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VITRALAB
Leonardo da Vinci Programme
LLP/LDV/TOI/2009/SK/93100530
Result 5
Handbook Automation and Robotics
Košice, September 2011
Obsah 1 Automation and robotics in manufacturing proces ...................................................................... 1
1.1 Industrial robot ................................................................................................................................ 2
1.2 Industrial robot functions ............................................................................................................ 2
1.3 Industrial robot structure............................................................................................................. 3
2 Kinematics ................................................................................................................................................... 7
2.1 Classification of kinematic structures according to structural layout ......................... 7
3 Control of robots ..................................................................................................................................... 13
3.1 Motion control of industrial robots ......................................................................................... 15
3.2 Interpolations ................................................................................................................................. 16
4 Robots Programming ............................................................................................................................. 19
4.1 On-line programming .................................................................................................................. 19
4.1.1 Coordinate system ................................................................................................................... 22
4.2 Off-line programming .................................................................................................................. 27
5 CNC machines .......................................................................................................................................... 34
5.1 Definition .......................................................................................................................................... 34
5.2 Scheme of CNC machine tool ................................................................................................... 34
5.3 Schemes of work CNC machining machine ......................................................................... 36
5.4 Coordinate system of the machine ........................................................................................ 37
5.5 Zero and reference points on CNC machines ..................................................................... 40
5.6 Determination of the zero point of the workpiece W ...................................................... 42
5.7 Tools correction ............................................................................................................................. 44
5.7.1 Length corrections .................................................................................................................... 45
5.8 Diametric (radius) corrections ................................................................................................. 45
6 Numerical control systems .................................................................................................................. 47
6.1 NC control systems ...................................................................................................................... 47
6.2 CNC control systems .................................................................................................................... 48
6.3 Digital systems according tool´s trajectory control to the workpiece ...................... 49
6.3.1 Continuous control systems ................................................................................................. 49
6.3.2 Coherental control systems .................................................................................................. 49
6.4 According to the programming method of tool location against the workpiece ... 50
6.4.1 Absolute programming (G 90) ............................................................................................. 50
6.4.2 Incremental programming (G 91) ...................................................................................... 51
6.5 Information processing in control system ........................................................................... 51
6.5.1 Geometric information ............................................................................................................ 51
6.5.2 Technology and support information ................................................................................ 52
7 CNC machines programming ............................................................................................................. 53
7.1 Structure of program ................................................................................................................... 53
7.2 Sub-programs ................................................................................................................................ 54
7.3 Cycles ................................................................................................................................................ 54
7.4 Sentence formats „Blocks“ ........................................................................................................ 54
8 Computer aided tool paths design – CAM ..................................................................................... 57
8.1 Technology ...................................................................................................................................... 57
8.2 Procedures for making technology ......................................................................................... 58
9 CNC machinery and the technological development ................................................................ 59
9.1 CNC machines, current status and trends of development .......................................... 59
9.2 CNC machining centers .............................................................................................................. 59
9.2.1 Requirements on modern CNC machines, production centers ................................ 60
9.3 Examples of modern CNC technology ................................................................................... 61
10 Sample of example ........................................................................................................................... 62
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1 Automation and robotics in manufacturing proces
Current needs in the process set out requirements on the application of automation and robotics in the manufacturing process. Quantity demands and quality of products have been continually increased as well as new complex technological processes and the construction of complex technical mechanisms. To meet these requirements it is necessary to develop new technological processes, design and development of construction of new automated and robotic equipment as well as modernization.
AUTOMATION:
Automation is a phase of technology development, which is characterized by the implementation of production, management and other processes without direct human intervention, coupled with the discovery of automated production lines, automatic plants and factories, the use of modern computing and control technology.
Automation does not exclude human fully. Human still controls and directs the work of general machinery (machine setting, enter the program, materials supply, maintenance), although the development of automation tools increasingly assume the following functions. It integrates them and makes management of technological processes more effective, Fig.1. Automation creates the possibility of a rapid increase in labour productivity growth in production, reducing production cost and improving product quality, it is the possibility of increasing the efficiency of production management. All this ultimately results in higher productivity and reduction of human labor (and hence the errors arising) in production.
Fig. 1. Automated line
ROBOTICS:
Partial or full implementation of robots in manufacturing and non-production processes to replace manual manpower by a robot according to Figure 2. Nevertheless, it is used in production processes and introduced more and more, it is necessary to note that no technical device completely replace the human factor.
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Fig. 2 Automatic robotized line for car assembling
1.1 Industrial robot
In literature, the term industrial robot means equipment which have the ability to solve independently a variety of handling tasks. At present, although an industrial robot is defined by the ISO, there is a number of other definitions and different interpretations but they all have the same essence.
At present, the general classification category includes robots:
Manipulator is a device with two-motion self-propelled units for management and automatic handling of workpieces, according to an established program and the time course of action in accordance with the production of machinery and other ancillary equipment.
Industrial-robot is a versatile multi-axis manipulator, motion available, which is freely programmable in movement. Robots can be equipped with tentacles, instruments or other means of production and may carry out handling, processing or assembly operations.
1.2 Industrial robot functions
Main robot functions include:
Handling capability, i.e. ability to grasp objects, transfer, orient and position them, including technological tools.
Versatility, this means that the robot does not serve only one purpose, but after the change, the end effector or tool, it can be used also for other purposes in other contexts and applied in iterative relations environment.
"Industrial Robot" is officially defined by ISO 8373:1994 as:
"Automatically controlled, programmable, multipurpose manipulator for action in three or more axes"
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The perception, the ability to perceive work and operating environment from internal and external sensors for the management of functions of the target program.
Autonomy, the ability to carry out independently required sequence of tasks, according to a specified program or in combination with some degree of self-decision on the selection process for the implementation of the task.
Integration, the ability of software and hardware to focus functional groups and major subsystems (a subsystem controller) into one compact unit if possible.
1.3 Industrial robot structure
The structure of an industrial robot can be divided into mechanical, control and programming section, Fig. 3
Robot/Hadrware
Pendant /Programing unit
Control system /Software
Data connectionPendant/Control
systemEngine power supply
Data connectionRobot/Control
system
End-effector
Fig. 3 The structure of the industrial robot
Mechanical section
Mechanical section of an industrial robot consists of links and joints, and joints are used to implement a robot motion and solids are links between them. Each joint provides a degree of freedom. Most robots have 5 possibly 6 degrees of freedom. The mechanical section of a robot consists of a base, carousel and arms, such as depicted in Fig. 4
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End-effectorArm 2
Arm 1
Robot Carousel
Robot Base
Joint 1
Joint 2
Joint 3
Fig. 4 A robot description and its sections
The end effector is a separate part of a robot, which serves for accommodating objects - griper or a technological head, such as a welding torch, Fig. 5. Together with industrial robots it is involved in the implementation of positioning and orientation of carried items . According to their intended use these are divided into gripers, head, integrated effectors and tools.
Joint 4 Joint 5 Joint 6
Flange
Grippers
Heads
Integrated effectors
Tools
En
d-e
ffe
cto
rs
Fig. 5 The end of a robot arm
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A robot control system
Its mission is based on information stored in the memory of a control computer and information obtained from sensors. This collected informatin is used for a robot action plan to decide on the actions to be performed. A block diagram of control of industrial robot is shown in Fig. 6
It includes all functions of management of positioning. In addition it offers the possibility of the current management of peripheral devices. Management of the robot is a microprocessor system, which operates under multitasking methods. Is it possible to handle simultaneously several sequential management processes.
Input and output level control is the choice of the design presented by either as a fieldbus technology or as discrete inputs and outputs. The serial interface is configurable and can be used to connect intelligent devices such as barcode scanners, image processing systems, etc.
Robot control systems are built on a PC base with a processor, equipped with a CD drive or floppy disk. As an external storage unit is used hard drive on which operating system is stored and real-time module to work in real time. The control system can be equipped with multifunctional card, which forms the interface between the programming unit, a PC security logic.
Programming unit
(Pendant)
Computer
Control system Drive Robot
ArmEnd-
effector
CNC machine
Backup generator Sensors
Fig. 6 Block diagram of industrial robot control
Control system allows:
The establishment of programs, editing and saving programs
Diagnosis of putting into operation
Path planning
Power control of servomodule
Communication with external modules
Programming unit
Programming a robot is done by so-called programming panel - pendant. This is a large, clear display, showing the progress of the program and its current status bar, switch between manual and automatic
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operation and selecting multiple imaging windows. By its sides it has function keys for various settings such as. speed, choice of coordinate system, and more.
Pendant also includes 6D mouse to control the robot in manual mode as well as buttons to control the robot separately in each axis, Fig. 7. As with any electrical device, pendant is equiped with a central stop for ensuring safety. To facilitate programming and diagnostics there is a software used with a number of additional features.
CENTRAL STOP
6D Mouse
Buttons for controlling the robot axes
Program
Function keys
Fig. 7 Pendant functions description
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2 Kinematics
The choice of the robot kinematics is mainly dependent on the mutual arrangement of a number of kinematic pairs (providing the individual movements). Kinetic properties of the robot are given by the number of rotational and translational axes and their arrangement.
Kinematic pairs (KP)
KPs are defined as two members of action mechanism movably connected. Mobility of one of the member to another is limited, the pair usually has one degree of freedom (pairs with more degrees of freedom in the design of robots are not often used). The members, which are connected together by sliding and rotating dynamic duos, it is possible to construct any kinematic chains.
The essence of a rotary kinematic pairs (KP) (Fig. 8) determines the potential curve only as a circular arc centered on the rotary body of KP with the A and the B bodies with a radius given by the length of arms of these bodies from the axis of rotary KD.
Object B
Object A
Rotation
Fig. 8 Rotary kinematic pair
The essence of sliding kinematic pairs (KP) (Fig. 9) defines itself on the linear trajectory or a section between the solid body A and a movable body B.
Fig. 9 Translational kinematic pair
2.1 Classification of kinematic structures according to structural layout
Kinematic pairs layout:
A) creating of kinematic chain with serial (consecutive) involving kinematic pairs - robot in Fig. 10 a) based on the serial mechanism principle
B) the establishment of a parallel kinematic chain (adjacent) involving kinematic pairs - robot in Fig. 10 b), the principle of parallel mechanis
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a) b)
Fig. 10 Ttypes of kinematic chains
The design of the robot is given by the kinematic structure, which is the type and sequence of arrangement of kinematic pairs in the kinematic chain by the tab.1.1. The most widespread concepts of an open kinematic chain are those which contains rotational and translational kinematic pairs. Based on the structure of a serial kinematic chain of the main drive system, existing robots can be classified into four basic groups:
Cartesian (TTT) Cylindrical (RTT) Spherical (RRT) Angularis (RRR),
Tab. 1 Prehľad priemyselných robotov podľa kinematickej štruktúry
Principle
Scheme of kinematic structure
Working area
Robot TTT
Kinematic structure – TTT – cartesian coordinate system /robot/gantry
Cartesian, Gantry robot
A kinematic chain composed of three, mutually perpendicular (orthogonal) translational kinematic pairs (sliding motion unit). It uses a rectangular coordinate system. This kinematic structure is very stable and in terms of kinematic analysis, it is the most accurate kinematic structure. It is easy to control it. The disadvantage is lower spatial mobility. It is mainly used for large spaces handling ares. Working space of robot consists of a cubic body, namely
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the prism or cube.
Robot RTT
Kinematic structure – RTT – cylindrical coordinate system /robot/ Cylindric
A kinematic chain composed of one rotational kinematic pair (rotational motion unit) and two mutually perpendicular, to each other, translational kinematic pairs (sliding motion unit). It is characterized by its robustness and easy control. Working space of robot consists of a cylindrical body, namely the cylinder, or a part of it.
Robot RRT
Kinematic structure – RRT – spheric coordinate system/robot/Spherick
A kinematic chain composed of two rotational kinematic pairs (rotary motion unit) and one translational kinematic pairs (sliding motion unit). The kinematic structure has been proposed as one of the first configuration. The workspace is bounded by spherical surface.
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Robot RRR
Kinematic structure – RRR – angular coordinate system/ robot/ Angular
A kinematic chain composed of three rotational kinematic pairs (rotary motion unit). Kinematic structure is characterized by good manipulative skills and thereby it avoids obstacles well. This structure is recently the most common in the construction of robots. Working space of robot consists angular or multi-angle body.
Robot of SCARA type
Kinematic structure of SCARA type
A kinematic chain composed of two rotational kinematic pairs (rotary motion unit) and one translational kinematic pairs (sliding motion unit). The advantage of this type of kinematic structure is well-positioned service area and higher mobility. It has, however, a smaller working space and more complex control. This structure is destined for the operations performed vertically from above and it is applied for the printed circuit assembly. It reaches high velocity and high acceleration. Working space of robot consists of a ring.
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Robot with parallel
kinematic structure
Parallel kinematic structure
Mechanisms in a parallel kinematic structure (Hexapoda, 3-pod), have three to six parallel members (arms) that are connected between the base and platform, or output member. Parallel mechanisms generally comprise two platforms, one of which is controlled by a length variable arms, working in parallel. Actuators is defined as a mobile platform, which has three to six degrees of freedom to the other platform - the base. It can be moved individually in each of the three linear and three angular directions or in any combination. The resulting movement of the platform is the current movement and control of these arms. Workspace of parallel kinematic robot structure is not fixed and it needs to be calculated. The length of each joint and rotation of joints must be taken into account.
Robot with two arms
Kinematic structure with two arms
An industrial robot with two arms is equipped with 13 degrees of freedom of movement, each arm has 6 degrees of freedom and the rotation around the vertical axis of the robot is added as well. The parameters of the robot determine it for mounting or handling applications with high level of manipulation, similar to humans.
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Multi-joint robot
Multi-joint structure
A kinematic structure of multi-joint arrangement offers an excellent flexibility. It differs primarily in the fact that it contains no classical translational or rotational kinematic pair. The structure uses a system of steel wires for perfect control of arm, which are interwoven through a series of plates arranged according to the structure of the spine of a human, to create a workspace of a ballshape with a flat bottom. Robot workspace is characterized by very good manipulative skills in difficult to reach areas such as enclosed areas of car bodies, etc.
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3 Control of robots
Robot control is achieved through the robot control system using information obtained from sensors. The control system enables to guide the robot to the desired position by means of programming unit (pendant). Through Iinputs / Outputs it is possible to attach various devices on the robot workstation operated by robot control, such as(conveyor, positioning tables,...). The control system is able to manage directly the unit as an axis. Modern control systems are equipped with connectivity to one of many technological hubs (DeviceNet, Profibus, Interbus, Ethernet, ...) and connect the robot to better structure the manufacturing system (CIM). Robots are equipped with industrial applications that simulate the programming unit of the PC. Controlling the robot and its programming can be implemented as follows directly from the PC. The governance structure of the robot is in Fig.11.
Engine
Feedback Sensor
Control system
Programming unit
PC
Conveyor Positioning unit
PLC
Fig. 11 Structure of robot control
The control system ensures the generation of signals for each axis of the robot. To ensure the required action of a robot, the control system must receive feedback information from the sensors (speed, torque, position, ...). Block diagram of control power unit with electric drive is shown in Figure 12.
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ENGINE
SENSOR 1
SENSOR 2
SENSOR 3
ELECTRIC CONVERTER
CONTROL SYSTEM
POWER SUPPLY
MECHANICAL CONVERTER(REDUCTOR)
EXECUTIVE UNIT
Fig. 12 Scheme of control of robot electric propulsion units
The main task of the robot control system is to generate signals for servo propulsion of a robot created by the program in automatic mode, or generate signals based on the functions of movement counterpart. Control system processes information from internal sensors juging the state of the system, but also information from external sensors around. For this purpose, control system is equipped with a number of digital inputs / outputs as well as several analog inputs / outputs. The internal structure of the robot control system is in Figure 13.
Central
control
unit
of robot
USB
Ethernet
Communication module
Data bus
Serial port
User Interface
Control panelSensors
Sensors interface
Motion module
Module I/OSystem memory
Program memory
User memory
Fig. 13 The internal structure of the robot control system
The control system can be divided into a central control unit that processes and executes the robot program. Communication module for interfacing the robot with the environment through technology hub and a module for motion control and management of the powertrain. Among the standard features of robot control systems are included:
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Multitasking operation system Built-in mathematical functions Discontinuation treatment Axial, linear and circular interpolation Tracing the conveyor belt Connection of camera systems Possibility to create macros and subprograms Built-in palletizing Management of multiple axes The cooperation of several robots in a common workspace Digital inputs and outputs
3.1 Motion control of industrial robots According to the nature of the motion control we distinguish management of industrial robots:
Point control (PTP - Point to Point) this type of management is used when it is necessary to achieve certain points in robot workplace, between whom there is no link.
Track control (CP - continuous path) this type of management is used if we need to drive the robot throughout the path of movement.
Point control is going through a sequence of discrete points in space. Figure 14 shows a possible sequence of movements P1-P2-P3 at various points with example of a program formulated in natural language. Trajectory between the points is not defined, axis move without a functional context. Point control is used mainly for handling and spot welding.
Pi - robot head position
Ai - robot activity in required position
Step Activity
1 Start in P1
2 Go to position P2
3 When P2 reached, execute activity A2
4 After finishing A2, go to position P3
5 When P3 reached, execute activity A3
Fig. 14 An example of PTP robot motion control
The robot passes each point with a positioning accuracy. After reaching the exact location of the command it causes the execution of activity A2-A3. Sometimes the accuracy is not required (for example - in circumvention of obstacles), and time loss for positioning works rather distracting. After reaching a defined point of the surrounding of auxiliary point movement is not interrupted, but continues with given rate at the next point. For example, if Figure 4. is such a point P2 (A2 may come off), shall enter an order no. 2 shapes: 2 Go through the auxiliary point P2. Control with path behavior allows programming and navigating through defined motion paths with a functional relationship in movement in different axes. In doing so, there are two possibilities:
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1. Multipoint control (MP) program includes motion in the form of a dense sequence of points in space, that are enterd in a fast time sequence (after 10 to 100 ms) from the axis position controller. These procedures are shown in Figure 15. Activity A1 is performed when the value entered into the coordinates of a point P4 position controller, regardless of whether that position has been reached or not. A small loss of time, which in fact occurs, is usually acceptable.
Pi - robot head position
Ai - robot activity in required position
Step Activity
1 Start in position P1
2 Go to position P2
3 Go to position P3
4 Go to position P4
5 Execute required activity A1 in position P4
6 Go to position P5
Fig. 15 An example of MP robot motion control
Multipoint control is mainly used in paint spraying robots, but also for spot welding and surfaces processing such as grinding, polishing. Programming is done mainly by the method of direct teaching. 2. Path control (CP) allows you to scroll through mathematically defined pathways. An example is shown in Figure 16. Programming is performed directly by "teach-in" or through the text. Computer (interpolator) determines certain number of values while evaluating the same motion on a curve path and enter them into the position controller in accordance with the program speed. A typical example of path control/management is arc welding.
Pi - robot head position Ai - robot activity in required position
Step Activity
1 Start in position P1
2 Go to position P2 via line
3 Execute activity A1 in position P2
4 Go to poisition P4 via P3 via circle;
5 Continue via circle to position P5
Fig. 16 An example of path control robot motion
3.2 Interpolations Interpolation is the process of defining the functions, which, according to certain values, passes given points. The robotic technology uses point, linear and circular interpolation. When moving PTP (point-to-point) movement begins and ends for all axes simultaneously. PTP mode is used for preparatory movements, which requires the robot move as quickly as possible to the desired position. When you move the robot to the desired point, approximation can be applied, which allows us to
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move smoothly without unnecessary slowdown. In case of Kuka robot, approximation is indicated in welding as a percentage (0-100%). When 0% is a robot with an explanation to the selected point in the case of other values that point is bypassed by the set value of approximation. In the approximation of 100% and linear motion, the robot begins to circumvent the desired point in the middle of the path between the start and end point. Fig.17 shows the type PTP movement without approximation. The track of robotś arm movement can not be determined in advance in this case. Endpoints are defined , in which the robot will come exactly or circumvent them according to the approximation parameters, Figure 18.
The shortest distance
Possible PTP paths
PTP - motion without approximation P2 is point of exact positioning
Fig. 17 PTP motion without approximation
PTP - motion with approximation P2 is point of approximation
Possible PTP approximation paths
The shortest distance
Fig. 18 PTP motion with approxomation
If necessary of keeping the track in the desired direction arm movements can be performed by LIN type (motion in a straight line) and CIR (Circular motion). When the movement type LIN, robot arm moves along in a straight line. This type of movement is slower than the PTP, since there is a need to calculate the points of robot path. Movement in a straight line is used when you need accurate placing of the end of effector to the desired position, for example. during installation, or circumvention of obstacles in the robot workspace. Figure 19 illustrates the movement in a straight line without setting a parameter of approximation and Fig. 20 using the approximation.
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LIN - motion without approximation P2 is point of exact positioning
The shortest distance
Fig. 19 LIN motion without approximation
LIN - motion with approximation P2 is point of approximation
Two parabolic branches(symmetric at the same speed )
approximation areain % by KLIN in mm
Fig. 20 LIN motion with approximation
The last type of motion is circular - CIR. It is needed to enter not only the start and the end point but an auxiliary point as well into the control system so that it can then realize the type of motion. Again, it is possible to use motion without approximation. Approximation does not apply to an auxiliary point, fig.21 and Fig. 22.
Fig. 21 CIR motion without approximation Fig. 22 CIR motion with approximation
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4 Robots Programming
Robot is operating under a pre-established program. The program is defined as a sequence of instructions which lead to execution of required activity. Programming of robot is defined as the compilation and creation of program based on algorithm. According to the approach to the development of the program the programming is divided:
on-line programming (programming by robot using pendant)
off-line programming (programming outside robot using PC)
4.1 On-line programming
On-line programming is done directly by an operator through required handling points and robot is controlled manually to single points which allows him to put these points into memory and save the points. As step No2 logical part of controlling and periphery devices must be programmed. In this section, the speeds of the movement paths of the robot are set. The main advantage of this mode is programming and in the real environment which avoids accuracy problems as well as functional test can be done. See fig. 23.
Information from sensors
Robot
Robot control system
Programmer (programming using
pendant)
Fig. 23 The procedure for on-line programming of robots
Nowadays, modern programming units are already built on a PC platform. Operation is easy via function keys. The display has an option to view several windows for visual display features of a robot, or technology program and their parameters. Built-in color display allows the operator to program directly through the I / O of their activities. Some programming unit (Coma Robotics) are capable of transmitting data to the control system wireless, Fig.24.
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Fig. 24 Programming units of OTC Daihen and Comau Robotics
The disadvantage of on-line programming is a relatively long programming time, physical burden on programmer in handling complex movements and long cycles. Another disadvantage is that all workplace of production is out of order when programming the robot, only some of the devices may work in limited mode.
Play-back mode programming
Entire working process is controlled manualy and control unit remembers the movement evry 20ms and records information about positions, points and orientation. Such programming can be used at simple, inaccurate robots like painting robots. When an automated mode is launched robot plays recorded path and operations. Repeating paths is not exact. Another disadvantage of this mode is the presence of operating staff. Programme producing is fast and quick and is suitable for low production too.
Teach-in programming
Robot arm is guided by robot staff using the control panel keys. Coordinates of defined positions and tools orientation are saved in memory. Speed information is also set at this stage. Then in automated mode robot uses saved datas. Single points of position and tools orientation are entered manually. Other function are programmed using Path control (PC). Fig. 25.
Obr. 25 Teach-in programming
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Description of selected features of the programming unit depicted in Fig. 26.
ESC
Menu keys
Status keysCentral STOP
Status keys
Space mouse
Softkeys
enter
Cursor keys
ASCII Block of characters
Numeric block
Program start forward
stop
Window selection key
Modes key
Dirve On
Dirve Off
Fig. 26 Programming unit - pendant for robot programming
Description of programming unit functions in Tab. 2
Table 2
Key Description
ESC Any activity can be stopped at any time, datas not saved, opend windows closed
Window selection key
Switching over opend windows if windows accessible. Selected window marked with color.
Stop Stops active programme which is in automated mode.
Start forward Strats selected programm
Starts backward Robot moves opposite programmed direction, moves are copleted backwards way to START position.
Number keys Entering numbers. On second level the num. section is substituted by operating keys.
Enter Enter or Return
6D mouse For manual robot operating in all 6 axes. Measures the deviation and adjusts movement speed. +/- alternative keys
Emergency The most importatnt security key. Red color
Stop In case of emergency, robot movements stop, before another operation the key must be unblocked.
Drive On Starts movements
Drive Off Stops movements
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Operation mode Manual mode- robot operates only when confirming key pressed. External mode- robot executes programme at programmed speed. Operating done using by operating key or by SPS (PLC)
Menu keys Opening menu options, closing with Escape key
Status key Left or right next to display, selecting the operation mode, values setting, functions
Softkeys Selecting the options or functions in the soft-key. Functions modifying according to requests, soft-key changes visually
Programming unit allows monitoring of input/output and of system information, writing programs in the editor, allowing access to production data (average cycle time, number of production cycles, ...), set operating parameters, eg. welding directly from the pendant. Modern units have analytical capabilities for optimizing robot work.
4.1.1 Coordinate system
A robot operates in a standard Cartesian coordinate system World. If necessary, it can be selected for a robot guidance a tool coordinate system or an external coordinate system, which is situated outside the robot, to get the robot to the desired position. If individual robot axes are necessary for a robot guidance an axially oriented system to be selected.
Axial coordinate system
TOOL / Tool Coordinate system TOOL
BASE / External Coordinate system BASE
WORLD / Basic Coordinate system WORLD
For manual robot operating to the required position in manual mode it is necessary to set the desired coordinate system. Each programming unit is equipped with buttons to manipulate individual axes of a robot arm, then we move the robot to the desired position. When adjusting the positions of the robot programmer can choose one of the options (Fig. 27). Choice of coordinate system is performed by setting appropriate positions according to the robot technology used.
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Fig. 27 Coordinate system of Kuka robot
Axial coordinate system
Every axis of robot is possible to move independently in the positive or negative direction of the axis. Movements are performed using the operating keys. Movement of the axis of robot in axial coordinate system is shown in fig. 28.
Fig. 28 Axial coordinate system
Pri pohybe jednotlivých osí sú k dispozícií nasledujúce prevádzkové klávesy a pohybové smery 6D myši:
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prevádzkové klávesy space mouse
Coordinate system WORLD
Relative coordinate system WORLD is absolute cartesian rectangular coordinate system. Its beginning lies inside the cell center of robot, fig. 29. The zero point of the system does not move.
Fig. 29 Coordinate system WORLD
Pri pohybe jednotlivých osí sú k dispozícií nasledujúce prevádzkové klávesy a pohybové smery 6D myši:
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prevádzkové klávesy pre 6D myš
ručnú prevádzku
Coordinate system BASE
Relative coordinate system BASE is cartesian rectangular (right-angled) coordinate system. Its center lies outside the cell, in external tool such as welding pliers, fig. 30. External tool coordinate system is decisive while working in BASE. The workpiece is being moved around or alongside the axes.
externý nástroj robot s obrábaným dielom
Fig. 30 Coordinate system BASE
Pri pohybe jednotlivých osí sú k dispozícií nasledujúce prevádzkové klávesy, poprípade pohybové smery 6D myši:
Pri dodávke leží začiatok súradnicového systému WORLD v päte robota.
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prevádzkové klávesy pre 6D myš
ručnú prevádzku
Coordinate system TOOL
Relative coordinate system TOOL is cartesian rectangular (right-angled) coordinate system, its center lies in the tool, fig. 31. Orientation of this coordinates system is choosen so that its axis X is identical to working instrument direction. Coordinate system TOOl always follows the tool movements.
Fig. 31 Coordinate system TOOL
Pri pohybe jednotlivých osí sú k dispozícií nasledujúce prevádzkové klávesy, poprípade pohybové smery 6D myši:
Pri dodávke leží začiatok súradnicového systému BASE v päte robota.
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prevádzkové klávesy pre 6D myš
ručnú prevádzku
4.2 Off-line programming
Paradigm of technical development of production systems clearly shifts the training activities and programming of NC machines and robots from real workplaces to work with their computer models based on increasingly smarter software packages. Today, training programs for NC machines in the environment of CAD/CAM represents almost 70% and this trend will shortly reach the robots. The advantage of off-line programming is a real possibility outside the workplace to create an optimal program in advance of the actual realization, before implementing a project. Off-line programming allows to describe a complex task, experimenting with the structure of the workplace, to eliminate conflict situations, verify program in 3D representation. The fact that programming is an off-site, greatly reduces the downtime due to transition to another production program.
Off-line programming is performed in computer models of the real robot cell including its surroundings in 3D presentation, Fig. 32. Programming is done in advance, the system allows direct import of objects from different CAD systems. The disadvantage is that this approach requires additional investment outside the robot, but on the other hand, such results, whether the robot reaches all equipment, are known before physical implementation.
Each virtual robot model has three parts: a model of the manipulator, model of the control unit and a program. Manipulator model is a 3D solid model, the control unit contains the actual robot controller program and specifies the role that the robot will perform. For other devices such as NC machine, plant, conveyor etc. a model can be created as a model for the robot. Communication between elements of the model corresponding connection between the models. Data exchange between models of the production system and CAD / CAM is supported by the STEP standard. The library contains models of robots, NC machines, peripheral devices, which are then imported into the simulation model. Simulation can be run in real-time 3D presentations. The evaluation model is implemented on the basis of simulation results. After reaching the optimal alternative the program is translated into the language of the robot and imported into the real robot control system. Fig. 32.
Pri dodávke leží začiatok súradnicového systému TOOL v strede príruby robota.
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Import from CAD:
- robot- tool- peripheral devices
Calibration
Program creating phase
Simulation and verification
Program and model
modification
Program Translating and Transmiting
On-line program repairs
Fig. 32 Operation procedures in an off-line programming
Off-line programming allows the use of PTP, LIN, or CIRC interpolation. Off-line programming allows a detailed 3D simulation which can detect conflict situations and to verify the changes of the future, test handling points. This allows the user to search not only the optimum deployment of equipment in the manufacturing cell, but the optimum handling of their operating cycles. Many off-line programming systems monitor the real time course of robot activities, support the selection of appropriate tools, technology or process parameters. Connectivity between robot and CAD system is depicted in fig. 33.
Objects prepared in a CAD system can be transferred (eg STEP format) to the off-line robot programming (eg KukaSim, RobCad, RobotStudio, etc..), where the working environment can be modeled with the selected robot and imported objects. Duty cycle is created by putting the functional model to the desired position. Duty cycle can be simulated in the off-line programming environment. This allows us to check the cycle and remove the conflict between the conflicts of the robot and objects. The last step is to generate a program for the robot controller. This program is transferred to the robot is a gradual pacing verified and if necessary adjusted to a final podobytak that it can be applied in service.
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Control system
Robot
Programming unit
PCOff-line program
PCCAD/CAM system
Fig. 33 CAD system connectivity with robolt during off-line programming
Off-line program preparation allows:
Minimizing re-arrange time
Production maximizing
Reducing program failurs
Finding dangerous situations and unreal tasks
All technologiocal parameters programming
Automatic path searching with obstacles avoiding
Working cycle optimalization
Programming itself is not dependant on existence of workplace
Minimizing downtime robotic workstation
Simulation of the complete process on your PC
Detection of conflicts and potential problems before the production stage
Test of deliverability of individual points
Programming of all technological parameters
Elimination of errors in the program
Generating code for robot control systems
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Direct link of off-line programs for CAD systems
Graphical presentation of "real" programming panel Fig. 34 gives the possibility of programming on-line, which is preferably used as a training tool for teaching on-line programming. Systems off-line programming have an event table/chart, which is an ideal tool for verification of program structure, logic functions and I / O status, Fig. 35.
Fig. 34 A graphic presentation of programming panel in PC
Fig. 35 RobCad programm for off-line robot programming
During the implementation of programs created in the CAD system we can monitor all movements of the robot and visualize with diagnostic functions contained in the CAD system. Is it possible to link on-line between the robot and CAD systems. Every movement of the robot in real environment will be shown in the visualization environment. Thus it is possible to verify the quality of the proposed program and if necessary just to make the required adjustments.
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Within the Robot Studio we can perform simulations of collision situations, Fig. 36 and 37. Welding gun and welding assembly parts depicted while tongs are at a safe distance from the elements of the preparation so there is no conflict.
Fig. 36 A simulation of tongs approaching towards welding parts – pre-collision situation
Fig. 35 collision showed where encountering tongs are within the reach of clamping elements, which are shown in red highlighting.
Fig. 37 A simulation of tongs approaching towards welding parts – collision situation
Paradigm of technical development of production systems clearly shifts the training activities and programming of NC machines and robots from real workplaces to work with their computer models based on increasingly smarter software packages. Today, training programs for NC machines in the environment of
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CAD / CAM represents almost 70% and this trend will shortly reach the robots. The advantage of off-line programming is a real possibility outside the workplace to create an optimal program in advance of the actual realization, before implementing a project. Off-line programming allows to describe a complex task, experimenting with the structure of the workplace, to eliminate conflict situations, verify program in 3D representation. The fact that programming is an off-site, greatly reduces the downtime due to transition to another production program. Off-line programming is performed in computer models of the real robot cell including its surroundings in 3D presentation. Programming is done in advance, the system allows direct import of objects from different CAD systems. The disadvantage is that this approach requires additional investment outside the robot, but on the other hand, such results, whether the robot reaches all equipment, are known before physical implementation.
Testing the accessibility of tongs towards welding parts is possible with feature settings of collision situations where you can specify a minimum distance between elements, allowing us to determine the location of the collision situations. As an example, the accessibility detecting in fig. 38 where the first figure represents the distance from the pneumatic clamp pliers and it is sufficient, in this case 10 mm.
Fig. 38 Tested accessibility is in required range
Fig. 39 shows a smaller distance between ticks and pneumatic clamping, which is indicated by yellow staining conflicting elements.
Fig. 39 Tested accessibility exceeded required range
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Each of the methods of programming robots (on-line and off-line) has its advantages and disadvantages. By taking advantage of both these methods of programming techniques we can achieve the optimal solution. Generally, such programming is labeled as hybrid. Robot program mainly consists of two parts: location (position), the programming logic (communication calculations). Program logic can be effectively developed off-line, since an effective debugging and incentive funds are available here. Much of motion orders may be generated off-line with the re-use of data from CAD with the interaction of the programmer. Motion orders for locating the workpiece in place of robot cells may be programmed on-line if necessary. In this way, the benefits of both methods can be used.
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5 CNC machines
5.1 Definition
Computer numeric control production machines (CNC) are characterized by central control system, driving main and auxiliary machine functions by program. Information is in a program written by alphanumeric characters. The program itself is given by sequence of separate group of characters called blocks or sentences. The program is designed to manage power elements of the machine and guarantees the manufacturing of the workpiece.
Machines are flexible, can quickly adapt for different production and work in automatic cycle which is managed by numerical control. CNC machines applied in all sectors of industrial production (machining, forming, assembling, measuring). Their typical representatives are lathes and milling machines used for training programmers and operators.
The information in the program can be divided into:
Geometric – describe the tool path, which are given by workpiece dimensions, machining methods and describe feeding of the tool to the workpiece and from it. It is a description of the tool tracks in Cartesian coordinates, when the creation of the program needs the dimensions of workpice blueprint. Description in program is in X,Z axis for the lathe, in axis X, Y, Z for milling machine (and also by other axes depending on construction of machine and workpiece complexity), by given functions which provides ISO and the individual producers of control systems.
Technological – provide machining technology in terms of cutting conditions (especially the speed or cutting speed, feed or depth).
Auxiliary - it's information, commands for the machine for some auxiliary functions (such as switching on coolant pump, direction of spindle rotation etc.)
5.2 Scheme of CNC machine tool
Computer – it is an industrial computer with pre-recorded control system, which is part of the machine. Is given by a screen and control panel. Via control panel is possible to perform requested steps during manual servicing, for adjusting CNC machining and work in other modes of machine. The computer enables, by using the software control system, to create the required CNC program.
Control circuits - In these circuits the logic signals are converted to high-voltage electrical signals, which directly control each part of the machine - the spindle and feed motor, valves, etc.
Interpolator - Managing the tool path, which is given by geometry, calculations of the length and radius corrections of tool. So it calculated equidistant movement, which is shifted from the calculated correction of the geometric contour. Guarantees the geometric accuracy of the product.
Comparative circuit - The machine must be equipped with the feedback (with exceptions for simple CNC machines for staff training), which transmits information about the geometric values in coordinate axes at various points within the range of motion. These coordinates are compared with the values that are given by the program (and modified in interpolator). If a difference appears, feed drives receive the command to achieve the desired coordinate values. The machine must be equipped with a transducer, which is used to obtain the coordinates.
Term CNC (Computer Numerical Control) means: Computer (numerically) controlled machine.
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Fig.40 Block diagram of the CNC machine tool – symplified
Control panel – (can be solved as a figure 41) divided into several parts, which differ with their meanings:
data input – alpha numeric section, which is used to manually write for example a program, data instruments, adjusted for machinery, etc.;
machine control – special section used to tool or workpiece motion, triggers the spindle speed, affects the size of the hand-feeds, speeds, etc.;
choice of operation mode - you can choose the manual mode, automatic mode, workshop programming, etc,;
memory activation - induce different types of memory; tests activating – calling tests of programs and test of machine, simulation of programs; screen - used to control process; portable panel - for controlling the basic physical functions of the machine as a basic part of
thekeypad. Allows the operator to go to places that offer the possibility of more accurate and more complete visual inspection.
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Fig.41 CNC machine control panel – examplle of the on of many design
5.3 Schemes of work CNC machining machine
During operations, we may encounter several types of operations of the machine or only types of machine control system. They can be set on the control panel by buttons. Typically, control systems have these schemes:
Manual mode - is used for resetting tool or measuring equipment in the desired position, tool change, approaching to the workpiece, start-up speeds, etc.
Automatic mode - a smooth implementation of the program. After the block processing machine reads and processes the next block automatically - smooth machining process.
Mode B - B (block by block) - the machine stops after processing the block and after re-start reads and processes next block. BB scheme is one of the options for checking correctness of CNC program.
Setting (impact speed, work shift, fast feed) - The amount of movement can affect by hand control, by potentiometer, where you can adjust range usually between 5-150% of the value set in manual or automatic mode.
Tool memory mode (the tool data memory) - you can save and recall tools data, including corrections.
Teach in mode ("learning" or "lead-in and storage”) - the machine has the "ability" to learn. Operator manually (via keyboard) perform required movements to manufacture workpiece.
EDIT mode program - a program for processing is entered directly into the editor of the machine or is "loaded" into the machine control system externally. In the editor of the machine programs can be repaired as required.
Diagnostic mode – reports, locates, diagnoses defects for quick removal. It also allows remote service.
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5.4 Coordinate system of the machine
Production machines use a Cartesian coordinate system. The system is right-handed, rectangular with axes X, Y, Z, rotary motion, whose axes are parallel to the axes X, Y, Z, marked A, B, C - Figure 42. True that the Z axis is parallel to the axis of the work spindle, and a positive sense takes place from the workpiece to the tool. Values are present also in the negative field of coordinates.
Fig.42 Definition of Cartesian coordinates – right-handed system
Cartesian coordinate system is necessary for the machine control and for the measuring of the tools. Tool, in the machine, moves according to orders from the CNC machine control panel or under the CNC program commands. If necessary, coordinate system can move and rotate. In the case of measurement instruments (surveys corrections) is a Cartesian system placed in a point of exchange tools or tool tip.
The coordinate system is placed in the machine according to the following rules:
1) Start from a stationary workpiece.
2) Always must be defined X-axis.
3) The X axis lies in the plane of the fixture or the workpiece or is parallel to its plane.
4) Z-axis is identical or parallel to the axis of work spindle, which grants main cutting movement.
5) A positive axis sense goes from the workpiece to a tool in the direction of workpiece growing.
6) If there are other additional movements in the axes X, Y, Z on the machine, these are called U, V, W.
7) If the workpiece is moved against the tool, coordinates are called X ', Y' and Z '.
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Fig. 43 Lathe coordinate system (spindle without driven tools)
Fig.44 Multi-axes lathe
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Fig.45 Coordinate system for CNC milling and drilling
Fig.46 Coordinate system of 5-axes centrer
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Fig. 47 Coordinate system of maching center
On top of the basic coordinate system is necessary to reference points define in the workspace of the machine, which help determine the relative position of machine, tool and workpiece.
5.5 Zero and reference points on CNC machines
After switching CNC control system on the machine, coordinate system in its own machine is activated. The coordinate system has its origin - the zero point, which must be specified. According to the application the zero points have their names. The CNC machines have other important points:
M – zero point of the machine
This is the beginning point of the coordinate system of the machine work area. It is a fixed structure (usually the intersection of the main spindle axis and workpiece mounting plane) and can`t be changed. It's an absolute beginning of the coordinates.
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W – zero point of the workpiece
It is the beginning of the workpiece coordinate system. The position chosen freely by the programmer and can be changed during the program. Zero point is usually chosen in the axis of symmetry and at the upper surface of the workpiece (semifinnished).
R – reference point of the machine
It is a place on the machine (usually in the working space of the machine), in the maximum possible distance from the zero point of the machine, due to end switches in each axis. Only after moving the reference point relative to the point M, machine "knows where it is”. Distance from reference point and the zero point is stored in the machine table of the machine constants. Without moving the reference point R, machine can’t work in absolute coordinates input.
P – point of the tool tip
It is necessary for determining the length correction and subsequent radius correction (nose compensation). It is a point which movement is theoretical programmed (if using radius correction).
F – reference point of the slide or spindle
It is a point on the fixture (seating) area of the media tools (for example end of the spindle in the spindle axis). This point manages the control system according to the program. In the point F has the tool zero value, so it is therefore necessary to correct the actual tool path. Corrections of the tool are applied to this point.
E – set-point machine
Point of the tool mounting, which is identical with F pint after workpiece fixation (it is necessary to ensure the correction of the tool on the device outside the machine).
Fig. 48 Reference lathe points
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Fig. 49 Reference milling points
At the beginning of processing (programming) it is necessary to move the coordinate system from the machine zero point into the zero point of the workpiece.
The current system allows two types of beginning displacement:
absolute (set) offset – calls by preparatory function in the program (G54 - G57) – individual displacements are absolute - they indicate the distance from point W to the point M - each new shift cancels the previous
programmable (additive) offset (G58 - G59) - is relative - indicates the distance from the W hotspot - added to the absolute displacement - applied only in the sentence, which was called
Fig. 50 Offset of workpiece zero point – W
5.6 Determination of the zero point of the workpiece W
scratch by tool - it is not accurate (ovality, throwing blank, operator skills), but don`t requires the equipment costs
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by measuring eccentric touch using a probe using optical devices
Fig.51 Scratch by tool
Fig.52 Eccentric measuring contact
Eccentric contact has two parts - clamping and touch. Touch part move to the semiproduct. Eccentricity is reduced to zero - at this point will be position deducted. A little touch of overrunning evoke the vibrated eccentrically again.
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Fig.53 Measuring probe – optical device
5.7 Tools correction
Location of media tools in machine coordinate system is relative to point F (zero-point on the machine carriers). The surface of the workpiece is created by the tool tip, point F shall therefore describe ecvidistants so therefore must be activated corrections, which automatically handle the interpolator. One other reason for the use of corrections is that different instruments have different dimensions. If it was not treated by corrections, the various instruments in the same sentence of the program held a variety of tracks to the workpiece. On the following picture the shape of the workpiece is made by the black tool with black color. Red tool, which has a tip after the clamping into the fixture in another place under the same program without correction created the red shaded shape.
Fig.54 Workpiece shape changing in machining with various uncorrected tools
It is true that in many cases it is possible to set the instrument into the module clamps so that the edge of each instrument was set to the same point, but it is tedious and difficult.
All corrections are stored in memory of corrections.
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Corrections are dividen into:
length diametric (radius)
Tools corrections are usually measured on a special machine outside the workplace in order to maximize machine time. To that are used special optical instruments.
5.7.1 Length corrections
They are used both in turning and in milling.
When turning the surface it does not follow the required theoretical tool tip (with zero radius), but the actual tip with radius of a certain size. This results in the bevels and rounds the variations of the theoretical and actual shape. Therefore it is necessary in memory of correstions specify a tool nose radius and tool position due to the machined surface, in order interpolator can calculate the ecvidistant of the track.
Fig.55 Contour defect without correction of tip radius
5.8 Diametric (radius) corrections
For the activation radius compensation are used preparatory functions G41 or G42. These functions are socalled modal (it means valid until further notice). The validity of the functions is terminated by a preparatory function G40.
G 41 - CORRECTION OF THE TOOL RADIUS IN THE LEFT OF OUTLINE
G 42 – CORRECTION OF THE TOOL RADIUS IN THE RIGHT OF OUTLINE
Evaluation if the tool is on the left or right is done from the perspective of the tool feed direction.
When we are not using averaging correction (G41, G42), then the system operates a zero tool holder (F) as the tool axis. This means that if we use tools with different diameters would be during the execution of the program made components of different sizes. Sizes of ground-plans machined using various tool diameters are shown in the next picture.
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Fig.56 Workpiece dimensions without diameter corrections
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6 Numerical control systems
Numerical control systems can be divided into two groups:
NC CNC
Computer Control Systems (CNC), for all its advantages prevail, whereas the NC systems are both technically and morally obsolete and are used only in the depletion of their life.
6.1 NC control systems
Into the memory system is read only one sentence which will be executed. After the sentence is read, loads a new one. When the new sentence loads, the current content of memory is overwritten. Information is entered into the program on paper tape, or manually from the keyboard. Program on paper tape is read again and again during the production of other items. For making the next piece the tape has to be rewind to its beginning. Any treatment of the program is possible only by adjusting the paper tape. In the program can not be used parameters and user subroutines, program can not branch out.
Fig. 57 Scheme of NC control system
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6.2 CNC control systems
System is reading whole program from diskette or other medium for storing data, or from LAN net (cabel or wireless). Difference from NC systems is, that interpolator is not hardware but software. To generate profile of trajectory is possible to use mathematical description. So it is also possible to generate parabolas and high-order curves. Systems with better processor performance can realize dimensional circular interpolation, but in practical use linear and circular interpolation is sufficient.
Programmable logic controller (PLC) is used to processing technological information for CNC systems.
CNC systems benefits:
easy to edit program expand program to use parameters work with sub-programs to use graphic simulation of machining to use diagnostic programs to offset inaccurancies of system and machines parts
Fig. 58 Scheme of CNC control system
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6.3 Digital systems according tool´s trajectory control to the workpiece
6.3.1 Continuous control systems
Coordinates system input
Interpolation is missing. Tool is moved with rapid feed to the programed point. Carried trajectory is not issue (tools is
moved in a plane of one axis an then in a plane of second axis to the designated point). After reaching designated point, movement in other axix is performed Useful for drillers and forming machines.
Rectangular control
Tool movement is parallel with cocrdinates systems. There is movement in one axis, after finishing movement in other one. Useful for drillers and forming machines and lathes.
6.3.2 Coherental control systems
Systems enabling computiong of corrections and geometry.
Tools is moved in plane X-Z (2D) in lathes For millers, linear interpolations are possible in one plane, X-Y, X-Z, Y-Z (2,5D). By using
powerful processor, it is possible to machine various shapes and 3-D surfaces. If other movements, out of movements in axis, are possible (rotations), we are talking about 4D and 5D control.
Fig.59 2D control Fig.60 2,5 D control
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Fig.61 2D control Fig.62 2D control
6.4 According to the programming method of tool location against the workpiece
6.4.1 Absolute programming (G 90)
all the programmed tool path points are related to a pre-selected point – zero point of the program (W), the location chosen arbitrarily by programmer
for needs of absolute programming is better to use quotations from the base (grid dimensions)
Fig. 63 Absolute programming – dimensions
!! In program the end-point position is adjusted !!
During setting of dimensional words (X,Y,Z) in absolute programming is the basic question: What distance from the zero point of the program should the tool reaches (in each axis)?
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6.4.2 Incremental programming (G 91)
coordinates of all programmed points are given due to the previous point, which is regarded as an initial
for needs of incremental programming are so used string dimensions
Fig. 64 Incremental programming – dimensions
6.5 Information processing in control system
Information which management system needs to correct action can be divided into:
geometrical technology and support necessary for the organization of the program
6.5.1 Geometric information
Information about track media of tool are processed in the interpolator. Interpolator is an arithmetic unit which calculates the path elements in each coordinate axis so that the resulting movement between two given points is:
linear – linear interpolation around circular arc – circular interpolation parabola or a general curve
Interpolator generates signal of the desired path. Measuring device generates a signal on the actual track. Both signals are compared in a differential element - their difference is the regulation divergence, which after amplification and transformation creates a action quantity. In other words - differential member sends
During setting of dimensional words (X,Y,Z) in absolute programming is the basic question: What kind of distance should tool draw forward from endpoint of preceding movement (in each axis)?
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impulses to the motor until rest reached the desired position. Measuring devices work after some non-zero "jumping" – increments. Increment Is the smallest measurable and therefore programmable path. At present is widely used increment 0.001 mm.
Fig. 65 Circular interpolation – interpolar function
Operation principle of interpolator of circular interpolation clockwise (G02) is on the previous figure:
1. Creates an equation of a circle in the XY plane (X-0,026)2 + (Y-0,001)2 = 0,022
2. Send a unit impulse in the direction+X
3. Substituting the coordinates of point 1 in the equation of a circle and find that the left side of the equation is smaller than the right. This means that the point 1 lies within the arc.
4. Change the direction of movement and sends unit pulses until it finds that the point lies outside the arc, see section 2)
5. Repeats the previous paragraphs, until it gets to the end point.
6.5.2 Technology and support information
The control system must handle not only information about the geometry of movement, but also its speed, then feed per revolution or per unit of time, cooling type, blowing etc. Matching Logic deals with other helpful information - the logical relationships between the control commands and signals from the machine, which report the status of the various mechanisms – for example:
spindle starts only when the chuck is clamped shut and the housing is closed during spin the spindle working shifts starting to work shifts and speeds of spindle stops working when open the door of the working place translation program doesn´t run in a loss of information on the reference.
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7 CNC machines programming
7.1 Structure of program
Program is sequence of sentences. Every sentence is sequence of words.
Program is bounded:
At the begining by sentence. At the end of the program has to be one of the assictance functions M02 or M30.
Every sentence is bounded by agreed characters:
Beginning of the sentence. End of the sentence.
Beginning of the sentence:
Character N. : (colon) - for some systems for main sentence – sentence, which has all necessary dates for
continuing program. So called subordinate sentence starting with character N has only finktions, which has been changed from the last sentence.
End of sentence
With character LF or EOB. There could be character / (slash) in front of the first character of the sentence, which is marking
sentence not used in the program. Example:
Numbering of sentences is arbitrary. Same numbering can’t be used for more than one sentence. Some systems are ignoring sequence of numbering and using sequence of sentences. Which means, as in following example, sentence 1000 will be executed before sentence 5.
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7.2 Sub-programs
Is a closed part of the program, which could be repeated several time in the main program, or could be used in other program,
Is made by programmer, is mentioned behind main program in some systems, but usually it is independent part of code, which is called by other program (main or by sub-program), · has similar structure as main
program, is re-called by word (for SINUMERIK) with address L <number of program>, could be re-called numerous times by using word (for SINUMERIK) with address P <number>, podprogramy je možné vnořovat, ends with word M17 and sends control back to main program
7.3 Cycles
Is a sub-program added and fixed by manufacturer of control system. Cycles are used, for example in turning, for:
roughing lenghtwise and crosswise grooving drilling holes threading
for milling:
drilling pocketing grooving etc.
7.4 Sentence formats „Blocks“
Form of the sentence can be divided by the length:
With fixed (constant) lenght With variable lenght
In formats with fixed lenght is necessary to use, according to the type of used word, syntactically complete words.
In the format of variable length sentence it is not necessary, system retrieves the specified word from memory of words, which pulls the contents of memory and the sentence is carried out by substituting. So until there is no change in the words, it is not necessary to write the word in the sentence.
Each phrase (block) includes characters in addition to the beginning and end of several groups of characters, known words.
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Each word consist of two parts:
adress semantic
Example:
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8 Computer aided tool paths design – CAM
Computer aided tool paths design, part of an integrated production system, not only generates NC code for the machine (this is a fundamental output), but output may be (depending on application) as well as drawings, data on the use of materials, tools and machines, and more.
When working with the CAM system is need to select, as input information, information about:
workpiece (geometry, material) technology (material, cutting conditions) machine on which runs the final control program
GEOMETRY OF THE WORKPIECE
CAM system uses geometry in digital form. Geometric elements that characterize the shape of the workpiece or semiproduct, may constitute such contours, surfaces, and 3D models.
Applicable digital data can arise:
In the CAD part of CAM application. Retrieved from another application. By model digitization.
Getting geometry is shown in more detail in next image.
Fig.66 Capture of geometry of workpiece for CAM aplocations
8.1 Technology
The most popular technology used in CAD / CAM systems are shown in the following diagram.
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Fig. 67 Technology supported by CAM
8.2 Procedures for making technology
Before the start of production technology is needed to know some basic information regarding the machining process. These values include the default information for creating the NC program, such as:
Definition of the workpiece
material of the workpiece default semiproduct
Definition of the tool
selection of library tools creation of new tools
Data of the machine and control system
postprocesor
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9 CNC machinery and the technological development
9.1 CNC machines, current status and trends of development
Status of development in the modernization and automation, the use of CNC technology in the manufacturing sector shows the following picture. Intensity of production and number of units on the axes of the graph illustrates how a given state corresponds to the use of production techniques and the type of programming. The conventional technique is likely to have future success only in single piece production and repair.
Fig. 68 Deployment of production machines – equipment in factories in dependence of type and labor intensity
Continuous development and upgrading of machine tools is rapidly applied in practice. This is because reduction of prices of machinery and control equipment due to their increasing utility value. Machines provide more convenience in programming, include more features, and reduce production downtimes. This leads to a reduction in traditional conventional machines deployed in production
9.2 CNC machining centers
Diagram (Figure 30) shows a sorting machining machines, originally dedicated, sorted by technology of machining (figure doesn´t capture all the technologies and their combinations). There are very few parts which are made of only one technology, such as for turning the shaft is needed to mill the groove. Economy of operation leads to the integration of several methods of machining in one machine (center). The reasons are in the reduction (removal) in the operation time, it also increases the accuracy of operation production. Further integration of technology into the machine leads to the universal machining centers. That means for the economy:
Reducing lead times and increased accuracy of work. Reducing the costs of production (instead of several machines be drawn one - saving production
areas, saving depreciation costs). Possibility to easily automate the production (construction of flexible production lines - CIM). For machines with HSC technology is provided as a fivefold increase in productivity, this ratio
can be expected in economic savings.
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Fig. 69 Evolution from simple machines to machining centers
9.2.1 Requirements on modern CNC machines, production centers
Diagram (Fig. 30) demonstrates the current requirements for developed and sold by CNC machines (center), which are economically successful. Already in the development of the machine are taken into account the economic demands, giving rise to technological requirements and lead to the construction, design machines with advanced manufacturing technology HSC. That the machine complies with those requirements, the design shall also include other advanced features and accessories.
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9.3 Examples of modern CNC technology
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10 Sample of example
Example 1 (programming in control program FANUC)
Contouring, pocket
O0002 (CVIC1) N5 T1 M6 N91 G91 N10 G43 H1 N100 G1 Z-4 F200 N15 M3 S1800 N105 G1 X5 N20 G0 X50 Y-22 Z2 N106 G17 N25 G1 Z-2 F200 N110 G3 X-10 R5 N30 G41 H11 N115 G3 X10 R5 N35 G1 Y5 F400 N120 G1 X5 N40 G1 X35 N125 G3 X-20 R10 N45 G2 Y55 R25 N130 G3 X20 R10 N50 G1 X95 C10 N135 G90 N55 G1 Y5 C10 N140 G0 Z0 N60 G1 X48 N145 G0 Z50 N65 G1 Y-22 G40 N150 G0 X-50 Y100 N70 G0 Z50 N155 M30 N75 T2 M6 N80 G43 H2 N85 M3 S2400 N90 G0 X35 Y30 Z2
