Industrial Robotics

Edited by Prof. A. Del SoleWith free resources from the internet

industrial definition by RIA (Robotic Institute of America):re-programmable multi-functional manipulator designed to move materials, parts, tools, or specialized devices through variable programmed motions for the performance of a variety of tasks, which also acquire information from the environment and move intelligently in response.

Standard definition by ISO 8373:automatically controlled, reprogrammable, multipurpose manipulator programmable in three or more axes.

DEFINITIONS ► ROBOT:

ISO 8373 - Manipulating industrial robots

It is the ISO standard that defines terms relevant to manipulating industrial robots operated in a manufacturing environment.

ROBOT: complex machine composed by:a mechanical system for interacting with the environmentan actuation system for task executiona sensory system for getting proper informationa control system for the run-time control and programming.

ROBOTICS: inter-disciplinary science, with competencies inthe fields of:MechanicsElectronicsComputer ScienceAutomatic ControlSensorsActuatorsMaterialsC.

DEFINITIONS ►

Robot

The name derives from the czech word robota (“hard work”), used to indicate artificial humanlike creatures built for being inexpensive workers in the theater play Rossum’s Universal Robots (R.U.R.) written by Karel Capek in 1920 and translated in English.

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1750 (ca): J. de Vaucanson builds several mechanical dolls, with dimensions similar to the human ones and able to play music

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1892: S. Babbitt (U.S.A.) builds a motorized crane with a gripperto be used in a furnace

This is not a robot properly, it shares characteristics of manipulator arms only.

1954: G.C. Devol design a “programmable pick-and-placemechanism”, patented in 1961.

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Devol proposes the name UNIMATION (Universal Automation) for the first robotic industry, and

Unimation robots were also called programmable transfer machines since their main use at first was to transfer objects from one point to another.They used hydraulic actuators and were programmed in joint coordinates, i.e. the angles of the various joints were stored during a teaching phase and replayed in operation.

UNIMATE was the first industrial robot, which worked on a General Motors assembly line, in 1961.

1969 Victor Scheinman at Stanford University invented the STANDFORD ARM, an all-electric, 6-axis articulated robot designed to permit an arm solution.

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1973: SRI International (an independent, nonprofit research center) develops WAVE, the first programming language.

1974: AL (Assembly Language). From WAVE and AL, thecommercial programming language VAL has been developed (Unimation, V. Scheinmann and B. Shimano)

This allowed it accurately to follow arbitrary paths in space and widened the potential use of the robot to more sophisticated applications such as assembly and welding.

1973: At Cincinnati Milacron Corporation, Richard Hohn developed the robot called The Tomorrow Tool or T3.

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The T3 was the first commercially available industrial robot controlled by a microcomputer as well as the first U.S. robot to use the revolute configuration (a number of rigid arms connected by rotary joints).

Industrial robotics took off quite quickly in Europe, with both ABB Robotics and KUKA Robotics bringing robots to the market in 1973.

T3 robot was used in applications such as welding automobile bodies, transferring automobile bumpers and loading machine tools. In 1975, T3 was introduced for drilling applications. And in the same year, the T3 became the first robot to be used in aerospace.

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Interest in robotics increased in the late 1970s and many US companies entered the field, including large firms like General Electric, and General Motors.At the height of the robot boom in 1984, Unimation was acquired by Westinghouse Electric Corporation

1975: OLIVETTI commercializes the SIGMA robot, for assembly operations; one of the first robot applications in this field.1976: robot manipulators are used in the Viking 1 and 2 space missions on Mars.

Only a few non-Japanese companies ultimately managed to survive in this market, the major ones being: Adept Technology, Stäubli-Unimation, the Swedish-Swiss company ABB Asea Brown Boveri, the German company KUKA Robotics and the Italian company Comau.

There are a number of ways in which industrial robots may be classified. Such classifications describe important features possessed by the robots.

ConfigurationGrouped according to there structure or design. For example some robots have arms that rotate while others can only move in straight lines.

Control SystemImportant considerations when selecting a robot concern its positioning accuracy, its repeatability and its ability to traverse smooth and often complex contours. Such considerations are a function of control system employed.

Power TransmissionIndustrial robots may be powered by hydraulic, pneumatic, electrical and mechanical devices eg a high power lifting function will dictate a hydraulically powered robot to be specified.

ApplicationParticular task for which the robots are employed: welding, assembly, painting, material handling, etc.

Classification of Industrial Robots

Translation: This refers to linear movement in the X, Y or Z direction. The term is sometimes used to describe the linear offset distance of a rotational or revolute joint.

Repeatability: Perfect accuracy is unattainable and so some dimensional tolerance must be applied. The repeatability is a measure of how close a Robot arm can return to a previously held position. A typical repeatability specification for an industrial Robot would be + or - 0.2 mm.

Manipulation: The task of picking up an object and changing its position and orientation in space. The manipulation in Robotics often takes the form of a human (anthropomorphic) arm.

Instability: Instability is the tendency of the system to oscillate about a desired position. A Robot arm traveling at high speed may have too much inertia to stop when it reaches the desired position and as a result it will overshoot its target and feedback an error signal. This will cause the arm to try again to reach the desired position.

Response: The response time is the time lag between the application of the input signal and the arm reaching its desired position. Response time is always a compromise between minimal lag time and stability of the system.

Common Robot Terminology

Degrees of Freedom relates to the locating or positioning of a body in space. Any body in space has six degrees of freedom: It can have linear movement along three mutually perpendicular axes and rotational movement about the same three axes. The three linear movements, allow the body to be moved to a desired position in space and the three rotational movements allow the body to be orientated about that position.

Degree of Freedom and Axis of Movement

Axes of Movement relates to the number of axes in which the Robot may move. In one particular Robot configuration the axes of movement coincides with the joints of the human body indeed they are called waist, shoulder, elbow and wrist movements.

In order for a Robot to reach all sides of a component, its movements should include all six degrees of freedom. It is not necessary for the Robot to provide all six axes, as us usually three are provided by the end effector.

Industrial robots can take many physical forms and there is no absolute "best" configuration, the best will depend on the particular application as different configurations have different advantages which make them more suitable for certain tasks.

There are seven basic industrial robot design configurations:

Cartesian or Rectangular

Cylindrical

Polar or spherical

Scara

Revolute (or articulated) - Anthropomorphic

Robot Configuration

The Cartesian Configuration provides for three linear axis of movement at right angles to each other, in the Cartesian X, Y and Z space. It can also be called Rectangular Configuration as its working range sweeps a rectangular volume.

AdvantagesEasily programmed and controlled movementsGood accuracySimple control systemFast operationInherent stiff structureLarge payload capacityStructural simplicity, giving good reliability

ApplicationsApplications include areas where linear movements of high accuracy are demanded: manipulation of components (pick and place), milling, drawing machines, 3D printing where a pen or router translates across an x-y plane while a tool is raised and lowered onto a surface to create a precise design.

Cartesian or Rectangular Configuration

The Cylindrical configuration combines both vertical and horizontal linear movement, with rotary movement in the horizontal plane about the vertical axis.

AdvantagesEasily controlled and programmed movementsSimple control systemGood accuracyFast operationGood access to front and sidesStructural simplicity giving good reliability

ApplicationsApplications include small circular manufacturing cells or loading and unloading operations: assembly, handling at machine tools, spot welding and handling at die casting machines.

Cylindrical Configuration

This combines rotational movement in both the horizontal and vertical planes with a singular linear in/out movement of the arm. It is sometimes referred to as the gun Turret configuration.

AdvantagesEasily controlled and programmedmovements.Large payload capacity.Fast operation.Accuracy and repeatability at long reaches.

ApplicationsSuited to lifting and shifting operations and to reaching into horizontal and inclined tunnels.

Polar or Spherical Configuration

The term Scara stands for Selective Compliance Assembly Robot Arm.

It is a combination of the cylindrical and revolute configurations operating in the horizontal plane.

AdvantagesExtremely good maneuverability withinthe work area.Fast operation.High accuracyHigh payload in the vertical plane.

ApplicationsThe SCARA configuration was developed primarily for assembly tasks which require movement in the horizontal plane coupled with simple vertical movement for picking, placing and insertion operations.

Scara Configuration

The Revolute configuration comprises a number of rigid arms connected by rotary joints, rotary movement at the base is also provided. Since all movements are by angular rotation of the joints complex calculations are often needed to move the arm in straight lines.

AdvantagesExtremely good maneuverabilityAbility to reach over obstructionsEasy front, side, rear, and overhead access.Large reach for small floor area.Slim design, allows integration into restrictedworkspace.Fast movements due to rotary joints.Can traverse complex continuous paths.

ApplicationsSpot and arc welding, adhesive placing, assembly, painting, material handling, etc

These robots are also called anthropomorphic for their human arm similarity

Revolute (or Articulated) Configuration

These robots are also called anthropomorphic for their human arm similarity

Revolute (or Articulated) Configuration

Axes or Degrees of Movement – two axes are required to reach any point in a plane; three axes are required to reach any point in space. To fully control the orientation of the end of the arm three more axes are required. Some designs (e.g. the SCARA robot) trade limitations in motion possibilities for cost, speed, and accuracy.This term is often confused with Degrees of Freedom. The distinction is important as they relate to different aspects of the Robots capability. The term Degrees of Freedom relates to the locating or positioning of a body in space. Any body in space has six degrees of freedom. It can have linear movement along three mutually perpendicular axes and rotational movement about the same three axes. The three linear movements (Translational movements), allow the body to be moved to a desired position in space and the three rotational movements allow the body to be orientated about that position. In order for a Robot to reach all sides of a component, its movements should include all six degrees of freedom. It is not necessary for the Robot configuration to provide all six as us usually three are provided by the end effector.The term Axes of Movement relates to the number of axes in which the Robot may move. Working envelope – the region of space a robot can reach.Kinematics – the actual arrangement of rigid members and joints in the robot, which determines the robot's possible motions. Classes of robot kinematics include articulated, cartesian, parallel and SCARA.

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Carrying capacity or payload – how much weight a robot can lift.Speed – how fast the robot can position the end of its arm. This may be defined in terms of the angular or linear speed of each axis or as a compound speed i.e. the speed of the end of the arm when all axes are moving.Acceleration – how quickly an axis can accelerate. Since this is a limiting factor a robot may not be able to reach its specified maximum speed for movements over a short distance or a complex path requiring frequent changes of direction.Accuracy – how closely a robot can reach a commanded position. When the absolute position of the robot is measured and compared to the commanded position the error is a measure of accuracy. Accuracy can be improved with external sensing for example a vision system or Infra-Red. Accuracy can vary with speed and position within the working envelope and with payload.Repeatability – how well the robot will return to a programmed position. This is not the same as accuracy. It may be that when told to go to a certain X-Y-Z position that it gets only to within 1 mm of that position. This would be its accuracy which may be improved by calibration. But if that position is taught into controller memory and each time it is sent there it returns to within 0.1mm of the taught position then the repeatability will be within 0.1mm.

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Motion control – for some applications, such as simple pick-and-place assembly, the robot need merely return repeatably to a limited number of pre-taught positions. For more sophisticated applications, such as welding and finishing (spray painting), motion must be continuously controlled to follow a path in space, with controlled orientation and velocity.Power source – some robots use electric motors, others use hydraulic actuators. The former are faster, the latter are stronger and advantageous in applications (such as spray painting), where a spark could set off an explosion.Drive – some robots connect electric motors to the joints via gears; others connect the motor to the joint directly (direct drive). Using gears results in measurable 'backlash' which is free movement in an axis. Smaller robot arms frequently employ high speed, low torque DC motors, which generally require high gearing ratios; this has the disadvantage of backlash. Compliance - this is a measure of the amount in angle or distance that a robot axis will move when a force is applied to it. Because of compliance when a robot goes to a position carrying its maximum payload it will be at a position slightly lower than when it is carrying no payload. Compliance can also be responsible for overshoot when carrying high payloads in which case acceleration would need to be reduced.

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The mechanical structure of an industrial robot is made up of a sequence of link and joint combinations. The links are the rigid members connecting the joints. The joints (also called axes) are the movable components of the robot that cause relative motion between adjacent links. There are five principal types of mechanical joints used to construct the manipulator. Two of the joints are linear, in which the relative motion between adjacent links is translational, and three are rotary types, in which the relative motion involves rotation between links.

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The computer system that controls the manipulator must be programmed to teach the robot the particular motion sequence and other actions that must be performed in order to accomplish its task. There are several ways that industrial robots are programmed. Lead-through programming: The manipulator is driven through the various motions needed to perform a given task, recording the motions into the robot’s computer memory. This can be done either by physically moving (Lead-by-the-nose) the manipulator through the motion sequence [this technique is popular for tasks such as paint spraying] or by using a control box (Teach pendant) to drive the manipulator through the sequence.

A second method of programming involves the use of a programming language very much like a computer programming language. However, in addition to many of the capabilities of a computer programming language, the robot language also includes statements specifically designed for robot control:Motion-control commands are used to direct the robot to move its manipulator to some defined position in space. Input/output commands are employed to control the receipt of signals from sensors and other devices in the work cell and to initiate control signals to other pieces of equipment in the cell.

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Welding: the use of robots completely automate a welding process by both performing the weld and handling the part.

Applications of robots (Tasks)

Robot welding is commonly used for resistance spot welding and arc welding in high production applications, such as the automotive industry.

Painting/Coating: Robot painting produces top quality results. Once properly programmed, an industrial painting robot can apply material without leaving behind drips, inconsistencies, overspray, etc. Paint and/or coating is applied precisely and consistently.

Applications of robots (Tasks)

Robotic painters also protect workers. The painting application is a hazardous and taxing job. Workers can be exposed to unsafe VOCs (Volatile Organic Compounds), isocyanides and carcinogens.

Assembly: robots are used for lean industrial processes and have expanded production capabilities in the manufacturing world. An assembly line robot can increase production speed and consistency.

Applications of robots (Tasks)

Assembly robots also save workers from tedious and dull assembly line jobs.

Packaging: robots are extremely flexible, fast, precise and cost-efficient. With the right end of arm tooling, a robot can complete any packaging process.

Applications of robots (Tasks)

Vision technology, and software upgrades have also improved the abilities of packaging robots.

Palletizing: A palletizer or palletiser is a machine which provides automatic means for stacking cases of goods or products onto a pallet.Manually placing boxes on pallets can be time consuming and expensive; it can also put unusual stress on workers.

Applications of robots (Tasks)

Robotic palletizers have an end of arm tool (end effector) to grab the product from a conveyor or layer table and position it onto a pallet.

Pick and Place: Robotic pick and place automation speeds up the process of picking parts up and placing them in new locations, increasing production rates.

Applications of robots (Tasks)

The robots can be easily programmed and tooled to provide multiple applications.

Human and machine work hand in hand. The human operator controls and monitors production, the robots perform the physically strenuous work.

Human-robot collaboration (HRC)

The machine does not replace the human, but complements his capabilities and relieves him of arduous tasks.

In the short term history of robotics, a few key points have been observed about the integration of robots in the work place. The first point we will look at is rigid automation, which consists of a fixed path followed by an industrial robot. This kind of automation is still used in manufacturing lines where security devices are implanted or where heavy loads are transported in the robot working area. The security features are usually security cages and pressure sensors that can stop the robot if an impact is detected.

Human-robot collaboration (HRC)

In the past couple of years, collaborative robots have seen an incredible rise in the robotics market. These kinds of robots are used for applications that require humans working along with robots. They are mainly used for assembly tasks with low payloads. The security features of collaborative robots are highly sensitive pressure sensors that detect a human presence. Those robots are able to learn and to adapt their path to their environment. In brief, collaborative robots don’t need protective cages because they use different security devices and because of the low speed at which they function. This is key to future human-robot collaboration.

The next iteration in robotic security is the use of 3D cameras in the robot environment. This device allows the robot to not only be stopped when an impact is felt by the pressure sensor, but also prevents impact by anticipating the motion.

Robot Security 2.0

Laws of Robotics (I. Asimov - 1942)● A robot may not injure a human being

or, through inaction, allow a human being to come to harm.

● A robot must obey orders given to it by human beings, except where such orders would conflict with the First Law.

● A robot must protect its own existence as long as such protection does not conflict with the First or Second Law

Isaac Asimov è stato uno scrittore e biochimico sovietico naturalizzato statunitense. I Robot è una raccolta di suoi racconti di fantascienza; contiene 9 storie che hanno per protagonisti i robot positronici, macchine programmate per agire secondo le tre leggi della robotica. Le storie sono basate sul tema delle tre leggi della robotica, sulle loro contraddizioni e le loro apparenti falle. Le storie sono scritte in modo da essere ognuna indipendente dalle altre e hanno un tema che conduce all'interazione fra il genere umano, i robot e la morale.