embedded systems & Robotics training with project for final year b tech students

TECNOCRATS INFOTECH @ 9540854414

Definition:

Alternate definition:

“A robot is a one-armed, blind idiot with limited memory and which cannot speak, see, or hear.”


Ideal TasksTasks which are: Dangerous

Space exploration chemical spill cleanup disarming bombs disaster cleanup

Boring and/or repetitive Welding car frames part pick and place manufacturing parts.

High precision or high speed Electronics testing Surgery precision machining.


Automation vs. robotsAutomation –Machinery designed to carry out a specific taskBottling machineDishwasherPaint sprayer

Robots – machinery designed to carry out a variety of tasks

Pick and place armsMobile robotsComputer Numerical Control machines


Types of robotsPick and place

Moves items between points

Continuous path controlMoves along a programmable path

SensoryEmploys sensors for feedback


Pick and Place Moves items from one point to

another

Does not need to follow a specific path between points

Uses include loading and unloading machines, placing components on circuit boards, and moving parts off conveyor belts.


Continuous path control

Moves along a specific path

Uses include welding, cutting, machining parts.


SensoryUses sensors for feedback.

Closed-loop robots use sensors in conjunction with actuators to gain higher accuracy – servo motors.

Uses include mobile robotics, telepresence, search and rescue, pick and place with machine vision.


Measures of performance

Working volume The space within which the robot operates. Larger volume costs more but can increase the

capabilities of a robot

Speed and acceleration Faster speed often reduces resolution or

increases cost Varies depending on position, load. Speed can be limited by the task the robot

performs (welding, cutting)

Resolution Often a speed tradeoff The smallest step the robot can take


• Accuracy

–The difference between the actual position of the robot and the programmed position

• Repeatability

Will the robot always return to the same point under the same control conditions?

Increased cost

Varies depending on position, load

Performance (cont.)


Control

•Open loop, i.e., no feedback, deterministic

•Closed loop, i.e., feedback, maybe a sense of

touch and/or vision


Kinematics and dynamicsDegrees of freedom—number of independent motions

Translation--3 independent directionsRotation-- 3 independent axes2D motion = 3 degrees of freedom: 2

translation, 1 rotation3D motion = 6 degrees of freedom: 3

translation, 3 rotation


Kinematics and dynamics (cont.)Actions

Simple joints prismatic—sliding joint, e.g., square cylinder in square

tube revolute—hinge joint

Compound joints ball and socket = 3 revolute joints round cylinder in tube = 1 prismatic, 1 revolute

MobilityWheelsmultipedal (multi-legged with a sequence of actions)


Kinematics and dynamics (cont.)

Work areasrectangular (x,y,z)cylindrical (r,,z)spherical (r,,)

Coordinates

World coordinate frameEnd effector frame How to get from coordinate system x” to

x’ to x

x

x''

x'


TransformationsGeneral coordinate transformation from x’ to x

is x = Bx’ + p , where B is a rotation matrix and p is a translation vector

More conveniently, one can create an augmented matrix

which allows the above equation to be expressed as x = A x’.

Coordinate transformations of multilink systems are represented as

x0 = A01 A12A23. . .A(n-1)(n)xn


DynamicsVelocity, acceleration of end actuator

power transmissionactuator

solenoid –two positions , e.g., in, out motor+gears, belts, screws, levers—continuum of

positions stepper motor—range of positions in discrete

increments


A 2-D “binary” robot segment Example of a 2D robotic link having

three solenoids to determine geometry. All members are linked by pin joints; members A,B,C have two states—in, out—controlled by in-line solenoids. Note that the geometry of such a link can be represented in terms of three binary digits corresponding to the states of A,B,C, e.g., 010 represents A,C in, B out. Links can be chained together and controlled by sets of three bit codes.

A CB A CB A CB A CB

A CB A CBA CB A CB


ProblemsJoint play, compounded through N joints

Accelerating masses produce vibration, elastic deformations in links

Torques, stresses transmitted depending on end actuator loads


Control and programming Position of end actuator

multiple solutions

Trajectory of end actuator: how to get from point A to Bprogramming for coordinated motion of each linkproblem—sometimes no closed-form solution


Control and programming (cont.)Example: end actuator (tip) problem with no closed

solution.Two-segment arm with arm lengths L1 = L2, and stepper -motor control of angles 1 and 2.

Problem: control 1 and 2 such that arm tip traverses its range at constant height y, or with no more variation than y.Geometry is easy: position of arm tipx = L1 (cos 1 + cos 2)y = L1 (sin 1 + sin 2)

1

2

L1

L2

y


Control and programming (cont.)Arm tip moves by changing 1 and 2 as a function of

time.Therefore

So, as 1 and 2 are changed, x and y are affected.

To satisfy y = constant, we must have

. So the rates at which 1 and 2 are changed depend on the values of 1 and 2.

)sin(sin 22111 Lx

0)cos(cos 22111 Ly

2

112 cos

cos


Control and programming (cont.)There is no closed-form solution to this problem. One must use approximations, and accept some minor variations in y. Moving the arm tip through its maximum range of x might have to be accomplished through a sequence of program steps that define different rates of changing 1 and 2.

Possible approaches: Program the rates of change of 1 and 2 for y = const. for

initial values of 1 and 2 . When arm tip exceeds y, reprogram for new values of 1 and 2.

Program the rates of change of 1 and 2 at the initial point and at some other point for y = const. Take the average of these two rates, and hope that y is not exceeded. If it is exceeded, reprogram for a shorter distance. Continue program segments until the arm tip has traversed its range.


Control and programming (cont.)Program the rates of change of 1 and 2 at the initial point

and at some other point for y = const. Take the average of these two rates, and hope that y is not exceeded. If it is exceeded, reprogram for a shorter distance. Continue program segments until the arm tip has traversed its range.

The rate of change of 1 and 2 can be changed in a programming segment, i.e., the rates of change need not be uniform over time. This programming strategy incorporates approaches 1) and 2). Start with rates of change for the initial values of 1 and 2 , then add an acceleration component so that y = const. will also be satisfied at a distant position.


Feedback control

Rotation encodersCamerasPressure sensorsTemperature

sensorsLimit switchesOptical sensorsSonar


New directions

• Haptics--tactile sensing

• Other kinematic mechanisms,

e.g. snake motion

• Robots that can learn


Technology

embedded systems & Robotics training with project for final year b tech students