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Definition:
Alternate definition:
“A robot is a one-armed, blind idiot with limited memory and which cannot speak, see, or hear.”
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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.
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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
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Types of robotsPick and place
Moves items between points
Continuous path controlMoves along a programmable path
SensoryEmploys sensors for feedback
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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.
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Continuous path control
Moves along a specific path
Uses include welding, cutting, machining parts.
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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.
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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
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• 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.)
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Control
•Open loop, i.e., no feedback, deterministic
•Closed loop, i.e., feedback, maybe a sense of
touch and/or vision
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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
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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)
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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'
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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)xnwww.technogroovy.com , 07500347448 ,07533940322
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
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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
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ProblemsJoint play, compounded through N joints
Accelerating masses produce vibration, elastic deformations in links
Torques, stresses transmitted depending on end actuator loads
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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
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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
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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
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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.
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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.
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Feedback control
Rotation encodersCamerasPressure sensorsTemperature
sensorsLimit switchesOptical sensorsSonar
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New directions
• Haptics--tactile sensing
• Other kinematic mechanisms,
e.g. snake motion
• Robots that can learn
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