robotics (vii semester, b.tech. mechatronics) prepared by: nehul j. thakkar asst. professor...
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ROBOTICSROBOTICS(VII Semester, B.Tech. Mechatronics)(VII Semester, B.Tech. Mechatronics)
Prepared By:Nehul J. ThakkarAsst. ProfessorU.V.Patel College of EngineeringGanpat University
Chapter 2: Fundamentals of Chapter 2: Fundamentals of Robot TechnologyRobot Technology
Robot Anatomy Robot Motions Work Volume Degree of Freedom (DOF) Robot Drive Systems Speed of Motions Load-carrying Capacity Control Systems Dynamic Performance Compliance End Effectors Sensors
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Robot AnatomyRobot Anatomy
The physical construction of the body, arm and wrist of the machine
The wrist is oriented in a variety of positions Relative movements between various components of body, arm
and wrist are provided by a series of joints Joints provide either sliding or rotating motions The assembly of body, arm and wrist is called “Manipulator”
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Robot Anatomy..Robot Anatomy..
Attached to the robot’s wrist is a hand which is called “end effector”
The body and arm joints position the end effector and wrist joints orient the end effector
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Robot Anatomy..Robot Anatomy..Robot Configurations Variety of sizes, shapes and physical configuration
1. Cartesian Coordinates Configuration2. Cylindrical Configuration3. Polar or Spherical Configuration4. Articulated or Jointed-arm Configuration5. Selective Compliance Assembly Robot Arm (SCARA) Configuration
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Robot Anatomy..Robot Anatomy..1. Cartesian Coordinate Configuration Uses three perpendicular slides to construct x , y and z axes X-axis represents right and left motions, Y-axis represents forward-backward
motions and Z-axis represents up-down motions Kinematic designation is PPP/LLL Other names are xyz robot or Rectilinear robot or Gantry robot Operate within a rectangular work volume
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Robot Anatomy..Robot Anatomy..1. Cartesian Coordinate Configuration..
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Robot Anatomy..Robot Anatomy..1. Cartesian Coordinate Configuration.. Advantages
Linear motion in three dimension Simple kinematic model Rigid structure Higher repeatability and accuracy High lift-carrying capacity as it doesn’t vary at different locations in work volume Easily visualize Can increase work volume easily Inexpensive pneumatic drive can be used for P&P operation
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Robot Anatomy..Robot Anatomy..1. Cartesian Coordinate Configuration.. Disadvantages
requires a large volume to operate in work space is smaller than robot volume unable to reach areas under objects must be covered from dust
Applications Assembly Palletizing and loading-unloading machine
tools, Handling Welding
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Robot Anatomy..Robot Anatomy..2. Cylindrical Configuration Use vertical column which rotates and a slide that can be moved up or down
along the column Arm is attached to slide which can be moved in and out Kinematic designation is RPP Operate within a cylinder work volume Work volume may be restricted at the back side
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Robot Anatomy..Robot Anatomy..2. Cylindrical Configuration..
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Robot Anatomy..Robot Anatomy..2. Cylindrical Configuration.. Advantages
Simple kinematic model Rigid structure & high lift-carrying capacity Easily visualize Very powerful when hydraulic drives used
Disadvantages Restricted work space Lower repeatability and accuracy Require more sophisticated control
Applications Palletizing, Loading and unloading Material transfer, foundry and forging
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Robot Anatomy..Robot Anatomy..3. Polar or Spherical Configuration Earliest machine configuration Has one linear motion and two rotary
motions First motion is a base rotation, Second
motion correspond to an elbow rotation and Third motion is radial or in-out motion
Kinematic designation is RRP Capability to move its arm within a
spherical space, hence known as ‘Spherical’ robot
Elbow rotation and arm reach limit the design of full spherical motion
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Robot Anatomy..Robot Anatomy..3. Polar or Spherical Configuration..
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Robot Anatomy..Robot Anatomy..3. Polar or Spherical Configuration.. Advantages
Covers a large volume Can bend down to pick objects up off the
floor Higher reach ability
Disadvantages Complex kinematic model Difficult to visualize
Applications Palletizing Handling of heavy loads e.g. casting,
forging
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Robot Anatomy..Robot Anatomy..4. Jointed Arm Configuration Similar to human arm Consists of two straight components like human forearm and upper arm,
mounted o a vertical pedestal Components are connected by two rotary joints corresponding to the shoulder
and elbow Kinematic designation is RRR Work volume is spherical
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Robot Anatomy..Robot Anatomy..4. Jointed Arm Configuration..
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Robot Anatomy..Robot Anatomy..4. Jointed Arm Configuration..
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Robot Anatomy..Robot Anatomy..4. Jointed Arm Configuration.. Advantages
Maximum flexibility Cover large space relative to work volume
objects up off the floor Suits electric motors Higher reach ability
Disadvantages Complex kinematic model Difficult to visualize Structure not rigid at full reach
Applications Spot welding, Arc welding
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Robot Anatomy..Robot Anatomy..5. SCARA Configuration Most common in assembly robot Arm consists of two horizontal revolute joints at the waist and elbow and a final
prismatic joint Can reach at any point within horizontal planar defined by two concentric circles Kinematic designation is RRP Work volume is cylindrical in nature Most assembly operations involve building up assembly by placing parts on top of a
partially complete assembly
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Robot Anatomy..Robot Anatomy..5. SCARA Configuration..
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Robot Anatomy..Robot Anatomy..5. SCARA Configuration..
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Robot Anatomy..Robot Anatomy..5. SCARA Configuration.. Advantages
Floor area is small compare to work area
Compliance Disadvantages
Rectilinear motion requires complex control of the revolute joints
Applications Assembly operations Inspection and measurements Transfer or components
April 21, 2023 Cont.23
Robot MotionsRobot Motions Industrial robots perform productive work To move body, arm and wrist through a series of motions and positions End effector is used to perform a specific task Robot’s movements divided into two categories:
1. Arm and body motions2. Wrist motions
Individual joint motions referred as ‘ DOF ’ Motions are accomplished by powered joints
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Robot Motions..Robot Motions.. Three joints are associated with the action of arm
and body Two or three used to actuate the wrist Rigid members are used to connect manipulator
joints are called links Input link is closest to the base Output link moves with respect to the input link
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Robot Motions..Robot Motions.. Joints involve relative motions of the adjoining links that may be linear
or rotational Linear joints involve a sliding or translational motion which can be
achieved by piston, telescopic mechanism May be called ‘Prismatic’ joint Represented as L or P joint Three types of rotating motion:
1. Rotational (R)2. Twisting (T)3. Revolving (V)
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Robot Motions..Robot Motions..
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Robot Motions..Robot Motions.. Physical configuration of the robot can be
described by a joint notation scheme Considering the arm and body first Starting with the joint closest to the base till
the joint connected to the wrist Examples are LLL, TLL, TRL, TRR, VVR Wrist joints can be included for notation From joint closest to the arm to the
mounting plate for the end effector have either T or R type
Examples are TRL : TRT, TRR : RT The scheme also provide that robot move
on a track or fixed to a platform Example TRL : TRT, L-TRL : TRT
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Robot Motions..Robot Motions..
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Robot Motions..Robot Motions..
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Robot Motions..Robot Motions..
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Robot Work VolumeRobot Work Volume The space within which the robot can
manipulate its wrist end different end effector might be
attached to wrist but not counted as part of the robot’s work space
Long end effector add to the extension of the robot compared to smaller end effector
End effector may not be capable of reaching certain points within the robot’s normal work volume
Larger volume costs more but can increase capabilities of robot
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Robot Work Volume..Robot Work Volume.. It depends upon following physical
characteristics: Robot’s configuration Size of the body, arm and wrist components Limits of the robot’s joint movements
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Robot Work Volume..Robot Work Volume..
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Robot Work Volume..Robot Work Volume..
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Degree of Freedom (DOF)Degree of Freedom (DOF)
Rotate Base of ArmPivot Base of ArmBend ElbowWrist Up and DownWrist Left and RightRotate Wrist
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Degree of Freedom..Degree of Freedom.. It is a joint , a place where it can
bend or rotate or translate Can identify by the number of
actuators on the arm Few DOF allowed for an application
because each degree requires motor, complicated algorithm and cost
Each configurations discussed before utilizes three DOF in the arm and the body
Three DOF located in the wrist give the end effector all the flexibility
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Degree of Freedom..Degree of Freedom.. A total 6 DOF is needed to locate a
robot’s hand at any point in its work space
The arm and body joints move end effector to a desired position within the limits of robot’s size and joint movements
Polar, cylindrical and jointed arm configuration consist 3 DOF with the arm and body motions are:
1. Rotational traverse: Rotation of the arm about vertical axis such as left-and-right swivel of the robot arm about a base
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Degree of Freedom..Degree of Freedom..
2. Radial traverse: Involve the extension and retraction (in or out movement) of the arm relative to the base
3. Vertical traverse: Provide up-and-down motion of the arm
For a Cartesian coordinate robot, 3 DOF are vertical movement (z-axis motion), in-and-out movement (y-axis motion), and right-and-left movement (x-axis motion) which are achieved by slides of the robot arm
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Degree of Freedom..Degree of Freedom..
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Degree of Freedom..Degree of Freedom.. Wrist movement enable the robot to
orient the end effector properly to perform a task
Provided with up to 3 DOF which are:
1. Wrist Pitch/Bend: Provide up-and-down rotation to the wrist
2. Wrist Yaw: Involve right-and-left rotation of the wrist
3. Wrist Roll/Swivel: Is the rotation of the wrist about the arm axis
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Degree of Freedom..Degree of Freedom..
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Degree of Freedom..Degree of Freedom..
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Drive SystemsDrive Systems Capacity to move robot’s body, arm
and wrist Determine speed of the arm
movements, strength of the robot & dynamic performance
Type of applications that the robot can accomplish
Powered by three types of drive systems:1. Hydraulic2. Pneumatic 3. Electric
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Drive Systems..Drive Systems..
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Drive Systems..Drive Systems..1. Hydraulic Drive
Associated with large robot Provide greater speed & strength Add floor space Leakage of oil Provide either rotational or linear
motions Applications such as:
• Spray coating robot• Heavy part loading robot• Material handling robot• Translatory motions in cartesian robot• Gripper mechanism
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Drive Systems..Drive Systems..1. Hydraulic Drive..
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Drive Systems..Drive Systems..1. Hydraulic Drive..
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Drive Systems..Drive Systems..2. Pneumatic Drive
Reserved for smaller robot Limited to “pick-and-place” operations
with fast cycles Drift under load as air is compressible Provide either rotational or linear
motions Simple and low cost components Used to open and close gripper
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Drive Systems..Drive Systems..
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Drive Systems..Drive Systems..3. Electric Drive
Rotor, stator, brush and commutator assembly
Rotor has got windings of armature and stator has got magnets
The brush and the commutator assembly switch the current in armature windings
The most commonly used are DC servomotors, AC servomotors and stepper motors
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Drive Systems..Drive Systems..3. Electric Drive..
ServomotorApril 21, 2023 Cont.52
Drive Systems..Drive Systems..3. Electric Drive..
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Drive Systems..Drive Systems..3. Electric Drive..
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Speed of MotionSpeed of Motion Speed determines how quickly the
robot can accomplish a given work cycle
Desirable in production to minimize cycle time
Industrial robot speed range up to a maximum of 1.7 m/s
Speed would be measured at wrist Highest speed can be obtained by
large robot with fully extended arm
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Speed of Motion..Speed of Motion.. Most desirable speed depends on factors:
Accuracy Weight of the object Distance
Inverse relation between the accuracy and the speed
Heavier objects must be handled more slowly
Capable of traveling one long distance in less time than a sequence short distances whose sum is equal to the long distance
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Speed of Motion..Speed of Motion.. Short distance may not permit for
programmed operating speed
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Load-Carrying CapacityLoad-Carrying Capacity It depends upon size, configuration,
construction and drive system Robot arm must be in its weakest
position to calculate load-carrying capacity
In polar, cylindrical and jointed-arm, the robot arm is at maximum extension
Ranges from less than a pond to several thousand pounds
Gross weight include the weight of the end effector
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Control SystemsControl Systems Controlling drive system to properly
regulate its motions Four categories according to control
systems1. Limited-sequence robot2. Playback robots with PTP control3. Playback robots with continuous path control4. Intelligent robot
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Speed of Response & Speed of Response & StabilityStability The speed of response refers to the
capability of the robot to move to the next position in a short amount of time
Stability is defined as a measure of the oscillations which occur in the arm during movement from one position to the next
Good stability exhibit little or no oscillation and poor stability indicated by a large amount of stability
Damping control stability but reduces the speed of response
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Speed of Response & Speed of Response & Stability..Stability..
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Spatial ResolutionSpatial Resolution
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Spatial Resolution..Spatial Resolution.. Defined as smallest increment of
movement into which the robot can divide its work volume
Depends on two factors: system’s control resolution and the robot’s mechanical inaccuracies
Control resolution is determined by robot’s position control system and its feedback measurement system
Ability to divide total range of movement for the particular joint into individual increments that can be addressed in the controllerApril 21, 2023 Cont.63
Spatial Resolution..Spatial Resolution.. Joint range depends on the bit storage
capacity in the control memory Number of increments for a axis is given by Number of Increments = 2n
Have a control resolution for each joint in case of several DOF
Resolution for each joint to be summed vectorially
Total control resolution depend on the wrist motions as well as the body and arm motions
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Spatial Resolution..Spatial Resolution.. Mechanical inaccuracies come from
elastic deflection in the structure elements, gear backlash, stretching of pulley cords, leakage of hydraulic fluids and other imperfections in the mechanical system
Also affected by load being handled, the speed of arm moving, condition of maintenance of robot
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AccuracyAccuracy Ability to position its wrist end at a
desired target point within the work volume
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Accuracy..Accuracy.. Depends on spatial resolution means
how closely the robot can define the control increments
Lie in the middle between two adjacent control increments
One half of the control resolution
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Accuracy..Accuracy.. Depends on spatial resolution means how closely
the robot can define the control increments Lie in the middle between two adjacent control
increments One half of the control resolution Same anywhere in work volume It may be changed in work volume due to
mechanical inaccuracies
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Accuracy..Accuracy.. Affected by many factors
Mechanical inaccuracies Work range Weight
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RepeatabilityRepeatability Ability to position its wrist at a point in space that
had been taught Accuracy relates to its capacity to be programmed
to achieve a given target point Programmed point and target point may be different
due to limitations of resolution Repeatability refers to ability to return to the
programmed point when commanded to do so
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Repeatability..Repeatability..
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ComplianceCompliance Displacement of the wrist end in response to a force or a torque
exerted against it High compliance means that wrist is displaced a large amount
by small force known as ‘Springy’ Reduce the robot precision of movement under load Directional feature Reaction force of the part may cause deflection to the
manipulator
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Thank YouThank You
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