ROBOTICS (VII Semester, B.Tech. Mechatronics)

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ROBOTICS(VII Semester, B.Tech.
Mechatronics)

• Prepared By
• Nehul J. Thakkar
• Asst. Professor
• U.V.Patel College of Engineering
• Ganpat University

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Chapter 2 Fundamentals of Robot 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 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..

• Attached to the robots 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 Configurations
• Variety of sizes, shapes and physical
  configuration
• Cartesian Coordinates Configuration
• Cylindrical Configuration
• Polar or Spherical Configuration
• Articulated or Jointed-arm Configuration
• Selective Compliance Assembly Robot Arm (SCARA)
  Configuration

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Robot Anatomy..

• 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..

• Cartesian Coordinate Configuration..

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Robot Anatomy..

• Cartesian Coordinate Configuration..
• Advantages
• Linear motion in three dimension
• Simple kinematic model
• Rigid structure
• Higher repeatability and accuracy
• High lift-carrying capacity as it doesnt vary at
  different locations in work volume
• Easily visualize
• Can increase work volume easily
• Inexpensive pneumatic drive can be used for PP
  operation

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Robot Anatomy..

• 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..

• 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..

• Cylindrical Configuration..

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Robot Anatomy..

• 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..

• 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..

• Polar or Spherical Configuration..

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Robot Anatomy..

• 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..

• 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..

• Jointed Arm Configuration..

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Robot Anatomy..

• Jointed Arm Configuration..

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Robot Anatomy..

• 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..

• 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..

• SCARA Configuration..

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Robot Anatomy..

• SCARA Configuration..

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Robot Anatomy..

• 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

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Robot 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
• Robots movements divided into two categories
• Arm and body motions
• Wrist motions
• Individual joint motions referred as DOF
• Motions are accomplished by powered joints

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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..

• 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
• Rotational (R)
• Twisting (T)
• Revolving (V)

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Robot Motions..
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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..
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Robot Motions..
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Robot Motions..
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Robot 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 robots 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 robots normal work
  volume
• Larger volume costs more but can increase
  capabilities of robot

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Robot Work Volume..

• It depends upon following physical
  characteristics
• Robots configuration
• Size of the body, arm and wrist components
• Limits of the robots joint movements

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Robot Work Volume..
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Robot Work Volume..
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Degree of Freedom (DOF)

• Rotate Base of Arm
• Pivot Base of Arm
• Bend Elbow
• Wrist Up and Down
• Wrist Left and Right
• Rotate Wrist
  
  

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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..

• A total 6 DOF is needed to locate a robots hand
  at any point in its work space
• The arm and body joints move end effector to a
  desired position within the limits of robots
  size and joint movements
• Polar, cylindrical and jointed arm configuration
  consist 3 DOF with the arm and body motions are
• 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..

• Radial traverse Involve the extension and
  retraction (in or out movement) of the arm
  relative to the base
• 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..
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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
• Wrist Pitch/Bend Provide up-and-down rotation to
  the wrist
• Wrist Yaw Involve right-and-left rotation of the
  wrist
• Wrist Roll/Swivel Is the rotation of the wrist
  about the arm axis

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Degree of Freedom..
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Degree of Freedom..
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Drive Systems

• Capacity to move robots 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
• Hydraulic
• Pneumatic
• Electric

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Drive Systems..
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Drive Systems..

• 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..

• Hydraulic Drive..

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Drive Systems..

• Hydraulic Drive..

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Drive Systems..

• 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..
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Drive Systems..

• 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..

• Electric Drive..
• Servomotor

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Drive Systems..

• Electric Drive..

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Drive Systems..

• Electric Drive..

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Speed 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..

• 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..

• Short distance may not permit for programmed
  operating speed

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Load-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 Systems

• Controlling drive system to properly regulate its
  motions
• Four categories according to control systems
• Limited-sequence robot
• Playback robots with PTP control
• Playback robots with continuous path control
• Intelligent robot

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Speed of Response Stability

• 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 Stability..
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Spatial Resolution
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Spatial Resolution..

• Defined as smallest increment of movement into
  which the robot can divide its work volume
• Depends on two factors systems control
  resolution and the robots mechanical
  inaccuracies
• Control resolution is determined by robots
  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 controller

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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..

• 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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Accuracy

• Ability to position its wrist end at a desired
  target point within the work volume

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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..

• 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..

• Affected by many factors
• Mechanical inaccuracies
• Work range
• Weight

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Repeatability

• 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..

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Compliance

• 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 You