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FUNDAMENTALS OF ROBOTICS��Module 2���- Dr. Adithya Hegde�Assistant Professor�Department of Robotics and AI, MITE, Moodabidre

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About the course – Module 2

Module 2 – Robot Anatomy and Motion Analysis (8 Hrs.)

  • Robot configurations: polar, cylindrical, Cartesian, and jointed arm configurations
  • Robot links and joints
  • Degrees of freedom
  • Types of movements: vertical, radial and rotational traverse, roll, pitch and yaw
  • Work volume
  • Robot kinematics: direct and inverse kinematics
  • Transformations and rotation matrix.

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Robot Anatomy

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Robot Anatomy

  • Manipulator consists of joints and links
    • Joints provide relative motion
    • Links are rigid members between joints
    • Various joint types: linear and rotary
    • Each joint provides a “degree-of-freedom”
    • Most robots possess five or six degrees-of-freedom
  • Robot manipulator consists of two sections:
    • Body-and-arm – for positioning of objects in the robot's work volume
    • Wrist assembly – for orientation of objects

Base

Link0

Joint1

Link2

Link3

Joint3

End of Arm

Link1

Joint2

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Manipulator Joints

  • Translational motion
    • Linear joint (type L)
    • Orthogonal joint (type O)

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  • Rotary motion
    • Rotational joint (type R)
    • Twisting joint (type T)
    • Revolving joint (type V)

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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 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:
      • 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..

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      • 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
  1. 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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  • Robots: Axis and Orientation of Movement - Pitch, Roll, Yaw
  • https://www.youtube.com/watch?v=EjvdpkX9fD8

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Degree of Freedom..

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Degree of Freedom..

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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..

  1. Cartesian Coordinate Configuration
  2. Uses three perpendicular slides to construct x , y and z axes
  3. X-axis represents right and left motions, Y-axis represents forward-backward motions and Z-axis represents up-down motions
  4. Kinematic designation is PPP/LLL
  5. Other names are xyz robot or Rectilinear robot or Gantry robot
  6. Operate within a rectangular work volume

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Robot Anatomy..

  1. Cartesian Coordinate Configuration..

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Robot Anatomy..

  1. Cartesian Coordinate Configuration..
  2. 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..

  1. Cartesian Coordinate Configuration..
  2. 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

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  • Applications
      • Assembly
      • Palletizing and loading-unloading machine tools,
      • Handling
      • Welding

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Robot Anatomy..

  1. Cylindrical Configuration..

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Robot Anatomy..

  1. Cylindrical Configuration..
  2. Advantages
      • Simple kinematic model
      • Rigid structure & high lift-carrying capacity
      • Easily visualize
      • Very powerful when hydraulic drives used
  3. Disadvantages
      • Restricted work space
      • Lower repeatability and accuracy
      • Require more sophisticated control
  4. Applications
      • Palletizing, Loading and unloading
      • Material transfer, foundry and forging

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  1. Polar or Spherical Configuration
  2. Earliest machine configuration
  3. Has one linear motion and two rotary motions
  4. First motion is a base rotation, Second motion correspond to an elbow rotation and Third motion is radial or in-out motion
  5. Kinematic designation is RRP
  6. Capability to move its arm within a spherical space, hence known as ‘Spherical’ robot
  7. Elbow rotation and arm reach limit the design of full spherical motion

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    • Polar or Spherical Configuration..

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Robot Anatomy..

  1. Polar or Spherical Configuration..
  2. Advantages
      • Covers a large volume
      • Can bend down to pick objects up off the floor
      • Higher reach ability
  3. Disadvantages
      • Complex kinematic model
      • Difficult to visualize
  4. Applications
      • Palletizing
      • Handling of heavy loads e.g. casting, forging

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  1. Jointed Arm Configuration
  2. Similar to human arm
  3. Consists of two straight components like human forearm and upper arm, mounted o a vertical pedestal
  4. Components are connected by two rotary joints corresponding to the shoulder and elbow
  5. Kinematic designation is RRR
  6. Work volume is spherical

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Robot Anatomy..

    • Jointed Arm Configuration..

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Robot Anatomy..

  1. Jointed Arm Configuration..
  2. Advantages
      • Maximum flexibility
      • Cover large space relative to work volume objects up off the floor
      • Suits electric motors
      • Higher reach ability
  3. Disadvantages
      • Complex kinematic model
      • Difficult to visualize
      • Structure not rigid at full reach
  4. Applications
      • Spot welding, Arc welding

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  1. SCARA Configuration
  2. Most common in assembly robot
  3. Arm consists of two horizontal revolute joints at the waist and elbow and a final prismatic joint
  4. Can reach at any point within horizontal planar defined by two concentric circles
  5. Kinematic designation is RRP
  6. Work volume is cylindrical in nature
  7. 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..

  1. SCARA Configuration..
  2. Advantages
      • Floor area is small compare to work area
      • Compliance
  3. Disadvantages
      • Rectilinear motion requires complex control of the revolute joints
  4. Applications
      • Assembly operations
      • Inspection and measurements
      • Transfer or components

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Work Envelope

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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 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..

  • 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..

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Robot Work Volume..

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Spatial resolution

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Robot Reach

  • Robot reach is the distance from the center of the robot to the fullest extension of the robotic arm.
  • This measurement determines the robot's work envelope.

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  • Pay load = End effector wt (or tooling wt.) + Part wt.

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End of Module 2

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