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ROBOTICS: ROBOT MORPHOLOGY

ROBOTICS: ROBOT MORPHOLOGY. Josep Amat and Alícia Casals Automatic Control and Computer Engineering Department . Components of a Robot. External Sensors. Environment. Programming. Net. Internal Sensors. Control Unit. Actuators. Mechanical Structure. User.

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ROBOTICS: ROBOT MORPHOLOGY

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  1. ROBOTICS: ROBOT MORPHOLOGY Josep Amat and Alícia Casals Automatic Control and Computer Engineering Department

  2. Components of a Robot External Sensors Environment Programming Net Internal Sensors Control Unit Actuators Mechanical Structure User

  3. Chapter 2. Robot Morphology Basic characteristics: - Kinematics chain - Degree of freedom - Maneuvering degree - Architecture - Precision - Working space - Accessibility - Payload

  4. Degrees of freedom Degrees of freedom correspond to the number of actuators that produce different robot movements D o F A joint adds a degree of freedom to the manipulator structure, if it offers a new movement to the end effector that can not be produced by any other joint or a combination of them.

  5. P z Reference frame origin x y Degrees of freedom Positioning Positioning the end effector in the 3D space, requires three DoF, either obtained from rotations or displacements.

  6. roll tilt P pan z Reference frame origin x y Degrees of freedom Orientation Orienting the end effector in the 3D space, requires three additional DoF to produce the three rotations.

  7. Chapter 2. Robot Morphology Basic characteristics: - Kinematics chain - Degree of freedom - Maneuvering degree - Architecture - Precision - Working space - Accessibility - Payload

  8. Maneuvering degree Maneuvering degree is the number of actuators that although producing new movements do not contribute to new degrees of freedom.

  9. Degrees of maneuverability (redundant) Multiple access (with redundant DoF) Forced access (without redundancy)

  10. Chapter 2. Robot Morphology Basic characteristics: - Kinematics chain - Degree of freedom - Maneuvering degree - Architecture - Precision - Working space - Accessibility - Payload

  11. Robot architecture Robot architecture is the combination and disposition of the different kind of joints that configure the robot kinematical chain.

  12. Mechanical Structure Kinematics chain: Sequence of rigid elements linked through active joints in order to perform a task efficiently Closed (Parallel): Open:

  13. Nomenclature: Elbow Arm Wrist Shoulder Trunk Base

  14. Characteristics derived from the mechanical structure: • Degrees of freedom • Work Space • Accessibility • Payload • Precision

  15. Characteristics derived from the mechanical structure: • Degrees of freedom Tridimensional positioning: (x,y,z ) Minimum: 3 Degrees of freedom

  16. Characteristics derived from the mechanical structure: q   • Degrees of freedom Positioning + orientation: (x,y,z,,,q ) Minimum: 3 + 3 Degrees of freedom Architecture: Configuration and kind of articulations of the kinematical chain that determine the working volume and accessibility

  17. Kind of possible joints: In red, those usually used in robotics as they can be motorized without problems

  18. Basic characteristics. Definitions • Degrees of freedom: • Number of complementary movements. • Movement capability: • Working volume, Accessibility and Maneuvering • Movement precision: • Resolution, Repetitiveness, Precision and Compliance • Dynamical characteristics: • Payload, Speed and Stability

  19. ey Coordinates of the target ex Movement precision • Precision (Accuracy) • Capacity to place the end effector into a given position and orientation (pose) within the robot working volume, from a random initial position. • e increases with the distance to the robot axis. • Precision depends on: • Mechanical play (backlash) • Sensors offset • Sensors resolution • Misalignments in the position and size of rigid elements, specially the end-effector E.E. Points reached in different tests

  20. ey Coordinates of the target ex e offset Movement precision • Precision (Accuracy) • Capacity to place the end effector into a given position and orientation (pose) within the robot working volume, from a random initial position. • e increases with the distance • to the robot axis. Precision + R

  21. ey Coordinates of the target ex Movement precision • Repetitiveness • Capacity to place the end effector into a given position and orientation (pose) within the robot working volume, from a given initial position. Repetitiveness error • Repetitiveness depends on: • Mechanical play (backlash) • Target position • Speed and direction when reaching the target Precision + R

  22. Movement precision (Statics) • Resolution: • Minimal displacement the EE can achieve and / or the control unit can measure. • Determined by mechanical joints and the number of bits of the sensors tied to the robot joints. • Error resolution of the sensor = Measurement Rank / 2n

  23. Joint 1 Joint 2 Joint 3 Joint 4 Joint 5 Joint 6 Examples of Joints (movements between articulated bodies) Mechanical Structure Joint 1 Joint 4 Joint 3 Joint 5 Joint 2

  24. Example of a section of a working volume

  25. Architectures Architecture: Configuration and kind of articulations of the kinematical chain that determine the working volume and accessibility Classical Architectures: Cartesian Cylindrical Polar Angular

  26. Classical Architectures Cartesian Work Space (D+D+D)

  27. Classical Architectures Example of a Cartesian Work Space Robot (D+D+D)

  28. Classical Architectures Cylindrical Work Space (R+D+D)

  29. Classical Architectures Example of a Cylindrical Work Space Robot (R+D+D)

  30. Classical Architectures Polar Work Space (R+R+D)

  31. Classical Architectures Example of a Polar Work Space Robot (R+R+D)

  32. Classical Architectures Angular Work Space (R+R+D)

  33. Classical Architectures Angular Work Space (R+R+R)

  34. Classical Architectures Example of Angular Work Space Robots (R+R+R)

  35. Working space of a robot with angular joints

  36. Inverted robot: Increase the useful working volume

  37. Architecture “SCARA” Architecture R-R-D with cylindrical coordinates ( SCARA: Selective Compliance Assembly Robotic Arm )

  38. SCARA Robot : examples

  39. · constant resolution Drawbacks: · requires a large working volume · the working volume is smaller than the robot volume (crane structure) · requires free area between the robot and the object to manipulate · guides protection Resume Cartesian Robot Characteristics Robot Joints Observations Cartesian 1a. Linear: X Advantages: : 2a. · Linear: Y linear movement in three dimensions · simple kinematical model Linear: Z 3a. · rigid structure · easy to display · possibility of using pneumatic actuators, which are cheap, in pick&place operations

  40. Resume Cylindrical Robot Characteristics Robot Joints Observations Cylindrical 1a. Rotation: q Advantages: simple kinematical model 2a. · Linear: Z · easy to display Linear: r 3a. · good accessibility to cavities and open machines · large forces when using hydraulic actuators Drawbacks: · restricted working volume · requires guides protection (linear) · the back side can surpass the working volume

  41. Resume Polar Robot Characteristics Robot Joints Observations Polar 1a. Rotation: q Advantages: 2a. Rotation: j · large reach from a central support 3a. Linear: r · It can bend to reach objects on the floor · motors 1 and 2 close to the base Drawbacks: · complex kinematics model · difficult to visualize

  42. q 1 q 2 q 3 Resume Angular Robot Characteristics Robot Joints Observations Angular 1a. rotation : Advantages: 2a. rotation · maximum flexibility · large working volume with respect to the robot size 3a. rotation · joints easy to protect (angular) · can reach the upper and lower side of an object Drawbacks: · complex kinematical model · difficult to display · linear movements are difficult · no rigid structure when stretched

  43. SCARA 1a. rotation 2a. rotation 3a. rotation q 2 q 3 Resume SCARA Robot Characteristics Observations Robot Joints : q Advantages: 1 • high speed and precision Drawbacks: • only vertical access

  44. Dynamic Characteristics • Payload: • The load (in Kg) the robot is able to transport in a continuous and precise way (stable) to the most distance point • The values usually used are the maximum load and nominal at acceleration = 0 • The load of the End-Effector is not included. Example of Map of admitted loads, in function of the distance to the main axis

  45. speed Vmax Long movement Short movements time Dynamic Characteristics • Velocity • Maximum speed (mm/sec.) to which the robot can move the End-Effector. • It has to be considered that more than a joint is involved. • If a joint is slow, all the movements in which it takes part will be slowed down. • For shorts movements it can be more interesting the measure of acceleration.

  46. Architectures - Classical Architectures: Cartesian Cylindrical Polar Angular - Special configurations

  47. Special Configurations. Pendulum Robot GGD

  48. Example of a Pendulum Robot RRD

  49. Special Configurations. Elephant Trunk Classical Degrees of freedom Concatenated Degrees of freedom (elephant trunk)

  50. Special Configurations. Elephant Trunk Classical Degrees of freedom Concatenated Degrees of freedom (elephant trunk)

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