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

2. User Components of a Robot Environment Net External Sensors
Control Unit
Programming
External
Sensors
Environment
Internal
Actuators
Mechanical Structure
Net
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. Reference frame origin
Degrees of freedom
Positioning x y z P
Reference frame origin
Positioning the end effector in the 3D space, requires three DoF, either obtained from rotations or displacements.

6. Reference frame origin
Degrees of freedom
Orientation x y z P
Reference frame origin
roll
pan
tilt
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. Positioning + orientation: (x,y,z,,,q )
Characteristics derived from the mechanical structure:
Degrees of freedom   q
Positioning + orientation: (x,y,z,,,q )
Minimum: 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 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. ex ey
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.
Coordinates
of the target
Points reached in different tests

20. ey ex Movement precision e increases with the distance
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. ex ey
Coordinates
of the target
e offset
Precision + R

21. ey 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 ex ey
Repetitiveness depends on:
Mechanical play (backlash)
Target position
Speed and direction when reaching the target
Coordinates
of 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. Mechanical Structure
Examples of Joints (movements between articulated bodies)
Joint 1
Joint 2
Joint 5
Joint 3
Joint 4
Joint 6
Joint 1
Joint 4
Joint 3
Joint 5
Joint 2

24. Example of a section of a working volume

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

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

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

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

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

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

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

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

33. Angular Work Space (R+R+R)
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 R-R-D with cylindrical coordinates
Architecture “SCARA”
Architecture R-R-D with cylindrical coordinates
( SCARA: Selective Compliance Assembly Robotic Arm )

38. SCARA Robot :
examples

39. Resume Cartesian Robot Characteristics
Joints
Observations
Cartesian
1a.
Linear: X
Advantages: :
2a.
Linear: Y
linear movement in three dimensions
simple kinematical model
3a.
Linear: Z
rigid structure
easy to display
possibility of using pneumatic actuators,
which are cheap, in pick&place
operations
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

40. Resume Cylindrical Robot Characteristics
Joints
Observations
Cylindrical
1a.
Rotation: q
Advantages:
2a.
Linear: Z
simple kinematical model
easy to display
3a.
Linear: r
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
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. Resume Angular Robot Characteristics
Joints
Observations
Angular
1a.
rotation q 1 2 3 :
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. Resume SCARA Robot Characteristics
Joints
Observations
SCARA
1a.
rotation
2a.
3a. q : 1
Advantages: q 2
high speed and precision q 3
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. 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.
Vmax
time
speed
Short movements
Long movement

46. - 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)

51. Special Configurations. Elephant Trunk
Increase of accessibility

52. Special Configurations. Elephant Trunk
Distributed Degrees of Freedom.

53. Elephant Trunk Examples Applications

54. Special Configurations. Stewart Platform
6 Displacements  6 DoF.
+ X,
+ Y,
+ Z
+ j,
+ f,
+ q
Special Configurations. Stewart Platform

55. Platform “Stewart” Example
Workspace

56. Example of
“Stewart” Robot

57. D Robots
6 Rotations  6 DoF.

58. Movement capabilities
1. Working volume (Workspace):
Set of positions reachable by the robot end-effector.
Shape is more important than the volume (m3)
2. Accessibility:
Capacity to change the orientation at a given position.
Strongly depend on the joint limits.
3. Maneuverability
Capacity to reach a given position and orientation (pose) from different paths (different configurations).
Usually implies the presence of redundant joints
(degrees of manipulability or degrees of redundancy).

59. Coupled movements
Decoupled movements

60. Coupled movements
The rotation of a link is propagated to the rest of the chain

61. Decoupled movements
The rotation of a link is not propagated to the rest of the chain

62. Decoupling achieved with a parallelepiped structure
Mechanical decoupling architectures l2 l1 Ma l1 l2
Decoupling achieved with a parallelepiped structure

63. Example of a decoupled structure with a parallelepiped structure

64. l2 l1 Ma Mb Mechanical decoupling solutions
Structure decoupled with connecting rods

65. Decoupling with connecting rodsMa
By transmitting the movement with connecting rods, the rotation of a joint does not propagates to the following.

66. Ma Mb Decoupling with connecting rods a b
By transmitting the movement with connecting rods, the rotation of a joint does not propagates to the following.

67. Mb Ma Mb Decoupling with connecting rods Mj Ma Mj
Transmission with connecting rods through two consecutive joints maintains the orientation of the E.E.

68. Mechanical decoupling solutions
Structure decoupled with chains

69. Decoupling with chainsMj Mj
Transmission movements with chains

70. Decoupling with chainsMj Mj
Transmission systems with chains produce decoupled movements

71. Points potentially weak in mechanical design
Weak points
Mechanical correction
Increase rigidness
Permanent deformation
of the whole structure
and the components
Weight reduction
Counterweight
Increase rigidness
Reduction of the mass
to move
Dynamic deformation
Weight distribution
Reduce gear clearances
Backlash
Use more rigid
transmission elements

72. Points potentially weak in the mechanical design
Weak points
Mechanical correction
Axes clearance
Use pre stressed axes
Improve clearance in axes
Friction
Increase lubrication
Thermal effects
Isolate heat source
Improve mechanical
connection
Bad transducers
connection
Search for a better location
Protect the environment