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

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Presentation on theme: "ROBOTICS: ROBOT MORPHOLOGY Josep Amat and Alícia Casals Automatic Control and Computer Engineering Department."— Presentation transcript:

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

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

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

4 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. Degrees of freedom

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

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

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

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

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

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

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

13 Nomenclature: Arm Wrist Elbow Shoulder Trunk Base

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

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

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

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

18 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 Basic characteristics. Definitions

19 xx yy 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.  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 Coordinates of the target

20 xx yy Coordinates of the target Precision + R  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.  increases with the distance to the robot axis.

21 xx yy Repetitiveness depends on: Mechanical play (backlash) Target position Speed and direction when reaching the target Repetitiveness error Precision + R 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. Coordinates of the target

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 / 2 n

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

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

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

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

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

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

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

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

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

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: S elective C ompliance A ssembly R obotic A rm )

38 SCARA Robot : examples

39 Resume Cartesian Robot Characteristics RobotJointsObservations Cartesian1a.Linear: X 2a. 3a. Advantages: :  linear movement in three dimensions  simple kinematical model  rigid structure  easy to display  possibility of using pneumatic actuators, which are cheap, in pick&place operations Linear: Y Linear: Z  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 Cylindrical1a. Rotation:  2a. 3a.    good accessibility to cavities and open machines  large forces when using hydraulic actuators  restricted working volume  requires guides protection (linear)  the back side can surpass the working volume RobotJointsObservations Linear: Z Linear:  Advantages: simple kinematical model easy to display Drawbacks:

41 Resume Polar Robot Characteristics Polar1a. Rotation:  2a. Rotation:  3a. Linear:   large reach from a central support  It can bend to reach objects on the floor  motors 1 and 2 close to the base  complex kinematics model  difficult to visualize RobotJointsObservations Drawbacks: Advantages:

42 Angular1a.rotation 2a.rotation 3a.rotation  1  2  3 :  maximum flexibility  large working volume with respect to the robot size  joints easy to protect (angular)  can reach the upper and lower side of an object  complex kinematical model  difficult to display  linear movements are difficult  no rigid structure when stretched Resume Angular Robot Characteristics RobotJointsObservations Advantages: Drawbacks:

43 high speed and precision only vertical access : SCARA1a.rotation 2a.rotation 3a.rotation  1  2  3 Resume SCARA Robot Characteristics RobotJoints Observations Advantages: Drawbacks:

44 Example of Map of admitted loads, in function of the distance to the main axis 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.

45 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 Dynamic Characteristics

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

47 Special Configurations. Pendulum Robot GGD

48 Example of a Pendulum Robot RRD

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

50 Classical Degrees of freedom Concatenated Degrees of freedom (elephant trunk)

51 Increase of accessibility Special Configurations. Elephant Trunk

52 Distributed Degrees of Freedom. Special Configurations. Elephant Trunk

53 Elephant Trunk Examples Applications

54 6 Displacements  6 DoF. + X, + Y, + Z + , + , +  Special Configurations. Stewart Platform

55 Platform “Stewart” Example Workspace

56 Example of “Stewart” Robot

57  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 (m 3) 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 Mechanical decoupling architectures l1l1 l2l2 l2l2  l1l1 Decoupling achieved with a parallelepiped structure

63 Example of a decoupled structure with a parallelepiped structure

64  Structure decoupled with connecting rods l1l1 l1l1 l2l2 l2l2  Mechanical decoupling solutions

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

66     Decoupling with connecting rods

67       Transmission with connecting rods through two consecutive joints maintains the orientation of the E.E. Decoupling with connecting rods

68 Structure decoupled with chains Mechanical decoupling solutions

69   Transmission movements with chains Decoupling with chains

70   Transmission systems with chains produce decoupled movements Decoupling with chains

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

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


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