Presentation on theme: "ROBOTICS: ROBOT MORPHOLOGY"— Presentation transcript:
1 ROBOTICS: ROBOT MORPHOLOGY Josep Amat and Alícia CasalsAutomatic Control and Computer Engineering Department
2 User Components of a Robot Environment Net External Sensors Control UnitProgrammingExternalSensorsEnvironmentInternalActuatorsMechanical StructureNetUser
3 Chapter 2. Robot Morphology Basic characteristics:- Kinematics chain- Degree of freedom- Maneuvering degree- Architecture- Precision- Working space- Accessibility- Payload
4 Degrees of freedomDegrees of freedom correspond to the number of actuators that produce different robot movementsD o FA 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 freedomPositioningxyzPReference frame originPositioning the end effector in the 3D space, requires three DoF, either obtained from rotations or displacements.
6 Reference frame origin Degrees of freedomOrientationxyzPReference frame originrollpantiltOrienting 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 degreeManeuvering degree is the number of actuators that although producing new movements do not contribute to new degrees of freedom.
14 Characteristics derived from the mechanical structure: Degrees of freedomWork SpaceAccessibilityPayloadPrecision
15 Characteristics derived from the mechanical structure: Degrees of freedomTridimensional positioning: (x,y,z )Minimum: 3 Degrees of freedom
16 Positioning + orientation: (x,y,z,,,q ) Characteristics derived from the mechanical structure:Degrees of freedomqPositioning + orientation: (x,y,z,,,q )Minimum: Degrees of freedomArchitecture: 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 ManeuveringMovement precision:Resolution, Repetitiveness, Precision and ComplianceDynamical 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.exeyPrecision depends on:Mechanical play (backlash)Sensors offsetSensors resolutionMisalignments in the position and size of rigid elements, specially the end-effector E.E.Coordinatesof the targetPoints 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 distanceto the robot axis.exeyCoordinatesof the targete offsetPrecision+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 errorexeyRepetitiveness depends on:Mechanical play (backlash)Target positionSpeed and direction when reaching the targetCoordinatesof the targetPrecision+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 StructureExamples of Joints (movements between articulated bodies)Joint 1Joint 2Joint 5Joint 3Joint 4Joint 6Joint 1Joint 4Joint 3Joint 5Joint 2
25 Classical Architectures: Cartesian Cylindrical Polar Angular Architecture: Configuration and kind of articulations of the kinematical chain that determine the working volume and accessibilityClassical Architectures: CartesianCylindricalPolarAngular
26 Cartesian Work Space (D+D+D) Classical ArchitecturesCartesian 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 ArchitecturesCylindrical 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 ArchitecturesPolar 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 ArchitecturesAngular Work Space (R+R+D)
33 Angular Work Space (R+R+R) Classical ArchitecturesAngular Work Space (R+R+R)
34 Classical Architectures Example of Angular Work Space Robots (R+R+R)
39 Resume Cartesian Robot Characteristics JointsObservationsCartesian1a.Linear: XAdvantages::2a.Linear: Ylinear movement in three dimensionssimple kinematical model3a.Linear: Zrigid structureeasy to displaypossibility of using pneumatic actuators,which are cheap, in pick&placeoperationsconstant resolutionDrawbacks:requires a large working volumethe working volume is smaller thanthe robot volume (crane structure)requires free area between the robotand the object to manipulateguides protection
40 Resume Cylindrical Robot Characteristics JointsObservationsCylindrical1a.Rotation: qAdvantages:2a.Linear: Zsimple kinematical modeleasy to display3a.Linear: rgood accessibility to cavities andopen machineslarge forces when using hydraulicactuatorsDrawbacks:restricted working volumerequires guides protection (linear)the back side can surpass theworking volume
41 Resume Polar Robot Characteristics JointsObservationsPolar1a.Rotation: qAdvantages:2a.Rotation: jlarge reach from a central support3a.Linear: rIt can bend to reach objects on the floormotors 1 and 2 close to the baseDrawbacks:complex kinematics modeldifficult to visualize
42 Resume Angular Robot Characteristics JointsObservationsAngular1a.rotationq123:Advantages:2a.rotationmaximum flexibilitylarge working volume with respectto the robot size3a.rotationjoints easy to protect (angular)can reach the upper and lower side of an objectDrawbacks:complex kinematical modeldifficult to displaylinear movements are difficultno rigid structure when stretched
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 pointThe values usually used are the maximum load and nominal at acceleration = 0The 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 VelocityMaximum 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.VmaxtimespeedShort movementsLong movement
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. ManeuverabilityCapacity 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).
60 Coupled movementsThe rotation of a link is propagated to the rest of the chain
61 Decoupled movementsThe rotation of a link is not propagated to the rest of the chain
62 Decoupling achieved with a parallelepiped structure Mechanical decoupling architecturesl2l1Mal1l2Decoupling 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 rods MaBy 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 chains MjMjTransmission movements with chains
70 Decoupling with chains MjMjTransmission systems with chains produce decoupled movements
71 Points potentially weak in mechanical design Weak pointsMechanical correctionIncrease rigidnessPermanent deformationof the whole structureand the componentsWeight reductionCounterweightIncrease rigidnessReduction of the massto moveDynamic deformationWeight distributionReduce gear clearancesBacklashUse more rigidtransmission elements
72 Points potentially weak in the mechanical design Weak pointsMechanical correctionAxes clearanceUse pre stressed axesImprove clearance in axesFrictionIncrease lubricationThermal effectsIsolate heat sourceImprove mechanicalconnectionBad transducersconnectionSearch for a better locationProtect the environment