Chapter 3 - Manipulators And End Effectors

Question 1

Manipulators?

Answer 1

Composed of links and joints.

Links - rigid sections that make up the mechanism and support the load carried by the robot.

Joints - the connection between two links

Question 2

Revolute Joints?

Answer 2

Allows relative rotation about on axis.

Has 1 degree of freedom and 5 constraints.

Permits only angular motion.

Question 3

Three Types of Revolute Joint Motions?

Answer 3

Rotational joint- arm lengths stay the same but joints have relative position changes.

Twisting joint- rotation about an axis, that is parallel to both links

Revolving joint - rotation about an axis, that is perpendicular to a link

Question 4

Cylindrical Joint?

Answer 4

Allows relative rotation and translation about one axis.

2 degrees of freedom and 4 constraints

Question 5

Prismatic joints?

Answer 5

Allows relative translation about one axis (linear motion)

1 degree of freedom and 5 constraints.

Question 6

Spherical Joints?

Answer 6

Allows three degrees of rotational freedom about the center of the joint. Also called a ball and socket joint.

Question 7

Planar Joints?

Answer 7

Allows relative translation on a plane and relative rotation about an axis perpendicular to the plane.

Question 8

Classification of Manipulators by Motion

Answer 8

Planar Manipulator - all the moving links move in planes parallel to one another

Spherical Manipulator - if all the links perform spherical motions about a common stationary point

Spatial Manipulator - if at least one of the links of the mechanism possesses a general spatial motion

Question 9

Classification of Manipulator by Kinematic Structure?

Answer 9

Open-loop: if all the links form an open loop chain

Parallel: if it is made up of a closed-loop chain

Hybrid: if it consists of open loop and closed loop chains

Question 10

Four Categories of Robot Manipulation?

Answer 10

Mobility Analysis - measurement of the DOF of the manipulator system

Kinematic Analysis - all first order differential motions

Velocity Manipulability - functionality of a manipulator system in the velocity domain

Velocity Workspace Analysis - determines the velocity bounds achievable by the system within the capability bounds of the joint actuators.

Question 11

Active and Passive Joints?

Answer 11

Active joints are joints that can be actuated directly. Passive Joints are joints that are incorporated by kinematic constraints arising from contact.

Question 12

Phased-Based Manipulation?

Answer 12

Simplifies the programming and control of complex robot applications by segmenting the tasks down into phases and relates it to the dexterity of the human hand for context and scope.

Ex: Simply grabbing a glass involves velocity control, contact sensors, gripping control and sensing the movement of the glass off the table.

Question 13

Three Wrist Movements of a Robot?

Answer 13

Yaw - wrist movement from side to side (lateral)

Pitch - rotation about a horizontal axis (up + down)

Roll - twisting of the wrist (360 degree rotation)

Question 14

Gantry Robot?

Answer 14

A Cartesian Co-ordinate robot mounted from above in a rectangular frame. It’s base is mounted on a track but it is considered a stationary robot.

Have high positional accuracy (able to place objects in the desired location)

Well suited for pick and place operations

Question 15

Cylindrical Coordinate Robot?

Answer 15

If the first joint of a Cartesian coordinate robot is replaced with a revolute joint, it becomes a cylindrical robot.

The R joint swings the arm back and forth about a vertical base axis. The P joints then move the wrists up and down along the vertical axis and in and out along a radial axis.

Has 3 degrees of freedom.

Question 16

Spherical Coordinate Robot?

Answer 16

Is produced by replacing the 2nd joint of a cylindrical robot with a revolute joint.

The 2nd joint pitches the arm up and down a horizontal shoulder axis.

Question 17

SCARA Robot?

Answer 17

Selective Compliance Assembly Robot Arm (SCARA) is a manipulator used for assembly robots in high speed assembly operations.

Has 2 revolute joints and 1 prismatic joint. Making capable of simulating human like movements.

Question 18

PUMA robot?

Answer 18

When the last prismatic joint is replaced with a revolute joint this produces an articulated coordinate robot a.k.a programmable universal machine for assembly or PUMA.

It is a dual of the Cartesian robot with 3R instead of 3P and is considered anthropomorphic.

If differs from SCARA robots in that it is able to a complex area from the base of the robot to a point directly overhead.

Question 19

Work Envelope?

Answer 19

The boundary of positions in space that the robot can reach.

The size and shape of the work envelope is determined by the extent, number, type and order of a robots axes and programmed instructions.

The major axes determine the shape, the minor axes determine the orientation of the end effector.

Question 20

End Effectors?

Answer 20

Devices at that handle objects during transfer or processing. Classified as either: grippers or end-of-arm tooling (EOAT).

The Tool Center Point (TCP) - is the tip of the end effector and is used when referring to the robots position.

Automatic tool changing allows robots to use several tools sequentially.

Question 21

EOAT End Effectors and Use Cases?

Answer 21

Welding: used for simple & compound curved joints and running multiple short welds

Ladle-type: handling of hot materials

Spot-weld: stop and go production line operations

Spray gun: spraying with controlled velocity

Question 22

Grippers?

Answer 22

Used to move objects.

Can be driven hydraulically, pneumatically and electrically.

Either friction (relies on squeezing with force) or encompassing (cradling the part with force).