Robotics and Automation Expert
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Performance Criteria for Redundant Robot Inverse Kinematics (page 4)

The inertial performance criteria have their basis in dynamic models of forces and torques within the robot and are essential to the intelligent design and application of robots. The rate of change of inertial criteria measure how fast the robot can respond to torque and force demands. They are especially important because larger actuators or higher gear ratios can supply more torque, but both will slow the overall response of the robot to external disturbances.

The compliance criteria describe the robot's ability to perform precision operations under load. They also correspond to the vibratory modes of the robot. Of the compliance criteria, the potential energy partition values, are particularly important. The potential energy partition values measure the distribution of compliance energy and how it changes as the robot moves. An unusually high compliance energy content in any part of the robot indicates a problem with the robot's design. Rapid changes in compliance energy indicate large local forces, which correspond to large actuator demands and decreased precision.

The kinetic energy performance criteria address high-level issues represented in relatively simple formulations. Large changes in kinetic energy correspond to very large demands on actuator power. Very rapid changes in the kinetic energy represent shocks to the robot.

Dual Arm Robot Example - This example completes the development of the assist interface for the DAW. After deriving a closed-form inverse kinematics solution, the example concludes with a discussion of the software implementation and the simulation results. The DAWM has 17 Degrees Of Freedom (DOF) arranged in 2 serial chains each having 8 independent DOF and sharing 1 common center rotational joint. Schilling Titan II manipulators form the last six DOF for each arm (Figure 3.).

Figure 4. shows a schematic of the Schilling arm. The offset at the wrist prevents the last three joint axes from intersecting at a point (no spherical wrist). This complicates the analysis somewhat. The following provides a solution involving polynomials of degree 2 or less. The analysis follows three basic steps. The first step uses the constraints on position and orientation. The next step removes the effects of the wrist offset. After this, step three solves for for the remaining angles as if the robot had a spherical wrist..


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