Research Papers

Actuator Gain Distributions to Analytically Meet Specified Performance Capabilities in Serial Robot Manipulators

[+] Author and Article Information
Oziel Rios1

Robotics Research Group, Department of Mechanical Engineering, University of Texas at Austin, Austin, TX 78758oziel_rios@mail.utexas.edu

Delbert Tesar

Robotics Research Group, Department of Mechanical Engineering, University of Texas at Austin, Austin, TX 78758tesar@mail.utexas.edu

It should be noted that in this article we present methods by which to design serial mechanisms addressing the basic parameters affecting speed, force, and accuracy. The more complex dynamic parameters affecting the operation of the system are beyond the scope of this work.

Note that in Eq. 16, the sum starts at j=i to include the weight of link i. Note also that for the actuators, Laiic=0 for all i since we are assuming that actuator i is located on axis i.

The accuracy estimation derivation presented here based on an encoder can be extended to other position sensing methods such as potentiometers or resolvers.

According to PowerCube™ specifications, changing the transmission reduction ratio will not change the weight of the overall actuator as given in Table 1.

Like for the PowerCube™ actuators, changing the transmission reduction ratio has no effect on the total actuator weight.


Corresponding author.

J. Mech. Des 131(2), 021010 (Jan 21, 2009) (9 pages) doi:10.1115/1.3066625 History: Received October 08, 2007; Revised December 04, 2008; Published January 21, 2009

A serial robotic manipulator arm is a complex electromechanical system whose performance is characterized by its actuators. The actuator itself is a complex nonlinear system whose performance can be characterized by the speed and torque capabilities of its motor, and its accuracy depends on the resolution of the encoder as well as its ability to resist deformations under load. The mechanical gain associated with the transmission is critical to the overall performance of the actuator since it amplifies the motor torque, thus improving the force capability of the manipulator housing it, reduces the motor speed to a suitable output speed operating range, and amplifies the stiffness improving the precision under load of the overall system. In this work, a basic analytic process that can be used to manage the actuator gain parameter to obtain an improved arm design based on a set of desired/required performance specifications will be laid out. Key to this analytic process is the mapping of the actuator parameters (speed, torque, stiffness, and encoder resolution) to their effective values at the system output via the mechanical gains of the actuators as well as the effective mechanical gains of the manipulator. This forward mapping of the actuator parameters allows the designer to determine how each of the parameters influences the functional capacity of the serial manipulator arm. The actuator gains are then distributed along the effective length of the manipulator to determine their effects on the performance capabilities of the system. The analytic formulation is also demonstrated to be effective in addressing the issue of configuration management of serial robotic manipulators where the goal is to assemble a system that meets some required performance specifications. To this end, two examples demonstrating a solution of the configuration management problem are presented. The analytic process developed based on the mapping of the mechanical parameters of the actuator to their effective values at the system output is shown to dramatically reduce the effort in the initial phases of the design process, meaning that the number of design iterations can be dramatically reduced.

Copyright © 2009 by American Society of Mechanical Engineers
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Grahic Jump Location
Figure 1

Transformations the motor parameters undergo to be represented in the manipulator’s task-space

Grahic Jump Location
Figure 2

Distribution of actuator gain functions

Grahic Jump Location
Figure 3

6DOF manipulator composed of PowerCube™ actuators




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