A Stewart Platform- Based Manipulator: General Theory and Practical Construction

Abstract

The Stewart Platform is one example of a parallel connection robot manipulator. This paper summarizes work that has been done at Oregon State University over the past several years on this topic. The work has fallen into two general areas: theoretical consideration of the generalized Stewart Platform and practical considerations for building a working machine. Both of these areas are covered in this paper.

The theoretical part of the paper discusses the following four problems:

1. Given the position and orientation of the end effector, what are the actuator coordinates?

2. Given the velocity, position, and orientation of the end effector, what are the actuator velocities?

3. Given the forces exerted on the end effector by the external world and the accelerations of the end effèc tor, what are the forces at the actuators?

4. What are the singular configurations of the manipu lator? For the Stewart Platform, the singular configu rations are positions where the end effector gains one or more degrees of freedom.

After the theoretical problems have been solved, there are still a group of practical problems to be tackled when a real machine is built. How can the general configuration be sim plified to make the solution of the equations practical? Once a configuration is decided upon, what are the construction considerations for building a real machine? What is the range of motion of the end effector? What are the necessary ranges of motion of the joints? What are the implications of the singularities of the Stewart Platform and what are some practical ways of solving the problems they cause?

In the process of doing this research, three machines were built and a computer simulation was written and used. The most recent machine and the computer simulation will be described in this paper.

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