Development of a parallel mechanism test machine with six degree-of-freedom position and force control

Understanding physical properties and system responses is currently limited by the capability of test machines to adequately simulate the actual loading structures experience in their environment. One such structure that has not been tested adequately with respect to its real loading environment is the human spine, in particular vertebral motion segments.; This paper discusses the theoretical background, development, implementation, and capabilities of a 6 degree of freedom (DOF) testing machine with position and force control. The machine is designed for testing vertebral motion segments. The principles involved in developing the machine and its design can be implemented for testing a multitude of components that experience 6 DOF loading in their actual environment.; All of the design issues addressed are presented and discussed. Design topics covered include kinematics, geometry optimization, structure and mechanical design, hydraulics, and integrated control system development. The design process is discussed in its entirety with rationale provided for design choices. The primary unique features of this design are utilization of a parallel mechanism for a position and force control testing machine and use of on/off valves for controlling the system. The use of a parallel mechanism results in a much stiffer mechanism than would be achieved with serial manipulators. The use of on/off valves instead of proportional hydraulic valves results in a much more cost effective system which is very easily controlled from a PC with a data acquisition system.; The control theory that supports the 6 DOF position and force control is discussed and its implementation in code is presented. The code was written in Windows based C++ to provide a user friendly interface. The results of position and force control are presented. In addition to 6 DOF position and 6 DOF force control, alternatives for controlling combinations of position and force simultaneously are considered.; The limitations of this technology as well as its capabilities for providing a useful test platform are discussed. The technology developed was examined in great detail in this research, but there are also opportunities for future work in the development and implementation of this technology.