Four axial structural and material test machine

Structural tests of complex motion segments, such as those found in numerous joints in the body, require a flexible test bed capable of coordinated multiple axis control and a thorough understanding of the forces and moments. Past experience with such tests on the wrist, elbow, foot and spine joints pointed to the inadequacies of conventional test machines not designed for such purposes. Therefore, a PC-based four-axial benchtop test machine suited for more flexible, sophisticated, biomechanical testing has been developed and built. The test machine consists of a rigid aluminum frame incorporating three translational and one rotational axis driven by micro-stepping motors. The tester is controlled by an industry standard 486 PC including a motor indexer and analog-to-digital (A-D) board. The custom motion control software (not limited to four channels) is designed to accommodate both stepper and servo controllers in displacement or load control modes, or a feedback mode utilizing any number of A-D inputs to control axis velocity. Each axis can act independently, or dependently as a function of another axis. A six-component load cell was also incorporated for force and moment measurement. This new test machine has been found to be quite feasible and easy to operate in the analysis of joint constraint and laxity measurement.