Development of a general 6-DOF parallel robotic system: Load-control methodology for spine biomechanics testing

Parallel robots have gained popularity for applications requiring large payloads and accurate multi-degree-of-freedom (DOF) motion. This project focused on the development of a parallel robotic system to examine the injury mechanics of the structures of the lumbar intervertebral joint. Six-DOF position- and load-control algorithms were programmed for machine operation. The positional accuracy of the machine was considered substandard. The kinematic errors were attributed to problems in machine deformation, manufacturing, and assembly. These errors led to poor load-control in porcine lumbar spine tests. A 3-DOF approach improved load-control tests since the other 3-DOF loads were not explicitly controlled. Forces and the principal bending moment were satisfied within ±25N and 1Nm in 6-DOF, and ±10N and 0.25Nm in 3-DOF. The developed methods are specific to 6-DOF joint testing with parallel robots. The incorporation of these methods into a 6-DOF parallel robot with sub-millimetre accuracy is warranted for improved multidimensional joint testing.