Two Mitigation Strategies for Motion System Limits

Limited workspace is a challenge for all motion-based simulators, whether they are large excursion systems, like the NADS, or smaller simulators utilizing only Stewart Platforms. Two approaches for addressing this challenge are nonlinear washout scaling and software displacement limiting. This paper presents new algorithms developed for these approaches. The nonlinear scaling method makes use of the cubic Hermite interpolation polynomial to smooth the corner in the scaled output at the limit. A software displacement limiting method is introduced that generates control signals in the simulator frame of reference. As a result, unwanted acceleration artifacts caused by unbalanced limiting of the actuators can be avoided. The methods are described, and off-line simulation results using the new displacement limiting method are presented.