Operating system-induced jitter in force display computations

Haptic interfaces require a consistent rate of force computation for stable high-frequency displays. This paper reports measurements of force computation consistency under Windows 2000 and XP in single- and dual-processor systems. The median time was accurate at 1 ms. However, as the computation in the force loop increased to 500 μs/iteration, release time jitter in the single-processor system increased up to 52%. Jitter was also introduced by network load. Contention from other real-time applications, such as audio and video display, dramatically increased the jitter, up to 100%. These high levels of jitter could perceptibly degrade force display for some tasks. Jitter was substantially lower for the dual-processor system. Haptic applications requiring consistent force computation should consider dual-processor configurations.