Numerical Methods for the Force Reflection of Contact

Abstract

An important problem in the field of force-reflecting systems and telerobotics is poor rendering of contact, particularly of contact with stiff surfaces. There are numerous possible sources of poor performance, including poor contact models, sampling errors, and delays due to computation or data transmission. In this paper we examine effects due to sample-and-hold, which is a fundamental property of both the discrete domain and also of the sensors and power amplifiers used in a force-reflecting system. We propose sample-and-hold be generalized to sample-estimate-hold. We show why ordinary sample-and-hold generates an active contact interface, and provide ways of improving the feeling of the interface. We have developed a suite of numerical methods for improving the performance of rendering of surfaces by force reflection. We have conducted both simulations and experiments to demonstrate the efficacy of the proposed .scheme. Our contributions are a new method of digitally processing force data, and a systematic method for coupling force-processing systems that run at different rates.

Implicit Multibody Penalty-BasedDistributed Contact

“…A frictional model for penaltybased simulation was proposed in [14], and we adopt their frictional model in our work. Many authors improved the definition of penetration depth and temporal stability of penalty forces [15], [16], [17]. Stiff springs can be replaced for potential barriers [18], or integrated at a higher rate than the rest of the system [19].…”

“…We then find its connected components (contact islands) [39]. The contact islands are decoupled from each other in (15) and are solved independently, which often greatly decreases the system solve time.…”

High-fidelity passive force-reflecting virtual environments

“…That these two signals are not the same is cause for loss of passivity of a complete system, even when the combination of and represents a passive system, termed here the "nominal system." This spurious energy production was called "energy leak" [10], or "energy error" [9]. We can express the combined effects of zero-order hold conversion and computational delay by (3) where is the sampling period and is a pulse otherwise.…”

Stable Haptic Rendering Using a Pipelined Threading Architecture

“…Gillespie and Cutkosky [16] developed controllers based on half-sample predictions and based on the design in the digital domain to eliminate "energy leaks" in the system. Ellis et al [17] suggested a sampleestimate-hold concept and a suite of numerical methods to improve the performance of force reflections. Lu and Song [18] developed an energy-compensating control method to improve haptic system performance through calculating and eliminating "work difference" between the sampleddata haptic system and an ideal continuous-time haptic system.…”

“…As in [17], the maximum stiffness Kmax is defined as the maximum value of spring stiffness K under which the human operator cannot cause the system to be unstable with any free behaviours. Considering the fdevice of the DHD is around 4.0 KHz (Table 1), the maximum number of haptic threads was set to four conservatively.…”