Reliable and Enhanced Stiffness Perception in Soft-tissue Telemanipulation

Abstract

Haptic feedback is one of the missing links in robotized minimally invasive telesurgery. The teleoperation controllers are optimized so as to offer the surgeon a reliable perception of the stiffness of soft tissue, rather than following the traditional approach where tracking and force reflection fidelity are considered. The experimental results show that optimization allows for better focus on the quality of the haptic information in the performance-stability trade-off. A force sensor to measure the interaction forces with the environment is found to be indispensable for high-quality touch feedback. Next to optimization for realistic feedback of the environment stiffness, in this paper we describe how to extend human perception beyond differential thresholds and thus enhance sensitivity. Experiments on a one-dimensional system demonstrate that the operator is able to discriminate tinier differences using a telemanipulation system with enhanced sensitivity than through direct manipulation.

Transparent and Shaped Stiffness Reflection for Telesurgery

“…The perception and differentiation of the tissue's stiffness is essential during surgical palpation tasks (De Gersem et al, 2005a). Palpation is the technique of examining parts of the body by touching and pressing them.…”

“…However, from such plots, it is difficult to analyse what the human operator feels. For this purpose, it is more useful to present the experimental data on force versus position plots, as done by De Gersem et al (2005a); Mahvash & Okamura (2007); Tzafestas et al (2008); Willaert et al (2008b). Both ways of plotting the experimental data in the time-domain are employed in this chapter.…”

“…The problem of the differential thresholds is addressed in this chapter. Inspired by the idea of Impedance Shaping (Colgate, 1993), De Gersem et al introduced the idea to overcome the differential thresholds by means of teleoperation control (De Gersem et al, 2005a;b). As stated in the introduction, the minimal change in stiffness that can be discriminated by a human operator is a constant fraction c of the nominal stiffness.…”

“…The design of haptic teleoperation controllers for interaction with these types of environments is receiving growing interest from the research community (Cavusoglu et al, 2002;De Gersem et al, 2005a;Malysz & Siroupour, 2007;Misra & Okamura, 2006;Tavakoli et al, 2006) and forms the topic of this chapter.…”

“…To increase the stiffness discrimination ability, this generalized version of the SRC, applies a nonlinear shaping function to the estimated stiffness before reflection to the master. This principle of enhanced sensitivity (De Gersem et al, 2005a;b;Malysz & Siroupour, 2007;Son & Lee, 2008), allows the human operator to feel a difference in stiffness that is smaller than one he/she can detect by manual palpation. This chapter describes a practical implementation of the generalized version of the SRC (gSRC) and shows the feasibility of enhanced sensitivity based on a set of psychophysical user tests.…”