The characteristics of force sensor and reaction force esti-
mation observer are observed by the experiment. The experimental system in Fig. 2 is composed of LDSM, a optical encoder (RGH24, Encoder resolution 0.1 μm, by Renishaw), and a load cell (LUR-A-50NSA1, Rated Capacity 50N, Natural Frequency 2kHz, by Kyouwa Co.).