Friction analysis according to pretension of laparoscopy surgical robot instrument

Abstract

Surgical robot instruments are driven by using cable-pulley structure. The elasticity at cable-pulley structure causes slack effect of cable. Elastic region of cable must be compensated for preventing the slack. The surgical instrument inputs a pretension for compensation at cable’s elastic region. Therefore pretension is an important factor in the design of a surgical instrument. However, the pretension is related with friction force which is affected by normal force at the driving shaft pulley. The shaft and contact surface of the pulley consist of sliding bearing structure. Typically, the friction coefficient in the sliding bearing structure is determined by the Petroff equation. The pressure of Petroff equation is related to the denominator of the equation. Therefore increasing normal force brings about an effect which decreases friction coefficient. Eventually, in theoretically, that means the pretension can be increased to infinity to decrease friction coefficient. However actual result comes out different. Therefore in this paper, the friction analysis method according to a pretension is proposed and an experiment method for the analysis of the friction is introduced. The correlation between pretension and friction is estimated by the analysis. The estimated result is compared with the experiment one and is analyzed. Also finally this paper suggests an appropriate pretension for surgical robot instrument by the friction analysis result.