Accuracy Improvement of Torque Estimation Between a Surgical Robot Instrument and Environment in Single-DOF Motion
Strain gauges attached to the driving pulleys of the instrument of surgical robots allow estimation of the torque between the instrument and environment. Friction in the torque transmission, however, deteriorates accuracy of the estimation. This paper pro
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Abstract. Strain gauges attached to the driving pulleys of the instrument of surgical robots allow estimation of the torque between the instrument and environment. Friction in the torque transmission, however, deteriorates accuracy of the estimation. This paper proposes a method to reduce the estimation error using a friction model and Butterworth low-pass filter. The friction model is developed based on Dahl model and reflects the characteristics of the particular driving mechanism. Experimental results show that the relative error can be reduced to 3.49 % in case of a sine wave motion. Keywords: Surgical robot model
Haptic feedback
Torque estimation
Friction
1 Introduction Haptic feedback to the surgeon is sometimes necessary during the operation especially for complex tasks such as coronary suturing [1]. The current commercialized surgical robot systems, however, do not provide haptic feedback. This makes it difficult to discriminate the amount of force being applied to the patient’s tissues, and it reduces performance of the operation [2, 3]. Measuring interaction force between the surgical instrument and environment is required to provide high-fidelity haptic feedback. It is difficult to measure the contact force directly by attaching a force sensor to the tip of surgical robot instrument because of technical limitations such as sterilization, insulation, and size limitation [4]. Various methods have been developed in the literature to estimate force and torque by isolating the surgical instrument from the part where the force sensors are mounted [5–7]. Kang and Lee [6] and Spiers et al. [7] proposed the method to estimate the interaction torque between the surgical instrument and environment by sensing torque generated at driving pulleys of the surgical instrument. The interaction torque can be estimated since the driving pulley and the surgical instrument tip are connected through wire-tendon mechanism. This estimation method induces error in the torque measurement due to friction, inertia, etc. These factors occur in the torque transmission. The friction is the most significant factor among these elements [8]. Kang and Lee [6] tried to reduce the estimation error using a friction model which includes viscous and Coulomb friction. The proposed friction model, however, did not accurately reflect the © Springer International Publishing Switzerland 2016 F. Bello et al. (Eds.): EuroHaptics 2016, Part II, LNCS 9775, pp. 187–195, 2016. DOI: 10.1007/978-3-319-42324-1_19
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characteristics of wire-tendon mechanism in the instrument. Mahvash and Okamura [9] used Dahl model to compensate friction occurring in manipulators with wire-tendon mechanism. They applied the model to compensate friction in a slave robot to estimate insertion force. This method, however, cannot be directly applied to the surgical instruments. Spiers et al. [7] conducted experiment using a tissue with properties similar to those of human liver. They found the relationship between the torque measured from the torque se
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