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Nonparametric Identification of the Surgeon's Hand Vibration in Haptic Devices

Surgical handcontrollers are evolved in the last two decades by adding haptic feedback and vibration sensation. Haptic feedback can provide a realistic simulation of low frequency phenomena, while adding vibration to handcontrollers simulate high frequency vibration phenomena such as bone drilling. Two main methods of adding vibration to haptic devices are back drivable robot arms and adding vibration actuators to the handle (stylus) of the hand controllers. In both of these methods, a high fidelity method to investigate the dynamics at the grasping point of the handcontrollers is required to properly design the vibration generators. Developed dynamic models of the user hand while holding the stylus of the haptic devices includes a combination of experimental setups, and SDOF/MDOF dynamic models. The current dynamic models are limited by the range of excitation frequency where the tool was held with different styles. This grasping style affects the model parameters, which has not been investigated in previous studies. In this study, an experimental setup is developed to investigate a dynamic model of the grasping point of the haptic endeffectors. The system was modeled by its frequency response with a non-parametric identification method. The amplitude and phase of the frequency response of the operator's hand are plotted as a function of frequency. The natural frequency of the hand model is in agreement with the assumed SDOF model. The phase difference and the coherence spectrum is analyzed to investigate the natural frequencies and amplitude ratios at different grasping configurations and finger styles. The results showed changes in the natural frequencies and amplitude ratios for different hand configurations and finger styles. The developed model in this study can be used in conjunction with the vibration generators in haptic handcontrollers to more accurately render the developed vibration at surgical corridors at the end-user hand.