Adaptable Haptic Shared Control based on Grip Force

Abstract

An important design choice for Haptic Shared Control is the magnitude of assisting forces: high assisting forces are beneficial during agreement between operator and controller, but also result in larger conflict forces in case of disagreement. In order to use higher forces without increasing conflict forces, literature proposes Adaptable Haptic Shared Control: using real-time operator grip force measurements to smoothly scale the magnitude of assisting forces. For full hand grip force no objective measurements comparing Haptic Shared Control versus Adaptable Haptic Shared Control are known and only very limited data on this comparison is available for finger pinching and subjective measurements.
In order to prove that, using grip force to adapt the magnitude of assisting forces indeed leads to reduced conflict forces while maintaining the regular Haptic Shared Control performance during agreement, an experiment is required.
It is hypothesized that Adaptable Haptic Shared Control will reduce conflict forces during disagreement and that the larger the disagreement the higher the grip force.
Both an Adaptable and regular Haptic Shared Controller are designed and implemented on an actuated joystick, which is extended with a 2D dynamometer to allow real-time grip measurements. Eighteen subjects participated in an experiment where they used the Triar joystick to steer a virtual object along a path consisting of a multisine (agreement) interspersed with straight sections containing obstacles that needed to be avoided (conflict). After the adaptable and regular haptic shared control condition a Vanderlaan questionnaire was provided to the participant with the question to score them compared to manual control.
During the path following task, both the Adaptable Haptic Shared controller and regular haptic shared controller provide similar increased performance in lateral deviation compared to manual control (p<0.01). During obstacle avoidance, the Adaptable Haptic shared control significantly decreased conflict forces compared to haptic shared control (p<0.01), but at a price of brief increased grip force. No significant difference in grip force was found between obstacles sizes (conflict). The subjective usefulness and satisfying score of adaptable and regular haptic shared control are both positive compared to manual but do not significantly differ from each other. Result show that with Adaptable Haptic Shared Control humans prefer increasing their grip force to lower the Haptic Shared Control forces during disagreement. Additionally during non-conflict situations they maintain the beneficial forces of Haptic Shared Control.