Integrated Grasping Controller Leveraging Optical Proximity Sensors for Simultaneous Contact, Impact Reduction, and Force Control

TL;DR

A new idea of virtual dynamics that treats multiple fingers comprehensively is introduced, which enables the function of simultaneous contact without compromising the other two functions.

Abstract

Grasping an unknown object is difficult for robot hands. When the characteristics of the object are unknown, knowing how to plan the speed at and width to which the fingers are narrowed is difficult. In this paper, we propose a method to realize the three functions of simultaneous finger contact, impact reduction, and contact force control, which enable effective grasping of an unknown object. We accomplish this by using a control framework called multiple impedance control, which was proposed in a previous study. The advantage of this control is that multiple functions can be realized without switching control laws. The previous study achieved two functions, impact reduction and contact force control, with a two layers of impedance control which was applied independently to individual fingers. In this paper, a new idea of virtual dynamics that treats multiple fingers comprehensively is introduced, which enables the function of simultaneous contact without compromising the other two functions. This research provides a method to achieve delicate grasping by using proximity sensors. For the effectiveness of the proposed method, please refer to https://youtu.be/q0OrJBal4yA.

Figures (10)

• Figure 1: Block diagram of the proposed controller using multiple impedance control. It consists of three layers of impedance control, with each layer playing the role of simultaneous contact, impact reduction, or contact force control.
• Figure 2: Experimental device used to verify whether the proposed method can achieve both the simultaneous contact and impact reduction functions.
• Figure 3: Relationship between the sensor--object distance and proximity sensor output when the object surface is white. The blue curve represents the experimental data, and the red curve represents the fitted curve.
• Figure 4: Time series data of the contact forces acting on each finger. The blue line shows the contact force acting on finger $j=1$, and the red line shows the contact force acting on finger $j=2$. The dashed line represents the results for Case 1, and the solid line represents Case 2.
• Figure 5: Time series data of the target position. The dotted line represents the center position of the grasped object, the dashed line represents the results for Case 1, and the solid line represents Case 2.