Dynamic manipulation of unknown string by robot arm: realizing momentary string shapes

Abstract

We propose a method to realize the dynamic manipulation of a string with unknown characteristics via a high-speed robot arm. We use a mass-spring-damper model for the string and repeat three steps: motion generation, real manipulation, and parameter estimation. Robot motion is given by the joint angular velocities expressed by the Bezier curves. Their control points are randomly positioned to generate various robot motion for dynamic string manipulation. The generated motion is performed by a wire-driven robot arm and, real string movement is captured by the camera. These time-series images are used for the parameter estimation of string. The best parameter set is determined via comparison between real and simulated string movement after changing parameter randomly and logarithmically. This parameter set is not unique, but it simulates the actual string movement well. Since the estimated string parameter is used for the robot motion generation after repeating the above 3 steps, the motion generation reflects string property and motion objective can success without special tests in advance. This is an advantage of our method because it is difficult to know all of string property with very complicated non-linearity beforehand. We focus on realizing the momentary string shape in 2 dimensions in this paper. We confirmed the effectiveness of our proposed method by realizing five momentary shapes and 3 kinds of string properties. We also discussed the reproducibility and compatibility of estimated parameters and motion generation.

Casting Manipulation With Unknown String via Motion Generation, Actual Manipulation, and Parameter Estimation

“…The authors have realized several motion objectives for strings with unknown properties by repeating motion generation, actual manipulation, and parameter estimation [22] [23] [24]. Specifically, our proposed method differs from previous research as it does not acquire training samples by manipulating the robot in the real world in advance, as in previous studies.…”

“…The reason for adopting this approach is that the proposed method utilizes parameters derived from the actual manipulation of the robot arm, thus the parameters are estimated to the specific motion of the string. Therefore, if the direction of the force applied to the string differs significantly, the estimated parameters may not be valid, as demonstrated in [22].…”