Motion teaching method for complex robot links using motor current

Abstract

Conventional robot motion teaching methods use a teaching pendant or a motion capture device and are not the most convenient or intuitive ways to teach a robot sophisticated and fluid movements such as martial arts motions. Ideally, a robot could be set up as if it were a clothing mannequin that has light limbs and flexible yet frictional joints which can be positioned at desirable shape and hold all the positions. To do the same with a robot, an operator could pull or push the links with minor forces until the desired robot posture is attained. For this, a robot should measure the applied external force by using torque sensors at the robot joints. However, torque sensors are bulky and expensive to install in every DOF joints while keeping a compact design, which is essential to humanoid robots. In this paper, we use only motor current readings to acquire joint torques. The equations used to compensate for the effect of gravity on the joint torques and the self-calibration method to earn link parameters are presented. Additionally, kinematic restrictions can be imposed on the robot's arms to simplify the motion teaching. Here, we teach the Kendo training robot with this method and the robot's learnt martial art motions are demonstrated.

A systematic survey of martial art using motion capture technologies: the importance of extrinsic feedback

“…Studies in robotic field were done by Chen, et al [7] for Tai Chi using Humanoid Robot of Metal Fighter with Gait Algorithm and by Lee [31] for Kendo martial art using equations for acquiring joint torques. In term of motion clip, Tai Chi Chuan were studied for purposes of searching method based on a well-structured index mechanism to retrieve human motion efficiently [51], synthesizing new motions from a given corpus of motion data [5], synthesizing new motions from a given sequence of continuous motion capture data [8] and constructing a content-based human motion retrieval system [9].…”

Encoderless position estimation and error correction techniques for miniature mobile robots

“…(19) to the new model, as shown in Eq. (20). Figure 3 illustrates the block diagram of the proposed system, including the position estimation using the displacement functions and the error correction using feedback from the motors.…”

“…It relies on the applied voltage and the motor's manufacturing characteristics [19]. The use of the motor current was previously proposed in [20] to estimate the joint torque of a humanoid robot's arm. It utilized the motor current to detect and measure the applied force without using any hardware components.…”

Control System Design for a Surface Cleaning Robot

“…The motor armature series resistance has shortcomings, such as it is unstable at low speeds, the speed is not continuous, etc. In addition, the method of reducing the supply voltage does not change the mechanical characteristics of the motor and the speed control is smoother [13].…”