Calibration Considering the Direction of Rotation for Contact Type Three-Dimensional Position-Measuring Instruments

Abstract

In Japan, the aging of sewage facilities due to long-term use has become a significant social issue. As a result, there has been a growing interest in portable and easy-to-operate standalone pipe inspection robots in recent years. However, the pipes being inspected not only have level differences due to joint connections but also pose a high risk of toppling over due to deterioration, collapses, and sludge caused by external disturbances. Many standalone robots address this by suppressing tipping through tire shape and axle adjustments. However, this method is for suppression and not complete prevention. Therefore, we are exploring a software-based approach to prevent tipping through control of robot movement and aiming to achieve advanced self-position estimation. Currently, we are in the stage of verifying this self-position estimation. However, due to the curved nature of the pipes, it is difficult to accurately measure the robot's position and orientation using conventional measurement instruments. Thus, we have developed a specialized three-dimensional position measurement instrument for pipe inspection robots. Furthermore, although we performed calibration in the translational direction of the instrument, while improvements in accuracy were observed in the translational direction, the accuracy in the rotational direction deteriorated. In this paper, we propose a method to simultaneously calibrate the translational and rotational accuracy of the instrument to address this issue. We discuss the mechanism model, calibration parameters, elimination of redundant parameters by introducing redundancy, and parameter estimation using the Newton method. Additionally, through comparative validation using the instrument, we confirm that the position accuracy after calibration is within the range of approximately ±1.0 mm, and the orientation accuracy is within the range of approximately ±0.3 degrees. This demonstrates the effectiveness of the proposed method.