Translational Calibration for Contact Type Three-Dimensional Position-Measuring Instruments

In Japan, as the number of sewerage management facilities increases, continuous maintenance of drainage pipes and sewage pipes is considered important. However, it is grinding for operators to perform the expansive in-pipe inspection. Therefore, in recent years, inspections using stand-alone type piping inspection robots have been actively used. Inside of the pipe, there are disturbances such as unevenness, sludge, or dents at pipe joints which cause slips and tumbles of the robot. Therefore, the conventional ways of approaching those disturbances have been adjusting the size of the robot and tires according to the diameter of the pipe to prevent tipping over. We are exploring tip-over prevention measures by the software approach through advanced straight-ahead control. Currently, we are in the stage of verifying the self-position estimation necessary to realize straight-ahead control, and equipment for that purpose is required. However, to measure the position and posture of the robot inside the curved pipe, a special three-dimensional position-measuring device is required. Therefore, we have developed a three-dimensional position-measuring instrument for pipe inspection robots, but there is still an error in the absolute positioning accuracy. In this paper, to solve this error problem and make it precise, we propose a method to apply the calibration method used in the manipulator to the measuring instrument. Also, the kinematic model and its calibration parameters are explained, and a method of deleting unnecessary redundant parameters and parameter estimation by Newton's method is presented. Furthermore, in a comparative verification using a measuring instrument proposed in the paper, the positional accuracy after calibration is within a range of approximately ±1.0 mm, and the variation is also within a range of ±0.5 mm, which shows that the proposed method is effective.