Improvement of position and orientation tracking accuracy by fusing HTC Vive trackers and Inertia Measurement Units
Creators: name: Weber, Mitchell
Publisher: name: Graduate Studies
Year: 2023
Subjects: subject: Engineering--Mechanical

description: Position tracking systems have been used for calibration, error compensation and navigation of robots to enable higher precision machining, assembly, or control. Laser trackers are the most common position tracking system in the aerospace industry despite the high price. They can track minute position changes with micrometre accuracy. Vision-based tracking systems such as an OptiTrack Motion Capture system have also been used for navigation, pick-and-place, or less precise machining. The price of the vision-based tracking system is lower than laser trackers, but its performance can degrade with sub-optimal ambient lighting. A new position-tracking system has been designed with recent developments in virtual reality (VR) hardware. One of the VR systems, the HTC Vive, uses tracking devices (i.e,Vive trackers) and base stations. The position of the Vive tracker is calculated based on the time of arrival of the Infrared (IR) laser pulses emitted from the base stations detected by the photodiodes on the tracker. The Vive system costs only $1000 to $1500 but provides centimeter accuracy. A less expensive position tracking system with micrometer accuracy would be an enormous boon to many industries. This study has investigated a new design of a position tracking system with high accuracy and a low-cost. This study has investigated a new design of a position tracking system with high accuracy and a low-cost using HTC Vive trackers and multiple Inertial Measurement Units (IMUs). Sensor fusion algorithms such as the Extended Kalman Filter (EKF) and the Unscented Kalman Filter (UKF) have been developed to combine Vive trackers and IMUs. For the system setup, the base stations are placed above the tracking space and their positions are calculated using a Vive tracker placed at a given origin (0,0,0 for Vive system). Hand-eye calibration is done to find the coordinate-frame transformation between the Vive tracker’s frame and the robot’s frame. After the calibration step, the Kalman filter algorithms are used to estimate the position of the end-effector as the robot moves. A Leica Absolute Tracker AT960 laser tracker provides a reference tracking position, which can be used to evaluate the tracking accuracy of the proposed system. Multiple tool paths having a variety of operating conditions, such as different linear accelerations and angular velocities, have been used with various tracking spaces, and a different number of base stations and Vive trackers for testing. The HTC Vive tracking system has a tracking error of over 1 cm. On the other hand, the results of the developed algorithms have shown that the proposed tracking system can achieve 6 to 2 or 5.5 to 1 mm of error with EKF and UKF, respectively. Multiple trackers can improve the accuracy by up to 1 mm with the EKF, but to a lesser extent with the UKF. This study has found that improvements can be made to the stock HTC Vive system by using the customized EKF or UKF, fusing multiple trackers and fusing multiple IMUs. The proposed tracking system can be used for error compensation for tasks such as machining, welding, or pick-and-place.