Dynamic 6DOF metrology for evaluating a visual servoing system

Abstract

In this paper we demonstrate the use of a dynamic, six-degree-offreedom (6DOF) laser tracker to empirically evaluate the performance of a real-time visual servoing implementation, with the objective of establishing a general method for evaluating realtime 6DOF dimensional measurements. The laser tracker provides highly accurate ground truth reference measurements of position and orientation of an object under motion, and can be used as an objective standard for calibration and evaluation of visual servoing and robot control algorithms. The real-time visual servoing implementation used in this study was developed at the Purdue Robot Vision Lab with a subsumptive, hierarchical, and distributed vision-based architecture. Data were taken simultaneously from the laser tracker and visual servoing implementation, enabling comparison of the data streams.

Mathematical metrology for evaluating a 6DOF visual servoing system

“…The algorithm in 5.1 that constructed the best homogeneous matrix H to fit two streams of 6DOF data was applied to data streams that were collected from the Purdue system and a laser tracker system at Purdue University in April of 2008 [2]. These data streams were obtained from two experiments (see Section 3).…”

“…Therefore in this paper, we are searching for LTHRB where LT is the output of the laser tracker system and RB is the output of the Purdue system. In [2], a description of the methodology for the output of both the Purdue system and the laser tracker system is provided. A review is given in Section 3.…”

“…STSHLT = (LTHSTS) −1 and LTHO is constructed by using the laser tracker along with a spherically mounted reflector (SMR) to calculate the Cartesian coordinate position of three features on the object. These three features are enough information to identify the object's reference frame [2].…”

“…For the Purdue Line tracker system each position was in the 2600 mm to 2700 mm range with a standard deviation of 0.560 to 0.630 standard deviation. More details can be found in [2]. Overall, the laser tracker system is two orders of magnitude more accurate than the Purdue system.…”

“…In previous work [2] we reported on experiments in the evaluation of the performance of a real-time visual servoing system using a highly accurate, dynamic, six degree of freedom (6DOF) laser tracker. The purpose of the experiments was to demonstrate a method for evaluating real-time 6DOF dimensional measurements of an object or assembly component under moderately constrained motion.…”