Performance measurement of a mobile manipulator-on-a-cart and coordinate registration methods for manufacturing applications

Abstract

Mobile manipulators, which consist of a robotic manipulator arm on a vehicular base, enable more flexible and dynamic workflows in manufacturing processes by freeing the manipulator arm from the restriction of working on a single, calibrated workspace. A mobile manipulator-on-cart further enhances job concurrency since the manipulator arm is mounted to a detachable cart rather than directly to the vehicle payload structure. With this increase in flexibility, there is a need to understand new sources of position and orientation uncertainty. This uncertainty can degrade the accuracy and precision of the mobile manipulator position and orientation in addition to the coordination capability between the manipulator and vehicle. To facilitate performance evaluation and uncertainty characterization, the National Institute of Standards and Technology (NIST) has developed an artifact-based measurement methodology for mobile manipulator-on-a-cart systems. The artifact, which is re-configurable, simulates mock-assembly tasks for manufacturing applications, and is compared to a ground truth consisting of an optical tracking system (OTS). This report documents experimental procedures, data analysis methods, and results in measuring the performance of the manipulator-on-a-cart system. The speed and accuracy of two example coordinate registration techniques to be used by the mobile manipulator-on-a-cart to reduce position and orientation uncertainty are also compared.

Design and implementation of a closed-loop mobile manipulator control system

“…The Type A CMMA has been used to measure the static and indexed performance of an Automatic Guided Vehicle (AGV) mobile manipulator [20][21][22][23][24], the indexed performance of an Autonomous Mobile Robot (AMR) mobile manipulator [25], and the indexed performance of a mobile manipulator-on-a-cart, in which an Autonomous Mobile Robot Cart Transporter (AMR-CT) coordinated with a manipulator mounted on a detachable cart [26].…”

“…Furthermore, the AMR-CT mobile manipulator could allow for increased hardware utilization (e.g., allowing the AMR-CT to tend other carts and/or payloads) and concurrent workfows. In addition to evaluating mobile robot docking uncertainty and manipulator position accuracy/repeatability, the CMMA can also be used to compare the performance of coordinate registration methods and algorithms, as demonstrated with various laser-based and visual marker-based coordinate registration test implementations [23,26].…”

“…The CMMA evaluation of the laser-based edge rapid coordinate registration method from Ref. [26] only partially represented this scenario because the registration method took between 15 s and 23 s to run. Therefore, multiple or continuous small perturbations after initial registration could not be tested using this implementation.…”

“…[1,[35][36][37][38][39] provide a specifc example where feedback from a 6 DoF iGPS was applied to the end-effector of an AGV and industrial robot arm mobile manipulator to achieve closed loop control for laser paint removal of aircraft wings. However, the accuracy requirement of this application was 254 mm and it has been observed that, in comparing previous experiments with the CMMA, mobile manipulators that use AMR bases can have more docking uncertainty than those that use AGV bases [25,26,39].…”

“…In the work, it was noted that the assumption of a horizontal, fat surface with no wheel slippage (among other assumptions) was made for the model of the mobile manipulator representing the relationship between the actuator torques and generalized forces and torques. Prior experiments with the mobile manipulator-on-a-cart demonstrated an environment that may not meet such assumptions, which can introduce additional performance uncertainty [26]. Therefore, usage of the CMMA could bolster further advances in control scheme development by allowing for a standardized, reproducible test method for evaluation in a variety of environmental conditions.…”