Metrology Referenced Roving Accurate Manipulator (MR ROAM), 10-R8019

Principal Investigators
Glynn Bartlett
Paul Hvass

Inclusive Dates:  01/01/09 – 12/31/09

Background - Modern industrial robots are generally monolithic assemblies, either floor-mounted or gantry-mounted, whose accuracy is largely determined by the error stack-up through each joint and link from a ground reference to the robot's end effector. The fact that the systems rely upon a physical link to the ground reference means that there is limited robot market penetration both for large-scale applications and for operation at remote sites. However, the recent availability of large scale metrology systems to provide real-time, noncontact position data (e.g. incremental Global Positioning System (iGPS) or motion capture technology), enables a signal-based link to ground reference that can replace the physical link. The robotics industry is ripe for rapid expansion utilizing off-the-shelf manipulators on mobile platforms, in conjunction with an external metrology system, for large scale and remote site tasks where accuracy and repeatability are required over large working envelopes.

Approach - A demonstration system will be developed using a small, commercially available platform and manipulator. The first step will be to develop the software necessary to combine the mobile platform with the robotic manipulator so they work as a single kinematic unit and to mechanically join the robotic manipulator and mobile platform. The next step will be to incorporate the external metrology device. The metrology device will provide a six degree-of-freedom (DOF) base pose correction to the mobile platform position, implemented at specified rates. Once the mobile platform has the corrected base pose, the robotic manipulator may be corrected to world space using a standard base transformation matrix and the manipulator inverse kinematic solution. In addition, the system will implement closed loop control for the mobile platform motion with the new feedback loop so the reach of the manipulator is not exceeded while tracking a world path. Once the MR ROAM system has been integrated, empirical testing will be conducted to determine the repeatability and capability of the system. The experimental variables will consist of the measurement update rate, tool point velocity, and path profile. To measure performance, the motion capture marker constellation will be attached to both the end effector and to the mobile platform. The markers on the mobile platform will be used for dynamic corrections of the base pose, and the markers on the end effector will be used to track accuracy and repeatability of the complete system to follow a specified world path.

Accomplishments - This project was completed December 31, 2009. The basic integration of the three individual systems occurred over the first two quarters. This integration included mechanical, electrical, and software components. During the third quarter, calibration of the system and different control algorithms were tested to evaluate performance. System level testing started at the end of the third quarter. During the fourth quarter the system concept was proven operational through both numerical analysis of tool point data and paint deposition on a complex surface that was approximately 10 times the length and twice the width of the mobile platform wheel base.

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