2011 IR&D Annual Report

Metrology Referenced Roving Accurate Manipulator Phase 2 (MR ROAM 2), 10-R8205

Principal Investigators
Glynn Bartlett
Paul Hvass

Inclusive Dates:  01/01/11 – 01/01/12

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 non-contact position data enables a signal-based link to ground reference that can replace the physical link. The robotics industry is ripe for rapid expansion using 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 envelops.

Figure 1: Integrated MR ROAM 2 System
Figure 1. Integrated MR ROAM 2 System.

Approach — A demonstration system was developed using a commercially available platform and manipulator. The first step was to port the software developed during phase 1 and update it as necessary to match the new robotic manipulator and mobile platform. The next step was to incorporate the new external metrology system. The metrology system provided was a six degree-of-freedom (DOF) base pose correction to the mobile platform position, implemented at specified rates. Software was developed to correct the tool point based on the feedback from the metrology device. The robotic manipulator was corrected to a world path plan using an incremental real-time correction implemented through the robotic controller. The project ported from phase 1 the closed loop control developed for the mobile platform motion using an external metrology device. The closed-loop path control of the mobile platform maintained the manipulator tool point within reach of an independent tool path. Once the MR ROAM 2 system was integrated, empirical testing was conducted to determine the repeatability and capability of the system. The experimental variables consisted of the tool-point velocity at one specific update rate and two different part locations within the field of view of the metrology device. Metrology receivers were attached to the mobile platform to track its position for the feedback loop. Metrology receivers, mounted on the end effector, were used to both make real-time path corrections, and track accuracy and repeatability of the complete system to follow a specified world path.

Accomplishments — 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. Final testing finished at the end of the third quarter, and analysis was completed during the fourth quarter. Data indicates the positional accuracy is less than one-half inch and repeatability is one-quarter inch according to ISO standard 9283. The system maintained a standard deviation of less than one-quarter inch in all coordinate directions.


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