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When Millimeters Count, Count on WVRTC Engineers to Deliver

WVRTC Robot Characterization

How well can a robot position itself? How well can it repeat going to the same position? How about when it has to lift a heavy object? Or when it’s moving slow as opposed to moving fast?

When conducting robotics research, these are important questions and the answers need to be well understood. WVRTC has been the primary source for providing this data on all of the industrial robots both at NASA Goddard Space Flight Center (GSFC) and the WVRTC facility in Fairmont. While the industrial robots will remain on earth, they serve as analogs to the actual robotic manipulators that will soon be in space repairing satellites and plucking boulders off the surfaces of asteroids. Understanding their capabilities and limitations is important since it drives the design of the flight software, robotic tools, and overall mission objectives.

Robot characterization began as a rigid implementation of an American National Standards Institute (ANSI) procedure. This standard provides a common way for establishing the robot’s position accuracy (how close can the robot get to where it was commanded), the position repeatability (how close can the robot get to where it was previously), the path accuracy (similar to position accuracy, only with the robot moving), and the path repeatability. WVRTC used its knowledge and expertise to completely automate the ANSI procedure which greatly reduces the amount of time necessary to characterize a robot. It also ensures that the procedure is highly repeatable and not subject to human operator error.

While the standard provides a way to compare the performance of various robotics manipulators, it has some inherent drawbacks. The drawback is that the robot is characterized in a small portion of its workspace. Depending on the source of the position error, the accuracy of the robot can be drastically different if the robot is positioned in an area other than where it was characterized. The ANSI procedure also does not provide any indication as to where the error is originating. This is where WVRTC has taken the robot characterization process to another level.

By implementing a custom procedure, in addition to the ANSI standard, WVRTC can characterize a robot through its entire workspace. The large amount of data collected during the process can then be run through a custom optimization routine to identify how the accuracy of the robot could be improved. As a byproduct, the source of most errors can be identified and corrected. This process has already proven extremely useful at improving the performance of the robots, even uncovering a bug in the manufacturers’ custom control software.

WVRTC continues to expand its work on robot characterization, making further improvements to its automated testing and data processing routines. Recently, the team has expanded their capabilities to fully capture the effects that increasing the payload has on the robot’s accuracy. Through additional testing and optimization, the team can now predict with high certainty the amount of deflection the robot will experience due to its load. All told, WVRTC has shown that on certain manipulators, the position accuracy can be improved by a factor of twenty. The team looks to continue this work and to assist with the characterization of the engineering development unit at GSFC for satellite servicing.  In addition, WVRTC capability with robot characterization will serve multiple robotic operations in space exploration, ranging from autonomous capture to cooperative assembly tasks.

 

A WVRTC Robot Undergoing ANSI Characterization (with payload)

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