This project will further develop a recently proposed novel control strategy, Passive Velocity Field Control (PVFC), for mechanical systems in the context of application areas where the system must interact safely with its environment and where coordination is one of the key prime control objectives. Specifically, the new control method will be developed for two important application areas:
- robotic deburring; and
- control of teleoperated manipulators.
The PVFC control paradigm is ideally suited for these applications because it possesses two unique features:
- it makes explicit any coordinate requirements of the task for the system, and
- it preserves the passivity property of the closed loop system.
Most previous strategies involve the decomposition of a control task into the design of a timed trajectory, and the design of a controller to track the trajectory at each instant in time. In contrast, the present strategy captures the coordination requirement by merely defining a velocity field that guides the system to satisfy the coordination requirement, without the extraneously timing information that can over constrain the system. By ensuring that the closed loop system is passive with respect to the power input from the environment, the interaction of the closed loop system with any strictly passive physical system will remain stable. Previous controllers generally do not possess this property, so that as the closed loop system comes in contact with the environment, interaction stability can be compromised.
Because of these features, the new control paradigm is expected to be suited for applications where there is a strong coordination requirement and where the stable and intimate interactions with uncertain physical environment are needed for safe operation. Since robotic deburring and teleoperated manipulation applications share these salient features, these will be studied simultaneously.
In robotic deburring, the coordination requirement is imposed by the constraint that the tool must follow precisely the prescribed tool path to avoid unintended material removal. Moreover, the deburring tool must also interact with the work piece to be deburred. Because of the imprecise knowledge of the geometry of the surface and of the dimensions of the burrs present, the interaction forces experienced by the tool can vary up to 200%. Inappropriate interaction between the tool and the work piece can lead to instability, damage to the tool, and poor deburring quality.
The coordination requirement for teleoperated manipulator systems is imposed by the fact that the motions of both the manipulator that interacts with the human and of the manipulator performing the actual manipulation must mimic each other. In addition, a teleoperated manipulator must physically interact with both the human operator and the work environment, so that the safety of the human and the possibly delicate work environment (such as in robotic surgery) must be guaranteed. This becomes critical as many telemanipulation applications demands that the force and the power interaction between human and the machine should be a scaled multiple of that between the environment and the machine.
Part finishing operations currently account for 35% of manufacturing costs due to the labor intensive manual operations. Thus, effective robotic deburring strategies can lead to increased productivity and significant cost saving. Teleoperation with kinesthetic feedback, can potentially combine the superior mechanical capability, strength, size and endurance of machines with the real time information processing capability of human. Thus, such human-in-the-loop approach can be applied to mechanically challenging tasks that need to be performed in uncertain and unstructured environments. These situations include minimally invasive surgeries, toxic inspection and cleanup, health care robotics and operations in unstructured manufacturing floors etc..
A combined theoretical and experimental approach is being taken in this research. Controller design and analysis will utilize concepts from differential geometry, especially Riemannian geometry. Experimental verification will be performed on a direct drive manipulator system, powered by Moog 416 and 420 series DC brushless motors. The manipulator system serves the dual purpose of the deburring robot and the teleoperator system.
Graduate students:
- Jing-Lei Li M.S. Oct 2000. Now at Seagate, MN.
- Dongjun Lee PhD candidate
Undergraduate students
- Benjamin Peirce B.S. (Hons), August 2000. Now at Harvard.
Publications to date:
- D. J. Li and P. Y. Li, "Passive Approaches to the Control of Bilateral Teleoperated Manipulators: Theory and Experiments", Proceedings of the 2001 American Control Conference, Arlington VA, June 2001.
- J. Li and P. Y. Li, "Passive velocity field control approach to robot force control and contour following", Proceedings of the 2000 Japan USA Symposium on Flexible Automation Ann Arbor, MI, July, 2000
- P. Y. Li and D. J. Lee, "Passive feedforward approach to bilateral teleoperated manipulators", Proceedings of the 2000 Symposium on Haptic Interfaces and Teleoperators, ASME IMECE. November, 2000.
- P. Y. Li, “Adaptive Passive Velocity Field Control”, Proceedings of the 1999 American Control Conference, San Diego.
- P. Y. Li, “Passive Control of Bilateral Teleoperated Manipulators”, Proceedings of the 1998 American Control Conference, Philadelphia, June 1998.
- P. Y. Li and R. Horowitz, "Passive Velocity Field Control. Part 1: Geometry and Robustness", IEEE Transactions on Automatic Control, (Accepted for publication)
- P. Y. Li and R. Horowitz, "Passive Velocity Field Control. Part 2: Application to Robot Contour Following Problems ", IEEE Transactions on Automatic Control (Accepted for publication)
- P. Y. Li and R. Horowitz, "Passive Velocity Field Control of Mechanical Manipulators" IEEE Transaction on Robotics and Automation August 1999
Sponsors:
- National Science Foundation (Grant CMS-9870013)
- Matching funds provided by Center for Advanced Manufacturing, Design and Control (CAMDAC) of the University of Minnesota.
