BRACING MICROMACRO MA"ULAT0RS CONTROL Jae Young Lew Automation and Measurement Sciences Department Pacific Northwest Laboratoory' Wayne J. Book The George W. Woodruff School of Mechanical Engineering Georgia Institute of Technology This paper proposes a bracing strategy for micro/macro manipidatom. The bnwing micro/macro manipulator can provide advantages in accurate positioning, large work- space, and contact-task capability. However, in exchange for improvement in performance, one must accept the complex control problem along with the complex dynam- ics. This research develops a control scheme for a bracing manipulator which makes multiple contacts with the environment. Experimental d t s show the feasibility of the proposed ideas for real world applications. 1. Introduction In general, a micro arm is mounted on the end of a macro manipulator. The macro manipulator would c ~ v r y the micro arm to the place of interest in a large work- space. Then, the micro arm would perform fine motions. One of the inherent problems with this serial configuration of microlmacro manipulators is the structural flexibility of the macro manipulator. Bracing a microlmacro manipula- tor can be one effective way to reduce or damp out its structural vibration. For example, the manipulator would brace against a stationary frame, and the end effector would perform line motion control just as a human braces the wrist for accurate writing. By forming a close kinematic chain, bracing will stiffen its structure and secure the end point positioning. Bracing requires a special type of control strategy due to its complex constrained dynamics. This research generalizes the bracing arm control problem as a hybrid control of flexible manipulators with multiple contacts. For example, the end effector works against a workpiece, and the other part of the manipulator may brace against a stationary frame. Then, the manipulator should be able to control the position/ force not only at the end effector, but also at the bracing point. This requires hybrid control of multiple contacts with the environment. This paper presents a hybrid pitiodforce controller for flexible link manipulators which make contact with environment at more than one point. First, a mathe- matical formulation of the umshined dynamics is obtained. Their dynamics are transformed into two using the singular value decomposition of constraint equations. The force and position controllers are devel- oped based on the orthogonality of these two subspaces. This work has been developed in a generic form for broad application. Theoretical study proves its asymptotic stability, and experimental results show promising feasibil- ity of bracing strategy for red world application. subspm such a~ Constrained and constraint-free space^ 2. ProblemStatement The bracing arm control problem is generalized to a hybrid control of flexible manipulators with multiple contacts with the environment. Figure 1 shows the general case of a bracing manipulator with n joints, all active, constrained by m contacts with the environment. Figure 1 A Flexible Mauipulntor with Multiple Contact with E n v i " m t The objective is to control the positiodforce of the end effector while satisfying all the constraints and maintaining desired contact forces at the bracing points. A bracing manipulator, which is a redundant manipulator, 'PNL is operated for the U.S. Department of Energy by Battelle Memorial Institute under Contract DE-ACM- 76RLO 1830. 1050-4729/94 $03.00 0 1994 IEEE 2362