Technical Reports (CIS)

Document Type

Technical Report

Date of this Version

May 1992


University of Pennsylvania Department of Computer and Information Science Technical Report No. MS-CIS-92-63.


The design and control of an in-parallel, pneumatically actuated manipulator is presented. In-parallel manipulators offer superior dynamic characteristics because of their high stiffness, low inertia, and potential for direct drive actuation. In this thesis, the three degree of freedom tripod manipulator is studied. The three degrees of freedom of the manipulator are exactly those that are required for force control perpendicular to a surface. These degrees of freedom are translations along the approach direction and rotations about the axes perpendicular to the approach direction. This body of research can be grouped into three parts. First the area of force control is examined with two purposes in mind, improving pneumatic force control, and understanding how force control has been traditionally implemented and the reasons for its limitations. Next, the improvement of the response of the mechanism and the implementation of different force control schemes are investigated. To improve the response of the system, shorter transmission lengths and an inner pressure feedback loop are added. Position control, force control, stiffness/compliance control, and impedance control, are all investigated, Lastly, a discussion of the advantages and possible uses of this mechanism is presented. The advantage of the parallel mechanism is the ability to regulate the force perpendicular to the surface. Thus, the mechanism can control the force perpendicular to the surface, while an arm attached to the mechanism can control the position of the end effector. This mechanism thus allows the hybrid position and force control problem to be decoupled. Obvious uses for applying a force perpendicular to a surface are tasks such as deburring or polishing. Another possible use could be peg insertion; a new design for peg insertion will be discussed. Lastly, this mechanism could be used as an ankle for a walking machine or a writ for a serial robot. The mechanism can adjust for unforeseen impacts and allow the system to be used in an unstructured environment.



Date Posted: 25 July 2007