Title
Design of a Six Degree of Freedom Haptic Interface

Abstract
A six degree-of-freedom manipulandum with force-feedback capabilities was designed for the use as an interface in virtual environments and teleoperators. Of specific interest is its application to astronaut training. The manipulandum should be able to simulate the mechanical behavior of a wide range of tools in a zero gravity environment. The device is made up of two, three degree-of-freedom mechanisms coupled by a variable length linkage which also serves as the manipulandum's handle. The tip of each 3 dof mechanism can be positioned arbitrarily in 3-space. A fixed-length rod connecting the two tips would have five controlled dof, but would be unable to rotate about its own axis. However, expanding and contracting the variable length linkage will rotate the handle about the axis of the linkage resulting in the sixth degree of freedom. A cable driven differential transmission is used for each of the three degree of freedom mechanisms allowing all six actuators to be fixed to ground. The kinematic parameters were chosen such that the usable workspace, with no singularities, is approximately one cubic foot in translational motion, and plus/minus ninety degrees in endpoint orientation space.

Source: Masters Thesis, Northwestern University; August, 1996

Title
Motor Selection and Damper Design for a Six Degree of Freedom Haptic Display

Abstract
The overall thrust of this research was to design a motor/damper system for a proposed six degree of freedom haptic device designed by Burns [2]. First, the thesis addresses the importance of damping in providing stable and "real" touch feedback to the user. Second, the work addresses motor issues regarding advantages/disadvantages to brushed versus brushless motors, different commutation methods, and position feedback sensors. Finally, damper design issues are discussed. These issues include: 1) torque sensor selection and setup, 2) cancellation of noise caused by internal and external loads, and 3) advantages of damper adjustability.

Source: Masters Thesis, Northwestern University; March, 1997

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