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A traditional haptic device utilizes motors to impose feedback motion constraints on a user interacting with it. However, primary concerns with human-robot interaction include safety, stability, and ease of manufacturing. It is therefore desired to develop a passive haptic device that users can interact with by moving the system along constrained single degree of freedom (SDOF) paths while restricting motion in other directions. The goal of the project is to develop a planar passive haptic system that can restrict motion paths while allowing only the prescribed SDOF paths.
The device is required to have at least six SDOF paths and force resistance capable of blocking the user when they deviate away from an SDOF path and preventing them from damaging the device. Additionally, the minimum angle between adjacent SDOF paths must be less than 90 degrees.
The design that we chose was a system of six linkages connected by brakes at each joint. These brakes are pneumatically powered and turn on and off to hold and release the motion of the linkages. Rotary encoders are mounted at the bottom of the brakes to track the relative position of the joints and the handle that is moved by the user. The primary requirements were that the system had at least 6 SDOF paths and could resist a maximum torque of 11Nm, produced by a user at the handle.
To test that the device matched the characteristics and requirements that it was designed, the assembled prototype was subject to many tests, as well as virtual simulations. Some requirements and constraints were achieved simply by nature of the design. For example, the six SDOF paths are inherently included in the design by the addition of 6 brakes, and therefore it does not need to be confirmed through testing. However, some tests were performed to test the functionality, including both angle measurement and force testing for one linkage, as well as the full system. In addition, MATLAB simulations verified the angle change between the different degrees of freedom paths. Each of these tests verified different parts of the requirements. All of these tests were successful.
There are no major modifications that need to be made to the device moving forward. All requirements for design have been met. However, there are modifications that should be made to increase the ability and accuracy of the device. Currently there is too much slack in the joints that will not only affect force, but position measurements as well. This issue should be address to improve the device.
Matteson, Lydia; Jones, Morgan; and Hinojosa, Sam, "HaptX Team Final Project Report" (2020). Engineering Senior Design Reports. 42.