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A spherical five-bar linkage generally has two degrees-of-freedom. However, some configurations arise where the mechanism is able to move with an additional degree-of-freedom, even with both input angles fixed. These configurations are termed exceptional. They appear in a configuration surface as embedded straight lines in the direction of its outputs. Without prior knowledge, these lines can be discovered by structured slicing of the configuration surface using the tools of polynomial homotopy continuation. This search procedure is conducted for spherical five-bars of equal-link-length. Cases for adjacent and nonadjacent input angles are analyzed. An equal-link-length spherical five-bar with 90 deg links is used for the design of a deployable control surface for an aircraft. Taking advantage of the exceptional sets in the mechanism, one motor is able to lock, deploy, and articulate the control surface.
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Output Mode Switching for Parallel Five-bar Manipulators Using a Projection-based Direct Collocation Method
For a given endpoint position, a five-bar manipu-lator may assume several separate configurations, with each offering distinct differential kinematics. The corresponding configurations are separated by output singularities and are said to belong to different output modes. In this work, a procedure for dynamically switching between output modes is proposed, with each mode offering different directional force/velocity transmission ratios. The procedure involves solving an optimal control problem using a projection-based direct collocation method for constrained mechanisms to find an optimal trajectory along which the mechanism changes output modes. Using this procedure, a five-bar mechanism configured at a given end-effector position is shown to switch to another output mode where the electrical energy consumed by the actuators to statically hold the mechanism reduces by 80%. Furthermore, the computed trajectories are seen to cross input singularities, a maneuver made possible by momentum planning since actuator authority is impaired at these configurations.
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- Award ID(s):
- 2144732
- PAR ID:
- 10562616
- Publisher / Repository:
- IEEE
- Date Published:
- ISBN:
- 979-8-3503-9596-9
- Page Range / eLocation ID:
- 1-8
- Format(s):
- Medium: X
- Location:
- Chicago, IL, USA
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1109/ReMAR61031.2024.10617557
