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There are many ways for a gripper to estimate the forces between its fingers. If powered by direct-drive brushless motors, then one technique is to measure their current. This is not the most accurate technique, but it is simple, keeps the sensor remote, and requires no new components. The estimation involves multiplying current signals through by the torque constant and the inverse transpose of the Jacobian. The Jacobian either amplifies the signal from fingertip force to motor current (at the cost of tip force production), or diminishes it (with the gain of tip force production), indicating an inherent trade-off. However, the Jacobian is a function of configuration, and for any workspace point there are multiple configurations (multiple inverse kinematics solutions), therefore a selection of Jacobian exists. For a given workspace point, the number of Jacobian choices is just a few, but these choices can be designed (through dimensional synthesis) to overcome the trade-off. The problem can be framed as velocity ellipse synthesis over multiple output modes. In this work, we conduct optimal synthesis to compute a new gripper design. The gripper was built and tested. It transitions between two different modes: sense mode and grip mode. Sense mode can sense forces 3 times smaller than grip mode. Grip mode can exert forces 4 times greater than sense mode.
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Direct Drive Hands: Force-Motion Transparency in Gripper Design
The Direct Drive Hand (DDHand) project is exploring an alternative design philosophy for grippers. The conventional approach is to prioritize clamping force, leading to high gear ratios, slow motion, and poor transmission of force/motion signals. Instead, the DDHand prioritizes transparency: we view the gripper as a signal transmission channel, and seek high-bandwidth, highfidelity transmission of force and motion signals in both directions. The resulting design has no gears and no springs, occupying a new quadrant in the servo gripper design space. This paper presents the direct drive gripper design philosophy, compares the performance of different design choices, describes our current design and implementation, and demonstrates a fly-by “smack and snatch” grasping motion to show the gripper’s ability to safely detect and respond quickly to variations in the task environment.
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- Award ID(s):
- 1813920
- PAR ID:
- 10105126
- Date Published:
- Journal Name:
- Robotics: science and systems
- ISSN:
- 2330-7668
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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