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Actuators 2013, 2(2), 45-58; doi:10.3390/act2020045

Optimal Passive Dynamics for Physical Interaction: Catching a Mass

2,* , 3
1 Meka Robotics, 255 Potrero Ave, San Francisco, CA 94103, USA 2 Dynamic Robotics Laboratory, Department of Mechanical Engineering, Oregon State University, Corvallis, OR 97331, USA 3 Ekso Bionics, 1414 Harbour Way South Suite 1201, Richmond, CA 94804, USA
* Author to whom correspondence should be addressed.
Received: 4 March 2013 / Revised: 12 April 2013 / Accepted: 22 April 2013 / Published: 2 May 2013
(This article belongs to the Special Issue Human Centered Actuators)
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For manipulation tasks in uncertain environments, intentionally designed series impedance in mechanical systems can provide significant benefits that cannot be achieved in software. Traditionally, the design of actuated systems revolves around sizing torques, speeds, and control strategies without considering the system’s passive dynamics. However, the passive dynamics of the mechanical system, including inertia, stiffness, and damping along with other parameters such as torque and stroke limits often impose performance limitations that cannot be overcome with software control. In this paper, we develop relationships between an actuator’s passive dynamics and the resulting performance for the purpose of better understanding how to tune the passive dynamics for catching an unexpected object. We use a mathematically optimal controller subject to force limitations to stop the incoming object without breaking contact and bouncing. The use of an optimal controller is important so that our results directly reflect the physical system’s performance. We analytically calculate the maximum velocity that can be caught by a realistic actuator with limitations such as force and stroke limits. The results show that in order to maximize the velocity of an object that can be caught without exceeding the actuator’s torque and stroke limits, a soft spring along with a strong damper will be desired.
Keywords: passive dynamics; impedance; catching passive dynamics; impedance; catching
This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Kemper, K.; Vejdani, H.R.; Piercy, B.; Hurst, J. Optimal Passive Dynamics for Physical Interaction: Catching a Mass. Actuators 2013, 2, 45-58.

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