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Research Papers

Cam Profile Generation for Cam-Spring Mechanism With Desired Torque

[+] Author and Article Information
Fei Gao

Mem. ASME
Department of Mechanical and
Automation Engineering,
The Chinese University of Hong Kong,
Shatin 999077, NT, Hong Kong
e-mail: fgao2@mae.cuhk.edu.hk

Yannan Liu

Department of Mechanical and
Automation Engineering,
The Chinese University of Hong Kong,
Shatin 999077, NT, Hong Kong
e-mail: lyn2014hk@gmail.com

Wei-Hsin Liao

Professor
Fellow ASME
Department of Mechanical and
Automation Engineering,
The Chinese University of Hong Kong,
Shatin 999077, NT, Hong Kong
e-mail: whliao@cuhk.edu.hk

1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the JOURNAL OF MECHANISMS AND ROBOTICS. Manuscript received August 23, 2017; final manuscript received April 18, 2018; published online May 31, 2018. Assoc. Editor: Jian S. Dai.

J. Mechanisms Robotics 10(4), 041009 (May 31, 2018) (7 pages) Paper No: JMR-17-1265; doi: 10.1115/1.4040270 History: Received August 23, 2017; Revised April 18, 2018

Commercial springs have linear characteristics. Nevertheless, in some cases, nonlinear behavior (e.g., nonlinear torque) is desired. To handle that, a cam-spring mechanism with a specified cam profile was proposed in our previous work. In this paper, to further study the cam profile generation, a new convenient design method is proposed. First, the model of cam-spring mechanism considering the friction force is analyzed. Based on this model, sorts of derivation processes are conducted for obtaining the expression of spring torque. When the friction coefficient is zero, the analytical solution of the equation (spring deformation) is derived. However, in practice, where the friction coefficient is not zero, an analytical solution is not available. Therefore, a numerical solution is sought. Then, with the obtained spring deformation, the cam profile and pitch curve are generated. Results of an experiment conducted to verify the new method show that the cam profile generated by the direct derivation method can precisely mimic the desired torque characteristics. In addition, the hysteresis induced by the friction force in the cam-spring mechanism is also studied. By increasing the spring stiffness, spring free length, and the cam eccentricity, the hysteresis in the cam-spring mechanism can be decreased.

FIGURES IN THIS ARTICLE
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Copyright © 2018 by ASME
Topics: Torque , Springs , Friction
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Figures

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Fig. 1

Cam-spring mechanism for desired torque characteristics

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Fig. 2

Powered ankle-foot prosthesis: (a) prototype and (b) schematic diagram

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Fig. 3

Geometric model of the cam-spring mechanism

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Fig. 4

Cam profile generation: (a) with undercutting and (b) without undercutting

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Fig. 5

Generated cam profiles via different design methods

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Fig. 6

Simulation results of spring torques in the cam-spring mechanism

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Fig. 7

Effect of l0 on the hysteresis in the cam-spring mechanism

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Fig. 8

Effect of spring stiffness k on the hysteresis in the cam-spring mechanism

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Fig. 9

Effect of eccentricity e on the hysteresis in the cam-spring mechanism

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Fig. 10

Cam profile generation: (a) cam profile and (b) fabricated cam model

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Fig. 11

Experimental setup for testing the cam-spring mechanism

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Fig. 12

Measured torque versus angle curve in the cam-spring mechanism

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