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Research Papers: Design of Mechanisms and Robotic Systems

Avoiding Early Failures in Conjugate Cam Mechanism by Means of Different Design Strategies

[+] Author and Article Information
Pau Català

Department of Mechanical Engineering,
Universitat Politècnica de Catalunya,
Avda. Diagonal 647,
Barcelona 08028, Spain
e-mail: pau.catala@upc.edu

Maria Antònia De los Santos, Joaquim M. Veciana, Salvador Cardona

Department of Mechanical Engineering,
Universitat Politècnica de Catalunya,
Avda. Diagonal 647,
Barcelona 08028, Spain

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the JOURNAL OF MECHANICAL DESIGN. Manuscript received May 30, 2015; final manuscript received September 30, 2015; published online November 16, 2015. Assoc. Editor: Ettore Pennestri.

J. Mech. Des 138(1), 012302 (Nov 16, 2015) (9 pages) Paper No: MD-15-1401; doi: 10.1115/1.4031805 History: Received May 30, 2015; Revised September 30, 2015

To solve the indetermination of forces existing in a form-closed cam mechanism formed by conjugate cams, where the contact between the cams and the follower rollers is constantly ensured by only the geometry of the elements, dynamic models that consider the elasticity of the elements must be proposed. Because the stiffness of the main elements is associated with the elasticity of the solids, tight variations in manufacturing and assembly errors modify the effective interference fit, which significantly affects the expected fatigue life of the mechanism, leading to a premature failure of the elements due to surface fatigue. Based on a real industrial application of a conjugate cam mechanism and using lumped-parameter models, the objectives of this paper are: first, to show that it is difficult to achieve a pure form-closed conjugate cam mechanism, with the expected fatigue life of the mechanism, by using only standard tolerance specifications; second, to compare the expected fatigue life and motor torque with other cam mechanism design strategies such as force-closed and the combination of force-closed and form-closed strategies, known as force-closed conjugate cam strategy. This paper based on simulation results demonstrates that this latest strategy can, thanks to a better control of the preload, easily achieve results very similar to the theoretical ones of a form-closed conjugate cam mechanism. A prototype of the mechanism of the force-closed conjugate cam strategy is also built.

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References

Figures

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Fig. 5

Form-closed contact forces

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Fig. 6

Form-closed motor torque

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Fig. 7

Form-closed contact pressures

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Fig. 4

Free-body diagram of conjugate cams

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Fig. 3

Linear displacement functions imposed on the roller centers

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Fig. 2

Scheme of the dynamic model for pure form-closed

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Fig. 1

Current form-closed conjugate cam mechanism

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Fig. 12

Scheme of the dynamic model for force-closed conjugate cam strategy

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Fig. 8

Scheme of the dynamic model for force-closed strategy

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Fig. 9

Free-body diagram of cam

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Fig. 10

CAD model with a feasible constructive solution

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Fig. 11

Force-closed conjugate cam strategy prototype

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Fig. 13

Force-closed strategy forces

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Fig. 14

Bottom follower accelerations for different springs for the force-closed conjugate cam mechanism

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Fig. 15

Comparison of spring forces for the force-closed conjugate cam mechanism

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Fig. 16

Forces for the force-closed conjugate cam strategy

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Fig. 17

Contact pressures for new alternatives design strategies

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Fig. 18

Motor torque for new alternatives design strategies

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