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Technical Briefs

Torque Measurement With Compliant Mechanisms

[+] Author and Article Information
Edward Sung, Martin L. Culpepper

Precision Compliant Systems Laboratory,
Department of Mechanical Engineering,
Massachusetts Institute of Technology,
Cambridge, MA 02139

Jonathan F. Bean

Harvard Medical School,
Department of Physical Medicine and Rehabilitation,
Spaulding Cambridge Outpatient Center,
Cambridge, MA 02138

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the Journal of Mechanical Design. Manuscript received July 19, 2011; final manuscript received March 13, 2012; published online January 17, 2013. Assoc. Editor: Mary Frecker.

J. Mech. Des 135(3), 034502 (Jan 17, 2013) (5 pages) Paper No: MD-11-1313; doi: 10.1115/1.4023326 History: Received July 19, 2011; Revised March 13, 2012

This work focuses on the design, development, and testing of an inexpensive, low-profile, cartwheel flexure mechanism for torque measurement. It has been designed primarily for use in a rehabilitation and diagnostics instrument for the treatment of ankle injuries. The sensor is manufactured rapidly and at low-cost using an Omax™ abrasive waterjet machine. Strain gauges are bonded to the flexure beams to measure applied strain using a full wheatstone bridge circuit. Displacement, force, and torque are then calculated from the measured circuit voltage; power and velocity can also be determined if required by the application. Experimental results show that there exists a linear relationship between applied torque and output voltage of the wheatstone bridge for the nested cartwheel flexure design. Furthermore, results of preliminary tests of an ankle rehabilitation device show that it fulfills a need not currently satisfied by current rehabilitation and diagnostic technology in physical medicine and rehabilitation.

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References

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Figures

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Fig. 1

Ankle rehabilitation device utilizing cartwheel flexures as torque sensors

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Fig. 2

Simplified model of flexure deformation

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Fig. 3

Cartwheel flexure deformation

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Fig. 4

(a) Schematic of cartwheel flexure circuit; (b) calibration setup utilizing weights to apply a known, repeatable torque to the cartwheel flexure

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Fig. 5

Cartwheel flexure designs

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Fig. 6

FEA results for cartwheel flexure designs (a) one; (b) two, with increased ROM; and (c) three, with increased load capacity

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Fig. 7

Strain distribution along cartwheel flexure beam

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Fig. 8

Common Wheatstone bridge circuit

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Fig. 9

Calibration date for the three (1-(a), 2-(b), 3-(c)) cartwheel flexure designs

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Fig. 10

Example measurement of the inversion/eversion and plantarflexion/dorsiflexion motions of the AJC

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