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Design Innovation

Design and Validation of a General Purpose Robotic Testing System for Musculoskeletal Applications

[+] Author and Article Information
Lawrence D. Noble, Robb W. Colbrunn, Antonie J. van den Bogert

Department of Biomedical Engineering, Lerner Research Institute, and Orthopaedic and Rheumatologic Research Center, Cleveland Clinic, Cleveland, OH 44195

Dong-Gil Lee

Department of Biomedical Engineering, Lerner Research Institute, and Orthopaedic and Rheumatologic Research Center, Cleveland Clinic, Cleveland, OH 44195; Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, WA 98195

Brian L. Davis1

Department of Biomedical Engineering, Lerner Research Institute, and Orthopaedic and Rheumatologic Research Center, Cleveland Clinic, Cleveland, OH 44195davisb3@ccf.org

1

Corresponding author.

J Biomech Eng 132(2), 025001 (Jan 28, 2010) (12 pages) doi:10.1115/1.4000851 History: Received December 18, 2006; Revised October 15, 2009; Posted December 17, 2009; Published January 28, 2010; Online January 28, 2010

Orthopaedic research on in vitro forces applied to bones, tendons, and ligaments during joint loading has been difficult to perform because of limitations with existing robotic simulators in applying full-physiological loading to the joint under investigation in real time. The objectives of the current work are as follows: (1) describe the design of a musculoskeletal simulator developed to support in vitro testing of cadaveric joint systems, (2) provide component and system-level validation results, and (3) demonstrate the simulator’s usefulness for specific applications of the foot-ankle complex and knee. The musculoskeletal simulator allows researchers to simulate a variety of loading conditions on cadaver joints via motorized actuators that simulate muscle forces while simultaneously contacting the joint with an external load applied by a specialized robot. Multiple foot and knee studies have been completed at the Cleveland Clinic to demonstrate the simulator’s capabilities. Using a variety of general-use components, experiments can be designed to test other musculoskeletal joints as well (e.g., hip, shoulder, facet joints of the spine). The accuracy of the tendon actuators to generate a target force profile during simulated walking was found to be highly variable and dependent on stance position. Repeatability (the ability of the system to generate the same tendon forces when the same experimental conditions are repeated) results showed that repeat forces were within the measurement accuracy of the system. It was determined that synchronization system accuracy was 6.7±2.0ms and was based on timing measurements from the robot and tendon actuators. The positioning error of the robot ranged from 10μm to 359μm, depending on measurement condition (e.g., loaded or unloaded, quasistatic or dynamic motion, centralized movements or extremes of travel, maximum value, or root-mean-square, and x-, y- or z-axis motion). Algorithms and methods for controlling specimen interactions with the robot (with and without muscle forces) to duplicate physiological loading of the joints through iterative pseudo-fuzzy logic and real-time hybrid control are described. Results from the tests of the musculoskeletal simulator have demonstrated that the speed and accuracy of the components, the synchronization timing, the force and position control methods, and the system software can adequately replicate the biomechanics of human motion required to conduct meaningful cadaveric joint investigations.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Simplified illustration of the musculoskeletal simulator, as it would be configured for a foot study. The various coordinate systems shown illustrate the necessary mathematical transformations required to achieve motion of the force platform against the foot to simulate gait (GND: force plate; MIC: MicroScribe; PLA: rotopod platform; ROB: rotopod base; TIB: tibia). Reprinted with permission, Cleveland Clinic Center for Medical Art & Photography ©2009. All Rights Reserved.

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Figure 2

Musculoskeletal simulator, demonstrating cadaver foot mounting and attachment of five tendons to the actuators through freeze clamps, cables, and pulleys

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Figure 3

Simplified illustration of the musculoskeletal simulator, as it would be configured for a knee study. The various coordinate systems shown illustrate the necessary mathematical transformations required to achieve motion of the knee fixture to cause knee flexion (FEM: femur; FIX: knee flexion fixture; LOD: six-axis load cell; MIC: MicroScribe; PLA: rotopod platform; ROB: rotopod base). Reprinted with permission, Cleveland Clinic Center for Medical Art & Photography ©2009. All Rights Reserved.

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Figure 4

Musculoskeletal simulator block diagram showing general components required for foot experiments. The synch bus allows synchronization between the rotopod, strain gauge data acquisition, and tendon actuators during simulated gait (DOF, degrees of freedom)-

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Figure 5

Tendon actuator accuracy results for two experiments of three runs each, in which under closed-loop feedback, the actuator of the musculoskeletal simulator simulates muscle contractions. Muscles included (a) triceps surae, (b) tibialis anterior, (c) tibialis posterior, (d) peroneus longus, and (e) flexor hallucis longus. Note that absolute error is shown as a mean ±1 standard deviation. Target force is included as a reference.

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Figure 6

Tendon actuator repeatability results for two experiments of three runs each, in which under closed-loop feedback, the actuator of the musculoskeletal simulator simulates muscle contractions. Muscles included (a) triceps surae, (b) tibialis anterior, (c) tibialis posterior, (d) peroneus longus, and (e) flexor hallucis longus. Note that relative accuracy can be seen in deviation from the theoretical line.

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Figure 7

Optimization results for seven experiments, showing convergence of superior force against the target toe-off region profile during simulated gait using the musculoskeletal simulator.

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Figure 8

Selected results from the foot bone strain study using the musculoskeletal simulator are shown. Full-physiological loading is demonstrated through (a) the superior and (b) anterior ground reaction forces, (c) anterior center of pressure, and (d) muscle forces. Results shown are indicative of a typical experiment run.

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Figure 9

Representative superior compression force profile of the real-time proportional-integral-derivative (PID) hybrid control for a knee experiment using the musculoskeletal simulator.

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