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Research Papers

Torque Mode Control of a Cable-Driven Actuating System by Sensor Fusion

[+] Author and Article Information
Kyoungchul Kong

Assistant Professor
Mem. ASME
Robotic Systems Control Laboratory,
Department of Mechanical Engineering,
Sogang University,
Seoul 121-742, Korea
e-mail: kckong@sogang.ac.kr

Joonbum Bae

Assistant Professor
Mem. ASME
School of Mechanical and Advanced Materials Engineering,
UNIST,
Ulsan 689-798, Korea
e-mail: jbbae@unist.ac.kr

Masayoshi Tomizuka

Cheryl and John Neerhout, Jr.,
Distinguished Professor
Fellow ASME
Department or Mechanical Engineering,
University of California,
Berkeley, CA 94720
e-mail: tomizuka@me.berkeley.edu

1Corresponding authors.

Contributed by the Dynamic Systems Division of ASME for publication in the JOURNAL OF DYNAMIC SYSTEMS, MEASUREMENT, AND CONTROL. Manuscript received December 4, 2011; final manuscript received October 12, 2012; published online February 21, 2013. Editor: J. Karl Hedrick.

J. Dyn. Sys., Meas., Control 135(3), 031003 (Feb 21, 2013) (7 pages) Paper No: DS-11-1371; doi: 10.1115/1.4023064 History: Received December 04, 2011; Revised October 12, 2012

A cable-driven actuating system is proposed in this paper. The proposed system is attractive for rehabilitation systems because the weight of the actuator is not imposed on the human body. Since the end-effector and the actuators are connected by Bowden cables, the humans are allowed to freely move in a certain range while being assisted. However, it is a challenge to account for the variable friction of the Bowden cable and the inertia and friction of the actuator in the design of control algorithms. In this paper, a hierarchical control strategy is adopted to control the proposed cable-driven actuating system. To determine the reference trajectory of the motor in real-time, a sensor-fusion method based on a kinematic Kalman filter with MEMS accelerometers is proposed. By the proposed control methods, the cable-driven actuating system realizes a precise force-mode actuation. The system performance is evaluated by experiments.

Copyright © 2013 by ASME
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References

Figures

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Fig. 1

Schematic of the cable-driven human assistive system

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Fig. 2

Two rotary series elastic actuators that pull cables

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Fig. 3

End-effector of the cable-driven system

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Fig. 4

Friction identification of the geared motor

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Fig. 5

Open loop system model: (a) geared motor with friction compensation loop, (b) approximated open loop model after the friction compensation

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Fig. 6

Frequency responses with and without friction compensation

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Fig. 7

A hierarchical controller structure

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Fig. 8

Closed loop system with a PD controller and a feedforward controller

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Fig. 9

An encoder with two accelerometers; (a) encoder disk, (b) optical reader, (c) MEMS accelerometers

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Fig. 10

Angular velocity of reel by differentiating encoder signal and by a kinematic Kalman filter

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Fig. 11

Feedforward filter with a kinematic Kalman filter

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Fig. 12

Reference trajectory of the motor (θRf in Fig. 8) when the desired cable tension is zero

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Fig. 13

Change of cable friction

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Fig. 14

Estimation of cable friction. The notions of ① to ④ in the figure correspond to those in Fig. 13.

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Fig. 15

Performance of the overall controller without friction compensation

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Fig. 16

Performance of the overall controller with friction compensation

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