Abstract
Modulation of arm mechanical impedance is a fundamental aspect for interaction with the external environment and its regulation is essential for stability preservation during manipulation. Even though past research on human arm movements has suggested that models of human finger impedance would benefit the study of neural control mechanisms and the design of novel hand prostheses, relatively few studies have focused on finger and hand impedance. This article touches on the two main aspects of this research topic: first it introduces a mechanical refinement of a device that can be used to effectively measure finger impedance during manipulation tasks; then, it describes a pilot study aimed at identifying the inertia of the finger and the viscous and elastic properties of finger muscles. The proposed wearable exoskeleton, which has been designed to measure finger posture and impedance modulation while leaving the palm free, is capable of applying fast displacements while monitoring the interaction forces between the human finger and the robotic links. Moreover, due to the relatively small inertia of the fingers, it allows us to meet some stringent specifications, performing relatively large displacements (∼45°) before the stretch reflex intervenes (∼25 ms). The results of measurements on five subjects show that inertia, damping, and stiffness can be effectively identified and that the parameters obtained are comparable with values from previous studies.
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Notes
The motors used in this device are Maxon RE 25 (∅25 mm, graphite brushes, 20 W brushed DC motor), available from http://shop.maxonmotor.com/ishop/article/article/118752.xml
The encoder mounted on the motor’s shaft is a 3 channel rotary encoder. Its resolution is equal to 1000 CPT (Count per Turn).
Austriamicrosystems AS5045 12-bit programmable magnetic rotary encoder.
Micron Instruments semiconductor backed gauges.
References
Bennett, D. J. Torques generated at the human elbow joint in response to constant position errors imposed during voluntary movements. Exp. Brain Res. 95(3):488–498, 1993.
Bennett, D. J., J. M. Hollerbach, Y. Xu, and I. W. Hunter. Time-varying stiffness of human elbow joint during cyclic voluntary movement. Exp. Brain Res. 88(2):433–442, 1992.
Burdet, E., R. Osu, D. Franklin, and M. Kawato. The central nervous system stabilizes unstable dynamics by learning optimal impedance. Nature 414(6862):446–449, 2001.
Chao, E. Y. S., K.-N. An, W. P. Cooney, and R. L. Linscheid. Biomechanics of the Hand—A Basic Research Study. Singapore: World Scientific Publishing Company, 1989.
Dong, R. G., T. W. McDowell, and D. E. Welcome. Biodynamic response at the palm of the human hand subjected to a random vibration. Ind. Health 43(1):241–255, 2005.
Fiorilla, A. E., N. G. Tsagarakis, F. Nori, and G. Sandini. Design of a 2-finger hand exoskeleton for finger stiffness measurements. Appl. Bionics Biomech. 6:217–228, 2009.
Friedman, J., and T. Flash. Task-dependent selection of grasp kinematics and stiffness in human object manipulation. Cortex 43(3):444–460, 2007.
Fu, C., and M. Oliver. Direct measurement of index finger mechanical impedance at low force. First Joint Eurohaptics Conference, 2005 and Symposium on Haptic Interfaces for Virtual Environment and Teleoperator Systems, 2005. World Haptics 2005, pp. 657–659, 2005. doi:10.1109/WHC.2005.40.
Gomi, H., and M. Kawato. Human arm stiffness and equilibrium-point trajectory during multi-joint movement. Biol. Cybern. 76(3):163–171, 1997.
Grinyagin, I. V., E. V. Biryukova, and M. A. Maier. Kinematic and dynamic synergies of human precision-grip movements. J. Neurophysiol. 94(4):2284–2294, 2005. doi:10.1152/jn.01310.2004.
Hajian, A. Z., and R. D. Howe. Identification of the mechanical impedance at the human finger tip. J. Biomech. Eng. 119(1):109–114, 1997.
Hogan, N. The mechanics of multi-joint posture and movement control. Biol. Cybern. 52(5):315–331, 1985.
Jones, L. A., and I. W. Hunter. Influence of the mechanical properties of a manipulandum on human operator dynamics. 1. Elastic stiffness. Biol. Cybern. 62(4):299–307, 1990.
Kao, I., M. Cutkosky, and R. Johansson. Robotic stiffness control and calibration as applied to human grasping tasks. IEEE Trans. Robotics Autom. 13(4):557–566, 1997. doi:10.1109/70.611319.
Lacquaniti, F., M. Carrozzo, and N. A. Borghese. Time-varying mechanical behavior of multijointed arm in man. J. Neurophysiol. 69(5):1443–1464, 1993.
Milner, T., and D. Franklin. Characterization of multijoint finger stiffness: dependence on finger posture and force direction. IEEE Trans. Biomed. Eng. 45(11):1363–1375, 1998. doi:10.1109/10.725333.
Mussa-Ivaldi, F. A., N. Hogan, and E. Bizzi. Neural, mechanical, and geometric factors subserving arm posture in humans. J. Neurosci. 5(10):2732–2743, 1985.
Perreault, E. J., R. F. Kirsch, and A. M. Acosta. Multiple-input, multiple-output system identification for characterization of limb stiffness dynamics. Biol. Cybern. 80(5):327–337, 1999.
Pisano, F., G. Miscio, R. Colombo, and P. Pinelli. Quantitative evaluation of normal muscle tone. J. Neurol. Sci. 135(2):168–172, 1996.
Serres, S. J. D., and T. E. Milner. Wrist muscle activation patterns and stiffness associated with stable and unstable mechanical loads. Exp. Brain Res. 86(2):451–458, 1991.
Sharon, A. The Macro/Micro Manipulator: An Improved Architecture for Robot Control. Ph.D. thesis, Department of Mechanical Engineering, Massachusetts Institute of Technology, 1989.
Tubiana, R. The Hand. Philadelphia: W.B. Saunders Company, 1981.
Acknowledgments
This work was partially funded by the European Commission’s Sixth Framework Programme as part of the VIACTORS project under Grant no. 231554. We want to acknowledge the RobotCub consortium for designing and maintaining the development of the electronic devices included in this project.
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Associate Editor Thurmon E. Lockhart oversaw the review of this article.
Appendix A: Exoskeleton Finger Kinematics—Denavit–Hartenberg Representation
Appendix A: Exoskeleton Finger Kinematics—Denavit–Hartenberg Representation
The kinematics of the mechanical chain that actuates each finger can be represented using the Denavit–Hartenberg convention in Table 3.
L 0, L 1, L 2, and L 3 are the distances between the finger MCP joint and the motor shaft and the length of the three joints of the exoskeleton, while θ1, θ2, θ3, and θ4 are the angles of the motor cantilever and of the three joints of each finger of the exoskeleton (see Fig. 7).
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Fiorilla, A.E., Nori, F., Masia, L. et al. Finger Impedance Evaluation by Means of Hand Exoskeleton. Ann Biomed Eng 39, 2945–2954 (2011). https://doi.org/10.1007/s10439-011-0381-7
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DOI: https://doi.org/10.1007/s10439-011-0381-7