Kinetostatic Analysis of Robotic Fingers
Two main approaches dominate the literature on robotic grasping, namely, on one hand purely theoretical work on grasping and manipulation and, on the other hand, the rather intuitive design of functional prototypes. This chapter attempts to bridge this ga
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Quapropter bono christiano siue mathematici siue quilibet inpie diuinantium, maxime dicentes uera, cauendi sunt, ne consortio daemoniorium animam deceptam pacto quodam societatis inretiant. The good Christian should beware of mathematicians and all those who make empty prophecies. The danger already exists that mathematicians have made a covenant with the devil to darken the spirit and confine man in the bonds of Hell. Saint Augustine, De Genesi ad Litteram, Book II-xviii-37, 401-415. in which a fundamental basis for the analysis of underactuated robotic fingers is established. A method to determine the ability of an underactuated finger to generate an external wrench onto a fixed object is presented. This method is based on the introduction of two new matrices which completely describe the relationship between the input torque of the finger actuator and the contact forces on the phalanges.
3.1 Introduction Two main approaches dominate the literature on robotic grasping, namely, on one hand purely theoretical work on grasping and manipulation and, on the other hand, the rather intuitive design of functional prototypes. This chapter attempts to bridge this gap for the special case of underactuated fingers. Indeed, although the development of underactuated fingers aims at overcoming the theoretical difficulties of general manipulation issues and at obtaining prototypes of practical relevance, the capabilities of these fingers remain not well known. Prototypes have often been built through intuitive design, without a generic knowledge of the resulting behaviour and based mainly on special purpose computer-aided simulation. This chapter presents an effort to establish a common framework using simple theoretical bases to analyze the contact forces generated by robotic fingers during enveloping grasps. The fundamental goal of underactuation being simplicity, the objective of this work is to provide practical tools for the analysis L. Birglen, T. Lalibert´ e, & C. Gosselin: Underactuated Robot. Hands, STAR 40, pp. 33–60, 2008. c Springer-Verlag Berlin Heidelberg 2008 springerlink.com
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Kinetostatic Analysis of Robotic Fingers
and comparison of underactuated fingers. Indeed, some issues have been overlooked in previous work and should be systematically addressed. For instance, the grasp force distribution, the capability of the finger to actually exert forces on a grasped object, the stability of the grasp and others will be covered in this chapter. Underactuation in robotic hands generates intriguing properties, e.g. underactuated hands cannot always ensure full whole-hand grasping. Indeed, the distribution of the forces between the different phalanges is governed by the mechanical design of the hand since only one actuator is used and some phalanges may not be able to actually exert any effort in certain configurations. This uncontrollable force distribution can also lead to unstable grasps: a continuous closing motion of the actuator tending to eject the object, as discussed in more details in Chapter 4. A new method to study t
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