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I will discuss two representations of friction and two manipulation systems. The first system is a sensorless parts orienter developed in 1985 by Matthew Mason and myself. That system was based on a configuration space representation of friction. The second system is a recent system in which two robot arms manipulate parts using their "palms". This system is based on a frictional representation for modeling relative sliding motions between a part and moving constraints.
In the past, part orienters and feeders have suffered from the "frozen hardware" problem. Too much of the mechanics of the task has been compiled into hardware, in the form of fixed feeder gates and orienting shapes. At the other extreme, general purpose robots have suffered from too much generality and too little reliable software. An important intermediate architecture consists of a sequence of simple manipulators under software control. The research presented in this talk is a step towards the creation of such simple manipulators.
The long-term goal of this research is two-fold: to design fast, precise parts feeders and to improve nonprehensile robotic manipulation. The two goals are closely related. A good architecture for a parts feeder exploits nonprehensile contact, by pipelining fast-acting low-degree of freedom manipulators along the feeder. Manipulation of objects by humans or animals often involves nonprehensile contact in which the object undergoes a series of partial grasps, shuffled back and forth between various states of prehension. More broadly, I seek to understand the mechanics of contact, and in particular the tradeoffs between hardware, software, and sensing, by exploring extreme points in the space of manipulation strategies. The two systems described in this talk constitute two such points, highlighting the mechanics of contact.
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