Grasp Analysis and Planning Research

We are motivated by a class of important robotic planning problems which are not handled by current motion-planning systems. Examples are a ``snake-like'' robot that crawls inside a tunnel by embracing against its sides, or a limbed robot (analogous to a ``monkey'') that climbs a truss structure by pushing and pulling. In these examples, the robot is an articulated mechanism whose motions must be planned so as to achieve high-level goals. However, the robot's motion is generated by the reaction forces which arise from stably bracing and/or pushing against the environment. These interaction forces must be planned and controlled so as to achieve stability of the robot mechanism. It should be noted that the practically important industrial work-holding or ``fixturing'' problem is a special case of this class of problems. Multi-fingered grasping and manipulation is also a related problem. For example, during finger gaiting, the finger tip reaction forces are used to stably secure the grasped object.

In all of these cases, the interaction forces must be planned and controlled so as to achieve stability of the robot mechanism. In this proposal, we are primarily concerned with planning and maintaining quasistatic stability . That is, in motion where the inertial effects due to the moving parts of the robot are small relative to the forces-torques of interaction between the robot and its environment. The quasistatic assumption is immediately applicable to planning the ``hand-hold'' states (analogous to the hand-holds used by rock climbers between dynamically moving states) where the grasped object, or the robot mechanism in the dual case, is at a static equilibrium. Moreover, if the mechanism's motion between these static states is sufficiently ``slow,'' then the quasistatic assumption will hold throughout.

Quasistatic motion planning problems are especially attractive for two reasons. First, these problems are a natural middle ground between classical path planning and tasks that involve the full dynamics of the robot and the objects it manipulates, such as hopping, running, or juggling. Second, there is a vast array of robotic tasks that fall within this category.

To date, our work has focused on developing a basic mobility theory to describe the mobility of multiply contacting bodies. We have recently extended the theory to include the effects of compliance, friction, and gravity. Our current efforts are focused on using the basic methodology to develop quasi-static motion planning techniques and algorithms for optimal grasp and fixture selection.

Students that work in this area:

Selected Papers

This work is done in collaboration with Prof. Elon Rimon of the Technion (Israel Institute of Technology).