Compliant motion occurs when the manipulator position is constrained by the task geometry . Compliant motion may be produced either by a pass ive m~chanica comp liance built into the manipulator , or by an active compliance implemented in the control servo loop . The second method , called force controj/is the subject of this report. In particular , this repor t presents a theory of force control based on formal models of the manipulator and the task geometry .The ideal effector is used to model the manipulator , and the task geometry is I' ;3:I Ø 7 ~~~ (continued)modeled by the Lideal surface, which is the locus of all positions accessible to the ideal effector. Models are also defined for the goal trajectory , position control , and force control.These models are useful in two repects. First , the model of force control provides a precise semantics for force control primi tives in manipulator programming languages .The model also defines a simple interface between the manipulator and the programeer , Isolating the programmer from the fundamental complexity of low-leve l manipulator control.Second , the formalism provides a method of synthesizing force control programs for compliant motion . A force control program is modeled as a set of equations in the components of manipulator velocity (angular velocity) and force (torque). The task geometry constra ints can be modeled similarly. The control program synthesis problem is to construct a program whose equations , wh~~ combined with the task geometry equations , have a s ingle unique solution equal ~o the goal trajectory. We show that to obtain good performance in the presence of p1 nning model error , it is also desirable that these two sets of equations be or~~%ogonal and non-redundant .This report describes research done at the Artificial Intelligence Laboratory of ABSTRACTCompliant motion occurs when the manipulator position is constrained by the task geometry. Compliant motion may be produced either by a passive mechanical compliance built in to the manipulator, or by an active compliance implemented in the control servo loop. The second method, called force control, is the subject of this report. In particular , this report presents a theory of force control based on formal models of the manipulator and the task geometry. The ideal effeaor is used to model the manipulator, and the task geometry is modeled by the ideal surface, which is the locus of all positions accessible to the ideal effector. Models are also defined for the goal trajectory, position control, and force control.These m odels are useful In two respects. First, the model of force control provides a precise semantics for force control primitives in manipulator programming languages. The model defines a simple interface between the manipulator and the programmer , isolating the programmer from the fundamental compkxity of low-level manipulator control.

Active compliance enables robots to carry out tasks in the presence of significant sensing and control errors. Compliant motions are quite difficult for humans to specify, however. Furthermore, robot programs are quite sensitive to details of geometry and to error characteristics and must, therefore, be constructed anew for each task. These factors motivate the search for automatic synthesis tools for robot program ming, especially for compliant motion. This paper describes a formal approach to the synthesis of compliant-motion strategies from geometric descriptions of assembly operations and explicit estimates of errors in sensing and control. A key aspect of the approach is that it provides criteriafor correct ness of compliant-motion strategies.

We would like to give robots the ability to position and orient parts in the plane by pushing, particularly when the parts are too large or heavy to be grasped and lifted. Unfortunately, the motion of a pushed object is generally unpredictable due to unknown support friction forces. With multiple pushing contact points, however, it is possible to find pushing directions that cause the object to remain fixed to the manipulator. These are called stable pushing directions. In this article we consider the problem of planning pushing paths using stable pushes. Pushing imposes a set of nonholonomic velocity constraints on the motion of the object, and we study the issues of local and global controllability during pushing with point contact or stable line contact. We describe a planner for finding stable pushing paths among obstacles, and the planner is demon strated on several manipulation tasks.

Pushing is an essential component of many manipulator operations. This paper presents a theoretical exploration of the mechanics of pushing and demonstrates application of the theory to analysis and synthesis of robotic manipulator operations.

The book presents the most current research in manipulator design and control of direct-drive robot arms. In direct-drive robots the shafts of revolute joints are directly coupled to the

An autonomous robotic manipulator can reduce unby motion strategies. This paper explores the use of motion strategies demonstrated within the context of a simple method to orient planar to eliminate uncertainty, without the use of sensors. The approach is objects. A randomly oriented object is dropped into a tray. When the tray is tilted, the object can slide into walls, along walls, and into corners, sometimes with the effect of reducing the number of possible orientations. For some objects a sequence of tilting operations exists that leaves the object's orientation completely determined. The paper describes an automatic planner that constructs such a tilting program, implemented, the resulting programs have been executed using a tray using a simple model of the mechanics of sliding. The planner has been attached to an industrial manipulator, and sometimes the programs work. The paper also explores the issue of sensorless manipulation, tray-tilting in particular, within the context of a formal framework first described by Lozano-Pkrez, Mason, and Taylor [1984]. It is observed that sensorless motion strategies perform conditional actions using mechanical decisions in place of environmental inquiries.

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This paper presents an analysis of a two-dimensional rigid-body collision with dry friction. We use Routh’s graphical method to describe an impact process and to determine the frictional impulse. We classify the possible modes of impact, and derive analytical expressions for impulse, using both Poisson’s and Newton’s models of restitution. We also address a new class of impacts, tangential impact, with zero initial approach velocity. Some methods for rigid-body impact violate energy conservation principles, yielding solutions that increase system energy during an impact. To avoid such anomalies, we show that Poisson’s hypothesis should be used, rather than Newton’s law of restitution. In addition, correct identification of the contact mode of impact is essential.