Nominal Motion Plan Research Articles

A compliant controller dynamically updating the compliance center by contact localization

This paper presents a compliant control method for insertion of complex objects with concavities. Most work on robot assembly using compliant motion control schemes focuses on overcoming jamming conditions for simple peg-in-hole problems, and cannot be used for complex shapes frequently encountered in assembly applications. When an object is being inserted to a hole or slot with a small clearance, a contact path is issued to compensate for uncertainties. When the object shape is complex, however, the contact state changes several times and severely, making compliant control difficult. The algorithm presented here is capable of generating satisfactory compliant motion control in spite of changing contact states. During the execution of a nominal motion plan, it computes the actual position of the contact point from the force/torque sensor reading using a contact localization algorithm. It then dynamically updates the center for compliance to the computed contact point, and minimize the chance of jamming and unwanted collisions. The control scheme has been implemented on hardware and tested on the task of inserting a T-shape into a C-shape involving a very tight tolerance. The insertion motion was accomplished by a sequence of 2 translational and 1 rotational compliant motions, and successfully executed by the proposed compliant motion controller.

Assembly of complex shaped objects: A stiffness control with contact localization

This paper presents a compliant control method for insertion of complex objects with concavities. The control algorithm presented here is capable of generating satisfactory compliant motion control in spite of changing contact states. During the execution of a nominal motion plan, it computes the actual position of the contact point from the force/torque sensor reading using a contact localization algorithm. It then dynamically updates the center of compliance to the computed contact point, and minimizes the chance of jamming and unwanted collisions. The control scheme has been implemented on hardware and tested on the task of inserting a T-shaped object into a C-shaped cavity with a very tight tolerance. The insertion motion, which involves a sequence of 2 translational and 1 rotational compliant motions, was successfully executed by the proposed compliant motion controller.

Simulating physical interactions between an articulated mobile vehicle and a terrain

This paper deals with the problem of planning the motion of a complex land vehicle moving in a natural environment. The contribution presented here is a motion generator which predicts the dynamic behaviour of the vehicle when executing a given nominal motion plan. This plan is expressed in terms of a channel that must be followed and of a set of intermediate subgoals that must be reached. Solving this motion generation problem requires to explicitly reason about the geometric and the physical aspects of the movements that the vehicle has to execute. In our approach, this is done by using two basic constructions derived from the concept of physical model: the ‘generalized obstacles’ are used to physically guide the movements of the vehicle using an explicit model of the vehicle-terrain interactions, and the ‘physical targets’ are used to map the strategic information onto our physical representation of the world and to introduce the force feedback gestural control.

Physical simulation of land vehicles with obstacle avoidance and various terrain interactions

AbstractProgramming the motions of an autonomous planetary robot moving in an hostile and hazardous environment is a complex task which requires both the construction of nominal motion plans and the anticipation as far as possible of the effects of the interactions existing between the vehicle and the terrain. In this paper we show how physical models and dynamic simulation tools can be used for amending and completing a nominal motion plan provided by a classical geometrical path planner. The purpose of our physical modeller‐simulator is to anticipate the dynamic behaviour of the vehicle while executing the nominal motion plan. Then the obtained simulation results can be used to assess and optimize the nominal motion plan. In the first part, we outline the physical models that have been used for modelling the different types of vehicle, of terrain and of vehicle‐surface interactions. Then we formulate the motion planning problem through the definition of two basic abstract constructions derived from physical model: the concept of generalized obstacle and the concept of physical target. We show with various examples how it is possible, when using this method, to solve the locomotion problem and the obstacle avoidance problem simultaneously and, furthermore, to provide the human operator with a true force feedback gestural control over the simulated robot.