Admittance matrix design for force-guided assembly

Abstract-Indirect force control (IFC) architectures are a common approach for dealing with unknown environments. What all IFC schemes have in common, is that the relation between the set-point and the actual configuration of the robot is determined by a mechanical relationship (e.g. a mass-spring-damper system). In this work, we propose a setpoint generation method for IFC schemes, enabling intuitive specification of mixed force and positioning tasks on joint and Cartesian level. In addition, the formulation of equality and inequality tasks is supported and a passivity based stability proof is formulated using the concept of virtual energy storage.The resulting task programming interface is demonstrated on a 7 degree of freedom robot, running a joint space impedance controller. One sample task demonstrates the application of the developed approach and highlights the basic features. I. MOTIVATIONCompliant control involving force and positioning tasks has been investigated elaborately in the last decades. A popular approach to realize compliance is provided by indirect force controllers, where the motion and interaction forces of the physical robot are indirectly controlled by moving a virtual robot, which is coupled to the physical robot via a virtual mechanical relationship. Fig. 1 depicts the basic idea. The most popular variation of an IFC is the well known impedance control paradigm, introduced by Hogan in his seminal paper [1], but also simpler variants, like stiffness control or an ordinary PD-controller with compensation of the gravitational torques and sufficiently low proportional gain. This control scheme has also nice stability properties which are basically independent from the environmental dynamics. Furthermore, series elastic actuator (SEA) robots, which are equipped with physical springs in their joints, can also be considered as IFC's.The set-point selection for the virtual robot is also referred to as virtual trajectory generation and while there is an extensive amount of work, having the purpose of improving the accuracy of the virtual mechanical relationship or proposing different extensions or variations for IFC's (for impedance control in particular), the literature covering pure virtual trajectory generation is very sparse.The present work is meant to fill the gap between the low level control design and high level application programming by introducing an additional control layer, which we call set-pointgenerator (SPG). The purpose of the SPG is to provide set-points for the virtual manipulator according to the specified tasks, using only information on the current joint state. These tasks are defined by the application programmer via a task specification interface, where a set of hierarchically ordered force and positioning subtasks on joint and Cartesian level is determined. To our best knowledge, there is no work treating virtual set-point generation for joint level IFC's in order to achieve mixed force and positioning tasks without additional sensory feedback, like force or vision.In [...

show abstract

“…Several investigations have also been made targeting the construction of compliances, optimized for specific tasks [7], [8].…”

Section: A Indirect Force Controlmentioning

confidence: 99%

Hierarchical Force and Positioning Task Specification for Indirect Force Controlled Robots

2018

View full text Add to dashboard Cite

show abstract

“…Brost and Goldberg [6] present amn algorithm which, given a two-dimensional part geometry, selects the optimal fixture design from the set of all fixture designs which are possible using a modular fixturing system. Schimmels and Peshkin [25] present a method for designing a manipulator admittance matrix to be realized by the manipulator controller which leads to contact forces that always act so as to reduce the degree of misalignment between a part and the fixture into which it is being guided. is identical for the contact identification and fixturing problems, but the underlying assumptions are different.…”

Section: Fixturingmentioning

confidence: 99%

“…A closely related body of work has been done by Brost and Goldberg [6], Schim mels and Peshkin [25], Bausch and Youcef-Toumi [4], and Asada [2] on the synthesis of optimal pin fixtures for the constraint and alignment given small initial misalign ment of parts of known geometry in a plane. The work proposed here considers a related problem: the synthesis of a moving part geometry i.e.…”

Section: Introductionmentioning

confidence: 99%

Advances in grasping and vehicle contact identification : analysis, design and testing of robust methods for underwater robot manipulation

Snow¹

1999

View full text Add to dashboard Cite

This thesis focuses on improving the productivity of autonomous and telemanipula tion systems consisting of a manipulator arm mounted to a free flying underwater vehicle.Part I minimizes system sensitivity to misalignment by developing a gripper and a suite of handles that passively self align when grasped. After presenting a gripper guaranteed to passively align cylinders we present several other self aligning handles. The mix of handle alignment and load resisting properties enables handles to be matched to the needs of each task. Part I concludes with a discussion of successful field use of the system on the Jason Remotely Operated Undersea Vehicle operated by the Woods Hole Oceanographic Institution.To enable the exploitation of contact with the environment to help stabilze the vehicle, Part II develops a technique which identifies the contact state of a planar vehicle interacting with a fixed environment. Knowing the vehicle geometry and velocity we identify kinematically feasible contact points, from which we construct the set of feasible contact models. The measured vehicle data violates each model's constraints; we use the asociated violation power and work to select the best overall model. Part II concludes with experimental confirmation of the contact identification techniqu&s efficacy.

show abstract

“…The approach is referred to as force-assembly and has been successful for workpart into fixture insertion when errors are infinitesimal [5], [6], [7] .…”

Section: Section I Introductionmentioning

confidence: 99%

Admittance selection for planar force-guided assembly for single-point contact with friction

Huang

Schimmels

2003 IEEE International Conference on Robotics and Automation (Cat. No.03CH37422)

Self Cite

View full text Add to dashboard Cite

Abstract:This paper identifies procedures for selecting the appropriate admittance to achieve reliable planar force-guided assembly for single-point frictional contact cases. A set of conditions that are imposed on the admittance matrix is presented. These conditions ensure that the motion that results from contact reduces part misalignment. We show that, for bounded misalignments, if an admittance satisfies the misalignment-reduction conditions at a finite number of contact configurations and a given coefficient of friction /spl mu//sub M/) then the admittance will also ensure that the conditions are satisfied at all intermediate configurations for all coefficients less than /spl mu//sub M/.

show abstract

Admittance matrix design for force-guided assembly

Cited by 103 publications

References 13 publications

Hierarchical Force and Positioning Task Specification for Indirect Force Controlled Robots

Hierarchical Force and Positioning Task Specification for Indirect Force Controlled Robots

Advances in grasping and vehicle contact identification : analysis, design and testing of robust methods for underwater robot manipulation

Admittance selection for planar force-guided assembly for single-point contact with friction

Contact Info

Product

Resources

About