Ernest D. Fasse

Haptic interaction with virtual objects Spatial perception and motor control

Abstract. This paper considers interaction of the human arm with “virtual” objects simulated mechanically by a planar robot. Haptic perception of spatial properties of objects is distorted. It is reasonable to expect that it may be distorted in a geometrically consistent way. Three experiments were performed to quantify perceptual distortion of length, angle and orientation. We found that spatial perception is geometrically inconsistent across these perceptual tasks. Given that spatial perception is distorted, it is plausible that motor behavior may be distorted in a way consistent with perceptual distortion. In a fourth experiment, subjects were asked to draw circles. The results were geometrically inconsistent with those of the length perception experiment. Interestingly, although the results were inconsistent (statistically different), this difference was not strong (the relative distortion between the observed distributions was small). Some computational implications of this research for haptic perception and motor planning are discussed.

Spatio-geometric impedance control of Gough-Stewart platforms

This paper looks at the control of mechanical impedance of the so-called Gough-Stewart class of parallel platforms. Two methods of compliance control are presented. One is based on global potential energy functions that have previously been applied to controlling serial manipulators and electrodynamically levitated platforms. The second method uses the exponential map to associate finite displacements of the platform from equilibrium with twist displacements. Compliant wrenches are then proportional to the twist displacements. Control of spatial damping is addressed as well, justifying the classification as impedance control. Control algorithms and simulation results are given.

Spatial Compliance Modeling Using a Quaternion-Based Potential Function Method

This paper looks at the modeling of elastically coupled rigidbodies. The elastic deformation is assumed to be localized, which is aparticularly valid assumption for flexural joints. A generic, lumpedparameter, Euclidean geometric, potential function based approach ispresented using quaternion calculus. The potential functions are similarto the functions presented in the spatial compliance control literature.Rigid body displacements are represented using a combination ofCartesian coordinates and quaternions. To demonstrate the utility of theproposed methods for computer analysis, a nontrivial example isconsidered. The system consists of two rigid bodies coupled by anasymmetric flexure incorporating crossed leaf springs. While thecompliant constitutive equations are well defined for arbitrary rigidbody displacements, it is only claimed that the model is accurate forsmall displacements.

Control of Physical Contact and Dynamic Interaction

This paper considers the influence of physical contact and mechanical interaction on the dynamics and control of manipulators. Manipulation fundamentally requires contact with the object(s) being manipulated; contact implies mechanical interaction; and mechanical interaction can have a profound influence on manipulator dynamics and control - for example, controller stability is easily jeopardized. In many present robot applications the dynamic effects of physical contact may be neglected either because contact forces are relatively small or because they need not be controlled accurately. However, the dynamics of physical contact are likely to become more prominent as newer robot designs permit relatively larger payloads and robots are applied to tasks requiring more precise control of mechanical interaction, e.g., applications involving intimate physical interaction with humans such as haptic virtual environments or personal-care robots.

Retrieval of similarly shaped parts from a CAD database

The increased use of Computer Aided Design (CAD) tools have resulted in the obvious need to efficiently retrieve specific and groups of similar parts from CAD databases for group technology (GT) applications; Current classification and retrieval methods from CAD databases are typically code based. The disadvantage of such a retrieval scheme is application dependency. We propose an application independent scheme and utilize it in retrieving similarly shaped parts on the basis of form-features and the inter-feature relationships. We address the issues of completeness of spatial interactions vocabulary and multiple interpretations for a part.

Sliding mode attitude control of a small satellite for ground tracking maneuvers

This paper deals with spacecraft attitude control using sliding mode techniques. Two distinctions of the proposed method from most reported methods are: 1) the measure of attitude error used is intrinsically defined, Euclidean-geometric, and intuitive; and 2) a novel, dynamically nonlinear sliding function is used that results in a simple control law. As an example we consider the ground station tracking of UASat.

Determining feasible contact states of pairs of spatial polyhedra

Recent research uses qualitative contact models for compliant motion planning and control. Although these methods have great potential, generation of qualitative contact models of nonconvex polyhedra is difficult. Qualitative contact models could be generated in a generate-and-test fashion if a predicate were available for verifying contact hypotheses. In general, a contact hypothesis does not fully constrain the relative configuration of the objects making verification of the hypothesis difficult. This paper presents an optimization-based method to verify geometric feasibility of contact hypotheses that do not fully constrain the relative configuration. This method has been implemented and applied to test contact hypotheses of nontrivial object pairs.

On the spatial impedance control of Gough-Stewart platforms

Looks at the control of mechanical impedance of the so-called Gough-Stewart class of parallel platforms. Two methods of compliance control are presented. One is based on global potential energy functions that have previously been applied to controlling serial manipulators and electrodynamically levitated platforms. The second uses the exponential map to associate finite displacements of the platform from equilibrium with screw displacements. Compliant wrenches are then proportional to the screw displacements. Control of spatial damping is addressed as well, justifying the classification as impedance control. Control algorithms and simulation results are given.

A methodology for automatic retrieval of similarly shaped machinable components

A methodology that can intelligently search a CAD database of 2.5D machinable components and retrieve components and sub-pieces with similar shape characteristics has been presented. The proposed methodology has the potential to reduce both the development time and cost of new designs by effectively re-using existing designs more efficiently. This is accomplished by searching a database of parts with their associated plans and extracting parts of those plans that are required for the query part. These plan parts can subsequently be merged to develop the entire plan for the query part. The methodology utilizes qualitative matrices to represent the spatial relationship between the maximal features of the query component. These feature-spatial relationship pairs are matched against those present in existing components within the database. The query can be relaxed based upon TAH structures that allow for generalizing of features and spatial relationships to allow for the best match to be found if no exact match is found.

Quantitative measurement of haptic perception

Development and evaluation of teleoperators and haptic virtual environment technologies require objective quantitative measures of haptic quality. In this paper a theoretical framework and experimental procedures are introduced for quantitative assessment of haptic perception. Human haptic perception of objects is distorted and uncertain as well. Perceptual distortion is defined to be a systematic bias of perception with respect to an objective standard. Perceptual uncertainty is defined to be a measure of statistical distribution of percepts. A set of mathematical tools is presented to quantify perceptual distortion and uncertainty. Two experiments are presented which apply these tools to investigate the fundamental structure of human haptic perception.<<ETX>>