Wyatt S. Newman

High speed robot control and obstacle avoidance using dynamic potential functions

Time-optimal control of robot motion for dynamically decoupled manipulators is described in terms of potential functions. Avoidance of moving obstacles is incorporated via protective potential functions. An energy interpretation of the potential functions leads to rules for construction of avoidance functions and logical operations among them. Simple expressions for combining obstacle fields with an obstacle-free time-optimal solution result in the minimum safe influence of obstacles. Simulation results are given demonstrating high-speed target interception in the presence of obstacles.

Stabilization of a mobile robot climbing stairs

Remotecs Andros VI mobile robot is physically capable of ascending and descending stairs. However, the teleoperated control of the robot climbing stairs is difficult, as the operators feedback is limited to visual and audio cues only. Our analysis and experiments show that this tracked mobile robot is inherently unstable in open-loop stair climbing, and the robot under telemanipulation is prone to falling. We describe the design and validation of a feedback system for automatic heading control for stabilization of stair climbing. The design incorporates solid-state attitude sensors as inputs to an on-board multiprocessor system. We have experimentally demonstrated stability of the robot in stair climbing, even in the presence of large disturbances and noise. With the addition of the on-board computing, control of the robot is elevated from teleoperation to supervisory control.<<ETX>>

Augmented impedance control: an approach to compliant control of kinematically redundant manipulators

A control method that achieves impedance control of redundant degree-of-freedom manipulators is proposed. The technique combines reduced-order impedance control with configuration control to achieve impedance control of the hand and integrable control of the redundancy. The resulting controlled dynamics is shown to present a passive physical equivalent impedance, thus guaranteeing stability in contact with arbitrary passive environment. In addition, it is shown that there are severe restrictions in choosing the desired hand inertia.<<ETX>>

A human-robot interface based on electrooculography

Design and implementation of an electrooculography based gaze-controlled robotic system is presented. The robot system consists of signal acquisition, pattern recognition, control strategy and robot motion modules. The users eye gaze movements are reconstructed from electrooculogram (EOG) signals, which are recorded from the face in real time. The eye movement patterns, e.g., saccades, fixation and blinks are detected from the raw eye gaze movement data by a pattern recognition module. The control strategy module interprets the users intention from the eye movement patterns based on predefined protocols. A horizontally mounted robot, emulating the skeletomuscular configuration of the human arm, is controlled by the robot motion control module to execute the interpreted user intention. The performance results of two control strategies are discussed.

Reflexive collision avoidance: a generalized approach

A generalized approach to reflexive obstacle avoidance is proposed. Reflex control is a method that guarantees collision avoidance with minimum nonessential influence on higher-level controls. The reflex controller described consists of two sub-modules: the C-space inspector and the active reflex controller. The C-space inspector inspects and approves prisms in C-space that are free from obstacles. The active reflex controller acts like a filter with respect to collision avoidance, which approves or replaces higher-level commands based on the free-space prisms returned from the C-space inspector. The reflex controller serves well as a building block in obstacle avoidance and path planning algorithms.<<ETX>>

Stable interaction control and coulomb friction compensation using natural admittance control

A new control system design formulation is presented for achieving high-performance, guaranteed-stable impedance control. While the bandwidth of the resulting controller is no higher than alternative techniques, the new formulation significantly improves performance when Coulomb friction is present in the system. The technique requires a careful choice of the target impedance. The resulting feedback compensators are causal and have stable poles, although they are often non-minimum phase. General rules for controller synthesis are derived. Experimental performance results are presented for a two-mass system with internal compliance and Coulomb friction. Results demonstrate that the technique is successful in rejecting internal friction force disturbances while maintaining a passive driving-point impedance.

An agile manufacturing workcell design

This paper introduces a design for agile manufacturing workcells intended for light mechanical assembly of products made from similar components (i.e., parts families). We define agile manufacturing as the ability to accomplish rapid changeover from the assembly of one product to the assembly of a different product. Rapid hardware changeover is made possible through the use of robots, flexible part feeders, modular grippers, and modular assembly hardware. The division of assembly, feeding, and unloading tasks between multiple robots is examined with prioritization based upon assembly time. Rapid software changeover will be facilitated by the use of a real-time, object-oriented software environment utilizing graphical simulations for off-line software development. An innovative dual VMEbus controller architecture permits an open software environment while accommodating the closed nature of most commercial robot controllers. These agile features permit new products to be introduced with minimal downtime and system reconfiguration.

Calibration of a Motoman P8 robot based on laser tracking

Calibration of a Motoman P8 robot using an SMX, Inc. laser-based coordinate measuring system is presented. Since the coordinate measuring device is capable of reporting absolute coordinates, unconstrained by any calibration template, it offers highly accurate measurement of poses selected for convenience of parameter identification. It is shown that measurements obtained using the circle-point analysis technique and the highly accurate SMX coordinate measuring device provide insight into the ability to successfully calibrate an industrial robot.

Advances in agile manufacturing

An agile workcell has been developed for light mechanical assembly in collaboration with industrial sponsors. The workcell includes multiple Adept robots, a Bosch conveyor system, multiple flexible parts feeders at each robots workstation, CCD cameras for parts feeding and hardware registration, and a dual VMEbus control system. Our flexible pairs feeder design uses multiple conveyors to singulate the parts and machine vision to locate them. Specialized hardware is encapsulated on modular grippers and modular worktables which can be quickly interchanged for assembly of different products. Object-oriented software (C++) running under VxWorks, a real-time operating system, is used for workcell control. An agile software architecture was developed for rapid introduction of new assemblies through code re-use. A simulation of the workcell was developed so that controller software could be written and tested off-line, enabling the rapid introduction of new products.

A new method for kinematic parameter calibration via laser line tracking

A robot kinematic calibration technique is presented. The process assumes the use of an optical detector mounted on the robots end-effector, which is used in position feedback. By this method, calibration data can be acquired for detector positions along a straight laser beam, and the detector is precisely centered on the laser line at each sample point. By structuring the data collection process this way, post processing to deduce kinematic parameters is simplified. A goodness-of-fit metric is given which exploits the straight-line constraint of the data. This metric is well suited for use within a numerical search for best-fit kinematic parameters. Illustrations of the techniques virtues and limitations are presented. An experimental apparatus for evaluating the technique on industrial robots is described. The approach is shown to be simple, inexpensive, and feasible.<<ETX>>