Seat support surface optimization using force feedback.

The development, implementation and evaluation of an algorithm designed to find optimal seat support surfaces is presented. The algorithm has been developed and implemented on an active contour measurement device. The device consists of an array of positioning elements equipped with force sensors for feedback. With a patient seated on the array, the algorithm is designed to find a seat contour that optimally satisfies given performance criteria. The performance criteria are based on measured stiffness of the soft tissues. A theoretical development of the algorithm is presented along with the modifications made to the algorithm during implementation. The results from several tests using man-made test bodies and a prototype contour gage are presented to verify the algorithm's performance.

A closed loop automated seating system.

This technical report presents the recent progress in the design and construction of a closed loop automated seating system. Preliminary test results are reported. The system is designed to measure seating surface forces and control the seating surface geometry of a seated human. It uses force information as feedback to determine custom seating contours which produce desired seating characteristics. Ultimately, the system is intended to be used for research studies with patients. The system consists of an electronically actuated, force-sensing seating surface which is controlled by a computer. Stepper motors are used to move force sensing probes up or down until the desired seating surface characteristic is attained. Preliminary test results are presented and analyzed. A force-equalizing control algorithm has been written and found to produce relatively uniform force distributions for soft, hemispherical loads of various weights.

An adaptable optimal controller for electric wheelchairs.

A microcomputer-based optimal control system for electric wheelchairs is presented. As the weight of a wheelchair is generally small compared to that of a user, the user's actual weight can have a tremendous impact on the dynamics of the wheelchair. The velocity feedback controller presented here was designed to give an optimal response for all users by incorporating a measure of the individual user's weight into the control algorithm. This allows optimal control of the motor velocities while assuring the constant stability of the system. Control of the system is managed by a modified proportional-integral-derivative (PID) controller, and the adaptability is handled by use of variable-structure control. The factors and considerations involved in such a system are identified, as are the advantages and disadvantages of the particular control strategy used. Experimental results are presented.

Range measurements by a mobile robot using a navigation line.

A continuous, straight-edged line is used for the visual navigation of an autonomous mobile robot in a factor environment. This line, which resides on the floor and contrasts with background, may also be used to determine range information. Two methods are developed for determining the range of an object in the sensor's field of view. The effects of various error conditions in the system geometry on each ranging method are determined. Equations are derived which yield the percent error in calculating ranges given estimates of these error conditions. Numerical examples using typical sensor parameters are given.

Sensing error for a mobile robot using line navigation.

The use of a contrasting line for the visual navigation of autonomous mobile robots in a factory environment is developed. Minimum and maximum linewidths are determined analytically by considering sensor geometry, field of view, and error conditions present in the system. The effects of these error conditions on the width of the line, as seen in the image plane, determines the optimal linewidth. Numerical examples using typical sensor parameters are given.

Machine vision applied to vehicle guidance.

Research on the semiautonomous operation of mobile robots in typical pathways is described. The image of the pathway will consist of two nearly vertical lines bounding a region with little texture (the pathway) after correction for perspective. In order to identify pathway boundaries, regions in the image space are examined using an edge detection algorithm, edges between regions are determined by the algorithm, and those corresponding to straight or nearly straight lines with large slope (path boundaries) are identified by means of the Hough transform. Once the path boundaries are identified, the horizontal distance from camera to road edge is determined. Next, a method to detect cubics in the roadway (i.e., obstacles) is presented. The region of interest in the roadway (from the camera to some predetermined distance in front of it) is known from the path boundary algorithm. The interior of this region is examined for edges. If edges are detected, it means that obstacles or shadows are present. A method to separate obstacles from shadows using stere vision is then presented.

CCD Implementation of a Three-Dimensional Video-Tracking Algorithm.

Implementation of a three-dimensional video tracking algorithm using CCD's is presented. The algorithm does not require conventional pattern recognition or continuous segmentation updating. The only requirements, for the class of targets presented, are that the sampling lattice contain only points inside the target and that the background vary slowly. Several well-known segmentation techniques are available for initial segmentation and determination of target points. The use of CCD devices simplifies the architecture of the processor and permits real time processing at a high sampling rate. Some of the vector and matrix operations require either the use of continuously variable tapweight transversal filters or analog multipliers. The use of analog multipliers, which can be on-chip, reduces the number of components and offers higher accuracy than presently available variable tap weight transversal filters.