June 12, 2001Jeong-Su Han

An Autonomous Vehicle for People with Motor Disabilities

by G. Bourhis, O.Horn, O.Habert and A. Pruski

Paper Review

Contents

1. Objectives of this project

2. VAHM Robot

3. Hardware Architecture

4. Software Architecture

5. Discussion

Objectives

- To provide an aid to mobility for disabled people who find it difficult of impossible to drive a conventional wheelchair.- Not to make the robot as autonomous as possible but to take full advantage of the user’s abilities without burdening him with too much workload.

Objectives

respirator VoiceJoystick

VAHM Robot

First prototype of the VAHM robot- began in 1989- Robuter mobile base- A wheelchair seat- PC 486 computer- a belt of ultrasonic sensors- man-machine interface (graphic screen)

Current prototype of the VAHM robot

Control mode

- the machine is only used to transmit and adapt data from the user and the mobility task.

Manual Mode

- the machine has complete control of the system, once a goal is selected.

Automatic Mode

- control is divided between the user and the machine.- sharing degrees of liberty. e.g.) the user: choose way to go, the machine: obstacle avoidance

Semiautonomous Mode

Hardware Architecture

Ultrasonic Sensors

Hardware ConnectionsGraphic Interface

Incremental Encoders

- a belt of 16 ultrasonic sensors.- cover each side of wheelchair.- updates the measurement table every 100ms.

- mounted on the shaft of each engine.- provide relative localization data through position and orientation.

- DX (Control Dynamics) bus is used.- can be connected the various electronic modules.

Software Architecture

Perception control

- Localization- Static localization vs. Dynamic localization

- Free space detection- Relatively large area ( a radius of 2 m around the robot) will be considered as an obstacle in free space detection.

Localization

- Ultrasonic measurement and the user’s indication is used. e.g.) ‘sitting-room entrance’, ‘near the bed’- The principle: to look for the best possible correspondence between the environment grid and the measurement grid.- The cell size: 10 by 10 cm, The search area: 1.5 by 1.5 m.

Static Localization

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: the values of cells in local and global grids: cover all the cells in the local grid: the corresponding cells of the global grid: the translation and rotation of the local grid as compared with the global grid

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Cell value: -1 for empty cell, 1 for occupied cell, 0 for unknown cell

- 10 cm, 7 acceptable, 99% success rate.- In dynamic localization, discrepancy btw. local map points and global map straight lines is corrected in the sense of least-squared.

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Navigation control

- Wheelchair to move toward a set of geometrical points.- Environment model is fed into the machine prior to any planning.- 2-D space divided by 256 by 256 cells.

- based on the wheelchair’s behavior.- Behavior is defined by the orientation of a straight line going through the frame’s origin.- The direction is equal to the average of the behaviors weighted by measured value’s inverse.

Navigation control

Obstacle avoidance

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: the number of sensors: the robot’s behavior associated to sensor i: the distance measured by sensor i: the angle of the straight line

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- The relatively large area (a radius of 2 m around the robot) will be considered as an obstacle.

Free space search

- The user tells the robot which direction to proceed in using a designation system or a joystick.- The wheelchair will move along this direction.

Navigation control

Direction following

- Following the straight line parallel to a wall.- The equation of the straight line is computed from the data sent by the three ultrasonic sensors located on the side of the wheelchair facing the wall that is to be followed.- If the wall is too close or is not straight, obstacle avoidance algorithm is used.

Wall following

- The environmental model is fed into the machine prior to any planning.- 2-D space, 256 by 256 cells.

1. The size and position of the obstacles have been introduced using a graphic editor, the environmental model is obtained.2. The current position point and the goal to reach are known, path planning for a punctual robot in an area covering the 1.5 times width of the wheelchair is computed.3. The trajectory is turned into a sequence of arcs or circles to take into account the fact that the mobile is nonholonomic.4. The robot moves in accordance with the navigation algorithm.

- not optimal solution, processing time is under 1s.

Navigation control

Path planning

Communication control

- Man-machine interface is essential to ensure the efficiency of technical aids.- A wide range of sensors is used for powered wheelchair.- hand- and chin-controlled joysticks, mechanical switches, breath sensors, speech recognition. switches or analog sensors.

- a single-switch case: an icon or an area of the screen is used for scanning over several possible choices, then validating.

- analog sensors case: the disabled person can control a proportional sensor by moving a virtual joystick displayed on the screen.

Discussion

- The second prototype of the VAHM robot as described.- The choice of the automation level usually depends on parameters that are easily apprehended: - single-switch or proportional man-machine interface sensors. - modeled or non-modeled environment. - this control selection is currently left up to the user.

- The user is left with only two controls: - choosing the direction. - stopping the wheelchair.

Discussion