March 2002, Koichi Hirata and Teppei Kono

When a wheelchair is driven on a waving ship, the operation becomes very hard, and it has highly dangerous, such as reckless driving and falling. In this study, we consider the operation of a wheelchair to have a small side-rolling motion. Then we develop an assistance device for a waving condition.

A hand-operated wheelchair runs snaky on a waving ship. Thus, we consider several assistance devices for evasion of the snaky running.

A. Turning angle control of front tires
Turning angle of front tires has free rotating motions. The free turning angle brings easy handling and small turning diameter. However, when the floor is waving or slanting, the front tires fall down, then the wheelchair turns against the will. Because there is no force to keep the straight cource for the front tires. Therefore we think that a turning angle control device for the front tires is useful on the waving ship.

B. Additional drive power control
A wheelchair turns with the difference of the drive power of the left and theright rear wheels. When the floor is waving or slanting, the assistance device, which assist power to the lower wheel, brings stable running. The assistance device requires high quality control method. Otherwise, the wheelchair drives recklessly by the additional drive power device.

C. Brake control of rear tires
The brake control device also brings the stable running instead of the additional drive power device. This concept is the automatic control for braking operation.

D. Control of the center of gravity
The center of gravity of the wheelchair affects the running characteristics strongly. That is, the control of the center of gravity also brings easy handling on a waving ship.

After the above discussions, we adopted "C. Brake control of rear tires" for the first assistance device. Because, it was considered that the brake control device can be set easily to any wheelchairs, also it is accurate and safety.

The follows pictures shows the developed assistance device. When a person drives a wheelchair on a waving condition, he must control brake force suitably. This assistance device has a microcomputer and a R/C servomotor, and can adjust the brake force optionally. Also, we developed a slope angle sensor with a pendulum. The sensor has micro-switches, and they perceive at slope angle of 3 and 5 deg. The microcomputer controls the brake force based on the signals of the switches.

Structure of the Assistance Device

Photograph of the Assistance Device

In order to investigate effects of the assistance device to the operation, we experimented on 'a Simple Experimental Slope to Image a Waving Ship (a Waving Slope)'. The waving slope has about 10 m of length. A spacer is located at the right side of the center of the slope. The figure to the right shows the experimental results at slope angle of 5 deg. From the figure, when the brake was not controled, a driver put on the brake with his hill-side hand. On the other hand, when the assistance device controled the brake force, the driver did not operate the brake with his hands, and similar torques were given to the both wheels. From such experiments, it was confirmed that the developed assistance device can produce the easy operation of the driver on the waving slope.

Experimental Results (5 deg.)

In this study, it was confirmed that the assistance device produces the easy operation of a driver on the waving slope. However, as the waving of a real ship is too complex, it is considered that the pendulum sensor, which was developed in this study, cannot measure a condition of a wheelchair suitably. We think that the assistance device becomes high performance by adoption of a multi-axis gravitation acceleration sensor. Also, the assistance device works at every condition increasing the time to add the drive power to hand-rims. Then a driver feels often to disturb the operation. If the assistance device has the torque sensor, which senses whether the driver adds the power, and if the device works only the time of inertia running, the device will have more better operation feeling.

Development Diary of the Assistance Device
Demonstration Movie of the Assistance Device (MPEG-1 format, 1.3 MB�j