Hideyuki Tanaka

Optical Occupant Position Sensor for Airbag System

An occupant position sensor is the key device for the smart airbag system to increase the reliability of conventional airbag systems. In the smart airbag system, the degree of airbag explosion is controlled by the data from the occupant position sensor. High accurate occupant position sensing is needed, which might be difficult by supersonic technologies.This paper reports a novel optical occupant position sensing device suitable for the smart airbag system, which measures the distances from the sensor to 2 dimensional multiple points on the occupant. The method to measure the distances is optical triangulation using photo-diode array pairs and a data processing IC.In this paper. the occupant position recognition is demonstrated using the data obtained by 2 dimensional distance measurement of the occupant position sensing device, in the accuracy of 3cm at the distances of 75cm within the optical view angle of 35 and 53 degrees in horizontal and vertical respectively. Total distance measurement points of this device are 4×44. This paper also describes the recognition possibility of 4 basic occupant position using these distance data, which is needed for airbag explosion control in smart airbag system.

Low-transmission-loss prism for optical switches designed by means of optical-power-evaluation computer program

We have developed a low transmission loss prism for optical switches suitable for optical fiber systems which monitor and control factory equipment. We have realized the low transmission loss prism by using the geometrical property of ellipsoids and a newly developed optical power evaluation computer program which facilitates estimating the coupling efficiency between two optical fibers considering total reflection phenomena, numerical aperture and far field pattern of the optical fiber for an aspherical optical system. The transmission loss of the present ellipsoidal prism is 5 dB for the plastic fiber with the core diameter of 1 mm, and 5.8 dB for polymer clad fiber with core diameter of 0.2 mm. The present ellipsoidal prism improves transmission loss by 4 dB as compared with the conventional spherical prism for the optical fibers usually adopted to the optical fiber systems. The calculated loss and experimental loss agreed well. This agreement confirms the usefulness of our computer program.

Plastic molded optical switch designed by means of optical power evaluation computer program

This paper reports a novel reflection type plastic molded optical switch which comprises two spherical prisms for totally reflecting incident light and a shutter positioned between the prisms for controlling the transmission loss of the light. The switch shows insertion loss of 9.7 dB when the switch is used in conjunction with optical fibers with 1 mm core diameter and extinction ratio of 35.1 dB. The insertion loss is lower by 8 dB than the conventional reflection type switch that employs flat reflection type prisms. In designing the switch, we evaluated the switch performance by means of a newly developed ray tracing computer program that considers optical power for each ray trace, that has not been done by the conventional evaluation technique. Discrepancy between the experimental and calculated insertion losses is +/- 1 dB. This small discrepancy confirms usefulness of our computer program.