(a) Field of the Invention
The present invention relates to a method for minimizing errors in sensors used for a recording apparatus of car accidents, and more particularly, to a method to enable precise recordation of car accidents by minimizing errors in sensors.
(b) Description of the Related Art
A recording apparatus of a car accident is provided to enable scientific research of the cause and the process of the car accident.
The apparatus may use sensors to detect the beginning of a collision of a car or it may distinguish the accident from a switch operation of the driver or from a signal of airbag operation.
During a period of time around the instant of the accident, the apparatus records the road conditions where the accident occurred, as well as the driver""s operation of equipment, the motion of the car, and other movement circumstances.
Accordingly, the recording apparatus needs to be designed to protect data from heat and submergence in such situations as when the car catches fire during a collision or when it is submerged in water.
And the recording apparatus, being mounted on a car driven on the road, needs to be designed so that sensor error due to road conditions and driving circumstances is as small as possible. Of the sensors used for the recording apparatus, data from the acceleration sensor and rotational angular velocity sensor have an important role in reconstructing the accident. A rotational angular velocity sensor is also known as a yaw-rate sensor. But the two sensors exhibit a zero offset drift phenomena, the phenomena being that the zero point of the sensors drifts.
FIG. 1 is a diagram showing a relationship between zero offset errors and the total error caused by zero offset errors.
When the acceleration sensor shows zero G, G meaning the unit of gravitation, or when the yaw-rate sensor shows zero deg/sec, the output of the sensor is said to have/show zero offset or zero output, or it is said to be zero biased. But the datum point when the sensor shows zero offset changes because of environmental factors such as temperature which cause sensor error, the aforementioned zero offset drift error or zero bias drift error.
The zero offset error accumulates when integration is taken, so that the sum of errors becomes fatal in most cases, especially for reconstructing the trajectory of a car, because a second order integration is needed to reconstruct the trajectory. That is, a very small zero offset error may cause a fatal error in calculation of position on the trajectory.
Many methods to correct the zero offset error are devised such as a method using a high frequency tube and filter, and a method using a heat insulating means. But those methods can not perfectly remove errors caused by the zero offset drift phenomena. Accordingly, a proper correction has to be made in the stage of accident analysis, and the correction has to be made manually in the process of using a computer program for accident reconstruction.
The present invention has been made in an effort to solve the above problem of the prior art.
It is an objective of this invention to provide a method for minimizing errors in sensors used for a recording apparatus of car accidents, automatically correcting the data measured by an acceleration sensor and a yaw-rate sensor on the basis of the vehicle speed measured at the transmission and of the steering angle measured by a steering angle sensor.
In a method for minimizing errors in sensors used for a recording apparatus of car accidents, data including acceleration, yaw-rate, vehicle speed measured at the transmission, and steering angle are first measured by sensors, then error in forward acceleration is corrected on the basis of vehicle speed measured at the transmission. Next, error in lateral acceleration is corrected on the basis of vehicle speed and steering angle measured by a steering angle sensor, then error in rotational angular velocity is corrected on the basis of steering angle and vehicle speed. Finally, data is recorded as corrected values.