JPS63111471A - Vehicle speed measuring instrument - Google Patents

Abstract

PURPOSE:To eliminate an error in the measurement of a speed due to variation in vehicle height measured by a vehicle height sensor by correcting the power of an optical system with the vehicle height measured by a vehicle speed sensor which uses a spatial filter. CONSTITUTION:Reflected light from a road surface 15 which is converted by a lens 2 is projected on the spatial filter 1, and converted photoelectrically and then inputted to a differential amplifier 3. Its differential output is inputted to an amplifier 8 and amplified with a specific gain. The output of the amplifier 8 is inputted to a microcomputer 13 through an A/D converter 12, and the microcomputer 13 controls the gain of the amplifier 8 so that the value is constant. A pulse sent by a transmitter 4 is reflected by a road surface and received by a receiver 5. A measurement part 6 measures the time difference between the sent and received pulses and the computer 13 inputs the difference to compensate variation in the power of the optical system due to variation in the vehicle height.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a speed measuring device for an automobile, and more particularly to a speed measuring device using a spatial filter.

[Conventional technology]

Vehicle speed measurement using a spatial filter is carried out based on equation (1) in an arrangement as shown in FIG.

v=f-M-P...(1)
Here, ■ is the speed, M is the magnification of the optical system, P is the pitch of the spatial filter, and f is the output signal frequency of the spatial filter. The magnification M of the optical system is the lens 100 and the spatial filter 10.
1 is the distance a, and the distance between the road surface 102 and the lens 100 is y = b / a...
・(2) [“One problem that Ming is trying to solve”]・
1. In the above speed measurement using a spatial filter, the distance between the road surface and the lens due to the vertical movement of the vehicle body! ] value changes,
Even when the vehicle is traveling at a constant speed, the measured speed value may fluctuate. For this reason, conventionally, JP-A-52-1
43081, a method is adopted in which a light shielding plate having a small hole is rearranged on the focal point of the lens between the lens and the spatial filter, and only the light that passes through the small hole on the focal point is introduced into the spatial filter. was. However, in this conventional method, since the amount of light passing through the small holes is very small, a powerful light source is required, resulting in an increase in the size of the device and high power consumption.

The purpose of the present invention is to eliminate erroneous speed measurement due to changes in vehicle height,
An object of the present invention is to provide a speed measuring device for an automobile using a spatial filter, which is small in size and has low ntffl power.

[Means for solving problems]

The above object is achieved by a vehicle height sensor that measures the distance between a lens and a road surface, and a vehicle height measured by this sensor.

[Effect]

A vehicle height sensor measures the height of the vehicle while it is running, and calculates the distance bo from the Lensto road surface. When this distance at rest is b, M in equation (2) may be modified to Mo according to the following equation, and this may be used as the value in equation (1).

MO2M-bo/b...(3)
In this case, there is no need to use small holes, so there is no reduction in the amount of light, and there is no need to increase the size of the light source or increase power consumption.

〔Example〕

Two embodiments of the present invention will be described below with reference to the drawings. 1st
The figure shows an embodiment of the device of the present invention, in which reflected light from a road surface 15 is focused by a lens 2, is projected onto a spatial filter 1, photoelectrically converted, and then input into a differential intensifier 3. Ru.

Here, an example of the configuration of the spatial filter 1 is shown in FIG. 3. This filter is of a differential type, and light receiving elements 50 are arranged facing each other at a pitch P. Light receiving elements 5 facing each other
The pitch of 0 is P/2.

Returning to FIG. 1, the outputs of both light receiving elements are amplified by a differential intensifier 3 to obtain a differential output. This differential output is the amplifier 8
and is amplified with a predetermined gain. The output of the amplifier 8 is sent to the microcomputer 1 via the A/D converter 12.
3, and the microcomputer 13 controls the gain of the amplifier 8 so that this input value is constant. The purpose of this gain control is to prevent the amplifier 8 from becoming saturated due to a sudden increase in the amount of light when the vehicle passes over, for example, a white line for traffic display on a road. The signal amplified by the amplifier 8 is sent to a variable center frequency bandpass filter 10. Such a bandpass filter can be realized by, for example, comprising a Swissotito capacitor filter and controlling its clock frequency with a numerically controlled oscillator (Neo) 9.

Further, the numerically controlled oscillator can be realized by a PLL synthesizer or the like. The center frequency of this bandpass filter is changed, and its output is given to the microcomputer 13 via the A/D converter 11. From this input, the microcomputer 13 estimates the average frequency of the narrowband irregular signal that is the spatial filter output signal.

FIG. 4A shows the processing flow for estimating the average frequency, and in process 200, the initial value f of the estimated center frequency is determined by the following equation.

f = v c / (MX P ) Here, VC is the current vehicle speed, MX is the current optical system magnification obtained from the vehicle height sensor (described later), and P is the pitch (constant) of the spatial filter. A value f is set in the numerically controlled oscillator 9. In process 202, the output value A of the A/D converter 11 at the initial value frequency f is read. In the judgment process 203, the previously captured A/D converter output Ao is compared with the currently captured output A. If the difference is within the predetermined value i, the process proceeds to step 209, where the estimated center frequency value is set as fcttf. Otherwise, the process proceeds to determination processing 204. Note that the current value A is initialized to 0 only for the first time. In judgment process 204, the above-mentioned A/D is determined. If Ao>A, the coefficient α of the frequency increase step is set to -1 in process 205, and if Ao<A, α=1 is set in process 206. Next, in process 207, the previous value A of the A/D converter output value is
Update o to A to prepare for the next process. In process 208, the estimated center frequency is determined using the α value determined in process 205 or 206. That is, f is replaced by f+α·Δf.

Here, Δf is the positive width of one time. After correcting f in this way, return to process 201, set the corrected frequency f to the numerically controlled oscillator 9, and repeat the following processes, thus estimating the average center frequency fc of the spatial filter output narrowband signal. .

The output of the amplifier 8 is then led to the comparator 15 of FIG. ! It is compared with the voltage er and shaped into a rectangular wave. The differentiating circuit 16 converts the rectangular waveform into a pulse waveform as shown in FIG. 5, and inputs it to the microcomputer 13 as an interrupt signal IRQ.

The above-described gain control process is started by this interrupt signal. This processing flow is shown in FIG. 4B.
9 Judgment process 2 of reading the output value of the D converter 12 three times
In step 14, it is checked whether all of the A/D output values read three times are equal to or greater than a specified value A. This specified value is determined through experiments, etc. If all values are above the specified value A1, the A/
This is a case where the D output value is at a high level, and gain control is performed in process 215 only in such a case.
If the average value of the output values is Ao, then the current gain line g (A) and the normal gain line go are shown in Fig. 6.
Gain G can be found from (A). In this case, the A/D converter output value is set to the AIIXK. Incidentally, Gc in Fig. 1 is the gain before gain control, and is a margin (about =O, S), and go(A) and g(A) are parallel.

In process 216, the interrupt mask is canceled and in process 217, the fourth
Start the gain monitoring program shown in Figure C.

In this program, in process 218, the A/D converter 1
Load 2-output A engineering. In the judgment process 219, as shown in FIG. 6, it is judged whether the value of g-'' (go (AI)) exceeds A.This is to raise the reduced gain value back to the normal state. If it exceeds, in step 222, the previous value AO of the A/D conversion value in step 203 of FIG. 4A is changed to Ao 4-g(1-
” (g (Ao)). This is because the gain has been lowered in the gain control program, so the A/D output has also decreased.
This is because if this continues, correct estimation cannot be made when estimating the center frequency, so it is necessary to correct the A/D output value at the time when the gain is lowered. In process 219, g +
If z(go(AX)) does not exceed A, the process proceeds to process 220, where the gain G is increased by 1, and in process 221, the gain control is performed so that the same gain correction is performed in the process 222 described above. while estimating the average center frequency fc.

Next is a vehicle height sensor that corrects the magnification of the optical system. In this embodiment, an ultrasonic sensor is used as the vehicle height sensor. That is, the transmitted pulse emitted from the transmitter 4 in FIG. 1 is reflected on the road surface and received by the receiver 5, but as shown in FIG. 7, the transmitted and received pulses have a time difference τ corresponding to the vehicle height. Then, the height of the vehicle, that is, the distance bo between the lens 2 and the road surface 14 is expressed as: bo = vs t/2 - (4). Here vs is the speed of sound. Then, the time difference is measured by the time difference measuring section 6, digitized by the counter 7, and taken into the microcomputer 3.The microcomputer 3 calculates the vehicle height bo from equation (4), and uses this and the estimated average center frequency fc. , the speed V is v=fc-P''(bo/b)' M ・
"(5). Here, p is the pitch of the spatial filter, b is the distance between the lens and the road surface when it is stationary, and M is the magnification of the optical system when it is stationary.

〔Effect of the invention〕

According to the present invention, in a military law sensor using a spatial filter, it is possible to prevent measurement errors caused by changes in the magnification of the optical system due to changes in vehicle height, and also eliminates the need for a powerful light source, resulting in miniaturization of the device. This also has the effect of reducing power consumption.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the device of the present invention, FIG. 2 is a diagram showing the positional relationship between the spatial filter and the lens, FIG. 3 is a diagram showing an example of the configuration of the spatial filter, and FIG. 4A is a diagram showing the spatial relationship between the spatial filter and the lens. Figures 4B and 4C are flowcharts of the process of estimating the average frequency of the filter output, Figures 4B and 4C are flowcharts of the process of controlling the level of the spatial filter output to a constant level, and Figure 5 is a flowchart of the interrupt generation mechanism that starts the process of Figure 4B. Explanatory diagram, Figure 6 is the 4th
FIG. B and FIG. 4C are explanatory diagrams of the processing, and FIG. 7 is an explanatory diagram of the operation of the vehicle height sensor. 1... Spatial filter, 2... Lens, 3... Differential amplifier. 4... Transmitter, 5... Receiver, 6... Time difference measuring section, 7... Counter, 8... Amplifier, 9... Numerical control layer oscillator. 10... Band pass filter, 11, 12... A/
D 20th 4th. Area A Figure 4e1 Figure 4c

Claims (1)

[Claims] 1. The reflected light from the road surface is taken into a spatial filter via an optical system, the average frequency in the spatial filter output signal is detected, and the value proportional to the magnification of the optical system and the detected average frequency is calculated as a value proportional to the vehicle's running. A vehicle speed measuring device configured to determine speed includes a vehicle height sensor that measures the height of a fixed position of the vehicle from the road surface, a height of the vehicle at the fixed position when the vehicle is stationary, and a height detected by the vehicle height sensor. A vehicle speed measuring device characterized in that it is provided with means for calculating the magnification of the optical system when the vehicle is traveling.