JPH06324059A - Speed measuring apparatus of space filter type and speed controlling system and automobile equipped with the apparatus - Google Patents

Abstract

PURPOSE:To provide a speed measuring apparatus of a space filter type capable of obtaining accurate measuring values without being influenced by the surrounding temperature, and a speed controlling system and an automobile each equipped with the measuring apparatus. CONSTITUTION:The light from a to-be-measured object is detected by a space filter type photodetector 3 through a photodetecting lens 1 and a slit 2, whereby the speed of the object is calculated by a signal processing circuit 4. At this time, the temperature in the vicinity of the photodetecting lens 1 is detected by a temperature sensitive element 5. A temperature compensating circuit 6 makes a correction based on the detected temperature to the process to calculate the speed in the signal processing circuit 4. Accordingly, an error in the measuring value of the speed resulting from the temperature in the vicinity of the photodetecting lens 1 is restricted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spatial filter type speed measuring device, a speed control system including the same, and a vehicle, and more particularly to a correction processing technique for suppressing a measurement error due to temperature in the device.

[0002]

2. Description of the Related Art Conventionally, in this type of spatial filter type velocity measuring device, various materials are used for a light receiving lens for receiving light from a measurement object.

[0003]

However, when the material of the light receiving lens is made of low-cost plastic, the lens undergoes thermal expansion due to ambient temperature changes and the refractive index changes, so that the focus of the lens is reduced. The distance changes. For this reason, as will be described later, the magnification of the optical system changes, so that a predetermined measurement accuracy cannot be maintained over a wide ambient temperature range, that is, there is a problem that the temperature characteristic is poor.

A specific example is shown in FIG.
Is the initial state, which is the ideal imaging state of this optical system, (b)
Indicates the image formation state when the ambient temperature is lowered. The distance between the light receiving lens 51 and the target object 54 is a, and the light receiving lens 5 is
The initial focal length of 1 is f, and the slit 5 is arranged on the focal plane of the light receiving lens 51 and allows only light passing near the optical axis to pass.
The distance between 2 and the spatial filter type photodetector 53 is b. Further, the focal length of the light receiving lens 51 when the focal length changes with the change of the ambient temperature is f ′. As shown in "Measurement and Control" Vol. 7, No. 11, P9 to P20, the detected speed V in the spatial filter type speed measuring device
Is calculated as V = P · fc / m by the magnification m of the optical system, the spatial filter pitch P, and the measurement frequency fc.

As shown in FIG. 3A, in the ideal image forming state of the optical system, only the light rays parallel to the optical axis reach the spatial filter type photodetector 53, so that the magnification m is irrespective of the value of a. , M = x / y = b / f. Here, x is an image of the object y. On the other hand, as shown in (b) of the figure, when the ambient temperature is lowered, the focal length of the lens is f '(<f), so the length of the target object with respect to the image x having the same length as (a). Becomes y '(<y), the magnification m'becomes m' = x / y '(> m). Therefore, comparing (a) and (b) in the figure, since the magnifications of the optical system are different between m and m ′, the detection speeds V and V ′ (V ′ corresponding to the same measurement frequency fc are lower than the ambient temperature decrease). V'is (V'-V) with respect to V
It has a relative error of / V. For example, the material of the light receiving lens 51 is polycarbonate, the initial focal length f is 80 mm, and the distance a between the light receiving lens 51 and the target object 54 is 500 m.
m and a change in ambient temperature of 40 ° C., a relative error of about 7% occurs.

As another example, the material of the light receiving lens 51 is polycarbonate, the initial focal length f is 65 mm, the material of the casing of the speed measuring device is ABS resin, and the distance a between the light receiving lens 51 and the target object 54 is 380 mm. , Standard temperature 2
The case of 5 ° C. will be described. The focal length of the light receiving lens 51 has a positive temperature coefficient of about 2.58 × 10 −4% / ° C. due to a decrease in the refractive index and an increase in the radius of curvature as the temperature rises. On the other hand, the linear expansion coefficient of ABS resin is 0.7 × 10 −4.
% / ° C., the distance between the lens focal point and the slit 52 has a positive temperature coefficient of 1.88 × 10 −4% / ° C. subtracted. In other words, the higher the temperature,
The slit 52 is displaced from the lens focal position in the direction toward the light receiving lens 51. Therefore, under the standard temperature condition, of the reflected light from the target surface, the component parallel to the optical axis is selected and enters the slit 52, whereas under the high temperature condition, it converges toward the optical axis. The ingredient to be selected is selected. This corresponds to a reduction in the spatial frequency selected by the spatial filter, and as a result, the measurement speed proportional to the spatial frequency also decreases, and the measured speed has a negative temperature characteristic. FIG. 8 shows the calculation result under the above conditions. The temperature coefficient of measurement speed is constant at about −0.1% / ° C. in the range of −50 ° C. to 100 ° C.

The present invention solves the above-mentioned problems and is affected by the ambient temperature by measuring the ambient temperature of the device and correcting the speed calculation process by the circuit process according to this temperature. It is an object of the present invention to provide a spatial filter type speed measuring device capable of obtaining a highly accurate measured value, a speed control system including the same, and an automobile.

[0008]

To achieve the above object, the invention of claim 1 provides an optical system and a photodetector for receiving light from an object to be measured, and a signal detected by the photodetector. In a spatial filter type velocity measuring device having a signal processing circuit for calculating the velocity of the measurement object based on,
A temperature-sensing element that detects the temperature in the vicinity of the optical system, and a temperature compensation circuit that corrects the speed calculation processing of the measurement object in the signal processing circuit according to the output of the temperature-sensing element. is there. According to a second aspect of the present invention, in the spatial filter type velocity measuring device according to the first aspect, the temperature sensing element is a thermistor, a temperature measuring resistance element, a thermocouple, or a semiconductor temperature sensor utilizing temperature dependency of PN junction voltage drop. Any of its integrated temperature sensors. According to a third aspect of the present invention, in the spatial filter type velocity measuring device according to the first and second aspects, one or a plurality of temperature sensitive elements are provided,
At least one of them is arranged in the immediate vicinity of or in contact with the lens of the optical system. According to a fourth aspect of the present invention, in the spatial filter type velocity measuring device according to the first aspect, the signal processing circuit has a frequency / voltage conversion circuit for converting the frequency of the detection signal into a voltage, and the correction processing by the temperature compensation circuit is This is performed by adjusting the gain of the output from the frequency / voltage conversion circuit or the final output of the signal processing circuit.

According to a fifth aspect of the present invention, in the spatial filter type velocity measuring apparatus according to the first aspect, the signal processing circuit has a counter for counting the number of pulses obtained from the detection signal,
The correction process by the temperature compensation circuit is performed by adjusting the counting time in the counter. According to a sixth aspect of the present invention, in the spatial filter type velocity measuring device according to the first aspect, the signal processing circuit has a high frequency pulse oscillator for measuring a cycle of the detection signal,
The correction process by the temperature compensation circuit is performed by adjusting the output frequency of the high frequency pulse oscillator. The invention according to claim 7 is provided with the spatial filter type speed measuring device according to any one of claims 1 to 6 and a wheel speed sensor, and the speed is controlled by controlling the brake or the accelerator by the output of these. System. The invention according to claim 8 is an automobile equipped with the speed control system according to claim 7.

[0010]

According to the present invention, the light from the object to be measured is received by the photodetector via the optical system, and the speed of the object to be measured is calculated in the signal processing circuit. At this time, the temperature near the optical system is detected by the temperature sensitive element, and the temperature compensating circuit corrects the speed calculation processing of the signal processing circuit according to the detected temperature. This suppresses the error in the speed measurement value due to the temperature near the optical system. According to the configuration of claim 3, the temperature in the vicinity of the lens of the optical system is detected by the temperature sensitive element, and the temperature compensating circuit corrects the speed calculation processing of the signal processing circuit according to the detected temperature. Therefore, an accurate velocity of the measuring object can be calculated in consideration of the change in the focal length of the lens due to the temperature. According to the configurations of claims 4 to 6, the speed measurement value can be corrected by adjusting the gain, adjusting the counting time in the counter, and adjusting the output frequency of the high-frequency pulse oscillator, and taking the influence of temperature into consideration. The velocity of the measuring object with high accuracy is calculated. According to the configurations of claims 7 and 8, efficient braking and acceleration can be performed.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment according to the present invention will be described below with reference to FIG.
Will be described with reference to. The spatial filter type velocity measuring device includes a light receiving lens 1 for receiving light from an object to be measured, a slit 2 having a small hole at a focal position of the light receiving lens 1, and a space for receiving light passing through the small hole of the slit 2. The filter type photodetector 3, the signal processing circuit 4 for performing speed calculation processing of the measuring object from the signal detected by the photodetector 3, and the light receiving lens 1 are provided in the vicinity of or in contact with the light receiving lens 1. The temperature-sensitive element 5 detects the ambient temperature of the lens 1, and the temperature compensation circuit 6 outputs a signal for temperature correction to the signal processing circuit 4 according to the temperature detected by the temperature-sensitive element 5. The light receiving lens 1 is made of low-cost plastic, and its focal length changes depending on the temperature. The temperature sensing element 5 includes, for example, a thermistor, a temperature measuring resistance element, a thermocouple,
There is a semiconductor temperature sensor or its integrated temperature sensor that utilizes the temperature dependence of the PN junction voltage drop. Further, the temperature measuring resistance element includes those made of platinum or copper.

To explain the operation, the light from the object to be measured is received by the light receiving lens 1, passes through the small hole of the slit 2, and is received by the spatial filter type photodetector 3. The detection signal from the photodetector 3 is input to the signal processing circuit 4. On the other hand, the temperature in the vicinity of the light receiving lens 1 is detected by the temperature sensing element 5, and the temperature compensating circuit 6 is detected according to the detected signal.
Outputs a signal for performing temperature correction to the signal processing circuit 4. As a result, the signal processing circuit 4 calculates and outputs a temperature-corrected velocity signal of the measurement object. Therefore, even if the material of the light receiving lens 1 is low-cost plastic, the speed measurement value can be obtained in consideration of the change in the focal length of the light receiving lens 1 due to the temperature, and the measurement accuracy can be improved. It should be noted that not only one temperature sensitive element 5 but also a plurality of temperature sensitive elements are provided, and the temperature at multiple points is measured, so that the temperature distribution in the device is considered more accurately than the temperature in the vicinity of the light receiving lens 1. This enables accurate temperature correction. For example, by separately estimating the change in the focal length of the light receiving lens 1 due to temperature and the change in the small hole of the slit 2 due to thermal expansion and thermal contraction of the optical holder, comprehensive temperature correction can be performed in speed calculation. it can.

FIG. 2 shows the above-mentioned first device provided with two temperature sensitive elements.
The modification of an Example is shown. In addition to the temperature-sensitive element 5a arranged in the vicinity of or in contact with the light-receiving lens 1, a temperature-sensitive element 5b is arranged in the vicinity of or in contact with the slit 2. The detection signals from the temperature sensitive elements 5a and 5b are both input to the temperature compensation circuit 6. Since the temperature near the slit 2 is detected by the temperature sensitive element 5b, the temperature compensating circuit 6
Outputs a signal that takes into account not only the change in the focal length of the light receiving lens 1 but also the change in the small hole of the slit 2 due to heat contraction. Therefore, it is possible to calculate the velocity of the measuring object with less error.

In the second to fourth embodiments, the correction processing by the temperature compensation circuit 6 will be described in detail below. 3 and 4 show a second embodiment. The signal processing circuit and the temperature compensation circuit include a waveform shaping circuit 22 that converts an analog signal from the photodetector 21 into a pulse signal, and an F that converts a frequency into a voltage.
It is composed of a / V (frequency / voltage) conversion circuit 23 and an amplifier 25 whose amplification degree changes according to the temperature detected by a thermistor 24 which is a temperature sensitive element 4 for detecting the temperature near the optical system. The output from the F / V conversion circuit 23 is an amplifier 25.
The amplification degree is adjusted according to the temperature at
The velocity measurements are temperature corrected.

FIG. 4 shows the thermistor 24 and the amplifier 2 of FIG.
5 is a detailed circuit diagram of FIG. The feedback resistor of the amplifier 25 is provided with a thermistor 24 having a temperature coefficient of + 0.2% / ° C., and the inverting input terminal of the amplifier 25 is connected to a variable resistor 26 whose one end is grounded. The variable resistor 26 adjusts the output of the amplifier 25. When the output of the F / V conversion circuit 23 is VF (T) and the output of the amplifier 25 is V0 (T),

[0016]

[Equation 1]

Is represented by When the variable resistor 26 is adjusted so that VR = r,

[0018]

[Equation 2]

It becomes In this way, since the output of the amplifier 25 can be controlled to be substantially equal to the output of the F / V conversion circuit 23 at 25 ° C., effective temperature correction can be realized.

FIG. 5 shows a third embodiment. The signal processing circuit and the temperature compensation circuit include a waveform shaping circuit 22 that converts an analog signal from the photodetector 21 into a pulse signal, and a counter 2 that counts the number of pulses output from the waveform shaping circuit 22.
7, a D / A converter 28, and a timer 29 for setting the count time of the counter 27. A thermistor 24, which is a resistor that determines the time constant, is connected to the timer 29. The timer 29 outputs two pulse signals for causing the counter 27 to perform the counting start operation and the counting end operation according to the temperature detected by the thermistor 24. As a result, the count time of the counter 27 is changed according to the temperature, and the measured value becomes accurate without being affected by the temperature.

FIG. 6 shows a fourth embodiment. The signal processing circuit and the temperature compensation circuit include a high frequency pulse oscillator 30 that outputs a high frequency pulse, a waveform shaping circuit 22 that converts an analog signal from the photodetector 21 into a pulse signal, and a pulse output from the waveform shaping circuit 22. A counter 2 for counting the output frequency of the high-frequency pulse oscillator 30 to measure the period
7, a reciprocal arithmetic circuit 31, and a D / A converter 28. A thermistor 24, which is a resistor that determines the time constant, is connected to the high-frequency pulse oscillator 30. The output frequency of the high frequency pulse oscillator 30 is changed according to the temperature detected by the thermistor 24, and the counter 27 counts the number of high frequency pulses in one cycle of the signal from the waveform shaping circuit 22 and is inversely proportional to this count number. The analog voltage is output from the D / A converter 28. As a result, the measured value is temperature-corrected.

An antilock brake system (ABS) for controlling the brake so as not to lock and an accelerator are controlled by using both outputs of the spatial filter type speed measuring device and the wheel speed sensor provided separately. Traction control system (TC
It is also possible to construct a speed control system such as L). In addition, for cars such as passenger cars, trucks, trailers, and buses,
Equipped with this speed control system, efficient braking / acceleration capability can be obtained.

[0023]

As described above, according to the first and second aspects of the present invention, since the speed calculation process in the signal processing circuit is corrected according to the temperature near the optical system, the correction is performed regardless of the temperature near the optical system. In addition, speed measurement with high accuracy becomes possible. Further, even if a low-cost plastic material is used for the optical system and the housing, the temperature characteristics do not deteriorate, so that the cost of the entire device can be suppressed. According to the invention of claim 3, the temperature in the vicinity of the lens is measured by the temperature sensitive element, and the speed calculation process in the signal processing circuit can be corrected in accordance with the change in the focal length of the lens, so that the speed measurement can be performed. The error can be suppressed. Further, a plastic material can be used for the lens, and the cost of the device can be reduced.

According to the invention of claims 4 to 6, the correction processing for the signal processing circuit which brings about the above-mentioned effects is performed by adjusting the gain of the output from the frequency / voltage conversion circuit or the final output of the signal processing circuit, This can be performed by adjusting the counting time in the counter or adjusting the output frequency of the high frequency pulse oscillator, and the same effect as described above can be obtained. According to the invention of claim 7, since a highly accurate speed measurement value can be obtained, it becomes possible to perform efficient brake or accelerator control by this output, and it is expected that the braking distance is shortened or good acceleration is achieved. According to the invention of claim 8, since the braking distance is shortened and the acceleration performance is improved,
The safety of the car is increased.

[Brief description of drawings]

FIG. 1 is a block diagram of a spatial filter type velocity measuring device according to a first embodiment of the present invention.

FIG. 2 is a block diagram of a spatial filter type velocity measuring device according to a modification of the present embodiment.

FIG. 3 is a block diagram of a signal processing circuit and a temperature compensation circuit according to a second embodiment.

FIG. 4 is a circuit diagram of a temperature compensation circuit according to the present embodiment.

FIG. 5 is a block diagram of a signal processing circuit and a temperature compensation circuit according to a third embodiment.

FIG. 6 is a block diagram of a signal processing circuit and a temperature compensation circuit according to a fourth embodiment.

FIG. 7 is a diagram for explaining a difference in image forming state due to ambient temperature, in which (a) is an initial state that is an ideal image forming state;
(B) shows the image formation state when the ambient temperature changes.

FIG. 8 is a diagram showing temperature characteristics of speed measurement error.

[Explanation of symbols]

 1 Light receiving lens 2 Slit 3 Spatial filter type photodetector 4 Signal processing circuit 5, 5a, 5b Temperature sensing element 6 Temperature compensation circuit 24 Thermistor 25 Amplifier 27 Counter 29 Timer 30 High frequency pulse oscillator

Claims (8)

[Claims] 1. An optical system and a photodetector for receiving light from a measurement object, and a signal processing circuit for calculating the speed of the measurement object based on a signal detected by the photodetector. In the spatial filter type velocity measuring device, a temperature-sensing element for detecting the temperature in the vicinity of the optical system, and a temperature for correcting the velocity calculation processing of the measurement object in the signal processing circuit according to the output of the temperature-sensing element. A spatial filter type velocity measuring device comprising: a compensation circuit. 2. The spatial filter type velocity measuring device according to claim 1, wherein the temperature sensing element is a thermistor, a temperature measuring resistance element, a thermocouple, or a PN.
A spatial filter type speed measuring device, which is either a semiconductor temperature sensor utilizing the temperature dependence of a junction voltage drop or an integrated temperature sensor thereof. 3. The spatial filter type velocity measuring device according to claim 1, wherein one or a plurality of temperature sensitive elements are provided, and at least one of the temperature sensitive elements is in the vicinity of or in contact with the lens of the optical system. A spatial filter type velocity measuring device, characterized in that 4. The spatial filter type velocity measuring device according to claim 1, wherein the signal processing circuit has a frequency / voltage conversion circuit for converting the frequency of the detection signal into a voltage, and the correction processing by the temperature compensation circuit is the frequency / A spatial filter type speed measuring device characterized in that it is performed by adjusting the gain of the output from the voltage conversion circuit or the final output of the signal processing circuit. 5. The spatial filter type velocity measuring device according to claim 1, wherein the signal processing circuit has a counter for counting the number of pulses obtained from the detection signal, and the correction processing by the temperature compensation circuit performs counting by the counter. A spatial filter type velocity measuring device characterized in that it is performed by adjusting time. 6. The spatial filter type velocity measuring device according to claim 1, wherein the signal processing circuit has a high frequency pulse oscillator for measuring the cycle of the detection signal, and the correction process by the temperature compensation circuit is the high frequency pulse oscillator. The spatial filter type velocity measuring device is characterized in that it is performed by adjusting the output frequency of the. 7. The spatial filter type speed measuring device according to any one of claims 1 to 6 and a wheel speed sensor are provided, and the speed is controlled by controlling a brake or an accelerator according to the outputs of them. Speed control system. 8. An automobile equipped with the speed control system according to claim 7.