JPH06109746A - Speed detector - Google Patents

Abstract

PURPOSE:To provide a compact space filter type speed detector at a low cost by forming a tracking filter with a simple circuit structure. CONSTITUTION:The electric signal having the frequency corresponding to the moving speed of an object to be measured is outputted from a space filter 1, and the signal in the noise frequency range contained in the electric signal is cut off by a tracking filter 3. The signal passing through the tracking filter 3 is converted into voltage by a F/V converter 4 and outputted. The output voltage is fed back to the tracking filter 3 via a level converter 5. The frequency range where noises are cut off is controlled in response to the output voltage, noises are surely removed, and accurate speed is detected.

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 detecting device for detecting the ground speed of a vehicle in a non-contact manner, and to a technique for removing a noise frequency range of a detected electric signal.

[0002]

2. Description of the Related Art Conventionally, in a spatial filter type velocity detecting device, grating slits are arranged at regular intervals, and a light receiving element for receiving light transmitted through the slits is arranged behind the slits, and this light receiving element is There is generally known a method of obtaining a time / frequency signal by alternately connecting wires every other pair and combining them into two sets, and by taking a differential between two sets of signal outputs of this light receiving element. However, in this detection method, a noise frequency component other than the center frequency corresponding to the moving speed of the measurement target is also included in the detected signal, so it is necessary to remove the noise frequency component through a filter. A tracking filter (mainly a center frequency tracking type band pass filter) is usually used for this filter because of its wide speed detection range.
As shown in Japanese Patent Laid-Open No. 15170, a PLL (Phase Locked Loop) is also used.

[0003]

However, such a conventional tracking filter has a problem that the circuit size becomes large and uneconomical, and it is not possible to reduce the size and cost of the entire apparatus.

The present invention solves the above-mentioned problems, and an object of the present invention is to provide a spatial filter type velocity detecting device which is compact and low in cost by using a simple tracking filter circuit configuration.

[0005]

[Means for Solving the Problems] To achieve the above object
The invention according to claim 1 is characterized in that the light from the object to be measured is special.
Selectively receive light with a constant spatial frequency component, and
A sky that outputs an electrical signal with a frequency that corresponds to the moving speed of an object.
Filter and the electrical signal output from the above spatial filter
The electrical signal of the noise frequency component of the signal frequency is cut off.
Noise blocking means and electrical signals that have passed through the noise blocking means.
Signal frequency is converted to a voltage proportional to the frequency and output
Frequency / voltage conversion means for
Of the measurement object based on the voltage output from the replacement means
Spatial filter type speed detector for detecting moving speed
Then, the noise blocking means adjusts the moving speed of the measuring object.
The frequency domain that cuts off the noise is controlled accordingly.
It was made. The invention according to claim 2 provides the above noise shielding.
The disconnecting means controls noise by controlling the applied voltage.
The cutoff frequency region is controlled. Claim 3
The invention described above is output from the frequency / voltage converting means.
A level converter for converting the level of the voltage
Apply the output voltage of the converter to the noise blocking means.
It is the one. According to a fourth aspect of the present invention, the noise shielding is provided.
The disconnecting means includes a variable resistance element, a capacitor and an operational amplifier.
A low-pass filter that attenuates high frequencies using
Low frequency using variable resistance element, capacitor and operational amplifier
It consists of a high-pass filter that attenuates a few frequencies.
It According to a fifth aspect of the present invention, the noise blocking means is configured to
The frequency of the electrical signal passing through the sound blocking means is
To match the center frequency of the electrical signal output by
In addition, it controls the frequency range in which noise is cut off.

[0006]

According to the above construction, the spatial filter outputs the electric signal having the frequency corresponding to the moving speed of the object to be measured, and the noise cutoff means cuts off the signal in the noise frequency range included in the electric signal. To be done. At this time, the frequency region for blocking the noise is controlled according to the moving speed, the noise is reliably removed, and the moving speed of the measurement object is correctly detected.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment embodying the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram of a spatial filter type velocity detecting device. This speed detection device includes two sets of spatial filters 1 that output an electric signal having a frequency corresponding to the moving speed of a measurement object (not shown), and a differential that amplifies the two sets of spatial filter outputs by taking the differential. The amplifier 2 includes a tracking filter 3 that cuts off an electric signal having a noise frequency component, an F / V converter 4 that converts a frequency into a voltage, and a level converter 5 that converts a voltage into a level. The output signal from the spatial filter 1 is input to the tracking filter 3 via the differential amplifier 2, and the electric signal of the noise frequency component is cut off in the tracking filter 3. That is, only the signal having the frequency within the pass band of the tracking filter 3 is selected. Then, the signal that has passed through the tracking filter 3 is input to the F / V converter 4, and by the F / V converter 4,
An analog voltage proportional to the selected frequency is output.
The moving speed of the measuring object is output based on the analog output voltage.

The output voltage is fed back to the control input section of the tracking filter 3 via the level converter 5. Therefore, since the cutoff frequency of the tracking filter 3 changes in proportion to the output voltage, that is, in proportion to the selected frequency, the frequency passing through the tracking filter 3 is only the frequency component indicating the moving speed of the measurement object, It is possible to improve the SN ratio.

FIG. 2 is a specific circuit diagram of the tracking filter 3. In the figure, a field effect transistor (FET) 1
A low-pass filter is composed of 1, the capacitor 12, and the operational amplifier 13, and the high frequency band is attenuated by this filter. Further, the FET 21, the capacitor 22, and the operational amplifier 23 constitute a high-pass filter, and the low frequency range is attenuated by this filter. A bandpass filter is configured by the above two filters.

A signal from the differential amplifier 2 is input to the drain of the FET 11. The source of the FET 11 and the other end of the capacitor 12 whose one end is grounded are connected to the operational amplifier 13
Of the operational amplifier 13, and the negative input terminal of the operational amplifier 13 is connected to the output terminal of the operational amplifier 13. The output terminal of the operational amplifier 13 is connected to one end of the capacitor 22, and the attenuated signal in the high frequency range is input to one end of the capacitor 22. The other end of the capacitor 22 and the drain of the FET 21 whose source is grounded are connected to the operational amplifier 2
3 is connected to the + input terminal of the operational amplifier 23, and the-input terminal of the operational amplifier 23 is connected to the output terminal of the operational amplifier 23. A signal of the selected frequency is sent from the output terminal of the operational amplifier 23 to the F / V converter 4. In addition, FET11,
A voltage from the level converter 5 is applied to the gate of 21. The operational amplifiers 13 and 23 function as buffers.

The control voltage, which is appropriately level-converted from the final output by the level converter 5, is applied to the gates of the FETs 11 and 21. The drain current ID of the FET 11 is
As shown in FIG. 3, it is determined only by the gate potential VGS, not by the drain-source voltage VDS. That is, when the FETs 11 and 21 are regarded as resistance elements, the resistance value R is VDS / ID, and therefore, the control is possible by the gate potential VGS. Therefore, by controlling the gate potential VGS, the pass frequency 1 / (2πRC) of the tracking filter 3 can be controlled. The passing frequency of the tracking filter 3 is controlled so that only the frequency component indicating the velocity of the measurement target passes through the tracking filter 3. As a result, noise is removed and the SN ratio is improved.

According to the present invention, a flexible circuit structure is possible according to the required speed detection accuracy. For example, the tracking filter 3 may have a circuit configuration of a primary filter using one set of a capacitor and a variable resistance element or a circuit configuration of a multi-order filter using a plurality of sets. Further, either a passive filter or an active filter may be used. Furthermore, instead of the band pass filter, only a low pass filter or only a high pass filter may be used as the tracking filter.

[0013]

As described above, according to the first and second aspects of the present invention, the voltage applied to the noise blocking means can be controlled to remove the noise accurately, so that the circuit scale of the device can be reduced and the cost can be reduced. Can be achieved. Further, a flexible circuit configuration can be realized according to the required speed detection accuracy. According to the invention of claim 3, in addition to the same effect as described above, the output voltage of the frequency / voltage converting means is fed back to the noise blocking means via the level converter, so that the noise is proportional to the selected frequency. The cutoff frequency of the cutoff means changes. Therefore, the frequency passing through the noise blocking means is only the frequency component indicating the velocity of the measurement object, and the SN ratio is improved. According to the invention of claim 4, in addition to the same effect as described above, it is possible to attenuate the frequencies on both the high and low sides of a certain specific frequency, so that the noise frequency component can be reliably removed to obtain the desired frequency. Only the electric signal of can be taken out. Therefore, noise is reliably removed, the SN ratio is improved, and the speed detection accuracy of the present device is increased. Claim 5
According to the invention, in addition to the effects similar to those described above, since the frequency of the electric signal passing through the noise blocking unit matches the center frequency of the electric signal output by the spatial filter, it corresponds to the moving speed of the measuring object. A stable voltage output can be obtained.

[Brief description of drawings]

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

FIG. 2 is a circuit diagram of a tracking filter in the device.

FIG. 3 is a diagram showing a relationship between a drain-source voltage, a drain current, and a gate potential in an FET in a tracking filter.

[Explanation of reference numerals] 1 spatial filter 3 tracking filter 4 F / V converter 5 level converter 11 and 21 field effect transistor (FET) 12 and 22 capacitor 13 and 23 operational amplifier

Claims (5)

[Claims] 1. A spatial filter for selectively receiving light of a specific spatial frequency component of light from an object to be measured and outputting an electric signal having a frequency corresponding to the moving speed of the object to be measured, and the space. Of the frequencies of the electric signal output from the filter, noise blocking means for blocking the electrical signal of the noise frequency component, and the frequency of the electrical signal that has passed through the noise blocking means is converted into a voltage proportional to the frequency and output. frequency/
In a spatial filter type velocity detecting device comprising a voltage converting means and detecting a moving speed of the measuring object on the basis of a voltage output from the frequency / voltage converting means, the noise blocking means is used for the measuring object. A spatial filter type velocity detecting device characterized in that a frequency region for blocking noise is controlled according to a moving velocity. 2. The spatial filter type velocity detecting device according to claim 1, wherein the noise blocking means controls a frequency region for blocking noise by controlling an applied voltage. 3. A level converter for level-converting the voltage output from the frequency / voltage converting means, wherein the output voltage of the level converter is applied to the noise blocking means. The spatial filter type velocity detecting device according to claim 2. 4. The low-pass filter for attenuating a high frequency band using a variable resistance element, a capacitor and an operational amplifier, and the high-pass filter for attenuating a low frequency band using a variable resistance element, a capacitor and an operational amplifier. 4. The spatial filter type velocity detecting device according to claim 3, comprising a band pass filter. 5. The noise blocking means controls the frequency domain for blocking noise so that the frequency of the electrical signal passing through the noise blocking means matches the center frequency of the electrical signal output by the spatial filter. Claim 1, characterized in that
The spatial filter type velocity detection device according to 2 or 3.