JP3329237B2 - Distance measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring device for measuring a distance to an external target by measuring a time until a pulsed measuring light is emitted and a reflected light returns. .

[0002]

2. Description of the Related Art Conventionally, as a distance measuring device, for example, as disclosed in JP-A-7-71957,
The laser diode is driven by a pulse-like drive signal to emit laser light (measurement light) from the light emitting unit, and the reflected light, which is reflected by the measurement light hitting an external target, is received by a light receiving unit such as a photodiode. , The time ΔT (see FIG. 9A) from the light emission time of the light emitting unit to the light reception time of the reflected light by the light receiving unit is measured, and the distance to the target is determined based on the time ΔT. Devices configured to calculate are known.

In this type of apparatus, an amplifier 5 for amplifying a light receiving signal from the light receiving unit is usually provided in a signal processing system for processing a light receiving signal from the light receiving unit, as shown in FIG.
2. STC (Sens) that further amplifies the output from the amplifier 52
itivity Time Control) circuit 54 and STC circuit 5
4 is provided with a comparator 56 for determining whether or not the reflected light is received by the light receiving unit based on whether or not the output from the light receiving unit 4 is equal to or higher than a preset light receiving determination level Vth. The light receiving timing is detected.

The amplifier 52 and the STC circuit 54 respectively provide a signal component of the reflected light reflected from the target (that is, a signal component for emitting the measuring light from the light emitting unit) in the light receiving signal output from the light receiving unit. This is for amplifying only the AC signal component corresponding to the frequency of the pulsed drive signal used, and outputting the amplified signal to the STC circuit 54 and the comparator 56 at the subsequent stage. Connected by a coupling capacitor.

[0005] In addition, the STC circuit 54 receives an STC signal (see FIG. 9 (a)) output from a control circuit (not shown), and emits a measuring light as a signal from the light emitting section to emit a measuring light. The amplification factor is controlled so that the output level becomes higher. In other words, as shown in FIG. 9A, the light receiving signal from the light receiving unit is, as shown in FIG. The shorter the time until incidence), the higher the signal level. Therefore, if the light receiving signal from the light receiving unit is always amplified at a constant amplification factor, for example,
The measurement light emitted from the light emitting unit leaks in a direction different from the direction in which the target is to be measured, and weak light reflected by an object near the measuring device located in that direction enters the light receiving unit. Alternatively, even if the measurement light is reflected by rain or the like and weak light is incident on the light receiving unit, the comparator 56
Will receive a high-level signal equal to or higher than the light reception determination level Vth, and will not be able to detect reflected light from the target that should be originally detected, making it impossible to accurately measure the distance to the target. I will.

Therefore, in a distance measuring device, usually, an STC circuit 54 is provided in a signal processing system of a received light signal,
Suppresses the amplification factor of the received light signal in the area where the elapsed time after the measurement light emission is short, and prevents the weak reflected light in the short distance area from being detected as the reflected light from the target whose distance is to be measured. -ing

An amplifier 52 provided before the STC circuit 54 adjusts the detection sensitivity of the reflected light by the comparator 56 so that the noise signal component flowing through the signal processing system of the received light signal is not erroneously detected as the reflected light. This is for maximizing the measurable distance.

That is, the signal level of the light-receiving signal from the light-receiving section becomes lower as the distance from the target becomes longer. Therefore, to increase the measurable distance, the amplification factor of the light-receiving signal is increased and the comparator 56 However, in the signal processing system of the received light signal, the noise signal component is also amplified. Therefore, if the amplification factor of the received light signal is excessively increased, the noise signal component is reduced to the light reception determination level Vth. , The reception of the reflected light is erroneously detected by the comparator 56.

Therefore, in the distance measuring device, usually, the S
An amplifier (a so-called variable gain amplifier) 52 whose gain can be adjusted is provided separately from the TC circuit 54, and the gain of the amplifier 52 is adjusted by a gain control signal from a control circuit (not shown), so that a comparator 56 is provided. Is set to the maximum sensitivity within a range in which a noise signal component is not erroneously detected as reflected light.

Next, the comparator 56 compares the output from the STC circuit 54 with the light reception determination level Vth as described above, and when the output from the STC circuit 54 is higher than the light reception determination level Vth, the light receiving section The light reception timing of the reflected light required for calculating the distance is detected from the result of the determination as follows, for example.

That is, since the signal level of the light receiving signal varies depending on the distance from the target, the output from the STC circuit 54 becomes equal to or higher than the light receiving determination level Vth.
If the time at which the output from 6 changes is detected as the light receiving timing, the detected light receiving timing is shifted due to the difference in the level of the light receiving signal. Therefore, FIG.
As shown in the figure, from the time T1 when the output from the STC circuit 54 exceeds the light receiving determination level Vth, the STC circuit 54
Is detected as the pulse width W of the received light signal, and the center time T3 of the received light signal is calculated from the pulse width W, and this time is used to receive the reflected light. Timing.

When calculating the distance to the target, the distance from the center time T0 of the measurement light emitted from the light emitting unit is calculated as follows:
The light receiving timing of the reflected light obtained as described above (time T3
), And convert this time to distance.

[0013]

By the way, in the conventional distance measuring device configured as described above, the STC circuit 54 determines the amplification factor in the signal processing system of the received light signal.
Since the gain increases with the lapse of time after the measurement light is emitted, the change in the amplification factor changes the signal input level to the comparator 56, and sometimes the light reception timing of the reflected light cannot be accurately detected. .

That is, in the STC circuit 54, a so-called multiplier composed of, for example, a double balanced mixer (double balanced modulator) as shown in FIG.
By multiplying the input signal from the light receiving section by the STC signal, a signal obtained by amplifying the input signal at an amplification factor corresponding to the STC signal is output. May leak to the output side (feedthrough).

If the change in the STC signal is significantly different from the frequency range of the reflected light, the feedthrough component is cut off by the above-described coupling capacitor or the like, and the signal input level to the comparator 56 is reduced Although it is possible to prevent the influence of the through light, as described above, in order to prevent erroneous detection of reflected light from a short distance, ST
In the device provided with the C circuit 56, since the STC signal and the light receiving signal change in a frequency region extremely close to each other, when feedthrough occurs, the signal should be originally input to the comparator 56 as shown in FIG. The light receiving signal A becomes the light receiving signal B which changes in the positive potential (+) direction in response to the change of the STC signal under the influence of the feedthrough, and
The light receiving signal C changes in the negative potential (-) direction according to the change of the C signal.

In the light receiving signal B, the comparator 5
6 is higher than normal, the reflected light is erroneously detected by the comparator 56 immediately after the measurement light is emitted. Conversely, the input signal to the comparator 56 is lower than normal in the received light signal C. Therefore, the reflected light is not detected by the comparator 56.

The double balanced mixer shown in FIG. 10A has a pair of transistors (Q1 and Q1).
2, Q3 and Q4, Q5 and Q6) and a constant current source 68, and each of the symmetrically arranged differential circuits 62 and 64 to the differential circuit 66 A constant current flows to the constant current source 68 via the transistors Q5 and Q6. In this double balanced mixer, an STC signal is applied between the transistors Q1, Q2 and Q4, Q3 of the differential circuits 62, 64, respectively, and light is received between the transistors Q5, Q6 of the differential circuit 66. When signals from the unit side are applied, the differential circuits 62, 6
A multiplied signal obtained by multiplying each signal is output from the output terminal on the fourth side. The configuration and operation of such a double balanced mixer are well known in the art (for example, CQ Publishing Co., Transistor Technology, February 1994, February). , Etc.), and a detailed description thereof will be omitted.

Such a problem occurs not only when a double balanced mixer is used for the STC circuit 54 but also when, for example, a multiplier including an operational amplifier or a variable gain amplifier is used for the STC circuit 54. Occurs. On the other hand, since the above-described problem occurs when the DC signal component output from the STC circuit 54 is changed by the STC signal, a DC voltage is applied to the signal input terminal of the STC circuit 54, and the STC circuit 54 This can be solved by offsetting the DC signal component in 54.

However, S output from the STC circuit 54
Since the amount of change in the TC signal also changes due to environmental changes such as temperature, simply applying a DC voltage to the signal input terminal of the STC circuit 54 changes the STC circuit 54 when the use environment of the distance measuring device changes. As a result, the distance to the target cannot be measured accurately.

The present invention has been made in view of such a problem, and in a distance measuring apparatus having the above-described STC circuit, a distance can always be accurately measured without being affected by feedthrough of the STC circuit. The purpose is to be.

[0021]

In order to achieve the above object, in the distance measuring device according to the first aspect, when the distance calculating means is operating, first, the light emitting means is turned on by the distance calculating means. , And emits the measurement light. Then, when the light receiving means receives the reflected light from which the measuring light is reflected by hitting the external target and outputs a light receiving signal, the amplifying means amplifies the light receiving signal. Then, the light receiving detecting means takes in the AC signal component output from the amplifying means and detects the reception of the reflected light by the light receiving means from the signal.

Further, the distance calculating means outputs a pulse-like driving signal to the light emitting means and simultaneously activates the amplification factor controlling means. As a result, the amplification factor of the amplifying unit increases as time elapses after the light emitting unit emits the measurement light. In other words, the amplifying unit functions as the above-described STC circuit, and prevents the light reception detection unit from detecting unnecessary reception of reflected light from a short distance.

The distance calculating means measures the time from the emission of the measuring light from the light emitting means to the detection of the reflected light by the light receiving detecting means, and the distance from the measured time to the target. Is calculated. That is, the distance measuring device of the present invention measures the distance to the target by the same operation as the above-described conventional device.

On the other hand, in the present invention, the reference level measuring means,
The operating level measuring means and the DC voltage setting means are arranged such that the DC voltage applying means is connected to the signal input terminal of the amplifying means in order to suppress the AC signal component output from the amplifying means due to the gain control by the gain controlling means. The DC voltage to be applied is set as follows.

That is, first, when there is no signal input to the amplifying means, the reference level measuring means measures the level of the AC signal component from the amplifying means detected by the level detecting means as a reference level. Further, the operating level measuring means changes the gain of the amplifying means by activating the gain controlling means, and changes the level of the AC signal component detected by the level detecting means at the time of operating the gain controlling means. It is measured as an operation level. When the reference level and the operation level are respectively measured in this way, the DC voltage setting means sets the DC voltage so that the measured operation level becomes the reference level.

That is, when the distance to the target is measured by the operation of the distance calculating means, the output from the amplifying means changes in accordance with the gain controlled by the gain controlling means. Occurs, the signal level input to the light receiving detecting means changes, so that the light receiving detecting means cannot accurately detect the reception of the reflected light from the light receiving means, and the calculation result (distance) of the distance calculating means has an error. Will occur.

Therefore, in the present invention, the level (reference level) of the AC signal component output from the amplifying means when there is no signal input to the amplifying means and the amplification factor does not change.
And measuring the level (operation level) of the AC signal component output from the amplification means when the amplification rate of the amplification means is changed by operating the amplification rate control means so that the operation level becomes the reference level. By setting a DC voltage to be applied to the signal input terminal of the amplifying means, it is possible to reliably prevent feedthrough caused by a change in amplification factor in the amplifying means.

Therefore, according to the present invention, it is possible to reliably prevent feedthrough caused by a change in the amplification factor of the amplifying means during distance measurement, and to measure the distance to the target with high accuracy. Also, in particular, in the present invention, the DC voltage applying means applies the DC voltage applied to the signal input terminal of the amplifying means to cancel the feedthrough to the level detecting means, the reference level measuring means, the operation level measuring means, and the DC voltage setting. Since it can be set at any time by the operation of the means, if the reference level measuring means, the operating level measuring means and the DC voltage setting means are operated periodically, for example, in a cycle shorter than the ambient temperature change of the device,
It is also possible to reliably prevent a change in feedthrough due to a change in ambient temperature, and to constantly measure the distance to a target with high accuracy.

Here, in order to measure the feedthrough of the amplifying means, it is only necessary to measure the output from the amplifying means functioning as the STC circuit as the reference level and the operation level, respectively, as described above. Since the feedthrough is an AC signal component, it is desirable to use, as a level detecting means for measuring the signal level, a means capable of detecting the maximum level of the output from the amplifying means, such as a peak hold circuit.

However, when the maximum value detecting means such as a peak hold circuit is used as the level detecting means, FIG.
If the feedthrough goes negative as shown in
It becomes impossible to distinguish whether the feedthrough is “0” or negative. Therefore, in the apparatus according to the first aspect, as in the second aspect, the input of the light receiving signal to the amplifying means is cut off, and the pseudo light receiving signal in the form of a pulse is input to the amplifying means. The light receiving signal input means is provided, and the level detecting means is configured to detect the maximum level of the AC signal component output from the amplifying means (that is, configured by the maximum value detecting means). When measuring the reference level, the amplification factor of the amplification unit is set to the maximum amplification ratio controlled by the amplification ratio control unit, the pseudo signal input unit is operated, and the operation level measurement unit measures the operation level. In this case, the amplification factor control means may be activated to change the amplification rate of the amplification means, and the pseudo signal input means may be operated at a predetermined timing at which the amplification rate of the amplification means becomes the maximum amplification rate. Hope Arbitrariness.

That is, when the reference level and the operation level are measured as described above, the pseudo light receiving signal is input to the amplifying means, and the signal is obtained when the amplifying means amplifies the pseudo light receiving signal at the same amplification factor (maximum amplification factor). By measuring the maximum level of the output from the amplifying means, it is possible to always change the output of the amplifying means to the positive side irrespective of the presence or absence of feedthrough, and accurately detect the feedthrough of the amplifying means You can do it. In this way, according to the apparatus of the second aspect, since the feedthrough can always be detected accurately, the DC voltage for canceling the feedthrough can be set accurately, and the distance measurement error due to the feedthrough of the amplifying means can be reduced. , Can be reduced more reliably.

When the maximum value detecting means such as a peak hold circuit is used as the level detecting means as described above, the maximum value detecting means such as the peak hold circuit usually uses an optimum voltage range (maximum level) for measuring the maximum level. (A so-called dynamic range) is set, and if the input voltage is out of this voltage range, the maximum level may not be measured accurately.

For this reason, it is more preferable that the signal path from the light receiving means to the amplifying means is provided in the signal path as described in claim 3.
Second amplification means for amplifying and outputting the input signal is provided, and when the reference level measurement means measures the reference level, the second amplification means sets the reference level to a predetermined level optimal for the operation of the level detection means. It is preferable to set the amplification factor of the means.

As the second amplifying means, a variable gain amplifier (an amplifier 5 shown in FIG. 9 (b)) usually provided in a stage prior to the STC circuit as the amplifying means in the conventional device.
2) may be used. Further, the maximum value detecting means such as a peak hold circuit outputs an offset voltage even when there is no signal input, and this offset voltage changes depending on individual differences of circuits, temperature, and the like. Therefore, as described in claim 3,
Even if the amplification factor of the second amplifying unit is set so that the reference level measured by using the level detecting unit becomes an optimal level for the operation of the level detecting unit, the measured reference level includes the offset voltage. Therefore, when the offset voltage fluctuates so as not to be ignored with respect to the optimum input level of the level detecting means, the level of the output signal from the amplifying means (and the feedthrough of the amplifying means) is reduced by using the level detecting means. Measurement cannot be performed well.

Therefore, in the apparatus according to the third aspect,
In order to more reliably cancel the feedthrough of the amplifying means, the level detecting means is operated without a signal before the reference level is measured by the reference level measuring means. Providing an offset value measuring means for measuring the maximum level detected by the detecting means as an offset value of the level detecting means, and setting the reference level measuring means and the operation level measuring means from the maximum level detected by the level detecting means. It is desirable that the value obtained by subtracting the offset value be measured as the reference level and the operation level, respectively.

In the case where the distance measuring device is configured as described in claim 3 or 4, if the reference level can be set to a predetermined level by the reference level measuring means, the predetermined level is set as the reference level. Although it is preferable, the reference level cannot always be set to a predetermined level.
The reference level measuring means is configured to set the amplification factor of the second amplifying means and then perform the measurement of the reference level again, and the DC voltage setting means sets the second level by the reference level measuring means. It is desirable to set the DC voltage using the reference level measured after setting the amplification factor of the amplification means.

In the DC voltage setting means, when the DC voltage is updated by a periodic operation when the DC voltage has already been set, the operation level and the reference level are set as described in claim 6. A deviation from the current level is obtained, and if the deviation is equal to or more than a predetermined level, a changed voltage value obtained by changing the current voltage value set as the current DC voltage by a predetermined voltage in a direction in which the deviation decreases becomes a new DC voltage. If the deviation is smaller than a predetermined level, a weighted average voltage value obtained by weighting the current voltage value and the changed voltage value to the current voltage value and averaging them may be set as a new DC voltage. .

That is, although the feedthrough changes depending on the temperature, the temperature does not change suddenly, and the DC voltage does not greatly deviate from the optimum value once it is set. Therefore, when the DC voltage is updated, it is desirable to reduce the amount of change so that the DC voltage does not greatly change under the influence of disturbance noise or the like. However, when the operating voltage or the like of the device changes, the optimum value of the DC voltage may also change suddenly. In such a case, the DC voltage needs to be largely changed accordingly.

Therefore, in the distance measuring device according to the present invention, when the deviation between the operating level and the reference level is equal to or more than a predetermined level, it is determined that the operating voltage or the like has suddenly changed, and the current DC voltage is determined. By setting a changed voltage value obtained by adding (or subtracting) a predetermined voltage to a new DC voltage, the DC voltage is largely changed in a direction in which the deviation of each signal level is eliminated, and the deviation between the operation level and the reference level is reduced. When the voltage is smaller than the predetermined level, a voltage value obtained by weighting and averaging the current voltage value and the changed voltage value is set as a new DC voltage. They change it gradually. Therefore, according to the distance measuring device of the sixth aspect, the DC voltage can be updated according to the degree of deviation of each signal level, and the DC voltage can be controlled to an optimum value.

Further, the distance measuring device of the present invention (claims 1 to 6) can measure the distance to the target with high accuracy without being affected by a change in feedthrough due to temperature. In particular, as described in claim 7, for a vehicle that is mounted on a vehicle such as an automobile whose use temperature environment greatly changes and measures the distance to a target located in front of the vehicle in the traveling direction. If used as a distance measuring device, more effects can be exhibited.

[0041]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. First, FIG. 1 is a block diagram showing a configuration of a vehicle distance measuring apparatus to which the present invention is applied.

As shown in FIG. 1, the vehicle distance measuring device of this embodiment is a light emitting section (light emitting means) 4 composed of a laser diode which is energized by the drive circuit 2 and emits laser light (measuring light) forward of the vehicle. And a light receiving section (light receiving means) 8 composed of a photodiode for receiving reflected light in which the laser light emitted from the light emitting section 4 strikes a target ahead of the vehicle such as the preceding vehicle 6 and is reflected.

The light receiving signal from the light receiving section 8 is amplified by the amplifier 10 and input to the variable gain amplifier (hereinafter simply referred to as an amplifier) 14 as the second amplifying means via the signal switching circuit 12. Note that this amplifier 14 has the configuration shown in FIG.
This is similar to the amplifier 52 shown in FIG.
The gain is controlled by a gain control voltage VGC output from a well-known microcomputer (hereinafter, simply referred to as CPU) 30 mainly composed of U, ROM, RAM and the like.

The signal switching circuit 12 is for switching whether the input of the amplifier 14 is connected to the light receiving signal input path of the light receiving section 8 or to the filter 16. Is switched to one of them. Note that the signal switching circuit 12 is normally switched to the light receiving unit 8 side, and the filter 1 is temporarily turned off when performing a feed-through canceling process described later.
6 is switched. The filter 16 includes a resistor
It consists of a differentiation circuit consisting of a capacitor, etc.
When a control signal (High level) is input from the PU 30,
This is differentiated to generate a pulsed pseudo light receiving signal (hereinafter simply referred to as a pseudo signal). And in this embodiment,
The filter 16 and the signal switching circuit 12 function as a pseudo light receiving signal input unit of the present invention.

Next, the output signal from the amplifier 14 is STC
Circuit (amplifying means) 18, but the STC circuit 18
Is provided with a voltage superimposing circuit (DC voltage applying means) 20 for applying a DC voltage VDC, and an STC circuit 18 applies a DC signal to an output signal (AC signal component) from the amplifier 14. A signal on which the voltage VDC is superimposed is input. This DC voltage VDC is for canceling the feedthrough of the STC circuit 18.

The STC circuit 18 is composed of the double balanced mixer shown in FIG. 10A, and its amplification factor (in other words, the multiplication value for the input signal) is
The voltage is controlled so as to increase with time by the STC voltage Vstc generated by the C voltage generation circuit 22.

That is, when the STC voltage generation circuit 22 receives a control signal output from the CPU 30 at a predetermined timing, such as when a laser beam is emitted from the light-emitting unit 4, the time elapses from the minimum level to the maximum level. S increases with
It is configured to generate a TC voltage Vstc.
The C circuit 18 amplifies and outputs an input signal at an amplification factor that changes (increases) according to the change of the STC voltage Vstc.

Note that the STC voltage generation circuit 22
When the control signal is received from 0, the STC voltage Vstc is changed from the minimum level to the maximum level.
After stc reaches the maximum level (in other words, STC circuit 1
8) (after the gain reaches the maximum gain), the state is maintained until the next control signal is input from the CPU 30.

Next, the output signal from the STC circuit 18 is
It is input to the comparator 24. The comparator 24
The output signal from the STC circuit 18 and the light reception determination level Vth are compared in magnitude, and when the output from the STC circuit 18 is higher than the light reception determination level Vth, a High level signal is output from the output terminal, and the inverted output terminal outputs a Low level signal. Output level signal. Each output terminal of the comparator 24 is connected to the time measurement IC 26.
Monitors the rise of the output signal from each output terminal of the comparator 24, and measures the times T1 and T2 shown in FIG. 9A.

That is, the time measurement IC 26 determines that the input signal to the comparator 24 is higher than the light reception determination level Vth and the output from the output terminal rises at T1, and that the input signal to the comparator 24 is higher than the light reception determination level Vth. Time T at which the output from the inverted output terminal rises and becomes smaller
2 are detected respectively.

The CPU 30 outputs a pulse-like drive signal to the drive circuit 2 to emit a laser beam from the light emitting section 4 to the front of the vehicle and activates the time measurement IC 26 at the same time. Actually, the elapsed time from the time when the laser light is emitted (time T0 shown in FIG. 9A) is measured.

Then, the CPU 30 determines the time T1 measured by the time measurement IC 26 as described in the section of the prior art.
, T2 (elapsed time), the pulse width W of the received light signal
Is measured to determine the light receiving center time T3, the time from the laser light emission time (center time) T0 to the light receiving center time T3 is calculated, and the distance to the target ahead of the vehicle is calculated from the time. That is, in the present embodiment, the function as the distance calculation unit is realized by the CPU 30 and the time measurement IC 26.

An output terminal of the STC circuit 18 is connected to a peak hold circuit 28 as a level detecting means.
The maximum level of the signal output from the device can be detected. The maximum level (peak hold voltage VPH) detected by the peak hold circuit 28 is equal to C
It is input to PU30.

All the components of the signal processing system from the light receiving section 8 to the comparator 24 and the peak hold circuit 28 except for the signal path between the voltage superposition circuit 20 and the STC circuit 18 are all cups for cutting DC signal components. They are connected by a ring capacitor, and can transmit only an AC signal component necessary for distance measurement, such as a light receiving signal from the light receiving unit 8.

In the distance measuring apparatus of the present embodiment configured as described above, the CPU 30 operates according to a preset control program to execute the above-described distance measurement and various controls for optimally performing the distance measurement (for example, In this case, a feed-through canceling process, which is a main process according to the present invention and executed by the CPU 30, will be described.

FIG. 2 is a flowchart showing the entire flow of the feed-through cancel process. As shown in FIG. 2, this processing is performed only once immediately after the CPU 30 is started, an initial offset value obtaining processing (S110; S represents a step), an initial reference value obtaining processing (S120), and an initial voltage setting processing. (S130), and thereafter, a normal offset value obtaining process (S150), a normal reference value obtaining process (S160), and a normal voltage setting process (S170) executed each time a predetermined time elapses (S140; YES). Is achieved.

Then, the offset value acquisition processing (S11)
0, S120), a process as an offset value measuring means for measuring the offset value of the peak hold circuit 28 used for detecting the feedthrough of the STC circuit 18 is executed. In the reference value acquisition process (S120, S160), In a state where the amplification factor of the STC circuit 18 is kept constant (maximum amplification factor), a pseudo signal is input to the amplifier 14, and the signal level (maximum level) of the pseudo signal detected by the peak hold circuit 28 at that time is read. A process as a reference level measuring means for setting the value as a reference level is executed. In the voltage setting process (S130, S170), the STC is set.
The amplification factor of the circuit 18 is changed in the same manner as in the distance measurement, and a pseudo signal is input to the amplifier 14 immediately after the amplification factor reaches the maximum, and the signal level of the pseudo signal detected by the peak hold circuit 28 at that time ( Operating level measuring means for determining a DC voltage value for setting the operating level to the reference level and setting a DC voltage VDC to be applied to a signal input terminal of the STC circuit 18. Executes processing as voltage setting means. Further, in the reference value acquisition processing (S120, S160), the amplification factor of the amplifier 14 is set so that the signal level of the pseudo signal input to the peak hold circuit 28 becomes an optimum value for the operation of the peak hold circuit 28. (Specifically, a process of setting the gain control voltage VGC) is also executed.

Hereinafter, each of the above processes (S110 to S130,
The flow of S150 to S170) will be described in detail with reference to the flowcharts shown in FIGS. FIG. 3 is a flowchart showing the initial offset value acquisition processing (S110). As shown in FIG. 3, in the initial offset value acquisition processing, first, in S210, the signal switching circuit 12
6 to cut off the signal input to the amplifier 14,
By setting the gain control voltage VGC (and hence the amplification factor of the amplifier 14) to zero, the peak hold circuit 28 is set to a state where no signal is input, and the peak hold voltage VPH is read.

Then, in S220, it is determined whether or not the peak hold voltage VPH has been acquired n times (for example, 8 times) in S210.
Is performed, the peak hold voltage VPH is acquired n times by the process of S210. Then, when the peak hold voltage VPH can be acquired n times, the process proceeds to subsequent S230.

In S230, the average value VPAV (n) is calculated from the n peak hold voltages VPH obtained as described above, and in S240, the average value of the n peak hold voltages VPH obtained this time is calculated. The peak hold voltage VPH in the range of the value VPAV ± α (α; for example, 20 mV) is
It is determined whether there are m (for example, 5) or more.

If the number of the peak hold voltages VPH within the range of the average value VPAV ± α is equal to or more than m, it is determined that the peak hold voltage VPH has been normally obtained, and S25
0, and the average value V PHAV ± α (α; for example, 20 mV)
The average value V PHAV (α) is calculated from the m or more peak hold voltages V PH within the range of
The calculated average value VPAV (α) is set as an offset value (initial value) of the peak hold circuit 28.

If it is determined in step S240 that there are no more than m peak hold voltages VPH within the range of the average value VPHAV ± α, the flow shifts to step S270, and the n peak hold voltages in steps S210 and S220 are performed. It is determined whether or not the voltage VPH acquisition operation has been performed X times (for example, 5 times). If the acquisition operation has not been performed x times, S210
And the operation of acquiring the n peak hold voltages VPH is executed again.

On the other hand, if the operation of acquiring the n peak hold voltages VPH in S210 and S220 has already been performed X times, it is determined that the n peak hold voltages VPH acquired this time are normal and the process proceeds to S260. Is set as the offset value (initial value) of the peak hold circuit 28.

When the offset value (initial value) of the peak hold circuit 28 is set in S260, the CPU 30 terminates the initial offset acquisition processing and starts the next initial reference value setting processing. Next, FIG.
Is a flowchart showing a normal offset value acquisition process (S150) that is periodically executed to update the offset value after the offset value of the peak hold circuit 28 is once acquired in the initial offset value acquisition process (S110).

As shown in FIG. 4, in the normal offset value acquiring process, the peak hold voltage VPH is read n times by setting the peak hold circuit 28 to the signal non-input state similarly to the initial offset value acquiring process (S110) (S310, S310). 32
0), an average value VPAV (n) is calculated from the read n peak hold voltages VPH (330), and the average value VPAVAV is calculated.
It is determined whether there are m or more peak hold voltages VPH within the range of ± α (S340). If the peak hold voltage VPH within the range of the average value VPAV ± α is m or more, the range is determined. M or more peak hold voltages V
The average value VPAV (α) is calculated from the PH (350), and the flow shifts to S360 for updating the offset value.

On the other hand, if it is determined that there are no more than m peak hold voltages VPH within the range of the average value VPHAV ± α (S340: NO), in S370, an initial or normal offset value acquisition process is performed. In step S360, the offset value acquired last time (previous value; that is, the current offset value) is set as the average value VPAV of the peak hold voltage VPH.
Move to

Then, in S360, S350 or S3
From the average value VPAV set at 70 and the previous value, an average value obtained by weighting the previous value is calculated (so-called weighted average), and the value is set as a new offset value. This calculation is performed, for example, according to the following equation (1).

Offset value = (previous value × 9 + average value V PHAV) / 10 (1) As described above, in the normal offset value acquisition processing, the offset value (previous value) has already been set. By setting a weighted average value with the average value obtained this time as an offset value, it is possible to prevent the offset value from largely fluctuating due to disturbance noise or the like.

FIG. 5 shows an initial reference value acquisition process (S12).
It is a flowchart showing 0). As shown in FIG.
In the initial reference value acquisition process, first, in S410, a series of level measurement operations described below are performed with the gain control voltage VGC.
Is repeated while changing the peak hold voltage VPH, the signal level VGJ of the pseudo signal obtained by subtracting the offset value from the peak hold voltage VPH becomes the gain control voltage VGC at which the optimal value (for example, 500 mV) for the operation of the peak hold circuit 28 is obtained. Explore.

Level measurement operation: The amplification factor of the STC circuit 18 is fixed to the maximum amplification factor, and a control signal is output to the filter 16 while the signal switching circuit 12 is switched to the filter 16 side. Input the signal,
At this time, the peak hold voltage VP obtained by the peak hold circuit 28 is read, and the signal level VGJ of the pseudo signal is measured by subtracting the offset value of the peak hold circuit 28 from the value VPH.

In this search, the CPU 30 changes the data (for example, 8 bits) used to control the gain control voltage VGC in order from the upper bit, and sets the signal level of the pseudo signal obtained by the level measurement operation. V
A so-called binary search technique of searching for a point at which GJ becomes a set value is used.

When the gain control voltage VGC at which the signal level VGJ of the pseudo signal reaches the set value is searched by this search operation, in subsequent S420, the search has been performed j times (for example, 8 times). Judge whether or not
If the search operation has not been performed a number of times, the search operation in S410 is performed j times in a procedure such as shifting to S410 again.

When the search operation in S410 is executed j times, the flow shifts to S430, where the j gain control voltages VGC obtained by the search operation are
The average value VGCAV (j) is calculated, and in S435, the gain control voltage within the range of the average value VGCAV (j) ± β (β; for example, 20 mV) is obtained from the j gain control voltages VGC obtained this time. The voltage VG is k (for example, 5
Number) or not.

If the number of the gain control voltages VGC within the range of the average value VGCAV ± β is equal to or more than k, it is determined that the search for the gain control voltage VGC has been normally performed, and the process shifts to S440. The average value VGCAV (β) is calculated from the k or more gain control voltages VG in the range of VGCAV ± β, and in S450, the calculated average value VGCAV (β) is used as the reference gain control value ( (Initial value; for example, 10-bit data).

If it is determined in step S435 that there are no more than k gain control voltages VGC within the range of the average value VGCAV ± β, the flow shifts to step S460 to execute step S41.
It is determined whether or not the series (j times) of the search operation by 0 and S420 has been performed y times (for example, 5 times). If the series of search operations has not been performed y times, the flow shifts to S410 to execute the above series of search operations again.

On the other hand, if the series of search operations in S410 and S420 have already been performed y times, it is determined that the j gain control voltages VGC obtained by the current search operation are normal, and the flow shifts to S450, and in S430. The calculated average value VGCAV (j) is set as a reference gain control value (initial value).

Then, when the reference gain control value is set in S450, the CPU 30 then sets the gain control voltage VGC output to the amplifier 14
Is controlled by the reference gain control value. The control of the gain control voltage VGC is performed by using upper-order several bits (for example, 8 bits) of the reference gain control value that can be used by the CPU 30 to control the gain control voltage VGC using the D / A converter. And output this data to a D / A converter to obtain a D / A
The gain control voltage VGC is controlled via the converter.

That is, when the CPU 30 controls the gain control voltage VGC, the D / A converter is used.
The reference gain control value is the average value of the gain control voltage VGC controlled via the D / A converter, and the gain control voltage VGC controllable via the D / A converter is represented by a value after the decimal point. When the gain control voltage VGC is subsequently controlled by the reference gain control value, the value obtained by removing the value after the decimal point from the gain control value (rounding, rounding down, or rounding up) is D / A converted. The gain control voltage VGC is controlled by outputting the gain control voltage VGC.

When the reference gain control value is set in S450, the signal level VGJ of the pseudo signal actually obtained when the gain control voltage VG is controlled by the reference gain control value is measured. ,
This is set as the reference level of the pseudo signal.

That is, first, in S470, the above-described series of level measurement operations is repeated j times (for example, 8 times), so that the signal level VGJ of the pseudo signal when the gain of the STC circuit 18 is fixed to the maximum gain is obtained. j is acquired, and the following S4
At 80, an average value VGJAV (j) is calculated from the obtained j signal levels VGJ, and at S490, the average value VGJAV ± γ (γ; of the j signal levels VGJ obtained this time is calculated.
For example, the signal level VGJ in the range of 50 mV) is k
It is determined whether there are more than five (for example, five).

If the number of signal levels VGJ within the range of the average value VGJAV ± γ is k or more, it is determined that the signal level VGJ of the pseudo signal has been normally obtained, and the flow shifts to S500, where the average value VGJAV An average value VGJAV (γ) is calculated from k or more signal levels VGJ in the range of ± γ, and the following S
At 510, the calculated average value VGJAV (γ) is
This is set as the reference level (initial value) of the pseudo signal output from the C circuit 18.

If it is determined in step S490 that there are no more than k signal levels VGJ within the range of the average value VGJAV ± γ, the flow shifts to step S520 to obtain j signal levels VGJ in step S470. It is determined whether the operation has been performed y times (for example, 5 times). If the obtaining operation has not been performed y times, the process proceeds to S470, and the obtaining operation of the j signal levels VGJ is performed again.

On the other hand, j signal levels V in S470
If the GJ acquisition operation has already been performed y times, it is determined that the current acquisition operation has been successfully performed, and the process proceeds to S510.
The average value VGJAV (n) calculated in 480 is set as the reference level (initial value) of the pseudo signal.

When the reference level (initial value) of the pseudo signal is set in S510, the CPU 30
Ends the initial reference value acquisition processing and starts the next initial voltage setting processing. Next, FIG. 6 shows a case where the reference gain control value and the reference level of the pseudo signal are once acquired in the initial reference value acquisition processing (S120), and then the normal reference value periodically executed for updating these reference values is obtained. Acquisition processing (S1
It is a flowchart showing 60).

As shown in FIG. 6, in the normal reference value acquisition processing, first, in S610, the series of level measurement operations is repeated j times (for example, 8 times) in the same manner as in S470, whereby the amplification of the STC circuit 18 is performed. The j signal levels VGJ of the pseudo signal when the rate is fixed to the maximum amplification rate are obtained.

Then, in S615, the average value VGJAV (j) is obtained from the j signal levels VGJ obtained in S610.
, And in S620, the average value VGJAV ± δ (δ; for example, 20 m) of the j signal levels VGJ acquired this time.
V), there are k signal levels VGJ (for example, 5
Number) or not.

If the number of signal levels VGJ within the range of the average value VGJAV ± δ is k or more, it is determined that the signal level VGJ of the pseudo signal has been normally obtained, and the flow shifts to S625, where the average value VGJAV ± δ VGJAV is calculated from k or more signal levels VGJ in the range. Also S6
At 20, when it is determined that there are no more than k signal levels VGJ within the range of the average value VGJAV ± δ, the flow shifts to S 630, where the pseudo signal obtained at the last time in the initial or normal reference value obtaining process is obtained. The reference level (previous value; that is, the current reference level) is set as it is as the average value VGJAV.

When the average value VGJAV of the signal level VGJ of the pseudo signal is calculated or set in S625 or S630, the calculated or set average value VGJAV and the set value of the pseudo signal are set in S635. (For example, 500 mV)
Compare with Then, if the average value VGJAV matches the set value, the process directly proceeds to S650. If the average value VGJAV is lower than the set value, the current value is increased in S640 to increase the signal level of the pseudo signal. Data value controlling the gain control voltage VGC (data value obtained by removing the value below the decimal point for the controllable voltage from the reference gain control value, hereinafter referred to as the VGC control data value)
After adding “1” to the new value, a new VGC control data value is set, and then the flow shifts to S650.

On the other hand, when the average value VGJAV is higher than the set value, in order to lower the signal level of the pseudo signal,
At S645, a value obtained by subtracting the value “1” from the VG control data value is set as a new VG control data value.
Move to 650. Note that V is determined in S640 and S645.
When the GC control data value is updated, the gain control voltage VG rises or falls by the minimum variable voltage determined by the resolution of the D / A converter.

Next, when the gain control voltage VGC is updated in this manner, this update is again performed in order to determine whether or not the signal level VGJ of the pseudo signal has been brought close to the set value by the update. , The signal level V of the pseudo signal
GJ (specifically, the average value VGJAV) is measured.

That is, first, in S650, the above series of level measurement operations is repeated j times (for example, 8 times) to obtain j signal levels VGJ of the pseudo signal, and then in S6
At 55, the average value VGJAV (j) is calculated. And
In subsequent S660, similarly to the above-described S490, the average value VGJAV ± γ (γ;
For example, the signal level VGJ in the range of 50 mV) is k
Number (for example, 5) or more, and determine the average value VGJ
If the number of signal levels VGJ in the range of AV ± γ is k or more, the process proceeds to S665, and the average value VGJAV is calculated from the k or more signal levels VGJ in the range of average values VGJAV ± γ.
If there are not k or more signal levels VGJ within the range of the average value VGJAV ± γ, the flow shifts to S660, and the previous value is directly set as the average value VGJAV.

When the average value VGJAV of the signal level VGJ of the pseudo signal after updating the gain control voltage is obtained in this manner, this average value VGJAV and this average value VGJAV and S625 (or S630) before changing the gain control voltage are obtained. By comparing the calculated average value VGJAV, it is determined which average value is closer to the set value (for example, 500 mV).

If the average value VGJAV before the change is close to the set value, in S680, the VGC control data value (the value before the change) corresponding to the gain control voltage VGC before the change
And a reference gain control value obtained last time in the initial or normal reference value acquisition processing (an average value obtained by weighting the previous value from the previous value is calculated (so-called weighted average), and that value is calculated as a new reference gain control value. Conversely, if the changed average value VGJAV is close to the set value, S
The flow shifts to 685, where a weighted average of the VGC control data value (changed value) corresponding to the changed gain control voltage and the previous value is set, and that value is set as a new reference gain control value.

The weighted averaging is performed in the same manner as in S360 described above. Also, the value before change or the value after change (VGC control data value) corresponds to data of several upper bits of the reference gain control value that can control the gain control voltage VGC using the reference gain control value. , S680, and S685, when calculating the weighted average of these values, a value “0” is added to the lower bit of the VGC control data value that is the pre-change value or the post-change value, and the digits of these values are added. After adding the numbers, a weighted average value is calculated by weighting the current reference gain control value.

Next, when the reference gain control value is set as described above, the signal level VGJ of the pseudo signal is measured again, and the reference level is updated from the value. That is, first, in S690, the above series of level measurement operations is repeated j times (for example, 8 times) to obtain j signal levels VGJ of the pseudo signal, and in S695, the average value VGJ is obtained.
Calculate AV (j). Then, in S700, the average value VGJAV ± γ of the j signal levels VGJ obtained this time is obtained.
(Γ; for example, 50 mV).
Is determined if there are k or more (for example, 5) or more, and if the number of signal levels VGJ within the range of the average value VGJAV ± γ is k or more, the flow shifts to S705, where the average value VGJAV ± γ The average value VGJAV is calculated from the k or more signal levels VGJ in the range. If the k or more signal levels VGJ in the average value VGJAV ± γ do not exist, the process proceeds to S710. , The previous value is set as the average value VGJAV. Then, when the average value VGJAV of the signal level VGJ of the pseudo signal is obtained in this manner, the flow shifts to S715, where the average value VGJAV is set as the reference level, and the process ends.

FIG. 7 shows an initial voltage setting process (S13).
It is a flowchart showing 0). As shown in FIG.
In the initial voltage setting process, first, in S810, the following series of level measurement operations are repeatedly performed while changing the DC voltage VDC input to the STC circuit 18 to thereby reduce the pseudo value obtained by subtracting the offset value from the peak hold voltage VPH. A search is made for a DC voltage VDC at which the signal level VGJ of the signal becomes the reference level.

Level measurement operation: The signal switching circuit 12 is switched to the filter 16 side, a control signal is output to the STC voltage generation circuit 22, and the amplification factor of the STC circuit 18 is changed, and a predetermined timing at which the amplification factor is maximized Outputs a control signal to the filter 16 to input a pseudo signal to the amplifier 14. At this time, the peak hold voltage VPH obtained by the peak hold circuit 28 is read, and the value VPH is read.
Then, the signal level (operation level) VGJ of the pseudo signal is measured by subtracting the offset value of the peak hold circuit 28 from.

In this search, data (for example, 8 bits) used to control the DC voltage VDC is changed in order from the most significant bit, and the signal level VGJ of the pseudo signal obtained by the above level measurement operation is used as a reference. A so-called binary search method of searching for a point serving as a level is used.

When the DC voltage VDC at which the signal level VGJ of the pseudo signal becomes the reference level is searched by this search operation, at 820, whether or not the search has been performed i times (for example, 8 times) And if it has not been executed i times, the process returns to S810 again.
The search operation of S810 is executed i times.

When the search operation in S810 is executed i times, the flow shifts to S830, and the average value VDC is obtained from the i DC voltages VDC obtained by the search operation.
AV (i) is calculated, and in S840, the DC voltage VDC within the range of the average value VDCAV (i) ± ε (ε; for example, 50 mV) of the i DC voltages VDC obtained this time is s. It is determined whether there are more than five (for example, five).

If the number of DC voltages VDC within the range of the average value VDCAV ± ε is s or more, it is determined that the search for the DC voltage VDC has been performed normally, and the flow shifts to S850, where the average value VDCAV ± ε is determined. s or more DC voltages VDC within the range of ε
, The average value VDCAV (ε) is calculated from
, The calculated average value VDCAV (ε) is set as a DC voltage value (initial value) for feedthrough cancellation.

If it is determined in S840 that there are no more than s DC voltages VDC within the range of the average value VDCAV ± ε, the flow shifts to S860, where S810 and S820 are executed.
(I times) by z times (for example, 5 times)
It is determined whether or not it has been performed. If the series of search operations has not been performed z times, the flow shifts to S810 to execute the above series of search operations again.

On the other hand, if a series of search operations in S810 and S820 have already been performed z times, it is determined that the i DC voltages VDC obtained by the current search operation are normal.
Proceeding to S870, the average value VDCAV calculated in S830 is obtained.
(i) is set as the DC voltage value (initial value).

When the DC voltage value is set in S870 as described above, the CPU 30 then sets the DC voltage VDC applied to the signal input terminal of the STC circuit 18 via the voltage superposition circuit 20 to the set value. Control with the applied DC voltage value. Note that the control of the DC voltage VDC includes the CPU 3 of the DC voltage values in the same manner as the control of the gain control voltage VGC.
0 is data of several upper bits that can control the DC voltage VDC using the D / A converter (hereinafter referred to as VDC control data value)
Is used to output the VDC control data value to the D / A converter, so that the DC voltage VDC is output through the D / A converter.
Control.

FIG. 8 shows an initial voltage setting process (S13).
0) is a flowchart showing a normal voltage setting process (S170) that is periodically executed after setting a DC voltage for feedthrough cancellation in order to prevent the DC voltage from deviating from an optimum value due to a temperature change or the like. is there.

As shown in FIG. 8, in the normal voltage setting process, first, in S905, a series of level measurement operations similar to the above S810 is repeated i times (for example, 8 times). I of the signal level (operation level) VGJ are obtained. Then, in S910, the average value VGJAV (i) is calculated from the i signal levels VGJ obtained in S905, and in S915, the average value VGJAV (i) is compared with the reference level, and the average is compared. Value V
If GJAV (i) matches the reference level, the flow shifts to step S920, where the VDC control data value (the upper few bits (for example, 8 bits) of the DC voltage value) which is actually controlling the DC voltage VDC. Value) and a DC voltage value (a data value that has a larger number of bits than the VDC control data value (for example, 10 bits) and includes a value after the decimal point with respect to a minimum variable voltage that can control VDC by the D / A converter). , An average value obtained by weighting the DC voltage value is calculated (a so-called weighted average), and the subsequent S925
After setting the average value as a DC voltage value, the process ends. Note that this weighted average is calculated in S68 described above.
0, S685.

On the other hand, if it is determined in S915 that the average value VGJAV (i) is larger than the reference level, the process proceeds to S930.
Then, it is determined whether or not the difference is equal to or higher than a predetermined voltage κ (for example, 25 mV). If the difference is equal to or higher than the predetermined voltage κ and the average value VGJAV (i) is larger than the reference level by the predetermined voltage κ or more, the process proceeds to S935, and the VDC corresponding to the DC voltage VDC currently controlled. By setting a data value obtained by adding the value "1" to the control data value as a new DC voltage value, the DC voltage VDC is quickly increased by the minimum variable voltage determined by the resolution of the D / A converter,
The process ends.

On the contrary, in S930, the average value VGJAV (i)
When it is determined that the difference between the DC voltage and the reference level is less than the predetermined voltage κ, the process proceeds to S940, where the DC voltage value is obtained by adding the value “1” to the VDC control data value and the DC voltage value. An average value weighted to the value is calculated (weighted average), and in S945, the average value is set as a DC voltage value, and then the process ends. The weighted average is S920
Is performed in the same manner as described above.

Next, in S915, the average value VGJAV (i)
Is determined to be smaller than the reference level, S9
50, the difference is a predetermined voltage κ (for example, 25 m
V) It is determined whether or not it is not less than. If the difference is equal to or more than the predetermined voltage κ and the average value VGJAV (i) is smaller than the reference level by the predetermined voltage κ or more, the process proceeds to S955, and the VDC corresponding to the DC voltage VDC currently controlled. By setting a data value obtained by subtracting the value “1” from the control data value as a new DC voltage value, the DC voltage VDC is changed to D /
The voltage is immediately reduced by the minimum variable voltage determined by the resolution of the A-converter, and the process ends.

Conversely, in S950, the average value VGJAV (i)
If it is determined that the difference between the reference voltage and the reference level is less than the predetermined voltage κ, the process proceeds to S960, and the DC voltage value is obtained by subtracting the value “1” from the VDC control data value and the DC voltage value. An average value weighted to the value is calculated (weighted average), and in S965, the average value is set as a DC voltage value, and the process ends. The weighted average is S92
Performed in the same way as 0.

Note that S940, S945, and S960,
The process 965 is a process for stabilizing the operation of the signal processing system of the received signal by suppressing the frequency of the DC voltage VDC actually changing. That is, in each of these processes, the DC voltage value is updated by the weighted average, so that even if there is a deviation between the average value VGJAV (i) of the signal level VGJ of the pseudo signal and the reference level, the difference is less than the predetermined voltage κ. Sometimes,
The DC voltage value changes slowly, and the DC voltage VDC actually controlled changes only when each of the above-described processes is continuously performed a plurality of times. Therefore, the STC circuit 18 and the peak hold circuit 2
In the case where the DC voltage in 8 has temporarily fluctuated, it is possible to prevent the DC voltage VDC from being changed, and the subsequent accuracy of distance measurement to be deteriorated.

As described above, in this embodiment, the pseudo signal is input to the amplifier 14 while the gain of the STC circuit 18 is kept constant (maximum gain) by the reference value acquisition processing (S120, S160). Then, the signal level (maximum level) of the pseudo signal detected by the peak hold circuit 28 is read, the value is set as the reference level, and the voltage setting process (S130, S170) performs the STC circuit 1
8, the pseudo signal is input to the amplifier 14 immediately after the amplification factor reaches the maximum, and the signal level of the pseudo signal detected by the peak hold circuit 28 at that time ( The maximum level is read, a DC voltage value for controlling the signal level (operation level) to the reference level is obtained, and a DC voltage VDC applied to the signal input terminal of the STC circuit 18 is set.

For this reason, according to the present embodiment, the AC signal component (feedthrough) output due to the change in the amplification factor of the STC circuit 18 at the time of distance measurement is applied to the DC signal applied to the signal input terminal of the STC circuit 18. With the voltage VDC, cancellation can be performed accurately, and at the time of distance measurement, the distance to the target located in front of the vehicle can be measured without being affected by feedthrough of the STC circuit 18.
Therefore, according to the present embodiment, it is possible to extremely accurately measure the distance to the preceding vehicle traveling in front of the vehicle and the distance to the obstacle, and it is possible to improve the safety during traveling of the vehicle,
In a device that performs inter-vehicle distance control that causes the own vehicle to follow a preceding vehicle at a predetermined inter-vehicle distance, the inter-vehicle distance control can be performed with extremely high accuracy.

In this embodiment, the reference value acquisition processing (S
120, S160) and voltage setting processing (S130, S1)
Before executing (70), the offset value acquisition processing (S11)
0, S150), the offset value of the peak hold circuit 28 used for detecting the output signal level (maximum level) from the STC circuit 18 is detected, and in the reference value acquisition processing (S120, S160), the pseudo value is detected. The voltage value (signal level VGJ) corresponding to the pseudo signal obtained by subtracting the offset value from the peak hold voltage obtained by the peak hold circuit 28 at the time of signal input is set to an optimal set value for the operation of the peak hold circuit 28. The amplification factor of the amplification factor 14 (specifically, the gain control voltage VGC) is set. For this reason, the feedthrough of the STC circuit 18 can always be accurately detected using the peak hold circuit 28, and the DC voltage VDC is always optimized without being affected by the operation characteristics of the peak hold circuit 28. Can be set.

In the normal voltage setting process (S170) for updating the DC voltage VDC, the average value VGJAV of the signal level VGC of the pseudo signal obtained when the amplification factor of the STC circuit 18 is changed (that is, the present invention) When the deviation between the operating level) and the reference level is equal to or greater than the predetermined voltage κ, the DC voltage VDC is used as the minimum variable voltage determined by the resolution of the D / A converter used by the CPU 30 to output the DC voltage VDC. If the deviation is less than the predetermined voltage κ, the operating voltage value used for controlling the DC voltage VDC is updated in a direction in which the deviation decreases so that the DC voltage VDC changes slowly. Therefore, when the deviation is small, the change in the DC voltage VDC can be suppressed, and the stability of the control can be improved. Only when the deviation is large, the DC voltage VDC can be largely changed to improve the responsiveness of the control. And so on.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.
Various embodiments can be adopted. For example, in the above embodiment, the case where the present invention is applied to an automobile distance measuring device has been described.However, the present invention is applicable to a distance measuring device for other moving objects such as an aircraft, or from a fixed station. The present invention can also be applied to a distance measuring device for a fixed station that emits measurement light and monitors surrounding moving objects and the like.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an entire distance measuring apparatus according to an embodiment.

FIG. 2 is a flowchart illustrating a flow of a feed-through cancellation process executed by a CPU according to the embodiment.

FIG. 3 is a flowchart illustrating an initial offset value acquisition process executed in S110 of FIG. 2;

FIG. 4 is a flowchart illustrating a normal offset value acquisition process executed in S150 of FIG. 2;

FIG. 5 is a flowchart illustrating an initial reference value acquisition process executed in S120 of FIG. 2;

FIG. 6 is a flowchart illustrating a normal reference value acquisition process executed in S160 of FIG. 2;

FIG. 7 is a flowchart illustrating an initial voltage setting process executed in S130 of FIG. 2;

FIG. 8 is a flowchart showing a normal voltage setting process executed in S170 of FIG. 2;

FIG. 9 is an explanatory diagram illustrating the configuration and operation of a conventional distance measuring device.

FIG. 10 is an explanatory diagram for explaining a problem of a conventional distance measuring device.

[Explanation of symbols]

4 light emitting section 8 light receiving section 12 signal switching circuit
DESCRIPTION OF SYMBOLS 14 ... Amplifier 16 ... Filter 18 ... STC circuit 20 ... Voltage superposition circuit 22 ... STC voltage generation circuit 24 ... Comparator
26: time measurement IC 30: CPU (microcomputer)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-4-318483 (JP, A) JP-A-5-188136 (JP, A) JP-A-7-71957 (JP, A) JP-A-9-97 236661 (JP, A) JP-A-54-161290 (JP, A) JP-A-57-29875 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01S 7/00-7 / 64 G01S 13/00-17/95 G01B 11/00-11/30 G01C 3/00-3/32

Claims (7)

(57) [Claims] A light-emitting means for emitting measurement light; a light-receiving means for receiving reflected light in which the measurement light emitted by the light-emitting means hits an external target and reflecting the light; and outputting a light-receiving signal; Amplifying means for amplifying the received light signal from the amplifying means, an amplifying rate controlling means for controlling the amplifying rate of the amplifying means so as to increase with time, and an AC signal component outputted from the amplifying means. Capture
Light-receiving detection means for detecting the reception of the reflected light by the light-receiving means from the signal; and outputting a pulse-like drive signal to the light-emitting means to emit the measurement light, activating the amplification factor control means, and thereafter, A distance measuring unit that measures a time until the reception of the reflected light by the light receiving unit is detected by the light receiving detection unit, and calculates a distance from the measured time to the target. A DC voltage application unit that applies a DC voltage to a signal input terminal of the amplification unit in order to suppress an AC signal component output from the amplification unit due to amplification ratio control by the amplification ratio control unit; Take in the AC signal component output from the means,
Level detection means for detecting the level of the signal; reference level measurement means for measuring, as a reference level, the level of the AC signal component detected by the level detection means when there is no signal input to the amplification means; Activating the amplification factor control means to change the amplification factor of the amplification means, and the level of the AC signal component detected by the level detection means at that time is set as an operation level at the time of operation of the amplification rate control means. Operating level measuring means for measuring; and a DC voltage applying means for inputting a signal to the amplifying means such that an operating level measured by the operating level measuring means becomes a reference level measured by the reference level measuring means. A distance measuring device comprising: a DC voltage setting means for setting a DC voltage applied to a terminal. 2. A pseudo light receiving signal inputting means for interrupting the input of a light receiving signal to said amplifying means and inputting a pulsed pseudo light receiving signal to said amplifying means, wherein said level detecting means comprises: Detecting the maximum level of the output AC signal component, and when the reference level measuring means measures the reference level, sets the amplification factor of the amplification means to the maximum amplification factor controlled by the amplification factor control means. Then, the pseudo signal input means is operated, and when the operation level measuring means measures the operation level, the amplification rate control means is activated to change the amplification rate of the amplification means, The distance measuring apparatus according to claim 1, wherein the pseudo signal input means is operated at a predetermined timing when the amplification factor of the means becomes a maximum amplification factor. 3. A signal path from the light receiving means to the amplifying means, comprising: a second amplifying means for amplifying and outputting an input signal, wherein the reference level measuring means is configured to determine whether the reference level is equal to the level of the level detecting means. The distance measuring apparatus according to claim 2, wherein an amplification factor of the second amplification unit is set so as to be a predetermined level optimal for operation. 4. The level detecting means is operated without a signal before the reference level is measured by the reference level measuring means, and the maximum level detected by the level detecting means at that time is used as the level detecting means. Providing an offset value measuring means for measuring as an offset value of the reference level measuring means and the operation level measuring means, a value obtained by subtracting the offset value from the maximum level detected by the level detecting means, the reference level and 4. The distance measuring apparatus according to claim 3, wherein each of the operation levels is measured. 5. The reference level measuring means sets the amplification factor of the second amplifying means and then measures the reference level again, and the DC voltage setting means sets the amplification factor of the second amplifying means. 5. The distance measuring apparatus according to claim 3, wherein the DC voltage is set using a reference level measured after setting the amplification factor of the two amplifying units. 6. The DC voltage setting means obtains a deviation between the operation level and the reference level, and if the deviation is equal to or more than a predetermined level, reduces the current voltage value currently set as the DC voltage with a small deviation. A changed voltage value changed by a predetermined voltage in a direction is set as a new DC voltage, and if the deviation is smaller than a predetermined level, the current voltage value and the changed voltage value are weighted to the current voltage value. The distance measuring apparatus according to any one of claims 1 to 5, wherein the weighted average voltage value averaged is set as a new DC voltage. 7. The distance measuring device is mounted on a vehicle,
2. A vehicle distance measuring device for measuring a distance to a target located in front of a traveling direction of a vehicle.
The distance measuring device according to claim 6.