JPH11281743A - Distance detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a distance detector the manufacturing cost of which is reduced by reducing the number of parts. SOLUTION: A time measuring means, which starts time measurement upon receiving a control pulse from a light emission control means, is provided with a first switch means 26 which lets the control pulse from the light emission control means pass and stops the passing of the pulse by means of the leading edge of the output of a comparing means 22; first integration circuits 28 and 29 which integrate the light emission control pulse passed through the first switch means 26; a second switch 27 which is connected in parallel with the first switch means 26, lets the control pulse from the light emission control means pass, and stops the passing of the pulse by means of the trailing edge of the output of the comparing means 22; and second CR integration circuits which integrate the light emission control pulse passed through the second switch means 27, and supply the integrated outputs of the first and second integrating means to a distance calculating means which calculates the distance to a front target.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance detecting device for use in a vehicle anti-collision device which detects the distance between a host vehicle and a target ahead and issues an alarm for preventing collision if necessary. About.

[0002]

2. Description of the Related Art Japanese Patent Laid-Open Publication No.
Japanese Patent Application Laid-Open No. 119152/1992 discloses such a device, which will be described below with reference to FIGS. That is, 1 is a laser diode, 2 is a laser diode driving section, 3 is a high voltage generation section, 4 is a timer control circuit, and a laser pulse is supplied from the timer control circuit 4 to the laser diode driving section 2 by a start pulse. Light is emitted, and this start pulse is input to the measuring unit 5 as a start signal for distance measurement.

On the other hand, the reflected light reflected by the target is received by a light receiving diode 6, a signal based on the reflected light is detected by a light receiving amplifier 7 and a peak hold amplifier 8, and a stop pulse is input from a pulse generator 9 to a measuring unit 5. And a first point in time when a start pulse is issued by the measuring unit 5;
The time between the second time when the stop pulse is issued is measured, and the distance to the target is calculated from the measured time.

The measuring section 5 will be described in detail with reference to FIG. 4. The measuring section 5 includes a reference DC voltage source 10 for supplying a reference DC voltage Vref. It is connected to the input terminal of the integration circuit 11 via the first switch S1 (FIG. 5B) closed by (FIG. 5A). Integration circuit 11
5 comprises an operational amplifier 12, a resistor R and a capacitor C1, and is supplied through the first switch S1 in FIG.
The voltage of (c) is integrated (FIG. 5 (d)). Integration circuit 11
Is connected to the output terminal of the second switch S2 (FIG. 5 (f)) in which the stop pulse (FIG. 5 (e)) is closed by the pulse whose polarity is inverted by the inverter 13.
A capacitor C2 is connected, and an A / D converter 14 for converting the terminal voltage of the capacitor C2 into a distance is connected to perform A / D conversion (FIG. 5 (g)). A third switch S3, which is closed by a stop pulse, is connected to both ends of the first capacitor C1 in the integration circuit 11.

[0005]

However, in such a conventional distance detecting circuit, the number of components is large because the measuring section 5 is configured as described above. In addition, especially in the integration circuit, C
There is a problem that an operational amplifier that is more expensive than the R element is used. SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a distance detection device that reduces the number of components and reduces costs.

[0006]

According to a first aspect of the present invention, there is provided a distance detecting apparatus which emits light in response to a control pulse from the light emission control means for outputting a control pulse for controlling a light emission output. Light emitting means, fired from the light emitting means,
A light receiving element for receiving the light reflected by the front target, a comparison circuit for inverting the output while the voltage value of the light receiving signal by the light receiving element exceeds a reference value, and a control pulse from the light emission control means; Time measuring means for starting the time measurement, and stopping each time measuring operation when each of the leading edge and the trailing edge of the output of the comparison circuit is detected, based on two times measured by the time measuring means. A distance calculating device for calculating a distance to the front target, wherein the time measuring device receives a control pulse from the light emission control device, passes the control pulse, and passes the control pulse. A first switch for stopping passage by the leading edge of the output, a first integration circuit for integrating a light emission control pulse passing through the first switch, and a parallel connection to the first switch. Second switch means for receiving and passing a control pulse from the light emission control means and stopping the passage by the trailing edge of the output of the comparing means; and integrating the light emission control pulse passing through the second switch means. And a second integration circuit that supplies integrated outputs of the first and second integration circuits to the distance calculation means.

In another aspect of the present invention, the first and second integrating circuits are constituted only by a capacitor and a resistor.

In another aspect of the present invention, the first and second switch means have high-speed switch characteristics.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 FIG. 1 shows an embodiment.
This will be described below based on A light receiving element 20 is supplied with power by the step-up power supply 19 and receives reflected light output from a light emitting element described later. Reference numeral 21 denotes an automatic gain control amplifying circuit (hereinafter abbreviated as "amplifying circuit") for amplifying a light receiving signal accompanying the light receiving from the light receiving element 20. Thus, the amplification factor is changed in accordance with the amplitude value based on the integrated waveform, so that the noisy output signal from the light receiving element 20 is not unnecessarily amplified while the laser light emitting element 33 described later emits light. Then, during this light emission, a large power supply noise may be generated because the second current flows through the circuit, so that appropriate amplification is achieved.

Reference numeral 22 denotes a comparison circuit, which compares a light receiving signal from the amplifying circuit 21 with a reference value to separate noise including a DC component to extract a light receiving signal with less noise. When extracted, the output is set to a high level and supplied to the measuring unit 23 having the same function as the measuring unit 5 in FIG. This measuring unit 23
As will be described later, the falling detection circuit (first
Switch means) 24, rise detection circuit (second switch means) 25, first switch circuit (first switch means)
26, second switch circuit (second switch means) 27, first CR integration circuit 28, second CR integration circuit 29, and CPU
It is composed of 30 distance calculation functions.

The CPU 30 inputs an integrated value indicating time from the first and second CR integrators 28 and 29, calculates a half value of a simple average value of the integrated value, and corresponds to the calculated value. Is calculated, and a distance corresponding to the calculated time is calculated. If the calculated distance is smaller than the safe inter-vehicle distance compared with the safe inter-vehicle distance calculated based on a vehicle speed signal v or the like supplied from a vehicle speed sensor (not shown), an alarm signal is generated and the inter-vehicle distance is generated. Is small and there is a danger of collision, and is output to activate the alarm device. Further, the CPU 30 generates a light emission timing signal of a fixed period and supplies the light emission driver 32 to the light emission driver 32 in synchronization with the power being turned on. The light emission timing signal is supplied to the first and second switch circuits 26 and 27 as a signal indicating the start of light emission, and is supplied to the amplifier circuit 21 as a signal for determining the amplification factor of the received light signal. It is supplied via an unshown integration circuit.

Reference numeral 31 denotes a light emitting system power supply circuit, and 33 denotes a laser light emitting element. The laser light emitting element receives a driving pulse from the light emitting driver 32 and emits light at regular intervals.
The light is reflected by a mirror 36 attached to a shaft of a motor 35 which alternately alternates between normal rotation and reversal in a rotation angle range of, for example, 10 degrees by the PU 30 and is emitted forward of the vehicle. Next, the detailed configuration of the measurement unit 23 will be described in the order of the fall detection circuit 24, the rise detection circuit 25, the first switch circuit 26, the second switch circuit 27, the first CR integration circuit 28, and the second CR integration circuit 29.

The falling detection circuit 24 receives a light receiving signal (see FIG. 2B) output from the comparing circuit 22, detects a falling edge of the light receiving signal, and outputs a detection signal (see FIG. 2B). (See FIG. 2C). The rising detection circuit 25 receives a light receiving signal (see FIG. 2B) output from the comparing circuit 22 similarly to the falling detecting circuit 24, detects a rising edge of the light receiving signal, and performs detection. A signal (see FIG. 2D) is output.

The first switch circuit 26 receives a detection signal from the fall detection circuit 24 as a control signal, turns off the input and output, and normally turns on the input and output when no supply of the detection signal is received. ing. Second switch circuit 27
Has a function similar to that of the first switch circuit 26,
A detection signal is input as a control signal from the rise detection circuit 25, the input and output are turned off, and the input and output are turned on in normal times when the supply of the detection signal is not received.

The first CR integration circuit 28 is composed of two circuit elements, a resistor R and a capacitor C, has a non-linear integration characteristic, and uses even the non-linear part. The light emission timing signal A supplied from the switch circuit 26 is integrated, and the integrated value is output as a time signal (see FIG. 2E). The second CR integration circuit 29 is a circuit similar to the first CR integration circuit 28, and includes two circuit elements of a resistor R and a capacitor C.
It has a non-linear integration characteristic and is used even up to the non-linear part. The light emission timing signal A supplied from the second switch circuit 27 is integrated, and the integrated value is output as a time signal. (See FIG. 2F).

When the integrating circuit is used as a timer for measuring time, an integrating circuit of a system for integrating a constant current is usually used in order to emphasize accuracy. The one that integrates the timing signal A is used. It is generally known that the method of integrating a constant voltage is used as a linear characteristic until the time required to reach a saturation region is 1/10 of the integration characteristic. Integral characteristics up to near saturation are used.

That is, in this embodiment, a linear integration characteristic and a non-linear integration characteristic are selectively used. The linear portion is used in a range where the inter-vehicle distance that requires the accuracy of the alarm is short, and the non-linear portion is used in a range where the inter-vehicle distance that does not require the accuracy of the alarm is long. In other words, at short inter-vehicle distances, the danger is very likely to be imminent and the need for alarms is very high,
This is because, while the demand for the accuracy of time is high, when the distance between the vehicles is large, the importance of the warning is low and the accuracy of time is not so required.

Next, the operation of the above configuration will be described below with reference to FIG. That is, when the power is supplied, the motor 35 is driven while alternately repeating the normal rotation and the reversal at a fixed cycle, and the CPU 30 supplies the light emission timing signal A of the fixed cycle to the light emission driver 32 and the laser light emitting element 33. From the laser beam is emitted at a constant period. As a result, the laser light is reflected forward of the vehicle by the mirror 36 attached to the rotation shaft of the motor 35.

When this power is supplied, a high-level light emission timing signal A is supplied from the CPU 30 to the light emission driver 32, so that the laser light is emitted from the laser light emitting element 33,
The first and second CR integrators 28 and 29 start the integration operation as shown in FIGS. 2E and 2F with the same integration characteristics.

As a result, the laser beam reflected in front of the vehicle (see FIG. 2A) is reflected by a front target such as a front vehicle located ahead, received by the light receiving element 20, and received by the light receiving element 20. The received light signal (Fig. 2
(See FIG. 2B) is supplied to the comparison circuit 22 via the amplifier circuit 21 and is converted into a binarized light receiving signal (equivalent to the light receiving signal shown in FIG. 2B). The falling edge of the light receiving signal B is detected by the falling detection circuit 24 (see FIG. 2C), and the input and output of the first switch circuit 26 are turned off. The rising edge is detected by the rising detection circuit 25 (see FIG. 2D), and the input and output of the second switch circuit 27 are turned off.

As a result, the first and second CR integration circuits 2
The simple average value of the integration results at 8 and 29 is supplied to the CPU 30, and the CPU 30 calculates the distance between the host vehicle and the target ahead.

When a laser beam is emitted from the laser light emitting element 33, a large current flows through the circuit pattern.
So that the rising edge of the light emission timing signal from the CPU 30 is rounded with a large time constant by an integrator (not shown) so as not to amplify the light reception signal in the same manner as a regular light reception signal. The function of the amplifier circuit 21 is temporarily reduced while operating on the light emission timing signal.

[0023]

As described above, according to the present invention, there is an effect that the cost can be reduced by reducing the number of parts. Also, the first
The configuration is simplified by configuring the second integration circuit with only the capacitor and the resistor. In addition, by configuring the first and second switch means with high-speed switches, the effect of improving measurement accuracy can be exhibited.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram illustrating a configuration of a first embodiment of a distance measuring device according to the present invention.

FIG. 2 is an operation explanatory diagram for explaining the operation of the circuit block in FIG. 1;

FIG. 3 is a circuit block diagram of a conventional distance measuring device.

FIG. 4 is an explanatory diagram of a specific circuit of a measuring unit in FIG. 3;

FIG. 5 is a timing chart for explaining the operation of the circuit of FIG. 4;

[Explanation of symbols]

 REFERENCE SIGNS LIST 20 light receiving element 21 automatic gain control type amplifier circuit 22 comparison circuit 23 measuring section 24 fall detection circuit (first switch means) 25 rise detection circuit (second switch means) 26 first switch circuit (first switch means) 27 2 switch circuit (second switch means) 28, 29 CR integration circuit 30 CPU 31 Light emitting system power supply circuit 32 Light emitting driver 33 Laser light emitting element 35 Motor

Claims (3)

[Claims] 1. A light emission control means for outputting a control pulse for controlling a light emission output; a light emission means for receiving a control pulse from the light emission control means to emit light;
A light receiving element for receiving the light reflected by the front target, a comparison circuit for inverting the output while the voltage value of the light receiving signal by the light receiving element exceeds a reference value, and a control pulse from the light emission control means; Time measuring means for starting the time measurement, and stopping each time measuring operation when each of the leading edge and the trailing edge of the output of the comparison circuit is detected, based on two times measured by the time measuring means. A distance calculating device for calculating a distance to the front target, wherein the time measuring device receives a control pulse from the light emission control device, passes the control pulse, and passes the control pulse. A first switch for stopping passage by the leading edge of the output, a first integration circuit for integrating a light emission control pulse passing through the first switch, and a parallel connection to the first switch. A second switch for receiving a control pulse from the light emission control unit, passing the control pulse therethrough, and stopping the passage by a trailing edge of the output of the comparison unit; and a light emission control pulse passing through the second switch unit. A distance detecting device, comprising: a second integrating circuit for integrating, and supplying an integral output of the first and second integrating circuits to the distance calculating means. 2. The distance detecting device according to claim 1, wherein said first and second integrating circuits are constituted only by a capacitor and a resistor. 3. The distance detecting device according to claim 1, wherein said first and second switch means have high-speed switch characteristics.