JPH0119112Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is an optical radar device that calculates the distance to the object to be measured based on the delay time from the time when the light pulse is generated from the emitter to the time when the reflected light pulse is received by the receiver. In particular, the present invention relates to an optical radar device that detects the delay time with high accuracy.

As shown in FIG. 1, a conventional optical radar device is generally composed of a light emitter 1, a light receiver 2, and a control circuit 3.

The light projector 1 receives a driving signal A from the pulse generator 6 of the control circuit 3, which has a repetition period Tp and a pulse width Tw as shown in FIG. As shown in FIG. 3b, the light emitting element 4 generates a coherent optical pulse Lt (wavelength is λ) such as a laser beam that is pulse-modulated by the drive signal A. Ru.

This light pulse Lt is shaped into a radiation beam with a spread angle θt by the condensing lens 9, and is irradiated toward the target object whose distance is to be determined in front (hereinafter referred to as the object to be measured). .

The reflected light pulse Lr from which the light pulse Lt is reflected by the object to be measured and returns is weak as shown in FIG. 3c, and this reflected light pulse Lr is
The light is collected by the condensing lens 10 of the light receiver 2, and after removing backlight noise (sunlight, artificial illumination light, etc.) through the interference filter 11, the received light is placed at the focal point of the condensing lens. The light is incident on the element 5.

Then, a light receiving signal B as shown in FIG. 2d is output from the light receiving element 5 and is supplied to the control circuit 3.

The received light signal B is amplified and pulse-shaped by a pulse detector 7, and then a distance detection circuit 8
supplied to When performing the above pulse shaping,
Detecting the leading edge of the pulse of the above-mentioned light reception signal B, FIG.
The trigger signal D is shaped as shown in FIG.

In addition to the trigger signal D, the distance detection circuit 8 is supplied with a trigger signal C that is generated in synchronization with the drive signal A as shown in FIG. 3e. , the delay time τ of the trigger signal D is calculated, and the distance data E
It is output as .

As shown in FIG. 2, for example, the distance detection circuit 8 includes a flip-flop 81 that is set and reset by the trigger signal C and the reflected light pulse signal D, a high frequency oscillator 82, and an AND gate 8.
3 and a high-speed counter 84.

Then, the AND gate 83 is opened by the output F of the flip-flop 81 as shown in FIG. 3g for a period of delay time τ, and the output G of the high frequency oscillator 82 as shown in FIG. Among them, as shown in FIG. 3i, a signal H having a number of pulses corresponding to the delay time τ is supplied to the high-speed counter 84.

As a result, the high speed counter 84 outputs distance data E proportional to the delay time τ.

This distance data E is supplied to an arithmetic circuit such as a microcomputer, and the distance R (R=(speed of light)·τ/2) to the object to be measured is calculated.

However, in the conventional optical radar device as described above, the pulse leading edge of the reflected light pulse Lr is detected to determine the delay time τ. Due to changes in distance and reflectance of the object to be measured, the reflected light pulse Lr as shown in outputs B1 and B2 shown in FIG.
If the peak value of the received light output changes greatly, the delay times τ ₁ and τ ₂ detected based on the above-mentioned received light outputs B1 and B2 will be greatly different. Therefore, it is difficult to accurately determine the distance to the object to be measured. I won't be able to do that.

This idea was made in view of the above circumstances, and it detects the time from the generation of a light pulse to the leading edge of the received reflected light pulse and the time to the trailing edge of the reflected light pulse. By providing a means for alternately selecting and outputting the detected delayed signals and extracting a DC voltage signal proportional to the average value of the pulse widths of both detection signals, it is possible to accurately and easily measure the distance to the object to be measured. An object of the present invention is to provide an optical radar device that can be detected by a method.

Hereinafter, one embodiment of this invention will be described in detail using the drawings from FIG. 5 onwards.

FIG. 5 is a circuit diagram showing an embodiment of the optical radar device according to the present invention. In this embodiment, the pulse detector 7 and distance detection circuit 8 of the conventional example shown in FIG. 1 are improved, and all other components are the same as those of the conventional example. Therefore, their illustration and description will be omitted.

As shown in FIG. 5, the reflected light pulse light reception signal B from the light receiving element 5 shown in FIG. 1 and the trigger signal C from the pulse generator 6 are applied to input terminals 11 and 12, respectively.

The above trigger signal C is the leading edge detection circuit 13 and 1/2
The light reception signal B is supplied to the trailing edge detection circuit 15 and the leading edge detection circuit 13.

The leading edge detection circuit 13 includes an inverter 13a and an AND gate 13b that detect the rise of the trigger signal C and output a high-speed pulse H, and is set by the high-speed pulse H, and is set by the rise of the light reception signal B. , that is, a flip-flop 13c that is reset by the leading edge of the pulse, and the flip-flop 13c detects the leading edge corresponding to the delay time from the rise of the trigger signal C to the leading edge of the pulse of the received light signal B. Signal K is output.

The trailing edge detection circuit 15 includes an inverter 15a that detects the end point of the fall of the light reception signal B, that is, the trailing edge of the pulse, and outputs a high-speed pulse I.
NAND gate 15b and the leading edge detection circuit 13
is set by the high-speed pulse H from the AND gate 13b, and the NAND gate 1
A flip-flop 15c is reset by a high-speed pulse I from 5b.
A trailing edge detection signal J corresponding to the delay time from the rise of the trigger signal C to the trailing edge of the pulse of the light reception signal B is output from the flip-flop 15c.

Leading edge detection signal K and trailing edge detection signal J output from the two flip-flops 13c and 15c.
are supplied to AND gates 16 and 17 together with the output M and Q output L of the 1/2 period 14, respectively,
The outputs N and O of the AND gates 16 and 17 are supplied to an averaging circuit 19 via an OR gate 18.

The averaging circuit 19 is composed of a high-speed transistor (a high-speed FET may be used) 20 that switches in response to the output P of the OR circuit 18, and a smoothing circuit 21 that converts the switching output of this transistor 20 into a DC voltage signal. has been done.

FIG. 6 is a time chart showing the output waveforms of each of the above components.

As shown in the figure, a light pulse is emitted from the projector 1.
In response to the trigger signal C output in synchronization with the timing of generating Lt, the leading edge detection circuit 13
A high-speed pulse H is output from the AND gate 13b.

This high-speed pulse H sets the two flip-flops 15c and 13c, and their outputs J and K become "H".

Next, when the reflected light pulse Lr is received and a light reception signal B is supplied from the light reception element 5, the leading edge detection circuit 1
3 flip-flop 13c is reset,
The output K becomes "L".

Furthermore, at the trailing edge of the pulse of the light reception signal B,
A high speed pulse I is output from the NAND gate 15b of the trailing edge detection circuit 15, and the flip-flop 15c is reset.

Thereafter, the above operation is repeated.

Since the AND gates 16 and 17 are alternately opened and closed every cycle of the trigger signal C by the outputs M and L of the 1/2 cycle 14,
The leading edge detection signal K and the trailing edge detection signal J are output from the gates 16 and 17 every other gate, and therefore, the leading edge detection signal K and the trailing edge detection signal are outputted from the OR circuit 18. A signal P in which J and J appear alternately will be output.

The signal P output from the OR circuit 18 is supplied to the averaging circuit 19 and converted into a DC voltage signal R proportional to the average value of the pulse widths of the leading edge detection signal K and the trailing edge detection signal J. is output.

That is, as shown in FIG. 7, the pulse width of the leading edge detection signal K is τ ₃ , the pulse width of the trailing edge detection signal J is τ ₄ , and the repetition period Tp of the trigger signal C and the two pulse widths τ Let the difference between ₃ and τ ₄ be τ ₅ and τ ₆ , respectively.
If voltage changes corresponding to τ ₃ , τ ₄ , τ ₅ , and τ ₆ in the collector potential signal Q of the transistor 20 are respectively V ₁ , V ₂ , V ₃ , and V ₄ , the following relationship holds true.

V ₁ = It・τ ₃ /C ₂ …(1) V ₂ = (Vo・τ ₅ )/(R ₁・C ₂ )…(2) V ₃ = It・τ ₄ /C ₂ …(3) V ₄ = (Vo・τ ₆ )/(R ₁・C ₂ )…(4) However, It is a constant current source determined by the peak value of the collector potential signal Q and the emitter resistance Re, and C ₂
is the capacitance of capacitor C ₂ , R ₁ is the resistance value of resistor R ₁ ,
Vo is the voltage drop value of the collector potential signal Q from the power supply voltage Vcc.

Furthermore, if the integrating circuit consisting of the resistor R ₁ and the capacitor C ₂ is in a steady state, V ₁ + V ₃ = V ₂ + V ₄ ...(5) holds true, so the equation (1) can be changed to the above equation (5). ) ~ (4), It (τ ₃ + τ ₄ ) / C ₂ = Vo (τ ₅ + τ ₆ ) / R ₁・C ₂ …(6) Here, 2Tp≫ (τ ₃ + τ ₄ ) and If Tp is set so that It(τ ₃ +τ ₄ )=2VoTp/R ₁ …(7) Therefore, Vo∝(τ ₃ +τ ₄ )/2…(8) Therefore, the above formula ( As is clear from 8), the output R of the averaging circuit 19 becomes a DC voltage signal proportional to the average value of the pulse widths τ ₃ and τ ₄ of the leading edge detection signal K and the trailing edge detection signal J.

That is, as shown in FIG. 8, the DC voltage signal R is a signal proportional to the delay time τr from the generation point S of the pulsed light Lt to the pulse center of the received light signal B of the reflected light pulse Lr.

As mentioned above, by averaging the delay time from the time of generation of the optical pulse Lt to the leading edge and trailing edge of the pulse of the reflected light Lr, an accurate signal that does not fluctuate due to changes in the intensity of the received light signal B can be obtained. Distance data can be obtained.

Further, unlike the conventional example shown in FIG. 2, expensive parts such as a high frequency oscillator and a high speed counter are not required, and the manufacturing cost of the device can be reduced.

As explained in detail above, the optical radar device according to this invention can measure the distance to the object to be measured without being affected by the distance to the object to be measured or changes in the reflectance of the object to be measured. It has the advantage of being able to be determined stably and accurately.

In addition, since this invention measures the time interval from the transmitted light pulse to the reflected light using an integrating circuit, it does not require high-speed logic circuits such as high-speed clock generation circuits and high-speed counters, making the device inexpensive. This has the effect that it can be realized.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a conventional optical radar device, FIG. 2 is a diagram showing the configuration of the distance detection circuit in FIG. 1,
Fig. 3 is a time chart showing each main output of the optical radar device shown in Fig. 1, Fig. 4 is a waveform chart showing the ranging operation of the conventional optical radar device, and Fig. 5 is the optical radar according to the present invention. FIG. 6 is a block circuit diagram showing one embodiment of the device, FIG. 6 is a time chart showing each main output of the device, FIG. 7 is a waveform diagram to explain the operation of the averaging circuit of the device, and FIG. FIG. 3 is a waveform diagram showing a distance measuring operation of the device. 1... Emitter, 2... Light receiver, Lt... Light pulse, Lr... Reflected light pulse, 3... Control circuit, 1
3... Leading edge detection circuit, 15... Trailing edge detection circuit, 1
9...Averaging circuit.

Claims (1)

[Scope of Claim for Utility Model Registration] The period from the time when a light pulse is generated from a projector toward a distance-measuring object to the time when a light receiver receives a reflected light pulse reflected from the light pulse toward a distance-measuring object. In an optical radar device for a vehicle that determines the distance to the object to be measured based on time; a first delay for detecting the time from the generation point of the optical pulse to the pulse leading edge of the received reflected optical pulse; time detection means; second delay time detection means for detecting the time from the generation point of the light pulse to the pulse trailing edge of the received reflected light pulse; generated from the light projector toward the object to be measured; means for alternately selecting and outputting the delayed signal detected by the first delay time detection means and the delay signal detected by the second delay time detection means for each period of the optical pulse signal; a semiconductor switch that switches in response to the alternately selected and output delayed signals and functions as a constant current source; a resistor connected in series with the semiconductor switch and to which a power supply voltage is applied; and a capacitor connected in parallel with the semiconductor switch. and means for outputting a DC voltage signal corresponding to the distance from a connection point between the resistor and the capacitor.