JPS6312543B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pulse reflection type distance measuring device that measures the distance to an object based on the round trip time of electromagnetic wave pulses such as radio waves or light to the object.

Conventionally, this type of device measures the time interval between the emitted pulse and the reflected pulse by counting reference clock pulses and converts the counted amount into distance, and the first method measures the time interval between the emitted pulse and the reflected pulse. Some have adopted the second method of converting the distance into voltage and converting the voltage into distance.

However, these methods handle radio waves and light at extremely high speeds of 3×10 ⁸ m/s, so errors in time processing have a large impact on accuracy, for example, 2/3
An error of ×10 ^-8 seconds is equivalent to 1 meter.

In particular, the first method requires a high-frequency (for example, 150 MHz with an accuracy of ±1 m) reference clock pulse in order to improve measurement accuracy, and the counter, etc., is also required to have a high-speed response, so the circuit The disadvantage is that the configuration is complicated and very expensive.

On the other hand, the second method requires fewer high-speed response parts and has a simpler circuit configuration than the first method, but because it handles analog voltages, it is greatly affected by temperature and cannot achieve practical accuracy. was difficult and impossible to put into practical use.

For this reason, there has been a desire for a distance measuring device that has a certain level of accuracy (approximately ±1 m) and is inexpensive, so that it can be mounted on a vehicle and used as a device for measuring inter-vehicle distance.

The present invention was made in view of such conventional problems, and although it adopts a method of converting time intervals into voltage, it is inexpensive and accurate by making it unaffected by environmental conditions such as temperature. The purpose is to provide a distance measuring device with good performance.

Embodiments of the present invention will be described below with reference to the drawings.
In this embodiment, when converting a time interval into a distance voltage, the reference voltage is converted to the reference voltage at different timings by the same conversion means and compared, so that even if the distance voltage changes due to temperature, At the same time, the reference voltage also changes, making it unaffected by temperature and other factors. In addition, to detect reflected light, it is necessary to detect the center position of the reflected pulse to avoid detection errors caused by the size of the reflected pulse, and also to emit a sharp pulse and directly receive and amplify the pulse. The high-speed response part is kept to the necessary minimum.

In FIG. 1, 1 is a sequence control circuit that controls the whole, and sends a drive pulse a at a predetermined period to a drive circuit 3 that drives a laser diode 2. (Shortest distance) Timing pulse b is the time
A distance voltage sampling pulse _d is sent to the delay circuit 4 and the operation start input of the constant gradient ramp voltage generation circuit 5, and is further sent to the sampling hold circuit 6. is output at a time T _c delayed by more than time T ₀ from the drive pulse a, and then the constant slope gradient voltage generation circuit is reset, and a 75 m (maximum distance) voltage sampling pulse d is output at a further delayed time T _d ,
The voltage sampling pulse e is further delayed by the time T _e
Put it out.

Reference numeral 7 denotes a first light receiving element, which guides the light emitted by the laser diode 2 through a glass fiber and receives the light directly (at a distance of 0 m). Then, the output is amplified by a reference standard amplifier 8, and the output of the amplifier 8 is a waveform signal with a peak value as shown in FIG. The differential signal is converted into a differential signal that crosses zero at the zero-crossing point, and a pulse that rises at the zero-crossing point is outputted from the differential signal by the next-stage zero-crossing detection circuit 10 and input to the delay circuit 4. Then, the signal delayed by the time T ₀ in the delay circuit 4 becomes a stop signal for the voltage increasing operation of the constant slope ramp voltage generation circuit 5.

In addition, the above-mentioned differentiation circuit 9 and zero cross detection circuit 1
The reason why the center position of the output waveform of the amplifier 8 is detected by 0 is as follows.If this method is not adopted, the output waveform of the laser diode needs to be a very thin square wave. In addition, the light receiving element,
Amplifiers and the like must also use elements that faithfully reproduce the waveform. That is, in general, in the case of a simple laser diode drive system, the output waveform is not a square wave but a mountain-shaped waveform with a rounded shape, and the response characteristics of the first light receiving element 7, the amplifier 8, etc. make the output waveform even more rounded. On the other hand, since random noise is superimposed on the light incident on the first light receiving element 7 as shown in Fig. 3, it is necessary to set a threshold at an appropriate level to detect the original signal. In this case, a signal with a rounded waveform has a rise time from a threshold value that differs depending on its magnitude, and as a result, when the rise is detected, the detection time differs depending on the magnitude of the signal, resulting in an error. However, if the center position of the waveform is detected, time errors due to the size of the waveform will not occur.

Reference numeral 11 denotes a second light receiving element that receives the light emitted from the laser diode 2 and reflected by the target object, which has the same performance as the first light receiving element 7. The output of this light receiving element 11 is amplified by a light receiving amplifier 12 similar to the reference standard amplifier 8, and is inputted to a differentiating circuit 14 and a peak holding circuit 15 via a gate 13. The gate 13 is for removing random noise that enters the light receiving element 11, such as background noise of the target object, and the gate 13 is used to remove random noise that enters the light receiving element ₁₁ , such as background noise of the target object. Open only for a long time. The differentiating circuit 14 detects the center position of the rounded signal waveform using the next-stage zero-cross detecting circuit 16, similar to the combination of the differentiating circuit 9 and the zero-cross detecting circuit 10. The output of the zero cross detection circuit 16 is input to the operation start input of the constant slope ramp voltage generation circuit 5. The peak holding circuit 15 is a circuit that holds the peak value of the input signal from the gate 13, as shown in FIG. A differential pulse that is slightly earlier in time than the position) is obtained,
The differential pulse is compared with the comparison level in the comparator 18 at the next stage, and a detection output having a rising edge slightly earlier than the peak value is obtained, which is input to the reset input of the constant slope voltage generation circuit 5. enter. Note that the peak holding circuit 15 is cleared by the sequence control circuit 1 at the timing when the distance voltage sampling pulse c is output.

Therefore, on the output side of the constant slope ramp voltage generation circuit 5, there is a voltage output that is reset to zero by the output pulse of the comparator 18, starts operating with the output pulse of the zero cross detection circuit 16, and increases at a constant slope. Get out. This output is reset every maximum pulse among the output pulses of the gate 13, and has a sawtooth waveform. Therefore, after starting with the largest reflected signal having the maximum value, it is not reset. Then, when a pulse is output from the delay circuit 4 when time T ₀ has elapsed, the output voltage of the constant slope ramp voltage generation circuit 5 is
The voltage at that time is maintained. The voltage is then internally reset to zero after a predetermined period of time.

When the sampling and holding circuit 6 receives the distance voltage sampling pulse c from the sequence control circuit 1, it continues to output the current output voltage (distance voltage V _x ) of the constant slope gradient voltage generation circuit 5 to the output terminal 6a, and also outputs the 0 m voltage. Output voltage of circuit 5 when sampling pulse e is received (0m voltage V ₀ )
continues to be outputted to the output terminal 6b, and when the 75m voltage sampling pulse d is further received, the output voltage of the circuit 5 at that time (75m voltage V ₇₅ ) is continued to be outputted to the output terminal 6c. Then, the above sampling pulse c,
The contents are updated by receiving e and d. 19
~21 is the distance voltage V _x , 0m voltage updated one after another
V ₀ , 75m Voltage V ₇₅ 10-100 of laser emission pulse
This is an averaging circuit that averages the deviations, thereby improving the accuracy of the distance voltage V _x , 0 m voltage V ₀ , and 75 m voltage V ₇₅ .

Note that the longer the round trip time of the laser emission pulse to the target object, the lower the distance voltage V _x becomes.
The voltage V ₀ is the maximum voltage, and the 75m voltage V ₇₅ is the minimum (zero). In other words, the relationship is V ₀ > V _x > V ₇₅ .

22 is a first difference detection circuit that outputs the difference V ₀ −V _x =V _0x between the output voltage V ₀ of the averaging circuit 20 and the output voltage V _x of the averaging circuit 19; 23 is the averaging circuit 20;
This is a second difference detection circuit that outputs the difference V ₀ -V ₇₅ =V ₀₇₅ between the output voltage V ₀ of the averaging circuit 21 and _the output voltage V 75 of the averaging circuit 21 . And these voltages V _0x and V ₀₇₅ are
A/D converter 24 compares V _0x /V ₀₇₅ and converts the resulting analog voltage into a digital signal. In this case, the voltage V _0x changes depending on the ambient temperature, etc., but at the same time, the voltage V ₀₇₅ changes in the same way, so the value of V _0x /V ₀₇₅ does not change depending on the temperature, etc. The value of V _0x /V ₀₇₅ is proportional to the distance to the target object. The converted digital signal is then applied to the distance indicator 25 to display the distance. In addition, by adding a signal of the minimum distance to be detected (for example, the minimum inter-vehicle distance in a car) to the comparator 26 given as a comparison standard, if a target object exists at a distance shorter than the minimum distance, the comparison can be made. A comparison output is output from the device 26, and the alarm device 27 is activated. A timing chart of the entire operation described above is shown in FIG. T _x is the round trip time of the firing pulse to the target object.

As explained above, the present invention converts the round trip time of an electromagnetic wave pulse to a target object at a first timing using a converting means and holds it as a distance voltage. The gist of the present invention is that the distance voltage is converted at another second timing and held as a reference voltage, and the distance is detected by comparing the distance voltage with the reference voltage.

Therefore, according to the present invention, even if the distance voltage and the reference voltage are affected by temperature, they change in the same way, so the comparison result does not change, and therefore, there is no adverse effect due to temperature.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an apparatus according to an embodiment of the present invention, and FIGS. 2 to 5 are timing charts for explaining the operation. 2... Laser diode, 7... First light receiving element, 8
...Reference light reference amplifier, 11...Second light receiving element, 15
...Peak holding circuit, 22, 23...First and second difference detection circuits.

Claims (1)

[Claims] 1. In a pulse reflection type ranging device that emits an electromagnetic wave pulse, converts the round trip time of the electromagnetic wave pulse to a target object into a voltage signal, and detects the voltage signal as a distance signal to the target object, the electromagnetic wave pulse The time-voltage conversion means converts the round trip time into a voltage at a first timing and holds it as a distance voltage, and the time-voltage conversion means converts the predetermined reference time into a voltage at another second timing. 1. A pulse reflection type distance measuring device, characterized in that the distance voltage is converted and held as a reference voltage, and distance detection is performed by comparing the distance voltage with the reference voltage.