JPS5837576A - Pulse reflecting type range finder - Google Patents

Abstract

PURPOSE:To prevent the accuracy of the titled device from being reduced temperature by changing a standard voltage in the same manner as the change of range voltage in accordance with the temperature change. CONSTITUTION:The light from a laser diode 2 is directly led to a photodetector 7 reflected by an object to be measured and led to a photodetector 11. Outputs from these photodetectors 7, 11 are amplified by amplifiers 8, 12 and inputted to a voltage generating circuit 5 with constant gradient inclination through the processing such as differentiation and zero-cross detection. A sampling/holding circuit 6 holds the standard and range voltages and difference detecting circuits 22, 23 compares these voltages to calculate the distance. The culculated result is displayed on a distance display device 25 through an A/D converter 24.

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 has a first method in which the time interval between the emitted pulse and the reflected pulse is measured by counting reference clock pulses, and the counted amount is converted into distance; Some have adopted a second method in which the time interval between pulses is converted into voltage, and the voltage is converted into distance.

However, these methods handle radio waves and light at a speed of 3
Since it is extremely fast at x 10 m/j, errors in time processing have a large impact on accuracy, for example, 2/3 x 10 m/j.
The error in seconds is equivalent to 1 meter.

In particular, the first method requires a high-frequency reference clock pulse (for example, 150 MHz with +1 tn accuracy) in order to improve measurement accuracy, and counters and the like are also required to have a high-speed response. The circuit configuration becomes complicated,
The disadvantage is that it is 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, it has a certain level of accuracy (±1m) when used as a device to measure the distance between vehicles when mounted on a vehicle.
There was a desire for an inexpensive distance measuring device that would provide accurate results.

The present invention was made in view of such conventional problems, and while adopting a method of converting time intervals into voltage,
The object is to provide a distance measuring device that is inexpensive and has high accuracy by making it unaffected by environmental conditions such as temperature.

Embodiments of the present invention will be described below with reference to the drawings.

In this embodiment, when converting a time interval to 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, the reference voltage is It takes advantage of the fact that the voltage also changes, making it unaffected by temperature and other factors. 1. To detect the reflected light, detect the center position of the reflected pulse to avoid detection errors due to the size of the reflected pulse, and emit a sharp pulse and directly transmit the pulse. It eliminates the need to amplify the received light and keeps the high-speed response part to the necessary minimum.

In FIG. 1, reference numeral 1 denotes a sequence control circuit that controls the entire system, and it sends a drive pulse IL at a predetermined period to a drive circuit 3 that drives a laser diode 2, and also sends a drive pulse IL with a phase shift of about 180 degrees from the drive pulse a. (Shortest distance) Timing pulse b IIMTo (Maximum distance 75 to be described later)
FF+ is sent to the delay circuit 4 (time required for light to travel back and forth) and the operation start input of the constant gradient ramp voltage generation circuit 5, and the distance voltage sampling pulse d is sent from the drive pulse a to the sampling hold circuit 6. Time T. After that, the constant gradient ramp voltage generating circuit is reset, the r5mC1iA long distance) voltage sampling pulse d is outputted at a further delayed time TdK, and the 0m voltage sampling pulse e is outputted at a further delayed time T0.

Reference numeral 7 denotes a tg1 light receiving element, which guides the light emitted by the laser diode 2 through a glass fiber and directly receives the light (at a distance Om). Then, the output is amplified by the reference standard amplifier 8, and the output #-i of the amplifier 8 is a waveform signal with a peak value as shown in FIG. That is, it is converted into a differential signal that crosses zero at the center position, and a pulse that rises at the time of zero cross is outputted from the differential signal by the next stage zero cross detection circuit 1a, and is input to the delay circuit 4. Then, the delay circuit 4 calculates the time T. The delayed signal becomes a stop signal for the voltage increasing operation of the constant slope #slant voltage generation circuit 5.

The reason why the center position of the output waveform of the amplifier 8 is detected by the differentiating circuit 9 and the zero-cross detection circuit 10 is as follows. If this method is not adopted, the output waveform of the laser diode will be very A thin square wave is required, and it is also necessary to use a light receiving element, an amplifier, etc. that can faithfully reproduce the waveform. That is, in the case of a simple laser diode driving method, the output waveform is generally not a square wave but a mountain-shaped waveform with a rounded shape, and the response characteristics of the first light receiving element T, 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 T, as shown in Figure t43, a threshold value of an appropriate level is set.

In this case, the rounded waveform signal has different rise times from the threshold depending on its size, and as a result, when the rising edge is detected, the detection time differs depending on the signal size. Errors will occur. However, if you detect the center position of the waveform,
No time error occurs due to the size of the waveform.

Reference numeral 11 denotes a second light receiving element that receives the light emitted from the laser diode 2 and reflected by hitting the target object, which has the same performance as the first light receiving element T. and,
The output of this light-receiving element 11 is amplified by a light-receiving amplifier 12 similar to the reference amplifier 8, and is input to a differentiating circuit 14 and a peak holding circuit 15 via a gate 13. gate 13
is for removing random noise incident on the light-receiving element 11 such as background noise of the target object, and the delay time τ is set slightly before the laser beam is emitted by the control circuit 1. Open for a slightly longer period of time. The differentiating circuit 14 and the next-stage zero-cross detecting circuit 16 detect the center position of the rounded signal waveform, similar to the combination of the differentiating circuit S and the Xerox 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.
The rising edge is differentiated by the next stage differentiating circuit 1T to obtain a differentiated pulse that is slightly earlier in time than the peak value (center position), and this differentiated pulse is compared with the comparison level by the next stage comparator 18. From K, a detection output with a rising 9 edge slightly earlier than the above peak value is obtained,
Enters the reset input of the constant slope ramp voltage generation circuit 5.

Note that the peak holding circuit 15 is cleared by the sequence control circuit 1 at the timing when the distance voltage sampling pulse (C1) is output.

Therefore, on the output side of this constant slope ramp voltage generation circuit 5,
The comparator is reset to zero with the output pulse of the first day, and starts operating with the output pulse of the zero cross detection circuit 16, producing a voltage output that increases at a constant slope. This output is reset and set every o maximum pulses 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, the time τ is output from the delay circuit 4. If a pulse appears when the time elapses,
The output voltage of the constant slope ramp voltage generation circuit 5 maintains the voltage at that time. The voltage is then internally reset to zero after a predetermined period of time.

The sampling hold circuit 6 is connected to the sequence control circuit 1.
When receiving the distance voltage sampling pulse C from
x ) to the output terminal 6a for 11", and when receiving the Qmi pressure sampling pulse θ, continue to output the output voltage of the circuit 5 at that time (Qm pressure V.) to the output terminal 6b, and further 75m' When the voltage sampling pulse d is received, the output voltage C75mt pressure v, 5) of the circuit 5 at that time continues to be output from the output terminal 601C. Then, the contents are updated by receiving the sampling pulses c, e, and d again.

1''9~21 are the distance voltage V, Om voltage V., 15m voltage V?5 updated one after another, and 10~1 of the laser emission pulse.
This is an averaging circuit that averages 00 shots, thereby improving the accuracy of distance voltage Vx, Qm voltage V6%75m voltage v0.

Note that the distance voltage v8 becomes lower as the round trip time of the light emitting pulse to the target object becomes longer; the om voltage vo is the maximum voltage, and the ys rrr tFE''/ra is the minimum (zero).
It is. The relationship is vo>vx>v7ff.

22 is the output voltage VD of the averaging circuit 2o and the averaging circuit 19
The difference V from the output voltage V□. -V engineering=first difference detection circuit that outputs vox; 23 is the output voltage v0 of the averaging circuit 20;
and the output voltage of the averaging circuit 21 〒5 difference V o V
ys-VO? 6 k output f is the second difference detection circuit. And these voltages vox and vol are A
In the /D converter 24, a comparison of "VO?5" is performed, and the resulting analog voltage is converted into a digital signal.In this case, the voltage v0 varies depending on the ambient temperature, etc., but at the same time, the voltage Wool is also the same. Therefore, the value of ``voys'' does not change depending on the temperature or the like.

This “”VO? The value of 6 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 M1 in a car) to the comparator 26 provided as a comparison standard, if a target object exists at a known distance from the minimum distance, the signal can be detected. A comparison output is output from the comparator 26, and the alarm 2T is activated.

A timing chart of the entire operation described above is shown in FIG. Tx is the round trip time of the firing pulse to the target object.

As explained above, the present invention converts the travel 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, and converts a predetermined reference time to the converting means. 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

Claims (1)

[Claims] 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 round trip time of the electromagnetic wave pulse Converting time into voltage at a first timing by the time-voltage converting means and holding it as a distance voltage, and converting the predetermined reference time into voltage at another second timing by the time-voltage converting means. A pulse reflection type distance measuring device, wherein the distance voltage is held as a reference voltage, and distance detection is performed by comparing the distance voltage with the reference voltage.