JPH0367113A - Distance measuring instrument - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention is a distance measuring method that measures distance by emitting infrared light toward an object, receiving the infrared light reflected from the object, and using a triangulation method. This relates to a measuring device.

Such distance measuring devices include various cameras, surveying equipment, position detection sensors, robots, and object detectors.

It can be used in collision avoiders, automatic doors, etc.

(Prior art) Distance measurement using a position detection device (PSD) that emits infrared light toward an object, receives the infrared light reflected from the object, and outputs a signal according to the receiving position. equipment is used.

The principle of distance*m in such a distance measuring device is explained in the sixth section.
This will be explained using figures.

The LED 20, which is a light emitting element, is caused to emit light intermittently as a sine wave or a rectangular wave having a certain frequency. Lens 2
The diffused reflected light is made to enter a lens 23 which is a distance S from the lens 21, and is made to hit the PSD 24. At this time, currents I,, I, corresponding to the positions hit by the light flow from the PSD 24.

1, = k (c/2-d) --
(1) I, = k (c/2 + d)
-------- There is the relationship (2). Here, k is a distance-dependent constant, C is the length of PSD24, and d is PSD2
This is the amount of deviation from the center of the spot light that is focused on 4.

Meanwhile, as shown in FIG.

S/L=d/f There is a relationship as shown in (3). S is the distance between the light projecting lens 2 and the light receiving lens 23, L is the distance from the light projecting lens 21 to the distance measurement target 22, and f is the distance from the light receiving lens 23 to the PSD 24. The above equations (1) and (2) are I, = k (c/2-f-s/L) -" (4) F2 = k (c/2+f-8/L)...・(
5), and from this relationship I, /l2=(c/2-f-S/L)/(c/2+f'
S/L) """ The relationship (6) is obtained. c, f
, S are predetermined, so the distance is uniquely determined by detecting the ratio of ■□ and work 2.

According to this distance measurement principle, the ratio of the outputs of the PSD 24 is used as a distance measurement signal, and the value thereof is determined by the amount of deviation d of the spot light on the PSD 24, so that relatively accurate distance measurement can be performed.

However, when the distance to the object to be measured is further than about 10 m, the output of the PSD 24 becomes small and the accuracy deteriorates significantly. Further, even if the distance @L to the object to be measured is short, the distance cannot be measured accurately if there is strong external light.

In order to improve these problems, it is conceivable to increase the output of one light emitting element, but this would shorten the life of the light emitting element.

Another method is to blink one light emitting element at a certain frequency, detect the light at that frequency and distinguish it from outside light, and use a gain control circuit to reduce the output of the PSD 24 when the object to be measured is far away. For example, a distance measuring device that automatically increases the gain of an amplifier has been proposed (Utility Model Application No. 15907/1989).
(see publication).

(Problems to be Solved by the Invention) The distance measuring device shown in the above-mentioned document (Utility Model Application Publication No. 15907/1983) uses a detector, so the distance measuring accuracy is good, but the distance measuring device is It takes time for the signal to stabilize, which slows down the operation speed.

The present invention blinks a light emitting element at a constant frequency as a countermeasure against external light, extracts the light at that frequency with a filter, and automatically changes the gain of the amplifier to perform accurate distance measurement and speed up the operation. The object of the present invention is to provide a distance measuring device that is faster.

(Means for Solving the Problems) Therefore, the distance measuring device of the present invention includes a light emitting element that blinks at a constant frequency and emits infrared light toward an object, and a light emitting element that emits infrared light toward an object and receives infrared light reflected from the object. a position detection element that outputs a signal according to the light receiving position, two amplifiers that amplify the re-output signals of the position detection element, and a blinking frequency band of the light emitting element included in the output signal of each amplifier. Two filters that pass the signal, and the signals that have passed through each filter are rectified and smoothed to extract only the signal corresponding to the infrared light component from the light emitting element, which is then used for distance measurement calculations.
and a gain control circuit that controls the gain of each of the amplifiers, and the gain control circuit includes a window comparator that compares the output of one of the rectification and smoothing circuits with a reference voltage. , an up/down counter that uses the output of the window comparator as an up/down control input, and a selection circuit that selects a resistance value that determines the gain of each amplifier based on the output of the up/down counter.

(Example) FIG. 1 schematically represents the invention.

The LED 20, which is a light emitting element, emits near-infrared light toward an object. The LED 20 has a constant frequency (e.g. several 10 to several 1
It is driven via a movement circuit 26 in response to a signal from an oscillator 25 that oscillates a signal of 00 KHz). LED2
The infrared light from 0 is reflected by the distance measurement object and enters the light receiving surface of the PSD 24 as a spot light at a position corresponding to the distance to the distance measurement object.

Reference numeral 2.3 denotes a variable gain amplifier, which inputs and amplifies the signal current I ty 2 corresponding to the position of the spot light from the PSD 24, respectively. 4 and 5 are filters that pass the blinking frequency components of the LED 20 from the output signals of the amplifiers 2 and 3, respectively. The filters 4 and 5 are band-pass filters whose pass frequency is the blinking frequency band of the LED 20, and for example, a tank circuit or a ceramic filter can be used. 6 and 7 are rectifier/smoothing circuits which each input the output signal of the filter 4.5 and rectify and smooth it into a DC voltage signal. 9 is a differential amplifier;
The difference between the output signals of both rectifier/smoothing circuits 6 and 7 is taken out as a ranging signal. This distance measurement signal is used, for example, for automatic focus adjustment in a camera.

8 is a gain control circuit, and the output signal of one rectifier/smoothing circuit 6 (or 7) is input to the gain control circuit 8. A control signal is generated in the gain control circuit N8, and this control signal controls the gains of the amplifiers 2 and 3.

This allows the gains of amplifiers 2 and 3 to be controlled by automatic gain control (AGC).
), and as shown in FIG.
Or, even if the current input to the amplifiers 2 and 3 changes, the output of 7) will have a smaller amount of change corresponding to the change. This means that
This means that the output of the rectifier/smoothing circuit 6.7 has little effect on the distance to the m-square object, and accuracy is ensured even in distant distance measurement. As shown in equation (6), the distance measurement signal is determined not by the absolute value of the current and the current, but by the ratio.
Since the current ratio It/Iz is maintained regardless of the magnitude of the control gain, distance measurement is not affected.

Next, a specific configuration will be explained using FIG. 2.

FIG. 2 specifically shows the rectifier/smoothing circuit 6 and the gain control circuit 8.

Signal current generators 1 and 1□ from the PSD 24 each convert the current into voltage and pass through an amplifier for amplification.

It is input to the non-inverting input terminal of each operational amplifier of variable gain amplifiers 2 and 3.

In the rectification/smoothing circuit 6 (the rectification/smoothing circuit 7 also has the same configuration, only the rectification/smoothing circuit 6 will be explained).
The output terminal of the filter 4 is connected to the base of a transistor Q5, the emitter of which is connected to a power supply Vce through a diode D1 and a resistor RIO, and the collector of which transistor Q5 is connected to a Veefi source below the ground (GND) level. The connection of the resistor RIO and the diode D1 is connected to the base of the transistor Q6, the collector of the transistor Q6 is connected to the power supply Vce, and the emitter of the transistor Q6 is connected to the diode D1.
2 and grounded through the differential amplifier 9 through the resistor R11.
is connected to one input terminal of the C1 is a smoothing capacitor.

In order to configure the gain control circuit 8, the output No. 3 V of one rectifier/smoothing circuit 6 is used. 1 as input, base 4! ! A window comparator 30 is provided to compare the magnitude with the voltage, and the output of the window comparator 30 is increased.
An up/down counter 31 is provided as a down control input. To determine the gain of the amplifier 2, a series resistance circuit of resistors R1, R2, R3 is connected between the output terminal and the inverting input terminal of the operational amplifier. Resistance R1, R
2゜R3 each has a switch SW that constitutes a selection circuit.
1. ．． SW2. SW3 is connected in parallel.

The same applies to amplifier 3, with resistors R4, R5゜R6
A series resistor circuit is connected between the output terminal and the inverting input terminal of the operational amplifier, and the resistors R4, R5, and R6 are connected to switches SW4. SW5. SW
6 are connected in parallel.

The resistances R1, R2, and R3 are weighted, and the ratio thereof is, for example, R1:R2:R3=1:2:4. The same applies to the resistors R4, R5, and R6 of the other amplifier 3, and the ratio thereof is, for example, R4:R5:R6=1.
:2:4.

Switches SWI and SW4 are up/down counters 31
It is controlled on/off by the output 01 of the switch SW2.
and SW5 are controlled on/off by the output 02 of the up/down counter 31, and the switches SW3 and SW6 are controlled on/off by the output o3 of the up/down counter 31. Each switch 5WI-8W6 is turned off when the output of the up/down counter 31 is at a high level.

Turns on when low level.

In the up/down counter 31, when the signal input from the window comparator 30 is an up signal, the high level output signal moves in the direction of 01 → 02 → 03,
Conversely, when it is a down signal, the high level output signal changes from 03 to 0.
Move in the direction of 2→01.

A specific example of the window comparator 30 is shown in FIG.

Input terminal A is a terminal to which reference voltage Vr is input, and constant current source 43. It is connected to a connection point between resistors 44 and 45 of a series circuit of resistors 44 and 45 and a constant current source 46. A connection point between constant current source 43 and resistor 44 is connected to an inverting input terminal of comparator 47.

A connection point between the resistor 45 and the constant current source 46 is connected to an inverting input terminal of a comparator 48. Comparator 47, 4
The output V of the rectifier/smoothing circuit 6 is input to the non-inverting input terminal 8 via the input terminal B. , is input. comparator 47,
The output terminal of 48 is connected to AND gate 49, and
The output C of the gate 49 becomes a signal that causes the up/down counter 31 to perform a down operation. comparator 47,
The output terminal of 48 is also connected to a NOR gate 50,
The output of NOR gate 50 is up/down counter 3
This is a signal that causes the up operation of 1 to be performed.

In the window comparator shown in FIG. 3, if the current of the constant current source 43, 46 is I, and the resistance value of the resistor 44.45 is R, then the high-level side threshold level of this window comparator is V r + I. becomes R,
The lower threshold level is Vr-I.R. Comparators 47 and 48 are input from terminal B.

, with each threshold level, gate 49.5
A down signal and an up signal are output through terminals C and D through 0.

The outputs of the comparators 47 and 48, the signal levels of the terminals C and D, and the operation of the up/down counter 31 are shown in the table below.

The operation of the window comparator 30 is further illustrated in FIG. 4 as shown in FIG.

Now, assume that the reference voltage Vr is F, the high-level side threshold level is E, and the low-level side threshold level is G. If V is in the state of Vl, for example, the window comparator 30 outputs a signal to cause the up/down counter 3 to operate down from the above table. Conversely, if v and i are in the state of v2, for example, the window comparator 30 outputs a signal that causes the up/down counter 31 to operate up. If vo, for example vO, is between levels E and G, the signal from window comparator 30 will neither go up nor go down.

Next, the operation of this embodiment will be explained.

In Figure 2, when the distance measurement target is close, the PSD24
If the incident light is strong <, the output current from the PSD 24 I0. I
, is large, the output signal V Oi of the rectifier/smoothing circuit 6
increases, a down signal is output from the window comparator 30, and the output of the up/down counter 31 moves in the direction of 03→02→01, which causes the resistance that determines the gain in amplifiers 2 and 3 to change from R3→ R2→R
1, and the gains of amplifiers 2 and 3 become smaller. As a result, the output signals of the rectifier/smoothing circuits 6 and 7 become smaller, and eventually the output signal vo of the rectifier/smoothing circuit 6 becomes smaller.
falls between the two threshold levels E and G of the window comparator 30, the window
Depending on the output from the comparator 30, the state of the up/down counter 31- does not change.

On the other hand, if the incident light to the PSD 24 is weak and the output current from the PSD 24 is small, such as when the distance measurement target is far away, the output signal of the rectifier/smoothing circuit 6 becomes small, and the window comparator 30 outputs an up signal, and the output of up/down counter 31 changes from 01 to Q.
As a result, the resistors that determine the gains in amplifiers 2 and 3 are switched in the direction of R1→R2→R3, and the gains of amplifiers 2 and 3 become larger. This increases the output signals of the rectifier/smoothing circuits 6 and 7,
Eventually, the output signal ■ of the rectifier/smoothing circuit 6. When □ falls between the two threshold levels E and G of the window comparator 30, the state of the up/down counter 3 no longer changes depending on the output from the window comparator 30.

As the output signal of the rectifying/smoothing circuit that operates the gain control circuit 8, the other rectifying/smoothing circuit? The output signal Vo of the lt circuit 7 may also be used.

Note that a frequency divider may be provided after the oscillator 25, and the output of this frequency divider (No. 4) may drive the LED 20.

Further, the filters 4 and 5 can also be configured by switched capacitor filters in which the capacitors are switched using a switch to provide filter characteristics.

Elements other than LEDs may be used as the light emitting elements.

(Effects of the Invention) In the present invention, each of the two output signals of the PSD is amplified, passed through a filter, rectified and smoothed, and used for distance measurement calculation, and one of the outputs of the two rectification/smoothing circuits is used to output the PSD. By controlling the gains of the two amplifier circuits that amplify the two outputs, stable outputs can be obtained whether the object to be measured is close or far away. It becomes possible to realize a device that can be extended to

Also, since the present invention does not use a detector, the distance measurement 73
It can quickly stabilize the signal and increase the operating speed.

[Brief explanation of drawings]

Fig. 1 is a block diagram schematically showing one embodiment, Fig. 2 is a circuit diagram specifically showing the same embodiment, and Fig. 3 is a window diagram.
A circuit diagram showing an example of a frame comparator, FIG. 4 is a diagram showing the operation of a window comparator, FIG. 5 is a diagram showing AGC characteristics in an example, and FIG. 6 is a diagram showing the principle of distance measurement using a light emitting element and PSD. FIG. 3 is an optical layout diagram. 2.3...Amplifier, 4,5...Filter, 67...Rectifier/smoothing circuit, 8...
Gain control circuit, 20...LED, 24...
...PSD, 30...Window comparator, 31...Up/down counter, R1-
R6...Resistor, SWI~SW6...Switch. Figure 1

Claims (1)

[Claims] (1) A light emitting element that blinks at a constant frequency and emits infrared light toward an object, and a position detection element that receives the infrared light reflected from the object and outputs a signal according to the receiving position. ,
two amplifiers that amplify both output signals of the position detection element, and two filters that pass the signal in the blinking frequency band of the light emitting element included in the output signal of each amplifier;
Two rectifying/smoothing circuits that rectify and smooth the signals that have passed through each filter to extract only the signal corresponding to the infrared light component from the light emitting element and use it for distance measurement calculations, and the gain of each of the amplifiers. The gain control circuit includes a window comparator that compares the output of one of the rectifier/smoothing circuits with a reference voltage, and an up/down control input for the output of the window comparator. A distance measuring device comprising: an up/down counter; and a selection circuit that selects a resistance value that determines the gain of each of the amplifiers based on the output of the up/down counter.