JPS63302313A - Distance measuring apparatus - Google Patents

Abstract

PURPOSE:To enable reduction in the shortest measurable distance without lengthening a position detector (PSD), by arranging the center of a light receiving section to be deviated on the side opposite to an infrared ray emitting device (IRED) from the optical axis of a lens for receiving light. CONSTITUTION:The optical axis of a lens 4 for receiving light is arranged to match one end of a light receiving section of a PSD5, not the center thereof. A signal current at the one end of the light receiving section is supplied to a changeover switch 10. A first terminal (a) of the switch 10 is connected to an electrode 8 as intact to supply current I2 to a signal processing circuit 1. On the other hand, a second terminal (b) is connected to an electrode 9 through a resistance 6 to supply a current I2' to the signal processing circuit 11. A current I1 is supplied to the signal processing circuit 11 from a current 7 at the other end of the PSD5. The signal processing circuit 11 determines a distance based on I1/I2 or I1/I2'. Then, an image of light projected from an IRED1 and reflected on an object 3 is formed on the PSD5 with the lens 4 for receiving light. This enables reduction in the shortest measurable distance without lengthening the PSD.

Description

[Detailed Description of the Invention] [Technical Field] The present invention provides a position sensing element (hereinafter referred to as PSD) that projects light onto an object to be measured and detects the reflected light from the object by a baseline length from the light projecting element. ) The present invention relates to a distance measuring device that measures the distance to an object by receiving light at a distance.

[Prior art]

A conventional example of such a distance measuring device is shown in Figure 7.

Infrared light for distance measurement from an infrared light emitting element (hereinafter referred to as I RED) 1 is focused through a projection lens 2, and is focused on a subject 3.
is irradiated. The reflected light is passed through the light receiving lens 4,
The image is formed on the PSD S. Here, the center of the PSD 5 is aligned with the optical axis of the light receiving lens 4.

The imaging position, that is, the distance X from the optical axis of the light-receiving lens 4 (dotted chain S in the figure) is
The distance between the light receiving lens 4 and the PSD 5 is f.
, where S is the deviation (baseline length) between the optical axis and the subject 3, it is expressed as follows.

x=S-f/l...(1) Here, assuming that the length of the light receiving part of the PSD 5 is t, and the optical axis of the light receiving lens 4 and the center of the PSD 5 match, the image formation Signal current 11 output from electrodes at both ends of PSD 5 at position X. The ratio of I2 is as follows.

I, /Iz=(H+x)/(7-x) If equation (2) is rewritten with respect to distance t, the following equation is obtained.

That is, it can be seen that if the ratio of the signal currents I, I, I2 output from both end electrodes of the PSD 5 is determined, the distance to the subject can be determined.

FIG. 8 shows the relationship between the imaging position X and the signal current ratio 11/I. When the subject is at infinity, x=0.

Since I = I, I, /I, = 1. Also,
Equation (1) is X0CI/l, and the horizontal axis X in FIG. 8 is proportional to the reciprocal of the subject distance t. When the subject distance t becomes smaller, X becomes larger. Therefore, the closest pressure that can be measured is l171! t' is when x=t/2, and (
1) It can be found from the equation as follows.

t'=2・S −f/l ・・
- (4) [Problems to be solved by the invention] As described above, in a distance measuring device using a PSD.

Due to its principle, there was a limit to the closest distance that could be measured. To reduce the closest distance t', from equation (4), PSD
It can be seen that the length t of the light receiving section No. 5 can be increased.

However, since the PSD 5 has a uniform resistive layer made of a single P layer as a light receiving section, the longer the resistive layer becomes, the worse the IJ nearness of the resistive layer becomes, and the accuracy of distance measurement deteriorates. Furthermore, there were drawbacks such as the high cost of producing long elements.

An object of the present invention is to provide a distance measuring device that can shorten the closest distance that can be measured without increasing the PSD.

Another object of the present invention is to provide a distance measuring device that can increase the accuracy of distance measurement on the far side when the closest distance that can be measured is shortened.

A PSD 5 disposed off the optical axis of the light receiving lens 4 on the opposite side of the IRED 1, and at least one of the PSDs 5.
A resistor 6 selectively connected to two electrodes by a changeover switch 10 is provided.

[Effect]

According to this invention, the center of the light receiving section of the PSD is shifted from the optical axis of the light receiving lens to the side opposite to IRED 1, thereby shortening the closest distance that can be measured compared to when the centers are aligned. You can do this. Furthermore, by connecting a resistor in series to the PSD on the far side, 9. There is always a one-to-one correspondence between the ratio of the output signal of the PSD and the subject distance, and erroneous distance measurement can be prevented.

〔Example〕

An embodiment of a distance measuring device according to the present invention will be described below with reference to one drawing. FIG. 1 is a schematic diagram showing the optical system. Portions that are consistent with the conventional example shown in FIG. 7 are given the same reference numerals. In this embodiment, the optical axis of the light receiving lens 4 is PSD 5
It is aligned with one end of the light receiving area, not the center. The signal current at one end is supplied to the changeover switch IQ. The first terminal a of the changeover switch 10 is directly connected to the electrode 8.

A current generator 2 is supplied to the signal processing circuit 11. The second terminal is connected to the electrode 9 via the resistor 6, and supplies a current 2' to the signal processing circuit 11. A current is supplied from the electrode 7 at the other end of the PSD 5 to the signal processing circuit 11 . The signal processing circuit 11 is I /I or 11/12'1 2
Find the distance based on ′. The spot light image projected from IREDJ and reflected by the subject 3 is converted to P by the light receiving lens 4.
Imaged on SD5. Although this spot light image actually has a finite size, it is treated as a point here for convenience of explanation.

In this example as well, x=Sf/l. The closest measurable distance t is when x = t, and is as follows.

t'=s-f/l...
(5) That is, by aligning one end of the PSD 5 with the optical axis, the closest distance can be shortened to 1/2 than when the center of the PSD 5 is aligned with the optical axis.

Note that it is not necessarily necessary to shift one end of the PSD 5 to the optical axis of the light-receiving lens 4, and it is only necessary that the center of the PSD 5 be shifted from the optical axis to the side opposite to IREDJ.

The output signal ratio I, /I2 is as follows when the switch 10 is connected to the a side.

That is, when the position X of the spot light image is at the center of the PSD 5 (x=t/2), the equation 2=1.

At this time, the imaging position due to the reflected light from the object closer to the object distance is x) t/2, so! , /I,>1, and the imaging position due to the reflected light from the object further away is X<t/2, so I,
/I2<1. This is shown by solid line A in FIG.

However, in reality, the amount of incident light changes depending on the distance, so the amount of incident light decreases on the far side (X km).
Since i=ikio(!:fx), I,/l2=1, and changes as shown by the broken line.

Next, the ratio of the output signals when the switch 10 is connected to the b side (in this case, 11/I,') is determined. Assuming that the resistance between both ends of the PSD 5 is 1t-R4, and the resistance value of the resistor 6 is R2 (Fig. 3 (a)), when the switch 10 is connected to the b side and both are connected in series, the resistance value of both is R1 + R2.
PSD5' of is equal to equal parsimony (Fig. 3(b)
)). Of course, the photocurrent generated by the incident light is
In this example, the light reflected from the subject only moves on the PSDs.
The resistor 6 does not require a photoelectric conversion function, and only a resistance component is required.

Now, if R1=R2, the length of PSD 5/ is 2t. Its center coincides with the optical axis. Therefore.

Current 11 taken out from i-poles 7 and 9. The ratio of I2' is as follows.

The relationship between I, /I,' (≧1) and X is shown by a solid line B in FIG.

As described above, according to the present embodiment, by switching the switch 10, two distance measurement principles can be used, but both have advantages and disadvantages. When switch 10 is connected to side a, x = t/2 and x = 0, and ■1
/I2 are equal, and on the far side of x≦t/2, I, /I
There are two points of X with the same value of 2, and there is a drawback that a single output corresponding to the distance cannot be obtained. In other words, the distance will be incorrectly measured in the range of X≦t/2.

Characteristics obtained by connecting switch 10 to side b (solid line B)
F1 has lower accuracy than solid line A for the following reasons. Generally, in such a distance measuring device, the amount of signal light reflected from the object and incident on the PSD is extremely small, and noise components are often added to the output signal due to circuit noise and the like. Therefore, it is desirable that the change in the output signal with respect to the change in distance be large.

FIG. 4 shows changes in characteristics when noise is added to characteristics A and B in FIG. 2, respectively. + for characteristic A.

-The characteristics when noise is added are A'.

AI, and the case where similar noise is added to characteristic B is Bl
, Bl. Here, it is assumed that the width of noise at a certain distance X is equal to both A and B. Now, if we use the signal output VB according to the characteristic B to determine the distance X, then Bl,
131F, there is a judgment width of ΔxB. Similarly, when the signal output VA based on the characteristic A is used, there is a judgment width of ΔxA. Since characteristic A has a larger slope, ΔxA (ΔxB), and characteristic A has better accuracy.

Therefore, in this embodiment, the distance measurement range is changed using the switch 10, and on the close side (X≧t/2), the switch 10 is connected to the 1 side, distance measurement is performed from I, /I, and on the far side (X <
t/2), connect the switch 10 to the b side.

Measure the distance from I, /I2'. Therefore, it is possible to shorten the closest distance measurement and eliminate erroneous distance measurement on the far side.

FIG. 5 shows a detailed diagram of the distance measuring device according to this embodiment, and the same reference numerals as in FIG. 1 are given to the same parts.

The control circuit 20 connects IRED 1 via the transistor 21
control the light emission. The first electrode A of PSD 5 is resistor 2
5 to an operational amplifier 26 to which negative feedback is applied. The second electrode B is connected via an analog switch 23 to an operational amplifier 29 which is also provided with negative feedback by a resistor 28. Terminal B is also connected to an operational amplifier 29 via a resistor 6 and an analog switch 24 . The analog switches 23 and 24 are controlled by control signals (signals from terminals) from the control circuit 20. A terminal control signal is supplied directly to the analog switch 23 and to the analog switch 24 via the inverter 22. Therefore, when one of the analog switches 23 and 24d is on, the other is always off.

Operational amplifiers 26 and 29 constitute a current/voltage conversion circuit,
The output of the PSD 5 [current I, , I2i is converted into a voltage, respectively. The outputs of the operational amplifiers 26, 29 are supplied to the signal processing circuit 3) via filter circuits 27, 30, respectively. The filter circuits 27 and 30 detect a change in the photocurrent generated by the reflected light from the object due to the projection of the IRED 1 from the photocurrent constantly generated by background light or the like. The signal processing circuit 31 outputs from a terminal C a distance signal corresponding to the ratio I, /I of the human force signals, that is, the subject distance t.

A voltage divider consisting of resistors J7 &~37f connected in series to make a constant 1! It is connected between the current source 36 and a constant voltage terminal. A contact point between the constant current source 36 and the resistor 37h.

Connection points of the resistors 371 to 37f and constant voltage terminals are connected to inverting input terminals of the comparators 35a to 35g, respectively.

That is, the comparators 35a to 35g constitute an A/D converter 35.

The output terminals of comparators 35h to 35g are AND gates 381
~38g is followed by a first input terminal. The terminal control signal is AND Dart 31J*, 38c, 38e, 38g4
:) is supplied to the second input terminal. A control signal from the terminal is passed through an inverter 39 to AND gates 38b and 38d.

38f is supplied to the second input terminal. AND dart 38
h to 31Jgf@configured in selection circuit sg7. AN
The output signal of DN-DART&~38g is sent to the lens drive circuit (
(not shown). The distance signal at terminal C is compared with a reference value V eom by comparator 32 . The output of comparator 32 is supplied to control circuit 20.

In such a configuration, when a start signal is input, the control circuit 20 turns on the transistor 21 and sets the terminal to H level. This allows IREDJ
emits light, and a spot image is formed on PSD j by the reflected light from the subject. The photocurrent of PSD5 is divided into electrodes A and H according to the incident position of the spot image, and I4.
A signal current I2 is generated. Here, the terminal is H
level, the analog switch 23 is turned on and the analog switch 24 is turned off. For this purpose, electrode B is connected to an amplifier 29 via an analog switch 24. For this reason, the signal currents I, , I, are each converted into a current/voltage by a resistor 25, an operational amplifier 26, a resistor 28, and an operational amplifier 29, and the filter circuit 27.3
After being separated from the light t a due to the constant concentration light by 0, the light is input to the signal processing circuit 3 . The output V at the output terminal C of the signal processing circuit 3 is v=r (11/I2). This is a function related to fH current/voltage conversion. Therefore, if the optical system is set as shown in FIG. 1, an analog output V proportional to the reciprocal of the subject distance t is generated at the output terminal C as shown in FIG. 8g6. When the analog output v1 is greater than or equal to the base value Vcom, the output of the comparator 32 becomes H level, and upon receiving this, the control circuit 20 ends the first ranging operation. The reference value Vcom is used to switch distance measurement based on characteristics A and B shown in FIG. 2, and is set to a value slightly larger than 1.

That is, during the first distance measuring operation, the solid line portion of the analog output v1 is conveniently used as the distance signal. At this time, since the terminal is at H level, AND e -) 38b, 38
d and 38f become non-conductive, and of the outputs of the A/D converter 35, only the outputs of the comparators 35h+35c and 35e+35g are supplied to the lens drive circuit as the A/Di conversion f of the distance signal.

When the analog output V becomes less than the reference value V com.

The output of the comparator 32 becomes L level, and the control circuit 20 turns off the transistor 21 and ends the first distance measurement operation.
In order to start the 20th distance measuring operation after a certain period of time, the terminal is set to L level. Thereby, electrode B is connected to operational amplifier 29 via resistor 6. Then, after a certain period of time, the transistor 21 is turned on to emit IREDlt-light. The photocurrent of PSD 5 due to the reflected light from the subject is:
The PSD 5 and the resistor 6 divide the current into electrodes A and B depending on the incident position on the newly constructed PSD equivalent element. Flowing,.

The signal 2 is converted into a current/voltage in a similar manner, filtered, and input to the signal processing circuit 3. At this time, an analog output v2 as shown in FIG. 6 is obtained from the signal processing circuit 31. At this time, terminal D [is at L level, so A
ND? '-) 38 m, 38 c, 38
e.

38g is not conductive, and among the outputs of the A/D converter 35, only the outputs of the comparators 35b, 35d, and 35f are supplied to the lens drive circuit as A/D converted values of distance signals.

As explained above, according to the first embodiment, in the subject distance range where the analog output v1 in the tenth distance measuring operation is equal to or higher than the reference value Vcom, the terminal voltage does not reach H level, and the sixth distance measuring operation does not reach the H level.
The solid line portion of the analog output V in the figure is used as the subject distance signal. When the analog output V, becomes less than the reference value v com, the terminal becomes L level, a resistor is connected in series to the PSD, a second distance measurement operation is performed, and the solid line part of the analog output v2 in Fig. 6 is Used as a subject distance signal. In this way, it is possible to distinguish whether the distance measurement result is the analog output v1 or v2 depending on whether the terminal is at the H level or the L level.

Note that in this embodiment, the size of the image reflected by the subject 3 and formed on the PSD j by the light-receiving lens 4 is assumed to be a point, but in reality, the size of the image Vi is a certain finite size. Therefore, in Fig. 1, the light receiving lens 4
The best solution is to move the PSD 5 to the left by a length corresponding to the radius of the spot image with respect to the optical axis. In this case, it is easy to align the center of the PSD equivalent element newly constructed by the resistor 6 and PSD 5 with the optical axis of the light receiving lens 4.

Also, 1st. Although the second distance measuring operation is switched based on I, /I2, the present invention is not limited thereto, and may be switched according to the object distance, for example, according to I, +I. That is, I and Earthwork 2 affect the amount of light received by the PSD 5, and when the subject is far away, the amount of light received is small, and as the subject is closer, the amount of light received increases.

〔Effect of the invention〕

As explained above, according to the present invention, by shifting the center of the PSD from the optical axis of the light-receiving lens to the side opposite to the IRED, the closest distance i that can be measured can be shortened, and Selectively connect a resistor to PSD using
By changing the characteristics of the ratio of the output signals, a distance measuring device that can always perform highly accurate distance measurement is provided.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of an optical system of one embodiment of a distance measuring device according to the present invention, and Fig. 2 shows the P when the changeover switch shown in Fig. 1 is switched.
A diagram showing changes in the output characteristics of the SD, Figure 3 (a) e (
b) is a circuit diagram showing a PSD equivalent element in which a resistor is connected in series with the PSD, Fig. 4 is a diagram showing the change in characteristics when noise is added to the characteristics in Fig. 2, and Fig. 5 is an example of this implementation. A concrete block diagram of the example, FIG. 6 is a diagram showing the characteristics of the ranging signal of the ranging device shown in FIG. 5, and FIG. 7 is a diagram showing the optical system of a conventional example of the nine ranging devices using PSD. 8 are diagrams showing the characteristics of a distance measurement signal in a conventional example. 1... Infrared light emitting element (IRED), 2... Lens for light projection. 3... Subject, 4... Light receiving lens, 5... Position detection element (PSD), 6... Resistor, 10... Changeover switch, 11... Signal processing circuit, 20... Control circuit, 23.24...Analog switch, 26.29.
...Operation amplifier, 27.30...Filter circuit, 31
...Division circuit, 32...Comparator. Applicant's representative Patent attorney Uki Tsuboi Figure 3 Figure 4

Claims (4)

[Claims] (1) A means for projecting a light beam onto an object; and a means for projecting a light beam arranged at a distance from the light beam projection means by a baseline length, receiving reflected light from the object, and having a ratio according to the receiving position of the reflected light. In a distance measuring device that includes a position detection means that outputs a signal and measures the distance to an object based on the ratio of the two signals, the position detection means has a light receiving section whose center is aligned with the optical axis of the light receiving lens. A distance measuring device comprising means for selectively connecting a resistor to at least one output terminal of the position detecting means, the distance measuring device being arranged to be offset from the light beam projecting means on a side opposite to the light beam projecting means. (2) The distance measuring device according to claim 1, wherein the resistor is connected when the object is farther than a predetermined distance. (3) The distance measurement according to claim 1 or 2, wherein the position detecting means is arranged such that one end of the light receiving portion thereof is aligned with the optical axis of the light receiving lens. Device. (4) The distance measuring device according to any one of claims 1 to 3, wherein the resistance value of the resistor is equal to the resistance value of the light receiving section of the position detection means.