JPS5960426A - Range finder of camera - Google Patents

Abstract

PURPOSE:To prevent an overcurrent to a light projecting element and circuits even when a subject is at infinite distance or has a low coefficient of reflection by providing a control circuit which controls a projected light output with a limiting means which limits the output of a light projecting means so that the output value does not exceeds an upper limit value. CONSTITUTION:When the output -Q of an RSFF6 goes up to a high level, transistor TRs 7 and 8 turn on and a capacitor C11 is discharged through a resistance R19; and a voltage applied to an IR photodiode rises gradually and turns on an AC basis synchronously with a CLK. An OP Amp operates as a constant voltage circuit together with TRs 13-15. Reflected light from a subject is incident to a semiconductor position detector 21 and IA and IB from electrodes A and B are inputted to switches 36 and 37 through OP Amps 24 and 25, frequency selecting circuits 26 and 27, etc., to calculate integral values VA and VB. Then, the output of the diode is increased by the sum signal and compared by a comparator 58 with VR1; when it is greater than VR1, an FF6 is set to prevent the overcurrent.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a distance measuring device that obtains distance information by projecting light from the camera body side and receiving the rapidly emitted light.

Conventionally, a light emitting element and a light receiving element are provided separated by a predetermined distance (baseline length), and the direction of the light emitting element or the light receiving element is changed in conjunction with the movement of the photographic lens, and the output of the light receiving element is adjusted according to the subject distance. Active type distance measuring devices are widely known in which the movement of the photographing lens is stopped when the peak value is reached, and a focusing operation is performed.

However, the active method requires a mechanism to change the direction of the light emitting element or light receiving element, and the distance measurement operation is performed simultaneously with the movement of the photographic lens, so it is not possible to know the distance information in advance before the release operation. Can not.

Furthermore, special measures are required for prefocus photography, which measures the distance of an arbitrary object within the viewfinder field frame before the release operation. In addition, as an automatic focus control device capable of prefocusing, a double-coupling system using a charge-coupled device is also known, but the charge-coupled device is expensive in this double-coupling system. (The processing arithmetic circuit is also complicated, making it unsuitable for small compact cameras.

Therefore, it is possible to obtain a distance signal from a difference signal between two outputs of a semiconductor device detector using a light emitting element.
This is proposed in Japanese Patent No. 44809. In this proposal, in order to make the difference signal correspond accurately to the distance signal,
Pulse modulation is applied to the light projecting element using the sum signal of the two outputs, and the output of the light projecting element is feedback-controlled so that the sum signal of the two outputs is always constant regardless of the distance to the object to be measured.

However, when using such a proposal as a distance measuring device for a camera, it is difficult to project light when the distance to the subject is far and the photographic lens is at the infinity end, or when the reflectance from the subject is low. There were problems in that the output of the element became excessive, the current consumption increased, and the light emitting element and the light emitting control circuit were destroyed.

SUMMARY OF THE INVENTION An object of the present invention is to provide a distance measuring device for a camera that can solve the above-mentioned problems and prevent an increase in current consumption and damage to a light projecting means and a light projecting control circuit. .

In order to achieve this object, the present invention is characterized in that a control circuit for controlling the output of the light projecting means is provided with a limit means for limiting the output of the light projecting means so that it does not exceed an upper limit value.

Hereinafter, the present invention will be explained in detail based on illustrated embodiments.

1 and 2 show a circuit diagram and a semiconductor device detector showing an embodiment of the present invention. 1 is the power battery, 2 is the power switch,
3 is a single pulse generation circuit that generates a single pulse power-up clear signal PUC when the power switch 2 is turned on; 4 is a constant voltage generation circuit that generates constant voltages KVC and VC;
5 is a clock generation circuit that generates a clock pulse CLK; 6 is an RSS free lag flop; 8 is a transistor;
9. 10 is a voltage dividing resistor, 11 is a time constant capacitor, 12 is an operational amplifier, 13 is a transistor, 14 and 15 are voltage dividing resistors, and 16 is a transistor, which is turned on and off by inputting the clock pulse CLK (K). In return, the infrared light emitting diode 17 is turned on with alternating current.
20 is a light receiving lens; 21 is a light receiving surface 22; and a semiconductor device detector having electrodes A and B (details will be described later); 23 is connected to the semiconductor device detector 21; This is a bias power supply.

Reference numerals 24 and 25 designate operational amplifiers, each of which has its inverting input terminal connected to electrode A1 and electrode B of the semiconductor device detector 21, and its non-inverting input terminal receiving a constant voltage VC. 26.
27 is a frequency selection circuit that constitutes a no-pass filter together with operational amplifiers 24 and 25; 28, 29, and 30 are resistors;
31 is an operational amplifier, 32, 33, 34 is a resistor, 35 is an operational amplifier, 36, 37 is an analog switch, 38 is an integration circuit composed of a resistor 39 and a capacitor 40, 41 is composed of a resistor 42 and a canister 43. Integrating circuit,
44.45 is an operational amplifier that amplifies the signal integrated by the integrating circuit 38.41 and outputs a signal voltage ■ and a signal voltage ■, respectively; 46 is composed of resistors 47, 48, 49, 50, and an operational amplifier 51. The subtraction circuit outputs a difference signal (V, -Vs) between the signal voltages (2) and (2). 5
Reference numeral 2 denotes an adder circuit composed of resistors 53, 54, 55, 56 and an operational amplifier 57, which outputs a sum signal (■, +■) of the signal voltage ■ and the signal voltage η. Difference signal (M, -V,)
, the sum signal (VA0V,) is a tonal proportional to the difference and sum of the signal currents 6 and II1 of the semiconductor device detector 21, respectively. 58 is a comparator, the inverting input terminal receives the reference level ■1 of the reference level generator 59 (set by a constant voltage KVC and a potentiometer), and the non-inverting input terminal receives the sum signal (V, +V) from the adder circuit 52. , ) are input respectively.

60 is a latch circuit that is latched when the RS flip-flop 6 is set, 61 is an inverter, and 62 is a comparator.The reference level generator 630 has a reference level at its inverting input terminal, and a timer at its non-inverting input terminal. The voltage is input to the charging of the constant capacitor 11. 64 is an AND gate, which opens when a high level signal is input from the inverter 61 and the converter 62, and outputs the infinite end signal i.
NFNT is output.

Next, the operation will be explained. First, the operation of the semiconductor device detector 21 shown in FIG. 2 will be explained. The semiconductor device detector 21 is biased by a power source 23 for noise, and when light is incident on the light receiving surface 22, it generates a photocurrent I according to the amount of incident light, and converts this photocurrent ■ into two signals. The current is divided into 4 and IB (1.+I□=I) and output from electrodes A and B. That is, the signal current IA,
will undergo contradictory changes depending on the incident angle of the reflected light.

Now, calculate the distance between electrodes A and B of the semiconductor device detector 21,
If the distance from electrode A to the light receiving point is X, the light receiving surface 22
Since is a uniform resistor, there is a relationship of ■O=Work ×. Therefore, the signal current IA, 1. distance
(that is, the position of the light receiving point), and according to this distance X, the distance X to the subject can be measured based on the principle of triangulation. That is, IA-11=I-2I.

Therefore, by controlling the photocurrent I (= 1.+1.) constant, 1. -1. The absolute value of can be associated with the distance.

The first stroke of the release button on the camera body causes
When the power switch 2 is turned on, a power-up clear signal PUC is generated from the single pulse generation circuit 3, the RS flip-flop 6 is reset, and the output of the output terminal Q is inverted to the NO level. Further, the constant voltage generation circuit 4 generates two constant voltages VC, KVC, (KVC>■e), and the clock generation circuit 5 generates a voltage of several tens of KHz.
Clock pulses CI, K are generated. When the output of the output terminal Q of the RS flip-flop 6 is inverted to a no-y level, the transistor 7 is turned on, and at the same time, the transistor 8 is also turned on, and the time-setting capacitor 11 is charged via the resistor 9. The input level at the non-inverting input terminal of the operational amplifier 12 gradually increases by 1°C, and by turning on the transistor 13, the voltage applied to the infrared light emitting diode 17 also rises by 1. The light emitting output increases.The transistor 16 is turned on and off repeatedly by the clock pulse CLK, so the infrared light emitting diode 17 performs AC lighting in synchronization with the clock pulse CLK.Also, the voltage dividing resistor 14.150 min. Since the pressure point is connected to the inverting input terminal of operational amplifier 120, operational amplifier 1
2 works as a constant voltage circuit together with transistor 13 and voltage dividing resistors 14 and 15.

The light emission output from the infrared light emitting diode 17 is transmitted through the light emission lens 1.
8, the light is projected onto the object 19, and the reflected light passes through the light receiving lens 20 and reaches the light receiving surface 22 of the semiconductor detector 2.
01 point.

Depending on the angle of incidence, signal currents IA, 1. can be obtained respectively. Each signal current IA,
1. are operational amplifiers 24.25 and frequency selection circuits 26.
27, only high frequency components are selected and amplified. The two outputs are further amplified by resistors 28 to 30 and operational amplifier 31, and resistors 32 to 34 and operational amplifier 35, and are input to analog switches 36 and 37, respectively. In the analog switch 36.37, the instantaneous value of the output of the operational amplifier 31.35 is detected in synchronization with the blinking cycle of the infrared light emitting diode 17 by inputting the clock pulse CLK, and the value is held and integrated. circuit 38
．． 41 respectively. The two inputs are integrated by the integrating circuits 38 and 41, and the integrated values are passed through an operational amplifier 44 to a subtraction circuit 46 as a signal voltage ■, and through an operational amplifier 45 to an addition circuit 52 as a signal voltage ■. Output.

Here, the resistance values R47 to Rs of each of the resistors 47 to 50, which constitute a part of the subtraction circuit 46 and the addition circuit 52, and 53 to 56 are
The following relational expression is established between Rss and R56.

Therefore, the difference signal (VA-V,) from the subtraction circuit 46 is
The adder circuit 52 outputs a sum signal (VA+■), respectively. The sum signal (V, +V,) from the adder circuit 52 is
The infrared light emitting diode 170 increases in accordance with the rise in the light emitting output, and the comparator 58 causes the reference level generator 5 to increase.
9, the output of the comparator 58 is inverted to high level, and the tS flip-flop 6 is set. Therefore, the output of its output terminal Q becomes low. The transistor 7 and the transistor 8 are turned off, charging of the time-limiting capacitor 11 is stopped, and the operational amplifier 12 is inverted.
The increase in the output of the infrared light emitting diode 170 also stops, and the increase in the light emitting output of the infrared light emitting diode 170 also stops.

Moreover, when the It_S free lag flop 6 is set,
The output of the output terminal Q is inverted to high level, and the latch circuit 6
0, the difference signal from the subtraction circuit 46 at that time (
VA-V,) is latched.

Therefore, the difference signal (V, -■) is the phase signal (■+V11
) reaches a predetermined value, and according to the principle described above, it corresponds accurately to the subject distance. Needless to say, it is easy to display the distance using the difference signal (■-V) using the conventional technology.

Next, a case where the subject 19 is located near infinity will be described. When the subject 19 is far away, the reflectance of the reflected light from the subject 19 is low, so the sum signal (VA+V
l) hardly increases despite the increase in the light output from the infrared light emitting diode 17. Therefore, the output of the comparator 58 does not easily invert to high level, and R
Since the SS free-lag flop is also not set, charging of the time-fixing capacitor 11 continues.

The charge level of this time-fixing capacitor 11 is determined by the voltage dividing resistor 9.
Since the potential does not exceed the upper limit value, which is the potential of the 100 voltage division point, when the charge level of the time-fixing capacitor 11 reaches the upper limit value, the light emitting output of the infrared light emitting diode 17 does not increase.
will be restricted. At the same time, the output of the comparator 62 is inverted to high level, and since the output of the comparator 58 is low level, it is inverted by the inverter 61 and becomes high level, so the AND gate 64 is opened and the infinite end signal is 1 NFNT is output 1, furthermore,
A reference level generator 6 is connected to the inverting input terminal of the comparator 62.
This reference level VB2 is set slightly lower than the upper limit value set by the voltage dividing resistor 9.10.

The voltage dividing ratio of the voltage dividing resistors 9 and 1O in this embodiment is appropriately set based on the maximum rated power of the infrared light emitting diode 17, the driving ability of its control circuit, and the like. Also, comparator 5
The reference level input to the inverting input terminal of 8 is determined by the hyperfocal distance of the camera to which the present invention is applied, the standard reflectance of the subject, the amplification degree of each operational amplifier shown in FIG. It is set appropriately in consideration of sensitivity and the like.

In other words, at the maximum light emitting output of the infrared light emitting diode 17,
According to Honjitsu, the output of the comparator 58 is set so as not to be reversed for the subject 19 of standard reflectance located within the hyperfocal distance range, and the consumption is It is possible to prevent the control circuit including the infrared light emitting diode 17, the transistor 13, etc. from being destroyed due to an increase in current. Furthermore, when the limit means operates and the sum signal (VA+vll) does not reach the reference level VRI, the infinite far end signal iNFNT can be output. Furthermore, since the infrared light emitting diode 17 is turned on with alternating current and the output of the semiconductor device detector 21 is synchronously detected by the analog switches 36 and 37, the influence of background light on the semiconductor device detector 21 can be removed. .

In this embodiment, the infrared light emitting diode 17 corresponds to the light projecting means, the semiconductor device detector 21 corresponds to the light receiving means,
The subtraction circuit 50 and the latch circuit 60 constitute an example of distance information detection means, and the circuit including the R87 lip-flop 6 or the transistor 16, the addition circuit 52, the comparator 58,
The reference level generator 59 constitutes an example of a control circuit, and the voltage dividing resistor 9.10 constitutes an example of the limiting means of the present invention.

In this embodiment, a semiconductor device detector 21 is used, but
The invention is not limited to this, and it is also easy to use two light receiving elements. The two light-receiving elements are arranged at positions where their outputs change in opposite ways depending on the incident angle of the light reflected from the subject 19.

At this time, the outputs from the two light receiving elements may be connected to the inverting input terminals of the operational amplifiers 24 and 250, respectively.

In addition, in this example, the signal ′[ of the semiconductor device detector 21
ni fluent ■. is converted into signal voltages ■ and ■, and the sum signal (V
A+V, ), difference signal (VA-■) is generated, but the signal current is directly generated from sum signal (1, +I, l),
A difference signal (1, -1,) may be generated.

As described above, according to the present invention, the limit means for limiting the output of the light projecting means from exceeding the upper limit value is provided in the control circuit that controls the output direction of the light projecting means, so that current consumption increases. However, the light projecting means and the light projecting control circuit can be prevented from being destroyed.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, and Fig. 2 is a circuit diagram showing an embodiment of the present invention.
It is a figure which shows the semiconductor device detector in a figure. ■...-Power supply battery, 3...Single pulse generation circuit, 5.
... Clock generation circuit, 6... RS flip-flop 02, 9.10... Voltage dividing resistor, 11... Time-fixing capacitor, 17... Infrared light emitting diode, 19... Subject, 21 --- Semiconductor device detector, 38.41 --- Integrating circuit, 44.45 --- Operational amplifier, 46 --- Subtraction circuit, 52 --- Adding circuit, 58 --- Comparator, 5
9...Reference level generator, 6o...Latch circuit, ■
・-・Photocurrent, ■■１・-Signal current, ■, L...Signal voltage, VnIs VB2-"Reference level, CLK-・
- CI Fookles, PUC...Power up clear signal, iNFNT:...Infinity End No. 411. Patent applicant Minoru Nakamura, Canon Co., Ltd. agent

Claims (1)

[Claims] 1. A light projector that projects light onto the subject, a light receiver that changes two outputs contradictoryly depending on the angle of incidence of the reflected light from the subject, and a direct or indirect sum of the two outputs of the light receiver. A control circuit that controls the output of the light projecting means so that the output becomes a predetermined value, and a distance information detection that obtains the difference between the two outputs of the light receiving means as distance information when the sum of the two outputs of the light receiving means is a predetermined value. In a camera heat output measuring device comprising:
A distance measuring device for a camera, characterized in that the control circuit is provided with a limit means for limiting the output of the light projecting means so that it does not exceed an upper limit value.