JPS6138584A - Detector for light projection signal - Google Patents

Abstract

PURPOSE:To detect a reflected light from an object with a high precision even if a quantity of ambient light is varied, by alternating a projection-nonprojection cycle and the nonprojection-projection cycle of a light projecting means by a light projection control means. CONSTITUTION:A control pulse CF2 controls a projected luminous flux, and the high level indicates the light projection state, and the low level indicates the nonprojection state. An ambient light quantity PA2 changing with time indicates that the quantity of ambient light is constant with respect to time, and period from a time t20 to a time t21 is a projection section, and the period from the time t21 to a time t22 is a nonprojection section, and the period from the time t22 to a time t23 is a nonprojection section, and the period from the time t23 to a time t24 is a projection section. Since the projection-nonprojection cycle, and the nonprojection-projection cycle are alternated in this manner, a true light projection signal as the difference between an integral signal for projection and that for nonprojection is detected with a high precision when the quantity of ambient light is not only constant but also varied as shown by PD2. Thus, the drift of an output signal ID2 at times t22 and t24-t27 is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light projection signal detection device [@], and in particular to a light projection signal detection device that can project a luminous flux from a light projecting means toward an object and detect the reflected light from the object with high precision. This relates to device K. Furthermore, the present invention is applicable to a focus detection device in a camera such as a photographic camera or a video camera, which projects light from a light projecting means on the camera side toward an object side and performs focus detection using reflected light from the object. The present invention relates to a light projection signal detection device suitable for.

Conventionally, in order to project light onto an object 1RII and detect the reflected light from the object, for example, the projecting light is modulated and the output of the photoelectric conversion element of the light receiving means is amplified by AC, and then the output is converted into a signal for a certain period of time. We are trying to improve the VN ratio. However, this method requires complicated signal processing circuits and
Since noise is introduced during C amplification, accurate detection is difficult when the reflected light is weak.

The applicant first converted i+tt light from an object into 41'j li
For good detection, the light generated in the photoelectric conversion element ``L'J i
A light projection signal detection device was proposed in Japanese Patent Application No. 16362/1983, which allows for the direct integration of /lt+. This device integrates the output signal from the light receiving means with opposite polarity when the light emitting means emits light and when it does not emit light (7). Based on this integration result, noise due to ambient light (i" A signal based only on the luminous flux from the optical means, i.e., a true light projection signal, is detected.

However, if the surrounding scene changes with the time 1jl, the difference in the light t;: when the light is emitted and when the light is not emitted becomes an error in detecting the true light emitting signal.

Therefore, with the above method, it is difficult to detect the true light emitting signal with good accuracy when there are many fluctuations in the amount of ambient light or when the amount of reflected light from an object is small. It is an object of the present invention to provide a light projection IJ number detection device capable of detecting reflected light from an object with good viscosity even if the viscosity varies. A further object of the present invention is to provide a light emitting unit suitable for a focus detection device I'1 of a camera, etc., which can detect the entire light emitting signal of an object even if the reflected light from an object is weak. :Providing the No. 1 detection device. In order to achieve the object of the present invention, the main features of the light projection signal detection device include a light projection means for projecting light toward an object, and a projection device that periodically repeats light projection and non-projection of light by the light projection means. A light control means, a light receiving means for receiving the reflected light from the object side and generating a light emitter signal and a non-emitter signal, and an iJQ light emitter and a light emitter control means, which are generated by the front self-receiving means; In a light projection signal detection device having an integrating means for integrating a non-light projection signal, the light projection control means alternately operates a light projection-non-light projection period and a non-light projection-light projection period of the light projection means. That's true.

In this way, the present invention makes it possible to accurately detect a true light projection signal even if the amount of ambient light changes. In order to better achieve the object of the present invention, the integrating means integrates the light emitting signal and the non-light emitting signal with opposite polarities, and detects the true light emitting signal based on the output from the integrating means. It is preferable to do so.

Next, one embodiment f+'1J of the present invention will be explained with reference to each drawing.

First, FIG. 1 shows a schematic diagram of a conventional light projection signal detection device when detecting a light projection signal. - In the figure, CFI is 1 for controlling the projected light flux 'x 1iilJ from the projecting means.
When the control pulse is at a high level, it indicates a light emitting state, and when it is at a low level, it indicates a non-light emitting state.

PAL indicates the amount of light when the ambient light is constant over time. Next, the influence of ambient light in the projection state and the non-projection state will be described. Time t10 ``'''' 1 □ 0 The period corresponding to the illumination condition is reached, and if it is lined up, an integral signal IAI based on the @quaternary is generated below. In the corresponding interval 89, an integral signal IAI based on the surrounding pt is generated above the sequence, that is, at time 11°-10
If the amount of ambient light is constant between 2 and 2, the 4λ signal in the light emission section and the non-light emission section will be the same, and if it is enclosed, the integral due to the ambient light during light emission and non-light emission (i74+ with opposite polarity) 6j, the influence of ambient light can be removed at time t-2. Therefore, to find the difference signal between light emission and non-light emission when r=1 at time 11o-102, it is true. 1g of '
You will get the number.

If the amount of ambient light is kept constant over time in this way, the drift of integral No. 16 IAI due to ambient light will be zero. This means that the subsequent time jx3 + L4. The same applies to t-work, . . . . Therefore, the true light projection signal is correctly detected.

Next, when the amount of ambient light changes over time as shown by PBI and PCI in the figure, the integral of the amount of ambient light in the light projection section and the non-light projection section will be different. Therefore, the integral signal IBI
, ICI is integrated at time t and 2 even if it is integrated with opposite polarity as mentioned above.
Then, at time t□4, the integral value v, the phase
An error will occur by the amount that corresponds.

The light emitting signal detection device of the present invention alternately operates the light emitting-non-emitting cycle and the non-emitting-light emitting cycle of the light projecting means, thereby detecting the true light emitting signal due to fluctuations in the ambient light area. This is to minimize the amount of

FIG. 2 shows an explanatory diagram for explaining the principle of the light projection signal detection device of the present invention. In the figure, CF2 is a control pulse for controlling the emitted light flux of the light emitting means, and as in Fig. 1, when it is at a high level, it is in the light emitting state, and when it is at a low level, it is in the non-emitting state. shows.

PA2 indicates a state in which the ambient light is constant over time, and at time t2
0 "" t2□ is a light projection section, time t2□ to t2□ is a non-light projection section, time t2□ to t23 is a non-light projection section, time t2
3 to t24 is the light projection section. As described above, according to the present invention, as shown in FIG.
By alternating the light projection period, when the amount of ambient light is constant, the amount of ambient light can be reduced to V! +1 is PD2
Even if the signal changes as shown in FIG. 251
Doria)k of output signal ID2 at t26 and t27
IBI and ICI shown in FIG. 1 can be significantly smaller than IBI and ICI.

Next, an embodiment in which the present invention is applied to a focus detection device such as a camera will be described with reference to each drawing.

Figures 3 (&), (b), and (e) are explanatory diagrams of the detection principle when the present invention is applied to a focus detection device such as a camera. In this figure, SA and SR represent light reflected from an object. The charging conversion element SP constituting the light receiving means for detection is a reflected light spot formed when a light projecting means (not shown) projects a luminous flux toward the object, and the reflected light spot SP is reflected by an objective lens (not shown). For example, in a camera, the photographing lens)
It moves left and right in the figure depending on the focal state of the image. In addition,
The configuration for moving the reflected light spot 5P in this manner is well known from, for example, Japanese Patent Laid-Open Nos. 54-151829 and 1982-155832, and therefore the description thereof will be omitted here. Based on photoelectric conversion elements SA and SB
Reflected light spora when the i1 objective lens is in the normal state) It is provided with the center of SP as the boundary. Figure 3 (
a) is the photoelectric conversion element S when the objective lens is in focus
The relationship between A, 8B and the reflected light spot SP is shown.

A, B are reflected light spora) SP K is the output amount of the true light emitting signal generated in each of the two photoelectric conversion elements SA, SB, A, B are the ambient light OO. , 8B conceptually shows the output Jl generated in each of the photoelectric conversion elements SA and SB.
0), (B+B0) are obtained, and the output amounts A and B are obtained when the light is not emitted.
0 is obtained. In the present invention, the output amount (A+A0) held in each of the first and second integrating means (not shown), (
B180) directly through differential circuit 0 to output amount A0.
By subtracting Bo'i, the output quantities A and B as shown in FIG. 3(b) are obtained. Therefore, the sum of the output amounts A and B when light emission and non-light emission are repeated periodically ΣA
, ΣB are also held in each of the first and second integrating means.

In the present invention, the focal state of the objective lens is determined using the sums ΣA and ΣB. That is, as shown in FIG. 3(c)K,
Focus when Σperson-ΣB, front focus when SA>ΣB, SA
When ΣB, it is determined that it is the rear bin.

At this time, it is preferable to keep Σλ+ΣB at a constant value of 1 because the inclination of ΣA-ΣB near the in-focus position can be made substantially constant, and the focusing accuracy can always be kept constant.

FIG. 4 shows an embodiment of a signal processing circuit when the present invention is applied to a focus detection device.
SB is a silicon/photodiode which becomes the photoelectric conversion element mentioned above, LD is a light emitting element which becomes a light projecting means, CA, C
B is a capacitor serving as the first and second integrating means, AG
I-AC3 and BGI to BG4 d These are analog gates that form a differential circuit. The light emitting element LD is connected to a power source (not shown) via a resistor R1, and grounded via a transistor Tri. Therefore, clock pulse φI
Transistor Tr is connected to RK through Tabassa amplifier BA
By turning on and off i, the light emitting element LD emits modulated light and projects light onto the object OB. Conversion element S to light '1
One end of A, SB is an analog gate AGI, BG
A
It is connected to the inverting inputs of operational amplifiers MA, MB with high input impedance via C3 and BO2. Also,
The other end of each is connected to the inverting inputs VC of the amplifiers MA and MB via analog terminals AC3 and BO2, and is grounded via analog terminals AC3 and BO3. The non-inverting inputs of operational amplifiers MA and MB are grounded. Capacitor CA, C
B is provided in the negative feedback path of operational amplifiers MA and MB. AC3, BO2 are capacitors〇A, C
An analog gate provided in parallel with B and a signal φ.

is turned on by Both RAI and RBI have resistor tubes of R, and +(xA +JR) is output at the connection point between them. Next, resistors RA2, RA3, RB
2.

RB3 and operational amplifier BP constitute a differential amplifier circuit,
(Σto-ΣB) occurs at its output.

O20 is an oscillator that generates clock pulses, DIV is a frequency divider that divides the clock pulse, and RFI is a frequency divider D.
The output of IV is connected to the T input, and DFi is a D-type 7 flip-flop that latches the output of the comparator CP.IN1 to IN4 are inverters, and ON1 to ON4 are synchronized with the rising edge of the input pulse. One-shot circuit, OR gate, AN1 to AN
2 is an AND gate, RCl is a pull-up resistor, and these circuits generate control pulses φC, φIR2φ8.

φE and sample hold circuit SHI, 5) I2
control. The photographic lens control circuit CKT controls the photographic lens in a well-known manner based on the outputs of the sample and hold circuits SHI and SR2.Using this principle, the operation of the nine-lens array is shown in FIG. I will explain using FIG. 5 shows each signal φIR'φ. , φ□, and φ8, and a timing chart of the main parts of FIG. 4.

As is clear from the figure, φ8 has the same waveform as the clock pulse φIR in the effective integration period, and φA has the same waveform as the clock pulse φIR. That is, when φA is at a high level, l
If φB is low level, and if φA is low level, φ
B is a high level.

In FIG. 5, time t. When the normally open focus detection switch SWI shown in FIG. 4 is turned on, the frequency divider D is turned on at time t.
In synchronization with the rising edge of Iv, R8T flip 7q
The Tsubu RFI is set, so it's one-shot) times m
A one-shot pulse is generated from ONI, and capacitors CA and CB are connected to analog gates AG5 and BO2.
is reset via . After that, at time t2, which is between time t0 and I3, when φC is inverted to the low level side at the same time as ON1 is inverted to the low level side, the analog gate AGE is activated.

Since BO2 is turned off, capacitors CA and CB
starts integrating the photocurrent generated in the photoelectric conversion elements SA and SB.

Between R time tz and t3, φIR is inverted, so the light emitting element LD lights up and the photoelectric conversion element SA,
Reflected light from an object due to light projection and ambient light enter the SR. At this time, φ.

becomes high level AC3, AC4, BO2, BO2
turns on and the corresponding photocurrents i(A+A0), (B+B,
) is integrated by capacitors CA and CB K.

During time t-I4, φIR remains at a low level, so the light emitting element LDa is turned off and only ambient light enters the photoelectric conversion elements SA and SRK.

During this time, since φA is at a high level, the analog games AGI, AC2, BGI, and 13G2 are turned on, and the corresponding photocurrents taA and lBo are divided into four and six parts by the capacitors CA and CB.

Therefore, at time t4, the following photocurrents are integrated between t2 and t3 and are integrated between the photocurrent amounts (A+A0) and (B+B0) and 1 -1.
, 34
.

That is, the difference in light intensity depends on the ratio of reflected light generated by light projection and incident on the photoelectric conversion elements SA and 8B. Flow rate A, B
are held in capacitors CA and CB, respectively.

Next, during time t "" ts, the signal generated from the photoelectric conversion element when not emitting light is integrated, and between time t5 and t6, the signal from the photoelectric conversion element when emitting light is integrated in the opposite direction. This makes it possible to minimize errors caused by fluctuations in ambient light.

If the light-emitting element LD is periodically turned off and on in accordance with φIR, a true light emitting signal, that is, a photocurrent ff1AtBo)
Total jA, AB yyhtciHsu7 A/j
is generated at the respective output terminals of operational amplifiers MA and MB. − The sum of the true light emission signals ΣA and ΣB (ΣA + ΣB)
For example, if it reaches the reference level at time t8 and is 9, then
Since the comparator CP is inverted to the high level, the Q terminal of the flip-flop DPI is inverted to the high level side, and the one-shot ON2 is activated.

OH2 generates a one-shot pulse and inverter N
2, IN3, Antogame) ANI, ANZ
φ and φA are set to a low level via the input signal, and the acquisition of new signals is stopped.

Between times 1 and 19, the differential output from the operational amplifier BP (
ΣA-ΣB) f: is used to determine the focal state of the objective lens and move the objective lens in the focusing direction. Note that such control, that is, control that detects the focus state from the output difference (ΣA - ΣB) when the output sum (ΣA + ΣB) is constant, is as follows:
For example, it is well known in Japanese Patent Application Laid-Open No. 57-175904, so a detailed explanation thereof will be omitted.

Since the one-shot circuit ON4 generates a one-shot pulse between times 1 and 16, φc is inverted to high level and the analog signal is turned on (AC3 and BGS are turned on to clear the capacitors CA and CB. After that, the next pulse starts from time t6. Starts focus detection.

Note that time t. -1 construction. Based on the sum of the sums (Σλ + ΣB) and the difference between the sums (Σ - ΣB), the discrimination information is stored in the sample and hold circuit SHI until the next focus discrimination information is obtained.
, held in SB2.

As described above, according to the present invention, it is possible to achieve a light projection signal detection device that can accurately detect a light projection signal based on reflected light from an object even if the amount of ambient light changes over time.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of light emitting signal detection in a conventional light emitting signal detecting device, Fig. 2 is an explanatory diagram showing the principle of the light emitting signal detecting device of the present invention, and Figs. FIG. 2 is an explanatory diagram of an embodiment in which the invention is applied to a focus detection device such as a camera. In the figure, CFI and CF2 are control pulses, PAN and P
A2. PBi, PCI, PD2 are the amount of ambient light that changes with time, SA, SB are the photoelectric conversion elements, SP is the spora of reflected light), A, B are the output amounts from the photoelectric conversion elements SA, SR, respectively, when emitting light, A and B are O
O is the output amount from the photoelectric conversion elements SA and SB when no light is emitted. 1st note 3 Figure (C) Z bar ΣB position

Claims (2)

[Claims] (1) A light projection means for projecting light to the object side; a light projection control means for periodically repeatedly emitting and non-emitting light from the light projection means; and a light projection control means for receiving reflected light from the object side and projecting light. In the light emitting signal detection device, the light emitting signal detection device includes a light receiving means for generating a light emitting signal and a light emitting non-emitting signal, and an integrating means for integrating the light emitting and light emitting signals generated by the light receiving means in synchronization with the light emitting control means. A light projection signal detection device characterized in that a light control means alternately operates a light projection-non-light projection period and a non-light projection-light projection period of the light projection means. (2) The scope of the claim characterized in that the integrating means integrates the light emitting signal and the non-light emitting signal with opposite polarities, and detects the true light emitting signal based on the output from the integrating means. 1st
The light emitting signal detection device described in .