JPH07119883B2 - Optical projection type distance measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a light projection type distance measuring device, and more specifically, it projects continuous pulsed light such as infrared light onto a subject and reflects light from the subject. The present invention relates to a light projection type distance measuring device for measuring a subject distance based on the above.

[Prior Art] An autofocus (hereinafter abbreviated as AF) device applied to a still camera, a video camera or the like is roughly classified into two types. One is a passive method that uses the brightness distribution information of the subject, and the other is a so-called active method that has its own light projecting means and measures the distance by the reflected light of the projected signal. The active system has a high penetration rate due to its simple structure and low cost, but the biggest drawback is that the magnitude of the reflected light decreases as the subject distance increases, and the S /
Since the AF calculation becomes inaccurate due to the deterioration of the N ratio, the range that can be measured is limited to a relatively short distance.
In particular, for subjects that are said to be at infinity, such as landscapes where reflected light does not return at all, AF calculation will be performed only by the noise component in the circuit, but noise is generated randomly. Therefore, the farther the distance, the higher the possibility of erroneous distance measurement.

Therefore, conventionally, there has been proposed a means for judging the infinity by comparing the intensity of reflected light with a certain reference voltage (see JP-A-59-228212 and JP-A-60-244807). ).

[Problems to be Solved by the Invention] However, since the conventional infinity determination means performs comparison with a certain level, when the distance starts to be measured from a short distance and the object distance is gradually increased, Then the judgment of infinity is suddenly made. In other words, the AF result sometimes flew unnaturally from a certain distance. For this reason, when measuring a subject with low reflectance, for example, a black subject, the reflected light level is also reduced, and even at a short distance, it may be determined to be infinity, which may result in a so-called out-of-focus photograph. This was probably there.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an optical projection type distance measuring device capable of eliminating an erroneous distance measurement at infinity and performing a highly accurate AF operation.

[Means and Actions for Solving Problems] The present invention relates to a projection unit that projects distance measuring light onto a subject,
A light receiving unit that receives the reflected signal light from the subject and outputs two signals depending on the incident position of the reflected signal light, and a division calculation based on the two outputs of the light receiving unit are performed to calculate the subject distance. In a light projection type distance measuring device having an arithmetic circuit, the arithmetic circuit is provided with an input means for inputting a compensation signal irrelevant to an incident position on the light receiving means, and the compensation is performed when the subject is at infinity. It is characterized in that the operation result of the operation circuit is determined by the signal level.
When the amount of light incident on the light receiving means decreases, the distance measurement result is gradually changed to smoothly determine infinity.

[Example] Next, an example of the present invention will be described.

FIG. 2 is an AF (autofocus) to which the present invention is applied.
It is a block diagram which shows the structure of the principal part of a camera. This second
In the AF camera shown in the figure, the light emitted by the IRED1 is condensed by the light projecting lens 2 and irradiated toward the subject 3, and the reflected light is received by the light receiving lens 4 which is a well-known position detector (hereinafter referred to as a position detector) composed of a semiconductor element. , Abbreviated as PSD) 5. This PSD 5 has photocurrents I ₁ and I ₂ depending on its imaging position.
Are shunted, and the shunted photocurrents I ₁ and I ₂ are
Is supplied to. The AF IC 6 pulse-drives the IRED1 via the IRED controlling transistor 1A and also controls the PSD.
Distance measurement data based on photocurrents I ₁ and I ₂ from 5 is supplied to the CPU 7.

On the other hand, the light receiving element 8 for exposure control (hereinafter abbreviated as EE) that converts the brightness of the subject into an electric signal is combined with the IC 9 for EE to control the proper exposure. Further, the CPU 7 controls the sequence of the entire camera and also performs calculations for driving the shutter opening time and the focus adjustment lens. The output of the CPU 7 drives the motor 11 which is a power source for the shutter, film winding and lens extension by the driver 10.

Here, the operation principle of the infrared light projection type triangulation for measuring the object distance by the PSD 5 will be described. When the optical axis of the light receiving lens 4 is aligned with the center line of the PSD 5 and this is the origin, the incident position of the reflected light is x, the light projecting lens 2 and the light receiving lens 4
And the distance between the principal points, that is, the base line length is s, and the light receiving lens 4
Assuming that the focal length of is f ₀ , the subject distance l is given by l = s · f ₀ / x (1)

The photocurrents I ₁ and I ₂ generated by the PSD 5 due to the reflected light of the subject due to IRED ₁ are both proportional to the reflected light intensity, but the photocurrent ratio I ₁ /
I ₂ does not depend on the intensity of reflected light and is determined only by the incident light position x. If the total length of PSD5 is t, Becomes Substituting equation (1) into the above equation, Therefore, if the photocurrent I ₁ / I _{2 of} the SPD ₅ is obtained, the subject distance 1 is uniquely determined.

By the way, as is clear from the equation (2), the photocurrent
I ₁ and I ₂ are always in a relation of I ₁ > I ₂ . However, I ₁ / I ₂ = 1 only when l → ∞, but this is not possible because the reflected light itself does not return when the subject distance 1 is infinity.

Also, when performing AF calculation based on the above formula (2), if the calculation result is AFDATA, Becomes That is, theoretically, the larger the subject distance 1, the smaller the AFDATA. However, in reality, there is noise, so if this is I _N1 , I _N2 , As described above, since the noises I _N1 and I _N2 are generated at random, the influence of the noises I _N1 and I _N2 becomes dominant when the distance 1 increases and the photocurrents I ₁ and I ₂ decrease. That is, as the distance 1 increases, the inverse phenomenon that AFDATA increases depending on the noise generated at that time, contrary to the theory, may occur.

Therefore, when a compensating current I _c having a magnitude that satisfies the relationship of I _c > I _N1 and I _N2 is added to the numerator and denominator on the right side of the above formula (4), the calculation result AFDATA shown in the following formula (5) is obtained. ′ Is obtained.

In this formula (5), when I ₁ and I ₂ → 0, the calculation result AFDAT
A'will definitely be 1 or less, and the inversion phenomenon can be prevented and infinity compensation can be performed.

Further, when I ₁ and I ₂ >> 0 at a short distance, the relationship that is substantially the same as the theoretical value is maintained as in the expression (3).

Therefore, in this AF camera, by adding the compensation current I _c based on the above theory, the distance measurement accuracy in the long distance of the optical projection type distance measuring device using the PSD 5 is improved.

FIG. 1 shows the AF IC 6 in the AF camera shown in FIG.
3 is a block diagram of the electric circuit of FIG.

In FIG. ₁ , the photocurrents I ₁ and I ₂ from the PSD ₅ are applied to the voltage signals V ₁ and V ₂ , respectively, in the current-voltage conversion circuits 12 and 13 having low input impedance, that is, to the light intensity barycenter position of the incident light to the PSD 5. After being converted into a corresponding voltage, it is supplied to the channel changeover switches 14 and 15, respectively. The channel changeover switches 14 and 15 are each constituted by an analog switch or the like. The switch 14 is controlled directly, and the switch 15 is controlled by a channel changeover signal d from a channel changeover circuit 20 described later via an inverter 27. In accordance with the logic level of the channel switching signal d, either of the voltage signals V ₁ and V ₂ is time-divisionally divided into a bandpass filter (hereinafter referred to as BPF).
Abbreviated as 16). The BPF 16 selectively passes only certain frequency components. This frequency is the oscillation frequency of the oscillator 25, that is, the IRED drive circuit 26.
Is selected so as to have the same frequency as that of the drive pulse signal a for causing the IRED1 to emit continuous pulses through the. Therefore BP
In F16, the background light is removed from the photocurrent of the PSD 5, and the signal component obtained by photoelectrically converting only the reflected light from the subject 3 is selectively amplified and passed. The BPF 16 is provided with an offset adjusting resistor 30 which is a variable resistor. As will be described later, the offset voltage is applied by the offset adjusting resistor 30 so that the same effect as the application of the compensation current I _c can be obtained. The integration switch 17 is composed of an analog switch or the like, and supplies the filter output b of the BPF 16 to the integrator 18 in synchronization with the signal from the integration timing pulse circuit 28. Integral output of integrator 18
V ₁ is supplied to the inverting input terminal of the comparator 19. The reference voltage Vref is applied to the non-inverting input terminal of the comparator 19. The comparison output c of the comparator 19 is supplied to a channel switching circuit 20 composed of a D-type flip-flop or the like,
The channel changeover signal d output from 20 controls the channel changeover switches 14 and 15. The switching signal d is an AND gate 21 for controlling the input pulse of the positive integration counter 22 and an integration timing pulse circuit.
Also supplied to 28. Positive integration circuit counter 22
Is also a shift register, the channel switching signal d from the channel switching circuit 20 becomes "H" level, the gate 21 opens, and the synchronous integration at the time of positive integration when the channel switching switch 14 is turned on. It counts the number of times, and AF data is transferred from the built-in shift register to the CPU 7 shown in FIG. 2 after the AF operation is completed. Further, the total integration number counter 23 configured by a preset counter or the like counts the total number of synchronous integrations, that is, the timing pulse e from the integration timing pulse circuit 28, and terminates the AF processing when the set number is reached. An end signal is supplied to 24.

The operation of the present embodiment thus configured will be described with reference to the time chart of FIG.

FIG. 3 is a time chart of the signal waveform of the AF IC 6 in the distance measuring mode. The AF operation is started when the AF IC 6 receives the AF start signal and the basic clock signal from the CPU 7. The IRED1 starts pulse light emission driven by the pulse signal a having a duty ratio of 50% at 16 KHz, for example. Photocurrent I ₁ and I ₂ supplied from PSD5 that received the subject light
The output voltages V ₁ and V ₂ of the voltage conversion circuits 12 and 13 have waveforms as shown in FIG. 3, and the ratio of the peak values of these two voltage waveforms V ₁ and V ₂ is I ₁ / I ₂ described above. equal. When the AF start signal is received, the channel switching circuit 20, the positive integration counter 22 and the total integration counter 23 are reset. At this time, the channel switching signal d from the channel switching circuit 20
Is "L", the channel selection switch 14 is turned off and the switch 15 is turned on, so that the voltage V ₂ proportional to the photocurrent I ₂ is applied to the BPF 16. Therefore, first, the timing pulse e is sent from the integration timing pulse circuit 28 at a timing when it becomes "H" at approximately the center of "H" of the drive pulse signal a as shown in FIG. At this time, the output of the BPF 16 supplies the integrator 18 with a voltage proportional to the photocurrent I ₂ . Therefore, since the integrated output V _I of the integrator 18 is integrated at the positive peak b ₁ of the filter output signal b of the BPF 16, it is integrated in the negative direction, that is, inverse integrated.
It changes like V _I-1 , and this integration operation is repeated until it falls below the reference voltage Vref. The integrated output V _I is the reference voltage V ref
When it further decreases, the comparison output c of the comparator 19 changes from "L" to "H".
The channel switching signal d from the channel switching circuit 20 becomes "L" in synchronization with the falling edge of the timing pulse e _1.
To "H", this time change the channel selection switch 14
Turns on and the switch 15 turns off. Then, the voltage signal by the photocurrent I ₁ is input to the BPF 16 in place of the photocurrent I ₂ , but at this time, the integration timing pulse circuit 28 uses the timing pulse e as timing pulse e as compared with when the channel changeover switch 15 is turned on. , And outputs a timing pulse e _{2 obtained} by delaying the frequency of the IRED drive pulse signal a by a half cycle. Therefore,
Negative peak b of filter output signal b output from BPF16
_{Since the} integration is performed at ₂ , the integration is performed in the positive direction this time, that is, the positive integration is performed. Thus, every time the integrated output V _I exceeds the reference voltage Vref, signals proportional to the photocurrents I ₁ and I ₂ in the direction approaching the reference voltage Vref are integrated in the opposite directions.

Now, assuming that the total number of integrations is N ₀ , the relationship between the number of positive integrations N _S and the number of inverse integrations N _G is N ₀ = N _S + N _G (6). The relationship between the number of positive integrations N _S and the number of total integrations N ₀ is N _S = {I ₂ / (I ₁ + I ₂ )} N ₀ (7) Substituting the expression (2) in equation (7), and _{N S = (1/2-} s · f o / l · t) N 0 ...... (8). Therefore, since the total integration number N ₀ counted by the total integration number counter 23 is always kept constant by the termination circuit 24, the subject distance 1 is obtained from the positive integration number N _S counted by the positive integration number counter 22. .

The above operation is an AF operation in an ideal situation in which noise and electric circuit mismatch are ignored. Actually, as described above, since the distance measurement value causes an error as the distance increases, compensation for infinity will be described below.

Although the virtual compensation signal called the compensation current I _c has already been described, the noises I _N1 and I _N2 are actually minute currents of 100 pico-order, and the compensation current I _c is also injected in the same order. There is a need to. The larger the compensation current I _c is, the larger the compensation effect is, but this becomes an error at a short distance, so that it is better to be close to the order of the noises I _N1 and I _N2 . However, it is not easy to actually make a minute current of 100 pico-order.

Therefore, in the BPF 16 after the AF signal is amplified, the offset adjustment resistor 30 inputs a compensation signal in the form of an offset voltage. If the BPF 16 inputs a compensation signal of about 1 mV, it is possible to set the input-converted current value of the current-voltage conversion circuits 12 and 13 to 100 pico-order value.
Specifically, for example, if the current-voltage conversion rate of the current-voltage conversion circuits 12 and 13 is 2 MΩ and the gain of the BPF 16 is 5 times, 1 m
An offset voltage V _c of V as creating by adjusting the offset adjustment resistor 30, the offset voltage V _c Current - when converted to an input current signal of the voltage conversion circuit 12,13, 1mV / (2MΩ × 5 ) = 100 pA, and it can be seen that the same effect as when the compensation current I _c is input is obtained.

Next, a more specific electrical circuit configuration of the BPF 16, integration switch 17 and integrator 18 in FIG. 1 will be described with reference to FIG.

The BPF 16 includes an operational amplifier 31, the offset adjusting resistor 30, resistors 32 to 34, and a capacitor 35. That is, in the BPF 16, the inverting input terminal of the operational amplifier 31 having the offset adjusting resistor 30 is connected to the current-voltage conversion circuit 12, 1.
The output of 3 is input via the resistor 32 and the capacitor 36, and the reference voltage Vref is applied to the non-inverting input terminal. The reference voltage Vref is applied to the connection point between the resistor 32 and the capacitor 36 via the resistor 33. Further, this connection point is connected to the output terminal of the operational amplifier 31 via the capacitor 35, and the inverting input terminal of the operational amplifier 31 is connected to the output terminal of the operational amplifier 31. The integrator 18 is
Operational amplifier where the reference voltage Vref is applied to the non-inverting input terminal
36, an integrating resistor 37 connected between the inverting input terminal of the operational amplifier 36 and the integrating switch 17, and an integrating capacitor 38 connected between the inverting input terminal and the output terminal of the operational amplifier 36. There is.

Here, input offset voltage V ₀₁ , V of each operational amplifier 31,36
_{If 02} is ignored, the output voltage V _I of the integrator 18 is: the gain of the BPF 16, A _V ; the on-time of the integration switch 17, τ;
If the resistance value of 7 is R _I and the capacitance of the integrating capacitor 38 is C _I , the input voltage V _B of BPF16 Becomes

However, in reality, if the offset voltage of the BPF 16 is V ₀₁ and the offset voltage of the integrator 18 is V ₀₂ , Becomes In order to perform the correct AF calculation, it is necessary to make an adjustment of V ₀₁ + V ₀₂ = 0. This is performed by the offset adjusting resistor 30 of the BPF 16, but if the above-mentioned compensation signal is added as V _{C at} this time, infinity compensation is possible at the same time. In other words, adjust so that the adjusted relationship between V _I and V _B is as follows.

In this way, V _C is ignored when the input voltage V _{B of} BPF 16 is sufficiently large, but V _C begins to take effect when the subject distance increases and V _B gradually decreases. And, at the time of distance measurement at infinity, V _B becomes 0 but V _C remains, so V _I is always a negative value. Therefore, by the above-described operation, V _I is integrated in the negative direction regardless of whether the logic attempts to integrate in the positive direction or the negative direction. As described above, when the output V _I of the integrator 18 becomes equal to or lower than the reference voltage V ref, the logic tries to integrate in the positive direction and the number of positive integration times N _S is counted. So at infinity, N _S = N ₀ .

If such infinity compensation is not performed, at infinity, the integrated output result V _{I obtained} by one-time integration is positive in the positive direction due to noise that is smaller than the compensation signal V _C but is randomly generated.
The number of integrations in the positive direction, which is the final AF signal, was not random in both negative directions, and there was a high possibility of false range finding. Therefore, according to the equation (8), the number N _S of positive integrations is
When the change is as shown by the line L ₁ in FIG. 5 and the subject distance 1 is infinity, theoretically N _S = (1/2) N ₀ , but when the compensation signal V _C is not added. Actually, N _S varies widely in the shaded area in FIG. 7 depending on the magnitude of noise, and can take any value from 0 to N _{0 at} infinity, and is determined to be a short distance at a long distance. False distance measurement will occur.

Therefore, the theoretical formula of the number N _S of positive integrations when the compensation signal V _C is added is that the optical signal incident on the PSD 5 at a distance of 1 m is I _o, and the current-voltage conversion rate of the current-voltage conversion circuits 12 and 13 is When Z, it becomes like the following formula (12).

When this is graphed, it becomes as shown by the line L ₂ in FIG. Therefore, even if actually variations in N _S by noise, range of variation, as indicated by hatching in FIG. 6 is a permissible range comparable to the short distance of the variation range.

As described above, in the present embodiment, by adjusting the offset adjusting resistor 30 of the BPF 16, the offset of the BPF 16 and the integrator 18 are adjusted, and at the same time, the infinity compensation signal can be input and the infinity compensation can be performed. it can.

[Effects of the Invention] As described above, according to the present invention, even if the object distance becomes a long distance, the reflected light signal becomes small, and the S / N ratio deteriorates, a long-range distance is generated due to noise randomly generated. Does not cause an erroneous operation such as erroneously determining that the distance is short, and since the influence of the compensation signal changes due to the change in distance, the distance measurement result does not fly unnaturally.
It is possible to realize AF capable of measuring distances with high accuracy even at a long distance.

[Brief description of drawings]

1 is a block diagram of an electric circuit of an AF IC included in the AF camera shown in FIG. 2, and FIG. 2 is a block diagram showing a configuration of a main part of an AF camera to which the present invention is applied. 3 is a time chart of a signal waveform in the distance measuring mode of the AF IC shown in FIG. 1, FIG. 4 is a circuit diagram showing a detailed configuration of an electric circuit of a main part in FIG. 1, and FIG. ~ Fig. 7 is a diagram showing the number of times of positive integration with respect to distance. 1 …… IRED (light emitting means) 5 …… PSD (light receiving means) 30 …… Offset adjusting resistor (means for adding signals) 31 …… Op-amp

Claims (1)

[Claims] 1. A projection means for projecting distance measuring light to a subject, and a light receiving means for receiving reflected signal light from the subject and outputting two signals depending on the incident position of the reflected signal light. In a light projection type distance measuring device having a calculation circuit for calculating a subject distance by performing a division calculation based on two outputs of the light receiving means, a compensation signal which is irrelevant to the incident position on the light receiving means is input to the calculation circuit. An optical projection type distance measuring device, characterized in that the calculation result of the calculation circuit is determined by the level of the compensation signal when the subject is at infinity.