JP3214991B2 - Distance measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring apparatus, and more particularly to an active distance measuring apparatus used for a camera or the like.

[0002]

2. Description of the Related Art A conventional active distance measuring device for a camera generally includes an infrared light emitting diode (hereinafter, referred to as "IRED") and a position detecting element (hereinafter, referred to as "IRED") which receives infrared light emitted from the IRED and reflected by a subject. Hereinafter, "PSD"
That. ), The signal current output from the PSD is subjected to arithmetic processing by a signal processing circuit and an arithmetic circuit, and is output as distance information.
U ". ) To detect the distance.

In some cases, an error may occur in a distance measurement using only one light emission.
It is general to perform multiple rounds to obtain a plurality of distance information and integrate the plurality of distance information. For this reason, a conventional distance measuring device is generally provided with an integrating circuit for integrating an output signal from an arithmetic circuit.

FIG. 4 is a circuit diagram showing a configuration of an integrating circuit in a conventional distance measuring device. The integrating circuit 16 includes a switch 1 connected to an output terminal of the arithmetic circuit 15 and an integrating capacitor 2 connected to the other end of the switch 1. A constant current source 4 is connected to the integrating capacitor 2 via a switch 3, and an operational amplifier 5 for charging the integrating capacitor 2 is connected. One terminal of a switch 6 is connected to the (−) input terminal of the operational amplifier 5, and the output terminal of the operational amplifier 5 is connected to the other end of the switch 6. A reference power supply 7 is connected to a (+) input terminal of the operational amplifier 5. Switch 1,
3 and 6 are controlled by the CPU 19.

In such an integrating circuit 16, when the main power of the camera is turned on and the release button is half-pressed, the switch 6 is turned on by a control signal from the CPU 19, and the integrating capacitor 2 is charged. Will be Thereby, as schematically shown in FIG. 5, the integrating capacitor 2 is connected to the reference voltage (V
_REF ). After charging, the switch 6 is turned off and is kept as it is.

After that, the IRED emits a pulse of infrared light, and the switch 1 is synchronized with the time of about half of the emission width.
Is turned on and off. As a result, the output from the arithmetic circuit corresponding to each infrared light emission is sequentially input to the integration capacitor 2. The output from the arithmetic circuit 15 is input to the integrating capacitor 2 as a negative voltage, and as shown in FIG. 5, the charging voltage of the integrating capacitor 2 is reduced stepwise by a voltage corresponding to the distance (first). Integration).

When the input (discharge) of the negative voltage for the predetermined number of pulse emission times (for example, 256 times) to the integrating capacitor 2 is completed, the switch 3 is turned on by the control signal of the CPU 19. As a result, the integration capacitor 2 is charged at a constant speed determined by the rating of the constant current source 4 (second integration). This charging allows the integration capacitor 2
Is returned to the reference voltage (V _REF ), the CPU 19 turns off the switch 3 to stop charging the integrating capacitor 2.

The terminal 2a of the integration capacitor 2 is connected to the CPU via the comparator 8, and the CPU 19 can measure only the time when the output of the comparator is high and can measure the time required for the second integration. Since the charging speed is constant by the constant current source 4, from the time required for the second integration,
The total sum of the signal voltages input to the integration capacitor 2, that is, the distance to the subject can be obtained by one distance measurement.

After that, in the second and subsequent distance measurement, the charging of the integrating capacitor 2 is already performed by the constant current source 4, so that the switch 3 is kept open unless particularly used for a long time. You.

[0010]

In the active type distance measuring device as described above, an expensive film capacitor is used as the integrating capacitor 2 of the integrating circuit. The use of is desired. However, ceramic capacitors have a problem in that the charging voltage drops due to dielectric absorption.

Immediately after the start of the first charging, the capacitor C forms an equivalent circuit as shown in FIG. For this reason,
When opening the switch SW to the first time after charging, constant voltage drop by the resistance component R _X in FIG. 6 is observed. Such a phenomenon is called dielectric absorption.

When a ceramic capacitor is used as the integrating capacitor 2 due to such dielectric absorption, a relatively large voltage drop (ΔV) occurs when the switch 6 is opened during the first distance measurement, as shown in FIG. After that, the first integration is started. Therefore, the time required for charging at the time of the second integration includes ΔV corresponding to the voltage drop of ΔV.
A delay of t occurs. This delay is a distance measurement error. It should be noted that a voltage drop due to dielectric absorption also occurs in the film capacitor, but the drop amount is extremely small and has little effect on distance measurement.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide an active distance measuring apparatus which can prevent a distance measuring error due to dielectric absorption of an integrating capacitor. .

[0014]

To achieve the above object, a distance measuring apparatus according to the first aspect of the present invention comprises a light emitting means for projecting light toward a distance measuring object, and a light emitting means for emitting light from the light emitting means. A light receiving means for receiving the reflected light of the light projected on the object and outputting a signal in accordance with the light receiving position; and a signal corresponding to the distance to the object to be measured based on the signal from the light receiving means And an integration capacitor for outputting the signal from the calculation means, and integrating the signal from the calculation means by discharging the integration capacitor in accordance with the signal from the calculation means, and corresponding to the integration result obtained by charging the integration capacitor. Integration means for outputting a signal to be measured, detection means for detecting the distance to the object to be measured based on the signal from the integration means, and an integration capacitor before the first distance measurement is performed after the main power is turned on. To charge for a predetermined time Characterized in that it comprises a charging means for performing.

According to a third aspect of the present invention, in the distance measuring apparatus according to the first aspect of the present invention, the first charging means after the main power is turned on is used instead of the charging means.
It is characterized in that it has a charging means for charging the integrating capacitor for a time long enough to prevent a voltage drop due to dielectric absorption at the time of the second distance measurement.

[0016]

In the distance measuring apparatus according to the first aspect of the present invention, a voltage drop due to dielectric absorption is forcibly generated before the distance measurement by charging the integrating capacitor before performing the first distance measurement. I am going to let it. Since the voltage drop due to dielectric absorption does not substantially occur in the second or subsequent charging, an error due to dielectric absorption is avoided in the first distance measurement.

Further, in the distance measuring apparatus according to the third aspect of the present invention, the charging time for the first distance measurement is extended, but the voltage drop due to dielectric absorption is
This is based on the finding that when the battery is charged for a long time, it becomes extremely small.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram schematically showing a configuration of an active distance measuring apparatus according to the present invention which can be applied as a distance measuring apparatus of an automatic focusing camera. This ranging device
The configuration is substantially the same as the conventional configuration. An infrared light emitting diode (IRED) 10 for projecting an infrared ray to a subject (object for distance measurement) via a projection lens (not shown),
A driver 11 for driving the RED 10 and an IRED 1
A position detection element (PSD) that receives infrared rays emitted from the object and reflected by the subject through a light receiving lens (not shown)
12 are provided.

The distance measuring device further includes a first signal processing circuit 13 and a second signal processing circuit 14 for processing the signal current I ₁ and the signal current I ₂ output from the PSD ₁₂ , respectively. A calculating circuit 15 for calculating and outputting distance information to the subject based on the signal output from the integrating circuit 14; an integrating circuit 16 for integrating the output from the calculating circuit 15; And a microcomputer (CPU) 19 for controlling the lens drive circuit 17 to move the taking lens 18 to the in-focus position. First and second signal processing circuits 13 and 14, arithmetic circuit 15 and integrating circuit 16
Is usually housed in an autofocus integrated circuit (hereinafter, referred to as “AFIC”) 20 and mounted on a camera.

The operation of the distance measuring device is controlled by the CPU 19. The operation is outlined below.
Infrared rays are projected from the ED 10 to the subject via a projection lens (not shown). This infrared light is reflected by the subject and received by the PSD 12 via a light receiving lens (not shown). The PSD 12 is a photodiode that distributes and outputs a current from two electrodes in accordance with a position where infrared rays are received, and outputs a signal current I ₁ and a signal current I ₂ output from the PSD 12 to the first signal processing circuit 13, respectively. After being appropriately processed by the second signal processing circuit 14, the signal is input to the arithmetic circuit 15. In the arithmetic circuit 15, data corresponding to the output ratio I ₁ / (I ₁ + I ₂ ) of the PSD 12 is obtained, and this data is output as a distance information signal.

In one ranging operation, the IRED emits infrared pulses a plurality of times (for example, 256 times).
The arithmetic circuit 15 outputs signals of the distance information for the number of times. Therefore, the integration circuit 16 integrates the same number of signals as the input number of times of light emission, and outputs the sum to the CPU 19 as one distance information. The CPU 19 calculates the distance to the subject based on the input distance information, and controls the lens driving circuit 17 to move the photographing lens 18 to the focusing position.

Here, the integration circuit 16 will be described in more detail. The integrating circuit 16 in the present embodiment includes a ceramic capacitor as the integrating capacitor 2, and the integrating capacitor 2 is externally attached to the AFIC 20. Since the integrating circuit 16 of the present embodiment has the same configuration as the conventional one, referring to FIG. 4, one terminal 2b of the integrating capacitor 2 is connected to the ground, and the other terminal 2a is connected to the C terminal.
It is connected to one end of the switch 1 controlled by a signal from the PU 19. The other end of the switch 1 is connected to the output terminal of the arithmetic circuit 15. An AFIC 20 (comparator 8) is connected to a terminal 2a of the integrating capacitor 2.
A constant current source 4 is connected via a switch 3 controlled by the control circuit, and a (-) input terminal of an operational amplifier 5 for charging the integrating capacitor 2 is connected. The CPU 1 is connected between the (−) input terminal and the output terminal of the operational amplifier 5.
The switch 6 controlled by the switch 9 is connected, and the reference power supply 7 is connected to the (+) input terminal of the operational amplifier 5.

In this embodiment, the operation of the integrating circuit is performed as shown in the timing chart of FIG. That is, as shown in (a), (c), (d) and (e) of FIG.
When the main power supply of the camera is turned on, the power supply voltage of the AFIC 20 rises and the integration capacitor 2 is charged. This charging is performed by turning on the switch 6 by the control signal sent from the CPU 19 at the timing shown in FIG. 2D, whereby the integrating capacitor 2 is connected to the reference The battery is charged until the voltage (V _REF ) is _reached . Hereinafter, this charging is referred to as precharging. Then, after a lapse of a certain time, the power of the AFIC 20 is turned off, and at the same time, the switch 6 is turned off, and the charging of the integrating capacitor 2 is stopped.

Next, as shown in FIG. 2 (b), when the release button of the camera is half-pressed to enter a distance measuring state, the power supply voltage of the AFIC 20 is raised again, and
The switch 6 is turned on, and the integration capacitor 2 is charged until it reaches the reference voltage (V _REF ). After charging is complete,
The switch 6 is turned off and kept in that state.

As shown in FIG. 2F, the IRED 10
Is driven by a light emission timing signal having a duty ratio output from the CPU 19 to the driver 11, and emits infrared pulses a plurality of times (for example, 256 times per distance measurement). The infrared light emitted from the IRED 10 is reflected by the object and then received by the PSD 12, so that the output ratio I ₁ / (I ₁ +) determined by the arithmetic circuit 15 for each light emission.
The data of I ₂ ) is sequentially input to the integration circuit 16.
The CPU 19 controls the switch 1 at a timing corresponding to the pulse emission of the IRED 10, and inputs a negative voltage corresponding to the output ratio to the integrating capacitor 2.

FIG. 3 is a timing chart schematically showing a change over time of the charging voltage of the integrating capacitor 2. As shown in FIG. The integration capacitor 2 is discharged by the signal from the arithmetic circuit 15, and the potential of the terminal 2a decreases stepwise with time (first integration). Although the voltage drop amount of each step is itself distance information corresponding to the distance to the subject, in the present embodiment, the distance information is the sum of the voltage drop amounts obtained by the pulse emission of the IRED 10.

When the input of the number of times of pulse emission (256 times) to the integrating capacitor 2 is completed, the switch 6 is kept off and the switch 3 is turned on by a signal from the CPU 19. As a result, the integration capacitor 2 is charged at a constant speed determined by the rating of the constant current source 4 (second integration). This charging allows the integration capacitor 2
Returns to the reference voltage (V _REF ), the comparator 8
Turns off the switch 3 to stop charging the integrating capacitor 2.

The terminal 2a of the integrating capacitor 2 is connected to the CPU 19 via the comparator 8. The comparator 8 outputs a high pulse from the AFIC 20 until the reference voltage (V _REF ) is reached from the start of charging. The CPU 19 outputs the output of the comparator 8
Only the high time is measured, and the time from the start of charging of the integration capacitor 2 until the potential of the terminal 2a reaches the reference potential (V _REF ), that is, the time required for the second integration is measured. Since the charging speed of the integration capacitor 2 is constant, the sum of the signal voltages input to the integration capacitor 2 can be obtained by one distance measurement from the time required for the second integration. This is the output ratio I obtained from the signal current of PSD12.
₁ / (I ₁ + I ₂ ). Therefore, the distance to the subject can be obtained by using this data. Thereafter, when the release button is completely pressed, the CPU 19 controls the lens driving circuit 17 based on the obtained distance to cause the photographing lens 18 to perform an appropriate focusing operation.

Although the first distance measurement is completed in this way, as understood from FIG. 3, since the integrating capacitor 2 is charged in advance before the distance measurement is started, the voltage drop due to dielectric absorption ( ΔV) occurs when the precharge is stopped. Due to the characteristics of the capacitor, a voltage drop due to dielectric absorption does not occur in the second charge, so that no voltage drop occurs in the charge performed after the precharge, that is, in the charge in the first distance measurement. Therefore, in the first distance measurement, there is no delay in the charging time of the second integration due to the voltage drop, and no distance measurement error occurs.

After the second charging, the charging by the reference power source 7 is not performed before the distance measurement routine (the distance measurement routine includes the charging by the reference power source 7). 6 is kept off in principle.
However, if you do not use the distance measuring device for a long time,
In some cases, the voltage of the integrating capacitor 2 decreases and falls below the reference voltage (V _REF ). Therefore, if the distance measurement has not been performed for a long time, the switch 6 is turned on in the distance measurement routine, and charging is performed by the reference power supply 7. At this time, the voltage drop due to dielectric absorption is also performed. Problems may occur.

Therefore, when the distance measurement is not performed for a long time, the switch 6 is closed at regular time intervals and the integration capacitor 2 is charged. This is preferable because no descent is observed and a distance measurement error is prevented from occurring.

Further, in the above embodiment, at the time of precharging, the integration capacitor 2 is charged by the reference power supply 7 until the integration capacitor 2 reaches the reference voltage (V _REF ). Alternatively, charging may be performed using the power supply of the AFIC 20 until the voltage (Vcc) of the AFIC 20 is reached.

Further, even when the charging time for the integration capacitor 2 is sufficiently long, no voltage drop occurs due to dielectric absorption of the integration capacitor 2. Therefore, even if the above-described pre-charging is not performed, or if the charging time by the reference power supply 7 in the first distance measurement is made longer than before in the first distance measurement, the occurrence of the distance measurement error can be prevented. The charging time in this case is preferably set to a minimum time in which a voltage drop due to dielectric absorption can be substantially eliminated, from the viewpoint of preventing a delay in the distance measurement operation. Of course, the method of extending the charging time can be applied to the case where the switch 6 is closed again and the integrating capacitor 2 is charged by the reference power supply 7 when the distance measurement is not performed for a long time.

In the case where the charging / discharging of the integrating circuit is opposite to that in the above-described embodiment, that is, the integration is performed such that the charging is performed a plurality of times so that the charging voltage increases stepwise and then the discharging is performed only once. The present invention can be applied to a circuit.

[0036]

As described above, according to the present invention, no voltage drop due to dielectric absorption of the integrating capacitor is observed during distance measurement, and the problem of distance measurement error due to such voltage drop is avoided. In the case of a focus camera, the taking lens can be accurately moved to the in-focus position. This is an effect obtained regardless of the type of the integration capacitor. Therefore, an inexpensive ceramic capacitor can be used as an integrating capacitor instead of an expensive film capacitor, and the manufacturing cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a camera distance measuring apparatus to which the present invention can be applied.

FIG. 2 is a timing chart for explaining the operation of the distance measuring apparatus in FIG. 1;

FIG. 3 is a timing chart schematically showing a change over time of a charging voltage of an integration capacitor.

FIG. 4 is a block diagram illustrating a configuration of an integration circuit in FIG. 1;

FIG. 5 is a timing chart schematically showing a change over time of a charging voltage of an integrating capacitor in a conventional distance measuring device.

FIG. 6 is a circuit diagram of an equivalent circuit for explaining the principle of dielectric absorption of a capacitor.

[Explanation of symbols]

1 switch, 2 integration capacitor, 3 switch, 4
... constant current source, 5 ... operational amplifier, 6 ... switch, 7 ... reference power supply, 8 ... comparator, 10 ... IRED (infrared light emitting diode), 11 ... driver, 12 ... PSD (position detection element), 13 ... first signal processing Circuit, 14: second signal processing circuit, 15: arithmetic circuit, 16: integrating circuit, 17: lens driving circuit, 18: photographing lens, 19: CPU (microcomputer), 20: AFIC (integrated circuit for automatic focusing)

Claims (3)

(57) [Claims] A light emitting means for projecting light toward the object to be measured; a light receiving means for receiving reflected light of the light emitted from the light emitting means to the object to be measured; and outputting a signal in accordance with a light receiving position. A light receiving unit, a calculating unit that performs a calculation based on a signal from the light receiving unit, and outputs a signal corresponding to a distance to the object to be measured, and an integrating capacitor, and according to a signal from the calculating unit. Integrating the signal from the calculating means by discharging from the integrating capacitor, and outputting a signal corresponding to the integration result obtained by charging the integrating capacitor; based on the signal from the integrating means A distance measuring device comprising: detecting means for detecting a distance to an object to be measured; and charging means for charging the integrating capacitor with a reference voltage at the start of each distance measurement, the charging means comprising: After power-on, before charging at the start of the first distance measurement, separately from the first distance measurement, a period of time sufficient to prevent a voltage drop due to dielectric absorption. Wherein the integrating capacitor is charged by the following method. 2. A charging device according to claim 1, wherein, when the distance measurement is not performed for more than a predetermined time, independently of the distance measurement, the charging means sets the integrating capacitor long enough to prevent a voltage drop due to dielectric absorption. 2. The distance measuring apparatus according to claim 1, wherein the charging is performed in a short time. 3. A light emitting means for projecting light toward the object to be measured, receiving reflected light of light projected from the light emitting means on the object to be measured, and outputting a signal in accordance with a light receiving position. A light receiving unit, a calculating unit that performs a calculation based on a signal from the light receiving unit, and outputs a signal corresponding to a distance to the object to be measured, and an integrating capacitor, and according to a signal from the calculating unit. Integrating the signal from the calculating means by discharging from the integrating capacitor, and outputting a signal corresponding to the integration result obtained by charging the integrating capacitor; based on the signal from the integrating means A distance measuring device comprising: detecting means for detecting a distance to an object to be measured; and charging means for charging the integration capacitor with a reference voltage at the start of each distance measurement, the charging means comprising: When the power is turned on, separately from the distance measurement, the integrating capacitor is charged for a time long enough to prevent a voltage drop due to dielectric absorption.