JP3137544B2 - 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. 5 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. 6, 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 turned on / off for a time (integration period) that is about half of the light emission width. As a result, the output from the arithmetic circuit 15 corresponding to each infrared light emission is sequentially output to the integrating capacitor 2.
Is input to The output from the arithmetic circuit 15 is input to the integrating capacitor 2 as a negative voltage, and as shown in FIG. 6, the voltage charged in the integrating capacitor 2 is reduced stepwise by a voltage corresponding to the distance ( 1st 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 integrating capacitor 2 is connected to the CPU 19 via the comparator 8,
Can measure only the time when the comparator output is high (switch 3 is on), and can measure the time required for the second integration. Since the charging speed is constant by the constant current source 4, the second
From the time required for the 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.

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

[0010]

In the active type distance measuring apparatus as described above, an expensive film capacitor is used as the integrating capacitor 2 of the integrating circuit 16, but an inexpensive ceramic is used due to a demand for reducing the manufacturing cost. The use of capacitors 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 charge, the capacitor 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. 7 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]

In order to achieve the above object, a distance measuring apparatus according to the present invention comprises: a light emitting means for projecting light toward an object to be measured; and a light emitting means for projecting light from the light emitting means to the object to be measured. A light receiving means for receiving the reflected light of the obtained light and outputting a signal according to the light receiving position, and a calculation for performing a calculation based on a signal from the light receiving means and outputting a signal corresponding to a distance to the object to be measured Means for integrating the signal from the calculating means by discharging the integrating capacitor according to the signal from the calculating means, and outputting a signal corresponding to the integration result obtained by charging the integrating capacitor. Integrating means, detecting means for detecting the distance to the object to be measured based on a signal from the integrating means, and when performing distance measurement, before integration, a predetermined reference voltage is applied to the integrating capacitor. Apply large voltage After, it is characterized by and a charging means for charging as the charging voltage of the integration capacitor is restored to the reference voltage.

More specifically, the charging means includes a first power supply for applying the reference voltage to the integration capacitor, a second power supply for applying a voltage higher than the reference voltage to the integration capacitor, and a first power supply. A first switch for controlling the power supply to the integrating capacitor from the second power supply, a second switch for controlling the power supply to the integrating capacitor from the second power supply, and the second switch after turning on the first and second switches. Switch off,
Then, there is provided control means for turning off the first switch.

[0016]

In the distance measuring apparatus according to the present invention, a voltage higher than the reference voltage is applied to the integrating capacitor and then returned to the reference voltage, so that a voltage drop due to dielectric absorption occurs before returning to the reference voltage. Voltage drop can be prevented.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals.

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 is provided.

The distance measuring apparatus 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 this 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 the position of receiving infrared light, 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. Arithmetic circuit 15
, The output ratio I ₁ / (I ₁ + I ₂ ) of the PSD 12
Is obtained, and this data is output as a signal of distance information.

In one distance measurement operation, the IRED 10 emits infrared light pulses a plurality of times (for example, 256 times). Therefore, the arithmetic circuit 15 outputs signals of 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. In the integrating circuit 16 of the present embodiment, as shown in FIG. 2, one terminal 2b of the integrating capacitor 2 is connected to the ground,
The other terminal 2 a is connected to one end of the switch 1 controlled by a signal from the CPU 19. The other end of the switch 1 is connected to the output terminal of the arithmetic circuit 15. A constant current source 4 is connected to a terminal 2a of the integrating capacitor 2 via a switch 3 controlled by a comparator 8.
And the (-) input terminal of the operational amplifier 5 for charging the integration capacitor 2 is connected. Between the (-) input terminal and the output terminal of the operational amplifier 5, C
Switch controlled by PU19 (first switch)
The reference power supply (first power supply) 7 is connected to a (+) input terminal of the operational amplifier 5. Furthermore,
This integration circuit 16 is different from the conventional integration circuit described with reference to FIG.
A power supply (second power supply) 21 of the FIC 20 is connected via a switch (second switch) 22 controlled by the CPU 19.

In this embodiment, the operation of the integrating circuit 16 is performed as shown in the timing chart of FIG. That is, as shown in FIGS. 3A to 3E, after the main power of the camera is turned on and the release button of the camera is half-pressed to perform the first distance measurement, the AFIC 20 is turned on.
The power supply 21 is turned on, and after a certain stabilization time has elapsed, the switches 6 and 22 are turned on. As a result, as shown in FIG. 3 (h), the integrating capacitor 2 is charged, and the potential of the terminal 2a becomes the voltage (Vcc) of the power supply 21. Next, after a lapse of a predetermined time, the switch 6 is maintained in the on state, and only the switch 22 is turned off. As a result, the charging voltage of the integrating capacitor 2 is fixed to the reference voltage (V _REF ) of the reference power supply 7. Then, when a predetermined charging time has elapsed, the switch 6 is turned off and held in that state.

Next, as shown in FIG.
D10 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 received by the PSD 12 after being reflected by the subject.
The output ratio I ₁ / (I ₁
+ 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. 4 is a timing chart schematically showing the change over time of the charging voltage of the integrating capacitor 2. 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 light emission (256 times) to the integrating capacitor 2 is completed, (d) to (d) of FIG.
As shown in (f), the switches 6 and 22 are 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). When the voltage of the integrating capacitor 2 returns to the reference voltage (V _REF ) by this charging, the AFIC 20 turns off the switch 3 by the comparator 8 to stop the charging of the integrating capacitor 2.

The terminal 2a of the integrating capacitor 2 is connected to the CPU 19 via the comparator 8. CPU19
Is measured only during the time when the output of the comparator 8 is HIGH, and the time from when the charging of the integrating capacitor 2 starts to when the potential of the terminal 2a reaches the reference potential (V _REF ), that is, the second time
The time required for 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 PSD12
Corresponding to the output ratio I ₁ / (I ₁ + I ₂ ) obtained from the signal current of Therefore, the distance to the subject can be obtained by using this data. Thereafter, when the release button is completely pressed, the CPU is determined based on the obtained distance.
Reference numeral 19 controls the lens driving circuit 17 so that
Perform an appropriate focusing operation.

In this manner, the first distance measurement is completed. However, as understood from FIG. 4, before the charging voltage of the integrating capacitor 2 is fixed to the reference voltage (V _REF ), since a large voltage (Vcc) is applied than the reference voltage (V _REF), when turning off the switch 22, the voltage (V
When the voltage drops from (cc) to the reference voltage (V _REF ), a voltage drop (ΔV) due to dielectric absorption appears. In other words, the voltage drop (ΔV) due to dielectric absorption is absorbed by increasing the charging voltage. From the characteristics of the capacitor, usually
Since the voltage drop due to dielectric absorption does not occur again, the first integration will be started from the reference voltage (V _REF ) after the switch 6 is turned off. 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.

When the distance measuring device is not used for a long time, the voltage of the integrating capacitor 2 drops and the reference voltage (V
_REF ). Therefore, if the distance measurement has not been performed for a long time, the switch 6 is turned on and charging is performed by the reference power supply 7. At this time, there is a possibility that a problem of a voltage drop due to dielectric absorption may occur. is there. Therefore, when the distance measurement is restarted after the state where the distance measurement is not performed for a long time, such a case is also treated as the first distance measurement, and the switches 3, 6, 22 and the like are operated at the same timing as in FIG. It is preferable to perform the control because the occurrence of a distance measurement error due to dielectric absorption is prevented.

In the above embodiment, the power supply 21 of the AFIC 20
To charge the integration capacitor 2 by
A dedicated power supply may be provided separately. The voltage is
Any voltage can be absorbed as long as it can absorb the voltage drop due to dielectric absorption. However, in order to perform processing in a short time, it is preferable that the voltage is equal to or more than the voltage drop (ΔV) and higher than the reference voltage (V _REF ). It is.

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

[0032]

As described above, the present invention forcibly absorbs the voltage drop due to dielectric absorption by applying a voltage higher than the reference voltage to the integrating capacitor, and thus measures the distance due to the voltage drop. This solves the problem of error. Therefore, for example, when the distance measuring device of the present invention is used for an autofocus camera, it is possible to accurately move the taking lens to the in-focus position.

Further, according to the present invention, it becomes possible to use an inexpensive ceramic capacitor as an integrating capacitor instead of an expensive film capacitor, and it is possible to reduce the manufacturing cost.

Further, it is conceivable to reduce the voltage drop due to dielectric absorption by extending the charging time for the integrating capacitor. However, according to the present invention, the above-described effect can be obtained even if the charging time for the integrating capacitor is relatively short. Is obtained, and an increase in shutter time lag can be prevented.

[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 block diagram showing a configuration of an integrating circuit in the distance measuring apparatus according to the present invention.

FIG. 3 is a timing chart illustrating the operation of the distance measuring apparatus according to the present invention.

4 is a timing chart schematically showing a change over time of a charging voltage of an integration capacitor in the integration circuit of FIG. 2;

FIG. 5 is a block diagram showing a configuration of an integrating circuit in a conventional distance measuring device.

FIG. 6 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. 7 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 (first switch), 7 ... reference power supply (first power supply), 8 ... comparator, 10 ... IRED (infrared light emitting diode), 11
... Driver, 12 PSD (Position Detector), 13 ...
1st signal processing circuit, 14 ... 2nd signal processing circuit, 15 ... arithmetic circuit, 16 ... integration circuit, 17 ... lens drive circuit, 18
... a photographing lens, 19 ... a CPU (microcomputer), 20 ... AFIC (automatic focus integrated circuit), 21 ...
AFIC power supply (second power supply), 22... Switch (second power supply)
Switch).

Claims (2)

(57) [Claims] A light emitting means for projecting light toward the object to be measured; a light receiving means for receiving reflected light of 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 Detecting means for detecting the distance to the object to be measured; and, when performing distance measurement, applying a voltage higher than a predetermined reference voltage to the integrating capacitor before performing the integration. Distance measuring apparatus charging voltage and a charging means for charging to return to the reference voltage. A second power supply for applying a voltage higher than the reference voltage to the integration capacitor; a first power supply for applying the reference voltage to the integration capacitor; a second power supply for applying a voltage higher than the reference voltage to the integration capacitor; A first switch for controlling power supply from the power supply to the integration capacitor; a second switch for controlling power supply to the integration capacitor from the second power supply;
2. The distance measuring apparatus according to claim 1, further comprising: switch control means for turning off the second switch after turning on the first and second switches, and thereafter turning off the first switch.