JPH0738896Y2 - Auto focus device - Google Patents

Description

[Detailed description of the device]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing device using a motor servo to drive a lens.

[0002]

2. Description of the Related Art Conventionally, there has been an automatic focusing device in which a pulse width is changed according to an image shift amount and a motor is driven by a current having the changed pulse width to move a photographing lens. For example, in the specification and drawings of Japanese Utility Model Publication No. 54-84940,
An autofocus device is disclosed in which the amount of deviation between the position of the photographing lens and the position of the subject is detected by the external light triangulation method, and the width of the pulsed current is changed according to the detected amount of deviation to drive the motor. . There is also an automatic focusing device that uses a motor servo to drive the lens. In such an automatic focusing device, three modes of forward rotation, reverse rotation, and stop are set in the motor servo, the output signal generated at the output of the motor servo is compared with the input signal, and the output signal and the input signal are compared. The motor servo is driven while confirming the coincidence.

[0003]

[Problems to be solved by the device]
The autofocus device disclosed in Japanese Patent No. 84940 can increase the drive amount of the motor when the displacement amount is large, and can reduce the drive amount of the motor when the displacement amount is small, but the photographing lens is driven to the vicinity of the in-focus position. Then, the width of the pulsed current becomes so small that the motor cannot be driven by the load of the photographing lens or the like. Therefore, it is possible to drive the taking lens from the out-of-focus position to the vicinity of the in-focus position, but if the power supply voltage condition deteriorates or there is a temperature change in the environment, move the taking lens to the in-focus position. There is a problem that it is not possible to drive the lens from the vicinity of to the accurate focus position, and accurate focus control cannot be performed. Also,
When the motor is a motor servo, if the speed of the motor servo is too fast, the response due to the weight of the backlash mechanical system may not be able to confirm the match between the input signal and the output signal, which may cause hunting. .

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to solve these drawbacks and to provide an autofocusing device which has a high motor operating speed, a narrow dead zone, that is, a fast operating speed and a high precision. In particular, it is an object to provide a motor servo device for such an autofocus device.

In the present invention, the motor is driven by the pulse signal, and the rotation speed of the motor is changed by the pulse width (duty ratio) of the pulse signal. That is, when the focus is largely deviated, the pulse width is increased (that is, the time for supplying power to the motor is increased), and the pulse width is decreased (the supply time is decreased) as the focus is approached. With that alone, the pulse width becomes too small near the in-focus point and the motor stops responding to the pulse signal, and it stops before focusing. Therefore, in the present invention, means for defining the minimum value of the pulse width is provided so that the speed of the motor does not fall below a predetermined value.

[0006] Among the autofocus cameras, there is a camera that drives a photographing lens or the like by a servomotor to focus the image. Generally, a signal required by a servo device of this type of camera is a signal representing a so-called front pinning state in which an image forming surface formed by a photographing lens is formed in front of a film surface, and a back pinning state in the opposite case. There are three signals, a signal representing a focus state and a signal representing a focus state. The servo device operates as follows by these three signals. When the photographic lens catches the subject, if it is in the front focus state, a signal indicating the front focus is output and the motor is rotated in one direction to move the photographic lens in the focusing direction. When in-focus is achieved, a signal indicating in-focus is issued, the motor is stopped, and the taking lens is held in that position. In the rear focus state, a signal indicating the rear focus is output, and the motor is rotated in the opposite direction to that in the previous case to achieve focusing. In order to perform the above operation, the servo device includes a focus detector that outputs the above-mentioned three signals, and the like.
An example is shown in Japanese Patent Application Laid-Open No. 54-104859 "Automatic Focus Detection Device". In this focus detection device, two sinusoidal detection signals are output from the subject light that has passed through the photographing lens or the like. This detection signal discriminates the above-mentioned three states based on the phase difference. That is, when the phase of one of the two detection signals is ahead of that of the other signal, for example, it is determined to be the front pin, the opposite pin to the rear, and the focus when there is almost no phase difference. Has been. Further, the transfer amount is proportional to the deviation from the focus. Therefore, if the phase difference is detected from these two signals and the motor is driven, the servo device of the autofocus camera can be achieved.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An autofocus device according to an embodiment of the present invention, which receives such two signals and operates according to the phase difference between them, will be described below with reference to the drawings.

FIG. 1 shows a servo motor drive circuit according to a first embodiment of the present invention, and FIG. 2 shows signal waveforms in the circuit of FIG. Input terminals 1 and 2 receive the two detected sine wave signals from the focus detector described above. Comparators 3 and 4 convert the two detected sine wave signals into a square wave signal-binary signal shown in FIGS. 2A and 2B. Initially, the signal B is ahead of the signal A in phase, and at this time, the lens is in the front focus state. Assuming that focusing is achieved at time T in FIG. 2, the phase of signal B is ahead of that of signal A until time T. The two rectangular wave signals A and B are input to the exclusive OR gate (hereinafter referred to as EX-OR) 6 and output as the signal C in FIG. The signal C has a pulse width corresponding to the amount of phase difference between the two rectangular wave signals. The signal M basically drives the motor M. Further, the two rectangular wave signals A and B are connected to the OR gate 7.
2 and is output as the signal D in FIG. The signal D is the trigger input for the two one-shot multis 8 and 9. The one-shot multis 8 and 9 operate at the rising edge of the signal D (in this example, the rising edge of the signal B whose phase is advanced), and are determined by the resistor R ₁ and the capacitor C _1, and the resistor R ₂ and the capacitor C _2. It outputs signals E and F having pulse widths t ₁ and t ₂ . The output signal E of the one-shot multi 8 becomes narrower as the pulse width of the pulse for driving the motor M, that is, the pulse width of the signal C becomes closer to the focus, and the pulse width becomes extremely small in the vicinity of the focus so that the motor does not operate. Necessary to prevent, the pulse width t ₁ means the minimum pulse width at which the motor can operate. The signals C and E are input to the OR gate 10 and output as the signal H in FIG. The signal H depends on the pulse width of the signal C while the phase shift is large, that is, when the focus is considerably out of focus, and depends on the pulse width of the signal E when the phase shift is small, that is, when the focus is substantially reached. Therefore, the pulse width of the signal H is maintained at t ₁ or more. Since the output of the one-shot multi 9 is taken from the inverting output terminal of Q, its output waveform becomes like the signal F, and the pulse width t ₂ determines the focusing zone (dead zone width). This width t ₂ is chosen smaller than t ₁ . The D slip flop 11 receives the C signal as a data input, reads the C signal which is a data input at the rising edge of the F signal input as a clock signal, and latches it. The D flip-flop 11 outputs a logic "1" from the Q terminal when the pulse width of the logic "1" of the C signal is wider than the width t ₂ of the logic "0" of the F signal, and outputs a logic "0" when the width is narrow. . The output of the D flip-flop 11 becomes the G signal of FIG. That is, when the focus state is approached and the phase difference between the two detection signals becomes smaller than a certain value determined by the width of the logical "0" of the F signal, the G signal becomes the logical "0". The signal H and the signal G are logically ANDed by the AND gate 12, and the output of the AND gate 12 becomes the signal of FIG. 2I. On the other hand, the D flip-flop 5 receives the A signal as the data input and reads the A signal as the data input at the rising edge of the B signal which is the clock signal. In this example, the B signal is A from the front focus state to the in-focus state.
Q of flip-flop 5 because the phase is ahead of the signal
The output is a logical "0". This Q output is shown as the J signal in FIG. If it is in the rear pin state, the phase of the A signal is ahead of that of the B signal, and the J signal is logic "1". The J signal and the I signal are input to the EX-OR K and output as the K signal in FIG. The K signal coincides with the I signal because the G signal is logical "0". The current IM flowing in the motor M is generated by the voltage difference between the K signal and the J signal, and the direction of the flowing current is the direction of the arrow in the drawing. If the J signal is a logical "1", the K signal is the inverse of the I signal,
The flowing current is in the direction opposite to the arrow in the drawing. However, the amount of current flowing does not depend on the direction. As can be seen from the above description, the drive current of the motor has a pulse shape, and the pulse width thereof corresponds to the amount of deviation from the focus. However, when the phase difference of the detection signals becomes less than a certain value t ₂ where t _{1 is} less than t ₁ , there is no drive signal to the motor M and the motor M is stopped.

In the embodiment of FIG. 1, the motor M has a K signal and a J signal.
The signal is controlled so that it will not be driven when the pulse of the K signal disappears (that is, when the signals between the terminals of the motor M both become logic "1" or "0"). Therefore, it is not configured to generate a stop signal. When it is desired to suddenly stop the motor according to the stop signal, the motor drive circuit of the second embodiment shown in FIG. 3 is applied. The two detection signals are input to input terminals 1 and 2 and converted into rectangular wave signals A'and B'in FIG. 4 by comparators 20 and 21, respectively. The EX-OR 23 inputs the signals A'and B ', and outputs the C'signal of FIG. The one-shot multi 29, which is triggered by the C'signal, has a resistor R ₁ and a capacitor C _1.
The output pulse such as G 'signal of Figure 4 having a pulse width t ₁ determined by ₁ to output from the Q terminal. Noah Gate 27
Outputs the signal I'in FIG. 4 by ORing the signals C'and G '. The I'signal corresponds to the H signal in FIG. Signals A'and B'are also input to AND gate 24 and OR gate 25 to produce signals E'and F'of FIG. 4, respectively. In this example, the rising edge of the E'signal coincides with the rising edge of the A'signal and the rising edge of the F'signal coincides with the rising edge of the B'signal.

The one-shot multi 26 is triggered by the F'signal and sends a pulse having a pulse width t ₂ determined by the resistor R ₂ and the capacitor C ₂ to its Q terminal like the H'signal in FIG. This H'signal corresponds to the F signal in FIG. The one-shot multi 28 receives the E'signal as a data input and reads it at the rising edge of the H'signal which is a clock signal. The falling edge of the H'signal coincides with the rising edge of the B'signal. Therefore, the difference between the rising edges of the A ′ signal and the B ′ signal,
That is, when the phase difference becomes smaller than the pulse width t _{2 of the} H'signal, the D flip-flop 28 outputs a logic "1" to its Q terminal. As a result, the pulse width t ₂ becomes the focusing zone as in the apparatus of FIG. The Q output of the one-shot multi 28 is inverted by the inverter 36 and becomes the J'signal in FIG. The D flip-flop 22 is for reading data by using the clock signal of the B'signal with the A'signal as a data input. In this example, since the B'signal leads the A'signal in phase, the Q output has a logic "0" as the output M'in FIG. The NAND gate 31 has an M'signal,
The inverted logical product of the J ′ signal and the I ′ signal is output to the output terminal 33. However, since the M ′ signal is a logical “0”, the output at the output terminal 33 is a logical “1”. The NAND gate 34 outputs an inverted logical product of the M'inverted logical signal, the J'signal and the I'signal to the output terminal 34. The inverted logical signal of M'is a logical "1" and the J'signal is a time T. Since it is a logical "1" until the time (when the focus state is reached) and then a logical "0", an inverted version of the I'signal occurs until the time T and becomes a logical "1" thereafter. A pulse like the signal K'in FIG. 4 is output to the output terminal 34. A J'signal is generated at the output terminal 35, which serves as a motor stop signal.

Motor control circuit terminals 33, 34 and 35 of FIG. 3 are input terminals 33 ', 34' of the motor drive circuit of FIG.
And 35 '. The basic configuration of the motor drive circuit of FIG. 5 is transistors 100, 101, 102 and 103.
The motor 14 is connected between the middle points a and b of the bridge circuit, and when the transistors 101 and 102 are ON, the current flows from a to b to rotate the motor 14 in one direction, and when the transistors 100 and 103 are ON, the current flows. Flows from b to a to rotate the motor 14 in the other direction. In this example, a high level is applied to the terminal 33 ', a K'signal is applied to the terminal 34', and a J 'signal is applied to the terminal 35'. Therefore, the transistor 105 is turned off, the transistors 100 and 103 are turned off, and the transistor 106 is turned on when the K'signal is low level.
When 1 and 102 are turned on, a current flows to the motor 14 from a to b. When focusing is achieved, both terminals 33 'and 34'
The pulse becomes high level and the pulse for driving the motor 14 disappears. Also, since the terminal 35 'becomes low level, the transistor 107 turns on and the transistors 101 and 103 turn on.
To do. This forms a short circuit closed loop of the transistor 101, the motor 14 and the transistor 103,
The reverse operation of the collector and the emitter of one of the transistors causes a dynamic braking to realize an abrupt stop.

The motor drive circuit of FIGS. 6 and 7 is another embodiment to which the motor control circuit of FIG. 3 can be connected. 6 and 7
When focusing is achieved, the transistors 100-1
All of 03 are turned off, the coil of the relay 40 is excited, the contacts are closed, and the dynamic braking is generated. Although the ground connection of the transistors 100 to 103 in the circuit of FIG. 7 is different from that of FIGS. 5 and 6, this connection is suitable when the power supply voltage has a margin.

Contrary to the above-mentioned signal form, Hi is connected to the terminal 34 '.
When the gh level signal and the K'signal are applied to the terminal 33 ', the rotation direction of the motor is reversed.

The focusing operation by the device of the present invention will be described.
When the photographing lens is the subject, the focus detection device described above outputs two detection signals having a phase difference according to the front focus state or the rear focus state. When the focus shift is large and the phase difference is large, the duty ratio of the pulsed current flowing through the motor also becomes large, the motor rotates at a high speed, and the photographing lens moves at a high speed in the focusing direction. As the focus state is approached, the phase difference between the two detection signals becomes smaller, the duty ratio of the current flowing through the motor becomes smaller, and the rotation speed of the motor becomes slower.

[0015]

As described above, according to the present invention, the relative displacement amount signal proportional to the focus displacement amount is generated, so that the motor can be driven at high speed when the displacement amount with the pin is large, When the shift amount is small, the motor can be driven at a low speed, and quick focusing operation and high-level focusing can be performed. Further, since the drive sustaining signal capable of driving the motor is generated, the pulse width does not become so small that the motor cannot be driven. That is, even if the photographing lens is driven near the in-focus position and the relative displacement amount signal becomes small, the motor can be driven by the drive maintaining signal. Therefore, it is possible to reliably drive the taking lens to an accurate in-focus position without stopping the taking lens near the in-focus position.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a motor driving device according to the present invention.

FIG. 2 is a signal waveform diagram in the circuit of FIG.

FIG. 3 is a circuit diagram of a motor drive controller according to the present invention.

FIG. 4 is a signal waveform diagram of the circuit of FIG.

5 is a circuit diagram of a motor drive device to which the device of FIG. 3 is connected.

6 is a circuit diagram of a motor drive device to which the device of FIG. 3 is connected.

7 is a circuit diagram of a motor drive device to which the device of FIG. 3 is connected.

[Explanation of symbols]

6,23 Pulsed signal generation circuit 8,10,27,29 Circuit for maintaining pulse width above a predetermined value

Claims (2)

[Scope of utility model registration request] 1. A photographing lens drive motor (14), a pair of photoelectric conversion means (1, 2) for receiving light from a subject and generating photoelectric conversion signals corresponding to an optical image corresponding to the subject, respectively. Based on the photoelectric conversion signal from the pair of photoelectric conversion means,
Focus detection means (3, 4) for detecting the amount of relative deviation between the optical images in the pair of photoelectric conversion means, and relative having a pulse width proportional to the amount of relative deviation between the optical images. Generate a displacement amount signal (C) and a drive maintaining signal (E) having a minimum pulse width capable of driving the motor,
A drive control signal (H) is further generated by the logical sum of the relative displacement amount signal and the drive maintaining signal, and the drive control signal is given to the photographic lens drive motor to stop the photographic lens to the in-focus position. An automatic focus detection device comprising drive control means (6, 7, 8, 10) for surely moving without performing. 2. The pulse width maintaining means includes means for generating a pulse signal having the predetermined pulse width, and a pulse signal obtained by a logical sum of the pulse signal having the predetermined pulse width and the pulse signal of the pulsed current. The autofocus device according to claim 1, wherein the motor is driven by the following method.