JPH0232605B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an automatic focusing device that uses a motor servo to drive a lens.

Conventionally, motor servo sets the motor in three modes: forward rotation, reverse rotation, and stop, compares the input signal with the output signal generated by the motor output, and drives the motor until the two signals match. ing. This conventional method has disadvantages such as the speed of the motor cannot be increased very much due to the response due to the weight of the backlash mechanical system of the gear train, and the dead zone must be wide. If this happens, hunting may occur and the motor will not stop, resulting in the inconvenience that even in motor servos used in camera autofocus devices, the photographic lens may not stop accurately at the predetermined position. A situation has arisen.

SUMMARY OF THE INVENTION The present invention aims to solve these drawbacks and provide an automatic focusing device that has a faster motor operating speed, a narrower dead zone, and thus operates faster and has higher accuracy. In particular, the object is to provide a motor servo device for such an autofocus device.

In the present invention, the motor is driven by a pulse signal, and the rotational speed of the motor is varied by the pulse width (duty ratio) of the pulse signal. That is, the pulse width is increased when the pulse width is significantly deviated from the in-focus point (that is, the time for supplying power to the motor is lengthened), and it is decreased as the pulse width approaches the in-focus point (the time for supplying power to the motor is shortened). If that's all you do, the pulse width near the in-focus point will become too small and the motor will no longer respond to the pulse signal, resulting in the motor stopping before focusing. Therefore, in the present invention, a means for specifying the minimum value of the pulse width is provided to prevent the speed of the motor from falling below a predetermined value.

Among autofocus cameras, there are cameras that drive a photographic lens or the like using a servo motor to achieve focusing. In general, the signals required by the servo device of this type of camera are those that represent the so-called front focus state, in which the imaging surface of the photographing lens is formed in front of the film surface, and vice versa, the signals that represent the rear focus state. There are three signals: a signal representing the focus state, and a signal representing the in-focus state. The servo device operates as follows based on these three signals. When the photographic lens captures the subject, assuming that it is in the front focus state, a signal indicating the front focus is output, which causes the motor to rotate in one direction and move the photographic lens in the focusing direction. When focus is achieved, a signal indicating focus is output, stopping the motor and holding the photographic lens in that position. Also, if the camera is in the rear focus state, a signal indicating rear focus is output, and the motor is rotated in the opposite direction to achieve focus. In order to perform the above operations, the servo device includes a focus detector etc. that outputs the three signals mentioned above, but the servo device includes a focus detector etc. that outputs the three signals mentioned above.
An example is shown below. This focus detection device outputs two sinusoidal detection signals from subject light that has passed through a photographic lens or the like. The above-mentioned three states are discriminated from this detection signal based on the phase difference. That is, when the phase of one of these two detection signals is ahead of that of the other signal, the front focus is determined, for example, when the phase is opposite, the rear focus is determined, and when there is almost no phase difference, the focus is determined. It is being Furthermore, the amount of phase shift is proportional to the deviation from focus. Therefore, by detecting the phase difference from these two signals and driving the motor, a servo device for an autofocus camera can be achieved.

An automatic focusing 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 two detected sinusoidal signals from the aforementioned focus detector. Comparators 3 and 4 convert the two detected sinusoidal signals into square wave signals--binary signals shown in FIG. 2A and B. It is assumed that signal B is initially ahead of 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 signal B until time T
is ahead of signal A in phase. The two rectangular wave signals A and B are input to an exclusive OR gate (hereinafter referred to as EX-OR) 6 and output as 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 motor M is basically driven by this signal C. Further, the two rectangular wave signals A and B are input to the OR gate 7 and output as the signal D in FIG. Signal D serves as a trigger input for two one-shot multis 8 and 9. One shot multi 8
and 9 operate at the rising edge of signal D (in this example, at the rising edge of signal B, which is ahead in phase), and resistors
It outputs signals E and F having pulse widths t _{1 and} t 2 determined by R ₁ , capacitor C ₁ , resistor R _{2 ,} and capacitor C ₂ . The output signal E of the one-shot multi 8 is such that the pulse width of the pulse that drives the motor M, that is, the pulse width of the signal C, narrows as the focus approaches, and the pulse width becomes extremely small near the focus, causing the motor to stop operating. This is necessary to prevent
Pulse width t ₁ means the minimum pulse width at which the motor can operate. Signals C and E are input to OR gate 10 and output as signal H in FIG. 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 becomes small, that is, when the image is almost in focus. Therefore, the pulse width of signal H is
t maintained above ₁ . Since the output of the one-shot multi 9 is taken from the terminal, its output waveform is like signal F, and the pulse width _t2 determines the focusing zone (dead zone width). This width t ₂ is the width
t is chosen to be smaller than ₁ . The D flip-flop 11 receives the C signal as a data input, and reads and latches the C signal as a data input at the rising edge of the F signal inputted as a clock signal. When the pulse width of the logic "1" of the C signal is wider than the width _t2 of the logic "0" of the F signal, the D flip-flop 11 outputs a logic "1" from the Q terminal, and when it becomes narrower, it outputs a logic "0". . The output of this D flip-flop 11 becomes the G signal shown in FIG. That is, when the in-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 logic "0" of the F signal, the G signal becomes logic "0". The signal H and the signal G are ANDed by an AND gate 12, and the output of the AND gate 12 becomes the signal I in FIG. On the other hand, the D flip-flop 5 receives the A signal as a data input, and reads the A signal as a data input at the rising edge of the B signal, which is a clock signal. In this example, the B signal leads the A signal in phase from the front focus state to the in-focus state, and the Q output of the flip-flop 5 is logic "0". This Q output is shown as the J signal in FIG. If it is in the rear pin state, the A signal leads the B signal in phase and the J signal is logic "1". The J signal and I signal are input to EX-OR K and output as the K signal in FIG. This K signal matches the I signal since the G signal is logic "0". A current IM flowing through the motor M is generated by the voltage difference between the K signal and the J signal, and the direction of the current flowing is indicated by the arrow in the drawing. If the J signal is a logic "1", the K signal is the inverse of the I signal, and the current flowing is in the opposite direction to the arrow in the drawing. However, the amount of current flowing is not related to the direction. As can be seen from the above explanation, the motor drive current is in the form of a pulse, and the pulse width corresponds to the amount of deviation from focus, and the pulse width becomes smaller near focus, but the motor M is unable to rotate. _The motor _M
There is no drive signal to the motor M, and the motor M is stopped.

In the embodiment of FIG. 1, the motor M is controlled by the K signal and the J signal, and when the pulse of the K signal disappears (that is, the signals between the terminals of the motor M both become logic "1" or "0". (When you get used to it) It will no longer be driven. Therefore, it is not particularly configured to generate a stop signal. When it is desired to suddenly stop the motor in response to a 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 by comparators 20 and 21 into rectangular wave signals A' and B' shown in FIG. EX-OR 23 inputs signals A' and B' and outputs signal C' shown in FIG. The one-shot multi 29, triggered by the C' signal, outputs an output pulse from the Q terminal, such as the G' signal of FIG. 4, with a pulse width t ₁ determined by _the resistor R ₁ and the capacitor C 1 . NOR gate 27 logically ORs signals C' and G' and outputs signal I' in FIG. The I' signal corresponds to the H signal in FIG. signal A′ and
B' is also AND gate 24 and OR gate 25
and produce signals E' and F' shown in 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 outputs a pulse having a pulse width t ₂ determined by the resistor R ₂ and the capacitor C ₂ to its terminal as shown in the H' signal in FIG. This H' signal corresponds to the F signal in FIG. The one-shot multi 28 uses 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′ and B′ signals, that is, the phase difference, is
When the pulse width of the H' signal becomes smaller than _t2 , the D flip-flop 28 outputs a logic "1" to its Q terminal. This results in pulse width t ₂ being the focal zone, similar to the device of FIG. The Q output of the one-shot multi 28 is inverted by the inverter 36 and output to the fourth
This becomes the J′ signal in the figure. D flip-flop 22 is
The A' signal is used as a data input, and the data is read and latched by the B' clock signal. In this example, the B' signal leads the A' signal in phase, so the Q output is a logic "0" like the signal M' in Figure 4.
becomes. The NAND gate 31 outputs the inverted AND of the M' signal, J' signal, and I' signal to the output terminal 33, but since the M' signal is logic "0", the output at the output terminal 33 is logic "1". ” is. The NAND gate 34 outputs the inverted AND of the 'signal, J' signal, and I' signal to the output terminal 34, but the 'signal is logic "1" and the J' signal is at time T (the point in time when the in-focus state is reached). Since the logic is "1" until then and the logic is "0" thereafter, an inverted version of the I' signal is generated until time T, and thereafter it becomes logic "1". A pulse such as 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 3 in Figure 3
5 is the input terminal 33' of the motor drive circuit shown in FIG.
34' and 35'. The basic configuration of the motor drive circuit in FIG. 5 is transistors 100, 10.
A motor 14 is connected between midpoints a and b of a bridge circuit consisting of transistors 101 and 102, and when transistors 101 and 102 are turned on, current flows from a to b, rotating the motor 14 in one direction. When 103 is ON, current flows from b to a, rotating the motor 14 in the other direction. In this example, the High level is applied to the terminal 33', the K' signal is applied to the terminal 34', and the J' signal is applied to the terminal 35'. Therefore, the transistor 105 is
OFF and transistors 100 and 103 are OFF
However, transistor 106 is turned on when the K' signal is at low level, and transistors 101 and 102 are turned on.
When turned on, current flows to the motor 14 from a to b. When focus is achieved, both terminals 33' and 34'
It becomes a high level and there is no pulse to drive the motor 14. Also, since the terminal 35' becomes low level, transistor 107 is turned on and transistor 1 is turned on.
Turn on 01 and 103. As a result, transistor 101, motor 14, and transistor 10
A short-circuit closed loop of No. 3 is formed, but when the collector and emitter of one of the transistors operate in reverse, a dynamic brake is generated and a sudden stop can be realized.

Further, the motor drive circuits shown in FIGS. 6 and 7 are other embodiments to which the motor control circuit shown in FIG. 3 can be connected. In FIGS. 6 and 7, when focusing is achieved, all transistors 100 to 103 are turned off, the coil of relay 40 is energized, the contacts are closed, and a dynamic brake is generated. Transistor 10 of the circuit of FIG.
Although the ground connections 0 to 103 are different from those shown in FIGS. 5 and 6, this connection is suitable when there is sufficient power supply voltage.

Contrary to the above-described signal format, when a high level signal is applied to the terminal 34' and a K' signal is applied to the terminal 33', the direction of rotation of the motor is reversed.

A focusing operation by the device of the present invention will be explained. When the photographic lens is placed on the subject, the aforementioned focus detection device outputs two detection signals having a phase difference depending on the front focus or 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 rotational speed of the motor is fast, and the photographing lens moves at high speed in the direction of focusing. As the focus state approaches, the phase difference between the two detection signals becomes smaller, the duty ratio of the current flowing through the motor becomes smaller, and the rotational speed of the motor becomes slower. This effect of the present invention makes it possible to reduce the effects of inertia, backlash, etc. when the motor stops. Another effect of the present invention is that the duty ratio does not become so small that the motor cannot be driven, so even if the duty ratio is made small as described above, the problem of the motor being stopped before focusing does not occur.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a motor drive device according to the present invention. FIG. 2 is a signal waveform diagram in the circuit of FIG. 1. FIG. 3 is a circuit diagram of a motor drive control device according to the present invention. FIG. 4 is a signal waveform diagram of the circuit of FIG. 3. 5, 6 and 7 are circuit diagrams of a motor drive device to which the device of FIG. 3 is connected. Explanation of the symbols of the main parts: Pulse signal generation circuit...6, 23; Circuit for maintaining the pulse width above a predetermined value...8, 10, 29, 27.

Claims (1)

[Scope of Claims] 1. Photoelectric conversion means for receiving a pair of optical images, respectively; Focus detection means for detecting a relative displacement amount of the pair of structures based on a pair of photoelectric signals from the photoelectric conversion means; In an automatic focusing device equipped with a motor that drives a photographing lens based on the relative deviation amount, the relative deviation is such that when the relative deviation amount is large, the pulse width is wide, and when the relative deviation amount is small, the pulse width is narrow. drive control means for intermittently driving the motor with a pulsed current having a pulse width proportional to the amount of the pulsed current; An automatic focusing device comprising: a pulse width maintaining means for maintaining the predetermined pulse width, the pulse width maintaining means maintaining the predetermined pulse width even if the relative shift amount becomes equal to or less than a predetermined value. 2. The pulse width maintaining means includes means for generating a pulse signal with the predetermined pulse width, and controls the motor with a pulse signal obtained by logically adding the pulse signal with the predetermined pulse width and the pulse signal of the pulsed current. An automatic focusing device according to claim 1, characterized in that the automatic focusing device is driven.