JPS61282810A - Automatic focus detecting device - Google Patents

Abstract

PURPOSE:To prevent an automatic focus detecting device from malfunctionining by starting a motor for lens driving at the start of focusing detection control and moving a lens from its start point, and inhibiting discrimination operation for focusing until the motor reaches a specific rotating speed. CONSTITUTION:A power source 1 is connected to an automatic focus circuit 3 with a changeover switch 2, a ligth emitting element 5 is activated, and reflected light from an object is photodetected 6 to output an L signal S0 until focusing is detected. A signal S1 is H and the output S7 of a NAND circuit 9 which constitutes an R-SFF is H. Transistor TRs 7, 19 and 22 turn on when the signal S7 is H to rotate the motor 23 forward. A signal from a encoder which is not shown in figure is inputted to a preliminary run section setting circuit 12 and the signal S6 is L until the motor reaches the normal rotating speed. When the motor 23 rotates forward and fucusing is obtained, the signals S5 and S6 go up to H and the signal S7 is inverted to L. One-shot multivibrator circuits 14 and 15 and an OR circuit 18 cooperate to turn off the TRs 19 and 22 and turn on TRs 20 and 1 for a specific time, braking the motor 23 electrically. Thus, malfunction is prevented and focusing precision is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to an automatic focus detection device, and in particular to control of a drive motor when performing a so-called focusing operation while moving a photographic lens along the optical axis using a drive motor. Regarding circuits.

(Background of the Invention) In general, an automatic focus detection device for a camera equipped with an autofocus function includes a motor control circuit that controls a drive motor that moves a photographic lens forward and backward in the optical axis direction, and a motor control circuit that controls a drive motor that moves the photographic lens forward and backward in the optical axis direction. The camera is equipped with a focus detection circuit which, when detecting this, instructs the motor control circuit to stop the drive motor to keep the photographic lens stationary.

Here, when the shutter release button is pressed, the focus detection circuit starts a focus detection operation to detect whether the photographing lens is at the in-focus position, and at the same time, the motor control circuit starts energizing the drive mode. to move the photographing lens from the predetermined starting position.

When the focus detection circuit detects that the photographic lens has come to the optimal focus position due to this movement, it commands the motor control circuit to stop energizing the drive motor, causing the photographic lens to stop at the focus position, and then It is now possible to take pictures in a focused state.

(Problems to be Solved by the Invention) However, such conventional automatic focus detection devices have the following problems.

First, as mentioned above, the focus detection operation by the focus detection circuit and the control operation of the drive motor by the motor control circuit are started simultaneously in conjunction with the shutter release button, but at startup, a large current flows through the drive motor. This causes a problem in that the power supply voltage suddenly drops below the operating rated voltage of the automatic focus detection device, resulting in unstable operation.

Next, when the focus detection circuit detects the focused state of the photographing lens, it causes the motor control circuit to stop supplying current to the drive motor and causes the drive motor to perform a braking operation. Therefore, the drive motor rotates forward by a certain amount due to inertia and then stops, and the photographing lens also remains at the position at the time of the stop. In order to keep the photographic lens stationary at the optimal focus position, correction control is performed to set the start time of the brake operation a predetermined time before the photographic lens reaches the in-focus position.

However, in a so-called start-up state in which the drive motor, which has started rotating in conjunction with the shutter release button, has not yet reached its steady state rotation speed, when the focus detection circuit finishes detecting the focus, the rotation speed of the drive motor decreases. The brake operation will be performed when it is uncertain. For this reason, when the correction control described above is performed, the photographic lens cannot be stopped at an optimal focusing position, and a problem arises in that the focus detection accuracy is deteriorated due to variations in the resting position.

Furthermore, we focused on the fact that the shorter the time required for the brake operation, that is, the time it takes for the drive motor to rotate due to inertia until it stops, the more accurately the photographic lens can be stopped at the in-focus position. Some devices are equipped with a motor control circuit that improves the braking force by supplying current, but in this case, the drive motor that starts rotating in conjunction with the shutter release button has not yet reached its steady state rotation speed. When focus detection by the focus detection circuit is completed within a certain period of time, the drive motor performs a reverse rotation using a reverse rotation current from the point at which it once stopped. For this reason, the photographing lens ends up stopping at a position that is further back than the optimal focusing position, resulting in deterioration of focusing accuracy.

(Objective of the Invention) An object of the present invention is to solve these drawbacks and provide an automatic focus detection device that operates reliably and has high focusing accuracy.

(Summary of the Invention) In order to achieve this object, the present invention provides a means for inhibiting a focus determination operation during a focusing operation until the drive motor for moving the photographing lens reaches a steady state rotation speed. This is the technical point.

(Example) Hereinafter, an example of an automatic focus detection device according to the present invention will be described with reference to the drawings.

Fig. 1 shows the main circuit configuration of the motor control circuit in this embodiment, where 1 is a power source such as a battery, 2 is an on/off switch for focus detection operation, and 3 is an autofocus circuit that performs focus detection. be.

A light emitting element 5 that emits light when a current is supplied through the NPN transistor 4 connected to the control signal output terminal T of the circuit 3.
is connected to the output terminal side of selector switch 2, and input terminal 1
1. I2. A pair of light receiving elements 6 are connected to the I3 side.

Here, during a focusing operation to be described later, the autofocus circuit 3 emits infrared light or the like from a light emitting element 5 toward a subject, receives reflected light from the subject by a light receiving element 6, and receives each light. When the amounts of light received by the elements become equal, it is determined that focus is achieved, and a focus control signal indicating that focus has been detected is output from output terminal Q.

A resistor 7 is connected between the output terminal of the changeover switch 2 and the ground terminal of the power supply 1, and the output terminal of the changeover switch 2 is connected to one input terminal S of a NAND circuit 9 via an inverter circuit 8. The NAND circuit 10 constitutes an R-S flip-flop circuit (hereinafter referred to as R-3FF) together with the NAND circuit 9, and one input terminal R is connected to the output terminal of the NAND circuit 11.

Each input terminal of the NAND circuit 11 is connected to an output terminal Q of the autofocus circuit 3 and a run-up section setting circuit 1.
2 output terminal Y is connected.

The output terminal X of the NAND circuit 9 is connected to the inverter circuit 13,
One-shot multivibrator circuit 14.2 manual OR
It is connected to each input terminal of the circuit 17, and the output terminal of the one-shot multivibrator circuit 14 is further connected to each input terminal of the second one-shot multivibrator circuit 15, the inverter circuit 16, and the human-powered OR circuit 18. are doing.

Furthermore, a second one-shot multivibrator circuit 15
The output terminal of is connected to the other input terminal of the OR circuit 17.18.

PNP type transistors 19, 20 and NPN type transistors 21, 22 constitute a drive circuit that supplies power to a drive motor 23 that moves the photographic lens in a forward and reverse manner. The inverter circuit 16 and transistor 21 are O
The R circuit 18 and the transistor 22 are turned on and off according to respective control signals from the OR circuit 17, and the current input terminal of the drive motor 23 is connected between the connection point of the transistor 19.21 and the connection point of the transistor 20.22. ing.

FIG. 2 shows a drive mechanism for the photographing lens 24 that is moved by the drive motor 23 shown in FIG.
The photographic lens 24 is moved along the optical axis along the optical axis by a drive motor 23 (FIG. 1) together with the base plate 26.

Here, during a focusing operation, when a shutter release button (not shown) is pressed, the photographing lens 24 is moved to a predetermined position (start position) outside the focusing range, for example, at the position closest to the camera body 25.
It is extended by a drive motor 23 from a position close to the object toward the subject.

The absolute amount of movement of the photographing lens 24 from the starting position at this time is determined by the distance between the rack 28 fixed to the base plate 26 and the pinion 29.
The signal is transmitted to the encoder board 30 via the rotation of the encoder board 30, and as the brush 31 as a detector slides on the encoder pattern 30a, it is detected as a code signal from the output terminal of the brush 31. This code signal is sent to the run-up section setting circuit 12 in FIG.
is supplied to.

Next, the operation of the circuit shown in FIG. 1 will be explained together with the timing chart shown in FIG. In FIG. 3, Sl is the voltage appearing at the output terminal of the selector switch 2, S2. S3. S4 is the approach section setting circuit 1 from the encoder brush 31 in FIG.
2, S5 is a signal appearing at output terminal Y of approach section setting circuit 12, S6 is a focusing signal output from output terminal Q of autofocus circuit 3,
S7 is the output signal of the output terminal X of the NAND circuit 9, S8 is the output signal of the one-shot multivibrator circuit 14,
S9 indicates the output signal of the one-shot multivibrator circuit 15, and S10 indicates the voltage polarity applied between the current supply terminals of the drive motor 23.

Selector switch 2 closes together with the shutter release button (
At time t1), the circuit is supplied with power and starts a focus detection operation.

First, the transistor 4 is turned on by an on signal output from below the control signal output terminal of the autofocus circuit 3, and infrared light is emitted from the light emitting element 5 toward the subject. A pair of light-receiving elements 6 receive the reflected infrared light, and when the amount of light received by each light-receiving element becomes equal, the autofocus circuit 3 determines that the photographic lens 24 is in focus, and outputs a signal from the output terminal Q. A focusing signal S6, which will be described later, is generated.

At time t1, the photographing lens 24 is outside the focus adjustment range, that is, at the starting position where focusing is not possible, so the output of the output terminal Q of the autofocus circuit 3 is at the "LOW" level, and the output terminal of the changeover switch 2 is at the "LOW" level. The level becomes “High”. Therefore, a "'Low" level signal is applied to the set input terminal S of the NAND circuit 9, and a "Hiqh" level signal is applied to the reset input terminal R of the NAND circuit 10. The output signal S7 of the circuit 9 becomes "High" level from time t1.

This output signal S7 is passed through an NPN transistor 22 via an OR circuit 17 and a PNP via an inverter circuit 13.
Since the voltage is applied to the NP-type transistor 19, the drive motor 23 receives a voltage of the normal polarity shown in S10, and the voltage is applied to the dotted line a.
As shown in , current flows and forward rotation occurs. Furthermore, at this time,
Since the one-shot multivibrator circuits 14 and 15 are not activated, their respective output signals 38 and 39 are at the "LOW" level, and the transistors 20 and 21 are both off.

As the photographing lens 24 moves due to the forward rotation of the drive motor 23, code signals 32, 33, 34 from the encoder are supplied to the run-up section setting circuit 12, and the code signals 32, 33, 34 become "LOW". , “Hiah”,
At time t2 when it becomes “High”, the signal S5 becomes ')li
In addition, the setting code of the code message @S2.33.34 is L when the drive motor 23 reaches a steady state and the photographing lens enters the focus adjustment range and can be focused.
OW”, “High”, “l-1-1i
”.

For example, when starting at time 11, a large current flows through the drive motor 23 and the power supply voltage drops, which causes the autofocus circuit 3 to malfunction and output a "High" level focusing signal S6 (indicated by a broken line). Even if the signal S5 is at the 'Low' level until time t2, the focus signal S6 is masked by the NAND circuit 11, and the level of the signal S7 does not change, so that the drive motor 23 does not rotate in the normal direction. will continue.

As a result, the driving motor 23 performs the focusing operation without malfunctioning.

Next, at time t3, when the autofocus circuit 3 detects the in-focus position of the photographing lens 24, a rectangular focus signal S6 of the "I (ioh") level is output from the output terminal Q. At this time t3 , the run-up section setting circuit 1
Since the output signal S5 of 2 is "l-1-1i", the focus signal S6 is applied to the reset terminal R of the NAND circuit 10, and the output signal S7 of the NAND circuit 9 is "LOW".
Flip to level.

In synchronization with the fall of this output signal S7 from "High" to "Low", the one-shot multivibrator circuit 14 is activated and the "Hr
A rectangular signal S8 is output, and this output signal S9 is supplied to the drive motor 23 via the inverter circuit 16, the PNP transistor 20, the OR circuit, and the NPN transistor 21. Both 20 and 21 are turned on, and a reverse current is supplied to the drive motor 23 as shown by the dotted line only during the time width τ1, and the drive motor 23 performs a braking operation against inertia.

Note that when the signal S7 becomes "LOW" level, the transistor 19 is turned off, and the NPN type transistor 22 is turned off.
Output signal S of one-shot multivibrator circuit 15
It is turned off while 9 is "1ow".

Next, the one-shot multivibrator circuit 15 is activated in synchronization with the fall of the signal S8 (time 14), and a rectangular signal S9 that becomes "High" in a preset time width τ2 is output. This signal S9 is the OR circuit 17.1
Since the transistors 21 and 22 are both turned on, and the PNP transistors 19 and 20 are turned off at this point, the drive motor 23 is stopped because no current is supplied to it. do.

Note that the photographing lens 24 is returned to the start position after the exposure operation is completed.

As explained above, the run-up section setting circuit 12 detects the absolute amount of movement of the photographing lens 24, determines based on this absolute amount of movement that the drive motor is rotating in a steady state,
After that, the drive motor 23 can be controlled to stop. Therefore, since the drive motor 23 does not stop before reaching a certain rotation speed, the photographing lens 24 can be accurately stopped at the in-focus position.

In the above embodiment, the run-up section setting circuit sets the stop prohibition period of the drive motor based on the encoder output turn, but the circuit is not limited to this, and the operation may start in synchronization with the pressing of the shutter release button. , a timer circuit may be used to count the time until the drive motor reaches a predetermined rotation speed. .

(Effects of the Invention) As explained above, according to the present invention, stopping of the drive motor due to focus detection is prohibited until the drive motor reaches a predetermined number of rotations, so that at the start of the focusing operation, Malfunctions are prevented even if a large current flows through the drive motor and the power supply voltage fluctuates.Furthermore, the rotation of the drive motor is controlled to stop when it reaches a predetermined rotation speed, allowing the photographic lens to remain at a reliable focusing position. It is possible to improve focusing accuracy.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a main part of an embodiment of an automatic focus detection device according to the present invention, FIG. 2 is an explanatory diagram showing an overview of the photographing lens drive mechanism, and FIG. 3 is an explanatory diagram of the operation of the circuit in FIG. 1. be. 8.13.16: Inverter circuit 9.10, 11: NAND circuit 12: Run-up section setting circuit 14.15: One-shot multivibrator circuit 17
．． 18: OR circuit 19.20, 21.22: Transistor 23: Drive motor 24: Li shadow lens 31: Brush

Claims (1)

[Claims] Automatic system that moves the photographic lens in the optical axis direction by a drive motor, detects that the photographic lens has come to the in-focus position, stops the drive motor, and stops the photographic lens at the in-focus position. In an automatic focus detection device that performs focus adjustment, the drive motor is rotated at the start of the focus detection control to move the photographing lens from a predetermined starting position, and the drive motor is rotated until the amount of movement reaches a predetermined amount. An automatic focus detection device characterized by comprising a motor control means for prohibiting the motor from stopping.