JPH0721578B2 - Automatic focusing device - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to drive control of a photographing lens by an automatic focusing device.

(Background of the Invention) A conventional automatic focusing device drives a photographing lens by a motor based on a shift amount to a focus position of a photographing lens and a defocus amount corresponding to the shift direction, and when the driving is finished. The next focus detection is performed, or the drive is performed again based on the defocus amount obtained by performing the next focus detection while driving the same, and the defocus amount is repeated within a predetermined value that can be considered to be in focus. At some point, driving of the taking lens was stopped and a focus signal was output to the exposure control unit, the focus display unit, and the like. For example, as one of the shooting modes of a camera, a so-called one-shot that accepts a shutter release only after an automatic focusing device outputs a focusing signal.
Although there is an AF mode, if the focus detection method as described above is used, the detection immediately before the focus signal is output is spent merely for confirming the focus state, and a charge storage device such as CCD. In the automatic focusing device using as a light receiving element, the photographer feels that the charge accumulation time of the light receiving element and the passing time of the AF algorithm after the shooting lens is stopped are the delay time between receiving the shutter release, It had the drawback of poor responsiveness.

(Object of the Invention) An object of the present invention is to provide an automatic focusing device having excellent responsiveness to drive control of a taking lens.

(Summary of the Invention) The present invention sets a first zone that can be almost regarded as a focused state and a second zone that can sufficiently ensure the detection accuracy of an automatic focusing device, and sets the defocus amount to the first zone and the second zone. When the value is between the zone and the value, the shooting lens is driven based on this defocus amount, and the focus signal is output immediately after driving, so that the delay from the end of driving the shooting lens until the focus signal is output. The technical point is that there is no time.

(Embodiment) FIGS. 1 to 5 show an embodiment of the present invention. FIG. 1 is a general block diagram of an automatic focusing device that drives a photographing lens by a motor to automatically support a focused state. The light flux that has passed through the taking lens 1 in response to the automatic focusing device forms an image on a light receiving portion 2 (for example, a charge storage type light receiving element such as a CCD) of the automatic focusing device in the camera body, and a signal of this optical image. Is transmitted to the central control unit CPU4 via the interface 3.
This optical image pattern is AD-converted by the interface 3 and transmitted to the CPU 4, or is directly AD-converted by an AD converter incorporated in the CPU 4. The AD-converted optical image pattern is subjected to data processing by the CPU 4 by a predetermined AF algorithm, and a movement amount prediction value (hereinafter, referred to as a defocus amount) of the photographing lens necessary for bringing into a focused state is calculated.
Since the specific optical detection system and algorithm are already known, the description is omitted.

FIG. 2 illustrates the defocus amount detected by the automatic focusing device. In FIG. 2, the defocus amount corresponds to the position where the light beam that has passed through the taking lens 1 forms an image and the relative amount (image plane shift amount) ΔZ to the film surface. When the imaging surface of the taking lens 1 is on the film surface f ₀ , it indicates a focused state, when it is fα, it indicates a front focus state, and when it is fβ, it indicates a rear focus state. The light receiving unit 2 of the automatic focusing device is located at a position substantially equivalent to the film surface, and the light image of the light receiving unit 2 is sent to the central control unit CPU4 via the interface 3 to perform arithmetic processing for focus detection. The defocus amount ΔZ is calculated. In order to form (focus) the light image on the film surface, the defocus amount ΔZα in the front focus state or the defocus ΔZ in the rear focus state.
It is sufficient to drive the taking lens 1 back and forth by an amount corresponding to β.

The moving amount of the taking lens 1 is monitored by a feedback pulse by an encoder 6 (a photo interrupter provided on the output shaft of the servo motor 7) provided in the drive servo system, and the CPU 4 causes the actual moving amount of the taking lens 1 to move. While monitoring, the AF drive circuit 5 drives the servo motor 7 to drive the taking lens 1 to the in-focus position. Therefore, the defocus amount ΔZ calculated by the CPU 4 is actually converted into the count number of this feedback pulse to control the drive of the taking lens 1.

FIG. 3 is a specific circuit example of the AF drive circuit 5 of FIG. 1, which will be described below.

In FIG. 3, digital signals of an H level signal and an L level signal are applied as control signals to the two control terminals T2 and T3, and each of the transistors B3 to Q6 of the blit configuration for supplying a current to the motor 7 is selectively selected. Is turned on / off. The L level signal of the control signal corresponds to the voltage of the ground terminal GND, and the H level signal corresponds to the voltage of the power supply terminal V _CC or higher.

The control modes of the circuit of FIG. 3 will be described with respect to various states of control signals applied to the control terminals T2 and T3.

(1) When an H level signal is applied to both terminals T2 and T3 (standby state) PNP transistors Q1, Q2 and Q7, Q8 are connected to their bases through resistors R1 to R3 and resistors R6 to R8. Since the H level voltage is applied, all of them are turned off. Therefore, the PNP transistors Q3 and Q5 and the NPN transistors Q4 and Q6 forming the blit are also turned off, and the motor 7 is not supplied with power and is stationary. In this case, all the transistors in the circuit are off, the current consumption of the circuit is 0, and the servo standby state is set.

(2) When the control signal of the L level signal is applied to the terminal T2 and the H level signal is applied to the terminal T3 (forward rotation drive state) Current is supplied to the base of the transistor Q2 via the resistor R3, and the transistor Q2 is turned on. become. As a result, the transistors Q3 and Q6 are turned on, so that a current flows in the motor 7 in the direction of arrow A to drive the motor 7. On the other hand, the transistor
Since Q7 is off, transistors Q4, Q5 and Q8 are off. At this time, the transistor Q1 is turned on, but the transistors Q5 and Q7 are turned off, so there is no influence on the circuit operation.

(3) When the control signal of the H level signal is applied to the terminal T2 and the L level signal is applied to the terminal T3 (reverse rotation drive state) The circuit operation is opposite to the case of (2), that is, in the direction of the arrow B, that is, ( The motor drive current flows in the opposite direction to the case of 2), and the motor 7 is driven in the reverse rotation to that in the case of (2).

(4) When an L level control signal is applied to both terminals T2 and T3 (brake operating state) Transistors Q2 and Q7 are turned on
Since Q1 and Q8 are also turned on, the emitter current of transistor Q7 is supplied from transistor Q1 and the emitter current of transistor Q2 is supplied from transistor Q8. Also, the V _CE saturation voltage of transistors Q1 and Q8 is less than the V _BE required to turn on transistors Q5 and Q3, so
3 and Q5 turn off, only transistors Q4 and Q6 turn on. A loop consisting of the transistors Q4 and Q6 and the motor 7 serves to brake and brake the motor 7 being driven.
This is because the motor 7, which is rotating by inertia after the motor drive current is cut off, temporarily acts as a generator and causes a current to flow in the short-circuit loop, and rotational energy is released as heat energy, which brakes the rotation of the motor 7. Of. At this time, the rotation of the motor 7 causes one of the transistors Q4 and Q6 to operate in a reverse transistor mode (in which the roles of the emitter and the collector are reversed, and in the case of an NPN transistor, current flows from the emitter to the collector). There is.

The encoder 6 shown in FIG. 1 is composed of a photo interrupter composed of a light emitting diode LED1 and a phototransistor Q10. The encoder 6 monitors the actual movement amount of the taking lens 1 and feeds it as a feedback pulse to the CPU 4 from the terminal T1. Is output. The encoder 6 converts the movement amount (rotation amount) of the taking lens 1 into a pulse signal, which is output from the terminal T1.

The above is a description of the static control mode. However, in the vicinity of the servo target (focus position), the motor speed is reduced to improve the braking when the servo target is reached. To be done.

FIGS. 4A to 4C are examples of time charts showing the states of the control signals until the servo target is reached. FIG. 4 (A) is a chart showing a control signal input to the control terminal T2, and FIG. 4 (B) is a chart showing a control signal input to the control terminal T3. C) is terminal T1
It is a chart figure which shows the feedback pulse output from.

In FIGS. 4A and 4B, when the drive circuit 5 is operated by the CPU 4, a control signal for driving is input to the control terminal T2, and the control terminal T3 is at the L level while the motor 7 is being driven. It can be seen that the signal is being input. The driving circuit 5 gradually reduces the duty of the energization time to the servo motor 7 as the driving of the taking lens 1 to the servo target by the servo motor 7 from the time point t0 to improve the braking characteristic. In the driving circuit 5, the driving torque is controlled by alternately driving and braking during intermittent driving, but there is also a method of turning off energization instead of braking.
In this drive circuit 5, the duty of the drive time is 100%.
(Time points t0 to t1), 50% (Time points t1 to t2), 25% (Time points
The speed is changed in four steps from t2 to t3) and 12.5% (time points t3 to t4) to smoothly decelerate to the servo target position and shorten the servo time as much as possible.

When the driving circuit 5 drives and controls the photographing lens 1, the actual movement amount of the photographing lens 1 at that time is monitored by the encoder 6, and the feedback detected by the encoder 6 in FIG. 4 (C). The pulse is represented. As can be seen from FIG. 4 (C), as the duty of the control signal input to the control terminal T2 of the drive circuit 5 decreases, the drive speed of the photographing lens 1 also decreases,
The output interval of the feedback pulse signal output from T1 becomes longer. The amount of movement of the photographing lens 1 during servo is monitored by monitoring this feedback pulse, and as the servo target is approached, the drive speed is controlled based on this pulse signal to switch the duty.

Next, a drive control method when the photographing lens 1 reaches the servo target will be described with reference to FIG. The larger the defocus amount ΔZ calculated by the automatic focusing device, the more the accuracy deteriorates due to the capability of the light receiving unit 2 and the optical capability of the detection optical system including the taking lens 1. Therefore, in the embodiment shown in FIG. 5, the automatic focusing device has the first zone X formed around the focusing position Φ where the defocus amount is sufficiently small and the photographing lens can be determined to be in the focusing state. And a second zone Y which is larger than the first zone X and which can expect the detection accuracy of the automatic focusing device. More specifically, when the defocus amount ΔZ calculated by the automatic focusing device is smaller than the second zone Y, it is possible to estimate that the photographing lens 1 is almost at the focusing position by performing servo based on this. There is. The taking lens 1 is drive-controlled based on the first zone X and the second zone Y set in this way.

(1) When the defocus amount Z is within the first zone X (ΔZ <X), the photographic lens 1 is not driven and a focus signal is output.

(2) When the defocus amount ΔZ is larger than the first zone X and smaller than the second zone Y (X ≦ ΔZ ≦ Y),
The photographing lens 1 is driven based on the defocus amount ΔZ, and a focusing signal is output immediately after the driving is completed.

This focus signal is normally sent by the CPU 4 when the taking lens 1 is stopped.
And is used as a signal that enables exposure control such as shutter release operation. By providing two focus determination zones in this way (except for the case (1) when the focus state is initially set), refocus detection for confirming the focus state and focusing by the passage time of the AF algorithm are performed. It is possible to eliminate the delay in the operation response. Specifically, in the case of (2) described above, since the focus detection operation is not performed again after driving the taking lens 1 based on the defocus amount ΔZ, the taking lens 1 stops immediately after the taking lens 1 is stopped. A focus signal will be output.

Attached Table 1 explains the drive control of the photographing release performed by the CPU 4 of the camera based on a flowchart.

Steps S1 to S4 are a flow for calculating a defocus amount (image image movement amount on the film surface) using a general charge storage element. In step S5,
If the calculated defocus amount ΔZ is smaller than the second zone Y, the flag FLG is set to FLG = 1 (step S
6) If larger, set FLG = 0 (step S7). With this flag, after the lens drive of the taking lens is finished,
It is possible to distinguish whether the driving is performed from within the second zone Y or from outside the second zone Y. In step S8, the defocus amount ΔZ is the first zone X.
Check if it is within. If the defocus amount ΔZ is within the first zone X (ΔZ <X), the process proceeds to step S12, and since FLG = 1 at this time, the focus signal is immediately output in step S13. In step S8, the defocus amount ΔZ
If is larger than the first zone X, proceed to step S9,
The defocus amount ΔZ is converted into the number of pulses by the image movement coefficient unique to the taking lens 1 so that it can be compared with the feedback pulse. It should be noted that this coefficient is output from the storage means (ROM or the like) provided in the taking lens to the CPU 4 in the camera prior to the drive control of the taking lens 1. Step S1
At 0, the drive control of the taking lens 1 is started by the motor 7. In step S11, the drive control described in FIG. 4 is performed.

In step S12, the flag FLG is determined and the FLG
= 1, the defocus amount ΔZ is located between the first zone X and the second zone Y (X ≦ ΔZ ≦
Since it is Y), the focus signal is immediately output (step S13). Further, when FLG = 0 in step S12, it means that the defocus amount ΔZ is larger than the second zone Y (ΔZ> Y). Therefore, the focusing signal is not output,
The process returns to step S1 again, and the focus detection operation is performed.

In step S14, the AF mode of the camera is one-shot AF
It is determined whether or not it is the mode (AF mode in which the focus detection operation is not performed after the focus state is detected once, and the shutter release operation is possible), and in the one-shot AF mode, the shutter release operation can be performed immediately. Yes (step S15). If it is not the one-shot AF mode, that is, if it is the continuous AF mode (the AF mode in which the focus detection feature is repeatedly performed after the focus detection and the subject is a moving body is continuously followed), the step S1 Then, the focus detection operation is continued.

Therefore, in the embodiment, the magnitude of the defocus amount ΔZ is taken into consideration, and when the defocus amount ΔZ is between the first zone and the second zone, the defocus amount ΔZ is sufficiently reliable. Defocus amount Δ
The photographing lens is drive-controlled based on Z, and a focus signal is output at the same time when the drive control is completed. Therefore, the focus detection time for confirming the focus can be eliminated, and an automatic focusing device with good responsiveness can be obtained.

(Effects of the Invention) According to the present invention as described below, in order to drive and control the taking lens in consideration of the size of the defocus amount detected by the automatic focusing device, focusing is performed from the end of driving the taking lens. The time until signal output can be shortened, and good response with no delay time can be obtained.

[Brief description of drawings]

1 to 5 show an embodiment of the present invention. FIG. 1 is a block diagram of an automatic focusing device for automatically servoing a photographing lens by a motor to a focused state, and FIG. 2 is a photographing lens. FIG. 3 is an explanatory view showing an image forming state, FIG. 3 is a drive circuit diagram of a photographing lens, FIG. 4 is a timing chart of signals of terminals T1 to T3, and FIG. 5 is a defocus amount and a first zone and a second zone. It is explanatory drawing which shows the relationship of. (Explanation of symbols of main parts) 1 ... Photography lens, 4 ... CPU, 5 ... Drive circuit, 7 ... Motor

Claims (1)

[Claims] 1. An automatic focusing device having a defocus calculation means for calculating a defocus amount corresponding to a shift amount of a photographing lens to a focus position and a shift direction thereof, the focus being substantially centered on the focus position. A first zone indicating a state and a second zone larger than the first zone are set, and when the defocus amount is larger than the first zone and smaller than the second zone, the photographing lens is driven based on the defocus amount. An automatic focusing device characterized by being controlled and outputting a focusing signal indicating the focused state immediately after completion of the drive control.