JPH07128569A - Driving controller for movable lens of photographing device - Google Patents

Abstract

PURPOSE:To unnecessitate a speed sensor, to reduce the number of sensors and to reduce manufacturing cost of a photographing device by differentiating position information from a position sensor obtain moving speed information of a movable lens, and servo-controlling the movable lens to the target position by position information and moving speed information. CONSTITUTION:This device is provided with a lens driving means 6 which drives a variable lens, a lens position detecting means 7 which detects an actual position of the variable lens, and a differentiation means 10 which differentiates position information from the position detecting means 7 and converts it to moving speed information of the variable lens. And a control means 9 controls the lens driving means 6 so that a position of the variable lens is aligned with a target position based on position information and moving speed information obtained from the lens position detecting means 7 and the differentiation means 10 respectively and given target position information. By using this constitution, position information and moving speed information of the variable lens can be obtained by only the position detecting means 7, a speed sensor is not required, manufacturing cost of the photographing device can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive control device for a movable lens provided in a photographing device such as various cameras or video cameras.

[0002]

2. Description of the Related Art In recent years, most photographing devices such as cameras and video cameras have an autofocus function and an electric zoom function. The lens barrel of such an image pickup apparatus is provided with a drive means for moving the movable lens for focusing and the movable lens for zooming in the optical axis direction thereof. As the drive means of this type, a coil and a magnet are used. An electromagnetically-driven actuator having is used. As an example of such an imaging device, a device using a voice coil motor (hereinafter, referred to as VCM) as an actuator is proposed in, for example, Japanese Patent Laid-Open No. 4-25811.

This is, as shown in FIG. 5, a movable lens group 1
A ring-shaped coil 3 is attached to the lens holding member 2 that holds the lens so as to be concentric with the optical axis center. On the other hand, a ring-shaped magnet 4 is fixed to the member 5 on the outer shell side concentrically with the ring-shaped coil 3 as shown in the figure. Since the magnet 4 is magnetized in the radial direction of the center of the axis, the magnetic flux and the current are spatially orthogonal to each other when a current is applied to the ring-shaped coil 3, so that the ring-shaped coil 3 is made to follow the optical axis by Fleming's left-hand rule. The lens holding member 2 fixing the ring-shaped coil 3 is moved in the optical axis direction because it is movably held in the optical axis direction. It will move in the optical axis direction. The moving direction changes depending on the direction of the current flowing through the ring-shaped coil 3. The ring-shaped coil 3 and the ring-shaped magnet 4 constitute a VCM 6.

However, since only moving the current through the ring-shaped coil 3 simply keeps it moving, the VCM 6 of this type consisting of the ring-shaped coil 3 and the ring-shaped magnet 4 is actually operated by the position sensor 7. Based on the lens position information, a so-called feedback system servo control system as shown in the block diagram of FIG. 6 is configured to control the position of the movable lens group 1. The position sensor 7 is composed of an inclined magnet 7A having an inclined front end and a Hall element 7B arranged to face the inclined portion of the inclined magnet 7A, and the Hall element 7B is moved according to the movement of the movable lens group 1.
The magnetic flux density from the inclined magnet 7A with respect to changes the output voltage from the Hall element 7B,
This voltage corresponds to the position of the movable lens group 1.

The operation of the servo control system in FIG. 6 has a certain amplification factor (indicated by servo gain G (s)) which is the difference between the position command information (target position information) and the position information obtained by the position sensor 7. Send it to VCM6. The lens position changed by the current flowing into the VCM 6 is constantly detected and fed back by the position sensor 7, and the current corresponding to the difference from the position command information is sent to the VCM 6, so the lens position is constantly the target position based on the position command information. Try to follow. The block diagram of FIG. 6 can be realized very easily by an electric circuit as shown in FIG.

In FIG. 7, an operational amplifier Q1 outputs position command information Vx and a position sensor output Vs indicating an actual lens position.
Is to make a difference Vo of
Since it is doubled (= servo gain G (s) = R _f / R) and −AVo is obtained by the operational amplifier Q3, 2AVo is input to the ring-shaped coil 3 of the VCM 6. Further, a speed feedback gain (H in FIG. 6) based on moving speed information from a speed sensor 8 described later is input to the operational amplifier Q1.
(Indicated by (s)) is also input. These operational amplifiers Q
1-Q3 and resistors R ₂ , R _f , R, R ₃ etc.
A control device 9 for driving and controlling M6 is configured.

Here, if the equation governing the mechanism of FIG. 5 and the equation governing the electric circuit of FIG. 7 are combined, the following equation (1) can be expressed.

[0008]

[Equation 1]

M: total mass of moving object (movable lens group 1 + lens holding member 2 + ring coil 3) L: inductance of ring coil 3 K _f : thrust constant (= 2πrN) r: ring coil 3
, N: number of turns x: position of movable lens group B: axial viscous friction between lens holding member 2 and bearing R: resistance value of ring coil 3 Ke: back electromotive force constant of ring coil 3 (≡ K _f = 2π
rN) A: Servo gain R _b : Resistance value of damping coil 8A of speed sensor 8 R ₂ : Circuit constant (see FIG. 7) R ₃ : Circuit constant (see FIG. 7) K _b : Electromotive force constant of damping coil 8A ( = 2πr _b
N _b ) r _b : Radius of damping coil 8A, N _b : Number of turns Vx: Position command (target position) Here, if a sine wave is input to the position command Vx of the formula (1) of the above mathematical expression 1, the lens position x also The sine wave solution is obtained following the position command, but its amplitude and phase change finely depending on the input and the frequency of the input sine wave.

FIG. 8 shows the result of actually calculating the input and output amplitudes and phases by substituting the actual numerical values into the equation (1). Figure 8
In the figure, the horizontal axis represents the frequency of the input sine wave, and the vertical axis represents the input / output ratio of the amplitude of the sine wave and the phase shift amount of the input / output. Generally, a servo control system has its own resonance frequency, which is 100 Hz in this example.
It exists in the vicinity. When the input frequency is sufficiently lower than the resonance frequency, the input / output amplitude ratio is 1, and the phase difference is also approximately 0 °. However, as the input frequency approaches the resonance frequency, the resonance characteristics shown in the figure As shown.

By the way, the purpose of the servo control system of the movable lens group 1 of the photographing apparatus is to perform position control, but as shown in FIG.
Speed feedback (speed feedback gain is H
(Indicated by (s)) must also be performed. If there is no velocity feedback (H (s) = 0), the amplitude ratio exceeds 1 at the resonance frequency as shown in FIG. 8, and in some cases the amplitude becomes extremely large, so-called resonance phenomenon occurs, and the control cannot be performed. Will be. In addition, in the region above the resonance frequency, the amplitude sharply decreases, and the phase also deviates, so to say that tracking is not possible, but the upper limit frequency that can be used is that the amplitude ratio is about 0.7 (- 3d
Generally, the frequency is B). As shown in FIG. 8, applying velocity feedback slightly lowers the upper limit frequency, which is equivalent to trying to use the phase difference between input and output as small as possible. Of course, excessively increasing the velocity feedback gain causes overcorrection, and narrows the frequency range that can be meaninglessly used.

According to the control theory, as long as the phase difference does not exceed -180 °, it belongs to the stable region as a system, but the smaller the phase difference is, the easier the control is. Therefore, each gain is determined according to the purpose. Since the resonance frequency rises when the servo gain is increased, the servo frequency and speed feedback gain are adjusted while keeping the amplitude ratio and phase difference in mind, and the resonance frequency is increased as much as possible to obtain a flat frequency characteristic over a wide frequency range. It is common to do so.

By the way, how to detect the lens moving speed for applying the speed feedback is as follows.
In the prior art example shown in FIG. 5, the most common speed sensor 8
Is proposed to be used. In FIG. 5, a bar magnet 8A having a magnetizing direction parallel to the optical axis is fixed to the lens holding member 2 as shown in the figure. A damping coil 8B is fixed to a part of the fixed outer shell member 5 so as to be located around the bar magnet 8A. Here, when the lens holding member 2 moves in the optical axis direction, the bar magnet 8A moves in and out of the damping coil 8B, and a voltage is generated in the damping coil 8B by the principle of electromagnetic induction. Moreover, since the generated voltage is proportional to the moving speed of the bar magnet 8A, that is, the moving speed of the movable lens group 1, it is proportional to the moving speed by inputting this voltage to the operational amplifier Q1 as shown in FIG. You can give feedback.

[0014]

However, in recent years, cameras and video cameras tend to be low in price, and only one control mechanism, that is, movement control of a movable lens, is used like the above-mentioned conventional apparatus. 2 of position sensor 7 and speed sensor 8
Although it is necessary in principle to use two sensors,
When commercializing, there is a problem in terms of cost.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a movable lens drive control device that does not require a speed sensor, thereby reducing the cost of a photographing device.

[0016]

For this reason, the movable lens drive control device of the photographing apparatus of the present invention comprises a lens drive means for driving the movable lens, and a lens position detection means for detecting the actual position of the movable lens. Differentiating means for differentiating the position information from the lens position detecting means into moving speed information of the movable lens, and position information and moving speed information respectively obtained from the lens position detecting means and differentiating means and a given target. And a control means for controlling the lens driving means so as to match the movable lens position with the target position based on the position information.

[0017]

According to this structure, the position information and the moving speed information of the movable lens can be obtained only by the position sensor, and the cost of the photographing apparatus can be reduced without providing the speed sensor.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a block diagram of a servo control system showing an embodiment of a movable lens drive controller according to the present invention, and FIG. 2 shows a concrete control circuit diagram thereof. The movable lens mechanism of this embodiment is the same as the conventional device shown in FIG. 5 except that the speed sensor 8 is omitted, and the same parts are designated by the same reference numerals.

In the block diagram of this embodiment shown in FIG. 1, speed information is obtained based on position information and speed feedback is applied. In FIG. 2 showing a specific circuit configuration of this servo control system, a position sensor 7 as a lens position detecting means for detecting the position of the movable lens group 1, a VCM 6 as a lens driving means for driving the movable lens group 1, and control. The control device 9 as means has the same configuration as the conventional one.

In the present embodiment, the moving speed information for speed feedback is the output Vs from the position sensor 7.
Is obtained by a differentiating circuit 10 as a differentiating means composed of operational amplifiers Q4 and Q5 and input to the control device 9. The differentiating circuit 10 outputs the output V from the position sensor 7.
s is differentiated by the operational amplifier Q4, the differential output is multiplied by the speed feedback gain H (s) by the operational amplifier Q5 and output as moving speed information, and this moving speed information output is input to the operational amplifier Q1 of the control device 9. Is. The operation of each operational amplifier Q1 to Q3 in the control device 9 is similar to that of the conventional circuit shown in FIG.

Next, FIGS. 3A to 3C show input / output conditions when the servo control system of this embodiment is applied to the lens driving mechanism of FIG. First, the upper part of (A) shows the position command Vx. Here, + 1.0mm, -1.0mm
The target is step operation with a frequency of 1.0 Hz.
The lower part of (A) is the position sensor output Vs. That is, this is the actual movement of the movable lens group 1. The transient response of the natural frequency is shown for each step.

The upper stage of (B) shows the output of the position sensor output Vs, that is, the output of the operational amplifier Q4. (B)
The lower row shows the movement of the movable lens group 1 as in the lower row of (A). The output of this operational amplifier Q4 is the operational amplifier Q
When the output of the differentiating circuit 10 amplified in 5 is given to the input of the operational amplifier Q1 of the control device 9 and feedback is applied, the transient response disappears as shown in the lower stage of (C), and the movement is almost the same as the position command. I understand.

Next, as in the simulation shown in FIG. 8, the position command Vx is a sine wave, and the result of examining the amplitude ratio and phase difference between the position command and the actual lens movement over a wide frequency range from 1.0 Hz is shown. As shown in FIG. The horizontal axis is the input sine wave frequency. First, the ● data in the figure shows the case where there is no velocity feedback. In this case, the resonance frequency is in the vicinity of 70 Hz, which shows a remarkable resonance,
The amplitude ratio at this frequency has reached more than 5 times, -3
At about 100 Hz, which is the upper limit frequency of dB, the phase difference is almost 180 degrees and the phase is inverted, and if this is left as it is, the resonance is scary and very unusable.

Next, the data of ◯ is an example in which speed feedback is applied by the speed sensor 8 using a magnet and a coil which is a conventional example. In this case, the amplitude ratio is almost 1 even at the resonance frequency, and at the resonance frequency and above, the amplitude gradually decreases and the frequency of -3 dB is about 100 Hz, which is almost unchanged from the case without speed feedback. Also,
The phase difference near 100 Hz is slightly improved to about −150 ° as compared with the case where there is no speed feedback, but it will be improved a little if the speed feedback gain is increased a little more. This is because the amplitude ratio is close to the resonance frequency and exceeds a little more than 1, which is no wonder.

Finally, the data of this embodiment is indicated by Δ. The amplitude ratio shows an extremely flat frequency characteristic up to the resonance frequency, and gently decreases as it is, and the frequency of -3 dB is almost 100 Hz and hardly changes. The phase difference is also improved and reaches −110 ° near 100 Hz. From the above experimental results, it is possible to obtain almost the same result as the conventional device by the device of the present embodiment, or more excellent result of the conventional device, and it is possible to realize a significant cost reduction by omitting the speed sensor 8.

[0026]

As described above, according to the present invention, the position information from the position sensor is differentiated to obtain the moving speed information of the movable lens, and the movable lens is moved to the target position based on the position information and the moving speed information. Since the servo control is performed, a speed sensor is not required, the number of sensors can be reduced, and the cost of the image capturing apparatus can be reduced. Also, the control accuracy can be the same as or higher than that of the conventional one.

[Brief description of drawings]

FIG. 1 is a system block diagram of an embodiment of the present invention.

FIG. 2 is an electric circuit diagram corresponding to the above system block diagram.

FIG. 3 is a diagram showing an operation example of the embodiment.

FIG. 4 is a frequency characteristic diagram for comparing the present embodiment with a conventional example.

FIG. 5 is a configuration diagram of a movable lens drive unit to which the present invention is applied.

FIG. 6 is a conventional system block diagram.

FIG. 7 is an electric circuit diagram corresponding to the conventional system block diagram of the above.

FIG. 8 is a diagram showing a calculation simulation result of frequency characteristics of a conventional example.

[Explanation of symbols]

 1 Movable Lens Group 6 VCM 7 Position Sensor 9 Control Device 10 Differentiation Circuit

Claims (1)

[Claims] 1. A movable lens drive control device for a photographing apparatus, which servo-controls a movable lens position so as to match a given target position, the lens drive means driving the movable lens, and the actual position of the movable lens. Position detecting means for detecting the position information, differentiating means for differentiating the position information from the lens position detecting means and converting it into moving speed information of the movable lens, and position information respectively obtained from the lens position detecting means and the differentiating means. And a control means for controlling the lens driving means to match the movable lens position with the target position based on the moving speed information and the given target position information. Lens drive control device.