JP2013081294A - Drive circuit and drive method of voice coil motor with spring return mechanism and lens module using them and electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress vibration of VCM with a spring return mechanism.SOLUTION: A control unit 30 receives a command value designating the target stroke volume of a voice coil motor 110, and generates a control signal V2. A control signal S2 changes linearly from an initial value corresponding to the stroke volume before movement toward a target value corresponding to the target stroke volume, over a transition time that is equal to an integer times of the reciprocal of resonance frequency of the voice coil motor 110. A drive current generation unit 10 supplies a drive current Idrv corresponding to the control signal S2 to the coil of the voice coil motor 110.

Description

  The present invention relates to a control technique for a voice coil motor with a spring return mechanism.

  An actuator for positioning a focusing lens is provided in a digital still camera, a digital video camera, or an electronic device (for example, a mobile phone) with an imaging function. As the actuator, a stepping motor method, a piezo method, a voice coil motor (VCM) method, or the like is employed.

  The VCM can generate a propulsive force in a linear direction corresponding to the direction of the current flowing through the coil. For example, when an H bridge circuit is connected to the VCM, the direction of the coil current can be switched, and a driving force can be obtained in the positive direction and the negative direction.

  On the other hand, a VCM with a spring return mechanism may be used. A VCM with a spring return mechanism generates a propulsive force in a first direction by supplying a drive current to a coil, and a propulsive force in a second direction opposite to that of a spring (spring) attached to the mover. It has a structure that uses force to generate. That is, electric drive and dynamic drive are used together. When driving a VCM with a spring return mechanism, it is sufficient to supply a drive current only in one direction of the coil, and the drive circuit can be simplified.

JP 2004-12492 A Japanese Patent Laid-Open No. 9-298430 JP 2008-113506 A JP 2008-043171 A

The vibration system having a spring has a spring constant K and a resonance frequency fr determined by the mass M.
fr = √ (K / M) / 2π (1)
Along with the downsizing of electronic equipment, downsizing of a VCM with a spring return mechanism is required. When the VCM is reduced in size, the inductance of the coil is reduced and the weight of the mover is reduced, which causes a problem that the mover, that is, the lens vibrates due to the force of the spring.

  In order to suppress the vibration of the lens, a method of driving the VCM with a drive current having a spectrum from which the frequency component of the resonance frequency fr is removed has been proposed. Specifically, (1) a step waveform is shaped by a band elimination filter BEF that removes the resonance frequency to generate a drive current, or (2) a waveform shaped drive signal is calculated in advance by calculation. There has been proposed a method of storing it in a memory and reading it out during driving. These methods have a problem that the scale of hardware increases because a filter, a memory, and the like are required.

  The present invention has been made in view of the above problems, and one of the exemplary purposes of the certain aspect is to provide a control technique capable of suppressing the vibration of the VCM with a spring return mechanism.

  One embodiment of the present invention relates to a drive circuit for a voice coil motor with a spring return mechanism. The drive circuit receives a command value indicating a target stroke amount (also referred to as a slide amount) of the voice coil motor, generates a control signal, and applies a drive current corresponding to the control signal to the coil of the voice coil motor. A drive current generation unit to be supplied. The control unit linearly changes the control signal from the initial value corresponding to the stroke amount before movement to the target value corresponding to the target stroke amount over a transition time that is an integral multiple of the reciprocal of the resonance frequency of the voice coil motor. Let

  According to this aspect, the residual amplitude of the mover can be suppressed and the settling time can be shortened.

  The transition time may be 1 times the reciprocal of the resonance frequency. In this case, the settling time can be minimized.

  The control unit may include a calculation unit that generates a digital control signal. When the transition time is τ, the control signal sampling period is Ts, the initial stroke amount is x1, and the target value is x2, the calculation unit changes the control signal value by (x2−x1) × Ts / τ. You may let them.

  Another aspect of the present invention relates to a lens module. The lens module includes a focusing lens, a voice coil motor with a return mechanism in which a movable element is coupled to the focusing lens, and a drive circuit according to any one of the above-described modes for driving the voice coil motor.

  Another aspect of the present invention relates to a lens module. The lens module includes a camera shake correction lens, a voice coil motor with a return mechanism whose movable element is coupled to the camera shake correction lens, and a drive circuit according to any one of the above-described modes for driving the voice coil motor.

  Another embodiment of the present invention relates to an electronic device. The electronic apparatus includes any one of the lens modules described above and an imaging device that images light that has passed through the lens module.

  According to the present invention, vibration of the mover can be suppressed.

It is a circuit diagram which shows the structure of the drive circuit which concerns on embodiment. It is a wave form diagram which shows operation | movement of the drive circuit of FIG. It is a figure which shows the relationship between step amount, a residual amplitude, and transition time when changing stroke amount from 0 to 160. FIG. It is a circuit diagram which shows the structure of the control part which concerns on a modification.

  FIG. 1 is a circuit diagram showing a configuration of a drive circuit 100 according to the embodiment. FIG. 1 shows the entire electronic device 2 including the drive circuit 100.

  The electronic device 2 is a mobile phone with an imaging function, a digital camera, a video camera, or the like, and includes a CPU (Central Processing Unit) 3, a lens module 116, and an imaging device 118.

  The lens module 116 is provided to realize a so-called autofocus function, and includes a focusing lens 114, a voice coil motor 110, and a drive circuit 100.

  The voice coil motor 110 is an actuator that positions the focusing lens 114, and the mover is coupled to the focusing lens 114. The voice coil motor 110 includes a return spring mechanism, and the mover is connected to the spring 112.

  The drive circuit 100 supplies a drive current Idrv to the coil L1 of the voice coil motor 110 and controls the position of the lens 114. Specifically, the drive circuit 100 displaces the mover in the first direction by causing the drive current Idrv to flow through the coil L1. The spring 112 acts to push the mover back in a second direction opposite to the first direction.

  The CPU 3 determines a target position of the focusing lens 114 so that an image that has passed through the focusing lens 114 forms an image on the imaging device 118, and instructs the stroke amount of the voice coil motor 110 according to the target position. The value S1 is output to the drive circuit 100.

  The above is the configuration of the entire electronic device 2. Next, the configuration of the drive circuit 100 will be described.

  The drive circuit 100 includes a drive terminal P1, a drive current generation unit 10, and a control unit 30.

  The drive terminal P1 is connected to one end of the coil L1. The other end of coil L1 is connected to a fixed voltage terminal (for example, power supply terminal Vdd). When the drive circuit 100 operates by receiving a negative power supply, the fixed voltage terminal may be a ground terminal. 1 is configured as a sink type that sucks the drive current from the coil L1, but those skilled in the art will understand that it can also be configured as a source type that flows the drive current Idrv into the coil L1. In the case of the source type, the other end of the coil L1 is connected to a ground terminal.

The control unit 30 receives an instruction value S1 instructing a target stroke amount of the voice coil motor 110 from the electronic device 2, and generates an analog control signal V2. The vibration system including the voice coil motor 110, the spring 112, and the focusing lens 114 has a spring constant K and a resonance frequency fr determined by the mass M.
fr = √ (K / M) / 2π (1)

Data corresponding to the resonance frequency fr or its reciprocal 1 / fr is stored in the drive circuit 100 in advance, or the data can be received from the CPU 3. The control unit 30 linearly changes the control signal V2 over a certain transition time τ from the initial value x1 corresponding to the stroke amount before movement to the target value x2 corresponding to the target stroke amount. The transition time τ is set according to the equation (2) represented by the integer n and the reciprocal 1 / fr of the resonance frequency fr.
τ = n / fr (2)
In this embodiment, n = 1. That is, the transition time τ is equal to the reciprocal of the resonance frequency fr.

The control unit 30 includes a calculation unit 32 and a D / A converter 34. The calculation unit 32 generates a digital control signal S2. The D / A converter 34 converts the digital control signal S2 into an analog control signal V2.
When the sampling period of the control signal S2 is Ts, the calculation unit 32 changes the value of the control signal S2 by the step amount Δx of Expression (3).
Δx = (x2−x1) × Ts / τ (3)
Such a calculation unit 32 can be easily generated using a counter, and a specific generation algorithm is not particularly limited.

  The drive current generator 10 supplies the drive current Idrv corresponding to the control signal V2 to the coil L1 of the voice coil motor 110. For example, the drive current generation unit 10 includes an operational amplifier 12, a transistor 14, and a resistor R2.

The transistor 14 and the resistor R2 are provided in series between the drive terminal P1 and the fixed voltage terminal (ground terminal), that is, on the path of the drive current Idrv flowing through the coil L1. The control signal V2 is input to the non-inverting input terminal of the operational amplifier 12. The voltage at the connection point between the transistor 14 and the resistor R2 is fed back to the inverting input terminal of the operational amplifier 12. The drive current Idrv generated by the drive current generator 10 is given below.
Idrv = V2 / R2

  The configuration of the drive current generator 10 is not limited to that shown in FIG. 1, and other types of current sources or voltage sources may be used.

The above is the overall configuration of the drive circuit 100. Next, an outline of the operation will be described.
FIG. 2 is a waveform diagram showing the operation of the drive circuit 100 of FIG. The solid line (i) indicates the control signal S2 (that is, the drive current Idrv generated by the drive current generator 10), and the broken line (ii) indicates the actual stroke amount when the control signal S2 is applied.

When the resonance frequency fr is 85.333 Hz, the transition time τ is set to τ = 1 / 85.333 = 11.7 (msec). For example, it is assumed that an initial value x1 = 0 of the stroke amount and a command value S1 instructing a target value x2 = 160 is input from the CPU 3. If the sampling time Ts of the control signal S2 is 0.98 ms (sampling frequency fs = 1024 Hz), the step amount Δx is in accordance with the equation (3):
Δx = (x2−x1) × Ts / τ
= (160-0) /11.7*0.98=13.4
Given in.

  The control unit 30 increments the value of the control signal S2 by Δx = 13.4 every sampling. As a result, the drive current Idrv generated by the drive current generator 10 changes linearly over the transition time τ from the current value corresponding to the initial value x1 to the current value corresponding to the target value x2.

  As indicated by the broken line (ii), in the middle of the transition time τ, an error δ occurs in the control signal S2 and the actual stroke amount due to the vibration. Then, after the transition time τ has elapsed, the stroke amount is stabilized near the target value. The vibration after the transition time τ (referred to as residual amplitude) falls within a sufficiently allowable range in actual use, and may be considered to be settled at the transition time τ. That is, the transition time τ and the settling time are equal.

  As described above, according to the drive circuit 100 according to the embodiment, the stroke amount can be stabilized at the target value in the sufficiently short transition time τ of 11.7 ms. In various lens modules, since the resonance frequency fr is about several tens Hz to several hundreds of Hz, even if fr = 30 Hz, the transition time τ is about 33 ms, so that sufficiently high-speed control is possible. It is.

  Further, the drive circuit 100 does not require a conventional filter for removing the resonance frequency from the spectrum of the drive current and a memory for storing the control signal from which the resonance frequency has been removed, so that the hardware scale can be reduced. Can do.

  FIG. 3 is a diagram showing the relationship between the step amount Δx, the residual amplitude, and the transition time when the stroke amount is changed from 0 to 160. It should be noted that the relationship shown in FIG. 3 should not be regarded as general technical common knowledge of those skilled in the art, but was first found by the present inventors.

  As a generally known tendency, the smaller the step amount Δx, the smaller the amplitude during transition and the residual amplitude. However, if the step amount Δx is reduced, the transition time τ becomes longer. On the other hand, if the step amount Δx is increased, the transition time τ can be shortened, but the residual amplitude is increased, resulting in an increase in the settling time.

  The present inventors examined the relationship between the step amount Δx and the residual amplitude in more detail, and found that the residual amplitude becomes small when the step amount takes a discrete value as shown in FIG. The step amount that minimizes the residual amplitude gives a transition time τ that is an integral multiple of the reciprocal 1 / fr of the resonance frequency fr. In other words, by setting the transition time τ to an integral multiple of the reciprocal 1 / fr of the resonance frequency fr, the residual amplitude can be reduced even if the step amount Δx is increased.

  In the embodiment, the case where n = 1 has been described, but n may be 2 or more. However, since the transition time (settling time) τ becomes longer as n is increased, the case where n = 1 is most preferable.

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are within the scope of the present invention. is there. Hereinafter, such modifications will be described.

  In the embodiment, the control unit 30 including the calculation unit 32 and the D / A converter 34 has been described, but the means for generating the control signal V2 is not limited to this. FIG. 4 is a circuit diagram illustrating a configuration of a control unit 30a according to a modification.

  The control unit 30 includes a capacitor C1, a first current source CS1, a second current source CS2, and a calculation unit 32. The first current source CS1 and the second current source CS2 are variable current sources, and are configured to be able to generate a specified current amount for a specified period. When the capacitor C1 is charged with the current Ic1 generated by the first current source CS1, the analog control signal V2 rises with a certain slope. When the capacitor C1 is discharged by the current Ic2 generated by the second current source CS2, the analog control signal V2 falls with a constant slope.

  The arithmetic unit 32 determines that the analog control signal V2 is an integer multiple of the reciprocal (1 / fr) of the resonance frequency fr from the initial value x1 corresponding to the stroke amount before movement to the target value x2 corresponding to the target stroke amount. The first current source CS1 and the second current source CS2 are controlled so as to change linearly over the transition time τ. The transition time τ is given by the above-described equation (2).

When increasing the stroke amount, the computing unit 32 deactivates the second current source CS2 and activates the first current source CS1 during the transition time τ. At this time, the current Ic1 to be generated by the first current source CS1 is given by Expression (4).
Ic1 = C1 × (x2−x1) / τ (4)

When reducing the stroke amount, the calculation unit 32 deactivates the first current source CS1 and activates the second current source CS2 during the transition time τ. At this time, the current Ic2 to be generated by the second current source CS2 is given by Expression (5).
Ic2 = −C1 × (x2−x1) / τ (5)

  According to this configuration, the analog control signal V2 can be generated in the same manner as the set of the control unit 30 and the D / A converter 34 in FIG.

  A person skilled in the art can design a circuit for generating the control signal S2 or V2 in addition to the configuration of FIG. 1 or FIG. 4, and such a circuit is also included in the scope of the present invention.

  In the embodiment, the lens module for focusing has been described, but the application of the drive circuit 100 is not limited thereto. For example, the voice coil motor 110 may drive a camera shake correction lens.

  Although the present invention has been described using specific terms based on the embodiments, the embodiments only illustrate the principles and applications of the present invention, and the embodiments are defined in the claims. Many modifications and arrangements can be made without departing from the spirit of the present invention.

L1 ... Coil, P1 ... Drive terminal, 2 ... Electronic device, 10 ... Drive current generator, R2 ... Resistance, 12 ... Operational amplifier, 14 ... Transistor, 30 ... Control part, 32 ... Calculation part, 34 ... D / A converter DESCRIPTION OF SYMBOLS 100 ... Drive circuit 110 ... Voice coil motor 112 ... Spring 114 ... Focusing lens 116 ... Lens module 118 ... Imaging device

Claims (8)

A drive circuit for a voice coil motor with a spring return mechanism,
A control unit that receives a command value instructing a target stroke amount of the voice coil motor and generates a control signal, the control signal corresponding to the target stroke amount from an initial value corresponding to a stroke amount before movement. A control unit that changes linearly over a transition time that is an integral multiple of the reciprocal of the resonance frequency of the voice coil motor toward the target value;
A drive current generator for supplying a drive current according to the control signal to the coil of the voice coil motor;
A drive circuit comprising:   The drive circuit according to claim 1, wherein the transition time is one time the inverse of the resonance frequency. The control unit includes a calculation unit that generates a digital control signal,
When the transition time is τ, the sampling period of the control signal is Ts, the initial value of the stroke amount is x1, and the target value is x2, the calculation unit sets the value of the control signal to (x2−x1) × The drive circuit according to claim 2, wherein the drive circuit is changed by Ts / τ. The controller is
A capacitor;
A first current source for charging the capacitor;
A second current source for discharging the capacitor;
An arithmetic unit for controlling the first current source and the second current source;
With
The voltage generated in the capacitor is output as the control signal,
The arithmetic unit activates the first current source during the transition time when increasing the control signal, and activates the second current source during the transition time when decreasing the control signal. The drive circuit according to claim 1, wherein: Focusing lens,
A voice coil motor with a return mechanism in which the mover is connected to the focusing lens;
The drive circuit according to any one of claims 1 to 3, which drives the voice coil motor;
A lens module comprising: An image stabilization lens,
A voice coil motor with a return mechanism in which the mover is connected to the camera shake correction lens;
The drive circuit according to any one of claims 1 to 3, which drives the voice coil motor;
A lens module comprising: The lens module according to claim 5 or 6,
An imaging device for imaging light passing through the lens module;
An electronic device comprising: A method for driving a voice coil motor with a spring return mechanism,
Generating a command value indicating a target stroke amount of the voice coil motor;
A control signal that linearly changes from an initial value corresponding to the stroke amount before movement to a final value corresponding to the target stroke amount over a transition time that is an integral multiple of the reciprocal of the resonance frequency of the voice coil motor. Steps,
Supplying a drive current corresponding to the control signal to the coil of the voice coil motor;
A method comprising the steps of:

Images