JP2010078732A - Actuator device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an actuator device capable of achieving fine and high-speed position control. <P>SOLUTION: The device includes a high input-resistance differential amplifying circuit 61 for detecting a resistance value of a shape memory alloy 2, and for output of the first detection signal; a high input-resistance differential amplifying circuit 62 for detecting a resistance value of a reference resistance, and for output of the second detection signal; logarithmic amplifying circuits 63, 64 for performing logarithmic conversion processing respectively to the first and second detection signals, and for output of the first and second logarithmic signals; a subtraction circuit 65 for output of a difference signal between the first and second logarithmic signals; an inverse logarithmic amplifying circuit 66 for performing inverse logarithmic conversion processing to the difference signal, and for output of a ratio signal between the resistance value of the shape memory alloy 2 and the resistance value of the reference resistance; and a feedback control part 6 for detecting displacement of a lens position based on the ratio signal, and for output of a feedback signal S1 to a PWM driving part 1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an actuator device. More specifically, the present invention relates to an actuator device using a shape memory alloy.

  In recent years, proposals have been made to use shape memory alloys as means for displacing the position of a lens in a lens barrel in an autofocus mechanism of a camera or other imaging device. The shape memory alloy is composed of, for example, a fine wire or a coil spring. Such a shape memory alloy has the property that when it is heated by passing an electric current, it shrinks and its resistance value changes. Therefore, the position of the lens of the autofocus mechanism can be displaced using the property that the shape memory alloy expands and contracts according to the current.

  As means for supplying power to the shape memory alloy, voltage control or PWM (pulse width modulation) control is used. In particular, in the case of PWM control, the power supplied to the shape memory alloy is controlled by a digital signal by changing the duty ratio of a pulse signal having a constant amplitude and period, so a feedback circuit using a microcomputer or the like is compared. Can be constructed easily.

  As position control using a shape memory alloy, for example, in the SMA actuator device of Patent Document 1, the shape memory alloy is applied to a lens module having a camera autofocus or zoom mechanism, and is measured by a reference clock. Heating control is performed alternately. According to Patent Document 1, the potential of the position setting unit of the bridge circuit is compared with the potential of the SMA actuator. When the reference clock becomes high, the potential of the SMA actuator is set according to the output signal of the comparator. The SMA actuator is energized and heated when the electric potential is higher than the electric potential of the SMA actuator, and the SMA actuator is not energized when the electric potential of the SMA actuator is equal to or lower than the potential of the set portion. It has become.

  Further, in the position control device of Patent Document 2, a shape memory alloy is applied to the bending amount control of the bending portion of the endoscope, and the actuator operates based on the displacement of the shape memory alloy. According to Patent Document 2, immediately before the actuator is driven, the maximum value and the minimum value of the resistance values of the two shape memory alloys are detected and stored in the storage unit. Specifically, the shape memory alloy is sufficiently cooled, the maximum value of the resistance value at that time is detected and stored, and sufficient time is supplied to supply the sufficient current to finish the deformation operation of the shape memory alloy. After elapses, the minimum resistance value at that time is detected and stored.

Japanese Unexamined Patent Publication No. 2007-2111754 (paragraph number 0007, see FIG. 1) Japanese Patent No. 2769351 (see Examples)

  However, in the case of Patent Document 1, the position of the lens module is not controlled by measuring an unknown resistance value of the shape memory alloy. For example, in FIG. 1, the potential at point A (midpoint of R3, R4, and R5) of the bridge circuit 2 is compared with the potential at point B (midpoint of SMA7 and R2) by a comparator (comparator 3). Since the configuration is such that the energization of the shape memory alloy is ON / OFF controlled based on the binary comparison result of the high level or the low level, it is difficult to finely control the lens position of the autofocus mechanism.

  On the other hand, in the case of Patent Document 2, it is necessary to sufficiently cool the shape memory alloy to detect the maximum resistance value every time position control is performed, and then to sufficiently heat the shape memory alloy to detect the minimum resistance value. Therefore, for example, when high-speed position control is required, such as control of the lens position of the autofocus mechanism of the imaging apparatus, appropriate control cannot be performed.

  The present invention solves the above-described problems, and an object thereof is to provide an actuator device that can realize fine and high-speed position control.

  In order to achieve the above object, an actuator device according to the present invention includes a shape memory alloy that expands and contracts according to a supplied drive signal to displace a predetermined control object, and a reference resistor connected to the shape memory alloy, Drive means for supplying a drive signal to the shape memory alloy and the reference resistance; first detection means for detecting a resistance value of the shape memory alloy and outputting a first detection signal; Second detection means for detecting a resistance value and outputting a second detection signal; and first logarithmic conversion means for performing a logarithmic conversion process on the first detection signal and outputting a second logarithmic signal. A second logarithmic conversion unit that performs logarithmic conversion processing on the second detection signal and outputs a second logarithmic signal; and a difference between the first logarithmic signal and the second logarithmic signal. Subtracting means for calculating and outputting a difference signal; An inverse logarithmic conversion means for performing a reverse logarithmic conversion process on the signal and outputting a ratio signal representing a ratio between the resistance value of the shape memory alloy and the resistance value of the reference resistance; and the control object based on the ratio signal And feedback control means for outputting a feedback signal carrying information to be fed back to the driving means.

  In the actuator device according to the present invention, the first detection means detects a resistance value that changes simultaneously with expansion and contraction according to the current value of the drive signal supplied to the shape memory alloy, and the feedback control means The displacement amount of the controlled object due to expansion and contraction of the shape memory alloy is detected based on a change in resistance value.

  Further, in the actuator device according to the present invention, the drive means supplies a drive signal having a current value independent of a change in the resistance value of the shape memory alloy to the shape memory alloy and the reference resistor, and The detecting means and the second detecting means detect each terminal voltage represented by a product of a current value and a resistance value flowing through the shape memory alloy and the reference resistance.

  In the actuator device according to the present invention, the control target is an imaging device having an optical unit of an autofocus mechanism, and the shape memory alloy expands and contracts according to a drive signal supplied from the drive unit. The lens of the autofocus mechanism is displaced.

  According to the present invention, fine and high-speed position control can be realized. Therefore, for example, an actuator device suitable for controlling the lens position of an autofocus mechanism of an imaging device of a digital camera or a mobile phone with a camera can be provided.

  Hereinafter, with respect to the first to third embodiments and modifications of the actuator device according to the present invention, taking as an example a case where an imaging device having an autofocus mechanism such as a digital camera or a mobile phone with a camera is a control target, This will be described with reference to the drawings.

  FIG. 1 is a block diagram showing the configuration of the actuator device according to the first embodiment. In FIG. 1, a PWM drive unit 1 is composed of a D / A conversion circuit, a PWM signal generation circuit, a 6-bit microcomputer, and the like (none of them are shown), and 64 according to a 6-bit input signal S1. The step duty ratio PWM signal S2 is output.

  The SMA (Shape Memory Alloy) 2 is composed of, for example, a thin wire, and expands and contracts in accordance with the current value of the PWM signal input from the PWM drive unit 1 to act on the autofocus mechanism of the optical system 3. The position of the lens is adjusted by changing the force A1.

  The optical system 3 includes an autofocus mechanism in which the lens position is adjusted by the acting force of the SMA 2, an image pickup device such as a CCD or CMOS, an image processing circuit, and the like (none of which are shown). The optical system 3 outputs a 10-bit edge signal S3 obtained from the image of the contour of the subject from the image processing circuit. The edge signal S3 has a maximum level when the focus is achieved, and the level decreases as the focus is removed. Therefore, the edge signal S3 is widely used as an autofocus detection signal.

  The feedback control unit 4 performs signal processing such as amplification processing, waveform shaping processing, and impedance conversion processing based on the edge signal S3 for detecting the focus state output from the optical system 3 and the target value signal S5. Thus, a 10-bit feedback signal S4 carrying information to be fed back to the PWM drive unit 1 is output. The target value signal S5 is, for example, a zoom setting value for far-field shooting or foreground shooting set by operating a mechanical part of the lens barrel or a switch.

  The delta-sigma modulation unit 5 performs bit conversion (reduction) of the 10-bit feedback signal S4 input from the feedback control unit 4 into a 6-bit digital signal, and outputs it as the input signal S1 to be supplied to the PWM drive unit 1 . Details of the bit conversion will be described later.

  In FIG. 1, the PWM drive unit 1 is configured to supply the generated digital PWM signal directly to the SMA 2. However, as a modification of the first embodiment, the PWM signal is converted from digital to analog to convert the SMA 2. May be supplied. FIG. 2 is a block diagram and a circuit diagram showing a PWM drive unit 1 according to a modification of the first embodiment. 2 (1), the PWM generation circuit 11 outputs a PWM signal S11 having a duty ratio of 64 steps in accordance with the 6-bit input signal S1 supplied from the delta-sigma modulation unit 5 in FIG. An LPF (low-pass filter) circuit or smoothing circuit 12 integrates the PWM signal S11, converts it into a sawtooth analog signal, and outputs it. The V / I conversion circuit 13 converts the sawtooth analog signal into a current and outputs the current.

  FIG. 2B is a circuit diagram of a specific example of the LPF circuit 12 and the V / I conversion circuit 13 of FIG. In FIG. 2 (2), a passive primary LPF circuit 12 is an integrating circuit composed of a series resistor Ri and a parallel capacitor C, and integrates (filters) the PWM signal S11 to provide a sawtooth wave analog signal having a voltage Vc. Convert to S12 and output. The V / I conversion circuit 13 includes an operational amplifier OP having a high input impedance, a current setting resistor (feedback resistor) Rf, an NPN transistor Tr, and protective resistors Rp1 and Rp2. In the V / I conversion circuit 13, the voltage at the inverting input of the operational amplifier OP is equal to Vc at the non-inverting input. Therefore, If · Rf = Vc, and the input signal S2 of the current If proportional to the voltage Vc represented by If = Vc / Rf is supplied to the SMA2. That is, even if the resistance value of the load SMA2 changes, the load current If does not change, and the voltage across the SMA2 changes.

  FIG. 3 is a block diagram showing an internal circuit of the delta-sigma modulation unit 5 of FIG. In FIG. 3, the delta sigma modulation unit 5 includes a quantization circuit 51, an addition circuit (or subtraction circuit) 52, a delay circuit 53, a multiplication circuit 54, and an addition circuit 55. That is, as shown in FIG. 3, the delta-sigma modulation unit 5 performs a primary noise shaping operation that gives a differential characteristic that rises higher by returning the quantization noise generated in the quantization circuit 51 to the input side. .

As described above, the 10-bit feedback signal S4 is input to the delta-sigma modulation unit 5, and is input to the quantization circuit 51 via the addition circuit 55. In the quantization circuit 51, a quantization noise Nq having no correlation with the input signal S51 is generated. The quantization noise Nq is output (extracted) as S52 by subtracting the input signal S51 to the quantization circuit 51 from the output signal S1 of the quantization circuit 51 in the addition circuit 52. The quantization noise component of the output signal S52 (= Nq) of the adder circuit 52 is input to the delay circuit 53 of the transfer function of z ⁻¹ and is delayed by one sampling time fs. The output signal S53 (= Nq · z ⁻¹ ) of the delay circuit 53 is input to the multiplication circuit 54, multiplied by the coefficient a1 (in this case, −1), and the output signal S54 (= −Nq · z ⁻¹ ). Is added to the adder circuit 55 and added to the input signal S4 to become the input signal S51 (= S4-Nq · z ⁻¹ ) of the quantizer 51. As a result, the output signal of the quantization circuit 51, that is, the output signal S1 of the delta-sigma modulation unit 5 is expressed by the following equation.
S1 = S4 + Nq (1-z ⁻¹ )

  FIG. 4 is a diagram showing the contents of the 10-bit input signal S4 converted into the 6-bit output signal by the delta-sigma modulation unit 5 of FIG. Excluding 0 representing no signal, the 10-bit input bit signal S4 is represented by level 1 to level 1023 from “0000000001” to “1111111111”. On the other hand, the 6-bit output bit signal S1 is represented by level 1 to level 63 from “000001” to “111111”. In addition, the correspondence between the two is indicated by a decimal display that is a normalized number.

In FIG. 4, when the input bit signal S4 is “1000000000” (512 level), the normalized number corresponds to “0.5”, that is, 50% of the full scale, and the output bit signal S1 is “100,000” (32 Level). For example, when an input bit signal S4 of 522 (512 + 10) level is input,
S4 = 0.5 + 10/1024
It becomes. In this state, when the sampling time t is 0, Ts, 2Ts, 3Ts, 4Ts, 5Ts (more than 6Ts is omitted), the input signal S51, the output signal S1, and the quantization noise Nq of the quantization circuit 51 are expressed by the following equations. Is done.
S51 (t = 0) = 0.5 + 10/1024
S51 (t = Ts) = 0.5 + 20/1024
S51 (t = 2Ts) = 0.5 + 14/1024
S51 (t = 3Ts) = 0.5 + 24/1024
S51 (t = 4Ts) = 0.5 + 18/1024
S51 (t = 5Ts) = 0.5 + 12/1024
S1 (t = 0) = 32 levels = 32/64 = 0.5
S1 (t = Ts) = 32 level = 33/64 = 0.5 + 1/64
S1 (t = 2Ts) = 32 levels = 32/64 = 0.5
S1 (t = 3Ts) = 32 levels = 33/64 = 0.5 + 1/64
S1 (t = 4Ts) = 32 levels = 33/64 = 0.5 + 1/64
S1 (t = 5Ts) = 32 levels = 32/64 = 0.5
Nq (t = 0) = − 10/1024
Nq (t = Ts) = − 4/1024
Nq (t = 2Ts) = − 14/1024
Nq (t = 3Ts) = − 8/1024
Nq (t = 4Ts) = − 2/1024
Nq (t = 5Ts) = − 12/1024

  FIG. 5 shows that when a 522 level input bit signal S4 is input, the input signal S51 of the quantization circuit 51 when the sampling time t is 0, Ts, 2Ts, 3Ts, 4Ts, 5Ts, The transition of the output signal, that is, the output signal S1 of the delta-sigma modulation unit 5 is shown. In FIG. 5, L1 indicates 0.5 level, L2 indicates 0.5 + 1/64, and L3 indicates 0.5 + 1/32.

  FIG. 6 shows the duty ratio of 64 steps of the PWM signal when the output signal S1 of the delta-sigma modulation unit 5 is from 0 level to 63 level.

FIG. 7 is a diagram illustrating a reduction effect of quantization noise in the vicinity of direct current by the primary noise shaper of the delta-sigma modulation unit 5 of FIG. Energy Nq ² spectrum Nq of the quantization noise in the frequency f is represented by the sampling frequency fs by the following equation.
Nq ² = 4 {sin (ω / fs)} ²
However, ω = 2πf
In FIG. 7, among the quantization noise energy Nq ² in the range from direct current (f = 0) to 1/2 of the sampling frequency fs, the noise component from direct current to 1/6 of the sampling frequency fs is the sampling frequency fs. Is reduced by the primary noise shaper of the delta-sigma modulation unit 5 in comparison with a high-frequency noise component of 1/6 or more.

  FIG. 8 is a modification of the first embodiment, and shows an internal circuit of the delta-sigma modulation unit 5 of FIG. In FIG. 8, the delta sigma modulation unit 5 includes a quantization circuit 51, an addition circuit (or subtraction circuit) 52, a delay circuit 53, a multiplication circuit 54, a delay circuit 56, a multiplication circuit 57, and an addition circuit 55. That is, as shown in FIG. 8, the delta-sigma modulation unit 5 returns the quantization noise generated in the quantization circuit 51 to the input side twice, thereby increasing the high frequency more rapidly than the first-order noise shaping. Next noise shaping operation is performed.

The quantization noise Nq of the quantization circuit 51 in FIG. 8 is output (extracted) as S52 by subtracting the input signal S51 to the quantization circuit 51 from the output signal S1 of the quantization circuit 51 in the addition circuit 52. The quantization noise of the output signal S52 (= Nq) of the adder circuit 52 is input to the delay circuit 53 of the transfer function of z ⁻¹ and is delayed by one sampling time fs. The output signal S53 (= Nq · z ⁻¹ ) of the delay circuit 53 is input to the multiplication circuit 54, multiplied by the coefficient a1 (in this case −2), and the output signal S54 (= −2Nq · z ⁻¹ ). Is input to the adder circuit 55. The output signal S53 in the delay circuit 53 (= Nq · ^{z -1) is} input to the delay circuit 56 of the transfer function of ^{z -1,} the output signal ^{S56 (= Nq (z -1)} 2) is multiplied by The signal is input to the circuit 57 and multiplied by a coefficient a2 (in this case, 1). Therefore, the output signal S54 (= −2Nq · z ⁻¹ ) of the multiplication circuit 54 and the output signal S57 (= Nq (z ⁻¹ ) ² ) of the multiplication circuit 57 are added to the input signal S4 in the addition circuit 55. . Therefore, the input signal S51 of the quantization circuit 51 is S4 + Nq (z ⁻¹ ) ² −2Nq · z ⁻¹ . In the quantization circuit 51, the generated quantization noise Nq is added to S51. As a result, the output signal of the quantization circuit 51, that is, the output signal S1 of the delta-sigma modulation unit 5 is expressed by the following equation.
S1 = S4 + Nq-2Nq · z ⁻¹ + Nq (z ⁻¹ ) ² = S4 + Nq (1-z ⁻¹ ) ²

FIG. 9 is a diagram illustrating the effect of reducing quantization noise in the vicinity of direct current by the secondary noise shaper of the delta-sigma modulation unit 5 in FIG. Energy Nq ² spectrum Nq of the quantization noise in the frequency f is represented by the sampling frequency fs by the following equation.
Nq ² = 16 {sin (ω / fs)} ⁴
However, ω = 2πf
In FIG. 9, among the quantization noise energy Nq ² in the range from DC (f = 0) to 1/2 of the sampling frequency fs, the noise component from DC to 1/6 of the sampling frequency fs is the sampling frequency fs. Is significantly reduced by the secondary noise shaper of the delta-sigma modulation unit 5 in comparison with a high-frequency noise component of 1/6 or more.

  As described above, the actuator device according to the first embodiment includes the SMA (shape memory alloy) 2 that expands and contracts according to the supplied drive signal and displaces the lens of the autofocus mechanism of the optical system 3 of the imaging device. The PWM drive unit 1 that supplies a drive signal to the SMA 2 and the change in the focus state of the imaging device of the lens displaced by the SMA 2 are detected, and information to be fed back to the PWM drive unit 1 according to the change state A feedback control unit 4 that outputs a responsible feedback signal, and a delta-sigma modulation unit 5 that is input to the PWM drive unit 1 by reducing the number of bits that is the amount of digital data information of the feedback signal output by the feedback control unit 4 It is equipped with.

  In this case, the PWM drive unit 1 generates a PWM signal based on the digital data input from the delta-sigma modulation unit 5 as a drive signal.

  In this case, the delta-sigma modulation unit 5 also includes a quantization circuit 51 that quantizes the feedback signal output from the feedback control unit 4 and a delay circuit 53 that delays the quantization noise generated in the quantization circuit 51 (further, Includes a delay circuit 56) and an adder circuit 55 that combines the quantization noise delayed by the delay circuit 53 and the like with the feedback signal output by the feedback control unit 4 and feeds back to the quantization circuit 51.

  In this case, the PWM drive unit 1 may include a low-pass filter circuit or a smoothing circuit that smoothes the generated PWM signal and converts it into an analog drive signal.

  Therefore, according to the first embodiment and the modification described above, a PWM signal is supplied to the SMA 2 as a drive signal, and the position of the lens of the autofocus mechanism of the optical system 3 of the imaging apparatus is controlled using the property that the SMA 2 expands and contracts. In this case, an inexpensive product can be obtained by eliminating the inconsistency of the digital signal between the feedback signal for position detection obtained from the optical system 3 of the imaging device and the input signal to the PWM drive unit 1. Can be realized.

  Further, according to the first embodiment, when a PWM signal is supplied to the SMA 2 as a drive signal and the position of the lens of the autofocus mechanism of the optical system 3 of the imaging apparatus is controlled using the property that the SMA 2 expands and contracts, An optimal feedback loop can be configured by generating a drive signal corresponding to the response speed of SMA2.

  Next, a second embodiment of the present invention will be described. FIG. 10 is a block diagram illustrating a configuration of the actuator device according to the second embodiment. In FIG. 10, a PWM drive unit 1 (drive means) is composed of a D / A conversion circuit, a PWM signal generation circuit, a 6-bit microcomputer, etc. (all not shown), and a 6-bit input signal S1. In response, a PWM signal S2 having a duty ratio of 64 steps is output.

  The SMA (Shape Memory Alloy) 2 is composed of a thin wire, for example, and is deformed according to the current value by the PWM signal input from the PWM drive unit 1 to act on the autofocus mechanism of the optical system 3. The position of the lens is adjusted by changing the force A1.

  The optical system 3 (optical means) includes an autofocus mechanism in which the lens position is adjusted by the acting force of the SMA 2, an image pickup device such as a CCD or CMOS, an image processing circuit, etc. (none of which are shown).

  The feedback control unit 6 detects a change in the resistance value of the SMA 2 and outputs a 6-bit feedback signal S1. Since the resistance value of the SMA 2 changes at the same time as it contracts due to heating by the supplied current, the amount of contraction can be detected by detecting the change of the resistance value. The target value signal S7 is, for example, a zoom setting value for far-field shooting or foreground shooting set by operating a mechanical part of the lens barrel or a switch.

FIG. 11 is a block diagram showing an internal configuration of the feedback control unit 6 and the PWM drive unit 1 of FIG. In FIG. 11, a resistor Rsma is an equivalent circuit of the SMA 2 in FIG. 10, and expands and contracts according to the current value I supplied from the PWM drive unit 1 and changes in resistance value (referred to as “Rsma” for convenience). The resistor Rref (reference resistor) is a reference fixed resistor having a fixed resistance value (for convenience, “Rref”). Therefore, the voltages Vsma and Vref at both ends of the resistor Rsma and the resistor Rref are expressed by the following formulas depending on the supplied current value I.
Vsma = Rsma · I
Vref = Rref · I

  The high input resistance differential amplifier circuit 61 (first detection means) amplifies the voltage Vsma across the resistor Rsma and outputs a first detection signal k1 · Vsma. Further, the high input resistance differential amplifier circuit 62 (second detection means) amplifies the voltage Vref across the resistor Rref and outputs a second detection signal k1 · Vref.

  The logarithmic amplifier circuit 63 (first logarithmic conversion means) logarithmically amplifies the first detection signal k1 · Vsma output from the high input resistance differential amplifier circuit 61 and outputs the signal k2 · ln (k1 · Vsma). To do. Further, the logarithmic amplifier circuit 64 (second logarithmic conversion means) logarithmically amplifies the second detection signal k1 · Vref output from the high input resistance differential amplifier circuit 62 to generate a signal k2 · ln (k1 · Vref). Is output.

  The subtraction circuit 65 (subtraction means) has a positive input terminal connected to the logarithmic amplifier circuit 63, a negative input terminal connected to the logarithmic amplifier circuit 64, and a signal k2 · ln (k1 · Vsma) output from the logarithmic amplifier circuit 63. And the difference between the signal k2 · ln (k1 · Vref) output from the logarithmic amplifier circuit 64 and the difference signal k2 · ln (Vsma / Vref) is output.

  The inverse logarithmic amplifier circuit 66 (antilogarithmic conversion means) performs inverse logarithmic conversion on k2 · ln (Vsma / Vref) output from the subtracting circuit 65, and the ratio between the resistance value Rsma of the SMA2 and the resistance value Rref of the reference resistance. A ratio signal k3 · (Vsma / Vref) is output.

  Although not shown in the figure, the control circuit 67 (feedback control means) comprising an MPU (microcomputer) or the like has a control program ROM, work RAM, sample hold circuit, A / D conversion circuit, etc. The ratio signal k3 · (Vsma / Vref) output from the inverse logarithmic amplifier circuit 66 is sampled and held, A / D converted, and PWM as an input signal S1 of 6-bit digital data corresponding to an error from the target value S7. Feedback is provided to the drive unit 1.

  FIG. 12 is a flowchart showing an autofocus operation executed by the control circuit 67. First, after processing of the RAM work area, for example, initialization processing (step S1) such as clearing the timer T to 0, the value of the timer T is from 0 to a predetermined time T1, which is an interval for measuring SMA. It is determined whether or not it has been reached (step S2). If the predetermined time has not been reached, another process as the imaging device is executed (step S3). As other processes, for example, there are a timer interrupt process that occurs at regular intervals and other interrupt processes.

  In step S2, when the value of the timer T reaches T1, the signal k3 · (Vsma / Vref) output from the antilogarithmic amplifier circuit 66 of FIG. 11 is sampled and held, and A / D is converted into 6-bit digital data. Conversion is performed and the resistance value Rsma of SMA is taken in (step S4). Next, the resistance value of SMA is detected (step S5), and the displacement amount of the position of an optical component such as a lens is calculated (step S6).

  Next, an error between the target position and the detected position is calculated based on the calculated displacement amount (step S7), and a feedback signal is generated based on the calculation result (step S8). Next, the generated feedback signal is output to the PWM drive unit 1 (step S9). Thereafter, the timer T is cleared to 0 (step S10), the process proceeds to step S2, and the loop process up to step S10 is repeated every time the predetermined time T1 elapses.

  As described above, the actuator device according to the second embodiment includes the SMA 2 that expands and contracts according to the supplied drive signal and displaces the lens position of the autofocus mechanism of the optical system 3, and the reference resistor connected to the SMA 2. A PWM drive unit 1 that supplies a drive signal to the SMA 2 and the reference resistor, a high input resistance differential amplifier circuit 61 that detects the resistance value Rsma of the SMA 2 and outputs a first detection signal, and a reference resistor A high input resistance differential amplifier circuit 62 that detects the resistance value Rref and outputs a second detection signal, and a logarithmic amplifier circuit that performs logarithmic conversion processing on the first detection signal and outputs a second logarithmic signal 63, a logarithmic amplification circuit 64 that performs logarithmic conversion processing on the second detection signal and outputs a second logarithmic signal, and calculates a difference between the first logarithmic signal and the second logarithmic signal. Output signal A sub-logarithm amplification circuit 66 for performing a reverse logarithmic conversion process on the difference signal and outputting a ratio signal representing a ratio between the resistance value Rsma of the SMA 2 and the resistance value Rref of the reference resistance; And a feedback control unit 6 that detects a displacement amount of the lens position based on the information and outputs a feedback signal S1 that carries information to be fed back to the PWM drive unit 1.

  As described above, according to the second embodiment, the lens position of the autofocus mechanism detected by the ratio of the first detection signal of the resistance value of SMA2 and the second detection signal of the resistance value of the reference resistor. In the case of feeding back the error to the PWM drive unit 1, instead of using a complicated division circuit that directly calculates the ratio of the first detection signal and the second detection signal, the first detection signal and the second detection signal The detection signal is logarithmically converted and the difference between these is calculated to detect the ratio between the resistance value of the SMA 2 and the reference resistance value, so that high-speed calculation processing can be performed compared to calculation processing of the division circuit. This makes it possible to realize fine and fast control of the lens position.

  Next, a third embodiment of the present invention will be described. FIG. 13 is a block diagram illustrating the configuration of the actuator device according to the third embodiment. As shown in FIG. 13, the third embodiment has a configuration in which the delta-sigma modulation unit 5 in the first embodiment is incorporated into the configuration of the second embodiment shown in FIG. The other components are the same as those in the second embodiment, and are thus denoted by the same reference numerals and the description thereof is omitted.

  In the second embodiment, the microcomputer output of the control circuit 67 in FIG. 11 has a 6-bit configuration, and a 6-bit feedback signal adapted to generate a PWM signal in the PWM drive unit 1 is generated. A configuration in which the circuit 67 controls the entire imaging apparatus is also conceivable. As the microcomputer in this case, it is general to use a microcomputer having 10 bits or more, for example, a 16-bit structure, rather than a 6-bit structure. For this reason, there is a problem that the consistency of the digital signal cannot be obtained with the PWM signal having a resolution with a duty ratio of 64 steps, so that the expansion and contraction of the shape memory alloy cannot respond to a high-speed change of the drive signal. It is necessary to reduce the number of 16-bit to 32-bit feedback signals output from the control circuit 67 and to convert the feedback signals into bits suitable for the generation of the PWM signal in the PWM drive unit 1 using the characteristics. is there.

  In FIG. 13, the feedback control unit 6 detects the ratio between the resistance value of the SMA 2 and the reference resistance value without using a divider circuit, as in the second embodiment. When the microcomputer of the feedback control unit 6 that processes the detection signal has a general-purpose 16-bit or more configuration, a delta-sigma modulation unit 5 outputs a feedback signal of 10-bit or more as in the case of the first embodiment. It is converted into a 6-bit feedback signal and supplied to the PWM drive unit 1.

  Therefore, according to the third embodiment, it is possible to perform high-speed arithmetic processing as compared with the arithmetic processing of a complicated division circuit, and high-speed autofocus control can be realized. Further, an inexpensive product can be realized by eliminating the inconsistency of the digital signal between the feedback signal from the feedback control unit 6 and the input signal to the PWM drive unit 1. Furthermore, an optimal feedback loop can be configured by generating a drive signal corresponding to the response speed of SMA2.

  The above embodiments are for explaining the present invention, and the present invention is not limited to the above embodiments, and other embodiments and other embodiments that can be considered by those skilled in the art without departing from the scope of the claims. Modifications also belong to the present invention.

  For example, in the above-described embodiment, the actuator device whose control target is the autofocus mechanism of a camera or other imaging device has been described. However, the control target of the actuator device of the present invention is not limited to the autofocus mechanism. The present invention is effective as any actuator device that requires high-precision and high-speed position control in devices or parts other than the imaging device, as well as being usable for controlling the iris mechanism and shutter mechanism of the imaging device. It is clear that there is.

It is a block diagram which shows the structure of the actuator apparatus in 1st Embodiment of this invention. It is a figure which shows the PWM drive part by the modification of 1st Embodiment, (1) is the block diagram, (2) is the circuit diagram. It is a block diagram which shows the internal circuit of the delta-sigma modulation part of FIG. It is a figure which shows the content by which a 10-bit input signal is converted into a 6-bit output signal by the delta-sigma modulation part of FIG. It is a figure which shows transition of the output signal of the delta-sigma modulation part of FIG. It is a figure showing the duty ratio of the PWM signal corresponding to the level of the output signal of the delta-sigma modulation part of FIG. It is a figure which shows the reduction effect of the quantization noise near direct current | flow by the primary noise shaper of the delta-sigma modulation part of FIG. It is a circuit diagram of the delta-sigma modulation part of FIG. 1 in the modification of 1st Embodiment. It is a figure which shows the reduction effect of the quantization noise near direct current | flow by the secondary noise shaper of the delta-sigma modulation circuit of FIG. It is a block diagram which shows the structure of the actuator apparatus in 2nd Embodiment of this invention. It is a block diagram which shows the internal structure of the feedback control part of FIG. 10, and a PWM drive part. 12 is a flowchart illustrating an autofocus operation executed by the control circuit of FIG. 11. It is a block diagram which shows the structure of the actuator apparatus in 3rd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 PWM drive part 2 Shape memory alloy 3 Optical system 4,6 Feedback control part 5 Delta-sigma modulation part 51 Quantization circuit 53,56 Delay circuit 52,55 Addition circuit 61,62 High input resistance differential amplification circuit 63,64 Logarithm Amplifier circuit 65 Subtractor circuit 66 Reverse logarithmic amplifier circuit 67 Control circuit

Claims (4)

A shape memory alloy that expands and contracts according to a supplied drive signal to displace a predetermined control object;
A reference resistor connected to the shape memory alloy;
Drive means for supplying drive signals to the shape memory alloy and the reference resistance;
First detection means for detecting a resistance value of the shape memory alloy and outputting a first detection signal;
Second detection means for detecting a resistance value of the reference resistor and outputting a second detection signal;
First logarithmic conversion means for performing logarithmic conversion processing on the first detection signal and outputting a second logarithmic signal;
Second logarithmic conversion means for performing logarithmic conversion processing on the second detection signal and outputting a second logarithmic signal;
Subtracting means for calculating a difference between the first log signal and the second log signal and outputting a difference signal;
An inverse logarithmic conversion means for performing a reverse logarithmic conversion process on the difference signal and outputting a ratio signal representing a ratio between a resistance value of the shape memory alloy and a resistance value of the reference resistance;
Feedback control means for detecting a displacement amount of the control object based on the ratio signal and outputting a feedback signal carrying information to be fed back to the driving means;
An actuator device comprising:   The first detection means detects a resistance value that changes simultaneously with expansion and contraction according to the current value of the drive signal supplied to the shape memory alloy, and the feedback control means detects the resistance value based on the change in the resistance value. The actuator device according to claim 1, wherein a displacement amount of the controlled object due to expansion and contraction of the shape memory alloy is detected.   The drive means supplies a drive signal having a current value independent of a change in the resistance value of the shape memory alloy to the shape memory alloy and the reference resistance, and the first detection means and the second detection means The actuator device according to claim 1, wherein each terminal voltage represented by a product of a current value and a resistance value flowing through the shape memory alloy and the reference resistance is detected.   The control target is an imaging device having an optical means of an autofocus mechanism, and the shape memory alloy expands and contracts according to a drive signal supplied from the drive means to displace the lens of the autofocus mechanism. The actuator device according to any one of claims 1 to 3, characterized in that:

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