WO2013121581A1

WO2013121581A1 - Mirror driving device

Info

Publication number: WO2013121581A1
Application number: PCT/JP2012/053845
Authority: WO
Inventors: 宏之榎本
Original assignee: パイオニア株式会社
Priority date: 2012-02-17
Filing date: 2012-02-17
Publication date: 2013-08-22

Abstract

This mirror driving device has a base unit, a mirror unit connected to the base part via connecting part so as to be able to oscillate, a first coil and second coil for causing the mirror part to oscillate, and a switching means for selectively switching the supply of electric current to either or both of the first coil and second coil. A resonance frequency can thereby be appropriately controlled without leading to an increase in the size or power consumption of the device.

Description

Mirror drive device

The present invention relates to a technical field for driving a mirror used in an image display device.

2. Description of the Related Art Conventionally, an image display device that displays an image by scanning (scanning) a laser beam with a mirror is known. In general, a mirror used in an image display device adjusts the driving frequency to the resonance frequency of the structure for the purpose of increasing the deflection angle while reducing the driving current and reducing fluctuations due to disturbance. . For example, Patent Documents 1 and 2 describe techniques relating to the control of the resonance frequency of such a mirror.

Patent Document 1 discloses a technique for controlling the resonance frequency of a vibrating mirror by heating the torsion bar with a heating element, with respect to a vibrating mirror that deflects a laser beam by reciprocally vibrating a mirror substrate about a torsion bar as a rotation axis. Are listed. In Patent Document 2, the temperature of the torsion bar is raised and lowered using a temperature control device such as a Peltier element or a fan motor so that the torsion bar has a target temperature that exhibits a spring constant corresponding to a predetermined drive frequency. The technology to be described is described.

Japanese Patent Laid-Open No. 2004-69731 JP 2008-9188 A

However, the techniques described in Patent Documents 1 and 2 require an external device (such as a heating element, a Peltier element, and a fan motor) for controlling the resonance frequency in addition to the device that drives the mirror. There was a tendency for the overall size of the apparatus to increase. Therefore, it has been difficult to apply the technology to small devices. In the techniques described in Patent Documents 1 and 2, since the temperature of the torsion bar is controlled by the external device, power consumption tends to increase due to the control of the external device.

Examples of the problem to be solved by the present invention include the above. An object of the present invention is to provide a mirror driving device capable of appropriately controlling a resonance frequency without causing an increase in size of the device or an increase in power consumption.

In the first aspect of the invention, the mirror driving device includes a base portion, a mirror portion that is swingably connected via the base portion and the connecting portion, and a first coil for swinging the mirror portion. And a second coil, and switching means for selectively switching the supply of current to one or both of the first coil and the second coil.

In the invention according to claim 8, the mirror driving device includes a base portion, a mirror portion that is swingably connected via the base portion and the connecting portion, and a plurality of coils for swinging the mirror portion. And a switching means for switching the number of coils that supply current among the plurality of coils.

1 shows an overall configuration of a mirror driving device according to the present embodiment. The figure for demonstrating the specific structure of a switch part is shown. An example of a change in resolution when the resonance frequency changes is shown. The figure for demonstrating the reason which can control a resonance frequency, without increasing the emitted-heat amount (power consumption) in the whole apparatus by a present Example is shown. The processing flow for the resonant frequency control which concerns on a present Example is shown. The processing flow for the resonant frequency detection which concerns on a present Example is shown. The figure for demonstrating the reason for making the drive frequency in case a phase difference (absolute value) is 90 degree | times into a resonant frequency is shown.

In one aspect of the present invention, a mirror driving device includes a base portion, a mirror portion that is swingably connected via the base portion and a connection portion, a first coil for swinging the mirror portion, and And a switching means for selectively switching supply of current to one or both of the first coil and the second coil.

The above mirror driving device is suitably applied to an image display device that displays an image by scanning (scanning) laser light with a mirror portion. The mirror part is swingably connected via a base part and a connection part (for example, a torsion bar), and is swung by the first coil and the second coil. The switching means selectively switches the supply of current to one or both of the first coil and the second coil. By performing such switching, the coil power consumption (that is, the heat generation amount) changes due to the change in coil impedance. As a result, the temperature of the connecting portion can be controlled using the change in the amount of heat generated by the coil, and the resonance frequency can be controlled. Therefore, according to the above mirror driving device, it is possible to appropriately control the resonance frequency without causing an increase in the size of the device or an increase in power consumption.

Preferably, the first coil and the second coil are formed so as to surround the mirror part, and are disposed in the vicinity of the connection part. Thereby, temperature control of a connection part can be performed appropriately, ensuring the rotational torque for rocking | fluctuating a mirror part.

In one aspect of the above mirror driving device, the first coil and the second coil are wound in parallel. Thereby, it becomes possible to improve the mountability to the mirror drive device of a 1st coil and a 2nd coil.

In another aspect of the above mirror driving device, the mirror driving device further includes a detecting unit that detects a resonance frequency of the oscillating mirror unit, and the switching unit selectively supplies the current according to the resonance frequency. Switch to. As a result, the resonance frequency can be appropriately set to a desired frequency (reference resonance frequency).

Preferably, in the above mirror driving device, the switching means switches so as to supply a current to one of the first coil and the second coil when the resonance frequency is equal to or higher than a reference resonance frequency. When the resonance frequency is lower than the reference resonance frequency, switching can be performed so as to supply current to both the first coil and the second coil.

In the above mirror driving device, preferably, the switching means supplies the current to one of the first coil and the second coil, and both the first coil and the second coil. It is possible to perform control for continuously switching between the current supply and the timing for performing the switching according to the resonance frequency.

In another aspect of the above mirror driving device, the phase difference between the drive signal for swinging the mirror portion and the detection signal of the sensor for detecting the swing of the mirror portion due to the drive signal is 90 degrees. The control means further controls the frequency of the drive signal, and the detection means determines the frequency of the drive signal when the phase difference is 90 degrees as a result of control by the control means. Detect as. Thereby, it is possible to appropriately detect the resonance frequency and appropriately control the switching based on the resonance frequency.

In another aspect of the present invention, a mirror driving device includes a base portion, a mirror portion that is swingably connected via the base portion and a connection portion, and a plurality of coils for swinging the mirror portion. And a switching unit that switches the number of coils that supply current among the plurality of coils.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

[Device configuration]
FIG. 1 is a schematic diagram illustrating an overall configuration of a mirror driving device 100 according to the present embodiment. The mirror drive device 100 mainly includes a mirror drive control unit 1, a vibrating mirror 2, and a switch unit 3. The mirror driving device 100 is applied to an image display device (not shown), and operates to scan with laser light to draw an image.

The mirror drive control unit 1 includes a drive control unit 11, a switch control unit 12, a resonance frequency detection unit 13, and a phase comparison unit 14. The vibrating mirror 2 includes a mirror part 21, a base part 22, a torsion bar 23,

magnets

24a and 24b,

coils

25a, 25b and 25c, and a position sensor 26. The mirror drive control unit 1 corresponds to a drive circuit (actuator drive circuit) that swings the mirror unit 21 using the

coils

25a, 25b, and 25c in the vibration mirror 2 as actuators.

First, the mirror drive control unit 1 will be described. The drive control unit 11 outputs a drive signal S11 (corresponding to a current) for driving the

coils

25a, 25b, and 25c in the vibrating mirror 2. The drive signal S11 is supplied to the

coils

25a, 25b, and 25c via the switch unit 3.

The switch control unit 12 supplies a control signal S12 for controlling the switch unit 3 to the switch unit 3. The switch control unit 12 generates a control signal S12 based on the resonance frequency detected by the resonance frequency detection unit 13. The switch control unit 12 (which may include the switch unit 3) corresponds to an example of the “switching unit” in the present invention.

The phase comparison unit 14 obtains the phase difference between the drive signal S11 of the drive control unit 11 and the detection signal S26 of the position sensor 26 in the vibration mirror 2. Specifically, the phase comparison unit 14 obtains a phase difference between the frequency corresponding to the drive signal S11 of the drive control unit 11 and the frequency corresponding to the actual swinging operation of the vibrating mirror 2 by the drive signal S11.

The resonance frequency detection unit 13 detects the resonance frequency in the oscillating mirror 2 based on the phase difference obtained by the phase comparison unit 14. Specifically, the resonance frequency detection unit 13 detects the frequency of the drive signal S11 when the phase difference is 90 degrees as the resonance frequency.

The switch unit 3 has a plurality of switches (not shown) for switching the output destination of the drive signal S11 of the drive control unit 11. Specifically, the switch unit 3 supplies the drive signal S11 to at least one of the

coils

25a, 25b, and 25c by switching a plurality of switches according to the control signal S12 of the switch control unit 12. . In FIG. 1, a drive signal S25a is supplied from the switch unit 3 to the coil 25a, a drive signal S25b is supplied from the switch unit 3 to the coil 25b, and a drive signal S25c is supplied from the switch unit 3 to the coil 25c ( The drive signals S25a, S25b, and S25c correspond to currents).

Hereinafter, when the

coils

25a, 25b, and 25c are not distinguished from each other, they are appropriately described as “coil 25”, and when the drive signals S25a, S25b, and S25c are not distinguished from each other, they are appropriately described as “drive signal S25”. .

Next, the vibrating mirror 2 will be described. The mirror part 21 is supported by a torsion bar 23 and is configured to be swingable with respect to the base part 22 (in other words, the frame part). The mirror unit 21 receives laser light and reflects the laser light toward a screen (not shown). For example, the mirror unit 21 swings so as to scan the laser beam in the horizontal direction (main scanning direction). The torsion bar 23 has elasticity that connects the mirror part 21 and the base part 22 and rotates the mirror part 21 about an axis along one direction as a central axis.

The above-described resonance frequency is a frequency mainly determined by the configuration of the mirror unit 21 and the torsion bar 23. For example, the resonance frequency is determined by the moment of inertia of the mirror portion 21 and the spring constant (torsional elastic coefficient) of the torsion bar 23. Further, the resonance frequency tends to change depending on the temperature of the torsion bar 23. Specifically, the resonance frequency tends to decrease as the temperature of the torsion bar 23 increases, and the resonance frequency tends to increase as the temperature of the torsion bar 23 decreases.

The

coils

25 a, 25 b, and 25 c are formed so as to surround the mirror part 21 and swing together with the mirror part 21. Each of the

coils

25a, 25b, and 25c is made of the same material and has the same wire diameter, and is disposed by being wound in parallel, that is, a plurality of one-turn windings are connected in parallel. Has been. In FIG. 1, the

coils

25a, 25b, and 25c are shown with only one turn (one turn) for convenience of explanation, but are actually composed of a plurality of turns (the number of turns of the

coils

25a, 25b, and 25c (the number of turns). ) Is the same). The

coils

25a, 25b, and 25c are supplied with drive signals S25a, S25b, and S25c (corresponding to current) under the control of the switch unit 3 by the switch control unit 12, respectively. When a current is passed through the coil 25 in the presence of a magnetic field (a magnetic field in a direction perpendicular to the torsion bar 23) by the

magnets

24a and 24b, a rotational torque due to Lorentz force is generated. Thereby, the mirror part 21 will rock | fluctuate.

A position sensor 26 is provided in the vicinity of the torsion bar 23. The position sensor 26 is configured to be able to detect the position of the mirror unit 21, and supplies a detection signal S 26 corresponding to the detected position of the mirror unit 21 to the phase comparison unit 14. For example, the position sensor 26 is configured by an angle sensor that detects an angle (rotation angle) of the mirror unit 21.

Next, a specific configuration of the switch unit 3 will be described with reference to FIG. In FIG. 2, only the minimum components necessary for the description of the switch unit 3 are illustrated for convenience of description. As shown in FIG. 2, the switch unit 3 includes first switches 3a1 and 3a2 and second switches 3b1 and 3b2.

The first switches 3a1, 3a2 are switched between on and off by a control signal S12a (shown by a broken line) from the switch control unit 12. The first switches 3a1, 3a2 operate in conjunction with the control signal S12a and are set to the same state. The second switches 3b1 and 3b2 are switched between on and off by a control signal S12b (shown by a broken line) from the switch control unit 12. The second switches 3b1 and 3b2 operate in conjunction with the control signal S12b and are set to the same state. Hereinafter, when the first switches 3a1 and 3a2 are not distinguished from each other, they are referred to as “first switches 3a”, and when the second switches 3b1 and 3b2 are not distinguished from each other, they are referred to as “second switches 3b”.

When both the first switch 3a and the second switch 3b are off, a current (drive signal S25a) is supplied only to the coil 25a. In addition, when the first switch 3a is on and the second switch 3b is off, current (drive signals S25a and S25b) is supplied to the

coils

25a and 25b. When both the first switch 3a and the second switch 3b are on, current (drive signals S25a, S25b, S25c) is supplied to all the

coils

25a, 25b, 25c.

The coil impedance of the oscillating mirror 2 is changed by changing the number of the coils 25 through which the current flows according to the setting of the first switch 3a and the second switch 3b. The conditions of the

coils

25a, 25b, and 25c are the same, and the

coils

25a, 25b, and 25c are connected in parallel. Therefore, the larger the number of the coils 25 through which the current flows, the lower the coil impedance. In other words, the smaller the number of coils 25 through which current flows, the higher the coil impedance.

Specifically, when both the first switch 3a and the second switch 3b are turned off, the current is supplied only to the coil 25a, so that the coil impedance becomes the highest (hereinafter, the coil impedance is “ Also called “high coil impedance”). On the other hand, when both the first switch 3a and the second switch 3b are turned on, current is supplied to all of the

coils

25a, 25b, and 25c, so that the coil impedance is the lowest (hereinafter, The coil impedance is also referred to as “low coil impedance”).

On the other hand, when the first switch 3a is turned on and the second switch 3b is turned off, since current is supplied to the

coils

25a and 25b, both the first switch 3a and the second switch 3b are turned off. Although the coil impedance is lower than the case, the coil impedance is higher than when both the first switch 3a and the second switch 3b are turned on. The same coil impedance is obtained when the first switch 3a is turned off and the second switch 3b is turned on. Hereinafter, the coil impedance is also referred to as “standard coil impedance”.

[Control method]
Next, the control method according to the present embodiment will be specifically described. In the present embodiment, as described above, the resonance frequency in the oscillating mirror 2 is controlled by changing the coil impedance by the control of the switch unit 3 by the switch control unit 12. Specifically, the fluctuation of the resonant frequency is suppressed by controlling the power consumption of the coil 25 (that is, the amount of heat generated by the coil 25) by changing the coil impedance. That is, in this embodiment, the resonance frequency is set to a desired frequency (hereinafter referred to as “reference resonance frequency”) by controlling the temperature of the torsion bar 23 using the self-heating of the coil 25. The reference resonance frequency is a fixed frequency that is set in advance in accordance with image drawing by the image display device.

More specifically, in this embodiment, when the resonance frequency detected by the resonance frequency detector 13 (hereinafter referred to as “detected resonance frequency”) is equal to or higher than the reference resonance frequency, the coil impedance is increased to increase the coil 25. The switch control unit 12 controls the switch unit 3 so as to decrease the resonance frequency by increasing the heat generation amount (that is, by increasing the temperature of the torsion bar 23). Specifically, the switch control unit 12 controls the switch unit 3 so that both the first switch 3a and the second switch 3b are set to off, thereby causing a current to flow only in the coil 25a, thereby increasing the high coil impedance. Set to.

On the other hand, when the detected resonance frequency is lower than the reference resonance frequency, the resonance frequency is increased by decreasing the coil impedance to decrease the amount of heat generated by the coil 25 (that is, by decreasing the temperature of the torsion bar 23). In order to do this, the switch control unit 12 controls the switch unit 3. Specifically, the switch control unit 12 controls the switch unit 3 so that both the first switch 3a and the second switch 3b are set to ON, so that a current flows through all of the

coils

25a, 25b, and 25c. Therefore, the coil impedance is set to be low.

On the other hand, when the detected resonance frequency is approximately the reference resonance frequency, the switch control unit 12 controls the switch unit 3 so as to set the first switch 3a on and the second switch 3b off. Then, the current is passed through the

coils

25a and 25c, or the current is passed through the

coils

25a and 25c by controlling the switch unit 3 so that the first switch 3a is turned off and the second switch 3b is turned on. . That is, the switch control unit 12 sets the standard coil impedance.

Here, the reason for controlling the resonance frequency as described above will be described. In general, the vibrating mirror 2 used in the image display device has a resonance frequency as a driving frequency for the purpose of increasing a swing angle while reducing the driving current of the mirror unit 21 and reducing fluctuations due to disturbance. Is controlled by using. Such a resonance frequency tends to change depending on the temperature in the vibrating mirror 2 (specifically, the temperature of the torsion bar 23). Specifically, the resonance frequency tends to change from the reference resonance frequency. As a coping method when the resonance frequency changes in this way, a method is known in which the image is not distorted by synchronizing the image signal and performing shift correction such as pixel data and scanning line interpolation. However, this method tends to reduce the resolution.

FIG. 3 shows an example of a change in resolution when the resonance frequency changes. FIG. 3 shows the horizontal scanning direction (main scanning direction) in the substantially horizontal direction and the vertical scanning direction (sub-scanning direction) in the vertical direction. Specifically, FIG. 3 shows the horizontal resolution and the vertical resolution in a part of the image.

FIG. 3A shows a diagram when the resonance frequency is not shifted, specifically, when the resonance frequency matches the reference resonance frequency. In this case, the horizontal resolution is four and the vertical resolution is four. FIG. 3B shows a diagram when the resonance frequency is lower than the reference resonance frequency. In this case, since there are three vertical resolutions, it can be said that the vertical resolution is lowered as compared with the case where the resonance frequency shown in FIG. On the other hand, the horizontal resolution is equivalent to six lines by interpolation (interpolated points are indicated by broken lines), but the actual amount of information is four. FIG. 3C shows a diagram when the resonance frequency is higher than the reference resonance frequency. In this case, since there are three horizontal resolutions, it can be said that the horizontal resolution is lowered as compared with the case where the resonance frequency shown in FIG. On the other hand, the vertical resolution is equivalent to six by interpolation (interpolated lines are indicated by broken lines), but the actual amount of information is four.

As described above, it can be seen that when the resonance frequency changes, the resolution tends to decrease even if image correction is performed accordingly. In order to suppress such a change in the resonance frequency, a technique for controlling the temperature of the torsion bar 23 (for example, a technique described in Patent Documents 1 and 2) is known. However, as described in “Problems to be Solved by the Invention”, in this technique, an external device (for example, a heat source such as a heater or a cooling device such as a fan or a Peltier element) for resonance frequency control is used. This is necessary separately and tends to increase the overall size of the apparatus. Moreover, in the said technique, there existed a tendency for power consumption to increase by using such an external device.

In contrast, in this embodiment, the switch control unit 12 controls the resonance frequency by changing the coil impedance by performing control to switch the coil 25 to be used. That is, in this embodiment, the temperature of the torsion bar 23 is adjusted by changing the coil impedance to control the amount of heat generated by the coil 25, and the resonance frequency is set to the reference resonance frequency. According to such a present Example, a resonant frequency can be controlled appropriately, without adding the external device for temperature control like the technique described in patent document 1,2. Therefore, according to the present Example, the enlargement of an apparatus can be suppressed and it can apply appropriately to a small apparatus.

In this embodiment, a method of controlling the temperature using the self-heating of the coil 25 is used. However, since this method uses the current necessary for driving the coil 25 as it is, Temperature control can be appropriately realized without increasing current consumption. That is, in this embodiment, it is not necessary to increase the current for temperature control.

Furthermore, according to the present embodiment, the temperature change amount (power consumption change amount) on the vibrating mirror 2 side can be offset by the temperature change amount (power consumption change amount) on the mirror drive control unit 1 side. The resonance frequency can be controlled without increasing the power consumption of the entire apparatus. That is, the heat generation amount of the entire mirror driving device 100 corresponds to the sum of the loss on the mirror drive control unit 1 side and the heat generation on the vibrating mirror 2 side, but control for changing the coil impedance as in this embodiment. According to this, since the heat generation amount can be distributed between the mirror drive control unit 1 side and the vibrating mirror 2 side, the heat generation amount (power consumption) in the entire apparatus can be maintained substantially constant.

Here, with reference to FIG. 4, the reason why the resonance frequency can be controlled without increasing the heat generation amount (power consumption) in the entire mirror driving device 100 according to the present embodiment will be described.

FIG. 4 shows the voltage, current, and heat generation on the mirror drive control unit 1 side on the left side, and the voltage, current, and heat generation on the vibration mirror 2 side on the right side. Specifically, graphs A11, B11, and C11 indicate drive voltages on the mirror drive control unit 1 side, and graphs A12, B12, and C12 indicate currents on the mirror drive control unit 1 side. Graphs A13, B13, and C13 show the heat generation amount (voltage × current) on the mirror drive control unit 1 side. The heat generation amounts A13, B13, and C13 are amounts corresponding to “power supply voltage−drive voltage”, and indicate losses on the mirror drive control unit 1 side. As can be seen from the expression “power supply voltage−drive voltage”, on the mirror drive control unit 1 side, the higher the drive voltage, the smaller the heat generation amount (that is, the smaller the loss), and the lower the drive voltage, the greater the heat generation amount. (In other words, loss increases). On the other hand, graphs A21, B21, and C21 show voltages on the vibrating mirror 2 side, graphs A22, B22, and C22 show currents on the vibrating mirror 2 side, and graphs A23, B23, and C23 show The amount of heat generation (voltage × current) on the vibrating mirror 2 side is shown.

FIG. 4 (a) shows a diagram when temperature control is not particularly performed because the detected resonance frequency is approximately the reference resonance frequency. Specifically, a diagram in the case of using standard coil impedance is shown. FIG. 4B shows a diagram in the case where temperature control for increasing the temperature is performed because the detected resonance frequency is equal to or higher than the reference resonance frequency. Specifically, a diagram in the case of using a high coil impedance is shown.

Comparing FIG. 4A and FIG. 4B, when the high coil impedance is used, the drive voltage on the mirror drive control unit 1 side is higher than when the standard coil impedance is used. However, it can be seen that the current on the mirror drive control unit 1 side does not change (see graphs A12 and B12). As the drive voltage is increased in this way, when the high coil impedance is used, the amount of heat generated (loss) on the mirror drive control unit 1 side is reduced as compared with the case where the standard coil impedance is used. (See graphs A13 and B13). On the other hand, it can be seen that when the high coil impedance is used, the amount of heat generated on the vibrating mirror 2 side is increased as compared with the case where the standard coil impedance is used (see A23 and B23). The current does not change on the mirror drive control unit 1 side because the displacement due to the coil driving force is determined by “current × number of turns (number of turns)”, but the number of turns does not change, so it is necessary even if the coil impedance changes. This is because the current for obtaining a proper coil displacement does not change. The reason why the drive voltage is high when high coil impedance is used is that it is necessary to increase the drive voltage in order to obtain the same current even if the coil impedance increases.

As described above, when the high coil impedance is used, the amount of heat generated on the vibrating mirror 2 side is increased as compared with the case where the standard coil impedance is used. However, when the drive voltage is increased, the mirror drive control unit 1 side is increased. The amount of heat generated (loss) decreases. Therefore, the amount of heat generation (power consumption) in the entire mirror driving device 100 does not change between when the high coil impedance is used and when the standard coil impedance is used. That is, according to the configuration according to the present embodiment, even if the coil impedance is increased, it can be said that the heat generation amount (power consumption) in the entire mirror driving device 100 does not change.

Next, FIG. 4C shows a diagram in the case where the temperature control for reducing the temperature is performed because the detected resonance frequency is lower than the reference resonance frequency. Specifically, a diagram in the case of using a low coil impedance is shown. Comparing FIG. 4A and FIG. 4C, when the low coil impedance is used, the drive voltage on the mirror drive control unit 1 side is lower than when the standard coil impedance is used. However, it can be seen that the current on the mirror drive control unit 1 side does not change (see graphs A12 and C12). Since the drive voltage is reduced in this way, the amount of heat generated (loss) on the mirror drive control unit 1 side is increased when the low coil impedance is used than when the standard coil impedance is used. (See graphs A13 and C13). On the other hand, it can be seen that when the low coil impedance is used, the amount of heat generated on the vibrating mirror 2 side is reduced as compared with the case where the standard coil impedance is used (see A23 and C23). The current does not change on the mirror drive control unit 1 side because the displacement due to the coil driving force is determined by “current × number of turns (number of turns)”. This is because the current for obtaining a proper coil displacement does not change. The reason why the drive voltage is low when the low coil impedance is used is that the drive voltage needs to be lowered in order to obtain the same current even if the coil impedance is reduced.

As described above, when the low coil impedance is used, the amount of heat generated on the vibrating mirror 2 side is reduced as compared with the case where the standard coil impedance is used. However, when the driving voltage is lowered, the mirror driving control unit 1 side is reduced. The calorific value (loss) increases. Therefore, the amount of heat generated (power consumption) in the entire mirror driving device 100 does not change between when the low coil impedance is used and when the standard coil impedance is used. That is, according to the configuration according to the present embodiment, even if the coil impedance is decreased, it can be said that the heat generation amount (power consumption) in the entire mirror driving device 100 does not change.

As can be seen from the above description, according to the present embodiment, it is possible to appropriately control the temperature while maintaining the heat generation amount (power consumption) of the entire mirror driving device 100 constant.

[Processing flow]
Next, the processing flow according to the present embodiment will be described in detail with reference to FIGS.

FIG. 5 shows a processing flow for resonance frequency control. This processing flow is repeatedly executed by the mirror drive control unit 1 during normal operation of the image display device, for example.

First, in step S101, the resonance frequency detection unit 13 in the mirror drive control unit 1 detects the resonance frequency in the vibration mirror 2. Then, the process proceeds to step S102. The specific processing related to the detection of the resonance frequency will be described later in detail.

In step S102, the switch controller 12 in the mirror drive controller 1 determines whether or not the resonance frequency (detected resonance frequency) acquired in step S101 matches the reference resonance frequency. If the detected resonance frequency does not match the reference resonance frequency (step S102: Yes), the process proceeds to step S103. In step S103 and subsequent steps, temperature control for setting the detected resonance frequency to the reference resonance frequency is performed. On the other hand, when the detected resonance frequency matches the reference resonance frequency (step S102: No), the process ends. In this case, temperature control is not performed.

Note that, in step S102 of FIG. 5, it may be determined whether or not the detected resonance frequency and the reference resonance frequency are substantially the same. That is, it is not necessary to determine whether or not the detected resonance frequency and the reference resonance frequency are exactly the same. In such a case, when the detected resonance frequency and the reference resonance frequency are substantially the same, the resonance frequency control process is terminated.

In step S103, the switch control unit 12 determines whether or not the detected resonance frequency is less than the reference resonance frequency. If the detected resonance frequency is less than the reference resonance frequency (step S103: Yes), the process proceeds to step S104. In this case, the switch control unit 12 controls the switch unit 3 so as to lower the coil impedance in order to increase the resonance frequency by reducing the amount of heat generated by the coil 25 (step S104). Specifically, the switch control unit 12 uses all of the

coils

25a, 25b, and 25c by controlling the switch unit 3 so that both the first switch 3a and the second switch 3b are set to ON. Thus, the low coil impedance is set. Then, the process proceeds to step S106.

On the other hand, when the detected resonance frequency is equal to or higher than the reference resonance frequency (step S103: No), the process proceeds to step S105. In this case, the switch control unit 12 controls the switch unit 3 to increase the coil impedance in order to decrease the resonance frequency by increasing the amount of heat generated by the coil 25 (step S105). Specifically, the switch control unit 12 controls the switch unit 3 so as to set both the first switch 3a and the second switch 3b to be off, so that only the coil 25a is used, so that a high coil impedance is obtained. Set to. Then, the process proceeds to step S106.

In step S106, the apparatus waits for a predetermined time in order to wait for a temperature change caused by the coil impedance control as described above. Then, the process proceeds to step S107.

In step S107, the resonance frequency detector 13 detects the resonance frequency in the oscillating mirror 2 again. Then, the process proceeds to step S108. The specific processing related to the detection of the resonance frequency will be described later in detail.

In step S108, the switch control unit 12 determines whether or not the resonance frequency (detection resonance frequency) acquired in step S107 is within a predetermined range. The predetermined range is a frequency range defined with reference to the reference resonance frequency.

If the detected resonance frequency is within the predetermined range (step S108: Yes), it can be said that the resonance frequency is close to the reference resonance frequency to some extent, so the processing ends. On the other hand, when the detected resonance frequency is not within the predetermined range (step S108: No), it can be said that the resonance frequency is away from the reference resonance frequency, and thus the process returns to step S102. In this case, the process after step S102 is performed again.

Next, FIG. 6 shows a processing flow for detecting the resonance frequency. This processing flow is executed in steps S101 and S107 of the processing flow shown in FIG. Here, the outline of the processing flow of FIG. 6 will be briefly described. In this processing flow, the drive frequency is controlled so that the phase difference (absolute value) between the drive signal S11 of the drive control unit 11 and the detection signal S26 of the position sensor 26 is 90 degrees, and the phase difference (absolute value) is The drive frequency at 90 degrees is detected as the resonance frequency.

Referring to FIG. 7, the reason why the drive frequency when the phase difference (absolute value) is 90 degrees is used as the resonance frequency will be described. FIG. 7 shows the transfer characteristics of the actuator (coil 25, etc.) of the vibrating mirror 2 on the upper side, and shows the phase difference between the drive signal S11 of the drive control unit 11 and the detection signal S26 of the position sensor 26 on the lower side. Yes. As shown in FIG. 7, it can be seen that when the phase difference (absolute value) is 90 degrees, a peak occurs in the transfer characteristic of the actuator, that is, resonance occurs. From this, it can be said that the drive frequency when the phase difference (absolute value) is 90 degrees is the resonance frequency in the oscillating mirror 2.

Referring back to FIG. 6, the processing flow for detecting the resonance frequency will be described. First, in step S201, the phase comparison unit 14 in the mirror drive control unit 1 detects the phase difference between the drive signal S11 of the drive control unit 11 and the detection signal S26 of the position sensor 26. Then, the process proceeds to step S202.

In step S202, the phase comparison unit 14 determines whether or not the phase difference (absolute value) acquired in step S201 is 90 degrees. When the phase difference (absolute value) is 90 degrees (step S202: Yes), the process proceeds to step S203. In this case, the resonance frequency detection unit 13 in the mirror drive control unit 1 detects the currently set drive frequency of the vibrating mirror 2 as the resonance frequency (step S203). Then, the process ends.

On the other hand, when the phase difference (absolute value) is not 90 degrees (step S202: No), the process proceeds to step S204. In step S204, the phase comparison unit 14 determines whether or not the phase difference (absolute value) is greater than 90 degrees.

If the phase difference (absolute value) is larger than 90 degrees (step S204: Yes), the process proceeds to step S205. In this case, in order to reduce the phase difference (absolute value), the drive control unit 11 in the mirror drive control unit 1 performs control to reduce the drive frequency of the oscillating mirror 2 (step S205). Then, the process returns to step S201.

On the other hand, when the phase difference (absolute value) is 90 degrees or less (step S204: No), the process proceeds to step S206. In this case, in order to increase the phase difference (absolute value), the drive control unit 11 performs control to increase the drive frequency of the vibrating mirror 2 (step S206). Then, the process returns to step S201.

According to the processing flow of FIGS. 5 and 6 described above, temperature control is appropriately realized by changing the coil impedance so as to set the resonance frequency to the reference resonance frequency while appropriately detecting the resonance frequency. Is possible.

In step S202 in FIG. 6, it may be determined whether or not the phase difference (absolute value) is approximately 90 degrees. That is, it is not necessary to determine whether or not the phase difference (absolute value) is strictly 90 degrees. In such a case, the drive frequency when the phase difference (absolute value) is approximately 90 degrees is detected as the resonance frequency.

[Modification]
Below, the modification suitable for said Example is demonstrated. It should be noted that the following modifications can be applied to the above-described embodiments in any combination.

(Modification 1)
In the above description, an example in which three coils 25 are used has been described. However, only two coils 25 may be used, or four or more coils 25 may be used. When two coils 25 are used, the number of settable coil impedances is small, but the apparatus configuration can be simplified. When four or more coils 25 are used, the device configuration tends to be complicated. However, since the number of settable coil impedances increases, it is possible to appropriately realize subtle temperature changes and large temperature changes. It becomes possible.

(Modification 2)
In the above description, the embodiment using the plurality of coils 25 having the same conditions (material, wire diameter, number of turns, etc.) is shown, but the present invention is not limited to this. In the modified example, a plurality of coils made of different materials, different wire diameters, different numbers of turns, and the like can be used. In the above-described embodiment, the coil impedance is changed by switching the number of coils to be used. However, in the modification, the coil impedance can be changed by switching the coil itself to be used. Needless to say, even in this modification, the coil impedance may be changed by switching the number of coils to be used.

(Modification 3)
In the above-described embodiment, when changing the coil impedance, the coil impedance to be used (high coil impedance, low coil impedance, or standard coil impedance) is switched according to the detected resonance frequency. In the modified example, the coil impedance can be continuously changed by continuously switching the coil that supplies the current according to the switching time ratio. In this example, the coil impedance can be arbitrarily controlled between the high coil impedance and the low coil impedance in accordance with the detected resonance frequency.

For example, using two coils having the same conditions (hereinafter referred to as “coil A” and “coil B”), supply of current to coil A and supply of current to coil A and coil B Can be controlled continuously in a relatively short cycle. In one example, when the detected resonance frequency is equal to or higher than the reference resonance frequency, the period in which current is supplied to the coil A in the period in which the switching is performed is longer than the period in which current is supplied to the coil A and the coil B. Also, make continuous switching. On the other hand, when the detected resonance frequency is lower than the reference resonance frequency, the period during which current is supplied to the coil A and the coil B in one cycle in which the switching is performed is greater than the period during which current is supplied to the coil A. Also, make continuous switching.

Further, the above-described modification uses two coils having different conditions (hereinafter referred to as “coil C” and “coil D”. The coil C has a higher impedance than the coil D). It can also be applied to. In this example, it is possible to perform control for continuously switching between supply of current to the coil C and supply of current to the coil D at a relatively short cycle. In one example, when the detected resonance frequency is equal to or higher than the reference resonance frequency, the period for supplying current to the coil C is longer than the period for supplying current to the coil D in one cycle for performing the switching. Switch continuously. On the other hand, when the detected resonance frequency is lower than the reference resonance frequency, the period for supplying the current to the coil D is set longer than the period for supplying the current to the coil C in one cycle for performing the switching. Switch continuously.

It should be noted that the above-described modification can be similarly applied to a configuration using three or more coils.

(Modification 4)
In the above, the embodiment in which the present invention is applied to the configuration in which the laser beam is scanned in the horizontal direction (main scanning direction) has been described. However, the present invention has a configuration in which the laser beam is scanned in the vertical direction (sub scanning direction). Can be applied similarly.

(Modification 5)
The present invention is not limited to application to an image display device that displays an image by scanning a laser beam. The present invention can also be applied to sensor devices such as a foreign matter sensor and a temperature sensor.

The present invention can be used for an image display device.

DESCRIPTION OF SYMBOLS 1 Mirror drive control part 2 Vibration mirror 3 Switch part 3a1, 3a2 1st switch 3b1, 3b2 2nd switch 11 Drive control part 12 Switch control part 13 Resonance frequency detection part 14 Phase comparison part 21 Mirror part 22 Base part 23

Torsion bar

25a , 25b, 25c Coil 26 Position sensor 100 Mirror drive device

Claims

A base part;
A mirror part swingably connected via the base part and a connection part;
A first coil and a second coil for swinging the mirror part;
And a switching unit that selectively switches the supply of current to one or both of the first coil and the second coil.
The mirror driving device according to claim 1, wherein the first coil and the second coil are wound and arranged in parallel.
3. The mirror driving device according to claim 1, wherein the first coil and the second coil are formed so as to surround the mirror portion and are disposed in the vicinity of the connection portion. 4. .
It further has detection means for detecting the resonance frequency of the mirror part that swings,
4. The mirror driving device according to claim 1, wherein the switching unit selectively switches the supply of the current according to the resonance frequency. 5.
The switching means performs switching so as to supply a current to one of the first coil and the second coil when the resonance frequency is equal to or higher than a reference resonance frequency, and the resonance frequency is the reference resonance. 5. The mirror driving device according to claim 4, wherein when the frequency is less than the frequency, switching is performed so that a current is supplied to both the first coil and the second coil.
The switching means is a control for continuously switching the supply of the current to one of the first coil and the second coil and the supply of the current to both the first coil and the second coil. The mirror driving device according to claim 4, wherein the switching timing is controlled according to the resonance frequency.
The frequency of the drive signal is controlled so that the phase difference between the drive signal for swinging the mirror part and the detection signal of the sensor that detects the swing of the mirror part by the drive signal is 90 degrees. Further comprising control means,
The detection means detects the frequency of the drive signal when the phase difference is 90 degrees as controlled by the control means as the resonance frequency. The mirror drive device described in 1.
A base part;
A mirror part swingably connected via the base part and a connection part;
A coil portion having a plurality of coils for swinging the mirror portion;
A mirror driving device comprising switching means for switching the number of coils that supply current among the plurality of coils.