Optical path control device, display device, and optical path control method

Abstract

To stably oscillate an optical section.SOLUTION: An optical path control device comprises: an oscillating section including an optical member on which light is incident; an actuator that oscillates the oscillating section; and a driving section that applies a driving signal of a waveform, including a first period TA1 that changes a current value from a first current value A1 to a second current value A2, and a second period TB1 that is continuous with the first period TA1 and holds the current value in the second current value A2, to the actuator to cause the actuator to oscillate the oscillating section and control an optical path. The driving section applies the driving signal so that the length of the first period TA1 corresponds to the natural frequency of the oscillating section.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an optical path control device, a display device, and an optical path control method. [Background technology]

[0002] For example, an optical device is known that shifts the optical axis by swinging an optical section into which light is incident, as shown in Patent Document 1. Patent Document 1 describes that by swinging the optical section to shift the optical path of light passing through the optical section, it is possible to increase the resolution of a projected image beyond the resolution of a light modulation device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6451187 Summary of the Invention [Problem to be solved by the invention]

[0004] When shifting the optical path in this way, it is necessary to oscillate the optical section at high speed and to keep it stationary stably.

[0005] In view of the above problems, an object of the present invention is to provide a light path control device, a display device, and a light path control method that can oscillate an optical unit at high speed and stop it stably. [Means for solving the problem]

[0006] An optical path control device according to one embodiment of the present invention includes an oscillating unit including an optical member into which light is incident, an actuator that oscillates the oscillating unit, and a drive unit that applies to the actuator a drive signal having a waveform that includes a first period in which a current value is changed from a first current value to a second current value, and a second period that is continuous with the first period and in which the current value is maintained at the second current value, thereby causing the actuator to oscillate the oscillating unit and controlling the optical path, and the drive unit applies the drive signal so that the length of the first period becomes a value that corresponds to the natural frequency of the oscillating unit.

[0007] A display device according to an aspect of the present invention includes the light path control device and an irradiation device that irradiates the optical member with light.

[0008] An optical path control method according to one aspect of the present invention is an optical path control method for controlling an optical path by applying a drive signal to an actuator that oscillates an oscillating part including an optical element into which light is incident, the method comprising the steps of applying to the actuator the drive signal having a waveform including a first period in which a current value is changed from a first current value to a second current value, and a second period that is continuous with the first period and in which the current value is maintained at the second current value, thereby causing the actuator to oscillate the oscillating part, and a length of the first period is set to a value corresponding to the natural frequency of the oscillating part. Effect of the Invention

[0009] According to the present invention, the optical portion can be swung at high speed and then stopped stably. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram of a display device according to a first embodiment. [Diagram 2] FIG. 2 is a block diagram illustrating a schematic circuit configuration of the display device. [Diagram 3] FIG. 3 is a schematic diagram of the optical path control mechanism. [Figure 4] FIG. 4 is a cross-sectional view taken along line AA of FIG. [Diagram 5]FIG. 5 is a graph illustrating the waveform of a driving signal according to the first embodiment. [Figure 6] FIG. 6 is a graph illustrating the oscillation pattern of the optical portion according to the first embodiment. [Figure 7] FIG. 7 is a block diagram illustrating a schematic circuit configuration of a display device according to the second embodiment. [Figure 8] FIG. 8 is a graph illustrating the waveform of a drive signal according to the second embodiment. [Figure 9] FIG. 9 is a graph illustrating a swing pattern of the optical portion according to the second embodiment. [Figure 10] FIG. 10 is a graph illustrating the waveform of a driving signal according to the third embodiment. [Figure 11] FIG. 11 is a graph illustrating a swing pattern of the optical portion according to the third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiment described below.

[0012] (First embodiment) (display device) FIG. 1 is a schematic diagram of a display device according to the first embodiment. As shown in FIG. 1, the display device 1 according to the first embodiment has a light path control device 10 and an irradiation device 100. The irradiation device 100 is a device that irradiates light L for an image, and the light path control device 10 is a device that controls the optical path of the light L. In this embodiment, the light path control device 10 shifts the position of the image displayed by the light L by shifting the optical axis of the light L, thereby making the resolution of the projected image higher than the resolution of the image by the irradiation device 100 (i.e., the number of pixels of a display element 106 described later).

[0013] 1, the irradiation device 100 includes a light source 101, polarizing plates 105R, 105G, and 105B, display elements 106R, 106G, and 106B, polarizing plates 107R, 107G, and 107B, a color synthesis prism 108, a projection lens 109, dichroic mirrors 120 and 121, reflecting mirrors 130 and 131, lenses 140 to 145, a polarization conversion element 150, and a video signal processing circuit 160. When the display elements 106R, 106G, and 106B are not to be distinguished from one another, they will be referred to as display elements 106.

[0014] The light source 101 is a light source that generates and irradiates light. The light source 101 irradiates incident light L0. In this embodiment, the light source 101 is used as a light source that irradiates the incident light L0, but the light source 101 may have another optical device for generating the incident light L0.

[0015] Incident light L0 from the light source 101 is incident on the lens 140. The lenses 140 and 141 are, for example, fly-eye lenses. The illumination distribution of the incident light L0 is homogenized by the lenses 140 and 141, and the incident light L0 is incident on the polarization conversion element 150. The polarization conversion element 150 is an element that aligns the polarization of the incident light L0, and has, for example, a polarizing beam splitter and a retardation plate. For example, the polarization conversion element 150 aligns the incident light L0 to p-polarized light.

[0016] The incident light L0, the polarization of which has been aligned by the polarization conversion element 150, is irradiated onto the dichroic mirror 120 via the lens 142. The lens 142 is, for example, a condenser lens.

[0017] The dichroic mirror 120 separates the incident light L0 into yellow light LRG and blue light LB containing a blue band component. The yellow illumination light LRG separated by the dichroic mirror 120 is reflected by the reflecting mirror 130 and enters the dichroic mirror 121.

[0018] The dichroic mirror 121 separates the incident yellow light LRG into red light LR containing a component in the red wavelength range and green light LG containing a component in the green wavelength range.

[0019] The red light LR separated by the dichroic mirror 121 is applied to the polarizing plate 105R via the lens 143. The green light LG separated by the dichroic mirror 121 is applied to the polarizing plate 105G via the lens 144. The blue light LB separated by the dichroic mirror 120 is reflected by the reflecting mirror 131 and applied to the polarizing plate 105B via the lens 145.

[0020] The polarizing plates 105R, 105G, and 105B have the property of reflecting either s-polarized light or p-polarized light and transmitting the other. For example, the polarizing plates 105R, 105G, and 105B reflect s-polarized light and transmit p-polarized light. The polarizing plates 105R, 105G, and 105B are also called reflective polarizing plates.

[0021] The p-polarized red light LR is transmitted through polarizing plate 105R and is irradiated onto display element 106R. The p-polarized green light LG is transmitted through polarizing plate 105G and is irradiated onto display element 106G. The p-polarized blue light LB is transmitted through polarizing plate 105B and is irradiated onto display element 106B.

[0022] The display element 106R, the display element 106G, and the display element 106B are, for example, reflective liquid crystal display elements. In this embodiment, the display element 106R, the display element 106G, and the display element 106B are reflective liquid crystal display elements, but they are not limited to the reflective type and may be configured to use transmissive liquid crystal display elements. In addition, various applications are possible to configurations using other display elements instead of liquid crystal display elements.

[0023] The display element 106R is controlled by the video signal processing circuit 160. The video signal processing circuit 160 drives and controls the display element 106R based on image data of the red component. The display element 106R optically modulates the p-polarized red light LR in accordance with the control of the video signal processing circuit 160 to generate the s-polarized red light LR. The display element 106G is controlled by the video signal processing circuit 160. The video signal processing circuit 160 drives and controls the display element 106G in accordance with image data of the green component. The display element 106G optically modulates the p-polarized green light LG in accordance with the control of the video signal processing circuit 160 to generate the s-polarized green light LG. The display element 106B is controlled by the video signal processing circuit 160. The video signal processing circuit 160 drives and controls the display element 106B in accordance with image data of the blue component. Display element 106B optically modulates p-polarized blue light LB based on image data of the blue component under the control of video signal processing circuit 160, to generate s-polarized blue light LB.

[0024] The polarizing plates 107R, 107G, and 107B have the property of transmitting either s-polarized light or p-polarized light and reflecting or absorbing the other. For example, the polarizing plates 107R, 107G, and 107B transmit s-polarized light and absorb unnecessary p-polarized light.

[0025] The s-polarized red light LR generated by display element 106R is reflected by polarizing plate 105R, passes through polarizing plate 107R, and is irradiated onto color synthesis prism 108. The s-polarized green light LG generated by display element 106G is reflected by polarizing plate 105G, passes through polarizing plate 107G, and is irradiated onto color synthesis prism 108. The s-polarized blue light LB generated by display element 106B is reflected by polarizing plate 105B, passes through polarizing plate 107B, and is irradiated onto color synthesis prism 108.

[0026] The color synthesis prism 108 synthesizes the incident red light LR, green light LG, and blue light LB, and irradiates the resulting light L for image display onto a projection lens 109. The light L is projected via the projection lens 109 onto a screen (not shown) or the like.

[0027] Although the irradiation device 100 has the above-mentioned configuration, the configuration is not limited to the above description and may be any configuration.

[0028] The light path control device 10 has a light path control mechanism 12, a control circuit (control unit) 14, and a drive circuit (drive unit) 16. The light path control mechanism 12 is a mechanism that oscillates when driven by the drive circuit 16. The light path control mechanism 12 is provided between a color synthesis prism 108 and a projection lens 109 in a direction along the light path of the light L. The light path control mechanism 12 oscillates while receiving the light L from the color synthesis prism 108, shifting the traveling direction (light path) of the light L and outputting it toward the projection lens 109. In this way, the light path control device 10 controls the light path of the light L so that the light path of the light L is shifted. The position at which the light path control mechanism 12 is provided is not limited to between the color synthesis prism 108 and the projection lens 109, and may be any position.

[0029] FIG. 2 is a block diagram showing a schematic circuit configuration of the display device. As shown in FIG. 2, the video signal processing circuit 160 controls the display elements 106R, 106B, and 106G. The video signal processing circuit 160 receives a video signal including image data for controlling the display elements 106R, 106B, and 106G and a synchronization signal. The video signal processing circuit 160 controls the display elements 106R, 106B, and 106G based on the image data while synchronizing the timing based on the synchronization signal. The control circuit 14 has a digital circuit 14A and a converter 14B. The digital circuit 14A receives a synchronization signal from the video signal processing circuit 160. The digital circuit 14A generates a digital drive signal for driving the optical path control mechanism 12 while synchronizing the timing based on the synchronization signal. The converter 14B is a DA converter that converts a digital signal into an analog signal. The converter 14B converts the digital drive signal generated by the digital circuit 14A into an analog drive signal. The drive circuit 16 receives the analog drive signal from the converter 14B, amplifies the analog drive signal, and outputs it to an actuator 12B of the optical path control mechanism 12, which will be described later. The actuator 12B is driven in response to the drive signal to oscillate a oscillating portion 12A, which will be described later.

[0030] (Optical path control mechanism) The configuration of the light path control mechanism 12 will be described in more detail. Fig. 3 is a schematic diagram of the light path control mechanism, and Fig. 4 is a cross-sectional view taken along line AA in Fig. 3. As shown in Figs. 3 and 4, the light path control mechanism 12 has a swinging part 12A including an optical member 20 onto which light L is incident, and an actuator 12B that swings the swinging part 12A. More specifically, the light path control mechanism 12 has the optical member 20, a movable part 22, a support part 24, an axis part 25, a coil 26, a yoke 27, and a magnet 28.

[0031] The optical member 20 is a member that transmits the incident light L. The optical member 20 receives the light L from one surface, transmits the incident light L, and emits the light L from the other surface. In this embodiment, the optical member 20 is a glass plate, but the material and shape of the optical member 20 may be arbitrary.

[0032] The movable part 22 is a member that supports the optical member 20. The movable part 22 is fixed to the optical member 20. Specifically, the movable part 22 in this embodiment is a plate-like member with a through hole formed in the center. The optical member 20 is fixed to the movable part 22 in a state where it is fitted into the through hole of the movable part 22. Note that the optical member 20 is fixed to the movable part 22 via a fixing member or adhesive for fixing to the movable part 22, but the method of fixing the optical member 20 to the movable part 22 may be arbitrary.

[0033] The support 24 is a member that supports the movable part 22 on which the optical member 20 is provided so as to be able to swing. In this embodiment, the support 24 is a frame-shaped member that is provided so as to surround the outer periphery of the movable part 22. The shaft 25 is a member that connects the movable part 22 to the support 24 so as to be able to swing. In this embodiment, two shafts 25 are provided. The shafts 25 are provided at positions near the vertices of the rectangular optical member 20 that face each other. The movable part 22 swings around a swing axis AX that is an axis that connects the shafts 25. When the movable part 22 swings around the swing axis AX, the attitude of the optical member 20 provided on the movable part 22 changes, and the optical path of the light L that passes through the optical member 20 is shifted.

[0034] The coil 26 is attached to the movable part 22 and fixed to the movable part 22. The coil 26 is provided at each of both ends of the movable part 22. The yoke 27 is a member that forms a magnetic path. The yoke 27 is attached to the support part 24 and fixed to the support part 24. The coil 26 is provided at each of both ends of the movable part 22 corresponding to the coil 26. The magnet 28 is a permanent magnet. The magnet 28 is attached to the yoke 27 and fixed to the yoke 27. The magnet 28 is disposed at a position adjacent to each of the coils 26. A drive signal from the drive circuit 16 is input to the coil 26. In the example of FIG. 4, the magnet 28 is attached to one side of the U-shaped yoke 27, and an air gap is formed between the surface of the magnet 28 that is not attached and the opposing side of the U-shaped yoke 27. The coil 26 is disposed in this air gap. A drive signal is input to the coil 26. As a result, a current flows through coil 26, which is a conductor within the magnetic field of magnet 28, generating a force that oscillates movable part 22 (oscillating part 12A) fixed to coil 26. In other words, actuator 12B according to this embodiment can be said to be an electromagnetic actuator constituted by coil 26, yoke 27, and magnet 28.

[0035] In this embodiment, since the movable part 22 provided with the optical member 20 oscillates in this manner, it can be said that the optical member 20, the movable part 22, and the coil 26 constitute the oscillating part 12A. In other words, it can be said that the part of the optical path control mechanism 12 that oscillates relative to the support part 24 corresponds to the oscillating part 12A. Note that, in cases where a fixing member or adhesive for fixing the optical member 20 to the movable part 22, a substrate or lead wire for passing a current through the coil 26, or the like are provided, these also oscillate relative to the support part 24, and are therefore included in the oscillating part 12A.

[0036] Although the actuator of the present embodiment is a so-called moving coil type in which the coil 26 is disposed in the movable part 22, the actuator is not limited thereto, and may be, for example, a so-called moving magnet type in which the magnet 28 is disposed in the movable part 22 and the coil 26 is disposed in the support part 24. In this case, since the magnet 28 is oscillated together with the optical member 20, the magnet 28 is included in the oscillating part 12A instead of the coil 26.

[0037] The optical path control mechanism 12 is configured as described above, but is not limited to this and may have any configuration in which the optical part can shift the optical path of light L by oscillating the optical part due to an actuator to which a drive signal is applied.

[0038] In the light path control mechanism 12, the actuator 12B swings the swinging part 12A in response to the drive signal. That is, the actuator 12B swings the swinging part 12A in response to the drive signal so that the swinging part 12A repeats a change in posture from a first angle D1 to a second angle D2 around the swing axis AX and a change in posture from the second angle D2 to the first angle D1. The swinging part 12A repeats swinging between the first angle D1 and the second angle D2, so that the optical axis of the light L repeatedly shifts from the first position to the second position and from the second position to the first position. In this embodiment, the image projected on the screen by the light L when the optical axis is at the first position and the image projected on the screen by the light L when the optical axis is at the second position are shifted by half a pixel. That is, the image projected on the screen repeatedly shifts by half a pixel and returns by half a pixel. This increases the apparent number of pixels, and the image projected on the screen can be made high-resolution. In this manner, since the shift amount of the optical axis in this embodiment is half a pixel of the image, the first angle D1 and the second angle D2 are set to angles that allow the image to be shifted by half a pixel. Note that the shift amount of the image is not limited to half a pixel, and may be any amount, such as ¼ or ⅛ of a pixel. The first angle D1 and the second angle D2 may also be set appropriately according to the shift amount of the image.

[0039] (Drive signal) Next, the drive signal applied from the drive circuit 16 to the actuator 12B will be described.

[0040] FIG. 5 is a graph for explaining the waveform of the drive signal according to the first embodiment. The drive signal applied from the drive circuit 16 to the actuator 12B is an electric signal, and as shown in FIG. 5, the current value changes over time. Hereinafter, the waveform representing the change in the current value of the drive signal over time will be referred to as the waveform of the drive signal. In FIG. 5, the waveform of the drive signal is shown by a solid line. In the first embodiment, the drive signal has the same waveform repeated every cycle T. The cycle T includes a period T1 and a period T2 that follows the period T1 and is continuous with the period T1. The period T1 corresponds to a period during which an image (here, an image that is not shifted by half a pixel) is displayed when the optical axis of the light L is at a first position, and the period T2 corresponds to a period during which an image (here, an image that is shifted by half a pixel) is displayed when the optical axis of the light L is at a second position.

[0041] In the first period TA1 of the period T1, the current value of the drive signal changes from the first current value A1 to the second current value A2. More specifically, in the first period TA1, the current value of the drive signal changes linearly from the first current value A1 to the second current value A2 as time passes. That is, the current value of the drive signal is the first current value A1 at the start timing of the first period TA1, and then the current value changes linearly from the first current value A1 to the second current value A2 at the end timing of the first period TA1. The first current value A1 is a current value that can hold the oscillating part 12A at the first angle D1 and is set according to the value of the first angle D1. The second current value A2 is a current value that can hold the oscillating part 12A at the second angle D2 and is set according to the value of the second angle D2. The first current value A1 and the second current value A2 are current values ​​whose positive and negative signs are opposite to each other, and their absolute values ​​may be equal. FIG. 5 illustrates an example in which the first current value A1 is negative and the second current value A2 is positive.

[0042] The length of the first period TA1 is a value corresponding to the natural frequency of the oscillating part 12A. As described above, the oscillating part 12A refers to the part of the optical path control mechanism 12 that oscillates with respect to the support part 24 (the optical member 20, the movable part 22, and the coil 26 in the example of this embodiment). That is, it can be said that the length of the first period TA1 is a value corresponding to the natural frequency of the part that oscillates with respect to the support part 24. More specifically, the length of the first period TA1 is preferably approximately the same value as the natural period of the oscillating part 12A, and more preferably the same value as the natural period. Here, the natural period is the reciprocal of the natural frequency. In addition, "approximately the same value" means that a value that is deviated from the natural period by the degree of the error range is also acceptable. For example, when the deviation from the natural period is within 5% of the value of the natural period, it may be considered to be "approximately the same value". Hereinafter, the expression "approximately the same value" has the same meaning. The value of the natural vibration (the inverse of the natural frequency) is expressed as "1 / f" [s], where f [Hz] is the natural frequency.

[0043] The natural frequency of the oscillating part 12A may be measured in advance. For example, a sine wave may be applied (swept) to the actuator 12B while gradually increasing the frequency from 0 Hz to measure the vibration of the oscillating part 12A, and the frequency at which the oscillating part 12A vibrates most may be set as the natural frequency of the oscillating part 12A. A microdisplacement meter may be used to measure the vibration. In this embodiment, the length of the first period TA1 is set based on the natural frequency of the oscillating part 12A measured in this manner, and the waveform of the drive signal is set so that the current changes from the first current value A1 to the second current value A2 during the first period TA1 of the set length.

[0044] In the second period TB1 of the period T1, the current value of the drive signal is held at the second current value A2. The second period TB1 is a period following the first period TA1 and continuing to the first period TA1. It is preferable to increase the natural frequency of the oscillating part 12A, since it is possible to shorten the first period TA1 and lengthen the second period TB1 (for example, to make it longer than the first period TA1). It is not limited to the current value not strictly changing from the second current value A2, but may also include the current value deviating from the second current value A2 within a range of a predetermined value. The predetermined value here may be set arbitrarily, and may be, for example, 10% of the second current value A2.

[0045] In this way, during period T1, the current value of the drive signal gradually changes from the first current value A1 to the second current value A2, and when the current value reaches the second current value A2, the current value is maintained at the second current value A2.

[0046] In the third period TA2 of the period T2, the current value of the drive signal changes from the second current value A2 to the first current value A1. The third period TA2 is a period that follows the second period TB1 and is continuous with the second period TB1. More specifically, in the third period TA2, the current value of the drive signal changes linearly over time from the second current value A2 to the first current value A1. That is, at the start timing of the third period TA2, the current value of the drive signal is the second current value A2, and then the current value changes linearly from the second current value A2 to become the first current value A1 at the end timing of the third period TA2.

[0047] The length of the third period TA2 corresponds to the natural frequency of the oscillating part 12A. More specifically, the length of the third period TA2 is preferably approximately the same as the natural period (the inverse of the natural frequency) of the oscillating part 12A, and more preferably the same as the natural period. Third Period TA2 In this embodiment, the length of the third period TA2 is equal to the length of the first period TA1.

[0048] In the fourth period TB2 of the period T2, the current value of the drive signal is held at the first current value A1. The fourth period TB2 is a period that follows the third period TA2 and is continuous with the third period TA2. The fourth period TB2 is a period that follows the first period TA1 and is continuous with the first period TA1. In this embodiment, the fourth period TB2 is equal to the second period TB1. By increasing the natural frequency of the oscillating part 12A, the third period TA2 can be shortened and the fourth period TB2 can be lengthened (for example, longer than the third period TA2), which is preferable. Note that being held at the first current value A1 is not limited to the current value not strictly changing from the first current value A1, and may also include the current value deviating from the first current value A1 within a range of a predetermined value. The predetermined value here may be set arbitrarily, and may be, for example, 10% of the first current value A1.

[0049] In this way, during period T2, the current value of the drive signal gradually changes from the second current value A2 to the first current value A1, and when the current value reaches the first current value A1, the current value is maintained at the first current value A1.

[0050] As described above, in the first embodiment, the waveform of the drive signal is trapezoidal, and the first periods TA1 and TA2 during which the current value changes have values ​​that correspond to the natural frequency of the oscillating part 12A.

[0051] 5 indicates the period during which the light L is irradiated. It is preferable that the irradiation device 100 does not irradiate the light L in the first period TA1, and irradiates the light L in the second period TB1. It is also preferable that the irradiation device 100 does not irradiate the light L in the third period TA2, and irradiates the light L in the fourth period TB2.

[0052] (Oscillation pattern) Next, the oscillation pattern of the oscillating unit 12A due to application of a drive signal will be described. Fig. 6 is a graph illustrating the oscillation pattern of the optical unit according to the first embodiment. The oscillation pattern of the oscillating unit 12A refers to the displacement angle (angle around the oscillation axis AX) of the oscillating unit 12A per unit time when a drive signal is applied to the actuator 12B. In Fig. 6, the oscillation pattern is shown by a solid line.

[0053] In the first period TA1, the current value of the drive signal changes from a first current value A1 to a second current value A2, so that the displacement angle of the oscillating part 12A changes from a first angle D1 to a second angle D2 in the first period TA1.

[0054] In the second period TB1, the current value of the drive signal is held at the second current value A2. As a result, the displacement angle of the oscillating part 12A is held at the second angle D2 in the second period TB1. Note that being held at the second angle D2 does not necessarily mean that the displacement angle does not change strictly from the second angle D2, but may also include the displacement angle deviating from the second angle D2 within a range of a predetermined value. The predetermined value here may be set arbitrarily, and may be, for example, a value of 10% of the second angle D2.

[0055] In the third period TA2, the current value of the drive signal changes from the second current value A2 to the first current value A1, so that the displacement angle of the oscillating part 12A changes from the second angle D2 to the first angle D1 in the third period TA2.

[0056] In the fourth period TB2, the current value of the drive signal is held at the first current value A1. As a result, the displacement angle of the oscillating part 12A is held at the first angle D1 in the fourth period TB2. Note that being held at the first angle D1 does not necessarily mean that the displacement angle does not change strictly from the first angle D1, but may also include the displacement angle deviating from the first angle D1 within a range of a predetermined value. The predetermined value here may be set arbitrarily, and may be, for example, a value of 10% of the first angle D1.

[0057] The light L is irradiated during the second periods TB1 and TB2. Therefore, during the second period TB1, the light L is irradiated onto the oscillating portion 12A held at the second angle D2, and the optical path of the light L is at the first position. During the fourth period TB2, the light L is irradiated onto the oscillating portion 12A held at the first angle D1, and the optical path of the light L is shifted to the second position, and the image is shifted by half a pixel.

[0058] In an optical path control device that shifts an optical path by swinging an optical unit, it is required to swing the optical unit stably. As a result of intensive research, the present inventor discovered that by setting the length of the first periods TA1 and TA2 to a value corresponding to the natural frequency of the swing unit 12A, it is possible to suppress the swing unit 12A from vibrating in the second periods TB1 and TB2 and swing the swing unit 12A stably. That is, in this embodiment, since the length of the first periods TA1 and TA2 is a value corresponding to the natural frequency of the swing unit 12A, it is possible to suppress the vibration of the swing unit 12A in the second periods TB1 and TB2 and swing the swing unit 12A stably. Therefore, according to this embodiment, it is possible to swing the swing unit 12A at high speed and stop it stably, thereby suppressing deterioration of an image.

[0059] (effect) As described above, the light path control device 10 according to this embodiment includes a swinging unit 12A including an optical member 20 on which light L is incident, an actuator 12B that swings the swinging unit 12A, and a drive circuit 16 (drive unit) that applies a drive signal to the actuator 12B to cause the actuator 12B to swing the swinging unit 12A and control the light path. The drive circuit 16 applies a drive signal to the actuator 12B, the drive signal having a waveform including a first period TA1 in which the current value is changed from a first current value A1 to a second current value A2, and a second period TB1 that is continuous with the first period TA1 and in which the current value is maintained at the second current value A2. The drive circuit 16 applies the drive signal so that the length of the first period TA1 corresponds to the natural frequency of the swinging unit 12A.

[0060] In this way, in the first embodiment, by setting the length of the first period TA1 to a value corresponding to the natural frequency of the oscillating part 12A, it is possible to suppress the oscillation of the oscillating part 12A in the second period TB1 and stably oscillate the oscillating part 12A. Also, by changing the current value in the first period TA1, which has a length corresponding to the natural frequency of the oscillating part 12A, and setting a waveform that maintains the current value in the subsequent second period TB1, it is possible to easily set a waveform that can stably oscillate the oscillating part 12A without complicating the setting of the waveform.

[0061] Moreover, the drive circuit 16 applies the drive signal so that the length of the first period TA1 is the reciprocal of the natural frequency of the oscillating part 12A. By setting the length of the first period TA1 to the reciprocal of the natural frequency of the oscillating part 12A, it is possible to make the oscillating part 12A oscillate more stably.

[0062] Moreover, the drive circuit 16 applies a drive signal so that the current value changes linearly from the first current value A1 to the second current value A2 during the first period TA1. By making the change in the current value during the first period TA1 linear, the oscillation part 12A can be oscillated more stably.

[0063] Moreover, the display device 1 according to this embodiment includes a light path control device 10 and an irradiation device 100 that irradiates the oscillation part 12A with light L. By including the light path control device 10, the display device 1 according to this embodiment can stably oscillate the oscillation part 12A and suppress image degradation.

[0064] Furthermore, in the second period TB1, the irradiation device 100 irradiates the oscillating portion 12A with the light L. By irradiating the light L in the second period TB1, it becomes possible to appropriately shift the optical path.

[0065] Moreover, the light path control method according to the present embodiment controls the light path by applying a drive signal to the actuator 12B that swings the oscillating part 12A on which the light L is incident. This method has a step of applying a drive signal having a waveform including a first period TA1 in which the current value is changed from a first current value A1 to a second current value A2, and a second period TB1 that is continuous with the first period TA1 and in which the current value is maintained at the second current value A2, to the actuator 12B, thereby causing the actuator 12B to swing the oscillating part 12A. In this method, the length of the first period TA1 is set to a value corresponding to the natural frequency of the oscillating part 12A. According to this method, the oscillating part 12A can be stably oscillated.

[0066] Second embodiment Next, a second embodiment will be described. In the second embodiment, the waveform of the drive signal is different from that in the first embodiment. Descriptions of parts of the second embodiment that are common to the first embodiment will be omitted.

[0067] FIG. 7 is a block diagram showing a schematic circuit configuration of a display device according to the second embodiment. As shown in FIG. 7, the control circuit 14 according to the second embodiment includes a digital circuit 14A, and does not have a DA converter (converter 14B) as in the first embodiment. In the second embodiment, a digital drive signal generated by the digital circuit 14A is input to the drive circuit 16, which amplifies the digital drive signal and outputs it to the actuator 12B. The actuator 12B is driven according to the drive signal to swing the swinging part 12A. Thus, in the second embodiment, a digital drive signal is input to the drive circuit 16, but is not limited thereto, and a drive signal converted to analog by the converter 14B may be input as in the first embodiment.

[0068] (Drive waveform) Fig. 8 is a graph illustrating the waveform of the drive signal according to the second embodiment. As shown in Fig. 8, in the second embodiment, the current value is held at zero in the first period TA1. In this embodiment, since the digital circuit 14A and the like include a digital switching circuit, the supply of current to the actuator 12B can be stopped, and the period during which the supply of current is stopped is the period during which the current value is set to zero.

[0069] The length of the first period TA1 is a value corresponding to the natural frequency of the oscillating part 12A. More specifically, the length of the first period TA1 is preferably approximately the same as half the natural period (the reciprocal of the natural frequency) of the oscillating part 12A, and more preferably the same as half the natural period (the reciprocal of the natural frequency). Note that half the natural period is expressed as "1 / (2·f)" [s], where the natural frequency is f [Hz].

[0070] In the second period TB1, the current value of the drive signal is maintained at the second current value A2. The second period TB1 is a period following the first period TA1 and continuing to the first period TA1. That is, at the start timing of the second period TB1 (the timing when the first period TA1 switches to the second period TB1), the current value switches from zero to the second current value A2, and the current value is maintained at the second current value A2 until the end timing of the second period TB1.

[0071] Thus, in the second embodiment, the drive signal in period T1 has a current value held at zero during the first period TA1, the current value switches to the second current value A2 at the start of the second period TB1, and the current value is held at the second current value A2 during the second period TB1.

[0072] In the second embodiment, the current value is held at zero during the third period TA2. The third period TA2 is a period that follows the second period TB1 and is continuous with the second period TB1. That is, at the start timing of the third period TA2 (the timing when the second period TB1 switches to the third period TA2), the current value switches from the second current value A2 to zero, and is held at zero until the end timing of the third period TA2.

[0073] The length of the third period TA2 corresponds to the natural frequency of the oscillating part 12A. More specifically, the length of the third period TA2 is preferably approximately equal to half the natural period (the reciprocal of the natural frequency) of the oscillating part 12A, and more preferably equal to half the natural period (the reciprocal of the natural frequency). In this embodiment, the length of the third period TA2 is equal to the length of the first period TA1.

[0074] In the fourth period TB2, the current value of the drive signal is maintained at the first current value A1. The fourth period TB2 is a period following the third period TA2. That is, at the start timing of the fourth period TB2 (the timing when the third period TA2 switches to the fourth period TB2), the current value switches from zero to the first current value A1, and is maintained at the first current value A1 until the end timing of the fourth period TB2.

[0075] Thus, in the second embodiment, the drive signal in period T2 has a current value held at zero during the third period TA2, the current value switches to the first current value A1 at the start of the fourth period TB2, and the current value is held at the first current value A1 during the fourth period TB2.

[0076] In the first period TA1 following the fourth period TB2, the current value is held at zero as described above. That is, at the start timing of the first period TA1 (the timing when the fourth period TB2 switches to the first period TA1), the current value switches from the first current value A1 to zero, and is held at zero until the end timing of the first period TA1.

[0077] 8 indicates a period during which the light L is irradiated. It is preferable that the irradiation device 100 does not irradiate the light L in the first period TA1, and irradiates the light L in the second period TB1. It is also preferable that the irradiation device 100 does not irradiate the light L in the third period TA2, and irradiates the light L in the fourth period TB2.

[0078] (Oscillation pattern) Next, the oscillation pattern of the oscillation section 12A caused by application of a drive signal will be described below. Fig. 9 is a graph illustrating the oscillation pattern of the optical section according to the second embodiment.

[0079] At the start of the first period TA1, the current value of the drive signal is switched from the first current value A1 to zero, and the current value is maintained at zero until the end of the first period TA1. As a result, the displacement angle of the oscillating part 12A changes from the first angle D1 to the second angle D2 during the first period TA1. More specifically, the oscillating part 12A, which has been twisted to the first angle D1 and maintained at the first current value A1, is released from the twist and returns to the neutral position as the current becomes zero, and is further twisted to the second angle D2 on the opposite side by the action of inertia force, thereby reaching the second angle D2.

[0080] At the start of the second period TB1, the current value of the drive signal is switched from zero to the second current value A2, and the current value is maintained at the second current value A2 until the end of the second period TB1. As a result, the displacement angle of the oscillating part 12A is maintained at the second angle D2 during the second period TB1. That is, the force of the oscillating part 12A twisted to the second angle D2 balances the force of the second current value A2 that tries to return to the neutral position, and the displacement angle is maintained at the second angle D2.

[0081] At the start of the third period TA2, the current value of the drive signal is switched from the second current value A2 to zero, and the current value is kept at zero until the end of the third period TA2. As a result, the displacement angle of the oscillating part 12A changes from the second angle D2 to the first angle D1 in the third period TA2.

[0082] At the start of the fourth period TB2, the current value of the drive signal is switched from zero to the first current value A1, and the current value is maintained at the first current value A1 until the end of the fourth period TB2. As a result, the displacement angle of the oscillating part 12A is maintained at the first angle D1 during the fourth period TB2.

[0083] In the second embodiment, the length of the first periods TA1 and TA2 during which the current value is switched to zero and maintained at zero corresponds to the natural frequency of the oscillating part 12A, so that the oscillation of the oscillating part 12A during the second periods TB1 and TB2 can be suppressed and the oscillating part 12A can be oscillated stably. Therefore, according to this embodiment, image degradation can be suppressed. Furthermore, by setting the current value to zero during the first periods TA1 and TA2, it is possible to shorten the length of the first periods TA1 and TA2 and lengthen the length of the second periods TB1 and TB2, rather than gradually switching the current value as in the first embodiment. This makes it possible to lengthen the period during which the light L is irradiated, and to more suitably suppress image degradation.

[0084] (effect) As described above, the light path control device 10 according to the second embodiment includes a swinging unit 12A on which light L is incident, an actuator 12B that swings the swinging unit 12A, and a drive circuit 16 (drive unit) that applies a drive signal to the actuator 12B to cause the actuator 12B to swing the swinging unit 12A and control the light path. The drive circuit 16 applies a drive signal to the actuator 12B, the drive signal having a waveform including a first period TA1 in which the current value is zero, and a second period TB1 that follows the first period TA1 and is continuous with the first period TA1, and in which the current value is maintained at a second current value A2. The drive circuit 16 applies the drive signal so that the length of the first period TA1 corresponds to the natural frequency of the swinging unit 12A.

[0085] In this way, in the second embodiment, by setting the length of the first period TA1 to a value corresponding to the natural frequency of the oscillating part 12A, it is possible to suppress the oscillation of the oscillating part 12A in the second period TB1, and to stably oscillate the oscillating part 12A. Also, by setting the current value to zero in the first period TA1 having a length corresponding to the natural frequency of the oscillating part 12A, and then switching to and maintaining the second current value A2 in the subsequent second period TB1, it is possible to easily set a waveform that can stably oscillate the oscillating part 12A without making the waveform setting complicated.

[0086] Moreover, the drive circuit 16 applies the drive signal so that the length of the first period TA1 is approximately equal to half the natural period (the reciprocal of the natural frequency) of the oscillating part 12A. By setting the length of the first period TA1 to the reciprocal of the natural frequency of the oscillating part 12A, it is possible to make the oscillating part 12A oscillate more stably.

[0087] Furthermore, the drive circuit 16 applies a drive signal so that the current value is maintained at the first current value A1, which is opposite in sign to the second current value A2, during a fourth period TB2 (third period) that precedes the first period TA1 and is subsequent to the first period TA1. By applying current values ​​that are opposite in sign to the first period TA1 in this manner, the oscillating part 12A can be oscillated stably and appropriately.

[0088] Third embodiment Next, a third embodiment will be described. In the third embodiment, the waveform of the drive signal is different from that in the first embodiment. Descriptions of the configurations of the third embodiment and the first embodiment will be omitted.

[0089] The control circuit 14 according to the third embodiment includes the digital circuit 14A as in the second embodiment, and may not have a DA converter (converter 14B) as in the first embodiment. That is, in the third embodiment, a digital drive signal generated by the digital circuit 14A is input to the drive circuit 16, and the drive circuit 16 switches the positive and negative current of the drive signal using a switching circuit (not shown), that is, switches the current so that the direction is reversed and the current value is the same, and outputs the current to the actuator 12B. In this way, in the third embodiment, a digital drive signal is input to the drive circuit 16, but this is not limiting, and a drive signal converted to analog by the converter 14B may be input as in the first embodiment.

[0090] (Drive waveform) FIG. 10 is a graph for explaining the waveform of the driving signal according to the third embodiment. As shown in FIG. 10, in the third embodiment, in the first period TA1, the current value is held at the second current value A2, and then the current value is held at the first current value A1. That is, in the period TA1a of the first period TA1, the current value is held at the second current value A2, and in the period TA1b of the first period TA1, the current value is held at the first current value A1. The period TA1b is a period following the period TA1a and continuing to the period TA1a. That is, at the start timing of the period TA1b (the timing at which the period TA1a switches to the period TA1b), the current value switches from the second current value A2 to the first current value A1, and the current value is held at the first current value A1 until the end timing of the period TA1b.

[0091] The length of the first period TA1 corresponds to the natural frequency of the oscillating part 12A. The length of the first period TA1 is preferably approximately equal to one-third of the natural period (the reciprocal of the natural frequency) of the oscillating part 12A, and more preferably equal to one-third of the natural period. Note that one-third of the natural period (the reciprocal of the natural frequency) is expressed as "1 / (3·f)" [s], where the natural frequency is f [Hz].

[0092] More specifically, the length of the period TA1a and the length of the period TA1b in the first period TA1 correspond to the natural frequency of the oscillating part 12A. It is preferable that the length of the period TA1a and the length of the period TA1b are the same. More specifically, it is preferable that the length of the period TA1a and the length of the period TA1b are approximately the same as one-sixth of the natural period (the reciprocal of the natural frequency) of the oscillating part 12A, and more preferably, they are the same as one-sixth of the natural period. Note that, when the natural frequency is f [Hz], the one-sixth of the reciprocal of the natural frequency is expressed as "1 / (6·f)" [s].

[0093] In the second period TB1, the current value of the drive signal is maintained at the second current value A2. The second period TB1 is a period that follows the first period TA1 (period TA1b) and is continuous with the first period TA1 (period TA1b). That is, at the start timing of the second period TB1 (the timing when period TA1b switches to the second period TB1), the current value switches from the first current value A1 to the second current value A2, and is maintained at the second current value A2 until the end timing of the second period TB1.

[0094] Thus, in the third embodiment, the drive signal in period T1 has a current value maintained at the second current value A2 in period TA1a, a current value switched to and maintained at the first current value A1 in period TA1b, and a current value switched to and maintained at the second current value A2 in the second period TB1.

[0095] In the third embodiment, in the third period TA2, the current value is held at the first current value A1, and then held at the second current value A2. That is, at the start timing of the period TA2a of the third period TA2 (the timing when the second period TB1 switches to the period TA2a), the current value switches from the second current value A2 to the first current value A1, and is held at the first current value A1 until the end timing of the period TA2a. The period TA2b is a period that follows the period TA2a and is continuous with the period TA2a. That is, at the start timing of the period TA2b (the timing when the period TA2a switches to the period TA2b), the current value switches from the first current value A1 to the second current value A2, and is held at the second current value A2 until the end timing of the period TA2b.

[0096] The length of the third period TA2 corresponds to the natural frequency of the oscillating part 12A. The length of the third period TA2 is preferably approximately equal to one third of the natural period (the reciprocal of the natural frequency) of the oscillating part 12A, and more preferably equal to one third of the natural period. In this embodiment, the length of the third period TA2 is equal to the length of the first period TA1.

[0097] More specifically, the length of the period TA2a and the length of the period TA2b in the third period TA2 correspond to the natural frequency of the oscillating part 12A. The length of the period TA2a and the length of the period TA2b are preferably the same. More specifically, the length of the period TA2a and the length of the period TA2b are preferably approximately the same as one-sixth of the reciprocal of the natural frequency of the oscillating part 12A, and more preferably the same as one-sixth of the natural period. In this embodiment, the length of the period TA2a is equal to the length of the period TA1a, and the length of the period TA2b is equal to the length of the period TA1b.

[0098] In the fourth period TB2, the current value of the drive signal is maintained at the first current value A1. The fourth period TB2 is a period following the third period TA2 (period TA2b) and continuing to the third period TA2 (period TA2b). That is, at the start timing of the fourth period TB2 (the timing when the period TA2b switches to the fourth period TB2), the current value switches from the second current value A2 to the first current value A1, and is maintained at the first current value A1 until the end timing of the fourth period TB2.

[0099] Thus, in the third embodiment, the current value of the drive signal in period T2 is maintained at the first current value A1 in period TA2a, the current value is switched to and maintained at the second current value A2 in period TA2b, and the current value is switched to and maintained at the first current value A1 in the fourth period TB2.

[0100] In the period TA1a following the fourth period TB2, the current value is held at the second current value A2 as described above. That is, at the start timing of the period TA1a (the timing when the fourth period TB2 switches to the period TA1a), the current value switches from the first current value A1 to the second current value A2, and is held at the second current value A2 until the end timing of the period TA1a.

[0101] 10 indicates a period during which the light L is irradiated. It is preferable that the irradiation device 100 does not irradiate the light L in the first period TA1, and irradiates the light L in the second period TB1. It is also preferable that the irradiation device 100 does not irradiate the light L in the third period TA2, and irradiates the light L in the fourth period TB2.

[0102] (Oscillation pattern) Next, the oscillation pattern of the oscillation section 12A caused by application of a drive signal will be described below. Fig. 11 is a graph illustrating the oscillation pattern of the optical section according to the third embodiment.

[0103] The drive signal switches the current value from the first current value A1 to the second current value A2 at the start of the period TA1a, and the current value is held at the second current value A2 until the end of the period TA1a. At the start of the period TA1b, the current value switches from the second current value A2 to the first current value A1, and the current value is held at the first current value A1 until the end of the period TA1b. As a result, the displacement angle of the oscillating part 12A changes from the first angle D1 to the second angle D2 during the first period TA1 (periods TA1a and TA1b). More specifically, a force is applied in the direction of returning at the second current value A2 to the force that tries to twist back at the first angle D1, and the oscillating part 12A is accelerated in the direction of the second angle D2. If it is left as it is, it will be twisted further than the second angle D2 due to inertia, so in this embodiment, the first current value A1 is applied thereafter to apply the brakes. Therefore, it is possible to achieve even faster oscillation than in the second embodiment.

[0104] At the start of the second period TB1, the current value of the drive signal is switched from the first current value A1 to the second current value A2, and the current value is maintained at the second current value A2 until the end of the second period TB1. As a result, the displacement angle of the oscillating part 12A is maintained at the second angle D2 during the second period TB1.

[0105] The drive signal switches the current value from the second current value A2 to the first current value A1 at the start of the period TA2a and maintains the current value at the first current value A1 until the end of the period TA2a, and switches the current value from the first current value A1 to the second current value A2 at the start of the period TA2b and maintains the current value at the second current value A2 until the end of the period TA2b. As a result, the displacement angle of the oscillating part 12A changes from the second angle D2 to the first angle D1 during the third period TA2 (periods TA2a and TA2b).

[0106] At the start of the fourth period TB2, the current value of the drive signal is switched from the second current value A2 to the first current value A1, and the current value is maintained at the first current value A1 until the end of the fourth period TB2. As a result, the displacement angle of the oscillating part 12A is maintained at the first angle D1 during the fourth period TB2.

[0107] In the third embodiment, the length of the first periods TA1 and TA2 in which the current value is switched between positive and negative corresponds to the natural frequency of the oscillating part 12A, so that the oscillation of the oscillating part 12A in the second periods TB1 and TB2 can be suppressed and the oscillating part 12A can be oscillated stably. Therefore, according to this embodiment, image degradation can be suppressed. Furthermore, by switching the current value between positive and negative in the first periods TA1 and TA2, the length of the first periods TA1 and TA2 can be shortened and the length of the second periods TB1 and TB2 can be lengthened, for example, compared to the first and second embodiments. This makes it possible to extend the period in which the light L is irradiated, and to more suitably suppress image degradation.

[0108] (effect) As described above, the light path control device 10 according to the third embodiment includes a swinging unit 12A on which light L is incident, an actuator 12B that swings the swinging unit 12A, and a drive circuit 16 (drive unit) that applies a drive signal to the actuator 12B to swing the swinging unit 12A and control the light path. The drive circuit 16 applies to the actuator 12B a drive signal having a waveform including a first period TA1 in which the current value is held at a second current value A2 and then a first current value A1 having a polarity opposite to that of the second current value A2, and a second period TB1 that is continuous with the first period TA1 and in which the current value is held at the second current value A2. The drive circuit 16 applies the drive signal so that the length of the first period TA1 corresponds to the natural frequency of the swinging unit 12A.

[0109] In this way, in the third embodiment, by setting the length of the first period TA1 to a value corresponding to the natural frequency of the oscillating part 12A, it is possible to suppress the oscillation of the oscillating part 12A in the second period TB1, and to stably oscillate the oscillating part 12A. Also, by switching the positive and negative current values ​​in the first period TA1 having a length corresponding to the natural frequency of the oscillating part 12A, and then switching to and maintaining the second current value A2 in the subsequent second period TB1, it is possible to easily set a waveform that can stably oscillate the oscillating part 12A without making the waveform setting complicated.

[0110] Moreover, the drive circuit 16 applies the drive signal so that the length of the period TA1a during which the current is held at the second current value A2 in the first period TA1 is equal to the length of the period TA1b during which the current is held at the first current value A1 in the first period TA1. By making the lengths of the periods TA1a and TA1b equal, the oscillating part 12A can be oscillated more stably.

[0111] Moreover, the drive circuit 16 applies the drive signal so that the length of the period TA1a during which the current is held at the second current value A2 in the first period TA1 and the length of the period TA1b during which the current is held at the first current value A1 in the first period TA1 are substantially equal to one-sixth of the reciprocal of the natural frequency of the oscillating part 12A. By setting the length of the first period TA1 within this range, the oscillating part 12A can be oscillated more stably.

[0112] Although the embodiments of the present invention have been described above, the embodiments are not limited to the contents of these embodiments. The above-described components include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the above-described components can be appropriately combined, and the configurations of each embodiment can also be combined. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the gist of the above-described embodiments. [Explanation of symbols]

[0113] 1 Display device 10 Optical path control device 12 Optical path control mechanism 12A Optical section 12B Actuator 16 Drive circuit (drive section) 100 Irradiation device A1 First current value A2 Second current value D1 1st angle D2 2nd angle L light TA1, TA2 1st Period TB1, TB2 2nd Period

Claims

1. a swinging portion having an optical member to which light is incident; An actuator that swings the swinging portion; a drive unit that applies to the actuator a drive signal having a waveform including a first period during which a current value is changed from a first current value to a second current value, and a second period that is continuous with the first period and during which the current value is maintained at the second current value, thereby causing the actuator to swing the swing unit and controlling the optical path; having The drive unit applies the drive signal so that a length of the first period has the same value as an inverse of a natural frequency of the oscillator. Optical path control device.

2. 2 . The light path control device according to claim 1 , wherein the drive section applies the drive signal such that a current value changes linearly from the first current value to the second current value during the first period.

3. 3. A light path control device comprising: the light path control device according to claim 1 or 2; and an irradiation device that irradiates the optical member with light. Display device.

4. The display device according to claim 3 , wherein the irradiation device irradiates the optical member with light during the second period.

5. An optical path control method for controlling an optical path by applying a drive signal to an actuator that oscillates an oscillating unit including an optical member into which light is incident, comprising: a step of applying to the actuator the drive signal having a waveform including a first period during which a current value is changed from a first current value to a second current value, and a second period subsequent to the first period during which the current value is maintained at the second current value, thereby causing the actuator to swing the swinging portion; The length of the first period is set to the same value as the reciprocal of the natural frequency of the oscillation portion. Optical path control method.

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