Patent Description:
For example, as shown in <CIT>, there are known optical devices shifting an optical axis by oscillating an optical part on which light is made incident. <CIT> states that the resolution of a projected image can be made higher than the resolution of an optical modulation apparatus by oscillating the optical part to shift the optical path of light passing through the optical part.

When shifting the optical path in this way, it is required that the optical part be oscillated at high speed and be stopped stably.

<CIT> discloses a driving method of lens actuator by setting a time of a rising portion to a period corresponding to a natural frequency of a driving source.

<CIT> discloses an optical device which includes a movable section including an optical section that deflects video light in accordance with the angle of incidence of the video light incident on a light incident surface and outputs the deflected video light and a holder that supports the optical section, an actuator that rotates the movable section around a first axis, an actuator that rotates the movable section around a second axis, a drive circuit that supplies the actuator with a first drive signal and the actuator with a second drive signal, and a sensor disposed in a position different from the positions on the first and second axes detects the position of the optical section, and the drive circuit adjusts the first and second drive signals in accordance with the position of the optical section detected with the sensor.

<CIT> discloses a method for controlling an optical device including a movable section including an optical section that refracts incident video image light and outputs the refracted video image light and a holding section that supports the optical section, and an actuator that causes the movable section to swing, the method including applying a drive signal to the actuator to cause the movable section to swing. The drive signal is a wave having a trapezoidal waveform, and the trapezoidal wave has a first flat section where first voltage is applied for a first period, a second flat section where second voltage higher than the first voltage is applied for a second period, and a third flat section where third voltage higher than the first voltage and lower than the second voltage is applied for a third period after the first voltage is applied and before the second voltage is applied.

<CIT> discloses an optical path controller which includes: two leaf springs 14a and 14b which support a holding member so that an optical path changing plate and the holding member rotate around a rotary shaft parallel to the optical path changing plate and which are parallel to the rotary shaft; a coil which is attached to an opening installed in the holding member; a driving circuit which controls current flowing in the coil; and magnetic field-generating parts that generate a magnetic field at least in a part of a space in which the coil exists. At least one leaf spring is arranged so as to form a prescribed angle which is not parallel to the acting force vertical plane that is a plane vertical to the direction of a force acting on the coil.

<CIT> discloses a method of increasing a perceived resolution of a display which includes directing light at a optical dithering element and repeatedly transitioning the optical dithering element from a first position to a second position and then back to the first position such that the mirror alternately reflects light to a first position on the display and then to a second position on the display. Each transition of the mirror includes controlling any overshoot or ringing in the position of the optical dithering element by providing a predetermined drive signal to the optical dithering element to smoothly accelerate and decelerate the element during the traverse between the first and second positions.

In accordance with the present invention, an optical path control apparatus as set forth in the appended claims is provided. In particular, an optical path control apparatus according to an embodiment includes: an oscillating part having an optical member on which light is made incident; an actuator configured to oscillate the oscillating part; and a drive unit configured to apply to the actuator a drive signal with a waveform including a first period in which a current value is changed and including a second period that is continuous with the first period and in which the current value is held, to cause the actuator to oscillate the oscillating part and to control an optical path, the drive unit applying the drive signal so that a length of the first period is a value corresponding to a natural frequency of the oscillating part.

A display apparatus according to an embodiment includes: the above-described optical path control apparatus; and an irradiation apparatus applying light to the optical member.

A method according to an embodiment is of controlling an optical path by applying a drive signal to an actuator configured to oscillate an oscillating part including an optical member on which light is made incident. The method includes: applying to the actuator the drive signal with a waveform including a first period in which a current value is changed and including a second period that is continuous with the first period and in which the current value is held, to cause the actuator to oscillate the oscillating part. A length of the first period is set to a value corresponding to a natural frequency of the oscillating part.

The following describes the present embodiments in detail based on the accompanying drawings. The embodiments described below do not limit the present invention.

<FIG> is a schematic diagram of a display apparatus according to a first embodiment, representing an embodiment not according to the claimed subject-matter. As illustrated in <FIG>, this display apparatus <NUM> according to the first embodiment has an optical path control apparatus <NUM> and an irradiation apparatus <NUM>. The irradiation apparatus <NUM> is an apparatus applying light L for images, whereas the optical path control apparatus <NUM> is an apparatus controlling an optical path of the light L. In the present embodiment, the optical path control apparatus <NUM> shifts the optical axis of the light L to shift the position of an image displayed by the light L and to make the resolution of a projected image higher than the resolution of an image by the irradiation apparatus <NUM> (that is, the number of pixels of a display element <NUM> described below).

As illustrated in <FIG>, the irradiation apparatus <NUM> includes a light source <NUM>, polarizing plates 105R, <NUM>, and 105B, display elements 106R, <NUM>, and 106B, polarizing plates 107R, <NUM>, and 107B, a color combining prism <NUM>, a projection lens <NUM>, dichroic mirrors <NUM> and <NUM>, reflective mirrors <NUM> and <NUM>, lenses <NUM> to <NUM>, a polarization conversion element <NUM>, and an image signal processing circuit <NUM>. When the display element 106R, the display element <NUM>, and the display element 106B are not distinguished from each other, they are referred to as the display element <NUM>.

The light source <NUM> is a light source generating light and applying it. The light source <NUM> applies incident light L0. The present embodiment, which takes using one light source <NUM> as the light source applying the incident light L0 as an example, may have another optical apparatus for generating the incident light L0.

The incident light L0 from the light source <NUM> is made incident on the lens <NUM>. The lenses <NUM> and <NUM> are, for example, fly-eye lenses. The incident light L0 is made uniform in illumination distribution by the lenses <NUM> and <NUM> and is made incident on the polarization conversion element <NUM>. The polarization conversion element <NUM> is an element aligning the polarization of the incident light L0 and has, for example, a polarization beam splitter and a retardation plate. For example, the polarization conversion element <NUM> aligns the incident light L0 to the p-polarized light.

The incident light L0, the polarization of which has been aligned by the polarization conversion element <NUM>, is applied to the dichroic mirror <NUM> through the lens <NUM>. The lens <NUM> is, for example, a condenser lens.

The dichroic mirror <NUM> separates the incident light L0 made incident thereon into yellow light LRG and blue light LB, which contains blue band components. The yellow illumination light LRG separated by the dichroic mirror <NUM> reflects off the reflective mirror <NUM> and is made incident on the dichroic mirror <NUM>.

The dichroic mirror <NUM> separates the yellow light LRG made incident thereon into red light LR, which contains red band components, and green light LG, which contains green band components.

The red light LR separated by the dichroic mirror <NUM> is applied to the polarizing plate 105R through the lens <NUM>. The green light LG separated by the dichroic mirror <NUM> is applied to the polarizing plate <NUM> through the lens <NUM>. The blue light LB separated by dichroic mirror <NUM> reflects off the reflective mirror <NUM> and is applied to the polarizing plate 105B through the lens <NUM>.

The polarizing plates 105R, <NUM>, and 105B have the property of reflecting either the s-polarized light or the p-polarized light and passing the other. For example, the polarizing plates 105R, <NUM>, and 105B reflect the s-polarized light and pass the p-polarized light. The polarizing plates 105R, <NUM>, and 105B are also referred to as reflective polarizing plates.

The red light LR, which is the p-polarized light, passes through the polarizing plate 105R and is applied to the display element 106R. The green light LG, which is the p-polarized light, passes through the polarizing plate <NUM> and is applied to the display element <NUM>. The blue light LB, which is the p-polarized light, passes through the polarizing plate 105B and is applied to the display element 106B.

The display element 106R, the display element <NUM>, and the display element 106B are, for example, reflective liquid crystal display elements. The present embodiment describes a case in which the display element 106R, the display element <NUM>, and the display element 106B are reflective liquid crystal display elements as an example; not limited to the reflective type, transmissive liquid crystal display elements may also be used. They can also be applied in various ways to configurations including other display elements in place of the liquid crystal display elements.

The display element 106R is controlled by the image signal processing circuit <NUM>. The image signal processing circuit <NUM> drives and controls the display element 106R based on red component image data. The display element 106R optically modulates the red light LR as the p-polarized light in accordance with the control of the image signal processing circuit <NUM> to generate the red light LR as the s-polarized light. The display element <NUM> is controlled by the image signal processing circuit <NUM>. The image signal processing circuit <NUM> drives and controls the display element <NUM> based on green component image data. The display element <NUM> optically modulates the green light LG as the p-polarized light in accordance with the control of the image signal processing circuit <NUM> to generate the green light LG as the s-polarized light. The display element 106B is controlled by the image signal processing circuit <NUM>. The image signal processing circuit <NUM> drives and controls the display element 106B based on blue component image data. The display element 106B optically modulates the blue light LB as the p-polarized light based on the blue component image data in accordance with the control of the image signal processing circuit <NUM> to generate the blue light LB as the s-polarized light.

The polarizing plates 107R, <NUM>, and 107B have the property of passing either the s-polarized light or the p-polarized light and reflecting or absorbing the other. For example, the polarizing plates 107R, <NUM>, and 107B pass the s-polarized light and absorb the p-polarized light, which is unnecessary.

The red light LR as the s-polarized light generated by the display element 106R is reflected by the polarizing plate 105R, passes through the polarizing plate 107R, and is applied to the color combining prism <NUM>. The green light LG as the s-polarized light generated by the display element <NUM> is reflected by the polarizing plate <NUM>, passes through the polarizing plate <NUM>, and is applied to the color combining prism <NUM>. The blue light LB as the s-polarized light generated by the display element 106B is reflected by the polarizing plate 105B, passes through the polarizing plate 107B, and is applied to the color combining prism <NUM>.

The color combining prism <NUM> combines the red light LR, the green light LG, and the blue light LB made incident and applies them as the light L for image display to the projection lens <NUM>. The light L is projected onto a screen or the like, not illustrated, through the projection lens <NUM>.

Although the irradiation apparatus <NUM> is configured as described above, its configuration is not limited to the above description; any configuration may be employed.

The optical path control apparatus <NUM> has an optical path control mechanism <NUM>, a control circuit (a controller) <NUM>, and a drive circuit (a drive unit) <NUM>. The optical path control mechanism <NUM> is a mechanism oscillating by being driven by the drive circuit <NUM>. The optical path control mechanism <NUM> is provided between the color combining prism <NUM> and the projection lens <NUM> in a direction along the optical path of the light L. The optical path control mechanism <NUM> oscillates while the light L from the color combining prism <NUM> is made incident thereon, thereby shifting the travel direction (the optical path) of the light L and emitting it toward the projection lens <NUM>. Thus, the optical path control apparatus <NUM> controls the optical path of the light L so as to shift the optical path of the light L. The position in which the optical path control mechanism <NUM> is provided is not limited to between the color combining prism <NUM> and the projection lens <NUM> but may be any position.

<FIG> is a block diagram schematically illustrating a circuit configuration of the display apparatus. As illustrated in <FIG>, the image signal processing circuit <NUM> controls the display elements 106R, 106B, and <NUM>. An image signal including image data for controlling the display elements 106R, 106B, and <NUM> and a synchronization signal is input to the image signal processing circuit <NUM>. The image signal processing circuit <NUM> controls the display elements 106R, 106B, and <NUM> based on the image data while synchronizing timing based on the synchronization signal. A control circuit <NUM> has a digital circuit 14A and a converter 14B. The synchronization signal from the image signal processing circuit <NUM> is input to the digital circuit 14A. The digital circuit 14A generates a digital drive signal to drive the optical path control mechanism <NUM> while synchronizing timing based on the synchronization signal. The converter 14B is a digital-to-analog (DA) converter converting a digital signal to 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 <NUM> receives input of the analog drive signal from the converter 14B, amplifies the analog drive signal, and outputs it to actuators 12B of the optical path control mechanism <NUM> described below. The actuators 12B are driven in response to the drive signal to oscillate an oscillating part 12A described below.

The following describes the configuration of the optical path control mechanism <NUM> more specifically. <FIG> is a schematic diagram of the optical path control mechanism, whereas <FIG> is an A-A sectional view of <FIG>. As illustrated in <FIG> and <FIG>, the optical path control mechanism <NUM> has the oscillating part 12A including an optical member <NUM> on which the light L is made incident, and the actuators 12B oscillating the oscillating part 12A. In more detail, the optical path control mechanism <NUM> has the optical member <NUM>, a movable part <NUM>, a support part <NUM>, shaft parts <NUM>, coils <NUM>, yokes <NUM>, and magnets <NUM>.

The optical member <NUM> is a member passing the light L made incident thereon. The optical member <NUM> makes the light L incident on one surface, passes the light L made incident thereon, and emits the light L from the other surface. The optical member <NUM> is a glass plate in the present embodiment; any material and shape may be employed.

The movable part <NUM> is a member supporting the optical member <NUM>. The movable part <NUM> is fixed to the optical member <NUM>. Specifically, the movable part <NUM> of the present embodiment is a plate-like member formed with a through hole at the center. The optical member <NUM> is fixed to the movable part <NUM> fit into the through hole of the movable part <NUM>. The optical member <NUM> is fixed to the movable part <NUM> via a fixing member or adhesive to be fixed to the movable part <NUM>; any method for fixing the optical member <NUM> to the movable part <NUM> may be employed.

The support part <NUM> is a member supporting the movable part <NUM> provided with the optical member <NUM> in an oscillatable manner. In the present embodiment, the support part <NUM> is a frame-like member and is provided so as to surround the outer perimeter of the movable part <NUM>. The shaft parts <NUM> are members coupling the movable part <NUM> to the support part <NUM> in an oscillatable manner. In the present embodiment, two shaft parts <NUM> are provided. The shaft parts <NUM> are provided at respective positions near the apexes of the rectangular-shaped optical member <NUM> facing each other. The movable part <NUM> oscillates about an oscillation axis AX, which is an axis connecting the shaft parts <NUM> to each other. The movable part <NUM> oscillates about the oscillation axis AX, whereby the attitude of the optical member <NUM> provided in the movable part <NUM> changes, thus shifting the optical path of the light L passing through the optical member <NUM>.

The coils <NUM> are mounted on the movable part <NUM> and are fixed to the movable part <NUM>. The coils <NUM> are provided at the respective ends of the movable part <NUM>.

The yokes <NUM> are members forming a magnetic path. The yokes <NUM> are mounted on the support part <NUM> and are fixed to the support part <NUM>. The yokes <NUM> are provided at the respective ends of the movable part <NUM> in correspondence with the coils <NUM>. The magnets <NUM> are permanent magnets. The magnets <NUM> are mounted on the respective yokes <NUM> and are fixed to the respective yokes <NUM>. The magnets <NUM> are placed at positions adjacent to the respective coils <NUM>. The drive signal from the drive circuit <NUM> is input to the coils <NUM>. In the example in <FIG>, the magnet <NUM> is bonded to one side of the U-shaped yoke <NUM>, forming an air gap between the face of the magnet <NUM> that is not bonded and the U-shaped opposing side of the yoke <NUM>. The coil <NUM> is placed within this air gap. The drive signal is input to the coils <NUM>. This causes a current to flow through the coils <NUM>, which are conductors within magnetic fields caused by the magnets <NUM> to generate a force, and this force causes the movable part <NUM> (the oscillating part 12A) fixed to the coils <NUM> to oscillate. That is to say, it can be said that the actuator 12B according to the present embodiment is an electromagnetic actuator including the coil <NUM>, the yoke <NUM>, and the magnet <NUM>.

In the present embodiment, the movable part <NUM> provided with the optical member <NUM> thus oscillates, and thus it can be said that the optical member <NUM>, the movable part <NUM>, and the coils <NUM> form the oscillating part 12A. That is to say, it can be said that the part of the optical path control mechanism <NUM> oscillating with respect to the support part <NUM> refers to the oscillating part 12A. When fixing members or adhesive for fixing the optical member <NUM> to the movable part <NUM> or a substrate or lead wires for passing a current through the coils <NUM> are provided, they also oscillate with respect to the support part <NUM> and are thus also included in the oscillating part 12A.

Although the actuator of the present embodiment is of what is called a moving coil type, in which the coils <NUM> are placed in the movable part <NUM>, this is not limiting; for example, it may be what is called a moving magnet type, in which the magnets <NUM> are placed in the movable part <NUM>, whereas the coils <NUM> are placed in the support part <NUM>. In this case, the magnets <NUM> are oscillated together with the optical member <NUM>, and thus the magnets <NUM> are included in the oscillating part 12A in place of the coils <NUM>.

Although the optical path control mechanism <NUM> is configured as described above, this is not limiting; any configuration in which the optical part oscillates by the actuator to which the drive signal has been applied to enable the shift of the optical path of the light L by the optical part may be employed.

In the optical path control mechanism <NUM>, the actuators 12B oscillate the oscillating part 12A in accordance with the drive signal. That is to say, the actuators 12B oscillate the oscillating part 12A in such a manner that the oscillating part 12A repeats an attitude change from a first angle D1 to a second angle D2 about the oscillation axis AX and an attitude change from the second angle D2 to the first angle D1 in accordance with the drive signal. The oscillating part 12A repeats the oscillation between the first angle D1 and the second angle D2, whereby the optical axis of the light L repeats a shift from a first position to a second position and a shift from the second position to the first position. In the present embodiment, an image projected onto the screen by the light L when the optical axis is in the first position and an image projected onto the screen by the light L when the optical axis is in the second position are shifted by half a pixel. That is to say, the image projected on the screen repeats shifts by half a pixel and returns by half a pixel. This increases an apparent number of pixels and enables images projected onto the screen to have a higher resolution. Thus, the optical axis shift amount in the present embodiment is equivalent to half a pixel of the image, and thus the first angle D1 and the second angle D2 are set to angles that can shift the image by half a pixel. The image shift amount is not limited to being equivalent to half a pixel but may be any amount such as <NUM>/<NUM> or <NUM>/<NUM> of a pixel, for example. The first angle D1 and the second angles D2 may be set as appropriate in line with the image shift amount.

The following describes the drive signal applied from the drive circuit <NUM> to the actuators 12B.

<FIG> is a graph illustrating a waveform of the drive signal according to the first embodiment. The drive signal applied from the drive circuit <NUM> to the actuators 12B is an electric signal, and as illustrated in <FIG>, the current value changes with the passage of time. In the following, the waveform representing a change in the current value with time of the drive signal is referred to as the waveform of the drive signal. In <FIG>, 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, which is after the period T1 and is continuous with the period T1. The period T1 corresponds to a period in which the image when the optical axis of the light L is in the first position (in this case, the image not shifted by half a pixel) is displayed, whereas the period T2 corresponds to a period in which the image when the optical axis of the light L is in the second position (in this case, the image shifted by half a pixel) is displayed.

In a first period TA1 of the period T1, the drive signal changes the current value from a first current value A1 to a second current value A2. More specifically, in the first period TA1, the drive signal changes the current value linearly from the first current value A1 to the second current value A2 with the passage of time. That is to say, the drive signal has a current value of the first current value A1 at the start timing of the first period TA1, then changes the current value linearly from the first current value A1, and has a current value of 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 in accordance with 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 in accordance with the value of the second angle D2. The first current value A1 and the second current value A2 are current values opposite to each other in polarity, and their absolute values may be equal. <FIG> exemplifies that the first current value A1 is negative, whereas the second current value A2 is positive.

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 <NUM> oscillating with respect to the support part <NUM> (the optical member <NUM>, the movable part <NUM>, and the coils <NUM> in the example of the present embodiment). That is to say, the length of the first period TA1 can be said to be a value corresponding to the natural frequency of the part oscillating with respect to the support part <NUM>. More specifically, the length of the first period TA1 is preferably substantially the same value as the natural period of the oscillating part 12A and more preferably the same value as the natural period. The natural period is the inverse of the natural frequency. The term "substantially the same value" means that values that deviate from the natural period by about an error range are also acceptable. For example, when the deviation with respect to the natural period is within <NUM>% of the value of the natural period, it may also be "substantially the same value. " In the following, too, the description "substantially the same value" refers to the same meaning. The value of the natural vibration (the inverse of the natural frequency) is expressed as "<NUM>/f" [s] when the natural frequency is f [Hz].

The natural frequency of the oscillating part 12A may be measured in advance. For example, a sine wave may be applied (swept) to the actuators 12B with gradually increasing frequency from <NUM> to measure the vibration of the oscillating part 12A, and the frequency at which the oscillating part 12A vibrates the most may be used as the natural frequency of the oscillating part 12A. A micro-displacement meter may be used to measure vibration. In the present embodiment, the length of the first period TA1 is set based on the natural frequency of the oscillating part 12A measured in this way, and the waveform of the drive signal is set in such a manner that the current value changes from the first current value A1 to the second current value A2 in the first period TA1 of the set length.

The drive signal holds the current value at the second current value A2 in a second period TB1 of the period T1. The second period TB1 is a period that is after the first period TA1 and is continuous with the first period TA1. Increasing the natural frequency of the oscillating part 12A is desirable, because doing so can shorten the first period TA1 and lengthen the second period TB1 (can lengthen it than the first period TA1, for example). Holding at the second current value A2 is not limited to the current value not changing strictly from the second current value A2 but may also include the current value shifting from the second current value A2 within the range of a certain value. The certain value here may be set to any value and may be a value <NUM>% of the second current value A2, for example.

Thus, in the period T1, the drive signal gradually changes the current value from the first current value A1 to the second current value A2 and, when the current value reaches the second current value A2, holds the current value at the second current value A2.

In a third period TA2 of the period T2, the drive signal changes the current value from the second current value A2 to the first current value A1. The third period TA2 can be said to be a period that is after the second period TB1 and is continuous with the second period TB1. More specifically, in the third period TA2, the drive signal changes the current value linearly from the second current value A2 to the first current value A1 with the passage of time. That is to say, the drive signal has a current value of the second current value A2 at the start timing of the third period TA2, then changes the current value linearly from the second current value A2, and has a current value of the first current value A1 at the end timing of the third period TA2.

The length of the third period TA2 is the value corresponding to the natural frequency of the oscillating part 12A. More specifically, the length of the third period TA2 is preferably substantially the same value as the natural period (the inverse of the natural frequency) of the oscillating part 12A and more preferably the same value as the natural period. As to the third period TA2 in this embodiment, the length of the third period TA2 is equal to the length of the first period TA1.

In a fourth period TB2 of the period T2, the drive signal holds the current value at the first current value A1. The fourth period TB2 is a period that is after the third period TA2 and is continuous with the third period TA2. The fourth period TB2 is a period that is before the first period TA1 and is continuous with the first period TA1. The fourth period TB2 is equal to the second period TB1 in the present embodiment. Increasing the natural frequency of the oscillating part 12A is desirable, because doing so can shorten the third period TA2 and lengthen the fourth period TB2 (can lengthen it longer than the third period TA2, for example). Holding at the first current value A1 is not limited to the current value not changing strictly from the first current value A1 but may also include the current value shifting from the first current value A1 within the range of a certain value. The certain value here may be set to any value and may be a value <NUM>% of the first current value A1, for example.

Thus, in the period T2, the drive signal gradually changes the current value from the second current value A2 to the first current value A1 and, when the current value reaches the first current value A1, holds the current value at the first current value A1.

As described above, in the first embodiment, the waveform of the drive signal is trapezoidal, and the first periods TA1 and TA2, in which the current value changes, are the value corresponding to the natural frequency of the oscillating part 12A.

The broken line in <FIG> shows periods during which the light L is applied. It is preferable that the irradiation apparatus <NUM> do not apply the light L in the first period TA1 and apply the light L in the second period TB1. It is preferable that the irradiation apparatus <NUM> do not apply the light L in the third period TA2 and apply the light L in the fourth period TB2.

The following describes an oscillation pattern of the oscillating part 12A by the application of the drive signal. <FIG> is a graph illustrating an oscillation pattern of the optical part according to the first embodiment. The oscillation pattern of the oscillating part 12A refers to the displacement angle (an angle about the oscillation axis AX) of the oscillating part 12A with time when the drive signal is applied to the actuators 12B. In <FIG>, the oscillation pattern is shown by a solid line.

In the first period TA1, the drive signal changes the current value from the first current value A1 to the second current value A2. Thus, the oscillating part 12A changes the displacement angle from the first angle D1 to the second angle D2 in the first period TA1.

In the second period TB1, the drive signal holds the current value at the second current value A2. Thus, the oscillating part 12A holds the displacement angle at the second angle D2 in the second period TB1. Holding at the second angle D2 is not limited to the displacement angle not changing strictly from the second angle D2 but may also include the displacement angle shifting from the second angle D2 within the range of a certain value. The certain value here may be set to any value and may be a value <NUM>% of the second angle D2, for example.

In the third period TA2, the drive signal changes the current value from the second current value A2 to the first current value A1. Thus, the oscillating part 12A changes the displacement angle from the second angle D2 to the first angle D1 in the third period TA2.

In the fourth period TB2, the drive signal holds the current value at the first current value A1. Thus, the oscillating part 12A holds the displacement angle at the first angle D1 in the fourth period TB2. Holding at the first angle D1 is not limited to the displacement angle not changing strictly from the first angle D1 but may also include the displacement angle shifting from the first angle D1 within the range of a certain value. The certain value here may be set to any value and may be a value <NUM>% of the first angle D1, for example.

The light L is applied in the second periods TB1 and TB2. Thus, in the second period TB1, the light L is applied to the oscillating part 12A held at the second angle D2, making the light path of the light L the first position. In the fourth period TB2, the light L is applied to the oscillating part 12A held at the first angle D1, shifting the light path of the light L to the second position, and shifting the image by half a pixel.

In optical path control apparatuses shifting the optical path by oscillating the optical part, the optical part is required to be stably oscillated. After diligent research, the inventor of the present invention has discovered that by setting the lengths of the first periods TA1 and TA2 to the value corresponding to the natural frequency of the oscillating part 12A, the oscillating part 12A is suppressed from vibrating in the second periods TB1 and TB2, and the oscillating part 12A can be oscillated stably. That is to say, in the present embodiment, the lengths of the first periods TA1 and TA2 are the value corresponding to the natural frequency of the oscillating part 12A, and thus the vibration of the oscillating part 12A in the second periods TB1 and TB2 is suppressed, and the oscillating part 12A can be oscillated stably. Thus, according to the present embodiment, the oscillating part 12A is oscillated at high speed and is stopped stably, and thus image degradation can be suppressed.

As described above, the optical path control apparatus <NUM> according to the present embodiment has the oscillating part 12A including the optical member <NUM> on which the light L is made incident, the actuators 12B oscillating the oscillating part 12A, and the drive circuit <NUM> (the drive unit) applying the drive signal to the actuators 12B to cause the actuators 12B to oscillate the oscillating part 12A and to control the optical path. The drive circuit <NUM> applies the drive signal with a waveform including the first period TA1, in which the current value is changed from the first current value A1 to the second current value A2, and the second period TB1, which is continuous with the first period TA1 and in which the current value is held at the second current value A2, to the actuators 12B. The drive circuit <NUM> applies the drive signal in such a manner that the length of the first period TA1 is the value corresponding to the natural frequency of the oscillating part 12A.

Thus, in the first embodiment, by setting the length of the first period TA1 to the value corresponding to the natural frequency of the oscillating part 12A, the oscillating part 12A is suppressed from vibrating in the second period TB1, and the oscillating part 12A can be oscillated stably. Owing to the waveform changing the current value in the first period TA1, the length of which corresponds to the natural frequency of the oscillating part 12A, and holding the current value in the subsequent second period TB1, the waveform capable of stably oscillating the oscillating part 12A can be easily set without making waveform setting complicated.

The drive circuit <NUM> applies the drive signal in such a manner that the length of the first period TA1 is the inverse of the natural frequency of the oscillating part 12A. By making the length of the first period TA1 the inverse of the natural frequency of the oscillating part 12A, the oscillating part 12A can be oscillated more stably.

The drive circuit <NUM> applies the drive signal in such a manner that the current value varies linearly changes from the first current value A1 to the second current value A2 in the first period TA1. By making the change in the current value in the first period TA1 linear, the oscillating part 12A can be oscillated more stably.

The display apparatus <NUM> according to the present embodiment includes the optical path control apparatus <NUM> and the irradiation apparatus <NUM> applying the light L to the oscillating part 12A. The display apparatus <NUM> according to the present embodiment includes the optical path control apparatus <NUM> and can thereby stably oscillate the oscillating part 12A and suppress image degradation.

The irradiation apparatus <NUM> applies the light L to the oscillating part 12A in the second period TB1. By applying the light L in the second period TB1, the light path can be shifted appropriately.

The method of optical path control according to the present embodiment applies the drive signal to the actuators 12B oscillating the oscillating part 12A on which the light L is made incident to control the optical path. The present method has a step of applying the drive signal with a waveform including the first period TA1, in which the current value is changed from the first current value A1 to the second current value A2, and the second period TB1, which is continuous with the first period TA1 and in which the current value is held at the second current value A2, to the actuators 12B to cause the actuators 12B to oscillate the oscillating part 12A. In the present method, the length of the first period TA1 is the value corresponding to the natural frequency of the oscillating part 12A. The present method can stably oscillate the oscillating part 12A.

The following describes a second embodiment, representing an embodiment according to the claimed subject-matter. The second embodiment differs from the first embodiment in the waveform of the drive signal. In the second embodiment, for the parts common to those of the first embodiment in configuration, descriptions thereof are omitted.

<FIG> is a block diagram schematically illustrating a circuit configuration of the display apparatus in the second embodiment. As illustrated in <FIG>, the control circuit <NUM> according to the second embodiment includes a digital circuit 14A and does not have a DA converter (the 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 <NUM>, and the drive circuit <NUM> amplifies the digital drive signal and outputs it to the actuators 12B. The actuators 12B are driven in response to the drive signal to oscillate the oscillating part 12A. Although the digital drive signal is thus input to the drive circuit <NUM> in the second embodiment, this is not limiting; the drive signal analog-converted by the converter 14B may be input as in the first embodiment.

<FIG> is a graph illustrating the waveform of the drive signal according to the second embodiment. As illustrated in <FIG>, in the second embodiment, the current value is held at zero in the first period TA1. In the present embodiment, the digital circuit 14A or the like includes a digital switching circuit, and thus the current supply to the actuators 12B can be stopped, and the period during which the current supply is stopped is a period during which the current value is set to zero.

The length of the first period TA1 is the value corresponding to the natural frequency of the oscillating part 12A. More specifically, the length of the first period TA1 is preferably substantially the same value as the half value of the natural period (the inverse of the natural frequency) of the oscillating part 12A and more preferably the same value as the half value of the natural period (the inverse of the natural frequency). The half value of the natural period is expressed as "<NUM>/(<NUM>·f)" [s] when the natural frequency is f [Hz].

The drive signal holds the current value at the second current value A2 in the second period TB1. The second period TB1 is a period that is after the first period TA1 and is continuous with the first period TA1. That is to say, at the start timing of the second period TB1 (the timing of switching from the first period TA1 to the second period TB1), the current value switches from zero to the second current value A2, and the current value is held at the second current value A2 until the end timing of the second period TB1.

Thus, in the second embodiment, the drive signal in the period T1 holds the current value at zero in the first period TA1, switches the current value to the second current value A2 at the start timing of the second period TB1, and holds the current value at the second current value A2 in the second period TB1.

In the second embodiment, the current value is held at zero in the third period TA2. The third period TA2 can be said to be a period that is after the second period TB1 and is continuous with the second period TB1. That is to say, at the start timing of the third period TA2 (the timing of switching from the second period TB1 to the third period TA2), the current value switches from the second current value A2 to zero, and the current value is held at zero until the end timing of the third period TA2.

The length of the third period TA2 is the value corresponding to the natural frequency of the oscillating part 12A. More specifically, the length of the third period TA2 is preferably substantially the same value as the half value of the natural period (the inverse of the natural frequency) of the oscillating part 12A and more preferably the same value as the half value of the natural period (the inverse of the natural frequency). In the present embodiment, the length of the third period TA2 is equal to the length of the first period TA1.

The drive signal holds the current value at the first current value A1 in the fourth period TB2. The fourth period TB2 is a period that is after the third period TA2 and is continuous with the third period TA2. That is to say, at the start timing of the fourth period TB2 (the timing of switching from the third period TA2 to the fourth period TB2), the current value switches from zero to the first current value A1, and the current value is held at the first current value A1 until the end timing of the fourth period TB2.

Thus, in the second embodiment, the drive signal in the period T2 holds the current value at zero in the third period TA2, switches the current value to the first current value A1 at the start timing of the fourth period TB2, and holds the current value at the first current value A1 in the fourth period TB2.

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

The following describes an oscillation pattern of the oscillating part 12A by the application of the drive signal. <FIG> is a graph illustrating the oscillation pattern of the optical part according to the second embodiment.

The drive signal switches the current value from the first current value A1 to zero at the start timing of the first period TA1 and holds the current value at zero until the end timing of the first period TA1. Thus, the oscillating part 12A changes the displacement angle from the first angle D1 to the second angle D2 in the first period TA1. More specifically, the oscillating part 12A, which has been twisted to the first angle D1 and held at the first current value A1, is released from the twisting and returns to a neutral position owing to the current becoming zero and is twisted to the opposite second angle D2 to reach the second angle D2 owing to an inertial force further acting thereon.

The drive signal switches the current value from zero to the second current value A2 at the start timing of the second period TB1 and holds the current value at the second current value A2 until the end timing of the second period TB1. Thus, the oscillating part 12A holds the displacement angle at the second angle D2 in the second period TB1. That is to say, the oscillating part 12A, which has been twisted to the second angle D2, is held at the second angle D2 owing to a balance between a force to return to the neutral position and a force caused by the second current value A2.

The drive signal switches the current value from the second current value A2 to zero at the start timing of the third period TA2 and holds the current value at zero until the end timing of the third period TA2. Thus, the oscillating part 12A changes the displacement angle from the second angle D2 to the first angle D1 in the third period TA2.

The drive signal switches the current value from zero to the first current value A1 at the start timing of the fourth period TB2 and holds the current value at the first current value A1 until the end timing of the fourth period TB2. Thus, the oscillating part 12A holds the displacement angle at the first angle D1 in the fourth period TB2.

In the second embodiment, the lengths of the first periods TA1 and TA2, in which the current value is switched to zero and held at zero, are the value corresponding to the natural frequency of the oscillating part 12A, and thus the vibration of the oscillating part 12A in the second periods TB1 and TB2 is suppressed, and the oscillating part 12A can be oscillated stably. Thus, according to the present embodiment, image degradation can be suppressed. More specifically, by setting the current value to zero in the first periods TA1 and TA2, the lengths of the first periods TA1 and TA2 can be shortened and the lengths of the second periods TB1 and TB2 can be lengthened compared with gradually switching the current value as in the first embodiment, for example. This lengthens the period during which the light L is applied and can thus suppress image degradation more suitably.

As described above, the optical path control apparatus <NUM> according to the second embodiment has the oscillating part 12A on which the light L is made incident, the actuators 12B oscillating the oscillating part 12A, and the drive circuit <NUM> (the drive unit) applying the drive signal to the actuators 12B to cause the actuators 12B to oscillate the oscillating part 12A and to control the optical path. The drive circuit <NUM> applies the drive signal with a waveform including the first period TA1, in which the current value is set to zero, and the second period TB1, which is after the first period TA1 and is continuous with the first period TA1 and in which the current value is held at the second current value A2, to the actuators 12B. The drive circuit <NUM> applies the drive signal in such a manner that the length of the first period TA1 is the value corresponding to the natural frequency of the oscillating part 12A.

Thus, in the second embodiment, by setting the length of the first period TA1 to the value corresponding to the natural frequency of the oscillating part 12A, the oscillating part 12A is suppressed from vibrating in the second period TB1, and the oscillating part 12A can be oscillated stably. Owing to the waveform setting the current value to zero in the first period TA1, the length of which corresponds to the natural frequency of the oscillating part 12A, and switching the current value to the second current value A2 and holding it in the subsequent second period TB1, the waveform capable of stably oscillating the oscillating part 12A can be easily set without making waveform setting complicated.

The drive circuit <NUM> applies the drive signal in such a manner that the length of the first period TA1 is substantially the same value as the half value of the natural period (the inverse of the natural frequency) of the oscillating part 12A. By making the length of the first period TA1 the inverse of the natural frequency of the oscillating part 12A, the oscillating part 12A can be oscillated more stably.

The drive circuit <NUM> applies the drive signal in such a manner that in the fourth period TB2 (the third period), which is before the first period TA1 and is continuous with the first period TA1, the current value is held at the first current value A1, which is opposite to the second current value A2 in polarity. Thus, by applying the current values opposite to each other in polarity before and after the first period TA1, the oscillating part 12A can be oscillated stably and appropriately.

The following describes a third embodiment, representing an embodiment not according to the claimed subject-matter. The third embodiment differs from the first embodiment in the waveform of the drive signal. In the third embodiment, for the parts common to those of the first embodiment in configuration, descriptions thereof are omitted.

The control circuit <NUM> according to the third embodiment, like the second embodiment, also includes the digital circuit 14A and does not necessarily have a DA converter (the converter 14B) as in the first embodiment. That is to say, in the third embodiment, the digital drive signal generated by the digital circuit 14A is input to the drive circuit <NUM>, and the drive circuit <NUM> switches the polarity of the current of the drive signal by a switching circuit, not illustrated, that is, switches the current so as to be opposite in direction and the same in the current value, and outputs the current to the actuators 12B. Although the digital drive signal is thus input to the drive circuit <NUM> in the third embodiment, this is not limiting; the drive signal analog-converted by the converter 14B may be input as in the first embodiment.

<FIG> is a graph illustrating the waveform of the drive signal according to the third embodiment. As illustrated in <FIG>, 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 to say, in a period TAla of the first period TA1, the current value is held at the second current value A2, whereas in a period TA1b of the first period TA1, the current value is held at the first current value A1. The period TA1b is a period that is after the period TAla and is continuous with the period TAla. That is to say, at the start timing of the period TA1b (the timing of switching from the period TAla 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.

The length of the first period TA1 is the value corresponding to the natural frequency of the oscillating part 12A. The length of the first period TA1 is preferably substantially the same value as the one-third value of the natural period (the inverse of the natural frequency) of the oscillating part 12A and more preferably the same value as the one-third value of the natural period. The one-third value of the natural period (the inverse of the natural frequency) is expressed as "<NUM>/(<NUM>·f)" [s] when the natural frequency is f [Hz].

More specifically, the length of the period TAla and the length of the period TA1b of the first period TA1 are the value corresponding to the natural frequency of the oscillating part 12A. The length of the period TAla and the length of the period TA1b are preferably the same. More specifically, the length of the period TAla and the length of the period TA1b are preferably substantially the same value as the one-sixth value of the natural period (the inverse of the natural frequency) of the oscillating part 12A and more preferably the same value as the one-sixth value of the natural period. The one-sixth value of the inverse of the natural frequency is expressed as "<NUM>/(<NUM>·f)" [s] when the natural frequency is f [Hz].

The drive signal holds the current value at the second current value A2 in the second period TB1. The second period TB1 is a period that is after the first period TA1 (the period TA1b) and is continuous with the first period TA1 (the period TA1b). That is to say, at the start timing of the second period TB1 (the timing of switching from the period TA1b to the second period TB1), the current value switches from the first current value A1 to the second current value A2, and the current value is held at the second current value A2 until the end timing of the second period TB1.

Thus, in the third embodiment, the drive signal in the period T1 holds the current value at the second current value A2 in the period TAla, holds the current value at the switched first current value A1 in the period TA1b, and holds the current value at the switched second current value A2 in the second period TB1.

In the third embodiment, in the third period TA2, the current value is held at the first current value A1, and then the current value is held at the second current value A2. That is to say, at the start timing of the period TA2a of the third period TA2 (the timing of switching from the second period TB1 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 is after the period TA2a and is continuous with the period TA2a. That is to say, at the start timing of the period TA2b (the timing of switching from the period TA2a to the period TA2b), the current value switches from the first current value A1 to the second current value A2, and the current value is held at the second current value A2 until the end timing of the period TA2b.

The length of the third period TA2 is the value corresponding to the natural frequency of the oscillating part 12A. The length of the third period TA2 is preferably substantially the same value as the one-third value of the natural period (the inverse of the natural frequency) of the oscillating part 12A and more preferably the same value as the one-third value of the natural period. In the present embodiment, the length of the third period TA2 is equal to the length of the first period TA1.

More specifically, the length of the period TA2a and the length of the period TA2b of the third period TA2 are the value corresponding 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 substantially the same value as the one-sixth value of the inverse of the natural frequency of the oscillating part 12A and more preferably the same value as the one-sixth value of the natural period. In the present embodiment, the length of the period TA2a is equal to the length of the period TAla, whereas the length of the period TA2b is equal to the length of the period TA1b.

The drive signal holds the current value at the first current value A1 in the fourth period TB2. The fourth period TB2 is a period that is after the third period TA2 (the period TA2b) and is continuous with the third period TA2 (the period TA2b). That is to say, at the start timing of the fourth period TB2 (the timing of switching from the period TA2b to the fourth period TB2), 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 fourth period TB2.

Thus, in the third embodiment, the drive signal in the period T2 holds the current value at the first current value A1 in the period TA2a, holds the current value at the switched second current value A2 in the period TA2b, and holds the current value at the switched first current value A1 in the fourth period TB2.

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

The following describes an oscillation pattern of the oscillating part 12A by the application of the drive signal. <FIG> is a graph illustrating the oscillation pattern of the optical part according to the third embodiment.

The drive signal switches the current value from the first current value A1 to the second current value A2 at the start timing of the period TAla, holds the current value at the second current value A2 until the end timing of the period TAla, switches the current value from the second current value A2 to the first current value A1 at the start timing of the period TA1b, and holds the current value at the first current value A1 until the end timing of the period TA1b. Thus, the oscillating part 12A changes the displacement angle from the first angle D1 to the second angle D2 in the first period TA1 (the periods TAla and TA1b). More specifically, in addition to a force to twist back at the first angle D1, a force is further applied in a returning direction by the second current value A2 to accelerate the oscillating part 12A in a direction of the second angle D2. If being left as it is, the oscillating part 12A will be further twisted beyond the second angle D2 due to inertia, and thus in the present embodiment, the first current value A1 is passed after that to apply braking. Thus, the oscillating part 12A can be oscillated even faster than in the second embodiment.

The drive signal switches the current value from the first current value A1 to the second current value A2 at the start timing of the second period TB1 and holds the current value at the second current value A2 until the end timing of the second period TB1. Thus, the oscillating part 12A holds the displacement angle at the second angle D2 in the second period TB1.

The drive signal switches the current value from the second current value A2 to the first current value A1 at the start timing of the period TA2a, holds the current value at the first current value A1 until the end timing of the period TA2a, switches the current value from the first current value A1 to the second current value A2 at the start timing of the period TA2b, and holds the current value at the second current value A2 until the end timing of the period TA2b. Thus, the oscillating part 12A changes the displacement angle from the second angle D2 to the first angle D1 in the third period TA2 (the periods TA2a and TA2b).

The drive signal switches the current value from the second current value A2 to the first current value A1 at the start timing of the fourth period TB2 and holds the current value at the first current value A1 until the end timing of the fourth period TB2. Thus, the oscillating part 12A holds the displacement angle at the first angle D1 in the fourth period TB2.

In the third embodiment, the lengths of the first periods TA1 and TA2, in which the polarity of the current value is switched, are the value corresponding to the natural frequency of the oscillating part 12A, and thus the vibration of the oscillating part 12A in the second periods TB1 and TB2 is suppressed, and the oscillating part 12A can be oscillated stably. Thus, according to the present embodiment, image degradation can be suppressed. More specifically, by switching the polarity of the current value in the first periods TA1 and TA2, the lengths of the first periods TA1 and TA2 can be shortened and the lengths of the second periods TB1 and TB2 can be lengthened compared with the first embodiment and the second embodiment, for example. This lengthens the period during which the light L is applied and can thus suppress image degradation more suitably.

As described above, the optical path control apparatus <NUM> according to the third embodiment has the oscillating part 12A on which the light L is made incident, the actuators 12B oscillating the oscillating part 12A, and the drive circuit <NUM> (the drive unit) applying the drive signal to the actuators 12B to cause the actuators 12B to oscillate the oscillating part 12A and to control the optical path. The drive circuit <NUM> applies the drive signal with a waveform including the first period TA1, in which the current value is held at the second current value A2, and then the current value is held at the first current value A1, which is opposite to the second current value A2 in polarity, and the second period TB1, which is continuous with the first period TA1 and in which the current value is held at the second current value A2, to the actuators 12B. The drive circuit <NUM> applies the drive signal in such a manner that the length of the first period TA1 is the value corresponding to the natural frequency of the oscillating part 12A.

Thus, in the third embodiment, by setting the length of the first period TA1 to the value corresponding to the natural frequency of the oscillating part 12A, the oscillating part 12A is suppressed from vibrating in the second period TB1, and the oscillating part 12A can be oscillated stably. Owing to the waveform switching the polarity of the current value in the first period TA1, the length of which corresponds to the natural frequency of the oscillating part 12A, and switching the current value to the second current value A2 and holding it in the subsequent second period TB1, the waveform capable of stably oscillating the oscillating part 12A can be easily set without making waveform setting complicated.

The drive circuit <NUM> applies the drive signal in such a manner that the length of the period TAla, in which the current value is held at the second current value A2 in the first period TA1, and the length of the period TA1b, in which the current value is held at the first current value A1 in the first period TA1, are the same. By making the lengths of the periods TAla and TA1b equal, the oscillating part 12A can be oscillated more stably.

The drive circuit <NUM> applies the drive signal in such a manner that the length of the period TAla, in which the current value is held at the second current value A2 in the first period TA1, and the length of the period TA1b, in which the current value is held at the first current value A1 in the first period TA1, are substantially the same value as the one-sixth value of the inverse of the natural frequency of the oscillating part 12A. By setting the length of the first period TA1 to this range, the oscillating part 12A can be oscillated more stably.

According to the above-described embodiments, it is possible that the optical part is oscillated at high speed and is stopped stably.

Claim 1:
An optical path control apparatus (<NUM>) comprising:
an oscillating part (12A) having an optical member (<NUM>) on which light is made incident;
an electromagnetic actuator (12B) configured to oscillate the oscillating part (12A); and
a drive unit (<NUM>) configured to periodically apply to the actuator (12B) a drive signal, which is between a first current value (A1) to a second current value (A2), with a waveform to cause the actuator (<NUM>) to oscillate the oscillating part (12A) and to control an optical path, wherein
the first current value (A1) and the second current value (A2) are current values opposite to each other in polarity,
absolute values of the first current value (A1) and the second current value (A2) are equal,
the oscillating part (12A) is held at a displacement angle of a first angle (D1) for the first current value (A1), and
the oscillating part (12A) is held at a displacement angle of a second angle (D2) for the second current value (A2), wherein
the waveform includes a first period (TA1) in which a current value is changed from the first current value (A1) to zero at the start timing of the first period (TA1) and the current value is held at zero until the end timing of the first period (TA1),
a second period (TB1) that is continuous with the first period (TA1) and in which the current value is changed from zero to the second current value (A2) at the start timing of the second period (TB1) and the current value is held at the second current value (A2) until the end timing of the second period (TB1), a third period (TA2) that is continuous with the second period (TB1) and in which the current value is changed from the second current value (A2) to zero at the start timing of the third period (TA2) and the current value is held at zero until the end timing of the third period (TA2), and a fourth period (TB2) that is continuous with the third period (TA2) and in which the current value is changed from zero to the first current value (A1) at the start timing of the fourth period (TB2) and the current value is held at the first current value (A1) until the end timing of the fourth period (TB2), and
the drive unit (<NUM>) is configured to apply the drive signal so that a length of the first period (TA1) and the third period (TA2) is substantially a same value as a half value of an inverse of a natural frequency of the oscillating part (12A).