OPTICAL DEVICE AND IMAGE FORMING UNIT WITH OPTICAL DEVICE

Abstract

The present disclosure provides an optical device in which foreign matters adhering to the surface of a light-transmitting body can be sufficiently removed without complicating the formation, and an image forming unit provided with the optical device. An optical device (10) is provided with an outermost-layer lens (1) (light-transmitting body), a housing (2), a vibrating body (3), a piezoelectric element (5), and a driving circuit (6). The driving circuit (6) causes a voltage (Vp-p_1) of a driving signal that drives the piezoelectric element (5) in a sputtering mode (first vibration mode) among a plurality of vibration modes that vibrate the outermost-layer lens (1) and a voltage (Vp-p_(underline)2) of a driving signal that drives the piezoelectric element (5) in a heating mode (second vibration mode) to be equal.The driving circuit (6) drives the piezoelectric element (5) such that an effective voltage (Veff_1) applied to the piezoelectric element (5) within a predetermined period of the sputtering mode and an effective voltage (Veff_2) applied to the piezoelectric element (5) within the predetermined period of the heating mode are different.

Description

Technical field

[0001] The present disclosure relates to an optical device and an image forming unit having an optical device. Background technology

[0002] Safety equipment has been controlled and driving assistance control has been performed by providing an image generation unit at a front and / or rear of a vehicle and utilizing an image captured by the image generation unit. In many cases, such an image generation unit is provided outside a vehicle, and thus, foreign matter such as raindrops (water droplets), mud, dust, and the like may adhere to a light-transmitting body (a protective cover or a lens) covering the outside of the image generation unit. Furthermore, in cold weather, ice or frost may adhere to a surface of the light-transmitting body of the image generation unit provided outside the vehicle, making it difficult to obtain clear images.

[0003] In this regard, in a lens cleaning system described in Patent Document 1, a light-transmitting body is vibrated through a plurality of driving sequences, including a dehydration sequence and a heating sequence, thereby removing foreign matter adhering to a surface of the light-transmitting body. This lens cleaning system varies the voltage applied to a transducer, a time duration and frequency of vibration of the light-transmitting body, and the like according to a type of driving sequence. Reference listPatent document

[0004] Patent Document 1: US Patent Application Publication No. 2020 / 0282435 Summary of the inventionTechnical problem

[0005] However, the system according to Patent Document 1 requires a drive circuit including an amplifier circuit for changing the voltage applied to the converter, which increases the manufacturing cost of the drive circuit. Furthermore, the system according to Patent Document 1 performs maximum power driving during vibration of the light-transmitting body. Therefore, a circuit and wiring that can withstand the maximum power are required, which may cause system complexity.

[0006] In this context, an object of the present disclosure is to provide an optical device capable of removing foreign matter adhering to a surface of a light-transmitting body without configuration complexity, and an image forming unit having an optical device. Solution to the problem

[0007] An optical device according to one aspect of the present disclosure includes: a light-transmitting body configured to transmit light having a predetermined wavelength; a housing configured to hold the light-transmitting body; a vibrating body configured to contact the light-transmitting body held by the housing; a piezoelectric element provided on the vibrating body and configured to vibrate the vibrating body; and a driving circuit configured to drive the piezoelectric element. The vibrating body is a cylindrical body and includes a first end and a second end on a side opposite to the first end, the first end contacting the light-transmitting body, and the piezoelectric element is provided at the second end.The driving circuit causes a voltage Vp-p_1 of an AC signal that drives the piezoelectric element in a first vibration mode among a plurality of vibration modes to vibrate the light-transmitting body to be the same as a voltage Vp-p_(underline)2 of an AC signal that drives the piezoelectric element in a second vibration mode among the plurality of vibration modes, and drives the piezoelectric element such that an effective voltage Veff_1 applied to the piezoelectric element within a predetermined time period in the first vibration mode is different from an effective voltage Veff_2 applied to the piezoelectric element within the predetermined time period in the second vibration mode.

[0008] An image forming unit according to one aspect of the present disclosure includes: the optical device described above; and an image forming element arranged such that the light-transmitting body is arranged in a viewing direction thereof. Advantageous effects of the invention

[0009] According to the present disclosure, the piezoelectric element is driven such that the voltage of an AC signal driving the piezoelectric element is the same in the first vibration mode and the second vibration mode, and the effective voltage Veff_1 in the first vibration mode is different from the effective voltage Veff_2 in the second vibration mode. Therefore, foreign matter adhering to the surface of the light-transmitting body can be removed by vibrating the light-transmitting body at different frequencies without configuration complexity. Brief description of the drawings Fig. 1 is a half-sectional view of an image forming unit according to Embodiment 1. Fig. 2 is a block diagram for explaining a configuration of a driving circuit according to Embodiment 1. Fig. 3 is a graph showing a relationship between a frequency and an impedance when an optical device according to Embodiment 1 is vibrated. Fig. 4 is a diagram for explaining a drive signal that drives a piezoelectric element by the drive circuit according to Embodiment 1. Fig. 5 is a graph for explaining a relationship between a displacement of a light transmitting body and a duty ratio of a driving signal. Fig. 6 is a graph for explaining a change in a maximum displacement of a light transmitting body according to a change in a duty ratio of a driving signal. Fig. 7 is a graph for explaining a transient response of vibration when a light-transmitting body is excited using a driving signal. Fig. 8 is a circuit diagram for explaining a configuration of a driving circuit according to Embodiment 2. Fig. 9 is a diagram for explaining a drive signal that drives a piezoelectric element by a drive circuit according to Embodiment 3. Fig. 10 is a circuit diagram for explaining a configuration of a driving circuit according to Embodiment 4. Fig. 11 is a graph for explaining characteristics of a filter circuit included in the driving circuit according to Embodiment 4. Description of the embodiments

[0010] Hereinafter, an optical device and an image forming unit including the optical device according to embodiments will be described in detail with reference to the drawings. In the drawings, the same reference numerals denote the same or corresponding portions. The optical device described below is applied, for example, to an in-vehicle image forming unit and is capable of vibrating a light-transmitting body (for example, an outermost layer lens) to remove foreign matter adhering to the surface of the light-transmitting body. The optical device is not limited to an in-vehicle image forming unit. For example, the optical device can also be applied to a security monitoring camera, an image forming unit for a drone, and the like. (Example 1)

[0011] Fig. 1 is a half-sectional view of an image forming unit 100 according to Embodiment 1. Note that an X-direction and a Z-direction in the drawings indicate a lateral direction and a height direction of the image forming unit 100, respectively. A one-dot chain line in Fig. 1 indicates a portion of the image forming unit 100 passing through a central axis thereof. The image forming unit 100 includes an optical device 10 and an image forming element 20 arranged such that an outermost layer lens 1 and an inner layer lens 4 are arranged in a viewing direction thereof. The image forming element 20 is, for example, an image sensor such as a CCD (charge coupled device) sensor and a CMOS (complementary metal-oxide-semiconductor) sensor, and is mounted on a circuit board, which is not shown.

[0012] The optical device 10 includes the outermost layer lens 1, a housing 2, a vibrating body 3, the inner-layer lens 4, a piezoelectric element 5, and a driving circuit 6. Note that in the present disclosure, the optical device 10 includes at least the outermost layer lens 1, the housing 2, the vibrating body 3, the piezoelectric element 5, and the driving circuit 6, and the inner-layer lens 4 may be included in the image forming unit 100. In the optical device 10, the outermost layer lens 1 and the inner-layer lens 4 are adjusted to be aligned, and then a housing including the image forming element 20 is attached to the optical device 10, thereby forming the image forming unit 100.

[0013] The outermost layer lens 1 is a light-transmitting body that transmits light having a predetermined wavelength (e.g., a wavelength of visible light, a wavelength detectable by an imaging element, or the like), and is, for example, a convex meniscus lens. The optical device 10 may use a transparent member such as a protective cover instead of the outermost layer lens 1. The protective cover is made of glass or resin, such as transparent plastics.

[0014] One end portion of the outermost layer lens 1 is held by one end portion of a disc spring 2a extending from the housing 2. Note that a space between the outermost layer lens 1 and a holder 2b, which is one end portion of the disc spring 2a, is filled with an adhesive 2c. Furthermore, although the end portion of the disc spring 2a holds the outermost layer lens 1, the housing 2 may directly or indirectly hold the outermost layer lens 1. In order to vibrate the outermost layer lens 1 held by the housing 2, the optical device 10 is further provided with the vibrating body 3 at a position in contact with the outermost layer lens 1.

[0015] The vibrating body 3 is a cylindrical body, and one end portion 31 (first end) thereof is in contact with the outermost layer lens 1, and the other end portion 32 (second end) thereof, which is located on a side opposite to the one end portion, is provided with the piezoelectric element 5. The vibrating body 3 has a configuration in which the one end portion 31 and the other end portion 32 are connected to each other by a support member 33. Note that a cross-sectional shape of the support member 33 is an S-shape. As shown in Fig. 1, the inner layer lens 4 is arranged within the cylinder of the vibrating body 3.

[0016] The one end portion 31 has a shape extending in a radial direction (X and Y directions) of the cylindrical body and can be stably connected to a peripheral edge portion of the outermost layer lens 1. The other end portion 32 is a portion that vibrates when the piezoelectric element 5 vibrates and has a thickness greater than that of other portions. Therefore, vibration of the piezoelectric element 5 can be transmitted to the outermost layer lens 1 more efficiently. The support member 33 is a portion that supports the one end portion 31 and transmits vibration of the other end portion 32 to the one end portion 31. It is noted that the one end portion 31, the other end portion 32, and the support member 33 may be integrally formed or may be formed separately. Furthermore, as shown in Fig. 1, a maximum outer dimension of the support part 33 is larger than a maximum outer dimension of the one end portion 31, and a maximum outer dimension of the other end portion 32 is larger than the maximum outer dimension of the support part 33. Therefore, vibration of the other end portion 32 (i.e., vibration of the piezoelectric element 5) can be efficiently transmitted to the outermost layer lens 1 (light-transmitting body).

[0017] The piezoelectric element 5 is provided at the other end portion 32. The piezoelectric element 5 has a hollow circular shape and vibrates, for example, by polarization in a thickness direction. The piezoelectric element 5 is made of PZT-based piezoelectric ceramics. However, other piezoelectric ceramics, such as (K, Na)NbO3, may be used. A piezoelectric single crystal, such as LiTaO3, may also be used. The piezoelectric element 5 is connected to the drive circuit 6 and vibrates the outermost layer lens 1 based on a signal from the circuit.

[0018] The driving circuit 6 can drive the piezoelectric element 5 in a sputtering mode. In the sputtering mode, the driving circuit 6 vibrates the outermost layer lens 1 at a resonant frequency of the vibrating body 3 to remove foreign matter, such as raindrops, mud, and dust, adhering to the outermost layer lens 1. Furthermore, the driving circuit 6 can drive the piezoelectric element 5 in a heating mode. In the heating mode, the driving circuit 6 vibrates the outermost layer lens 1 at a natural vibration frequency of the outermost layer lens 1 to remove foreign matter, such as ice and frost, adhering to the outermost layer lens 1. The driving circuit 6 can drive the piezoelectric element 5 while switching between a plurality of vibration modes, including the sputtering mode and the heating mode.The driving circuit 6 also serves as a switching part that switches the mode for vibrating the outermost layer lens 1 among the plurality of vibration modes.

[0019] The driver circuit 6 will be described in detail with reference to the drawings. Fig. 2 is a block diagram for explaining a configuration of the driver circuit 6 according to Embodiment 1. Fig. 2 illustrates an example in which the piezoelectric element 5 is connected to the driver circuit 6 in a single-ended manner. However, this connection method is merely an example and is not limited thereto. A reference potential of the piezoelectric element 5 may be, for example, ground or may be body ground connected to a negative terminal of a battery.

[0020] The driving circuit 6 includes a control circuit 61 and an output circuit 62. The control circuit 61 controls the output circuit 62 to convert a voltage Vout supplied from a driving power supply circuit 7 into a driving voltage Vdrv to be output to the piezoelectric element 5. The driving circuit 6 sets the driving voltage Vdrv to be output to the piezoelectric element 5 to drive the piezoelectric element 5 while switching between the plurality of vibration modes including the atomization mode and the heating mode. Although it is described that the driving circuit 6 does not include the driving power supply circuit 7, the driving circuit 6 may include the driving power supply circuit 7.

[0021] The control circuit 61 controls a switching frequency of a plurality of switches included in the output circuit 62, thereby adjusting a frequency of a drive signal. The control circuit 61 includes a general-purpose processor, such as a CPU or an MPU, that executes a program to implement a predetermined function. The control circuit 61 is communicable with a storage device and calls and executes a calculation program or the like stored in the storage device to implement various types of processing, such as switching processing of the plurality of switches, in the control circuit 61 and the like.The control circuit 61 is not limited to having an aspect in which hardware resources and software cooperate to implement a predetermined function, but may be a hardware circuit designed only to implement a predetermined function. That is, the control circuit 61 may be implemented by various processors other than a CPU or an MPU, such as a GPU, an FPGA, a DSP, and an ASIC. Such a control circuit 61 may include, for example, a signal processing circuit that is a semiconductor integrated circuit.

[0022] When a driving signal is applied to the piezoelectric element 5, an impedance of the piezoelectric element 5 changes according to a frequency of the driving signal. Fig. 3 is a graph showing a relationship between a frequency and an impedance when the optical device 10 according to Embodiment 1 is vibrated. As in Fig. As illustrated in Figure 3, the piezoelectric element 5 has a plurality of frequencies at which impedance decreases locally. These frequencies correspond to resonance frequencies of the vibrating body 3. The optical device 10 according to this embodiment has resonance frequencies at, for example, approximately 30 kHz (arrow I) and approximately 550 kHz (arrow II).

[0023] When the piezoelectric element 5 receives the input of a drive signal corresponding to one of these resonant frequencies, the piezoelectric element 5 vibrates the outermost layer lens 1 in a vibration mode that varies depending on a frequency. For example, in a case where a drive signal at a frequency of about 30 kHz is input, the piezoelectric element 5 vibrates the outermost layer lens 1 with the vibrating body 3 interposed therebetween in a first vibration mode. The first vibration mode is a vibration mode for vibrating the outermost layer lens 1 as a whole. The first vibration mode is the atomization mode capable of atomizing and thus removing foreign matter, such as a droplet, adhering to the outermost layer lens 1.

[0024] Furthermore, in a case where a drive signal at a frequency of about 550 kHz is input, the piezoelectric element 5 vibrates the outermost layer lens 1 with the vibrating body 3 interposed therebetween in a second vibration mode (heating mode) in which the temperature of the outermost layer lens 1 is slightly increased. The vibration in an environment of about 550 kHz causes the outermost layer lens 1 to vibrate in a higher-order vibration mode with a larger number of nodes than that of the vibration at about 30 kHz. In the heating mode, the piezoelectric element 5 has a small impedance, and thus a large amount of power is supplied to the piezoelectric element 5, which allows the temperature of the outermost layer lens 1 to be rapidly increased.

[0025] It should be noted that at a frequency of about 110 kHz, between the first vibration mode and the second vibration mode, there is a frequency that resonates with the natural vibration of the outermost layer lens 1. When a drive signal is input at this frequency, the piezoelectric element 5 vibrates a central portion of the outermost layer lens 1 more strongly than a peripheral edge portion of the outermost layer lens 1 with the vibrating body 3 interposed therebetween. The piezoelectric element 5 can cause vibration other than the vibration modes described above for the outermost layer lens 1. Furthermore, the resonance frequencies described above are merely an example and can be changed according to a shape, material, and the like of the optical device 10.

[0026] As in Fig. 3, when a driving signal at the frequency corresponding to the resonance frequency is input to the piezoelectric element 5, an impedance of the piezoelectric element 5 becomes locally minimum.

[0027] Conventionally, in a case where the drive circuit 6 drives the piezoelectric element 5 while switching between a plurality of vibration modes as described above, the drive circuit 6 adjusts a voltage to be applied to the piezoelectric element 5 according to the switched vibration mode. However, in order for the drive circuit 6 to adjust a voltage to be applied to the piezoelectric element 5, it is necessary to provide the drive circuit 6 with an amplifier circuit, which increases the manufacturing cost of the drive circuit 6. Furthermore, the sputtering mode and the heating mode have different conditions from each other in terms of vibration acceleration required for a vibration to be excited, and the like.For example, in the atomization mode, it is preferable that a frequency of a vibration to be excited is several tens of kilohertz and a vibration acceleration is more than 8.0 × 10. 5 m / s 2 On the other hand, in heating mode, a frequency of a vibration to be excited is several hundred kilohertz, and a power sufficient for thawing and preventing overheating must be supplied to the piezoelectric element 5.

[0028] Furthermore, the sputtering mode and the heating mode have different optimal vibration magnitudes from each other, and voltages to be applied to the piezoelectric element 5 to realize these optimal vibration magnitudes are thus different. Generally, a resonance resistance in the heating mode is significantly lower than a resonance resistance in the sputtering mode. In a case where the same voltage is applied to the piezoelectric element 5 in the heating mode, damage due to overheating and / or an increase in power consumption may be caused. Therefore, in a drive circuit that supplies a square wave using a half-bridge circuit or the like, an amplifier circuit is required to adjust a voltage to be applied to the piezoelectric element 5, which increases the manufacturing cost of the drive circuit.

[0029] In this regard, in the optical device 10 according to this embodiment, the vibration mode is switchable by adjusting a waveform itself of a drive signal to be input without changing a voltage to be applied from the drive circuit 6 to the piezoelectric element 5. Fig. Fig. 4 is a diagram for explaining a drive signal that drives the piezoelectric element 5 by the drive circuit 6 according to Embodiment 1. As shown by a waveform a in Fig. 4, the driving circuit 6 outputs to the piezoelectric element 5 as a driving signal a rectangular wave in which a high-time period th having a voltage at a positive value and a low-time period tl having a voltage at a negative value form one period.

[0030] The driving circuit 6 adjusts a length of the high-voltage period th and a length of the low-voltage period tl according to the vibration mode without changing a voltage value of the high-voltage period th and a voltage value of the low-voltage period tl. That is, the driving circuit 6 makes a voltage Vp-p_1 of a driving signal (AC signal) that drives the piezoelectric element 5 in the sputtering mode to vibrate the outermost layer lens 1 the same as a voltage Vp-p_(underline)2 of a driving signal that drives the piezoelectric element 5 in the heating mode (Vp-p_1 = Vp-p_2).Note that, assuming that the driving circuit 6 includes the driving power supply circuit and the output circuit that converts a DC voltage output from the driving power supply circuit into an AC signal, the DC voltage output from the driving power supply circuit can be defined to be the same in the plurality of vibration modes. That is, the driving circuit 6 causes a DC voltage Vout_1 for generating a drive signal (AC signal) that drives the piezoelectric element 5 in the sputtering mode to vibrate the outermost layer lens 1 to be the same as a DC voltage Vout_(underline)2 for generating a drive signal that drives the piezoelectric element 5 in the heating mode (Vout_1 = Vout_2).

[0031] Furthermore, the driving circuit 6 drives the piezoelectric element 5 such that an effective voltage Veff_1 applied to the piezoelectric element 5 within a predetermined time period in the sputtering mode is different from an effective voltage Veff_2 applied to the piezoelectric element 5 within the predetermined time period in the heating mode (Veff_1 ≠ Veff_2).

[0032] Here, a voltage Vp-p is the voltage of the difference (a peak-to-peak value) between a maximum value (+Vpp) and a minimum value (-Vpp) of a drive signal (AC signal). Furthermore, an effective voltage Veff indicates a voltage value supplied as vibration to the outermost layer lens 1 when the piezoelectric element 5 is driven by the drive signal at the voltage Vp-p. The drive circuit 6 adjusts the length of the high-voltage period th and the length of the low-voltage period tl to change the effective voltage Veff, thereby switching between the sputtering mode and the heating mode.From a perspective of preventing overheating of the outermost layer lens 1 in the heating mode, the effective voltage Veff_1 applied to the piezoelectric element 5 within the predetermined time period in the sputtering mode is preferably higher than the effective voltage Veff_2 applied to the piezoelectric element 5 within the predetermined time period in the heating mode (Veff_1 > Veff_2).

[0033] Furthermore, it is assumed that a displacement amount upon vibration of the outermost layer lens 1 is a vibration amplitude Av, and a power input for exciting the outermost layer lens 1 is a power Pv. In the case where the drive circuit 6 drives the piezoelectric element 5 in the sputtering mode to enable sputtering and thus removal of foreign matter, such as a droplet, adhering to the outermost layer lens 1, it is required that the vibration amplitude Av of the outermost layer lens 1 is larger than that in the case where the piezoelectric element 5 is driven in the heating mode. That is, the driving circuit 6 preferably has a larger vibration amplitude Av_1 of the outermost layer lens 1 in the sputtering mode than a vibration amplitude Av_2 of the outermost layer lens 1 in the heating mode (Av_1 > Av_2).

[0034] In addition, as in Fig. As shown in Figure 3, when the piezoelectric element 5 is driven in the heating mode, the resonance resistance is lower than when the piezoelectric element 5 is driven in the sputtering mode, increasing the input power Pv. That is, the drive circuit 6 preferably has a lower input power Pv_1 in the sputtering mode than an input power Pv_2 in the heating mode (Pv_1 < Pv_2). Therefore, the drive circuit 6 can efficiently drive the piezoelectric element 5 in each vibration mode of the sputtering mode and the heating mode.

[0035] Assuming that a shorter time period min(th, tl) of the peak period th and the low time period tl is an active time period ta, a duty cycle of a drive signal can be represented by min(th, tl) / (th + tl) = ta / (th + tl). Adjusting the length of the peak period th and the length of the low time period tl also means adjusting a duty cycle of a drive signal. Therefore, the drive circuit 6 can change the effective voltage Veff by adjusting a duty cycle of a drive signal and can switch between the sputtering mode and the heating mode without changing the voltage Vp-p to be applied to the piezoelectric element 5.

[0036] A generalized relationship between a drive signal in atomization mode and a drive signal in heating mode by using a duty cycle of a drive signal is a relationship as represented by Formula 1. ∫{ta_1 / (th_1+tl_1)}dt>∫{ta_2 / (th_2+tl_2)}dt

[0037] Here, it is assumed that the sputtering mode includes a peak period th_1, a low time period tl_1, and an active time period ta_1, and the heating mode includes a peak period th_2, a low time period tl_2, and an active time period ta_2. That is, in a case where the driving circuit 6 drives the piezoelectric element 5 for a predetermined time period dt, the driving circuit 6 preferably has a first integral value that is greater than a second integral value. The first integral value is an integral of a duty ratio of a driving signal that drives the piezoelectric element 5 in the sputtering mode over the predetermined time period dt. The second integral value is an integral of a duty ratio of a driving signal that drives the piezoelectric element 5 in the heating mode over the predetermined time period dt.In this way, the driver circuit 6 can provide an arbitrary adjustment of the effective voltage Veff by changing a duty cycle of a driver signal.

[0038] With further reference to Fig. 4 is responsive to changing a duty cycle of a drive signal as the low time period tl increases, as indicated by a waveform b in Fig. 4, an average voltage value over a plurality of periods is not 0 (zero) V, but takes a negative value. If the average voltage value of the drive signal is not 0 (zero) V, an offset DC voltage is applied to the piezoelectric element 5, and electrochemical migration may be caused between both electrodes of the piezoelectric element 5.

[0039] In this respect, as shown by a waveform c in Fig. 4, the driver circuit 6 each period a period with a longer low time period tl and a period with a longer high time period th, thereby generating a drive signal such that the number of periods with the longer low time period tl and the number of periods with the longer high time period th are equal within the predetermined time period dt. In particular, the drive signal in the waveform c in Fig. 4, the first high-voltage period th1 and the second low-voltage period tl2 have the same length, and the first low-voltage period tl1 and the second high-voltage period th2 have the same length. Therefore, the driving circuit 6 can drive the piezoelectric element 5 such that an average value of a voltage applied to the piezoelectric element 5 over the predetermined time period dt is 0 (zero) V, and electrochemical migration caused between both electrodes of the piezoelectric element 5 can be prevented.

[0040] Next, it is described that changing a duty ratio of a driving signal can adjust a vibration level of the outermost layer lens 1. Fig. 5 is a graph for explaining a relationship between a displacement of a light transmitting body (outermost layer lens 1) and a duty ratio of a driving signal. Fig. 6 is a graph for explaining a change in a maximum displacement of a light transmitting body (outermost layer lens 1) according to a change in a duty ratio of a driving signal.

[0041] In Fig. 5, a displacement of the outermost layer lens 1 in a case where a duty cycle of a driving signal is changed from 10% to 50% is plotted, where a horizontal axis indicates a frequency (kHz) and a vertical axis indicates a displacement (µm) of the outermost layer lens 1. In Fig. 6, maximum displacements of the outermost layer lens 1 in cases where the voltage Vp-p is 30 V and 50 V are plotted, where a horizontal axis indicates a duty ratio (%) of a drive signal and a vertical axis indicates a maximum displacement (µm) of the outermost layer lens 1. Note that a displacement of the outermost layer lens 1 is measurable using, for example, a laser Doppler displacement meter.

[0042] As in Fig. 5 and Fig. As illustrated in FIG. 6, the driving circuit 6 can increase the maximum displacement of the outermost layer lens 1 by changing a duty cycle of a driving signal from 10% to 50% in the case of driving the piezoelectric element 5 in the sputtering mode. Therefore, the driving circuit 6 can adjust the maximum displacement (vibration level) of the outermost layer lens 1 based on a duty cycle of a driving signal in the sputtering mode. Similarly, the driving circuit 6 can change the maximum displacement of the outermost layer lens 1 based on a duty cycle of a driving signal in the heating mode, thereby being able to accurately adjust a heating value of the outermost layer lens 1.In particular, in the case of driving the piezoelectric element 5 in the heating mode, the driving circuit 6 can prevent overheating and insufficient thawing performance of the outermost layer lens 1 by adjusting a heating value based on a duty ratio of a driving signal.

[0043] Furthermore, from a mechanical resonance perspective, it can be described that changing a duty cycle of a driving signal adjusts a vibration level of the outermost layer lens 1. Fig. Figure 7 is a graph for explaining a transient behavior of vibration when a light-transmitting body (outermost layer lens 1) is excited using a driving signal. Fig. 7, a horizontal axis indicates time and a vertical axis indicates a displacement of the outermost layer lens 1.

[0044] When vibrating the outermost layer lens 1, the outermost layer lens 1 does not reach the maximum displacement at a moment when voltage is applied to the piezoelectric element 5, but a vibration of the outermost layer lens 1 is accelerated by vibration over several periods according to a quality factor of the vibrating body 3, and then the outermost layer lens 1 reaches the maximum displacement. Therefore, as shown in Fig. 7 illustrates that, in a case where a duty ratio of a drive signal is low, vibration is turned off in a state where vibration of the outermost layer lens 1 does not increase sufficiently. As a result, a displacement of the outermost layer lens 1 hits a peak without reaching the maximum displacement and remains a small displacement. On the other hand, in a case where a duty ratio of a drive signal is high, vibration is turned off in a state where vibration of the outermost layer lens 1 has increased sufficiently. Therefore, a displacement of the outermost layer lens 1 reaches the maximum displacement. (Example 2)

[0045] Embodiment 1 describes the optical device 10 capable of switching between the sputtering mode and the heating mode by changing the effective voltage Veff by thoroughly adjusting a duty cycle of a drive signal without changing the voltage Vp-p. Whether a frequency of a voltage applied to the piezoelectric element 5 is a resonant frequency can be determined by detecting a value of a current flowing through the piezoelectric element 5. In this regard, Embodiment 2 describes an optical device that adjusts a vibration level according to a value of a current flowing through a piezoelectric element.

[0046] The optical device according to Embodiment 2 has the same configurations as the optical device 10 according to Embodiment 1, and therefore, the same configurations will be described using the same reference numerals to avoid repeating the detailed description. Fig. 8 is a circuit diagram for explaining a configuration of a driving circuit 6A according to Embodiment 2. The driving circuit 6A includes the control circuit 61, the output circuit 62, a current detection circuit 63, a capacitor 64, and a resistor 65.

[0047] The output circuit 62 is connected to a driving power supply circuit. The output circuit 62 includes a series circuit comprising a first switch 62a, to which a voltage Vout is input from the driving power supply circuit, and a second switch 62b. A connection point C1 between the first switch 62a and the second switch 62b is connected to the piezoelectric element 5, with the capacitor 64 interposed therebetween. Each of the first switch 62a and the second switch 62b is, for example, a MOSFET (metal-oxide-semiconductor field-effect transistor), but is not limited thereto.

[0048] The current detection circuit 63 can detect at least one of a current flowing through the first switch 62a and a current flowing through the second switch 62b and output a detection signal indicative of a magnitude of the detected current to the control circuit 61. The current detection circuit 63 includes a current-to-voltage conversion element 63a, a low-pass filter 63b, and an analog-to-digital (AD) conversion circuit 63c.

[0049] The current-to-voltage conversion element 63a can convert a current flowing through the conversion element 63a into a voltage corresponding to a magnitude of the current flowing through the conversion element 63a. The conversion element 63a is a resistor (shunt resistor) with a predetermined resistance value. The conversion element 63a is not limited to a shunt resistor but may be a Hall element.

[0050] The low-pass filter 63b is a filter circuit that removes a signal having a frequency component higher than a cutoff frequency. In this embodiment, the low-pass filter 63b is connected to a connection point between the conversion element 63a and the second switch 62b. The low-pass filter 63b smoothes a voltage input from the conversion element 63a and outputs the smoothed voltage to an AD conversion circuit 45.

[0051] The AD conversion circuit 63c is a circuit that converts the voltage (analog signal) smoothed by the low-pass filter 63b into a digital signal that can be input to the control circuit 61. The AD conversion circuit 63c outputs the digital signal as a detection signal to the control circuit 61. The current detection circuit 63 does not necessarily include the AD conversion circuit 63c, and the low-pass filter 63b can output a smoothed voltage as a detection signal to the control circuit 61.

[0052] The current detection circuit 63 outputs to the control circuit 61 a detection signal that is a digital signal generated based on the magnitude of the current flowing through the second switch 62b, but the current detection circuit 63 is not limited to this. For example, the current detection circuit 63 may include only the conversion element 63a and the low-pass filter 63b and output to the control circuit 61 a detection signal that is not a digital signal but an analog signal.

[0053] In a first state described later, the capacitor 64 can charge based on the voltage Vout applied by the drive power supply circuit. In a second state described later, the capacitor 64 can discharge to a ground potential via the second switch 62b. Therefore, through the control circuit 61 controlling switching processing of the first switch 62a and the second switch 62b, the drive circuit 6A can flow a current I1 and a current I2 to the piezoelectric element 5.

[0054] The resistor 65 is connected between the ground potential and a connection point between the piezoelectric element 5 and the capacitor 64. The piezoelectric element 5 has a one-end side connected to the ground potential, with the resistor 65 interposed therebetween, and thus, once the switching processing by the control circuit 61 ends, the one-end side and the other-end side of the piezoelectric element 5 have an equipotential.

[0055] The control circuit 61 of the drive circuit 6A performs switching processing, complementarily switching the first switch 62a and the second switch 62b at a switching frequency. That is, the control circuit 61 controls the first switch 62a and the second switch 62b such that the second switch 62b is in an OFF state when the first switch 62a is ON (first state). Furthermore, the control circuit 61 controls the first switch 62a and the second switch 62b such that the second switch 62b is in an ON state when the first switch 62a is OFF (second state). The control circuit 61 complementarily switches the first switch 62a and the second switch 62b so that the control circuit 61 applies a drive voltage Vdrv as a drive signal to the piezoelectric element 5 based on the voltage Vout from the drive power supply circuit.The drive voltage Vdrv has a frequency that corresponds to the switching frequency.

[0056] In the first state, the current I1 flows through the first switch 62a into the driver circuit 6A. In Fig. 8, the current I1 is indicated by a dashed arrow. As in Fig. 8, the current I1 flows from the drive power supply circuit to the piezoelectric element 5 via the first switch 62a. Therefore, a voltage having a higher potential on the drive circuit 6A side is applied to the piezoelectric element 5.

[0057] In the driver circuit 6A, when a voltage is applied to the piezoelectric element 5 in the first state, the capacitor 64, which is connected between the output circuit 62 and the piezoelectric element 5, accumulates a positive charge on the output circuit 62 side and a negative charge on the ground potential side. When the control circuit 61 changes the output circuit 62 from the first state to the second state, the capacitor 64 and the piezoelectric element 5 discharge. In the second state, the discharge flows as the current I2 into the driver circuit 6A via the second switch 62b. Fig. 8, the current I2 is indicated by a one-dot chain line arrow. As in Fig. As illustrated in Figure 8, the current I2 flows from the piezoelectric element 5 to the ground potential via the second switch 62b. Furthermore, the capacitor 64 accumulates a negative charge on the output circuit 62 side and a positive charge on the piezoelectric element 5 side. Therefore, a voltage having a lower potential on the drive circuit 6A side is applied to the piezoelectric element 5.

[0058] As described above, the drive circuit 6A can output a drive signal with a polarity inverted at a predetermined frequency to the piezoelectric element 5 by switching the first switch 62a and the second switch 62b. Therefore, the drive circuit 6A can adjust a frequency of a drive signal by controlling a switching frequency for switching the first switch 62a and the second switch 62b.

[0059] Furthermore, the driving circuit 6A can determine a resonance frequency of the vibrating body 3 by changing a switching frequency within a predetermined frequency range. Specifically, the driving circuit 6A changes the switching frequency at a predetermined increase (or decrease) rate within a predetermined frequency range and determines, as the resonance frequency, a switching frequency with a largest current value detected by the current detection circuit 63. Therefore, the driving circuit 6A can determine a vibration level based on a current value detected by the current detection circuit 63 and can change a duty cycle of a driving signal in such a way as to correspond to the determined vibration level.That is, the driving circuit 6A can change a duty ratio of a driving signal according to a current value detected by the current detecting circuit 63, thereby being able to adjust a behavior difference attributable to an individual difference of devices and temperature characteristics. (Example 3)

[0060] Embodiment 1 describes the optical device 10 capable of changing the effective voltage Veff by adjusting a duty cycle of a drive signal. However, a method for changing the effective voltage Veff is not limited to this, but may be a method of decimating a part of a pulse signal from a drive signal, which is a pulse signal that repeats a high-voltage period and a low-voltage period. Embodiment 3 describes an optical device capable of reducing an effective voltage by decimating a pulse signal for every specific period from a drive signal. The optical device according to Embodiment 3 has the same configurations as the optical device 10 according to Embodiment 1, and therefore, the same configurations will be described using the same reference numerals to avoid repeating the detailed description.

[0061] Fig. 9 is a diagram for explaining a drive signal that drives the piezoelectric element 5 by the drive circuit 6 according to Embodiment 3. As shown by a waveform a in Fig. 9, the driving circuit 6 uses, as a driving signal to be output to the piezoelectric element 5, a rectangular wave in which the high-wave period th having a voltage at a positive value and the low-wave period tl having a voltage at a negative value form one period.

[0062] In order to change the effective voltage Veff, the driver circuit 6 fixes the voltage to a low level (-Vpp) in a decimation time period tz, as shown by a waveform b in Fig. 9. In waveform b in Fig. 9, the decimation time period tz includes two periods and a pulse signal is decimated for every two periods. It is noted that in the waveform b in Fig. 9, the voltage in the decimation time period tz is fixed to the low level (-Vpp), but the voltage in the decimation time period tz may be fixed to a high level (+Vpp).

[0063] In the case where the voltage in the decimation time period tz is fixed to the low level (-Vpp) or the high level (+Vpp) as shown by the waveform b in Fig. As shown in Figure 9, an average voltage over a plurality of periods does not become 0 (zero) V, but takes a negative value (in the case of fixing at the high level (+Vpp), the average voltage takes a positive value). When the average voltage of the drive signal is not 0 (zero) V, an offset DC voltage is applied to the piezoelectric element 5, and electrochemical migration between both electrodes of the piezoelectric element 5 may be caused.

[0064] In this respect, fixed as by a waveform c in Fig. 9, the driver circuit 6 does not drive the voltage to the low level (-Vpp) or the high level (+Vpp) in the decimation time period tz, but fixes it to 0 (zero) V (GND). Specifically, in the case where the output circuit 62 is a half-bridge circuit including the first switch 62a and the second switch 62b shown in Fig. 8, the voltage in the decimation time period tz may be fixed to 0 (zero) V (GND) by the first switch 62a and the second switch 62b being in the OFF state.

[0065] Although the optical device 10 according to Embodiment 3 is described to change the effective voltage Veff by providing the decimation time period tz to a drive signal, this can be combined with the method described in Embodiment 1 in which the effective voltage Veff is changed by adjusting a duty ratio of a drive signal.

[0066] A generalized relationship between a drive signal in atomization mode and a drive signal in heating mode by using the decimation time period tz and a duty cycle of a drive signal is a relationship as represented by Formula 2. ∫{ta_1 / (th_1+tl_1+tz)}dt>∫{ta_2 / (th_2+tl_2+tz)}dt

[0067] Here, it is assumed that the sputtering mode includes the peak period th_1, the low time period tl_1, and the active time period ta_1, and the heating mode includes the peak period th_2, the low time period tl_2, and the active time period ta_2. Decimation time periods for the sputtering mode and the heating mode are both assumed to be the decimation time period tz. Further, the drive signal represented by Formula 2 preferably sets the peak period th_1 and the low time period tl_1 in the sputtering mode and the peak period th_2 and the low time period tl_2 in the heating mode such that an average value of a voltage over the predetermined time period dt is 0 (zero) V. (Example 4)

[0068] Embodiment 1 describes the optical device 10 capable of changing the effective voltage Veff by adjusting a duty cycle of a drive signal. However, the method for changing the effective voltage Veff is not limited to this, and a method for changing a load of a drive circuit may be employed. Embodiment 4 describes an optical device capable of reducing an effective voltage by inserting a filter circuit between a drive circuit and a piezoelectric element to change a load of the drive circuit. The optical device according to Embodiment 4 has the same configurations as the optical device 10 according to Embodiment 1, and therefore, the same configurations will be described using the same reference numerals to avoid repeating the detailed description.

[0069] Fig. 10 is a circuit diagram for explaining a configuration of a driving circuit 6B according to Embodiment 4. The driving circuit 6B includes the control circuit 61, the output circuit 62, the current detection circuit 63, the capacitor 64, the resistor 65, and a filter circuit 66. The filter circuit 66 is not necessarily included in the driving circuit, but the filter circuit 66 may be inserted between the driving circuit 6 and the piezoelectric element 5 shown in Fig. 2, or may be inserted between the driver circuit 6A and the piezoelectric element 5 shown in Fig. 8. It is noted that with respect to the driver circuit 6B shown in Fig. 10, the same configurations as those of the driver circuit 6A shown in Fig. 8 are designated by the same reference numerals in order not to repeat the detailed description.

[0070] The filter circuit 66 is a low-pass filter (LPF) comprising a resistor 66a and a capacitor 66b. The filter circuit 66 can output, in a signal form approximating a triangular wave, a square-wave drive signal obtained by switching the first switch 62a and the second switch 62b at a switching frequency significantly higher than (for example, about one-tenth) a time constant (RC). Fig. 11 is a graph for explaining characteristics of the filter circuit 66 included in the driver circuit 6B according to Embodiment 4. In Fig. 11 a horizontal axis indicates time and a vertical axis indicates response.

[0071] The filter circuit 66 outputs in a form of a signal approximating a triangular wave as shown in Fig. 11, an input square wave drive signal, thereby being able to reduce an effective voltage of the drive signal. In a case where the voltage of the difference (peak-to-peak value) between a maximum value and a minimum value of a signal approximating a triangular wave is the same as the voltage of the difference (peak-to-peak value) between a maximum value (+Vpp) and a minimum value (-Vpp) of a drive signal, an effective voltage of the signal approximating a triangular wave is about half of an effective voltage of the drive signal. It is noted that in the case of the signal approximating a triangular wave as in Fig. 11, the driving circuit 6B causes the DC voltage Vout_1 for generating a driving signal (AC signal) that drives the piezoelectric element 5 in the sputtering mode to vibrate the outermost layer lens 1 to be the same as the DC voltage Vout_(underline)2 for generating a driving signal that drives the piezoelectric element 5 in the heating mode (Vout_1 = Vout_2).

[0072] The driver circuit 6B, which is Fig. 10 includes one stage of the filter circuit 66 inserted between the output circuit 62 and the piezoelectric element 5. However, the configuration is not limited to this, and multiple stages of the filter circuit 66 may be inserted in the drive circuit 6B. The drive circuit 6B may include multiple stages of the filter circuit 66 inserted between the output circuit 62 and the piezoelectric element 5 to output a sine wave drive signal.

[0073] As in Fig.As illustrated in FIG. 3, a frequency of a drive signal that drives the piezoelectric element 5 in the sputtering mode is lower than a frequency of a drive signal that drives the piezoelectric element 5 in the heating mode. Therefore, the drive circuit 6B causes the time constant (RC) to be less than half a period of a drive signal that drives the piezoelectric element 5 in the sputtering mode and more than half a period of a drive signal that drives the piezoelectric element 5 in the heating mode. In this way, the effective voltage Veff_1 in the sputtering mode can be higher than the effective voltage Veff_2 in the heating mode (Veff_1>Veff_2).

[0074] Furthermore, the resistor 66a and the capacitor 66b included in the filter circuit 66 may have a variable resistance and a variable capacitance, respectively, so that the driver circuit 6B can change a resistance value of the resistor 66a and a capacitance value of the capacitor 66b according to a current value detected by the current detection circuit 63. The driver circuit 6B changes the resistance value of the resistor 66a and the capacitance value of the capacitor 66b according to the current value detected by the current detection circuit 63, thereby being able to adjust a difference in behavior attributable to an individual difference of devices and temperature characteristics.

[0075] It is noted that the configuration of the driver circuit 6B according to Embodiment 4 may be combined with an optical device according to another embodiment. (Modifications)

[0076] In the optical device 10 according to the embodiments, the cross-sectional shape of the support part 33 is described as an S-shape. However, the cross-sectional shape of the support part is not limited to an S-shape as long as such a shape does not cause stress concentration on the vibrating body. For example, the cross-sectional shape of the support part 33 may be a shape in which a plurality of S-shapes are coupled together. Since the cross-sectional shape of the support part 33 may be any shape having a smaller portion with less stress concentration thereon in the support part 33, alternatively, the cross-sectional shape may be a curved shape having one half of an S-shape.

[0077] The imaging unit 100 according to the embodiments described above may include a camera, a LiDAR, a radar, and the like. Additionally, a plurality of imaging units 100 may be arranged side by side.

[0078] The image forming unit 100 according to the above-described embodiments is not limited to an image forming unit provided in a vehicle, but can similarly be applied to any image forming unit that includes an optical device and an image forming element, is arranged such that a light-transmitting body is arranged in a viewing direction thereof, and needs to remove foreign matter on a light-transmitting body. (Aspects) 1. An optical device according to the present disclosure comprises: a light-transmitting body configured to transmit light having a predetermined wavelength; a housing configured to hold the translucent body; a vibrating body configured to contact the translucent body held by the housing; a piezoelectric element provided on the vibrating body and configured to vibrate the vibrating body; and a driver circuit configured to drive the piezoelectric element, wherein the vibrating body is a cylindrical body and comprises a first end and a second end on a side opposite to the first end, the first end contacting the light-transmitting body, the piezoelectric element being provided at the second end, and the driver circuit causes a voltage Vp-p_1 of an alternating current signal that drives the piezoelectric element in a first vibration mode among a plurality of vibration modes to vibrate the light-transmitting body to be the same as a voltage Vp-p_(underline)2 of an alternating current signal that drives the piezoelectric element in a second vibration mode among the plurality of vibration modes, and drives the piezoelectric element such that an effective voltage Veff_1 applied to the piezoelectric element within a predetermined time period in the first vibration mode is different from an effective voltage Veff_2 applied to the piezoelectric element within the predetermined time period in the second vibration mode. 2. In the optical device according to (1), the driving circuit drives the piezoelectric element such that the effective voltage Veff_1 applied to the piezoelectric element within the predetermined time period in the first vibration mode is higher than the effective voltage Veff_2 applied to the piezoelectric element within the predetermined time period in the second vibration mode. 3. In the optical device according to (1) or (2), the driving circuit drives the piezoelectric element such that a vibration amplitude Av_1 of the light-transmitting body in the first vibration mode is larger than a vibration amplitude Av_2 of the light-transmitting body in the second vibration mode, and a power Pv_1 input in the first vibration mode is smaller than a power Pv_2 input in the second vibration mode. 4. In the optical device according to any one of (1) to (3), the drive circuit drives the piezoelectric element such that a first integral value is larger than a second integral value, wherein the first integral value is an integral of a duty ratio of an AC signal that drives the piezoelectric element in the first vibration mode over the predetermined time period, wherein the second integral value is an integral of a duty ratio of an AC signal that drives the piezoelectric element in the second vibration mode over the predetermined time period. 5. In the optical device according to (4), the driving circuit drives the piezoelectric element such that an average value of a voltage applied to the piezoelectric element over the predetermined time period is 0 (zero) V. 6. In the optical device according to (4) or (5), the driving circuit drives the piezoelectric element such that an AC signal driving the piezoelectric element includes a time period during which a voltage value is 0 (zero) and the first integral value is larger than the second integral value. 7. In the optical device according to any one of (1) to (6) includes the driver circuit a current detection circuit configured to detect a value of a current flowing through the piezoelectric element, and a control circuit configured to change a duty ratio of an AC signal driving the piezoelectric element according to the current value detected by the current detection circuit to perform control such that the effective voltage Veff_1 is greater than the effective voltage Veff_2. 8. In the optical device according to any one of (1) to (7) the driver circuit outputs an alternating current signal to the piezoelectric element via a filter circuit and a time constant of the filter circuit is less than half a period of an AC signal driving the piezoelectric element in the first vibration mode and more than half a period of an AC signal driving the piezoelectric element in the second vibration mode. 9. In the optical device according to any one of (1) to (8) the first vibration mode is a atomization mode in which the translucent body is vibrated to atomize foreign matter adhering to the translucent body, and the second vibration mode is a heating mode in which the translucent body is vibrated to heat the translucent body. 10. The optical device according to (9) further comprises: a switching part configured to switch a mode for vibrating the translucent body among the plurality of vibration modes, and the switching part switches between the atomization mode and the heating mode based on an image captured by an image forming element. 11. Another optical device according to the present disclosure comprises: a light-transmitting body configured to transmit light having a predetermined wavelength; a housing configured to hold the translucent body; a vibrating body configured to contact the translucent body held by the housing; a piezoelectric element provided on the vibrating body and configured to vibrate the vibrating body; and a driver circuit configured to drive the piezoelectric element, wherein the vibrating body is a cylindrical body and comprises a first end and a second end on a side opposite to the first end, the first end contacting the light-transmitting body, the piezoelectric element being provided at the second end, and the driver circuit a driver power supply circuit and an output circuit configured to convert a DC voltage output from the driver power supply circuit into an AC signal, causes the DC voltage Vout_1 for generating an AC signal that drives the piezoelectric element in a first vibration mode among a plurality of vibration modes to vibrate the light-transmitting body to be the same as the DC voltage Vout_(underline)2 for generating an AC signal that drives the piezoelectric element in a second vibration mode among the plurality of vibration modes, and drives the piezoelectric element such that an effective voltage Veff_1 applied to the piezoelectric element within a predetermined time period in the first vibration mode is different from an effective voltage Veff_2 applied to the piezoelectric element within the predetermined time period in the second vibration mode. 12. An image forming unit according to the present disclosure comprises: the optical device according to any one of (1) to (11); and an image forming element arranged such that the light-transmitting body is arranged in a viewing direction thereof.

[0079] The embodiments disclosed herein are to be considered in all respects as illustrative and not restrictive. The scope of the present disclosure is defined by the appended claims rather than by the foregoing description, and is intended to include any changes within the scope and meaning equivalent to the appended claims. List of reference symbols 1 outermost layer lens 2 housings 2a Disc spring 2b holder 3 vibration bodies 4 Inner layer lens 5 piezoelectric element 6, 6A, 6B driver circuit 7 Driver power supply circuit 10 optical device 20 imaging element 61 Control circuit 62 Output circuit 63 Current detection circuit 64, 66b capacitor 65, 66a resistance 66 filter circuit 100 image generation unit QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 2020 / 0282435

[0004]

Claims

[1] Optical device having the following features: a light-transmitting body configured to transmit light having a predetermined wavelength; a housing configured to hold the translucent body; a vibrating body configured to contact the translucent body held by the housing; a piezoelectric element provided on the vibrating body and configured to vibrate the vibrating body; and a driver circuit configured to drive the piezoelectric element, wherein the vibrating body is a cylindrical body and has a first end and a second end on a side opposite to the first end, the first end contacting the light-transmitting body, the piezoelectric element being provided at the second end, and the driver circuit causes a voltage Vp-p_1 of an alternating current signal that drives the piezoelectric element in a first vibration mode among a plurality of vibration modes to vibrate the light-transmitting body to be the same as a voltage Vp-p_(underline)2 of an alternating current signal that drives the piezoelectric element in a second vibration mode among the plurality of vibration modes, and drives the piezoelectric element such that an effective voltage Veff_1 applied to the piezoelectric element within a predetermined time period in the first vibration mode is different from an effective voltage Veff_2 applied to the piezoelectric element within the predetermined time period in the second vibration mode. [2] The optical device according to claim 1, wherein the driving circuit drives the piezoelectric element such that the effective voltage Veff_1 applied to the piezoelectric element within the predetermined time period in the first vibration mode is higher than the effective voltage Veff_2 applied to the piezoelectric element within the predetermined time period in the second vibration mode. [3] The optical device according to claim 1 or 2, wherein the driving circuit drives the piezoelectric element such that a vibration amplitude Av_1 of the light-transmitting body in the first vibration mode is larger than a vibration amplitude Av_2 of the light-transmitting body in the second vibration mode, and a power Pv_1 input in the first vibration mode is smaller than a power Pv_2 input in the second vibration mode. [4] The optical device according to any one of claims 1 to 3, wherein the driving circuit drives the piezoelectric element such that a first integral value is greater than a second integral value, the first integral value being an integral of a duty ratio of an AC signal driving the piezoelectric element in the first vibration mode over the predetermined time period, the second integral value being an integral of a duty ratio of an AC signal driving the piezoelectric element in the second vibration mode over the predetermined time period. [5] An optical device according to claim 4, wherein the driving circuit drives the piezoelectric element such that an average value of a voltage applied to the piezoelectric element over the predetermined time period is 0 (zero) V. [6] An optical device according to claim 4 or 5, wherein the driving circuit drives the piezoelectric element such that an AC signal driving the piezoelectric element has a time period during which a voltage value is 0 (zero) and the first integral value is larger than the second integral value. [7] Optical device according to one of claims 1 to 6, wherein the driver circuit has the following features: a current detection circuit configured to detect a value of a current flowing through the piezoelectric element, and a control circuit configured to change a duty ratio of an AC signal driving the piezoelectric element according to the current value detected by the current detection circuit to perform control such that the effective voltage Veff_1 is greater than the effective voltage Veff_2. [8] Optical device according to one of claims 1 to 7, in which the driver circuit outputs an alternating current signal to the piezoelectric element via a filter circuit and a time constant of the filter circuit is less than half a period of an AC signal driving the piezoelectric element in the first vibration mode and more than half a period of an AC signal driving the piezoelectric element in the second vibration mode. [9] Optical device according to one of claims 1 to 8, in which the first vibration mode is a atomization mode in which the translucent body is vibrated to atomize foreign matter adhering to the translucent body, and the second vibration mode is a heating mode in which the translucent body is vibrated to heat the translucent body. [10] Optical device according to claim 9, further comprising: a switching part configured to switch a mode for vibrating the translucent body among the plurality of vibration modes, wherein the switching part switches between the atomization mode and the heating mode based on an image captured by an image forming element. [11] Optical device having the following features: a light-transmitting body configured to transmit light having a predetermined wavelength; a housing configured to hold the translucent body; a vibrating body configured to contact the translucent body held by the housing; a piezoelectric element provided on the vibrating body and configured to vibrate the vibrating body; and a driver circuit configured to drive the piezoelectric element, wherein the vibrating body is a cylindrical body and comprises a first end and a second end on a side opposite to the first end, the first end contacting the light-transmitting body, the piezoelectric element being provided at the second end, and the driver circuit a driver power supply circuit and an output circuit configured to convert a DC voltage output from the driver power supply circuit into an AC signal, causes the DC voltage Vout_1 for generating an AC signal that drives the piezoelectric element in a first vibration mode among a plurality of vibration modes to vibrate the light-transmitting body to be the same as the DC voltage Vout_(underline)2 for generating an AC signal that drives the piezoelectric element in a second vibration mode among the plurality of vibration modes, and drives the piezoelectric element such that an effective voltage Veff_1 applied to the piezoelectric element within a predetermined time period in the first vibration mode is different from an effective voltage Veff_2 applied to the piezoelectric element within the predetermined time period in the second vibration mode. [12] Image forming unit having the following features: the optical device according to any one of claims 1 to 11; and an image forming element arranged such that the light-transmitting body is arranged in a viewing direction thereof.

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