Patent Description:
In recent years, an optical unit that includes an optical sensor such as an imaging element has been mounted on a front portion or a rear portion of a vehicle, and an image obtained by the optical unit has been used so as to control a safety device or so as to perform autonomous driving control. Since such an optical unit is often mounted on the outside of a vehicle, foreign matters such as raindrops, mud, and dust may sometimes adhere to a light-transmitting member (a lens or a protective cover) that covers the exterior of the optical unit. When a foreign matter adheres to the light-transmitting member, the adhered foreign matter is captured in an image that is obtained by the optical unit, so that a clear image cannot be obtained. In addition, in cold weather, ice or frost adheres to the surface of the light-transmitting member of the optical unit mounted on the outside of the vehicle, so that the optical unit cannot obtain a clear image.

Accordingly, an optical unit described in Patent Document <NUM> is capable of vibrating a light-transmitting member at a first frequency (in a cleaning mode) in order to remove a foreign matter adhering to a surface of the light-transmitting member and also vibrates the light-transmitting member at a second frequency (in a heating mode) in order to heat the light-transmitting member. More specifically, in the optical unit described in Patent Document <NUM>, a controller circuit switches the mode in which the light-transmitting member is vibrated between the cleaning mode and the heating mode.

In the optical unit described in Patent Document <NUM>, although the light-transmitting member is heated at the second frequency, which is different from the first frequency of the cleaning mode, a portion that is most desired to be vibrated and heated (e.g., the visual field range of the optical sensor) is not selectively heated, and the heating efficiency is low.

Document <CIT> discloses a vibration device making use of a piezoelectric element and used in a water droplet elimination device for a camera, an ultrasonic transducer device, a pump device, and the like, wherein the vibration device has drip-proof specifications such that the interior thereof is protected from liquid or outside air and a structure such that the piezoelectric element is not easily destroyed even with large amplitude. A vibration device is provided with a top plate elastic body and a cylindrical body having a first end part and a second end part and being linked to the top plate elastic body so as to hold the top plate elastic body on the first end part side. The cylindrical body is provided with an elongated ring shaped collar on the outer radial side of the cylindrical body on the second end part side. The vibration device is further provided with a piezoelectric element affixed to the ring-shaped collar so as to vibrate the cylindrical body.

<CIT> discloses another vibration device making use of vibrations of different frequencies.

Accordingly, it is an object of the present invention to provide an optical device capable of removing a foreign matter adhering to a light-transmitting member and selectively causing heat generation within the region of the light-transmitting member and an optical unit that includes an optical device.

In order to solve the above problem an optical unit according to claim <NUM> is provided.

According to the present invention, since a higher-order second vibration mode is selected so as to vibrate a light-transmitting member, a foreign matter adhering to the light-transmitting member can be removed, and heat generation can be selectively caused within the region of the light-transmitting member.

An optical unit according to an embodiment of the present invention will be described in detail below with reference to the drawings. Note that components denoted by the same reference signs in the drawings are the same or correspond to each other.

An optical unit according to a first embodiment will be described below with reference to the drawings. <FIG> is a schematic diagram illustrating the configuration of an optical unit <NUM> according to the first embodiment. <FIG> is a sectional view of the optical unit <NUM>, and <FIG> is a diagram illustrating the appearance of the optical unit <NUM>. The optical unit <NUM> is mounted on, for example, a front portion, a rear portion, or the like of a vehicle and is a unit that obtains information regarding the shape, the color, the temperature, and so forth of an object and information regarding, for example, the distance to an object. The optical unit <NUM> includes an optical sensor <NUM> that obtains information regarding the shape, the color, the temperature, and so forth of an object and information regarding, for example, the distance to an object and an optical device <NUM> that holds the optical sensor <NUM>. The optical device <NUM> includes an optical member that guides light to a sensor surface of the optical sensor <NUM>. The optical unit <NUM> is mounted on, for example, a vehicle as a result of the optical device <NUM> being fixed onto a support member <NUM>. Note that the optical unit <NUM> is not limited to being mounted on a vehicle and may be mounted on other apparatuses such as a ship or an aircraft.

When the optical unit <NUM> is used outside by being mounted on a vehicle or the like, foreign matters such as raindrops, mud, and dust may sometimes adhere to a light-transmitting member (a lens or a protective cover) that is arranged in the viewing direction of the optical sensor <NUM> and that covers the exterior of the optical sensor <NUM>. Accordingly, the optical device <NUM> includes removing means that removes a foreign matter adhering to the light-transmitting member.

More specifically, the optical device <NUM> includes a housing <NUM>, a transparent protective cover (light-transmitting member) <NUM> that is disposed on a surface of the housing <NUM>, and a vibrating body <NUM> that vibrates the protective cover <NUM>. The vibrating body <NUM> is connected to an excitation circuit <NUM> and vibrates the protective cover <NUM> on the basis of a signal from the circuit. The vibrating body <NUM> is the removing means and removes a foreign matter adhering to the protective cover <NUM> by vibrating the protective cover <NUM>. Note that the optical sensor <NUM> is disposed further inside than the protective cover <NUM> and is held by the housing <NUM>.

The housing <NUM> has a cylindrical shape and is made of, for example, a metal or a synthetic resin. Note that the housing <NUM> may have a different shape such as a rectangular columnar shape. The protective cover <NUM> is disposed at one end of the housing <NUM>, and the vibrating body <NUM> is disposed at the other end of the housing <NUM>.

For example, the vibrating body <NUM> is a piezoelectric vibrator (a piezoelectric element) that has a cylindrical shape or a shape obtained by dividing a cylindrical shape into a plurality of portions. The piezoelectric vibrator vibrates, for example, by being polarized in a thickness direction or a radial direction. The piezoelectric vibrator is made of a PZT-based piezoelectric ceramic. It goes without saying that a different piezoelectric ceramic such as (K, Na) NbO<NUM> may be used. Alternatively, a piezoelectric single crystal such as LiTaO<NUM> may be used.

The protective cover <NUM> has a dome-like shape extending from the one end of the housing <NUM>. In the present embodiment, this dome-like shape is a hemispherical shape. Note that the viewing angle of the optical sensor <NUM> is, for example, <NUM> degrees. Obviously, the dome-like shape is not limited to a hemispherical shape and may be a shape in which a cylinder is contiguous to a hemisphere or a shape having a surface curved less than a hemisphere. The protective cover <NUM> may be a flat plate. The entire protective cover <NUM> is at least transparent to light of a wave length targeted by the optical sensor <NUM>. Thus, the light that passes through the protective cover <NUM> may be visible light or invisible light.

In the present embodiment, the protective cover <NUM> is made of glass. However, the protective cover <NUM> is not limited to being made of glass and may be made of a resin such as a transparent plastic. Alternatively, the protective cover <NUM> may be made of a light-transmitting ceramic. Depending on the application, it is naturally preferable to use tempered glass. By using tempered glass, the strength of the protective cover <NUM> can be enhanced. In the case where the protective cover <NUM> is made of a resin, examples of the resin includes acrylic, cycloolefin, polycarbonate and polyester. In addition, a coating layer made of DLC or the like may be formed over a surface of the protective cover <NUM> in order to enhance the strength of the protective cover <NUM>, and a hydrophilic film, a water-repellent film, or an oleophilic or oleophobic coating layer may be formed for the purpose of, for example, imparting soil resistance to the surface or removing raindrops from the surface.

The protective cover <NUM> may be a simple glass cover or may be formed of an optical component such as a concave lens, a convex lens, or a flat lens. An additional optical component may be disposed further inside than the protective cover <NUM>. The method of joining the protective cover <NUM> and the housing <NUM> to each other is not particularly limited. The protective cover <NUM> and the housing <NUM> may be joined to each other by using an adhesive, by welding them together, by fitting them together, by press-fitting them together, or the like.

The above-mentioned optical sensor <NUM> is positioned further inside than the protective cover <NUM>. The optical sensor <NUM> may be an image sensor such as a complementary metal oxide semiconductor (CMOS) or a charge coupled device (CCD) or may be a light detection and ranging (LiDAR) sensor that uses a laser beam. In the case of using an image sensor as the optical sensor <NUM>, the optical sensor <NUM> captures an image of an image capturing target, which is present outside, through the protective cover <NUM>.

Another example of the removing means, which removes a foreign matter adhering to the light-transmitting member, besides the vibrating body <NUM> is a rotation mechanism that rotates the light-transmitting member. Such a rotation mechanism may be used in combination with the vibrating body <NUM> to form the removing means.

The vibrating body <NUM> is used as the removing means (driven in a cleaning mode) that removes a foreign matter adhering to the protective cover <NUM> by vibrating the protective cover <NUM>, and the vibrating body <NUM> can also be used as a heating unit (driven in a heating mode) that vibrates the protective cover <NUM> so as to heat the protective cover <NUM> by utilizing mechanical loss of vibration. Driving of the vibrating body <NUM> in the cleaning mode and driving of the vibrating body <NUM> in the heating mode will be described in detail below.

<FIG> is a schematic diagram illustrating the case in which the vibrating body <NUM> according to the first embodiment is driven in the cleaning mode. <FIG> illustrates the position of a maximum vibration displacement 12a of the protective cover <NUM> when the vibrating body <NUM> is driven in the cleaning mode. <FIG> illustrates the amplitude of vibration when the protective cover <NUM> is assumed to be a flat plate and vibrated in the cleaning mode. <FIG> illustrates a result of finite element method (FEM) analysis in the case where the vibrating body <NUM> is driven in the cleaning mode.

The vibrating body <NUM> can be driven in the cleaning mode by driving the vibrating body <NUM> at, for example, about <NUM>. When the vibrating body <NUM> is driven in the cleaning mode, as illustrated in <FIG>, the maximum vibration displacement 12a occurs at a center portion of the protective cover <NUM>. As illustrated in <FIG>, when the protective cover <NUM> is assumed to be a flat plate, a portion at which the amount of vibration displacement is large is the center portion of the protective cover <NUM> (antinode of vibration), and a portion at which the amount of vibration displacement is small is the peripheral edge portion of the protective cover <NUM> (node of vibration).

A mechanical vibration mode of a circular member can be expressed as a (x, y) vibration mode. Here, the letter x represents the number of nodes existing in a radial direction, and the letter y represents the number of nodes existing in a direction in which the circular member circulates. The letters x and y each represent an integer. In the protective cover <NUM> illustrated in <FIG>, since there are no nodes in the radial direction, x = <NUM> is satisfied, and since there are also no nodes in the direction in which the protective cover <NUM> circulates, y = <NUM> is satisfied. Thus, the vibration mode is a (<NUM>, <NUM>) vibration mode. As illustrated in <FIG>, the result of FEM analysis when the protective cover <NUM> is vibrated in the (<NUM>, <NUM>) vibration mode is a concentric circle mode in which a maximum vibration displacement portion <NUM> is located at the top portion (center portion) of the dome-like shape of the protective cover <NUM>.

<FIG> is a schematic diagram illustrating the case in which the vibrating body <NUM> according to the first embodiment is driven in the heating mode. <FIG> illustrates the position of the maximum vibration displacement 12a of the protective cover <NUM> when the vibrating body <NUM> is driven in the heating mode. <FIG> illustrates the amplitude of vibration when the protective cover <NUM> is assumed to be a flat plate and vibrated in the heating mode. <FIG> illustrates a result of FEM analysis in the case where the vibrating body <NUM> is driven in the heating mode.

The vibrating body <NUM> can be driven in the heating mode by driving the vibrating body <NUM> at, for example, about <NUM>. When the vibrating body <NUM> is driven in the heating mode, as illustrated in <FIG>, the maximum vibration displacement 12a occurs at the center portion of the protective cover <NUM>, and a node 12b occurs in a radial direction. As illustrated in <FIG>, when the protective cover <NUM> is assumed to be a flat plate, a portion at which the amount of vibration displacement is large is the center portion and the peripheral edge portion of the protective cover <NUM> (antinodes of vibration), and a portion at which the amount of vibration displacement is small is located at a position between the center portion of the protective cover <NUM> and the peripheral edge portion of the protective cover <NUM> (node of vibration). Note that the maximum vibration displacement 12a in the heating mode is within a region of the protective cover <NUM> that corresponds to the field of view of the optical sensor <NUM>. Thus, ice or frost formed within the region of the protective cover <NUM> corresponding to the field of view of the optical sensor <NUM> can be quickly removed.

In the protective cover <NUM> illustrated in <FIG>, since there is the node 12b in the radial direction, x = <NUM> is satisfied, and since there are no nodes in the direction in which the protective cover <NUM> circulates, y = <NUM> is satisfied. Thus, the vibration mode is a (<NUM>, <NUM>) vibration mode. As illustrated in <FIG>, the result of FEM analysis when the protective cover <NUM> is vibrated in the (<NUM>, <NUM>) vibration mode is a concentric circle mode in which a maximum vibration displacement portion <NUM> is located at the top portion of the dome-like shape of the protective cover <NUM>. Note that the number of nodes in the vibration mode of the cleaning mode is smaller than that in the vibration mode of the heating mode. In other words, when the number of nodes x = n(≥<NUM>), and the number of nodes x in the vibration mode of the heating mode = m(> <NUM>), the vibration mode of the cleaning mode is a higher-order vibration mode in which a relationship of n>m is satisfied.

<FIG> is a graph illustrating a relationship between the resonant frequency and the impedance of the piezoelectric vibrator when the vibrating body <NUM> according to the first embodiment is driven in the heating mode. As seen from <FIG>, the resonant frequency of the piezoelectric vibrator of the vibrating body <NUM> is around about <NUM>, and the impedance of the piezoelectric vibrator varies greatly. In this case, the coupling coefficient that indicates the efficiency with which electric energy applied to the piezoelectric vibrator is converted into mechanical energy is <NUM>%, which is a large value.

When the vibrating body <NUM> is driven in the heating mode, the piezoelectric vibrator of the vibrating body <NUM> is polarized over the entire surfaces of its cylindrical shape and vibrates in a width vibration mode and a higher-order vibration mode of the width vibration mode, or a thickness longitudinal vibration mode. The width vibration mode and the thickness longitudinal vibration mode will now be described. <FIG> is a schematic diagram illustrating vibration of the vibrating body <NUM> according to the first embodiment. <FIG> illustrates the width vibration of the vibrating body <NUM>. <FIG> illustrates the thickness longitudinal vibration of the vibrating body <NUM>.

The vibrating body <NUM> can vibrate in the width vibration mode, in which the vibrating body <NUM> expands and contracts in the radial direction, as a result of a poling treatment being performed on the entire surfaces of the cylindrical piezoelectric vibrator in the thickness direction. In other words, the width vibration mode is a vibration mode in which a position 13a of the vibrating body <NUM> expands and contracts in the directions of arrows illustrated in <FIG>.

In addition, the vibrating body <NUM> can vibrate in the thickness longitudinal vibration mode, in which the vibrating body <NUM> expands and contracts in the thickness direction, as a result of a poling treatment being performed on the entire surfaces of the cylindrical piezoelectric vibrator in the thickness direction. In other words, the thickness longitudinal vibration mode is a vibration mode in which a position 13b of the vibrating body <NUM> expands and contracts in the directions of arrows illustrated in <FIG>.

When the vibrating body <NUM> is vibrated in the heating mode, the efficiency of heating the protective cover <NUM> is increased by vibrating the vibrating body <NUM> in a vibration mode with a high coupling coefficient. In addition, by vibrating the top portion of the dome-shaped protective cover <NUM>, heat generation due to the mechanical loss of the vibration on the side on which the piezoelectric vibrator is located, heat generation due to the dielectric loss, and heat generation due to the mechanical loss of the vibration on the side on which the top portion of the dome-shaped protective cover <NUM> is located occur simultaneously, so that the efficiency of heating the protective cover <NUM> is increased.

Thus, the drive frequency in the heating mode (a second vibration mode) is about <NUM> and is higher than the drive frequency in the cleaning mode (a first vibration mode), which is about <NUM>. According to the claimed invention, the drive frequency in the heating mode (the second vibration mode) is five times or higher the drive frequency in the cleaning mode (the first vibration mode). However, since it is necessary to cause the piezoelectric vibrator of the vibrating body <NUM> to vibrate in the width vibration mode and the higher-order vibration mode of the width vibration mode or the thickness longitudinal vibration mode, the drive frequency in the heating mode (the second vibration mode) is set to <NUM> or lower.

Next, temperature changes in the protective cover <NUM> when the vibrating body <NUM> is vibrated in the heating mode will be described. <FIG> is a temperature profile of the protective cover <NUM> when the vibrating body <NUM> according to the first embodiment is driven in the heating mode. <FIG> illustrates temperature changes in the protective cover <NUM> in the heating mode, in which the vibrating body <NUM> is driven at <NUM> and temperature changes in the protective cover <NUM> in the cleaning mode, in which the vibrating body <NUM> is driven at <NUM>. Note that a driving signal that is applied to the vibrating body <NUM> is a signal having a sinusoidal waveform with an amplitude of <NUM> V.

As seen from <FIG>, when the vibrating body <NUM> is driven in the cleaning mode, the temperature of the protective cover <NUM> can be increased only by about <NUM> as a result of heating the protective cover <NUM> for <NUM> seconds. In contrast, when the vibrating body <NUM> is driven in the heating mode, the temperature of the protective cover <NUM> can be increased by about <NUM> as a result of heating the protective cover <NUM> for <NUM> seconds. In other words, in the cleaning mode, a foreign matter (e.g., a waterdrop or the like) adhering to the surface of the protective cover <NUM> can be atomized and removed by vibrating the center portion of the protective cover <NUM> to a large extent without heating the protective cover <NUM>. In contrast, in the heating mode, the protective cover <NUM> can be heated quickly by vibrating the center portion of the protective cover <NUM> to a large extent.

As described above, the optical device <NUM> according to the first embodiment includes the protective cover <NUM>, which is arranged in the viewing direction of the optical sensor <NUM>, the housing <NUM> at one end of which the protective cover <NUM> is held, and the vibrating body <NUM> that vibrates the protective cover <NUM> by using the piezoelectric vibrator (piezoelectric element) disposed along the other end of the housing <NUM>. The vibrating body <NUM> vibrates the protective cover <NUM> by selecting, from a plurality of vibration modes in which the protective cover <NUM> is vibrated, the cleaning mode (first vibration mode) in which the vibration displacement of the protective cover <NUM> becomes maximum and the higher-order heating mode (second vibration mode) in which the number of nodes of vibration (the number of nodes) is larger than that in the first vibration mode. In the heating mode, the position of the maximum vibration displacement in this vibration mode is within the region of the protective cover <NUM> corresponding to the field of view of the optical sensor <NUM>.

In the optical device <NUM> according to the first embodiment, since the higher-order heating mode is selected so as to vibrate the protective cover <NUM>, a foreign matter adhering to the protective cover <NUM> can be removed, and heat generation can be selectively caused within the region of the protective cover <NUM>. In addition, since the position of the maximum vibration displacement 12a in the heating mode is within the region of the protective cover <NUM> corresponding to the field of view of the optical sensor <NUM>, ice or frost formed within the region of the protective cover <NUM> corresponding to the field of view of the optical sensor <NUM> can be quickly removed.

The protective cover <NUM> may be excited in the heating mode by driving the piezoelectric vibrator of the vibrating body <NUM> in at least one of the width vibration mode, the higher-order vibration mode of the width vibration mode, and the thickness longitudinal vibration mode. As a result, the vibrating body <NUM> can be vibrated in a vibration mode with a high coupling coefficient, and the efficiency of heating the protective cover <NUM> is increased.

The cleaning mode may be a (n (≥<NUM>), <NUM>) vibration mode of the protective cover <NUM>, and the heating mode may be a (m (>n), <NUM>) vibration mode of the protective cover <NUM>. As a result, the efficiency with which the vibrating body <NUM> heats the protective cover <NUM> is increased.

In the heating mode, the position of the maximum vibration displacement 12a may be the center position in the region of the protective cover <NUM> corresponding to the field of view of the optical sensor <NUM>. As a result, ice or frost formed at the center position in the region of the protective cover <NUM> corresponding to the field of view of the optical sensor <NUM> can be quickly removed.

The optical unit <NUM> includes the optical sensor <NUM> and the above-described optical device <NUM>. Consequently, in the optical unit <NUM>, the higher-order heating mode is selected so as to vibrate the protective cover <NUM>. Thus, a foreign matter adhering to the protective cover <NUM> can be removed, and heat generation can be selectively caused within the region of the protective cover <NUM>.

The configuration of the optical device according to the first embodiment has been described above in which the vibrating body <NUM> vibrates the protective cover <NUM> in the cleaning mode or the heating mode. The configuration of an optical device according to a second embodiment will now be described in which the vibrating body <NUM> vibrates the protective cover <NUM> in the two vibration modes, which are the cleaning mode and the heating mode.

<FIG> is a diagram illustrating a driving signal that is supplied to the vibrating body <NUM> according to the second embodiment. <FIG> is an enlarged view of a period I illustrated in <FIG>. In <FIG> and <FIG>, the horizontal axis denotes time, and the vertical axis denotes voltage. Note that an optical unit according to the second embodiment has a configuration the same as that of the optical unit <NUM> illustrated in <FIG>. The same components will be denoted by the same reference signs, and detailed descriptions thereof will not be repeated. In addition, an optical device according to the second embodiment has a configuration the same as that of the optical device <NUM> illustrated in <FIG>. The same components will be denoted by the same reference signs, and detailed descriptions thereof will not be repeated.

The vibrating body <NUM> according to the second embodiment vibrates the protective cover <NUM> in the two vibration modes, which are the cleaning mode and the heating mode, and thus, a driving signal for the cleaning mode and a driving signal for the heating mode are superimposed as illustrated in <FIG>. In other words, the driving signal illustrated in <FIG> is obtained by superimposing a driving signal of <NUM> for causing the protective cover <NUM> to vibrate in the heating mode on a driving signal of <NUM> for causing the protective cover <NUM> to vibrate in the cleaning mode. The period I corresponds to one cycle of the driving signal of <NUM>, and as seen from <FIG>, during this one cycle, the driving signal fluctuates with a cycle of <NUM>.

The excitation circuit <NUM> simultaneously applies the driving signal having a frequency (e.g., <NUM>) for the cleaning mode, in which the maximum vibration displacement occurs at the top portion of the dome-shaped protective cover <NUM>, and the driving signal having a frequency (e.g., <NUM>) for the heating mode, in which the maximum vibration displacement occurs at the top portion of the dome-shaped protective cover <NUM> and in which the protective cover <NUM> is heated, to the vibrating body <NUM>, so that cleaning of the protective cover <NUM> and heating of the protective cover <NUM> can be simultaneously performed by superimposing the two vibration modes.

As described above, in the optical device according to the second embodiment, the vibrating body <NUM> vibrates the protective cover <NUM> by superimposing the heating mode on the cleaning mode. By superimposing the cleaning mode and the heating mode so as to vibrate the protective cover <NUM>, removal (cleaning) of a foreign matter adhering to the surface of the protective cover <NUM> and heating of the protective cover <NUM> can be performed simultaneously, and neither additional heating means nor a control unit that controls the additional heating means is necessary. Consequently, a reduction in the size of the optical device, a reduction in the manufacturing costs of the optical device, and an improvement in the reliability of the optical device can be achieved. In addition, removal (cleaning) of a foreign matter adhering to the surface of the protective cover <NUM> and melting of ice or frost formed on the surface of the protective cover <NUM> can be performed simultaneously, and the efficiency of removal of foreign matters is improved. Consequently, the visibility of the optical device can be improved in real time.

Note that, in <FIG>, the driving signal of <NUM> for vibrating the protective cover <NUM> in the heating mode is superimposed on the driving signal of <NUM> for vibrating the protective cover <NUM> in the cleaning mode in each period of the driving signal of <NUM>. However, the present invention is not limited to this, and the driving signal of <NUM> for vibrating the protective cover <NUM> in the heating mode may be superimposed on the driving signal of <NUM> for vibrating the protective cover <NUM> in the cleaning mode in some periods of the driving signal of <NUM>. In other words, the length of time over which the vibrating body <NUM> is driven so as to vibrate the protective cover <NUM> in the heating mode may be shorter than the length of time over which the vibrating body <NUM> is driven so as to vibrate the protective cover <NUM> in the cleaning mode.

Obviously, as described in the first embodiment, also in the case of driving the vibrating body <NUM> without superimposing the driving signal for vibrating the protective cover <NUM> in the cleaning mode and the driving signal for vibrating the protective cover <NUM> in the heating mode, the driving time in the heating mode may be shorter than the driving time in the cleaning mode.

The configuration of the optical device according to the first embodiment has been described above in which the protective cover <NUM> is vibrated in the heating mode, in which the maximum vibration displacement occurs at the top portion of the dome-shaped protective cover <NUM> and in which the protective cover <NUM> is heated. The configuration of an optical device according to a third embodiment will now be described in which the protective cover <NUM> is vibrated in the heating mode in which the maximum vibration displacement occurs at a portion of the protective cover <NUM> excluding the top portion of the dome-shaped protective cover <NUM> and in which the protective cover <NUM> is heated.

As illustrated in <FIG>, the position of a portion at which the amount of vibration displacement is large (antinode of vibration) and the position of a portion at which the amount of vibration displacement is small (node of vibration) change depending on the frequency of the driving signal for driving the vibrating body <NUM>. Thus, by changing the frequency of the driving signal for driving the vibrating body <NUM> such that the maximum vibration displacement occurs at a peripheral portion of the protective cover <NUM> excluding the top portion of the dome-shaped protective cover <NUM>, the peripheral portion of the protective cover excluding the top portion of the dome-shaped protective cover can be heated by using mechanical loss of vibration.

<FIG> is a diagram illustrating a result of FEM analysis in the case where the vibrating body according to the third embodiment is driven in the heating mode. <FIG> illustrates a result of FEM analysis in the case where the vibrating body <NUM> is driven by the driving signal having a frequency at which the maximum vibration displacement occurs at a peripheral portion of the protective cover <NUM> excluding the top portion of the dome-shaped protective cover <NUM>. <FIG> illustrates a result of FEM analysis in the case where the vibrating body <NUM> is driven by the driving signal having a frequency at which the maximum vibration displacement occurs at the top portion of the dome-shaped protective cover <NUM>.

<FIG> illustrates a vibration mode in which maximum vibration displacement portions 22a to <NUM> are located at a peripheral portion of the protective cover <NUM> excluding the top portion of the dome-shaped protective cover <NUM>, and the protective cover <NUM> can be heated by using the mechanical loss of the vibration at the positions of the maximum vibration displacement portions 22a to <NUM>. <FIG> illustrates a vibration mode in which a maximum vibration displacement portion <NUM> is located at the top portion of the dome-shaped protective cover <NUM>, and the protective cover <NUM> can be heated by using the mechanical loss of the vibration at the position of the maximum vibration displacement portion <NUM>.

The excitation circuit <NUM> illustrated in <FIG> can change frequency in order to switch between the vibration mode in which the maximum vibration displacement portions 22a to <NUM> are located at the positions illustrated in <FIG> and the vibration mode in which the maximum vibration displacement portion <NUM> is located at the position illustrated in <FIG>. In other words, the excitation circuit <NUM> also serves as a switching unit that switches the vibration mode in which the protective cover <NUM> is vibrated.

As described above, in the optical device according to the third embodiment, the excitation circuit <NUM> can switch to, as the heating mode, a vibration mode in which the maximum vibration displacement occurs at a position where heat generation is to be caused within the region of the protective cover <NUM> corresponding to the field of view of the optical sensor <NUM> in accordance with the position. As a result, an arbitrary portion of the protective cover <NUM> can be selected to be heated.

Note that, in order to easily change the position at which the maximum vibration displacement of the protective cover <NUM> occurs, instead of performing a poling treatment on the entire surfaces of the cylindrical piezoelectric vibrator of the vibrating body <NUM> in the thickness direction, it is desirable that the piezoelectric vibrator be divided into a plurality of portions and that a poling treatment be performed on the piezoelectric vibrator. <FIG> is a schematic diagram illustrating vibration of the vibrating body according to the third embodiment. <FIG> illustrates the case in which the piezoelectric vibrator of the vibrating body <NUM> is split into, for example, two portions and in which each of the piezoelectric vibrator portions is vibrated in the width vibration mode and the thickness longitudinal vibration mode. In <FIG>, vibrating bodies <NUM> and <NUM>, which are obtained by splitting the vibrating body <NUM> into two portions, are vibrated in the width vibration mode. In <FIG>, vibrating bodies <NUM> to <NUM>, which are obtained by splitting the vibrating body <NUM> into eight portions, are vibrated in the thickness longitudinal vibration mode.

The two separate vibrating bodies <NUM> and <NUM> are oppositely polarized to each other, or signals whose electric potentials are reversed so as to have phases differing from each other by <NUM> degrees are applied to the vibrating body <NUM> and the vibrating body <NUM>. As a result, as illustrated in <FIG>, vibration by which the vibrating body <NUM> expands in the horizontal direction indicated by arrows is excited, and vibration by which the vibrating body <NUM> contracts in the horizontal direction indicated by arrows is excited.

The two separate vibrating bodies <NUM> and <NUM> are oppositely polarized to each other, or signals whose electric potentials are reversed so as to have phases differing from each other by <NUM> degrees are applied to the vibrating body <NUM> and the vibrating body <NUM>. As a result, as illustrated in <FIG>, vibration by which the vibrating body <NUM> expands in the thickness direction indicated by arrows is excited, and vibration by which the vibrating body <NUM> contracts in the thickness direction indicated by arrows is excited.

By combining the vibrating bodies illustrated in <FIG>, various vibration modes can be easily formed. In other words, by inverting portions of the vibrating bodies that vibrate in the uniform vibration directions illustrated in <FIG>, the protective cover <NUM> can be vibrated in a new vibration mode that has a node in the radial direction and in which the direction of vibration is reversed at a split axis. When the protective cover <NUM> is vibrated in such a vibration mode, the protective cover <NUM> can be excited with higher efficiency than in the vibration mode illustrated in <FIG> as an example, and the bottom of the protective cover <NUM> can be effectively heated. In addition, for example, a vibrating body that is one of two vibrating bodies obtained by splitting a single vibrating body into two portions is driven in the thickness longitudinal vibration mode, so that the protective cover <NUM> can be locally heated by being vibrated only in the thickness direction. Note that, although <FIG> illustrates the case where the vibrating body is split into two portions, the present invention is not limited to this configuration, and the vibrating body may be split into three or more portions. In other words, the protective cover <NUM> is vibrated by using a piezoelectric vibrator that has been divided into a plurality of portions and that has undergone a poling treatment, so that the excitation circuit <NUM> can easily switch to, as the heating mode, a vibration mode in which the maximum vibration displacement occurs at a position where heat generation is to be caused within the region of the protective cover <NUM> corresponding to the field of view of the optical sensor <NUM> in accordance with the position. As a result, an arbitrary portion of the protective cover <NUM> can be selected to be heated.

Although the protective cover <NUM> has a dome-like shape in each of the optical devices according to the above-described embodiments, the protective cover <NUM> may have a plate-like shape.

Each of the optical units according to the above-described embodiments may include a camera, a LiDAR, a Rader, or the like.

Each of the optical units according to the above-described embodiments is not limited to an optical unit that is mounted onto a vehicle, and the present invention can also be applied to an optical unit for applications requiring cleaning of a light-transmitting member that is disposed in the field of view of the optical sensor.

Claim 1:
An optical unit comprising
an optical sensor; and
an optical device comprising:
a light-transmitting member that is arranged in a viewing direction of the optical sensor;
a cylindrical body at one end of which the light-transmitting member is held;
an excitation circuit configured to provide a signal according to a selection from a plurality of vibration modes; and
a vibrating body connected to the excitation circuit, wherein, based on a signal from the excitation circuit, the vibration body is configured to vibrate the light-transmitting member by using a piezoelectric element disposed along another end of the cylindrical body,
wherein the vibrating body is configured to vibrate the light-transmitting member in a first vibration mode of the plurality of vibration modes in which vibration displacement of the light-transmitting member becomes maximum and a higher-order second vibration mode of the plurality of vibration modes in which the number of nodes is larger than the number of nodes in the first vibration mode, and
wherein, in the second vibration mode, a position of a maximum vibration displacement in the second vibration mode is within a region of the light-transmitting member that corresponds to a field of view of the optical sensor,
wherein a drive frequency of the second vibration mode is five times or higher a drive frequency in the first vibration mode.