JP2012128029A - Liquid lens and control method for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid lens of which focal distance can be more highly accurately controlled by utilizing hysteresis characteristics and a control method of the liquid lens.SOLUTION: A liquid lens has hysteresis characteristics in which, between a first threshold value and a second threshold value of an applied voltage, a first range where a focal distance is different in a first operation for increasing the applied voltage and in a second operation for decreasing the applied voltage and the rate of change of the focal distance to the change in the applied voltage is smaller when performing the first operation than when performing the second operation, and a second range opposite to the first range are present. As to this liquid lens, when a change is made to the focal distance within the second range, the applied voltage value is placed in a state of equal to or more than the second threshold value once and then a control is made to change to a target voltage value, and when a change is made to the focal distance within the first range, the applied voltage value is placed in a state of equal to or less than the first threshold value once and then a control is made to change to a target voltage value.

Description

  The present invention relates to a variable focus liquid lens, and more particularly, to a liquid lens utilizing an electrowetting (hereinafter referred to as EW) phenomenon and a method for controlling optical characteristics of the liquid lens.

  In recent years, a variable focus liquid lens has attracted attention as an optical element. The liquid lens makes the focal length variable by changing the optical characteristics of the lens itself without providing a driving mechanism for moving the lens. As a liquid lens, one that performs electric drive control using the EW phenomenon has been proposed in Patent Document 1 and the like.

  The liquid lens based on the EW electric method described in Patent Document 1 is configured such that a droplet of an insulating liquid is immiscible with the droplet and is contained in a dielectric chamber together with a conductive liquid having a different refractive index. . The inner wall of the chamber is subjected to a surface treatment for improving the wettability of the conductor liquid. The first electrode is in contact with the conductor liquid. On the other hand, a second electrode having a circular opening is disposed on the outer surface of the chamber. And while applying a voltage between 1st and 2nd electrodes and controlling an applied voltage value, the shape of a droplet can be changed and a focal distance can be changed.

International Publication Number WO1999 / 018456

  On the other hand, the liquid lens based on the EW electrical method is focused on the same applied voltage value when the voltage value applied between the first and second electrodes is increased and when it is decreased. It is known to have so-called hysteresis characteristics with different distances.

  An object of the present invention is to provide a liquid lens capable of controlling the focal length with higher accuracy and its control method using the hysteresis characteristic.

  The liquid lens of the present invention that achieves the above object is a conductive or polar first liquid and an insulating or nonpolar material that does not mix with the first liquid and has a refractive index different from that of the first liquid. A container accommodated so as to form an interface having a curvature, a first electrode in contact with the first liquid, and the second liquid so as to face each other through an insulating layer. In the liquid lens including the provided second electrode and a voltage control unit that changes a focal length by controlling an applied voltage value applied between the first electrode and the second electrode. When the applied voltage value is equal to or less than the first threshold value or greater than or equal to the second threshold value, which is greater than the first threshold value, the focal length corresponds to the applied voltage value, and the applied voltage value is greater than the first threshold value. And less than the first threshold if less than the second threshold The focal length differs between when the first operation of increasing the voltage value from the state is performed and when performing the second operation of decreasing the voltage value from the state of the second threshold value or more, The rate of change of the focal length with respect to the change of the applied voltage value between the first and second focal lengths corresponding to the first and second threshold values is the first when the first operation is performed. The first range that is smaller than when the second operation is performed, and the rate of change of the focal length with respect to the change in the applied voltage value is smaller when the second operation is performed than when the first operation is performed. The voltage control unit changes the focal length from a state within or longer than the first range to a target focal length within the second range. After the applied voltage value is once set to a state equal to or higher than the second threshold value, the target focus is set. When the control is performed to change the voltage value corresponding to the separation, and the focal length is changed from the state within the second range or shorter than the target focal length within the first range, the applied voltage After the value is once brought to a state equal to or less than the first threshold value, control is performed to change the voltage value to a target focal length.

  In the control method of the present invention, in the above configuration, when the liquid lens is changed from a state in which the focal length is within the first range or longer than the target focal length in the second range, After the applied voltage value is once brought to a state equal to or greater than the second threshold value, control is performed to change the voltage value to a voltage value corresponding to a target focal length, and the liquid lens has a focal length within a second range or When changing from a shorter state to a target focal length within the first range, the voltage corresponding to the target focal length is set after the applied voltage value is once less than the first threshold. Control is performed to change the value.

  According to the present invention, the focal length can be controlled with higher accuracy.

1 is a schematic cross-sectional view of a liquid lens according to an embodiment of the present invention. The block diagram which shows the structural example of the voltage control part of FIG. The figure which shows the relationship between the applied voltage and focal distance in embodiment of FIG. The figure explaining the control method in case the target focal distance exists in the 2nd range in embodiment of FIG. The figure explaining the control method in case the target focal distance exists in the 1st range in the embodiment of FIG. The flowchart which shows the flow of control of the liquid lens in embodiment of FIG.

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

  FIG. 1 is a schematic cross-sectional view showing an embodiment of an EW electric type liquid lens according to the present invention. In FIG. 1, the symbol O indicates the optical axis of the liquid lens. The liquid lens has a rotationally symmetric shape with respect to the optical axis O. Each of the upper member 1 and the lower member 2 is made of a translucent flat plate member. These members 1 and 2 are arranged in parallel with each other at a predetermined interval by a frame or a spacer (not shown), and constitute a storage chamber (cell) that holds a liquid lens.

  On the inner surface of the lower member 2, a second electrode 3 having a circular opening 3a is provided. The second electrode 3 is made of a transparent electrode, and its opening has a rotationally symmetric shape with respect to the optical axis O. An insulating layer 4 is formed on the second electrode 3. A water-repellent layer 5 is formed in a circle around the optical axis O on the insulating layer 4, and a hydrophilic layer 6 is formed on the insulating layer 4 so as to surround the water-repellent layer 5. . These water repellent layer 5 and hydrophilic layer 6 constitute the inner wall of the storage chamber (cell).

  The accommodation chamber (cell) composed of the members 1 and 2 contains a conductive or polar first liquid 7 and an insulating or nonpolar second liquid 8. The first and second liquids do not mix with each other and have different refractive indexes. The second liquid 8 has hydrophobicity and is disposed so as to contact the water repellent layer 5. On the other hand, the first liquid 7 has hydrophilicity and is filled in the accommodation chamber so as to contact the hydrophilic layer 6 and surround the second liquid 8. As a result, an interface having a curvature as indicated by A is formed between these liquids. Since these liquids have different refractive indexes, a lens action is generated for light transmitted through the interface A. For example, as a commonly used material, the refractive index of the second liquid 8 that is insulative or polar is often higher than that of the first liquid 7 that is conductive or polar. In this case, the liquid lens functions as a convex lens.

  A hole is formed in a part of the storage chamber (cell), and a first electrode 9 made of a rod-like electrode is inserted therein and is in contact with the first liquid 7. The space between the hole and the first electrode 9 is sealed with an adhesive to maintain the sealing property of the storage chamber (cell). A voltage is applied by the voltage controller 10 between the first electrode 9 and the second electrode 3 described above. Moreover, the voltage control part 10 is comprised so that the applied voltage value applied between the 1st and 2nd electrodes can be controlled. The voltage control unit 10 is configured to exchange signals with other devices of the optical device equipped with a liquid lens, for example. The voltage applied by the voltage control unit 10 may be a DC voltage, but in order to suppress charge injection into the insulating layer 4, it is preferable to use an AC voltage of several tens Hz to several tens KHz.

  In the liquid lens of FIG. 1, for example, an acrylic transparent substrate can be used as the upper member 1 and the lower member 2. The second electrode 3 can be formed, for example, by forming a thin film of indium tin oxide (ITO) on the inner surface of the lower member 2 by sputtering and patterning the thin film. The circular opening 3a is preferably filled with an insulating material and flattened at the same height as the upper surface of the electrode. It is desirable that the insulating layer 4 on the second electrode 3 has a thickness of 1 μm or less so that the driving voltage of the voltage controller 10 does not increase. As such an insulating layer 4, for example, a film (LB film) formed by the Langmuir-Blodgett (LB) method can be used. If the LB method is used, a uniform defect-free thin film can be obtained at normal temperature and normal pressure. A cast coat film can also be used as the insulating layer 4. This film can be formed by applying an organic or inorganic compound (preferably a fluorine-based or silicon-based resin) onto a substrate together with a solvent using a technique such as dipping or spin coating. Further, as the insulating layer 4, a film made of metal oxide or silicon formed by sputtering can be used.

  The water repellent layer 5 is formed, for example, by applying a water repellent treatment agent on the insulating layer 4. As the water repellent agent, a fluorine compound or the like is preferably used. The water repellent layer 5 forms a surface layer in which the affinity (affinity) for the second liquid 8 is greater than the affinity for the first liquid 7. The hydrophilic layer 6 is formed, for example, by applying a hydrophilic treatment agent on the insulating layer 4. As the hydrophilic treatment agent, a surfactant, a hydrophilic polymer or the like is preferably used. In addition, the hydrophilic layer 6 may be formed using a generally known hydrophilic material.

  Examples of the first liquid 7 include an aqueous solution of an inorganic salt and an organic liquid such as a liquid having conductivity and polarity per se, or a liquid having conductivity and polarity by adding an ionic component. Used. As an example, an electrolytic solution in which water, ethyl alcohol, and sodium chloride are mixed at a predetermined ratio and has a density of 1.06 and a refractive index of 1.38 at room temperature can be used. In addition, the density and refractive index in this example are presented as one specification, and are not particularly limited thereto.

  As the second liquid 8, it is desirable to use a liquid that is colorless and transparent and has substantially the same density as the first liquid 7 in the operating temperature range of the liquid lens. If the difference in density between the first and second liquids is large, the interface between these liquids becomes asymmetrical, and coma aberration occurs. Here, “substantially the same density” means that the difference in density between the two liquids is less than 1% with respect to the density of the higher liquid. As the second liquid 8, for example, silicone oil having a density of 1.06 and a refractive index of 1.49 at room temperature can be used. Paraffin oil can also be used as the second liquid 8. As described above, the type of the second liquid 8 is not limited as long as it is an insulating or nonpolar liquid that does not mix with the first liquid 7.

  FIG. 2 is a block diagram illustrating a configuration example of the voltage control unit in the embodiment of the present invention described in FIG. 1.

  In FIG. 2, a voltage control unit 10 includes a CPU (Central Processing Unit) 11 that performs control calculation and drive signal generation, a ROM 13 and a RAM 14 that are connected to the bus of the CPU 11, a power supply 15 that generates an actual applied voltage, and a DC / DC It comprises a DC converter 16 and amplifiers 17 and 18 that amplify the voltage value. The CPU 11 is a built-in type that controls the applied voltage. The CPU 11 controls the applied voltage value, the application timing, and the duty ratio of the applied voltage in the case of PWM control. When the liquid lens of this embodiment is incorporated in an optical device such as an imaging device, the CPU 11 controls the entire optical device by exchanging signals with other devices of the optical device.

  The ROM 13 stores a reference table (LUT) for control and programs and data for causing the CPU 11 to execute various controls. As the ROM 13, a flash memory that is a nonvolatile memory or the like is used. The RAM 14 stores a work area used for the CPU 11 to perform various controls and processes, the state of the liquid lens, environment information of the apparatus, and the like. As the RAM 14, a suitable device is used in consideration of speed and cost, such as a DRAM that requires refreshing or an SRAM that does not require refreshing.

  As the power source 15, a DC power source such as a dry battery or a storage battery is used. The power supply 15 supplies power necessary for the operation of the control system such as the liquid lens as well as the CPU 11 and its peripheral circuits which are control systems. The DC / DC converter 16 boosts the voltage supplied from the power supply 15 to a desired voltage value according to the control signal of the CPU 11. In order to perform the electrowetting operation, a voltage of several hundred volts is generally required. In response to the control signal from the CPU 11, the output voltage of the power supply 15 is applied to the liquid lens by the DC / DC converter 16 and the amplifiers 17 and 18 at a desired voltage value, frequency, and duty. The amplifier 17 is connected to the first electrode 9 in the liquid lens shown in FIG. 1, and the amplifier 18 is connected to the second electrode 3, and a voltage is applied between these electrodes.

  Next, the operation of the liquid lens of the embodiment shown in FIG. 1 will be described. First, when a voltage is not applied to the first liquid 7, the interface between the first liquid 7 and the second liquid 8 is in the state A shown by the solid line in FIG. Here, the shape of the interface A includes the interfacial tension between the two liquids, the interfacial tension between the first liquid 7 and the water repellent layer 5 or the hydrophilic layer 6, and the second liquid 8 and the water repellent layer 5 or the hydrophilic layer 6. , And the volume of the second liquid 8. In this embodiment, the material is selected so that the interfacial tension between the silicone oil that is the second liquid 8 and the water repellent layer 5 is reduced. That is, since the wettability between the two materials is high, the outer edge of the lenticular droplet formed by the second liquid 8 has a tendency to spread, and is stabilized when the outer edge coincides with the application region of the water repellent layer 5. On the other hand, since both liquids have substantially the same density as described above, gravity does not act. Therefore, the interface A is a spherical surface, and the radius of curvature and the height of the apex (lens thickness) are determined by the volume of the second liquid 8.

  On the other hand, when a voltage is applied between the first liquid 7 and the second electrode 3 via the first electrode 9 from the voltage controller 10 shown in FIG. The balance of the interfacial energy between 7 and the hydrophilic layer 6 or the water repellent layer 5 changes. Then, the first liquid 7 gets over the boundary between the hydrophilic layer 6 and the water repellent layer 5 and enters the region where the water repellent layer 5 is applied. As a result, the diameter of the bottom surface of the lens formed by the second liquid 8 decreases, and the interface between the two liquids changes from the shape shown by the solid line A to the shape B shown by the broken line. In the present embodiment, the second liquid 8 has a higher refractive index than the first liquid 7, and the curvature radius of the interface becomes smaller due to the state (shape) change from the interface A to the interface B. The focal length of the liquid lens is shortened. In other words, the liquid lens functions as a so-called variable focus lens in which the focal length is changed by applying a voltage.

In FIG. 1, the contact angle when a voltage is applied between the first electrode 9 and the second electrode 3 is denoted by θ. Θ (V), which represents the contact angle θ as a function of the applied voltage V, is d for the thickness of the insulating layer 4, ε for the dielectric constant of the insulating layer 4, γ for the interfacial energy of the second liquid 8, and When the dielectric constant is ε ₀ , the following equation (1) is given.
cos θ (V) −cos θ (0) = ε ₀ · ε · V ² / (2d · γ) (1)

  From equation (1), it can be seen that the contact angle θ changes with the application of a voltage, and the interface shape between the first and second liquids can be controlled. That is, in the present embodiment, the focal length of the liquid lens changes depending on the applied voltage value. When a voltage is applied between the first electrode 9 and the second electrode 3 and the applied voltage value is gradually increased, the focal length of the liquid lens becomes shorter. On the other hand, when the voltage value is gradually decreased from a state in which a large voltage value is applied between the two electrodes, the focal length of the liquid lens gradually increases. Thus, the focal length of the liquid lens can be continuously changed by changing the applied voltage value.

  The configuration and operation of the liquid lens that is the premise of the present invention have been described above. Next, the control method that is a feature of the present invention will be described. The present invention makes it possible to perform control with higher accuracy when the focal length is controlled to a target value by using the hysteresis characteristic of an EW electric type liquid lens. First, the hysteresis characteristic of the liquid lens will be described with reference to FIG.

3A and 3B are diagrams showing the relationship between the applied voltage and the focal length in the embodiment of FIG. 3A and 3B, the horizontal axis indicates the voltage applied between the first electrode 9 and the second electrode 3 shown in FIG. 1, and the vertical axis indicates the focal length of the liquid lens. . In a state where no voltage is applied between the two electrodes, the focal length of the liquid lens is F _0. From this state, as shown in FIG. 3 (a), a voltage is applied between the electrodes, the gradually increasing the applied voltage, the focal length gradually becomes shorter as the curve C _1. Then, once the voltage value equal to or higher than the _second threshold value V ₂ is applied and then the applied voltage value is decreased, the focal length gradually increases according to the curve C ₂ . Furthermore, continue to decrease the applied voltage value once, after the first threshold value V ₁ the following conditions, when the applied voltage is increased, the focal length changes according to curve C ₁ again. As described above, the interface behavior of the liquid lens of FIG. 1 is nonlinear, so-called hysteresis characteristics.

When having such a hysteresis characteristic, greater than the applied voltage value is the first threshold value V _1, in the second range smaller than the threshold value V _2, even when applying the same voltage V, liquid The lenses show different focal lengths. For example, in FIG. 3 (a), by performing the first operation to go to increase the voltage value from the first threshold value V ₁ the following condition, the focal distance when the voltage value is V is F _A. On the other hand, the focal length when the voltage value is set to V by performing the second operation in which the voltage value is decreased from the state equal to or higher than the _second threshold value V ₂ becomes F _B different from F _A. . On the other hand, when the applied voltage value is less than or equal to the first threshold value V ₁ or greater than or equal to the second threshold value V ₂ , the focal length is uniquely determined from the applied voltage value. That is, in these cases, the liquid lens has one focal length corresponding to the applied voltage value.

In the liquid lens as described above, in the non-linear region the rate of change of the focal length is different with respect to a change in applied voltage value in the first curve C ₁ and the second curve C _2. In FIG. 3 (b), the first threshold value V ₁ and a second focal length corresponding to the threshold V ₂ of the applied voltage value, to the first focal length F ₁ and a second focal length F _2, respectively. Then, between the focal lengths F ₁ and F ₂ , the change rates of the focal lengths are equal between the curves C ₁ and C ₂ , that is, the slopes of the tangents of the curves C ₁ and C ₂ are equal. there is a focal length _{F 3.} In the first range R ₁ between the focal lengths F ₁ and F ₃ , the change rate of the focal length with respect to the change in the applied voltage value indicates that the second operation is performed when the first operation is performed. It will be smaller than when it was done. On the other hand, in the second range R ₂ between the focal lengths F ₃ and F ₂ , the change rate of the focal length with respect to the change of the applied voltage value is the first when the second operation is performed. Smaller than when the operation was performed.

In the characteristic as shown in FIG. 3B, when the target focal length is in the first range R ₁ , the rate of change with respect to the applied voltage value is smaller when the focal length is changed along the curve C _1. Therefore, more accurate control is possible. In contrast, if the focal length of the target is in the second range R _2, who was varied focal length along a curve C ₂ is more accurate control is possible. The present invention focuses on this point. That is, a case is considered where the focal length is to be changed from the state within the first range R ₁ or longer (the state longer than F ₁ ) to the target focal length within the _second range R ₂ . Try. In this case, once the applied voltage, after the second threshold value V ₂ or more states of, it performs control to change the voltage value corresponding to the focal length of the target. Also, consider a case where the focal length is to be changed from a state within the second range R ₂ or shorter (a state shorter than F ₂ ) to a target focal length within the _first range R ₁ . Try. In this case, control is performed to change the applied voltage value to a voltage value corresponding to the target focal length after the applied voltage value is once set to a state equal to or lower than the _first threshold value V1. By using such a method, the focal length can be changed on a curve having a smaller change rate of the focal length with respect to the applied voltage value, and control with higher accuracy is possible. Each case will be described in more detail below.

Figure 4 relates to the relationship between the applied voltage and the focal length there is shown the same characteristics as in FIG. 3, the focal length of the target for explaining a control method when it is in the second range R in ₂ FIG. As shown in FIG. 4A, it is assumed that the current state, that is, the state before the focal length is changed is the focal length F _S1 longer than F ₁ . The applied voltage value at this time is V _S1 . Since the target focal length _FT is within the second range R ₂ , the applied voltage value is increased from V _S1 and is temporarily set to a state equal to or greater than the _second threshold value V ₂ . Thereafter, the applied voltage value is decreased to a voltage value V _T corresponding to F _T. This is the same when the current state is the focal length F _S2 in the first range R ₁ . That is, the applied voltage value is once changed from V _S2 to a state equal to or higher than the _second threshold value V ₂ and then controlled to the voltage value V _T corresponding to F _T.

On the other hand, as shown in FIG. 4B, it is assumed that the current state is a focal length F _S1 shorter than F ₂ . In this case, the applied voltage value is controlled to gradually decrease from V _S1 and directly to V _T. That is, it is not necessary to temporarily set the applied voltage value to V ₁ or less. Similarly, when the current state is the focal length F _S2 in the second range R ₂ , the applied voltage value is directly changed from V _S2 to V _T.

Next, FIG. 5 shows the same characteristics as FIG. 3 with respect to the relationship between the applied voltage and the focal length, and the control method when the target focal length is in the first range R ₁ will be described. FIG. Assume that the current state is a focal length F _S1 shorter than F ₂ as shown in FIG. The applied voltage value at this time is V _S1 . Since the target focal length _FT is within the first range R ₁ , the applied voltage value is decreased from V _S1 , and is temporarily set to a state equal to or less than the _first threshold value V ₁ . Thereafter, the applied voltage value is increased to obtain a voltage value V _T corresponding to F _T. This is the same when the current state is the focal length F _S2 in the second range R ₂ . That is, the applied voltage value is once changed from V _S2 to a state equal to or lower than the _first threshold value V ₁ and then controlled to the voltage value V _T corresponding to F _T.

On the other hand, as shown in FIG. 5B, it is assumed that the current state is a focal length F _S1 longer than F ₁ . In this case, the applied voltage value is gradually increased from V _S1 and controlled so as to directly become V _T. In other words, once the applied voltage value, you need not be V ₂ or more. Similarly, when the current state is the focal length F _S2 in the first range R ₁ , the applied voltage value is directly changed from V _S2 to V _T.

In the control method described with reference to FIG. 4 and FIG. 5, at the focal length within the range R ₁ first, a state located on the curve C _2, and the state is on the curve C ₁ in the second range R within ₂ Not assumed. This is because such a state cannot be obtained as long as control is performed according to the method of the present invention.
In addition, when the target focal length is F ₁ or more or F ₂ or less, the focal length is uniquely determined with respect to the applied voltage value, and as shown in FIG. 4 (a) or FIG. 5 (a). No control is necessary. That is, in this case, the applied voltage may be controlled to direct V _T.

The above control is performed by the voltage controller 10 shown in FIG. In the voltage control unit 10, the ROM13 of the reference table (LUT), characteristics, i.e. including the curves C ₁ and C ₂ in the nonlinear region, the set applied voltage value corresponding to the focal distance and the focal length as shown in FIG. 3 Is stored in. The ROM 13 also includes first and second threshold values V ₁ and V ₂ , corresponding focal lengths F ₁ and F ₂ , and a focal point at the boundary between the first range R ₁ and the second range R _2. information of the distance F ₃ are stored. On the other hand, the RAM 14, and the current state, that is, the focal length F _S in a state before changing the focal length written. Based on the information stored in these memories, the CPU 11 determines the control method. Then, the CPU 11 controls the amplifiers 17 and 18 according to the determined control method to change the applied voltage value. Here, an example in which the reference table is stored in the ROM 13 has been shown. However, in order to reduce the memory capacity, the characteristics shown in FIG. .

  Also, since the characteristics as shown in FIG. 3 vary depending on environmental conditions, particularly the temperature of the liquid in the liquid lens storage chamber, it is desirable to have a plurality of reference tables corresponding to the environmental conditions. In this case, a sensor for measuring environmental conditions is required. Further, the measurement by this sensor may be performed at a predetermined timing such as when the driving of the liquid lens is started, and the reference table may be selected.

FIG. 6 is a flowchart showing a flow of control of the liquid lens in the embodiment of FIG.
6, in step 101 first, CPU 11 shown in FIG. 2 reads the current focal length _{F S} from RAM 14. Next, in step S102, CPU 11 of FIG. 2 reads the focal length _{F T} of the target instructed from other external devices. Here, as described above, the CPU 11 may be configured to control the entire optical apparatus in which the liquid lens is incorporated. In this case, the target focal length _FT is determined by the CPU 11 in accordance with a signal from another device (for example, a focus detection device).

Then, in step S103, CPU 11 of FIG. 2, the focal length _{F T} of the target to determine whether a first focal length _{F 1} (first corresponding to the threshold _{V 1)} or more. When F _T was at _{F 1} or more, the process proceeds to step S104, by controlling the applied voltage value _{V T,} adjust the focal length to the target value _{F T.} Thereafter, in step S105, the CPU 11 replaces the current focal length F _S in the RAM 14 with F _T and ends the process.

On the other hand, in step S103, when the focal length _{F T} that the target is not _{F 1} or more, and is determined, the process proceeds to step S106. In step S106, CPU 11 has a focal length _{F T} of the target to determine whether a second focal length _{F 2} (second corresponding to the threshold value _{V 2)} below. When F _T is was _{F 2} or less, the process proceeds to step S104. Thereafter, the foregoing description as well as the applied voltage value as V _T, after adjusting the focal length F _T, through step S105, the process ends.

In step S106, when the focal length _{F T} that the target is not _{F 2} or less, and is determined, the process proceeds to step S107. In step S107, CPU 11 has a focal length _{F T} of the target to determine whether the first range _R within _1. F _T is within _{R 1,} when it is determined that, the process proceeds to step S108. In step S108, is the current focal length F _S within the first range R ₁ or is F _S longer than the first range R ₁ (whether it is greater than or equal to the first focal length F ₁ )? ). When YES is determined in step S108, the process proceeds to step S104, the application voltage value as _{V T,} after adjusting the focal length _{F T,} through step S105, the process ends.

If NO is determined in step S108, the process proceeds to step S109. In step S109, CPU 11 has applied voltage temporarily, after the first threshold value _{V 1} or less, by controlling the applied voltage value _{V T,} adjust the focal length to the target value _{F T.} Thereafter, the process is terminated through step S105.

On the other hand, in step S107, NO _{(F T} is not in the first range _{R 1)} when it is determined that, the process proceeds to step S110. In step S110, is the current focal length F _S within the second range R ₂ or whether F _S is shorter than the second range R ₂ (whether it is less than or equal to the second focal length F ₂ )? ). When YES is determined in step S110, the process proceeds to step S104, the application voltage value as _{V T,} after adjusting the focal length _{F T,} through step S105, the process ends.

If NO is determined in step S110, the process proceeds to step S111. In step S 111, CPU 11 is the applied voltage once and, after the second threshold value _{V 2} or more, by controlling the applied voltage value _{V T,} adjust the focal length to the target value _{F T.} Thereafter, the process is terminated through step S105.

  In the above embodiment, an example in which the liquid lens functions as a convex lens has been shown. However, the second liquid has a smaller refractive index than the first liquid, and the liquid lens functions as a concave lens. The invention can be applied. As described above, the present invention can be applied in various ways, and the present invention includes all such application examples without departing from the scope of the claims.

DESCRIPTION OF SYMBOLS 3 2nd electrode 3a Circular opening 4 Insulating layer 5 Water repellent layer 6 Hydrophilic layer 7 1st liquid 8 2nd liquid 9 1st electrode 10 Voltage control part

Claims (2)

An interface in which a conductive or polar first liquid and an insulating or nonpolar second liquid that is not mixed with the first liquid and has a refractive index different from that of the first liquid have a curvature. Container accommodated to form,
A first electrode in contact with the first liquid;
A second electrode provided to face the second liquid through an insulating layer, and a focus by controlling an applied voltage value applied between the first electrode and the second electrode In a liquid lens with a voltage control unit that changes the distance,
When the applied voltage value is less than or equal to the first threshold value or greater than or equal to the second threshold value, which is greater than the first threshold value, one focal length corresponding to the applied voltage value is obtained, and the applied voltage value is greater than the first threshold value. When it is larger and smaller than the second threshold, the voltage value is increased when the first operation for increasing the voltage value from the state below the first threshold is performed and from the state above the second threshold. The focal length is different from the time when the second operation of decreasing the value is performed, and
Between the first and second focal lengths respectively corresponding to the first and second threshold values, the rate of change of the focal length with respect to the change of the applied voltage value is the second when the first operation is performed. A first range that is smaller than when the operation is performed, and a second rate at which the change rate of the focal length with respect to the change in the applied voltage value is smaller than that when the first operation is performed. And has a hysteresis characteristic in the range of
In the case where the voltage control unit changes the focal length within the first range or longer than the target focal length within the second range, the applied voltage value is once more than the second threshold value. Then, control is performed to change to a voltage value corresponding to the target focal length, and the target focus within the first range from the state where the focal length is within or shorter than the second range. In the case of changing to a distance, the liquid lens is characterized by performing control to change the applied voltage value to a voltage value corresponding to a target focal length after once changing the applied voltage value to a state equal to or less than a first threshold value. An interface in which a conductive or polar first liquid and an insulating or nonpolar second liquid that is not mixed with the first liquid and has a refractive index different from that of the first liquid have a curvature. A liquid provided with a container accommodated so as to form a first electrode, a first electrode in contact with the first liquid, and a second electrode provided to face the second liquid through an insulating layer In a control method for changing a focal length of the liquid lens by changing an applied voltage value applied between the first electrode and the second electrode with respect to the lens,
The liquid lens has one focal length corresponding to the applied voltage value when the applied voltage value is equal to or less than the first threshold value or greater than the second threshold value, which is greater than the first threshold value. When it is larger than the first threshold and smaller than the second threshold, the first operation for increasing the voltage value from the state below the first threshold is performed, and the second threshold or more The focal length is different from when the second operation of decreasing the voltage value from the state is performed, and
Between the first and second focal lengths respectively corresponding to the first and second threshold values, the rate of change of the focal length with respect to the change of the applied voltage value is the second when the first operation is performed. A first range that is smaller than when the operation is performed, and a second rate at which the change rate of the focal length with respect to the change in the applied voltage value is smaller than that when the first operation is performed. And has a hysteresis characteristic in the range of
When changing the liquid lens from a state in which the focal length is within or longer than the first range to a target focal length within the second range, the applied voltage value is once greater than or equal to the second threshold value. After changing to the state, control is performed to change to a voltage value corresponding to the target focal length, and the liquid lens is moved from the state where the focal length is within the second range or shorter than that within the first range. In the case of changing to the target focal length, the applied voltage value is once set to a state equal to or lower than the first threshold value, and then control is performed to change the voltage value to the target focal length. Liquid lens control method.

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