JP4787672B2 - Automatic focusing device - Google Patents

Description

  The present invention relates to an automatic focusing device, and in particular, uses a liquid crystal lens for adjusting a focal length, and detects a focal point from an image signal obtained from an optical image formed through the liquid crystal lens during a transient response operation of the liquid crystal lens. The present invention relates to an automatic focusing device.

  As a focusing mechanism that changes the focal length or the focal position of the optical system, a method of focusing by moving a lens is widely used. However, this method requires a lens driving mechanism, and thus has a drawback that the mechanism is complicated and a lens driving motor requires a relatively large amount of electric power. In addition, there is a drawback that the impact resistance is generally low.

  Thus, as a focusing mechanism that does not require a lens driving mechanism, a method of focusing by changing the refractive index of the liquid crystal lens has been proposed (for example, see Patent Document 1). Such a liquid crystal lens has a configuration in which a liquid crystal layer is sandwiched between two glass substrates provided with a pattern electrode and a common electrode. The pattern electrode has a central electrode and a plurality of annular electrodes, and the central electrode and each annular electrode are connected by a voltage drop resistor. A variable resistor is connected via a power amplifier to the lead electrode that is insulated from each ring electrode and connected to the center electrode, and the lead electrode connected to the ring electrode (outer peripheral electrode). Is connected to a variable resistor via an amplifier. Further, the AC voltage supplied from the AC source connected in parallel to these variable resistors is stepped down by the variable resistors. A voltage distribution is formed from the voltage signal applied to the extraction electrode and the voltage drop resistor, and a voltage distribution is formed in the liquid crystal layer. Then, by adjusting each variable resistance, various voltage distributions can be generated in the liquid crystal layer.

  Also, as a video camera autofocus (autofocus) system, a contour detection method is known in which information corresponding to image blur is extracted directly from a captured video signal, and the lens is climbed and controlled to minimize this blur. (For example, refer nonpatent literature 1.). Various autofocus devices using this hill-climbing control method have been proposed (see, for example, Patent Document 2, Patent Document 3, Patent Document 4, and Patent Document 5).

Japanese Patent No. 3047082 Japanese Utility Model Publication 2-44248 Japanese Patent No. 2742741 Japanese Patent Publication No.1-15188 Japanese Patent Publication No.2-1068 Kentaro Hanma, 4 others, “Contour Detection Autofocus Method”, Television Society Technical Report, November 29, 1982, p. 7-12

  However, no proposal has been made for focusing by controlling the change in the refractive index of the liquid crystal lens by the hill-climbing control method. As a reason, when a liquid crystal lens is used, it can be considered that it takes a long time to detect a focal point by hill-climbing control. Hereinafter, the time required to detect the focal point is compared between the method of moving the lens and the method of using the liquid crystal lens. In the comparison, it is assumed that there are 50 positions of the focal position set in advance for the near view, and the search is made for a peak of information corresponding to the blur in a certain direction, and an average of 25 positions is detected until the peak is found. Assuming that

  In the method of moving the lens, when the lens is moved to a position corresponding to a certain position and information corresponding to the blur at that time is acquired, the lens is moved to a position corresponding to the next position and information corresponding to the blur is obtained. The operation of obtaining is repeated. In this case, since the processing time per position is as short as 67 milliseconds, for example, the average time required to detect the in-focus point is about 1.7 seconds (= 67 milliseconds / position × 25 positions).

  On the other hand, in a method using a liquid crystal lens, the refractive index distribution of the liquid crystal lens is changed by changing a voltage (drive voltage) applied to the liquid crystal lens in order to drive the liquid crystal lens. Therefore, when a driving voltage corresponding to a certain position is applied to the liquid crystal lens and information corresponding to the blur at that time is obtained, a driving voltage corresponding to the next position is applied to the liquid crystal lens and information corresponding to the blur is again obtained. The operation of obtaining is repeated.

  However, in general, since the response of the liquid crystal to the change in the drive voltage is delayed, it is necessary to wait until the response of the liquid crystal becomes stable after changing the drive voltage. For this reason, the processing time per position becomes long, for example, 500 milliseconds, and it takes about 12.5 seconds (500 milliseconds / position × 25 positions) on average to detect the focal point. This is unrealistic.

  Further, according to Patent Document 1, the liquid crystal lens is configured to apply a voltage to both ends of the voltage drop resistor, and naturally, a voltage lower than the other end may be applied to one end. For example, when it is desired to act as a convex lens, a low voltage is applied to one extraction electrode and a high voltage is applied to the other extraction electrode.

  At this time, depending on the liquid crystal material of the liquid crystal layer used, the time for completing the transient response of the liquid crystal on the side to which the low voltage is applied is later than the time for completing the transient response of the liquid crystal on the side to which the high voltage is applied. As described above, when the operation of the liquid crystal lens is to be a convex lens, it is sufficient to respond according to the voltage applied over the entire surface of the liquid crystal layer. However, if a place where the transient response is late occurs until it functions as a convex lens. This time is determined by the response time of the liquid crystal on the side to which a low voltage is applied.

  In particular, when maximizing the power of the lens, the voltage difference between the central electrode and the peripheral electrode is maximized, so that the liquid crystal molecules in the liquid crystal layer are effective on the side where a low voltage is applied. Therefore, there is a problem that a long time is required until a lens having an appropriate refractive index profile in this portion is obtained (until the transient response is completed).

  Furthermore, in order to increase the power as a lens as much as possible, it is necessary to increase the birefringence of the liquid crystal material or increase the thickness of the liquid crystal layer. However, with such a configuration, the response of the liquid crystal becomes slow as described above, and there is a problem that it takes a long time to obtain a lens having an appropriate refractive index distribution.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an automatic focusing device that can solve the above-described problems caused by the prior art.

  In addition, the present invention detects a maximum value of the focus signal after extracting a plurality of focus signals corresponding to the degree of focus matching during the transient response operation of the liquid crystal lens, and at a sufficient speed in practical use. An object of the present invention is to provide an automatic focusing device capable of detecting a focusing point.

  In order to achieve the above object, an automatic focusing apparatus according to the present invention includes a liquid crystal lens whose focal length changes in accordance with an applied voltage, a liquid crystal lens driving unit that applies a predetermined voltage to the liquid crystal lens, and a liquid crystal lens. The photoelectric conversion means for generating an image signal from the transmitted optical image and the liquid crystal lens driving means are controlled to apply a predetermined voltage to the liquid crystal lens to perform a transient response operation. A plurality of focus signals are extracted by sampling at a period, and control means is provided for controlling the liquid crystal lens driving means so that the focus signal is maximized based on the extracted focus signals.

  Further, in the automatic focusing device according to the present invention, the control means controls the liquid crystal lens driving means to temporarily return the liquid crystal lens to an initial state, and then applies a predetermined voltage to operate the liquid crystal lens in a transient response operation. It is preferable to make it.

  Further, in the automatic focusing device according to the present invention, the liquid crystal lens includes a liquid crystal layer between two transparent substrates each having a pattern electrode having a central electrode and an outer peripheral electrode connected by resistance and a common electrode. It is preferable that the liquid crystal lens driving means applies different predetermined voltages to the central electrode and the outer peripheral electrode.

  Further, in the automatic focusing device according to the present invention, the control unit controls the liquid crystal lens driving unit to apply the maximum applied voltage to the center electrode and the outer peripheral electrode, thereby temporarily returning the liquid crystal lens to the initial state. It is preferable to make it.

  Furthermore, in the automatic focusing apparatus according to the present invention, it is preferable that the control means controls the liquid crystal lens driving means to apply a voltage for setting the liquid crystal lens in a state of a concave lens or a convex lens as a predetermined voltage.

  Further, in the automatic focusing device according to the present invention, the control means controls the liquid crystal lens driving means to set the liquid crystal lens in a convex lens state as a predetermined voltage, and the liquid crystal lens in a concave lens state. It is preferable to apply the 2nd voltage for making it at different timings.

  Further, in the automatic focusing device according to the present invention, the control means controls the liquid crystal lens driving means to temporarily return the liquid crystal lens to the initial state, and then place the liquid crystal lens in one of the concave lens and the convex lens. It is preferable to apply a second voltage for applying the first voltage to the other state of the concave lens and the convex lens after the liquid crystal lens is restored to the initial state again.

  According to the present invention, a liquid crystal lens is used for adjusting the focal length, and a plurality of focus signals corresponding to the focus matching degree are extracted at a time during the transient response operation of the liquid crystal lens, and the maximum value of the focus signals is determined. By detecting it, it becomes possible to detect the focal point at a sufficient speed in practical use.

  In addition, according to the present invention, after the liquid crystal lens is temporarily returned to the initial state, the liquid crystal lens is caused to perform a transient response operation, so that the reproducibility of the transient response operation is increased and an accurate in-focus position is obtained from the acquired focus signal. Can be detected.

  Hereinafter, an automatic focusing apparatus according to the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing a schematic configuration of the automatic focusing apparatus 100.

  As shown in FIG. 1, an automatic focusing device 100 includes a liquid crystal (LC) lens system 1, an optical lens system 2, an image sensor 3, a DSP (digital signal processor) 4, an autofocus (AF) controller 5, and a liquid crystal lens. A driver 6 and the like are provided. The liquid crystal lens system 1 has a configuration in which a P-wave liquid crystal lens and an S-wave liquid crystal lens are combined. The optical lens system 2 includes a diaphragm, a pan focus group lens, and an infrared cut filter. The image pickup device 3 includes an image sensor made of a solid-state image pickup device such as a CCD or a CMOS, and an analog-digital converter.

  An optical image formed through the liquid crystal lens system 1 and the optical lens system 2 is converted into an electric signal by the image sensor of the image sensor 3. The electrical signal output from the image sensor is converted into a digital signal by an analog-digital converter. The DSP 4 performs image processing on the digital signal output from the analog-digital converter. The autofocus controller 5 samples the image signal output from the DSP 4 at a predetermined period during the transient response operation period of the liquid crystal lens, thereby to obtain a plurality of focus signals corresponding to the degree of focus matching (hereinafter referred to as autofocus signal and autofocus signal). Extract). Then, the autofocus controller 5 determines the sampling timing when the level of the autofocus signal is maximized based on the plurality of extracted autofocus signals, and based on the determination result, the driving condition of the liquid crystal lens system 1 Control.

  The autofocus controller 5 includes a microprocessor 51 that performs the above-described series of controls, a storage unit 52, and the like. The storage unit 52 includes a read-only memory unit (ROM unit) that stores a program executed by the microprocessor 51 and various relationships necessary for obtaining an optimum driving voltage, and a write used by the microprocessor 51 as a work area. It has a possible memory part (RAM part). The liquid crystal lens driver 6 applies a voltage to the liquid crystal lens system 1 based on the control signal output from the autofocus controller 5.

  Details of processing executed by the autofocus controller 5 will be described later. The liquid crystal lens system 1 and the optical lens system 2 correspond to optical lens means. The image sensor 3 and the DSP 4 correspond to photoelectric conversion means. The autofocus controller 5 corresponds to means for controlling the focus signal extraction, the in-focus determination, and the liquid crystal lens driver 6. The liquid crystal lens driver 6 corresponds to means for driving the liquid crystal lens.

  2 and 3 are a front view and a sectional view showing a cell configuration of the P-wave liquid crystal lens 7.

  As shown in FIGS. 2 and 3, the P-wave liquid crystal lens 7 includes a pattern electrode 10 and a common electrode 11 that are disposed inside a pair of opposed glass substrates 8 and 9. 11, a liquid crystal panel is formed in which alignment films 12 and 13 are arranged to face each other and a liquid crystal layer 14 of, for example, homogeneous alignment is sealed between them.

  In the central portion of the P-wave liquid crystal lens 7, a lens portion 15 whose refractive index changes according to the applied voltage is provided. Further, the peripheral edge of the P-wave liquid crystal lens 7 is sealed with a seal member 16. The thickness of the liquid crystal layer 14 is kept constant by the spacer member 17. A flexible printed wiring board (FPC) 19 is connected to the electrode extraction portion 18 of the pattern electrode 10 using an anisotropic conductive film. A part of the electrode extraction part 18 is insulated from the pattern electrode 10 and connected to the common electrode 11.

  The length of one side of the glass substrates 8 and 9 is preferably about several mm to several tens of mm, for example, 10 mm. However, the size of the glass substrate 8 on the pattern electrode 10 side is the size excluding the portion of the pattern electrode 10 that covers the electrode extraction portion 18. The thickness of the glass substrates 8 and 9 is preferably about several hundred μm, for example, 300 μm. The thickness of the liquid crystal layer 14 is preferably about 10 to several tens of μm, for example, 23 μm. The diameter of the lens portion 15 is preferably about several mm, for example, 2.4 mm. In addition, said numerical value is an example, Comprising: It is not limited to this.

  FIG. 4 is a front view showing the configuration of the pattern electrode 10.

  As shown in FIG. 4, the pattern electrode 10 has a plurality of C-shaped annular electrodes 21 and 22 arranged around the circumference of a plurality of concentric circles having different radii around a circular center electrode 20. Have a different pattern. A space is formed between the center electrode 20 and the innermost ring electrode 21 and between the adjacent ring electrodes 21 and 22. The central electrode 20, the innermost annular electrode 21, and the adjacent annular electrodes 21, 22 are connected to each other via the annular connection part 23.

  From the center electrode 20, the center lead electrode 24 is separated from the other ring electrodes 21 and 22 and the ring connection part 23 (that is, in an insulated state). It extends to the outside of the outer peripheral electrode 22). On the other hand, the outer peripheral electrode 22 extends from the outer peripheral electrode 22 to the outer side in a state of being insulated from other electrodes. The pattern shown in FIG. 4 of the pattern electrode 10 is disposed so as to overlap the lens unit 15.

  In accordance with the voltages applied to the center extraction electrode 24 and the outer periphery extraction electrode 25, respectively, the center electrode 20 with respect to the common electrode 11, each annular electrode 21 between the center electrode 20 and the outer periphery electrode 22, and The voltage values of the outer peripheral electrodes 22 are different from each other. That is, a voltage distribution is generated in the lens unit 15 by the pattern electrode 10. By changing this voltage distribution, the refractive index distribution of the liquid crystal lens 7 changes, and the liquid crystal lens 7 can be made into a convex lens state, a parallel glass state, or a concave lens state.

  In FIG. 4, the total number of the center electrode 20, the outer peripheral electrode 22, and the annular electrode 21 therebetween is set to 7. However, the total number of the central electrode 20, the outer peripheral electrode 22, and the annular electrode 21 therebetween is, for example, 27 Is preferred. The diameter of the center electrode 20, the width of each annular electrode 21, and the width of the outer peripheral electrode 22 are selected so that a desired refractive index distribution can be obtained in the lens unit 15. The width of the space between adjacent ones of the center electrode 20, the ring electrode 21 and the outer peripheral electrode 22 is preferably 3 μm, for example. Further, the resistance value of each annular zone connecting portion 23 is preferably 1 kΩ, for example. The above numbers and numerical values are examples, and the present invention is not limited to these.

  FIG. 5 is a diagram showing the relationship between the driving voltage and the refractive index distribution in the liquid crystal lens.

  In FIG. 5, an example of a driving voltage (FIG. 5A) applied to the liquid crystal in a state where light having a polarization plane in the same direction as the alignment direction of the liquid crystal is transmitted through the liquid crystal and a change in the refractive index at that time ( FIG. 5 (b)) is shown.

  As shown in FIG. 5A, when the driving voltage V0 is applied to the liquid crystal from the outside, the refractive index of the liquid crystal corresponds to the driving voltage V0 with a delay of tf from the rising timing of the driving voltage V0. A state is reached (FIG. 5B). Further, the refractive index of the liquid crystal returns to the original state with a delay of time tr from the timing of falling of the drive voltage V0 (FIG. 5B). The times tf and tr are periods in which the liquid crystal is in a transient response operation, and the refractive index gradually changes. Here, as described above, the drive voltage V0 is, for example, an AC voltage subjected to pulse height modulation (PHM) or pulse width modulation (PWM).

  Using the P-wave liquid crystal lens 7 and the pattern electrode 10 whose dimensions and characteristic values are the values described above, the liquid crystal layer 14 has a refractive index ne for an extraordinary ray and a refractive index no for a normal ray of 1.75 and In this case, using a nematic liquid crystal having a birefringence Δn of 0.25, for example, the transient response operation time tf of the liquid crystal with respect to the rise of the drive voltage V0 (from 0 V to 5 V) and the rise of the drive voltage V0 The transient response operation time tr of the liquid crystal with respect to the fall (from 5 V to 0 V) is about 500 milliseconds.

  As described above, it takes a certain amount of time until the transient response operation of the liquid crystal is completed. Therefore, the automatic focusing device 100 samples an image signal generated from the optical image that has passed through the liquid crystal lens system 1 and the optical lens system 2 at a predetermined period during the transient response operation period of the liquid crystal.

  FIG. 6 is a diagram showing how the refractive index of the liquid crystal changes during the transient response operation period tf when the drive voltage rises, and how the focal length of the P-wave liquid crystal lens 7 changes.

  For example, as shown in FIG. 6A, the refractive index of the liquid crystal changes during the transient response operation period tf and becomes constant when the transient response operation period tf elapses. The refractive index of the liquid crystal portion corresponding to each annular electrode 21 and outer peripheral electrode 22 is also constant. Accordingly, when the transient response operation period tf elapses, the refractive index distribution of the P-wave liquid crystal lens 7 is determined to be a certain distribution, and the focal length f of the P-wave liquid crystal lens 7 is a certain constant according to the refractive index distribution. Converges to a value.

  The lines drawn above and below the horizontal axis in FIG. 6B represent changes in the focal length f when the P-wave liquid crystal lens 7 is in a convex lens state and a concave lens state, respectively. . For convenience of explanation, the focal length f when the P-wave liquid crystal lens 7 is in a convex lens state is represented by a positive numerical value, and the focal length f when the P-wave liquid crystal lens 7 is in a concave lens state is represented by a negative numerical value. Represents. In this way, when the focal length f of the P-wave liquid crystal lens 7 is positive or negative infinity, the P-wave liquid crystal lens 7 is in a parallel glass state.

  In the automatic focusing apparatus 100, the image signal is sampled at times t1, t2, t3, t4, t5, and t6 of the transient response operation period tf until the focal length f of the P-wave liquid crystal lens 7 converges to a constant value. At each sampling timing, the focal length f of the P-wave liquid crystal lens 7 is different. Accordingly, during one transient response operation period of the P-wave liquid crystal lens 7, the image signal generated from the optical image that has passed through the liquid crystal lens 7 with different focal lengths f can be sampled. A plurality of autofocus signals corresponding to the degree of matching can be extracted.

  Here, the sampling period ts is synchronized with the period of the frame, for example. The image signal may be sampled during the transient response operation period tr when the P-wave liquid crystal lens 7 falls. Further, the number of sampling is not limited to six.

  The sampling time and the P wave, such as the focal length f of the P wave liquid crystal lens 7 at the first sampling time t1 and the focal length f2 of the P wave liquid crystal lens 7 at the second sampling time t2. The relationship with the focal length of the liquid crystal lens 7 is required. This relationship is stored, for example, in the ROM section of the storage means 52 in the autofocus controller 5.

  Accordingly, the microprocessor 51 of the autofocus controller 5 obtains the focal length of the P-wave liquid crystal lens 7 at each sampling time based on the time when the image signal is sampled during the transient response operation period of the P-wave liquid crystal lens 7. be able to. As a result, the correspondence between each focal length of the P-wave liquid crystal lens 7 and the level of the autofocus signal can be obtained, so that the P when the level of the autofocus signal becomes maximum, that is, when the focus is achieved. The focal length of the wave liquid crystal lens 7 can be obtained.

  FIG. 7 shows an example of the relationship between the focal length of the P-wave liquid crystal lens 7 in a static state and the voltage applied to the liquid crystal lens 7 in order to set the focal length of the P-wave liquid crystal lens 7 to a certain value. FIG.

  As shown in FIG. 7, the values of the voltage Vouter of the outer peripheral electrode 22 and the voltage Vinner of the central electrode 20 when the focal length of the P-wave liquid crystal lens 7 becomes f1 in a static state in advance. The values of Vouter and Vinner when the focal length of the liquid crystal lens 7 becomes f2 in a static state, such as the focal length f of the P-wave liquid crystal lens 7 in the static state, and the P-wave liquid crystal lens 7 is also required to have a relationship with the driving voltage applied to the P-wave liquid crystal lens 7 in order to set the focal length f of the lens 7 to a certain value. This relationship is also stored in the ROM portion of the storage means 52 in the AF controller 5, for example.

  Therefore, in order to actually adjust the focus, that is, to adjust the focal length of the P-wave liquid crystal lens 7 to the focal length when the level of the autofocus signal is maximized, the microprocessor 51 uses the P-wave liquid crystal lens. It is possible to know how much drive voltage should be applied to 7.

  The P-wave liquid crystal lens 7 has been described with reference to FIGS. 2 to 7, but the S-wave liquid crystal lens is the same as the P-wave liquid crystal lens 7 described above, and thus the description thereof is omitted. However, the alignment direction of the liquid crystal layer in the S-wave liquid crystal lens is 90 ° different from the alignment direction of the liquid crystal layer 14 of the P-wave liquid crystal lens 7.

  When the refractive index distribution of the P-wave liquid crystal lens 7 is changed, light having a polarization plane in the same direction as the orientation direction of the P-wave liquid crystal lens 7 is affected by the change in the refractive index distribution. The light having the polarization plane in the direction orthogonal to the alignment direction of the liquid crystal lens 7 is not affected by the change in the refractive index distribution. The same applies to the S-wave liquid crystal lens. Therefore, the imaging optical system requires two liquid crystal lenses whose orientation directions are different by 90 °, that is, a P-wave liquid crystal lens 7 and an S-wave liquid crystal lens. The P-wave liquid crystal lens 7 and the S-wave liquid crystal lens are driven by a drive voltage having the same waveform. The drive voltage is, for example, an AC voltage that has been pulse height modulated (PHM) or pulse width modulated (PWM).

  Next, a voltage application pattern to the liquid crystal lens 7 when the liquid crystal lens 7 is changed to both a convex lens state and a concave lens state will be described. The liquid crystal lens 7 is in a convex lens state when the voltage Vouter applied to the outer peripheral electrode 22 of the pattern electrode 10 is higher than the voltage Vinner applied to the central electrode 20, and is in a concave lens state in the opposite case.

  FIG. 8 is a diagram showing an example of a voltage application pattern used in the automatic focusing apparatus 100 according to the present invention.

  8A shows the voltage Vouter applied to the outer peripheral electrode 22 of the pattern electrode 10, FIG. 8B shows the voltage Vinner applied to the center electrode 20 of the pattern electrode 10, and FIG. 8A and 8B show changes in the reciprocal of the focal length f of the P-wave liquid crystal lens 7 when the voltages shown in FIGS. 8A and 8B are applied, and FIG. 8D shows the results shown in FIGS. It is a figure which shows an example of the autofocus signal obtained when a voltage is applied.

  FIG. 9 is a diagram illustrating an example of retardation of a liquid crystal lens.

  9A shows an example of retardation of the P-wave liquid crystal lens 7 at time T1 in FIG. 8, FIG. 9B shows an example of retardation of the P-wave liquid crystal lens 7 at time T2 in FIG. FIG. 9C shows an example of retardation of the P-wave liquid crystal lens 7 at time T3 in FIG. 8, and FIG. 9D shows an example of retardation of the P-wave liquid crystal lens 7 at time T4 in FIG. Yes.

  In the voltage application pattern, as shown in FIGS. 8A and 8B, the voltage Vouter applied to the outer peripheral electrode 22 and the voltage Vinner applied to the central electrode 20 are respectively applied at the maximum at time T0. The voltage is V2. Next, at time T1, the voltage Vouter is changed to the applied minimum voltage V1, and the voltage Vinner is maintained at the applied maximum voltage V2. Next, at time T2, the voltage Vinner and the voltage Vouter are set to V2, which is the maximum applied voltage. Next, at time T3, the voltage Vouter is maintained at the applied maximum voltage V2, and the voltage Vinner is changed to the applied minimum voltage V1. Note that the voltage Vinner and the voltage Vouter before the time T0 indicate a state before the start of autofocus, and the voltage Vinner and the voltage Vouter after the time T4 are in-focus detected by the autofocus operation from the time T0 to the time T4. The hourly voltage is shown.

  In the P-wave liquid crystal lens 7, the retardation changes from the previous state from the rising timing of the voltage applied from time T 0, and at time T 1, as shown in FIG. That is, it becomes a state of flat glass. Since the transient response operation period of the liquid crystal is faster as the applied voltage is higher, the liquid crystal can be returned to the initial state more quickly by the applied maximum voltage V2. That is, the period from time T0 to time T1 may be determined in anticipation of the maximum value of the change of the liquid crystal to the sane state.

  Next, the retardation of the P-wave liquid crystal lens 7 changes from the falling timing at time T1, and the lens power gradually increases. At time T2, as shown in FIG. It becomes the state of the largest concave lens.

  Next, the retardation of the P-wave liquid crystal lens 7 changes from the rising timing of the voltage applied from time T2, and at time T3, as shown in FIG. It becomes a glass state. As described above, since the transient response operation period of the liquid crystal is faster as the applied voltage is higher, the liquid crystal can be returned to the initial state more quickly by the applied maximum voltage (V2).

  Next, the retardation of the P-wave liquid crystal lens 7 changes from the falling timing at time T3, and the lens power gradually increases. At time T4, as shown in FIG. It becomes the state of the maximum convex lens.

  As shown in FIG. 8C, the value of 1 / f of the P-wave liquid crystal lens 7 is substantially 0 at time T1, and changes from time T1 to time T2 so as to draw a downward convex curve. At time T2, the maximum negative value is obtained. Therefore, at time T2, the P-wave liquid crystal lens 7 is in a state of a concave lens having the maximum lens power. Further, the 1 / f value of the P-wave liquid crystal lens 7 returns to almost zero again at time T3, changes from time T3 to time T4 so as to draw a convex curve upward, and is positive at time T3. The maximum value of. Therefore, at time T4, the P-wave liquid crystal lens 7 is in a state of a convex lens having the maximum lens power. The S-wave liquid crystal lens is also operated simultaneously with the P-wave liquid crystal lens 7 by the same drive waveform as that of the P-wave liquid crystal lens 7 (see FIGS. 8A and 8B).

  Points 110 to 121 shown in FIG. 8C indicate an example of sampling time for obtaining the autofocus signal. That is, the AF controller 5 outputs six autofocus signals 135 to 130 at the six points 110 to 115 during the period in which the P-wave liquid crystal lens 7 is in a transient response operation and is in a concave lens state. Obtained from the DSP 4 and the six autofocus signals 136 to 141 at the six points 116 to 121 during the period in which the P-wave liquid crystal lens 7 is in the transient response operation and is in the state of the convex lens. Obtain from DSP4.

  FIG. 8D shows the obtained autofocus signals rearranged within the range of 1 / f to 1/100 to −1/100, and the sampling times 110 to 115 are autofocus. Corresponding to each of the signals 135 to 130, the sampling times 116 to 121 correspond to the autofocus signals 136 to 141, respectively.

  After sampling all scheduled autofocus signals, the AF controller 5 compares all the autofocus signals and detects the maximum value of the autofocus signals. In the example of FIG. 8D, in the lens system in which the liquid crystal lens system 1 and the optical lens system 2 are combined in a state where the autofocus signal 132 has the maximum value and the autofocus signal 132 is sampled, It seems that the camera is in focus. Therefore, the AF controller 5 drives the liquid crystal lens so as to be in a state corresponding to the maximum autofocus signal 132 after time T4. In the above example, six samplings are performed when the liquid crystal lens is in a concave lens state, and six samplings are performed when the liquid crystal lens is in a convex lens state. However, the number of samplings is limited to this. It is possible to select the optimum number of times according to the specifications of the automatic focusing device without any problem. Further, since the principle of the contour detection method in which the autofocus signal becomes the maximum when the subject is in focus is described in Non-Patent Document 1 described above, the description thereof is omitted here.

  For example, in the automatic focusing device 100 shown in FIG. 1, when the liquid crystal lens system 1 is in a flat lens state, the optical lens system 2 alone is designed so that the distance L to the subject is 200 mm and in focus. FIG. 8D shows a case where the distance L to the subject is longer than 200 mm, for example, a case where L is 350 mm. Therefore, when the P-wave liquid crystal lens 7 is in a concave lens state, the autofocus signal takes a maximum value.

  FIG. 10 is a diagram showing another example of a voltage application pattern used in the automatic focusing apparatus 100 according to the present invention.

  10A shows the voltage Vouter applied to the outer peripheral electrode 22 of the pattern electrode 10, FIG. 10B shows the voltage Vinner applied to the center electrode 20 of the pattern electrode 10, and FIG. FIGS. 10A and 10B show changes in the reciprocal of the focal length f of the P-wave liquid crystal lens 7 when the voltages in FIGS. 10A and 10B are applied, and FIG. 10D shows FIGS. 10A and 10B. It is a figure which shows an example of the autofocus signal obtained when a voltage is applied.

  In the example shown in FIG. 8, the autofocus signal is acquired by first setting the liquid crystal lens in a concave lens state, and then acquiring the autofocus signal by setting the liquid crystal lens in a convex lens state. On the other hand, in the example shown in FIG. 10, the autofocus signal is acquired by first setting the liquid crystal lens in a convex lens state, and then the autofocus signal is acquired by setting the liquid crystal lens in a concave lens state.

  In this voltage application pattern, as shown in FIGS. 10A and 10B, the voltage Vouter applied to the outer peripheral electrode 22 and the voltage Vinner applied to the central electrode 20 are respectively applied at the maximum at time T0. The voltage is V2. Next, at time T1, the voltage Vouter is maintained at the applied maximum voltage V2, and the voltage Vinner is changed to the applied minimum voltage V1. Next, at time T2, the voltage Vinner and the voltage Vouter are set to V2, which is the maximum applied voltage. Next, at time T3, the voltage Vouter is changed to V1, which is the minimum applied voltage, and the voltage Vinner is maintained at V2, which is the maximum applied voltage. Note that the voltage Vinner and the voltage Vouter before the time T0 indicate a state before the start of autofocus, and the voltage Vinner and the voltage Vouter after the time T4 are in-focus detected by the autofocus operation from the time T0 to the time T4. The hourly voltage is shown.

  In the P-wave liquid crystal lens 7, the retardation changes from the previous state from the rising timing of the voltage applied from time T 0, and at time T 1, as shown in FIG. That is, it becomes a state of flat glass. Since the transient response operation period of the liquid crystal is faster as the applied voltage is higher, the liquid crystal can be returned to the initial state more quickly by the applied maximum voltage V2. That is, the period from time T0 to time T1 may be determined in anticipation of the maximum value of the change of the liquid crystal to the sane state.

  Next, the retardation of the P-wave liquid crystal lens 7 changes from the falling timing at time T1, and the lens power gradually increases. At time T2, as shown in FIG. It becomes the state of the maximum convex lens.

  Next, the retardation of the P-wave liquid crystal lens 7 changes from the rising timing of the voltage applied from time T2, and at time T3, as shown in FIG. It becomes a glass state. As described above, since the transient response operation period of the liquid crystal is faster as the applied voltage is higher, the liquid crystal can be returned to the initial state more quickly by the applied maximum voltage (V2).

  Next, the retardation of the P-wave liquid crystal lens 7 changes from the falling timing at time T3, and the lens power gradually increases. At time T4, as shown in FIG. It becomes the state of the largest concave lens.

  As shown in FIG. 10 (c), the value of 1 / f of the P-wave liquid crystal lens 7 is substantially 0 at time T1, and changes from time T1 to time T2 so as to draw a convex curve upward. At time T2, the maximum positive value is obtained. Therefore, at time T2, the P-wave liquid crystal lens 7 is in a state of a concave lens having the maximum lens power. Further, the value of 1 / f of the P-wave liquid crystal lens 7 returns to almost zero again at time T3, changes from time T3 to time T4 so as to draw a downward convex curve, and is negative at time T4. The maximum value of. Therefore, at time T4, the P-wave liquid crystal lens 7 is in a state of a concave lens having the maximum lens power. Also in this example, the S-wave liquid crystal lens is operated simultaneously with the P-wave liquid crystal lens 7 by the same drive waveform as that of the P-wave liquid crystal lens 7 (see FIGS. 10A and 10B).

  Points 110 to 121 shown in FIG. 10C indicate an example of sampling time for obtaining an autofocus signal. That is, the AF controller 5 acquires six autofocus signals 135 to 130 at six points 110 to 115 during a period in which the P-wave liquid crystal lens 7 is in a transient response operation and is in a convex lens state. The six autofocus signals 136 to 141 are acquired at the six points 116 to 121 during the period in which the P-wave liquid crystal lens 7 is in the state of a concave lens during the transient response operation.

  FIG. 10D shows the obtained autofocus signals rearranged within the range of 1/100 to −1/100 in the value of 1 / f. Sampling times 110 to 115 are autofocus. Corresponding to each of the signals 135 to 130, the sampling times 116 to 121 correspond to the autofocus signals 136 to 141, respectively.

  After sampling all scheduled autofocus signals, the AF controller 5 compares all the autofocus signals and detects the maximum value of the autofocus signals. In the example of FIG. 10D, in the lens system in which the liquid crystal lens system 1 and the optical lens system 2 are combined in a state where the autofocus signal 139 has the maximum value and the autofocus signal 139 is sampled, It seems that the camera is in focus. Therefore, the AF controller 5 drives the liquid crystal lens so as to be in a state corresponding to the maximum autofocus signal 139 after time T4. In the above example, six samplings are performed when the liquid crystal lens is in a concave lens state, and six samplings are performed when the liquid crystal lens is in a convex lens state. However, the number of samplings is limited to this. It is possible to select the optimum number of times according to the specifications of the automatic focusing device without any problem.

  FIG. 11 is a diagram showing still another example of a voltage application pattern used in the automatic focusing apparatus 100 according to the present invention.

  FIG. 11A shows the voltage Vouter applied to the outer peripheral electrode 22 of the pattern electrode 10, and FIG. 11B shows the voltage Vinner applied to the central electrode 20 of the pattern electrode 10.

  In the example shown in FIG. 8, the voltage V2 or V1 is applied to the voltage Vinner and the voltage Vouter. On the other hand, in the example shown in FIG. 11, when the liquid crystal lens is initialized, the maximum voltage V0 is applied as the voltage Vinner and the voltage Vouter. In other cases, the voltage Vouter is applied to the outer peripheral electrode. Vo1 or Vo2 is applied, and Vi1 or Vi2 is applied as the voltage Vinner to the center electrode. That is, the example of FIG. 11 corresponds to a case where a predetermined voltage is individually applied to the center electrode and the outer peripheral electrode. In the case of FIG. 11, the relationship between the voltage Vinner and the voltage Vouter needs to satisfy the relationship of Vi1 <Vo1, Vi2> Vo2, and V0 ≧ Vi1, Vo2. Note that the example shown in FIG. 8 is a specific example of the example of FIG. 11 when Vi1 = Vo2 = V1 and V0 = Vi2 = Vo1 = V2.

  In this voltage application pattern, as shown in FIGS. 11A and 11B, at time T0, the voltage Vinner applied to the central electrode 20 and the voltage Vouter applied to the outer peripheral electrode 22 are respectively applied at the maximum. The voltage is V0. Next, at time T1, the voltage Vinner is changed to Vi2, and the voltage Vouter is changed to Vo2. Next, at time T2, the voltage Vinner and the voltage Vouter are set to V0, which is the maximum applied voltage. Next, at time T3, the voltage Vinner is changed to Vi1, and the voltage Vouter is changed to Vo1. Note that the voltage Vinner and the voltage Vouter before the time T0 indicate a state before the start of autofocus, and the voltage Vinner and the voltage Vouter after the time T4 are in-focus detected by the autofocus operation from the time T0 to the time T4. The hourly voltage is shown.

  In the P-wave liquid crystal lens 7, the retardation changes from the previous state from the rising timing of the voltage applied from time T 0, and at time T 1, as shown in FIG. That is, it becomes a state of flat glass. Since the transient response operation period of the liquid crystal is faster as the applied voltage is higher, the liquid crystal can be returned to the initial state more quickly by the applied maximum voltage V0.

  Next, the retardation of the P-wave liquid crystal lens 7 changes from the falling timing at time T1, and the lens power gradually increases. At time T2, as shown in FIG. It becomes the state of the largest concave lens.

  Next, the retardation of the P-wave liquid crystal lens 7 changes from the rising timing of the voltage applied from time T2, and at time T3, as shown in FIG. It becomes a glass state. As described above, since the transient response operation period of the liquid crystal is faster as the applied voltage is higher, the liquid crystal can be returned to the initial state earlier by the applied maximum voltage V0.

  Next, the retardation of the P-wave liquid crystal lens 7 changes from the falling timing at time T3, and the lens power gradually increases. At time T4, as shown in FIG. It becomes the state of the maximum convex lens. Also in this example, the S-wave liquid crystal lens is operated simultaneously with the P-wave liquid crystal lens 7 by the same driving waveform as that of the P-wave liquid crystal lens 7 (see FIGS. 11A and 11B).

  Since the change of the 1 / f value of the P-wave liquid crystal lens 7 and the sampling of the autofocus signal when the voltage pattern shown in FIG. 11 is applied are the same as those in FIGS. 8C and 8D, Description is omitted.

  Even when the voltage pattern shown in FIG. 11 is applied, the AF controller 5 compares all the autofocus signals after sampling all the planned autofocus signals, and detects the maximum value of the autofocus signals. Further, the AF controller 5 drives the liquid crystal lens so as to be in a state corresponding to the maximum autofocus signal after time T4.

  FIG. 12 is a diagram showing still another example of the voltage application pattern used in the automatic focusing apparatus 100 according to the present invention.

  12A shows the voltage Vouter applied to the outer peripheral electrode 22 of the pattern electrode 10, and FIG. 12B shows the voltage Vinner applied to the central electrode 20 of the pattern electrode 10.

  In the example shown in FIG. 10, the voltage V2 or V1 is applied to the voltage Vinner and the voltage Vouter. On the other hand, in the example shown in FIG. 12, when the liquid crystal lens is initialized, the maximum voltage V0 is applied as the voltage Vinner and the voltage Vouter. In other cases, the voltage Vouter is applied to the outer peripheral electrode. Vo1 or Vo2 is applied, and Vi1 or Vi2 is applied as the voltage Vinner to the center electrode. That is, the example of FIG. 12 corresponds to a case where a predetermined voltage is individually applied to the center electrode and the outer peripheral electrode. In the case of FIG. 12, the relationship between the voltage Vinner and the voltage Vouter needs to satisfy the relationship of Vi1 <Vo1, Vi2> Vo2, and V0 ≧ Vi1, Vo2. Note that the example shown in FIG. 10 is a specific example of the example of FIG. 12 when Vi1 = Vo2 = V1 and V0 = Vi2 = Vo1 = V2.

  In the example shown in FIG. 11, the autofocus signal is first acquired by setting the liquid crystal lens in a concave lens state, and then the autofocus signal is acquired by setting the liquid crystal lens in a convex lens state. On the other hand, the example shown in FIG. 12 is different in that an autofocus signal is acquired by first setting the liquid crystal lens in a convex lens state, and then an autofocus signal is acquired by setting the liquid crystal lens in a concave lens state.

  In this voltage application pattern, as shown in FIGS. 12A and 12B, at time T0, the voltage Vinner applied to the central electrode 20 and the voltage Vouter applied to the outer peripheral electrode 22 are respectively applied at the maximum. The voltage is V0. Next, at time T1, the voltage Vinner is changed to Vi1, and the voltage Vouter is changed to Vo1. Next, at time T2, the voltage Vinner and the voltage Vouter are set to V0, which is the maximum applied voltage. Next, at time T3, the voltage Vinner is changed to Vi2, and the voltage Vouter is changed to Vo2. Note that the voltage Vinner and the voltage Vouter before the time T0 indicate a state before the start of autofocus, and the voltage Vinner and the voltage Vouter after the time T4 are in-focus detected by the autofocus operation from the time T0 to the time T4. The hourly voltage is shown.

  In the P-wave liquid crystal lens 7, the retardation changes from the previous state from the rising timing of the voltage applied from time T 0, and at time T 1, as shown in FIG. That is, it becomes a state of flat glass. Since the transient response operation period of the liquid crystal is faster as the applied voltage is higher, the liquid crystal can be returned to the initial state more quickly by the applied maximum voltage V0.

  Next, the retardation of the P-wave liquid crystal lens 7 changes from the falling timing at time T1, and the lens power gradually increases. At time T2, as shown in FIG. It becomes the state of the maximum convex lens. In this example as well, the S-wave liquid crystal lens is operated simultaneously with the P-wave liquid crystal lens 7 by the same drive waveform as that of the P-wave liquid crystal lens 7 (see FIGS. 12A and 12B).

  Next, the retardation of the P-wave liquid crystal lens 7 changes from the rising timing of the voltage applied from time T2, and at time T3, as shown in FIG. It becomes a glass state. As described above, since the transient response operation period of the liquid crystal is faster as the applied voltage is higher, the liquid crystal can be returned to the initial state earlier by the applied maximum voltage V0.

  Next, the retardation of the P-wave liquid crystal lens 7 changes from the falling timing at time T3, and the lens power gradually increases. At time T4, as shown in FIG. It becomes the state of the largest concave lens.

  When the voltage pattern shown in FIG. 12 is applied, the change of the 1 / f value of the P-wave liquid crystal lens 7 and the sampling of the autofocus signal are the same as those in FIGS. 10C and 10D. Description is omitted.

  Even when the voltage pattern shown in FIG. 12 is applied, the AF controller 5 compares all the autofocus signals after sampling all scheduled autofocus signals, and detects the maximum value of the autofocus signals. Further, the AF controller 5 drives the liquid crystal lens so as to be in a state corresponding to the maximum autofocus signal after time T4.

  As described above, the automatic focusing device according to the present invention is useful for a device having an autofocus function, and is particularly mounted on a camera, a digital camera, a movie camera, a camera unit of a camera-equipped mobile phone, a car, or the like. It is suitable for an autofocus function such as a camera used for a rear confirmation monitor, a camera part of an endoscope, and glasses having a function of changing the degree of a lens.

FIG. 1 is a block diagram showing a schematic configuration of an automatic focusing apparatus according to the present invention. FIG. 2 is a front view showing the configuration of the liquid crystal lens. FIG. 3 is a cross-sectional view showing the configuration of the liquid crystal lens. FIG. 4 is a front view showing the configuration of the pattern electrode. FIG. 5 is an explanatory diagram showing a change in refractive index when a voltage is applied to the liquid crystal. FIG. 6 is an explanatory diagram showing changes in the refractive index of the liquid crystal and changes in the focal length of the liquid crystal lens during the transient response operation period. FIG. 7 is a diagram showing the relationship between the focal length of the liquid crystal lens and the driving voltage in a static state. FIG. 8 is a diagram showing an example of a voltage application pattern used in the automatic focusing apparatus according to the present invention. FIG. 9 is a diagram illustrating an example of retardation of a liquid crystal lens. FIG. 10 is a diagram showing another example of a voltage application pattern used in the automatic focusing apparatus according to the present invention. FIG. 11 is a diagram showing still another example of a voltage application pattern used in the automatic focusing apparatus according to the present invention. FIG. 12 is a diagram showing still another example of the voltage application pattern used in the automatic focusing apparatus according to the present invention.

Explanation of symbols

1 Liquid Crystal Lens System 2 Optical Lens System (Pan Focus Assembly Lens)
3 Photoelectric conversion means (image sensor)
4 Photoelectric conversion means (DSP)
5 AF Controller 6 Liquid Crystal Lens Driver 7 P Wave Liquid Crystal Lens 8, 9 Glass Substrate 10 Pattern Electrode 11 Common Electrode 12, 13 Alignment Film 14 Liquid Crystal Layer 15 Lens Part 16 Seal Member 17 Spacer Member 18 Electrode Extraction Part 19 Flexible Printed Wiring Board (FPC)
20 Center electrode 21 Ring electrode 22 Ring electrode (outer electrode)
23 Ring Zone Connection Portion 24 Center Part Extraction Electrode 25 Outer Periphery Part Extraction Electrode 51 Microprocessor 52 Storage Unit

Claims (3)

An automatic focusing device,
A liquid crystal lens whose focal length changes according to the applied voltage;
Liquid crystal lens driving means for applying a predetermined voltage to the liquid crystal lens;
Photoelectric conversion means for generating an image signal from an optical image transmitted through the liquid crystal lens;
By controlling the liquid crystal lens driving means and applying a predetermined voltage to the liquid crystal lens to perform a transient response operation, the image signal generated from the photoelectric conversion means is sampled at a predetermined period to obtain a plurality of focus signals. And a control means for controlling the liquid crystal lens driving means so as to maximize the focus signal based on the extracted plurality of focus signals ,
The control means controls the liquid crystal lens driving means to temporarily return the liquid crystal lens to an initial state, and then applies a predetermined voltage to cause the liquid crystal lens to perform a transient response operation.
An automatic focusing device characterized by that. The liquid crystal lens comprises a liquid crystal layer sandwiched between two transparent substrates each having a pattern electrode and a common electrode each having a central electrode and an outer peripheral electrode that are resistance-connected,
The liquid crystal lens driving means applies different predetermined voltages to the center electrode and the outer peripheral electrode,
The said control means controls the said liquid-crystal lens drive means, applies the maximum applied voltage to the said center part electrode and the said outer peripheral part electrode, and resets the said liquid-crystal lens once to an initial state. Automatic focusing device. The control means controls the liquid crystal lens driving means to apply a first voltage for bringing the liquid crystal lens into one of a concave lens and a convex lens after temporarily returning the liquid crystal lens to an initial state. 3. The automatic focusing device according to claim 1 , wherein after the liquid crystal lens is restored to the initial state again, a second voltage for applying the liquid crystal lens to the other state of the concave lens and the convex lens is applied.

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