Abstract:
A control device ( 4 ) controls a varifocal lens ( 2 ) having a first substrate ( 20 ), a second substrate ( 22 ) facing the first substrate ( 20 ), and a varifocal component ( 14 ) disposed between the first substrate ( 20 ) and the second substrate ( 22 ). When an off signal is inputted to the varifocal component ( 14 ), the control device ( 4 ) stops applying voltage to the varifocal component ( 14 ), then applies voltage for a specific length of time, and finally stops the voltage. This reduces the duration of hazing that occurs during the switching of voltage application to the varifocal component ( 14 ).

Description:
TECHNICAL FIELD 
     The present invention relates to the control of a varifocal lens. More specifically, it relates to the control of a lens with which the refractive index can be varied by using a liquid crystal material or the like. 
     BACKGROUND ART 
     A semi-finished blank for use in a varifocal liquid crystal lens is made up of a lower substrate whose surface has a convex curve, an upper substrate having a rear face with a concave curve that is joined to the upper face of the lower substrate face to face, and so forth. A varifocal component that is made up of a liquid crystal material is disposed between the upper and lower substrates. The refractive index of the varifocal component can be varied by applying voltage to the liquid crystal material. This semi-finished blank undergoes some processing and then is used as a lens for bifocal eyeglasses, for example (Patent Literature 1). 
     CITATION LIST 
     Patent Literature 
     Patent Literature 1: Specification of US Laid-Open Patent Application 2009/256977 
     SUMMARY 
     Technical Problem 
     When switching from a state in which voltage is applied to a liquid crystal material to a state in which no voltage is applied, there is a short period in which the lens becomes hazy as the liquid crystal material transitions from a homeotropic state to a planar state. This leads to a decrease in commercial value when this lens is used for bifocal eyeglasses. 
     In view of this, the present disclosure provides a control device for a varifocal lens with which the decrease in the commercial value of the varifocal lens can be suppressed by reducing the duration of the hazing that occurs during switching of the voltage applied to the varifocal lens. 
     Solution to Problem 
     The varifocal lens control device disclosed herein is configured to control a varifocal lens having a first substrate, a second substrate facing the first substrate, and a varifocal component disposed between the first substrate and the second substrate. When the control device switches a state of the varifocal lens to a state of no voltage application, the control device stops applying voltage to the varifocal component, then applies voltage to the varifocal component for a specific length of time, and finally stops applying voltage to the varifocal component. 
     The varifocal component may be, for example, a cholesteric liquid crystal material that has undergone horizontal orientation. 
     Also, a Fresnel lens may be formed on the first substrate so as to correspond to the varifocal component, for example. 
     Also, the control device may apply voltage to the varifocal component for the specific length of time after 20 to 600 milliseconds have elapsed since the control device stops applying voltage to the varifocal component, for example. 
     Also, after the control device stops applying voltage to the varifocal component, the control device may apply voltage to the varifocal component for the specific length of time prior to when transmissivity of the varifocal component is at its lowest, for example. 
     Also, the voltage to the varifocal component may be a square wave, for example. 
     Also, after the control device stops applying voltage to the varifocal component, the control device may apply voltage to the varifocal component for the specific length of time, in which the voltage is a square wave and is applied for a single period of the square wave or one-half the period of the square wave, for example. 
     Furthermore, an amplitude of the voltage applied to the varifocal component may be substantially the same as an amplitude of voltage used to drive the control device controlling the varifocal component. 
     Advantageous Effects 
     With the varifocal lens control device disclosed herein, there is less of a decrease in the commercial value of a varifocal lens. Specifically, the duration of hazing that occurs during the switching of voltage application to the varifocal component can be reduced. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is an oblique view of a pair of electronic eyeglasses pertaining to one Embodiment; 
         FIG. 2A  is a control block diagram for the electronic eyeglasses pertaining to the Embodiment, and  FIG. 2B  is a block diagram of a controller for the electronic eyeglasses pertaining to the Embodiment; 
         FIG. 3A  is a front view of an upper substrate constituting a semi-finished blank of the electronic eyeglasses pertaining to the Embodiment, and  FIG. 3B  is a front view of a lower substrate constituting a semi-finished blank of the electronic eyeglasses pertaining to the Embodiment; 
         FIG. 4  is a side view of a semi-finished blank of the electronic eyeglasses in the Embodiment; 
         FIG. 5  is a simplified and exploded cross section of the semi-finished blank in  FIG. 4 ; 
         FIG. 6  is a flowchart show part of the control of the electronic eyeglasses pertaining to the Embodiment; 
         FIG. 7  is a time transition diagram of the transmissivity of electronic eyeglasses to which the control pertaining to Example 1 has been applied; 
         FIG. 8  is a time transition diagram of the transmissivity of electronic eyeglasses to which the control pertaining to Example 2 has been applied; 
         FIG. 9  is a graph for comparison showing the time transition of transmissivity of the electronic eyeglasses when the control pertaining to the above-mentioned working examples is not applied; 
         FIG. 10  is a table of HCT when the fresh voltage in the control pertaining to the Embodiment is varied; and 
         FIG. 11  is a table of the time relation between the fresh voltage in the control pertaining to the Embodiment and the target transmissivity. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A controller  4  for controlling the varifocal lens  2  (an example of a varifocal lens) disclosed herein will now be described in detail through reference to the drawings. 
       FIG. 1  is a simplified diagram of a pair of electronic eyeglasses  8  equipped with the varifocal lens  2  obtained by specific processing, such as surfacing and edging, from a varifocal lens-use semi-finished blank  6 . The electronic eyeglasses  8  are constituted by an eyeglass frame  10  (an example of a frame), the varifocal lens  2 , the controller  4 , a sensor component  12 , and so forth. 
     As shown in  FIG. 1 , a varifocal component  14  that has a liquid crystal material (such as a cholesteric material) is formed in a region that is shifted downward from the center of the varifocal lens  2 . The refractive index of the varifocal lens  2  can be electrically varied with this varifocal component  14 . 
       FIG. 2A  is an electrical block diagram for the electronic eyeglasses  8 . The eyeglass frame  10  is provided with a power supply  16 , the sensor component  12 , the controller  4  (an example of a control device), and a circuit component  18  (an example of a driver). 
     A rechargeable battery and a booster circuit (neither of which is shown) are incorporated into the power supply  16 , and supply voltage to the sensor component  12 , the controller  4 , and the circuit component  18 . 
     The sensor component  12  may be constituted by an angular velocity sensor, a tilt sensor, or the like. This sensor detects movement of a head of the user wearing the electronic eyeglasses  8 , and outputs a signal to the controller  4 . The sensor component  12  may also output a signal to the controller  4  by sensing some operation by the user (including manipulation by the user) such as contact with the user&#39;s hand. 
     As will be discussed in detail below, the controller  4  changes the refractive index of the varifocal component  14  by controlling the voltage applied to the varifocal component  14  according to the signal from the sensor component  12 . The controller  4  is constituted by a memory or processor that executes various kinds of processing according to a program, for example. Into the circuit component  18  (an example of a driver) is incorporated a circuit for producing a lens drive waveform (not shown), etc., and voltage is applied to the varifocal component  14  according to a command signal from the controller  4 , thereby driving the varifocal component  14 . 
     The controller  4  functions as a control device. For example, as shown in  FIG. 2B , the controller  4  includes an input component  41  for inputting the on or off signal from the sensor component  12 , a determination component  42  for determining a switching signal from the sensor component  12 , and an output component  43  for outputting to the circuit component  18  a command signal that is the determination result outputted from the determination component  42 . The control device may include the controller  4  and the circuit component  18 . 
     The configuration of the varifocal component  14  will now be described.  FIG. 3B  is a front view of a lower substrate  20  (an example of a first substrate), and  FIG. 3A  is a front view of an upper substrate  22  (an example of a second substrate) that is joined to the lower substrate  20  face to face. A Fresnel lens  24  is formed in a partial region near the center of the lower substrate  20 . The semi-finished blank  6  shown in  FIG. 4  is constituted by forming a specific film between the lower substrate  20  and the upper substrate  22  and joining them. 
       FIG. 5  is a simplified and exploded cross section of the semi-finished blank  6  shown in  FIG. 4  in the thickness direction (the direction parallel to the plane of the drawing) passing through the varifocal component  14 . In a region facing the Fresnel lens  24  between the upper substrate  22  and the lower substrate  20 , a first transparent conductive film  26 , a first orientation film  28 , a liquid crystal material  30 , a second orientation film  32 , and a second transparent conductive film  34  are formed in that order, from the lower substrate  20  side toward the upper substrate  22 . In contrast, the region that does not face the Fresnel lens  24  is coated with a sealing agent  36  instead of the liquid crystal material  30 . Specifically, the liquid crystal material  30  coats just the region where the Fresnel lens  24  is formed, and the sealing agent  36  coats the remaining region. Similarly, the orientation films may be formed in just the region where the Fresnel lens  24  is formed. Here, the insulating films (such as a silicon dioxide film) that are disposed between the transparent conductive films and the orientation films are not depicted for the reason of simplifying the description. The semi-finished blank  6  that has thus been formed then undergoes specific processing, and as a result, a varifocal lens  2  can be obtained. 
     When the electronic eyeglasses  8  constituted as above are used, for example, as bifocal eyeglasses in which the refractive index can be varied in two stages, the refractive index of the varifocal component  14  is lower when the user looks down than when the user looks up so that near visual acuity will be better (refractive index for myopia). Conversely, when the user is looking in the horizontal direction, the sensor component senses this, and the controller  4  increases the refractive index of the varifocal component  14  so that distant visual acuity will be better (refractive index for hyperopia). 
     Next, the operation pertaining to the controller  4  that performs control of the varifocal component  14  electrically in this embodiment will be described in detail. In brief, the controller  4  halts the application of voltage to the varifocal component  14  when an off signal is inputted to the varifocal component  14 , then applies voltage for a specific length of time (fresh voltage), and then halts the voltage again.  FIG. 6  is a flowchart of the operation of the controller  4 , and the operation of the controller  4  will be described through reference to this flowchart. 
     When the power is switched on to the electronic eyeglasses  8 , voltage is supplied to the sensor component  12  (S 1 ). In this state, the drive voltage to the varifocal component  14  is off, and the varifocal component  14  is set to a refractive index for hyperopia as its initial state. When the user wearing the electronic eyeglasses  8  then moves his head, and more specifically when the sensor component  12  senses a change in the vertical angle of the electronic eyeglasses  8 , an on signal or off signal (an example of a specific switching signal) is outputted from the sensor component  12  to the controller  4  (S 2 ). For example, when the user looks down to read a book, the sensor component  12  that senses the specific angle of the head outputs an on signal to the controller  4 . Consequently, the circuit component  18  switches on the drive voltage to the varifocal component  14  (S 3 ). At this point, the varifocal component  14  is set to a refractive index for myopia, which is suited to reading a book. 
     When the user finishes his reading and raises his head to a horizontal position, the sensor component  12  senses this angle and outputs an off signal to the controller  4  (S 4 ), so that the drive voltage to the varifocal component  14  is switched off via the circuit component  18  (S 5 ). To measure the time that the varifocal component  14  is in an off state here, a timer (not shown) connected to the controller  4  is reset to zero. When the drive voltage to the varifocal component  14  is off, the refractive index of the varifocal component  14  is set to the hyperopia refractive index. 
     The controller  4  uses the timer count to determine whether or not the off state of the varifocal component  14  has exceeded a specific time, such as 100 milliseconds (S 6 ). If it is determined that the off state of the varifocal component  14  has exceeded this specific time, the controller  4  outputs to the circuit component  18  a signal for applying fresh voltage for just a short time to the varifocal component  14  (S 7 ). After the fresh voltage has been applied for a specific length of time, application of voltage to the varifocal component  14  is halted, resulting in an off state. 
       FIG. 7  shows the results of Example 1 in this embodiment. In this graph, the transmissivity of the varifocal component  14  is shown on the vertical axis, and the elapsed time on the horizontal axis. The fresh voltage used here is equivalent to one period of the pulse of the voltage used to drive the varifocal component  14  with a period (such as 50 Hz) and a voltage value (such as 10 V). The fresh voltage was applied 100 milliseconds after the drive voltage was shut off, at which the liquid crystal material  30  entered a focal conic state. For the sake of simplicity, we shall assume that the user does not notice any hazing that occurs when the drive voltage to the varifocal component  14  is switched off, as long as the transmissivity is at least 95%. As shown in this drawing, a transmissivity of 95% is reached approximately 740 milliseconds after the drive voltage to the varifocal component  14  is switched off (T=0). This is a pronounced difference as compared to  FIG. 9 , which illustrates a comparative example (discussed below). 
       FIG. 8  is a graph in which the application of fresh voltage is changed, and the fresh voltage used in  FIG. 7  is changed to one-half a period (such as approximately 25 Hz). Here again, it only takes about 730 milliseconds from the time the drive voltage goes off for the transmissivity of the varifocal component  14  to reach 95%. In the working examples shown in  FIGS. 7 and 8 , there is a sudden decrease in transmissivity immediately after the application of fresh voltage, but since this lasts such a short time, it cannot be discerned by a human. 
       FIG. 9  shows an example in which fresh voltage is not applied, as a comparative example to Examples 1 and 2. The liquid crystal material transitions to a focal conic state after the drive voltage to the varifocal component  14  is switched off, and the transmissivity of the varifocal component  14  decreases rapidly. After this, there is a gradual recovery, and the transmissivity reaches 95% about 1840 milliseconds after the drive voltage was switched off 
     Next, we will discuss the transmissivity recovery time when the fresh voltage value was varied and when the timing at which the fresh voltage was applied was varied. 
       FIG. 10  is a table of the HCT (haze clearing time) when the fresh voltage value was varied. HCT here shows the time it takes for the transmissivity of the varifocal component  14  to recover to 95%. For the fresh voltage, one period of a pulse of voltage that is the same as the drive voltage to the varifocal component  14  (such as 50 Hz) was used. Also, the fresh voltage was applied to the varifocal component  14  approximately 100 milliseconds after the point when the drive voltage to the varifocal component  14  was halted (T=0). It can be seen from this table that the amplitude is preferably either the same as or similar to that of the drive voltage of the varifocal component  14 . For instance, the HTC is preferably between approximately 20 and 600 milliseconds, and more preferably between approximately 50 and 300 milliseconds. 
       FIG. 11  shows the relation between HTC and the timing of fresh voltage application, that is, the time T from the point when the drive voltage to the varifocal component  14  is switched off until the fresh voltage is applied. As can be seen from  FIG. 11 , the timing of fresh voltage application is preferably 100 milliseconds after the varifocal component  14  has gone into its off state, or after a similar time has elapsed. Also, this timing of fresh voltage application is just prior to the time T at which transmissivity is lowest (approximately 230 milliseconds), as shown in  FIG. 9  in which fresh voltage is not applied. 
     As discussed above, when the drive voltage to the varifocal component  14  is switched off, fresh voltage is applied for a specific length of time so that the transition to a planar state will be accomplished quickly. Thus, the period in which hazing occurs can be shortened. This keeps the user from noticing any flickering of the lens  2  of the electronic eyeglasses  8 . 
     Other Embodiments 
     In the above embodiment, the sensor component  12  was an angular velocity sensor or a tilt sensor. Instead of using such sensor or in addition to using such sensor, the refractive index of the varifocal component  14  may be manually switched by the user. 
     Also, in the above embodiment, the varifocal component  14  was set to a hyperopia refractive index as the initial state of the electronic eyeglasses  8 , but this is not the only option. The varifocal component  14  may instead be set to a myopia refractive index as the initial state. 
     Also, whether or not the liquid crystal material  30  is in a focal conic state may be determined from whether or not the transmissivity has decreased. Therefore, the timing at which to apply the fresh voltage may be decided from the transmissivity, without keeping track of the time from when the drive voltage to the varifocal component  14  was switched off. In this case, a specific sensor (not shown) is provided to the electronic eyeglasses  8  to sense changes in the transmissivity. The controller  4  identifies a decrease in the transmissivity according to a signal from the specific sensor, and a command signal corresponding to this identification result, that is, a command to switch the voltage on or off to the varifocal component  14 , is outputted to the circuit component  18 . 
     INDUSTRIAL APPLICABILITY 
     The present invention is useful in electronic eyeglasses with which the refractive index can be varied. 
     REFERENCE SIGNS LIST 
       2  varifocal lens 
       4  controller 
       6  semi-finished blank for varifocal lens 
       8  electronic eyeglasses 
       10  eyeglass frame 
       12  sensor component 
       14  varifocal component 
       16  power supply 
       18  circuit component 
       20  lower substrate (first substrate) 
       22  upper substrate (second substrate) 
       24  Fresnel lens 
       26  first transparent conductive film 
       28  first orientation film 
       30  liquid crystal material 
       32  second orientation film 
       34  second transparent conductive film 
       36  sealing agent