JP4807179B2 - Memory liquid crystal panel and memory liquid crystal driving device - Google Patents

Description

  The present invention relates to a technique for supporting stable driving of a memory liquid crystal.

It is known that a cholesteric liquid crystal, which is one of memory liquid crystals, has three alignment states of homeotropic alignment, planar alignment, and focal conic alignment, and the alignment state is determined depending on an applied voltage. Patent Document 1 discloses a technique called DDS (Dynamic Drive Scheme) in which the orientation state of the cholesteric liquid crystal is changed at high speed by voltage control. In the DDS, the driving cycle of the cholesteric liquid crystal is divided into three stages of a preparation period, a selection period, and an evolution period, and a unique voltage is sequentially applied to the cholesteric liquid crystal for each period. More specifically, first, during the preparation period, a voltage is applied that causes all pixels of the line to be driven to transition to homeotropic alignment. In the selection period, a voltage is applied to select whether to maintain any pixel in the line to be driven in the homeotropic orientation or to allow relaxation to the transient planar. In the evolution period, the homeotropic orientation is applied. A voltage is applied to maintain the alignment state of the pixel and to shift the pixel having the planar alignment to the focal conic alignment. The DDS suppresses the time length required for rewriting per line to about 1 msec by applying the voltage in the preparation period and the voltage in the evolution period to each line of the cholesteric liquid crystal in a pipeline process. Has been successful.
US Pat. No. 5,748,277

  As disclosed in Patent Document 1, in the DDS, the subsequent alignment state is determined according to the magnitude of the voltage applied to the cholesteric liquid crystal during the selection period. In order to obtain a desired alignment state, this selection period It has been found that the voltage to be applied to the voltage fluctuates greatly under the influence of temperature. This will be described in more detail with reference to FIG. FIG. 14 is a diagram (V-R curve) schematically showing the relationship between the voltage applied during the selection period and the reflectance of the cholesteric liquid crystal, with the horizontal axis representing the voltage and the vertical axis representing the reflectance. The reflectance is a relative value when the reflection luminance of a standard white plate serving as a reference is 100%. A high reflectance (white level) means that the cholesteric liquid crystal is close to planar alignment and whiteness is strong, and a low reflectance (black level) means that the cholesteric liquid crystal is focal conic. It means that darkness is getting closer to the orientation. When the reflectance is between the white level and the black level, it means that a halftone (gray) between white and black appears.

Referring to the figure, for example, when the voltage V _H is applied to the cholesteric liquid crystal at 25 ° C., the white level is reached. However, when the voltage V _H is 27 ° C. or higher, the white level is not reached even when the voltage V _H is applied. Further, the reflectance of gray obtained when the voltage V _G1 or the voltage V _G2 is applied also varies depending on the temperature, and depending on the temperature, even if the same voltage is applied, it becomes completely white or black. Even if the variation in gray reflectance is within an allowable range, if the black level and the white level are reversed, it becomes impossible to read characters at all. Therefore, it is important to ensure the white level and the black level regardless of the temperature fluctuation. For this purpose, the difference between the voltage V _B applied when displaying black and the voltage V _H applied when displaying white (hereinafter, this difference is appropriately referred to as “temperature margin”) is used to absorb temperature fluctuations. You can see that you have to expand to the extent you want.
However, this has the following three problems.

(1) Problems due to the passive matrix method According to DDS, each pixel formed by sandwiching cholesteric liquid crystal between electrodes is driven by a so-called passive matrix method, so at least during the non-selection period (non-selection period), A voltage of V _H −V _B ) / 2 is applied to the pixel. Therefore, when the voltage V _H for displaying white is set higher in order to widen the temperature margin, the voltage of (V _H −V _B ) / 2 exceeds the threshold voltage to which the liquid crystal responds. Even the orientation state of the pixel that should not be made will transition. Even if the threshold voltage is not exceeded, if the voltage applied during the non-selection period increases, the reflectivity during the non-selection period decreases, and the reflectivity recovers after the power supply is completely erased. Therefore, when image rewriting is performed continuously, there is a possibility that a problem in which the reflectance is reduced and recovered continuously (hereinafter referred to as a blinking problem) may occur.
(2) Problem of power consumption Naturally, widening the temperature margin causes an increase in voltage applied during the selection period and the non-selection period, which means an increase in power consumption.
(3) Problem of multi-gradation display As is apparent from the VR curve shown in FIG. 14, even if a temperature margin is provided, halftone control becomes difficult if there is a temperature variation.
Further, the voltage indicating the halftone such as the voltage V _G1 and the voltage V _G2 shown in FIG. 14 does not generate individual voltages from the circuit surface, but instead generates pulse width modulation (hereinafter referred to as “PWM”). It is desirable to create by controlling the number of steps. Since the number of steps of the PWM is determined by the number of bits of the input data of the display body driving circuit, widening of the temperature margin leads to an increase in the width of one step in the PWM, and finely controls the voltage applied to the pixel. I can't do that.

Therefore, during normal times (when temperature unevenness does not occur), the temperature margin is set low to suppress flashing problems, power consumption, and gradation display problems, and only when temperature unevenness occurs in the screen. It is desirable to perform control to increase the value.
However, since it is not known in what form the temperature unevenness occurs, in order to detect the temperature unevenness, a very large number of temperature detection mechanisms are required, which is not realistic in terms of circuit scale and the like.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an efficient temperature unevenness detection means for providing a driving technique for a cholesteric liquid crystal that eliminates the adverse effects caused by widening the temperature margin. .

A memory liquid crystal panel according to a preferred embodiment of the present invention is a first pair of a memory liquid crystal and a substrate pair that sandwiches and seals the memory liquid crystal from above and below, and is provided with a transparent electrode connected by a scanning line. A substrate pair comprising a transparent electrode substrate and a second transparent electrode substrate provided with a transparent electrode connected by a data line intersecting the scanning line, the first transparent electrode substrate and the second transparent electrode substrate A plurality of temperature detecting means for detecting temperature and a heat radiating sheet for diffusing heat are attached to the lower surface of the substrate sandwiching the memory liquid crystal from below.
According to the present invention, since the temperature sensor and the heat radiation sheet are attached to the transparent electrode substrate that contacts the memory liquid crystal and receives the heat propagation, the locally increased temperature is diffused at the position where the memory liquid crystal is located. In addition, it can be detected by the temperature detecting means.

In this aspect, the plurality of temperature detection means may be attached to the lower surface with a predetermined distance interval, and the heat dissipation sheet may be attached to the lower surface so as to cover the plurality of temperature detection means.
According to this, since the heat radiation sheet is pasted so as to cover the temperature detecting means, the thermal diffusion effect can be further enhanced.

The heat dissipation sheet may be a graphite sheet made of a material having a structure in which carbon atoms are arranged in layers.
According to this, since the graphite sheet has the property that heat is not easily transmitted in the vertical direction and heat is easily transmitted in the horizontal direction, the locally increased temperature can be efficiently dispersed in the memory liquid crystal.

According to another aspect of the present invention, there is provided a memory-type liquid crystal driving device including a first transparent electrode substrate provided with a transparent electrode connected by a scanning line and a transparent electrode connected by a data line intersecting the scanning line. The memory liquid crystal is sandwiched and sealed from above and below by the second transparent electrode substrate, and the temperature is applied to the lower surface of the substrate that sandwiches the memory liquid crystal from below between the first transparent electrode substrate and the second transparent electrode substrate. A memory liquid crystal panel to which a plurality of temperature detecting means for detection and a heat radiating sheet for diffusing heat are affixed, and a temperature for specifying a temperature distribution of the memory liquid crystal based on the temperature detected by each of the plurality of temperature detecting means Distribution specifying means, and voltage for transitioning each alignment state of the storage liquid crystal between each transparent electrode provided on the first transparent electrode substrate and each transparent electrode provided on the second transparent electrode substrate The predetermined drive And means for sequentially applied to the scanning lines and the data lines according to cycle, and a driving means for switching in accordance with the waveform of the voltage to be the applied temperature distribution identified said temperature distribution identifying means.
According to the present invention, since the temperature sensor and the heat radiation sheet are attached to the transparent electrode substrate that contacts the memory liquid crystal and receives the heat propagation, the locally increased temperature is diffused at the position where the memory liquid crystal is located. In addition, the temperature detecting means can detect the temperature unevenness, and the occurrence of temperature unevenness can be efficiently determined based on the detected temperature.

In this aspect, the plurality of temperature detection means are affixed to the lower surface at a predetermined distance, and the heat dissipation sheet is affixed to the lower surface so as to cover the plurality of temperature detection means. Good.
According to this, since the heat radiation sheet is pasted so as to cover the temperature detecting means, the thermal diffusion effect can be further enhanced.

The heat dissipation sheet may be a graphite sheet made of a material having a structure in which carbon atoms are arranged in layers.
According to this, since the locally raised temperature can be efficiently dispersed in the memory liquid crystal, the occurrence of temperature unevenness in the memory liquid crystal can be efficiently detected using a limited number of temperature detection means. be able to.

Each of the condition provided identifier indicating that the temperature distribution of the memory liquid crystal panel satisfies a predetermined condition and the condition deficient identifier indicating that the condition is not satisfied, and the memory liquid crystal are shifted to various alignment states. A memory that associates and stores each set of drive parameters indicating a voltage waveform, and the drive means determines whether the temperature distribution specified by the temperature distribution specifying means satisfies the condition, and the determination result The waveform of the voltage to be sequentially applied to the scanning line and the data line may be switched to the waveform indicated by the drive parameter selected from the memory.
According to this, two patterns of drive parameters for determining the waveform of the voltage applied to the scanning line and the data line are prepared, and they are switched depending on whether or not temperature unevenness occurs. Therefore, while driving the storage liquid crystal in a mode that is advantageous in terms of power consumption and gradation, when temperature irregularities occur, switch to a special mode that can absorb the temperature difference between the display areas due to the temperature irregularities. By driving the memory liquid crystal, stable and efficient display control can be realized.

One of the plurality of temperature detection means is affixed at a position where the distance from the outer peripheral edge of the lower surface is equal to or greater than a predetermined value, and the remaining temperature detection means is located at a position where the distance is less than the predetermined value. A heat dissipating sheet is affixed to the lower surface so as to cover the temperature detecting means, and the driving means detects the temperature detected by the temperature detecting means affixed at a position where the distance from the outer peripheral edge of the lower surface is a predetermined value or more, and the remaining When the temperature difference detected by the temperature detection means exceeds a predetermined value, the drive parameter stored in the memory in association with the condition defect identifier is selected, and the scanning line and the waveform are displayed in the waveform indicated by the drive parameter. The waveform of the voltage sequentially applied to the data line may be switched.
According to this, since it is possible to identify the occurrence of temperature unevenness based on the difference between the temperature sensor at the position where the temperature change is most unlikely to occur and the detected temperature of the other temperature sensor, the accuracy of the identification is further increased. be able to.

(First embodiment)
A first embodiment of the present invention will be described.
FIG. 1 is a schematic hardware configuration diagram of a display device according to the present embodiment. As shown in the figure, the display device includes a cholesteric liquid crystal panel 10, a data electrode driving circuit 20, a scanning electrode driving circuit 30, an image rewriting button 40, and a control unit 50.
The cholesteric liquid crystal panel 10 is a member formed by sandwiching and sealing a cholesteric liquid crystal from above and below by two glass substrates provided with transparent electrodes, and affixing a plurality of temperature sensors and a heat radiation sheet to the lower surface of the lower glass substrate. is there. The display device according to the present embodiment applies a predetermined voltage to the transparent electrodes of both glass substrates of the cholesteric liquid crystal panel 10 through the data electrode driving circuit 20 and the scanning electrode driving circuit 30 under the control of the control unit 50. Then, the orientation state is changed to display an image.

  FIG. 2 is a diagram showing a cross section of the cholesteric liquid crystal panel 10 and types of alignment states of the cholesteric liquid crystal. The cholesteric liquid crystal panel 10 is formed by laminating an upper glass substrate 11, an upper transparent electrode 12, a cholesteric liquid crystal 13, a lower transparent electrode 14, a lower glass substrate 15, a light absorption plate 16, a temperature sensor 17, and a heat dissipation sheet 18. . Each of the upper transparent electrode 12 and the lower transparent electrode 14 shown in the drawing is provided with a data line and a scanning line for applying a voltage to the cholesteric liquid crystal 13.

As shown in FIG. 3, since the data lines and the scanning lines are wound on each of the upper and lower glass substrates in a substantially orthogonal direction, n rows of scanning lines (Y ₁ , Y ₁₎ are displayed in the display area of the cholesteric liquid crystal panel 10. ₂ ,..., Y _n ) and m columns of data lines (X ₁ , X ₂ ,..., X _m ) are formed. A voltage corresponding to the difference between the scanning line voltage and the data line voltage (hereinafter referred to as “driving voltage”) is applied to the cholesteric liquid crystal 13 sandwiched between the electrodes at each of the intersections of the two data lines. ) Is applied, and the alignment state changes individually according to the drive voltage. That is, each of the cholesteric liquid crystals 13 whose alignment state is individually shifted at each intersection of the scanning line and the data line plays a role of each pixel forming the image.
In the following description, each of the cholesteric liquid crystals 13 whose alignment state is individually shifted at each intersection of the scanning line and the data line is appropriately referred to as “electro-optical element 13a”.

  FIG. 4 is a top view of the cholesteric liquid crystal panel 10, and FIG. 5 is a right side view thereof. A total of five temperature sensors 17 (17a to d) are attached near the outer peripheral edge of the lower surface of the light absorbing plate 16 having a rectangular shape, and one (17e) is attached to the approximate center thereof. Two rectangular heat dissipating sheets 18a and 18b are attached so as to cover the four temperature sensors 17a to 17d two by two. Here, the thermal conductivity of the air around the temperature sensor 17 is 0.02 W / mK, and the thermal conductivity of the glass forming the back surface of the cholesteric liquid crystal panel 10 is about 1 W / mK. A so-called graphite-based sheet having a structure in which carbon molecules are arranged in layers and having a conductivity of about 200 to 300 W / mK is desirable, but a copper foil sheet having an equivalent thermal conductivity may be used instead. . In addition, the graphite sheet has a high thermal conductivity in the plane direction, but not in the vertical direction. Therefore, by attaching a heat dissipation sheet to cover the temperature sensor, more efficient thermal information can be obtained. It can be acquired.

  As shown in FIG. 6, each of the five temperature sensors 17 has one end of a thermistor 171 that is an element whose resistance value decreases as the temperature rises connected in series with a resistor 172, and the other end. Be grounded. Since the potential at the point 173 between the thermistor 171 and the resistor 172 of the temperature sensor 17 changes in accordance with the ratio between the resistance value of the thermistor 171 itself and the resistance value of the resistor 172, a signal output from the temperature sensor 17 The voltage of will vary depending on the temperature. The temperature is measured by converting this voltage value into digital data by the ADC.

In FIG. 2, the alignment state of the electro-optical element 13a (cholesteric liquid crystal) includes planar alignment (hereinafter referred to as “P alignment”) shown in (a) and focal conic alignment (hereinafter referred to as “F alignment”) shown in (b). Transition between three orientation states of homeotropic orientation (hereinafter referred to as “H orientation”) shown in FIG. In the P orientation state, light incident from the upper glass substrate 11 side is reflected, and white is expressed. On the other hand, in the F orientation state, incident light is transmitted and reaches the light absorbing plate 16, so that black is expressed. A halftone can also be expressed by mixing a P-alignment liquid crystal element and an F-alignment liquid crystal element by voltage control. Then, once this P orientation and F orientation transition, the state is maintained even if no voltage is applied. As will be described in detail later, when switching from the F orientation to the P orientation, it is necessary to undergo a transitional transition to the H orientation state, which is an orientation state that cannot be maintained without application of a voltage.
The transition of the alignment state shown in FIG. 2 is realized by changing the waveform of the voltage applied to the data line and the scanning line according to the driving cycle of the DDS driving.

  FIG. 7 is a diagram illustrating DDS driving. In DDS driving, the driving cycle of the cholesteric liquid crystal is divided into four stages including a preparation period (reset period), a selection period (selection period), and an evolution period (holding period) plus a non-selection period (non-selection period). In the three periods, a driving voltage unique to each is applied to the electro-optic element 13a via the scanning line and the data line, and the driving is performed until the liquid crystal alignment state does not change in the non-selection period (non-selection period). Reduce the voltage. The significance of the former three periods has also been explained in the background art section. In the preparation period, the drive voltage that causes all of the electro-optic elements 13a forming the line to be driven to transition to the H orientation is in the selection period. The drive voltage for selecting whether to maintain the arbitrary electro-optical element 13a of the line to be driven in the H orientation or to allow relaxation to the transient planar, the electro-optical element 13a that is in the H orientation during the evolution period. The driving voltage for applying the electro-optic element 13a having the P orientation to the F orientation while maintaining the orientation state of H is applied to the H orientation. Of these four periods, the orientation state is changed to P orientation and F in the subsequent Evolution period (holding period) to Non Selection period (non-selection period) according to the magnitude of the drive voltage applied in the Selection period (selection period). Transition to one of the orientations.

The relationship between the drive voltage during this selection period and the subsequent transition of the alignment state will be described in more detail with reference to FIGS.
FIG. 8 is a diagram showing the relationship between the drive voltage applied to the cholesteric liquid crystal that has been in each of the alignment states of the P orientation and the F orientation, and the reflectance after the drive voltage is rapidly removed. In the figure, the vertical axis represents reflectance, and the horizontal axis represents drive voltage. Further, V _{1 to} V ₄ given on the scale of the horizontal axis are drive voltage threshold values for transitioning the alignment state. As can be seen from this figure, when the cholesteric liquid crystal is in the P orientation state, while the drive voltage from V ₁ to V ₂ is being applied, the transparency gradually changes to the F orientation as the drive voltage increases. As a result, black, which is the color of the light absorbing plate 16, appears. The F alignment state is maintained while the drive voltage from V ₂ to V ₃ is applied, and the F alignment state is changed to the H alignment state while the drive voltage from V ₃ to V ₄ is applied. The reflectance increases again. On the other hand, when the cholesteric liquid crystal is in the F alignment state, the alignment state does not transition while the drive voltage of V ₁ to V ₃ is applied, and while the drive voltage of V ₄ or more is applied, The reflectance is increased by transition from the F alignment state to the H alignment state.

On the other hand, as shown in FIG. 9, in the DDS driving, the orientation state that transitions in the subsequent period is determined according to the magnitude of the driving voltage applied to each electro-optic element 13a in the Selection period. In more detail the contents of the figure, first, in the Preparation period, by V ₄ or more drive voltage shown in FIG. 8 is applied, no leakage of electro-optical element 13a has a P orientation state or F alignment state Transition to the H orientation state. In the selection period, a driving voltage corresponding to the orientation state of the color to be expressed is applied. In other words, the V ₂ or more if you want represents white, the V ₁ or less if you want represents black, its If you wish to represent the halftone intermediate driving voltage of both is being applied. Then, when a driving voltage of V ₁ or lower is applied, the transitional planar alignment (hereinafter referred to as “TP alignment”), which is an intermediate state between the H alignment and the P alignment, in which the helical structure of the liquid crystal molecules is slightly relaxed. first transition, and further transitions at Evolution period V ₄ below F alignment state when a driving voltage is applied as shown in FIG. 8, the state is maintained until the next drive cycle. On the other hand, if V ₂ or more drive voltage Selection period is applied to keep the H-orientation state, can drive voltage maintaining H orientation state in the subsequent Evolution period is applied, further in the subsequent Non Selection period When the driving voltage is rapidly removed, the state transits to the P orientation state, and this state is maintained until the next driving cycle.

FIG. 10 shows an example of waveforms applied to the data lines and the scanning lines in order to generate waveforms of drive voltages applied to the selection period and the non-selection period in order to represent white, black, and intermediate gray. FIG. In the waveform shown in this example, positive and negative voltages are alternately applied in order to prevent deterioration of the cholesteric liquid crystal.
First, each of the scanning lines constituting the matrix by intersecting with the data line is sequentially selected as the corresponding line in the selection period, and the scanning line that is the corresponding line in the selection period has zero in the first half and (V applying a _l + V _h) and becomes the scanning voltage _{V COM,} the scanning line of the line that is the Non Selection period, repeated rotation of applying a scanning voltage _{V COM} as the _{(V l + V h) /} 2. Then, while keeping the rotation and synchronization, the first half of the voltage V _h, the voltage _{V sel} of late voltage V _l (white), the first half of the voltage V _l, the voltage _{V sel} of late voltage V _h (black), or, One of the voltages V _sel (gray) in which the voltage V _h is superimposed on the voltage V _l as a pulse voltage having a width B is applied to each data line.

Here, when a voltage V _h having a voltage V _h in the first half and a voltage V _sel having a voltage V _{1 in} the second half is applied to a certain data line, the intersection position between the data line and the scanning line which is the corresponding line in the selection period is displayed. A drive voltage (V _sel −V _COM ) of V _h in the first half and −V _{h in} the second half is applied to the electro-optic element 13a. Therefore, in the DDS drive, the H alignment state is in the selection period. The electro-optical element 13a turns white when the non-selection period is reached. On the other hand, the electro-optic element 13a at the intersection of the scanning lines that is not the corresponding line in the selection period has (V _h −V _l ) / 2 in the first half and − (V _h −V _l ) / 2 in the second half. A drive voltage (V _sel −V _COM ) is applied, but since this drive voltage is smaller than V ₁ shown in FIG. 8, the alignment state of the liquid crystal cannot be changed. The same applies to the following two cases.
In addition, when a voltage V _{l of} a voltage V _l is applied to a certain data line and a voltage V _sel of a voltage V _h is applied to the second half, the electrical _potential at the intersection of the data line and the scanning line that is the corresponding line in the selection period is applied. Since the drive voltage (V _sel −V _COM ) of V ₁ in the first half and −V _{1 in} the second half is applied to the optical element 13a, the electro-optical element 13a is TP in the Selection period in the DDS drive. It changes to the alignment state and turns black when it reaches the Evolution period.
Further, when a voltage V _{sel in} which the voltage V _h is superimposed on the voltage V _l as a pulse voltage having a width B is applied to a certain data line, the data line and the scanning line that is the corresponding line in the selection period The electro-optic element 13a at the crossing position has a driving voltage (V _sel −V _COM ) in which the voltages V ₁ and V _h are superimposed on the first half and the voltages −V ₁ and −V _h are superimposed on the second half as pulse voltages. Since the electro-optical element 13a is applied, the electro-optical element 13a turns gray when the non-selection period is reached. It is also possible to change the tone of gray by PWM modulating the width B of the pulse voltage.

Returning to the description of FIG. The image rewriting button 40 is an operator for instructing rewriting of display contents of the cholesteric liquid crystal panel 10.
The control unit 50 includes an ADC (Analog / Digital Converter) 51, a data electrode power generation circuit 52, a scan electrode power generation circuit 53, a CPU 54, a RAM 55, a ROM 56, and a display body drive control circuit 57.
The ADC 51 supplies the CPU 54 with a digital signal obtained by converting an analog signal indicating the detected temperature of each temperature sensor 17, that is, a digital signal indicating the detected temperature of each temperature sensor 17. The data electrode power generation circuit 52 and the scan electrode power generation circuit 53 supply power to each of the data electrode drive circuit 20 and the scan electrode drive circuit 30.

The CPU 54 performs various processing calculations while using the RAM 55 as a work area. The display device according to the present embodiment operates in two modes, a binary mode and a gradation mode, and the ROM 56 has a drive applied to the electro-optical element 13a when operating in the binary mode. A drive parameter for determining the waveform of the voltage (hereinafter referred to as “binary mode drive parameter”) and a drive parameter for determining the waveform of the drive voltage applied to the electro-optical element 13a when operating in the gradation mode (hereinafter referred to as “binary mode drive parameter”). (Referred to as “gradation mode drive parameter”).
Here, the binary mode is a mode in which an image is displayed only by two colors of black and white, and the gradation mode is a mode in which an image is displayed by black, white, and intermediate gray. Therefore, the binary mode driving parameter determines the amplitudes of V _h and V _l for generating the white and black driving voltages shown in FIG. 10, whereas the gradation mode driving parameter is added to them. The pulse width B for creating the gray drive voltage shown in FIG. 10 is also determined.
FIG. 11 is a flowchart showing a characteristic operation of the control unit 50. The operation shown in the figure is started when the image rewriting button 40 is pressed.
When the image rewriting button 40 is pressed, the CPU 54 acquires a digital signal indicating the detected temperature of each temperature sensor 17 from the ADC 51 (step S100).
Subsequently, the CPU 54 determines whether or not temperature unevenness has occurred based on the detected temperature of each temperature sensor 17 specified from the digital signal acquired in step S100 (S110). “Temperature unevenness” refers to one of the detected temperatures of the four temperature sensors 17a to 17d attached near the outer peripheral edge of the light absorbing plate 16 and one temperature sensor 17e attached to the approximate center thereof. This means that the difference in the detected temperature exceeds the threshold value. Therefore, in this step S110, one of the detected temperatures of the four temperature sensors 17a to 17d attached near the outer peripheral edge of the light absorbing plate 16 and one temperature sensor 17e attached to the approximate center thereof. It is determined whether or not the difference between the detected temperatures exceeds a threshold value.

  The CPU 54 that has determined that the temperature unevenness has not occurred in step S110 supplies a signal instructing driving in the gradation mode to the display body drive control circuit 57 (S120). The display body drive control circuit 57 that has received this signal supplies the control signal generated based on the gradation mode drive parameter of the ROM 56 to the data electrode power generation circuit 52 and the scan electrode power generation circuit 53, and the data The electrode power generation circuit 52 and the scan electrode power generation circuit 53 apply voltages having waveforms according to the control signals to the scan electrode drive circuit and the data electrode drive circuit, respectively.

  On the other hand, the CPU 54 that has determined that the temperature unevenness has occurred in step S110 supplies a signal instructing driving in the binary mode to the display body drive control circuit 57 (S130). The display body drive control circuit 57 that has received this signal supplies the control signal generated based on the binary mode drive parameter of the ROM 56 to the data electrode power generation circuit 52 and the scan electrode power generation circuit 53, and the data The electrode power generation circuit 52 and the scan electrode power generation circuit 53 apply voltages having waveforms according to the control signals to the scan electrode drive circuit and the data electrode drive circuit, respectively.

As described above, in this embodiment, the five temperature sensors 17a to 17e are attached to the lower side of the light absorbing plate 16 of the cholesteric liquid crystal panel 10, and the temperature unevenness is based on the detected temperatures of the temperature sensors 17a to 17e. Determine whether or not there is an occurrence. When there is no temperature unevenness, it is operated in a gradation mode that displays a multi-gradation image with white and black mixed with clay, while when there is temperature unevenness, a white and black image is displayed. It is designed to operate in a binary mode that eliminates the effects of uneven color. Therefore, even when temperature unevenness occurs due to the user's fingers touching a part of the display surface of the cholesteric liquid crystal panel 10, a clean image can be displayed as much as possible.
In order to perform these mode switching, it is necessary to efficiently detect temperature unevenness. A thermistor is generally used to detect temperature unevenness on the panel surface, but the temperature range that can be detected by this thermistor is very narrow. Therefore, a large amount of thermistors are required to detect temperature unevenness over the entire screen, and the ADC circuit and the like increase accordingly, which is not realistic. Therefore, it is possible to efficiently identify the occurrence of temperature unevenness by spreading the heat generated in a part to the thermistor spaced apart by sticking the heat dissipation sheet 18 to the lower side of the light absorbing plate 16. It becomes possible.
Further, the detected temperature of the temperature sensor 17e at the center of the center where the user's finger is not in contact and the temperature fluctuation is small is used as a reference, and the detected temperature of the four temperature sensors 17a to 17d attached near the outer peripheral edge. Since the presence / absence of temperature unevenness is determined from the difference, the presence / absence of temperature unevenness can be accurately identified.

(Second Embodiment)
A second embodiment of the present invention will be described.
The display device according to the present embodiment operates in two modes: a normal mode and a temperature priority mode in which the temperature margin is wider than that in the normal mode. Drive parameters (hereinafter referred to as “normal mode drive parameters”) that determine the waveform (amplitude, pulse width) of each of the black, white, and gray drive voltages applied to the electro-optic element 13a, and operate in the temperature priority mode In this case, driving parameters (hereinafter referred to as “temperature priority mode driving parameters”) that determine the waveforms of the white, black, and gray driving voltages applied to the electro-optical element 13a are stored.

Here, in the temperature priority mode drive parameter, the difference between the voltage applied when expressing black and the voltage applied when expressing white, that is, the temperature margin is wider than the normal mode drive parameter. As described in the background section, the driving voltage for transitioning the alignment state of the cholesteric liquid crystal varies greatly under the influence of temperature. Therefore, in this embodiment, when temperature unevenness occurs, the drive parameters are switched so that good black and white display can be performed in both the region where the temperature is locally high or low and the region where the temperature is not high, and a wide temperature margin is provided. Control is performed so that the drive voltage is applied to each electro-optical element 13a.
FIG. 12 is a flowchart showing a characteristic operation of the control unit 50. The operation shown in the figure is started when the image rewriting button 40 is pressed.
Steps S100 to S110 shown in the figure are the same as those shown in FIG.
Then, the CPU 54 that has determined that the temperature unevenness has not occurred in step S110 supplies a signal instructing driving in the normal mode to the display body drive control circuit 57 (S121), while the temperature unevenness has occurred. The CPU 54 having determined that supplies a signal instructing driving in the temperature priority mode to the display body drive control circuit 57 (S131).
As described above, in the present embodiment, five temperature sensors 17 are attached to the lower side of the light absorption plate 16 of the cholesteric liquid crystal panel 10, and whether or not temperature unevenness occurs based on the detected temperatures of these temperature sensors 17. Judging. When temperature irregularities occur while driving the cholesteric liquid crystal based on the normal mode that is advantageous in characteristics such as power consumption and gradation, temperature priority that can absorb the temperature difference generated between the cholesteric liquid crystal regions The mode is switched to driving. Therefore, even if the user's finger touches a part of the display surface of the cholesteric liquid crystal panel 10 to cause temperature unevenness, black and white display can be performed satisfactorily.

(Other embodiments)
The present invention can be modified in various ways.
In the above embodiment, four temperature sensors 17 are attached in the vicinity of the outer peripheral edge of the lower surface of the light absorbing plate 16 and one in the approximate center, but the number of the temperature sensors 17 and their positional relationship. Is not limited to the above.
In the above embodiment, the occurrence of temperature unevenness is determined by the difference between the average of the detected temperatures of the four temperature sensors 17 near the outer peripheral edge of the lower surface of the light absorbing plate 16 and the detected temperature of the central temperature sensor 16 as a threshold value. However, in this method, the part where the distance from the outer peripheral edge is less than the predetermined value is when the user's fingers are touched or when a heat source is placed near the equipment. This is because it is preferable to determine the temperature unevenness based on the temperature sensor 17 at the center where the temperature is easily changed compared to the center and the distance from the outer peripheral edge is a predetermined value or more. Therefore, the presence or absence of temperature unevenness may be determined by another calculation using the temperature detected by the temperature sensor 17. For example, the temperature unevenness may be determined based on the average value of the detected temperatures of all the temperature sensors 17 including the center one and whether or not the difference between the detected temperatures exceeds a threshold value.
In the said embodiment, the heat-radiation sheet 18 was affixed in two pieces so that the four temperature sensors 17 near the outer peripheral end of the light absorption board 16 might be covered 2 each.
On the other hand, as shown in FIG. 13, the heat radiating sheet 18 is divided into four pieces (18a to d), and each of the four temperature sensors 17a to 17d near the outer peripheral end of the light absorbing plate 16 is not overlapped. It may be affixed to. According to this modification, the temperature can be individually detected for each of the four areas of the cholesteric liquid crystal panel 10, and thus the occurrence of temperature unevenness can be identified more efficiently.

It is a hardware schematic block diagram of a display apparatus. It is a figure which shows the cross section of a cholesteric liquid crystal panel, and the kind of orientation state of a cholesteric liquid crystal. It is a figure which shows a data line and a scanning line. It is a figure which shows the state of sticking of a temperature sensor and a thermal radiation sheet. It is a right view of a cholesteric liquid crystal panel. It is a figure which shows the structure of a temperature sensor. It is a figure which shows DDS drive. It is a figure explaining the relationship between a drive voltage and the transition of an orientation state. It is a figure explaining the relationship between the drive voltage in DDS drive, and the transition of an orientation state. It is a figure which shows an example of a voltage waveform. It is a flowchart which shows operation | movement of embodiment (1st Embodiment). It is a flowchart which shows operation | movement of embodiment (2nd Embodiment). It is a figure which shows the state of sticking of a temperature sensor and a heat radiating sheet (modification). It is a figure explaining background art.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Cholesteric liquid crystal panel, 11 ... Upper glass substrate, 12 ... Upper transparent electrode, 13 ... Cholesteric liquid crystal, 14 ... Lower transparent electrode, 15 ... Lower glass substrate, 16 ... Light absorption plate, 17 ... Temperature sensor, 18 ... Heat dissipation sheet, 20 ... data electrode drive circuit, 30 ... scan electrode drive circuit, 40 ... image rewrite button, 50 ... control unit, 51 ... ADC, 52 ... data electrode power generation circuit, 53 ... scan electrode power generation circuit, 54 ... CPU, 55 ... RAM, 56 ... ROM, 57 ... Display body drive control circuit, 140 ... Display device, 171 ... Thermistor, 172 ... Resistance

Claims (8)

Memory liquid crystal,
A pair of substrates for sealing the memory liquid crystal sandwiched from above and below, wherein a first transparent electrode substrate provided with a transparent electrode connected by a scanning line and a transparent electrode connected by a data line intersecting the scanning line are provided A substrate pair comprising a second transparent electrode substrate,
Of the first transparent electrode substrate and the second transparent electrode substrate, a plurality of temperature detecting means for detecting temperature and a heat radiating sheet for diffusing heat are attached to the lower surface of the substrate sandwiching the memory liquid crystal from below. Memory LCD panel. The memory liquid crystal panel according to claim 1,
The plurality of temperature detecting means includes
Affixed to the lower surface with a predetermined distance interval,
The heat dissipation sheet is
A memory liquid crystal panel attached to the lower surface so as to cover the plurality of temperature detecting means. The memory liquid crystal panel according to claim 1 or 2,
The heat dissipation sheet is a graphite sheet made of a material having a structure in which carbon atoms are arranged in layers. A storage liquid crystal is sandwiched from above and below by a first transparent electrode substrate provided with transparent electrodes connected by scanning lines and a second transparent electrode substrate provided with transparent electrodes connected by data lines intersecting the scanning lines. A plurality of temperature detecting means for detecting temperature and a heat dissipating sheet for diffusing heat are pasted on the lower surface of the first transparent electrode substrate and the second transparent electrode substrate that sandwich the memory liquid crystal from below. Memory LCD panel
Temperature distribution specifying means for specifying the temperature distribution of the memory liquid crystal based on the temperature detected by each of the plurality of temperature detecting means;
A voltage for changing the orientation state of each of the storage liquid crystals between each transparent electrode provided on the first transparent electrode substrate and each transparent electrode provided on the second transparent electrode substrate is set to a predetermined driving cycle. And a drive unit that sequentially applies the waveform of the applied voltage to the scanning line and the data line according to the temperature distribution specified by the temperature distribution specifying unit. The memory type liquid crystal driving device according to claim 4,
The plurality of temperature detecting means includes
Affixed to the lower surface with a predetermined distance interval,
The heat dissipation sheet is
A memory-type liquid crystal drive device attached to the lower surface so as to cover the plurality of temperature detecting means. The memory type liquid crystal driving device according to claim 4 or 5,
The heat dissipation sheet is a graphite sheet made of a material having a structure in which carbon atoms are arranged in layers. The memory liquid crystal driving device according to any one of claims 4 to 6,
Each of a condition provided identifier indicating that the temperature distribution of the memory liquid crystal panel satisfies a predetermined condition and a condition deficient identifier indicating that the temperature distribution does not satisfy the condition, and a voltage waveform for causing the memory liquid crystal to transition to various alignment states. A memory storing each set of drive parameters indicating
The driving means includes
It is determined whether the temperature distribution specified by the temperature distribution specifying means satisfies the condition, and based on the determination result, the waveform indicated by the drive parameter selected from the memory is sequentially applied to the scanning line and the data line. A memory-type liquid crystal drive device that switches the waveform of the voltage to be applied. The memory type liquid crystal driving device according to claim 7,
One of the plurality of temperature detection means is affixed at a position where the distance from the outer peripheral edge of the lower surface is a predetermined value or more, and the remaining temperature detection means and temperature detection are performed at a position where the distance is less than the predetermined value. A heat dissipation sheet is affixed to the lower surface to cover the means,
The driving means includes
When the difference between the temperature detected by the temperature detection means affixed at a position where the distance from the outer peripheral edge of the lower surface is equal to or greater than a predetermined value and the temperature detected by the remaining temperature detection means exceeds a predetermined value, the condition is not satisfied. A storage liquid crystal driving device that selects a driving parameter stored in the memory in association with an identifier, and switches a waveform of a voltage sequentially applied to the scanning line and the data line to a waveform indicated by the driving parameter.

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