Illumination device and driving method thereof

Abstract

This illumination device includes: a light source; an optical element including at least two liquid crystal cells stacked on each other above the light source; and a control device that drives the optical element. Each of the at least two liquid crystal cells includes: a plurality of first electrodes and a plurality of second electrodes alternately arranged in a stripe-like manner; a liquid crystal layer on the plurality of first electrodes and the plurality of second electrodes; and a plurality of third electrodes and a plurality of fourth electrodes that are disposed on the liquid crystal layer, cross the plurality of first electrodes and the plurality of second electrodes, and are alternately arranged in a stripe-like manner. The control device is configured such that a first input signal and a second input signal of a pulse width modulation method are input. Furthermore, the control device is configured so as to convert, in accordance with a duty ratio, the first input signal and the second input signal respectively to a first output signal and a second output signal of a pulse amplification method, and supply the converted signals to the optical element.

Description

[Technical Field]

[0001] 1. Field of the Invention One embodiment of the present invention relates to a lighting device and a driving method thereof. For example, one embodiment of the present invention relates to a lighting device that controls light distribution by utilizing the orientation of liquid crystals and a driving method thereof. [Background technology]

[0002] A known optical element, known as a liquid crystal lens, utilizes the fact that the refractive index of the liquid crystal layer changes by controlling the orientation of the liquid crystal through controlling the voltage applied to the liquid crystal. By placing this optical element over a light source and controlling the refractive index of the liquid crystal layer, it is possible to diffuse the light from the light source, thereby providing a lighting device with controllable light distribution (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2021-117344 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of one embodiment of the present invention is to provide a lighting device having a novel structure and a driving method thereof. For example, an object of one embodiment of the present invention is to provide a lighting device capable of controlling light distribution based on an input signal of a pulse width modulation system and a driving method thereof. [Means for solving the problem]

[0005] One embodiment of the present invention is an illumination device. The illumination device includes a light source, an optical element, and a control device that drives the optical element. The optical element includes at least two liquid crystal cells arranged to transmit light emitted from the light source and overlapping each other. Each of the at least two liquid crystal cells includes a plurality of first electrodes and a plurality of second electrodes arranged alternately in stripes, a liquid crystal layer on the plurality of first electrodes and the plurality of second electrodes, and a plurality of third electrodes and a plurality of fourth electrodes arranged alternately in stripes and intersecting the plurality of first electrodes and the plurality of second electrodes. The control device is configured to receive a first input signal and a second input signal of a pulse-width modulation type that specify the degree of diffusion of light by the optical element in the direction in which the plurality of first electrodes extend and the direction in which the plurality of third electrodes extend. The control device is further configured to convert the first input signal and the second input signal into a first output signal and a second output signal of a pulse amplitude type, respectively, according to a duty ratio, and supply them to the optical element.

[0006] One embodiment of the present invention is a method for driving a lighting device. The lighting device includes a light source, an optical element, and a control device for controlling the optical element. The optical element includes at least two liquid crystal cells arranged to transmit light emitted from the light source and overlapping each other. Each of the at least two liquid crystal cells includes a plurality of first electrodes and a plurality of second electrodes arranged alternately in stripes, a liquid crystal layer on the plurality of first electrodes and the plurality of second electrodes, and a plurality of third electrodes and a plurality of fourth electrodes arranged alternately in stripes and intersecting the plurality of first electrodes and the plurality of second electrodes. The driving method includes inputting, to the control device, first and second input signals of a pulse-width modulation type that specify the degree of diffusion of light by the optical element in the direction in which the plurality of first electrodes extend and the direction in which the plurality of third electrodes extend, and converting the first and second input signals into first and second output signals of a pulse amplitude type, respectively, according to a duty ratio, and supplying the converted signals to the optical element. [Brief explanation of the drawings]

[0007] [Figure 1]1 is a schematic perspective view of an illumination device according to an embodiment of the present invention. [Figure 2] 1 is a block diagram showing the configuration of an illumination device according to an embodiment of the present invention. [Figure 3] 1 is a schematic end view of an illumination device according to one embodiment of the present invention; [Figure 4] 1 is a schematic end view of an illumination device according to one embodiment of the present invention; [Figure 5] FIG. 2 is a schematic plan view showing an electrode pattern of a liquid crystal cell included in an optical element of an illumination device according to an embodiment of the present invention. [Figure 6] FIG. 2 is a schematic plan view showing an electrode pattern of a liquid crystal cell included in an optical element of an illumination device according to an embodiment of the present invention. [Figure 7] FIG. 2 is a schematic end view illustrating diffusion of light by an optical element of an illumination device according to an embodiment of the present invention. [Figure 8] FIG. 2 is a schematic end view illustrating diffusion of light by an optical element of an illumination device according to an embodiment of the present invention. [Figure 9] FIG. 1 is a block diagram showing the configuration of a control device for a lighting device according to an embodiment of the present invention. [Figure 10] 1A and 1B are schematic diagrams illustrating a method for driving a lighting device according to an embodiment of the present invention. [Figure 11] 4 is a flowchart illustrating an example of a method for driving a lighting device according to an embodiment of the present invention. [Figure 12] 4 is a flowchart illustrating an example of a method for driving a lighting device according to an embodiment of the present invention. [Figure 13] 1 is an equivalent circuit diagram of a processing circuit included in a drive circuit of a lighting device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, various embodiments of the present invention will be described with reference to the drawings, etc. However, the present invention can be embodied in various forms without departing from the spirit of the present invention, and should not be construed as being limited to the description of the embodiments exemplified below.

[0009] In order to clarify the description, the drawings may show the width, thickness, shape, etc. of each part schematically compared to the actual embodiment, but these are merely examples and do not limit the interpretation of the present invention. In this specification and each drawing, elements having the same function as those described in the previous drawings may be given the same reference numerals, and duplicated explanations may be omitted. This reference numeral is used to collectively represent multiple identical or similar structures, and when these are individually represented, a hyphen and a natural number are added after the reference numeral.

[0010] In this specification and claims, when expressing an aspect of placing another structure on top of a certain structure, the term "on top" is used, unless otherwise specified, to include both a case in which another structure is placed directly on top of a certain structure so as to be in contact with the certain structure, and a case in which another structure is placed above a certain structure via yet another structure.

[0011] In this specification and claims, the expression that two structures are "orthogonal" includes not only a state in which the two structures intersect perpendicularly (90°) but also a state in which the two structures intersect at an angle of 90°±10°. The expression that two structures are "parallel" includes a state in which the extension directions of the two structures form an angle of 0°±10°.

[0012] An illumination device 100 according to an embodiment of the present invention and a method for driving the same will now be described.

[0013] 1. Lighting device configuration Fig. 1 is a schematic perspective view showing the configuration of an illumination device 100 according to one embodiment of the present invention. As shown in Fig. 1, the illumination device 100 includes an optical element 110, a light source 102, and a control device (not shown in Fig. 1). The illumination device 100 may further include an input device (not shown in Fig. 1) for outputting a signal for controlling the optical element 110 and inputting it into the control device 150. The input device may be further configured to control the light intensity of the light source 102 via the control device or directly.

[0014] The light source 102 is configured and arranged to emit light to the optical element 110. There are no restrictions on the light emitting elements included in the light source 102, and examples thereof include light emitting diodes (LEDs) and cold cathode fluorescent lamps.

[0015] The optical element 110 is disposed above the light source 102 so as to transmit light emitted by the light source 102. The optical element 110 includes at least two liquid crystal cells 120 that overlap each other above the light source 102. The number of liquid crystal cells 120 included in the optical element 110 may be three or more. In the optical element 110 shown in FIG. 1, four liquid crystal cells (a first liquid crystal cell 120-1, a second liquid crystal cell 120-2, a third liquid crystal cell 120-3, and a fourth liquid crystal cell 120-4) are disposed above the light source 102 in order from the side closest to the light source 102. In the following description, an illumination device 100 including the optical element 110 that includes four liquid crystal cells 120 will be described as an example. The direction from the light source 102 to the optical element 110 is defined as the z direction.

[0016] Light emitted from light source 102 is incident on first liquid crystal cell 120-1 and is emitted from fourth liquid crystal cell 120-4. As will be described later, in lighting device 100, the diffusion of light is controlled by liquid crystal cell 120 included in optical element 110, and the light distribution of light emitted from optical element 110 can be changed. In other words, the light from light source 102 can be processed to change the shape of the surface (irradiation surface) on which the light irradiates an object.

[0017] Fig. 2 is a block diagram showing the configuration of the lighting device 100. As shown in Figs. 1 and 2, each liquid crystal cell 120 is connected to a connector 108 such as a flexible printed circuit (FPC) board, and is connected to a control device 150 via the connector 108. This allows the control device 150 to control the optical element 110. The control device 150 may be configured to be connected to the light source 102 and control the light source 102, or, although not shown, the light source 102 may be directly controlled by the input device 104 as described above. The control device 150 and the optical element 110 will be described in detail below.

[0018] 2. Optical elements 3 and 4 show schematic diagrams of the end faces of the optical element 110 taken along the dashed line AA' and the dashed line BB' perpendicular to the dashed line AA' in FIG. 1, respectively. As shown in these figures, each of the first to fourth liquid crystal cells 120-1 to 120-4 includes a first substrate 122 and a second substrate 124 facing each other, with a plurality of first electrodes 126-1, a plurality of second electrodes 126-2, a plurality of third electrodes 126-3, a plurality of fourth electrodes 126-4, a first alignment film 128-1, and a second alignment film 128-2 provided between them. The plurality of first electrodes 126-1 and the plurality of second electrodes 126-2 are provided on the first substrate 122, and the first alignment film 128-1 is formed on these electrodes. The plurality of third electrodes 126-3 and the plurality of fourth electrodes 126-4 are provided below the second substrate 124 and are disposed between the second substrate 124 and the second alignment film 128-2. The first substrate 122 and the second substrate 124 are fixed to each other by a sealant 132, and a liquid crystal layer 130 is sealed in a space surrounded by the first substrate 122, the second substrate 124, and the sealant 132. An adhesive 134 that transmits visible light is provided between adjacent liquid crystal cells 120, thereby fixing the adjacent liquid crystal cells 120 to each other. As the adhesive 134, for example, an acrylic resin adhesive or an epoxy resin adhesive can be used.

[0019] (1) Circuit board The first substrate 122 and the second substrate 124 are configured to transmit at least visible light of the light emitted by the light source 102. For example, the first substrate 122 and the second substrate 124 may be made of a light-transmitting substrate such as a glass substrate or a quartz substrate. The first substrate 122 and the second substrate 124 may contain a light-transmitting polymer such as polyimide, polyamide, polycarbonate, acrylic resin, or polysiloxane. The plurality of liquid crystal cells 120 are preferably arranged on the light source 102 such that the normal to the first substrate 122 and the second substrate 124 is the z direction and the principal surfaces are in the xy plane.

[0020] (2) Electrode Each of the electrodes 126 functions as an electrode for forming a transverse electric field in the liquid crystal layer 130. The electrodes 126 are made of a conductive oxide that transmits visible light, such as indium tin oxide (ITO) or indium zinc oxide (IZO). Alternatively, the electrodes 126 may contain a metal such as aluminum, tantalum, molybdenum, or tungsten, or an alloy thereof. However, to ensure transparency to visible light, the electrodes 126 are preferably formed in a mesh shape with a plurality of openings.

[0021] As can be seen from Figures 3 and 4, the first electrodes 126-1 and the second electrodes 126-2 are arranged in stripes, parallel to each other, and alternately. Therefore, one second electrode 126-2 is arranged between adjacent first electrodes 126-1, and one first electrode 126-1 is arranged between adjacent second electrodes 126-2. Similarly, the third electrodes 126-3 and the fourth electrodes 126-4 are arranged in stripes, parallel to each other, and alternately. Therefore, one fourth electrode 126-4 is arranged between adjacent third electrodes 126-3, and one third electrode 126-3 is arranged between adjacent fourth electrodes 126-4. However, the direction in which the first electrode 126-1 and the second electrode 126-2 extend intersects or is perpendicular to the direction in which the third electrode 126-3 and the fourth electrode 126-4 extend.

[0022] Here, between the first liquid crystal cell 120-1 and the second liquid crystal cell 120-2, the extension directions of the first electrode 126-1 and the second electrode 126-2 are the same, and the extension directions of the third electrode 126-3 and the fourth electrode 126-4 are also the same. This relationship is also the same between the third liquid crystal cell 120-3 and the fourth liquid crystal cell 120-4. However, between the second liquid crystal cell 120-2 and the third liquid crystal cell 120-3, the extension directions of the first electrode 126-1 (or the second electrode 126-2) are orthogonal to each other, and the extension directions of the third electrode 126-3 (or the fourth electrode 126-4) are also orthogonal to each other. Although not shown, when the optical element 110 is composed of two liquid crystal cells 120, the optical element 110 may be configured so that the extension directions of the first electrodes 126-1 (or second electrodes 126-2) are the same between these liquid crystal cells 120, and the extension directions of the third electrodes 126-3 (or fourth electrodes 126-4) are also the same between these liquid crystal cells 120. In the following description, as shown in Figures 3 and 4, the extension direction of the first electrode 126-1 and second electrode 126-2 of the first liquid crystal cell 120-1 is defined as the y direction, and the extension direction of the third electrode 126-3 and fourth electrode 126-4 is defined as the x direction.

[0023] As an example, FIGS. 5 and 6 are schematic plan views showing the patterns of electrodes 126 formed on the first substrate 122 and the second substrate 124 of the liquid crystal cell 120, respectively. As shown in FIG. 5, a plurality of first electrodes 126-1 and a plurality of second electrodes 126-2 arranged in a stripe pattern are provided on the first substrate 122. The plurality of first electrodes 126-1 are electrically connected to each other to form a comb-shaped pattern. Similarly, the plurality of second electrodes 126-2 are also electrically connected to each other to form a comb-shaped pattern. The comb-shaped pattern of the first electrodes 126-1 and the second electrodes 126-2 extends to one side of the first substrate 122 and is electrically connected to the connector 108 (see FIG. 1). Connection wiring 144 and 146 are provided on the first substrate 122 for electrically connecting the third electrode 126-3 and the fourth electrode 126-4 to the connector 108.

[0024] Similarly, a plurality of third electrodes 126-3 and a plurality of fourth electrodes 126-4 arranged in stripes are provided on the second substrate 124. The plurality of third electrodes 126-3 are electrically connected to each other to form a comb-shaped pattern, and the plurality of fourth electrodes 126-4 are also electrically connected to each other to form a comb-shaped pattern (see FIG. 6. Note that, for ease of understanding, FIG. 6 shows a plan view from the Z+ direction, similar to FIG. 5, and the electrodes that will be provided through the substrate are indicated by solid lines). The comb-shaped patterns of the third electrodes 126-3 and the fourth electrodes 126-4 extend to one side of the second substrate 124 to form terminals 140 and 142. When the first substrate 122 and the second substrate 124 are bonded together, the terminals 140 and 142 are electrically connected to connection wiring 144 and 146, respectively, via a conductive material (not shown). Therefore, a voltage is applied to all of the electrodes 126 from the control device 150 via the connector 108 arranged on the first substrate 122, and the liquid crystal cell 120 can be driven. The same applies to the other liquid crystal cells 120. Therefore, the multiple liquid crystal cells 120 can be driven independently of each other.

[0025] (3) Alignment film In each liquid crystal cell 120, a first alignment film 128-1 covers a plurality of first electrodes 126-1 and a plurality of second electrodes 126-2, and a second alignment film 128-2 covers a plurality of third electrodes 126-3 and a plurality of fourth electrodes 126-4. The alignment film 128 includes a polymer such as polyimide. Each alignment film 128 is given alignment characteristics by an alignment process such as a rubbing method or a photoalignment method, and thereby functions to align the liquid crystal molecules contained in the liquid crystal layer 130 in a certain direction. Hereinafter, the direction in which the alignment film 128 aligns the liquid crystal molecules so that their longitudinal directions are aligned is referred to as the alignment direction.

[0026] In each liquid crystal cell 120, the alignment direction of the first alignment film 128-1 is perpendicular to the direction in which the first electrode 126-1 and the second electrode 126-2 extend. Similarly, the alignment direction of the second alignment film 128-2 is perpendicular to the direction in which the third electrode 126-3 and the fourth electrode 126-4 extend. Therefore, in each liquid crystal cell 120, the alignment directions of the first alignment film 128-1 and the second alignment film 128-2 are perpendicular to each other.

[0027] (4) Liquid crystal layer The liquid crystal layer 130 can refract light passing through it or change the polarization state of the light passing through it depending on the orientation state of the liquid crystal molecules. Nematic liquid crystals or the like are used as the liquid crystals for the liquid crystal layer 130. The liquid crystals may be either positive or negative type. The liquid crystal layer 130 preferably contains a chiral agent that imparts a twist to the liquid crystals.

[0028] (5) Light distribution control Control of light distribution using optical element 110 will be described with reference to Figures 7 and 8. Figures 7 and 8 are schematic end views illustrating the optical characteristics of one liquid crystal cell 120, corresponding to the states where a voltage is not applied to electrode 126 and where a voltage is applied, respectively. In the figures, liquid crystal molecules contained in liquid crystal layer 130 are represented schematically as circles or ellipses.

[0029] 7, in accordance with the alignment direction of the alignment film 128, the liquid crystal molecules on the first substrate 122 side of the liquid crystal layer 130 are aligned in the x direction, and the liquid crystal molecules on the second substrate 124 side of the liquid crystal layer 130 are aligned in the y direction. Therefore, in a no-electric-field state in which no voltage is applied to any of the first electrode 126-1 to the fourth electrode 126-4, the liquid crystal molecules in the liquid crystal layer 130 are aligned so as to be twisted by 90° in the xy plane as they move from the first substrate 122 to the second substrate 124. Furthermore, the polarization plane (the polarization axis or the direction of the polarization component) of light transmitted through the liquid crystal layer 130 is rotated by 90° in accordance with the alignment direction of the liquid crystal molecules. That is, the light transmitted through the liquid crystal layer 130 (more specifically, the polarization component of the transmitted light) is optically rotated.

[0030] When a voltage is applied to the first electrode 126-1 to the fourth electrode 126-4 so as to generate a potential difference between adjacent electrodes 126, a transverse electric field is generated between the two adjacent electrodes 126. As a result, as shown in FIG. 8, the liquid crystal molecules in the liquid crystal layer 130 are aligned so as to be twisted 90° in the xy plane as they move from the first substrate 122 to the second substrate 124. At the same time, the liquid crystal molecules near the first substrate 122 side are aligned in a convex arc shape relative to the first substrate 122 by the transverse electric field between the first electrode 126-1 and the second electrode 126-2, and the liquid crystal molecules near the second substrate 124 side are aligned in a convex arc shape relative to the second substrate 124 by the transverse electric field between the third electrode 126-3 and the fourth electrode 126-4. The liquid crystal molecules aligned in a convex arc shape have a refractive index distribution, and light having a polarization axis that is the same as the alignment direction of the liquid crystal molecules is diffused. Furthermore, since the cell gap d, which is the distance between the first substrate 122 and the second substrate 124, is sufficiently larger than the distance between two adjacent transparent electrodes (for example, 8 μm≦d≦50 μm, more preferably 10 μm≦d≦30 μm, and even more preferably 15 μm≦d≦25 μm), the electric field formed between the electrodes 126 does not have much effect on the liquid crystal molecules located near the center between the first substrate 122 and the second substrate 124.

[0031] The light emitted from the light source 102 includes a polarized component in the x direction (P polarized component) and a polarized component in the y direction (S polarized component). However, for convenience, the light emitted from the light source 102 will be described below as being divided into light Lp having a P polarized component and light Ls having an S polarized component.

[0032] The polarization plane of light Lp incident from the first substrate 122 side is the same as the orientation direction of the liquid crystal molecules on the first substrate 122 side, so the light Lp is diffused in the x direction in accordance with the refractive index distribution of the liquid crystal molecules (see (1) in Figure 8). Furthermore, the light Lp is optically rotated while passing through the liquid crystal layer 130, and the polarization component changes from a P polarization component to an S polarization component. The polarization plane of the S polarization component of light Lp is the same as the orientation direction of the liquid crystal molecules on the second substrate 124 side, so the light Lp is diffused in the y direction in accordance with the refractive index distribution of the liquid crystal molecules (see (2) in Figure 8).

[0033] On the other hand, the polarization plane of light Ls incident from the first substrate 122 side is different (perpendicular) to the alignment direction of the liquid crystal molecules on the first substrate 122 side, so light Ls is not diffused (see (3) in Figure 8). Furthermore, light Ls is optically rotated while passing through the liquid crystal layer 130, and its polarization component changes from an S polarization component to a P polarization component. The P polarization component of light Ls is different (perpendicular) to the alignment direction of the liquid crystal molecules on the second substrate 124 side, so light Ls is not diffused (see (4) in Figure 8).

[0034] In this way, when light passes through one liquid crystal cell 120, one polarization component is selectively diffused. Although not shown, light Ls passing through the first liquid crystal cell 120-1 can be diffused in the x and y directions by the second liquid crystal cell 120-2 using the same principle. Therefore, by using two overlapping liquid crystal cells 120, all polarization components can be diffused in the x and y directions. Furthermore, the degree of diffusion (diffusion rate) can be changed by changing the voltage applied to the electrode 126. Therefore, by stacking multiple liquid crystal cells 120 and controlling the voltage applied to each electrode 126, light can be diffused as desired in the x and y directions. As a result, the shape of the surface illuminated by light from the light source 102 can be changed into various shapes, such as a circle, an ellipse, or a cross.

[0035] 3. Control device and method for driving lighting device using the control device (1) Control device configuration The control device 150 is a device that determines the voltage to be applied to the electrode 126 of the liquid crystal cell 120 of the optical element 110 in accordance with a pulse-width modulation type input signal input from the input device 104, and supplies a pulse-amplitude modulation type output signal to the electrode 126. As shown in the block diagram of FIG. 2, the power supply 106 is connected to the control device 150, thereby supplying power to the control device 150. The power supply 106 is configured to generate two different voltages V1 and V2. For example, the power supply 106 can generate voltages V1 and V2 of 3.3 V and 30 V, respectively.

[0036] The control device 150 includes a signal generation circuit unit 160 and a voltage application unit 190. The signal generation circuit unit 160 is an integrated circuit with a calculation function and operates based on a predetermined program. The signal generation circuit unit 160 may be configured, for example, with a central processing unit (CPU), a microprocessor (MPU), an integrated circuit (IC), an application-specific integrated circuit (ASIC), or a field-programmable gate array (FPGA). The signal generation circuit unit 160 may include a random access memory (RAM) as well as non-volatile memory such as a flash memory or a read-only memory. The signal generation circuit unit 160 receives a voltage V1 from the power supply 106 and performs calculations on an input signal input from the input device 104 according to a program. As described above, the lighting device 100 is configured to independently control the diffusion of light from the light source 102 in two directions (x and y directions). For this reason, the input signal from the input device 104 includes two independent signals (a first signal and a second signal, shown as PWM X and PWM Y in FIG. 2) for diffusion in the x and y directions, and both signals are input to the control device 150 using pulse width modulation. When the control device 150 controls the light source 102, the control device 150 may be configured so that a signal (Int.) for controlling the intensity and color of light from the light source 102 is input from the input device 104 to the signal generating circuit unit 160. The signal Int. is also input as a pulse width modulated signal.

[0037] 9 is a block diagram showing the configuration of the signal generation circuit unit 160. The signal generation circuit unit 160 includes signal conversion units (first signal conversion unit 162-1 and second signal conversion unit 162-2) for processing the first signal and the second signal, respectively, and each signal conversion unit 162 can include, as its main components, a counter circuit 164, a division circuit 166, a processing circuit 168, a filter circuit 170, a correction circuit 172, and a voltage calculation circuit 174 as an applied voltage calculation unit.

[0038] The counter circuit 164 and the divider circuit 166 calculate the duty ratio of the input signal input from the input device 104 to the signal generating circuit unit 160. When the duty ratio of the input signal is 1 (100%) or 0 (0%), the potential of the input signal is either high or low over multiple frame periods, which may prevent the counter circuit 164 and the divider circuit 166 from determining the duty ratio. Therefore, a processing circuit 168, which performs exceptional processing, generates a signal indicating that the duty ratio is 1 or 0. The filter circuit 170 filters the duty ratio obtained as a result of the calculation to remove exceptional values ​​or to reduce variations in the duty ratio caused by minute changes in the pulse width of the input signal from frame to frame. Examples of this processing include median filtering and averaging filtering. The correction circuit 172 determines the diffusion degree by referring to a lookup table indicating the relationship between the duty ratio of the input signal and the diffusion degree, which is the degree to which light from the light source 102 is diffused by the optical element 110. The voltage calculation circuit 174 calculates and determines the voltage to be supplied to each electrode 126 based on the diffusivity, generates a voltage signal, and supplies it to the voltage application unit 190. The lookup table is incorporated into a program that operates the signal generation circuit unit 160, or is stored in a non-volatile memory (not shown).

[0039] The voltage application unit 190 (see FIGS. 9 and 2) includes multiple pairs of digital-to-analog converters (DAC) 192 and amplifiers (AMP) 194, each corresponding to one of the electrodes 126 of the liquid crystal cell 120. In other words, a channel (ch) is formed by a pair of digital-to-analog converters 192 and amplifiers 194, and each electrode 126 is connected to the channel formed by the pair of digital-to-analog converters 192 and amplifiers 194. This allows voltages to be supplied to each electrode 126 independently. The digital-to-analog converters 192 are connected to the signal generation circuit unit 160 via a serial bus such as a serial peripheral interface (SPI). Voltages V1 and V2 are supplied to the digital-to-analog converters 192 and amplifiers 194, respectively, from the power supply 106. The voltage signal output from the signal generation circuit unit 160 is converted into a digital signal by the digital-to-analog converters 192, amplified by the amplifiers 194, and supplied to the electrodes 126 as a pulse amplitude modulated signal.

[0040] (2) Driving method of lighting device As described above, the first input signal and the second input signal input from the input device 104 are processed by the control device 150, but since these processes are identical, a method for driving the lighting device 100 will be described using one input signal.

[0041] As shown in FIG. 10 , in the lighting device 100, a pulse-width modulated input signal is used to input the degree of diffusion of light from the light source 102 in the x and y directions. During each frame period, a high potential (High) or low potential (Low) is input from the input device 104 for a period corresponding to the degree of diffusion. The period of the frame period is 30 Hz to 120 Hz, preferably 60 Hz to 120 Hz. When the period of one frame period is within the above range, the capacitance of the liquid crystal layer 130 can maintain the voltage applied to the electrodes 126. The control device 150 converts the duty ratio of this input signal (high potential period / frame period) into a voltage amplitude ratio of a pulse amplitude modulated output signal, and applies a voltage corresponding to the voltage amplitude ratio to each electrode 126. The input device 104 may be provided with, for example, a slider or tab (knob) for specifying the degree of diffusion of light. The degree of diffusion is input by sliding the slider or rotating the tab. The input device 104 may also be configured to adjust the brightness and color of the light from the light source 102.

[0042] 11 and 12 show an example of a flowchart illustrating this driving method. After one frame period starts, the control device 150 uses a clock signal to determine at regular intervals (for example, every 1 / 200 to 1 / 2000 of one frame period) whether the potential of the input signal is High or Low (S100). If it is determined that the potential of the input signal is High (S100: YES), the counter circuit 164 starts counting the High value (S102). At this time, if one frame period (i.e., the current frame period) has not yet elapsed, the High value counter is incremented by one (S104).

[0043] Subsequently, it is determined at regular intervals from the start of the frame period whether the input signal maintains a high potential (S106). If the potential of the input signal is still high, it is determined again whether the frame period has elapsed (S103). If the frame period has not elapsed (S103: NO), the high counter is incremented by one again (S104), and it is determined again whether the input signal maintains a high state (S106). If the duty ratio is greater than 0% but less than 100%, the potential of the input signal becomes low before the frame period elapses (S106: NO), and the counter count accumulated at the time the potential of the input signal becomes low corresponds to the high period. This high period is output from counter circuit 164 to divider circuit 166 (S108).

[0044] On the other hand, when the duty ratio is 100%, a low signal is not input over one frame period (a high potential is maintained over the frame period). Therefore, the loop of steps S103 to S106 is repeated over the frame period. Then, when the frame period has elapsed (S103: YES), a flag is set indicating that the input signal is always high, and a high potential, for example, is output to the processing circuit 168 as a flag potential indicating this (S110). The processing in the processing circuit 168 will be described later. Thereafter, if the input signal still remains high, the flag is maintained. However, the next time the input signal becomes low, the flag is cleared, and a low potential, for example, is output to the processing circuit 168 as a flag potential indicating that the input signal has become low (S112). That is, in the flowchart shown in FIG. 11, if the process goes to the end via step S108, it indicates that the input signal became low before the end of the frame period. In this case, the process returns to the start of the flowchart, passes through S100, and then goes to the flowchart of FIG. 12. On the other hand, if the process goes through step S112 and ends, it indicates that the frame period has been completed, and the process returns to the start of this flowchart and the next frame period begins.

[0045] Furthermore, if the potential of the input signal is maintained at Low at the start of a frame period, or if the potential of the input signal changes from High to Low during one frame period as described above (S100: No), the Low counter is started (FIG. 12, S120). If one frame period has not elapsed since the start of the frame period, the Low counter is incremented by one (S122). In this case, it is again determined at regular intervals whether the input signal is High or Low (S124). If the input signal still maintains a Low potential, it is again determined whether the frame period has elapsed (S121). If the frame period has not elapsed (S121: No), the Low counter is again incremented by one (S122), and it is again determined whether the input signal is maintaining a Low state (S124). If the duty ratio is greater than 0% but less than 100%, the input signal goes high before the end of the frame period (S124: NO), and the counter value accumulated at the time the input signal goes high corresponds to the low period. This low period is output to the division circuit 166 (S126).

[0046] On the other hand, when the duty ratio is 0%, no High signal is input during the frame period, and therefore, after the frame period has elapsed, a flag is set indicating that the input signal is always Low during the frame, and a flag potential indicating this, such as a High potential, is output to the processing circuit 168 (S128). The processing in the processing circuit 168 will be described later. Thereafter, if the input signal still remains Low, the flag is fixed, but the next time the input signal becomes High, the flag is released, and a flag potential indicating that the input signal has become High, such as a Low potential, is output to the processing circuit 168 (S130).

[0047] The duty ratio is calculated by the division circuit 166. The sum of the High period obtained in step S108 and the Low period obtained in step S126 is output as the frame period, the ratio of the High period to the frame period is calculated as the duty ratio, and a potential corresponding to the duty ratio is output to the processing circuit 168 (S132). Then, the counter circuit 164 is reset (S134). Thus, if the duty ratio is neither 0% nor 100%, the flow shown in FIGS. 11 and 12 starts from the start of FIG. 11, reaches step S108, then passes through step S100 again, moves to the flow chart of FIG. 12, and reaches step S134. Then, the frame period ends at step S134, and returns to the start of FIG. 11 with the start of the next frame period. Also, if the duty ratio is 0%, the flow starting from FIG. 11 passes through steps S100, S120, and S128, reaches S130, and the frame period ends. After that, the process returns to the start of Fig. 11 with the start of the next frame period. Also, if the duty ratio is 100%, the flow starting from Fig. 11 passes through steps S100 and S110 and reaches S112, at which point the frame period ends. After that, the process returns to the start of Fig. 11 with the start of the next frame period.

[0048] When the duty ratio is 100% or 0%, exception processing is performed in the processing circuit 168. An example of an equivalent circuit of the processing circuit 168 is shown in FIG. 13. The processing circuit 168 illustrated in FIG. 13 has an OR circuit 176, a first multiplexer 178, and a second multiplexer 180. Two input terminals of the OR circuit 176 are connected to the counter circuit 164, and flag signals indicating that the input signal is fixed to High and Low, respectively, are input. The output terminal of the OR circuit 176 is connected to a selection control input terminal of the second multiplexer 180. Therefore, when the input signal is fixed to High or Low, a High selection control signal is input to the second multiplexer 180. The two input terminals and the selection control input terminal of the first multiplexer 178 are connected to the counter circuit. A flag signal indicating that the input signal is fixed at a high potential is input to one input terminal and a selection control input terminal of the first multiplexer 178, and a flag signal indicating that the input signal is fixed at a low potential is input to the other input terminal. One input terminal of the second multiplexer 180 is connected to the division circuit 166 and receives an input of a potential corresponding to the duty ratio, and the other input terminal is connected to the output terminal of the first multiplexer 178.

[0049] Therefore, when a flag signal indicating that the potential of the input signal is fixed at High or Low is not input, the second multiplexer 180 outputs a potential corresponding to the duty ratio greater than 0% and less than 100% calculated by the division circuit 166. On the other hand, when a flag signal indicating that the potential of the input signal is fixed at High is input to the OR circuit 176, the second multiplexer 180 outputs a potential indicating a duty ratio of 100%. Conversely, when a flag signal indicating that the potential of the input signal is fixed at Low is input to the OR circuit 176, the second multiplexer 180 outputs a potential indicating a duty ratio of 0%. Note that the configuration of the processing circuit 168 is not limited to the above configuration, and any circuit configuration may be used as long as it can realize the above-mentioned functions.

[0050] After the above processing, the signal output from processing circuit 168 is processed by filter circuit 170 and correction circuit 172 to determine the degree of diffusion. Based on this degree of diffusion, voltage calculation circuit 174 calculates the voltage to be supplied to each electrode 126 and supplies it to voltage application unit 190 as a voltage signal.

[0051] The voltage signal output from the signal generating circuit section 160 is converted into a digital signal by a digital-to-analog conversion circuit 192, resulting in the generation of an output signal that is a pulse amplitude modulated signal having an amplitude corresponding to the duty ratio of the input signal. The voltage of this output signal is amplified by an amplifier circuit 194 and supplied to the electrodes 126 of the liquid crystal cell 120 via each channel.

[0052] As described above, in the lighting device according to one embodiment of the present invention, a pulse width modulation input signal input from the input device 104 is converted into a pulse amplitude modulation output signal, and this output signal can be used to control the optical element 110. This makes it possible to connect the lighting device to a wide range of devices regardless of the communication method.

[0053] The above-described embodiments of the present invention can be combined as appropriate as long as they are not mutually inconsistent. Furthermore, even if a person skilled in the art appropriately adds or deletes components or modifies the design of a display device of each embodiment, or adds or omits processes or modifies conditions, such a display device is included in the scope of the present invention as long as it includes the gist of the present invention.

[0054] Even if there are other effects and advantages different from those brought about by the aspects of each of the above-mentioned embodiments, those that are clear from the description in this specification or that can be easily predicted by a person skilled in the art are naturally understood to be brought about by the present invention. [Explanation of symbols]

[0055] 100: lighting device, 102: light source, 104: input device, 106: power supply, 108: connector, 110: optical element, 120: liquid crystal cell, 120-1: first liquid crystal cell, 120-2: second liquid crystal cell, 120-3: third liquid crystal cell, 120-4: fourth liquid crystal cell, 122: first substrate, 124: second substrate, 126: electrode, 126-1: first electrode, 126-2: second electrode, 126-3: third electrode, 126-4: fourth electrode, 128: alignment film, 128-1: first alignment film, 128-2: second alignment film, 130: liquid crystal layer, 132: sheet material, 134: adhesive, 140: terminal, 142: terminal, 144: connection wiring, 146: connection wiring, 150: control device, 160: signal generation circuit unit, 162: signal conversion unit, 162-1: first signal conversion unit, 162-2: second signal conversion unit, 164: counter circuit, 166: division circuit, 168: processing circuit, 170: filter circuit, 172: correction circuit, 174: voltage calculation circuit, 176: OR circuit, 178: first multiplexer, 180: second multiplexer, 190: voltage application unit, 192: digital-to-analog conversion circuit, 194: amplification circuit

Claims

1. light source, an optical element including at least two liquid crystal cells arranged to transmit light emitted from the light source and overlapping each other; a control device for controlling the optical element; Each of the at least two liquid crystal cells a plurality of first electrodes and a plurality of second electrodes arranged alternately in stripes; a liquid crystal layer on the plurality of first electrodes and the plurality of second electrodes; and a plurality of third electrodes and a plurality of fourth electrodes disposed on the liquid crystal layer, intersecting the plurality of first electrodes and the plurality of second electrodes, and alternately arranged in stripes; The control device a first input signal and a second input signal of a pulse width modulation type that specify a diffusion degree of the light by the optical element in a direction in which the plurality of first electrodes extend and a direction in which the plurality of third electrodes extend are input; an illumination device configured to convert the first input signal and the second input signal into a first output signal and a second output signal of a pulse amplitude type, respectively, in accordance with a duty ratio of the first input signal and the second input signal, and supply the converted output signals to the optical element.

2. the at least two liquid crystal cells include a first liquid crystal cell, a second liquid crystal cell, a third liquid crystal cell, and a fourth liquid crystal cell arranged from the light source side; 2. The lighting device according to claim 1, wherein the direction in which the plurality of first electrodes of the first liquid crystal cell and the second liquid crystal cell extend intersects with the direction in which the plurality of first electrodes of the third liquid crystal cell and the fourth liquid crystal cell extend.

3. The lighting device according to claim 1 , wherein the control device includes a signal conversion unit configured to calculate the duty ratio of each of the first input signal and the second input signal.

4. The signal conversion unit performs the following for each of the first input signal and the second input signal: a counter circuit and a division circuit for calculating the duty ratio; a processing circuit that performs exception processing when the duty ratio is 0 or 1; a filter circuit that performs a filtering process on the duty ratio; The lighting device according to claim 3 , further comprising a correction circuit that determines the degree of diffusion from the filtered duty ratio by referring to a look-up table.

5. the processing circuit includes an OR circuit, a first multiplexer, and a second multiplexer; two input terminals of the OR circuit are connected to the counter circuit, and an output terminal is connected to a selection control input terminal of the second multiplexer; the two input terminals and the selection control input terminal of the first multiplexer are connected to the counter circuit; 5. The lighting device according to claim 4, wherein one input terminal of the second multiplexer is connected to the division circuit, and the other input terminal is connected to the output terminal of the first multiplexer.

6. the control device includes an applied voltage calculation unit configured to calculate amplitudes of the first output signal and the second output signal based on the diffusion degree for each of the first input signal and the second input signal; and The lighting device according to claim 1 , further comprising a voltage application section that applies a voltage to the optical element in accordance with the amplitude of the first output signal and the second output signal.

7. 7. The lighting device according to claim 6, wherein the voltage application unit comprises a plurality of digital-to-analog converters and a plurality of amplifiers connected to the plurality of first electrodes, the plurality of second electrodes, the plurality of third electrodes, and the plurality of fourth electrodes of the at least two liquid crystal cells, respectively.

8. A method for driving a lighting device, The lighting device includes: light source, an optical element including at least two liquid crystal cells arranged to transmit light emitted from the light source and overlapping each other; a control device for controlling the optical element; Each of the at least two liquid crystal cells a plurality of first electrodes and a plurality of second electrodes arranged alternately in stripes; a liquid crystal layer on the plurality of first electrodes and the plurality of second electrodes; and a plurality of third electrodes and a plurality of fourth electrodes disposed on the liquid crystal layer, intersecting the plurality of first electrodes and the plurality of second electrodes, and alternately arranged in stripes; The driving method includes: inputting, to the control device, a first input signal and a second input signal of a pulse width modulation type that specify a diffusion degree of the light by the optical element in the direction in which the plurality of first electrodes extend and the direction in which the plurality of third electrodes extend; and A driving method comprising converting a first input signal and a second input signal into a first output signal and a second output signal of a pulse amplitude type, respectively, in accordance with a duty ratio, and supplying the first output signal and the second output signal to the optical element.

9. the at least two liquid crystal cells include a first liquid crystal cell, a second liquid crystal cell, a third liquid crystal cell, and a fourth liquid crystal cell arranged from the light source side; 9. The driving method according to claim 8, wherein the direction in which the plurality of first electrodes of the first liquid crystal cell and the second liquid crystal cell extend intersects with the direction in which the plurality of first electrodes of the third liquid crystal cell and the fourth liquid crystal cell extend.

10. the control device includes a signal conversion unit, The driving method according to claim 8 , further comprising calculating the duty ratio of each of the first input signal and the second input signal by the signal conversion unit.

11. the signal conversion unit includes a counter circuit, a division circuit, a processing circuit, a filter circuit, and a correction circuit for each of the first input signal and the second input signal; The driving method includes: calculating the duty ratio by the counter circuit and the division circuit; performing exception processing when the duty ratio is 0 or 1 by the processing circuit; performing a filtering process on the duty ratio by the filter circuit; 11. The driving method according to claim 10, further comprising: in the correction circuit, determining the diffusion factor from the filtered duty ratio by referring to a look-up table.

12. the processing circuit includes an OR circuit, a first multiplexer, and a second multiplexer; two input terminals of the OR circuit are connected to the counter circuit, and an output terminal is connected to a selection control input terminal of the second multiplexer; the two input terminals and the selection control input terminal of the first multiplexer are connected to the counter circuit; 12. The driving method according to claim 11, wherein one input terminal of the second multiplexer is connected to the division circuit, and the other input terminal is connected to the output terminal of the first multiplexer.

13. the control device includes an applied voltage calculation unit and a voltage application unit, The driving method includes: calculating amplitudes of the first output signal and the second output signal based on the diffusion degree by the applied voltage calculation unit for each of the first input signal and the second input signal; and The driving method according to claim 8 , further comprising applying a voltage to the optical element by the voltage application section in accordance with the amplitudes of the first output signal and the second output signal.

14. 14. The driving method according to claim 13, wherein the voltage application unit includes a plurality of digital-to-analog converters and a plurality of amplifiers connected to the plurality of first electrodes, the plurality of second electrodes, the plurality of third electrodes, and the plurality of fourth electrodes of the at least two liquid crystal cells, respectively.

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