Projection type display device

Abstract

The goal is to prevent the perceived resolution from decreasing due to temperature. [Solution] The projection display device 1 includes a lamp unit 2102, a liquid crystal panel having panel pixels into which light emitted from the lamp unit 2102 is incident, an optical path shift element 230 that shifts the optical path of the projected light emitted from the liquid crystal panel to change the position of the projected pixels onto which the panel pixels are projected, a sensor 240 that detects the temperature of the liquid crystal panel, and a control circuit 20. The control circuit 20 instructs the optical path shift element 230 to shift the optical path in four unit periods of one frame period, and changes the shift speed from the position of the projected pixels in one unit period to the projection position in the next unit period according to the temperature of the liquid crystal panel detected by the sensor 240, and instructs the lamp unit 2102 to turn off or dim the light for part or all of the period during which the optical path is shifted, according to the detected temperature.

Description

Technical Field

[0001] The present disclosure relates to a projection display device.

Background Art

[0002] In a projection display device, in order to pseudo-increase the resolution of an image, a technique of shifting the position of a pixel projected onto a screen or the like by a shift device is known (see, for example, Patent Document 1). By this technique, it is possible to make the user visually recognize that a resolution higher than the resolution of the liquid crystal panel is being projected. The shift device is an optical path shift element and is also called an optical axis shift element. In the technique of shifting the position of a pixel projected by an optical path shift element, a technique of displaying an image for a movement period during the shift period has been proposed (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, it has been pointed out that in the technique of displaying an image for a movement period during the shift period, when the usage conditions of the projection display device change, the quality of the projected image deteriorates.

Means for Solving the Problems

[0005] To solve the above problems, a projection display device according to one aspect of the present disclosure includes a light source that emits light, a liquid crystal panel having panel pixels into which light emitted from the light source is incident, an optical path shift element that shifts the optical path of the projected light emitted from the liquid crystal panel to change the position of the projected pixels onto which the panel pixels are projected, a sensor that detects the temperature of the liquid crystal panel, and a control circuit that controls the liquid crystal panel, the optical path shift element, and the light source, wherein the control circuit controls the optical path shift element for a period from the first unit period to the k (k is an integer of 2 or more) unit period included in one frame period. The optical path is shifted to change every k unit periods, and the shift speed from the position of the projected pixel in one unit period to the projection position in the next unit period is changed according to the temperature of the liquid crystal panel detected by the sensor, and the light source is turned off or dimmed according to the temperature of the liquid crystal panel detected by the sensor for part or all of the period during which the optical path is shifted, and a data signal corresponding to the gradation level specified by the pixel data constituting the video data is supplied to the panel pixels for each unit period. [Brief explanation of the drawing]

[0006] [Figure 1] This figure shows the optical configuration of the projection-type display device according to the first embodiment. [Figure 2] This block diagram shows the electrical configuration of a projection-type display device. [Figure 3] This diagram shows the relationship between frames and unit periods. [Figure 4] This diagram shows the relationship between image pixels and panel pixels. [Figure 5] This figure shows the relationship between the display pixels represented by the panel pixels and the projection position in the first mode. [Figure 6] This figure shows the relationship between the display pixels represented by the panel pixels and the projection position in the second mode. [Figure 7] This diagram shows the configuration of a liquid crystal panel in a projection-type display device. [Figure 8]This diagram shows the configuration of the pixel circuit in a liquid crystal panel. [Figure 9] This is a flowchart showing the processing of a projection display device. [Figure 10] This figure shows the selection process of scan lines in an LCD panel. [Figure 11] This diagram illustrates the optical response of the liquid crystal element in the first mode and the shift operation by the optical path shift element. [Figure 12] This is an explanatory diagram of the shift operation of the optical path shift element in the second mode. [Figure 13] This is a flowchart showing the processing of a projection-type display device according to the second embodiment. [Figure 14] This is a diagram illustrating the control of turning off lights in a projection-type display device. [Modes for carrying out the invention]

[0007] Embodiments will be described below with reference to the drawings. Note that the dimensions and scale of each part in the drawings have been appropriately altered from the actual dimensions. Furthermore, the embodiments described below are preferred examples and are subject to various technically preferred limitations. Therefore, the scope of this disclosure is not limited to these forms unless otherwise specifically stated in the following description.

[0008] Figure 1 shows the optical configuration of the projection-type display device 1 according to the first embodiment. In the figure, the image generated by the projection-type display device 1 is enlarged and projected onto the screen Scr. The left-right direction of the projection surface of the screen Scr is the front-to-back direction or depth direction of the paper, and the up-down direction of the projection surface is the up-to-down direction of the paper.

[0009] The projection display device 1 is a three-panel system including liquid crystal panels 100R, 100G, and 100B. Inside the projection display device 1 is a lamp unit 2102 consisting of a white light source such as a laser or LED. The light emitted from the lamp unit 2102 is separated into three primary colors, red (R), green (G), and blue (B), by three mirrors 2106 and two dichroic mirrors 2108 arranged inside. Of these, the R color light is incident on liquid crystal panel 100R, the G color light on liquid crystal panel 100G, and the B color light on liquid crystal panel 100B.

[0010] Note that the wavelength of colored light is shorter than the wavelength of green light, and the wavelength of green light is shorter than the wavelength of red light. Also, the optical path B is longer than the optical paths R and G. Therefore, to prevent loss in the long optical path, the colored light B is guided to the liquid crystal panel 100B via a relay lens system 2121 consisting of an incident lens 2122, a relay lens 2123, and an exit lens 2124.

[0011] The liquid crystal panel 100R has a pixel circuit arranged in a matrix in a planar view, as described later. The transmittance of light emitted from the liquid crystal elements included in the pixel circuit is controlled based on a data signal corresponding to R. In other words, in the liquid crystal panel 100R, the light emitted from the liquid crystal elements functions as the smallest unit of the image. Through this control, the liquid crystal panel 100R generates a modulated image (transmitted image) of R based on the data signal corresponding to R. Similarly, the liquid crystal panel 100G generates a modulated image of G based on the data signal corresponding to G, and the liquid crystal panel 100B generates a modulated image of B based on the data signal corresponding to B. The liquid crystal panel 100G is equipped with a sensor 240 that detects the temperature of the liquid crystal panel 100G.

[0012] The modulated images of each color respectively generated by the liquid crystal panels 100R, 100G, and 100B are incident on the dichroic prism 2112 from three directions. And in the dichroic prism 2112, the color lights of R and B are refracted at 90 degrees, while the color light of G travels straight. Therefore, the dichroic prism 2112 synthesizes the modulated images of each color light. The modulated image synthesized by the dichroic prism 2112 is incident on the projection lens 2114 through the optical path shift element 230. The optical path shift element 230 shifts the outgoing optical path from the dichroic prism 2112. Specifically, the optical path shift element 230 enables the image projected onto the screen Scr to be shifted in the left - right direction and the up - down direction over the projection surface. The left - right direction and the up - down direction respectively correspond to the horizontal direction and the vertical direction of the liquid crystal panels 100R, 100G, and 100B. The projection lens 2114 enlarges and projects the composite image passing through the optical path shift element 230 and the projection lens 2114 in sequence onto the screen Scr.

[0013] For the sake of convenience of explanation, in order to distinguish the pixels projected onto the screen Scr from the pixels of the liquid crystal panels 100R, 100G, and 100B, the pixels projected onto the screen Scr may be denoted as projection pixels, and the pixels of the liquid crystal panels 100R, 100G, and 100B may be denoted as panel pixels. Also, the position of the projection pixels passing through the optical path shift element 230 may be simply denoted as the projection position. Note that the modulated images by the liquid crystal panels 100R and 100B are projected after being reflected by the dichroic prism 2112, while the modulated image by the liquid crystal panel 100G travels straight through the dichroic prism 2112 and is projected. Therefore, each modulated image by the liquid crystal panels 100R and 100B has a left - right reversed relationship with respect to the modulated image of the liquid crystal panel 100G.

[0014] FIG. 2 is a block diagram showing the electrical configuration of the projection display device 1. As shown in the figure, the projection display device 1 includes a control circuit 20 in addition to the above - mentioned liquid crystal panels 100R, 100G, 100B, optical path shift element 23, and sensor 240.

[0015] Video data Vid-in is serially supplied to the control circuit 20 from a higher-level device such as a host device (not shown) in synchronization with a synchronization signal Sync. The video data Vid-in is data indicating an image to be displayed on the projection display device 1. Specifically, the gradation level of each pixel in the image is specified in 8 bits for each of, for example, RGB. For convenience of explanation, the pixels in the image indicated by the video data Vid-in are referred to as video pixels. The synchronization signal Sync includes a vertical synchronization signal for instructing the start of vertical scanning in the video data Vid-in, a horizontal synchronization signal for instructing the start of horizontal scanning, and a clock signal indicating the timing for one video pixel of the video data Vid-in.

[0016] In the present embodiment, the color image projected on the screen Scr is expressed by synthesizing the modulation images of the liquid crystal panels 100R, 100G, and 100B. Therefore, a pixel, which is the minimum unit of the color image, can be divided into a red panel pixel by the liquid crystal panel 100R, a green panel pixel by the liquid crystal panel 100G, and a blue panel pixel by the liquid crystal panel 100B. Note that the red panel pixel, the green panel pixel, and the blue panel pixel should strictly be referred to as sub-pixels, but in this description, they are referred to as panel pixels as described above.

[0017] For the liquid crystal panels 100R, 100G, and 100B, only the incident color light, that is, the wavelength is different, and the basic structure is common. Therefore, when it is not necessary to specifically describe the color for the liquid crystal panels 100R, 100G, and 100B, the reference numeral 100 is used.

[0018] The control circuit 20 includes a display control circuit 21 and a video processing circuit 22. In the present embodiment, the arrangement of the video pixels specified by the video data Vid-in is, for example, twice as large in the vertical direction and twice as large in the horizontal direction as compared with the arrangement of the panel pixels in the liquid crystal panel 100. In this case, video data Vid-in including information with a resolution four times that of the liquid crystal panel 100 is input from the higher-level device. In this embodiment, the projection position is shifted by the optical path shift element 230 in order to make the projected pixels visible at a resolution higher than the resolution of the panel pixels. Specifically, when displaying one frame of an image using video data Vid-in, the period for displaying the frame is divided into four unit periods, and the projection position is shifted for each unit period. Due to this shift, one panel pixel appears to be displayed as if it were four projected pixels within one frame period (four unit periods).

[0019] As will be explained in more detail later, the optical response of the liquid crystal element 120, that is, the characteristic change in transmittance of the liquid crystal element 120 in response to the applied voltage, changes slowly with a time delay. Specifically, the optical response of the liquid crystal element 120 becomes faster as the temperature increases and slower as the temperature decreases. On the other hand, the projection position by the optical path shift element 230 is shifted according to the levels of the control signals Px and Py, but it does not shift instantaneously according to the levels of the control signals Px and Py. Therefore, when shifting the projection position by the optical path shift element 230, the levels of the control signals Px and Py are not changed instantaneously, but rather changed with a certain degree of inclination (slope).

[0020] In this embodiment, when the temperature is high above a threshold, the operating mode is set to the first mode, and the slope of the level changes of the control signals Px and Py is set in accordance with the speed of the optical response of the liquid crystal element 120. For example, 65 degrees is used as the temperature threshold. On the other hand, in this embodiment, when the temperature is below a threshold, the optical response of the liquid crystal element 120 becomes slow. For this reason, in this embodiment, the operating mode is set to the second mode, the amount of shift of the optical path shift element 230 for each unit period is increased, and the lamp unit 2102 is turned off when shifting so that the shifting panel pixels are not visible.

[0021] Figure 3 is a diagram illustrating the relationship between a frame duration and a unit duration in this embodiment. In this embodiment, in both the first and second modes, a frame duration F is divided into four unit durations. To conveniently distinguish the four unit durations within a frame duration F, they are assigned the designations f1, f2, f3, and f4 in order of time. The temporal length of one frame period F is 16.7 milliseconds, assuming the frequency of the vertical synchronization signal included in the synchronization signal Sync is 60 Hz. In this case, the duration of each unit period f1 to f4 is 4.17 milliseconds.

[0022] Next, we will explain the relationship between the image pixels whose gradation level is specified in the image data Vid-in, the panel pixels of the liquid crystal panel 100, and the projection position of the optical path shift element 230. As mentioned above, the optical path shift element 230 shifts the projection pixels synthesized by the dichroic prism 2112, but for convenience, the amount of this shift is converted to the size of the panel pixels projected onto the screen Scr.

[0023] The left column in Figure 4 shows a portion of the display image represented by the video data Vid. The right column in Figure 4 shows a portion of the panel pixels that are related to the arrangement of the video pixels in the left column.

[0024] In the array of video pixels in the video data Vid shown in Figure 4, for convenience, the pixels are assigned codes A1-A6 in the first row, B1-B6 in the second row, C1-C6 in the third row, D1-D6 in the fourth row, E1-E6 in the fifth row, and F1-F6 in the sixth row, respectively, in order to distinguish them. In the panel pixel array shown in Figure 4, for convenience, the pixels are assigned codes a1 and a2 to the first row and b1 and b2 to the second row, respectively, in order to distinguish them.

[0025] Figure 5 is a diagram showing the first projection path in the first mode, illustrating at which projection position the panel pixels of the liquid crystal panel 100 display the video pixels indicated by the video data Vid-in. More specifically, Figure 5 is a diagram showing at which projection position panel pixel a1 in Figure 4 displays which video pixels in which unit period f1 to f4. In the first mode, during a unit period f1, panel pixel a1 represents image pixel A2 at the projection position P11 corresponding to image pixel A2. For the sake of explanation, the projection position corresponding to image pixel A2 is referred to as the reference position. Furthermore, for a panel pixel to represent an image pixel, it means that the liquid crystal element 120 of the panel pixel has a transmittance corresponding to the gradation level of the image pixel.

[0026] During a unit period f2, panel pixel a1 represents image pixel A3 at projection position P12, which is shifted 0.5 pixels to the right of the reference projection position P11. During a unit period f3, panel pixel a1 represents image pixel B3 at projection position P13, which is shifted 0.5 pixels downwards from projection position P12. During a unit period f4, panel pixel a1 represents image pixel B2 at projection position P14, which is shifted 0.5 pixels to the left of projection position P13. In the first mode, after a unit period f4, the projection position returns to the reference projection position P11, which is shifted 0.5 pixels upward from the projection position during the unit period f4.

[0027] Figure 6 shows the second projection path in the second mode, illustrating at which projection position the panel pixels of the liquid crystal panel 100 display the video pixels indicated by the video data Vid-in. In the second mode, during a unit period f1, panel pixel a1 represents image pixel A2 at the reference position, which is projection position P21. Although the reference position in Mode 1 and Mode 2 are the same location, for the sake of explanation, the reference position in Mode 1 will be referred to as projection position P11, and the reference position in Mode 2 as projection position P21.

[0028] In a unit period f2, panel pixel a1 represents image pixel B4 at projection position P22, which is shifted 1.0 pixel to the right and 0.5 pixels downward from the reference projection position P21. During a unit period f3, panel pixel a1 represents image pixel D3 at projection position P23, which is shifted 1.0 pixel downward and 0.5 pixels to the left of projection position P21. In a unit period f4, panel pixel a1 represents image pixel C1 at projection position P24, which is shifted 1.0 pixel to the left and 0.5 pixels upward from projection position P23. In the second mode, after a unit period f4, the projection position shifts 1.0 pixel upward and 0.5 pixels to the right in panel pixels from the projection position P24, returning to the reference projection position P24.

[0029] Returning to the explanation in Figure 2, the display control circuit 21 generates a control signal Ctr for controlling the liquid crystal panels 100R, 100G, and 100B. The display control circuit 21 outputs control signals Px and Py for controlling the projection position by the optical path shift element 230 at unit intervals. The level of the control signal Px specifies the projection position by the optical path shift element 230 in the left-right direction, and the level of the control signal Py specifies the projection position by the optical path shift element 230 in the up-down direction. The display control circuit 21 receives a signal Ts corresponding to the temperature output from the sensor 240, determines whether to use the first mode or the second mode, and changes the control signals Px and Py and the image pixels represented by the panel pixels according to the mode.

[0030] Furthermore, the display control circuit 21 outputs a control signal Lmp that instructs the lamp unit 2102 to turn on or off. Specifically, in the first mode, the display control circuit 21 instructs the lamp unit 2102 to stay lit, and in the second mode, it instructs the lamp to turn on (ON) when the projection position by the optical path shift element 230 is stagnant, and to turn it off (OFF) when the projection position shifts.

[0031] The video processing circuit 22 temporarily stores the video data Vid-in, reads out the video data corresponding to the video pixels represented by the panel pixels in a unit period from the stored video data Vid-in, converts the read video data into analog signals, and outputs them as data signals Vid-R, Vid-G, and Vid-B. Of these, data signal Vid-R is a signal obtained by converting the R component of the video data Vid-in and is supplied to the liquid crystal panel 100R. Similarly, data signal Vid-G is a signal obtained by converting the G component of the video data Vid-in and is supplied to the liquid crystal panel 100G. Data signal Vid-B is a signal obtained by converting the B component of the video data Vid-in and is supplied to the liquid crystal panel 100B.

[0032] Next, we will describe the LCD panels 100R, 100G, and 100B in general terms without specifying their colors.

[0033] Figure 7 is a block diagram showing the electrical configuration of the liquid crystal panel 100. The liquid crystal panel 100 is provided with a scan line drive circuit 130 and a data line drive circuit 140 around the periphery of the display area 10.

[0034] In the display area 10 of the liquid crystal panel 100, the pixel circuits 110 are arranged in a matrix. More specifically, in the display area 10, multiple scan lines 12 are provided extending horizontally in the figure, and multiple data lines 14 are provided extending vertically in the figure, maintaining electrical isolation from the scan lines 12. The pixel circuits 110 are then arranged in a matrix corresponding to the intersections of the multiple scan lines 12 and the multiple data lines 14.

[0035] If the number of scan lines 12 is m and the number of data lines 14 is n, the pixel circuits 110 are arranged in a matrix with m rows and n columns. Both m and n are integers greater than or equal to 2. In the scan lines 12 and pixel circuits 110, the rows of the matrix are sometimes referred to as rows 1, 2, 3, ..., m in the diagram from top to bottom. Similarly, in the data lines 14 and pixel circuits 110, the columns of the matrix are sometimes referred to as columns 1, 2, 3, ..., n in the diagram from left to right.

[0036] The scan line drive circuit 130 selects scan lines 12 one by one in the order of, for example, the 1st, 2nd, 3rd, ..., mth row, according to the control of the display control circuit 21, and sets the scan signal to the selected scan line 12 to the H level. The scan line drive circuit 130 also sets the scan signal to the scan lines 12 other than the selected scan line 12 to the L level. The data line drive circuit 140 latches one line of data signals supplied from the video processing circuit 22 according to the control of the display control circuit 21, and outputs it via the data line 14 to the pixel circuit 110 located on the scan line 12 during the period when the scan signal to the scan line 12 is at a high level.

[0037] Figure 8 shows the equivalent circuits of the pixel circuits 110, consisting of four 2x2 grids corresponding to the intersections of two adjacent scan lines 12 and two adjacent data lines 14. As shown in the figure, the pixel circuit 110 includes a transistor 116 and a liquid crystal element 120. The transistor 116 is, for example, an n-channel thin-film transistor. In the pixel circuit 110, the gate node of the transistor 116 is connected to the scan line 12, its source node is connected to the data line 14, and its drain node is connected to a pixel electrode 118 which is approximately square in plan view.

[0038] The liquid crystal panel 100 has a configuration in which an element substrate on which transistors 116 and pixel electrodes 118 are formed and a counter substrate on which common electrodes 108 are formed face each other, with the electrode formation surfaces facing each other, and the liquid crystal 105 is sealed inside. Therefore, for each pixel circuit 110, a liquid crystal element 120 is formed in which liquid crystal 105 is sandwiched between a pixel electrode 118 and a common electrode 108. Furthermore, the voltage LCcom is applied to the common electrode 108.

[0039] A storage capacitor 109 is provided in parallel with the liquid crystal element 120. One end of the storage capacitor 109 is connected to the pixel electrode 118, and the other end is connected to the capacitance line 107. A voltage constant over time, for example, the same voltage LCcom as the voltage applied to the common electrode 108, is applied to the capacitance line 107. The pixel circuit 110 is arranged in a matrix shape across the horizontal direction, which is the direction in which the scan lines 12 extend, and the vertical direction, which is the direction in which the data lines 14 extend. Therefore, the pixel electrodes 118 included in the pixel circuit 110 are also arranged across both the vertical and horizontal directions.

[0040] When the scanning signal reaches the H level on scan line 12, the transistor 116 of the pixel circuit 110, which is provided in conjunction with that scan line 12, turns ON. When transistor 116 is ON, the data line 14 and the pixel electrode 118 are electrically connected, so the data signal supplied to the data line 14 reaches the pixel electrode 118 via the ON transistor 116. When scan line 12 reaches the L level, transistor 116 turns OFF, but the voltage of the data signal that reached the pixel electrode 118 is maintained by the capacitive and storage capacitance 109 of the liquid crystal element 120.

[0041] In the liquid crystal element 120, the orientation of the liquid crystal molecules changes in response to the electric field generated by the pixel electrode 118 and the common electrode 108. Therefore, the liquid crystal element 120 has a transmittance corresponding to the effective value of the applied voltage. Furthermore, the region in the liquid crystal element 120 that functions as a panel pixel, that is, the region whose transmittance corresponds to the effective value of the voltage, is the region where the pixel electrode 118 and the common electrode 108 overlap when the liquid crystal panel 100 is viewed from above. Since the pixel electrode 118 is square when viewed from above, the shape of the pixel in the liquid crystal panel 100 is also square. Furthermore, in this embodiment, the liquid crystal 105 is a VA (Vertical Alignment) type, and operates in a normally black mode where the transmittance is lowest when the applied voltage to the liquid crystal element 120 is zero, and the transmittance increases as the applied voltage increases.

[0042] The operation of supplying data signals to the pixel electrodes 118 of the liquid crystal element 120 is performed in the order of row 1, 2, 3, ..., m row for each unit period. As a result, a voltage corresponding to the data signal is maintained in each of the liquid crystal elements 120 of the pixel circuit 110 arranged in m rows and n columns, so that each liquid crystal element 120 reaches the desired transmittance, and a transmitted image of the corresponding color is generated by the liquid crystal elements 120 arranged in m rows and n columns. In this way, the transmission image is generated for each RGB channel, and the resulting color image, created by combining the RGB channels, is projected onto the screen (Scr). The data signals Vid_R, Vid_G, and Vid_B, which are output in response to a certain unit period, correspond to the RGB components of the video data corresponding to that unit period. Therefore, a composite color image corresponding to the projection position is projected at that projection position during that unit period.

[0043] Figure 9 is a flowchart showing the processing procedure of the projection-type display device 1 according to the first embodiment. First, the display control circuit 21 obtains the temperature of the liquid crystal panel 100G from the signal Ts output from the sensor 240 (step Sa11). For example, if the sensor 240 is a resistive element, its resistance value changes according to the temperature, so the display control circuit 21 converts the resistance value indicated by the signal Ts to obtain the temperature of the liquid crystal panel 100G.

[0044] Next, the display control circuit 21 determines whether the acquired temperature is below a threshold (step Sa12). If the acquired temperature is below the threshold (if the result of the judgment in step Sa12 is "Yes"), the display control circuit 21 sets the operating mode to the first mode (step Sa13). If the acquired temperature is above the threshold (if the result of the judgment in step Sa12 is "No"), the display control circuit 21 sets the operating mode to the second mode (step Sa14). The display control circuit 21 sets the operating mode to either the first mode or the second mode, and then waits for a predetermined time, for example, just one minute, or for a predetermined period of multiple frames (step Sa15). After waiting, the display control circuit 21 returns the processing procedure to step Sa11. Therefore, the setting processes in steps Sa11 to Sa15 are repeated at the predetermined time intervals.

[0045] Before describing the operation when set to mode 1, we will explain the optical response to temperature.

[0046] Figure 10 shows an example of the relationship between the selection transition of the scan line 12, the optical response of the liquid crystal element 120, and the projection position by the optical path shift element 230 in the first mode.

[0047] In Figure 10, the selection transition of scan lines 12 is shown, with the vertical axis representing the first to mth lines of scan lines 12 and the horizontal axis representing elapsed time, illustrating how the selected scan lines 12 change over time. When the selected state of scan lines 12 is indicated by a thick black line, one scan line 12 is exclusively selected in each unit period f1 to f4. The order of this selection is, as mentioned above, the 1st, 2nd, 3rd, ..., mth lines. When a certain scan line 12 is selected during a certain unit period, a data signal is supplied to a certain data line 14 as follows. Specifically, the data signal supplied to the data line 14 is an analog conversion of the video data Vin-in of the video pixel at the position corresponding to the unit period among the four video pixels corresponding to the panel pixel.

[0048] For simplicity, the optical response of the liquid crystal element 120 is described here when all panel pixels are subjected to data signals corresponding to the highest gradation level in unit periods f1 and f3, and data signals corresponding to the lowest gradation level in unit periods f2 and f4. The optical responses of the liquid crystal elements 120 located in the first row, the mth row, and the intermediate (m / 2)th row are shown as representative examples.

[0049] Generally, the optical response of the liquid crystal element 120, that is, the characteristic change in transmittance of the liquid crystal element 120 in response to the applied voltage, changes slowly with a time delay. For example, in Figure 10, the transmittance of the liquid crystal element 120 located on the first scan line 12 does not immediately reach 100% even when a data signal corresponding to the highest gradation level is applied to the pixel electrode 118 of the liquid crystal element 120 at timing t1 when the first scan line 12 becomes H level, but gradually increases with an integrated waveform accompanied by a time delay. The applied voltage of the liquid crystal element 120 is the difference between the voltage applied to the pixel electrode 118 and the voltage applied to the common electrode 108.

[0050] As shown in the figure, the timing at which the voltage of the data signal is applied to the pixel electrode 118 of the liquid crystal element 120 is earlier the smaller the row of scan line 12 corresponding to the liquid crystal element 120, and later the larger the row. Since scanning is performed from the first row to the mth row, even when all panel pixels are rewritten to the same transmittance, a situation occurs where the transmittance differs in each row. In this case, the transmittance of the projection pixels that should be visible to the user at the projection position corresponding to each unit period is either 0% or 100%.

[0051] The optical path shift element 230 is controlled to be at the projection position for a given unit period, for example, during the period when the actual transmittance in the intermediate (m / 2) row approaches the target value, and is controlled to move the projection position during other periods. Specifically, for example, when a data signal corresponding to the highest gradation level is applied in unit period f1, the optical path shift element 230 is fixed at the reference position, projection position P11, during the period from timing t21 to t22 when the transmittance of the liquid crystal element 120 in the intermediate (m / 2) row becomes equivalent to the target 100%. Note that t22 is the timing when the scan line 12 of the (m / 2) row becomes H level in the next unit period f2, that is, the end of the period during which the transmittance maintains the target 100%. Similarly, for example, if a data signal corresponding to the lowest grayscale level is applied in a unit period f2, the optical path shift element 230 is fixed at the projection position P12 during the period from timing t23 to t24, when the transmittance of the liquid crystal element 120 in the (m / 2)th row becomes equivalent to the target 0%. Note that t24 is the timing when the scan line 12 of the (m / 2)th row becomes H level in a unit period f3, that is, the end of the period during which the transmittance maintains the target 0%. Furthermore, during the period from timing t25 to t26, the optical path shift element 230 is fixed at the projection position P13 for the unit period. Also, during the period from timing t27 to t20 of the next frame period F, the optical path shift element 230 is fixed at the projection position P14.

[0052] Furthermore, from timing t22 to t23, the optical path shift element 230 is controlled to shift from projection position P111 to projection position P12. Similarly, from timing t24 to t25, the optical path shift element 230 is controlled to shift from projection position P12 to projection position P13, from timing t26 to t27, from projection position P13 to projection position P14, and from timing t20 to t21 in the next frame period F, it is controlled to shift from projection position P14 to projection position P11.

[0053] Furthermore, when controlling the projection position of the optical path shift element 230 so that the transmittance of the liquid crystal element 120 in the intermediate (m / 2) row becomes the target value, the projection position for the other rows, especially the 1st row and the mth row, will be fixed with transmittances that deviate from the target value. However, since these positions are far from the center of the display area 10, this is unlikely to be visually noticeable as a decrease in display quality.

[0054] In the projection-type display device 1, the liquid crystal panels 100R, 100G, and 100B are incident on by extremely high luminous flux compared to a direct-view panel, causing significant temperature changes. On the other hand, in the liquid crystal element 120, the optical response to electrical changes becomes faster as the temperature increases. Therefore, if the shift operation of the optical path shift element 230 is not made to follow the optical response of the liquid crystal element 120, projected pixels that have not reached the desired transmittance will be visible at the predetermined projection position, reducing the effect of artificially increasing the resolution. This reduction in the effect of increasing the resolution is particularly noticeable in regions where the temperature is high and the optical response is fast. Therefore, in this embodiment, if the temperature detected by the sensor 240 is above a threshold, the first mode is used to control the shift operation of the optical path shift element 230 based on the detected temperature. Specifically, the higher the temperature, the shorter the period for shifting the projection position, and the longer the time for fixing the projection position.

[0055] Figure 11 shows an example of control signals Px and Py for circulating the projection position in the first mode along the first path shown in Figure 5. When the levels of control signals Px and Py are zero, the projection pixel is assumed to be at the reference projection position P11. When the level of control signal Px is +A / 2 (+0.5A), the projection position is shifted 0.5 pixels to the right of the reference position, and when the level of control signal Py is +A / 2, the projection position is shifted 0.5 pixels to the down of the reference position, using panel pixels.

[0056] The level of the control signal Px rises from zero to +A / 2 during the period from timing t22 to t23, remains at +A / 2 until timing t26, decreases from +A / 2 to zero during the period from timing t26 to t27, and remains at zero until timing t22 of the next frame period F. In other words, the projection position in the left-right direction remains fixed if the level of the control signal Px is constant, and shifts at a speed corresponding to the slope of the level change if the level of the control signal Px changes.

[0057] The level of the control signal Py decreases from +A / 2 to zero during the period from timing t20 to t21, remains at zero until timing t24, increases from zero to +A / 2 during the period from timing t24 to t25, and remains at +A / 2 until timing t20 of the next frame period F. In other words, the projection position in the vertical direction remains fixed if the level of the control signal Py is constant, and shifts at a speed corresponding to the slope of the level change if the level of the control signal Py changes.

[0058] Thus, in order to cycle the projection position along the first path in the first mode and to change the period for shifting the projection position according to the temperature, the display control circuit 21 performs the following control. The display control circuit 21 first has a lookup table that stores a pre-associated relationship between temperature and the magnitude of the level change (slope) of the control signals Px and Py, and converts the temperature detected by the sensor 240 into the magnitude of the slope by referring to the lookup table. Secondly, the display control circuit 21 applies the magnitude of the slope converted by referring to the lookup table to the control signals Px and Py. Specifically, the display control circuit 21 changes the slope of the control signal Px when it rises at timing t22, the slope when it falls at timing t26, the slope of the control signal Py when it falls at timing t20, and the slope when it rises at timing t24 to the magnitude of the slope obtained by conversion.

[0059] When the temperature of the liquid crystal panel 100G detected by the sensor 240 is above a threshold, the optical response of the liquid crystal element 120 accelerates starting from timings t20, t22, t24, and t26, as the detected temperature increases, as shown in Figure 11. In Figure 11, the dashed line in the optical response shows the optical response when the temperature is above the threshold (temperature T1), while the solid line shows the optical response when the temperature is higher than temperature T1 (temperature T2).

[0060] In the first mode, if the temperature of the liquid crystal panel 100G rises above a threshold, the shift period starting at timings t20, t22, t24, and t26 is shortened, and the period during which the projection position P11, P12, P13, or P14 is fixed is extended, thereby increasing the perceived resolution.

[0061] Figure 12 shows an example of control signals Px and Py for circulating the projection position in the second mode along the second path shown in Figure 6. In the second mode, when the level of the control signal Px is +A, the projection position is shifted 1.0 pixel to the right of the reference position, and when it is -A / 2 (-0.5A), the projection position is shifted 0.5 pixels to the left of the reference position. Also, when the level of the control signal Py is +A (+1.0A), the projection position is shifted 1.0 pixel to the downward position, and when it is +3A / 2 (+1.5A), the projection position is shifted 1.5 pixels to the downward position, and so on.

[0062] In the second mode, the level of the control signal Px is -A / 2 at the start of unit period f1, rises from -A / 2 to zero during the period from timing t31 to t32 in unit period f1, rises from zero to +A during the period from timing t33 ​​to t34 in unit period f2, falls from +A to +A / 2 during the period from timing t35 to t36 in unit period f3, and falls from +A / 2 to -A / 2 during the period from timing t37 to t38 in unit period f4.

[0063] In the second mode, the level of the control signal Py is +A at the start of unit period f1, decreases from +A to zero during the period from timing t31 to t32, increases from zero to +A / 2 during the period from timing t33 ​​to t34, increases from +A / 2 to +3A / 2 during the period from timing t35 to t36, and decreases from +3A / 2 to +A during the period from timing t37 to t38 in unit period f4.

[0064] In the second mode, unlike in the first mode, the display control circuit 21 controls the lamp unit 2102. In detail, in the second mode, the display control circuit 21 instructs the lamp unit 2102 to turn off via the control signal Lmp during part or all of the period during which the projection position is shifted by the optical path shift element 230, and to turn on during the other period. That is, the display control circuit 21 instructs the lamp to turn off during part or all of the periods from timing t31 to t32, timing t33 ​​to t34, timing t35 to t36, and timing t37 to t38, and to turn on during the other period. Figure 12 shows an example where the light is instructed to be turned off by the control signal Lmp during a portion of the period in which the projection position is shifted by the optical path shift element 230.

[0065] In the second mode, the temperature of the liquid crystal panel 100G is below the threshold and is low, so the optical response of the liquid crystal element 120 is low. Also, in the second mode, the lamp unit 2102 turns off when the projection position shifts. Therefore, the projected pixels are not visible at any point other than the target projection positions P21, P22, P23, and P24. Furthermore, in the second mode, the shift amount is larger compared to the first mode, so it is possible to reduce display unevenness caused by the uneven distribution of areas where the projection position overlaps due to the shift, compared to the first mode.

[0066] Thus, in the first embodiment, if the temperature of the liquid crystal panel 100G is above a threshold, the system enters the first mode. As the temperature increases, the shift period of the projection position shortens, and the period during which the projection position is fixed at P11, P12, P13, or P14 is extended. This allows for an improved perceived resolution. On the other hand, in the first embodiment, if the temperature of the liquid crystal panel 100G is below a threshold, it enters the second mode, and display unevenness is suppressed.

[0067] The timing for switching between the first and second modes is the beginning of one frame period F, that is, the start of unit period f1 where the projection position is the reference position and the same panel pixels represent the same image pixel A2.

[0068] In the first embodiment, the projection position path in the first mode and the projection position path in the second mode are not limited to the first path shown in Figure 5 and the second path shown in Figure 6, but may include a shift amount larger than the shift amount in the first mode.

[0069] Next, a projection-type display device 1 according to the second embodiment will be described. In the first embodiment, if the temperature of the liquid crystal panel 100G is above a threshold, the device enters a first mode, and the shift period of the projection position is shortened as the temperature increases. On the other hand, if the temperature is below the threshold, the device enters a second mode, and the amount of shift of the projection position is increased, and the lamp unit 2102 is turned off during the shift period. In the second embodiment, instead of distinguishing between first and second modes, as the temperature of the liquid crystal panel 100G increases, the projection position shift period is shortened in accordance with the temperature, while as the temperature decreases, the proportion of the period during which the lamp unit 2102 is turned off during the projection position shift period is increased.

[0070] Figure 13 is a flowchart showing the processing procedure of the projection-type display device 1 according to the second embodiment. First, the display control circuit 21 obtains the temperature of the liquid crystal panel 100G from the signal Ts output from the sensor 240, similar to step Sa11 (step Sb11).

[0071] In the second embodiment, the display control circuit 21 has a lookup table that stores a pre-associated relationship between temperature and the magnitude of the level change (slope) of the control signals Px and Py, similar to the first embodiment. However, in the second embodiment, there is no temperature threshold, so the magnitude of the slope is associated even in a relatively low temperature range. Specifically, for example, in the first embodiment, if the temperature is below 65°C, the system is set to the second mode, so in the temperature range below 65°C, it is not necessary to associate and store the magnitude of the slope when the levels of the control signals Px and Py change. However, in the second embodiment, even in the temperature range below 65°C, the magnitude of the slope of the control signals Px and Py is associated and stored in the lookup table. In the second embodiment, the lower limit of the temperature to which the magnitude of the slope of the temperature control signals Px and Py can be associated is set to 50°C.

[0072] As described above, as the temperature of the liquid crystal element 120 decreases, the optical response decreases, so the shift time of the projection position increases, and the period during which the projection pixel is at a location other than the target projection position also increases. For this reason, in the second embodiment, the off period in the lamp unit 2102 is also associated with the temperature and stored in the lookup table. Specifically, the off period is stored so that it becomes longer as the temperature decreases, while at high temperatures, the shift period becomes shorter, so the off period is set to zero.

[0073] For example, the duration of the lights-off period is stored in the lookup table as a duty cycle value obtained by dividing the duration of the lights-off period by the duration of the unit period. More specifically, regarding the period when the lights are off, the temperature is, If the temperature is between 50 and 60 degrees, then 20% If the temperature is between 60°C and 70°C, then 10% If the temperature is between 70°C and 80°C, then 5% If the temperature is 80℃ or higher, the percentage is 0%. It is stored in the lookup table as such. The display control circuit 21 reads the slope and duty cycle corresponding to the acquired temperature by referring to the lookup table (step Sb12).

[0074] Next, the display control circuit 21 applies the read slope to the slope when changing the levels of the control signals Px and Py, and instructs the control signal Lmp to turn off the lights for a period corresponding to the read duty cycle (step Sb13).

[0075] After step Sb13, the display control circuit 21 waits for a predetermined time, similar to step Sa15 (step Sb14). After waiting, the display control circuit 21 returns the processing procedure to step Sb11. Therefore, the processing in steps Sb11 to Sb14 is repeated at the predetermined time intervals.

[0076] Figure 14 shows an example of control signals Px, Py, and Lmp in the second embodiment. The control of the projection position by the temperature-dependent control signals Px and Py is the same as in the first mode in the first embodiment. In the second embodiment, the control signal Lmp controls the turning off of the lamp unit 2102 with a duty cycle corresponding to the temperature if the temperature is below 80 degrees. Specifically, the display control circuit 21 first controls the center of the projection position shift period, i.e., the center of time Cen when the control signal Px or Py changes level, to coincide with the center of the period during which the control signal Lmp specifies the off state of the lamp unit 2102. Furthermore, the display control circuit 21 second controls the quotient obtained by dividing the length Woff of the period specifying the off state in the control signal Lmp by the length WL of the unit period to coincide with a duty cycle corresponding to the temperature.

[0077] In Figure 14, the dashed line in the optical response shows the optical response when the temperature of the liquid crystal panel 100G is above the threshold temperature T3, and the dashed line for the control signal Lmp shows the light being off when the temperature is T3. Furthermore, the solid line shows the optical response when the temperature of the liquid crystal panel 100G is higher than temperature T3 (temperature T4), and the solid line of the control signal Lmp shows the light being off when the temperature is T4. In other words, in the second embodiment, if the temperature is low, the period of time the lights are off will be longer, so the average brightness during the projection position shift period will be lower if the temperature is low.

[0078] In the second embodiment, as the temperature of the liquid crystal panel 100G increases, the shift period of the projection position shortens in accordance with the temperature, so the period during which the projection position is fixed increases, and the perceived resolution can be enhanced. On the other hand, as the temperature decreases, the period during which the lamp unit 2102 is turned off increases in line with the lengthening of the shift period, so the projection position is less likely to be seen at a point other than the target position, and the deterioration of display quality is suppressed.

[0079] In the first and second embodiments, the reason why the sensor 240 is provided only on the liquid crystal panel 100G is that, generally, the visibility of green is higher than that of red and blue. Specifically, if the modulated image from the liquid crystal panel 100G is not visible at the intended projection position, the impact becomes significant and is likely to lead to a decrease in display quality. The number of sensors 240 increases, but the sensors 240 may also be provided on the liquid crystal panel 100R and / or the liquid crystal panel 100B.

[0080] The projection-type display device 1 is not limited to the first and second embodiments (hereinafter referred to as "embodiments, etc."), and various modifications described below are possible. Furthermore, embodiments and their respective modifications may be combined as appropriate.

[0081] In the embodiments, the explanation was given using normally black mode, but normally white mode may also be used. Furthermore, although the liquid crystal panels 100R, 100G, and 100B were described as transmissive, they may also be reflective. If the liquid crystal panels 100R, 100G, and 100B are reflective, the transmittance should be replaced with the reflectance.

[0082] In the embodiments, the frame period F was divided into four unit periods f1 to f4. That is, the number of unit periods k in the frame period F was described as "4," but k can be any integer greater than or equal to 2.

[0083] The purpose of turning off the lamp unit 2102 is to prevent the projected pixels from being visible at locations other than the target position during the projection position shift period. Therefore, the lamp may be reduced in brightness, not limited to being turned off, as long as this objective can be achieved. Reducing brightness means lowering the brightness of the light emitted from the light source compared to the previous state.

[0084] The projection display device 1 is a three-panel system including liquid crystal panels 100R, 100G, and 100B, but color reproduction can be improved by adding a yellow (Y) panel between G and R to create a four-panel system. Furthermore, it can also be applied to a single-panel system that displays monochrome images using only shades of gray, rather than color images.

[0085] The sensor 240 is not separate from the liquid crystal panel 100G; for example, it may be an internal type in which detection wiring is formed on the liquid crystal panel 100G and the resistance of said detection wiring changes with temperature. If it is internal, it may be configured in a way other than detecting the change in resistance of the above-mentioned detection wiring. Furthermore, the sensor 240 may be a separate sensor from the liquid crystal panel 100G, used in contact with the liquid crystal panel 100G, or it may be a non-contact sensor that detects the temperature of a part of the display area 10 that has a high correlation with the temperature.

[0086] From the embodiments described above, for example, the following embodiments can be understood.

[0087] A projection display device according to one embodiment 1 includes a light source that emits light, a liquid crystal panel having panel pixels into which light emitted from the light source is incident, an optical path shift element that shifts the optical path of the projected light emitted from the liquid crystal panel to change the position of the projected pixels onto which the panel pixels are projected, a sensor that detects the temperature of the liquid crystal panel, and a control circuit that controls the liquid crystal panel, the optical path shift element, and the light source, wherein the control circuit controls the optical path shift element for k units from the first unit period to the kth (k is an integer of 2 or more) unit period included in one frame period. The optical path is shifted to change with each unit period, and the shift speed from the position of the projected pixel in one unit period to the projection position in the next unit period is changed according to the temperature of the liquid crystal panel detected by the sensor, and the light source is turned off or dimmed according to the temperature of the liquid crystal panel detected by the sensor during part or all of the period in which the optical path is shifted, and a data signal corresponding to the grayscale level specified by the pixel data constituting the video data is supplied to the panel pixels for each unit period.

[0088] According to the projection display device of Embodiment 1, the shift speed of the projection position is controlled according to the temperature of the liquid crystal panel, and the brightness of the light source during the period when the optical path is shifted is controlled to be lower than the brightness of the light source during the period when the optical path is not shifted. For example, when the temperature is high, a longer period is ensured during which the projection position is fixed, so the resolution of the image that is perceived as pseudo-visible can be increased, while for example when the temperature is low, it is suppressed that the projected pixels are perceived at points other than the target position. The lamp unit 2102 is an example of a "light source".

[0089] In a projection display device according to a specific embodiment 2 of embodiment 1, the control circuit sets the shift speed of the optical path shift element to be lower when the temperature of the liquid crystal panel detected by the sensor is a first temperature (above a threshold) than the shift speed when the temperature is a second temperature (higher than the first temperature). According to the projection display device of embodiment 2, the period during which the projection position is fixed when the liquid crystal panel is at a second temperature higher than the first temperature can be made longer than the period during which the projection position is fixed when the panel is at the second temperature. Note that temperature T1, which is above the threshold, is an example of the "first temperature," and temperature T2 is an example of the "second temperature."

[0090] In a projection display device according to another specific embodiment 3 of embodiment 1, the control circuit makes the amount of optical path shift for each unit period when the temperature of the liquid crystal panel detected by the sensor is below a threshold greater than the amount of optical path shift for each unit period when the temperature is above the threshold. According to the projection display device of embodiment 3, if the temperature of the liquid crystal panel is below a threshold, the amount of shift increases in accordance with the slow optical response, so that display unevenness caused by the uneven distribution of areas where the projection position overlaps due to the shift is greater in some areas and less in others.

[0091] In a projection display device according to another specific embodiment 4 of embodiment 1, the control circuit lowers the brightness of the light source during the period when the optical path shifts when the temperature of the liquid crystal panel detected by the sensor is a third temperature, compared to the brightness during the period when the optical path shifts when the temperature is a fourth temperature higher than the third temperature. According to the projection display device of embodiment 4, when the liquid crystal panel is at a low third temperature, the brightness of the light source during the optical path shift period becomes low, which can suppress the projection pixels from being visible at locations other than the target position. Note that temperature T3 is an example of a "third temperature," and temperature T4 is an example of a "fourth temperature." [Explanation of symbols]

[0092] 1...Projection type display device, 20...Control circuit, 21...Display control circuit, 22...Image processing circuit, 100, 100R, 100G, 100B...Liquid crystal panel, 110...Pixel circuit, 120...Liquid crystal element, 230...Optical path shift element, 240...Sensor, 2102...Lamp unit.

Claims

1. A light source that emits light, A liquid crystal panel having panel pixels, into which light emitted from the light source is incident, An optical path shifting element that shifts the optical path of the projected light emitted from the liquid crystal panel, thereby changing the position of the projected pixels onto the panel pixels, A sensor for detecting the temperature of the liquid crystal panel, A control circuit that controls the liquid crystal panel, the optical path shift element, and the light source, Includes, The aforementioned control circuit is With respect to the optical path shift element, The optical path is shifted so as to change every k unit periods, from the first unit period to the kth (where k is an integer of 2 or more) unit periods, which are included in one frame period. In accordance with the temperature of the liquid crystal panel detected by the sensor, the shift speed from the position of the projection pixel in one unit period to the projection position in the next unit period is changed among the k unit periods. With respect to the aforementioned light source, During part or all of the period in which the optical path shifts, the light source is turned off or dimmed according to the temperature of the liquid crystal panel detected by the sensor. A data signal corresponding to the grayscale level specified by the pixel data constituting the video data is supplied to the panel pixels at each unit period. Projection type display device.

2. The aforementioned control circuit is With respect to the optical path shift element, When the temperature of the liquid crystal panel detected by the sensor is a first temperature which is above a threshold, the shift speed is set as follows: The shift speed is set lower than the shift speed when the second temperature is higher than the first temperature. The projection display device according to claim 1.

3. The aforementioned control circuit is With respect to the optical path shift element, When the temperature of the liquid crystal panel detected by the sensor is below a threshold, the amount of shift in the optical path for each unit period is, The amount of optical path shift for each unit period is made larger than the amount of optical path shift for each unit period when the temperature is above the threshold. The projection display device according to claim 1.

4. The aforementioned control circuit is With respect to the aforementioned light source, When the temperature of the liquid crystal panel detected by the sensor is the third temperature, the brightness during the period in which the optical path shifts is, When the fourth temperature is higher than the third temperature, the brightness is set lower than the brightness during the period when the optical path shifts. The projection display device according to claim 1.

Images