JP2013050628A - Projection type image display device and image display method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image display device that displays image in an optical wobbling system, in which burn-in and reliability deterioration of a liquid crystal material do not occur upon displaying a static image for a long time.SOLUTION: An image display device comprises: a field image creation circuit 101 for creating a plurality of field images for an original image; a liquid crystal display element 21R for displaying the plurality of field images by vertical scanning; a signal voltage supply unit 108 for supplying signal voltage corresponding to a field image W to the liquid crystal display element 21R; an optical path shift element 30 for shifting an optical path of modulated light from the liquid crystal display element 21R in accordance with the field image displayed by the liquid crystal display element 21R; a polarity inversion unit 107 for inverting polarity of the signal voltage for every vertical scanning period; and a field image switch unit 106 for switching the field image for every vertical scanning period and for switching a display order of the field images for every switching period specified as positive integral multiple of a polarity inversion period.

Description

  The present invention relates to a projection-type image display apparatus and an image display method for displaying an enlarged optical image of a display element.

  2. Description of the Related Art Conventionally, as a display device capable of displaying a large screen / high quality image, a light source device, a display element that modulates a light beam emitted from the light source device according to image information, and forms an optical image, and a display element Projection-type image display devices including a projection optical system for enlarging and projecting the luminous flux from the projector are widely used.

  In recent years, as represented by full high-definition, 4K × 2K (horizontal direction 4096 pixels, vertical direction 2160 pixels), etc., there is an increasing demand for higher-definition images and higher-definition images. There has also been significant progress in technology for increasing the number of pixels and increasing the definition of elements.

  However, there is a limit to the reduction in the pixel arrangement pitch of the display elements in the projection type image display device, and assuming the minimum pixel pitch that can be technically realized, the element size is increased by increasing the number of pixels, and the display The cost of the display element itself due to the influence of the element yield and the increase in cost due to the increase in size of the optical system are inevitable. In addition, as the number of display pixels increases, high-speed operation proportional to the number of pixels is also required for display element driving, so that the cost of the peripheral drive circuit section is also problematic.

  In order to solve this problem, so-called optical technology is used in which the pixel position of the projection image is shifted for each unit field (hereinafter also referred to as “pixel shift”), and an image with a shifted sampling point is displayed in a time-division manner in units of fields. An image display device using a wobbling method is disclosed (for example, see Patent Document 1).

  In Patent Document 1, one frame image is composed of a plurality of field images whose sampling points are spatially shifted, and on the projected image, the display pixel positions are shifted at a pitch corresponding to the sampling point shift of these field images. I do. A plurality of field images whose sampling points are in an interpolating relationship are integrated by the afterimage effect of human visual characteristics and perceived as a high resolution image. As a result, it is possible to cope with higher-definition image display that exceeds the limit of the number of pixels of the display element itself.

  Further, there is disclosed an image projection apparatus that uses a reflective liquid crystal display element as a display element and an optical path modulation element having an optical wobbling function disposed between a polarizing beam splitter and a projection lens, thereby enabling high-definition display ( For example, see Patent Document 2.)

JP-A-4-113308 JP 2003-5132 A

  By the way, as disclosed in Patent Document 2, a high-resolution image display device using an optical wobbling method is realized by using a liquid crystal display element such as a reflective liquid crystal display element that displays an image by a light modulation action of liquid crystal. In order to prevent image burn-in due to a DC voltage component and deterioration of the reliability of the liquid crystal material, it is necessary to drive the liquid crystal with a positive and negative symmetrical AC voltage. Specifically, when supplying a signal voltage corresponding to image data to be displayed to the liquid crystal display element, the “frame inversion driving method” is performed by inverting the signal voltage with respect to a predetermined reference potential every vertical scanning period. "Is often used.

  On the other hand, as described above, the image display device using the optical wobbling method displays a plurality of field images whose spatial sampling positions are interpolated with each other in a time-sharing manner, and supports spatial sampling points of each field image. Then, the optical path of the modulated light is shifted so that the observed pixel shifts. For this reason, the field to be displayed is basically updated every vertical scanning period of the display element.

  However, when different sampling image displays corresponding to the pixel shift are assigned to the fields before and after the polarity is reversed, the image sampling points are different between the alternating display images of the wobbling display. As for the picture portion, the signal voltage is asymmetric with positive and negative polarity. As a result, there has been a problem that liquid crystal burn-in occurs and the reliability of the liquid crystal material is remarkably lowered.

  In view of the above problems, an object of the present invention is to provide a projection-type image display apparatus and an image display method that do not cause burn-in in a long-time display of a still image or decrease in reliability of a liquid crystal material in image display by an optical wobbling method. That is.

  According to one aspect of the present invention, a field image generation circuit (101) that generates a plurality of field images (W1, W2) having sampling points complementary to an original image, and a plurality of field images (W1, W2). ) Are sequentially and periodically displayed by vertical scanning, and signal voltages corresponding to a plurality of field images (W1, W2) are supplied to the liquid crystal display elements (21R, 21G, 21B). In response to the signal voltage supply unit 108 to be supplied and the plurality of field images (W1, W2) displayed on the liquid crystal display elements (21R, 21G, 21B), the liquid crystal display elements (21R, 21G, 21B) are emitted. The polarity of the signal voltage is inverted every vertical scanning period of the optical path shift element (30) that shifts the optical path of the modulated light and the liquid crystal display elements (21R, 21G, 21B). The plurality of field images (W1, W2) displayed on the liquid crystal display elements (21R, 21G, 21B) are switched and the polarity of the signal voltage is inverted between positive and negative for each vertical inversion section (107) and vertical scanning period For each switching period (T1, T2) defined by a positive integer multiple of the polarity inversion period (F1, F2,..., F9), the polarity of the signal voltage and the liquid crystal display elements (21R, 21G, 21B) are displayed. Field image switching unit that switches the display order of the plurality of field images (W1, W2) so that the correspondence relationship with the plurality of field images (W1, W2) is reversed from the correspondence relationship of the immediately preceding switching period (T1, T2). (106) is provided.

  In one aspect of the present invention, a double speed conversion processing unit (104, 105) that doubles the vertical scanning rate of the field image (W1, W2) may be further provided.

  In one aspect of the present invention, the optical path shifting element (30) is a polarizing member that relatively rotates the polarization direction of the modulated light emitted from the liquid crystal display elements (21R, 21G, 21B) by 90 degrees by voltage on / off control. (31) and a birefringent member (32) that linearly refracts or refracts the modulated light according to the polarization direction of the modulated light from the polarizing member (31).

  In one embodiment of the present invention, the liquid crystal display elements (21R, 21G, 21B) may update the field images (W1, W2) simultaneously for all the display pixels.

  According to another aspect of the present invention, the step of generating a plurality of field images (W1, W2) having sampling points complementary to the original image, and the plurality of field images (W1, W2) are converted into liquid crystal display elements. (21R, 21G, 21B) sequentially and periodically displaying by vertical scanning, and supplying signal voltages corresponding to a plurality of field images (W1, W2) to the liquid crystal display elements (21R, 21G, 21B). Corresponding to the plurality of field images (W1, W2) displayed on the liquid crystal display elements (21R, 21G, 21B), the optical path of the modulated light emitted from the liquid crystal display elements (21R, 21G, 21B) is shifted. A step, a step of inverting the polarity of the signal voltage every vertical scanning period of the liquid crystal display elements (21R, 21G, and 21B), and a liquid crystal display every vertical scanning period. A step of switching a plurality of field images (W1, W2) displayed by the children (21R, 21G, 21B), and a positive polarity inversion period (F1, F2,..., F9) in which the polarity of the signal voltage is inverted between positive and negative For each switching period (T1, T2) defined by an integral multiple, the correspondence between the polarity of the signal voltage and the plurality of field images (W1, W2) displayed on the liquid crystal display elements (21R, 21G, 21B) is immediately before. The image display method includes a step of switching the display order of the plurality of field images (W1, W2) so as to reverse the correspondence relationship of the switching periods (T1, T2).

  According to the present invention, it is possible to provide a projection-type image display device and an image display method that do not cause image sticking in a long-time display of a still image or a decrease in reliability of a liquid crystal material in image display using an optical wobbling method.

It is a block diagram which shows an example of the control part which concerns on embodiment of this invention. It is the schematic which shows an example of the projection type image display apparatus which concerns on embodiment of this invention. It is the schematic which shows an example of the optical path shift element which concerns on embodiment of this invention. It is a perspective view of a half wave plate, an optical path shift element, and a projection lens concerning an embodiment of the invention. FIG. 5A is a schematic diagram showing sampling points of the odd field (W1) according to the embodiment of the present invention. FIG. 5B is a schematic diagram showing sampling points of the even field (W2) according to the embodiment of the present invention. FIG. 6A is a schematic diagram showing display pixel positions of odd fields on the projected image according to the embodiment of the present invention. FIG. 6B is a schematic diagram showing display pixel positions of even fields on the projection image according to the embodiment of the present invention. It is a timing chart for demonstrating an example of the image display method which concerns on embodiment of this invention. It is a block diagram which shows an example of the liquid crystal display element which concerns on the modification of embodiment of this invention. It is a timing chart for demonstrating operation | movement of the liquid crystal display element which concerns on the modification of embodiment of this invention. 6 is a timing chart for explaining an image display method according to a comparative example. It is another timing chart for demonstrating the image display method which concerns on a comparative example.

  Next, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the relationship between the thickness and the planar dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.

  Further, the embodiments described below exemplify apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention includes the material, shape, structure, The layout is not specified as follows. The technical idea of the present invention can be variously modified within the scope of the claims.

(Projection type image display device)
As a projection type image display apparatus according to an embodiment of the present invention, a projection type image display apparatus that performs color display using a reflective liquid crystal display element will be described as an example.

  As shown in FIG. 1, a projection-type image display apparatus according to an embodiment of the present invention includes a field image generation circuit 101 that generates a plurality of field images W1 and W2 having sampling points complementary to an original image. Liquid crystal display elements 21R, 21G, and 21B that sequentially and periodically display a plurality of field images W1 and W2 by vertical scanning, and signal voltages corresponding to the plurality of field images W1 and W2 are displayed on the liquid crystal display elements 21R, 21G, and 21B. The optical path of the modulated light emitted from the liquid crystal display elements 21R, 21G, 21B corresponding to the signal voltage supply unit 108 to be supplied to the plurality of field images W1, W2 displayed on the liquid crystal display elements 21R, 21G, 21B. For each vertical scanning period of the optical path shift element (pixel shift element) 30 that shifts and the liquid crystal display elements 21R, 21G, and 21B, the signal voltage Polarity reversing unit 107 for reversing the polarity, and polarity reversal by switching a plurality of field images W1, W2 displayed on the liquid crystal display elements 21R, 21G, 21B and reversing the polarity of the signal voltage between positive and negative for each vertical scanning period For each switching period defined by a positive integer multiple of the period, the correspondence between the polarity of the signal voltage and the plurality of field images W1, W2 displayed on the liquid crystal display elements 21R, 21G, 21B corresponds to the previous switching period. A field image switching unit 106 that switches the display order of the plurality of field images W1 and W2 is provided so as to reverse the relationship.

  As shown in FIG. 2, the projection type image display apparatus according to the embodiment of the present invention corresponds to the light source 10 and the three primary colors of red (R), green (G), and blue (B) as an overall configuration. Optical that illuminates the liquid crystal display elements 21R, 21G, and 21B using the liquid crystal display elements 21R, 21G, and 21B and the illumination light from the light source 10, and projects the modulated light emitted from the liquid crystal display elements 21R, 21G, and 21B The system 1 includes an optical path shift element 30 that shifts the optical path of modulated light emitted from the liquid crystal display elements 21R, 21G, and 21B, and a control unit 100 that controls the liquid crystal display elements 21R, 21G, and 21B and the optical path shift element 30. .

  The optical system 1 includes a condenser lens 11, a fly-eye lens pair 12, a polarization conversion optical element (PCS) 13, lenses 14, 18R, 18G, and 18B, dichroic mirrors 15 and 17, folding mirrors 16 and 16B, and a polarizing plate 19R. 19B, 19G, 22R, 22B, 22G, wire grid polarizing plates 20R, 20B, 20G, a dichroic prism 23, a half-wave plate 24, and a projection lens 25 are provided.

  Illumination light from the light source 10 passes through a condenser lens 11, a fly-eye lens pair 12, a polarization conversion optical element (PCS) 13, and a lens 14, and is decomposed into blue light and yellow light by a dichroic mirror 15, At 16B, the signal is folded back in each optical path direction. The yellow light is further decomposed into green light and red light by the dichroic mirror 17. Each of the red light, the green light, and the blue light is improved in the linear polarization degree of polarization by the polarizing plates 19R, 19B, and 19G through the lenses 18R, 18G, and 18B, and then the wire grid polarizing plate 20R that is disposed at an angle of 45 degrees. The light passes through 20B and 20G and enters each of the liquid crystal display elements 21R, 21G, and 21B.

  For example, LCOS (Liquid Crystal on Silicon) can be used as the liquid crystal display elements 21R, 21G, and 21B. The liquid crystal modulation member of each of the liquid crystal display elements 21R, 21G, and 21B has a signal voltage (as a drive signal) from the signal voltage supply unit 108 shown in FIG. Modulation voltage) is applied. The illumination light incident on each of the liquid crystal display elements 21R, 21G, and 21B is emitted after receiving a modulation action corresponding to the signal voltage.

  The modulated light emitted from each of the liquid crystal display elements 21R, 21G, and 21B is reflected by the wire grid polarizing plates 20R, 20B, and 20G arranged at 45 degrees, and an unnecessary polarization component is analyzed by the polarizing plates 22R, 22B, and 22G. After removal, color synthesis is performed by the dichroic prism 23. The emitted light color-synthesized by the dichroic prism 23 enters the optical path shift element 30 via the half-wave plate 24 and is projected from the projection lens 25 onto the screen 26.

  As shown in FIG. 3, the optical path shifting element 30 includes a polarizing member (polarizing switch) 31 disposed in the preceding stage and a birefringent plate 32 disposed on the exit side of the polarizing switch 31. The polarization switch 31 emits while maintaining the polarization direction of linearly polarized incident light when the control voltage (V) is off level, and changes the polarization direction of incident light by 90 degrees when the control voltage (V) is on-level voltage. Rotate. As the polarization switch 31, a liquid crystal cell in which liquid crystal is sealed in an opposing transparent electrode substrate can be used. When a voltage is applied to the liquid crystal cell, the arrangement state of molecules changes according to the voltage, and birefringence is exhibited with respect to light having a specific polarization direction component. If the phase difference in the optical path having the thickness d1 due to the birefringence is controlled to be ½ (180 degrees) of the incident light wavelength, the polarization direction of the emitted light is extracted as linearly polarized light rotated by 90 degrees. Can do. As a liquid crystal material / operation mode suitable for the polarization switch 31, for example, a ferroelectric liquid crystal having an extremely high switching speed, an OCB (Optically Compensated Bend) mode liquid crystal, or the like is used.

  As the birefringent plate 32, a crystal material having optical anisotropy such as a quartz plate can be used. When light having polarization components of ordinary and extraordinary rays is incident on the optical axis, the refractive index of ordinary rays is constant regardless of the angle of the incident light with respect to the optical axis, whereas incident light is incident on extraordinary rays. Depending on the angle with respect to the optical axis, and the angle with respect to the optical axis is maximized under a vertical condition. Thus, by switching the polarization of the light incident on the birefringent plate 32, the light refraction state changes, and the beam position on the exit surface can be shifted. Since the beam displacement amount by the optical path shift element 30 is determined by the relationship between the refraction angle and the thickness d2 of the birefringent plate 32, the displacement amount can be designed to an arbitrary value by changing the thickness d2 of the birefringent plate 32.

  As shown in FIG. 4, a half-wave plate 24 is disposed at the front stage of the optical path shift element 30. The half-wave plate 24 matches the polarization direction with the optical axis direction 45 degrees of the birefringent plate 32 in an example in which the pixel shift by the optical path shift element 30 is inclined at 45 degrees and pixel shift display is performed with two field images. It is for making it happen. By alternately controlling the control voltage (V) on the polarization switch 31 at the on and off levels, only one set of the optical path shift elements 30 is used, and the pixel position of the projected image is set to 45 degrees diagonally and horizontally and vertically 0 degrees each. .5 pixel pitch pixel shift can be accurately controlled. As shown in FIG. 4, the optical axis is shifted by switching the polarization switch 31 by voltage, and the pixel position of the projection image by the projection lens 25 can be shifted.

  As shown in FIG. 1, the control unit 100 includes a field image generation circuit 101, a control timing signal generation circuit 102, a data processing unit 103, a polarity inversion unit 107, a signal voltage supply unit 108, and an optical path shift control circuit 109. The data processing unit 103 includes first and second double speed conversion processing units 104 and 105 and a field image switching unit 106.

  As shown in FIG. 5A, the field image generation circuit 101 includes a field image W1 obtained by taking sampling points P1 every other pixel in the horizontal and vertical directions from the original image input from the outside, and FIG. As shown in FIG. 5, field images W2 are generated from the original image, taking sampling points P2 every other pixel in the horizontal and vertical directions. In the field images W1 and W2, the sampling points P1 and P2 of the field images are shifted by one pixel both vertically and horizontally with respect to the original image. As a result, the field images W1 and W2 have a complementary relationship with respect to the oblique 45 ° direction. For sampling and field pixel data generation for the original image, the original image can be generated by simply thinning out every other pixel, and if necessary, information on neighboring pixel data adjacent to the target pixel is weighted A sampling method including a filtering process reflected in the above may be used.

  The control timing signal generation circuit 102 shown in FIG. 1 outputs the control timing signal A to the polarity inversion unit 107 and the control timing signal E to the field image switching unit 106 according to the synchronization signal and the reference clock input from the outside. And a write control signal group WT_CTL and a read control signal group RD_CTL are output to the first and second double speed conversion processing units 104 and 105, respectively.

  Each of the first and second double speed conversion processing units 104 and 105 includes a field memory. For example, a first-in first-out (FIFO) memory can be used. The first and second double speed conversion processing units 104 and 105 perform read control at a rate twice that of write control according to the write control signal group WT_CTL and the read control signal group RD_CTL from the control timing signal generation circuit 102. As a result, the vertical scanning frequencies of the field images W1 and W2 are each doubled. For example, if the original image is a signal of 60 Hz, which is a general moving image vertical scanning rate, the vertical scanning rate of each field image is doubled to 120 Hz by this processing.

  The field image switching unit 106 is a data selector, for example. The field image switching unit 106 is synchronized with the control timing signal E from the control timing signal generation circuit 102, and outputs a plurality of field images W1 that are output after being subjected to double speed processing by the first and second double speed conversion processing units 104 and 105. , W2 is selected / switched and output. As a result, the two field images W1 and W2 are switched with the vertical scanning period doubled as the basic unit.

  The polarity inversion unit 107 synchronizes with the control timing signal (flag signal) A from the control timing signal generation circuit 102 in synchronization with the polarities of the field images W1 and W2 output from the field image switching unit 106 (digital codes 0 and 1). ) From positive polarity to negative polarity or from negative polarity to positive polarity. Since this control corresponds to the polarity inversion driving cycle of the liquid crystal display elements 21R, 21G, and 21B, switching is basically performed for each vertical scanning period.

  The signal voltage supply unit 108 supplies signal voltages corresponding to the field images W1 and W2 to the display pixels of the liquid crystal display elements 21R, 21G, and 21B. That is, the signal voltage supply unit 108 performs D / A conversion on the data of the field images W1 and W2 subjected to the polarity inversion processing by the polarity inversion unit 107 to convert them into analog signals, and drives the liquid crystal display elements 21R, 21G, and 21B. Voltage level conversion is performed to fit the signal voltage range. The generated analog signal voltage is supplied as a drive signal to the liquid crystal display elements 21R, 21G, and 21B.

  The optical path shift control circuit 109 outputs a control signal G to the optical path shift element 30 in synchronization with the control timing signal E of the field image switching unit 106. The optical path shift element 30 synchronizes with the display periods of the field images W1 and W2, as shown in FIGS. 6A and 6B, the pixel positions P, Shift to Q.

  As described above, the time-division display of the plurality of field images W1, W2 shifted from the sampling points P1, P2 shown in FIGS. 5 (a) and 5 (b), and FIGS. 6 (a) and 6 (b). With the optical wobbling method in which the shifts of the pixel positions P and Q of the projected image shown in FIG.

  Here, a comparative example in the case of performing image display by the optical wobbling method will be described with reference to FIG. FIG. 10A shows changes in the signal voltage in driving the liquid crystal display element, and FIG. 10B shows changes in the field images W1 and W2 displayed on the liquid crystal display element.

  When the field images W1 and W2 shown in FIG. 10B are assigned as they are to the polarity inversion periods F11 and F12 in which the polarity of the signal voltage shown in FIG. It is driven by the drive voltage based on the field image W1, and is always driven by the drive voltage based on the field image W2 during the negative polarity (−) period. Therefore, in this method, since the liquid crystal is driven based on the field images W1 and W2 that are different in the positive polarity period and the negative polarity period of the signal voltage, positive and negative symmetric AC driving that is the original purpose of polarity inversion driving is realized. The problem of being unable to do so occurs. In particular, since the difference between the data of the field images W1 and W2 supplied to the same pixel in the liquid crystal display element is large at the edge portion of the image, the influence of the asymmetry of the AC drive appears remarkably, and the burn-in and the reliability of the liquid crystal material Problems such as deterioration occur.

  As a countermeasure, when a plurality of field images W1 and W2 are displayed in a time-sharing manner, vertical scanning is performed n times (n is an integer of 2 or more) using each field signal within the same field display period. There is a method of reversing the polarity of a signal voltage for each unit of a plurality of vertical scanning periods. This method will be described with reference to FIG. FIG. 11A shows changes in the signal voltage in driving the liquid crystal display element, and FIG. 11B shows changes in the field images W1 and W2 displayed on the liquid crystal display element.

  The vertical scanning with the field images W1 and W2 shown in FIG. 11B is performed twice, and the signal voltages based on the same field images W1 and W2 are reliably applied symmetrically with both positive and negative polarities. According to this method, since there is no principle of asymmetry in the AC drive of the liquid crystal display element, the problems of burn-in and reliability deterioration can be solved.

  However, in the method of scanning a plurality of times with the same field images W1 and W2 shown in FIGS. 11A and 11B, the display update cycle of the field images W1 and W2 in the optical wobbling method, that is, wobbling. The display switching period extends to n times the vertical scanning period, and the field images W1 and W2 are alternately displayed at a low frequency in this cycle. For this reason, there is a problem in that blinking (flicker) in units of display pixels is easily visually recognized in the image edge portion and the fine pattern portion, and the display quality of the image is deteriorated.

(Image display method)
Next, an example of an image display method using the projection image display apparatus according to the embodiment of the present invention will be described with reference to the timing chart of FIG. FIGS. 7A to 7G show changes in the outputs of the points (nodes) A to G shown in FIG. FIG. 7H shows a mode of change in the pixel positions P and Q of the projection image shifted by the optical path shift element 30.

  As shown in FIG. 7A, the control timing signal (flag signal) A output from the control timing signal generation circuit 102 is a vertical scan that has been field doubled by the first and second double speed conversion processing units 104 and 105. It switches to high / low level every period.

  The polarity inversion unit 107 inverts the polarity of the signal voltage in synchronization with the control timing signal (flag signal) A every vertical scanning period with the field double speed. As a result, the signal voltage supplied from the signal voltage supply unit 108 to the liquid crystal display elements 21R, 21G, and 21B has a polarity of +, −, +, −, − for each vertical scanning period, as shown in FIG. Invert like .... Here, one set of the positive polarity period and the negative polarity period is defined as polarity inversion periods F1, F2, F3,. That is, the polarity inversion periods F1, F2, F3,..., F9 are twice as long as the vertical scanning period.

  As shown in FIGS. 7C and 7D, the first and second double speed conversion processing units 104 and 105 output field images W1 and W2 for each vertical scanning period at which the field double speed is achieved.

  As shown in FIG. 7E, the control timing signal generation circuit 102 generates a control timing signal E to the field image switching unit 106 that selects and outputs two series of field images W1 and W2.

  Here, the time division switching of the field image data based on the control timing signal E is defined not by a uniform cycle of every vertical scanning period but by a positive integer multiple of the polarity inversion cycles F1, F2, F3,. The switching periods T1, T2,... Are reversed as basic units.

  When attention is paid to the time-division output control of the display field in FIG. 7E and FIG. 7F, the field images are W1, W2, W1 in the first switching period T1 from time t = t0 to time t = t1. ,..., W1, W2 are displayed in this order. That is, in the first switching period T1, the field image W1 corresponds to the positive polarity period of the signal voltage, and the field image W2 corresponds to the negative polarity period of the signal voltage.

  In the second switching period T2 from the time t = t1 to the time t = t2, the correspondence relation between the field images W1 and W2 in the immediately preceding first switching period T1, the correspondence relation, and the polarity of the signal voltage is reversed. Thus, the field images are displayed in the order of W2, W1, W2,..., W2, W1. That is, in the second switching period T2, the field image W2 corresponds to the positive polarity period of the signal voltage, and the field image W1 corresponds to the negative polarity period of the signal voltage.

  Thereafter, by repeating this switching in the third, fourth,... Switching periods, the polarity asymmetry on the time integration is canceled for each of the field images W1, W2.

  As shown in FIG. 7G, the control signal G from the optical path shift control circuit 109 to the optical path shift element 30 is switched in synchronization with the control timing signal E for the field image switching unit 106. As shown in FIG. 7H, the optical path shift element 30 sets the pixel position of the projection image to the pixel position P in the display period of the field image W1, and sets the pixel position of the projection image to the pixel position P in the display period of the field image W2. Shift to position Q. In this way, display with a resolution higher than the number of effective pixels of the liquid crystal display elements 21R, 21G, and 21B can be realized by interlocking the sequential display of the field image W1 and the pixel shift by the optical wobbling method.

  As described above, according to the projection image display device and the image display method using the same according to the embodiment of the present invention, in the image display by the wobbling method, a plurality of fields are provided for each field period corresponding to each polarity of liquid crystal AC drive. Even when the field images W1 and W2 are alternately displayed, the polarity inversion and the association between the field images W1 and W2 are reversed in a predetermined switching period T1, T2,. In this case, the direct current component of the drive voltage at the image edge or the fine image pattern portion which becomes a particular problem can be canceled in terms of time average. As a result, it is possible to greatly reduce the burn-in in the long-time display of the still image and the deterioration of the liquid crystal material.

  If the image to be displayed is a moving image, strictly speaking, the frame information of the original image to be displayed is different in each of the first, second, third,... Period in FIG. Although the AC averaging between the two does not function completely, the influence of the image sticking of the liquid crystal and the DC voltage component is usually the condition in the long-time display of the still image in which the DC voltage is constantly applied under the constant condition. Since it is the most severe, the drive and display control of the present invention can provide a significant improvement effect of conventional problems.

(Modification)
Next, as a modification of the embodiment of the present invention, a liquid crystal display element more suitable for realizing an optical wobbling projection type image display apparatus will be described.

  The liquid crystal display element 21 according to the modification of the embodiment of the present invention includes a display unit 205, a horizontal scanning circuit 201, and a vertical scanning circuit 204, as shown in FIG. The display unit 205 includes m × n pixel circuits P11 to Pmn arranged in a matrix. Each pixel circuit P11 to Pmn includes two switching transistors Tr and Tr2, two capacitors C1 and C2 for holding a signal voltage, and a pixel electrode LC for applying and driving the signal voltage to the liquid crystal of each pixel. .

  The horizontal scanning circuit 201 includes a horizontal shift register 202 and sampling switch groups S1 to Sm. The horizontal shift register 202 is supplied with a horizontal scanning synchronous reference timing signal HST and a horizontal shift clock HCK, and sequentially sends out pulse signals to the control terminals of the output stage sampling switch groups S1 to Sm every horizontal scanning period. The input terminals of the sampling switch groups S1 to Sm are wired in common, the signal voltage Video to be written to the liquid crystal display element 21 is supplied, and the sampling switch groups S1 to Sm are sequentially turned on so that signals are supplied to the pixel unit signal lines. The voltage is sequentially sampled and held.

  The vertical scanning circuit 204 is supplied with a vertical scanning synchronization reference timing signal VST and a vertical shift clock VCK, and sequentially sends an ON pulse to a switching transistor Tr1 which is a writing switch for a pixel row corresponding to each output stage. Sequentially select write lines. By repeating this driving operation at a vertical scanning period, signal voltages for the display pixels are sequentially written to display an image.

  In the liquid crystal display element 21, two-stage series switching transistors Tr1 and Tr2 are formed in the pixel circuits P11 to Pmn. After the signal voltage is sequentially written by the switching transistor Tr1, the voltage held in the capacitor C1 is applied. The switching transistor Tr2 can retransfer to the holding capacitor C2 on the pixel electrode LC side at a timing different from the sequential scanning timing of each pixel row.

  Next, an example of the drive / display operation of the liquid crystal display element 21 according to a modification of the embodiment of the present invention will be described with reference to FIG.

  “F 1”, “F 2”, “F 3”, and “F 4” in the uppermost row in FIG. 9 represent drive signal inputs in each vertical scanning period supplied to the liquid crystal display element 21, and (W 1) and (W 2). ) Means to correspond to the field images W1 and W2.

  “A1” and “B1” in FIG. 9 correspond to the nodes A1 and B1 of the pixel circuit Pm1 in the first row (first row) of the vertical scanning shown in FIG. 8, and “A1” is held in the capacitor C1. The signal voltage “B1” indicates a change in the output node of the switching transistor Tr2, that is, the pixel electrode voltage that finally drives the liquid crystal.

  “An” and “Bn” in FIG. 9 correspond to the nodes An and Bn of the pixel circuit Pmn in the last row (n-th row) of the vertical scanning shown in FIG. 8, and “An” is held in the capacitor C1. The signal voltage “Bn” indicates a change in the output node voltage of the switching transistor Tr2.

  “TRIG” in FIG. 9 indicates a change mode of the common control signal TRIG shown in FIG. The lowermost part of FIG. 9 shows a change mode of the pixel positions P and Q shifted by the optical path shift element 30.

  As shown in “A1” and “An” in FIG. 9, the signal writing timing of the first scanning line (first line) and the last scanning line (nth line) has a time difference due to sequential scanning, and the time difference is vertical scanning. It is almost equivalent to the period. In the modification of the embodiment of the present invention, each of the pixel circuits P11 to Pmn includes a switching transistor Tr2, and on / off of the switching transistor Tr2 is controlled by a common control signal TRIG for all pixels. Specifically, the second switching transistors Tr2 of all the pixels are simultaneously turned on simultaneously by the control signal TRIG at a timing immediately after the signal writing in the last pixel row is completed in the vertical scanning. As a result, in “B1” and “Bn” in FIG. 9, the signal voltage that finally contributes to the liquid crystal drive changes simultaneously from the previous field to the information in the current field.

  As described above, according to the modification of the embodiment of the present invention, the time division / multiple field image display and the optical path shift control of the wobbling display method are affected by the scanning time difference in realizing the image display by the wobbling method. Can be controlled well without being affected. Therefore, it is possible to realize high-quality image display without problems such as in-plane nonuniformity of the wobbling display effect.

(Other embodiments)
As described above, the present invention has been described according to the embodiment. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  For example, in the embodiment of the present invention, as shown in FIG. 7, the display order of the field images W1, W2 is switched every switching period T1, T2 that is four times the unit of polarity inversion periods F1, F2,. However, this switching period is not limited to this. For example, in consideration of display characteristics, liquid crystal characteristics, and the like, it is possible to appropriately adopt switching periods of positive integer multiples of 2, 3, 5, or more than the polarity inversion periods F1, F2,. .

  In the embodiment of the present invention, as shown in FIG. 1, the case where the three-plate type liquid crystal display elements 21R, 21G, and 21B are used and synthesized by the dichroic prism 23 and then wobbling by the pixel shift element 30 has been described. Pixel shift elements may be arranged on the emission sides of the three-plate liquid crystal display elements 21R, 21G, and 21B, respectively, and wobbling may be performed individually. Further, instead of the three-plate type, a single-plate type liquid crystal display element may be used.

  In the embodiment of the present invention, the case where the original image is time-divided into two field images W1, W2 has been described. However, a plurality of (three, four,...) Fields having complementary sampling points. It may be divided into images. In that case, for example, a plurality of pixel shift elements 30 may be combined, and the pixel position of the projection image may be shifted corresponding to each of the plurality of field images.

  As described above, the present invention naturally includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.

DESCRIPTION OF SYMBOLS 1 ... Optical system 10 ... Light source 11 ... Condensing lens 12 ... Fly eye lens pair 14, 18R, 18G, 18B ... Lens 15, 17 ... Dichroic mirror 16, 16B ... Folding mirror 17 ... Dichroic mirror 19R, 19B, 19G, 22R , 22B, 22G ... polarizing plates 20R, 20B, 20G ... wire grid polarizing plates 21, 21R, 21G, 21B ... liquid crystal display elements 23 ... dichroic prisms 24 ... wavelength plates 25 ... projection lenses 30 ... optical path shifting elements 31 ... polarization switches 32 DESCRIPTION OF SYMBOLS ... Birefringent plate 100 ... Control part 101 ... Field image generation circuit 102 ... Control timing signal generation circuit 103 ... Data processing part 104 ... 1st double speed conversion process part 105 ... 2nd double speed conversion process part 106 ... Field image switching part 107: Polarity inversion unit 108 ... Signal power Pressure supply unit 109 ... Optical path shift control circuit 201 ... Horizontal scanning circuit 202 ... Horizontal shift register 204 ... Vertical scanning circuit 205 ... Display unit

Claims (5)

A field image generation circuit for generating a plurality of field images having sampling points complementary to the original image;
A liquid crystal display element for sequentially and periodically displaying the plurality of field images by vertical scanning;
A signal voltage supply unit for supplying a signal voltage corresponding to the plurality of field images to the liquid crystal display element;
An optical path shift element that shifts an optical path of modulated light emitted from the liquid crystal display element in correspondence with the plurality of field images displayed on the liquid crystal display element;
A polarity reversing unit that reverses the polarity of the signal voltage every vertical scanning period of the liquid crystal display element;
For each switching period defined by a positive integer multiple of a polarity inversion period in which the plurality of field images displayed on the liquid crystal display element are switched for each vertical scanning period and the polarity of the signal voltage is inverted between positive and negative. The field for switching the display order of the plurality of field images so that the correspondence relationship between the polarity of the signal voltage and the plurality of field images displayed on the liquid crystal display element is reversed from the correspondence relationship of the immediately preceding switching period. A projection-type image display device comprising: an image switching unit.   The projection type image display apparatus according to claim 1, further comprising a double speed conversion processing unit that performs double speed conversion on a vertical scanning rate of the field image. The optical path shift element is
A polarizing member that relatively rotates the polarization direction of modulated light emitted from the liquid crystal display element by 90 degrees by voltage on / off control;
The projection type image display device according to claim 1, further comprising: a birefringent member that linearly refracts or refracts the modulated light according to a polarization direction of the modulated light from the polarizing member.   The projection type image display device according to claim 1, wherein the liquid crystal display element simultaneously updates the field image for all display pixels. Generating a plurality of field images having sampling points complementary to the original image;
The liquid crystal display element sequentially and periodically displaying the plurality of field images by vertical scanning;
Supplying a signal voltage corresponding to the plurality of field images to the liquid crystal display element;
Shifting the optical path of the modulated light emitted from the liquid crystal display element corresponding to the plurality of field images displayed on the liquid crystal display element;
Reversing the polarity of the signal voltage every vertical scanning period of the liquid crystal display element;
Switching the plurality of field images displayed on the liquid crystal display element for each vertical scanning period;
Correspondence relationship between the polarity of the signal voltage and the plurality of field images displayed on the liquid crystal display element for each switching period defined by a positive integer multiple of the polarity inversion period obtained by inverting the polarity of the signal voltage between positive and negative Switching the display order of the plurality of field images so as to reverse the corresponding relationship of the immediately preceding switching period.

Images