JP2009193044A - Light modulator, projection type display device, and image projection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a projection type display device, projecting a projection image restrained from flickering. <P>SOLUTION: This light modulator includes liquid crystal display elements 12r, 12g, 12b and transmission type sheet polarizers 15r, 15g, 15b, which are disposed on an optical path of a first polarized light beam put in the linearly polarized state, which is obtained by polarizing and converting a light beam emitted from a light source 2, wherein photo sensors 21r, 21g, 21b are disposed at positions not overlapping the optical path of a light beam reflected by reflection type sheet polarizers 13r, 13g, 13b on the optical path of a light beam reflected by the transmission sheet polarizers 15r, 15g, 15b. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a light modulation device, a projection display device, and an image modulation device that suppress flicker caused by asymmetry of an alternating voltage applied between electrodes facing each other in a liquid crystal display element and improve the image quality of a projected image. The present invention relates to an image projection method.

The projection type display device irradiates the liquid crystal display element with light from a light source, forms an optical image corresponding to the input image signal, and enlarges and projects it. The liquid crystal display element is driven based on the input image signal. The electro-optical characteristics in doing so greatly affect the image quality of the projected image.
The liquid crystal display element has a common electrode, a pixel electrode including a large number of pixels that can be individually controlled by a driving transistor disposed opposite to the common electrode, and a liquid crystal interposed between the common electrode and the pixel electrode, An AC voltage that is inverted at a frame period or a line period is applied between the common electrode and the pixel electrode.

However, it is common due to variations in characteristics of pixel electrode driving transistors, variations in electro-optical characteristics of liquid crystal materials, variations in alignment conditions, mixing of impurities into the liquid crystal, and differences in the materials of the two opposing electrodes. Asymmetry occurs between the positive side and the negative side of the AC voltage applied to the electrode and pixel electrode voltages.
As a result, the common electrode voltage (Vcom), which is the DC voltage of the common electrode, deviates from the inversion center voltage, and a DC voltage component is applied to the liquid crystal display element, thereby causing flicker in the projected image.
When flicker occurs in the projected image, the black level of the projected image increases, thereby reducing the contrast and narrowing the display gradation. In addition, since a DC voltage component is applied to the liquid crystal display element, an ionic substance in the liquid crystal is attracted to one electrode, and the liquid crystal display element is seized, resulting in a decrease in operation reliability of the liquid crystal display element. .
Therefore, Patent Document 1 discloses a technique for suppressing flicker by adjusting the amount of Vcom applied to the common electrode of the liquid crystal display element.

Patent Document 1 generally describes as follows.
A projection display device described in Patent Document 1 includes a light source, a liquid crystal display element that irradiates light from the light source to form an optical image corresponding to an input image signal, a projection lens unit that magnifies and projects the optical image, and And an optical sensor for detecting the light intensity after irradiation of the display element, a drive circuit for driving the liquid crystal display element, and a correction circuit for controlling the drive circuit based on the light intensity detected by the optical sensor.
Here, the optical sensor detects flickering of light caused by flicker, and Patent Document 1 describes an outer peripheral edge of the screen or a projection lens unit as an installation position of the optical sensor.
In the display method of the projection display device, light emitted from a light source is irradiated onto a liquid crystal display element, an optical image corresponding to an input image signal is formed on the liquid crystal display element, and the formed optical image is enlarged by a projection lens. To project.
The magnified optical image is displayed as a projected image on a screen installed at the imaging position.

When the Vcom correction for suppressing flickering is started, the projection display device supplies a raster pattern signal, which is a test pattern stored in the drive circuit, from the drive circuit to the liquid crystal display element, and passes through the projection lens unit. A raster pattern image formed by the liquid crystal display element is projected onto the screen.
Then, the flicker state of the projected image is detected by measuring the light amount change of the image light of the raster pattern by the optical sensor installed in the outer peripheral edge of the screen or in the projection lens unit, and the liquid crystal display element is detected from the detection result. The amount of Vcom applied to the counter electrode is calculated. Based on the calculated Vcom amount, the correction circuit adjusts the Vcom amount so that flicker is not visually recognized in the projected image.

JP 2006-319950 A

However, in the projection type display device in which the optical sensor is installed on the outer peripheral edge of the screen described in Patent Document 1, the outer peripheral edge is always at the black level during projection and the amount of light is small. Therefore, in order to improve the accuracy of Vcom correction, a plurality of optical sensors are installed on the outer peripheral edge and the detection signal is integrated to increase the amplitude of the detection signal, or the measurement time at the optical sensor is extended to increase the integrated light quantity. It is necessary to increase. As a result, the installation space for the optical sensor is increased, and the time required for Vcom correction may be increased.
In addition, if an optical sensor is installed at the outer peripheral edge of the screen, when moving the projection display device, the optical sensor also needs to be moved separately and re-installed, which makes it difficult to move easily. It was.
Further, in the projection type display device in which the optical sensor is installed in the projection lens unit, since the optical sensor is located in the optical path projected from the projection lens unit liquid crystal display element onto the screen, the shadow of the optical sensor may be reflected on the screen. was there.
Furthermore, incorporating the optical sensor into the lens barrel of the projection lens unit increases the cost of the projection lens unit, and when replacing the projection lens according to the installation space of the projection display device, There was also a need to install an optical sensor.

In the projection type display device disclosed in Patent Document 1, R light, G light, and B light are sequentially irradiated and Vcom correction is performed by one optical sensor, or optical sensors for R, G, and B color lights are provided. It was necessary to correct the Vcom by installing and irradiating white light.
Therefore, in the case of one optical sensor, since it is necessary to irradiate three times with R light, G light, and B light, the time required for Vcom correction is long. Further, when optical sensors for R, G, and B color lights are respectively installed, the number of sensors and the installation area increase, so that it becomes more difficult to move the optical sensors when moving the projection display device.

Moreover, in the projection type display apparatus of patent document 1, it is necessary to install an optical sensor in the position away from the center of an optical path as much as possible so that the influence of the shadow of an optical sensor may not be given to a projection image. Yes.
For this reason, when performing Vcom correction, it is necessary to make adjustments based on the measurement results of a part of the outer edge of the projected image, and the occurrence of flicker is not uniform within the display area of the liquid crystal display element. Flicker could not be suppressed over the entire projected image.

The flicker appearing in the projected image includes, in addition to that caused by Vcom, flickering of discharge light that occurs depending on the electrode temperature of the light source and the surface state of the electrode of the light source, called lamp flicker.
However, in the conventional Vcom correction method, since Vcom correction is performed in a state including lamp flicker, the amount of Vcom is excessively adjusted, and flicker may not be removed even if Vcom correction is performed.

Accordingly, the present invention provides a light modulation device, a projection display device, and an image projection method that are easy to move, do not increase the cost of the projection lens, and do not cause the shadow of the optical sensor to appear in the projected image. Objective.
It is another object of the present invention to provide a light modulation device, a projection display device, and an image projection method that can perform Vcom correction with high accuracy and in a short time in addition to a small number of optical sensors.
Further, there is provided a light modulation device, a projection display device, and an image projection method that can suppress flicker even when flicker varies in a projected image and can suppress flicker caused by a liquid crystal display element separately from lamp flicker. The purpose is to provide.

1) In order to achieve the above object, the light modulation device α of the present embodiment converts the first polarized light beam in the first linear polarization state obtained by polarization-converting the light beam emitted from the light source 2, Liquid crystal display elements 12r, 12g, and 12b that modulate light into a first polarized light beam and a second polarized light beam in a second linearly polarized state orthogonal to the first polarized light beam based on the input image signal, and the first polarized light Reflective polarizing plates 13r, 13g, and 13b that transmit the light beam and reflect the second polarized light beam, and transmissive polarizing plates 15r, 15g, and 15b that transmit the second polarized light beam and reflect the first polarized light beam And optical sensors 21r, 21g, and 21b that detect the first polarized light beam reflected by the transmissive polarizing plates 15r, 15g, and 15b, and the liquid crystal display elements 12r, 12g, and 12b include the reflective polarizing plates 13r, Enter through 13g and 13b The first polarized light beam is modulated, and the light-modulated polarized light beam is reflected so as to be incident again on the reflective polarizing plates 13r, 13g, and 13b. The reflective polarizing plates 13r, 13g, and 13b are Of the polarized light beams that transmit the first polarized light beam from the light source 2 direction and are optically modulated by the liquid crystal display elements 12r, 12g, and 12b, the second polarized light beam is reflected in the direction of the transmissive polarizing plates 15r, 15g, and 15b. The optical sensors 21r, 21g, and 21b are disposed on the optical path of the light beam reflected by the transmissive polarizing plates 15r, 15g, and 15b, and the optical path of the light beam reflected by the reflective polarizing plates 13r, 13g, and 13b. It is arrange | positioned in the position which does not overlap with.
2) In order to achieve the above object, the light modulation device α described in 1) includes reflection type polarizing plates 13r, 13g, 13b, liquid crystal display elements 12r, 12g, 12b and transmission type polarizing plates 15r, 15g, 15b. The triangular sensors 20r, 20g, and 20b are disposed at positions corresponding to the three side surfaces, and the optical sensors 21r, 21g, and 21b are disposed at positions that are outside the substantially triangular columns 20r, 20g, and 20b. .
3) In order to achieve the above object, the light beam used in the light modulation device α described in 1) or 2) is one of red light, green light, and blue light.
4) In order to achieve the above object, the projection display device 1 of the present embodiment includes a light modulation device α according to any one of 1) to 3) and a white light beam emitted from the light source 2. Linearly polarized light having only the first linear polarization state by color-separating means for color-separating the light beam into red light beam, green light beam, and blue light beam, and converting the polarization angle after polarization-separating the incident light beam Each of the second linear polarization states of red light, green light, and blue light transmitted through the polarization conversion means 9b, 9rg that emits as a polarized light beam, and the transmissive polarizing plates 15r, 15g, 15b of the light modulation device α. Color synthesizing means 16 for synthesizing the polarized light flux.
5) In order to achieve the above object, in the projection type display device 1 described in 4), the liquid crystal display elements 12r, 12g, and 12b are a common electrode to which a common electrode voltage is applied while facing the pixel electrode. 24 and a liquid crystal sandwiched between the pixel electrode and the common electrode 24, and the optical sensors 21r, 21g, and 21b receive and detect the reflected light beams reflected from the transmissive polarizing plates 15r, 15g, and 15b. A liquid crystal drive that outputs a signal, supplies a pixel electrode voltage obtained by inverting the polarity of an input image signal for each vertical period with respect to a reference voltage to the pixel electrode, and outputs a switching period signal corresponding to one vertical period A maximum value on the positive side and a minimum value on the negative side of the polarity in one vertical period of the detection signal are obtained from the detection signals from the circuit 22, the optical sensors 21r, 21g, and 21b and the switching period signal, and the maximum value is obtained. of A detection circuit 23 that obtains a difference obtained by subtracting the absolute value of the minimum value from the pair value and outputs it as a difference signal; a difference signal from the detection circuit 23; Based on the common electrode voltage, if the difference signal is positive, the difference signal is subtracted from the common electrode voltage of the previous one vertical period, and if the difference signal is negative, the common electrode voltage of the previous one vertical period And a correction circuit 25 for obtaining a common electrode voltage by adding a difference signal to
6) In order to achieve the above object, the projection display device 1 described in 5) includes a control unit 38 that controls an operation for obtaining the common electrode correction voltage in the correction circuit 25 and a common circuit obtained by the correction circuit 25. The control unit 38 has an input corresponding to a predetermined image by the liquid crystal driving circuit 22 when a projection stop signal of the projection display device 1 is input. The image signal is input to the liquid crystal display elements 12r, 12g, and 12b to display a predetermined image as a projected image, and information on the common electrode correction voltage is obtained when the change rate of the obtained difference becomes a predetermined value or less. Is stored in the storage unit 39.
7) In order to achieve the above object, the control unit 38 of the projection display device 1 described in 6) displays an initial projection image that is initially projected when the power is turned on by the projection display device 1. Information on the common electrode correction voltage stored in the storage unit 39 is read out, and control is performed to display the initial projection image based on the read information on the common electrode correction voltage.
8) In order to achieve the above object, the correction circuit 25 of the projection display device 1 according to any one of 5) to 7) uses a signal in a frequency band corresponding to the inherent flickering of the light source 2 as a difference. It has a removal circuit 40 for removing from the signal.
9) In order to achieve the above object, the image projection method according to the present embodiment includes optical sensors 21r, 21g, and 21b that output detection signals in response to light reception, and switching period signals corresponding to one vertical period. Based on the detection signals from the optical sensors 21r, 21g, and 21b and the switching period signal from the liquid crystal driving circuit 22, the projection display device 1 having the liquid crystal driving circuit 22 that outputs the detection signal converts the detection signal to the positive side and the negative side of the polarity. Obtained in the difference signal calculation step, the difference signal calculation step, and the difference signal calculation step for calculating the difference between the peak values of the detection signal separated into the positive side and the negative side of the polarity, and outputting the difference signal Correction value calculating step for obtaining a common electrode correction voltage based on the difference signal, and an image projecting step for projecting an image by the projection display device using the common electrode correction voltage calculated in the correction value calculating step It has a correction value calculation step calculates a common electrode correction voltage from the difference signal obtained by calculating the result and the difference signal computing step of the directly previous vertical period and the correction value calculation step.
10) In order to achieve the above object, liquid crystal display elements 12r, 12g, and 12b that optically modulate incident polarized light beams, optical sensors 21r, 21g, and 21b that output detection signals in response to light reception, and information In the image projection method for projecting an image by the projection display device 1 having the storage unit 39 for storing the first common electrode immediately after the m-th power supply (m is an integer of 1 or more) of the projection display device 1. A first common electrode voltage detection step for obtaining a voltage; a second common electrode voltage detection step for obtaining a second common electrode voltage immediately before the m-th power-off of the projection display device 1; and a second common electrode voltage A common electrode voltage storage step of obtaining an m-th common electrode voltage change amount from the difference between the first common electrode voltage and the first common electrode voltage and storing it in the storage unit 39; Together The m-th common electrode voltage change amount read from the storage unit 39 is added to the third common electrode voltage detection step for obtaining the electrode voltage and the third common electrode voltage obtained in the third common electrode voltage detection step. A common electrode voltage calculating step using the obtained value as a common electrode voltage, and an image projecting step for projecting an image by applying the common electrode voltage obtained in the common electrode voltage calculating step to the liquid crystal display elements 12r, 12g, and 12b. And have.
11) In order to achieve the above object, in the image projection method according to 10), the first common electrode voltage detection step, the second common electrode voltage detection step, and the third common electrode voltage detection step include a liquid crystal display. Adder-side flicker that detects the amount of fluctuation of the light intensity of the projection light from the liquid crystal display elements 12r, 12g, and 12b by applying the first predetermined voltage to the reference common electrode voltage in the elements 12r, 12g, and 12b and applying it. The detection step and the first common voltage subtracted from the reference common electrode voltage in the liquid crystal display elements 12r, 12g, and 12b and applied to the light intensity fluctuation amount of the projection light from the liquid crystal display elements 12r, 12g, and 12b. The subtraction-side flicker detection step for detecting the first light intensity fluctuation amount obtained in the addition-side flicker detection step and the light intensity obtained in the subtraction-side flicker detection step. When the first fluctuation amount is larger than the second fluctuation amount, a voltage obtained by subtracting the second predetermined voltage from the common electrode voltage is used as a new common electrode voltage, and the second fluctuation amount is obtained. When the first fluctuation amount is smaller, the voltage obtained by adding the second predetermined voltage to the common electrode voltage is used as a new common electrode voltage. When the second fluctuation amount and the first fluctuation amount are equal, the common electrode When the common electrode voltage correction step, the addition-side flicker detection step, the subtraction-side flicker detection step, and the common electrode voltage correction step are combined into a common electrode voltage adjustment step using the voltage as a new common electrode voltage, A fluctuation amount adjusting step for calculating an optimum common electrode voltage by performing the electrode voltage adjusting step a predetermined number of times.

According to the present invention, since the optical sensor for detecting flicker of the projection light is installed in the apparatus other than the projection lens, the movement is easy, and the cost of the projection lens is not increased, and the optical sensor is added to the projection image. It is possible to provide a projection display device in which no shadow is reflected.
In addition, since an optical sensor corresponding to each of R light, G light, and B light is provided, a light modulation device, a projection display device, and an image projection method capable of performing Vcom correction with high accuracy in a short time are provided. be able to.
In addition, by installing an optical sensor in the device, the optical sensor can be placed close to the light source, so the amount of light detected by the optical sensor can be improved, and the number of optical sensors or measurement time can be reduced. It is possible to provide a light modulation device, a projection display device, and an image projection method that can be performed.
Further, there is provided a light modulation device, a projection display device, and an image projection method that can suppress flicker even when flicker varies in a projected image and can suppress flicker caused by a liquid crystal display element separately from lamp flicker. Can be provided.

Embodiments of a projection display device according to the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic plan view showing the configuration of the optical system of the projection display device of this embodiment. FIG. 2 is a schematic cross-sectional view showing a light modulation device used in the projection display device of the present embodiment. FIG. 3 is an explanatory diagram for explaining the principle of a polarizing plate used in the projection display device of this embodiment. FIG. 4 is an explanatory diagram for explaining an optical path emitted from the reflective liquid crystal display element used in the projection display device of this embodiment. FIG. 5 is an explanatory diagram for explaining an optical path incident on the reflective liquid crystal display element used in the projection display device of this embodiment. FIG. 6 is a block diagram showing the configuration of the Vcom correction circuit of the projection display device of this embodiment. FIG. 7 is a detailed block diagram showing the configuration of the Vcom correction circuit of the projection display device of this embodiment. FIG. 8 is a flowchart showing the operation of the Vcom correction circuit of the projection display device of this embodiment. FIG. 9 is an explanatory diagram in the case where Vcom correction is performed on a partial region of a projected image in the projection display device of the present embodiment. FIG. 10 is an explanatory diagram showing a detection signal of the optical sensor in the display area of the projected image in the projection display device of the present embodiment. FIG. 11 is a detailed block diagram showing another configuration of the Vcom correction circuit of the projection display device of the present embodiment. FIG. 12 is a flowchart showing the operation of another configuration of the Vcom correction circuit of the projection display device of this embodiment. FIG. 15 is a detailed block diagram showing still another configuration of the Vcom correction circuit of the projection display device according to the present embodiment.
Note that components having common functions are denoted by the same reference symbols throughout the drawings, and repeated descriptions of components once described are omitted.

<Example 1>
As shown in FIG. 1, the optical system of the projection display apparatus 1 of the embodiment includes a light source 2 having a xenon lamp 2a and a concave mirror 2b, and an infrared transmission filter that transmits infrared rays and reflects light beams in other wavelength bands. 3, an ultraviolet reflection filter 4 that reflects ultraviolet rays and transmits light beams in other wavelength bands, reflects blue (hereinafter referred to as “B”) light, and transmits red-green (hereinafter referred to as “RG”) light. Thus, the B dichroic mirror 5 that splits the incident light is sequentially disposed on the light beam emitted from the light source 2.

  Furthermore, on the optical path of the B light split by the B dichroic mirror 5, a reflection mirror 6, a first fly-eye lens 7b, a second fly-eye lens 8b, and a polarization conversion element that bend the optical path of the B light by 90 degrees 9b, condenser lens 10b, field lens 11b, reflective polarizing plate 13b, and incident linearly polarized light beam are modulated based on the input image signal, and the light beam that has been modulated and whose polarization state has changed is reflected and emitted. And a reflective liquid crystal display element 12b for the B light.

  Further, on the optical path of the RG light split by the B dichroic mirror 5, the first fly-eye lens 7rg, the second fly-eye lens 8rg, the polarization conversion element 9rg, the condenser lens 10rg, and the incident light flux An RG dichroic mirror 14 that reflects green (hereinafter referred to as “G”) light and disperses incident light by transmitting red (hereinafter referred to as “R”) light is disposed.

  Further, on the optical paths of the R light and G light split by the RG dichroic mirror 14, field lenses 11r and 11g, reflection type polarizing plates 13r and 13g, and incident linearly polarized light fluxes are input based on the input image signal. Reflective liquid crystal display elements 12r and 12g for R light and G light that reflect and emit light that has been light-modulated and light-modulated and whose polarization state has changed are disposed.

  Further, in the respective optical paths of the light beams reflected by the reflective liquid crystal display elements 12r, 12g, and 12b, reflective polarizing plates 13r, 13g, and 13b, transmissive polarizing plates 15r, 15g, and 15b, and a cross dichroic prism 16 are provided. And a projection lens 18 for enlarging and projecting the incident light beam onto the screen 17.

Here, each member will be described.
The first fly-eye lenses 7b and 7rg and the second fly-eye lenses 8b and 8rg make the shape of the light beam emitted from the light source 2 coincide with the shape of the display pixel area of the liquid crystal display element, and the illuminance on the liquid crystal display element. In order to make it uniform, it has a function of dividing an incident light beam into a plurality of partial light beams.
The polarization conversion elements 9b and 9rg have a function of converting a plurality of partial light beams that are randomly polarized light into a plurality of partial light beams that are linearly polarized light in one direction.
The condenser lenses 10b and 10rg have a function of combining a plurality of partial light beams converted into linearly polarized light in one direction by the polarization conversion elements 9b and 9rg and combining them into a light beam of linearly polarized light in one direction.
The field lenses 11r, 11g, and 11b have a function of converting incident linearly polarized light beams into telecentric illumination light.

The reflection-type polarizing plates 13r, 13g, and 13b transmit or reflect depending on the polarization state of the incident light beam, and polarization separate the light beam. In the case of the present embodiment, the light beams emitted from the field lenses 11r, 11g, and 11b are transmitted, and the light beams of components that are light-modulated by the reflective liquid crystal display elements 12r, 12g, and 12b are reflected.
The reflection type liquid crystal display elements 12r, 12g, and 12b are provided with the reflection type liquid crystal display elements 12r, 12g, and 12g in order to prevent the reflection type liquid crystal display elements 12r, 12g, and 12b from being heated to high temperatures and deteriorating the electro-optical characteristics. , 12b, heat sinks 19r, 19g, 19b are attached to the back surface.
The transmissive polarizing plates 15r, 15g, and 15b remove the unnecessary polarization light of the incident light beam that is reflected by the R, G, and B color light beams reflected by the reflective polarizing plate, respectively, and reduce the degree of polarization. It improves and improves contrast.
The cross dichroic prism 16 has a substantially quadrangular prism shape. The cross dichroic prism 16 color-synthesizes linearly polarized light beams of R, G, and B colors respectively incident from the three side surfaces thereof and emits them from the remaining one side surface.

Here, the reflective polarizing plates 13r, 13g, and 13b, the reflective liquid crystal display elements 12r, 12g, and 12b attached to the heat sinks 19r, 19g, and 19b for heat radiation, and the transmissive polarizing plates 15r, 15g, and 15b are as follows. These are fixed to the three side surfaces or the three virtual side surfaces of the substantially triangular prisms 20r, 20g, and 20b.
Further, optical sensors 21r, 21g, and 21b are disposed outside the substantially triangular prisms 20r, 20g, and 20b on the optical path of unnecessary polarized light reflected by the transmissive polarizing plates 15r, 15g, and 15b.
The optical sensors 21r, 21g, and 21b convert incident light into an electrical signal according to the amount of light, and convert the amount of light into voltage, current, frequency, or the like and output it as a detection signal.

Next, the operation of the optical system of the projection display device of the present invention will be described in detail with reference to FIGS.
FIG. 2 is an enlarged view of part A in FIG. 1, and includes reflective liquid crystal display elements 12r, 12g, 12b, reflective polarizing plates 13r, 13g, 13b, and transmissive polarizing plates 15r, 15g, 15b. This shows the light modulation device α.
In this embodiment, a xenon lamp 2 a that emits high-luminance light is used as the light source 2. Since the light flux of the xenon lamp 2a emitted from the light source 2 has a sharp emission line in the infrared band, the wavelength of the light beam having a wavelength of about 700 nm or more is transmitted when passing through the infrared transmission filter 3 disposed at an inclination of 45 degrees on the optical path. The light in the infrared band is removed, the light in the other wavelength band is reflected by the infrared transmission filter 3, and the optical path is bent 90 degrees.
The light beam from which the light in the infrared band is removed enters the ultraviolet transmission filter 4, and the ultraviolet transmission filter 4 reflects and removes ultraviolet light having a wavelength of about 400 nm or less. The luminous flux from which infrared rays and ultraviolet rays have been removed is emitted from the ultraviolet transmission filter 4.

The light flux from which infrared rays and ultraviolet rays have been removed is incident on a B dichroic mirror 5 that is disposed at an inclination of 45 degrees with respect to the optical path.
The B dichroic mirror 5 has a function of reflecting the B light of the incident light and transmitting the RG light, and the B light reflected by the B dichroic mirror 5 is disposed with an inclination of 45 degrees with respect to the optical path. The light path is reflected by the reflection mirror 6 and the optical path is bent 90 degrees.

The cross section of the light beam reflected by the reflection mirror 6 is circular based on the cross sectional shape in the direction orthogonal to the emission direction of the concave mirror 2b of the light source 2, and this light is applied to the effective pixel area of the rectangular liquid crystal display element. In order to apply efficiently, it is necessary to convert a circular light beam into a rectangular light beam.
Therefore, the light beam reflected by the reflection mirror 6 is divided into the first fly-eye lens 7b in which small rectangular convex lenses are formed in a matrix and the small rectangular convex lens disposed at the focal position of the first fly-eye lens 7b. The second fly's eye lens 8b formed in a matrix form is divided into a plurality of rectangular partial light beams, and the illuminance distribution of the light within the total light beams is made uniform.

Further, the B light, which is a plurality of rectangular partial light beams emitted from the second fly-eye lens 8b, is random polarized light with no polarization state. In order to convert this B light into linearly polarized light in one direction, a polarization conversion element 9b is used.
The polarization conversion element 9b is configured by a polarizing beam splitter array and a half-wave plate having birefringence selectively attached to a part of the exit surface of the polarizing beam splitter array, and is configured in a flat plate shape as a whole. Has been.

The light incident on the polarization conversion element 9b is first separated into a P-polarized component and an S-polarized component with respect to the polarization separation film surface by the polarization separation film surface of the polarization beam splitter array. At this time, a plurality of polarization separation film surfaces of the polarization conversion element 9b are provided in parallel and in a stripe shape, and each of them is formed with an inclination of 45 ° with respect to the main surface of the polarization conversion element 9b.
When light enters the polarization conversion element 9b, the P-polarized component of the incident light is transmitted through the polarization separation film surface and emitted to the back side of the polarization conversion element 9b, and the S-polarization component is reflected by the polarization separation film surface. The S-polarized component reflected by one polarization separation film surface and having its optical path bent by 90 ° is reflected again by another adjacent polarization separation film surface and the optical path is bent by 90 °, and is reflected on the back surface side of the polarization conversion element 9b. It is injected. A half-wave plate is provided in the region where the S-polarized component is emitted, and the S-polarized component transmitted through the half-wave plate is rotated by 90 ° in the polarization direction to be emitted as a P-polarized component. The In this way, the randomly polarized light from the light source 2 enters the polarization conversion element 9b and passes therethrough to become polarized light in one predetermined direction (P-polarized light).

  In the following description, polarized light in one predetermined direction obtained by the polarizing beam splitter array is described as P-polarized light. However, the present invention is not limited to this, and light emitted from the polarizing beam splitter array is polarized into S-polarized light. A method of conversion is also possible.

A plurality of partial light beams of B light converted into P-polarized light by the polarization conversion element 9b are combined into one P-polarized light beam by the condenser lens 10b.
The light beam of B light, which is P-polarized light emitted from the condenser lens 10b, is refracted by the field lens 11b in accordance with the size of the effective pixel area of the reflective liquid crystal display element 12b, and is inclined 45 degrees with respect to the optical path of the B light. Is incident on the reflective polarizing plate 13b fixed to one side surface of the substantially triangular prism 20b.
Of the B light beam incident on the reflective polarizing plate 13b, the P-polarized light component is transmitted, and a slight amount of the S-polarized light component contained in the B light beam is reflected, bent 90 degrees, and emitted to the outside of the substantially triangular prism 20b. The The light beam of B light, which is P-polarized light that has passed through the reflective polarizing plate 13b, is placed on a heat sink 19b fixed on one side surface of a substantially triangular prism 20b in a state orthogonal to the optical path of the B light. The light enters the reflective liquid crystal display element 12b.

As shown in FIG. 3, the reflective polarizing plate 13 b uses a wire grid polarizer, and a metal linear grid 102 such as aluminum is formed on an optical glass plate 101 with a pitch (P) of about 140 nm, for example. And having a reflecting surface regularly formed in a stripe shape. The reflection type polarizing plate 13b transmits the polarized light component (for example, P-polarized light) perpendicular to the grid 102 formed in a stripe shape out of the incident light beam as it is, and passes through the metal line 102 formed in the stripe shape. It has a characteristic of reflecting a parallel polarization component (for example, S-polarized light).
Furthermore, since the reflective polarizing plate 13b is a single plate-shaped polarization separation plate, it is lightweight. Further, since the reflective polarizing plate 13b is difficult to absorb the light incident from the light source 2, it is possible to suppress deterioration in the quality of the display image due to the birefringence of the glass caused by heat generation.

Similarly, substantially the same operation is performed on the RG light emitted from the B dichroic mirror 5.
That is, the RG light beam transmitted through the B dichroic mirror 5 is divided into a plurality of rectangular partial light beams by the first fly-eye lens 7 rg and the second fly-eye lens 8 rg disposed on the optical path, and the illuminance distribution of the light. Is made uniform.
A plurality of rectangular partial light beams of RG light, which is random polarization, emitted from the second fly-eye lens 8rg is converted into a plurality of partial light beams of RG light converted into P-polarized light by the polarization conversion element 9rg.

A plurality of partial light beams of RG light converted to P-polarized light by the polarization conversion element 9rg are combined into one P-polarized light beam by the condenser lens 10rg.
The luminous flux of RG light that is P-polarized light emitted from the condenser lens 10 rg is reflected by the dichroic mirror 14 that reflects G-band light and transmits R-band light, and P-polarized G light and P-polarized R light. Spectroscopy.
The G light and R light, which are P-polarized light dispersed by the dichroic mirror 14, are refracted by the field lenses 11g and 11r in accordance with the size of the effective pixel area of the reflective liquid crystal display elements 12g and 12r, respectively. The light is incident on the reflective polarizing plates 13r and 13g fixed to one side surface of the substantially triangular prisms 20r and 20g installed at an inclination of 45 degrees with respect to the respective optical paths of the light.

  Of the R and G light beams incident on the reflective polarizing plates 13r and 13g, the P-polarized light component is transmitted, and a slight amount of the S-polarized light component contained in the R and G light beams is reflected and bent by 90 degrees. Injected outside the substantially triangular prism 20b. The P-polarized R and G light beams transmitted through the reflective polarizing plates 13r and 13g are fixed to one side of the substantially triangular prisms 20r and 20g in a state orthogonal to the optical paths of the R and G lights, respectively. The light enters the reflective liquid crystal display element 12r for R light and the reflective liquid crystal display element 12g for G light installed on 19r and 19g.

In the reflective liquid crystal display elements 12r, 12g, and 12b, the alignment state of the liquid crystal is changed by applying a driving voltage based on the input image signal of each color to the liquid crystal of the reflective liquid crystal display elements 12r, 12g, and 12b of each color. Then, the P-polarized light flux of each color of R, G, and B incident is optically modulated and the light-modulated light flux is reflected.
The light-modulated light beams of R, G, and B colors are bent by 90 degrees in the S-polarized components of the respective colors by reflection type polarizing plates 13r, 13g, and 13b disposed at 45 degrees with respect to the optical path. The light enters the transmission type polarizing plates 15b, 15g, and 15r, which are unnecessary polarized light removing means, disposed on the other side surface of the triangular prisms 20r, 20g, and 20b.

The transmissive polarizing plates 15b, 15g, and 15r use wire grid polarizers, and the orientation of the metal linear grid 102 formed in a stripe shape with respect to the optical path is the reflective polarizing plates 13r, 13g, and 13b. Therefore, the transmissive polarizing plates 15b, 15g, and 15r transmit S-polarized light and reflect P-polarized light.
The transmissive polarizing plates 15b, 15g, and 15r serving as unnecessary polarized light removing means are reflective liquid crystal panels 12r, 12g, and 12b for each color light reflected by the reflective polarizing plates 13r, 13g, and 13b for each color light. Contrast is improved by removing unnecessary polarized light (P-polarized light) other than S-polarized light from the light-modulated light beams of the respective colors by the transmissive polarizing plates 15b, 15g, and 15r for the respective color lights. is there.

  The R-, G-, and B-colored S-polarized light beams transmitted through the transmissive polarizing plates 15b, 15g, and 15r are incident on the cross dichroic prism 16 from three incident surfaces except the exit surface 16a of the cross dichroic prism 16. In the cross dichroic prism 16, the incident R light, G light, and B light are color-combined and emitted from the exit surface 16a. The light emitted from the cross dichroic prism 16 is magnified by the projection lens 18 and projected onto the screen 17.

  On the other hand, the P-polarized light beams of the R, G, and B colors reflected by the transmissive polarizing plates 15b, 15g, and 15r are transmitted through the reflective polarizing plates 13r, 13g, and 13b for the respective color lights, and are substantially triangular prisms 20r, 20g. , 20b to the optical sensors 21r, 21g, 21b arranged outside.

  Next, in order to explain the position of the optical sensor, the optical path in the vicinity of the substantially triangular prisms 20r, 20g, 20b will be described in detail with reference to FIGS. Here, only the optical path of B light will be described, but the same applies to G light and R light.

The B light beam Ha, which is P-polarized light emitted from the condenser lens 10b, is refracted by the field lens 11b in accordance with the size of the display area of the reflective liquid crystal display element 12b, and is polarized into P-polarized light of the substantially triangular prism 20b. The light is incident on the reflective polarizing plate 13b installed on the side surface with an inclination of 45 degrees with respect to the optical path of light.
The reflective polarizing plate 13b has a property of transmitting P-polarized light, and the P-polarized light beam Hb transmitted through the reflective polarizing plate 13b is light-modulated by the reflective liquid crystal element 12b, and a part thereof is S-polarized. At the same time, it is reflected and reenters the reflective polarizing plate 13b.
The light beam Hb that has been light-modulated to become S-polarized light is reflected by the reflective polarizing plate 13b, bent by 90 degrees in the optical path, and incident on the transmissive polarizing plate 15b (Hc). The transmissive polarizing plate 15b improves the contrast of the projected image by transmitting S-polarized light and reflecting unnecessary P-polarized light as described above.
An optical sensor 21b is disposed on the P-polarized light beam Hd reflected by the transmissive polarizing plate 15b.

Further, in the reflective polarizing plate 13b, 100% of the incident P-polarized B light beam Ha is not transmitted, but a small proportion of the light is reflected and the S-polarized light slightly contained in the incident light beam Ha. Is also reflected.
Since the light beam Ha is reflected by the reflective polarizing plate 13b, the optical path is bent by 90 degrees, and the light beam He emitted from the substantially triangular prism 20b is not light-modulated by the reflective liquid crystal element 12b, the light beam Ha is reflected on the reflective liquid crystal display element 12b. The amount of light is large compared to the optical path Hd of the light beam reflected from the transmissive polarizing plate 15b affected by the flicker caused by the reflection type liquid crystal display element 12b.
Therefore, the optical sensor 21b needs to be disposed at a position on the light beam Hd reflected from the transmissive polarizing plate 15b and not affected by the light beam He reflected by the reflective polarizing plate 13b.

Next, the Vcom correction operation using the optical sensors 21r, 21g, and 21b will be described in detail with reference to FIGS. 6, 7, and 8. FIG.
Vcom correction is performed to obtain a common electrode voltage (Vcom) during main projection for emitting a light-modulated projection image based on an input image signal, and a specific image is projected to detect the optimum value of Vcom. To do.
FIG. 6 shows a Vcom correction circuit for the optical path of B light, but similar circuits are also provided for G light and R light.
As shown in FIG. 6, the Vcom correction circuit includes an optical sensor 21b disposed on the light beam Hd reflected from the transmissive polarizing plate 15b, a liquid crystal driving circuit 22b for supplying a reflective liquid crystal display element 12b driving signal, Based on the signal from the optical sensor 21b and the drive signal from the liquid crystal drive circuit 22b, a detection circuit 23b that detects the state of Vcom, and the common electrode voltage is calculated based on the state of Vcom detected by the detection circuit 23b. And a correction circuit 25b for supplying a common electrode voltage to the common electrode 24b of the reflective liquid crystal display element 21b.

Further, the Vcom correction circuit will be described in detail with reference to FIGS.
As shown in FIG. 7, the detection circuit 23b includes an AD converter (hereinafter referred to as ADC) 26, a timing pulse generator (hereinafter referred to as TG) 27, and a positive polarity data hold circuit (hereinafter referred to as DH-posi). 28), a negative polarity data hold circuit (hereinafter referred to as DH-negative) 29, a subtracter A30, a coefficient register (hereinafter referred to as DH-K) 31, a multiplier 32, and a multiplication And a resultant data hold circuit (hereinafter referred to as DH-DET-K) 33.
The correction circuit 25 includes a common electrode voltage data hold circuit (hereinafter referred to as DH-cc) 34, a subtractor B 35, and a DA converter 36.

The operation of the Vcom correction circuit shown in FIG. 7 will be described with reference to FIG. In the optical sensor 21b, the change in the amount of reflected light Hd from the transmissive polarizing plate 15b is converted into a detection signal that is an analog electrical signal, and the ADC 26 converts the analog signal into a digital signal. (S1)
The liquid crystal driving circuit 22b inverts the polarity of the input image signal for each vertical period (hereinafter referred to as a frame) of the image with respect to the reference voltage, and periodically inverts the polarity of the pixel electrode of the reflective liquid crystal display element 12b. The input image signal is supplied.
The clock signal and polarity switching signal generated for each frame output from the liquid crystal driving circuit 22b are input to the TG 27, and a positive trigger signal having a positive polarity and a negative trigger signal having a negative polarity and 1 of a projected image. A frame period signal corresponding to the frame is output. (S2)
Based on the positive and negative trigger signals output from the TG 27, the digital signal output from the ADC 26 is stored with the positive-side portion separated into DH-posi 28 and the negative-side portion separated into DH-negative 29. (S3)
The positive polarity side peak detection signal is output from the data stored in the DH-posi 28, and the negative polarity side peak detection signal is output from the data stored in the DH-negative 29, and is calculated by the subtractor A30. (S4)
When the difference in the subtracter A30 is 0, Vcom is not deviated and the process is terminated. When the difference in the subtracter A30 is other than 0, the process proceeds to the following steps (S5).
The difference data calculated by the subtractor A30 is amplified by the multiplier 32 according to the coefficient from DH-K31, and the result is stored in DH-DET-K33. (S6)
Here, the time required for Vcom correction can be shortened by increasing the coefficient from DH-K31.
The data stored in DH-DET-K33 is output as a difference signal only once per frame based on a signal corresponding to the frame period of the projection image from TG27. (S7)

The difference signal output from DH-DET-K33 is input to the subtractor B35, and the difference from the output value of the subtracter B one frame before stored in DH-cc34 is calculated. (S8)
The calculation result in the subtracter B35 is stored in the DH-cc 34 only once per frame based on a signal corresponding to the frame period of the projection image from the TG 27. (S9)
Further, the calculation result in the subtractor B35 is input to the DAC 36, converted from a digital signal to an analog signal (S10), and output as Vcom to the common electrode 24b. (S11)

The steps from the detection of the detection signal from the optical sensor 21b (S1) to the output of the Vcom correction value to the common electrode 24b (S11) are repeated for each frame until the difference (S5) in the subtractor A30 becomes zero. Thus, the Vcom value is corrected, and by using this Vcom value, flicker of the projected image can be suppressed during the main projection.
As a result, Vcom can be corrected without being affected by the light beam Ha of P-polarized B light incident on the reflective polarizing plate 13b, and a projected image with less flicker can be obtained.
Furthermore, each color light of R light, G light, and B light is detected by the independent optical sensors 21r, 21g, and 21b, and the Vcom correction value corresponding to each color light is calculated by the Vcom correction circuit. Vcom correction can be performed with high accuracy.
Furthermore, since the optical sensors 21r, 21g, and 21b are mounted inside the projection display device, the projection display device does not increase in size, and the projection display device can be easily moved.

<Example 2>
Next, as another embodiment of the present invention, an operation when performing Vcom correction of a specific area in a projection image will be described with reference to FIGS.
In the present embodiment, the configuration of the optical system and the Vcom correction circuit are the same as those in the first embodiment, and thus description thereof is omitted here.

In the Vcom correction for obtaining the Vcom value at the time of the main projection, the light amount of the light beam Hd incident on the optical sensor 21b varies depending on the state of light modulation by the reflective liquid crystal display element 12b.
In the light modulation, a driving voltage based on an input image signal is applied to the liquid crystal of the reflective liquid crystal display elements 12r, 12g, and 12b, and the polarization state of the incident R, G, and B colors is changed by changing the alignment state of the liquid crystal. This is caused by changing the polarization state of the light beam Hb.
Hereinafter, although the optical path of G light is demonstrated, it is the same also about B light and R light.

The optical characteristics (transmittance of the P-polarized component and transmittance of the S-polarized component) at the center wavelength of 550 nm of the G light of the reflective polarizing plate 13g and the transmissive polarizing plate 15g used in this example are compared.
The reflective polarizing plate 13g increases the extinction ratio (Tpw / Tsw) obtained by dividing the transmittance (Tpw) of the P-polarized component by the transmittance (Tsw) of the S-polarized component in order to improve the contrast of the transmitted light. ing. In addition, the transmissive polarizing plate 15g increases the transmittance (Tsa) of the S-polarized component in order to increase the transmittance.
For this reason, the reflective polarizing plate 13g has a small Tsw, and the transmissive polarizing plate 15g has a large Tsa.

On the other hand, the reflectance of the reflective polarizing plate 13g and the transmissive polarizing plate 15g is almost proportional to the transmittance because there is almost no optical loss (absorption) in the reflective polarizing plate 13g and the transmissive polarizing plate 15g. Become.
Therefore, Rsw is large in the reflective polarizing plate 13g, and Rsa is small in the transmissive polarizing plate 15g.
Actually, the reflectance at 550 nm, which is the central wavelength of G light, of the reflective polarizing plate 13g and the transmissive polarizing plate 15g used in this example is as follows.
Reflectivity (Rpw) of P-polarized light of reflective polarizing plate 13g = 1%
Reflectivity (Rsw) of reflection type polarizing plate 13g (Rsw) = 91%
Reflectivity (Rpa) of P-polarized light of transmission type polarizing plate 15g = 89%
S-polarized light reflectance (Rsa) of the transmissive polarizing plate 15g = 0.05%

When the input image signal applied to the reflective liquid crystal display element 12g is a black level (0%), the light beam reflected from the reflective liquid crystal display element 12g is P-polarized light. Therefore, in the reflective polarizing plate 13g, most of the P-polarized light is transmitted, but 1% is reflected (Rpw).
Further, a slight amount of the P-polarized light beam Hc reflected by the reflective polarizing plate 13g is incident on the transmissive polarizing plate 15g. In the transmissive polarizing plate 15g, 89% of the incident P-polarized light beam Hc is reflected (Rpa).

In other words, when the amount of light incident on the reflective liquid crystal display element 12g is 100%, the input polarizing plate 15g is reflected when the input image signal applied to the reflective liquid crystal display element 12g is at the black level (0%). The ratio (Ib) of the amount of light incident on the optical sensor 21g is as follows.
Ib = Rpw × Rpa = 1% × 89% = 0.89%
Here, it is assumed that there is no loss at the time of light modulation and reflection at the reflective liquid crystal display element 12g, and 100% reflection with respect to the light beam Hb of the incident light to the reflective liquid crystal display element 12g.

When the input image signal applied to the reflective liquid crystal display element 12g is a white level (100%), the light beam reflected from the reflective liquid crystal display element 12g is S-polarized light. Therefore, the reflective polarizing plate 13g reflects 91% of S-polarized light (Rsw).
The S-polarized light beam Hc reflected by the reflective polarizing plate 13g enters the transmissive polarizing plate 15g. In the transmissive polarizing plate 15g, most of the incident S-polarized light beam Hc is transmitted, but 0.05% is reflected (Rsa).

In other words, when the amount of light incident on the reflective liquid crystal display element 12g is 100%, the input image signal applied to the reflective liquid crystal display element 12g is reflected by the transmissive polarizing plate 15g when the white level (100%) is obtained. The ratio (Iw) of the amount of light incident on the optical sensor 21g is as follows.
Iw = Rsw × Rsa = 91% × 0.05% = 0.0455%
Here, it is assumed that there is no loss at the time of light modulation and reflection at the reflective liquid crystal display element 12g, and 100% reflection with respect to the light beam Hb of the incident light to the reflective liquid crystal display element 12g.

Accordingly, the optical sensor when the input image signal applied to the reflective liquid crystal display element 12g is incident on the optical sensor 21g at the black level (0%) and at the white level (100%). Comparing the amount of light Iw incident on 21g (0.0455%), the value is about 20 times larger when the input image signal is at the black level (0%).
Therefore, as shown in FIG. 9, the black level (0%) is displayed in the region where the Vcom correction of the projected image is to be performed, and the white level (100%) is displayed in the other region, thereby selectively displaying the black level. By performing Vcom correction of the area displaying (0%) and using the Vcom value obtained by this Vcom correction, flicker of the projected image can be suppressed during the main projection.

In general, the optical sensor detection signal when a Vcom shift occurs has a waveform very similar to a sine wave as shown in FIG.
As shown in FIG. 10, since the projection display device performs a line-sequential operation with respect to the vertical direction of the projected image, the detection of the optical sensor is performed according to the vertical area as shown in FIGS. 10 (a) to 10 (c). The phase of the signal changes.
Therefore, by changing the trigger position of the positive and negative trigger signals output from the TG 27, the vertical region of the projected image can be detected.
FIG. 10 shows a case where flicker occurs in the lower area of the projected image and Vcom deviation occurs.

<Example 3>
Next, as another embodiment of the present invention, an operation when Vcom correction is automatically performed will be described with reference to FIGS.
In the present embodiment, the configuration of the optical system is the same as that of the first embodiment, and thus the description thereof is omitted here. Further, the detection circuit 23b of the Vcom correction circuit is also the same as that of the first embodiment, and thus the description thereof is omitted.

  As shown in FIG. 11, in the first embodiment, the difference signal output from DH-DET-K33 is directly input to the subtractor B35, but in this embodiment, DH-DET-K33, subtractor B35, Is provided with a Vcom correction circuit start switch 37 for switching between starting and not starting the operation of the Vcom correction circuit, and a signal for controlling ON / OFF of the Vcom correction circuit start switch 37 based on an external signal. And a flash memory 39 for storing Vcom correction data are added to the correction circuit 25b of the first embodiment.

In order to accurately perform the Vcom correction for obtaining the Vcom value during the main projection, it is necessary to project an image of a specific pattern. In order to display an image of a specific pattern, it is efficient to perform Vcom correction when the projection display device 1 is started or when the operation ends.
In particular, Vcom is known to change depending on the temperature of the optical system of the projection display device 1 and the reflective liquid crystal display elements 21r, 21g, and 21b. Therefore, if Vcom correction is performed at the time of startup, the temperature of the optical system of the projection display device 1 and the reflective liquid crystal display elements 21r, 21g, and 21b is increased by the light from the light source 2 after the Vcom correction. Therefore, by performing Vcom correction at the end of the operation, the optical system of the projection display device 1 and the reflective liquid crystal display elements 21r, 21g, and 21b perform correction in a steady state that is sufficiently warmed by the light from the light source 2. And the accuracy of Vcom correction can be increased.

Hereinafter, the case where Vcom correction is performed at the end of the operation of the projection display apparatus 1 will be described with reference to FIG. 12, but the same may be performed when Vcom correction is performed when the projection display apparatus 1 is activated and during activation. it can.
As shown in FIG. 12, when a signal for ending projection of the projection display device 1 such as an external projection stop signal is input to the CPU 38, the CPU 38 outputs a Vcom correction circuit activation signal to the Vcom correction circuit activation switch 37. To do. (S101)
When the Vcom correction circuit activation signal is input to the Vcom correction circuit activation switch 37, the Vcom correction circuit activation switch 37 changes from the OFF state to the ON state. (S102)
When the Vcom correction circuit start switch 37 is turned on, the CPU 38 outputs a signal for displaying the Vcom correction image pattern to the liquid crystal drive circuit 22b. (S103)
When the image pattern for Vcom correction is displayed, difference signals are calculated in the order shown in the first embodiment, and Vcom correction is performed based on the calculated difference signal. Until the difference signal becomes 0, the ON state of the Vcom correction circuit activation switch 37 is held, and the calculation is repeated for each frame. (S104)

When the difference signal becomes 0, the CPU 38 outputs a Vcom correction circuit stop signal to the Vcom correction circuit start switch 37. (S105)
When the Vcom correction circuit stop signal is input to the Vcom correction circuit start switch 37, the Vcom correction circuit start switch 37 changes from the ON state to the OFF state. (S106)
The calculation result in the subtractor B35 when the difference signal becomes 0 is held in the flash memory 39 connected to the CPU. (S107)
After confirming that the calculation result in the subtracter B35 is stored in the flash memory 39, the power supply of the projection display device 1 is stopped.

As described above, when the stop signal of the projection display device 1 is input, the optical system and the reflective liquid crystal display elements 12r, 12g, and 12b are sufficiently warmed by the light from the light source 2 in order to perform Vcom correction. As a result, Vcom correction can be performed with the temperature stabilized.
Further, when the projection display device 1 is activated next time by storing the Vcom correction result in the flash memory 39, the projection display device 1 is used to perform the main projection when the Vcom correction result in the flash memory 39 is called. In this case, it is possible to display a projected image with little Vcom deviation from startup and with reduced flicker.
When Vcom correction is performed at the time of activation, the Vcom correction circuit activation switch 37 may be changed from the OFF state to the ON state when the activation signal of the projection display device 1 is input.

<Example 4>
In general, the amount of change in Vcom during the main projection of the projection display device 1 is the next (m + 1) operation start from the end of the previous operation of the projection display device 1 (mth, where m is an integer of 1 or more). It has been found that the longer the elapsed time, the greater the amount of change.
Therefore, in this embodiment, a projection image with a small Vcom deviation at the time of the main projection is obtained regardless of the elapsed time from the time of the first main projection at the time of power-on to the projection type display device 1 until the end of the operation due to the power stop. In order to perform projection, Vcom correction is performed at both timings immediately after power-on of projection-type display device 1 (at the time of startup) and immediately before power-off (at the end of operation).
The operation in the case of performing Vcom correction at both the start timing and the end timing of the projection display device 1 will be described with reference to FIGS.

When the projection display device 1 is activated, the temperature of the optical system of the projection display device 1 and the reflective liquid crystal display elements 21r, 21g, and 21b is heated by the light from the light source 2 and rises. The temperature rises rapidly immediately after start-up and becomes almost stable in about 30 minutes.
Therefore, when Vcom correction is performed at the time of startup, it is important to take into account the temperature change immediately after startup. In other words, when Vcom correction is performed at the time of startup, it is necessary to add a Vcom change amount α generated by a temperature rise after Vcom correction after obtaining a correction value (Vs) of Vcom.

Here, the change amount α of Vcom due to a temperature rise is obtained as follows, assuming that the Vcom correction amount at the start is Vst and the Vcom correction amount at the end of the operation is Ved.
α = Ved−Vst
The obtained change amount α of Vcom is stored in the flash memory 39, and is added to the Vcom correction amount (Vst) when the projection display device 1 is activated when the projection display device 1 is activated next time. Vcom correction can be performed in consideration of temperature changes of the optical system of the projection display device 1 and the reflective liquid crystal display elements 21r, 21g, and 21b.

Acquisition of the Vcom correction amount (Vst) at the start and acquisition of the Vcom correction amount (Ved) at the end of the operation are performed in the following procedure.
In the present embodiment, the configuration of the optical system is the same as that of the first embodiment, and thus the description thereof is omitted here. Further, the Vcom correction circuit is the same as that of the third embodiment, so that the description thereof is omitted.
Hereinafter, a method for acquiring the Vcom correction amount (Vst) at the time of activation will be described.
As shown in FIG. 13, when a signal such as an external projection start signal or projection stop signal is input to the CPU 38, the CPU 38 outputs a Vcom correction circuit activation signal to the Vcom correction circuit activation switch 37. (S201)
When the Vcom correction circuit activation signal is input to the Vcom correction circuit activation switch 37, the Vcom correction circuit activation switch 37 changes from the OFF state to the ON state. (S202)

When the Vcom correction circuit start switch 37 is turned on, the light intensity of the light source 2 is maximized in order to minimize flicker and increase the detection accuracy of Vcom. (S203)
Further, the CPU 38 outputs a signal for displaying the Vcom correction image pattern to the liquid crystal drive circuit 22b, and displays the Vcom correction image. As the Vcom corrected image, it is desirable to use a raster pattern having a brightness of about 50%. (S204)
Next, Vcom correction initial setting conditions are read from the flash memory 39. The initial setting conditions for Vcom correction include the current setting value (Vz ₀ ) of the Vcom correction amount described later, the loop count (L) of the Vcom automatic correction loop processing, the loop count (N) of the flicker amount automatic measurement loop, and the flicker amount. There are a change voltage amount (Vy) in automatic measurement, an addition amount (Vx) after correction of the Vcom shift direction, a correction coefficient (k), and the like. (S205)

After reading out the initial setting conditions for Vcom correction, a Vcom automatic correction loop process, which will be described later, is performed on each color light of R light, G light, and B light. In the Vcom automatic correction loop processing, R light, G light, and B light may be sequentially irradiated to set the Vcom correction amount for each color, or the R light, G light, and B light may be simultaneously irradiated to perform all of them at once. A color Vcom correction amount may be set. (S206)
When the setting of the Vcom correction amount is finished, the display of the Vcom correction image is finished (S207), and the light intensity of the light source 2 is returned to the steady level. (S208)

The Vcom automatic correction loop process is performed according to the following procedure.
As shown in FIG. 14, the Vcom automatic correction loop process performs the loop count (L) of the Vcom automatic correction loop process read from the flash memory 39 in S205. Here, a case where processing is performed with the loop count set to 5 will be described. (S301)
The reason why the loop processing is performed a plurality of times is to sufficiently increase the voltage range at the time of Vcom correction to provide a measurement margin.

First, based on the current setting value (Vz ₀ ) of the Vcom correction amount read from the flash memory 39 in S205 and the change voltage amount (Vy) in the flicker amount automatic measurement, the Vcom voltage is shifted to the plus side. A voltage (Vip = Vz ₀ + Vy) and an applied Vcom voltage (Vim = Vz ₀ −Vy) on the subtraction side obtained by shifting the Vcom voltage to the minus side are obtained.
The applied Vcom voltage (Vip) on the addition side is applied to the reflective liquid crystal display elements 12r, 12g, and 12b of the respective colors, the flicker amount (FLp) on the addition side is measured by a flicker amount automatic measurement loop described later, and then subtraction is performed. The applied Vcom voltage (Vim) on the side is applied to the reflective liquid crystal display elements 12r, 12g, and 12b for each color, and the flicker amount (FLm) on the subtraction side is measured by a flicker amount automatic measurement loop described later. (S302)

The addition side flicker amount (FLp) calculated in S302 is compared with the subtraction side flicker amount (FLm) (S303), and the addition side flicker amount (FLp) is larger than the subtraction side flicker amount (FLm). In order to shift the Vcom voltage to the negative side, the first Vcom correction amount (Vz ₁ ) is calculated using the following equation. (S304)
Vz ₁ = Vz ₀ −Vx × k (k = 1 when i = 1 to 3, k = 1 when i = 4 to 5)
Here, Vx and k are values read from the flash memory 39 in S205, Vx is an addition amount after determination of the Vcom shift direction, and k is a correction coefficient.

When the flicker amount (FLp) on the addition side is equal to or smaller than the flicker amount (FLm) on the subtraction side, it is determined whether the flicker amount (FLp) on the addition side and the flicker amount (FLm) on the subtraction side are the same value. (S305)
When the amount of flicker on the addition side (FLp) is equal to the amount of flicker on the subtraction side (FLm), the first Vcom correction amount (Vz ₁ ) is calculated using the following equation. (S306)
Vz ₁ = Vz ₀

When the flicker amount (FLp) on the addition side is not equal to the flicker amount (FLm) on the subtraction side, in order to shift the Vcom voltage to the positive side, the first Vcom correction amount (Vz ₁ ) is calculated using the following equation. . (S307)
Vz ₁ = Vz ₀ + Vx × k (k = 1 if i = 1-3, k = 1 if i = 4-5)

The processing from S301 to S307 is performed five times that is the loop count (L) of the Vcom automatic correction loop processing. (S308)
In the case of the second measurement, the second Vcom correction amount (Vz) is used by using the Vcom correction amount (Vz ₁ ) obtained in the first measurement instead of the current setting value (Vz ₀ ) of the Vcom correction amount. ₂ ) Calculate. Similarly, the Vcom correction amounts (Vz ₃ , Vz ₄ , Vz ₅ ) up to the _{fifth time} are sequentially measured and calculated using the previous Vcom correction amount (Vz _x ).

After the five Vcom automatic correction loop processes are completed, the polarities of the obtained five Vcom correction amounts (Vz ₁ , Vz ₂ , Vz ₃ , Vz ₄ , Vz ₅ ) are compared. (S309)
When the polarity is inverted between Vz _{1 and} Vz ₅ , it is determined that the flicker amount is the minimum value, and the fifth Vcom correction amount (Vz ₅ ) is set as the Vcom correction amount (Vst) at the time of activation.

If the obtained five Vcom correction amounts (Vz ₁ , Vz ₂ , Vz ₃ , Vz ₄ , Vz ₅ ) have the same polarity, it is determined that the flicker amount is not the minimum value, and the Vcom automatic correction loop process (hereinafter, referred to as “Fcom” correction process) (Referred to as retry processing). At this time, if retry processing has already been performed, the Vcom correction amount (Vz ₅ ) for the fifth time in the retry processing is set as the Vcom correction amount (Vst) at startup. (S310)
If the retry process is not performed in S309, the loop count is initialized to 0 (S311), and the Vcom automatic correction loop process of S301 to S308 is performed.

Note that the automatic measurement loop for the addition-side flicker amount (FLp) and the subtraction-side flicker amount (FLm) in S302 is performed according to the following procedure.
As shown in FIG. 15, the flicker amount automatic measurement loop performs the processing of the number of times (N) of the flicker amount automatic measurement loop read from the flash memory 39 in S205. Here, a description will be given of a case in which the flicker amount (FLp) on the addition side is measured with the number of loops set to 10. (S401)

First, from the current setting value (Vz ₀ ) of the Vcom correction amount read from the flash memory 39 in S205 and the change voltage amount (Vy) in the flicker amount automatic measurement, the applied Vcom voltage (Vip = Vz ₀ + Vy) on the addition side Is applied to the reflective liquid crystal display elements 12r, 12g, and 12b of the respective colors. (S402)
After the application side applied Vcom voltage (Vip) is applied, the first addition side flicker amount (FLp ₁ ) is measured after a time of one frame or more (for example, 50 msec). (S403)

Flicker of 10 additions side similarly after the measurement of the _{(FLp 1 ~FLp 10) (S404} ), the flicker amount of 10 times the adder of (FLp ₁ ~FLp ₁₀₎ Mean value calculated in the adder of The average flicker amount (FLp _ave ) is used. (S405)
An absolute value of an average value (FLp _ave ) of the flicker amount on the addition side is obtained and set as the flicker amount (FLp) on the addition side. (S406)

The Vcom correction amount (Vst) at the start-up of the projection display device 1 and the Vcom correction amount (Ved) at the end of the operation of the projection display device 1 are acquired by the above-described procedure, and the Vcom change amount α (α = Ved−Vst) is obtained and stored in the flash memory 39.
The latest change amount α of Vcom is stored in the flash memory 39 for the latest plural times (for example, 8 times in the embodiment) in order to reduce the error.
During the main projection of the projection display device 1, the measured Vcom correction amount (Vst) at the time of activation of the projection display device 1 is the latest multiple times stored in the flash memory 39 (for example, eight times in the embodiment). A value obtained by adding the average values of the change amounts α of Vcom is used as the Vcom value.

That is, during the main projection of the projection display device 1, a value obtained by adding the average value of the change amounts α of Vcom stored in the flash memory 39 to the Vcom correction amount (Vst) measured at startup is set as the Vcom value. By projecting the projected image, it is possible to project a projected image in consideration of the Vcom shift due to temperature during the main projection.
On the other hand, at the end of the operation of the projection display device 1, the Vcom correction amount (Ved) is measured, and a change amount α (α = Ved−Vst) of Vcom, which is a difference from the Vcom correction amount (Vst) at the time of activation, is obtained. And stored in the flash memory 39.
When the projection display device 1 is activated for the first time, an average change amount α0 of Vcom is stored in the flash memory 39 in advance at the time of factory shipment, and the change amount α0 of Vcom is set as the Vcom correction amount (Vst) at the time of initial activation. Is used as the Vcom value.

Here, when the Vcom value measured in the Vcom correction at the time of start-up and the Vcom value measured at the end of the previous operation stored in the rush memory 39 are compared and the difference is small, the Vcom value is almost changed. If not, Vx and k are not added to the Vcom value.
Specifically, when the difference between the Vcom value measured in the Vcom correction at the time of startup and the Vcom value measured at the end of the previous operation is equal to or less than Vx × k, which is an addition, Vcom × k is added to add Vcom × k. This is because the value may deviate from the optimum value.
More preferably, specifically, when the difference between the Vcom value measured in the Vcom correction at the time of startup and the Vcom value measured at the end of the previous operation is equal to or less than (Vx × k) / 2, the Vcom at the time of startup Vx × k is not added to the Vcom value measured in the correction, and the Vcom value measured in the Vcom correction at start-up is set as the Vcom value in the main projection.

Further, when the projection display device 1 is activated, the temperature of the optical system of the projection display device 1 and the reflective liquid crystal display elements 21r, 21g, and 21b is heated and increased by the light from the light source 2, and the temperature is about 30 minutes. However, after that, the temperature gradually changes and the optimum Vcom value also changes slightly.
Therefore, when the projection display device 1 is stopped within one hour from the start-up, the amount of change in Vcom due to the temperature rise that is the difference between the Vcom correction amount (Vst) at the start and the Vcom correction amount (Ved) at the end of the operation. α becomes small, and the difference from the change amount α of Vcom due to temperature rise when the projection display device 1 is operated for a long time becomes large.
Therefore, for example, when the projection display device 1 is stopped within one hour from the start-up, the measurement of Vcom correction at the end of the operation is not performed.

<Example 5>
Next, an operation for correcting Vcom by removing flicker caused by a change in light intensity (hereinafter referred to as lamp flicker) generated by thermal convection of xenon gas sealed in the xenon lamp 2a of the light source 2 will be described. .
The detection signals of the optical sensors 21r, 21g, and 21b include lamp flicker in addition to flicker caused by Vcom deviation.
Therefore, it is necessary to delete the lamp flicker from the detection signals of the optical sensors 21r, 21g, and 21b. An operation for correcting the Vcom by deleting the lamp flicker from the detection signals of the optical sensors 21r, 21g, and 21b will be described with reference to FIG.
In the present embodiment, the configuration of the optical system is the same as that of the first embodiment, and thus the description thereof is omitted here. In addition, the detection circuit 23 of the Vcom correction circuit is the same as that of the first embodiment, and a description thereof will be omitted.

  In the first embodiment, the difference signal output from the DH-DET-K33 is directly input to the subtractor B35. However, as shown in FIG. 15, in this embodiment, the DH-DET-K33 and the subtractor B35 are used. A low-pass filter (LPF) 40 for removing lamp flicker is added between the two.

In general, lamp flicker occurs in a certain frequency range. In the case of the light source 2 having a xenon lamp used in this example, the frequency of the lamp flicker was 40 Hz.
Therefore, the lamp flicker can be removed from the detection signal by removing the components in the frequency band of 40 Hz from the detection signals of the optical sensors 21r, 21g, and 21b by the LPF 40.
The LPF 40 may be disposed at any position between the optical sensors 21r, 21g, and 21b and the subtractor B35. In particular, the DH-DET-K33 and the subtractor B35 after detecting the difference signal. It is desirable to arrange | position between.
Thereby, the Vcom value from which the influence of the lamp flicker is deleted at the time of Vcom correction can be obtained, and by using this Vcom value, it is possible to project a projection image having no Vocm shift at the time of the main projection.
Further, as described above, since the frequency band in which lamp flicker is generated differs depending on the lamp used for the light source 2, it is necessary to change the characteristics of the LPF 40 according to the lamp used for the light source 2.

As described above, an optical sensor for detecting flicker of projection light is installed in the apparatus, and the projection lens can be replaced without being aware of the optical sensor when replacing the projection lens. It is possible to provide a light modulation device, a projection display device, and an image projection method that are easy, do not increase the cost of the projection lens, and do not cause the shadow of the optical sensor to appear in the projected image.
Furthermore, by installing an optical sensor in the apparatus, the amount of light detected by the optical sensor can be improved, and the number of optical sensors or the light modulation device, the projection display device, and the measurement time can be reduced. An image projection method can be provided.
Furthermore, since optical sensors are provided independently for each of the R, G, and B colors, white light is projected, and Vcom for each of the RGB colors can be corrected simultaneously and accurately, and light modulation that can suppress flicker An apparatus, a projection display device, and an image projection method can be provided.
Further, there is provided a light modulation device, a projection display device, and an image projection method capable of suppressing flicker even when flicker has a distribution in a projection image and capable of suppressing flicker caused by a liquid crystal display element separately from lamp flicker. Can be provided.

If the configuration of the Vcom correction circuit is a circuit that generates a difference between the positive side and the negative side based on the detection signal detected by the optical sensor 21b and corrects Vcom based on this difference value, It goes without saying that the present invention is not limited to this embodiment.
In addition, in the case of having modulation optical paths for a plurality of different colors, if the light modulation device α of the present invention is used for at least one optical path, it is effective for suppressing flicker. In particular, it is effective to use the light modulation device α of the present invention for G light having the highest brightness and flickering conspicuous or B light having a short wavelength and easily affecting an organic material.
In addition, the conventional method of installing the optical sensor in the vicinity of the projected image display area of the screen or in the projection lens may be used in combination with the present invention. Even in this case, Vcom can be corrected with high accuracy.

It is a schematic plan view which shows the structure of the optical system of the projection type display apparatus of this embodiment. It is a schematic sectional drawing which shows the structure of the light modulation apparatus used for the projection type display apparatus of this embodiment. It is explanatory drawing explaining the principle of the polarizing plate used for the projection type display apparatus of this embodiment. It is explanatory drawing explaining the optical path inject | emitted from the reflection type liquid crystal display element used for the projection type display apparatus of this embodiment. It is explanatory drawing explaining the optical path which injects into the reflection type liquid crystal display element used for the projection type display apparatus of this embodiment. It is a block diagram which shows the structure of the Vcom correction circuit of the projection type display apparatus of this embodiment. It is a detailed block diagram which shows the structure of the Vcom correction circuit of the projection type display apparatus of this embodiment. It is a flowchart which shows operation | movement of the Vcom correction circuit of the projection type display apparatus of this embodiment. It is explanatory drawing in the case of performing Vcom correction | amendment to the partial area | region of the projection image in the projection type display apparatus of this embodiment. It is explanatory drawing which shows the detection signal of the optical sensor by the display area of the projection image in the projection type display apparatus of this embodiment. It is a detailed block diagram which shows another structure of the Vcom correction circuit of the projection type display apparatus of this embodiment. It is a flowchart which shows operation | movement of another structure of the Vcom correction circuit of the projection type display apparatus of this embodiment. It is a flowchart which shows another operation | movement of the Vcom correction circuit of the projection type display apparatus of this embodiment. It is a flowchart which shows the operation | movement of the Vcom automatic correction | amendment loop process of the projection type display apparatus of this embodiment. It is a flowchart which shows the operation | movement of the flicker amount measurement loop process of the projection type display apparatus of this embodiment. It is a detailed block diagram which shows another structure of the Vcom correction circuit of the projection type display apparatus of this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Projection type display apparatus, 2 ... Light source, 2a ... Xenon lamp, 2b ... Concave mirror, 3 ... Infrared transmission filter, 4 ... Ultraviolet reflection filter, 5 ... B dichroic mirror, 6 ... Reflection mirror, 7b, 7rg ... 1st fly Eye lenses, 8b, 8rg ... second fly eye lens, 9b, 9rg ... polarization conversion element, 10b, 10rg ... condenser lens, 11r, 11g, 11b ... field lens, 12r, 12g, 12b ... reflection type liquid crystal display element, 13r , 13g, 13b ... reflective polarizing plate, 14 ... RG dichroic mirror, 15r, 15g, 15b ... transmissive polarizing plate, 16 ... cross dichroic prism, 16a ... exit surface, 17 ... screen, 18 ... projection lens, 19r, 19g , 19b ... heat sink, 20r, 20g, 20b ... triangular prism, 21r, 21g, 21b Optical sensor 22b Liquid crystal drive circuit 23b Detection circuit 24b Common electrode 25b Correction circuit 26 AD converter (ADC) 27 Timing pulse generator (TG) 28 Positive polarity data hold Circuit (DH-posi), 29... Negative polarity side data hold circuit (DH-negative), 30... Subtractor A, 31... Coefficient register (DH-K), 32. Circuit (DH-DET-K), 34 ... Common electrode voltage data hold circuit (DH-cc), 35 ... Subtractor B, 36 ... DA converter, 37 ... Vcom correction circuit start switch, 38 ... CPU, 39 ... Flash Memory, 40 ... Low-pass filter (LPF)

Claims (11)

A first polarized light beam in a first linear polarization state obtained by polarization conversion of a light beam emitted from a light source is orthogonal to the first polarized light beam and the first polarized light beam based on an input image signal. A liquid crystal display element that modulates light into a second polarized light beam in a second linear polarization state;
A reflective polarizing plate that transmits the first polarized light beam and reflects the second polarized light beam;
A transmissive polarizing plate that transmits the second polarized light beam and reflects the first polarized light beam;
An optical sensor for detecting the first polarized light beam reflected by the transmissive polarizing plate;
With
The liquid crystal display element is disposed so as to light-modulate the first polarized light beam that is transmitted through the reflective polarizing plate and to reflect the light-modulated polarized light beam so as to be incident on the reflective polarizing plate again. And
The reflective polarizing plate is disposed so as to transmit the first polarized light beam and reflect the second polarized light beam in the direction of the transmissive polarizing plate among the polarized light beams modulated by the liquid crystal display element. And
The optical sensor is disposed on a light path of a light beam reflected by the transmissive polarizing plate and at a position that does not overlap an optical path of the light beam reflected by the reflective polarizing plate. .   The reflective polarizing plate, the liquid crystal display element, and the transmissive polarizing plate are disposed at positions corresponding to three side surfaces of a substantially triangular prism, and the optical sensor is disposed at a position outside the substantially triangular prism. The light modulation device according to claim 1, wherein the light modulation device is disposed.   The light modulation device according to claim 1, wherein the light beam is a light beam of any one of red light, green light, and blue light. The light modulation device according to any one of claims 1 to 3,
Color separation means for color-separating the luminous flux of white light emitted from the light source into luminous fluxes of red light, green light, and blue light,
Polarization conversion means for emitting an incident light beam as a linearly polarized light beam having only a first linear polarization state by converting a polarization angle after polarization separation;
Color synthesizing means for synthesizing respective polarized light fluxes of the second linear polarization state of red light, green light, and blue light transmitted through the transmissive polarizing plate of the light modulator;
A projection lens for enlarging and projecting the polarized light beam emitted from the color synthesizing means as a projection image;
A projection type display device comprising: The liquid crystal display element includes a pixel electrode, a common electrode facing the pixel electrode, to which a common electrode voltage is applied, and a liquid crystal sandwiched between the pixel electrode and the common electrode,
The optical sensor receives a reflected light beam reflected from the transmissive polarizing plate and outputs a detection signal;
A liquid crystal driving circuit for supplying a pixel electrode voltage obtained by inverting the polarity of the input image signal for each vertical period with respect to a reference voltage to the pixel electrode and outputting a switching period signal corresponding to the one vertical period; ,
From the detection signal from the optical sensor and the switching period signal, a maximum value on the positive side and a minimum value on the negative side of the polarity in the one vertical period of the detection signal are obtained, and from the absolute value of the maximum value. A detection circuit that obtains a difference obtained by subtracting the absolute value of the minimum value and outputs the difference signal;
When the difference is positive based on the difference signal from the detection circuit and the common electrode voltage of the one vertical period one previous to the one vertical period for which the difference signal was obtained, the one vertical period of the previous one A correction circuit for subtracting the difference from a common electrode voltage and, when the difference is negative, adding the difference to the common electrode voltage of the previous one vertical period to obtain a common electrode correction voltage;
The projection display device according to claim 4, further comprising: A control unit for controlling an operation for obtaining the common electrode correction voltage in the correction circuit;
A storage unit for storing information on the common electrode correction voltage obtained by the correction circuit;
Have
When the control unit receives a projection stop signal of the projection display device,
The input image signal corresponding to a predetermined image is input to the liquid crystal display element by the liquid crystal driving circuit, and the predetermined image is displayed as a projection image,
When the obtained change rate of the difference becomes a predetermined value or less, the information on the common electrode correction voltage is stored in the storage unit,
The projection type display device according to claim 5. When the control unit displays an initial projection image that is initially projected when the power is turned on in the projection display device,
Read information of the common electrode correction voltage stored in the storage unit,
Based on the read information of the common electrode correction voltage, control to display the initial projection image,
The projection display device according to claim 6.   8. The projection according to claim 5, wherein the correction circuit includes a removal circuit that removes a signal in a frequency band corresponding to a flicker inherent to the light source from the difference signal. 9. Type display device. In an image projection method of projecting an image by a projection display device having an optical sensor that outputs a detection signal in response to light reception and a liquid crystal driving circuit that outputs a switching cycle signal corresponding to one vertical cycle,
A polarity separation step for separating the detection signal into a positive side and a negative side of polarity based on the detection signal from the photosensor and the switching period signal from the liquid crystal driving circuit;
Difference signal calculation for obtaining a difference between the peak values of the detection signals separated into the positive side and the negative side of the polarity for each vertical period of the projection image projected from the projection display device, and outputting a difference signal Steps,
A correction value calculating step for calculating a common electrode correction voltage based on the difference signal obtained in the difference signal calculating step;
An image projection step of projecting an image by the projection display device using the common electrode correction voltage calculated in the correction value calculation step;
Have
The image projection method characterized in that the correction value calculation step calculates a common electrode correction voltage from the calculation result in the correction value calculation step one vertical period before and the difference signal obtained in the difference signal calculation step. In an image projection method of projecting an image by a projection display device having a liquid crystal display element that optically modulates an incident polarized light beam, an optical sensor that outputs a detection signal in response to light reception, and a storage unit that stores information ,
A first common electrode voltage detection step of obtaining a first common electrode voltage immediately after power-on of the projection type display device m (m is an integer of 1 or more);
A second common electrode voltage detection step for obtaining a second common electrode voltage immediately before the m-th power supply stop of the projection display device;
A common electrode voltage storage step of obtaining an m-th common electrode voltage change amount from a difference between the second common electrode voltage and the first common electrode voltage and storing the change amount in the storage unit;
A third common electrode voltage detection step for obtaining a third common electrode voltage immediately after the (m + 1) th power-on of the projection display device;
The m-th common electrode voltage change amount read from the storage unit is added to the third common electrode voltage obtained in the third common electrode voltage detection step, and the obtained value is used as the common electrode voltage. A common electrode voltage calculation step;
An image projecting step of projecting an image by applying the common electrode voltage obtained in the common electrode voltage calculating step to the liquid crystal display element;
An image projection method comprising: The first common electrode voltage detection step, the second common electrode voltage detection step, and the third common electrode voltage detection step include:
An addition-side flicker detection step of adding a first predetermined voltage to a reference common electrode voltage in the liquid crystal display element and applying the first predetermined voltage to detect the amount of fluctuation of the light intensity of the projection light from the liquid crystal display element in an optical sensor; ,
Subtracting-side flicker detection step for subtracting and applying the first predetermined voltage to a reference common electrode voltage in the liquid crystal display element to detect a fluctuation amount of light intensity of projection light from the liquid crystal display element;
The first fluctuation amount of the light intensity obtained in the addition side flicker detection step is compared with the second fluctuation amount of the light intensity obtained in the subtraction side flicker detection step. When the first fluctuation amount is large, a voltage obtained by subtracting the second predetermined voltage from the common electrode voltage is set as a new common electrode voltage, and when the first fluctuation amount is smaller than the second fluctuation amount, A voltage obtained by adding the second predetermined voltage to the common electrode voltage is used as a new common electrode voltage. When the second fluctuation amount and the first fluctuation amount are equal, the common electrode voltage is set as a new common electrode voltage. A common electrode voltage correction step to be a voltage; and
By performing the common electrode voltage adjustment step a predetermined number of times when the addition side flicker detection step, the subtraction side flicker detection step, and the common electrode voltage correction step are combined into a common electrode voltage adjustment step, A fluctuation amount adjusting step for calculating the optimum common electrode voltage;
The image projection method according to claim 10, further comprising:

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