Patent Application
20070216440
1. Field of the Invention
The present invention relates to a sensor unit and an image display apparatus having the sensor unit.
2. Description of the Related Art
As a technique to provide a high-resolution image projection apparatus using a display device, such as an LCD, having a limited number of pixels, a wobbling technique is known which uses a polarization rotation liquid crystal cell and a birefringent plate in combination to perform pixel shifts.
With the wobbling technique, the timing of shifting light is dependent upon on and off of the polarization rotation liquid crystal cell. For this reason, to provide good display, it is important to drive control the polarization rotation liquid crystal cell taking its response into consideration. For example, JP-A No. 11-296135 (KOKAI) discloses a technique to determine an ideal drive signal of the polarization rotation liquid crystal cell. The response characteristic of the polarization rotation liquid crystal cell is temperature dependent. Thus, in order to apply an ideal drive signal to the liquid crystal cell even with temperature changed, a method has also been proposed by which the drive signal is changed on the basis of temperature information from a temperature sensor (see JP-A No. 11-326877 (KOKAI)).
With the proposal described in JP-A No. 11-326877, however, the temperature of the polarization rotation liquid crystal cell is measured; therefore, its response characteristic cannot be obtained. For this reason, it is required to determine the temperature versus response characteristic relationship of the polarization rotation liquid crystal cell in advance. However, it is not practical in terms of time and cost to determine in advance the temperature versus response characteristic relationship for all the polarization rotation liquid crystal cells actually manufactured. One might suggest a method to determine the temperature versus response characteristic relationship of a reference polarization rotation liquid crystal cell in advance. However, an ideal drive signal could not be obtained because the characteristic of the reference polarization rotation liquid crystal cell is not identical to those of polarization rotation liquid crystal cells actually manufactured.
JP-A No. 2000-284255 (KOKAI) discloses a method to calculate the temperature of a display liquid crystal panel from its response speed. However, this proposal does not relate to a polarization rotation liquid crystal cell for wobbling but relates to only a liquid crystal cell for display. In addition, to measure the temperature of the liquid crystal panel, its response speed is merely measured.
As described above, the wobbling technique is known as a technique to obtain a high-resolution image projector. Heretofore, it has been difficult to provide ideal driving of a polarization rotation liquid crystal cell taking its response characteristic into consideration.
The object of the present invention is to provide a sensor unit and an image display apparatus which allow the response characteristic of a polarization rotation liquid crystal cell to be obtained exactly.
A first aspect of the present invention, there is provided a sensor unit for measuring a response characteristic of a polarization rotation liquid crystal cell, comprising: a measurement light source which emits measurement light; a first polarization plate which has a first polarization direction and receives the measurement light from the measurement light source to output measurement light having the first polarization direction to a polarization rotation liquid crystal cell; a second polarization plate which has a second polarization direction and receives measurement light passed through the polarization rotation liquid crystal cell; a light receiving unit which receives measurement light passed through the second polarization plate; and a measurement unit which determines a response characteristic of the polarization rotation liquid crystal cell on the basis of a drive signal of the polarization rotation liquid crystal cell and the amount of measurement light received by the light receiving unit.
In the sensor unit, the first and second polarization directions are the same or perpendicular to each other.
In the sensor unit, the measurement light source is an LED which emits measurement light of green.
In the sensor unit, the LED has a condenser element.
In the sensor unit, the light receiving unit includes a photodiode.
A second aspect of the present invention, there is provided an image display apparatus which presents an image to an observer, comprising: an image modulation unit which produces modulated light modulated according to an image signal; a polarization rotation liquid crystal cell which is capable of rotating a direction of polarization of the modulated light produced by the image modulation unit; a birefringent plate which receives the modulated light from the polarization rotation liquid crystal cell; a display optical unit which presents the modulated light from the birefringent plate to the observer; a sensor unit configured to measure a response characteristic of the polarization rotation liquid crystal cell, the sensor unit including a measurement light source which emits measurement light, a first polarization plate which has a first polarization direction and receives the measurement light from the measurement light source to output measurement light having the first polarization direction to the polarization rotation liquid crystal cell, a second polarization plate which has a second polarization direction and receives measurement light passed through the polarization rotation liquid crystal cell, a light receiving unit which receives measurement light passed through the second polarization plate, and a measurement unit which determines a response characteristic of the polarization rotation liquid crystal cell on the basis of a drive signal of the polarization rotation liquid crystal cell and the amount of measurement light received by the light receiving unit; and a liquid crystal cell drive unit which drives the polarization rotation liquid crystal cell by a drive signal adjusted on the basis of the response characteristic determined by the measurement unit.
In the image display apparatus, the drive signal is adjusted taking into consideration the amount of light received by the light receiving unit when the polarization rotation liquid crystal cell has been set to a rotating state and the amount of light received by the light receiving unit when the polarization rotation liquid crystal cell has been set to a non-rotating state.
In the image display apparatus, the drive signal is adjusted so that the ratio or difference between a first amount of light received by the light receiving unit when the polarization rotation liquid crystal cell has been set to the rotating state and a second amount of light received by the light receiving unit when the polarization rotation liquid crystal cell has been set to the non-rotating state increases.
In the image display apparatus, the modulated light that the birefringent plate receives is separated into available light which arrives a target pixel and unavailable light which arrives a pixel next to the target pixel, and the drive signal is adjusted so that the ratio or difference between the amount of available light and the amount of unavailable light increases.
In the image display apparatus, an angle between a line that connects a center of the measurement light source and a center of the light receiving unit and a line normal to a light receiving surface of the polarization rotation liquid crystal cell is not more than 5 degrees.
In the image display apparatus, the sensor unit is placed in an area outside an area through which the modulated light from the image modulation unit passes.
In the image display apparatus, the image modulation unit is placed on the light receiving unit side of the polarization rotation liquid crystal cell.
In the image display apparatus, the drive signal is adjusted in real time.
In the image display apparatus, the measurement unit determines the response characteristic a plurality of times, and the drive signal is adjusted on the basis of a plurality of response characteristics determined.
In the image display apparatus, the drive signal is adjusted during a blanking period of the image signal.
A third aspect of the present invention, there is provided an image display apparatus which presents an image to an observer, comprising: an image modulation unit which produces modulated light modulated according to an image signal; a first polarization rotation liquid crystal cell which is capable of rotating a direction of polarization of the modulated light produced by the image modulation unit; a first birefringent plate which receives the modulated light from the first polarization rotation liquid crystal cell; a second polarization rotation liquid crystal cell which is capable of rotating a direction of polarization of the modulated light output from the first birefringent plate; a second birefringent plate which receives the modulated light from the second polarization rotation liquid crystal cell; a display optical unit which presents the modulated light from the second birefringent plate to the observer; a sensor unit configured to measure response characteristics of the first and second polarization rotation liquid crystal cells, the sensor unit including a measurement light source which emits measurement light, a first polarization plate which has a first polarization direction and receives the measurement light from the measurement light source to output measurement light having the first polarization direction to the first polarization rotation liquid crystal cell, a second polarization plate which has a second polarization direction and receives measurement light passed through the second polarization rotation liquid crystal cell, a light receiving unit which receives measurement light passed through the second polarization plate, and a measurement unit which determines response characteristics of the first and second polarization rotation liquid crystal cells on the basis of drive signals of the first and second polarization rotation liquid crystal cells and the amount of measurement light received by the light receiving unit; and a liquid crystal cell drive unit which drives the first and second polarization rotation liquid crystal cells by drive signals adjusted on the basis of the response characteristics determined by the measurement unit.
In the image display apparatus, the liquid crystal cell drive unit drives the first and second polarization rotation liquid crystal cells so that a transition timing of the drive signal of the first polarization rotation liquid crystal cell and a transition timing of the drive signal of the second polarization rotation liquid crystal cell are not coincident with each other.
In the image display apparatus, the polarization rotation liquid crystal cell has a display area through which the modulated light modulated by the image modulation unit passes and a measurement area through which the measurement light passes, and the liquid crystal cell drive unit drives each of the display area and the measurement area separately.
In the image display apparatus, the polarization rotation liquid crystal cell has a display area through which the modulated light modulated by the image modulation unit passes and a measurement area through which the measurement light passes, and further comprising a light-tight member between the display area and the measurement area to optically isolate the modulated light and the measurement light.
A fourth aspect of the present invention, there is provided an image display apparatus which presents an image to an observer, comprising: an image modulation unit which produces modulated light modulated according to an image signal; a first polarization rotation liquid crystal cell which is capable of rotating a direction of polarization of the modulated light produced by the image modulation unit; a first birefringent plate which receives the modulated light from the first polarization rotation liquid crystal cell; a second polarization rotation liquid crystal cell which is capable of rotating a direction of polarization of the modulated light output from the first birefringent plate; a second birefringent plate which receives the modulated light from the second polarization rotation liquid crystal cell; a display optical unit which presents the modulated light from the second birefringent plate to the observer; a sensor unit configured to measure a response characteristic of the first polarization rotation liquid crystal cell, the sensor unit including a measurement light source which emits measurement light, a first polarization plate which has a first polarization direction and receives the measurement light from the measurement light source to output measurement light having the first polarization direction to the first polarization rotation liquid crystal cell, a second polarization plate which has a second polarization direction and receives measurement light passed through the second polarization rotation liquid crystal cell, a light receiving unit which receives measurement light passed through the second polarization plate, and a measurement unit which determines a response characteristic of the first polarization rotation liquid crystal cell on the basis of a drive signal of the first polarization rotation liquid crystal cell and the amount of measurement light received by the light receiving unit; and a liquid crystal cell drive unit which drives the first polarization rotation liquid crystal cell by a drive signal adjusted on the basis of the response characteristic determined by the measurement unit and drives the second polarization rotation liquid crystal cell by a drive signal adjusted on the basis of a response characteristic estimated from the response characteristic determined by the measurement unit.
A fifth aspect of the present invention, there is provided an image display apparatus which presents an image to an observer, comprising: an image modulation unit which produces modulated light modulated according to an image signal; a first polarization rotation liquid crystal cell which is capable of rotating a direction of polarization of the modulated light produced by the image modulation unit; a first birefringent plate which receives the modulated light from the first polarization rotation liquid crystal cell; a second polarization rotation liquid crystal cell which is capable of rotating a direction of polarization of the modulated light output from the first birefringent plate; a second birefringent plate which receives the modulated light from the second polarization rotation liquid crystal cell; a display optical unit which presents the modulated light from the second birefringent plate to the observer; a sensor unit configured to measure a response characteristic of the second polarization rotation liquid crystal cell, the sensor unit including a measurement light source which emits measurement light, a first polarization plate which has a first polarization direction and receives the measurement light from the measurement light source to output measurement light having the first polarization direction to the first polarization rotation liquid crystal cell, a second polarization plate which has a second polarization direction and receives measurement light passed through the second polarization rotation liquid crystal cell, a light receiving unit which receives measurement light passed through the second polarization plate, and a measurement unit which determines a response characteristic of the second polarization rotation liquid crystal cell on the basis of a drive signal of the second polarization rotation liquid crystal cell and the amount of measurement light received by the light receiving unit; and a liquid crystal cell drive unit which drives the second polarization rotation liquid crystal cell by a drive signal adjusted on the basis of the response characteristic determined by the measurement unit and drives the first polarization rotation liquid crystal cell by a drive signal adjusted on the basis of a response characteristic estimated from the response characteristic determined by the measurement unit.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.
The embodiments of the present invention will be described hereinafter with reference to the accompanying drawings.
The projector 10 is equipped with an illumination unit 100, a display unit 200, a pixel shift unit 300, and a display optical unit 400. Image light emerging from the projector 10 is projected onto a screen 500 to present an image to an observer. In addition, the projector 10 is equipped with a sensor unit 600 in association with the pixel shift unit 300.
The illumination unit 100 is equipped with a light source 110 for display, a color wheel 120, a PS conversion device 130, an integrator rod 140, and an illumination optical system 150.
The display light source 110 is composed of a discharge lamp light source, such as an extra-high pressure mercury lamp, a metal halide lamp, or a xenon lamp, which produces white light and an elliptic reflector for concentrating the light from the discharge lamp. As the display light source 110 use may be made of an LED or a halogen lamp besides the discharge lamp. Illumination light from the display light source 110 is applied to the color wheel 120. The color wheel 120 has color filters of R (red), G (green), and B (blue) arranged in the circumferential direction. By rotating the color wheel 120, R light, G light and B light are output on a time-division basis from the color wheel 120. The illumination light from the color wheel 120 is applied via the PD conversion device 130 to the integrator rod 140. Setting the PS conversion device 130 allows the illumination light to be oriented efficiently in a specific direction of polarization. Setting the integrator rod 140 allows unevenness of illumination to be reduced. The illumination light from the integrator rod 140 is applied via the illumination optical system 150 to the display unit 200.
The display unit (image modulation unit) 200 modulates the illumination light with an input video signal (input image signal) to produce modulated light. Specifically, R, G and B images are displayed on the display unit 200 in synchronization with emergence of R, G and B light from the color wheel 120. Thereby, R modulated light, G modulated light and B modulated light are output from the display unit 200 and then combined in the time-axis direction. The display unit (image modulation unit) 200 is comprised of a transmissive LCD. The direction of polarization of illumination light by the PS conversion device 130 of the illumination unit 100 and the axis of polarized light transmission of the transmissive LCD are made to align in the same direction.
The illumination light modulated by the display unit 200 is applied to the pixel shift unit (wobbling unit) 300. The pixel shift unit 300 is constructed from a polarization rotation liquid crystal cell 310 and a birefringent plate 320. Its basic structure is the same as that disclosed in JP-A No. 11-296135 (KOKAI) or JP-A No. 11-326877 (KOKAI). In addition, the sensor unit 600 is set so that the polarization rotation liquid crystal cell 310 is inserted into it. The pixel shift unit 300 and the sensor unit 600 will be described in detail later.
The illumination light passed through the pixel shift unit 300 is applied to the screen 500 through the projection optical system 410 of the display optical unit 400. A conjugate image of the display unit 200 is projected with enlargement onto the screen 500.
Reference is first made to
Reference is next made to
As can be seen from the foregoing, whether to perform the shift operation in the birefringent plate 320 or not can be controlled by switching the polarization rotation liquid crystal cell 310 on or off. Therefore, by switching the polarization rotation liquid crystal cell 310 on and off in time sequence synchronously with the timing of modulation of the display unit 200, the display state of
The sensor unit 600 is equipped with a light source 610 for measurement, polarizing plates 620 and 630, and a light receiving device 640. The measurement light from the measurement light source 610 falls on the light receiving device 640 through the polarizing plate 620, the polarization rotation liquid crystal cell 310, and the polarizing plate 630. The response characteristic of the polarization rotation liquid crystal cell 310 can be measured by the sensor unit 600.
The measurement light source 610 is comprised of an LED and has a condenser lens to prevent the diffusion of light of the LED. In measuring the response characteristic of the polarization rotation liquid crystal cell 310 by the sensor unit 600, the measurement light source 610 emits light at all times. The measurement light from the measurement light source 610 is polarized in one direction by the polarizing plate 620 and then applied to the polarization rotation liquid crystal cell 310. The polarizing plate 630 is set to face the polarizing plate 620 with the polarization rotation liquid crystal cell 310 interposed therebetween. The polarizing plates 620 and 630 are placed so that their polarized-light transmission axes are aligned in the same direction. The measurement light passed through the polarizing plate 630 is directed to a light receiving area 641 of the light receiving device 640 which is comprised of a photodiode. The light receiving device 640 outputs a photoelectric conversion signal corresponding to the amount of received measurement light.
Reference is first made to
Reference is next made to
During the interval when the polarization rotation liquid crystal cell 310 goes from the off voltage applied state to the on voltage applied state or vice versa, it assumes an intermediate state between the off voltage applied state and the on voltage applied state. Even during this transition interval, therefore, an amount of measurement light which corresponds to the state of the polarization rotation liquid crystal cell 310 will fall on the light receiving device 640.
Thus, the amount of light received by the light receiving device 640 varies according to the state of the polarization rotation liquid crystal cell 310 and a photoelectric conversion signal corresponding to the amount of received light is output from the light receiving device 640.
As can be seen from the foregoing, by setting the sensor unit 600 to measure the amount of light received by the light receiving device 640 through the polarization rotation liquid crystal cell 310, the response characteristic of the polarization rotation liquid crystal cell 310 can be measured directly. It is therefore possible to exactly obtain the response characteristic of the polarization rotation liquid crystal cell 310 even if it varies with temperature.
As shown in
Also, as shown in
It is desirable that the measurement light source 610 use a green (G) LED. The response speed of liquid crystals is wavelength dependent. It is intrinsically desirable to measure the response characteristic over the entire range of wavelengths of the measurement light; in practice, however, it is difficult to make measurements over the entire range of wavelengths. The use of green light which has a wavelength in the neighborhood of the center of visible light and to which human eyes are highly sensitive allows exact measurements to be made.
Such a sensor unit as shown in
It is desirable that the polarized-light transmission axis be coincident with that of image light (modulated light) supplied from the display unit 200 and with the rubbing direction of the alignment layer of the polarization rotation liquid crystal cell 310. Furthermore, although it is desirable that the polarized-light transmission axes of the polarizing plates 620 and 630 be aligned in the same direction as described above, they may be perpendicular to each other.
As shown in
A field detection circuit 710 receives a predetermined synchronizing signal (for example, a synchronizing signal contained in an image signal (video signal) applied to the display unit 200) to produce a field synchronizing signal. Delayed signal producing circuits 720a and 720b produce delayed signals on the basis of the field synchronizing signal produced by the field detection circuit 710. Specifically, the delayed signal producing circuit 720a produces a delayed signal for determining the timing of the rising edge of a drive signal of the polarization rotation liquid crystal cell 310. The delayed signal producing circuit 720b produces a delayed signal for determining the timing of the falling edge of the drive signal. A liquid crystal cell drive signal producing circuit 730 receives the delayed signals from the delayed signal producing circuits 720a and 720b to produce the drive signal of the polarization rotation liquid crystal cell 310.
As described previously, by repeating on-off control of the polarization rotation liquid crystal cell 310, the display state of
The measurement light source 610 is responsive to a signal from a light source drive circuit 740 to emit measurement light, which in turn is directed to the light receiving device 640 through the polarization rotation liquid crystal cell 310. The light receiving device 640 produces a light detect signal (photoelectric conversion signal) corresponding to the response characteristic (transmission characteristic) of the polarization rotation liquid crystal cell 310. This signal is then amplified by an amplification circuit 750.
The light detect signal amplified by the amplification circuit 750 and the liquid crystal cell drive signal from the liquid crystal cell drive signal producing circuit 730 are applied to a liquid crystal characteristic detection circuit 760, which determines a relationship (temporal relationship) between the liquid crystal cell drive signal and the light detect signal. That is, the liquid crystal characteristic detection circuit 760 functions as measuring means for determining the response characteristic of the polarization rotation liquid crystal cell 310 on the basis of the amount of measurement light received by the light receiving device 640 and the drive signal of the polarization rotation liquid crystal cell 310.
Information obtained by the liquid crystal characteristic detection circuit 760 is sent via a data processing circuit 770 to a control circuit 780, which produces such a control signal as optimizes the liquid crystal cell drive signal on the basis of the information from the liquid crystal characteristic detection circuit 760. The control signal from the control circuit 780 is sent to the delayed signal producing circuits 720a and 720b, which adjust the delay time of each of the delayed signals on the basis of the control signal. That is, the liquid crystal cell drive signal is adjusted on the basis of the response characteristic of the polarization rotation liquid crystal cell 310 obtained by the liquid crystal characteristic detection circuit 760 and the polarization rotation liquid crystal cell 310 is driven by the adjusted drive signal.
By performing such feedback control at all times, allows the liquid crystal cell drive signal can be adjusted in real time. Therefore, even if the response characteristic of the polarization rotation liquid crystal cell 310 varies with temperature, it can be driven at all times with the optimum drive signal.
During the on period of
The interval from the time when application of the on voltage to the polarization rotation liquid crystal cell 310 is started until the output voltage of the light receiving device 640 rises to 90% of the maximum value Vp is taken as the rise time Ton. Also, the interval from the time when application of the on voltage to the polarization rotation liquid crystal cell 310 is stopped (application of the off voltage is started) until the output voltage of the light receiving device 640 falls to 10% of the maximum value Vp is taken as the fall time Toff. Determining these rise and fall times Ton and Toff and using these values for the aforementioned feedback control allow a proper liquid crystal cell drive signal to be produced.
In the example shown in
It is desirable to set the interval during which the liquid crystal cell drive signal is to be adjusted to a blanking interval (e.g., the vertical blanking interval) of an image signal (video signal). By adjusting the liquid crystal cell drive signal during the vertical blanking interval by way of example, drive signals can be adjusted without changing drive signals corresponding to one frame (i.e., one frame of image).
According to this embodiment, as described above, the provision of the sensor unit 600 allows the response characteristic of the polarization rotation liquid crystal cell 310 to be obtained directly and exactly even if it varies with temperature. Therefore, by adjusting the drive signal of the polarization rotation liquid crystal cell 310 on the basis of the obtained response characteristic information, it can be driven at all times with the optimum drive signal, allowing the display quality of the image display apparatus to be improved.
Next, a second embodiment of the present invention will be described. This embodiment remains unchanged from the first embodiment in the basic configuration of each of the sensor unit and the image display apparatus. Thus, description of the matters described in the first embodiment is omitted here.
In the first embodiment, the direction of polarization (the direction of polarized-light transmission axis) has been assumed to be ideal. However, in practice it is difficult to set the direction of polarization ideal because there are various error factors. For example, error factors include sticking errors of a polarizing plate on the LCD display unit 200, errors in the crystal axis direction of the birefringent plate 320, assembly errors, and errors caused by the applied voltage dependence of the characteristic of the polarization rotation liquid crystal cell 310. In
However, in practice there are various error factors as described above. For this reason, modulated light incident on the birefringent plate 320 is output therefrom divided into light (available light) which arrives at a target pixel position (for example, the pixel position A in
In the case of
In the case of
When the direction of polarization is not set ideal due to various error factors, the light receiving characteristic of the light receiving device 640 in the sensor unit 600 will also be different from that when the direction of polarization is set ideal as will be described below.
When the applied voltage to the polarization rotation liquid crystal cell 310 is changed from 0 through Vm and V1 to Vu, the output voltage of the light receiving device 640 will change from V1v through V2v and V1p to V2p. That is, when the applied voltage to the polarization rotation liquid crystal cell 310 is Vm, the output voltage of the light receiving device 640 is V2v (minimum value). When the applied voltage to the polarization rotation liquid crystal cell 310 is Vu, the output voltage of the light receiving device 640 is V2p, at which the output voltage is virtually saturated. Thus, the output voltage V2p can be taken as the maximum output voltage of the light receiving device 640.
As described above, the output voltage of the light receiving device 640 is minimum when the applied voltage to the polarization rotation liquid crystal cell 310 is Vm but not 0. That is, when the applied voltage to the polarization rotation liquid crystal cell 310 is Vm, the direction of polarization is set best (for example, such states as shown in
The characteristic curve shown in
This embodiment is equipped with a drive voltage varying circuit 790, which is capable of varying the drive voltage to the liquid crystal cell drive signal producing circuit 730. Thus, by varying the drive voltage to the liquid crystal cell drive signal producing circuit 730, such a relationship (relationship between the applied voltage to the polarization rotation liquid crystal cell 310 and the output voltage of the light receiving device 640) as shown in
As described previously with reference to
In obtaining such a relationship as shown in
According to the second embodiment, as described above, the same advantages as with the first embodiment can be obtained and moreover the drive voltages of the polarization rotation liquid crystal cell 310 can be optimized, thus allowing the display quality of the image display apparatus to be improved.
A third embodiment of the present invention will be described next. This embodiment remains unchanged from the first embodiment in the basic configuration of each of the sensor unit and the image display apparatus. Thus, description of the matters described in the first embodiment is omitted here.
Although the first and second embodiments have been described in terms of image display made on a two-point pixel shift basis, this embodiment provides image display on a four-point pixel shift basis.
With this embodiment, to make image display on a four-point pixel shift basis, the pixel shift unit (wobbling unit) 300 is constructed from a first polarization rotation liquid crystal cell 311, a first birefringent plate 321, a second polarization rotation liquid crystal cell 312, and a second birefringent plate 322.
In addition, in this embodiment, a light-tight member 350 is placed between the display area through which projection light (image light) from the display unit 200 passes and the measurement area through which measurement light measured by the sensor unit 600 passes. The light-tight member 350 can isolate the image light and the measurement light from each other to prevent them from influencing each other. It is therefore possible to prevent the image display quality from degrading and improve the measurement accuracy. As the light-tight member 350 use may be made of, for example, a light-tight black sheet or a light intercepting element (for example, a flocking sheet).
The operation illustrated in
The operation illustrated in
The operation illustrated in
The operation illustrated in
As can be seen from the foregoing, switching each of the polarization rotation liquid crystal cells 311 and 312 on or off allows the position on the screen 500 at which the image light arrives to be controlled. Therefore, by switching each of the polarization rotation liquid crystal cells 311 and 312 on or off in synchronization with the modulation timing of the display unit 200, the display states shown in
It is required to place the birefringent plates 321 and 322 in the display area through which image light from the display unit 200 passes (corresponding to the available area of
First, the operation of
Next, the operation of
Next, the operation of
Next, the operation of
As can be seen from the foregoing, the output voltage of the light receiving device 640 is low (Lo) in the cases of
In the comparative example shown in
At the time when a shift is made from pixel position D to pixel position A, the operation of the sensor unit 600 goes from the state of
At the time when a shift is made from pixel position A to pixel position C, the operation of the sensor unit 600 goes from the state of
At the time when a shift is made from pixel position C to pixel position B, the operation of the sensor unit 600 goes from the state of
At the time when a shift is made from pixel position B to pixel position D, the operation of the sensor unit 600 goes from the state of
Thus, with four-point pixel shifts such that the pixel positions are ordered A, C, B, D, it is possible to determine the response characteristic of the first polarization rotation liquid crystal cell 311 when its applied voltage is shifted from the off voltage to the on voltage. However, it is difficult to determine the response characteristic of the first polarization rotation liquid crystal cell 311 when its applied voltage is shifted from the on voltage to the off voltage and the response characteristic of the second polarization rotation liquid crystal cell 312.
In this embodiment, therefore, driving is performed such that the transition timing of the drive signal of the first polarization rotation liquid crystal cell 311 and the transition timing of the drive signal of the second polarization rotation liquid crystal cell 312 are not coincident with each other. For example, as shown in
At the time when a shift is made from pixel position B to pixel position A, the operation of the sensor unit 600 changes from the state of
At the time when a shift is made from pixel position A to pixel position D, the operation of the sensor unit 600 changes from the state of
At the time when a shift is made from pixel position D to pixel position C, the operation of the sensor unit 600 changes from the state of
At the time when a shift is made from pixel position C to pixel position B, the operation of the sensor unit 600 changes from the state of
Thus, with four-point pixel shifts such that the pixel positions are ordered A, D, C, B, the response characteristic of each of the first and second polarization rotation liquid crystal cells can be determined when its applied voltage is shifted from the off voltage to the on voltage and vice versa.
According to this embodiment, as described above, the pixel shifting sequence is defined such that the transition timing of the drive signal of the first polarization rotation liquid crystal cell 311 and the transition timing of the drive signal of the second polarization rotation liquid crystal cell 312 are not coincident with each other. Thereby, the response characteristic of each of the first and second polarization rotation liquid crystal cells 311 and 312 can be obtained with certainty.
A fourth embodiment of the present invention will be described next. The basic configuration of each of the sensor unit and the image display apparatus is the same as that in the third embodiment. Thus, description of the matters described in the third embodiment is omitted here. In this embodiment as well, as with the third embodiment, image display is made on a four-point pixel shift basis.
In this embodiment, the first and second polarization rotation liquid crystal cells 311 and 312 are each configured so that each of the display area through which image light from the display unit 200 passes (corresponding to the available area in
In the example shown in
In this embodiment, in order to separately drive each of the display and measurement areas of the polarization rotation liquid crystal cells 311 and 312, a liquid crystal cell measuring drive signal producing circuit 810 is set to drive the measurement area of each of the polarization rotation liquid crystal cells 311 and 312.
As described above, in this embodiment, the polarization rotation liquid crystal cells 311 and 312 are configured so as to be able to drive each of the display area and the measurement area separately. Thus, by applying a drive signal which is different from one for the display area to the measurement area, the response characteristic of each of the polarization rotation liquid crystal cells 311 and 312 can be obtained with certainty. That is, even if the pixel positions (A, B, C, D) are not set in a specific order of display as in the third embodiment, the response characteristics of the polarization rotation liquid crystal cells 311 and 312 can be obtained with certainty.
A fifth embodiment of the present invention will be described next. The basic configuration of each of the sensor unit and the image display apparatus is the same as that in the third embodiment. Thus, description of the matters described in the third embodiment is omitted here. In this embodiment as well, as with the third embodiment, image display is made on a four-point pixel shift basis.
In this embodiment as well, as with the third embodiment, image display is made on a four-point pixel shift basis. Thus, the pixel shift unit (wobbling unit) 300 is composed of a polarization rotation liquid crystal cell 311, a birefringent plate 321, a polarization rotation liquid crystal cell 312a, and a birefringent plate 322. In this embodiment, however, although the polarization rotation liquid crystal cell 311 has display and measurement areas, the polarization rotation liquid crystal cell 312a has a display area but not a measurement area. That is, the response characteristic of the polarization rotation liquid crystal cell 311 is measured but no response characteristic of the polarization rotation liquid crystal cell 312a is measured. The response characteristic of the polarization rotation liquid crystal cell 312a is estimated from that of the polarization rotation liquid crystal cell 311.
This embodiment is provided with an estimation circuit 820 to estimate the response characteristic of the polarization rotation liquid crystal cell 312a from that of the polarization rotation liquid crystal cell 311. For example, a relationship between the characteristics of the polarization rotation liquid crystal cells 311 and 312a is determined in advance. The response characteristic of the polarization rotation liquid crystal cell 312a is estimated on the basis of that relationship from the response characteristic of the polarization rotation liquid crystal cell 311. Further, the response characteristic of the polarization rotation liquid crystal cell 312a may be estimated assuming it to be identical to that of the polarization rotation liquid crystal cell 311.
A description is given of an example of a method of estimating the response characteristic of the polarization rotation liquid crystal cell 312a from that of the polarization rotation liquid crystal cell 311. For example, assume that a beam of light passed through the polarization rotation liquid crystal cell 311 falls on the polarization rotation liquid crystal cell 312a while diffusing. In this case, the amount of light passed through the unit area of the polarization rotation liquid crystal cell 312a falls below that of the polarization rotation liquid crystal cell 311. As a result, there arises a difference in response characteristic between the polarization rotation liquid crystal cells 311 and 312a according to a difference in the amount of light. The estimation circuit 820 is prepared so as to correct such a difference in response characteristic. Thereby, the response characteristic of the polarization rotation liquid crystal cell 312a can be estimated properly from the response characteristic of the polarization rotation liquid crystal cell 311.
The example of
With this embodiment, as described above, the response characteristic of one polarization rotation liquid crystal cell is estimated from that of the other polarization rotation liquid crystal cell. Therefore, such problems as described in connection with the comparative example of the third embodiment can be avoided because it is only required to measure the response characteristic of one polarization rotation liquid crystal cell. For this reason, unlike the third embodiment, the response characteristics of the polarization rotation liquid crystal cells 311 and 312 can be obtained without setting the order of display of the pixel positions (A, B, C, D) in a specific one.
Although, in the third through fifth embodiments, two sets of a polarization rotation liquid crystal cell and a birefringent plate are used, use may be made of three or more sets of a polarization rotation liquid crystal cell and a birefringent plate.
According to the present invention, the provision of a sensor unit allows the response characteristic of a polarization rotation liquid crystal cell to be obtained directly and exactly even if it varies with temperature. Accordingly, by adjusting a drive signal of the polarization rotation liquid crystal cell on the basis of the obtained response characteristic, the polarization rotation liquid crystal cell can be driven at all times by the optimized drive signals. As a result, the display quality of the image display apparatus can be improved.
Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-334736 | Nov 2004 | JP | national |
| 2005-202000 | Jul 2005 | JP | national |
This is a Continuation Application of PCT Application No. PCT/JP2005/021163, filed Nov. 17, 2005, which was published under PCT Article 21(2) in Japanese. This application is based upon and claims the benefit of priority from prior Japanese Patent Applications No. 2004-334736, filed Nov. 18, 2004; and No. 2005-202000, filed Jul. 11, 2005, the entire contents of both of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP05/21163 | Nov 2005 | US |
| Child | 11804768 | May 2007 | US |
