Liquid crystal display and driving method of liquid crystal display

A liquid crystal display includes: a transmissive liquid crystal display device having a display region made up of pixels arrayed in a matrix fashion. The liquid crystal display device includes a planar light source unit formed of planar light source units corresponding to respective display region units on an assumption that the display region is divided into the display region units and configured in such a manner that each planar light source unit irradiates a corresponding display region unit with light, and a drive circuit driving the liquid crystal display device and the planar light source device. The liquid crystal display device is scanned line-sequentially and the pixels making up each display region unit are scanned line-sequentially. A planar light source unit corresponding to a display region unit is held in a luminous state over a predetermined period since a line-sequential scan on the display region unit has been completed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display and a driving method of a liquid crystal display.

2. Description of the Related Art

In a liquid crystal display device, a liquid crystal material does not emit light by itself. Accordingly, for example, a planar light source device (backlight) that irradiates a display region of the liquid crystal display device with light is disposed behind the display region made up of a plurality of pixels. In a color liquid crystal display device, one pixel is formed of three types of sub-pixels including, for example, a red light emitting sub-pixel, a green light emitting sub-pixel, and a blue light emitting sub-pixel. An image is displayed by controlling a liquid crystal cell forming each pixel or each sub-pixel to operate as one type of light shutter (light valve), that is, by controlling light transmittance (numerical aperture) of each pixel or each sub-pixel and thereby controlling light transmittance of illumination light (for example, white light) emitted from the planar light source device.

In the past, a planar light source device employed in a liquid crystal display illuminates the entire display region uniformly at constant brightness. This configuration, however, causes deterioration of a moving picture display quality resulting from edge blurring. To overcome this inconvenience, there has been proposed a planar light source device formed of a plurality of planar light source units and controlled in such a manner that the respective planar light source units light on sequentially in synchronization with the completion of scans on portions of the liquid crystal display device corresponding to the respective planar light source units. For example, JP-A-2000-321551 describes a liquid crystal display provided with such a planar light source device. According to this liquid crystal display, blurring of a moving picture in an active matrix liquid crystal display device can be lessened. The moving picture display performance can be thus improved.

SUMMARY OF THE INVENTION

When a period to display the screen in black (black display period) is inserted between video display periods, a frame image and the following frame image are completely isolated in terms of time. Such isolation further enhances the moving image display characteristic. However, for example, given that the frame rate is 60 Hz in the absence of a black display period, then, in order to insert a black display period, it becomes necessary to drive the liquid crystal display in such a manner that a total of 120 video display periods and black display periods are present in one second. Further, for example, in order to set the video display periods and the black display periods to be of substantially the same length, in the case of a liquid crystal display provided with a planar light source device (hereinafter, referred to as the synchronous-type planar light source device for ease of description) controlled in such a manner that the respective light source units light on sequentially in synchronization with the completion of scans in portions of the liquid crystal display device corresponding to the respective planar light source units, it becomes necessary to scan the liquid crystal display device in about half the frame period of 1/60 (second). In addition, in a case where the liquid crystal display is used to alternately display right-eye images and left-eye images for a 3D image display, the actual frame period is shortened to half, that is, 1/120 (second). It therefore becomes necessary to drive the liquid crystal display in such a manner that a total of 240 video display periods and black display periods are present in one second. The liquid crystal display provided with the synchronous-type planar light source device has to shorten a scan period of the liquid crystal display device in order to insert a black display period. This raises a problem that a timing margin in a scan is reduced.

Thus, it is desirable to provide a liquid crystal display and a driving method of a liquid crystal display capable of lowering a degree of reduction of a timing margin in a scan on the liquid crystal display device caused by insertion of a black display period.

According to an embodiment of the present invention, there is provided a liquid crystal display including a transmissive liquid crystal display device having a display region made up of pixels arrayed in a matrix fashion, a planar light source device formed of a plurality of planar light source units corresponding to respective display region units on an assumption that the display region is divided into a plurality of the display region units and configured in such a manner that each planar light source unit irradiates a corresponding display region unit with light, and a drive circuit driving the liquid crystal display device and the planar light source device.

The liquid crystal display device is scanned line-sequentially and hence the pixels making up each display region unit are scanned line-sequentially. A planar light source unit corresponding to a display region unit is held in a luminous state over a predetermined period since a line-sequential scan on the display region unit has been completed. A luminous period of a planar light source unit corresponding to a display region unit on which the line-sequential scan is completed last in a given frame period and a luminous period of a planar light source unit corresponding to a display region unit on which the line-sequential scan is completed first in a frame period following the given frame period are set so as not to overlap each other. A wait time since the line-sequential scan on a display region unit has been completed until a planar light source unit corresponding to the display region unit changes to a luminous state is set in such a manner that a wait time in a display region unit on which the line-sequential scan is completed first and a wait time in a display region unit on which the line-sequential scan is completed last in one frame period become longest and shortest, respectively. Wait times in display region units positioned between the display region unit on which the line-sequential scan is completed first and the display region unit on which the line-sequential scan is completed last in the one frame are set so as to decrease in descending order in which the scan is completed.

According to another embodiment of the present invention, there is provided a driving method of a liquid crystal display including the steps of performing, with the use of the liquid crystal display described above, processing to scan the liquid crystal display device line-sequentially and hence to scan the pixels making up each display region unit line-sequentially, and performing processing to hold a planar light source unit corresponding to a display region unit in a luminous state over a predetermined period since a line-sequential scan on the display region unit has been completed.

A luminous period of a planar light source unit corresponding to a display region unit on which the line-sequential scan is completed last in a given frame period and a luminous period of a planar light source unit corresponding to a display region unit on which the line-sequential scan is completed first in a frame period following the given frame period are set so as not to overlap each other. A wait time since the line-sequential scan on a display region unit has been completed until a planar light source unit corresponding to the display region unit changes to a luminous state is set in such a manner that a wait time in a display region unit on which the line-sequential scan is completed first and a wait time in a display region unit on which the line-sequential scan is completed last in one frame period become longest and shortest, respectively. Wait times in display region units positioned between the display region unit on which the line-sequential scan is completed first and the display region unit on which the line-sequential scan is completed last in the one frame are set so as to decrease in descending order in which the scan is completed.

With the liquid crystal display and the driving method of a liquid crystal display according to the embodiments of the present invention, a wait time since the line-sequential scan on a display region unit has been completed until a planar light source unit corresponding to this display region unit changes to a luminous state is set in such a manner that a wait time in a display region unit on which the line-sequential scan is completed first becomes the longest and a wait time in a display region unit on which the line-sequential scan is completed last becomes the shortest. Also, wait times in display region units positioned between the display region unit on which the line-sequential scan is completed first and the display region unit on which the line-sequential scan is completed last are set so as to decrease in descending order in which the scan is completed. Accordingly, the scan period of the liquid crystal display device can be set longer than in a liquid crystal display provided with a synchronous-type planar light source device and by a driving method using this liquid crystal display.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a liquid crystal display and a driving method of a liquid crystal display according to embodiments of the invention will be described with reference to the drawings in the following order.

1. Detailed description of the present invention

2. Brief description of liquid crystal display employed in embodiment of the present invention

3. Embodiment of the present invention

DETAILED DESCRIPTION OF THE PRESENT INVENTION

For a liquid crystal display and a driving method of a liquid crystal display according to embodiments of the present invention, it can be configured in such a manner that a period between the beginning of a luminous period of a planar light source unit corresponding to a display region unit on which a line-sequential scan has been completed first in a given frame period and the end of a luminous period of a planar light source unit corresponding to a display region unit on which a line-sequential scan has been completed last in this frame period forms a video display period. Also, it can be configured in such a manner that a period between the end of a luminous period of a planar light source unit corresponding to a display region unit on which a line-sequential scan has been completed last in a given frame period and the beginning of a luminous period of a planar light source unit corresponding to a display area unit on which a line-sequential scan has been completed first in a frame period following this frame period forms a black display period.

Basically, virtual display region units of the liquid crystal display device are units divided so that each is made up of pixels in a predetermined number of rows and aligned in the scan direction. In a case where the liquid crystal display device has M0×N0pixels arrayed in a 2D matrix fashion and pixels in the first through N0'th rows are scanned sequentially, the minimum value and the maximum value of the virtual display region units are 2 and N0, respectively. The number of virtual display region units is basically determined according to the design of the planar light source units. The number of rows of pixels in the display region units can be either constant or different.

A light source for the planar light source units forming the planar light source device can be, for example, a light emitting diode (LED) or it can also be an electroluminescent (EL) device, a cold cathode field emission display (FED), a plasma display, and so forth. The light source may be a cold-cathode ray fluorescent lamp or a normal lamp as long as no trouble occurs in the control on a luminous state and non-luminous state. In a case where the light source is formed of a light emitting diode, white light can be obtained by forming the light source from a set of a red light emitting diode emitting red light having, for example, a wavelength of 640 nm, a green light emitting diode emitting green light having, for example, a wavelength of 530 nm, and a blue light emitting diode emitting blue light having, for example, a wavelength of 450 nm. Alternatively, white light can be obtained by light emission from a white light emitting diode (for example, alight emitting diode that emits white light by combining an ultraviolet or blue light emitting diode and phosphor particles). Further, light emitting diodes emitting light in a fourth color, a fifth color, and so on besides red, green, and blue light may be provided.

In a case where the light source is formed of light emitting diodes, a plurality of red light emitting diodes emitting red light, a plurality of green light emitting diodes emitting green light, and a plurality of blue light emitting diodes emitting blue light are disposed and arrayed in the planar light source units. To be more concrete, the light source can be formed of light emitting diode units including a combination of one red light emitting diode, one green light emitting diode, and one blue light emitting diode, a combination of one red light emitting diode, two green light emitting diodes, and one blue light emitting diode, a combination of two red light emitting diodes, two green light emitting diodes, and one blue light emitting diode, and so forth.

A light emitting diode can have a so-called face-up structure or a flip-chip structure. In other words, a light emitting diode is formed of a substrate and a luminous layer formed on the substrate. The light emitting diode may have either a structure in which light exits from the luminous layer to the outside or a structure in which light from the luminous layer exits to the outside by passing through the substrate. To be more concrete, the light emitting diode (LED) has a laminated structure including, for example, a first clad layer formed of a compound semiconductor layer having a first conductivity type (for example, n type) formed on the substrate, an active layer formed on the first clad layer, and a second clad layer formed of a compound semiconductor layer having a second conductivity type (for example, p type) formed on the active layer. The light emitting diode also includes a first electrode electrically connected to the first clad layer and a second electrode electrically connected to the second clad layer. Layers forming the light emitting diode are dependent on emission wavelengths and can be made of known compound semiconductor materials. In order to increase a light extraction efficiency from the light emitting diode, it is preferable to attach a semispherical resin material of a constant size to a light exiting portion of the light emitting diode. In a case where it is desired to emit light in a particular direction, for example, a 2D direction light-exiting structure by which light chiefly exits in a horizontal direction may be provided.

The planar light source device may be configured to further include a light diffusion plate and an optical functional sheet group including a diffusion sheet, a prism sheet, and a polarization conversion sheet as well as a reflection sheet. The optical functional sheet group may be formed of various types of sheets that are spaced apart from one another or laminated and formed into one integral body. Examples of a material of the light diffusion plate include polymethylmethacrylate (PMMA) and polycarbonate resin (PC). The light diffusion plate and the optical functional sheet group are disposed between the planar light source device and the liquid crystal display device.

A transmissive liquid crystal display device is formed, for example, of a front panel provided with a transparent first electrode, a rear panel provided with a transparent second electrode, and a liquid crystal material filled in a space between the front panel and the rear panel. The liquid crystal display device can be either a monochrome liquid crystal display device or a color liquid crystal display device.

To be more concrete, the front panel includes a first substrate formed of a glass substrate or a silicon substrate, a transparent first electrode (referred to also as a common electrode and made, for example, of ITO) provided on the outer surface of the first substrate, and a polarization film provided on the outer surface of the first substrate. In a transmissive color liquid crystal display device, a color filter coated with an overcoat layer made of acrylic resin or epoxy resin is further provided on the inner surface of the first substrate. Examples of the layout pattern of the color filter include a delta arrangement, a stripe arrangement, a diagonal arrangement, and a rectangle arrangement. The front panel is configured in such a manner that the transparent first electrode is formed on the overcoat layer. It should be noted that an oriented film is formed on the transparent first electrode. Meanwhile, to be more concrete, the rear panel includes, for example, a second substrate formed of a glass substrate or a silicon substrate, switching elements formed on the inner surface of the second substrate, transparent second electrodes (referred to also as the pixel electrodes and made, for example, of ITO) controlled to be conductive and nonconductive by the corresponding switching elements, and a polarization film provided on the outer surface of the second substrate. An oriented film is formed on the entire surface including the transparent second electrodes. Various members and the liquid crystal material forming the liquid crystal display device including a transmissive color liquid crystal display device can be known members and materials. Examples of the switching elements include but not limited to a 3-terminal element, such as an MOSFET and a thin film transistor (TFT) formed on a single-crystal silicon semiconductor substrate, and a 2-terminal element, such as an MIM element, a varistor element, and a diode.

An overlapping region of the transparent first electrode and each transparent second electrode including a liquid crystal cell corresponds to a pixel or a sub-pixel. In a transmissive color liquid crystal display device, one pixel includes a red light emitting sub-pixel (hereinafter, occasionally referred to as the sub-pixel [R]) that is formed of a combination of the region specified above and a color filter transmitting red, a green light emitting sub-pixel (hereinafter, occasionally referred to as the sub-pixel [G]) that is formed of a combination of the region specified above and a color filter transmitting green, and a blue light emitting sub-pixel (hereinafter, occasionally referred to as the sub-pixel [B]) that is formed of a combination of the region specified above and a color filter transmitting blue. A layout pattern of the sub-pixel [R], the sub-pixel [G], and the sub-pixel [B] coincides with the layout pattern of the color filter described above. It should be appreciated that a pixel is not necessarily formed of a set of three types of sub-pixels [R, G, B] including the sub-pixel [R], the sub-pixel [G], and the sub-pixel [B]. For example, a pixel may be formed of a set including these three types of sub-pixels [R, G, B] and an addition sub-pixel of one or more than one type (for example, a set including an additional sub-pixel emitting white light in order to enhance the luminance, a set including an additional sub-pixel emitting light of a complimentary color in order to broaden the color reproduction range, a set including an additional sub-pixel emitting yellow light in order to broaden the color reproduction range, or a set including additional sub-pixels emitting yellow and cyan light in order to broaden the color reproduction range).

Herein, let (M0, N0) be the number of pixels, M0×N0, arrayed in a 2D matrix fashion, then the value of (M0, N0) can be some types of resolution for image display, and more concretely, VGA(640, 480), S-VGA(800, 600), XGA(1024, 768), APRC(1152, 900), S-XGA(1280, 1024), U-XGA(1600, 1200), HD-TV(1920, 1080), and Q-XGA(2048, 1536) as well as (1920, 1035), (720, 480), and (1280, 960). The number of pixels, however, is not limited to the values specified above.

A drive circuit driving the liquid crystal display device and the planar light source device includes, for example, a planar light source unit drive circuit formed of a known circuit, such as a constant current circuit, a planar light source device control circuit formed of a known circuit, such as a logic circuit, and a liquid crystal display device drive circuit formed of a known circuit, such as a timing controller.

A time over which image information necessary to form one image is sent in the form of an electric signal is a frame period (unit: seconds) and the inverse of the frame period is a frame frequency (frame rate). It should be noted that a frame period contains a wait time since the image information necessary to form one image has been sent in the form of an electric signal until an electric signal to display the following image is sent.

Brief Description of Liquid Crystal Display Employed in Embodiment of the Present Invention

Hereinafter, a liquid crystal display and a driving method of a liquid crystal display according to embodiments of the present invention will be described with reference to the drawings. Prior to the description, a transmissive liquid crystal display device (to be more concrete, a transmissive color liquid crystal display device) and a planar light source device suitably employed in an embodiment of the present invention will be described briefly with reference toFIG. 1,FIG. 2A,FIG. 2B,FIG. 3, andFIG. 4.

As is shown in the conceptual view ofFIG. 1, a liquid crystal display includes:

(A) a transmissive color liquid crystal display device10having a display region11made up of pixels arrayed in a matrix fashion;

(B) a planar light source device40formed of a plurality of planar light source units41corresponding to respective display region units12on the assumption that the display region11is divided into a plurality of the display region units12and configured in such a manner that each planar light source unit41irradiates a corresponding display region unit12with light; and

(C) a drive circuit driving the liquid crystal display device10and the planar light source device40.

As is shown in the conceptual view ofFIG. 1, the transmissive color liquid display device10includes the display region11in which a total of M0×N0pixels are arrayed in a 2D matrix fashion, M0pixels along a first direction and N0pixels along a second direction. Herein, assume that the display region11is divided into a plurality (for example, P) virtual display region units12. For example, when the number of pixels, M0×N0, arrayed in a 2D matrix fashion and satisfying the VGA standards as resolution for image display is expressed as (M0, N0), then the number of pixels is expressed as (640, 480). Also, the display region11made up pixels arrayed in a 2D matrix fashion (a region encircled by an alternate long and short dashed line inFIG. 1) is divided into a plurality (for example, P) of virtual display region units12(boundaries are indicated by a dotted line). From a design viewpoint, P can take a value from 2 to N0. In an example shown inFIG. 1, P takes a value of 4. Each display region unit12is made up of a plurality of pixels. Each pixel is formed of a set of a plurality of sub-pixels each emitting light in a different color. To be more concrete, each pixel is formed of three types of sub-pixels including a red light emitting sub-pixel (sub-pixel [R]), a green light emitting sub-pixel (sub-pixel [G]), and a blue light emitting sub-pixel (sub-pixel [B]). The transmissive color liquid crystal display device10is driven line-sequentially. To be more concrete, the color liquid crystal display device10has scan electrodes (extending along the first direction) and data electrodes (extending along the second direction) intersecting in a matrix fashion. One screen is formed by inputting a scan signal into the scan electrodes to choose and scan the scan electrodes so that an image is displayed according to a control signal (basically, a signal based on an input signal) inputted into the data electrodes.

The liquid crystal display device10is scanned line-sequentially and hence the pixels forming each display region unit12are scanned line-sequentially. In the following description, assume that a scan is performed sequentially toward the second direction. As will be described below, the planar light source unit41corresponding to a display region unit12is held in a luminous state over a predetermined time since the line-sequential scan on this display region unit12has been completed. A driving method of the liquid crystal display according to an embodiment of the present invention includes the steps of performing processing to scan the liquid crystal display device10line-sequentially and hence to scan the pixels forming each display region unit12line-sequentially and performing processing to hold a planar light source unit41corresponding to a display region unit12in a luminous state over a predetermined period since the line-sequential scan on this display region unit12has been completed.

As is shown in a schematic partial cross section ofFIG. 4, the color liquid crystal display device10is formed of a front panel20provided with a transparent first electrode24, a rear panel30provided with transparent second electrodes34, and a liquid crystal material13filled in a space between the front panel20and the rear panel30.

The front panel20includes, for example, a first substrate21formed of a glass substrate, and a polarization film26provided on the outer surface of the first substrate21. A color filter22coated with an overcoat layer23made of acrylic resin or epoxy resin is provided on the inner surface of the first substrate21. The transparent first electrode (referred to also as the common electrode and made, for example, of ITO)24is formed on the overcoat layer23. An oriented film25is formed on the transparent first electrode24. Meanwhile, to be more concrete, the rear panel30includes, for example, a second substrate31formed of a glass substrate, switching elements (to be more concrete, thin film transistors (TFTs))32formed on the inner surface of the second substrate31, transparent second electrodes (referred to also as the pixel electrodes and made, for example, of ITO)34controlled to be conductive and non-conductive by the corresponding switching elements32, and a polarization film36provided on the outer surface of the second substrate31. An oriented film is provided across the entire surface including the transparent second electrodes34. The front panel20and the rear panel30are jointed to each other at the respective outer peripheral portions via a sealing member (not shown). It should be appreciated that the switching elements32are not limited to TFTs and, for example, they may be formed of MIM elements. Reference numeral37in the drawing denotes an insulation layer provided between one switching element32and another switching element32.

Various members and the liquid crystal material forming the transmissive color liquid crystal display device can be known members and materials. Accordingly, detailed descriptions are omitted herein.

A direct planar light source device (backlight)40includes a plurality (P) of planar light source units41corresponding to a plurality of respective virtual display region units12. Each planar light source unit41illuminates the display region unit12corresponding to the planar light source unit41from behind. Light sources provided to the planar light source unit41are controlled individually. Although the planar light source device40is positioned under the color liquid crystal display device10, the color liquid crystal display device10and the planar light source device40are shown separately inFIG. 1. The layout and the arrangement of partition walls and light emitting diodes in the planar light source device40are schematically shown in a plan view ofFIG. 2A. A schematic end view of the liquid crystal display according to the embodiment of the present invention is shown inFIG. 2B.FIG. 2Bshows major members. In the drawing, however, the hatching on a housing51, the color liquid crystal display device10, a light diffusion plate61, and so forth is omitted and a part of a diffusion plate20is notched. Further, a schematic partial cross section of the liquid crystal display formed of the color liquid crystal display device10and the planar light source device40is shown inFIG. 3. For ease of illustration, partition walls43are omitted inFIG. 3. Light sources are formed of light emitting diodes42(42R,42G, and42B) driven, for example, by the pulse width modulation (PWM) control method.

As is shown in a schematic partial cross section of the liquid crystal display ofFIG. 3, the planar light source device40is formed of the housing51provided with an outer frame53and an inner frame54. The end portion of the transmissive color liquid crystal display device10is held by being sandwiched between the outer frame53and the inner frame54via spacers55A and55B. A guide member56is disposed between the outer frame53and the inner frame54. It is therefore structured in such a manner that the color liquid crystal display device10sandwiched between the outer frame53and the inner frame54will not undergo displacement. The light diffusion plate61is attached to the inner frame54via a spacer55C and a bracket member57at the top inside the housing51. An optical functional sheet group including a diffusion sheet62, a prism sheet63, and a polarization conversion sheet64is laminated on the light diffusion plate61.

A reflection sheet65is provided at the bottom inside the housing51. Herein, the reflection sheet65is disposed so that the reflection surface opposes the light diffusion plate61and it is attached to the bottom surface52A of the housing51via an unillustrated attachment member. The reflection sheet65is formed, for example, of a silver sensitizing reflection film having a structure in which a silver reflection film, a low refractive film, and a high refractive film are sequentially laminated on a sheet base material. The reflection sheet65reflects light emitted from a plurality of light emitting diodes42(light sources42) and light reflected on the side surface52B of the housing51or the partition walls43shown inFIG. 2AandFIG. 2B. When configured in this manner, red light, green light, and blue light emitted, respectively, from a plurality of red light emitting diodes42R (light sources42R) emitting red light, a plurality of green light emitting diodes42G (light sources42G) emitting green light, a plurality of blue light emitting diode42B (light sources42B) emitting blue light are mixed. It thus becomes possible to obtain white light with high chromatic purity as illumination light. This illumination light passes through the light diffusion plate61and the optical functional sheet group including the diffusion sheet62, the prism sheet63, and the polarization conversion sheet64and illuminates the color liquid display device10from behind.

Regarding the arrangement of the light emitting diodes42R,42G, and42B, for example, it may be configured in such a manner that a light emitting diode unit is formed of a set of a red light emitting diode42R emitting red light (for example, wavelength of 640 nm), a green light emitting diode42G emitting green light (for example, wavelength of 530 nm), and a blue light emitting diode42B emitting blue light (for example, wavelength of 450 nm) and a plurality of light emitting diode units are arrayed in a horizontal direction and a vertical direction. In an example shown inFIG. 2AandFIG. 2B, four light emitting diode units are disposed in one planar light source unit41.

One planar light source unit41and another planar light source unit41forming the planar light source device40are partitioned by the partition wall43. In an example shown inFIG. 2AandFIG. 2B, the planar light source units41are surrounded by the side surfaces of the housing51and the partition walls43. To be more concrete, there are planar light source units41each of which is surrounded by two partition walls43and two side surfaces52B of the housing51and planar light source units41each of which is surrounded by one partition wall43and three side surfaces52B of the housing51. The partition walls43are attached to the bottom surface52A of the housing51via unillustrated attachment members.

As is shown inFIG. 1, a drive circuit that drives the planar light source device40and the color liquid crystal display device10according to an input signal and a clock signal from the outside (display circuit) includes a planar light source device control circuit70and planar light source unit drive circuits80that control emission and non-emission of light from the red light emitting diodes42R, the green light emitting diodes42G, and the blue light emitting diodes42B forming the planar light source device40as well as a liquid crystal display device drive circuit90. The planar light source device control circuit70is formed of a logic circuit and a shift register circuit. Meanwhile, each planar light source unit drive circuit80is formed, for example, of a light emitting diode drive power supply (constant current source). Known circuits or the like are available as circuits forming the planar light source device control circuit70and the planar light source unit drive circuits80.

The liquid crystal display device drive circuit90driving the color liquid crystal display device10is formed of known circuits, such as a timing controller91, a scan circuit92, and a source driver (not shown). The timing controller91generates a first clock signal CLK1on the basis of a clock signal CLK from the outside (display circuit) and supplies the scan circuit92with the first clock signal clock CLK1. The scan circuit92scans the scan electrodes SCL according to the first clock signal CLK1and drives the switching elements32formed of TFTs constituting the liquid crystal cells. The source driver applies a signal at a voltage corresponding to values of control signals [R, G, B] described below to unillustrated data electrodes.

The planar light source device control circuit70generates a second clock signal CLK2on the basis of the clock signal CLK from the outside (display circuit) and the first clock signal CLK1from the timing controller91. The sequentially shifted second clock signal CLK2is applied to respective control lines BCL. In the following description, assume that each planar light source unit41changes to a luminous state when the corresponding control line BCL is at a high level and each planar light source unit41changes to a non-luminous state when the corresponding control line BCL is at a low level.

The display region11made up of pixels arrayed in a 2D matrix fashion is divided into P display region units12. By describing this state using rows and columns, it can be said that the display region11is divided into display region units arrayed in P rows and one column.

Each display region unit12is made up of a plurality (M0×N) of pixels. By describing this state using rows and columns, it can be said that each display region unit12is formed of pixels arrayed in N rows and M0columns. In a case where the display region11is divided equally, it is basically expressed as N=N0/P. In a case where there is a surplus, the surplus is included in any display region unit12.

A red light emitting sub-pixel (sub-pixel [R]), a green light emitting sub-pixel (sub-pixel [G]), and a blue light emitting sub-pixel (sub-pixel [B]) are collectively referred to as the sub-pixels [R, G, B] in some cases. Also, a control signal for a red light emitting sub-pixel, a control signal for a green light emitting sub-pixel, and a control signal for a blue light emitting sub-pixel inputted into the sub-pixels [R, G, B] in order to control operations of the sub-pixels [R, G, B] (to be more concreted, to control the light transmittances (numerical apertures)) are collectively referred to as the controls signals [R, G, B] in some cases. Further, an input signal for a red light emitting sub-pixel, an input signal for a green light emitting sub-pixel, and an input signal for a blue light emitting sub-pixel inputted into the drive circuit from the outside in order to drive the sub-pixels [R, G, B] forming the display region units are collectively referred to as the input signals [R, G, B] in some cases.

As has been described, each pixel is formed as a set of three types of sub-pixels including a red light emitting sub-pixel (sub-pixel [R]), a green light emitting sub-pixel (sub-pixel [G]), and a blue light emitting sub-pixel (sub-pixel [B]). For example, the luminance of each of the sub-pixels [R, G, B] is controlled (gradation control) by an 8-bit numerical value and luminance has 28steps from 0 to 255. Each of values xR, xG, and xBof the input signals [R, G, B] inputted into the liquid crystal display device drive circuit90to drive the sub-pixels [R, G, B] in the respective pixels forming each display region unit12takes a value in 28steps. It should be appreciated that an embodiment of the present invention is not limited to this configuration. For example, the control may be performed using 10-bit numerical value in 210steps from 0 to 1023.

A control signal controlling the light transmittance of each pixel is supplied to the pixel from the drive circuit. To be more concrete, control signals [R, G, B] controlling light transmittances of the respective sub-pixels [R, G, B] are supplied to the respective sub-pixels [R, G, B] from the liquid crystal display device drive circuit90. In other words, the liquid crystal display device drive circuit90generates the control signals [R, G, B] from the input signals [R, G, B] inputted therein and the control signals [R, G, B] are supplied (outputted) to the sub-pixels [R, G, B], respectively. For example, in a case where a so-called gamma correction is applied to the values of the input signals, the control signals [R, G, B] are basically supplied to the color liquid crystal display device10by a known method as signals at voltages corresponding to the values of the input signals [R, G, B], xR, xG, and xB, raised to the 2.2th power. The switching elements32forming the respective sub-pixels are driven according to a scan signal applied to the scan electrodes SCL and the light transmittance (numerical aperture) of each sub-pixel is controlled by applying a desired voltage to the transparent first electrode24and the transparent second electrode34forming the liquid crystal cell according to the control signals [R, G, B]. Herein, the light transmittances (numerical apertures) of the sub-pixels [R, G, B] become larger as the values of the control signals [R, G, B] become larger.

Embodiment of the Present Invention

In order to clearly define the correspondence, descriptions will be given hereinafter on the assumption that N0=20 is given for M0×N0representing the number of pixels, the number of each of the display region units12and the planar light source units41is four, and each display region unit12has five rows of pixels. For example, as is shown inFIG. 8toFIG. 8Ddescribed below, four display region units12are indicated by reference numerals121,122,123, and124and the planar light source units41corresponding to the respective display region units12are indicated by reference numerals411,412,413, and414.

The scan electrodes SCL corresponding to 20 rows of pixels are indicted by alpha-numerals SCL1through SCL20in descending order of line-sequential scan. Then, the scan electrodes of five rows of pixels corresponding to the display region unit121are the scan electrode SCL1through the scan electrode SCL5. The scan electrodes of five rows of pixels corresponding to the display region unit122are the scan electrode SCL6through the scan electrode SCL10. The scan electrodes of five rows of pixels corresponding to the display region unit123are the scan electrode SCL11through the scan electrode SCL15. The scan electrodes of five rows of pixels corresponding to the display region unit124are the scan electrode SCL16through the scan electrode SCL20. The control lines BCL corresponding to the planar light source units411,412,413, and414are indicated by alpha-numerals BCL1, BCL2, BCL3, and BCL4, respectively.

In each frame period, the line-sequential scan on the display region unit121is completed first, the line-sequential scan on the display region unit122is completed next followed by the display region unit123and the display region unit124. In other words, the display region unit12on which the line-sequential scan is completed first in a given frame period is the display region unit121. Also, the display region unit12on which the line-sequential scan is completed last in a given frame period is the display region unit124.

A timing chart to drive the liquid crystal display according to a reference example is schematically shown inFIG. 5. Also, a timing chart to drive the liquid crystal display according to an embodiment of the present invention is schematically shown inFIG. 6.

Although it will be described in detail below, in an operation according to the reference example, a period from the beginning of a period T6to the end of a period T25shown inFIG. 5forms a video display period (seeFIG. 7A) and a period from the beginning of a period T26to the end of a period T5′ included in the following frame period shown inFIG. 5forms a black display period (seeFIG. 7B). By contrast, in an operation according to an embodiment of the present invention, a period from the beginning of a period T6to the end of a period T25shown inFIG. 6forms a black display period (seeFIG. 7C) and a period from the beginning of a period T26to the end of a period T5′ included in the following frame period shown inFIG. 6forms a video display period (seeFIG. 7D).

For ease of understanding of the present invention, an operation of the liquid crystal display according to the reference example will be described first. Herein, descriptions of the configuration of the liquid crystal display according to the reference example are omitted because it is substantially the same as the configuration of the liquid crystal display described above with reference toFIG. 1except for operation timing.

A period T1through a period T40shown inFIG. 5are respective horizontal scan periods in an operation according to the reference example. In an operation according to the reference example, let t0be the length of each horizontal scan period. For ease of description, assume that in operations according to both the reference example and an embodiment of the present invention described below, the length of the second clock signal CLK2is 5t0and the length of a period over which the control lines BCL stay at a high level is also 5t0.

In an operation according to the reference example, the respective planar light source units41are controlled to sequentially light on in synchronization with the completion of the scan in a portion of the liquid crystal display device10corresponding to the planar light source units41(to be more concrete, a portion of the display region11). To be more concrete, according to the reference example, the planar light source units41are controlled to start light emission at the same time when the line sequential scan on the corresponding display region units12is completed and to hold light emission for a predetermined period. In other words, a wait time since the line-sequential scan on a given display region unit12has been completed until the planar light source unit41corresponding to this display region unit12changes to a luminous state is 0 (nil).

Hereinafter, an operation according to the reference example will be described with reference toFIG. 5,FIG. 8AthroughFIG. 8D,FIG. 9AthroughFIG. 9D, andFIG. 10AthroughFIG. 10C.

A new frame period starts from the beginning of the period T1. As is shown inFIG. 5, the control line BCL1through the control line BCL4stay at a low level during these periods. As is shown inFIG. 8A, all the planar light source units411,412,413, and414are in a non-luminous state.

In the period T1through the period T5, the display region unit121is scanned line-sequentially. In other words, the scan electrode SCL1changes to a high level in the period T1and the light transmittances of the respective sub-pixels in the first row are controlled according to the control signals [R, G, B]. In the period T2through the period T5, too, the scan electrode SCL2through the scan electrode SCL5are scanned sequentially and the light transmittances of the respective sub-pixels in the second row through the fifth row are controlled in the same manner as above. InFIG. 8AthroughFIG. 8D, the line-sequentially scanned region is indicated as a newly scanned region. The same can be said in other drawings.

The display region units122,123, and124hold a state of having been scanned in the preceding frame period. InFIG. 8AthroughFIG. 8D, regions holding a state of having been scanned in the preceding frame period are indicated as previously scanned regions. The same can be said in other drawings.

As has been described, the display region unit121is scanned line-sequentially in the period T1through the period T5. All the planar light source units411,412,413, and414, however, remain in a non-luminous state. The liquid crystal display is therefore in a black display state.

In the period T6through the period T10, the display region unit122is scanned line-sequentially. Also, a new video display period starts from the beginning of the period T6. The scan electrode SCL6through the scan electrode SCL10are scanned sequentially and the light transmittances of the respective sub-pixels in the fifth row through the tenth row are controlled in the same manner as above.

Meanwhile, the control line BCL1changes from a low level to a high level at the beginning of the period T6and this state is maintained until the period T10. The control line BCL2through the control line BCL4stay at a low level. The planar light source unit411thus changes to a luminous state whereas the other planar light source units412,413, and414remain in a non-luminous state. Accordingly, a video corresponding to the light transmittances of the respective sub-pixels in the display region unit121is displayed.

In the period T11through the period T15, the display region unit123is scanned line-sequentially. The scan electrode SCL11through the scan electrode SCL15are scanned sequentially and the light transmittances of the respective sub-pixels in the eleventh row through the fifteenth row are controlled in the same manner as above.

The control line BCL1changes from a high level to a low level at the beginning of the period T10. The planar light source unit411thus changes to a non-luminous state. Meanwhile, the control line BCL2changes from a low level to a high level at the beginning of the period T10. The planar light source unit412thus changes to a luminous state. The control lines BCL3and BCL4stay at a low level. The planar light source units413and414therefore remain in a non-luminous state. Accordingly, a video corresponding to the light transmittances of the respective sub-pixels in the display region unit122is displayed.

In the period T16through the period T20, the display region unit124is scanned line-sequentially. The scan electrode SCL16through the scan electrode SCL20are scanned sequentially and the light transmittances of the respective sub-pixels in the sixteenth row through the twentieth row are controlled in the same manner as above.

The control line BCL2changes from a high level to a low level at the beginning of the period T16. The planar light source unit412thus changes to a non-luminous state. Meanwhile, the control line BCL3changes from a low level to a high level at the beginning of the period T16. The planar light source unit413thus changes to a luminous state. The control lines BCL1and BCL4stay at a low level. The planar light source units411and414therefore remain in a non-luminous state. Accordingly, a video corresponding to the light transmittances of the respective sub-pixels in the display region unit123is displayed.

In the period T21through the period T40described below, the scan electrode SCL1through the scan electrode SCL20are not scanned. The display region units121,122,123, and124therefore hold a previous state.

The control line BCL3changes from a high level to a low level at the beginning of the period T21. The planar light source unit413thus changes to a non-luminous state. Meanwhile, the control line BCL4changes from a low level to a high level at the beginning of the period T21. The planar light source unit414thus changes to a luminous state. The control lines BCL1and BCL2stay at a low level. The planar light source units411and412therefore remain in a non-luminous state. Accordingly, a video corresponding to the light transmittances of the respective sub-pixels in the display region unit124is displayed. The end of the period T25corresponds to the end of a video display period.

The control line BCL4changes from a high level to a low level at the beginning of the period T26. The planar light source unit414thus changes to a non-luminous state. The control lines BCL1, BCL2, and BCL3stay at a low level. The planar light source units411,412, and413therefore remain in a non-luminous state.

Hence, all the planar light source units411,412,413, and414are in a non-luminous state. The liquid crystal display thus changes to a black display state. The beginning of the period T26corresponds to the beginning of the black display period.

A next frame period starts from the beginning of the period T1′. As with the description of the period T1through the period T5above, the display region unit121is scanned line-sequentially and the light transmittances of the respective sub-pixels in the first row through the fifth row are controlled in the same manner as above. The display region units122,123, and124hold a state of having been scanned in the preceding frame period. The control line BCL1through the control line BCL4stay at a low level. All the planar light source units411,412,413, and414therefore remain in a non-luminous state. The liquid crystal display thus maintains a black display state. The end of the period T5′ corresponds to the end of the black display period.

In the period T6′ following the period T5′, as with the descriptions of the period T6above, the planar light source unit411changes to a luminous state and a video display period corresponding to the next frame period starts.

An operation according to the reference example has been described. As is obvious fromFIG. 5, in an operation according to the reference example, it is necessary to scan all the scan electrodes SCL in the period T1through the period T20, which is half the period T1through the period T40forming one field period. By contrast, in an operation according to an embodiment of the present invention, as will be described below, all the period T1through the period T40can be allocated to periods in which to scan all the scan electrodes SCL.

An operation according to an embodiment of the present invention will now be described. In an embodiment of the present invention, the length of the horizontal scan period is twice (2t0) the length of the horizontal scan period according to the reference example. It should be appreciated, however, that one field period inFIG. 6is also formed of the period T1through the period T40as inFIG. 5for ease of comparison with the reference example. In an embodiment of the present invention, two periods, such as the period T1and the period T2, together form one horizontal scan period.

In an embodiment of the present embodiment, a wait time since the line-sequential scan on a given display region unit12has been completed until the planar light source unit41corresponding to this display region unit12changes to a luminous state is set in such a manner that the wait time becomes the longest in the display region unit121on which the line-sequential scan is completed first in one frame period and the wait time becomes the shortest in the display region unit124on which the line-sequential scan is completed last in one frame period.

In other words, as is shown inFIG. 6, the wait time in the display region unit121on which the line-sequential scan is completed first is a time (15t0) from the beginning of the period T11to the end of the period T25. Meanwhile, the wait time in the display region unit124on which the line-sequential scan is completed last is a time from the beginning of the period T40to the end of the period T1′, that is, 0 (nil) as with the reference example.

Also, the wait times in the display region units122and123positioned between the display region unit121on which the line-sequential scan is completed first and the display region unit124on which the line-sequential scan is completed last in one frame period are set so as to decrease in descending order in which the scan is completed.

In other words, as is shown inFIG. 6, the wait time in the display region unit122is a time (10t0) from the beginning of the period T20to the end of the period T30. The wait time in the display region unit123is a time (5t0) from the beginning of the period T31to the end of the period T35.

It is set in such a manner that the luminous period of the planar light source unit414corresponding to the display region unit124on which the line-sequential scan is completed last in a given frame period and the luminous period of the planar light source unit411corresponding to the display region unit121on which the line-sequential scan is completed first in the frame period following the given frame period will not overlap each other.

As is shown inFIG. 6, the luminous period of the planar light source unit414corresponding to the display region unit124on which the line-sequential scan is completed last in the frame period starting from the period T1is from the period T1′ to the period T5′. Also, the luminous period of the planar light source unit411corresponding to the display region unit121on which the line-sequential scan is completed first in the following frame period starting from the period T1′ is from the period T26′ to the period T30′. In this manner, the former period and the latter period are set so as not to overlap each other.

Operation timing of the respective planar light source units41according to an embodiment of the present invention is the same as the operation timing of the planar light source units41according to the reference example described above except that the beginning is delayed by half the field period.

A period between the beginning of the luminous period of the planar light source unit411corresponding to the display region unit121on which the line-sequential scan has been completed first in a given frame period and the end of the luminous period of the planar light source unit414corresponding to the display region unit124on which the line-sequential scan has been completed last in this frame period forms the video display period. Also, a period between the end of the luminous period of the planar light source unit414corresponding to the display region unit124on which the line-sequential scan has been completed last in a give frame period and the beginning of the luminous period of the planar light source unit411corresponding to the display region unit121on which the line-sequential scan has been completed first in the frame period following the given frame period forms the black display period.

Hereinafter, an operation according to an embodiment of the present invention will be described with reference toFIG. 6,FIG. 11AthroughFIG. 11D,FIG. 12AthroughFIG. 12D, andFIG. 13AthroughFIG. 13C.

A new frame period starts from the beginning of the period T1. As is shown inFIG. 6, the control lines BCL1, BCL2, and BCL3stay at a low level and the control line BCL4stays at a high level during these periods. Hence, as is shown inFIG. 11A, the planar light source units411,412, and413are in a non-luminous state whereas the planar light source unit414is in a luminous state.

In the period T1through the period T5, a part of the display region unit121is scanned line-sequentially. In other words, in the period T1and the period T2, the scan electrode SCL2changes to a high level and the light transmittances of the respective sub-pixels in the first row are controlled according to the control signals [R, G, B]. In the period T3and the period T4, too, the scan electrode SCL2is scanned and the light transmittances of the respective sub-pixels in the second row are controlled in the same manner as above. In the period T5and in the period T6described below, the scan electrode SCL3is scanned and the light transmittances of the respective sub-pixels in the third row are controlled in the same manner as above.

A portion of the display region unit121that has not been scanned line-sequentially and the display region units122,123, and124hold a state of having been scanned in the preceding frame period.

As has been described, in the period T1through the period T5, a part of the display region unit121is scanned line-sequentially but the planar light source units411,412,413are in a non-luminous state whereas the planar light source unit414is in a luminous state. Accordingly, a video according to the light transmittances of the respective sub-pixels in the display region unit124is displayed. The end of the period T5corresponds to the end of the preceding video display period.

In the period T6through the period T25, the remaining portion of the display region unit121, the display region unit122, and a part of the display region unit123are scanned line-sequentially. Also, a new black display period starts from the beginning of the period T6.

The scan electrode SCL3is scanned in the period T5described above and in the period T6. The scan electrode SCL4is scanned in the period T7and the period T8. Thereafter, the scan electrodes SCL5through SCL13are scanned sequentially. It should be noted that the scan electrode SCL13is scanned in the period T25and in the period T26described below. The light transmittances of the respective sub-pixels in the fourth row through the thirteenth row are controlled in the same manner as above.

Meanwhile, the control line BCL4changes from a high level to a low level at the beginning of the period T6. The planar light source unit414thus changes to a non-luminous state. The control lines BCL2through BCL4stay at a low level. The planar light source units411,412, and413therefore remain in a non-luminous state. The liquid crystal display thus changes to a black display state. The beginning of the period T6corresponds to the beginning of the black display period and the end of the period T26corresponds to the end of the black display period.

In the period T26through the period T30, the remaining portion of the display region unit123is scanned line-sequentially. Also, a new video display period starts from the beginning of the period T26. The scan electrode SCL13is scanned in the period T25described above and in the period T26. The scan electrode SCL14is scanned in the period T27and the period T28and the scan electrode SCL15is scanned in the period T29and the period T30. The light transmittances of the respective sub-pixels in the fourteenth row and the fifteenth row are controlled in the same manner as above.

The control line BCL1changes from a low level to a high level at the beginning of the period T26. The planar light source unit411thus changes to a luminous state. Meanwhile, the control lines BCL2, BCL3, and BCL4stay at a low level. The planar light source units412,413, and414therefore remain in a non-luminous state. Accordingly, a video according to the light transmittances of the respective sub-pixels in the display region unit121is displayed.

In the period T31through the period T35, a part of the display region unit124is scanned line-sequentially. The scan electrode SCL16is scanned in the period T31and the period T32. The scan electrode SCL17is scanned in the period T33and the period T34and the scan electrode SCL18is scanned in the period T35and in the period T36described below. The light transmittances of the respective sub-pixels in the sixteenth row through the eighteenth row are controlled in the same manner as above.

The control line BCL2changes from a low level to a high level at the beginning of the period T31. The planar light source unit412thus changes to a luminous state. Meanwhile, the control line BCL1changes from a high level to a low level at the beginning of the period T31. The planar light source unit411thus changes to a non-luminous state. The control lines BCL3and BCL4stay at a low level. The planar light source units413and414therefore remain in a non-luminous state. Accordingly, a video corresponding to the light transmittances of the respective sub-pixels in the display region unit122is displayed.

In the period T36through the period T40, the remaining portion of the display region unit124is scanned line-sequentially. The scan electrode SCL18is scanned in the period T35described above and in the period T36. The scan electrode SCL19is scanned in the period T37and the period T38. The scan electrode SCL20is scanned in the period T39and the period T40. The light transmittances of the respective sub-pixels in the nineteenth row and the twentieth row are controlled in the same manner.

The control line BCL2changes from a high level to a low level at the beginning of the period T36. The planar light source unit412thus changes to a non-luminous state. Meanwhile, the control line BCL3changes from a low level to a high level at the beginning of the period T36. The planar light source unit413thus changes to a luminous state. The control lines BCL1and BCL4stay at a low level. The planar light source units411and414therefore remain in a non-luminous state. Accordingly, a video according to the light transmittances of the respective sub-pixels in the display region unit123is displayed.

The following frame period starts at the beginning of the period T1′. As with the description of the period T1through the period T5above, a part of the display region unit121is scanned line-sequentially and the light transmittances of the respective sub-pixels in the first row through the third row are controlled in the same manner as above. The remaining portion of the display region unit121and the display region units122,123, and124hold a state of having been scanned in the immediately preceding frame period.

The control line BCL3changes from a high level to a low level at the beginning of the period T1′. The planar light source unit413thus changes to a non-luminous state. Meanwhile, the control line BCL4changes from a low level to a high level at the begging of the period T1′. The planar light source unit414thus changes to a luminous state. The control lines BCL1and BCL2stay at a low level. The planar light source units411and412therefore remain in a non-luminous state. Accordingly, a video corresponding to the light transmittances of the respective sub-pixels in the display region unit124is displayed. The end of the period T5′ corresponds to the end of the video display period.

The operation according to the embodiment of the present invention has been described. As is shown inFIG. 7AtoFIG. 7D, both the video display periods and the black display periods account for half the frame period in each of the reference example and the embodiment of the present invention. Hence, the liquid crystal display exhibits the same moving picture characteristic in operations according to the reference example and the embodiment of the present invention.

According to the reference example, only half the frame period is allocated to the scan on the liquid crystal display device. On the contrary, according to the embodiment of the present invention, the entire frame period can be allocated to the scan on the liquid crystal display device. In other words, there is an advantage that a timing margin in the scan is not reduced because the scan period of the liquid crystal display device does not become shorter even when a black display period is inserted. Also, with the driving method according to the reference example, the scan frequency becomes higher as the scan period becomes shorter, which consequently causes an increase of power consumption in association with the scan on the liquid crystal display device. The embodiment of the present invention, however, also has an advantage that power consumption is not particularly increased in association with the scan on the liquid crystal display device.

In a case where right-eye images and left-eye images for a 3D image display are displayed alternately in the operation according to the embodiment of the present invention, for example, a right-eye image is displayed in the period T6through the period T25shown inFIG. 6and a left-eye image is displayed in the period T6′ through the period T25′. In this case, the right-eye image and the left-eye image are completely isolated in terms of time by the black display period in the period T26through the period T5′. Hence, when viewed via eye glasses that close the field of view of the left eye of the observer during a display period of a right-eye image and close the field of view of the right eye of the observer during a display period of a left-eye image, it becomes possible to obtain a satisfactory 3D image display.

In the operation ofFIG. 6, it is set in such a manner that the luminous periods of the planar light source unit411and the planar light source unit412, those of the luminous periods of the planar light source unit412and the planar light source unit413, and those the luminous periods of the planar light source unit413and the planar light source unit414do not over lap each other. It should be appreciated, however, that an embodiment of the present invention is not limited to this configuration. As is shown inFIG. 14, it may be configured in such a manner that the luminous period in a stage and the luminous period in the following stage may overlap partially.

While the embodiments of the present invention have been described, it should be appreciated that the present invention is not limited to the embodiments described above. The configurations and the structures of the transmissive color liquid crystal display device, the planar light source device, the planar light source units, the liquid crystal display, and the drive circuit described above are mere examples. In addition, members and materials forming the foregoing components are described by way of example and the driving process of the liquid crystal display is also described by way of example. It is therefore possible to change the members, the materials, and the driving process so as to suit the circumstances.

The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2009-017946 filed in the Japan Patent Office on Jan. 29, 2009, the entire contents of which is hereby incorporated by reference.