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Patent Issued for Optical Device and Projection Device Using the Optical Device Which Reduce Registration Shift Caused by Heat

September 10, 2014



By a News Reporter-Staff News Editor at Journal of Engineering -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventors Iwane, Tetsuaki (Kanagawa, JP); Aikoh, Yoshihisa (Aichi, JP); Yamamoto, Hideki (Kanagawa, JP); Homma, Keisuke (Kanagawa, JP), filed on May 17, 2011, was published online on August 26, 2014.

The patent's assignee for patent number 8814365 is Sony Corporation (JP).

News editors obtained the following quote from the background information supplied by the inventors: "The present invention relates to an optical device and a projecting device using the same.

"A front projector (projection device) which is one image display device often use a discharging lamp as a light source and a transmissive liquid crystal device or DMD (Digital Micromirror Device) as an image modulation element, and thus can be combined with devices and optical systems through various improvements. In addition, in recent years, projection type image display devices using reflective liquid crystal panels (reflective optical modulation elements) having higher resolution have been also put into practical use.

"In the market of front projectors, brightness of displayed images is an important factor for gaining superiority. The improvement in the brightness of projected images is a current trend, but is not easily realized since a difficult problem such as the need for a heat measure in the front projector device exists.

"For example, the increase in a temperature of the inside of the front projector device increases temperatures of constituent components. It is known that the linear expansion of the constituent component of which the temperature increases causes several defects. One of the defects is a registration shift. The registration shift is a phenomenon in which three image light beams of RGB do not overlap with each other at a correct position on a screen but are misaligned, and thus projected images look blurred.

"In the front projector using the reflective liquid crystal panels, three images overlap with each other on the screen using a projection lens by allowing the image light beams obtained by three reflective liquid crystal panels to pass through a reflective polarizer or a color synthesis prism which synthesizes the image light beams. The positions of the reflective liquid crystal panels are regulated such that three images overlap with each other on the screen and are fixed using an adhesive or the like. However, the linear expansion in the constituent elements after being fixed shifts the position of each reflective liquid crystal panel and causes the registration shift.

"Therefore, a projector has been proposed in which two fixing plates are joined to upper and lower edges of a light incidence surface of a color synthesis prism roughly parallel to each other, and the color synthesis prism, a reflective polarization element, and reflective liquid crystal panels are installed (for example, refer to Japanese Patent No. 4285462). According to the proposal, since the plate-shaped polarization element is fixed to the light incidence surface of the color synthesis prism via the fixing plate having a relative low linear expansion coefficient, it is possible to prevent the registration shift with a simple structure in the front projector.

"In addition, there has been proposed a reflective projection display device which includes reflective liquid crystal panels, a wave plate provided in a reflective polarizer, a wave plate holder which holds the wave plate and has a first aperture, and a transmission window (a second aperture) which is provided between the wave plate holder and the reflective polarizer and is smaller than the first aperture (for example, refer to JP-A-2007-108735). According to the proposal, since unnecessary light does not reach the wave plate holder due to the second aperture smaller than the first aperture of the wave plate holder, a temperature of the wave plate does not increase, and for this reason, it is possible to prevent shading from being generated in images on the screen due to birefringence occurring in the wave plate."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "However, as the causes of the registration shift, there are at least a thermal stress applied to the reflective polarization element and a thermal stress due to heat reception of an assembly forming the reflective liquid crystal devices. The registration shift caused by the former is improved by fixing the plate-shaped polarization element via the fixing plate having a relatively low linear expansion coefficient, but the registration shift caused by the latter has not been sufficiently improved yet.

"For example, a UV (ultraviolet) cured adhesive resin holding the reflective liquid crystal device itself receives heat via a light blocking plate (a panel side light blocking plate) which blocks light from reaching areas other than active areas of the reflective liquid crystal device, and generates the linear expansion. The linear expansion in the UV cured adhesive resin causes the reflection surface of the reflective liquid crystal device to be changed in three-axis directions of XYZ and to be shifted from a designed central position. The respective reflective liquid crystal devices of R, G and B are displaced differently from each other, and thereby the registration shift occurs.

"In addition, peripheral components of each of the reflective liquid crystal devices receive heat via the light blocking plate which blocks light from reaching the areas other than the active area of the reflective liquid crystal device, and each of the peripheral components generates the linear expansion. The thermal stress due to the linear expansion in the peripheral components also slightly shifts the incidence surfaces of the reflective liquid crystal devices from the designed central position in the three-axis directions of XYZ, and thus causes the registration shift.

"The solution is as follows. The periphery of the reflective light modulation device assembly is held by a solid component, and a material for the peripheral component is selected so as not to increase a temperature of the UV cured adhesive resin. Further, the structure thereof is designed so as to suppress the linear expansion due to heat from the peripheral component, and thus a variation amount in the reflective liquid crystal device is reduced.

"However, the more solid structure directly increases costs since the sizes of components or the number of components increase and materials are limited. In addition, when materials for preventing the linear expansion are selected, high heat dissipation is necessary, and the assembly strength is also necessary. Thus, it is not easy to select compatible components having different performances. An example of materials having the high heat dissipation includes aluminum, which does not have sufficient assembly strength.

"There has been proposed a method in which the increase in a temperature of the wave plate is suppressed so as not expose the wave plate holder to unnecessary light, but since a reflective polarization element is fixed as a solid part, it cannot be expected that registration shift will be improved.

"Thus, it is desirable to provide an optical device and a projection device capable of reducing the registration shift caused by heat reception of assembly forming reflective liquid crystal devices.

"According to an embodiment of the present invention, there is provided an optical device including a light synthesis prism, a light modulation unit, and a fixing member. The light synthesis prism synthesizes incident light beams which are incident to a plurality of incidence surfaces and outputs the synthesized light beams. The light modulation unit has an optical compensation element and a reflective light modulation device. The fixing member fixes a reflective polarization element and the light modulation unit to the light synthesis prism so as to correspond to one of the incidence surfaces. In addition, the light modulation unit includes a light blocking member and a heat insulating member. The light blocking member blocks light from reaching the light modulation unit and limits light with which the optical compensation element and the reflective light modulation device are irradiated, to light passing an aperture portion. The heat insulating member comes into contact with the light blocking member and the fixing member.

"According to another embodiment of the present invention, there is provided a projection device including a light source, an optical device, and a projection means. The optical device separates light beams emitted from the light source according to wavelength bands for modulation and synthesizes and emits the modulated light beams. The projection unit projects and outputs the light beams emitted from the optical device.

"In addition, the optical device includes a light synthesis prism, a light modulation unit, and a fixing member. The light synthesis prism synthesizes incident light beams which are incident to a plurality of incidence surfaces and outputs the synthesized light beams. The light modulation unit has an optical compensation element and a reflective light modulation device. The fixing member fixes a reflective polarization element and the light modulation unit to the light synthesis prism so as to correspond to one of the incidence surfaces. In addition, the light modulation unit includes a light blocking member and a heat insulating member. The light blocking member blocks light from reaching the light modulation unit and limits light with which the optical compensation element and the reflective light modulation device are irradiated, to light passing an aperture portion. The heat insulating member comes into contact with the light blocking member and the fixing member.

"According to the optical device and the projection device of the embodiments of the invention, it is possible to reduce the registration shift caused by heat reception of an assembly constituting reflective liquid crystal devices."

For additional information on this patent, see: Iwane, Tetsuaki; Aikoh, Yoshihisa; Yamamoto, Hideki; Homma, Keisuke. Optical Device and Projection Device Using the Optical Device Which Reduce Registration Shift Caused by Heat. U.S. Patent Number 8814365, filed May 17, 2011, and published online on August 26, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8814365.PN.&OS=PN/8814365RS=PN/8814365

Keywords for this news article include: Sony Corporation.

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Source: Journal of Engineering


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