GB2186989A - Light valve; polishing to improve contrast - Google Patents

Abstract

A method is described for improving the image contrast produced in a light valve including a matrix of pins of a metal embedded in a substrate of glass. The method involves polishing the surface of the matrix using an abrasive, such as aluminium oxide, having a hardness only slightly greater than that of the glass of the substrate. In use the matrix forms an interface between a liquid crystal and a vacuum tube producing an electron beam for addressing the liquid crystal.

Description

SPECIFICATION Light valve The present invention relates two a light valve for use in an image projection system and in particular is concerned with an improvement of the light valve described in PatentApplication No. 8325352.

The lig htvalve described in the above application includes a matrix of conductive pins embedded in an insulating glass substrate. This matrix is intended for use in a liquid crystal cell to constitute the vacuumtight interface between the liquid crystal and an electron beam for writing an image onto the cell. The conductive pins are very fine and serve to conduct the charge point by pointfrom one side of the matrix to the other without causing any charge spreading.

The above application also describes how such a matrix may be formed by forcing a molten metal into the holes of a glass filter. However, when used to produce an image, the lightvalve (which included this matrix) was found to give low image contrast and the present invention seeks to mitigate this problem.

According to the present invention, there is provided a method of improving the image contrast produced using a light valve including a matrix of pins of a metal embedded in a substrate of glass which method comprises polishing the surface ofthe matrix using an abrasive having a hardness only slightly greaterthan that of the glass of the substrate.

One reason for the low image contrast produced in the prior art is believed to have been an inadequate surface finish on the matrix. When light is reflected from the end surface ofthe conductive pins ittends to be scattered instead of being reflected, giving rise to a degradation in image contrast.

It is a difficult exercise to attempt to polish the ends of soft metal pins when they are surrounded byvery much harder glass. The polishing forces tend to cause separation of the glass and metal and the debris on the surface leaves deep grooves in the surface of the soft metal pins. For these and other reasons the matrix of the prior art which was polished by means of hard abrasives such as diamond was found to have low image contrast.

In the present invention, instead of using a hard abrasive which can abrade the glass with ease, it is proposed to use a relatively soft abrasive such as aluminium oxidewhich is only slightly harderthat the glass of the substrate. It has been found that using aluminium oxide with a particle size of approximately one micron, it is possible to polish the surface of the pins to leave a bright and smooth finish resulting in improved image contrast.

The polishing can be carried out in stages, gradually decreasing the particle size of the abrasive with each stage to improve the surface finish.

As with all polishing, it is importantto ensure that the surface remains properly lubricated during polishing to prevent overheating and dragging at the polishing surface.

The invention will now be described further by re ferenceto a specific example.

The manufacture ofthe matrixfora lightvalveis already described in the above patent specification and need not therefore be described in detail within the context of the present specification. It suffices to realise that at the end of the manufacturing step in which the molten metal is forced into the holes the glass filter material is left with an excess of metal adhering to its surface which mustfirst be removed.

This is effected by machining the end face ofthe filter until the glass is reached. The machining on a lathe leaves fine concentric grooves which are removed by polishing.

The polishing is carried out by resting the matrix on a polishing pad which is rotated or otherwise moved while the matrix is kept stationary. The polishing pad is lubricated by use of a suitable lubricant such as water to which small quantities of a soluble oil may be added. The abrasive powder placed on the polishing pad is aluminium oxide.

After coarse polishing steps using abrasives with large particle size, the matrix is transferred to a second polishing pad where an aluminium oxide powderwith a particle size of approximately one micron is used as the abrasive. Polishing should proceed until the ends ofthe pins are both smooth and bright. This can be ascertained by visual inspection.

1. A method of improving the image contrast produced using a light valve including a matrix of pins of a metal embedded in a substrate of glass which method comprises polishing the surface ofthe matrix using an abrasive having a hardness only slightly greater than that of the glass ofthe substrate.

2. A method as claimed in claim 1 ,wherein the abrasive employed is powdered aluminium oxide.

3. A method as claimed in claim 2, wherein the particle size of the abrasive powder employed in the last polishing step is approximately one micron.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Light valve The present invention relates two a light valve for use in an image projection system and in particular is concerned with an improvement of the light valve described in PatentApplication No. 8325352. The lig htvalve described in the above application includes a matrix of conductive pins embedded in an insulating glass substrate. This matrix is intended for use in a liquid crystal cell to constitute the vacuumtight interface between the liquid crystal and an electron beam for writing an image onto the cell. The conductive pins are very fine and serve to conduct the charge point by pointfrom one side of the matrix to the other without causing any charge spreading. The above application also describes how such a matrix may be formed by forcing a molten metal into the holes of a glass filter. However, when used to produce an image, the lightvalve (which included this matrix) was found to give low image contrast and the present invention seeks to mitigate this problem. According to the present invention, there is provided a method of improving the image contrast produced using a light valve including a matrix of pins of a metal embedded in a substrate of glass which method comprises polishing the surface ofthe matrix using an abrasive having a hardness only slightly greaterthan that of the glass of the substrate. One reason for the low image contrast produced in the prior art is believed to have been an inadequate surface finish on the matrix. When light is reflected from the end surface ofthe conductive pins ittends to be scattered instead of being reflected, giving rise to a degradation in image contrast. It is a difficult exercise to attempt to polish the ends of soft metal pins when they are surrounded byvery much harder glass. The polishing forces tend to cause separation of the glass and metal and the debris on the surface leaves deep grooves in the surface of the soft metal pins. For these and other reasons the matrix of the prior art which was polished by means of hard abrasives such as diamond was found to have low image contrast. In the present invention, instead of using a hard abrasive which can abrade the glass with ease, it is proposed to use a relatively soft abrasive such as aluminium oxidewhich is only slightly harderthat the glass of the substrate. It has been found that using aluminium oxide with a particle size of approximately one micron, it is possible to polish the surface of the pins to leave a bright and smooth finish resulting in improved image contrast. The polishing can be carried out in stages, gradually decreasing the particle size of the abrasive with each stage to improve the surface finish. As with all polishing, it is importantto ensure that the surface remains properly lubricated during polishing to prevent overheating and dragging at the polishing surface. The invention will now be described further by re ferenceto a specific example. The manufacture ofthe matrixfora lightvalveis already described in the above patent specification and need not therefore be described in detail within the context of the present specification. It suffices to realise that at the end of the manufacturing step in which the molten metal is forced into the holes the glass filter material is left with an excess of metal adhering to its surface which mustfirst be removed. This is effected by machining the end face ofthe filter until the glass is reached. The machining on a lathe leaves fine concentric grooves which are removed by polishing. The polishing is carried out by resting the matrix on a polishing pad which is rotated or otherwise moved while the matrix is kept stationary. The polishing pad is lubricated by use of a suitable lubricant such as water to which small quantities of a soluble oil may be added. The abrasive powder placed on the polishing pad is aluminium oxide. After coarse polishing steps using abrasives with large particle size, the matrix is transferred to a second polishing pad where an aluminium oxide powderwith a particle size of approximately one micron is used as the abrasive. Polishing should proceed until the ends ofthe pins are both smooth and bright. This can be ascertained by visual inspection. CLAIMS

1. A method of improving the image contrast produced using a light valve including a matrix of pins of a metal embedded in a substrate of glass which method comprises polishing the surface ofthe matrix using an abrasive having a hardness only slightly greater than that of the glass ofthe substrate.

2. A method as claimed in claim 1 ,wherein the abrasive employed is powdered aluminium oxide.

3. A method as claimed in claim 2, wherein the particle size of the abrasive powder employed in the last polishing step is approximately one micron.