Mechanical system for adjusting image centering and rotation in projection television apparatus

#Many systems use electronic adjustment of image centering and rotation. This invention relates to projection television apparatus, and is particularly advantageous with liquid crystal display (LCD) projection systems. With LCD projectors, electronic adjustment of centering and rotation adversely impacts picture performance. For electronic centering, there must be extra pixels outside of the image area to accommodate image shift. Therefore, some of the pixels are unused and resolution is reduced. For electronic rotation of the image, there is a similar result of wasted pixels, as well as a digital “stair-stepping” effect that occurs when a horizontal or vertical line is rotated and mapped to a rectangular pixel array.

#The projectors used in projection television apparatus must be properly adjusted in order to provide maximum picture accuracy. This invention allows a projector to be finely positioned such that the projected image is corrected to provide aiming and rotational accuracy.

#This invention provides an adjuster for positioning an element in a projection television apparatus. The adjuster comprises a bracket that mounts the element. First, second and third eccentric cams, positioned in substantially the same plane, mate with first, second and third slots in the bracket. The first cam has the ability to move the bracket in an X direction. The second cam has the ability to move the bracket in a Y direction perpendicular to said X direction, and the third cam has the ability to rotate the bracket in a plane defined by the X and Y directions.

#In the drawing:

#FIGS. 1a and 1b show the cam arrangement of the invention in two different positions.

#FIG. 2 is a cross section view of the inventive cam mechanism.

#Referring to FIGS. 1a and 1b, the invention provides a slotted bracket 1 that mounts the projector, and an eccentric cam arrangement that allows the bracket to be positioned accurately over a limited range. By using three cams 3, 5, and 7, in three slots 9, 11 and 13, X and Y motion, as well as rotation, can be achieved.

#FIG. 1a shows the cams in their nominal positions. Rotation of cam 5 produces horizontal motion of bracket 1 in an X direction. Rotation of cams 3 and 7 in the same direction produces vertical motion of bracket 1 in a Y direction. Differential rotation of cams 3 and 7 causes bracket 1 to rotate, as shown in FIG. 1b. Note that in FIG. 1b, cam 5 has been rotated by a small amount, which also translates bracket 1 in a horizontal direction.

#A feature of the invention comprises a cam serving double duty as both a hold-down function and an adjustment function. Referring to FIG. 2, mating part 15, which is rigidly coupled to a housing for the television apparatus, is held to bracket 1 by the cam arrangement. Only one of the three cams is shown in FIG. 2. However, the structure of the other cams is similar. Cam 5 has a flange 17 which holds bracket 1 to mating part 15. Screw 19 threads into mating part 15, through shoulder bushing 21, wavy washer spring 23 and cam 5. Because the thickness of cam 5 is matched to the thickness of bracket 1, flange 17 holds bracket 1 in frictional engagement with mating part 15, the amount of friction being determined by the pressure exerted by wavy washer spring 23.