Abstract:
A focusing arrangement has a lens disposed adjacent a lamp, a sensor for detecting a parameter which varies with a focal position of light focused by the lens, and a controller for adjusting the position of the lens based upon an output from the sensor in a manner which modifies the focal position of the light by the lens and maximizes the parameter detected by the sensor.

Description:
BACKGROUND  
       [0001]     When a projector such as that used in front or rear projection displays and the like, ages, the efficiency of light from the lamp that is coupled into the optical system drifts. One of the causes of this loss of efficiency can result from a misalignment occurring in the lamp focus at the entry of a light tunnel or the like type of light integrating device. This misalignment can be as a result of ageing of the entire projection system or just the ageing of the lamp burner. Ageing of the lamp burner might result in movement of the source of the arc inside the burner to shift its position. Any movement of the source of the arc inside the burner will result in a shift of the lamp focus at the coupling to the integrating device. This misalignment affects the functionality and the efficiency of the projector. It is therefore desirable to be able to align the lamp focus and maintain the projector efficiency with the passing of time. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0002]      FIG. 1  is a schematic depiction of an embodiment of the present invention.  
         [0003]      FIG. 2  is a schematic front view of a sensor arrangement which is used in the arrangement depicted in  FIG. 1 .  
         [0004]      FIG. 3  is a flow diagram which depicts the steps which are carried out in accordance with an embodiment of the invention in order to compensate for drift and loss of focus alignment.  
         [0005]      FIG. 4  is a schematic depiction of a further embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION  
       [0006]      FIG. 1  shows in schematic form an embodiment of the invention. In this arrangement, a parabolic mirror and lamp arrangement  102  along with an aspheric condenser lens  104 , is arranged to focus light through a color wheel  116  onto the entrance of an integrating device  106 . The integrating device homogenizes the light into a planar source of light at its exit. An illumination relay  160  images the light exiting from the integrating device  106  onto the optical modulator  120 . The optical modular  120  creates the images to be displayed. A projection lens  122  then images the optical modulator on the screen  114 .  
         [0007]     It should be appreciated that the arrangement depicted in  FIG. 1  shows an environment in which the embodiments of the invention can be deployed, and that the disclosed embodiments of the invention are in no way limited to this particular type of arrangement. For instance, instead of a parabolic reflector an elliptical reflector can be used. Instead of using a color wheel, a 2-3 panel optical modulator can be used where each panel handles one or more colors.  
         [0008]     The lamp arrangement  102  consists of a burner  101  and a reflector  103 . The light source is located inside the burner  101 . The reflector  103  can have a spherical shape, a conical shape (elliptical or parabola), a generic aspheric shape or can be a faceted one. The position of the light source inside the burner in relation to the focus of reflector affects the ability of the reflector  103  to collimate or focus the light outside the reflector  103 . This position of the light source in relation to the reflector  103  focus may vary slowly with time and as a result the light being reflected from the reflector  103  will shift from its intended target.  
         [0009]     The condenser lens  104  is responsible for focusing the light from the lamp  102  into the entrance of the integrating device  106  such that it maximizes the light coupled into the integrating device  106 . The condenser lens  104  may be a single lens or a combination of lenses. The condenser lens  104  or its constituents can be spherical or aspherical.  
         [0010]     The condensing lens  104  which can be an aspheric type condensing lens, is, in this embodiment, operatively connected with a motor(s) arrangement  108 , which is configured to move the lens  104  along or about three mutually perpendicular axes x, y and z. As will be appreciated, this movement can be linearly along the axes and/or rotational movement about at least the x and y axes. The goal of the condenser lens  104  movement is to position the focus of the condenser lens  104  in the relation to the center of the integrating device  106  in such a manner that maximizes the light going in the device. The plane x-y refers to the plane of the lens and z axis is the optical axis of the system or the centerline connecting the parabolic reflector and the integrating device  106 . The movement of lens  104  in the z direction adjusts the focus of the lens in this direction. The movement of lens in x-y direction or rotation about these axes results in the lateral (x-y plane) movement of the focused spot.  
         [0011]     The motor(s) arrangement  108  is controlled by signals inputted from a control circuit  110 . This control circuit  110 , as schematically shown, is, in this embodiment, connected with a light sensor  112  which is arranged to respond to a parameter which corresponds to the brightness or lumens which are generated at a screen  114 . The light sensor can, be a quad detector such as depicted in  FIG. 2 , which comprises a group of 4 detectors around the periphery of the integrating device  106 . The lateral or longitudinal displacement of the focused spot from the center of integrating device  106  can be detected by the unbalance or reduction of signals produced by the quad detector  112 .  
         [0012]     However, the light sensor  112  is not limited to the illustrated location or above-mentioned type, and can be located at any other location in the system where it can detect light as a function of lamp alignment with the integrating device  106 .  
         [0013]     The control circuit  110  can be configured to include a microprocessor (note shown) which runs an algorithm via which the operation of the motor(s)  108  can be controlled. An example of this algorithm is depicted in flow chart form in  FIG. 3 .  
         [0014]     As shown, the first step  1001  is to read in data from the set of quad detectors (sensor  112 ) placed at the entrance to the integrating device  106 . As will be appreciated, these detectors can be use to detect the displacement of the focused spot in the plane of the entrance to the integrating device  106 . More specifically, any imbalance in the signals generated by the quad detectors will indicate the direction of movement of focus in the plane of the entrance of the integrating device that is required to achieve an optimal focus. Following this, a parameter or parameters indicative of optimal focusing by the condensing lens  104  is evaluated and compared with a previously determined value(s) (step  1002 ).  
         [0015]     This predetermined value can represent the maximum value that can be expected to be produced for the age of the bulb and the like associated with the generation of the light which is focused by the condensing lens  104 . A look-up table and a clock sub-routine can be used to keep track of the age of the arrangement and to update the value with the passing of time. This, or another routine, can be made sensitive to bulb replacement if so desired.  
         [0016]     In the event that sensed value is not less then the predetermined value (step  1003 ), the routine ends in that no detrimental drift in lens focus is indicated.  
         [0017]     However, in the event that most recent value of the parameter being examined is lower than the predetermined value (step  1003 ), the routine flows to step  1004  wherein the appropriate lens adjustment is calculated and/or predicted and the motor(s) arrangement  108  energized to incrementally change the position of the lens  104  with respect to the integrating device  106 .  
         [0018]     The manner in which the motor(s) arrangement  108  is energized can be controlled in a number of ways which will be self-evident to those skilled in the feedback control art. Simply by way of example, an initial arbitrary adjustment can be selected. However, when implemented, if the sensor  112  is such as to provide an input indicative of the above mentioned parameter value reducing even further, the adjustment can be reversed and incremented in an opposite direction. This procedure can be repeated and/or conducted for each of the directions in which the condensing lens is arranged to be moved. If the maximum expected value is not determined to have been reached in step  1003  the process can cycle through a series of positional adjustments until the desired system efficiency is restored and screen lumens are maximized.  
         [0019]     In a further embodiment, shown in  FIG. 4 , in the case of DMD™ (Digital Micromirror Device™) or MMD™ (Micro Mirror Device™) based projectors, a single detector  182  can be used to detect the light deflected in the off-state  180  of the DMD type optical modulator. The position of the condenser lens  104  can be adjusted using this detection to maximize the signal at the detector. An algorithm of the nature shown in  FIG. 3  can be, merely by way of example, be used to implement the corrective motor energization. Placing the detector in the off state light region  180  of the DMD avoids the need for the detector to be placed in the projection path to the screen.  
         [0020]     As will be appreciated, the invention has been disclosed with reference to only a limited number of embodiments, however, the various changes and modifications which can be made without departing from the scope of the invention which is limited only by the appended claims, will, given the preceding disclosure, be self-evident to those skilled in the art of or circuit design or that which closely pertains thereto.  
         [0021]     For example, even though the arrangement shown in  FIG. 1  has been disclosed as including a DMD, it should be understood that this arrangement has been used merely by way of example and that other optical modulators such as Lcos, LCD or those based on inferometery may be used in place thereof. Further, the integrating device can take the form of an integrating tunnel, rod or fly&#39;s eye condenser lens, for example. For the purpose of illustration only, a rectangular apertured integrating tunnel has been illustrated in  FIG. 2 .