Abstract:
A system, method, and apparatus for sensing an operational condition of a projection device and generating a signal to be used in the adjustment of the relative disposition of a component of the projection device, are disclosed herein.

Description:
FIELD OF THE INVENTION 
     Disclosed embodiments of the present invention relate to the field of projection systems, and more particularly to adjusting the relative disposition of projection optics based on operational conditions. 
     BACKGROUND OF THE INVENTION 
     Rear-projection displays (RPDs) have become a popular technology for applications where a self-contained, large-screen display is required, for example rear-projection televisions (RPTs). RPTs are generally available with larger screen sizes than cathode ray tube (CRT) displays due to limitations inherent in the manufacture of large CRTs. More recently, RPDs have also found increased popularity for use in smaller applications, such as monitors. 
     An RPD includes many individual components that cooperate to display an image for a viewer. For example, a typical RPD has a body or cabinet housing a translucent screen, a light valve, light source, and projection optics. The light source illuminates the light valve, which modulates the light based on image data provided from an input device. The projection optics then project the image output from the light valve onto the screen for display. 
     During operation the components of an RPD create a significant amount of heat within the cabinet. This heat may cause a number of things to happen that ultimately affects the quality of the image of the light valve displayed at the screen. Increased heat may cause thermal drift between the system components due to physical expansion/contraction of the chassis that holds the components relative to one another. Heat may also have a thermalizing effect on the shape and/or index of refraction of lens elements of the projection optics. 
     Many design attempts have been presented in the prior art to try to mitigate the effects of thermal cycling within projection systems. One example includes a heater to preheat the components prior to operation in order to create a thermally constant environment. Another example consists of a design of combinations of positive and negative lens elements in an attempt to compensate for the thermalizing effect. However, any mitigative effect provided by these prior art designs falls short of compensating for the thermal cycling experienced throughout the life cycle of a typical projection system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings, in which the like references indicate similar elements and in which: 
         FIG. 1  illustrates a simplified schematic view of a projection device having a sensor to sense operating conditions within the projection device, in accordance with an embodiment of this invention; 
         FIG. 2  illustrates a simplified schematic view of a projection device adapted to sense an operational condition relating to a temperature measurement, in accordance with an embodiment of the present invention; 
         FIG. 3  illustrates a cross-sectional view of projection optics in accordance with one embodiment of the present invention; 
         FIG. 4  illustrates a simplified schematic view of a projection device adapted to sense an operational condition relating to a characteristic of a projected image, in accordance with an embodiment of the present invention; 
         FIG. 5  illustrates a flow diagram of a feedback loop implemented by the projection device according to an embodiment of the present invention; and 
         FIG. 6  illustrates a simplified schematic diagram of a projection device employing wavelength selective reflection to reflect the proxy image, in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Illustrative embodiments of the present invention include a projection device having a sensor to generate a signal, based at least in part upon sensed operating conditions, to be used in adjusting the relative positioning of components within the projection device, and methods practiced thereon. 
     Various aspects of the illustrative embodiments will be described using terms commonly employed by those skilled in the art to convey the substance of their work to others skilled in the art. However, it will be apparent to those skilled in the art that alternate embodiments may be practiced with only some of the described aspects. For purposes of explanation, specific materials and configurations are set forth in order to provide a thorough understanding of the illustrative embodiments. However, it will be apparent to one skilled in the art that alternate embodiments may be practiced without the specific details. In other instances, well-known features are omitted or simplified in order not to obscure the illustrative embodiments. In particular, a wide variety of optical components such as prisms, mirrors, lenses, integration elements, etc. may be used as appropriate to fold, bend, or modify the illumination for the intended application. Integration of these optical components into illustrated embodiments may not be specifically addressed unless it is necessary to develop relevant discussion of embodiments of the present invention. 
     Further, various operations will be described as multiple discrete operations, in turn, in a manner that is most helpful in understanding the present invention; however, the order of description should not be construed as to imply that these operations are necessarily order dependent. In particular, these operations need not be performed in the order of presentation. 
     The phrase “in one embodiment” is used repeatedly. The phrase generally does not refer to the same embodiment; however, it may. The terms “comprising,” “having,” and “including” are synonymous, unless the context dictates otherwise. 
       FIG. 1  illustrates a simplified schematic diagram of a projection device  100  having a sensor  104  to sense operating conditions within the projection device, in accordance with an embodiment of this invention. The projection device  100  may include an illumination arrangement  108  to provide light to a light valve  112 . The light valve  112  may modulate the received light in a manner to effectuate the output of a desired image. The desired image may be conveyed to the projection device  100  from an input device. The conveyed image may be, for example, image frames of a video. 
     For the purpose of this description, a still image may be considered as a degenerate or special video where there is only one frame. Accordingly, both still image and video terminologies may be used in the description to follow, and they are not to be construed to limit the embodiments of the present invention to the rendering of one or the other. 
     The image output from the light valve  112  may be conveyed by image rays travelling along a projection path and projected through projection optics  120  onto a viewing mechanism such as, but not limited to, a screen  124 . 
     Each of the components discussed herein may represent a wide range of devices designed to perform the component&#39;s respective function. For example, the illumination arrangement  108  may include a light source optically coupled to a series of illumination optics to process the illumination. The light source may be a polychromatic light source such as, but not limited to, an incandescent lamp (e.g., tungsten halogen) or a gaseous discharge lamp (e.g., a metal halide). In other embodiments, monochromatic light sources such as light-emitting diodes (LEDs), for example, may be used to produce light of a particular color. The illumination optics may include, but are not limited to, illumination lenses, integration devices, filters, and/or light-directing components (e.g., mirrors, prisms, light guides, etc.) designed to provide the illumination with the desired uniformity, angle, aspect ratio, color, and/or brightness to the light valve  112 . 
     The light valve  112  may include, but is not limited to, a digital micromirror device (DMD), a reflective liquid crystal on semiconductor (LCOS) device, and a liquid crystal device (LCD). In one embodiment, the light valve  112  may be sequentially illuminated with primary colors from the illumination arrangement  108  in a frame sequential modulation (FSM) manner. In various embodiments, the projection device  100  may also include more than one light valve  112 . For example, a color-specific light valve may be placed in each of a number of primary colored paths and be used to exclusively modulate the light of these paths. In these embodiments, the illumination arrangement  108  may include optics to facilitate the presentation of colored light to the appropriate light valves along the appropriate illumination paths. 
     In various embodiments, the input device may include a personal or laptop computer, a digital versatile disk (DVD), a set-top box (STB), a video camera, a video recorder, an integrated television tuner, or any other suitable device to transmit signals, e.g., video signals, to the projection device  100 . 
     The image rays from the projection optics  120  may converge to a focal point  128  that is a focal distance  132  away from the projection optics  120 . As the image rays converge to the focal point  128  their diameter of separation  136  gradually decreases, theoretically to zero. After the focal point  128 , and in the absence of the screen  124 , the image rays would then diverge with the diameter of separation  136  gradually increasing. The diameters of separation  136  may be symmetrical around the focal point  128 . A depth of focus  140  may exist throughout a range of diameters of separation  136  where the image may have a desired focal status. This may sometimes be referred to as the allowable blur circle. If the screen  124  is located within this depth of focus  140  the image may be focused upon the screen  124 . Due to the symmetry around the focal point  128 , if the focal point  128  is within +/−½ (depth of focus  140 ) distance to the screen  124 , the image may be focused on the screen  124 . 
     The focal distance  132  may be determined by a number of factors, including the number and type of elements that make up the projection optics  120  as well as their relative positioning to one another, and to the light valve  112 . Although the focal distance  132  may be largely fixed with the selection and arrangement of the components of the projection device  100 , there may be environmental situations experienced during operation that may affect the focal distance  132 . These environmental situations may cause focal drift, i.e., changes in the focal distance  132 . A significant focal drift may result in the depth of focus  140  drifting beyond the screen  124  resulting in an out-of-focus image at the screen  124 . 
     In one embodiment, the sensor  104  may sense an operational condition related to focal drift. Upon sensing the operational condition, the sensor  104  may output a sensor signal that may be used to counteract the focal drift. This may result in a focused image being achievable throughout a wide range of environmental situations. Additionally, this may result in design opportunities not previously realized due to compromises related to the depth of focus  140  dimension. 
     Prior art projection devices often choose projection optics having a large depth of focus dimension with the idea that more focal drift could be experienced through operation without resulting in an out-of-focus image. However, projection optics with a large depth of focus dimension may sacrifice a certain amount of light collection efficiency and/or compactness. 
     The depth of focus  140  dimension may be related to the projection optics&#39;  120  f-number, which is an expression denoting the ratio of the focal distance  132  to the diameter of the entrance pupil. Projection optics with small f-numbers may project light rays that converge, and subsequently diverge, at steeper angles than light rays from projection optics with a large f-number. These steep angles of convergence/divergence result in a relatively narrow depth of focus that is unaccommodating to focal drift. However, other considerations may tend towards the adoption of optics with small f-numbers. 
     Projection optics having small f-numbers may not only project light rays with steep angles but may also be capable of collecting light rays over a wide range of angles. With regards to the embodiment depicted in  FIG. 1 , this may facilitate the projection optics  120  collecting light rays from the light valve  112  over a wide range of angles thereby providing for an increased collection efficiency. Additionally, the relative positioning of the projection optics  120  to both the light valve  112  and to the screen  124  may be closer the smaller the f-number, resulting in a more compact projection device  100 . 
       FIG. 2  illustrates a simplified schematic view of a projection device  200  adapted to sense an operational condition and to adjust the relative disposition of a component based, at least in part, upon the sensed condition, in accordance with an embodiment of the present invention. In this embodiment, a mechanical actuator  204  may be coupled to a chassis  208  that provides for the relative disposition of the projection optics  120  and the light valve  112 . The projection optics  120  may include an entry lens  212 , an intermediate lens  216 , and an exit lens  220 . The lenses  212 ,  216 , and/or  220  may be simple lenses, i.e., one lens element having two refractive surfaces, or compound lenses, i.e., having more than one lens elements. A mechanical actuator  204  may operate to adjust the focal distance  132  by adjusting the disposition of at least one lens element of the projection optics  120  relative to the light valve  112 . 
       FIG. 3  illustrates a cross-sectional view of projection optics  120  in accordance with one embodiment of the present invention. As discussed above, the projection optics  120  may include the entry lens  212 , the intermediate lens  216 , and the exit lens  220 . The lens elements of the lenses  212 ,  216 , and  220  may be respectively disposed in tubes  304 ,  308 , and  312 . In this embodiment, the mechanical actuator  204  may include a piezoelectric device  316 . One end of the piezoelectric device  316  may be coupled to a brace  320 , which is coupled to the tube  308 . The other end of the piezoelectric device  316  may be coupled to an end of the tube  304 . In one embodiment the piezoelectric device  316  may have a ring-shape that corresponds to the interior diameter of the tube  312  and the end of the tube  308 . In other embodiments, the piezoelectric device  316  may include one or more discrete components. 
     Adjusting the voltage across the piezoelectric device  316  may cause linear motion through expansion/contraction in an axial direction, i.e., parallel to the projection path  324 . Adjusting the voltage in this way may cause precise adjustments to the relative disposition of the lens elements of the entry lens  212 . In a similar manner, the relative disposition of the Intermediate lens  216 , the exit lens  220 , and/or the light valve  112  may be adjusted. Additionally, in various embodiments the mechanical actuator  204  may be adapted to adjust the relative positioning of one or more of the individual lens elements. 
     In various embodiments, the mechanical actuator  204  may include a wide range of devices designed to adjust the relative disposition of components of the projection device  200 . For example, the mechanical actuator  204  could include, but is not limited to, a linear motor, a stepper motor, a solenoid, and/or a pneumatic cylinder. 
     Referring again to  FIG. 2 , a controller  224  may be coupled to the sensor  104  to receive a sensor signal that is based at least in part upon a sensed operating condition of the projection device  200 . The controller  224 , which may also be coupled to the mechanical actuator  204 , may output a control signal that is based at least in part upon the sensor signal. The control signal may cause the mechanical actuator  204  to adjust the relative disposition of at least one element of the projection optics  120  and the light valve  112 . 
     In one embodiment, the operating condition may be a temperature measurement and the sensor  104  may be a temperature sensor such as, for example, a thermocouple. A correlation between focal drift and the temperature measurement may be stored in a look-up table that is accessible by the controller  224 . The correlative data may be generated through empirical analysis performed through operation of a projection device with a similar optical architecture, or it could be the result of computational analysis based on known thermal effects of the components of the projection device  200 , e.g., thermal coefficients of the components. The controller  224  may receive the sensor signal representing a temperature measurement, access the look-up table to approximate the focal drift, and output the control signal that is adapted to at least partially counteract this focal drift. 
     In various embodiments the sensor  104  may be adapted to sense temperature measurements at more than one location. For example, the sensor may position one thermocouple adjacent to the projection optics  120  with another adjacent to the light valve  112 . 
       FIG. 4  illustrates a simplified schematic view of a projection device  400  adapted to sense an operational condition relating to a characteristic of a projected image, in accordance with an embodiment of the present invention. In this embodiment, the image of the light valve  112  may be projected onto the screen  124  through the projection optics  120  in a manner similar to the above embodiments. However, in this embodiment an image of a calibration object  404  may also be projected through the projection optics  120 . The image of the calibration object  404  may be projected onto the sensor  104 . Projecting both the light valve and calibration object images through the same projection optics may correlate the focal characteristics of the two images. For example, in one embodiment, the relative disposition of the components of the projection device  400  may be such that when the image of the calibration object  404  is focused upon the sensor  104 , the image of the light valve  112  is focused on the screen  124 . Due to this, or a similar, correlation of focal characteristics, the calibration object image may serve as a proxy for the light valve image. Therefore data analysis performed upon the former may give indication as to the status of the latter. Hereinafter the light valve image may also be referred to as the primary image, and the calibration object image may also be referred to as the proxy image. 
     In this embodiment, the sensor  104  may include an image capture device, and the proxy image may be projected onto a surface of the image capture device, which would then translate the image into electrical impulses of the sensor signal. The image capture device may be, e.g., a charge-coupled device (CCD) having an array of pixels with capacitors capable of detecting the amount of light that is incident upon the pixels and outputting electrical impulses representing that amount. 
     The sensor signal may be output to the controller  224 , which may perform analysis on the sensor signal to determine a focal characteristic of the proxy image. For example, a focal drift may occur that results in the proxy image going out of focus. The controller  224 , having determined an out-of-focus shift in the sensor signal, may output control signals to the mechanical actuator  204  that are designed to refocus the proxy image. The controller  224  may receive continual feedback from the sensor  104  to determine whether adjustments made to the relative disposition of the components have put the proxy image back into focus. 
       FIG. 5  illustrates a flow diagram of a feedback loop implemented by the projection device  400  according to an embodiment of the present invention ( FIG. 5  reference numbers in parentheses). Upon operation of the projection device  400  both the primary image and the proxy image may be projected through the projection optics  120  ( 500 ). The controller  224  may receive the sensor signal and determine the current focal status of the proxy image ( 504 ). The controller  224  may then compare the current focal status to an expected focal status of the proxy image ( 508 ). If the difference between the current focal status and the expected focal status is within a predetermined operating range, the controller  224  will refrain from actuating the mechanical actuator  204  and after a period of time the current focal status will be updated with more recent proxy image data from the sensor  104 . If the difference between the current and expected focal statuses is outside of the operating range, the controller  224  may generate control signals to actuate the mechanical actuator  204  to adjust the relative positioning of components of the projection device  400  ( 512 ) and then after a period of time the current focal status will be updated with more recent proxy image data from the sensor  104 . 
     In another embodiment, the controller  224  may generate the control signals based solely on the current focal status of the proxy image without comparing it to an expected focal status. 
     In one embodiment, the calibration object  404  may include a pattern that is designed to facilitate the focal characteristic analysis that is performed by the controller  224 . In one embodiment this pattern may include parallel lines of various widths and spacings. Other embodiments may include patterns having dots, concentric circles. The calibration object  404  may include a backlight source such as, but not limited to, an LED. 
     As depicted in  FIG. 4 , the calibration object  404  is distinct from the light valve; however, in other embodiments the calibration object  404  may be a part of the light valve  112 . In some embodiments, such as a rear-projection television (RPT), the image of the light valve  112  is projected in a manner to overfill the screen  124 . Therefore, in this embodiment, the sensor  104  may be placed adjacent to the screen  124  and the calibration object  404  may be a portion of the perimeter of the light valve  112 . 
     As depicted, the primary image may exit the projection optics with an upward trajectory, while the proxy image may exit the projection optics with a downward trajectory; however, other embodiments may have other trajectories. For example, in another embodiment the proxy image and the proxy image may exit the projection optics  120  with the same angular trajectory. 
       FIG. 6  illustrates a simplified schematic diagram of a projection device  600  employing wavelength selective reflection to reflect the proxy image, in accordance with an embodiment of the present invention. The illumination arrangement  108  may provide illumination with certain wavelengths designed to carry the primary image, and illumination having other wavelengths to carry the proxy image. For example, in one embodiment the primary image rays may have wavelengths within the visible spectrum, while the proxy image rays may have wavelengths within the infrared (IR) range. The primary image rays and the proxy image rays may be provided to the light valve  112  simultaneously or within respective time frames. 
     In one embodiment, the illumination arrangement  108  may include a polychromatic light source adapted to emit light over a wide range of wavelengths. The illumination arrangement  108  may have a color modulator with filter segments designed to receive the polychromatic light and transmit color sequential light to the light valve  112 . The color modulator may be a color wheel having primary color filters, e.g., red, green, and blue that are designed to emit colored light for modulation into the primary image. In one embodiment, the red filter may be designed to transmit illumination in both the visible red spectrum as well as the invisible infrared spectrum, thereby simultaneously providing the carrier for both the red portion of the primary image and the proxy image. 
     In another embodiment, monochromatic light sources such as colored LEDs may be used. These embodiments may have light sources that emit light within a relatively narrow spectrum of wavelengths. One embodiment may have primary light sources, e.g., red, green, and blue, that are designed to provide the primary image rays, and a calibration light source that is designed to provide the proxy image light rays. The calibration light source may be activated in its own time frame or, alternatively, activated in a time frame along with one or more of the primary colored light sources. 
     In this embodiment a dichroic reflector  604  may be optically coupled to the output of the projection optics  120 . The dichroic reflector  604  may be adapted to reflect the proxy image rays and transmit the primary image rays. More particularly, in one embodiment the dichroic reflector  604  may be adapted to reflect illumination having wavelengths over 700 nanometers (nm) (which includes the IR spectrum), while transmitting illumination having wavelengths less than 700 nm (which includes the visible spectrum). 
     The proxy image rays may be reflected towards the image capture device of the sensor  104 . An embodiment employing a CCD may be especially sensitive to proxy image rays within the IR spectrum. Similar to the above embodiment described and discussed with reference to  FIGS. 4-5 , the sensor  104 , controller  224 , and mechanical actuator  204  may cooperate to adjust the relative disposition of components of the projection device  600  in order to counteract focal drift that may result in the proxy and primary images going out of focus. 
     The novel aspects discussed and described with respect to the projection devices  100 ,  200 ,  400 , and  600  from the above embodiments may be used in a variety of applications including, but not limited to, a rear projection display (RPD) and a front-projection display (FPD). 
     Although specific embodiments have been illustrated and described herein for purposes of description of the preferred embodiment, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent implementations calculated to achieve the same purposes may be substituted for the specific embodiment shown and described without departing from the scope of the present invention. Those with skill in the art will readily appreciate that the present invention may be implemented in a very wide variety of embodiments. This application is intended to cover any adaptations or variations of the embodiments discussed herein. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.