Patent Description:
This application relates generally to projection systems and methods of driving a projection system.

Digital projection systems typically utilize a light source and an optical system to project an image onto a surface or screen. The optical system includes components such as mirrors, lenses, waveguides, optical fibers, beam splitters, diffusers, spatial light modulators (SLMs), and the like. The contrast of a projector indicates the brightest output of the projector relative to the darkest output of the projector. Contrast ratio is a quantifiable measure of contrast, defined as a ratio of the luminance of the projector's brightest output to the luminance of the projector's darkest output. This definition of contrast ratio is also referred to as "static" or "native" contrast ratio. Document <CIT> relates to an optical engine of a projection television in which a path of illumination emitted from a light source is aligned to correspond with the image producer by turning a screw of a mirror device. The object of the <CIT> can be achieved by an optical engine of a projection television including a light generator, a mirror device for reflecting illumination emitted from the light generator thereby changing a path of the illumination, in which a reflection angle of the illumination can be adjusted, and a projection apparatus for enlarging and projecting the image produced in the image producer on the screen by reflecting the image to an incident illumination from the mirror device, wherein the path of the illumination is aligned to correspond to the whole image produced in the image producer to be projected on the screen by adjusting the mirror device. Document <CIT> relates to the problem to improve, when a pattern is drawn on a substrate by scanning the substrate with plural light beams from plural light beam irradiation devices, the drawing quality by correcting variation in intensity distribution of diffraction light of the light beams due to variation in operation angle of a mirror of a spatial optical modulator. Solution in <CIT>: A pattern is drawn on a substrate by scanning the substrate with a plurality of light beams from a plurality of light beam irradiation devices including an illumination optical system for supplying a light beam, a spatial optical modulator for modulating the light beam by changing the angles of mirrors disposed in two directions, a driving circuit for driving the spatial optical modulator based on drawn data, and an irradiation optical system for emitting the light beam modulated by the spatial optical modulator in a manner that a chuck is moved relative to the plural light beam irradiation devices. The incidence angle of the light beam supplied to the spatial optical modulator of each light beam irradiation device is adjusted in accordance with the variation in operation angle of the mirror of the spatial optical modulator of each light beam irradiation device. <CIT> discloses that in order to align the optical components of a projection apparatus, more particularly a rear projection apparatus of a projection wall, wherein the projection apparatus comprises a light mixing rod, it is proposed to arrange an alignment deflecting mirror in the illumination path of the imaging device between the lamp and the light mixing rod, wherein said alignment deflecting mirror can be adjusted by means of servo motors. <CIT> relates to the problem to provide a mirror three-dimensionally held and positionally adjustable, so as to be fixed easily after a position adjustment. Solution in <CIT>: The curved mirror <NUM> comprises a reflection surface <NUM> formed in an axial-symmetry aspherical surface shape whose center is a first symmetry axis <NUM>, a sliding contact surface <NUM> spherically projecting and a positioning projection <NUM>. The sliding contact surface <NUM> fits in a bearing hole <NUM> of a bearing seat <NUM> provided upward on a base member. The bearing hole <NUM> is a concave portion formed in a spherical shape having a same diameter as that of the sliding contact surface <NUM>, and its opening end <NUM> fits to a part of the sliding contact surface <NUM>, so as to come in contact with and slidingly support the sliding contact surface <NUM>. A compression coil spring <NUM> is mounted in the positioning projection <NUM> and is pressed with a cover member. At this time, an end of the positioning projection <NUM> projects from an opening formed in the cover member, thereby allowing a positioning operation of the curved mirror <NUM>. An adhesive is applied between the positioning projection <NUM> and the opening <NUM> at a position where the reflection surface <NUM> is positionally adjusted, thereby fixing the curved mirror <NUM> at an optimum position. <CIT> discloses a multipath laser beam automatic collimation device. Multipath beam near-field and far-field reference synchronous images are transmitted to a photosensitive screen based on an image transmission automatic collimation structure of plug-in type fork wire arrays and fluorescence imaging by utilizing a double-cross fork wire array image transmission light path, and fluorescence imaging records of multiple beams generated by visible light CCD are utilized so that a problem of light path collimation near-field and far-field reference is solved, and integrated high-efficiency automatic collimation of multipath laser beams is also realized.

Some projection systems are based on SLMs that implement a spatial amplitude modulation. In such a system, the light source may provide a light field that embodies the brightest level that can be reproduced on the image, and light is attenuated or discarded in order to create the desired scene levels. Some high contrast examples of projection systems based on this architecture use a semi-collimated illumination system and Fourier stop in the projection optics to improve contrast. In such architectures, the illumination angle on the SLM has a substantial effect on the projected image, including but not limited to effects on the contrast ratio and the clarity of the projected image.

Various aspects of the present disclosure relate to devices, systems, and methods for projection display a high-contrast projection architecture.

In one exemplary aspect of the present disclosure, there is provided a projection system comprising a light source configured to emit a light in response to an image data; an illumination optical system configured to steer the light, the illumination optical system including a first mirror and a second mirror; a digital micromirror device including a plurality of micromirrors, wherein a respective micromirror is configured to reflect the steered light to a filter as on-state light in a case where the respective micromirror is in an on position and to reflect the steered light to a light dump as off-state light in a case where the respective micromirror is in an off position; and a controller configured to: determine a deviation between an actual angle of orientation of the digital micromirror device and an expected angle of orientation of the digital micromirror device, calculate a first amount of angle adjustment corresponding to the first mirror and a second amount of angle adjustment corresponding to the second mirror, and actuate the first mirror according to the first amount and the second mirror according to the second amount, thereby to maintain a position and a focus of the steered light on the digital micromirror device and to cause the on-state light to be incident within a predetermined distance from a center of the filter.

In another exemplary aspect of the present disclosure, there is provided a method of calibrating a projection system including a light source configured to emit a light in response to an image data, an illumination optical system configured to steer the light, the illumination optical system including a first mirror and a second mirror, and a digital micromirror device including a plurality of micromirrors respectively configured to reflect the steered light to a filter as on-state light in a case where the respective micromirror is in an on position and to reflect the steered light to a light dump as off-state light in a case where the respective micromirror is in an off position, the method comprising: determining a deviation between an actual angle of orientation of the digital micromirror device and an expected angle of orientation of the digital micromirror device, calculating a first amount of angle adjustment corresponding to the first mirror and a second amount of angle adjustment corresponding to the second mirror, and actuating the first mirror according to the first amount and the second mirror according to the second amount, thereby to maintain a position and a focus of the steered light on the digital micromirror device and to cause the on-state light to be incident within a predetermined distance from a center of the filter.

In another exemplary aspect of the present disclosure, there is provided a non-transitory computer-readable medium storing instructions that, when executed by a processor of a projection device including a light source configured to emit a light in response to an image data, an illumination optical system configured to steer the light, the illumination optical system including a first mirror and a second mirror, and a digital micromirror device including a plurality of micromirrors respectively configured to reflect the steered light to a filter as on-state light in a case where the respective micromirror is in an on position and to reflect the steered light to a light dump as off-state light in a case where the respective micromirror is in an off position, cause the projection device to perform operations comprising determining a deviation between an actual angle of orientation of the digital micromirror device and an expected angle of orientation of the digital micromirror device, calculating a first amount of angle adjustment corresponding to the first mirror and a second amount of angle adjustment corresponding to the second mirror, and actuating the first mirror according to the first amount and the second mirror according to the second amount, thereby to maintain a position and a focus of the steered light on the digital micromirror device and to cause the on-state light to be incident within a predetermined distance from a center of the filter.

In this manner, various aspects of the present disclosure provide for the display of images having a high dynamic range and high resolution, and effect improvements in at least the technical fields of image projection, holography, signal processing, and the like.

These and other more detailed and specific features of various embodiments are more fully disclosed in the following description, reference being had to the accompanying drawings, in which:.

This disclosure and aspects thereof can be embodied in various forms, including hardware, devices, or circuits controlled by computer-implemented methods, computer program products, computer systems and networks, user interfaces, and application programming interfaces; as well as hardware-implemented methods, signal processing circuits, memory arrays, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), and the like. The foregoing summary is intended solely to give a general idea of various aspects of the present disclosure, and does not limit the scope of the disclosure in any way.

In the following description, numerous details are set forth, such as optical device configurations, timings, operations, and the like, in order to provide an understanding of one or more aspects of the present disclosure. It will be readily apparent to one skilled in the art that these specific details are merely exemplary and not intended to limit the scope of this application.

Moreover, while the present disclosure focuses mainly on examples in which the various circuits are used in digital projection systems, it will be understood that this is merely one example of an implementation. It will further be understood that the disclosed systems and methods can be used in any device in which there is a need to project light; for example, cinema, consumer and other commercial projection systems, heads-up displays, virtual reality displays, and the like.

The optics of an SLM-based projection system may be broadly categorized into two parts: the optics located on the illumination side (i.e., optically upstream of the SLM) and the optics located on the projection side (i.e., optically downstream of the SLM). The SLM itself includes a plurality of modulating elements arranged in, for example, a two-dimensional array. Individual modulating elements receive light from the illumination optics and convey light to the projection optics. In some examples, the SLM may be implemented as a digital micromirror device (DMD); this will be discussed in more detail below. Generally, however, a DMD includes a two-dimensional array of reflective elements (micromirrors or simply "mirrors") which selectively reflect light towards the projection optics or discard light based on the position of the individual reflective elements.

As noted above, a high contrast projection system which uses a semi-collimated illumination system and Fourier stop in the projection optics may be greatly affected by differences in the angle of incidence light on the DMD. To prevent degradation in the projected image, a projection system may maintain the position and focus of an output of the illumination optics (e.g., light output from an integrating rod or other uniformity correcting device and subsequently reflected by one or more reflective elements) on the DMD, while at the same time keeping the reflected beam centered in the input of the projection optics (e.g., a filter aperture). However, the exact position of the first and second angle of the DMD mirrors may be subject to manufacturing or other tolerances, such that the actual first and second angles may vary by some amount. In order to compensate for differences in DMD mirror angle between different physical DMDs and ensure that the beam is appropriately centered, one may control the angle of light exiting (e.g., reflecting from) the DMD. Such control should be robust to variations in the first and second angle of the DMD mirrors. The robustness against angle variations may be provided by implementing an adjustment of the angle of incidence of the beam onto the DMD so that, when reflected by the DMD mirrors, the exit beam is always at (or substantially at) the nominal designed exit angle to the aperture. Moreover, because each color channel in color projection systems may have a different angle requirement, it is desirable to provide an adjustment for each color.

The architecture of such high contrast projection systems may provide particular constraints in addition to the adjustment and maintenance of proper illumination angle. For example, the projection systems may utilize a prism where the three colors are recombined and/or a fold mirror before the prism to reduce the size footprint of the optics and the projector itself. Moreover, because the illumination optics focuses an aperture onto the DMD, the optics may be constrained to maintain a constant distance between the aperture and the DMD. Furthermore, as noted above, the image of the aperture must be centered on the DMD. Herein, examples of projection systems are described which are capable of adjusting the input angle to the DMD without changing the focus or position of the integrating rod (or other uniformity correcting device) at the DMD.

<FIG> illustrates an exemplary high contrast projection system <NUM> according to various aspects of the present disclosure. In particular, <FIG> illustrates a projection system <NUM> which includes a light source <NUM> configured to emit a first light <NUM>; illumination optics <NUM> (one example of an illumination optical system in accordance with the present disclosure) configured to receive the first light <NUM> and redirect or otherwise modify it, thereby to generate a second light <NUM>; a DMD <NUM> configured to receive the second light <NUM> and selectively redirect and/or modulate it as a third light <NUM>; a filter <NUM> configured to filter the third light <NUM>, thereby to generate a fourth light <NUM>; and projection optics <NUM> configured to receive the fourth light <NUM> and project it as a fifth light <NUM> onto a screen <NUM>.

In practical implementations, the projection system <NUM> may include fewer optical components or may include additional optical components such as mirrors, lenses, waveguides, optical fibers, beam splitters, diffusers, and the like. With the exception of the screen <NUM>, the components illustrated in <FIG> may be integrated into a housing to provide a projection device. Such a projection device may include additional components such as a memory, input/output ports, communication circuitry, a power supply, and the like.

The light source <NUM> may be, for example, a laser light source, an LED, and the like. Generally, the light source <NUM> is any light emitter which emits coherent light. In some aspects of the present disclosure, the light source <NUM> may comprise multiple individual light emitters, each corresponding to a different wavelength or wavelength band. The light source <NUM> emits light in response to an image signal provided by the controller <NUM>; for example, one or more processors such as a central processing unit (CPU) of the projection system <NUM>. The image signal includes image data corresponding to a plurality of frames to be successively displayed. Individual elements in the projector system <NUM>, including the illumination optics <NUM> and/or the DMD <NUM>, may be controlled by the controller <NUM>. The image signal may originate from an external source in a streaming or cloud-based manner, may originate from an internal memory of the projection system <NUM> such as a hard disk, may originate from a removable medium that is operatively connected to the projection system <NUM>, or combinations thereof.

Although <FIG> illustrates a generally linear optical path, in practice the optical path is generally more complex. For example, in the projection system <NUM>, the second light <NUM> from the illumination optics <NUM> is steered to the DMD chip <NUM> (or chips) at a fixed angle, determined by the steering angle of the DMD mirrors.

To illustrate the effects of the angle of incidence and the DMD mirrors, <FIG> show an exemplary DMD <NUM> in accordance with various aspects of the present disclosure. <FIG> illustrates a plan view of the DMD <NUM>, and <FIG> illustrates partial cross-sectional view of the DMD <NUM>. The DMD <NUM> includes a plurality of square micromirrors <NUM> arranged in a two-dimensional rectangular array on a substrate <NUM>. In some examples, the DMD <NUM> may be a digital light processor (DLP) from Texas Instruments. Each micromirror <NUM> may correspond to one pixel of the eventual projection image, and may be configured to tilt about a rotation axis <NUM>, shown for one particular subset of the micromirrors <NUM>, by electrostatic or other actuation. The individual micromirrors <NUM> have a width <NUM> and are arranged with gaps of width <NUM> therebetween. The micromirrors <NUM> may be formed of or coated with any highly reflective material, such as aluminum or silver, to thereby specularly reflect light. The gaps between the micromirrors <NUM> may be absorptive, such that input light which enters a gap is absorbed by the substrate <NUM>.

While <FIG> expressly shows only some representative micromirrors <NUM>, in practice the DMD <NUM> may include many more individual micromirrors in an number equal to a resolution of the projector system <NUM>. In some examples, the resolution may be <NUM> (<NUM>×<NUM>), <NUM> (<NUM>×<NUM>), 1080p (<NUM>×<NUM>), consumer <NUM> (<NUM>×<NUM>), and the like. Moreover, in some examples the micromirrors <NUM> may be rectangular and arranged in the rectangular array; hexagonal and arranged in a hexagonal array, and the like. Moreover, while <FIG> illustrates the rotation axis <NUM> extending in an oblique direction, in some implementations the rotation axis <NUM> may extend vertically or horizontally.

As can be seen in <FIG>, each micromirror <NUM> may be connected to the substrate <NUM> by a yoke <NUM>, which is rotatably connected to the micromirror <NUM>. The substrate <NUM> includes a plurality of electrodes <NUM>. While only two electrodes <NUM> per micromirror <NUM> are visible in the cross-sectional view of <FIG>, each micromirror <NUM> may in practice include additional electrodes. While not particularly illustrated in <FIG>, the DMD <NUM> may further include spacer layers, support layers, hinge components to control the height or orientation of the micromirror <NUM>, and the like. The substrate <NUM> may include electronic circuitry associated with the DMD <NUM>, such as CMOS transistors, memory elements, and the like.

Depending on the particular operation and control of the electrodes <NUM>, the individual micromirrors <NUM> may be switched between an "on" position, an "off" position, and an unactuated or neutral position. If a micromirror <NUM> is in the on position, it is actuated to an angle of (for example ) -<NUM>° (that is, rotated counterclockwise by <NUM>° relative to the neutral position) to specularly reflect input light <NUM> into on-state light <NUM>. If a micromirror <NUM> is in the off position, it is actuated to an angle of (for example) +<NUM>° (that is, rotated clockwise by <NUM>° relative to the neutral position) to specularly reflect the input light <NUM> into off-state light <NUM>. The off-state light <NUM> may be directed toward a light dump that absorbs the off-state light <NUM>. In some instances, a micromirror <NUM> may be unactuated and lie parallel to the substrate <NUM>. The particular angles illustrated in <FIG> and described here are merely exemplary and not limiting. In some implementations, the on- and off-position angles may be between ±<NUM> and ±<NUM> degrees (inclusive), respectively.

In the context of <FIG>, where the DMD mirrors use an angle tilt of <NUM>° to reflect or discard light, the second light <NUM> is steered to the DMD chip <NUM> at a fixed angle of <NUM>°. When an individual mirror is tilted at a first predetermined angle (e.g., -<NUM>°), the mirror is considered to be in the on state and redirects light toward the filter <NUM> and the projection optics <NUM>. When an individual mirror is tilted at a second predetermined angle (e.g., +<NUM>°), the mirror is considered to be in the off state and redirects light to a light dump located outside the active image area.

In order to ensure that the image on the screen <NUM> has an acceptable clarity and contrast ratio, the illumination optics may be designed and/or controlled to ensure that the angle of incidence on the DMD <NUM> is correct, that aperture focus is maintained, and that aperture location is maintained, regardless of the presence of the prism and fold mirror in the projection system <NUM>.

In one exemplary implementation of the present disclosure, the above may be realized by using two mirrors located in series. <FIG> illustrate exemplary optical states of a partial optical system <NUM> in accordance with the present disclosure.

In particular, <FIG> illustrate an integrating rod <NUM>, a first light <NUM>, an illumination lens system <NUM> (which may comprise one or more individual lenses), a second light <NUM>, a first mirror <NUM>, a third light <NUM>, a second mirror <NUM>, a fourth light <NUM>, a DMD <NUM>, a fifth light <NUM>, an aperture <NUM>, and a sixth light <NUM>. Both the first mirror <NUM> and the second mirror <NUM> are configured for angle adjustment. Because the first mirror <NUM> is located optically upstream (and thus farther from the DMD) compared to the second mirror <NUM>, when the first mirror <NUM> changes its angle the location of the third light <NUM> on the second mirror <NUM> moves. In this manner, the first mirror <NUM> is configured to provide mostly translation (i.e., an effective translation function) and the second mirror <NUM> is configured to provide mostly angle adjustment. For explanation purposes, the partial optical system <NUM> in <FIG> is illustrated in an orientation where the first light <NUM> travels generally horizontally. Various elements illustrated in <FIG> may correspond to various elements (or parts of various elements) illustrated in <FIG>.

In some examples, the integrating rod <NUM> may be a component of the light source <NUM> which receives light from a light emitting element of the light source <NUM> and outputs light, such that the first light <NUM> corresponds to the first light <NUM>. In other examples, the integrating rod <NUM> may be a component of the illumination optics <NUM>, such that the integrating rod <NUM> receives the first light <NUM> and integrates it to form the first light <NUM>. In some examples, the illumination lens system <NUM>, the first mirror <NUM>, and the second mirror <NUM> are components of the illumination optics <NUM>, such that the fourth light <NUM> corresponds to the second light <NUM>. The first mirror <NUM> and/or the second mirror <NUM> may be formed of or coated with any highly reflective material, such as aluminum or silver, to thereby specularly reflect light.

The DMD <NUM> may correspond to the DMD <NUM>. For ease of explanation, the DMD <NUM> is illustrated as a flat surface; however, in practice the DMD <NUM> includes a plurality of individual reflective elements that may or may not be oriented along the same plane. In this manner, the DMD <NUM> may have a structure as illustrated in <FIG> so as to selectively reflect and direct the fourth light <NUM> (i.e., the second light <NUM>) depending on whether individual reflective components of the DMD <NUM> are in the on position, the off position, or the neutral position. Thus, the fifth light <NUM> may correspond to the third light <NUM>. In the claimed subject-matter, the aperture <NUM> is a component of the filter <NUM> thereby to provide filtered illumination to the projection optics, which are not illustrated in <FIG>. In order to provide an appropriate contrast ratio and image clarity, the fifth light <NUM> should be centered on the aperture <NUM>.

In the state illustrated in <FIG>, the surface of the DMD <NUM> is oriented at an angle of <NUM>° (measured from the vertical). In order to ensure that the fifth light <NUM> is centered on the aperture <NUM>, then, the first mirror <NUM> and the second mirror <NUM> are each oriented at an angle of <NUM>°. The first light <NUM> travels along a horizontal optical axis from the integrating rod <NUM> to the illumination lens system <NUM>. In practice, the first light <NUM> expands as it travels, such that it subtends a non-zero solid angle at a surface of the illumination lens system <NUM>. The illumination lens system <NUM> is configured to image the first light <NUM> onto the DMD <NUM>, such that the second light <NUM> is focused on a virtual point that is the same optical distance from an exit of the illumination lens system <NUM> as the DMD <NUM>. In other words, the focus of the illumination lens system <NUM> is located at a distance substantially equal to the sum of the optical path distances of the second light <NUM>, the third light <NUM>, and the fourth light <NUM>.

The second light <NUM> is specularly reflected by the first mirror <NUM>, such that the third light <NUM> travels vertically toward the second mirror <NUM>. The third light <NUM> is specularly reflected by the second mirror <NUM>, such that the fourth light <NUM> travels horizontally toward the DMD <NUM>, where it is reflected as the fifth light <NUM> toward the center of the aperture <NUM>.

In practice, however, any deviation in the angle of orientation of the DMD <NUM> will result in a shift in the point of incidence of the fifth light <NUM> on the aperture <NUM>. This shift may be counteracted by adjusting the first mirror <NUM> and the second mirror <NUM>. <FIG> illustrates such a countermeasure.

In the state illustrated in <FIG>, the surface of the DMD <NUM> is oriented at an angle of <NUM>° (measured from the vertical), which is a <NUM>° difference from the state illustrated in <FIG>. This angle difference is provided for ease of explanation in the visualization; in practical implementations, manufacturing and other tolerances in the DMD <NUM> may result in angle differences on the order of <NUM>° or less. In order to accommodate a change in the orientation of the DMD <NUM>, the input angle of the fourth light <NUM> to the DMD <NUM> may be changed. This may be effected by adjusting the first mirror <NUM> and the second mirror <NUM> appropriately.

The adjustments are such that the first mirror <NUM> is tilted to move the beam to the left. In the particular example illustrated in <FIG>, the first mirror <NUM> is provided with a <NUM>° counterclockwise tilt adjustment relative to the position in <FIG>. The second mirror <NUM> is tilted to move the beam up, which corresponds to a <NUM>° counterclockwise tilt adjustment relative to the position in <FIG>. Together, these tilt adjustments accommodate for the orientation deviation in the DMD <NUM>, such that the fifth light <NUM> remains centered on the aperture <NUM>. The first mirror <NUM> and the second mirror <NUM> may be actuated by, for example, servo motors.

The adjustments to the first mirror <NUM> and the second mirror <NUM> may be made during a calibration of the projection system <NUM>. The calibration may occur in real-time (e.g., after installation of the projection system <NUM> and before or during image projection) or during manufacture.

<FIG> illustrates an exemplary alignment method, which may be performed during the calibration of the partial optical system <NUM> illustrated in <FIG>. The alignment method of <FIG> may be performed in an automated manner; for example, through a computer program as will be described in more detail below.

At operation <NUM>, the alignment method determines an angle of orientation, or a deviation in the angle of orientation from the expected angle, of the DMD <NUM>. The angle of orientation may be determined directly by, for example, physically measuring the angle of orientation of the DMD <NUM> in the projection system <NUM>. Additionally or alternatively, the angle of orientation may be determined indirectly by, for example, illuminating the DMD <NUM> at a known angle and measuring the output angle of reflected light. In some implementations, operation <NUM> may be performed in a test fixture before the DMD <NUM> is installed on its prism assembly.

At operation <NUM>, the alignment method calculates the appropriate amount of angle adjustments for the first mirror <NUM> and the second mirror <NUM>, based on the measured angle of orientation (or deviation) of the DMD <NUM>. The appropriate amount of angle adjustments may be the amount which causes the fifth light <NUM> to be centered on the aperture <NUM>. The calculations of operation <NUM> may be performed through the use of a computer program that receives a single input (the angle of orientation of the DMD <NUM>, or the angle of orientation of the DMD <NUM> relative to the expected angle) and outputs angles of orientation for the first mirror <NUM> and the second mirror <NUM>. An exemplary calculation process, which takes as an input the difference between the angle of orientation of the DMD <NUM> and the expected angle ("dmddeltheta"), as depicted in Table <NUM> in a MATLAB-like pseudocode format to perform ray tracing.

The calculations of Table <NUM> output the adjusted angle of orientation of the first mirror <NUM> ("farmirrortheta"), the adjusted angle of orientation of the second mirror <NUM> ("nearmirrortheta), and the change in the focus point ("deltafocus"). The change in the focus point may result in some degree of defocus; however, depending on the f-number of the projection system <NUM>, the change in the focus point may not be detectable. The input and outputs of the calculations of Table <NUM> are depicted in <FIG>. Moreover, <FIG> illustrates the quantities farmirrortheta (<NUM>) and nearmirrortheta (<NUM>) as a function of dmdeltheta. While <FIG> illustrate an example in which the magnitude of farmirrortheta is between zero and <NUM> degrees and the magnitude of nearmirrortheta is between zero and <NUM> degrees, the present disclosure is not so limited. In some examples (and depending on the relative locations of the first mirror <NUM> and the second mirror <NUM>), the magnitude of farmirrortheta may be between zero and <NUM> degrees and the magnitude of nearmirrortheta may be between zero and <NUM> degrees.

As can be seen from <FIG>, any changes to the focus point of the system are small (<NUM> or less). Shifts in the focus point may not become apparent until the change exceeds ~<NUM> depending on the system parameters, and generally are more apparent for projection systems having a small f-number. In some implementations, the projection system <NUM> has an f-number of f15 or higher. In such implementations, the effects on the focal point of the system <NUM> are not detectable. If, however, the projection system <NUM> has a very small f-number, in one example at least one of the first mirror <NUM> or the second mirror <NUM> should translate in addition to its rotation. In another example, the position of the illumination lens system <NUM> along the optical axis of the first light <NUM> may be adjusted to maintain the focus.

The calculations of operation <NUM> may be carried out at a time of calibration, or may be performed beforehand and stored in a lookup table associated with the projection system <NUM>. In such an implementation, the calibration method may calculate the appropriate mirror angle adjustment by referencing the lookup table instead of by performing the operations illustrated in Table <NUM>.

After the above calculations of operation <NUM>, the alignment method actuates the mirrors at operation <NUM> to impart the calculated orientation thereon. This actuation may be implemented using a stepper motor, servo motor, or other appropriate adjustment mechanism. In the claimed subject-matter, the actuation is performed under the control of the controller <NUM> of <FIG>. In other examples not according to the claimed subject-matter, the actuation is performed under manual control.

While <FIG> illustrate a dual mirror implementation of the projection system <NUM>, the present disclosure is not so limited. In another exemplary implementation of the present disclosure, the above may be realized by using a single mirror and by adjusting both the angle of the mirror and its position.

In such any implementation, changes to the position of the mirror will result in changes to the focus of the aperture. As such, the illumination optics <NUM> should be refocused for each angle adjustment. However, the focus adjustment also results in small changes to the appropriate position of the mirror, such that multiple adjustments may be implemented to achieve the proper combination of focus, position, and angle.

<FIG> illustrates a partial optical system <NUM> in accordance with the present disclosure. In particular, <FIG> illustrates an illumination lens system <NUM> (which may comprise one or more individual lenses), a first light <NUM>, a mirror <NUM>, a second light <NUM>, a DMD <NUM>, a third light <NUM>, a virtual light path <NUM>, and a virtual pivot point <NUM>. For explanation purposes, the partial optical system <NUM> in <FIG> is illustrated in an orientation where the first light <NUM> travels generally vertically. Various elements illustrated in <FIG> may correspond to various elements (or parts of various elements) illustrated in <FIG>.

In some components, the illumination lens system <NUM> may be a component of the illumination optics <NUM> which receives either the first light <NUM> or intermediate light from upstream optical components within the illumination optics <NUM>. The illumination lens system <NUM> conveys the received light as the first light <NUM> to the mirror <NUM>, which may be formed of or coated with any highly reflective material, such as aluminum or silver, to thereby specularly reflect the first light <NUM> as the second light <NUM>.

The DMD <NUM> may correspond to the DMD <NUM>. For ease of explanation, the DMD <NUM> is illustrated as a flat surface; however, in practice the DMD <NUM> includes a plurality of individual reflective elements that may or may not be oriented along the same plane. In this manner, the DMD <NUM> may have a structure as illustrated in <FIG> so as to selectively reflect and direct the second light <NUM> depending on whether individual reflective components of the DMD <NUM> are in the on position, the off position, or the neutral position. Thus, the third light <NUM> may correspond to the third light <NUM>, and may be directed to and centered on downstream components so as to provide an appropriate contrast ratio and image clarity.

In a comparative example, if no mirror were present and thus an optical path from the illumination optics goes directly from the illumination aperture to the DMD at the correct angle and with the correct focus, and the system had a configuration in which the components had a single axis pivot point located at the center of a surface of the DMD, then the angle of the illumination could be adjusted without affecting the position or focus of the aperture image. However, this comparative example is not practical in a configuration including mirrors (such as a fold mirror or total internal reflection in a prism). Therefore, to recreate the effects of such a pivot, <FIG> further illustrates a virtual pivot simulation.

In <FIG>, because the individual reflective elements of the DMD <NUM> pivot on a single axis and because a sufficient contrast ratio and projected image clarity relies on a correction of different mirror pivot angles, then the optical path of light incident on the DMD <NUM> similarly may only pivot about the same single axis. To illustrate this, <FIG> further shows a virtual light path <NUM> and a virtual pivot point <NUM>. The virtual light path <NUM> traces the trajectory of the first light <NUM> if the mirror <NUM> were not present. The virtual pivot point <NUM> represents, but is not physically located on, the DMD <NUM> surface. While <FIG> illustrates an example in which only one reflective element exists in the optical path, the virtual pivot point <NUM> may be found even in systems with multiple reflective elements (e.g., mirrors, total internal reflection prisms, and so on) by unfolding all of the reflections (e.g., by determining and utilizing multiple virtual light paths). In any case, if the source of the first light <NUM> (e.g., the illumination lens system <NUM>) is rotated physically about the virtual pivot point, then the location and focus do not change when the angle of a reflective surface of the DMD <NUM> is adjusted. Mechanical linkages may be used to effect this rotation.

<FIG> illustrates one exemplary mechanical linkage configuration. In <FIG> (and subsequent figures), filled circles represent connector hinges that have a fixed location, which may be referred to as hinges that are "tied to ground. " Empty circles represent connector hinges which are free to translate. Thus, <FIG> illustrates a first fixed connector hinge <NUM>, a second fixed connector hinge <NUM>, a first connector <NUM> having a first end connected to the first fixed connector hinge <NUM>, a second connector <NUM> having a first end connected to the second fixed connector hinge <NUM>, a first free hinge <NUM> connected to a second end of the first connector <NUM>, a second free hinge <NUM> connected to a second end of the second connector <NUM>, a carrier body <NUM>, and a pivot point <NUM> which may be coincident with a third free hinge. The first connector <NUM>, the second connector <NUM>, and the carrier body <NUM> are rigid bodies. In the left portion of <FIG>, the carrier body <NUM> is in an unadjusted configuration. In such a configuration, the first connector <NUM> and the second connector <NUM> are pointed at the pivot point location. In the right portion of <FIG>, the carrier body <NUM> has been given a counterclockwise rotation to provide the desired rotation and accommodate the orientation angle of the DMD <NUM>.

The location of the pivot point <NUM> moves by only a small amount as a result of the counterclockwise rotation. The amount of change in the focus position depends on the respective lengths of the first connector <NUM> and the second connector <NUM>, and the amount of change in the location of the pivot point depends on the particular geometry of the linkage implementation.

<FIG> illustrates another exemplary linkage <NUM>. <FIG> illustrates a first fixed connector hinge <NUM>, a second fixed connector hinge <NUM>, a first connector <NUM> having a first end connected to the first fixed connector hinge <NUM>, a second connector <NUM> having a first end connected to the second fixed connector hinge <NUM>, a first free hinge <NUM> connected to a second end of the first connector <NUM>, a second free hinge <NUM> connected to a second end of the second connector <NUM>, a carrier body <NUM>, and a pivot point <NUM>. The first connector <NUM>, the second connector <NUM>, and the carrier body <NUM> are rigid bodies. The carrier body <NUM> has a generally coffin-like shape; however, because the pivot point <NUM> should not be a part of the optical surface, in practice the uppermost portion of the carrier body <NUM> may be cut off (represented by the dotted line in <FIG>). In one particular example, the optical path of a system including the exemplary linkage configuration of <FIG> has an optical path of about <NUM>, which is near the minimum practical length for D-Cinema DMD devices which are about <NUM> diagonal.

The linkage <NUM> of <FIG> is driven by a combination of a drive mechanism <NUM>, a drive hinge <NUM>, and a drive connector <NUM> which extends between the drive hinge <NUM> and a lower vertex of the carrier body <NUM>. The action of the drive mechanism, conveyed to the carrier body <NUM> via the drive connector <NUM>, provides the translation of the carrier body <NUM>. Compared to the linkage illustrated in <FIG>, the linkage <NUM> illustrated in <FIG> may result in an even smaller amount of change in the location of the pivot point <NUM>. In one particular example, the rotation applied to accommodate for an angle shift of the optical path from <NUM> to <NUM>° (e.g., as a result of a change in the angle of orientation of a reflective element of the DMD) may result in a translation of the pivot point of <NUM>. Such a translation would be undetectable. The position shift in the focus may be larger (e.g., ~<NUM>), which is likely to be undetectable with optical systems having a f-number of f20 or f15. In any event, the nature and architecture of the DMD may themselves mitigate the effects of a focus change or confine the effects to the edges.

In practical implementations, the effects of play in the bearings (e.g., the bearings in various ones of the hinges illustrated in <FIG>) may themselves affect the position of the virtual pivot point. This, however, may be alleviated by modifying the geometry of the linkage such that the linkage is more tolerant of the bearing play. <FIG> illustrate one such example of such a geometry for a linkage <NUM>.

<FIG> illustrate a first fixed connector hinge <NUM>, a second fixed connector hinge <NUM>, a first connector <NUM> having a first end connected to the first fixed connector hinge <NUM>, a second connector <NUM> having a first end connected to the second fixed connector hinge <NUM>, a first free hinge <NUM> connected to a second end of the first connector <NUM>, a second free hinge <NUM> connected to a second end of the second connector <NUM>, a carrier body <NUM>, and a pivot point <NUM>. The first connector <NUM>, the second connector <NUM>, and the carrier body <NUM> are rigid bodies. The carrier body <NUM> has a generally coffin-like shape; however, because the pivot point <NUM> should not be a part of the optical surface, in practice the uppermost portion of the carrier body <NUM> may be cut off (represented by the dotted line in <FIG> illustrates the linkage <NUM> in an unrotated position, and <FIG> illustrates the linkage <NUM> in a rotated position.

The linkage <NUM> is driven by a combination of a drive mechanism <NUM>, a drive hinge <NUM>, and a drive connector <NUM> which extends between the drive hinge <NUM> and a lower vertex of the carrier body <NUM>. The action of the drive mechanism, conveyed to the carrier body <NUM> via the drive connector <NUM>, provides the translation of the carrier body <NUM>.

Compared to the linkage <NUM> of <FIG>, the angle between the first and second connectors and (in <FIG>, the angle between the first connector <NUM> and the second connector <NUM>) is larger. The increase in angle increases the tolerance to bearing play of the linkage <NUM> up to an angle of <NUM>°, which is the particular angle between the first connector <NUM> and the second connector <NUM> illustrated in <FIG>. However, this change may result in slightly greater focal changes (e.g., <NUM> vs. <NUM>). In the event that this increase causes the change in focus to become noticeable, the lengths of the first connector <NUM> and the second connector <NUM> may be increased to compensate while the angle therebetween is maintained. The amount of increase in the lengths of the first connector <NUM> and the second connector <NUM> may be limited by the thermal expansion coefficient of the material of the first connector <NUM> and the second connector <NUM>.

To further reduce the amount of bearing play in the linkage <NUM>, it is possible to apply a preload to the bearings. In addition to an axial preload (e.g., with two bearings per pivot point), it is possible to add a spring that is attached to the bottom surface of the carrier body <NUM> at one end and attached to a fixed point (e.g., ground) at the other end. In some examples, the carrier body <NUM> is provided with a slot to allow a bolt (or other fastening mechanism) to lock the linkage <NUM> in place after adjustment. In some examples, the slot may be provided between the first connector <NUM> and the second connector <NUM> in a straight line.

In some implementations, the optical system <NUM> includes a linkage that has a coffin-like shape similar to the shape illustrated in <FIG> and <FIG> with an angle between the first and second connectors of between <NUM>° and <NUM>° and a length sufficient to maintain the required focus. In one particular example, the angle is <NUM>° and the length is greater than or equal to <NUM>.

Regardless of the particular linkage architecture used, various portions of the illumination optics <NUM>, including but not limited to those elements illustrated in <FIG>, may be mounted to the carrier body. <FIG> illustrates one such example of such a configuration using the linkage <NUM> of <FIG>. In <FIG>, a partial optical system <NUM> includes the linkage illustrated in <FIG>, an integrating rod <NUM>, and an illumination lens system <NUM> are mounted on the carrier body <NUM>. In some examples, the integrating rod <NUM> may be a component of the light source <NUM> which receives light from a light emitting element of the light source <NUM>; however, in other examples, the integrating rod <NUM> may be a component of the illumination optics <NUM>. Other methods to create a uniform illumination such as a fly's eye assembly may be used in place of the integrating rod.

The adjustments to the linkage to compensate for deviations in the angle of the DMD <NUM> may be made during a calibration of the projection system <NUM>. The calibration may occur in real-time (e.g., after installation of the projection system <NUM> and before or during image projection) or during manufacture.

<FIG> illustrates an exemplary alignment method, which may be performed during the calibration of the partial optical system <NUM> illustrated in <FIG>. The alignment method of <FIG> may be performed in part or in whole as an automated procedure.

At operation <NUM>, the alignment determines an angle of orientation of the DMD <NUM>. The angle of orientation may be determined directly by, for example, physically measuring the angle of orientation of the DMD <NUM> in the projection system <NUM>. Additionally or alternatively, the angle of orientation may be determined indirectly by, for example, illuminating the DMD <NUM> at a known angle and measuring the output angle of reflected light. In some implementations, operation <NUM> may be performed in a test fixture before the DMD <NUM> is installed on its prism assembly.

At operation <NUM>, the alignment method calculates the appropriate linkage adjustment for the linkage <NUM>, based on the measured angle of orientation of the DMD <NUM>. Operation <NUM> may include first calculating an appropriate rotational and/or translational adjustment to be made to the carrier body <NUM>, and then determining the corresponding linkage adjustment of the linkage <NUM> that would cause such a rotational and/or translational adjustment.

The calculations of operation <NUM> may be carried out at a time of calibration, or may be performed beforehand and stored in a lookup table associated with the projection system <NUM>. In such an implementation, the calibration method may calculate the appropriate rotational and/or translational adjustment by referencing the lookup table instead of by performing calculations at the time of calibration. In other examples, the calibration method may calculate the appropriate rotational and/or translational adjustment at the time of calibration, and may use a lookup table to determine the corresponding linkage adjustment.

After the calculations of operation <NUM>, the alignment method drives the linkage at operation <NUM> to impart the calculated orientation thereon. This actuation may be implemented by using a stepper motor, servo motor, or other appropriate adjustment mechanism as the drive mechanism <NUM>. The drive mechanism <NUM> may be controlled by the controller <NUM> illustrated in <FIG>. Operation <NUM> further includes securing the linkage after it has been driven to the appropriate orientation. In some examples, the securing and/or adjustment of the linkage may be performed manually.

The above projection systems and calibration methods may provide for a configuration having illumination optics which are able to adjust and maintain the proper illumination angle, maintain focus of the aperture, maintain the location of the aperture, and perform all this in an architecture which uses a prism and fold mirror.

With regard to the processes, systems, methods, heuristics, etc. described herein, it should be understood that, although the steps of such processes, etc. have been described as occurring according to a certain ordered sequence, such processes could be practiced with the described steps performed in an order other than the order described herein. It further should be understood that certain steps could be performed simultaneously, that other steps could be added, or that certain steps described herein could be omitted. In other words, the descriptions of processes herein are provided for the purpose of illustrating certain embodiments, and should in no way be construed so as to limit the claims.

Claim 1:
A projection system (<NUM>), comprising:
a light source (<NUM>) configured to emit a light in response to an image data;
an illumination optical system (<NUM>) configured to steer the light, the illumination optical system (<NUM>) including a first mirror (<NUM>) and a second mirror (<NUM>);
a digital micromirror device (<NUM>, <NUM>) including a plurality of micromirrors (<NUM>), wherein a respective micromirror (<NUM>) is configured to reflect the steered light to a filter (<NUM>) as on-state light in a case where the respective micromirror (<NUM>) is in an on position and to reflect the steered light to a light dump as off-state light in a case where the respective micromirror is in an off position, the projection system comprising the filter (<NUM>), wherein the filter includes an aperture (<NUM>); and
a controller (<NUM>) configured to:
determine a deviation between an actual angle of orientation of the digital micromirror device and an expected angle of orientation of the digital micromirror device,
calculate a first amount of angle adjustment corresponding to the first mirror and a second amount of angle adjustment corresponding to the second mirror, and
actuate the first mirror according to the first amount and the second mirror according to the second amount, thereby to maintain a position and a focus of the steered light on the digital micromirror device and to cause the on-state light to be incident within a predetermined distance from a center of the filter.