Patent Description:
This application relates generally to projection systems and methods of calibrating 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.

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 a small aperture 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 an integrating rod and a fold mirror; a digital micromirror device including a plurality of micromirrors, wherein a respective micromirror is configured to reflect the steered light to a predetermined location 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 a respective micromirror of the plurality of micromirrors of the digital micromirror device and a target angle of orientation of the respective micromirror of the plurality of micromirrors of the digital micromirror device, calculate a first amount of rotational adjustment corresponding to the fold mirror and a second amount of lateral adjustment corresponding to the integrating rod based on the deviation of the actual angle of orientation and the target angle of orientation of the respective micromirror of the plurality of micromirrors of the digital micromirror device, rotate the fold mirror by an angle corresponding to the first amount, and actuate the integrating rod in a first direction according to the second amount, wherein the second amount is based on the first amount and is configured to cause an angle of incidence of the steered light on the respective micromirror to change in response to the deviation and to maintain a position of the steered light on the respective micromirror.

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 an integrating rod and a fold mirror, and a digital micromirror device including a plurality of micromirrors respectively configured to reflect the steered light to a predetermined location 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 a respective micromirror of the plurality of micromirrors of the digital micromirror device and a target angle of orientation of a respective micromirror of the plurality of micromirrors of the digital micromirror device, calculating a first amount of rotational adjustment corresponding to the fold mirror and a second amount of lateral adjustment corresponding to the integrating rod based on the deviation of the actual angle of orientation and the target angle of orientation of the respective micromirror of the plurality of micromirrors of the digital micromirror device, rotating the fold mirror by an angle corresponding to the first direction, and actuating the integrating rod in a first direction according to the second amount, wherein the second amount is based on the first amount and is configured to cause an angle of incidence of the steered light on the respective micromirror to change in response to the deviation and to maintain a position of the steered light on the respective micromirror.

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 an integrating rod and a fold mirror, and a digital micromirror device including a plurality of micromirrors respectively configured to reflect the steered light to a predetermined location 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 a respective micromirror of the plurality of micromirrors of the digital micromirror device and an expected angle of orientation of the respective micromirror of the plurality of micromirrors of the digital micromirror device, calculating a first amount of rotational adjustment corresponding to the fold mirror and a second amount of lateral adjustment corresponding to the integrating rod based on the deviation of the actual angle of orientation and the target angle of orientation of the respective micromirror of the plurality of micromirrors of the digital micromirror device, rotating the fold mirror by an angle corresponding to the first direction, and actuating the integrating rod in a first direction according to the second amount, wherein the second amount is based on the first amount and is configured to cause an angle of incidence of the steered light on the respective micromirror to change in response to the deviation and to maintain a position of the steered light on the respective micromirror.

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 a small aperture stop in the projection optics may be greatly affected by differences in the angle of incidence of the light on the DMD (also referred to as an "input angle"). 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 aperture stop of the projection optics (e.g., a filter aperture). However, the exact position of the angles of the DMD mirrors (e.g., the respective angles of orientation of a DMD mirror in an "on" position and/or an "off" position as will be described in more detail below) may be subject to manufacturing or other tolerances, such that the actual 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 (also referred to as an "exit angle"). 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. Furthermore, as noted above, the image of the integrating rod should be centered on the DMD. Herein, examples of projection systems are described which are capable of adjusting the input angle of a beam to the DMD without changing the focus or position of the image 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>; first projection optics <NUM> configured to receive the third light <NUM> and project it as a fourth light <NUM>; a filter <NUM> configured to filter the fourth light <NUM>, thereby to generate a fifth light <NUM>; and second projection optics <NUM> configured to receive the fifth light <NUM> and project it as a sixth 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, in one implementation, be integrated into a housing to provide a projection device. In other implementations, the projection system <NUM> may include multiple housings. For example, the light source <NUM>, the illumination optics <NUM>, and the DMD <NUM> may be provided in a first housing, and the first projection optics <NUM>, the filter <NUM>, and the second projection optics <NUM> may be provided in a second housing which may be mated with the first housing. In some further implementations, one or more of the housings may themselves include subassemblies. The one or more housings of 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 light. In some implementations, the light is 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 projection 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 an oblique angle.

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. In particular, <FIG> illustrates a plan view of the DMD <NUM>, and <FIG> illustrates partial cross-sectional view of the DMD <NUM> taken along line II-B illustrated in <FIG>. 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). 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 type of 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 a number equal to a resolution of the projection 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 first projection optics <NUM>, the filter <NUM>, and the second projection optics <NUM> (e.g., a predetermined location). 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 <NUM> may be designed and/or controlled to ensure that the angle of incidence on the DMD <NUM> is correct, while maintaining the position of the second light <NUM> centered on the DMD <NUM>.

In one exemplary implementation of the present disclosure, the above may be realized by using an integrating rod and a fold mirror. <FIG> illustrate exemplary optical states of a partial optical system <NUM> in accordance with the present disclosure. The partial optical system <NUM> may be one example, at least in part, of the illumination optics <NUM> and the DMD <NUM>.

In particular, <FIG> illustrates an integrating rod <NUM> or other uniformity correcting device (of which only the output surface is illustrated), a first light <NUM>, a first lens group <NUM>, a second light <NUM>, a fold mirror <NUM>, a third light <NUM>, a second lens group <NUM>, a fourth light <NUM>, and a DMD <NUM>. For explanation purposes, the partial optical system <NUM> in <FIG> is illustrated in an orientation where the first light <NUM> travels generally vertically. Accordingly, the integrating rod <NUM> travels generally horizontally (perpendicular to the first light <NUM>). The integrating rod <NUM> is thus configured for lateral adjustment. The integrating rod <NUM> further has a range of motion defined by a first point and a second point. For example, the integrating rod <NUM> may be configured for movement up to -<NUM> millimeters (mm) and +<NUM> from a starting point (the position of the integrating rod <NUM> illustrated in <FIG>). In some implementations, the integrating rod <NUM> has a lateral size (e.g., diameter, aperture) large enough such that the first light <NUM> passes through the integrating rod <NUM> when the integrating rod <NUM> is positioned at the full extent of its range of motion. For example, the lateral size of the integrating rod <NUM> may be greater than or equal to twice a maximum value of the range of motion. The fold mirror <NUM> is configured for rotational adjustment. The fold mirror <NUM> has a range of motion defined by a third point and a fourth point. For example, the fold mirror <NUM> may be configured for movement among a range of <NUM>° to <NUM>°, where <NUM>° is defined as the fold mirror <NUM> being vertical. In some implementations, the fold mirror <NUM> has a lateral size (e.g., diameter) large enough such that the second light <NUM> reflects off a surface of the fold mirror <NUM> when the fold mirror <NUM> is positioned at the full extent of its range of motion. For example, a lateral size of the fold mirror <NUM> may be sufficiently large such that the light from the light source <NUM> (or the integrating rod <NUM>) remains incident on the fold mirror <NUM> even when the fold mirror <NUM> is at a maximum value of its range of motion and the integrating rod <NUM> is at a maximum value of its range of motion.

The integrating rod <NUM> is situated optically upstream (and thus farther from the DMD) compared to the fold mirror <NUM>. Additionally, the first lens group <NUM> is situated optically upstream compared to the second lens group <NUM>. In some implementations, the fold mirror <NUM> may be positioned after (e.g., downstream) the second lens group <NUM>. 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> (e.g., the light emitted by light source <NUM>). In such examples, the first light <NUM> is internal to the illumination optics <NUM>, and thus is not expressly illustrated in <FIG>. In some examples, the first lens group <NUM>, the fold mirror <NUM>, and the second lens group <NUM> are components of the illumination optics <NUM>, such that the fourth light <NUM> corresponds to the second light <NUM>. In some implementations, optical elements upstream from the integrating rod <NUM> (e.g., some or all optical components of the light source <NUM> and/or the illumination optics <NUM>) may be configured to travel with the integrating rod <NUM>. Such a configuration may be implemented to ensure uniformity and efficiency.

The first lens group <NUM> includes a first lens <NUM> and a second lens <NUM>. The second lens group <NUM> includes a third lens <NUM> and a fourth lens <NUM>. Although shown as including two lenses, the first lens group <NUM> and the second lens group <NUM> may be composed of any number of lenses to direct the first light <NUM> to the DMD <NUM> at the determined angle. Moreover, while each individual lens is separately illustrated, individual lenses within a group may be cemented to one another. Additionally, each lens group may be composed of any type of lenses, such as concave lenses, convex lenses, biconcave lenses, biconvex lenses, planoconcave lenses, planoconvex lenses, negative meniscus lenses, and positive meniscus lenses.

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. In order to provide an appropriate contrast ratio and image clarity, the fourth light <NUM>, once reflected by the DMD <NUM> (i.e., the third light <NUM>), should be centered on a predetermined location such as the aperture (e.g., the first projection optics <NUM>, the filter <NUM>, and the second projection optics <NUM>).

In the state illustrated in <FIG>, the surface of the DMD <NUM> is oriented normally to the fourth light <NUM>. The integrating rod <NUM> and the fold mirror <NUM> are each positioned such that the fourth light <NUM> that exits the second lens group <NUM> is centered on the DMD <NUM>. Typically, a DMD should be illuminated with light at twice the tilt angle of the micromirrors, but for simplicity of demonstrating the principle of this invention, <FIG> shows the fourth light <NUM> contacting the DMD <NUM> at <NUM>° relative to the surface normal of the DMD <NUM>. The first light <NUM> travels along a vertical optical axis from the integrating rod <NUM> to the first lens group <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 first lens group <NUM>. A surface of the first lens group <NUM> receives the first light <NUM> and directs the light, as the second light <NUM>, to the fold mirror <NUM>. A surface of the fold mirror <NUM> reflects the second light <NUM>, as the third light <NUM>, to the second lens group <NUM> such that the fourth light <NUM> is centered on the DMD <NUM>. When the micromirrors <NUM> are "on," the micromirror is tilted at a negative <NUM>°, and the fourth light <NUM> is projected through the projection lens. When the micromirrors <NUM> are "off," the mirror is tilted at a positive <NUM>°, and the fourth light <NUM> is projected to a light dump, as previously described.

In practice, however, any deviation in the nominal tilt angle of the micromirrors of the DMD <NUM> (or the DMD <NUM>) will result in a shift in the point of incidence of the third light <NUM> on the first projection optics <NUM>. Also, the fourth light <NUM> being angled at any other angle other than <NUM>° relative to the surface of the DMD <NUM> may no longer result in the third light <NUM> being centered in the aperture stop <NUM>. These shifts may be counteracted by adjusting the integrating rod <NUM> and the fold mirror <NUM>. For example, as illustrated in <FIG>, the integrating rod <NUM> may shift in a first direction <NUM>. The fold mirror <NUM> may rotate in a second direction <NUM>. The first direction <NUM> is perpendicular (e.g., lateral) to an optical axis of the integrating rod <NUM> (e.g., the direction of the first light <NUM>). The second direction <NUM> is an angular direction that indicates rotation of the fold mirror <NUM>. In <FIG>, the second direction <NUM> is a counter-clockwise, or negative, direction. The shift of the integrating rod <NUM> and the fold mirror <NUM> results in a shift in light, ultimately changing the direction of the fourth light <NUM>. However, movement of the integrating rod <NUM> and the fold mirror <NUM> may maintain the point of incidence of the fourth light <NUM> centered on the aperture. While the point of incidence is centered, the angle of the light is changed based on the amount of movement of the integrating rod <NUM> and the fold mirror <NUM>.

For example, in order to counteract a first exemplary deviation, the fourth light <NUM> as illustrated in <FIG> is angled at <NUM>° relative to the undeviated example of <FIG>, thereby to maintain a centered point of incidence on the DMD <NUM>. To achieve this, the integrating rod <NUM> is adjusted at a first amount (e.g., a first distance) in the first direction <NUM>, and the fold rod <NUM> is adjusted at a second amount (e.g., a second distance) in the second direction <NUM>.

In order to counteract a second exemplary deviation, the fourth light <NUM> as illustrated in <FIG> is angled at -<NUM>° relative to the undeviated example of <FIG>, thereby to maintain a centered point of incidence on the DMD <NUM>. To achieve this, the integrating rod <NUM> is adjusted at a first amount in a third direction <NUM>, and the fold mirror <NUM> is adjusted at a second amount in a fourth direction <NUM>. The third direction <NUM> may be opposite the first direction <NUM>. Additionally, the fourth direction <NUM> may be opposite the second direction <NUM> (e.g., clockwise or positive rotational direction).

The angles and angle adjustments illustrated in <FIG> are illustrative and not limiting. In practice, the particular angles and angle adjustments will depend on several factors including but not limited to tilt angle of the micromirrors of the DMD <NUM>, misalignments within the projection system, and system or performance parameters selected by the user of the system.

<FIG> illustrates an exemplary adjustment or alignment method, which may be performed during the calibration of the partial optical system <NUM> illustrated in <FIG>. The adjustment 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 adjustment method determines an angle of orientation, or a deviation in the angle of orientation from the expected angle, of the DMD micromirrors <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 adjustment method calculates the appropriate amount of lateral adjustment for the integrating rod <NUM> and the appropriate amount of rotational adjustment for the fold mirror <NUM>, based on the measured angle of the DMD micromirrors <NUM>. The appropriate amount of lateral adjustment and rotational adjustment may be the amount which causes the third light <NUM> to be centered on the DMD <NUM> and in the projection aperture <NUM>. The calculations of operation <NUM> may be performed through the use of a computer program that receives a single input (the tilt angle of the DMD micromirrors <NUM>, or the tilt angle of orientation of the DMD micromirrors <NUM> relative to the expected angle) and outputs an amount of lateral adjustment for the integrating rod <NUM> and an amount of rotational adjustment for the fold mirror <NUM>.

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.

After the above calculations of operation <NUM>, at operation <NUM>, the adjustment method actuates the integrating rod <NUM> and the fold mirror <NUM> to implement the calculated adjustments. This actuation may be implemented using a stepper motor, servomotor, or other appropriate adjustment mechanism. For example, the integrating rod <NUM> may be coupled to a first track, and the fold mirror <NUM> may be coupled to a servomotor. The first track and the servomotor may be coupled (e.g., by a mechanical linkage) such that a movement of the integrating rod <NUM> along the first track causes a corresponding movement of the fold mirror <NUM> by the servomotor. The integrating rod <NUM> may be actuated in the first direction <NUM> by actuating the first track such that the integrating rod <NUM> is at a first position, as calculated in operation <NUM>. In another implementation, the integrating rod <NUM> may be actuated in the third direction <NUM> by actuating the first track such that the integrating rod <NUM> is at a second position, as calculated in operation <NUM>. The fold mirror <NUM> may be actuated in the second direction <NUM> by actuating the servomotor such that the fold mirror <NUM> is at a first position, as calculated in operation <NUM>. In another implementation, the fold mirror <NUM> may be actuated in the fourth direction <NUM> by actuating the servomotor such that the fold mirror <NUM> is at a second position, as calculated in operation <NUM>. In the claimed invention, the actuation is performed under the control of the controller <NUM> of <FIG>. In other examples not according to the claimed invention, the actuation is performed under manual control.

<FIG> illustrates an exemplary partial optical system <NUM> for calibrating the projection system <NUM>. Some elements of the system <NUM> are equivalent to elements in the system <NUM> illustrated in <FIG>. Equivalent elements are illustrated using the same reference numerals. The system <NUM> includes the integrating rod <NUM>, the first light <NUM>, the first lens group <NUM>, the second light <NUM>, the fold mirror <NUM>, the third light <NUM>, the second lens group <NUM>, the fourth light <NUM>, and the DMD <NUM>. In some implementations, the partial optical system <NUM> further includes a prism <NUM>, such as a total internal reflection (TIR) prism. Additionally, the system <NUM> includes a fifth light <NUM>, a sixth light <NUM>, a first projection lens <NUM>, a beam splitter <NUM>, a second projection lens <NUM>, a first screen <NUM>, a third projection lens <NUM>, a second screen <NUM>, and an aperture stop <NUM>. The first projection lens <NUM>, the second projection lens <NUM>, and the first screen <NUM> may be the same as or similar to the first projection optics <NUM>, the second projection optics <NUM>, and the screen <NUM> illustrated in <FIG>, respectively. The fifth light <NUM>, represented by the long dash short dash lines, is marginal rays of the system. Where the rays of the fifth light <NUM> converge indicates the location of a projected image of the DMD <NUM>. The sixth light <NUM>, represented by half half dash lines, is chief rays of the system. Where the rays of the sixth light <NUM> converge indicates the aperture stop <NUM> or an image of the aperture stop <NUM>.

The beam splitter <NUM> splits the fifth light <NUM> and the sixth light <NUM> such that the rays of the fifth light <NUM> converge on the first screen <NUM> and the rays of the sixth light <NUM> converge on the second screen <NUM>. Accordingly, the image projected by the DMD <NUM> is reflected on the first screen <NUM>. Specifically, a diffraction pattern projected by the DMD <NUM> may be used for calibrating the projection system <NUM>. The image of the aperture stop <NUM> is projected on the second screen <NUM>. The first screen <NUM> may be, for example, the screen <NUM> of <FIG>. Each image may assist with calibrating the projection system <NUM>. For example, a technician of the projection system <NUM> may view both the diffraction pattern and the actual image of the aperture stop <NUM> on the second screen <NUM> while calibrating the projection system <NUM>. For purposes of calibration or testing, an assembly including the beam splitter <NUM> and the second lens <NUM> may be configured for insertion into the path of the fifth light <NUM> and the second light <NUM>. After calibration is complete, the assembly may be removed from the path.

<FIG> illustrates an exemplary calibration method, which may be performed during the calibration of the partial optical system <NUM> illustrated in <FIG>. The calibration method of <FIG> may be manually performed in order to set the initial positions of the integrating rod <NUM> and the fold mirror <NUM>.

At operation <NUM>, the integrating rod <NUM> and the fold mirror <NUM> are moved to the center of their range of travel. For example, the integrating rod <NUM> may move to the center of the first track, or the center of its range of motion, as previously described. The fold mirror <NUM> may move to the center of its range of motion, such as <NUM>°, as previously described.

At operation <NUM>, a projection aperture filter is installed, such as filter <NUM> of <FIG>. The filter <NUM> may include an aperture configured to pass a predetermined diffractive order, or predetermined illumination angle, of the fourth light <NUM>. For example, the filter <NUM> may include a "Fourier part" or "Fourier lens assembly" which refers to an optical system that spatially Fourier transforms modulated light (e.g., light from the DMD <NUM>) by focusing the modulated light onto a Fourier plane. The spatial Fourier transform imposed by the Fourier part converts the propagation angle of each diffraction order of the modulated light to a corresponding spatial position on the Fourier plane. The Fourier part thereby enables selection of desired diffraction orders, and rejection of undesired diffraction orders, by spatial filtering at the Fourier plane. For example, the Fourier part may be configured to pass projected light at an angle of <NUM>°. The spatial Fourier transform of the modulated light at the Fourier plane is equivalent to a Fraunhofer diffraction pattern of the modulated light.

At operation <NUM>, the fold mirror <NUM> is adjusted until the center of the diffraction pattern from the DMD <NUM> is centered on the second screen <NUM>. For example, the fifth light <NUM> may be a random noise pattern. When the fifth light <NUM> is projected onto the second screen <NUM>, the viewed diffraction pattern (e.g., spatial frequency) is asinc<NUM> function. As the fold mirror <NUM> is rotationally adjusted, the diffraction pattern of the fifth light <NUM> shifts. Once the diffraction pattern is centered, the fold mirror <NUM> is at a final calibration position. However, the image projected on the first screen <NUM> may no longer be fully illuminated. At operation <NUM>, the integrating rod <NUM> is adjusted until the image of the random noise pattern from the DMD <NUM> is fully illuminated on the first screen <NUM>. Once the DMD <NUM> is fully illuminated, the integrating rod <NUM> is at a final calibration position. The final calibration positions of the integrating rod <NUM> and the fold mirror <NUM> are stored in the memory of the controller <NUM> (e.g., the look-up table) as initial positions of the integrating rod <NUM> and the fold mirror <NUM>.

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 position of the illumination, and perform all this in an architecture which uses a an integrating rod and a 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.

Accordingly, it is to be understood that the above description is intended to be illustrative and not restrictive. Many embodiments and applications other than the examples provided would be apparent upon reading the above description. The scope of the invention should be determined with reference to the appended 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 including an integrating rod (<NUM>) and a fold mirror (<NUM>);
a first lens group (<NUM>) optically arranged between the integrating rod and the fold mirror;
a digital micromirror device (<NUM>, <NUM>, <NUM>) including a plurality of micromirrors (<NUM>), wherein a respective micromirror is configured to reflect the steered light to a predetermined location as on-state light (<NUM>) 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 (<NUM>) in a case where the respective micromirror is in an off position, wherein the light is projected onto the digital micromirror device at a first position;
a second lens group (<NUM>) is optically arranged between the fold mirror and the digital micromirror device; and
a controller (<NUM>) configured to:
determine a deviation between an actual angle of orientation of a respective micromirror of the plurality of micromirrors of the digital micromirror device and a target angle of orientation of the respective micromirror of the plurality of micromirrors of the digital micromirror device,
calculate a first amount of rotational adjustment corresponding to the fold mirror and a second amount of lateral adjustment corresponding to the integrating rod based on the deviation of the actual angle of orientation and the target angle of orientation of the respective micromirror of the plurality of micromirrors of the digital micromirror device,
rotate the fold mirror using a first actuator by an angle corresponding to the first amount, and
actuate the integrating rod using a second actuator in a first direction (<NUM>) according to the second amount,
wherein the second amount is based on the first amount and is configured to cause an angle of incidence of the steered light on the respective micromirror to change in response to the deviation and to maintain a position of the steered light on the respective micromirror.