Patent Application
20070041077
Conventional portable devices with physical display can not increase display size. But the portable device with projector can make a large display. Pocket-sized projectors can make people to see a high-resolution display from a camera, a cellular phone, an organizer, PDA, DVD player, laptop computer, and etc. Power consumption is an important issue for portable devices because the projector draws power from the device such as camera, cellular phone, an organizer, PDA, etc.
Spatial light modulators (SLM) have been used in projection display systems to increase image resolution and display brightness. For example, a Digital Micromirror Device (DMD) array, as described in U.S. Pat. Nos. 5,535,047 and 6,232,936, was used for two-dimensional image projection devices. According to this teaching, each micromirror of the DMD array has single-degree-of-freedom rotation about an axis, and works as a simple optical switch. Since the DMD array is merely an array of optical switches, the direction of light is limited. As shown in
There is a practical need for a pocket-sized two-dimensional image projection system that incorporates the advanced focusing capabilities of micromirror array lenses to improve brightness and power efficiency, and reducing size over existing projection systems. It is desired that such system be easy to manufacture and capable of being used with existing two-dimensional projections systems and devices.
The present invention is directed to a pocket-sized two-dimensional projection device for displaying two-dimensional images. The device comprises one micromirror array lens(MMAL) or array of MMAL. Each MMAL comprises an arbitrary group of micromirrors. The optical property of each group of micromirrors can vary according to the displayed image. The micromirrors are individually controlled electrostatically and/or electromagnetically by actuating components. The micromirrors are provided with three-degree-of-freedom motion; one translational motion along the normal axis to the plane of lens and two rotational motions about the axes in the plane. The translational motion is required to meet the phase matching condition to compensate for aberrations. The two rotational motions are required to deflect and focus the light, and are essential to the versatility of the array of MMAL.
In use, the device comprises a light source that generates collimated light which incidents from the light source to the lens array. The light is reflected from the micromirror array lenses and focused onto a projection surface where the resulting image is viewed. Since each micromirror array lens has the ability to scan the in-focused light along the projection surface, any two or more micromirror array lenses can simultaneously focus incident light onto different positions or at the same position on the projection surface. Because each micromirror array lens can scan the whole projection surface (i.e., focus the incident light at any position on the projection surface), the projected image can be generated.
When a MMAL or array of MMALs is applied to the pocket-sized two-dimensional image projection devices, the size of the device, the brightness of the projected image, and power consumption of the display device are greatly improved over prior art, DMD array devices and other projectors. The array of MMALs can use most incident light by adopting an optimized Random Scanning Technique. In accordance with this technique, a random scanning processor analyses brightness of each frame, and optimizes the focusing position and scanning speed of each micromirror array lens. For the purposes of the present invention, “random” means scanning is not to be sequential. Accordingly, in order to optimize the set of MMAL combinations which can minimize the movement, minimize construction and destruction of MMAL, and minimize scanning length for a frame rate, each micromirror array lens: (a) has an arbitrary number of micromirors; (b) scans a projection surface with different speeds; and (b) focus light at random positions in the projection surface.
The random scanning technique also enables the number of micromirrors to be less than the number of image pixels without deterioration of the resolution of projected images. Therefore, the size of device can be reduced. The gray scale of each pixel is easily achievable by controlling scanning speed and/or by controlling the number of micromirrors of each MMAL.
A MMAL or small sized array of MMALs can be implemented in portable electronic equipments such as mobile phones, personal digital assistants (PDA), camcorder, or even laser pointers. In such devices, a MMAL or the array of MMALs is combined with a laser diode modules and an automatic focusing unit to provide a very small pocket-sized two-dimensional image projector. Such devices also enable users to view large projected images from their mobile phones, personal digital assistants (PDA), and so on.
In conclusion, the advantages provided by the present invention over image projection systems of the prior art are:
It improves brightness and power consumption of a two-dimensional image projection systems;
It provides a portable, pocked-sized, and high quality two-dimensional image projectors;
The present invention may be used in a variety of applications because each micromirror array lens of the array of MMALs can be controlled independently to have different focal length, different optical axis, lens size, and lens shape;
Each micromirror array lens can be controlled to scan a projection surface with different speeds to easily control the light intensity of the displayed image; and
A group of micromirrors of the lens array can be controlled to scan the same point simultaneously to easily control the light intensity of the displayed image.
These and other features, aspects and advantages of the present invention will be better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, wherein:
FIGS. 4(a) and (b) are top views of the micromirror array lenses comprising the lens array of
In a particularly preferred embodiment of the invention, there is provided a pocket-sized two-dimensional image projection device comprising one micromirror array lens(MMAL) or array of MMAL. Each MMAL comprises a plurality of micromirrors, whose configurations may be adjusted to change the focal length, optical axis, lens size, the number of lenses, shape of lens, and others of the micromirror array lens. When applied to conventional two-dimensional display devices, the array of micromirror array lenses greatly improves the brightness of the projected image and the power consumption of the display device by increasing light efficiency and the size of projection device.
Referring to
The lens array 30 may comprise a series of micromirror array lenses 32, 34, and 36 arranged to form a substantially rectangular array. The basic configuration and operational principle of such a lens array is described in U.S. patent application Ser. No. 10/857,714 (filed May, 28, 2004), the entire disclosure of which is incorporated herein by reference.
As shown in FIGS. 4(a) and 4(b), each micromirror array lens comprises an arbitrary number of micromirrors 38 that may vary in size and shape. However, it is preferred that the micromirrors comprise a hexagonal, rectangular, and/or square shape. These shapes enable the micromirrors to be easily fabricated and controlled.
In other embodiments, a cylindrical lens array or mixed lens array comprising cylindrical and/or circular lenses may be constructed.
Each micromirror array lens exists for a given time. According to the image signal, many different micromirror array lenses are “constructed” and “destroyed” within the frame speed.
For example, one image frame may only require that the lens array 30 comprise only one micromirror array lens 32, as shown in
The micromirror array lens 32 produces an in-focus image pixel by converging collimated light 37 into one point M (see
The focal length F of the micromirror array lens 32 is changed by controlling the rotational and/or translational motions of each micromirror 38. Because the micromirrors can have rotational and translational motions, the micromirror array lens can be a Spatial Light Modulator (SLM). The micromirrors retract or elevate to lengthen or shorten the optical path length of light scattered from the image, to remove phase aberrations from the image.
The mechanical structures upholding the micromirrors 38 and the actuating components that rotate and translate the micromirrors are located under the micromirrors to enable the micromirrors to be positioned closer to one another. This increases the effective reflective area of the micromirror array lens 32. Also, electric circuits to operate the micromirrors can be replaced with known microelectronic technologies, such as MOS or CMOS. Applying the circuits under the micromirror array, the effective area can be increased by removing necessary area for the electrode pads and wires used to supply actuating power. Since the micromirrors are small in mass and generate small moments of inertia, their positions and attitudes may be changed at rate of approximately 10 kHz. Therefore, the micromirror array lens becomes a high speed variable focusing lens having a focusing response speed of approximately 10 kHz.
As discussed above, it is desired that each micromirror 38 have a curvature because the ideal shape of a conventional reflective lens has a curvature. However, since the aberration of the micromirror array lens 32 with flat micromirrors is not much different from a conventional lens with curvature if the size of the micromirrors is small enough, there is not much need to control the curvature of the micromirrors.
Accordingly, as shown in
At any given image frame, the optical axis of a micromirror array lens may vary. Similarly, at any given image frame, the number of micromirrors comprising a micromirror array lens and/or the focal length of a micromirror array lens may vary. Since each micromirror array lens has the ability to scan the in-focused light along the projection surface, any two or more micromirror array lenses can simultaneously focus incident light onto different positions or at the same position on the projection surface. Because each micromirror array lens can scan the partial or whole projection surface 60 (i.e., focus the incident light at any position on the projection surface), the projected image can be generated.
Pocket-sized two-dimensional image projection devices of the present invention may apply a random scanning technique (“RST”) to reduce the required number of micromirror array lenses comprising a lens array.
The technique begins with an image signal 110 that is received from an antenna, receiving means, or storage device. The signal is then processed by an image processor that analyses the average brightness of a frame 120. The image processor then analyses brightness of each pixel 130. Next, the image processor calculates the required light intensity and exposure time 140 for each pixel. The image processor then performs optimization 150. Through the optimization, the most optimized set of micromirror array lens combinations which can minimize the movement, minimize construction and destruction of the micromirror array lens, and minimize scanning length for a frame rate is generated. According to the optimized lens combinations, a control command for a frame is generated 160. The control signal is sent to lens array to generate images on the screen. Because the response speed of micromirror array lens (>10 kHz) is much faster than the frame speed (˜30 Hz), a pocket-sized two-dimensional image projection system using array of micromirror array lenses and the random scanning technique can display much more pixels than the number of micromirror array lenses. By changing the number of micromirrors of each micromirror array lens and/or scanning speed (i.e., the duration of light exposure time) of the micromirror array lenses, the gray scale can be expressed easily. The fact that the required number of micromirror array lens is much smaller than the number of pixels makes the array of micromirror array lenses very small in size.
A self diagnosis & correction technique (“SDCT”) may also be applied to a pocket-sized two-dimensional image projection device. During the SDTC, the image processor analyzes the deviations of each spot from a predetermined position and correct the scale factor of the corresponding micromirror. A simplified schematic diagram of the SDCT as applied to a pocket-sized two-dimensional image projection device of the present invention is shown in
This technique starts with the controller 240. The controller generates and sends a set of test signals to the lens array 220. Each of the micromirrors comprising the array is controlled by the test signal, and incident light from the light source 210 is deflected to several predetermined positions 235 along a projection surface 230 by the controlled micromirrors. The image sensor 250 comprises a photo detector that detects the light spots along the projection surface. The image sensor then sends an electrical signal comprising image data to the image processor 260. The image processor also decides the pass or failure for each micromirror. This test will be done for all micromirrors in the lens array. Because the response speeds of the micromirrors are slightly less than 10 kHz, the entire test can be completed for all micromirrors within a short time. The test also can be done while viewers are watching the image device. The test results for all micromirrors in the array is written in the ROM 270 and become reference data for the random signal processing. In the random scanning processing for a pocket-sized two-dimensional image displaying, the failed micromirrors are excluded in construction of micromirror array lenses.
Through the self diagnose process, failed micromirrors are identified. The random scanning processor optimizes the control signals to exclude failed micromirrors in operation and to compensate for aberrations by adjusting the micromirror array lens combination and scanning speed. By the SDCT, the displayed image can be maintained with the same quality even if as many as ten to twenty percent (10-20%) of micromirrors are failed. By applying SDCT, the reliability and operating lifetime of display device can be much improved.
When applying the present invention to a conventional two-dimensional display devices, the brightness of the projected image and power consumption of the display device are greatly improved by increasing light efficiency over prior art display devices. According to the prior art, the DMD array uses at most fifty percent (50%) of incident light because it has “on” and “off” positions. The light is dumped when the mirror is at “off” position. On the contrary, the array of micromirror array lenses can use most incident light by adopting the optimized Random Scanning Technique. In that regard, the most power consuming element in a two-dimensional display device is projection lamp, and light efficiency is directly related to power consumption.
Summarily, the present invention improves the brightness and power consumption of conventional two-dimensional image projection systems. The present invention may be adapted to provide portable, pocked-sized, and high quality two-dimensional image projection devices. Each of the micromirror array lenses may be controlled independently to have different focal length, different optical axis, lens size, and lens shape. This enables the lens array to be applied in many applications. Further, each of the micromirror array lenses may be controlled to scan a projection surface with different speeds, or a group of micromirror array lenses may be controlled to scan the same point on a projection surface simultaneously. This makes easy to control the light intensity on the screen.
The preceding description has been presented with reference to presently preferred embodiments of the invention. Workers skilled in the art and technology to which this invention pertains will appreciate that alterations and changes in the described structure may be practiced without meaningfully departing from the principal, spirit and scope of the invention.
Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and illustrated in the accompanying drawings, but rather should be read consistent with and as support to the following claims, which are to have their full and fair scope.
