Abstract:
A pen plotter capable of producing large 3-D stereo plots is described. The operating principles is based on micro-polarizer arrays and spatial multiplexing. Because of the vector based plotting and the continuous transfer of the ink from the pen to the paper, previous methods for making 3-D stereo printing cannot be used. Instead, a new &#34;pixel skipping pen&#34; and paper combination are devised which exploit the fact that water and oil do not mix. Dedicating oil-based inks for plotting the right perspectives on hydrophobic coating on the plotter paper, while water-based inks for plotting the left perspectives on hydrophilic coating, makes it possible to achieve 3-D stereo plotting with automatic registration on a single component 3-D plotting paper. Two other kinds of 3-D plotting papers are devised which use two and three specially treated sheets that are registered with pins.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates in general to the field of computer hard copy output devices. In particular it relates to pen plotters used to provide hardcopies for computer aided design, drafting and graphics. 
     2. Description of Related Art 
     All living creatures are endowed with a pair of eyes for 3-D stereoscopic vision. They have depended on this vision for their survival. Yet, in spite of the tremendous advances in information technology, there is no prior art teaching how to obtain hardcopy outputs from computers in the form of 3-D stereo plots. My co-pending application Ser. No. 7/554,742 teaches methods for producing 3-D stereo computer printers based on the micro-polarizer arrays and spatial multiplexing principles described in my co-pending applications Ser. No. 7/536,190, and Ser. No. 7/536,419. However, because pen plotters depend on the continuous transfer of ink from the pen onto the paper, the 3-D stereo printer operating principles described in Ser. No. 7/554,742 will not work for pen plotters. Therefore, there remains a need for generating large 3-D stereo plots for architectural and mechanical designs for which pen plotters are particularly suited. 
     SUMMARY OF THE INVENTION 
     The principal object of the present invention is to provide a 3-D stereo pen plotter which is based on micro-polarizer arrays (μPol) and spatial multiplexing. It comprises: 
     Means for manufacturing a special plotting paper having self-aligned features of the spatially multiplexed image with respect to the μPol. This plotting paper is based on the fact that water and oil do not mix and on the use of hydrophobic and hydrophillic coatings; and 
     Novel pen design which, even though continuously presses on the plotting paper, it plots only in the space intended for one perspective image, while skipping the space of the other perspective, to be filled with a different pen. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1a illustrates the principles behind the stereo plotter, spatial modulation and spatial multiplexing of the left and right images. 
     FIGS. 1b and 1c illustrate the use of micropolarizer sheets for demultiplexing and stereo viewing of the printed image by means of polarized spectacles. 
     FIGS. 2a-c show the 3-D stereo plot made of laminating a plotted micropolarizer sheet with a polarization preserving aluminum coated paper. 
     FIG. 3 shows the schematically the components of a pen plotter. 
     FIGS. 4a-c illustrate the manufacturing steps for producing a self-aligned μPol plotting paper. 
     FIG. 5 shows another plotting paper embodiment which is based on 2 components and registration pins. 
     FIG. 6 shows a third plotting paper embodiment which is based on 3 components and registration pins. 
     FIGS. 7A-B illustrate the special &#34;pixel skipping&#34; pens and their use in producing plots on a single component μPol 3-D plotting paper. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The invention is based on two fundamentally new concepts combined for the first time to record and display 3-D images. They are: Spatial Multiplexing of left and right images and Micro-Polarizers. These are described in my co-pending applications: &#34;A System For Producing 3-D Stereo Images&#34;, Ser. No. 536,190, and &#34;Methods For Manufacturing Micropolarizers&#34;, Ser. No. 536,419. FIG. 1a illustrates the spatial multiplexing principles. The data representing the left and right images are stored in a bit map format (other formats may also be used) in left memory array 1 (L-RAM), and right memory array 2 (R-RAM) respectively. Each pixel in the array has N-bits for color and gray-scale. Using a spatial checkerboard modulator MOD 3, the left image 1 is modulated and stored in the array 5. The right image is spatially modulated using the compliment of MOD 4 to produce the compliment pattern stored in array 6. The modulated images 5 and 6 are combined (multiplexed) using a spatial multiplexer 7 and the spatially multiplexed image (SMI) is stored in the array 8. The SMI 8 shows a combined left and right images side by side on a pixel by pixel basis and therefore caries the stereo information. The flow diagram of FIG. 1a is an algorithm to produce the SMI which can be implemented either in hardware or in software. In FIG. 1b the SMI 8 is combined with a spatial demultiplexer 9, a micropolarizer, μPol sheet described in applications Ser. Nos. 536,190, and 536,419 and a polarization decoder 10, a pair of spectacles with polarization states P1 and P2. The SMI and the μPol arrays 9 which have the same period are aligned such that the left pixels in the SMI illuminate the P2 cells in the μPol array and the right pixels illuminate the P1 cells. Thus, the left pixels become P2 polarized and the right pixels become P1 polarized. Because of the discriminating ability of the polarized eye glasses, the left eye which has a P2 polarizer can seen only the P2-polarized left pixels, and the right eye which has a P1 polarizer can see only the P1-polarized right pixels. To achieve the 3-D stereo sensation the human brain fuses the left and right images in the same manner it deals with natural 3-D scenes. FIG. 1c shows that the SMI 8 may also be placed top of the μPol. Choosing between the configurations of FIG. 1b and FIG. 1c depends on how the SMI is illuminated, and whether the transmissive mode or reflective mode of display is used; see Ser. No. 536,190. 
     To build a hardcopy plotter to output images from computers in stereo the above concept is used in conjunction with the principles taught in the embodiments described here. FIGS. 2a and 2b show how the final desired hardcopy stereo output is obtained. It comprises two sheets 11 and 12 laminated together to produce the output plot 16. The first sheet 11 is a μPol 9 on which the SMI 8 is plotted after proper alignment is ensured. The second sheet 12 consists of regular paper 13, coated with aluminum or silver flakes 14 and a clear adhesive layer 15. The aluminum or silver layer is needed to preserve the polarization and maximize the brightness. If paper only was used in 13, the polarized light striking its surface becomes depolarized and as it emerges from the μPol layer its brightness is reduced by at least 50%. FIG. 2c shows another simpler embodiment which eliminates the sheet 12 but achieves the same result by directly coating the back of the μPol 9 with a silver or aluminum film 14. 
     There are two classes of polarizer polymers; the absorptive class such as polyvinyl alcohol, PVA, and the reflective class such as cholesteric liquid crystal silicone, CLCS (see Robert Maurer et al, Society of Information Display SID 90 Digest, p. 110, 1990, and Martin Schadt, and Jurg Funfschilling, SID 90 Digest, p. 324, 1990). The absorptive class converts unpolarized light to linearly polarized light of state P1 by absorbing the orthogonal state P2. This absorbed light energy is converted to heat and is lost for ever. The polyvinyl alcohol, PVA, used to construct the μPols in Ser. Nos. 536,190, and 536,419 belongs to the absorptive class. Hard copies based on the absorptive class, in general, lose at least 50% of the illuminating light. The reflective class separates the incident unpolarized light into two circularly polarized states P1 and P2, one state P1 is transmitted and the other state P2 is reflected. In this case no light energy is lost to heat and therefore it is possible to convert 100% of the incident light into polarized light with the desired state of polarization. This is done by coating a sheet of CLCS with a reflective metallic film on one side, and illuminating it on the other side with unpolarized light. 50% of this light is reflected as P1, and the other 50% is transmitted as P2. This P2 light is then reflected by the metallic layer and converted into P1 (it is well known in the field of optics that a circularly polarized light of one state is converted to the orthogonal state as a result of reflection), thus all the incident light is converted to polarized light of state P1. This reflective class of polarizers when used to fabricate μPols, provides at least a factor of 2 brighter 3-D stereo plots than the absorptive class. 
     FIG. 3 illustrates schematically a pen plotter 17. Its main components are: the pen 18 which can be moved in the positive and negative X directions by means of an electromechanical X motion controller 20a; the paper 19 which can be moved in the positive and negative Y directions by means of an electromechanical Y motion controller 20b, and the computer 21. The computer translates the image to be plotted to vector quantities, and supplying the X and Y coordinates to the X and Y motion controllers relative to an initial position. Typical plotters also include a pen cartridge which holds 8 pens of different colors each of which is activated in turn for plotting. The main advantage of plotters over printers, is their ability to produce extremely wide and long plots. However, because conventional pen plotting is based on continuous ink transfer from an initial potion to a final position, spatial multiplexing of images is not possible unless a &#34;pixel skipping pen&#34; is found. 
     The &#34;pixel skipping pen&#34; concept is implemented by means of a special plotting paper manufactured according to the self-aligned process shown in FIG. 4. The μPol sheet 9 (FIG. 4a) is coated with a hydrophobic layer 23 (an oil based coating which repels water, similar to the coating used in making offset printing plates) and a photoresist layer 22. The laminate is exposed with a light source 25 through a sheet polarizer 24 with polarization state P2. The photoresist covering the P1 parts of the μPol 9 are not exposed by the P2 polarized light because the P1 parts do not transmit the P2 state. On the other hand the photoresist covering the P2 parts of the μPol 9 are exposed by the P2 polarized light because the P2 parts do transmit the P2 state. The next step FIG. 4b, is to develop the photoresist and chemically etch away the hydrophobic coating 23, leaving the P2 parts 26 of μPol 9 exposed. These exposed parts are hydrophilic, i.e., they attract water. The final step FIG. 4c is the removal of the photoresist, producing the final 3 -D plotting paper. FIG. 5 shows a second method for producing a 3-D plotting paper using two components 9a and 9b. These components are registered by means of registrations pins 28 going through the registration holes 27. The pins and holes are located in a least two locations in both 9a and 9b. The patterning of the coating 23 on 9a is accomplished by the same self-alignment method described in FIG. 4. The patterning of the coating 23 on 9a is also accomplished by the same self-alignment method described in FIG. 4, except for replacing the sheet polarizer P2 with a sheet polarizer P1. FIG. 6 shows yet a third method for producing a 3-D plotting paper using three components: clear plastic films 29a, 29b, and a μPol sheet 9. These components are registered by means of registrations pins 28 going through the registration holes 27. The pins and holes are located in a least two locations in 9, 29a, and 29b. The patterning of the coating 23 on 29a is accomplished by the same self-alignment method described in FIG. 4. The patterning of the coating 23 on 29b is also accomplished by the same self-alignment method described in FIG. 4 except for replacing the sheet polarizer P2 with a sheet polarizer P1. 
     3-D stereo plotting is demonstrated in FIG. 7a, using the single component plotting paper produced by the process described in FIG. 4, and a special pen design 36. The pen 36 has an oil-based ink 37 surrounded by a clear water based liquid 38. The purpose of the water-based liquid is to wet the hydrophilic regions on the P2 parts of μPol 9 before they are contacted by the center oil-based ink 37, making the water-wetted P2 parts forbidden to the oil ink. In the mean time, the coating 23 covering the P1 parts is hydrophobic, it repels the water-based liquid 38 and attracts the oil-based ink 37. The overall result is a pen that plots the P1 parts and skips the P2 parts. In order to achieve spatial multiplexing, the oil-based &#34;pixel skipping pen&#34; 36 plots only the right image on the P1 parts. In FIG. 7b, another water-based ink pen 39 is used to plot the left image only on the hydrophilic P2 parts while skipping the hydrophobic P1 pixels. Thus spatial multiplexing of the left and right perspectives is completed using pen plotting with automatic registration. 
     The second and third 3-D plotting papers in FIG. 5 and FIG. 6 do not require the special pen 36, instead, they use regular pens with either water-based inks or oil-based-inks. However, in this case plotting one perspective requires the removal of one layer, and then putting it back for plotting the second perspective. The registration pins 28 ensure proper alignment all the time.