Patent Publication Number: US-2023150200-A1

Title: Use of Dye-Type Polarizers in a Photopolymer Curing Device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This U.S. non-provisional patent application claims priority under 35 U.S.C. § 119(e) to U.S. provisional application 63/263,950 filed on Nov. 12, 2021 and to U.S. provisional patent application 63/266,733 filed on Jan. 13, 2022, the disclosures of which are considered part of the disclosure of this application and are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     This disclosure relates to a liquid crystal panel with enhanced polarizers for use in an additive fabrication system. 
     BACKGROUND 
     Additive fabrication, e.g., three-dimensional (3D) printing, provides techniques for fabricating objects, typically by causing portions of a building material to solidify at specific locations. Additive fabrication techniques may include stereolithography, selective or fused deposition modeling, direct composite manufacturing, laminated object manufacturing, selective phase area deposition, multi-phase jet solidification, ballistic particle manufacturing, particle deposition, laser sintering or combinations thereof. Many additive fabrication techniques build parts by forming successive layers, which are typically cross-sections of the desired object. Typically each layer is formed such that it adheres to either a previously formed layer or a build surface upon which the object is built. 
     In one approach to additive fabrication, known as stereolithography, solid objects are created by successively forming thin layers of a curable polymer resin, typically first onto a build surface and then one on top of another. Exposure to actinic radiation cures a thin layer of liquid resin, which causes it to harden and adhere to a bottom surface of the build surface or a previously cured layer on the bottom surface of the build surface. 
     Stereolithography printers generally contain a vat of photocurable resin that can be cured when the resin interacts with light, usually in the near ultraviolet (UV) wavelength (e.g., 365-415 nm), predominantly at 405 nm. Historically, lasers were used for light delivery, but in recent years, area projection technologies such as digital light processing (DLP) and liquid crystal display (LCD) have been used for light delivery. LCD optical systems consist of a UV backlight which transmits light through an LCD screen from the display industry. The LCD screen is used as a spatial mask layer by layer to trace out the geometry of each layer of the component to be printed. 
     SUMMARY 
     An aspect of the disclosure provides a curing system for an additive fabrication system. The curing system includes a light source, a liquid crystal cell, and a first polarizer. The light source is configured to emit light at a wavelength suitable for curing a photopolymerizable material. The liquid crystal cell is configured to receive the light from the light source. The first polarizer is disposed between the light source and the liquid crystal cell, wherein the first polarizer includes a polyvinyl alcohol (PVA) matrix and an organic dye impregnated into the PVA matrix. 
     This aspect of the disclosure may include one or more of the following optional features. In some examples, the wavelength of the light source is between 365 nm and 415 nm. In some examples, the light source is configured to provide a flux greater than 20 mW/cm 2  at the first polarizer. In some implementations, the light source is configured to provide a flux greater than 2 mW/cm 2  at the photopolymerizable material. In some configurations, the first polarizer is configured to operate at a temperature range from 10 to 120 degrees Celsius. 
     Optionally, the organic dye comprises at least one dye made from one or more of metal diazo compounds, trisazo compounds, biphenyldiazo, trisazo or disazomonoazoxy compounds, or metal-containing biphenyldisazo, trisazo or disazomonoazoxy compounds. In some examples, the first polarizer is spaced apart from the liquid crystal cell by a first distance. In some implementations, the first polarizer is laminated to the liquid crystal cell. In some configurations, the first polarizer is configured to be decoupled from the curing system. 
     In some examples, the light source comprises a high-power light emitting diode. In some implementations, a light-receiving surface of the liquid crystal cell has a size equal to or greater than a size of a light-emitting surface of the first polarizer. 
     In some configurations, the system further includes a collimating lens between the light source and the first polarizer. In some implementations, the system includes a diverging lens between the first polarizer and the liquid crystal cell. 
     In some configurations, the system includes a second polarizer situated on an opposite side of the liquid crystal cell compared to the first polarizer. In some examples, the second polarizer includes a PVA matrix and an organic dye impregnated into the PVA matrix. In some configurations, the second polarizer is spaced apart from the liquid crystal cell by a second distance. In some implementations, the second polarizer is laminated on the liquid crystal cell. In some examples, the second polarizer is configured to be decoupled from the curing system. 
     Another aspect of the disclosure provides a method of additive fabrication for curing a photopolymerizable material. The method includes a light source configured to emit light at a wavelength suitable for curing the photopolymerizable material. The light is received at a liquid crystal cell and polarized at a first polarizer disposed between the light source and the liquid crystal cell. The first polarizer includes a polyvinyl alcohol (PVA) matrix and an organic dye impregnated into the PVA matrix. In some examples, the method includes polarizing the light at a second polarizer disposed on an opposite side of the liquid crystal cell as the first polarizer. The second polarizer includes a polyvinyl alcohol (PVA) matrix and an organic dye impregnated into the PVA matrix. 
     The details of one or more implementations of the disclosure are set forth in the accompanying drawings and the description below. Other aspects, features, and advantages will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG.  1 A  shows a perspective view of an example additive fabrication system, where the system is arranged in an initial configuration. 
         FIG.  1 B  shows a perspective view of an example additive fabrication system, where the system is arranged in a fabricating configuration. 
         FIG.  1 C  shows a perspective view of an example additive fabrication system, where the system is arranged in a finished configuration. 
         FIG.  2 A  shows a perspective view of an example base of the additive fabrication system of  FIG.  1 A . 
         FIG.  2 B  shows a perspective view of the base of  FIG.  2 A , where components of a curing system of the base are partially sectioned to show a configuration of the curing system. 
         FIG.  3    is an exploded view of an example liquid crystal panel. 
         FIG.  4    is an exploded view of another example of a liquid crystal panel. 
         FIG.  5    is a schematic sectional view of an example polarized light generation system. 
         FIG.  6    is a schematic sectional view of another example of polarized light generation system. 
         FIG.  7    is a schematic sectional view of additional example of polarized light generation system. 
         FIG.  8    is a schematic sectional view of additional example of polarized light generation system. 
         FIG.  9    is a flowchart of an example arrangement of operations for a method curing a photopolymer resin. 
         FIG.  10    is a schematic partial sectional view of UV light measurement system. 
         FIG.  11    shows a perspective view of an example base including a plurality of photodiodes. 
     
    
    
     Like reference symbols in the various drawings indicate like elements. 
     DETAILED DESCRIPTION 
     The present disclosure relates to a curing system for an additive fabrication device (i.e., a 3D printer) that incorporates a liquid crystal panel configured to emit unfiltered monochromatic light to transform a liquid photopolymer resin into a solid layer of a fabricated component. Unlike conventional additive fabrication systems, which may include curing systems having lasers or DLP projectors, the curing system of the present disclosure includes the liquid crystal panel disposed adjacent to a basin that holds the liquid photopolymer resin to be cured. The liquid crystal panel is configured to emit unfiltered monochromatic light to the photopolymer resin within the basin at an optimal wavelength for curing the photopolymer resin. Using a liquid crystal panel according to the present disclosure offers the advantages over conventional laser and DLP curing systems, such as providing a high-resolution (e.g., up to 7,680×4,320 pixels) dimensional grid with a minimized optical path between the liquid crystal panel and the fabricated layer of the component. Reducing the optical path minimizes potential thermal drift between the curing system and the resin within the basin, ensuring a more precise definition of the fabricated part. 
     Referring to  FIGS.  1 A- 1 C , an additive fabrication device  100 , such as a stereolithographic printer, includes a base  110  and a dispensing system  120  coupled to the base  110 . The base  110  supports a fluid basin  130  configured to receive a photopolymer resin from the dispensing system  120 . The printer  100  further includes a build platform  140  positioned above the fluid basin  130  and operable to traverse a vertical axis (e.g., z-axis) between an initial position ( FIG.  1 A ) adjacent to a bottom surface  132  of the fluid basin  130  and a finished position ( FIG.  1 C ) spaced apart from the bottom surface  132  of the fluid basin  130 . 
     The base  110  of the printer  100  may house various mechanical, optical, electrical, and electronic components operable to fabricate objects using the device. In the illustrated example, the base  110  includes a computing system  150  including data processing hardware  152  and memory hardware  154 . The data processing hardware  152  is configured to execute instructions stored in the memory hardware  154  to perform computing tasks related to activities (e.g., movement and/or printing based activities) for the printer  100 . Generally speaking, the computing system  150  refers to one or more locations of data processing hardware  152  and/or memory hardware  154 . For example, the computing system  150  may be located locally on the printer  100  or as part of a remote system (e.g., a remote computer/server or a cloud-based environment). 
     The base  110  may further include a control panel  160  connected to the computing system  150 . The control panel  160  includes a display  162  configured to display operational information associated with the printer  100  and may further include an input device  164 , such as a keypad or selection button, for receiving commands from a user. In some examples, the display is a touch-sensitive display providing a graphical user interface (GUI) configured to receive the user commands from the user in addition to, or in lieu of, the input device  164 . 
     The base  110  houses a curing system  170  configured to transmit actinic radiation into the fluid basin  130  to incrementally cure layers of the photopolymer resin contained within the fluid basin  130 . The curing system  170  may include a projector or other radiation source configure to emit light at a wavelength suitable to cure the photopolymer resin within the basin. Thus, different light sources may be selected depending on the desired photopolymer resin to be used for fabricating a component C. In the present disclosure, the curing system  170  includes a liquid crystal panel  200  for curing the photopolymer resin within the fluid basin  130 . 
     As shown, the fluid basin  130  is disposed atop the base  110  adjacent to the curing system  170  and is configured to receive a supply of the resin R from the dispensing system  120 . The dispensing system  120  may include an internal reservoir  124  providing an enclosed space for storing the resin R until the resin R is needed in the fluid basin  130 . The dispensing system  120  further includes a dispensing nozzle  122  in communication with the fluid basin  130  to selectively supply the resin R from the internal reservoir  124  to the fluid basin  130 . 
     The build platform  140  may be movable along a vertical track or rail  142  (oriented along the z-axis direction, as shown in  FIGS.  1 A- 1 C ) such that the base-facing build surface  144  of the build platform  140  is positionable at a target distance D 1  along the z-axis from the bottom surface  132  of the fluid basin  130 . The target distance D 1  may be selected based on a desired thickness of a layer of solid material to be produced on the build surface  144  of the build platform  140  or onto a previously formed layer of the component C being fabricated. In some implementations, the build platform  140  may be removable from the printer  100 . For instance, the build platform  140  may be removably attached to the rail  142  by an arm  146  (e.g., pressure fit or fastened onto) and may be selectively removed from the printer  100  so that the fabricated component C attached to the build surface  144  can be removed via the techniques described above. 
     In the example of  FIGS.  1 A- 1 C , the bottom surface  132  of basin  130  may be transparent to actinic radiation that is generated by the curing system  170  located within the base  110 , such that liquid photopolymer resin located between the bottom surface  132  of the basin  130  and the build surface  144  of the build platform  140  or the component C being fabricated thereon, may be exposed to the radiation. Upon exposure to such actinic radiation, the liquid photopolymer may undergo a chemical reaction, sometimes referred to as “curing,” that substantially solidifies and attaches the exposed resin to the build surface  144  of the build platform  140  or to a bottom surface of the component C being fabricated thereon. 
     Following the curing of a layer of the fabrication material, the build platform  140  may incrementally advance upward along the rail  142  in order to reposition the build platform  140  for the formation of a new layer and/or to impose separation forces upon any bond with the bottom surface  132  of basin  130 . In addition, the basin  130  is mounted onto the base  110  such that the printer  100  may move the basin  130  along a horizontal axis of motion (e.g., x-axis). In an implementation, this motion may advantageously introduce additional separation forces. A wiper  134  is additionally provided, capable of motion along the horizontal axis of motion and which may be removably or otherwise mounted onto the base  110  or the fluid basin  130 . 
     With continued reference to  FIGS.  1 A- 1 C , the printer  100  is shown at different stages of the fabrication process. For example, at  FIG.  1 A , the printer is shown in an initial state prior to dispensing the resin R into the basin  130  from the reservoir  124  of the dispensing system  120 . Upon receipt of fabrication instructions, the printer  100  positions the build surface  144  of the build platform  140  at an initial distance D 1  from the bottom surface  132  of the basin  130  corresponding to a thickness of the first layer of resin R to be cured. The curing system  170  then emits an actinic radiation profile (i.e., an image) corresponding to the profile of the current layer of the component C to cure the current layer. Upon curing of the current layer, the build platform  140  incrementally advances upward along the z-axis to the next build position. The distance of each advancement increment corresponds to a thickness of the next layer to be fabricated. The curing system  170  then projects the profile of the component layer corresponding to the new position. The new component layer is cured on a bottom surface of the previous component layer. The curing and advancing steps repeat until the build platform  140  reaches the final position (see  FIG.  1 C ) corresponding to the finished component C. 
     Referring to  FIGS.  2 A and  2 B , the base  110  of the printer  100  is illustrated without the dispensing system  120 , the basin  130 , and the build platform  140  to show the curing system  170 .  FIG.  2 A  provides a perspective view of the base  110  and curing system  170  in a completed state while  FIG.  2 B  provides a perspective view of the base  110  showing the curing system  170  in partial sectional views to expose the interior components of the liquid crystal panel  200  of the curing system  170 .  FIG.  3    further provides a schematic view of the liquid crystal panel  200 . Note that, ratios among length, width, and thickness of each member in  FIGS.  2 A- 3    are different from those of an actual curing system  170  for clarity. 
     Referring to  FIGS.  1 A- 3   , the curing system  170  is configured to provide actinic radiation through the bottom surface  132  of the basin  130  to cure a layer of the photopolymer resin within the basin  130 . The curing system  170  of the present disclosure includes the liquid crystal panel  200  disposed adjacent to the basin  130 . Unlike conventional additive fabrication systems, which may include curing systems based on lasers or DLP projectors, use of the liquid crystal panel  200  offers the advantage of providing a high-resolution (e.g., up to 7,680×4,320 pixels) dimensional grid with a minimized optical path between the panel  200  and the bottom surface  132  of the basin  130 . Reducing the optical path minimizes potential thermal drift between the curing system  170  and the resin within the basin, ensuring more precise definition of the fabricated component C. 
     While off-the-shelf liquid crystal panels are available, these panels are typically optimized to output visible light for displaying an image for observation by the human eye. Thus, known liquid crystal panels (e.g., televisions or display monitors) generally emit various color components (e.g., blue, green, or red) within the visible part of the electromagnetic spectrum (e.g., 400 nm to 750 nm). However, many photopolymer resins used with additive fabrication devices  100  may be optimized to cure using a wavelength of between 365 nm and 415 nm. Because conventional liquid crystal panels are optimized to emit visible light, only approximately 1% of the light emitted from a conventional liquid crystal panel is output at the 365-415 nm wavelength. Accordingly, while functional, conventional liquid crystal panels are inefficient for use in a curing system  170 , as curing rates would be significantly slower than known systems (e.g., lasers, DLP) using comparable amounts of power (e.g., Watts). 
     The liquid crystal panel  200  of the present disclosure is optimized to provide a greater optical transmission efficiency (e.g., greater than 10%) compared to optical transmission rates of conventional liquid crystal panels (e.g., approximately 1%), particularly with respect to wavelengths typically used for curing photopolymer resins (e.g., approximately 405 nm). With reference to  FIGS.  2 B and  3   , the liquid crystal panel  200  includes a light unit  210 , a liquid crystal cell  220 , a first polarizer  230  disposed between the liquid crystal cell  220  and the light unit  210 , and a second polarizer  240  disposed on an opposite side of the liquid crystal cell  220  than the first polarizer  230 . The liquid crystal panel  200  may further include one or more glass layers  250  to provide support and protection for the liquid crystal panel  200 . Unlike conventional liquid crystal panels, which may further include a color filter disposed between the liquid crystal cell  220  and the second polarizer  240 , the liquid crystal panel  200  of the present disclosure does not include any color filter between the liquid crystal cell  220  and the second polarizer  240 . Thus, the second polarizer  240  is disposed immediately adjacent to the liquid crystal cell  220  and receives unfiltered light directly from the liquid crystal cell  220 . 
     The light unit  210  of the liquid crystal panel  200  includes a monochromatic light source  212  configured to emit an unpolarized light. In some implementations, the light source  212  is configured as a backlight provided adjacent to the first polarizer  230 . Furthermore, the light source  212  may be selected to emit light in a wavelength corresponding to the wavelength for curing the photopolymer resin. For example, where the resin is curable at a wavelength of 405 nm, the light source  212  may be selected or tuned to emit a 405 nm wavelength light. Accordingly, the light source  212  emits an unpolarized, monochromatic light having a wavelength suitable for curing the resin. In the illustrated example, the light source  212  includes a panel having an array of light-emitting diodes (LEDs)  214 . However, other light sources may be implemented as alternative or in addition to the panel array, including edge-lit LEDs and/or cold cathode fluorescent lamps. As discussed below, known light sources suitable for use in the light unit  210  generally have an optical transmission efficiency of approximately 50%, which must be accounted for when determining the overall optical efficiency of the curing system (see Table 1, below). 
     Referring to  FIG.  3   , the liquid crystal cell  220  includes a liquid crystal layer  222  and a substrate  224  disposed between the first polarizer  230  and a first side of the liquid crystal layer  222 . The liquid crystal layer  222  may include liquid crystal molecules arranged in a twist alignment in the absence of an electric field. The twist alignment generally refers to an alignment in which liquid crystal molecules in a liquid crystal layer are arranged substantially in parallel to the surface of the substrate  224 , and the arrangement direction thereof is twisted at a predetermined angle (e.g., 90° or 270°) on the substrate surface so that light reaching the second polarizer  240 , which is also oriented at the predetermined angle, can pass through the second polarizer  240  in the absence of the electric field at the liquid crystal layer  222 . Typical examples of the liquid crystal cell having a liquid crystal layer in such an alignment state include a liquid crystal cell  220  of a twisted nematic (TN) mode, a supertwisted nematic (STN) mode, in-plane switching (IPS), or an enhanced black nematic (EBN) mode. 
     The substrate  224  may include a plurality of switching elements  226  (e.g., thin-film transistors) each respectively associated with a pixel of the liquid crystal panel  200 . The switching elements  226  are selectively turned on and off to control whether a specific pixel of the liquid crystal panel  200  will be illuminated by twisting the corresponding liquid crystal of the liquid crystal layer  222 . Thus, in use, each of the switching elements  226  receives instructions from the computing system  150  corresponding to a profile P (see  FIG.  4   ) of a current build layer of the component C. The switching elements  226  of the substrate  224  are then switched on and off to illuminate pixels of the liquid crystal panel  200  corresponding to the profile P of the build layer. Specifically, when a switching element  226  is switched off, the light passing through liquid crystal corresponding to the switching element  226  is rotated such that it passes through the second polarizer  240  to illuminate the corresponding pixel. Conversely, when the switching element is turn on, the liquid crystals are twisted such that light passing through the liquid crystal is not rotated and does not pass through the second polarizer  240 . The substrate  224  may include an alignment film on the side facing the first side of the liquid crystal layer  222 . In some examples, the alignment film includes a surface subjected to an alignment treatment. Any suitable alignment technique may be adopted as long as liquid crystal molecules are arranged in a constant alignment state on the surface of the substrate  224 . 
     Each of the polarizers  230 ,  240  are configured to filter light having undefined or mixed polarization into light having a defined polarization. In an implementation, the first polarizer  230  and the second polarizer  240  may be oriented at a 90° angle relative to each other, such that the first polarizer  230  filters the unpolarized light received from the light source  212  and the second polarizer  240  further filters the rotated light received from the liquid crystal cell  220 . Specifically, the first polarizer  230  is configured to convert light received from the light source  212  into a first polarized light by filtering the light into a P-polarized light and an S-Polarized light. The P-polarized light then passes through the liquid crystal cell  220  and is rotated the predetermined angle (e.g., 90° or) 270° by the switching elements  226 . The second polarizer  240  is configured to allow the rotated light received from the liquid crystal cell  220  to pass through while filtering out light that is not rotated by the predetermined angle. Thus, rotated light associated with each pixel defining the profile P of the build layer passes through the second polarizer  240  such that second polarizer  240  emits the profile P of the current build layer. 
     Conventional liquid crystal panels may implement a single layer or a multi-layered polarizing film, or a laminate (so-called polarizing plate) including a substrate and a polarizing film, or in which a polarizing film is sandwiched between at least two substrates via any adhesion layer. When incident light is split into two perpendicular polarization components (i.e., S-polarized light and P-polarized light), polarizer films used in conventional liquid crystal panels have a function of transmitting one of the polarization components and absorbing the other one of the perpendicular polarization component. In the display industry, the polarizers are typically made from an extruded Polyvinyl Alcohol (PVA) film impregnated with iodine. When PVA is stretched, the molecules are aligned such that a preferred polarization state of the light is transmitted. The iodine is used to absorb the light of the polarization state that is perpendicular to the aligned PVA structure. These polarizing films are then laminated directly to the transistor/LC layers. The PVA/iodine polarizing films are extremely common and cost effective, with large volumes driven by the LCD display industry. However, data shows that absorptive polarizers that implement conventional polarizing films generally transmit only about 60% of incident energy. 
     In an implementation, the polarizers  230 ,  240  are optimized to maximize transmissivity of the 405 nm wavelength (or near-UV at 365-415 nm) through each polarizer  230 ,  240 . The first polarizer  230  and the second polarizer  240  may be the same or different. For example, each of the above polarizers  230 ,  240  may include a wire grid polarizer optimized for transmission of the 405 nm wavelength (or near-UV at 365-415 nm). Unlike conventional film-based polarizers (e.g., extruded PVA film impregnated with iodine), which may only transmit 60% of incident light (including light at the 405 nm wavelength), a wire grid polarizer may transmit approximately 80% of incident light at the 405 nm wavelength. Thus, implementing each of the first polarizer  230  and the second polarizer  240  as wire grid polarizer (80% optical efficiency) provides a 33% increase in optical transmission at each polarizer  230 ,  240  compared to film-based polarizers (60% optical efficiency). 
     Optionally or alternatively, the first polarizer  230 , the second polarizer  240 , or both, may include a thin-film dielectric polarizer optimized for transmission of the 405 nm wavelength. Thin-film dielectric polarizers may have an optical transmission rate of up to approximately 98% for light having a wavelength of 405 nm. However, thin-film dielectric polarizers operate at a relatively large incident angle (e.g., 45° or larger), which limits the practical use of thin-film dielectric polarizers to incorporation as the first polarizer  230  disposed adjacent to the light source  212 . Nevertheless, incorporating a thin-film dielectric polarizer (98% optical efficiency) as the first polarizer  230  provides a 63% increase in optical transmission at the first polarizer  230  compared to a film-based polarizer (60% optical efficiency). 
     Optionally or alternatively, the first polarizer  230 , the second polarizer  240 , or both, may be dye-type polarizers (e.g., PVA films containing dichroic dye). Implementing dye-type polarizers on a stereolithography printer provides several benefits over other configurations. Iodine-type and dye-type polarizers are both absorptive polarizers. This means that photons that do not get transmitted are absorbed and heat is created in the polarizer, which leads to a decline in transmission. This is in addition to the heat created as part of the stereolithography printing process, especially during photopolymerization. When heat is introduced to iodine/PVA polarizers, first the iodine is sublimated and the transmission of the polarizer increases. The heat causes polyene formation to occur in the PVA structure. Polyene formation in the polarizer film causes the polarizer film to turn brown which results in a rapid decline in transmission. As a result, users are required to replace the LCD screen within the typical lifetime of a stereolithography 3D printer. The LCD screen then becomes a consumable, which increases the total cost of ownership for a stereolithography printer and produces waste. This is one of the key hurdles holding back LCD projection as a widespread optical system used in stereolithography printers. 
     Alternatively, the organic dyes in many dye-type polarizers are much more robust to temperature relative to iodine, and the dye does not sublimate when exposed to typical stereolithography printing temperatures. Polyene formation in the PVA structure does occur in dye-type polarizers, but at a significantly slower rate than in Iodine-type polarizers due to the differences in chemistry. The result is that dye-type polarizers will last for the reasonable lifetime of a stereolithography printer, creating a tremendous advantage in customer value and reduces waste. 
     While crystalline, wire grid, and dielectric coating polarizers are more resistant to UV, near UV light, and heat compared to conventional PVA/iodine polarizers, these polarizers are orders of magnitude more expensive to produce in large sheets as required to span the typical LCD screen sizes found in stereolithography printers. 
     On the other hand, dye-type polarizers can be produced in a similar way as PVA/iodine polarizers, and therefore can be produced in large sheets to fit the dimension of LCD screen sizes in stereolithography printers without significantly increasing the cost. The PVA is extruded to align the molecules, and organic dye is impregnated into the PVA matrix instead of iodine. As a result, the dye-type polarizer film can be produced in large sheets to cover the size of a typical stereolithography printer LCD screen. The dye-type polarizers can be laminated to an LCD screen in the same way as a PVA/iodine polarizer, or they can be configured in the stereolithography printer as separate pieces in line with the transistor/liquid crystal layers. 
     Dye-type polarizers may include organic dyes that are resistant to UV light, near UV light, and heat. As a result, dye-type polarizers increases the lifetime of the LCD screen in a stereolithography printer. With properly configured dye-type polarizer (e.g., maximally transmissive to 365-415 nm yet resistant to degradation), the LCD screens will no longer be a consumable and can even exceed the lifetime of a stereolithography printer. In some implementations, the dye-type polarizer is configured to operate at an environment of between 10 and 120 degrees Celsius, and to receive a flux (e.g., from the light source) greater than 20 mW/cm. 2    
     Further, dye-type polarizers can be configured (e.g., by changing the type or concentration of dye) to achieve better or equal optical transmission at lower wavelength relative to that at 405 nm. There are some resin chemistries that are more sensitive to lower wavelength light, such as 365 nm, which would increase print speed. Additionally there are some material properties that can be improved (e.g., tensile strength) with lower wavelength light. This effect is difficult to achieve on PVA/iodine polarizers as there is a drop-off of about 20% in optical transmission between 405 nm and 365 nm for iodine. 
     In some implementations, the dye-type polarizers can include dyes made from one or more of metal diazo compounds, trisazo compounds, biphenyldiazo, trisazo or disazomonoazoxy compounds, and metal-containing biphenyldisazo, trisazo or disazomonoazoxy compounds. 
     As previously discussed, the liquid crystal panel  200  of the present disclosure omits the use of color filters employed by conventional liquid crystal panels, and thereby increases light transmission efficiency relative to conventional liquid crystal panels. For example, in Table 1 below, testing showed a 500% increase in optical transmission rates at the 405 nm wavelength for liquid crystal panels operated without a colored filter compared to liquid crystal panels operated with a colored filter. Thus, a color filter has an optical transmission efficiency of approximately 20%, which must be accounted for when determining the overall optical efficiency of the curing system (see Table 1 below). 
     As set forth above, implementing polarizers  230 ,  240  having a higher optical transmission efficiency in combination with no color filter provides a significant increase in the overall optical transmission efficiency of the liquid crystal panel  200 . Table 1 illustrates a comparison of the optical transmission efficiency of (i) a conventional, color-filtered liquid crystal panel including absorptive film polarizers, (ii) an unfiltered liquid crystal panel according to the present disclosure including two wire grid polarizers, (iii) an unfiltered liquid crystal panel according to the present disclosure including a thin-film dielectric polarizer and a wire grid polarizer, and (iv) an unfiltered liquid crystal panel according to the present disclosure including two dye-type polarizers. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Liquid Crystal Panel Optical Transmission Rates 
               
            
           
           
               
               
               
            
               
                   
                 No Color Filter; 
                   
               
            
           
           
               
               
               
               
            
               
                   
                 No Color 
                 Thin Film 
                   
               
            
           
           
               
               
               
               
               
            
               
                   
                 Color Filter; 
                 Filter; 
                 Dielectric &amp; 
                 No Color Filter; 
               
               
                   
                 Conventional 
                 Wire Grid 
                 Wire Grid 
                 Dye-type 
               
               
                   
                 Polarizers 
                 Polarizers 
                 Polarizers 
                 Polarizers 
               
            
           
           
               
               
            
               
                 Component 
                 Component Efficiency (Absolute Efficiency) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Light Unit 
                 50% 
                 (50%) 
                 50% 
                 (50%) 
                 50% 
                 (50%) 
                 50% 
                 (50%) 
               
               
                 Emission 
               
               
                 First Polarizer 
                 60% 
                 (30%) 
                 80% 
                 (40%) 
                 98% 
                 (49%) 
                 80% 
                 (40%) 
               
               
                 Liquid 
                 35% 
                 (10.5%) 
                 35% 
                 (14%) 
                 35% 
                 (17.2%) 
                 35% 
                 (14%) 
               
               
                 Crystal Layer 
               
            
           
           
               
               
               
               
               
               
            
               
                 RGB filter 
                 20% 
                 (2.1%) 
                 N/A 
                 N/A 
                 N/A 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Top polarizer 
                 60% 
                 (1.3%) 
                 80% 
                 (11.2%) 
                 80% 
                 (13.7%) 
                 80% 
                 (11.2%) 
               
            
           
           
               
               
               
               
               
            
               
                 Final Output 
                 1.3% 
                 11.2% 
                 13.70% 
                 11.2% 
               
               
                   
               
            
           
         
       
     
     As shown in Table 1, the conventional liquid crystal panel including the color filter and absorptive polarizers may only transmit approximately 1.26% of the light energy generated by the light emission unit. Removing the color filter and implementing first and second wire grid polarizers (80% efficient) increases overall optical efficiency to approximately 11.2%, while further replacing the first polarizer with a thin-film dielectric polarizer (98% efficient) further increases the overall efficiency of the liquid crystal panel to approximately 13.7%. Replacing the first and the top polarizers with dye-type polarizers (80%) also increases overall optical efficiency to approximately 11.2%, but at a much lower cost compared to using wire grid and thin film polarizers. 
     It is appreciated that other permutations of the polarizer arrangement not listed in Table 1 is also contemplated. For example, the first polarizer and the top polarizer may be any of the conventional polarizer, the wire grid polarizer, thin film dielectric, or the dye-type polarizer. 
     The increased optical transmission efficiency of the liquid crystal panel  200  of the present disclosure allows curing times to be significantly reduced compared to a curing system that may incorporate a conventional filtered liquid crystal panel. Process times may be further modified by adjusting the power input to the light unit. For example, the light unit may be configured to operate at a higher power level to increase the flux of the liquid crystal panel. In some examples, the light unit includes a power output ranging from 50 Watts to 100 Watts. However, higher-power light units  210  may also be implemented. Here, an increase in power may result in reduced lifespan of the liquid crystal panel  200  resulting from higher flux. Accordingly, a power of the light unit  210  may be selected to balance process cycle times and lifespan of the components of the liquid crystal panel  220 . In some examples, the liquid crystal panel  200  may operate at a power range to provide a flux ranging from 5 mW/cm 2  to 40 mW/cm 2 . 
     Referring to  FIGS.  3 - 4   , in some implementations, the light unit  210  of the liquid crystal panel includes a polarized light source  212  that implements LEDs  214 . In these implementations, the first polarizer  230  may be omitted from the liquid crystal panel  200  such that the light source  212  provides polarized light directly to the liquid crystal cell  220 , as shown in  FIG.  4   . Although polarized light sources  212  are typically more costly per watt than comparable unpolarized light sources, providing a direct source of polarized light may provide significantly reduced divergence of the actinic radiation compared to passing unpolarized light through a first polarizer, thereby providing a further improvement to optical transmission efficiency of the liquid crystal panel  200 . 
       FIG.  5    shows a schematic view of a system  500  for providing polarized light (i.e., P-polarized light), which may be incorporated as part of a curing system  170  in conjunction with the liquid crystal cell  220  and the second polarizer  240  discussed previously. As shown, the first polarizer  230  and the light unit  210  including the array of LEDs  214  are decoupled from, or not integrated to (e.g., not laminated to), the liquid crystal cell  220 . in accordance with some implementations. In these implementations, the first polarizer  230  is disposed at a location (e.g., positon or orientation) wherein a top side  235  of the first polarizer  230  is spaced apart from a bottom side  225  of the liquid crystal cell  220  by a first distance D 1  and the light source  210  including the array of LEDs  214  is disposed at a location (e.g., position or orientation) wherein a top side  216  of each LED  214  is spaced apart from the bottom side  225  of the liquid crystal cell  220  by a second distance D 2 , which is greater than the first distance D 1 . In some implementations, a bottom side  234  of the first polarizer  230  is spaced apart from the light source  210  by a third distance D 3 . As shown, the third distance D 3  is greater than the first distance D 1  in some implementations. However, in some implementations, the first distance D 1  is equal to or greater than the third distance D 3 . 
     In some implementations, it is beneficial to separate the first polarizer  230  and the light source  210  (including the array of the LEDs  214 ) from the liquid crystal cell  220 . For example, when the first polarizer  230  is separated from the liquid crystal cell  220  by a certain distance (e.g., first distance D 1 ), the first polarizer  230  can be easily replaced without damaging the liquid crystal cell  220 . In a situation that the first polarizer  230  is degraded to a certain point (e.g., discoloration), the user can easily replace the first polarizer  230  without damaging the liquid crystal cell  220 . Similarly, in some instances, it is beneficial to separate the light source  210  from the first polarizer  230  so the user can replace the light source  210  including the array of the LEDs  214  if at least one of the LEDs  214  is operating abnormally. These will substantially reduce the cost of ownership of the curing system  170 . 
     The first polarizer  230  may be at least one of PVA/iodine polarizer, wire grid type polarizer, dielectric film type polarizer, crystalline type polarizer, or dye type polarizer in some implementations. However, the first polarizer  230  is not limited to being constructed from the polarizer types mentioned above, but may be formed of other types of polarizer. 
       FIG.  6    shows a schematic sectional view of a curing subsystem  600  for providing the polarized light (i.e., P-polarized light), which may be incorporated as part of a curing system  170  in conjunction with the liquid crystal cell  220  and the second polarizer  240  discussed previously. As shown, the curing subsystem  600  includes a first polarizer  230   a  and the polarized light source  210  that are vertically spaced apart from the liquid crystal cell  220  and the second polarizer  240 . 
     In some implementations, as shown, the array of LEDs  214  included in the light source  210  are configured to provide the unpolarized light to the first polarizer  230   a . The first polarizer  230   a  implemented in the curing subsystem  600  is divided into individual polarizer units  232  that are laterally spaced apart from each other to reduce the overall material of the first polarizer  230  required to generate the polarized light from the light source  210 . In these implementation, each of the polarizer units  232  of the first polarizer  230   a  is disposed adjacent to and overlapped with a corresponding LED  214  to generate the polarized light. Since the first polarizer  230   a  (i.e., polarizer units  232  of the first polarizer  230 ) is disposed adjacent to the array of LEDs  214  and is separated from the liquid crystal cell  220 , the same or substantially equal amount of the polarized light can be generated with less material of the first polarizer  230  compared to polarized light generated by the first polarizer  230  in the curing subsystem  700  in the  FIG.  7   . Thus, the curing subsystem  700  may provide comparable performance characteristics to the system of  FIG.  6    while minimizing material costs. 
     As shown in  FIG.  6   , each of the polarizer units of the first polarizer  230   a  is disposed adjacent to and overlapped with the corresponding LED  214  in a direction (e.g., vertical direction or Z-axis) that the unpolarized light from the light source  210  is converted to the polarized light an early stage of dispersion. By converting the unpolarized light at the early stage of dispersion, the overall material of the first polarizer  230  is reduced. In other words, by placing the individual polarizer units  232  closer to the light source  210 , the respective sizes of the polarizer units  232  is minimized. 
     The first polarizer  230  implemented in the curing subsystem  600  may be at least one of PVA/iodine polarizer, wire grid type polarizer, dielectric film type polarizer, crystalline type polarizer, or dye type polarizer in some implementations. However, the first polarizer  230  is not limited to being constructed from the exemplary polarizer types mentioned above but maybe formed of other polarizer types. 
       FIG.  7    shows a schematic sectional view of a curing subsystem  700  for providing polarized light (i.e., P-polarized light), which may be incorporated as part of a curing system  170  in conjunction with the liquid crystal cell  220  and the second polarizer  240  discussed previously. As shown, the curing subsystem  700  includes a light unit  210   b  and a first polarizer  230   b  disposed adjacent to the light unit  210   b . In some implementations, as shown, the light unit  210   b  is a high-power LED  214   b , which is capable of providing adequate “backlight” to the liquid crystal cell  220 . 
     As shown, the size (i.e., length and/or width) of the first polarizer  230   b  implemented in the system  700  is substantially smaller than the size of the liquid crystal cell  220 . Since the first polarizer  230  is disposed adjacent to and overlapped with the high-power LED  214   b  of the light unit  210   b  in a first direction (e.g., vertical direction or Z-axis) and is separated from the liquid crystal cell  220 , the first polarizer  230   b  in the smaller size is capable of generating the polarized light that can cover the entire or substantial portion of the liquid crystal cell  220  using the diverging light from the high-power LED  214   b.    
     As shown in  FIG.  7   , the first polarizer  230  in the smaller size is disposed adjacent to and overlapped with the high power LED  214   b  of the light unit  210   b  in a direction (e.g., vertical direction or Z-axis) and the polarized light is generated using the (unpolarized) light from the light source  210   b  at an early stage of dispersion. By converting the light at the early stage of dispersion, the overall material of the first polarizer  230  is minimized. 
     In some instances, it is also helpful to utilize the high-power LED  214   b  of the light source  210   b  along with the first polarizer  230  disposed adjacent to the high-power LED  214   b  to reduce the cost of manufacturing by minimizing the size of first polarizer  230  required to generate the polarized light. 
     The first polarizer  230   b  implemented in the system  700  may be at least one of PVA/iodine polarizer, wire grid type polarizer, dielectric film type polarizer, crystalline type polarizer, or dye type polarizer in some implementations. However, the first polarizer  230   b  is not limited to being constructed from the exemplary polarizer types mentioned above but maybe formed of other types of polarizer. 
       FIG.  8    shows a schematic sectional view of a curing subsystem  800  for providing polarized light (i.e., P-polarized light), which may be incorporated as part of the curing system  170  in conjunction with the liquid crystal cell  220  and the second polarizer  240  discussed previously. As shown, the curing subsystem  800  includes the light unit  210 , a collimating lens  810 , a diverging lens  850 , the first polarizer  230   c  embodied as a dielectric polarizer (e.g., tilted polarizer) disposed between the collimating lens  810  and the diverging lens  850 . In some implementations, as shown, the light unit  210   b  is embodied as a high power light emitting diode which is capable of providing adequate “backlight” to the liquid crystal cell  220  and the second polarizer  240 . 
     As shown, when a dielectric polarizer is implemented as the first polarizer  230   c , the first polarizer  230   c  separates the (unpolarized) light received from the light source  210   b  into P-polarized light that is parallel to the plane of incidence, and S-polarized light that is perpendicular to the plane of incidence. In these implementations, the collimating lens  810  is disposed between the light source  210   b  and the first polarizer  230  to change the diverging light from the light source  210   b  (i.e., high-power LED) into a parallel beam and to provide the parallel beam to the first polarizer  230   c . The diverging lens  850  is disposed between the first polarizer  230   c  and the liquid crystal cell  220 . The diverging lens  850  is implemented to receive the P-polarized light of the parallel beam and to spread out the P-polarized light to the entirety or a substantial portion of the liquid crystal cell  220 . In these implementations, the high-power LED  214   b  of the light source  210   b , the collimating lens  810 , the first polarizer  230   c , the diverging lens  850 , and the liquid crystal cell  220  are aligned with each other in a first direction (e.g., vertical direction or Z-axis). 
     In some instances, it is beneficial to separate the first polarizer  230  and the light source  212  from the liquid crystal cell  220  as discussed previously. In some instances, it is also helpful to utilize the high-power LED  214   b  of the light source  210   b  along with the first polarizer  230  embodied as a dielectric polarizer (e.g., tilted polarizer) to reduce the cost of manufacturing by reducing the size of first polarizer  230  required to generate the polarized light. 
       FIG.  9    is a flowchart of an example arrangement of operations for a method  600  for curing a photopolymer resin using a liquid crystal panel  200  according to the present disclosure. At operation  902 , the method includes generating, by the liquid crystal panel  200 , a first polarized monochromatic light and receiving, by a liquid crystal cell  220  of the liquid crystal display  200 , the first polarized monochromatic light. As discussed above, the first polarized monochromatic light may be generated by subjecting unpolarized light generated by the light unit  210  to a first polarizer  230 , which may include a wire grid polarizer or a thin-film dielectric polarizer. In other implementations, the first polarized monochromatic light is generated by a polarized light unit  210   a . The first polarized monochromatic light has a wavelength selected for curing the particular photopolymer resin of the build component C, such as, for example, 405 nm. 
     At operation  904 , the method  900  includes rotating, by the liquid crystal cell  220 , in an absence of an electrical field, the first polarized monochromatic light. For instance, the liquid crystal cell  220  may rotate the first polarized monochromatic light by twisting the first polarized monochromatic light based on instructions corresponding to a profile P of a fabricated component C. For example, where the profile P of a corresponding build layer requires that one or more specific pixels of the liquid crystal panel  200  be illuminated, the instructions may cause one or more switching elements  226  each associated with a corresponding one of the one or more specific pixels to activate for twisting corresponding liquid crystal molecules of the liquid crystal cell  220  to rotate the first polarized monochromatic light by 90°. 
     At operation  906 , the method  900  includes receiving the rotated first polarized monochromatic light at the second polarizer  240  and polarizing, by the second polarizer  240 , the rotated first polarized monochromatic light a second time into second polarized monochromatic light having the profile P of the corresponding build layer. Here, the first polarized monochromatic light received by the second polarizer  240  is unfiltered. In other words, the rotated first polarized monochromatic light does not pass through a color filter prior to being received by the second polarizer  240 . At operation  908  of the method  900 , the second polarizer  240  transmits the second polarized monochromatic light having the profile P of the corresponding build layer onto the photopolymer resin to form the corresponding build layer of the build component C. This process is incrementally repeated for subsequent build layers, with each build layer including a unique profile P. 
     In some examples of the method  900 , generating the first polarized monochromatic light includes generating a first polarized monochromatic light having a wavelength of 405 nanometers. The first polarized monochromatic light may be generated by polarizing a non-polarized monochromatic light using the first polarizer  230 . In some configurations, the first polarizer  230  includes a thin film dielectric polarizer. In some examples, the first polarizer  230  includes a wire grid polarizer. Alternatively, generating the first polarized monochromatic light includes emitting the first polarized monochromatic light from LEDs  214  of the light source  212 . Optionally, rotated first monochromatic light may be polarized using a wire grid polarizer. 
     The method  900  may further include polarizing, by the first polarizer  230  of the liquid crystal panel  200  of the curing system  170 , a non-polarized monochromatic light into the first polarized monochromatic light comprising P-polarized light and a third polarized monochromatic light comprising S-polarized light. The method  900  may also include converting, by the half-wave plate  510  of the curing system  170 , the third polarized monochromatic light comprising S-polarized light into a fourth polarized monochromatic light comprising P-polarized light. The method  900  may further include transmitting, from the half-wave plate  510  of the curing system  170 , the fourth polarized monochromatic light comprising P-polarized light to the liquid crystal cell  220  of the curing system  170 . 
     In some examples, the method  900  includes combining, at the liquid crystal cell  220  of the liquid crystal panel  200 , the first polarized monochromatic light comprising the P-polarized light and the fourth polarized monochromatic light comprising P-polarized light. The method  900  may also include rotating, by the liquid crystal cell  220  of the liquid crystal panel  200 , the combined first polarized monochromatic light and fourth polarized monochromatic light, the rotated combined first polarized monochromatic light and fourth polarized monochromatic light having the profile of the corresponding build layer of the fabricated component C. 
       FIG.  10    shows a schematic partial sectional view of a system  1000  that is configured to measure the UV light exposure on the first polarizer  230   d . As discussed previously, the first polarizer  230   d  degrades with exposure to the UV light generated by the light unit  210 . As shown, the system  1000  includes one or more light sensors  1010  (e.g., photodiodes or UV light detectors) that are configured to measure the amount of the UV light (e.g., UV light intensity measurement in mW/cm 2 ) the first polarizer  230  is receives from the light unit  210 . In some implementations, as shown, the light sensors  1110  are located at the surrounding or peripheral portion of the liquid crystal panel  200 . In some implementations, to increase the accuracy of the UV light exposure measurement for the first polarizer  230   d , the second polarizer  240 , the liquid crystal cell  220 , and the glass layers  250  may be removed or etched off at the peripheral portion of the liquid crystal panel  200   d  and one or more light sensors  1010  are disposed on a peripheral portion of the first polarizer  230   d . In some implementations, to increase the accuracy of the UV light exposure measurement, the length and width of the second polarizer  240 , the liquid crystal cell  220 , and the glass layers  250  may be smaller than the length and width of the first polarizer  230   d  to provide sufficient space to place the light sensors  1010  at the peripheral portion of the liquid crystal panel  200   d . To further increase the accuracy of the UV light exposure measurement, the light sensor  1010  can be covered with a cover or shroud  1030  that is capable of blocking ambient UV light from external sources (e.g., sunlight). In some implementation, to increase the accuracy of the UV light exposure measurement, a side wall member  1050  is disposed between the light sensor  1010  and the end surface of at least one of the second polarizer  240 , the liquid crystal cell  220 , and the glass layers  250  to prevent the lateral intrusion of the UV light. As shown, the side wall member  1050  is constructed with a suitable material that is capable of blocking the UV light from entering through the side surface of the at least one of the second polarizer  240 , the liquid crystal cell  220 , and the glass layers  250 . 
     Referring to  FIG.  11   , the base  110  of the printer  100  is illustrated without the dispensing system  120 , the basin  130 , and the build platform  140  to show various UV light intensity measurement locations for the light sensors  1010  (e.g., photodiodes or UV light detector). In some implementations, light sensors  1010 ,  1010   a - 1010   h  are located or disposed at the peripheral portion of the liquid crystal panel  200 . The UV light measurements (e.g., UV light intensity measurement in mW/cm 2 ) collected by each of the light sensors  1010  are transmitted to the computing system  150  including the data processing hardware  152  and the memory hardware  154 . In some implementations, the amount of the UV light the first polarizer  230  is exposed to is determined using the data processing hardware  152  based on the UV light intensity measurements collected by the light sensors  1010  and corresponding light unit on-time (e.g., UV light intensity measurements (mW/cm 2 )×corresponding light unit on-time). 
     As shown in  FIG.  11   , the eight light sensors  1010   a - 1010   h  are disposed or located at the peripheral portion of the liquid crystal panel  200   d . However, the present disclosure does not limit the location and the number of the light sensors  1010  implemented to measure the amount of the UV light transmitted to the first polarizer  230   d . For example, more than eight light sensors  1010  are disposed or installed to measure the amount of the UV light the first polarizer  230   d  is exposed to at various locations. However, less than eight light sensors  1010  may disposed or installed to measure the amount of the UV light the first polarizer  230   d  is exposed to. In addition, one or more light sensors  1010  may be installed within the printing area (e.g., printing zones 1-4) or along the border between the printing area and the non-printing area. 
     It is helpful to have multiple light sensors  1010  to increase accuracy of the measurements. For example, the data processing hardware  152  is configured to determine or compute the amount of the UV light the first polarizer  230   d  is exposed to by averaging the UV light intensity measurements collected by the light sensors  1010  and monitoring the corresponding time the first polarizer  230   d  is exposed to the UV light (e.g., average of the UV light intensity measurements (mW/cm 2 )×corresponding light unit on-time). Each of the UV light measurements is stored in the memory hardware  154  and accessed by the data processing hardware  152  is to determine the UV light determine the total amount of the UV light the first polarizer  230   d  is exposed to. 
     In some implementations, each of the light sensors  1010   a - 1010   h  is assigned to a corresponding printing zone (e.g., printing zones 1-4). For example, the light sensors  1010   a ,  1010   h  adjacent to the printing zone 1 are assigned to the printing zone 1. The light sensors  1010   b ,  1010   c  adjacent to the printing zone 2 are assigned to the printing zone 2. The light sensors  1010   g ,  1010   f  adjacent to the printing zone 3 are assigned to the printing zone 3. The light sensors  1010   d ,  1010   e  adjacent to the printing zone 4 are assigned to the printing zone 4. 
     In some instances, the data processing hardware  152  is configured to determine or compute the amount of UV light the first polarizer  230   d  is exposed to for each of the printing zones using the measurement collected by the assigned light sensors  1110 . For example, the data processing hardware  152  is configured to determine the amount of UV light the printing zone 1 of the first polarizer  230   d  is exposed to by averaging the UV light measurements collected by the light sensors  1010   a ,  1010   h  associated with the printing area  1  and monitoring the corresponding time the printing area  1  of the first polarizer  230   d  is exposed to the UV light (e.g., average of the UV light intensity measurements (mW/cm 2 ) collected by assigned light sensors×corresponding light unit on-time). In these instances, the data processing hardware  152  is configured to add each of the UV light measurements together for a given printing zone. 
     In some implementations, the data processing hardware  152  is configured to determine or compute the amount of the UV light the first polarizer  230   d  is exposed to by selecting the greatest UV light measurement among the measurements collected by the light sensors  1010 . This method can be used for conservatively determining the amount of the UV light transmitted to the first polarizer  230   d  or a printing zone of the first polarizer  230 . Conversely, where a user desires to maximize the lifespan of the first polarizer, the data processing hardware  152  may configured to determine or compute the amount of the UV light the first polarizer  230   d  is exposed to by selecting the lowest UV light measurement among the measurements collected by the light sensor  1110 . 
     The data processing hardware  152  is configured to compute or determine the total amount of the UV light that is exposed to the first polarizer  230   d  by adding all of the UV light measurements in accordance with some implementations. For example, the data processing hardware  152  is configured to compute or determine the total amount of UV light that is exposed to the most exposed area (e.g., printing zone 1). 
     In some implementations, the data processing hardware  152  is configured to display the total amount of the UV light that is exposed to the first polarizer  230   d  (or the most exposed area of the first polarizer  230   d  such as printing zone 1 as example) or the remaining lifetime of the first polarizer  230   d . For example, as shown in  FIG.  11   , the display  162  of the control panel  160  may indicate the remaining lifetime of the first polarizer  230   d  based on the UV light measurements (e.g., average UV light intensity measurements (mW/cm 2 ) collected by the assigned light sensors in the most exposed area×corresponding light unit on-time) collected since installation or initialization of the first polarizer  230   d  and a predetermined or pre-computed amount of the UV light the first polarizer  230   d  can withstand before exceeding a known lifetime light exposure threshold for the first polarizer  230   d  (e.g., end of the lifetime). Based on the information on the display  162 , the user can minimize maintenance and service costs only replacing the first polarizer  230   d  at predetermined maintenance interval. The data processing hardware  152  is further configured to reset the remaining lifetime to 100% and reset the UV light exposure computation when the first polarizer  230   d  is replaced. 
     A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the disclosure. Accordingly, other implementations are within the scope of the following claims.