FR2692053A1 - Model prodn. by selective photopolymerisation of liq. or powder - using active liq. crystal mask or active light source controlled by computer instead of controlled movement focused laser - Google Patents

Abstract

Machine has an active mask or active source controlled by a CAD computer to absorb part of the emitted light but less pass selectively the wavelengths able to cause photopolymerisation. Active mask is a liq. crystal device absorbing part of the light from a laser or sundry lamp sources. Liq. crystal is either a screen exposing all the resin surface at once or a bar type lamp sweeps the surface. Active source is a video screen illuminating all the resin surface or a bar of laser diodes or a plasma discharge tube that are swept over the resin surface longitudinally or rotationally. Mask or source or both are computer controlled. Source of long wavelength light is pref. a series of lamps, the light is collimated then passed through two successive bar screen liq. crystal screens. Focussing system pref. follows to allow enlargement or redn. of the image. USE/ADVANTAGE - Machine makes objects by selective photopolymerisation of powders or liquids. Rapid prodn. of prototype models is obtd. in various materials. Useful in place of a controlled laser system an active mask or active light source is used.

Description

SELEC PHOTOPOLYMERIZATION OBJECT MANUFACTURING MACHINE
TIVE OF LIQUIDS OR POWDERS BY LAYERS, BASED ON MASK OR
ACTIVE SOURCE IN MOTION.

The technical field of the invention is that of rapid prototyping as regards its applications, and uses mechanical, optical, electronic and computer devices to operate.

The invention described relates to the use of various existing materials and methods for the purpose and according to arrangements not yet used in the technical field of the invention (rapid prototyping).

STATE OF THE ART
The concept of rapid prototyping by solidification of a layer of liquid resin or a powder, called by the term "stereolithography" appeared in the mid-80s, as a new method of manufacturing objects from computer files known as Computer-aided design (CAD). This Technology allows objects defined in CAD to be produced in surface or volume mode directly in a photopolymerizable resin, without machining, by solidification of a liquid or a powder.

In matters of stereolithography, there are today several systems allowing solidification by successive layers of solid or liquid resins. or the creation of an object by depositing a layer of molten material (Stratasys).

 Asavoir: 1) 3D systems (SLA), Dupont de Nemours (Somos), EOS (Stereos 400), as well as Sony and Mitsubishi machines etc ... see general principle Figure 1.

2) Stratasys type system.

3) Cubital type system (non-laser system).

4) DTM Type System (system based on powder sprayed and solidified by laser, layer by layer).

Actually, the 3D type system systeFs (The most widespread in the world) works like this:
By the use of an Ultraviolet source (Abbreviation: UV) focused at a single point: a laser, we polymerize in successive layers (Thanks to a plate descending in the liquid resin) and selectively, part of a resin Light-curing.

the laser, controlled by two mirrors themselves controlled by a computer system, scans the surface of the liquid with a tracing speed depending on the deflection mirrors. The complete tracing time of a layer is therefore dependent on the surface to be solidified.

In addition, the laser is generally controlled so as to solidify only part of the part to be produced (by drawing for example crossbars), in order to create a "load-bearing" structure, the rest of the resin then being solidified in an oven. says of Post Curing, with simple UV lamps. When a layer has been fully illuminated by the laser, all the parts of the liquid resin thus exposed have started a polymerization reaction. Then, a squeegee system comes to equalize the surface, the plate on which the workpiece is placed goes down one step in the liquid (not equal to the thickness of the layer to be solidified, i.e. generally 0.1 0.2 mm).

the process is thus repeated until the complete production of the part.

The advantages of this technique compared to conventional methods of producing objects (Machining by numerical control among others) being: - No need to create a toolpath.

- Complete creation of the object (Interior and Exterior) Simultaneously.

- Ability to produce parts that are not directly machinable in one piece.

 - Speed.

- Direct connection, via an Interface (STL) to the surface or volume CAD file.

The parts produced, being made of specific resin.

This technology has been distributed today to nearly 450 users around the world, and practically all suppliers of surface-assisted or solid-state computer-aided design software have the appropriate interface, called the interface.
STL.

The object of this invention relates to a complete sterolithography machine making it possible to create a resin prototype from solidification of successive layers of liquid photopolymerizable resin, avoiding some of the principles of the existing machines mentioned above and currently used.

The primary object of this invention is. instead of the laser method, to use an active "mask" and a source of insolation of the liquid situated behind this mask (Ultra violet source as regards the photopolymerizable resins currently available, or source of other length wave adapted to the resins that one wishes to harden). (Fig4), or an active emissive source (video screen type or laser diodes or plasma discharge tubes).

General principle
In order to solidify a layer of liquid, let's create a mask. This mask represents the layer to be solidified: the transparent part lets the photons of wavelength adapted to the resin which one wishes to polymerize pass (Ultraviolet wavelength in general, but which can be different depending on the resins used).

The photons that will touch the photopolymer liquid will allow the chemical reaction allowing the change of liquid -> solid state. The Dark part prevents the passage of photons and therefore prevents solidification.

This mask is associated with an optical focusing device, exactly like a slide projector or overhead projector (fresnel lens).

Each mask being in itself a kind of device. This makes it possible to have a clear image on the surface of the liquid and to solidify only what must be.

Different types of masks are possible, however, to be compatible with the working speeds envisaged as well as for the flexibility of the process, while mentioning them, we will not retain masks of the type: Photographic, Electrostatic by depositing a layer of toner on glass, tracing on transparent film (plotter or phototracer). Masks qualified as static. since it requires an additional intervention on the mask to modify it (photograph to be developed. toner to be erased then redeposit. tracing of a film by tracers of different types). Figure 3 (1 & 2)
The primary object of this patent relates to "active" masks in the sense that they are directly activated by a computer and electronic system to modify their state as a function of the layers to be solidified. This is the case for: - Video screens (Emissive) (Fig 3 (IV).

- Liquid crystal device (absorbing part of the radiation emitted by a UV or other source) (Fig 3 (III)
- Liquid crystal screen type. (Fig 4)
- bar type of liquid crystals. (Fig 5) - Device with laser diodes or plasma discharge tubes (Emissive)
- of diode or tube strip type (Fig 8)
- of the Laser diode or plasma discharge tube type (Fig 3 (V)), these active masks being faster than the masks previously described as passive, since they are controlled directly, the difference being that there is between a still image obtained by a Photographic or Photocopier or plotter type process, compared to an animated image
In the case of the video screen, this displays a direct image of the parts to be solidified (light part) and the parts not to solidify (opaque part of the screen). It is necessary that the photons emitted by the screen be adapted in frequency and intensity to the photopolymerization characteristics of the photopolymerizable liquid resins used.

Likewise, in the case of laser diodes placed in bars, it suffices to scan the surface of the liquid by displacement of the array of diodes, by controlling their illumination in order to reconstitute the image necessary for the desired polymerization. These diodes having to work at wavelength compatible with the photoplymerization characteristics of the photopolymerizable liquid resins used.

I) THE MASK:
This is the main part of the device and is made up of several ways 1: The slide or film mask. (Mask not active) Fig 3 (I and 11) It is possible to display each layer resulting from the so-called slicing operation (Slicing the surface or solid CAD file) on a computer video screen and photographing each layer. It only remains then to develop the film (Black and white) and to mount everything on a projector provided for this purpose with a source
UV (UV permeable film). Variants have been used, such as tracing by an electrostatic tracer, thus creating a UV-lightable film, an electrostatic toner layer on a glass pane. Each projected mask will allow to solidify in whole (and not in part) what must be on this layer.

2: The Video mask (Fig 3 (IV))
The Photographic film mask (never used for this specific technique) can be replaced by the Video screen itself. However, current video screens, whatever their definition have a low UV component, which remains impracticable in view of the current state of advancement of photopolymerizable resins, but may be used for any resin polymerizing to a length of wave that can be emitted by this type of screen. today or in the future (Color or black and white screens, or with modified photophores emitting in UV in the case of currently available resins ...) 3: The mask is an assembly incorporating a liquid crystal device.

In this case, this liquid crystal device serves as a mask. The liquid crystal device is backlit by a UV lamp (or a series of UV lamps, in the case of resins sensitive to UV, other possible wavelengths, depending on the resins used) and the whole is focused by a optical device on the liquid photopolymerizable resin.

As in the two previous cases (film type slide or video screen), there is total polymerization of the entire defined surface at one time.

The UV source being one or more wavelength lamps adapted to the desired effect. (in the case of an evolution of the type of resins used, the UV source could be replaced by a source working at other wavelengths).

The Liquid Crystal Device itself consists of several successive masks.

indeed, a single mask of this type will not offer a contrast greater than 70% between the transparent parts and those supposed to be completely opaque.

For this purpose. and this is the originality of the montage. we go up to the minimum two. and preferably three screens one behind the other with focusing optics between them as well as diaphragms. (Fig 4)
Thus we considerably increase the contrast between the opaque and transparent parts to the light.

The transparent part representing a very low intensity attenuation (except general attenuation due to the use of the diaphragm) compared to the opaque parts; ie 89% attenuation on the opaque parts compared to the transparent parts, with two screens, and 97% with three screens, which is in both cases sufficient to obtain a selective polymerization, as desired.

The principle is the same when using liquid crystal bars instead of screens (fig 5). F-diaphragms allow you to fine-tune both contrast and precision by increasing the depth of field.

Depending on the wavelength used, a liquid crystal device and a conventional projection optic may be used, or more specifically care will be taken to use materials which are transparent to the more distant UV, such as quartz.

4) The Bars of Laser Diodes. Strips of plasma discharge tubes.

In this case, an array of diodes or tubes can comprise several hundred or thousands of them, emitting at the desired wavelength (Example: the arrays used in laser printers), either arranged in line (Fig 8) or to form a screen of defined size. These bars are controlled to display one line of image at a time, and can thus illuminate the resin (either directly or by being focused by an optical device in order to increase the accuracy), the bar being moved by the equivalent of 'a line (By translation, or rotation), and the total image of the layer to solidify is thus transmitted to the bar, in synchronism with its movement mentdetranslation (or rotation). In the screen case, the image is transmitted only once, and there is no longer any translation necessary.

The primary object of this invention consists in the use of "active" masks as a source for the selective photoplymerization of liquid or powdered resins for the purpose of manufacturing objects from computer data (of CAD type, synthesis of image, etc ...).

These types of mask being: 1) Liquid crystal device and associated light source.

2) Video Screen Device.

3) Device with laser diodes or plasma discharge tubes.

these masks are directly controlled by a computer device and the display modification of each layer is done directly, without mechanical manipulation.

The rest of the device making it possible to solidify the successive layers which can then remain identical to the system developed by the company 3D systems (servo plate descending into the liquid). However this system requires the stabilization of the liquid between layers (a few seconds) and the passage of a squeegee to equalize the surface. Hence: II) POSITIONING OF THE MASK
The second object of this invention relates to the positioning of this mask:
In order to increase the manufacturing speed of the object, this time we have the image projected by the mask and the optical device, not on the surface of the liquid, but on the surface of a quartz glass, or any other material transparent to the wavelengths used, glass which will be sunk into the liquid (see Fig 1 1 or 12) We thus avoid three pitfalls: 1) the descending plate.

2) the problem of stabilization of the surface of the liquid.

3) The scraping.

In fact, the liquid being directly in contact with the glass, there is no possibility of wavelets on the surface of the liquid, and any problem of capillary effect on the newly solidified parts is eliminated by construction, since everything remains in the liquid.

The complete device works like this: 1st layer to solidify
The glass (projection screen) is positioned at the bottom of the resin tank, at a height from the bottom equal to the thickness of the layer to be solidified (ex: 1/10 th of a mm). The mask (The device integrating the liquid crystal, the video screen, or the device with laser diodes or plasma discharge tubes) displays the 1st layer (or line in the case of diode arrays and others): in black which is not to solidify, in white (therefore transparent to radiation) which needs to be solidified (image from a CAD file).

The UV lighting system (In the case of liquid crystals) then lights up (Flash type:
Intensity and duration depending on the type of resin used, or shutter system). The window is then raised by the height of a layer (eg: 1/10 th of a mm), the gap remains filled with liquid by pressure effect, no leveling is necessary. the liquid crystal screen displays the second layer to solidify and the lamp sends its second flash, etc.

At the end of the process, the device described is raised from the height of the part to be manufactured and has finished its work. The part is still entirely in the liquid. A plate fitted with an elevating device at the bottom of the liquid rises the finished and fully solidified part. The part is then removed from the tray, rinsed with a suitable solvent and available.

Sizes and details of the objects produced by this technique:
Taking into account the technologies used, the sizes of the manufacturable objects are not particularly limited, the optimum being located on volumes of 300 mm per cube for the smallest machines, to standard machines of 600 to 1000 mm per cube. Larger sizes are possible (Fig 13).

The manufacturing precision is entirely related to the precision of the lighting element, namely, liquid crystal cell or pixel of the video screen, or laser diode or discharge tube, multiplied by the magnification factor of the device. optical.

This optical device also makes it possible to illuminate different parts of the surface to be solidified, in several installments (example: a square of 30 centimeters on one side can be lit by 9 successive flashes each covering a square of 10 cm on one side; and in this case, the precision will be that of the square of 10 cm side) .In the case of a liquid crystal screen of 1000 points by 1000, and 200 mm side, the precision of each point is: 200 / 1000 mm, i.e.: 0.2 mm for a magnification factor of 1, and 0.1 mm for a magnification factor of 1/2 (reduction of the image by a factor of 2).

In the case of an array of diodes, Liquid crystals, discharge tubes, this precision will be of the same order, according to the arrangement of the elements on the array (in general from 300 to 600 points per inch, that is: 25, lmm for 300 at 600 points Direct precision, with magnification factor of 1: 25.1 / 300 to 25.1 / 600 or 0.085 to 0.043 mm.

By comparison, the precision of the machines currently supplied by the various manufacturers is no better than 0.2 mm on small objects.

Working speed:
Currently the machines delivered offer working speeds of around 1 solidified layer every 40 seconds on average. this time is due, on the one hand to the scanning speed of the laser, and on the other hand to the waiting time between layers: stabilization of the liquid and passage of the squeegee.

The process object of this invention eliminates the time of laser tracing, the stabilization of the liquid and the passage of the squeegee.

The manufacturing time per layer therefore drops to 2 seconds. for a polymerization of 0.1 mm deep. which makes it possible to produce an object 10 cm high, whatever its length, width, average thickness, in 2000 seconds, or approximately 35 minutes.

Industrial applications:
There are currently more than 400 stereolithography machines in the world. The estimated market for this type of technology, known as rapid prototyping, is around 300,000 units worldwide1 as long as the technology evolves and the machines offered are faster and easier to use and their cost is less than 50,000
Dollars (Figures extracted from a study carried out at the end of 1991 by the company Technicat Insights.

on rapid prototyping in the United States and worldwide). This figure of 500,000 units is to be compared to the number of installations in computer-aided design in mechanics worldwide (approximately 1,500,000 systems installed) and the number of plotters and machine tools 3 and 5 axes associated.

The need for rapid prototyping machines approaching the market for plotters of all types, mainly in the office environment.

The machine object of this invention is of the Office environment type, with a relatively low cost price, compared to the current costs of these machines, price being within the range estimated by the study of Technical Insights.

The areas affected now and in the future by existing machines and future machines are:
All the design offices of the companies manufacturing the objects:
Automotive, Aeronautics, Household appliances, Engineering, IT, Electricity, Electromechanical, Electronics, Telephony, Packaging, Glassmakers, Sports Equipment, Toys,
Eyewear, Medical ...

The French market alone is today estimated at more than 2,500 machines.

Figure 1: General principle of stereo laser lithography machines.

(la) Laser (1 b) Laser beam (2) set of deflection mirrors (used to orient the laser point on an XY plane) (3) Squeegee to equalize the level of the liquid. this moves in translation above the plane of the liquid in order to equalize the surface after each tracing of the laser.

(4) Light-curing liquid resin (5) Tank containing the resin (6) Tray descending into the liquid (7) Work in progress
Figure 2: Synoptic diagram of the Stereo-Lithography device and
Technological variants planned.

(1) Light Source (except in the case of an active source).

(I) Active source of Type Laser Diodes or Plasma discharge tubes (Screen or strips) (II) Active source of Video Type.

 (III) Mask of Slide Type.

 (1V) Active mask of Liquid Crystal type (Screen or bars).

 (2) Optical Focusing Device (3) Glass on which the image of the mask or active source (PI) is projected Immersed in the Liquid (PM) Mobile Part sinking into the resin tank (5) (5) Tank Resin Liquid Photopolymer (6) Tank bottom tray, Mobile (takes out the manufactured part, at the end of the process).

Figure 3: The different methods of selective photopolymerization (1) Seen on screen of what is to be solidified (in black) (2) Resin tank (3) Light source of wavelength allowing the photopolymerization reaction of the resin .

(4) focusing optics
The different methods that can be used to selectively solidify the photoplymerizable resin.

(I) Powder electrostatically deposited
(II) Slide or film
(here) Liquid crystal system
(Screen or barette)
(IV) Video screen
(V) laser diodes or plasma discharge tubes
(screen or bars).

(VI) mirror return device
(optional)
Figure 4: Liquid crystal screen base mask (1) Light source (2) Uniform light distribution device (3) Liquid crystal screen (4) Diaphragm (5) Focusing optics (6) Liquid crystal screen (7) Diaphragm (8) Focusing optics (projecting the image obtained on a transparent pane) With zoom possibilities (enlargement or reduction of the image).

(9) mechanical system integrating elements 1 to 8 (10) sealed tank sinking into the resin (11) glass plate or material transparent to the wavelengths used (12) Resin tank (13) Resin (14) Tray to reassemble the part at the end of manufacturing
Figure 5: Mask based on liquid crystal bar (1) Light source (2) Device for uniform light distribution.

(3) liquid crystal bar (5) diaphragm system (6) focusing lens system (7) liquid crystal bar (8) guide rail of the device allowing its translation (9) resin tank
Note: the mask thus formed is placed either directly in a watertight box sinking into the liquid, or behind a focusing optic and deflection mirrors.

A device slaved to the display of the line translates the whole.

Figure 6: first possibility of positioning the device described in Figure 5 (1) detailed assembly in Figure 5 (1 to 7) (2) Translattion device electronically controlled (3) Sealed container with transparent glass at the bottom, container immersed in resin (4 ) Resin tank
Figure 7: second possibility of positioning the device described in Figure 5 (1) detailed assembly in Figure 5 (1 to 7) (2) Transformation device electronically controlled (3) focusing optics of zoom type.

(4) Mirror (5) Watertight container with transparent glass at the bottom, tank immersed in resin (6) Resin tank
Figure 8: Source based on Laser diode array or discharge tubes (1) Laser diode array or plasma discharge tubes.

(2) optical focusing device (3) Guide rail for translating the assembly (1) and (2) (4) Resin tank
Figure 9: first possibility of positioning the device described in Figure 8 (1) detailed assembly in Figure 8 ((1) and (2)) (2) Translattion device electronically controlled (3) Sealed container with transparent glass at the bottom, container immersed in the resin (4) Resin tank
Figure 10: second possibility of positioning the device described in Figure 8 (1), detailed assembly in Figure 8 ((1) and (2)) (2) Transformation device electronically controlled (3) focusing optics of zoom type.

(4) Mirror (5) Watertight container with transparent glass at the bottom, tank immersed in resin (6) Resin tank
Figure 11: General Principle of Operation with box immersed in resin (1) light source
(in the case of an absorbent active mask: liquid crystals, see Figures 4 or 5).

(2) Device for uniform distribution of light (in the case of an absorbent active mask: liquid crystals see figure 4 or 5).

(3) Liquid crystal device (Figure 4 or 5) or active source (Diodes, tubes or video screen) (4) Focusing optics with Zoom (5) Deflection mirror (6) Sealed box device with transparent glass plunging into the resin tank (7) Transparent window on which the image from the source or mask is projected (8) Photopolymerizable resin (9) Work in progress (10) Resin tank
Figure 12: General principle of operation with box immersed in resin. Variant Without deflection mirror.

(1) device described in figure 4
(2) Sealed box device with transparent glass plunging into the resin tank (3) Transparent glass onto which the image from the source or mask is projected (4) Photopolymerizable resin (5) Resin tank (6) Piece during Manufacturing (7) Tray going up the part at the end of Manufacturing
Figure 13: Example of a device for making large objects.

(1) light source (in the case of an absorbent active mask: liquid crystals) (2) Active mask or active source (3) Focusing optics (Zoom) (4) Set of mirrors allowing the image to be reflected on a part of the surface of the resin tank (5) Sealed box device with transparent glass plunging into the resin tank (6) Resin tank (7) Transparent glass on which the image from the source is projected (8 ) Part in the course of manufacture (part already made).

Claims (4)

Claims 1) The machine for manufacturing objects by selective photopolymerization of liquids or photopolymerizable powders based on Active Mask or Active Source in motion from Computer files of computer-aided design or image synthesis is characterized by the integration of '' a mask absorbing part of the radiation emitted by a light source and allowing selectively the passage of light of wavelength suitable for the resin to be photopolymerized where it is to be photoplymerized or an active source: The name "active mask" is applied here to: - A liquid crystal device absorbing part of the radiation emitted by a suitable wavelength source, the source being monochromatic such as a laser or more simply a lamp or a series of lamps.  photopolymer resin surface will be lit in a single operation.  - Screen type with laser diodes or Plasma discharge tubes and in this case the  or tubes by translation or rotation  surface of the resin to be cured will be scanned by the diode array  - of the type of laser diode array or plasma discharge tubes in this case, the  riser will be lit in a single operation (Figure 3 (IV))  - of the Video Screen type, and in this case the surface of the photopolymer resin The name: "active source or emissive source" is here applied to devices generating their own light source. in an organized way:  tion or rotation (Figures 8,9,10)  light-curing will be scanned by the liquid crystal array by transla  - of the liquid crystal strip type and in this case, the surface of the resin to  light-curing will be illuminated in a single operation. (Figures 5, 6.7)  - of liquid crystal screen type, and in this case the surface of the resin to These masks or sources are called "active" in the sense that they are directly activated by a computer and electronic system to modify their state (display) according to the layers of photopolymers to be solidified, this by comparison with masks, called "passive". ", carne can themselves change state, because frozen by definition (Slides or Photographic film, Drawing made on transparent sheet, Layer of toner on a glass). 2) The liquid crystal mask device according to claim 1 is characterized in that it consists of one or more lamps, constituting the light source of wavelength allowing the photopolymerization reaction of the photopolymerizable resin, d '' a device for equalizing the light source (fresnel lens type or other) and several screens or bars arranged successively (at least 2) as well as at least one diaphragm according to Figure 4 (Screen) or Figures 5 to 7 (Barette), This arrangement increases the contrast between the transparent and opaque parts and allows the selective photopolymerization of a layer of photopolymerizable resin. 3) The device according to claim 1 is characterized in that this mask or active source is associated with an optical device in order to focus the image thus obtained on a window pane transparent to the wavelengths used, allowing the enlargement or reduction of the projected image. 4) The device according to claims 1,2 and 3 is characterized in that the assembly thus  constituted (the image projected by the mask or the active source and the optical device and the  glass) is immersed in the photopolymerizable resin in order to build the object, layer by  layer starting from the bottom of the tank and going up in steps equal to the layer height  light-cured until the object is completely manufactured.