Solid imaging apparatus and method with coating station

Abstract

A solid imaging apparatus and method produces an integral three-dimensional object from a multiplicity of cross sectional portions of the object by selectively exposing successive layers of a liquid photoformable composition to actinic radiation. The apparatus includes a vessel for containing the composition so as to present a free surface, and a movable platform disposed within the vessel below the free surface. Part of the composition is transferred above the free surface by lowering and raising a dispenser at predetermined positions located away from the platform. A doctor blade contacts the composition transferred above the free surface, and then moves over the platform to form a substantially uniform layer of the composition.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This is a continuation of application Ser. No. 07 / 884,030 filed May 18, 1992, which is a continuation-in-part of application Ser. No. 07 / 804,269, filed Dec. 5, 1991, now abandoned, which is a continuation of application Ser. No. 07 / 488,095, filed Mar. 1, 1990, now abandoned.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] This invention pertains to a solid imaging method and apparatus for fabricating an integral three-dimensional object from a multiplicity of cross sectional portions of the object. More particularly, the cross sectional portions correspond to solidified portions of contiguous layers of a photoformable composition. The method and apparatus use a dispenser in a coating station, which transfers part of the photoformable composition over the free surface of the composition so that a doctor blade may produce a uniform liquid layer. [0004] 2. Description of Related Art [0005] Many systems for production of ...

AI Technical Summary

Benefits of technology

[0010] U.S. Pat. No. 2,775,758, issued to O. J. Munz on Dec. 25, 1956, and the Scitex application describe methods by which the photoformable liquid is introduced into a vat by means of a pump or similar apparatus such that the

Problems solved by technology

The aforementioned methods of coating, however, are not capable of ensuring flat uniform layer thickness or of producing such layers quickly, or they do not effectively prevent damage or distortion to previously formed layers during the successive coating process and they involve coating only liquid formulations of preferably low viscosity.

Furthermore, they omit to recognize very important parameters involved in the coating process such as the effects of having both solid and liquid regions present during the formation of the thin liquid layers, the effects of fluid flow and rheological characteristics of the liquid, the tendency for thin photoformed layers to easily become distorted by fluid flow during coating, and the effects of weak forces such as hydrogen bonds and substantially stronger forces such as mechanical bonds and vacuum or pressure differential forces on those thin layers and on the part being formed.

Motion of the platform and parts, which have cantilevered or beam regions (unsupported in the Z direction by previous layer sections) within the liquid, creates deflections in the layers, contributing to a lack of tolerance in the finished part.

In addition, this method is rather slow.

Such methods have the aforementioned disadvantages of the Hull method except that the deflection of the layers during coating is reduced.

The methods described by Fudim do not address the problems inherent in separating such a transmitting material from a photopolymer formed in intimate contact with the surface of the transmitting material.

Whereas the effects of chemical bonding may be reduced significantly by suitable coatings or inherently suitable films, the mechanical bonds along with hydrogen bonds, vacuum forces, and the like are still present and in some cases substantial enough to cause damage or distortion to the photopolymer during removal from the transmitting material surface.

However, these methods require an exact amount of material or photoformable composition to be added in the vessel every time a layer has to be formed.

Because of this, the systems described in these patents have restrictions necessarily confining the photosensitive material between the doctor blade and part of the vessel at all times. Thus, it becomes very difficult to form a uniform layer in one continuous pass of the doctor blade without ending up with an excess or shortage of material at the end of the pass.

In other words, the doctored layer may be either lacking a part of it at the end of one doctoring operation or it may have an excess of material, which will be very difficult to redistribute in order to achieve the proper thickness and uniformity, due to the confined nature of the arrangement.

Also, the doctor blade has a tendency to create wave motion in the material surrounding the previously exposed layer causing a disturbing effect, particularly on parts of the previously exposed layer which are partially unsupported.

Use of a pump to recirculate a liquid of the nature used in solid imaging or stereolithography does not present a viable solution because the viscosity and mainly sensitivity of such compositions cause blockage of the paths and seizure of the pumping operation at an unacceptably high rate.

Premature polymerization within the higher-shear components of the pump seem to be the most probable cause of this problem.

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