GB2315700A

GB2315700A - Use of dynamic masks for object manufacture

Info

Publication number: GB2315700A
Application number: GB9615840A
Authority: GB
Inventors: Rupert Charles David Young; Chris Reginald Chatwin; Malcolm Ian Heywood
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-07-27
Filing date: 1996-07-27
Publication date: 1998-02-11
Also published as: GB9615840D0

Abstract

A dynamic mask (spatial light modulator) is used to produce a defined amplitude pattern in the imaging or Fourier plane of a lens system for application to object manufacture and rapid prototyping. The polarisation of an illuminating optical wavefront is amplitude or phase modulated by the spatial light modulator after transmission through, or reflection from, a polarising element. The pattern so generated is imaged or Fourier transformed to a photosensitive medium in order to create a specified level slice of the 3-D model or component under construction. Alternatively, a phase pattern is calculated and written to a phase modulating spatial light modulator. The pattern is calculated such that when optically Fourier transformed, an intensity pattern is generated in the back focal plane of the lens system. Derived from its CAD solid model, this will correspond to a given cross-section through the component or prototype under construction.

Description

Use of dynamic masks for object manufacture The invention relates to the use of a Spatial Light Modulator (SLM) to produce a defined amplitude pattern in the imaging or Fourier plane of a lens system for application to object manufacture and rapid prototyping.

Currently, laser scanning systems are used to write, one data point at a time, CAD model level slice data onto the surface of a photopolymer so as to induce a photopolymerisation reaction and create a solid layer of polymer corresponding in shape to the component at that level. The laser beam must be raster scanned over the surface in a serial manner which is inherently slow.

The invention described herein employs a dynamic mask, electrically or optically addressed with CAD level slice model data This modulates an optical wavefront with this information by spatially changing the polarisation or phase of the wavefront such that an amplitude pattern corresponding to the CAD level slice is projected onto the surface of the photopolymer or other substrate. The model or component is thus built layer by layer into a solid by displaying successive level slices from the CAD model on the SLM and exposing the photopolymer or other medium to the modulated illuminating radiation.

The polarisation of an illuminating optical wavefront is amplitude modulated by the SLM after transmission through, or reflection from, a polarising element. The pattern so generated is imaged or Fourier transformed to a photosensitive medium in order to create a specified level slice of the 3-D model under construction.

Alternatively, a phase pattern (binary or, preferably, multi-level phase) is calculated and written to a phase modulating spatial light modulator (PM-SLM). The pattern is calculated such that when optically Fourier transformed an intensity pattern is generated in the back focal plane of the lens system. This corresponds to a given cross-section through the component under construction which is derived from a CAD solid model of the component for which it is desired to produce the prototype.

To do this, the PM-SLM is illuminated by a TEMoo (Gaussian) mode coherent laser wavefront. Uniform illumination of the PM-SLM is not required since the intensity pattern is realised in the reciprocal space. Thus the Gaussian profile of the illuminating beam results in a convolution of the impulse response of the optical system with the generated intensity pattern which will be the Fourier transform of the illuminating Gaussian beam. The wavelength of the coherent wavefront may be from the ultra-violet to the visible dependant on the nature of the photopolymer being used.

The phase pattern is determined by an iterative technique such as one of the variations based on the Gerchberg-Saxton algorithm.

The imaging or Fourier plane of the lens system is arranged to be at the surface of or within the body of, the liquid photopolymer substrate that is photo-polymerised to a solid according to the pattern projected onto its surface. Thus a solid level-slice of the prototype under construction is generated that corresponds to the projected intensity pattern. Z-axis increments of the prototype in the photopolymer bath are carried out in order to build the entire component layer by layer. Thus, for each layer a new phase pattern is displayed on the PM-SLM and hence a new intensity distribution is generated at the particular z-plane under construction.

A specific embodiment is illustrated in the Figures below. The conventional scanning mirror system is replaced by the SLM projection technique. In Figure 1 a laser 1 passes through beam expansion optics 2 so as to illuminate the spatial light modulator 3. The lens 4 images or Fourier transforms the polarisation or phase modulated wave front onto the surface of the model currently being constructed such that the desired amplitude pattern is produced at the surface. In this particular embodiment, this is a photopolymerised model immersed in a photopolymer bath. Successive layers are built up by lowering the model into the bath after each layer is photopolymerised.

Figure 2 is an overall system diagram showing the data flow links to the CAD system.

Claims

Having described the invention the claims are:

1) The use of polarisation modulation, generated by whatsoever means, used so as to generate an intensity pattern when imaged or focused by a lens, to be used for cutting or solidifying a material.

2) The use of a programmable polarisation modulating mask (spatial light modulator) designed so as to generate an intensity pattern as in claim (1), to be used as in claim (1).

3) The use of a programmable polarisation modulating mask as in claim (2), to generate an intensity pattern as in claim (1), to be used in a rapid prototyping and/or manufacturing system using any material process whatsoever in order to generate a solid model layer by layer.

4) The use of a programmable polarisation modulating mask as in claim (2), to generate an intensity pattern as in claim (1), to be used in a rapid prototyping and/or manufacturing system as in claim (3), to solidify a photopolymer matrix containing any material whatsoever in order to generate a solid component object layer by layer.

5) The use of a programmable phase modulating mask as in claim (2), to generate an intensity pattern as in claim (1), to be used in a rapid prototyping and/or manufacturing system as in claim (3), to solidify a photopolymer in order to generate a solid model layer by layer.

5) The use of a programmable polarisation modulating mask as in claim (2), to generate an intensity pattern as in claim (1), to be used in a rapid prototyping and/or manufacturing system as in claim (3), to solidify a photopolymer matrix containing any material whatsoever in order to generate a solid object layer by layer.

6) The use of a phase mask, made by whatsoever means, designed so as to generate an intensity pattern when imaged or focused by a lens, to be used for cutting or solidifying a material.

7) The use of a programmable phase mask (phase modulating spatial light modulator) to display a phase profile designed so as to generate an intensity pattern as in claim (6), to be used as in claim (6).

8) The use of a programmable phase mask as in claim (7), to generate an intensity pattern as in claim (6), to be used in a rapid prototyping and/or manufacturing system using any material process whatsoever in order to generate a solid model layer by layer.

9) The use of a programmable phase mask as in claim (7), to generate an intensity pattern as in claim (6), to be used in a rapid prototyping and/or manufacturing system as in claim (8), to solidify a photopolymer matrix containing any material whatsoever in order to generate a solid model layer by layer.

10) The use of a programmable phase mask as in claim (7), to generate an intensity pattern as in claim (6), to be used in a rapid prototyping and/or manufacturing system as in claim (8), to solidify a photopolymer in order to generate a solid model layer by layer.

Amendments to the claims have been tiled as follows 1) The use of a phase mask, made by whatsoever means, designed so as to generate an intensity pattern when imaged or focused by a lens, to be used for cutting or solidifying a material.

2) The use of a programmable phase modulating mask (phase modulating spatial light modulator) to display a phase profile designed so as to generate an intensity pattern as in claim (1), to be used as in claim (1).

3) The use of a programmable phase modulating mask as in claim (2), to generate an intensity pattern as in claim (1), to be used in a rapid prototyping and/or manufacturing system using any material process whatsoever in order to generate a solid model layer by layer.

4) The use of a programmable phase modulating mask as in claim (2), to generate an intensity pattern as in claim (1), to be used in a rapid prototyping and/or manufacturing system as in claim (3), to solidify a photopolymer matrix containing any material whatsoever in order to generate a solid model layer by layer.