Electrophotography-Based Additive Manufacturing with Powder Density Detection and Utilization

• US 20150266236A1
• Filed: 03/18/2014
• Published: 09/24/2015
• Est. Priority Date: 03/18/2014
• Status: Active Grant

• Current Assignee: Evolve Additive Solutions, Inc.
• Original Assignee: Stratasys Incorporated
• Inventors: Farah, Zeiter S., Batchelder, J. Samuel
• Granted Patent: US 9,643,357 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B29L 2031/00 Other particular articles
• CPC Class Codes: B33Y 10/00 Processes of additive manufacturing
• CPC Class Codes: B33Y 30/00 Apparatus for additive manufacturing; Details thereof or accessories therefor
• CPC Class Codes: G01N 27/22 by investigating capacitance
• CPC Class Codes: G01R 1/18 Screening arrangements against electric or magnetic fields, e.g. against earth's field
• CPC Class Codes: G03G 15/1625 on a base other than paper
• CPC Class Codes: G03G 15/224 Machines for forming tactile or three dimensional images by electrographic means, e.g. braille, 3d printing
• CPC Class Codes: G03G 15/24 whereby at least two steps are performed simultaneously
• CPC Class Codes: G03G 2215/1695 at the second or higher order transfer point

Abstract

An additive manufacturing system for printing a three-dimensional part, which includes one or more electrophotography engines configured to develop layers of the three-dimensional part, a rotatable transfer belt configured to receive the developed layers from the electrophotography engine(s), a detector configured to measure powder densities of the developed layers on the rotatable transfer belt, and to transmit signals relating to the measured powder densities to a controller assembly, and a printing assembly configured to receive the developed layer from the rotatable transfer belt and to print the three-dimensional part from the developed layers.

Claims

1. An additive manufacturing system for printing a three-dimensional part, the additive manufacturing system comprising:

one or more electrophotography engines configured to develop layers of the three-dimensional part;

a rotatable transfer belt configured to receive the developed layers from the one or more electrophotography engines;

a detector configured to measure powder densities of the developed layers on the rotatable transfer belt, and to transmit signals relating to the measured powder densities;

a printing assembly configured to receive the developed layer from the rotatable transfer belt and to print the three-dimensional part from the developed layers; and

a controller assembly configured to receive the transmitted signals from the detector.

2. The additive manufacturing system of claim 1, wherein the detector comprises one or more capacitance sensors.

3. The additive manufacturing system of claim 2, wherein the one or more capacitance sensors comprise a plurality of capacitance sensors arranged in an array that is perpendicular to a movement direction of the rotatable transfer belt.

4. The additive manufacturing system of claim 2, wherein the detector further comprises a casing having one or more magnetic shielding materials, and which defines a slot for the rotatable transfer belt to move through, and wherein the one or more capacitance sensors are retained within the casing.

5. The additive manufacturing system of claim 2, wherein the detector further comprises a control board, and wherein each of the one or more capacitance sensors comprises:

an excitation electrode electrically connected to the control board;

a sense electrode electrically connected to the control board, and offset from the excitation electrode by a gap, wherein the rotatable transfer belt extends through the gap;

a first shield ground plate secured to the excitation electrode opposite of the gap; and

a second shield ground plate secured to the sense electrode opposite of the gap.

6. The additive manufacturing system of claim 5, and further comprising:

a first insulating film secured to the excitation electrode such that the first insulating film is located between the excitation electrode and the rotatable transfer belt; and

a second insulating film secured to the sense electrode such that the second insulating film is located between the sense electrode and the rotatable transfer belt.

7. The additive manufacturing system of claim 1, wherein the printing assembly comprises:

a heater configured to heat the developed layers;

a build platform; and

a pressing element configured to engage with the transfer assembly to press the heated developed layers into contact with a top surface of the three-dimensional part on the build platform in a layer-by-layer manner.

8. A method for printing a three-dimensional part with an additive manufacturing system, the method comprising:

producing a developed layer of a part material with an electrophotography engine of the additive manufacturing system;

transferring the developed layer from the electrophotography engine to a transfer belt of the additive manufacturing system;

rotating the transfer belt with the developed layer;

measuring a powder density of the developed layer on the rotating transfer belt; and

heating the developed layer on the rotating transfer belt after measuring the powder density; and

pressing the heated developed layer into contact with a top surface of the three-dimensional part.

9. The method of claim 8, wherein measuring the powder density of the developed layer on the rotating transfer belt comprises:

measuring one or more capacitance values of the developed layer on the rotating transfer belt;

transmitting signals relating to the one or more measured capacitance values for the developed layer to a controller assembly; and

determining a sample capacitance value with the controller assembly from the transmitted signals for the developed layer.

10. The method of claim 9, wherein measuring the powder density of the developed layer on the rotating transfer belt further comprises:

measuring one or more capacitance values of the rotating transfer belt in a clean state;

transmitting signals relating to the one or more measured capacitance values for the belt to the controller assembly;

determining a baseline capacitance value with the controller assembly from the transmitted signals for the belt; and

determining a difference between the sample capacitance value and the baseline capacitance value with the controller assembly.

11. The method of claim 8, wherein producing the developed layer of the part material comprises producing a test sample of the part material having predetermined dimensions, and wherein measuring the powder density of the developed layer on the rotating transfer belt comprises:

measuring one or more capacitance values of the test sample on the rotating transfer belt with the detector; and

transmitting signals relating to the one or more measured capacitance values for the test sample to a controller assembly.

12. The method of claim 8, and further comprising modifying imager data for the electrophotography engine based on the measured powder density.

13. The method of claim 8, and further comprising measuring z-heights of the heated developed layer pressed on the three-dimensional part.

14. A method for measuring a powder density of a developed layer, and utilizing the measured part density, in an additive manufacturing system, the method comprising:

rotating a transfer belt of the additive manufacturing system;

measuring one or more capacitance values of the rotating transfer belt in a clean state;

determining a baseline capacitance value from the one or more measured capacitance values for the rotating transfer belt;

producing the developed layer of a powder-based material with an electrophotography engine of the additive manufacturing system;

transferring the developed layer from the electrophotography engine to the rotating transfer belt;

measuring one or more capacitance values of the developed layer on the rotating transfer belt;

determining a sample capacitance value the one or more measured capacitance values for the developed layer on the rotating transfer belt; and

determining a difference between the sample capacitance value and the baseline capacitance value.

15. The method of claim 14, wherein producing the developed layer of the powder-based material comprises producing a test sample of the powder-based material for the developed layer, wherein the test sample has predetermined dimensions.

16. The method of claim 15, wherein measuring the one or more capacitance values of the developed layer on the rotating transfer belt comprises measuring one or more capacitance values of the test sample on the rotating transfer belt.

17. The method of claim 14, wherein measuring the one or more capacitance values of the developed layer on the rotating transfer belt comprises measuring a plurality of capacitance values of the of the developed layer on the rotating transfer belt with a plurality of capacitance sensors arranged in an array that extends perpendicular to a movement direction of the rotating transfer belt.

18. The method of claim 14, and further comprising insulating the plurality of capacitance sensors from spatially-varying potentials of the rotating transfer belt.

19. The method of claim 14, and further comprising modifying imager data for the electrophotography engine based on the determined difference between the sample capacitance value and the baseline capacitance value.

20. The method of claim 14, and further comprising modifying a triboelectric charge-to-mass (Q/M) ratio of the powder-based material based on the determined difference between the sample capacitance value and the baseline capacitance value.