REAL TIME IMPLEMENTATION OF GENERALIZED PREDICTIVE CONTROL ALGORITHM FOR THE CONTROL OF DIRECT METAL DEPOSITION (DMD) PROCESS

• US 20080223832A1
• Filed: 11/16/2007
• Published: 09/18/2008
• Est. Priority Date: 11/16/2006
• Status: Abandoned Application

• Current Assignee: DM3D Technology, LLC
• Original Assignee: The POM Group
• Inventors: Mazumder, Jyoti, Song, Lijun
• Application Number:
  US11/941,664
• Publication Number:
  US 20080223832A1
• Time in Patent Office: Days
• US Class Current: 219/121.66
• CPC Class Codes: B23K 2103/50 Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
• CPC Class Codes: B23K 26/03 Observing, e.g. monitoring, the workpiece
• CPC Class Codes: B23K 26/032 using optical means
• CPC Class Codes: B23K 26/034 Observing the temperature of the workpiece
• CPC Class Codes: B23K 26/0344 Observing the speed of the workpiece
• CPC Class Codes: B23K 26/123 in an atmosphere of particular gases
• CPC Class Codes: B23K 26/32 taking account of the properties of the material involved
• CPC Class Codes: B23K 26/34 Laser welding for purposes other than joining
• CPC Class Codes: B23K 35/0244 Powders, particles or spheres; Preforms made therefrom
• CPC Class Codes: G01J 5/004 by molten metals
• CPC Class Codes: G01J 5/0044 Furnaces, ovens, kilns G01J5/0007, G01J5/004 take precedence
• CPC Class Codes: G01J 5/02 Constructional details
• CPC Class Codes: G01J 5/025 Interfacing a pyrometer to an external device or network; User interface
• CPC Class Codes: G01J 5/60 using determination of colour temperature

Abstract

A linear model based generalized predictive control system controls the molten pool temperature during a Direct Metal Deposition (DMD) process. The molten pool temperature is monitored by a two-color pyrometer. A single-input single-output linear system that describes the dynamics between the molten pool temperature and the laser power is identified and validated. The incremental generalized predictive control algorithm with Kalman filter estimation is used to control the molten pool temperature.

Claims

1. A method of controlling a direct-metal deposition (DMD) process of type wherein a precisely controlled laser beam is used to melt powders in a melt pool on a substrate to form products, comprising the steps of:

identifying temperature dynamics associated with the melt pool; and

generating excitation signals to control the laser as a function of the temperature dynamics using a generalized predictive control algorithm with input constraints.

2. The method of claim 1, wherein the step of identifying temperature dynamics associated with the melt pool is carried out with a two-color pyrometer.

3. The method of claim 2, wherein the two-color pyrometer senses in regions of the spectrum different from that used by the laser used to form the melt pool.

4. The method of claim 3, wherein the laser used to form the melt pool is a diode laser, a fiber laser, or a CO₂ laser.

5. The method of claim 3, wherein the two-color pyrometer senses in bands at 1.3 μ

m and 1.64 μ

m.

6. The method of claim 1 wherein the excitation signals comprises random amplitudes or random durations in a predetermined range.

7. The method of claim 1, wherein the step of identifying temperature dynamics associated with the melt pool comprises model order selections, step response comparisons and residual analysis among different models structures.

8. The method of claim 1, wherein the generalized predictive control algorithm uses space-state models.

9. The method of claim 8, wherein the space-state models can be scaled into multiple-input and multiple-output systems to implement other control parameters such as the pool geometry and plume plasma radiation so as to control product dimensions or compositions.

10. The method of claim 1, wherein the generalized predictive control algorithm uses a dual active-set method with modifications.

20. The method of claim 1, wherein the controller implements a dual active-set method with modifications.

11. A direct-metal deposition (DMD) system, comprising:

a controllable laser beam to melt powders in a melt pool on a substrate to form products;

an instrument for identifying temperature dynamics associated with the melt pool; and

a generalized predictive controller with input constraints operative to generate excitation signals to control the laser as a function of the temperature dynamics identified by the instrument.

12. The system of claim 11, wherein the instrument used to identify temperature dynamics associated with the melt pool is a two-color pyrometer.

13. The method of claim 12, wherein the two-color pyrometer senses in regions of the spectrum different from that used by the laser used to form the melt pool.

14. The method of claim 13, wherein the laser used to form the melt pool is a diode laser, a fiber laser, or a CO₂ laser.

15. The method of claim 13, wherein the two-color pyrometer senses in bands at 1.3 μ

m and 1.64 μ

m.

16. The method of claim 11, wherein the excitation signals comprises random amplitudes or random durations in a predetermined range.

17. The method of claim 11, wherein the processor uses model order selections, step response comparisons and residual analysis among different models structures.

18. The method of claim 11, wherein the generalized predictive control algorithm uses space-state models.

19. The method of claim 18, wherein the space-state models can be scaled into multiple-input and multiple-output systems to implement other control parameters such as the pool geometry and plume plasma radiation so as to control product dimensions or compositions.