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Closed loop control of penetration depth during CO₂ laser lap welding processes.

Sibillano T, Rizzi D, Mezzapesa FP, Lugarà PM, Konuk AR, Aarts R, Veld BH, Ancona A - Sensors (Basel) (2012)

Bottom Line: Our novel approach is to analyze the optical emission from the laser generated plasma plume above the keyhole, to calculate its electron temperature as a process-monitoring signal.The sensor is able to correlate in real time the difference between the measured electron temperature and its reference value for the requested penetration depth.Accordingly the closed loop system adjusts the power, thus maintaining the penetration depth.

View Article: PubMed Central - PubMed

Affiliation: CNR-IFN Institute for Photonics and Nanotechnologies, UOS Bari, 70126 Bari, Italy. teresa.sibillano@fisica.uniba.it

ABSTRACT
In this paper we describe a novel spectroscopic closed loop control system capable of stabilizing the penetration depth during laser welding processes by controlling the laser power. Our novel approach is to analyze the optical emission from the laser generated plasma plume above the keyhole, to calculate its electron temperature as a process-monitoring signal. Laser power has been controlled by using a quantitative relationship between the penetration depth and the plasma electron temperature. The sensor is able to correlate in real time the difference between the measured electron temperature and its reference value for the requested penetration depth. Accordingly the closed loop system adjusts the power, thus maintaining the penetration depth.

No MeSH data available.


Controller layout.
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f2-sensors-12-11077: Controller layout.

Mentions: Figure 2 shows an overview of the controller operation. The electron temperature signal was used by the controller to stabilize the penetration depth at the desired value by adjusting the laser power. The core of the controller is a Proportional-Integral (PI) algorithm, based on the following equation:(1)C(s)=Kp(1+1sTi)in which Kp and Ti are constant parameters that denote controller gain and integral time constant parameters, respectively, and variable s indicates that the equation is expressed in the Laplace domain. The electron temperature set point Te,ref, for a desired penetration, has been determined according to the relation found in the preliminary welding tests and expressed in Figure 3. Like the P-only controller, the PI algorithm computes a controller output from its input. In our case the controller output was an analogic voltage signal (0–10 V) linearly related to the laser power level (0–2,500 W). The input signal was the difference ΔTe between the current electron temperature signal and its reference value. The computed output from the PI algorithm depends on the controller tuning parameters and the controller's input. The integral action ensures that the PI controller eliminates an offset, which is not possible with a P-only controller. To improve the controller performance at the start of the weld an initial laser power based on previous experiments is added to the controller output. Thus, PI controllers provide a balance of complexity and capability that makes them a widely used algorithm in process control applications.


Closed loop control of penetration depth during CO₂ laser lap welding processes.

Sibillano T, Rizzi D, Mezzapesa FP, Lugarà PM, Konuk AR, Aarts R, Veld BH, Ancona A - Sensors (Basel) (2012)

Controller layout.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3472874&req=5

f2-sensors-12-11077: Controller layout.
Mentions: Figure 2 shows an overview of the controller operation. The electron temperature signal was used by the controller to stabilize the penetration depth at the desired value by adjusting the laser power. The core of the controller is a Proportional-Integral (PI) algorithm, based on the following equation:(1)C(s)=Kp(1+1sTi)in which Kp and Ti are constant parameters that denote controller gain and integral time constant parameters, respectively, and variable s indicates that the equation is expressed in the Laplace domain. The electron temperature set point Te,ref, for a desired penetration, has been determined according to the relation found in the preliminary welding tests and expressed in Figure 3. Like the P-only controller, the PI algorithm computes a controller output from its input. In our case the controller output was an analogic voltage signal (0–10 V) linearly related to the laser power level (0–2,500 W). The input signal was the difference ΔTe between the current electron temperature signal and its reference value. The computed output from the PI algorithm depends on the controller tuning parameters and the controller's input. The integral action ensures that the PI controller eliminates an offset, which is not possible with a P-only controller. To improve the controller performance at the start of the weld an initial laser power based on previous experiments is added to the controller output. Thus, PI controllers provide a balance of complexity and capability that makes them a widely used algorithm in process control applications.

Bottom Line: Our novel approach is to analyze the optical emission from the laser generated plasma plume above the keyhole, to calculate its electron temperature as a process-monitoring signal.The sensor is able to correlate in real time the difference between the measured electron temperature and its reference value for the requested penetration depth.Accordingly the closed loop system adjusts the power, thus maintaining the penetration depth.

View Article: PubMed Central - PubMed

Affiliation: CNR-IFN Institute for Photonics and Nanotechnologies, UOS Bari, 70126 Bari, Italy. teresa.sibillano@fisica.uniba.it

ABSTRACT
In this paper we describe a novel spectroscopic closed loop control system capable of stabilizing the penetration depth during laser welding processes by controlling the laser power. Our novel approach is to analyze the optical emission from the laser generated plasma plume above the keyhole, to calculate its electron temperature as a process-monitoring signal. Laser power has been controlled by using a quantitative relationship between the penetration depth and the plasma electron temperature. The sensor is able to correlate in real time the difference between the measured electron temperature and its reference value for the requested penetration depth. Accordingly the closed loop system adjusts the power, thus maintaining the penetration depth.

No MeSH data available.