System Development

As described in section 4, in the initial phase of this work a control system was developed to control a band on pipe welding system. This work concerns the development of an adaptive control system for narrow groove pipeline welding. The system in development is a computer based monitoring and adaptive control system, intended to improve current results. It utilises feedback data from the laser vision sensor. The sensor is able to scan the joint providing measurement data such as gap, bevel angle or joint surface features while welding. Data coming from the vision sensor will be used together with feedback data from the welding power supplies and the motion controller, in the control algorithms. The intent of these control algorithms is to perform online adjustments to the motion and welding parameters. This aims for a more stable process with higher productivity.

The system being a computer based monitoring and control system it is capable of achieving current equipment results without depending so much on user intervention. It is able to acquire data from digital power supplies, laser stripe vision sensor and motion controller. This data provides information regarding the system status and is to be used in the adaptive control algorithms. The intent of these control algorithms is to perform online adjustments to the motion and welding parameters to compensate for variations in pipe setup. The foundations for this work are accurate monitoring and robust control algorithms. This novel system approach to pipeline welding will include seam tracking, torch height control and detection of previous seam shape for weld parameter adaption.

5.1.1 Hardware

This system is divided into four major components: welding, motion, vision and computer.

Each of these components will be described below. Once fully implemented they will communicate with each other through the control algorithms.

5.1.1.1 Welding

The welding system component contains the Lincoln Electric Power Wave F355i digital power supplies (Figure 5.1), wire feeders (Power Feed 10 Robotic K1780-2) and shielding gas supply (Figure 5.2). For this project these power supplies are controlled by the computer using Ethernet communication and the wire feeders and gas sub-systems are computer controlled through the corresponding power supply. The power supplies and computer exchange data bi-directionally. The computer regularly interrogates the power supplies on their status, and updates to the welding parameters will be sent by the computer to the power supplies. For more specific information about this PSs and the wire feeders check section 4.2.1.2 (page 32).

Figure 5.1 – Digital power supplies.

Figure 5.2 – Wire feed and gas equipment.

5.1.1.2 Motion

The motion system controls all three axes of movement in the welding head in order to place the welding torch(es) in the appropriate position to perform the weld. The three motion axes are responsible for: the travel around the pipe (X); torch oscillation (Y); and torch vertical displacement in relation to the pipe (Z), see Figure 5.4. The motion system is also responsible for retrieving information from two inclinometers inside the welding head. The welding head in

use is a Saturnax 5 with linear oscillation from Serimax. The motion controller used is a DMC-2280 controller together with a ICM/AMP 1900 interconnect module with internal amplifiers and an ICM 2900 interconnect modules with two servo amplifiers (12A8K) from Advanced Motions Controls, see Figure 5.3. The characteristics

Figure 5.3 – Motion controller equipment. Figure 5.4 – Welding head with tandem torch and laser sensor.

5.1.1.3 Welding Head

The Saturnax 5 commercial welding head from Serimax (Figure 4.6) as stated before had to be modified to be used in this system. The present configuration can be seen in Figure 4.7, the changes were required in order for the welding head to be capable of supporting a variety of welding torches and the laser camera.

5.1.1.4 Laser

The laser system components are a laser camera, control unit and ground fault detector from Servo Robot. The laser camera is a 3D laser vision camera MINI-I 60 based on a laser stripe system. The laser camera’s main physical characteristics can be seen in Figure 6.2, the camera uses a 50mW visible diode laser. Transmitted data to the control unit is 14340 points per second with 60 frames of 239 sampling points each. The control unit is pre-programmed with information related to the groove that will be scanned and sends data to the computer through a serial (RS-232) cable. More information concerning the laser sensor hardware can be found in section 6.1.1.1.

X Y

Z

5.1.1.5 Computer

A PC acts as central controller. An Intel Pentium III 844MHz processor, 384MB of RAM memory computer running Microsoft Windows XP is being used for development purposes.

The computer has the role of receiving information from the remaining parts of the system, processing it on-line with adaptive control algorithms and sending data back to the motion and welding systems with the necessary adjustments.

Figure 5.5 – Partial view of the system.

Legend:

1. PC (Personal Computer);

2. Motion Controller;

3. Laser Control Unit

5.1.2 Software

The user interface for this project will ultimately be a push button to initiate the welding. For the moment a User Interface (UI) was developed which is capable of controlling the system in manual and automatic modes. The manual mode was implemented in order to debug and better understand the way the hardware works. The UI in question is capable of controlling the power supplies and the welding head moving on a band.

The UI in question is SP5 – Pipe Girth Welding Software. A description of the features and capabilities of SP5 can be found in section 4.3.

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