The welding tracking sensor head consists of a CCD camera and one or two semiconductor lasers. The laser strip is projected onto the surface of the part at a predetermined angle as a structural light source. The camera directly observes the strip at the bottom of the sensor. The front of the camera has an optical filter that allows the laser to pass through while filtering out all other light, such as welding arcs. As a result, the sensor is positioned very close to the welding arc.
Fig. 1 The welding tracking sensor head.
The sensor is typically mounted on the front of the torch at a preset distance, known as the lead, to observe the weld. The installation height or distance between the sensor body and the workpiece varies depending on the type of sensor installed.
To ensure accurate observation, the welding gun must be positioned correctly above the weld so that the weld is close to the center of the strip, allowing the camera to observe both the laser strip and the weld.
Fig. 2 The position of the weld.
The laser range is projected at a specific angle. If the workpiece is very close to the sensor, the position of the laser strip will be relatively close. On the other hand, if the workpiece is far from the sensor, the position of the laser strip on the surface of the workpiece is relatively shifted backwards.
The camera observes the position of the laser strip and the sensor can measure the vertical distance from the workpiece. By analyzing the shape of the strip, the sensor can also determine the surface contour and position of the weld in the strip, allowing it to measure the transverse position of the weld.
Fig.3 Workpiece with normal distance
Fig. 4 Long distance workpiece
Fig. 5 Workpiece with close distance
The camera captures an image, which is processed by the controller and transformed into a digital laser stripe image. The software then segments the strip into multiple lines to form the weld. Based on the position of these lines, the system can calculate the position of the weld and convert it to a distance in millimeters using the calibration data stored in the sensor head.
During the tracking process, the system uses welding speed and forward distance to determine the delay time, ensuring that the torch follows the weld and not the sensor. The control strategy is designed to provide a smooth forward distance resulting in a smooth weld. If the sensor encounters a sudden change in path, it will respond smoothly, as illustrated in the figure below.
Fig. 6 A smooth response.
The sensor consists of several main components, including a CCD camera and filter, a semiconductor laser and optical elements, and a microprocessor for temperature monitoring and calibration data storage. The temperature monitor helps protect the laser from damage if the cooling system fails. It is important to note that if the laser operates beyond the temperature limit, its lifespan will be greatly reduced.
Storing calibration data makes it possible to exchange sensor heads without incurring additional costs or modifications, ensuring minimal downtime in the event of sensor damage or failure. The welding process is protected against soot and spatter by a black copper spatter guard, which is equipped with a transparent, replaceable plastic sheet that needs to be replaced regularly when dirt accumulates on its surface.
The sensor must be cooled using welding shielding gas or clean, dry, oil-free air to keep the temperature of the electronic components below 50°C, prevent dust accumulation, and protect the optical components. The typical gas flow rate used is 5 L/min.
If necessary, a water-cooled mounting plate can provide additional cooling for the sensor head. On the other hand, if the temperature of the semiconductor laser drops below +5°C, an optional heater must be installed on the sensor.
