The welding tracking sensor head includes a CCD camera and one or two semiconductor lasers. The laser is used as a structured light source to project laser fringes onto the surface of the workpiece under the sensor at a predetermined angle. The camera directly observes the stripes at the bottom of the sensor. On the front of the camera is an optical filter that allows the laser to pass through but filters out all other light, such as welding arcs. The sensor can therefore be very close to the welding arc.
The sensor is usually installed in the front of the welding gun at a preset distance (advanced), so it can observe the weld. The distance from the sensor body to the workpiece, that is, the installation height, depends on the type of sensor installed. When the welding torch is correctly positioned above the weld, the weld should be close to the center of the stripes, so that the camera can observe the laser stripes and the weld.
Since the laser fringe is projected at a certain angle, if the distance between the workpiece and the sensor is too close, the position of the laser fringe will be relatively forward. Conversely, if the workpiece is farther away from the sensor, the position of the laser stripes on the surface of the workpiece is relatively backward. The camera observes the position of the laser fringe, and the sensor can measure the vertical distance from the workpiece. From the perspective of the shape of the stripes, the sensor can also measure the contour of the surface and the position of the weld on the stripes, which allows the sensor to measure the lateral position of the weld.
The image observed from the camera is processed by the controller, and the image is first acquired and formed into a digitized laser fringe image. The software then uses specific settings to divide the stripes into many lines that form the weld. From the position of these lines, the system can measure the position of the weld and convert it into a distance calculated in mm. This conversion is done using the calibration data stored in the sensor head. When the system is tracking, the welding speed and the forward-looking distance are used to calculate the delay time. This ensures that the welding gun, not the sensor, travels along the weld. It should be pointed out that the control strategy provides a smooth forward looking distance to ensure the formation of a smooth weld. Therefore, if the sensor encounters a step change in the path, it will provide a smooth response, as shown in the figure below.
The key components of the sensor include: CCD cameras and filters, semiconductor lasers and optical components, microprocessors for temperature monitoring, and stored calibration data.
The temperature monitor protects the laser in case of failure of the cooling system. If the laser is used at a temperature exceeding the limit, its life will be significantly reduced.
The storage of calibration data makes the sensor heads completely interchangeable. Without additional costs and modifications. Thus, the minimum downtime in the event of sensor damage or failure is guaranteed.
The fumes and splashes of the welding process are protected by a black copper splash baffle to protect the optical components of the sensor head. This splash baffle is equipped with a clear and replaceable plastic sheet, which must be replaced regularly when dirt is on its surface.
The sensor must be welded with shielding gas or air cooling (clean, dry and oil-free) to maintain the temperature of the electronic components below 50°C, prevent smoke and dust, and protect the optical components. The gas flow rate used is typically 5L/min. If necessary, a water-cooled mounting plate can be used to provide additional cooling to the sensor head. Conversely, if the temperature of the semiconductor laser is lower than +5°C, the optional heater should be installed on the sensor.