Laser scanner, also called laser galvanometer, consists of X-Y optical scanning head, electronic drive amplifier and optical reflection lens. The signal provided by the computer controller drives the optical scanning head through the driving amplifier circuit, thereby controlling the deflection of the laser beam in the X-Y plane. Simply speaking, the galvanometer is a scanning galvanometer used in the laser industry. Its professional term is called high-speed scanning galvanometer Galvo scanning system. The so-called galvanometer can also be called an ammeter. Its design idea completely follows the design method of an ammeter. The lens replaces the needle, and the signal of the probe is replaced by a computer-controlled -5V-5V or -10V-+10V DC signal. , to complete the predetermined action. Like the rotating mirror scanning system, this typical control system uses a pair of retracting mirrors. The difference is that the stepper motor that drives this set of lenses is replaced by a servo motor. In this control system, a position sensor is used The design idea of and negative feedback loop further ensures the accuracy of the system, and the scanning speed and repeated positioning accuracy of the entire system reach a new level. The galvanometer scanning marking head is mainly composed of XY scanning mirror, field lens, galvanometer and computer-controlled marking software. Select corresponding optical components according to different laser wavelengths. Related options also include laser beam expanders, lasers, etc. In the laser demonstration system, the waveform of optical scanning is a vector scan, and the scanning speed of the system determines the stability of the laser pattern. In recent years, high-speed scanners have been developed, with scanning speeds reaching 45,000 points/second, making it possible to demonstrate complex laser animations.
5.1 Laser galvanometer welding joint
5.1.1 Definition and composition of galvanometer welding joint:
The collimation focusing head uses a mechanical device as a supporting platform. The mechanical device moves back and forth to achieve welding of different trajectory welds. The welding accuracy depends on the accuracy of the actuator, so there are problems such as low accuracy, slow response speed, and large inertia. The galvanometer scanning system uses a motor to carry the lens for deflection. The motor is driven by a certain current and has the advantages of high precision, small inertia, and fast response. When the beam is illuminated on the galvanometer lens, the deflection of the galvanometer changes the laser beam. Therefore, the laser beam can scan any trajectory in the scanning field of view through the galvanometer system.
The main components of the galvanometer scanning system are beam expansion collimator, focusing lens, XY two-axis scanning galvanometer, control board and host computer software system. The scanning galvanometer mainly refers to the two XY galvanometer scanning heads, which are driven by high-speed reciprocating servo motors. The dual-axis servo system drives the XY dual-axis scanning galvanometer to deflect along the X-axis and Y-axis respectively by sending command signals to the X and Y-axis servo motors. In this way, through the combined movement of the XY two-axis mirror lens, the control system can convert the signal through the galvanometer board according to the preset graphic template of the host computer software according to the set path, and quickly move on the workpiece plane to form a scanning trajectory.
5.1.2 Classification of galvanometer welding joints:
1. Front focusing scanning lens
According to the positional relationship between the focusing lens and the laser galvanometer, the scanning mode of the galvanometer can be divided into front focusing scanning (Figure 1 below) and rear focusing focusing scanning (Figure 2 below). Due to the existence of optical path difference when the laser beam is deflected to different positions (the beam transmission distance is different), the laser focal surface during the previous focusing mode scanning process is a hemispherical surface, as shown in the left figure. The post-focus scanning method is shown in the picture on the right. The objective lens is an F-plan lens. The F- plan mirror has a special optical design. By introducing optical correction, the hemispherical focal surface of the laser beam can be adjusted to flat. Post-focus scanning is mainly suitable for applications that require high processing accuracy and a small processing range, such as laser marking, laser microstructure welding, etc.
2.Rear focusing scanning lens
As the scanning area increases, the aperture of the f-theta lens also increases. Due to technical and material limitations, large-aperture f-theta lenses are very expensive and this solution is not accepted. The objective lens front galvanometer scanning system combined with the six-axis robot is a relatively feasible solution, which can reduce the dependence on the galvanometer equipment, has a considerable degree of system accuracy, and has good compatibility. This solution has been adopted by most integrators. Adopt, often referred to as flight welding. The welding of module busbar, including pole cleaning, has flight applications, which can increase the processing width flexibly and efficiently.
3.3D galvanometer:
Regardless of whether it is front-focused scanning or rear-focused scanning, the focus of the laser beam cannot be controlled for dynamic focusing. For the front focus scanning mode, when the workpiece to be processed is small, the focusing lens has a certain focal depth range, so it can perform focused scanning with a small format. However, when the plane to be scanned is large, the points near the periphery will be out of focus and cannot be focused on the surface of the workpiece to be processed because it exceeds the depth range of the laser focus. Therefore, when the laser beam is required to be well focused at any position on the scanning plane and the field of view is large, the use of a fixed focal length lens cannot meet the scanning requirements. The dynamic focusing system is a set of optical systems whose focal length can change as needed. Therefore, researchers propose using a dynamic focusing lens to compensate for the optical path difference, and use a concave lens (beam expander) to move linearly along the optical axis to control the focus position and achieve The surface to be processed dynamically compensates for the optical path difference at different positions. Compared with the 2D galvanometer, the composition of the 3D galvanometer mainly adds a “Z-axis optical system”, so that the 3D galvanometer can freely change the focus position during the welding process and perform spatial curved surface welding, without the need to change the carrier such as a machine tool, etc. like the 2D galvanometer. The height of the robot is used to adjust the welding focus position.
Post time: May-23-2024
