Considerations for system design of fiber laser cutting machine
The basic principle of this system is that the laser transmitter shoots the laser beam to the surface of the object to be measured through the lens. According to the reflection theorem of the optical path, the reflected laser beam is received by the photosensitive device through the camera lens. According to different distances, the camera can capture the light spot at different angles, and calculate the true object displacement value according to the position offset of the center and the position offset of the object to be measured.
The hardware composition of the triangulation ranging method of fiber laser cutting machine mainly includes light source, condenser lens and photosensitive device. Photosensitive devices are divided into charge-coupled devices CCD and position-sensitive devices PSD. Because CCD is sensitive to photoelectric gray scale, it has the characteristics of large dynamic range, good linearity, high precision, good stability, etc., while PSD determines the position of its light spot through the light distribution of its surface, which is prone to measurement errors. , Affect measurement accuracy. Therefore, CCD is generally used as a photosensitive device. At present, in the industrial market, products with a resolution of less than 125μm will use PSD, and products with a resolution of less than 2.5μm will use CCD, and most conventional fields involving computer vision will use CCD. Therefore, the system intends to use CCD as the photosensitive device.
Comparison of two triangulation ranging methods for fiber laser cutting machine
According to the difference between the angle between the laser beam and the surface normal of the object to be measured, the laser triangulation method can be divided It is the oblique laser triangulation method and the direct laser triangulation method.
The oblique laser triangulation method means that when the beam of the fiber laser cutting machine irradiates the surface of the object to be measured, the incident light will form a certain angle with the normal direction of the surface of the object to be measured. At this time, the laser beam is A certain amount of scattering and diffuse reflection occurs on the surface of the object to be measured, and a lens located at a specific position will pass these light rays to the photosensitive device through a narrow-band filter. When the object to be measured is displaced, the laser beam irradiates the surface of the object to be measured, and the light paths after the two displacements are scattered and diffusely reflected are different, resulting in a certain shift in the center position of the light spot on the photosensitive device. At this time, according to the geometric triangle relationship formed by the optical path system, the position offset of the spot center and the position offset of the object to be measured have a corresponding mathematical relationship. The actual displacement of the object is measured by calculating the offset of the center position of the spot.
The smaller the value is, the greater the change in the spot position of the imaging surface caused by the unit displacement of the surface to be measured. Lowering the sensitivity will help improve the accuracy of the sensor. Direct laser triangulation is a special case of oblique laser triangulation (when α is 0°), it will not be described here.
The oblique laser triangulation distance measurement mainly receives reflected light, which is suitable for the measured surface with low surface roughness. It is characterized by high resolution and small measurement range; direct laser triangulation distance measurement It mainly receives scattered light and diffuse reflected light, which is suitable for the measured surface with high surface roughness. It is characterized by low resolution, large measurement range, and low signal-to-noise ratio.
The parameter condition scheme of the system design of the fiber laser cutting machine and the choice of the hardware structure
Refer to the actual requirements of the industry for laser marking. The measurement accuracy is relatively low, and the marking target is For objects with high surface roughness and short-distance operation, the actual operation needs to be simple and easy to install. Therefore, the direct laser triangulation distance measurement method and the area array CCD are selected as the photosensitive device, and the condenser lens and the area array CCD are placed in parallel To design the light path. Since the imaging system of this fiber laser cutting machine cannot strictly meet the Scheimpflug condition, that is, the image plane, object plane, and lens plane intersect at one point, it is necessary to find out the conditions that can focus the optical path, and fix certain optical paths and other parameters that can affect the accuracy of the system. , So as to ensure that the accuracy requirements of the system can be achieved under this condition. Take MER-500-14GM model CCD photosensitive device as an example, its basic parameters: resolution: 2592*1944; pixel size: 2.2μm*2.2μm.
Considerations for the design of fiber laser cutting machine system
The design of the fiber laser cutting machine system mainly considers three parameters: The laser beam reflected light and the normal direction of the measured surface are clamped Angle θ(i), the accuracy requirement between the offset y of the measured surface and the image position offset x on the CCD photosensitive device, the positional relationship between the condenser lens and the reference surface.