What is a machine vision system for SMT processing
Machine vision system is the main factor that affects the assembly accuracy of parts During its operation, first confirm the position of PCB When the PCB is transported to the placement position, the CCD installed on the head of the mounter first identifies the positioning mark set on the PCB to confirm the PCB position. After the CCD confirms the positioning mark, it feeds back to the computer through the bus (BUS), calculates the patch dot position error (Ax, Ay), and echoes it back to the control system to realize the PCB identification process After confirming the PCB position, confirm whether the shape of components, including assemblies, is consistent with the program, whether the center of components is centered, and whether the component pins are coplanar and deformed The process of component alignment is: after placing the head absorption component, the vision system will image the component and convert it into digital image signal The geometric center and dimension of the part are analyzed by computer and compared with the data in the control program Compare, calculate the difference between the nozzle center and the component center at Ax. Ay and M, and feed back to the control system for correction in time to ensure that the component pin and PCB pad
Application requirements of SMT statistical technology
1) %,/Positioning system
%, 239； ¼ The positioning system is the key mechanism of the placement machine, and also the main index to evaluate the accuracy of the placement machine It includes, y transmission mechanism and * *, y servo system It has two functions: one is to support the placement head, that is, the placement head is installed on the% guide rail, and the guide rail moves along the y direction, thus realizing the whole process of wiring in the xy direction This structure is used for general mounters It is more common; The other is to support PCB bearing platform and realize PCB movement in the y direction This structure is usually used in rotary table tip mounters In this type of high-speed machine, the position of the rubber sheet head only rotates, and the placement process is completed by the horizontal movement of the feeder and the movement of the PCB load plane There is also a chip mounter The placement head is installed on the * rail and only moves in the% direction The two people complete the placement process together
There are two main types of driving mechanisms, one is the linear guide of ball screw, the other is the linear guide of synchronous belt. With the decrease of chip size and the continuous improvement of precision, the requirements for chip placement accuracy of the placement machine are getting higher and higher. In other words, the requirements for x and y positioning systems are getting higher and higher. The x ^ y positioning system is guaranteed by the x ^ y servo system, that is, the AC servo motor drives the inch drive mechanism and realizes accurate positioning under the command of the displacement sensor and the control system. Among them, the precision of displacement sensor plays a key role. The current mounter used in the displacement sensor functions as three types of circular grating encoder, magnetic scale and grating ruler. These three measurement methods can obtain high precision motion positioning accuracy, but only detect the navigation deviation for the single axis motion position, but cannot detect the orthogonal or rotation error caused by the deformation, bending and other factors of the navigation.
2) Z-axis positioning system
In an ordinary mounting machine, the base supporting the mounting head is fixed on the guide rail, and the base itself does not move in the z direction. The z-axis control system here specifically refers to the positioning of the nozzle placing the head in the moving process, which aims to meet the needs of components with different thicknesses of PCBs and different heights. Z-axis control system has two common forms: circular grating encoder ac/dc motor servo system and cylindrical cam control system.
3) Z-axis rotation positioning
The rotation control of the z-axis/nozzle of the early placement machine is realized by the cylinder and plug, which can only reach 0 ° and 90 °. During control, the current mounting machine directly installs the micro pulse motor in the mounting head. High precision control of direction. The resolution of the micro pulse motor of Panasonic MSR mounting machine is 0.072 °/pulse. It directly drives the suction nozzle device through high-precision harmonic drive (reduction ratio is 30:1). Because harmonic drive has the advantages of high concentricity between input shaft and output shaft, small clearance, low vibration, etc., the actual resolution of the oil suction nozzle in 6 directions can be as high as 0.0024/pulse, improving the placement accuracy.
The above is the explanation given by the editor of pcb circuit board company.
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