| Laser processing is a kind of advanced processing technology which causes photochemicaleffect on the material surface or evaporates surface material with high-energy density laserbeam. The laser processing has been widely used in many industrial areas such as automotive,aerospace, chemical, light industry, electrical and electronics, oil and metallurgical industriesbecause of its many advantages such as no mechanical contact between work piece and tools,no deformation suffered by work piece, fine machining quality, high machining speed, easilyintegrated with numerical control technology.High-performance motion control is the prerequisites to improve the accuracy andefficiency of CNC system. For laser processing CNC system, the high-precision andhigh-sensitivity laser power control and accurate synchronization control between laser powerand motion plays an important role in improving the accuracy and efficiency. Theinterpolation of complex trajectory interpolation is the core issues and hot issues of highspeed and high precision motion control, which received a great deal of research. However,there are still drawbacks such as the feedrate is fluctuant, the feedrate profile is not smoothand the jerk is terribly high, which reduces the system's dynamic performance and it isdifficult to achieve high precision as well as high-speed machining.To realize high-performance control of laser processing, curvature-adaptive look-aheadinterpolation schemes for CSLB (Continuous Small Line Blocks) and NURBS (Non-uniformRational B-Spline) are developed. In addition, three schemes are developed specially for thelaser processing applications, which are laser scan of closed NURBS contour, high precisionlaser power control scheme, as well as accurate synchronization control between laser powerand motion. Based on the above-mentioned schemes, a high-speed and high-precision flexiblemotion controller was developed for the field of laser processing. Main research contents andresearch results are as follows:1) Curvature-adaptive look-ahead interpolation scheme is developed for the complextrajectory expressed as CSLB. The curvature variation of complex CSLB trajectory isdescribed based on which feedrate of turning points is optimized. The turning feedratechanges following the curvature variation, that is, turning feedrate is high in low curvaturesections and low in high curvature sections. Under the constraint of Energy MinimizationPrinciple, the CSLB trajectory is cube fit into cube spline. The cube spline is continuous andsmooth, and it approaches to the original trajectory more closely than the CSLB trajectory.The cube spline is a third degree polynomial, so the interpolation calculation is easy to perform and the feedrate profile is smooth, the acceleration profile is continuous, which helpsto guarantee the accuracy meanwhile improve the efficiency.2) Curvature-adaptive look-ahead interpolation scheme is developed for the complextrajectory expressed as NURBS. The curvature variation of complex curve trajectory isdescribed based on which feedrate planning is performed. The feedrate changes following thecurvature variation, that is, turning feedrate is high in low curvature sections and low in highcurvature sections. The feedrate profile is smooth, the acceleration profile is continuous andthe jerk is limited, which helps to guarantee the accuracy meanwhile improve the efficiency.The function to calculate the parametric variable is formed with second-degree Taylorexpansion, which simplifies the interpolation calculation, minimizes the truncation error andthe generated feedrate profile matches the planned feedrate profile.3) High-speed and high-precision laser scan scheme is developed for the closed NURBScontour. An explicit rational polynomial NURBS expression is derived from the recurrencedefinition, based on which four essential modules involved are realized, namely calculatingintersection points of the scan line and the NURBS contour, compensating on-off delay,generating motion path, and real-time on-off control of laser. The laser scan of complexclosed NURBS contour fills the gaps at home and abroad.4) Laser power control scheme, as well as synchronization control between laser powerand motion scheme are developed. In laser processing, the constant laser energy density is animportant factor in guaranteeing the quality, which requires not only high-precision laserpower control, but also that laser power follows the processing speed by a constant rate ofchange in sync. With the analysis of material characteristic on laser processing and laserpower control features, the piecewise-linear approximation method is used to establish thequantitative between the material cutting quality and laser energy density as well as betweenlaser output power and control signals Then the closed-loop laser power control algorithm isdeveloped, ensuring high-precision laser power output. In addition, the relationship betweenlaser power and motion is studied and the laser power and motion position are renewedsynchronously in each interpolation cycle, which achieves the precise synchronization controlbetween the laser power and motion.5) The control requirements of a variety of laser processing equipment are analyzedbased on which the controller is developed for the field of laser processing. The hardware ofthe controller is configurable and reconfigurable. The hardware functions, in particular thecontrol interface can be redefined without changing the hardware circuitry. The software ofcontroller is modularized and configurable. All the functional units are abstracted into software modules with interoperability and interchangeability. Since the controller hardwareand software all have a high flexibility, rapid customization can be achieved for different laserprocessing equipment.Research and breakthrough of several key technologies of laser processing control helpsto improve performance of laser processing machine, to improve machining quality andmachining efficiency, to improve industrial competitiveness, which makes fine economic andsocial benefits.
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