Mechanism Study And Its Applications On Tension System Control Of Multi-wire Saw For Solar Silicon Wafer

Multi-wire saw (MWS) for solar silicon wafer is the key equipment in the solar silicon wafer manufacturing process in photovoltaic(PV) industry. The processing quality will directly affect the following the processing efficiency and yield. MWS, which gradually replace the traditional outer circle and inner circle cutting, has become the mainstream of wafer slicing technique for large diameter thin wafer production in PV industry. It has advantages such as high productivity, minimum warp, uniform thickness, and low kerf loss. The principle of MWS is that the abrasive slurry is fed from a plate to the wire and is carried by the wire to the silicon ingot through high-speed reciprocating motion of a steel wire, and the silicon ingot is pushed against the moving wire web and sliced into hundreds of thousands of wafers of a thickness somewhere between180and280μm at the same time. Tension control of MWS for solar silicon wafer is key technology for quality and efficiency in slicing processes. For lower kerf loss of silicon materials, a thin steel wire, which varies in size from0.12to0.16mm in diameter, is used in MWS. If the wire tension is too large, it results in wire breakage. The processing is interrupted. A costly silicon ingot is discarded as useless. If the wire tension is not large enough, it causes wire to vibrate. The amplitude and frequency of wire vibration influence the warp and total thickness variation of a silicon wafer. And the technology of MWS require that the wire tension is not the same in different stages for the same silicon ingot processing. The key technologies on tension control of MWS product development for solar silicon wafer are deeply studied in the dissertation.(1) The domestic and foreign study present situation of MWS for solar silicon wafer and tension control for industry field have been studied. The development trend of numerical control multi wire slice technology is described. According to the project requestment, the theory foundation have been deeply researched on tension control of MWS for solar silicon wafer. The research emphases and the conquered difficulties of the project have been pointed out. The project origin and project tasks undertaken by author are discussed. And main contents of this dissertation is given.(2) Tension mechanism of MWS is analyzed. The overall structure of MWS is introduced. The characteristics of MWS is described from the mechanical structure and control structure two aspects. The relationship among three tension sub system, including supply spool tension, take-up spool tension and slice tension, are discussed. Mathematical model of MWS tension system is set up through using the principle of Hooke, the principle of mass conservation and motion equation of motor axis. And control block diagram is given.(3) Aimed at the problem of tension detect for MWS, a new method of sensorless tension detect, which calculate tension by constructing a tension observer, is proposed. Tension estimation error equation are obtained through mathematical of MWS. And parameter stability conditions are gotten. The convergence speed of error is analyzed by defining Lyapunov function. The convergence speed of error is accelerated by the addition of compensation. So algebra tension observer is realized. Further by introducing the sign function, the improved algebraic tension observer is put forward. The stability and reliability of tension detect is enhanced and compensation factor is optimized by the use of particle swarm algorithm. The results of simulation verify the effectiveness and correctness of the proposed method. This method has characteristics such as low cost, strong anti-interference and high reliability.(4) The direct tension control method are proposed based on sliding mode control, fuzzy sliding mode control and model-free adaptive fuzzy sliding mode control. The sliding controller, including a velocity sliding controller and two tension sliding controllers, are designed. Integral sliding surface is defined based on tension error and velocity error respectively. The sgn(x) function reaching law method is adopted. The stability of algorithm is proved through Lyapunov function. Reaching law coefficient is optimized through fuzzy control. And sgn(x) function is replaced by tanh(x) function. It improves the dynamic performance, minishes the chattering bringing by sliding mode control and tracks the desired tension quickly and accurately. Then the model-free adaptive fuzzy sliding mode control algorithm is designed by introduction of model-free adaptive control,which compensate uncertain or part time-varying parameters of system. It make system has better robustness. Simulation is carried out on three algorithms. The results verify effectiveness and correctness of the proposed method.(5) The dynamic equation is established based on force analysis of the tension arm. The reasons of tension fluctuation are analyzed for MWS. A indirect tension control strategy is put forward based on three-axis synchronization. In this strategy, the supply/collect spool motor and main motor are considered the control objects. By defining the tracking error and the synchronization error for three-axis system, and introducing the speed error on the adjacent axis, A torque control scheme is designed based on the dynamic equations of the motor to make speed error and its derivative tend to zero, thus realizing three-axis synchronization. The convergence and stability of algorithm are proved by using Lyapunov function. Simulations show that this strategy provides the high synchronization precision, good stability and high convergence rate. Then the algorithm is extended to any number of axes under general conditions. Multi-axis synchronization control algorithm is designed. The convergence and stability are proved through Lyapunov function. Finally a simulation model is established in MATLAB to test the six-axis synchronization. Synchronization performance of the algorithm is verified.(6) According to the technical specification of MWS for solar silicon wafer, the hardware platform of tension control system is designed. The proposed various tension control strategy is used in applied research. The characteristics of various tension control strategies is analyzed through experimental result and data. XQ600A MWS is tested through slicing silicon ingot. The experimental result proved that the MWS product has characteristics such as high slice precision and high stability.XQ600A MWS product for solar silicon wafer is successfully developed. The sample machine completely meet the anticipated design requirements. At present as2011’s new product, it has been put into market applications. The key technologies study on tension control of MWS for solar silicon wafer enrich the design theory and technology system of MWS tension control. It provides important reference value for developing MWS product.