Research On The Servo Control For The WEDM Of Semiconductor Material Based On Linear Motor

Silicon is the most commonly used semiconductor material, silicon wafer is widely used in solar panels and integrated circuits after cutting processing. Wire-cut electrical discharge machining(WEDM) is a non-contact processing method which removes material using high-voltage pulse, it is quite suitable for cutting the brittle silicon. However, the special electrical properties of silicon are different from the metal, therefore the traditional WEDM servo control method is failed based on the identification of machining spark state. In addition, WEDM machine tools usually adopt step motor,the precision of which is lower, it is difficult to adapt to the machining of the material with variable thickness. This paper is aimed to research on the servo control for the WEDM of semiconductor material based on linear motor, the specific work are as follows:(1)In view of the current and voltage characteristics of the semiconductor silicon, a specific real-time detection circuit was developed. In analysis of silicon material discharge current and voltage variation in the WEDM processing, the inherent characteristics were found, and the evaluation function which fully reflect the gap state over a period of time was established, it provided decision-making for reciprocating progressive motion control.(2)The discharge current and voltage pulse detection circuit based on multi-threshold voltage and the motion controller based on FPGA were designed. The servo control system used for the WEDM of semiconductor material was set up. The motion controller detected and processed the voltage and current signals, and controls the movement of the motor in real time.(3) In order to avoid the occurrence of bending and broken wire phenomenon in the WEDM processing, the reciprocating progressive motion control strategy by means of back and forth feed was proposed. Reversible linear interpolation was deduced on the basis of a single step tracing algorithm.FPGA programming was written by the Verilog HDL language, the algorithm was verified through simulation in Model Sim, reciprocating progressive precision motion that makes the workpiece strictly move back in the original track was realized.(4)By the experiment of the WEDM for the semiconductor material, the relationship of current threshold voltage, the current pulse probability, the sampling numbers of voltage pulse and the feed speed was studied. Fuzzy control theory was applied in the servo control, fuzzy controller wasdesigned by MATLAB and FPGA using the average current deviation and its change rate as fuzzy input variables(5) On the WEDM machine tool, the experiments of cutting semiconductor silicon materials were conducted using the new servo motion control system. The validity of fuzzy control method was verified, the WEDM of semiconductor material was realized by detecting the probability of current pulse based on multi-threshold voltage.