Abstract: This paper outlines a brief development trend of 6-inch internal diameter cutting machines. The paper describes the implementation of a stepper motor for feed positioning, a hydraulic proportional valve for controlling the cylinder cutting speed, and a linear encoder for controlling the cutting stroke, all controlled by a logic control system designed by our company. Parameters are set and displayed via a touchscreen. Brief calculations demonstrate the feasibility of the equipment design, filling a gap in the domestic market for large-diameter cutting machines.
Keywords: 6-inch internal circle cutting machine, logic control, proportional flow valve, linear encoder
1. Introduction
Among the 6-inch internal circle cutting machines imported into China, the main manufacturers are M&B from Switzerland and Tokyo Seimitsu Corporation (TOKYO) from Japan.
The two companies produce internal circular cutting machines. M&B mainly focuses on horizontal models, while TOKYO mainly focuses on vertical models. Regarding the spindle support method, M&B focuses on air bearings, while TOKYO uses both rolling bearings and air bearings. Domestically, only the 45th Research Institute of the Ministry of Information Industry has developed internal circular cutting machines. Their internal circular slicing machines are used in the domestic silicon wafer cutting industry, covering slicing of silicon wafers from φ50mm to φ200mm. Our company's six-inch internal circular cutting machine, modeled after foreign machines, is a vertical model using air bearings. With our improvements, we have produced a domestically developed large-diameter internal circular cutting machine.
2. Feed control of the stepper motor in a 6-inch internal circle cutting machine
Our company's 6-inch internal circular cutting machine uses a Mitsubishi FX2n-64MT-001 transistor output PLC as its central processing unit. Control
A stepper motor drives the ball screw for feed. The stepper motor used is a 34HS300D two-phase hybrid stepper motor manufactured by Beijing Startech Co., Ltd., controlled by a stepper motor driver SH-2H090M. The cutting process of a six-inch inner circle cutting machine requires high precision in sheet thickness, parallelism, and consistency. This necessitates high accuracy in sheet thickness measurement. The two-phase hybrid stepper motor is used due to its low cost and stable operation. Microstepping eliminates low-frequency oscillations in the motor, increasing both output torque and resolution. The stepping pulses and direction are controlled by the dedicated pulse count outputs Y0 and Y1 of the PLC, outputting to the CP and DIR ports of the stepper motor driver. The interface control circuit is shown in the following diagram:
The stepping distance calculation process is as follows: If the cutting sheet thickness is set to D516 (PLC digital unit) in mm, the step angle of the two-phase stepper motor is 0.9°/1.8°, and the microstepping is set to 10, then the step angle after microstepping is 1.8° ÷ 10 = 0.18°. Therefore, the number of pulses required for one revolution of the stepper motor is 360° ÷ 0.18° = 2000 pulses. The feed uses a stepper motor with a ball screw drive. For every revolution of the stepper motor, the ball screw rotates one revolution. The ball screw pitch is 4mm, so 1mm corresponds to 2000 ÷ 4 = 500 stepper motor pulses. The sheet thickness D516 is a two-digit number with decimals, so the number of pulses required for the applied stepper motor is D516 * K5.
The stepper speed calculation process is as follows: Set the speed to D520 (PLC digital unit) in mm/min, and convert D520 ÷ K60 to mm/s. The number of pulses corresponding to 1 mm of stepper motor movement is 500. Therefore, the number of pulses required by the stepper motor per second at speed D520 is D522 * K500. Thus, the pulse period T = 1/d522 * K500. Finally, the pulse frequency F = 1/T = D522 * K500.
3. Control of the cutting stroke of a 6-inch internal circle cutting machine
Our company's 6-inch inner circle cutting machine's cutting process is divided into four parts: the initial cut, the entry cut, the middle cut, and the exit cut. Because the cutting area of the crystal differs in each segment, the force applied to the crystal during cutting changes in real time. Therefore, the speed used for each cutting stroke is variable depending on the cutting process. The required speed for each stroke is determined by monitoring with a linear encoder. Two phases of the linear encoder are connected to the PLC's X00 and X01 ports respectively, and counted by a dedicated high-speed counter C235 (the dedicated high-speed counter number configured on port X0). The encoder we use has a pulse accuracy of 0.02mm/pulse. Dividing the set cutting stroke by the pulse accuracy gives the required count value for the high-speed counter. When the count value is reached, the next cutting process begins while simultaneously resetting counter C235. The next stroke restarts high-speed counter C235. This process controls each stroke, providing signals for different speeds throughout the entire cutting process.
4. Control of cutting speed for a 6-inch internal circle cutting machine
Our company's 6-inch internal diameter cutting machine controls the cutting speed using a two-position proportional flow valve and a proportional amplifier. Simultaneously, a linear encoder detects the speed, achieving closed-loop control. The flow rate of the flow valve is adjusted in real-time to achieve the same speed as the set value. The specific wiring diagram is shown below.
The 0~±10V differential voltage signal is input from terminals 16a and 16c via the PLC analog module FX2n-4DA to control electromagnets A and B. The proportional amplifier is powered by 24V DC. Positive voltage controls electromagnet B, and negative voltage controls electromagnet A. It is crucial to note that the 0~±10V differential voltage signal is relative to terminals 16a and 16c; terminals 16a and 16c must never be connected to any terminals of the amplifier. The amplifier panel also features a potentiometer for adjusting the ramp time. If no delay time is required, the potentiometer can be turned counterclockwise to the end. Once the amplifier starts operating, the set speed and the linear encoder (using the programmable controller's SPD pulse density instruction) detect the number of pulses per unit time and calculate the actual speed of the cylinder. If the actual speed is greater than the set speed, the 0~±10V voltage value of the programmable controller is decreased; if the actual speed is less than the set speed, the 0~±10V voltage value of the programmable controller is increased. This achieves closed-loop control during the cutting process. During debugging, an approximate voltage can be provided based on experience to find the matching speed, reducing trial and error time. This is closely related to process parameters. During debugging, the solenoid valve may experience valve core vibration. This is caused by air inside the valve. In this case, start the hydraulic circuit, open the vent screw, and allow the valve core to reciprocate until the air is completely purged and the valve functions normally.
5. Six-inch inner circle cutting machine touch screen control
Our company selects Eview's 5.7-inch color series product for the touchscreen of our 6-inch internal circle cutting machine. This product has a long service life.
Moreover, it is safe and reliable. It transmits data to the PLC via a dedicated RS232 data cable. The touchscreen display mainly sets and displays parameters during the cutting process of the six-inch inner circle cutting machine. Its main functions include the following:
Setting the cutting disc thickness, cutting disc value, cutting speed for each segment, cutting stroke for each segment, and total cutting disc size.
Displays numerical values, the number of remaining unsliced pieces, and the status of each travel detection switch, etc.
The touchscreen is used by users to input process parameters and other information into the PLC through parameter settings. It serves as a bridge for human-machine interaction. These parameters that need to be set and displayed are designed using specialized software. After the software is organized, the data is downloaded to the touchscreen, and once the operating mode is entered, the system can begin operation.
6. Conclusion
By designing and producing a 6-inch internal circle cutting machine, and based on customer feedback, we filled a gap in the domestic market and replaced imported products. We will continue our research to improve the machine's reliability according to process requirements. The design of this 6-inch internal circle cutting machine has provided our company with more experience in developing and producing internal circle cutting machines for large-diameter crystals.
