1 Introduction In order to meet the requirements of mass production of coins, the factory needs a corresponding HC30 punching equipment to punch holes in the blanks with smooth edges. The electrical control system scheme is as follows: PLC is used for logic control, vector frequency converter is used for speed regulation, and a whole machine monitoring system is developed on the touch screen. In order to meet the requirements of machine tool structure, reduce noise and improve the safety factor of operation, an electric composite braking method is used to replace the mechanical brake to quickly brake the high-speed motor. The design of the electrical control system of this machine tool mainly includes the following aspects: (1) Design of automatic control system composed of PLC; (2) Implementation of speed regulation control; (3) Electric composite braking method is used for the main machine; (4) Implementation of detection and control of lubricating oil temperature; (5) Design of program difficulties; (6) Design of whole machine monitoring system developed on the touch screen. The specific content will be introduced in the following sections. 2 Control content and requirements (1) Operating mode This machine tool has three operating modes: jogging, single printing and continuous printing. • Jogging: mainly used for adjusting the machine tool status, the jogging speed is 75 pieces/minute; • Single printing: under pressure, only one blank is punched, the single printing speed is 380 pieces/minute; • Continuous printing: under no fault and pressure, blanks are punched continuously, the continuous printing speed is 380 rpm - 700 pieces/minute, stepless speed regulation. The three operating modes are switched according to the selected mode. (2) The content of the real-time monitoring of the touch screen mainly includes: main motor speed, crankshaft angle, real-time fault alarm, historical fault alarm, oil circuit and oil temperature monitoring, etc. (3) Fault detection and alarm serious fault content mainly includes: main drive failure, overload clutch overload, die ring overload, ejector overload, no cake failure, pattern cake failure, oil temperature too high, worktable not in position, cam worm gear box not in position, oil pressure too low, etc. After the above faults occur, the system automatically stops punching, and the spindle stop position is positioned within the range of ±40° to avoid system stalling. (4) Communication Function: The S7-300 PLC communicates with the main drive and touch screen via Profibus fieldbus communication. The S7-300 PLC can communicate with a remote computer via the MPI port, and the S7-300 PLC can communicate with pressure gauges via the CP340 module RS232, thus monitoring the pressure of the high-speed printing press. (5) Application of Electrical Composite Braking: While improving production efficiency, it is also important to prioritize the safety of operators. The application of electrical composite braking can reduce the harsh noise emitted by the mechanical brake during braking and meet the special requirements of a compact machine tool structure. Composite braking combines energy-consuming braking with DC braking, enabling rapid stopping. (6) System Openness: Siemens systems have excellent openness; therefore, any equipment control layer that conforms to the Siemens Profibus fieldbus protocol can be connected to this system. To improve management efficiency, the factory needs to implement ERP management. The touchscreen integrates an Ethernet port, allowing for convenient monitoring and management of the system. Data management can be achieved by connecting to ERP systems. 3. System Hardware Configuration and Implementation Methods 3.1 PLC Control Section To improve the reliability and flexibility of the control system, a PLC controller is used. The controller is a SIEMENS S7-300 series programmable logic controller, with a Siemens CPU315-2DP central processing unit. This system boasts high reliability and speed. The CPU315-2DP integrates one Profibus-DP interface and one combined DP/MPI interface, both of which can be configured as Profibus master or slave. Due to the use of a touchscreen, the number of PLC input points is significantly reduced. The PLC control section has 48 digital input points, 23 output points, for a total of 71 input/output points; 1 analog input point; and one high-speed electronic cam controller. The system hardware configuration materials are shown in the attached table. The PLC configuration diagram is shown in Figure 1. The following issues need to be noted when configuring Siemens S7-300 PLC: Figure 1 PLC configuration diagram (1) The number of modules that can be inserted (SM, FM, CP) is limited by the current value they obtain from the S7-300 PLC backplane bus. For the CPU315-2DP of this system, the current value obtained from the S7-300 PLC backplane bus by 8 modules mounted on one rack should not exceed 1.2A; (2) The arrangement order of S7-300 PLC modules is SM/FM/CP. 3.2 Speed ​​control The main drive adopts the speed control method of SIEMENS vector type MASTERDRIVE PLUS series frequency converter. MASTERDRIVE PLUS drive has the characteristics of small size, fast dynamic response speed and full integration. Through its own integrated Profibus-DP communication device, the drive and the main control system PLC can be easily connected. The open Profibus bus is used to realize the automatic control of the frequency converter. By adding or subtracting the BCD code data in the PLC reversible counter CNTR, and then sending the BCD code data in the reversible counter CNTR to the PLC-inverter connection channel as the setpoint for the AC inverter, the motor speed is controlled. The system organically combines various control functions such as manual and automatic speed increase, speed locking, and speed preset according to the process requirements. The system's jogging speed is 75 pieces/minute; the designed single printing speed is 380 pieces/minute; and the normal printing production speed is 380-700 pieces/minute, with stepless speed regulation. The speed of the die feeder is required to dynamically track the speed of the spindle, that is, when the spindle speed increases or decreases, the die feeder speed also increases or decreases accordingly, thus meeting the process requirements of different currencies. 3.3 The main machine braking adopts an electrical composite braking method. Composite braking combines the kinetic braking stopping method with the DC braking method. DC braking involves passing a DC current through the motor stator to generate braking torque. The physical process of DC braking is as follows: When DC current is applied, the stator magnetic field changes from a rotating state to a constant magnetic field with a fixed position and constant magnitude. Due to the influence of mechanical inertia, the rotor still rotates clockwise, and the rotor conductors cut the constant magnetic field. Since the cutting direction is opposite to that in the motoring state, the direction of the induced electromotive force and induced current generated in the rotor is also opposite to that in the motoring state, causing the motor torque to reverse and become counterclockwise. The torque M and the speed n are opposite in direction, which is the braking state. Under the combined action of its torque and the load torque, the motor quickly decelerates. When the speed is zero, the rotor conductors no longer cut the magnetic field, the induced electromotive force and induced current of the rotor decrease to zero, and the motor no longer generates electromagnetic torque, thus controlling the production machinery to stop quickly. Because a certain stall torque is generated after the motor stops, DC braking can replace mechanical braking to a certain extent. Kinetic braking can dissipate the energy fed back by the motor when it is running in the generating state in the braking resistor, thereby achieving the purpose of rapid stopping. When a frequency converter stops rapidly with a large inertia load, or when the load speed decreases, the motor may be in generator mode. The feedback energy will cause the DC bus voltage of the frequency converter to rise, leading to overcurrent tripping and even damage to the frequency converter. Therefore, a braking resistor should be installed to dissipate the feedback energy. The technical requirement for the HC30 type punching is a braking time of about 5 seconds, so a compound braking system can meet the requirement. SIEMENS' vector-type MASTERDRIVE PLUS series frequency converters all have a built-in braking control unit, which can be directly connected to the braking resistor. The wiring diagram between the MASTERDRIVE PLUS drive and the braking resistor is shown in Figure 2. Based on the mechanical requirements for normal operating torque, a 5.5kW power frequency converter of model 6SE7021-4EP60 is selected for the MASTERDRIVE PLUS series. Figure 2 Wiring diagram between the drive and the braking resistor. Based on the compound braking function diagram of the vector frequency converter (as shown in Figure 3), the compound braking is analyzed. Utilizing the compound braking function, that is, by injecting DC current into the asynchronous motor windings, a large braking torque is generated, which can stop the system in a very short time. When a serious system malfunction occurs, the control system issues an emergency stop signal, and DC braking is activated. Specifically, when vector inverter parameters P394.B=1 and P394.M=1, compound braking begins. The system decelerates according to the descent time set by parameter P397. When the system decelerates to frequency P398, the inverter pulse is blocked, and compound braking stops. Because the DC current flowing through the stator during compound braking generates a magnetic field, demagnetization is required to ensure normal motor startup next time. P603.M represents the motor demagnetization time range. This parameter is used to set the minimum waiting time from pulse blocking to pulse release. For safety, the motor is demagnetized by at least 90% when the pulse is released. Figure 3 shows the compound braking function of the vector inverter. 3.4 Oil Temperature Detection and Control The lubrication system of a machine tool is a crucial link in ensuring its normal operation, especially for the HC30 punching machine. As a high-speed punching machine with a maximum punching speed of 700 pieces/minute, the machine tool has very strict requirements for the temperature rise of the lubricating oil to ensure appropriate viscosity and good lubricity. When the lubricating oil temperature reaches 26℃, the oil cooling fan automatically starts to cool the lubricating oil; if the lubricating oil temperature reaches 46℃, the system automatically stops punching, and the spindle stops within a range of ±40°. For ease of operation and maintenance, the temperature measuring device selected is the AT303 integrated temperature transmitter, a new type of temperature measuring device that combines temperature display with 4-20mA current output. Because it uses a resistance temperature detector (RTD) as the measuring device, integrates cold junction compensation, and after processing through circuits such as voltage regulation filtering, operational amplification, nonlinear correction, V/I conversion, and constant current, it converts the signal into a 4-20mA current signal, thus reducing signal distortion and interference. The transmitter schematic diagram is shown in Figure 4. The AT303 integrated temperature transmitter outputs the lubricating oil temperature as an electrical signal to the analog module SM331. The SM331 has a 12-bit measurement accuracy and two input channels, capable of converting both current and voltage signals into digital signals. The analog signal is converted into a digital signal by the SM331 analog module, input to the PLC for data acquisition, and finally displayed on the touch screen. When using the domestic AT303 integrated temperature transmitter with the Siemens SM331 analog module, matching issues need to be considered. During hardware configuration, a 4-20mA current signal is selected. Practice has proven this method to be feasible, with the error between the actual and displayed temperatures being less than ±1℃. The display uses a high-brightness glow indicator, allowing operators or maintenance personnel to directly observe the oil temperature near the tank, thus demonstrating significant application value. The wiring diagram of the AT303 integrated temperature transmitter and the SM331 analog module is shown in Figure 5. Figure 5 Wiring diagram of transmitter and analog module SM331 3.5 Touchscreen Monitoring System The monitoring system adopts the powerful MP ​​270B multi-function touchscreen from SIEMENS. Because it integrates a Profibus communication port and the software is already integrated into the SIEMENS Step software package, it uses a high-speed Profibus fieldbus to communicate with the SIEMENS PLC without requiring a dedicated driver GSD file, resulting in a high performance-price ratio. The MP 270B is a 10.4-inch touchscreen with a resolution of 640×480 pixels. Its significant features are: the operating system is based on the Windows CE system, which is a currently popular embedded system; in addition, it integrates an Ethernet port, an MPI communication port, and a USB interface for connecting mice, keyboards, printers, etc., making it particularly suitable for Profibus fieldbus communication with SIEMENS PLCs. 4 System Software Programming and Implementation Methods 4.1 Program Design Method The system software is programmed using Siemens Step7 software. First, the hardware configuration of the system is performed using Step7 software, as shown in Figure 6. Then, Step7 software is used for programming, which allows for structured programs, meaning that the program can be decomposed into individual, self-contained programs. The machine decomposes the control system into three parts, namely three control function blocks FC. Finally, the three control function blocks FC are called through the system organization block OB1 (using the CALL instruction). FC1 mainly controls the speed of the host machine; FC2 mainly controls the printing and accurately controls the stop position according to the fault; FC3 mainly assists in operation, such as the operation of the cake conveyor, ejector, cam worm gear box, etc. This structure has the following advantages: large-scale programs are easy to understand, individual programs can be standardized, and program organization is simplified. The biggest advantage is that it is conducive to the debugging and maintenance of the entire control system. Figure 6 Hardware configuration of the system 4.2 Difficulties in program control (1) Control of accurate spindle stop When the machine tool is running at high speed, the control system issues a stop command, and the system automatically stops punching. The spindle stop position is located within the range of ±40° to avoid system stalling. The method involves inputting the positioning signal detected by the rotary encoder into a high-speed counter FM350-2 to measure the spindle angle, and then sending the angle signal to the PLC data area. When the control system issues a stop command, the PLC performs stop control based on the corresponding host speed value n and the corresponding angle α. First, no-load debugging is performed: start the spindle pressing, then stop the spindle pressing, and adjust the lead angle based on the distance before and after the stop position relative to the standard position to ensure the motor stops at a relatively ideal position. Then, with the motor under load, gradually increase the speed, repeating the previous steps, and correcting the data through multiple experiments. Based on the changes in the spindle speed, the stop angle is tabulated and stored in the PLC data area. The control algorithm can be written as: if n≥A(i) and n＜B(i) then α＝C(i) (i =1,2,3,…). Based on the sampled spindle speed, if a stop is required, the spindle will stop at a satisfactory position. To accurately control the stop, this system implements segmented control of the host speed, with each speed increase of 20 r/min constituting a segment. (2) Program control of compound braking When the machine tool is running at high speed, the system performs compound braking after issuing a stop command. During compound braking, the kinetic energy of the motor is converted into heat energy. If this state lasts for too long, it may cause the motor to overheat and damage the motor. Therefore, it is very important to control the braking time parameter P397 quickly and accurately. The compound braking time can be adjusted according to the different speeds of the host machine. The braking control of the host machine speed value n and the corresponding time t is established. The control algorithm can be written as if n≥E(j) and n＜F(j) then t＝G(j) (j =1,2,3,…). The PLC and the driver use Profibus bus communication control mode to quickly and accurately control parameters such as P394, P395, P396, and P397. The communication transmission rate is set to 1.5Mbps. The host machine speed is divided into segments, with each 50r/min increase in speed being a segment. Figure 7 is a flowchart of the program control. Figure 7. Program Control Flowchart 4.3 Human-Machine Interface Design Since the ring punching machine needs to monitor many parameters, developing a graphical human-machine interface with interactive operation functions can improve the system's data processing capabilities and facilitate maintenance and operation. A SIEMENS MP270B touch screen with touch operation function based on the Windows CE system was selected. The graphical monitoring screen was developed using SIEMENS' ProTool/Pro V6.0 software support, then downloaded to the touch screen, and normal communication settings were configured. The touch screen was designed with seven screens: screen display, parameter setting, fault display, auxiliary operation, and oil circuit monitoring. Each screen monitors a different object. 5. Conclusion The electrical design scheme of the HC30 ring punching machine has been proven feasible in practice. Some new control technologies, such as touch screens based on the Windows CE operating system, and the Windows CE system, are currently popular embedded operating systems. It is important to note that in practice, the specific process conditions of the HC30 ring punching machine should be taken into account. Special emphasis should be placed on the spindle stopping angle and related parameters of the electrical composite braking, such as the torque and braking time of the DC braking. These parameters should be adjusted and optimized in actual application to make the electrical control system more accurate, reliable and stable.