1 Introduction
Incremental shearing control in this system primarily involves cutting specific copper sheets to fixed lengths or incrementally as required. The cut copper sheets are then pressed into copper busbars to create flexible connectors, used for current introduction in electrical equipment such as control cabinets, meeting diverse customer specifications. Depending on the set increment, the flexible connectors can be bent at different angles, saving space, improving aesthetics, and offering better heat dissipation compared to connectors made from copper sheets of the same length. For small businesses or machining centers dealing with numerous small-volume, multi-variety customers, the need is for a relatively inexpensive shearing production line that guarantees shearing quality and precision, and is simple, convenient, and flexible to operate. Therefore, we developed an automatic copper sheet shearing control system. This system is now in actual production operation and is running stably and reliably.
2 System Design
2.1 Process Analysis
Figure 1 shows the process diagram of the shearing system, which mainly represents the mechanical parts of the shearing production line. It consists of five main parts: an uncoiler, a looper photoelectric switch for detection, a pinch roller, a shearing machine, and a feeding machine. The uncoiler is mainly controlled by a frequency converter motor and can complete the uncoiling and rewinding of raw materials. The photoelectric switch located in the buffer pit determines the uncoiler's operating speed based on the degree of copper sheet sag, ensuring normal feeding. The pinching mechanism is driven by an AC servo motor to rotate, completing the fixed-length and incremental conveying of the sheet metal. The shearing machine is controlled by high-pressure gas, alternating between left and right strokes, and is controlled by proximity switches on both sides.
Figure 1. Schematic diagram of incremental shearing system process.
2.2 Electrical Control System Design
System parameters are set and displayed via a touchscreen. The control section of the entire system is mainly controlled by a PLC and servo drives, as shown in Figure 2.
Figure 2 System control schematic diagram
Based on the system operation and control requirements, the Fuji Microx-SXSPB series PLC was selected. It is easy to use, powerful, offers the best performance-price ratio, and can meet various automation control needs. It also features a small size, is not limited by installation location, has large memory capacity, and high-speed instruction functions. Furthermore, it provides convenient, simple, and open communication functions and can be directly connected to a Pod. Therefore, the Microx-SXSPB series PLC can well meet the control requirements. The human-machine interface (HMI) is a Fuji UG221 series touchscreen, monochrome, 5.7 inches, used for parameter setting and display. The servo system uses servo drives from Wuhan Maixin and Huada motors. The frequency converter is a Fuji Frenic Multi series frequency converter.
3 Incremental shear control
3.1 Control Principle
The sheet metal cutting and incremental shearing sections are crucial to the entire system. Shearing occurs during material pauses; that is, the control system activates when the cutter blades separate, and the feeding length is jointly controlled by the PLC and servo drive. After triggering, the system directly calculates the operating speed curve using preset acceleration/deceleration rates, maximum speed, target length, and set increments as basic parameters, directly driving the servo motor for feeding. By setting the unit pulse movement and the number of pulses per encoder revolution, when the diameter of the clamping roller is fixed, the sheet metal movement length is determined by the angle or number of revolutions the clamping roller makes rotate. When the number of pulses emitted by the servo drive reaches the set pulse number (i.e., length), the PLC sends a signal, the AC servo motor stops rotating, and simultaneously, the electromagnet of the shearing system is energized, causing the cylinder to perform the shearing action. Each shearing action generates a pulse for the proximity switch, which is used to calculate the shearing quantity. This cycle repeats automatically, cutting the roll material into a certain number of fixed-length or incrementally length sheets.
3.2 Parameter Settings
(1) Determination of spindle speed (the same below when operating automatically) : The spindle speed must be determined by taking into account two aspects: production capacity and rotational inertia. The speed is not better the faster it is. If it is too fast, the rotational inertia is too large, and the requirement for precise stopping cannot be met, and the cutting length accuracy is not high; if it is too slow, the productivity requirement cannot be met. In this system, there is a reasonable speed range for users to choose from.
(2) Determination of Pulse Equivalent : In this example, the ability to perform high-precision length cutting and incremental shearing is essentially due to the precise control of the rotation angle (pulse equivalent) of each pulse of the pinch roller. When the diameter of the pinch roller is fixed, a certain angle it rotates corresponds to a certain arc length, which is the length of the sheet material movement. Theoretically, the smaller the pulse equivalent, the higher the cutting length accuracy, but the higher the requirements for the control system, making it uneconomical. Generally, the pulse equivalent only needs to be one order of magnitude higher than the processing accuracy; the cutting length of this system is generally between 2cm and 200cm, requiring an accuracy of 0.01cm . The servo motor spindle rotates four revolutions (50mm/revolution), and the pinch roller rotates one revolution (200mm/revolution), with a set pulse equivalent of 0.01mm /pulse, which is sufficient to meet the accuracy requirements.
4 System Software Design
The system software design includes two parts: the touch screen software design and the PLC operation control software design.
4.1 Software Design of Human-Computer Interface
All screens of the HMI in this system are designed using ug00s-cwv3 software and consist of four screens: power-on screen, manual screen, automatic screen, and information display screen. After successful compilation with ug00s-cwv3, the HMI is downloaded from a personal computer. If communication with the PLC is normal and the corresponding program on the PLC side is also correct, it is ready for use. The HMI connects directly to the PLC programmer port via an RS422 communication cable for command-based communication. Based on the request commands from the HMI, read and write operations can be performed on the PLC's internal memory. After processing, the PLC sends a response back to the external device. No special communication program needs to be written on the PLC side. Only the manual, data input, and automatic screens are shown here.
(1) Manual screen: The manual screen is mainly used to control and adjust the main mechanical parts during the installation of the sheet metal or after shearing.
Unwind and rewind buttons: Press to perform unwind and rewind actions, release to stop rotation; Feed and retract buttons: Press to perform servo feeding and retracting, release to stop servo rotation; Left punch button: Press once to punch left, if the punch does not move, it means the punch is on the left; Right punch button: Press once to punch right, if the punch does not move, it means the punch is on the right; Pull-out button: Press once to start slice feeding; Pull-out button: Press once to stop slice feeding; Return button: Return to the startup screen, as shown in Figure 3.
Figure 3 Manual screen
(2) Data Input and Automatic Screen: Previously, we needed the first chip length, chip length increment, total number of chips, and servo motor speed. In addition, the current chip count is used to replace chips if there are any missing chips during automatic operation, as shown in Figure 4.
Figure 4 Data Input Screen
4.2 PLC Software Design
The PLC program and the human-machine interface design work together to complete the system's functions. Using a PLC: manual control and automatic fixed-length or incremental shearing are performed.
The PLC program structure diagrams are shown in Figures 5, 6, and 7, respectively.
Figure 5 Main Program Structure Diagram
Figure 6 Manual Screen Structure Diagram
Figure 7 Automatic Screen Flowchart
5. Conclusion
By appropriately changing the pulse equivalent and the pinch roller diameter, the shearing accuracy can be improved by an order of magnitude; the actual operation of this system is good, and the shearing length, accuracy, and shearing speed fully meet the design requirements and user requirements.
