**1. Introduction**
Paper cutting machinery is one of the most widely used tools in the printing and packaging industry. A paper cutter is a device designed to cut flat sheets of paper, commonly used in the paper manufacturing sector. There are two main types: the sickle paper cutter and the flat knife paper cutter. The sickle paper cutter features a slitting mechanism with an upper and lower blade, as well as a cross-cutting mechanism that uses a rotating long blade and a fixed bottom blade. It can cut between 6 to 10 paper rolls simultaneously. On the other hand, the flat knife paper cutter allows the blade to be raised and lowered on a platform, enabling precise cutting of large sheets into smaller sizes.
The paper cutting machine includes both tissue paper cutters and industrial paper cutters, offering varying levels of automation. In China, there are two primary methods for upgrading the feed positioning system of paper cutting equipment. One approach involves using a microcontroller unit (MCU) with an inverter, while the other combines the MCU with a servo system. However, these solutions typically cost over 20,000 yuan. Moreover, the MCU systems are usually developed by specialized companies, which makes the technology conservative. If a fault occurs, it often requires professional repair or replacement, leading to long downtime and high maintenance costs, making them less favorable for post-upgrade use.
HMI, or Human-Machine Interface, refers to the interface that allows interaction between users and a system. It serves as a bridge for information exchange, converting internal data into a format that is easy for humans to understand. HMI products consist of both hardware and software components. The hardware includes a processor, display unit, input devices, communication interfaces, and storage units. The processor is the core component that determines the performance of the HMI. Depending on the product type, different processors such as 8-bit, 16-bit, or 32-bit may be used. The HMI software typically includes system software that runs on the hardware and screen configuration software that operates on a PC’s Windows environment. Users create project files using the configuration software and then download them to the HMI via a serial communication port.
**2. Feasibility Analysis of the Transformation**
Most modern PLCs come equipped with high-speed counter functions, allowing them to process pulse signals at frequencies up to tens or hundreds of kHz without the need for additional modules. Since the paper cutting machine does not require extremely high precision or fast response times for its feed system, this feature is well-suited for the application. By calculating the relevant parameters of the paper feed system, an appropriate encoder can be selected to ensure that the pulse frequency meets the accuracy requirements within the PLC's processing range.
During the feeding process, the PLC compares the received pulse count with a set value and controls the output frequency of the inverter based on the comparison result. This helps reduce system inertia when approaching the target position, thereby achieving more accurate positioning.
**3. Selection of Main Control Components**
**3.1 PLC Selection**
The required input and output signals for the device include: X0 and X1 as pulse inputs, X2 as front limit, X3 as rear limit, X4 as deceleration position, X5 as motor running signal, X6 as knife upper position, X7 as knife protection, X10 as paper press upper, X11 as photoelectric protection, X12 as car rear position, X13 as hand under the knife button, X14 as stop button, X15 as connecting rod protection, and X16 as knife returned in place.
For these input points, the FX1s-30MR PLC was chosen due to its affordability and sufficient functionality. Since an HMI is used, manual operations like forward, backward, and tool change are handled through the interface, eliminating the need to occupy additional PLC input points. The FX1s series PLC has a maximum of 16 input points and can process pulses up to 60 kHz, which is adequate for the paper cutting machine's requirements.
**3.2 Encoder Selection**
The encoder must meet two criteria: the highest pulse frequency the PLC can handle and the required feed accuracy. A 500P/R encoder was selected, providing 500 pulses per revolution. The maximum pulse frequency calculated is 25 revolutions per second × 500 pulses/rev × 2 (A/B phase) = 25 kHz. The theoretical feed resolution is 10 mm / 500 = 0.02 mm. Additionally, the system sends 50 pulses per 1 mm of encoder movement, which is crucial for PLC program calculations. Using two high-speed counters for A/B phase counting and applying high-speed positioning commands ensures the PLC can handle up to 30 kHz, meeting the first requirement. With a cutting accuracy of 0.2 mm, the theoretical accuracy is fully satisfied.
**3.3 Inverter and HMI Selection**
Mitsubishi products were selected for both components: the FR-E540-0.75K-CH inverter and the F920GOT-BBD-KC HMI. These components offer reliable performance and compatibility with the system, ensuring smooth operation and user-friendly control.
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