1 Introduction
Paper cutting machinery is one of the most commonly used pieces of equipment in the printing and packaging industries. A papercutter is a device used in the papermaking industry to cut sheets of paper. It is divided into two categories: rotary cutter (which is further divided into single-blade and double-blade types) and flat-blade cutter. A rotary cutter includes a longitudinal cutting mechanism consisting of an upper and lower blade, and a transverse cutting mechanism consisting of a rotating long blade and a fixed bottom blade. It can cut 6-10 paper rolls simultaneously. A flat-blade cutter has a platform with a liftable gate blade that cuts flat sheets of paper to a specified size. It is used to cut large sheets of paper into smaller sizes. Paper cutting machinery consists of household paper cutters and industrial paper cutters, with a wide variety and varying degrees of automation. Currently, there are two main ways to upgrade the feed positioning system of paper cutting equipment in China: one is to use a microcontroller combined with a frequency converter, and the other is to use a microcontroller combined with a servo system. However, both of these upgrade solutions cost over 20,000 yuan. Furthermore, microcontroller systems are designed by specialized development companies with conservative technology. If a fault occurs, the system can only be repaired or replaced by the original manufacturer, resulting in long repair cycles and high costs, which is detrimental to the maintenance and use of the modified equipment. HMI is an abbreviation for Human Machine Interface, also known as a human-machine interface. A human-machine interface (also called a user interface or user interface) is the medium for interaction and information exchange between a system and a user. It realizes the conversion between the internal form of information and a form that humans can understand. Human-machine interfaces exist in all fields involving human-machine information exchange.
Human-Machine Interface (HMI) products consist of two parts: hardware and software. The hardware includes a processor, display unit, input unit, communication interface, and data storage unit. The processor's performance determines the overall performance of the HMI product and is its core component. Depending on the product level, 8-bit, 16-bit, or 32-bit processors can be selected. HMI software generally consists of two parts: system software running on the HMI hardware and screen configuration software (such as JB-HMI screen configuration software) running on a PC with a Windows operating system. Users must first create a "project file" using the HMI screen configuration software, and then download the created "project file" to the HMI's processor for execution via the serial communication port between the PC and the HMI product.
2. Feasibility analysis of the renovation
Most modern PLCs have high-speed counter functions, capable of handling pulse signals with frequencies up to tens or hundreds of kHz without requiring additional special function units. Paper cutters, however, do not have very high requirements for the accuracy and response speed of their feeding systems. By calculating the relevant parameters of the paper cutter's feeding system and selecting an appropriate encoder, the pulse frequency can be kept within the PLC's processing range while still meeting the feeding accuracy requirements. During the feeding process, the PLC compares the received pulse count with a set value. Based on the comparison result, it drives the corresponding output point to control the frequency converter's output frequency. This slows down the feeding speed as it approaches the set value, reducing system inertia and achieving precise positioning.
3. Selection of main control components
3.1 PLC Selection
The device requires the following input/output signals:
x0 pulse input
x1 pulse input
x2 front limit
x3 rear limit, y3 forward!
x4 forward deceleration position y4 backward reversal
X5 motor operation signal; Y5 high speed.
X6 knife, Y6 medium speed.
X7 Slide Protection, Y7 Low Speed
X10 paper presser upper Y10
x11 photoelectric protection y11
x12 trolley rear position y12 feed clutch
X13 Dual-hand down-blade button; Y13 Pressure plate down.
X14 Stop Button, Y14 Knife Clutch
X15 linkage protection, Y15 motor start-prevention.
x16 knife returned in time
For these required input points, the FX1s-30MR PLC was selected. Because a human-machine interface (HMI) was chosen, other manual actions, such as forward, backward, and tool changing, are also performed through the HMI, without occupying PLC input points. This made it possible to choose the lower-priced FX1s series PLC, as the FX1s series PLC has a maximum of 16 input points. Furthermore, the high-speed counter of this series PLC has the ability to process pulses with frequencies up to 60 kHz, which is sufficient to meet the accuracy requirements of the paper cutter.
PLC stands for Programmable Logic Controller, a digital electronic system designed for industrial applications. It uses a programmable memory to store programs, execute user-oriented instructions for logic operations, sequential control, timing, counting, and arithmetic operations, and control various types of machinery or production processes through digital or analog input/output. It is a core component of industrial control. Early programmable controllers were called Programmable Logic Controllers (PLCs), primarily used to replace relays for logic control. With technological advancements, the functions of these microcomputer-based industrial control devices have far exceeded the scope of logic control; therefore, today such devices are called programmable controllers, abbreviated as PC. However, to avoid confusion with the abbreviation for Personal Computer, the abbreviation PLC is used. PLCs were first developed in 1966 by Digital Equipment Corporation (DEC) in the United States. Currently, programmable controllers from the United States, Japan, and Germany are of high quality and powerful functionality.
3.2 Encoder Selection
The encoder selection must meet two criteria: the highest pulse frequency received by the PLC and the feed accuracy. We selected an encoder with a resolution of 500 P/R (500 pulses per phase per revolution). Verification confirms that this resolution satisfies both conditions. The verification is as follows:
The highest pulse frequency of this system is 25 revolutions per second × 500 pulses per revolution × 2 (A/B phases) = 25 kHz.
Theoretical feed resolution = 10mm/500 = 0.02mm
Meanwhile, the data above shows that the encoder emits 50 pulse signals for every 1mm the feed system moves (this data is crucial and will be used in the PLC program's data processing). Since this project counts the A/B phase pulses of the encoder separately, using two high-speed counters, and applies high-speed positioning instructions in the program, the highest pulse frequency this PLC can handle is 30 kHz, thus satisfying the first condition. Our paper cutter's cutting accuracy requirement is 0.2mm, indicating that the theoretical accuracy fully meets this requirement.
3.3 Selection of Frequency Converter and HMI
We selected Mitsubishi products for both of these components: FR-E540-0.75K-CH and F920GOT-BBD-KC.
