[China Packaging Network News] In recent years, new electrical control technologies have been increasingly adopted in sheet-fed lithographic printing presses across China. Components such as PLCs, touchscreens, and inverters are now commonly used, offering improved reliability, energy efficiency, and enhanced functionality compared to older models. Despite these advancements, many printing companies still operate with outdated sheet-fed lithographic machines, which remain in use due to their cost-effectiveness and familiarity.
1. Process Characteristics of Press Operation Control
To effectively integrate an inverter-driven variable-frequency motor into a printing press, it is essential to first understand the operational characteristics of the press. This includes understanding what functional requirements the inverter must meet, selecting the appropriate model, and determining how to interface it with the existing system.
The operation of a sheet-fed lithographic press typically involves a motor driving the machine through belt, gear, or chain drives. Mechanical components such as rollers, impression cylinders, and other mechanisms are interconnected, meaning that the main motor controls the overall operation of the machine. During maintenance, adjustments, installation of PS plates, or cleaning, the machine often needs to be operated manually at low speeds—around 4 revolutions per minute (r/min).
During idle periods, the machine should run at a consistent speed to prevent damage to the PS plate and avoid ink drying. When formal production begins, the initial speed is usually around 3,000 r/min. As the paper feeder starts feeding sheets, the speed can increase to higher levels, typically between 6,000 and 8,000 r/min. A high-speed potentiometer allows operators to adjust the speed according to process requirements, and a speed meter displays the actual speed.
When transitioning from high-speed printing to the initial printing speed, two scenarios may occur: either the operator manually slows down using a button, or the system automatically decelerates due to issues like misfeeds, no paper, or double feeding. In such cases, the press will coordinate actions like pressure release, water stoppage, ink stoppage, and paper halt. At the end of production, pressing the stop button will bring the machine to a smooth stop in freewheel mode. Safety is also a key concern, so emergency stop buttons or safety switches are installed in hazardous areas. If activated, these switches will immediately halt the machine regardless of its current state.
2. Requirements for Inverter Functionality
(1) The inverter must support three-speed control and direction control to accommodate forward and reverse operations, low-speed settings, initial printing speed, and high-speed operation.
(2) The high-speed setting should be adjustable, ideally via a manual potentiometer for stepless speed adjustment to suit different process conditions.
(3) The machine’s speed must be clearly indicated on the display so that operators can monitor the current operating status.
(4) Acceleration and deceleration should be smooth and controlled, avoiding any sudden shocks. If the inverter detects a fault, it should immediately shut down the entire system.
3. Selection of Inverter Parameters
Based on these requirements, most general-purpose inverters can fulfill the necessary functions. For typical applications, a universal inverter is recommended. The voltage and power rating should match the original motor and power supply. For example, a 400V class inverter is suitable, with a 5.5kW inverter used for single-color presses and an 11kW unit for two-color models. With a wide range of options available, it's advisable to choose well-established brands known for quality, such as Mitsubishi A540 series, Yaskawa G5, or Delta. Although these products may be more expensive, they offer reliable performance and long-term value.
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