[China Packaging Network News] In recent years, new electrical control technologies have been widely adopted in sheet-fed lithographic printing presses across China. These include PLC systems, touchscreens, and inverters, which have significantly improved the performance of modern printing machines. Compared to older models from a few years ago, today's advanced sheet-fed presses offer higher reliability, energy efficiency, and more comprehensive functions. Despite these advancements, many printing companies still operate with older models, which continue to play an important role in their production lines.
1. Process Characteristics of Press Operation Control
To effectively integrate inverter-driven variable-frequency motors into printing presses and meet the demands of the production process, it is essential to first understand the operational characteristics of the press control system. This includes identifying the specific requirements that the inverter must fulfill, selecting the appropriate model, and determining how to modify the existing wiring setup.
Sheet-fed lithographic printing presses are typically driven by a motor connected through belts, gears, or chains, with various rollers, gear rows, and mechanisms working in coordination. The main drive motor controls the overall operation of the machine. During mechanical adjustments, inspections, installation of PS plates and blankets, and cleaning, manual forward and backward operation at around 4 rpm is often required. When the press is paused, it should run at a consistent speed to prevent damage to the PS plate and ink drying. Once formal production begins, the initial speed is usually around 3,000 rpm. As the paper feeder starts feeding paper, the machine can accelerate to higher speeds, typically between 6,000 and 8,000 rpm. A high-speed potentiometer allows for smooth speed adjustment to accommodate different production needs, and a speed meter displays the actual operating 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 press automatically decelerates due to issues like misfeeding, no paper, or double sheets. In such cases, the press performs coordinated actions, such as separating pressure, stopping water supply, halting ink flow, and stopping the paper feed. At the end of the production cycle, pressing the stop button will bring the machine to a smooth halt in freewheel mode. To ensure safety, emergency stop buttons or safety switches are installed at critical points on the press. If any of these are activated, the machine must stop immediately, regardless of its current state, and the entire system must be braked.
2. Requirements for Inverter Functionality
- The inverter must support three-speed control and direction control to handle forward and reverse operations, low-speed adjustments, and both initial and high-speed printing.
- High-speed operation should allow for variable speed settings, ideally adjusted smoothly via a hand-operated potentiometer to suit different process conditions.
- The machine's speed must be clearly displayed so operators can monitor the current status.
- Acceleration and deceleration should be smooth and controlled to avoid shocks. If the inverter detects a fault, it must immediately stop the entire system.
3. Selection of Inverter Parameters
Based on these requirements, most general-purpose inverters can meet the needs. For such applications, a universal inverter is typically chosen. The voltage and power rating should match the original machine’s power supply and motor specifications. In this case, a 400V class inverter is used, with a 5.5kW inverter for single-color presses and an 11kW inverter for two-color models. The market offers a wide range of options, and it is 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 provide reliable performance and long-term value.
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