Characteristic analysis of shaftless transmission of printing machine
Any mechanical movement is inseparable from the power, and the power of the printing press needs to have the following conditions: continuous stability; meet the printing operation requirements, and have the characteristics of continuous speed regulation.
Before the introduction of shaftless transmission in printing presses, newspaper printing presses experienced two generations of electric speed control. Before the 1970s, slip ring AC motors widely used in newspaper printing presses provided power. This control technology can be called the first generation of electric speed control of newspaper printing presses. After the 1970s, with the advancement of DC speed regulation technology, DC speed regulation and slip motor speed regulation have been widely used in printing machines. This control technology can be called the second generation of electric speed regulation of newspaper printing machines. Drag control. In 1992, Rexroth developed the first shaftless transmission system SYNAX for printing press drive. In the following ten years, shaftless speed regulation has replaced the speed control of other newspaper printing machines.
The first part of shaftless transmission overview shaftless transmission technology has gradually become a new concept of printing press technology. Breaking through the mechanical boundaries, the shaftless drive brings upgrades and breakthroughs to the design and manufacture of printing presses. The printing machine shaftless transmission technology is a printing machine transmission control technology developed based on the first shaftless transmission system SYNAX developed by Rexroth in 1992. It has been developed in many manufacturing drive professional systems worldwide. The company has this technology.
1 Standard for shaftless transmission of printing presses 1) Shaftless transmission communication Shaftless transmission technology adopts decentralized intelligent technology and adopts international transmission communication standard SERCOS (Serial Real Time Communication System) to design, through optical fiber to digital Control information is transmitted in real time. Each group of motors uses a distributed smart card that can control motors in 40 positions. The control information sent by the distributed smart card can flexibly control the operating position of the motor. The distributed smart card optical fiber communication technology connects 32 cards together to form a motor control group with up to 1000 positions.
2) The shaftless transmission of the printing machine The shaftless transmission of the synchronous printing machine is composed of three parts: an intelligent digital frequency converter, an AC motor and a 32-bit digital coding closed-loop feedback system. The shaftless transmission synchronization of the printing press relies on the 32-bit digital coding closed-loop feedback system control, which can complete the positioning of the AC motor 4000 times in one second. The intelligent digital frequency converter drives 2 million units of the AC motor step by step, and the network connection of the optical fiber digital transmission through the Ethernet interface fully meets the printing resolution and overprinting accuracy required by the printing quality. [next]
2 Advantages of shaftless transmission of printing machine to printing control 1) Decentralization and modularization of printing machine drive. To realize the miniaturization of the drive of the multi-paper path configuration, for example, Roland single-width double-diameter eight-color tower H-type printing machine, the drive motor is adjusted from the original single motor capacity ≥90kW to a single motor capacity ≤27kW The impact of the power grid has been reduced by more than 3 times;
2) Eliminate printing overprint errors caused by mechanical transmission. According to statistics, there are printing machines equipped with 8 printing devices, and there are motion tolerances for each component of each mechanically synchronized movement. The error between the first printing device and the eighth printing device is often higher than that of the first printing device and the second printing device. The error of the device is 7 times larger. It is not possible to eliminate this error until the mechanical gear and the rotating shaft reach a continuous motion state;
3) Reduce the preparation time for printing presses. The shaftless transmission technology can even realize the independent driving of each color group of the printing device, and the entire printing machine can be prepared by multiple people for printing. For example, the Roland eight-color tower printing press is driven by 4 motors, and the KBA eight-color tower printing press is driven by 8 motors;
4) The interchangeability of printing machine control. The shaftless transmission technology adopts the international transmission communication standard to perform the information transmission function, and any printing machine without shaft transmission has no patent restrictions;
5) Provide reliable fault diagnosis. Using serial real-time communication system, the manufacturer can formulate the operating standard parameters of the printing machine in the system, and then collect the operating parameters of the printing machine and compare it with it to know the location of the equipment failure;
6) The speed adjustment accuracy of the drive roller without shaft transmission can reach 0.01%, which can accurately control the speed of the printing paper tape pulling roller, effectively control the stability of the paper path printing, uniformity of tension, uniformity of cutting, etc. Of uncertainty;
7) The positioning accuracy of the shaftless transmission is used, which improves the reliability of automatic plate change, improves the reaction speed of printing overprinting and cutting register, and greatly reduces the rate of waste products. [next]
The second part frequency conversion technology
The realization of shaftless drive of printing press is closely related to the development and application of frequency conversion speed regulation technology. The variable frequency speed regulation technology applies the main characteristics of the three-phase asynchronous motor to realize the speed regulation of the motor.
1 Rotating speed characteristics of three-phase asynchronous motor Rotating speed of three-phase asynchronous motor: n = 60f / p, that is to say, the rotating speed n of three-phase asynchronous motor depends on the current frequency f and the number of magnetic field pole pairs p, and after the motor is manufactured, The number of magnetic pole pairs cannot be changed. Therefore, the speed of the three-phase asynchronous motor is proportional to the current frequency. The variable frequency speed regulation technology is to use this special property to adjust the speed of the motor output.
2 The principle of AC frequency conversion speed regulation for shaftless driving of printing presses In the late 1980s, a new type of field effect transistor (IGBT) came out. The characteristics of frequency conversion speed regulation motors have been improved. The printing machine began to introduce frequency conversion speed regulation technology. The frequency conversion speed regulation technology of the three-phase asynchronous motor is composed of a frequency converter and a three-phase asynchronous motor. The widely used frequency conversion form is the "AC-DC-AC" voltage type. Because the "AC-Straight-AC" type is easy to achieve constant current control, it is similar to the constant torque control characteristics of printing presses. The frequency conversion control of the printing machine adopts this "AC-Straight-AC" control form. This form of control has low power, and industrial control is also called AC servo control or AC control.
The work of the frequency converter is divided into two processes. In the first step, the three-phase (or single-phase) fixed-frequency AC power supply of the power supply is converted into DC through the rectifier bridge. The second step is to transform DC into AC. This process is called DC “inverterâ€. The frequency conversion speed regulation process is to control the frequency of the DC "inverter" output and the speed of the motor. The DC "inverter" process is the opposite of bridge rectification. The rectifier circuit is also called an "inverter" bridge circuit. The "inverter" bridge circuit of the shaftless drive of the printing press uses a field-effect transistor circuit for DC inversion, as shown in Figure 2. This is a voltage control device with low control power and high efficiency switching circuit with a switching frequency of ≤20kHz. It has the following characteristics: the current wave shape is closer to the AC power supply, and the controlled motor maintains the characteristics of more three-phase motors; the electromagnetic noise is small ; The circuit is simple; the self-processing ability of common faults is strong, the failure rate is small; the loss of the inverter itself is small. [next]
3 The basic method of AC frequency conversion speed control of the printing press The printing machine has a structure that determines the unevenness of the load, and the printability requires that the operation must be stable, the printing quality can be stable, and the effect of printing and copying can be achieved. Whether the printing machine changes from DC speed control drive to AC speed control drive, whether there is a change in the printing copy effect, or how to overcome the shortcomings of AC speed control, is what we want to know most. When using and maintaining the printing machine, you will notice that on the printing machine without shaft drive, some motors have encoders, and some motors do not have encoders. How do these two types of motors synchronize? You should first understand the AC frequency conversion speed control The basic way.
1) Vector control method DC motors have two mutually perpendicular magnetic fields to drive the motor to rotate, control the size of the vertical magnetic field, and realize the speed control while also controlling the mechanical characteristics of the motor. The three-phase AC asynchronous motor only has a vertical magnetic field for an instant. The basic point of AC frequency conversion speed control is to control the three-phase "inverter" bridge to control the instantaneous vertical magnetic field and improve the mechanical characteristics of AC frequency conversion speed control drive. This process of controlling the three-phase "inverter" bridge of the instantaneous vertical magnetic field is called the equivalent vector control method, as shown in Figure 3. Two processes of equivalent sub-vector control method:
In the first step, the given signal is processed. The inverter control circuit virtually decomposes the given signal into two rotating DC signals perpendicular to each other, which are called the magnetic field component iM and the torque component iT; the two magnetic fields of the DC motor are simulated.
The second step is equivalent conversion. According to the motor parameters, a series of equivalent transformations are performed on the mutually rotating DC magnetic field signals, and they are transformed into control signals iA, iB, and ic that control the three-phase inverter bridge.
2) No feedback vector control A type of motor common to shaftless printing presses does not have an encoder, but it is not an open-loop control without speed control. In the synchronization of this type of motor, by detecting the terminal voltage and current of the motor, the rotor flux and rotor angular velocity are calculated, and the magnetic field component iM and torque component iT in FIG. 3 are combined with specific motor parameters to perform equivalent conversion without feedback vector control. This type of control has a slightly poor dynamic response capability. The printing color sequence overprinting drive motor uses this control, and the overprinting of the printing machine will have slight differences due to speed changes.
3) Feedback vector control The shaftless drive printing machine needs to accurately control its speed according to the printability requirements, such as the determination of the production speed of the printing machine, the control of the printing color sequence overprinting speed, and so on. This type of motor is directly installed with an encoder on the motor to obtain the rotor speed of the motor, perform an equivalent transformation, realize vector control, and strictly control the speed of the motor to be synchronized with the given speed. This type of control has a strong dynamic response capability. The printing color sequence overprinting drive motor uses this control, and the overprinting of the printing machine will not change due to speed changes.
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