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In multi-unit drag applications such as paper making, textile printing and dyeing, because the product is very soft, if the tensile force is too large during the manufacturing process, the product will be broken, or the product will be too thin to meet the quality requirements; if the pulling force is too small, It will make the product too thick, not only does not meet the requirements, but also waste resources. To this end, multiple units are required to have synchronous drag control functions, and the solution has mechanical total axis synchronous control and master control. The synchronous control of the mechanical total axis makes the units tightly coupled together. The change of the motion state of any unit affects the operation of other units through the action of mechanical torque, so that the system has inherent synchronization characteristics, but the range and distance of the transmission are not very likely. Big. With the master control, the mutual distance of each unit is not limited. Since the units are loosely connected, they are flexible in use, but they lose the synchronization characteristics inherent in the synchronous control of the mechanical total shaft. How to retain the advantages of the master to control the physical loose connection, and obtain the inherent synchronization characteristics of the physical tight coupling in the mechanical total axis synchronous control is a subject to be studied.
2 Multi-motor synchronous control scheme The main synchronous mode is synchronous with the mechanical total axis. Due to the loss of the inherent synchronization characteristics of the traditional control mode, in the control process with strict synchronization requirements, it can only work normally under a specific working environment. For example, when the system is very disturbed and the following performance of each unit is the same. The virtual master axis control mode retains the advantages of the master control mode and the inherent synchronization characteristics of the conventional control mode, so it can be widely used in various occasions.
2.1 Mechanical total shaft synchronous control scheme The traditional mechanical total shaft synchronous mode is realized by mechanical components: a high-power motor drives a mechanical main shaft, and all the unit drives are meshed on the main shaft through the gear box, sharing the same input signal. The rotational speed and cumulative angle of a mechanical total shaft. When a unit changes its speed due to load changes, the shaft in the unit will generate a corresponding elastic torque, and the gearbox will be connected to the gearbox to transmit the torque to the mechanical main shaft, so that the rotation speed of the mechanical total shaft will follow the unit speed. Change in the same direction. The rotational angular velocity of the mechanical total axis is also a given signal for all units, so other unit speeds will also vary with the speed of the disturbed unit. It can be seen that the disturbance of the load not only changes the output of the unit, but also changes the output signal of each unit in the same direction. It is precisely because of these two effects that the out-of-synchronization caused by the disturbance of the load can quickly return to the synchronous operating state under the action of the mechanical shaft torque. But this kind of program has many shortcomings.
Dragging multiple loads with one motor limits the drag power of each load due to the limited capacity of the motor, which limits the output torque of the unit, which limits the load on the unit.
The mechanical total shaft is prone to oscillation. The viscosity coefficient of the mechanical total shaft system is small, so the oscillation phenomenon in the transfer function is highly prone to resonance (mechanical resonance). If the resonant frequency is low, it will affect the stability of the system. In a mechanical system, the damping coefficient cannot be adjusted, and it is difficult to achieve the desired dynamic performance.
Limited by the inherent elasticity of the mechanical total shaft, the maximum output torque that the mechanical main shaft can withstand is inversely proportional to the total shaft length, proportional to the cross-sectional area of ​​the shaft. When the production process requires a long distance between the motors, since the total shaft is long, in order to ensure that the total shaft can generate the torque required to drive the load, it is required to increase the cross-sectional area of ​​the total shaft, but this will increase the cost.
Since all mechanical units are connected together by mechanical components (gearboxes), the structure is relatively fixed. These mechanical components must be added or removed when it is necessary to increase or decrease the unit. Frequent unit changes can complicate the operation of the system.
Each unit of the total shaft drag needs to be equipped with a corresponding gear box. The processing of the gear box and its lubrication cost are high, and the equation of motion of the gear box is fixed and not programmable.
When it is necessary to adjust the speed ratio through the gearbox, only the gear can be replaced and thus it is not flexible.
2.2 The master control plan 圄 1 is the structural frame of the program. In this way, all units of the system share an input signal, the signal. There is no coupling between the units, and the disturbance of any unit will not affect the motion state of other units. Since the input signal (master signal) of the system directly acts on the driver of each unit, each unit obtains a consistent input signal, which is not affected by other factors, that is, the disturbance of any unit does not affect the working status of other units. . If it is only the fluctuation of the master signal, the synchronization of each unit at this time mainly depends on the consistent follow-up of the master signal by each unit. However, when a unit is disturbed, the synchronization of the system is not guaranteed. Compared with the mechanical total shaft mode, this method is mainly due to the loss of mutual feedback between the units, thus losing the inherent synchronization characteristics of the mechanical total axis synchronization mode. However, with respect to the mechanical synchronization mode, since each unit is driven by a motor alone, this mode has a large output power.
It can be seen that when the performance of each unit is similar, only the given case can achieve synchronization well. When any motor is disturbed, it will seriously affect the synchronous operation of the system.
2.3 Virtual Total Axis Control Scheme The virtual total axis solution simulates the physical characteristics of the mechanical total axis and thus has an inherent synchronization characteristic similar to the mechanical total axis. With the introduction of the virtual master axis synchronization method, the above problems have been greatly improved, and the system has better dynamic performance. The virtual master axis mode not only has the large-capacity feature of the master synchronization mode, but also retains the inherent synchronization characteristics of the traditional synchronization mode, and also enables the system to have a flexible topology.圄2 is the fluctuation of the signal, and when any motor is not disturbed, the structure of the scheme is framed.
The structure box contains the virtual total axis (including the total axis drive), the virtual inner axis, and the mechanical unit load.
Since it simulates mechanical parts, according to Hooke's theorem, the mechanical shaft torque can be derived as: Tt=KtrX 0, where Ktr is the elastic coefficient and e is the angular displacement. When considering the attenuation coefficient, the mechanical torque is also added to the mechanical attenuation. At this time, Tt=KtrX 0+KsXw, where Ks is the attenuation coefficient and w is the angular velocity. The torque in the virtual total axis system is TT=Ktr0err+KsWerr, where -0,w -w, Ktr is the elastic coefficient of the inner axis of the virtual machine, Ks is the attenuation coefficient of the inner axis of the virtual machine, and w is the output angular velocity of the partition motor 0 is the output angular displacement of the partition motor, w' is the angular velocity (the output angular velocity of the virtual total axis), and 0' is the angular displacement (the output angular displacement of the virtual total axis).
After the system input signal of the virtual master axis system passes through the total axis, the signal of the unit driver is obtained, that is, the input angular displacement and the input angular velocity. That is, the unit driver is synchronized with the input signal instead of the system's input signal. Since the signal is a filtered signal obtained after the total axis, the signal is more easily tracked by the unit driver, thereby improving synchronization performance.
The input signal of the mechanical part of each unit is the electromagnetic torque Te, the load and the disturbance T1, the output is the angular velocity W, and Te-TL=J Xdw/dt.J is the moment of inertia of the mechanical system. The electromagnetic torque Te is the output of the current (torque) regulator.
Similar to the mechanical total shaft, when the load is disturbed, on the one hand, the speed of the disturbed unit changes in the direction of decreasing the speed difference between the shaft and the other shaft; on the other hand, the input signal also changes, under the input signal, Other unit shaft speeds also change in a direction that reduces the speed difference between the axes. These two aspects enable the system to be synchronized quickly, so the virtual master axis system has the inherent synchronization characteristics of the mechanical master axis.
The virtual mechanical part of the virtual master axis system is implemented in software and is easy to adjust parameters. Resonance can be avoided by adjusting the parameters. When the attenuation parameter is adjusted to change the damping coefficient of the system, the system can also have better dynamic performance. This overcomes the drawback that the mechanical total shaft system is prone to resonance.
Each unit is driven by a separate drive motor and has a much larger capacity than the traditional mechanical total shaft system.
The system has a "plug and play" nature. That is, the topology of the system can be changed by a simple wiring operation, unlike mechanical total shafts that require the addition or removal of mechanical components.
Through the electronic circuit connection, the system working in the virtual total axis mode can operate normally in a large range, and theoretically there is no distance limitation.
The virtual total axis system was simulated with Matlab: the unit 1 was applied to the motor 1 at 3 seconds, and the motor 2 was not subjected to any disturbance. The torque and speed changes are as follows: 圄3~圄6. f The output torque of the motor 2 is shown by 圄4. When one motor is disturbed, the speed of the other motor will change accordingly, making it worse. The value is smaller to achieve better synchronization. Since the signal and the speed signal of the undisturbed motor are close to each other, in order to see the effect, in the comparison of the two signals, the range of the time axis is narrowed so that their changes can be clearly seen. As can be seen from 圄5 and 6, when a motor is disturbed, the speed of each zone motor is directly given, that is, the signal also changes. It is this signal change that causes the speed of the motor that is not disturbed to follow the motor of the victim. The speed changes, which is also the key to the synchronization of the mechanical total axle system, and the virtual total axle system reproduces this. As can be seen from 圄5 and 6, at the moment when the system is disturbed, the signal size is between the disturbed motor speed and the undisturbed motor speed. After a period of time, the speed of the undisturbed motor is over-adjusted. The value of the time signal is greater than the output speed of all motors, and then the output speed of each motor is gradually increased by the action of this signal, and finally reaches the stable state before the disturbance. During the whole process, when the state of the system changes, the speed of each motor is not well synchronized with the given signal of the whole system, but can be combined with the signal of each motor (this signal is the output of the system given signal through the virtual total axis) The signal is well synchronized, but this does not prevent the system from working properly, because the main performance indicator of the system is the synchronization between the motors, not the synchronization of the motor with a given signal.
3 Conclusion Tian Fuxiang's advanced electronic shaft technology and its application. Journal of Qingdao Institute of Civil Engineering and Architecture, 1990. Xiong Guangkai, Xiao Tianyuan, et al. Computer simulation application. Beijing: Tsinghua University Press, 1988. The above describes and compares several common multi-motor synchronous control schemes, and concludes that the virtual total axis synchronization method has good comprehensive performance. The virtual total axis synchronization method is a Promising control solution.
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