Analysis of Multi-motor Synchronous Drive Control System

In the multi-unit dragging applications such as papermaking and textile printing and dyeing, due to the great flexibility of the product, if the tensile force is too great during the manufacturing process, the product will break, or the product will be too thin to meet the quality requirements; if the tensile force is too small, It will make the product too thick, not only does not meet the requirements, but also cause waste of resources. For this reason, multiple units are required to have a synchronous drag control function, and the scheme thereof is a synchronous control of the mechanical axis and a master control. The synchronous control of the mechanical axis makes all units closely coupled together. The change of the movement state of any unit will affect 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 cannot be very Big. With master control, the mutual distance of each unit is not limited. Since the units are loosely connected and flexible in use, they lose the synchronization characteristics inherent to the synchronous control of the mechanical axis. How to retain the advantage of the physical loose connection of the master control and obtain the inherent synchronization characteristics of the physical close coupling in the synchronous control of the mechanical axis is a subject to be studied.

2 The multi-motor synchronous control scheme master synchronization method is more synchronous than the mechanical axis synchronization method. Due to the loss of the inherent synchronization characteristics of the traditional control method, in the control process with strict synchronization requirements, it can only work in a specific working environment. For example, when the system is lightly disturbed and the following performance of the units is the same. The virtual axis control mode retains the advantages of the master control mode and the inherent synchronization characteristics of the traditional control mode, so it can be widely used in various occasions.

2.1 Synchronous control of the mechanical axis The traditional method of synchronizing the mechanical axis is realized by mechanical components: a high-power motor drags a mechanical axis, and all the unit drivers mesh with the gear shaft through the gear box, sharing the same input signal. The rotational speed and cumulative angle of a mechanical shaft. When a unit changes its rotation speed due to a change in load, the shaft in the unit will generate a corresponding elastic torque, which is transmitted to the gearbox through this gearbox to transmit the torque to the general axis of the machine, causing the rotation speed of the general axis to follow the unit rotation speed. The same direction changes. The rotational angular velocity of the mechanical axis is also a given signal for all cells, so other cell velocities will also vary with the speed of the disturbed cell. 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 functions that the imbalance caused by the disturbance of the load can quickly return to the synchronous operation state under the action of the mechanical shaft torque. However, this program has many deficiencies.

Dragging a plurality of loads with one motor, due to the limited capacity of the motor, limits the dragging power of each load, resulting in a limited output torque of the unit, which limits the load of the unit.

The mechanical axis is prone to oscillation. The viscous coefficient of the mechanical axis system is very small, so the resonance phenomenon (mechanical resonance) can easily occur in the oscillation part of the transfer function. If the resonant frequency is low, it will affect the stability of the system. In mechanical systems, this damping factor cannot be adjusted and it is difficult to achieve the desired dynamic performance.

Due to the inherent elasticity of the mechanical shaft, the maximum output torque the mechanical 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 that the distance between the motors is long, the total shaft length is long, and 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 shaft, but this will increase the cost.

Since all mechanical units are connected together with mechanical parts (gearboxes), the structure is relatively fixed. When it is necessary to add or remove units, these mechanical components must be added or removed. Frequent unit changes can complicate the operation of the system.

Each unit driven by the total axis needs to be equipped with a corresponding gear box. The gear box has high processing and lubrication costs, and the gear box has a fixed motion equation and is not programmable.

When it is necessary to adjust the rotation speed ratio through the gear box, only the gears can be replaced, so it is not flexible.

2.2 The master control plan 圄1 is the structural frame of the plan. In this way, all units of the system share one input signal, the signal. There is no coupling between the elements, and the disturbance of any element will not affect the motion of other elements. Because the input signal of the system (main command signal) acts directly on the driver of each unit, each unit obtains a consistent input signal, which is not affected by other factors, ie, the disturbance of any unit does not affect the working status of other units. . If only the master signal fluctuates, then the synchronization of the units depends on the unit's consistent follow of the master signal. However, when a unit is disturbed, the synchronization of the system cannot be guaranteed. Compared with the mechanical axis method, this method is mainly due to the loss of the mutual feedback links between the units, and thus loses the inherent synchronization characteristics of the synchronous mode of the mechanical axis. However, with respect to the mechanical synchronization method, since each unit is individually driven by a motor, this method has a large output power.

It can be seen that when the performance of each unit is similar, only the given case can achieve better synchronization. Any disturbance in the motor will seriously affect the synchronous operation of the system.

2.3 Virtual Total Shaft Control Scheme The virtual total shaft scheme simulates the physical characteristics of the mechanical shaft and therefore has similar inherent synchronism with the mechanical shaft. With the proposed virtual axis synchronization method, the above problems have been greatly improved, and the system has better dynamic performance. The virtual axis method not only has the large-capacity characteristics of the master-sequence synchronization method, but also retains the inherent synchronization characteristics of the traditional synchronization method, and also makes the system have a flexible topology.圄2 is the fluctuation of the signal, and any motor will not be disturbed.

The structure box includes a virtual total axis (including a master axis driver), a virtual inner axis, and a mechanical unit load.

Since it simulates a mechanical part, according to Hooke's theorem, the torque of the mechanical shaft 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 also adds the role of 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, whose -0, w -w, Ktr are the elastic coefficients 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 speed of the partitioned 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 total axis system passes the role of 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 synchronizes with the input signal instead of the system input signal. Since the signal is a filtered signal obtained after the action of the total axis, the signal is more easily tracked by the unit driver, thereby improving the synchronization performance.

The input signal of the mechanical part of each unit is electromagnetic torque Te, load and disturbance T1, output is angular speed W, 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 axis, when the load generates a disturbance, on the one hand, the speed of the disturbed unit changes in a direction that reduces the speed difference between the axis and the other axis; on the other hand, the input signal also changes, under the input signal, Other unit shaft speeds also change in the direction of decreasing the speed difference between the shafts. These two functions can make the system synchronize quickly, so the virtual total axis system has the inherent synchronization characteristics of the mechanical total axis mode.

The virtual mechanical part of the virtual total axis system is implemented in software and it is easy to adjust parameters. Resonance can be avoided by adjusting the parameters. When adjusting the attenuation parameter to change the system damping coefficient, the system can also have better dynamic performance. This overcomes the disadvantages of the mechanical shaft system being susceptible to resonance.

Each unit is driven by a separate drive motor, and its capacity can be much larger than the system capacity of conventional mechanical total-axis systems.

The system has "plug and play" nature. In other words, the topology of the system can be changed through a simple connection operation, unlike the mechanical axis that requires the addition or removal of mechanical components.

Through the electronic circuit connection, the system working in the virtual axis system can operate normally in a relatively large range. Theoretically there is no distance limit.

Simulation of the virtual total axis system with Matlab: A unit perturbation was applied to motor 1 for 3 seconds, and motor 2 was not disturbed. The torque and speed changes are as follows: 圄3~圄6. f Output Torque The output torque of motor 2 can be seen from 圄4. When one motor is disturbed, the speed of the other motor will change accordingly, making it worse. The value becomes smaller for 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 changing process can be clearly seen. According to 圄5 and 可知6, when a motor is disturbed, the direct reference of the speed of each motor is changed, that is, the signal also changes. It is this signal change that causes the speed of the undisturbed motor to follow the disturbed motor. The change in speed is also the key to the synchronization of the mechanical axis system, and the virtual total axis system reproduces this point. From 圄5,6 we can also see that at the moment of disturbance in the system, the size of the signal is between the speed of the disturbed motor and the speed of the undisturbed motor. After a period of time, the speed of the undisturbed motor overshoots. The value of the time signal is greater than the output speed of all motors, and then the output speed of each motor gradually increases under the action of this signal, and finally reaches a stable state before being disturbed. In the whole process, when the state of the system changes, the speed of each motor does not synchronize well with the given signal of the entire system, but it can output the signal of each motor (the signal is output after the system given signal passes the virtual total axis The signals are 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 rather than the synchronization of the motor and the given signal.

3 Conclusion Tian Fuxiang advanced electronic axis technology and its applications. Journal of Qingdao Institute of Architecture and Engineering, 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 mode has a very good overall performance. The conclusion is that the virtual total axis synchronization mode is a Promising control scheme.