Electric motor drive unit

Abstract

To provide an electric motor driving device that can improve control response of a rolling machine as a whole, while achieving load balance between driving devices for upper and lower rolls.SOLUTION: An electric motor driving device according to an embodiment comprises a master-side control part and a follower-side control part. The master-side control part controls a speed of a master-side electric motor. The follower-side control part calculates a ratio of a follower-side torque reference with respect to a master-side torque reference, memorizes the ratio when the ratio is in a predetermined range, outputs a value determined by multiplying the memorized ratio by the master-side torque reference, and controls a speed of the follower-side electric motor. The follower-side control part controls a speed of the follower-side electric motor when the ratio is out of the predetermined range.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] An embodiment of the present invention relates to an electric motor drive device for a rolling mill with separate upper and lower drives. [Background technology]

[0002] In a rolling mill with separate top and bottom drive, the top and bottom rolls are not mechanically connected before the material is bitten in or after it is released, so it is not possible to apply master-follower control, where one roll (the master) is speed controlled and the other (the follower) is torque controlled.For this reason, the speed of the top roll and the bottom roll are generally controlled separately.

[0003] On the other hand, while the material is being bitten, the upper and lower rolls are mechanically coupled via the material. Therefore, if the upper and lower rolls are controlled only by speed control, the load may be unevenly distributed on one of the drive units. If the load imbalance is significant, one drive unit will be in a powering state and the other in a regenerative state, resulting in an insufficient torque for rolling in the entire rolling mill. In such cases, load balance control is required in a rolling mill with separate upper and lower drive units.

[0004] Conventionally, load balance control and drooping control have been used to control the load balance of rolling mills with separate top and bottom drives. With load balance control, the target value for the load balance between the two upper and lower drive units is set in advance as a load balance gain, and the load on the two rolls is controlled by this. For example, in the case of a rolling mill with separate top and bottom drives used to roll shaped steel, the shapes of the upper and lower rolls may differ, and it is not always optimal to have a 1:1 load sharing ratio, making it difficult to set an appropriate gain.

[0005] Drooping control is a control method for distributing the load on each motor when multiple motors are driven by one drive. It applies a negative correction amount to the speed reference of the motor with the highest load, thereby lowering the speed reference. By lowering the speed of the motor with the highest load, the other motor can share more of the load. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 9-295016 Summary of the Invention [Problem to be solved by the invention]

[0007] In conventional load balance control, such as load balancing control and drooping control, load balancing is achieved by correcting the speed reference of the follower side of the two driving devices. This method reduces the control response of the speed control system, causing problems such as delayed response during acceleration / deceleration of rolling while the material is being bitten, and reduced accuracy of inter-stand free tension control (FTC) performed between other rolling mills.

[0008] The embodiments of the present invention have been made to solve the above-mentioned problems, and have an object to provide an electric motor drive device that improves the control response of the entire rolling mill while balancing the load between the drive devices for the upper and lower rolls. [Means for solving the problem]

[0009] An embodiment of the present invention includes a master-side controller that controls a first electric motor that drives one of two rolls, and a follower-side controller that controls a second electric motor that drives the other of the two rolls. The master-side controller outputs a first torque reference to control the first electric motor so that the speed of the first electric motor follows a predetermined first speed reference. The follower-side controller generates a second torque reference so that the speed of the second electric motor follows a predetermined second speed reference. The follower-side controller has a load balance control function that corrects the second torque reference based on the first torque reference, a torque correction unit that calculates a ratio of the second torque reference to the first torque reference, monitors whether the ratio is within a predetermined range, stores the ratio as a constant when the ratio falls within the range, multiplies the constant by the first torque reference, and outputs the result as a third torque reference, and a switch that selectively outputs the second torque reference or the third torque reference. The switch outputs the second torque reference to control the second motor when the ratio is outside the range, and outputs the third torque reference to control the second motor when the ratio is within the range. [Effects of the Invention]

[0010] According to the embodiment, an electric motor drive device is provided that improves the control response of the entire rolling mill while balancing the load between the drive devices for the upper and lower rolls. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic block diagram illustrating an electric motor drive device according to an embodiment; [Figure 2] FIG. 4 is a schematic graph illustrating the operation of the electric motor drive device according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Each embodiment will be described below with reference to the drawings. The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc. are not necessarily the same as those in reality. Furthermore, even when the same part is shown, the dimensions and ratios may be different depending on the drawing. In the present specification and the drawings, elements similar to those described above with reference to the previous drawings are designated by the same reference numerals, and detailed descriptions thereof will be omitted as appropriate.

[0013] FIG. 1 is a schematic block diagram illustrating an electric motor drive device according to an embodiment. As shown in Fig. 1, the electric motor drive device 10 includes a master-side control unit 10a and a follower-side control unit 10b. Although not shown, the master-side control unit 10a and the follower-side control unit 10b output torque references to torque control units of the electric motors they respectively drive. The master-side electric motors and follower-side electric motors drive work rolls in accordance with their respective torque references. The master-side control unit 10a and the follower-side control unit 10b input speed feedback of the electric motors they respectively drive, and perform feedback control so that the speed feedback follows the speed references input to the master-side control unit 10a and the follower-side control unit 10b, respectively.

[0014] The configuration of the master control unit 10a will be described. The master-side control unit 10a has a master-side PI controller 26a. A speed reference (first speed reference) for the master-side electric motor (first electric motor) set in a programmable logic controller (PLC), for example, as in this example, is input to the master-side speed reference input 22a. A speed feedback detection value detected by a speed detector provided in the master-side electric motor is input to the master-side speed feedback input 24a.

[0015] The difference between the speed reference and the speed feedback is input to the master-side PI controller 26a. The master-side torque reference output 28a outputs a master-side torque reference (first torque reference) calculated by proportional-plus-integral operation of the difference between the speed reference and the speed feedback.

[0016] The configuration of the follower-side control unit 10b will be described. The follower-side control unit 10b has a follower-side PI controller 26b, a torque correction unit 30b, and a switch 27b. For example, as in this example, a speed reference (second speed reference) for the follower-side electric motor (second electric motor) set in the PLC is input to the follower-side speed reference input 22b. The speed reference for the follower-side electric motor is set according to the respective shapes of the upper and lower rolls. Depending on the respective shapes of the upper and lower rolls, the speed reference for the follower-side electric motor may be set to the same value as the speed reference for the master-side electric motor, or may be set to a different value. The speed reference for the master-side electric motor and the speed reference for the follower-side electric motor are not necessarily constant over time, but may be recalculated depending on the progress of the rolling process, etc., and set as a time-varying speed pattern.

[0017] A speed feedback detection value detected by a speed detector provided in the follower-side electric motor is input to the follower-side speed feedback input 24b. Similar to the master-side control unit 10a, the follower-side PI controller 26b receives the difference between the speed reference and the speed feedback, performs proportional-plus-integral calculation, and generates and outputs a follower-side torque reference (second torque reference).

[0018] In this example, a drooping correction is added to the follower-side control unit 10b. A correction value for the drooping correction is input to the drooping correction input 23b. The correction value for the drooping correction is added to the speed reference on the follower side. This correction value is calculated based on the torque reference on the master side and is set so as to distribute a portion of the torque reference on the master side to the follower side. The correction value is calculated, for example, by multiplying the torque reference on the master side by a preset constant. In other words, the larger the torque reference on the master side, the larger the correction value for the drooping correction, and the speed reference on the follower side becomes a larger value according to the torque reference on the master side.

[0019] The torque correction unit 30b includes a torque ratio calculation unit 34b, a memory 36b, and a switching command unit 38b. The torque ratio calculation unit 34b receives the follower-side torque reference (A) generated by the follower-side PI controller 26b and the master-side torque reference (first torque reference, B) generated by the master-side PI controller 26a. The torque ratio calculation unit 34b divides the follower-side torque reference by the master-side torque reference to calculate the torque ratio (A / B). If the calculated torque ratio is determined to be within a predetermined range, the torque correction unit 30b multiplies the torque ratio stored in the memory 36b by the master-side torque reference and outputs the result to the switch 27b. Whether the torque ratio is within the predetermined range is determined, for example, by determining whether the torque ratio is within the predetermined range within a predetermined period of time.

[0020] The switching command unit 38b outputs a constant torque ratio control switching command to the switcher 27b at the timing when the torque ratio calculation unit 34b outputs the torque ratio determined to be a constant value to the memory 36b. One input of the switcher 27b is connected to the output of the follower-side PI controller 26b, and the other input of the switcher 27b is connected to the output of the torque correction unit 30b. When the switching command unit 38b does not output a switching command, the switcher 27b outputs the torque reference (second torque reference, A) generated by the follower-side PI controller 26b. When a switching command is output, the switcher 27b outputs the corrected torque reference (third torque reference, C) output by the torque correction unit 30b.

[0021] The torque ratio calculation unit 34b continues to calculate the torque ratio even during the period when the switch 27b is outputting the output of the torque correction unit 30b as the torque reference on the follower side. If the calculated torque ratio falls outside a predetermined range, the torque ratio calculation unit 34b determines that the rolled material has left the rolls and outputs an independent control switchover command to the switch 27b. The switch 27b outputs the output of the follower-side PI controller 26b as the torque reference on the follower side.

[0022] The electric motor drive device 10 according to the embodiment determines whether the material to be rolled is bitten into the rolls or disengaged from the rolls based on a torque reference ratio. After the material to be rolled is bitten into the rolls, the follower-side control unit 10b maintains a constant torque ratio, and performs independent speed control before the material to be rolled is bitten into the rolls and after it disengages from the rolls. This makes it possible to realize an electric motor drive device for a rolling mill with separate top and bottom drives that operates stably, regardless of whether the material to be rolled is bitten or not.

[0023] The operation of the electric motor drive device 10 according to the embodiment will be described. FIG. 2 is a schematic graph illustrating the operation of the electric motor drive device according to the embodiment. Figure 2 shows the time changes in the upper roll speed N(u), upper roll torque reference Tq(u), torque ratio Tq(u) / Tq(L), lower roll speed N(L), and lower roll torque reference Tq(L). The upper roll speed N(u), upper roll torque reference Tq(U), torque ratio Tq(U) / Tq(L), lower roll speed N(L), and lower roll torque reference Tq(L) are plotted in this order from top to bottom. The graph in Figure 2 shows the tendency of time changes in each characteristic. The vertical axis of the graph is an arbitrary scale and does not represent the absolute magnitude of each characteristic or the relative magnitude relationships between characteristics.

[0024] In the example of Figure 2, at time t0, the material to be rolled is assumed to be caught between the upper and lower rolls. Also, in the example of Figure 2, of the upper and lower rolls, the speed of the lower roll is controlled by the master-side controller 10a, and the upper roll is controlled by the follower-side controller 10b. The period from time t0 to time t1 is a control delay until control by drooping correction begins. In the period from time t1 to time t2, load balance control by drooping correction is performed, and from time t2 onwards, load balance control by constant torque ratio control is performed.

[0025] As shown in Figure 2, when the workpiece to be rolled is caught between the upper and lower rolls at time t0, the master-side controller 10a controls the speed of the lower roll to follow the master-side speed reference, and the master-side controller 10a generates and outputs a torque reference corresponding to the difference between the speed reference and speed feedback for the master-side electric motor. During the period from time t0 to time t1, the speed N(L) of the upper roll is, for example, approximately constant.

[0026] During the period from time t0 to time t1, control by drooping correction is not enabled, so the speed of the upper roll motor is controlled by the follower-side control unit 10b independently of the master-side control unit 10a. During this period, the speed N(u) of the upper roll is controlled to follow the speed reference.

[0027] During the period from time t0 to time t1, both the master-side torque reference and the follower-side torque reference are generated according to the speed difference by their respective control units, but the torque distribution between them can fluctuate over time due to the biting of the rolled material. Therefore, during this period, the torque reference is not necessarily a constant value, and the torque ratio Tq(U) / Tq(L) fluctuates over time, as in this example.

[0028] When the drooping control is started, for example, if the load on the lower roll is large, the speed N(u) of the upper roll controlled by the follower-side control unit 10b decreases over time during the period from time t1 to time t2, and the torque reference Tq(U) also decreases over time.

[0029] Due to the drooping correction, the torque on the master side is distributed to the follower side, and therefore the temporal fluctuation of the torque ratio Tq(U) / Tq(L) in the period from time t1 to time t2 is smaller than the fluctuation in the period from time t0 to time t1.

[0030] Since time t0, the torque ratio calculation unit 34b of the torque correction unit 30b has continuously calculated the value of the torque ratio Tq(U) / Tq(L) and monitored whether it is within a predetermined range. At time t2, the torque ratio calculation unit 34b determines that the torque ratio Tq(U) / Tq(L) is within the predetermined range and stores the value K in the memory 36b. At the same time, the torque ratio calculation unit 34b outputs a constant torque ratio control switch command to the switch 27b. The torque correction unit 30b multiplies the master-side torque reference Tq(L) by the constant torque ratio value K and outputs the result to the switch 27b. The follower-side control unit 10b outputs K×Tq(L) as the follower-side torque reference.

[0031] As a result of the above processing, from time t2 onwards, the master side speed N(L) is controlled to follow the set speed reference, for example, to a substantially constant speed. Since the torque ratio between the master side and the follower side is controlled to a constant value K, the master side torque reference Tq(L), follower side torque reference Tq(U) and follower side speed N(u) will change, for example, fluctuating over time, depending on the torque ratio K and torque distribution due to the biting of the rolled material.

[0032] In constant torque ratio control after time t2, for example, if the torque reference Tq(L) on the master side changes to increase, the torque reference Tq(U) on the follower side also increases in accordance with the change in the torque reference Tq(L) on the master side. Conversely, if the torque reference Tq(L) on the master side changes to decrease, the torque reference Tq(U) on the follower side also decreases in accordance with the change in the torque reference Tq(L) on the master side. Because the response of the torque reference on the follower side to the torque reference on the master side is calculated using a linear formula, the control response is sufficiently high.

[0033] Although not shown, when the rolled material comes off the rolls, the torque ratio Tq(U) / Tq(L) falls outside the specified range, and the master-side control unit 10a and the follower-side control unit 10b each perform independent speed control.

[0034] The effects of the electric motor drive device 10 according to the embodiment will be described. The electric motor drive device 10 according to the embodiment includes a torque correction unit 30b. The torque correction unit 30b monitors the ratio between the torque references generated and output by the corresponding control units of the upper and lower rolls as a torque ratio, and when the torque ratio reaches a certain value and stabilizes, the follower-side control unit 10b multiplies the torque reference output by the master-side control unit 10a by the torque ratio and outputs the result as the torque reference of the follower-side control unit 10b. Therefore, even if the shapes of the upper and lower rolls are different, appropriate load sharing can be achieved.

[0035] For example, in the technology described in Patent Document 1, the speeds of the upper and lower rolls are controlled based on the difference between their speeds. The roll speed control is performed via a control system with a first- or second-order delay, such as PI control, which has the problem of being prone to response delays.

[0036] In contrast, in the electric motor drive device 10 according to the embodiment, after both the master side and the follower side generate and output torque references, the follower side is controlled based on the ratio of the torque references on the master side and the follower side. Therefore, the speed control system is not included in the response to load fluctuations, making it possible to achieve a high-speed response. Therefore, in a rolling mill with separate top and bottom drives, a high-speed response is possible even when accelerating or decelerating while the material is being bitten or when FTC is performed, making it possible to achieve a highly accurate rolling process.

[0037] By combining the constant torque ratio control with the drooping correction control, part of the load sharing can be assigned to the drooping correction, reducing the control burden of the constant torque ratio control. Therefore, more appropriate load sharing can be achieved.

[0038] In this way, it is possible to realize an electric motor drive unit that improves the control response of the entire rolling mill while balancing the load between the drive units for the upper and lower rolls.

[0039] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0040] 10...electric motor drive device, 10a...master side control unit, 10b...follower side control unit, 22a...master side speed reference input, 22b...follower side speed reference input, 23b...drooping correction input, 24a...master side speed feedback input, 24b...follower side speed feedback input, 26a...master side PI controller, 26b...follower side PI controller, 27b...switcher, 28a...master side torque reference output, 28b...follower side torque reference output, 30b...torque correction unit, 34b...torque ratio calculation unit, 36b...memory, 38b...switching command unit

Claims

1. a master-side control unit that controls a first electric motor that drives one of the two rolls; a follower-side control unit that controls a second electric motor that drives the other of the two rolls; Equipped with the master-side control unit outputs a first torque reference to control the first electric motor so that the speed of the first electric motor follows a preset first speed reference; the follower-side control unit generates a second torque reference so that the speed of the second electric motor follows a preset second speed reference; The follower-side control unit a load balance control function that corrects the second speed reference based on the first torque reference; a torque correction unit that calculates a ratio of the second torque reference to the first torque reference, monitors whether the ratio is within a preset range, and stores the ratio as a constant when the ratio falls within the range, multiplies the constant by the first torque reference, and outputs the result as a third torque reference; a switch that selectively outputs the second torque reference and the third torque reference; and The switch is When the ratio is outside the range, outputting the second torque reference to control the second electric motor; an electric motor drive device that outputs the third torque reference to control the second electric motor when the ratio is within the range;

2. 2. The electric motor drive device according to claim 1, wherein the load balance control function includes a drooping correction function that corrects the second speed reference with a correction speed set based on the first torque reference.

Images