JPS6392286A - Speed controller for dc motor - Google Patents

Abstract

PURPOSE:To obtain a current value to meet the load in starting, by providing a means to reduce the value of a drooping characteristic element in a low rotating speed. CONSTITUTION:A drooping characteristic element 22 outputs a drooping signal Dr on the basis of the power command I1. An amplifier 30 amplifies the signal of difference between the speed command V0 and the drooping signal Dr and outputs the speed command V1. A speed command regulator 34 multiplies the speed command V1 by (1-alpha) and outputs the speed command Va through a polarity changeover device 36. A speed command regulator 38 multiplies the speed signal V0 by alpha and outputs the speed command Vb. An amplifier 42 compares the sum value of the speed commands Va and Vb with the speed feedback signal Vf and outputs the current command I1. The polarity changeover device 36 is changed over according to the polarity of the speed command V0.

Description

[Detailed description of the invention] [Industrial application field]

This research relates to a speed control device for a DC motor, and in particular,
The present invention relates to an improvement in a speed control device for a DC motor in which the rotational speed is controlled by a feedback control system having a droop characteristic element with respect to the load, which is suitable for application to a DC motor for driving a steel rolling line or a process line.

[Conventional technology]

Conventionally, DC motors have been used as drive sources for machining or transportation in various manufacturing processes because of their excellent controllability of rotational speed and torque. Here, in Fig. 3, which shows a block diagram of an example of a speed control system for controlling a DC motor, the DC motor V
110 is configured to rotate when supplied with voltage and current by a voltage generator 12 using a thyristor. The rotational speed of the DC motor 10 is determined by a speed detector 1 attached to the DC motor 10, for example, having a pulse generator.
Detected by 4. And the DC electric tlllo
When the speed is controlled, an automatic speed regulator (Auto
+at 1cSpeed Regulator (hereinafter referred to as ASR) 16, the external speed command Vo
and the speed feedback signal V from the speed detector 14
The difference in f is determined and input at the addition point 18. In this case, the speed feedback signal "■" is the speed command 70
The rotational speed of the DC motor 10 is adjusted by the ASR 16 so that the speed is increased when the speed feedback signal vf is not higher than the speed command (2o), and the speed is decreased when the speed feedback signal vf is larger than the speed command (2o). By the way, the output signal of the ASR 16 is sent to the automatic current regulator (Auto+atic Curre) as the current command 11.
The current command 11 is input to the ntRegulator (hereinafter referred to as ACR) 20, but the current command 11 is
An output signal (hereinafter referred to as a do looping signal) D of a predetermined ratio determined by the dou looping (ping, dou looping) element 22
r, and is returned to the ASR 16 via the addition point 18. In this case, the value of the draw looping signal D' is very important in adjusting and determining the relationship between the speed of the DC motor 10 and the load (current), that is, in determining the degree to which the rotational speed decreases according to the load. Note that the value of the current flowing into the DC motor 10 from the voltage generator is calculated as the current feedback If at the addition point 24.
It is fed back to the ACR 20 via. In the figure, numeral 25 indicates a draw looping control section, and the other portion 27 indicates a current control section. Further, the symbol Io is a current command for the voltage generator 12. FIG. 4 shows the speed characteristics with respect to the current value of a large current WIJ machine whose speed is being controlled. If the drooping signal p' is not input from the drooping characteristic element 22, the symbol N in the figure is shown.
As indicated by E1, the DC motor 10 rotates at a constant speed regardless of the load (indicated by the current value). On the other hand, when the dou looping signal Dr is added, the symbol N in the figure
As shown by E2, the speed of the DC motor 10 decreases as the load increases (e$, flow value increases). By the way, examples in which DC motors are used for speed control that requires a large number of motors and accurate speed include steel rolling lines and process lines. When a DC motor is used to control the speed 1tlII in such a line,
Speed command V to balance the load of each DC electric gJJ machine
It is normal to reduce the dow looping signal D by a few percent from . The level of the speed command signal (V o −−Vf −D r ) input to the
The characteristic indicated by the symbol NE2 in FIG. 4 is obtained. Furthermore, when the ratio of the draw looping signal D'' to the current command 11 is increased, the downward slope to the right of the graph indicated by the symbol N E 2 in the figure further increases, and the degree of decrease in speed relative to the load increases. Therefore, By adjusting the value of the drooping signal D'' by adjusting the drooping characteristic element 22, the line speed of the steel rolling line or the like can be gently started, accelerated or decelerated.

[Problems to be solved by the invention]

However, when the speed control system increases the value of the drooping signal D of the droop characteristic element 22 to start the entire line, when a very heavy load is applied (for example, when the rolls of a rolling mill (When the load becomes heavy) Since the load current cannot be increased to the upper limit current value of ACR20, when the rolling roll stops with the material to be rolled caught, rolling cannot be continued for the following reasons. There is a problem that the drooping signal D of the drooping characteristic element 22 may
As the value of Vf increases, and when the difference (Vo-Dr) between each speed command VO and the dow looping signal D becomes zero, the speed control system as shown in FIG. The output current 1o becomes a stable value even in a state where there is no interference, and the torque to escape the jam is generated by the DC electric motor t!
110. In other words, when the value of the draw looping Dr is set to zero or a small value in a state where the DC motor 10 does not rotate, the value of the current command 1o becomes the current limit value I n as shown by the symbol Id1 in FIG.
ax, and the maximum torque of the DC motor 10 can be obtained.On the other hand, if the value of the dowel looping signal Dr is increased, the value of the current command The current limit value I lax cannot be reached, and the maximum torque of the DC motor 10 cannot be obtained.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and is aimed at improving the acceleration/deceleration of a DC motor even if the output signal amount of the drooping characteristic element is increased. It is an object of the present invention to provide a speed control device for a DC motor that can obtain a current value commensurate with the motor load when the load is heavy.

[Means to solve the problem]

The present invention provides a speed control device for a DC motor in which the rotational speed is controlled by a feedback control system having a drooping characteristic element with respect to a load, comprising means for reducing the value of the drooping characteristic element at low rotational speed. Thus, the above objective has been achieved.

[Effect]

Normally, some DC motors have their rotational speed controlled by a feedback control system that has a drooping characteristic element with respect to the load in order to improve acceleration and deceleration.In the present invention, the output of this drooping characteristic element is Even when the signal is set to a large value, the value of the droop characteristic element is decreased at low rotational speeds in order to maintain sufficient rotational torque for the load.Therefore, when starting or when the load is heavy, It is possible to obtain a current value and thus a rotational torque commensurate with the motor load. Conventionally, it was not possible to increase the input current to the DC motor up to the current limit value, so it was not possible to increase the output signal of the drooping characteristic element. For example, in a rolling line, etc., the material to be rolled is strongly pulled when starting the line, which may cause defects.However, according to the present invention, the output signal of the drooping characteristic element is changed to when the rotation speed is low, such as when starting the line. It is now possible to start the line gently by reducing it to a desired value, and therefore, it is possible to prevent flaws from occurring in the rolled material at the time of starting.

【Example】

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a speed control device for a DC motor according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the circuit configuration of a speed control device according to this embodiment. The speed control device is equipped with a dow looping control section 25A as shown in FIG. 1 instead of the dow looping control section 25 of the conventional speed control device shown in FIG. Reference numeral 27 has a configuration similar to that of the conventional speed regulating device, and illustration thereof is omitted. The dow looping control unit 25A amplifies the signal (VoDr) of the difference between the speed command V obtained at the addition point 28 and the dow looping signal Dr, and basically outputs the dow looping signal Dr. An ASRI multiplier (amplifier) 30 for creating a speed command that takes into account the value, an inverter 32 for reversing the polarity of the speed command (1) output from the ASRI amplifier 30, and an inverted speed command (1) a first speed command regulator 34 for determining the ratio at which the current is reflected in the current command IO to the DC motor (not shown); and a polarity switcher for switching the polarity of the output signal of the first speed command regulator 34. 36, a second speed command regulator 38 for outputting a speed command Vb by multiplying the speed command VO by a predetermined coefficient α to be described later, and a second speed command regulator 38 for determining the polarity of the speed command VD and switching the polarity switch 36. the sum of the speed command Va output from the polarity switch 36 and the speed command Vb output from the second speed command regulator 38 (hereinafter referred to as speed reference V
s) and an ASR2 amplifier 42 for forming a current command value to be sent to the DC motor from the speed command obtained from the speed feedback Vf from the speed detector 14 shown in FIG. . The polarity switch 36 is composed of diodes of opposite polarity and contacts for interlocking the diodes. The speed command Va is a speed command that is influenced by the dow looping signal D, and the speed command vb is a speed command that is not affected by the dow looping signal Dr.The ratio of these speed commands Va and Vb is adjusted. are the first and second speed command regulators 34 and 38.The coefficient α that determines the ratio at which these speed commands Va and Vb are reflected in the current command Io is α, and the first speed command regulator 34 generates a value of (1-α) for the speed command, and the second speed command regulator 38 multiplies the value of α.These speed commands Va and Vb are summed at an addition point 44. The speed reference Vs is determined, and the difference (vs - Vf) from the speed feedback signal vf from the speed detector (not shown) similar to that shown in FIG. 3 is calculated at the addition point 46.
A current command unit 1 to a current control unit (not shown) is controlled so that the speed of the DC motor becomes the same value as a speed reference Vs. The effects of the embodiment will be explained below. When the load current of the DC motor is zero, the speed command ■0=speed reference Vs. Then, the load becomes heavy and the current command 1
1 increases, the effect of the draw looping signal D'' appears and the value of the speed command Va decreases.If the load becomes heavier and the current command 11 increases and the value of the speed command Va becomes zero, Speed command vb from second speed command regulator 38
Since the output of is constant, speed reference Vs = speed command vb
Therefore, the speed standard ■s does not become zero. Here, the relationship between load current and speed when controlling a DC motor using the speed reference vs. as described above is shown in Fig. 2.
In this case, the horizontal axis represents the current value and the vertical axis represents the speed. The figure shows that as the current increases from zero, the speed decreases, but the decrease stops at a certain point, and after that, the speed standard remains constant even if the current increases. be understood. Note that the slope of the speed and the slope of the value of the coefficient α are determined by the drooping characteristic element 22 and the first and second speed command regulators 3.
It can be adjusted by 4.38. The graph indicated by reference numeral S1 in the drawing shows the case where the coefficient α is large and the ratio of the dow looping signal Dr is small, and the graph shown by reference numeral $2 shows the case where the coefficient α is small and the ratio is large. From the above, if the speed control of a DC motor is performed by increasing the value of the drooping signal Dr using the circuit shown in Figure 1, the speed base *Vs will be zero even when the load is heavy and the current command is large. It can be seen that it always has a certain value. Therefore, when the speed control device is used, for example, to control the speed of a rolling roll, even when the rolling roll is heavy and the DC motor stops rotating, the value of the difference between the speed reference Vs and the speed feedback ■t (Vs - In order to maintain a certain value (Vf), the rolling rolls remain locked and the ASR2 amplifier 42 is saturated, allowing the current command (1), which is the output of the ASR2 amplifier 42, to rise up to the current limit of the DC motor. Therefore, even if the value of the dow looping signal Dr is increased, the load current can be made to flow up to the current limit when the roll is in the locked state, so the mill roll can be released from the roll locked state. In the above embodiment, the present invention was applied to a speed control device as shown in FIG. 1, but the speed control device to which the present invention is applied is not limited to that shown in the figure, The present invention can also be applied to a speed control device of this type. Further, in the above embodiments, a DC motor used in a steel rolling line or a process line was exemplified as a DC motor controlled by the speed control device according to the present invention, but the present invention may also be applied to a DC motor used for other purposes. It is clear that control can be achieved with such a speed control device.

【Effect of the invention】

As explained above, according to the present invention, even if the output signal of the droop characteristic element is increased in order to improve the acceleration/deceleration of the DC motor, a current value commensurate with the load can be obtained at the time of starting. Therefore, when the output signal of the droop characteristic element is made small, the material to be rolled is strongly pulled at the start of a line such as a rolling line, which may cause flaws. can be increased to a desired value, the line can be started more easily, and excellent effects such as being able to eliminate flaws in the rolled material that occur during startup as described above can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a circuit configuration of an embodiment of a speed control device for a DC motor according to the present invention, and FIG. 2 is an example of speed control characteristics with respect to load current to explain the operation of the embodiment. FIG. 3 is a block diagram showing an example of a conventional speed control device; FIG. 4 is a diagram showing an example of speed characteristics when a DC motor is controlled by the conventional speed control device; FIG. 5' is a diagram showing an example of a change in the current command value depending on the magnitude of dow looping. DESCRIPTION OF SYMBOLS 10... DC motor, 20... Automatic current regulator, 22... Drooping characteristic element, 25A... Drooping control part, 28.44.46... Addition point, 30.42... Automatic speed regulator amplifier (ASRI amplifier, ASR2 amplifier), 34. 38... First and second speed command regulator, 36... Polarity switch, 40... Polarity discriminator.

Claims (1)

[Claims] (1) A speed control device for a DC motor in which the rotation speed is controlled by a feedback control system having a droop characteristic element with respect to the load, comprising means for reducing the value of the droop characteristic element at low rotation speeds. Features: Speed control device for DC motors.