JPS623670B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control device for a DC motor that drives rolling rolls of a rolling mill that rolls materials such as ferrous and non-ferrous materials.

Conventionally, this type of DC motor control device generally
It is configured as shown in the figure.

In the apparatus shown in FIG. 1, there is a reference control circuit 2 for adjusting the speed reference signal 1 to a predetermined acceleration/deceleration slope based on the rolling schedule, etc. A speed control circuit 5 that obtains an output according to the difference with the speed feedback signal 4, a current limiting circuit 6 that limits the output of the speed control circuit 5, that is, the current reference signal, from exceeding the allowable current value of the DC motor, and the speed. A current control circuit 9 obtains an output according to the difference between the output of the control circuit 5 and the current feedback signal 8 from the current detector 7, and ignites the power supply converter 11 for driving a DC motor according to the output of the current control circuit 9. a phase control circuit 10 for controlling;
A control device is constituted by the power supply converter 11 for supplying DC power from the AC supply power source 12 to the DC motor 13 in accordance with the output of the phase control circuit 10. Rotation of DC motor 13 (rotation speed 1
4) is transmitted to the rolls 15 of the rolling mill, and rolls the steel material 16 passing between the rolls. The speed detector 3 detects the rotational speed of the DC motor 13, and the current detector 7 detects the current flowing through the DC motor 13 on the AC side of the power converter 11. A separately excited DC motor is generally used as the DC motor 13, but its field winding circuit is not shown.

FIG. 2 shows the characteristics obtained by the control device of FIG. 1 over time on the horizontal axis. As shown in FIG. 2, when a speed reference signal 1 is given as a step input, a slope reference signal 1a is output from the reference control circuit 2, and speed control, current control, and phase control are performed based on this output signal. As a result, an output rotational speed 14 is obtained. Here, the output rotational speed 14 initially rises along the inclination reference signal 1a, but once drops at the time T1 when the material 16 is bitten, the output rotational speed is controlled by the speed control circuit 5 to increase the output rotational speed and tends to rise. have.

When selecting the capacity of the DC motor used to drive the rolls of a rolling mill, it is ideal to have sufficient capacity, but from the viewpoint of price and size, it is necessary to select a DC motor that is suitable for the load torque, and to determine the maximum capacity required for rolling. The load capacity is usually up to the overload capacity of the DC motor. Therefore, during rolling, it is necessary to use the DC motor to its full capacity, and as a current reference signal, which is the output signal of the speed control circuit 5, the actual speed tends to always lag behind the speed reference signal by a speed difference of 17. Reflecting this, when the current limit value set by the current limit circuit 6 is reached, the current is input to the current control circuit 9, and control is performed to flow an output current commensurate with the load capacity such as rolling torque. Become.

As time passes and the rolling of the material 16 is completed and the material reaches the end point T2, the load capacity rapidly decreases due to the lack of material, but due to the speed difference 17, the current control circuit 9 As the output current was being controlled in the direction of increasing the output current, it would temporarily accelerate after reaching the bottom, and in the worst case, the detection setting value of the electrical or mechanical overspeed detector could be reached. In order to protect the DC motor and other moving parts, it is necessary to stop the motor immediately.

In summary, the conventional device shown in FIG. 1 has the following drawbacks (1) to (3).

(1) Unnecessary acceleration occurs.

(2) Therefore, the time until stopping becomes longer.

(3) Most rolling mills operate reversibly, but the longer time it takes to stop the mill affects the entire rolling schedule.

SUMMARY OF THE INVENTION An object of the present invention is to provide a DC motor control device that can eliminate the above-mentioned drawbacks and easily and reliably suppress acceleration when the material runs out, that is, when the load suddenly decreases.

In order to achieve this object, the present invention is equipped with an actual current detection circuit and a speed difference calculation circuit to automatically suppress acceleration when the load suddenly decreases. explain.

FIG. 3 shows an embodiment of the present invention.
In FIG. 3, the same reference numerals as in FIG. 1 represent the same constituent parts, and the explanation of the structure of those parts will be omitted. Here, according to the invention, a comparator 18 and a speed difference calculation circuit 21 are provided. A current feedback signal 8 from the current detector 7 is fed back to the current control circuit 9 and is also input to the comparator 18 at the same time. The comparator 18 compares this input current value with the current limit value set by the current limit value setter 19, and closes the signal switch 20 only when the former reaches the latter. The speed difference calculation circuit 21 is connected to the speed detector 3
The deviation, that is, the speed difference, between the speed feedback signal 4 and the speed reference signal 1 from the The reference control circuit 2 has a polarity opposite to that of the reference signal 1 (i.e., a subtraction signal).
give to

Since the speed feedback signal 4 always lags behind the speed reference signal 1 due to delays in the control system, a speed difference 17 is detected as already explained with reference to FIG. The speed difference calculation circuit 21 sets a signal amount slightly smaller than the speed difference 17 using a setter provided therein, and outputs it. In this way, under the condition that the signal switch 20 is closed,
After the reference control is performed with apparently the same content as that in which the speed reference signal 1 is decreased, the signal is input to the speed control circuit 5.

As a result, in the conventional method (Fig. 1), the speed difference was 17
However, in the present invention (FIG. 3), during rolling, the auxiliary reference signal 1b with a value slightly smaller than the speed difference 17 is given, so the speed control circuit The control contents of 5 are speed difference 17 - auxiliary reference signal 1b
Therefore, the current reference signal applied to the current control circuit 9 is reduced compared to the conventional one, and the response speed of the control system becomes faster. Therefore, it is possible to obtain a circuit operation that suppresses temporary acceleration when the material bottoms out in the rolling mill.

The characteristics obtained by the present invention are shown in FIG.
Here, the meanings of each symbol are the same as in FIG. 2. Newly added code 1b (dashed line)
is the auxiliary reference signal. Since the slope reference signal 1a is reduced based on the subtraction of the auxiliary reference signal 1b,
The difference between the reference signal 1a, which is the target value, and the actual speed 14 is small, and it is shown that the acceleration operation at the time of tailing off is suppressed, and the time until stopping after the tailing off is shortened. .

As described above, according to the present invention, the following effects can be obtained by lowering the speed reference value when the load current reaches a predetermined limit value.

(1) Unnecessary acceleration operations can be suppressed, and therefore the time until stopping can be shortened.

(2) Especially in the case of reversible operation in a rolling mill, the rolling schedule can be shortened.

(3) Conventionally, rolling speed pattern control performed using an electronic computer was based on predictions, but this method uses a control method that captures the actual load condition, which allows for more precise control. This can be accomplished easily and at low cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional control device, FIG. 2 is a diagram showing control characteristics of the device in FIG. 1, and FIG. 3 is a block diagram showing an embodiment of the control device of the present invention.
FIG. 4 is a diagram showing the control characteristics of the device of FIG. 3. 2...Reference control circuit, 5...Speed control circuit, 6
...Current limit circuit, 9...Current control circuit, 10...
...Phase control circuit, 11...Power converter, 13...
DC motor, 15...Rolling mill roll, 18...Comparator, 20...Signal switch, 21...Speed difference calculation circuit.

Claims (1)

[Claims] 1. A reference control circuit that obtains a slope reference signal by limiting a speed reference signal to a predetermined acceleration/deceleration slope; a current control circuit that obtains an output according to the difference between the slope reference signal and the speed feedback signal; a forward converter that converts the power into electric power and supplies the power to a controlled DC motor; a phase control circuit that controls the firing phase of the forward converter according to the output of the current control circuit; and an actual current and a current limit value. a comparator that compares and outputs an operation signal when the actual current reaches a current limit value; a speed difference calculation circuit that outputs a signal slightly smaller than the difference between the speed reference signal and the speed feedback signal; 1. A control device for a DC motor, comprising: a signal switch which is closed by an operation output of a switch, and which adds an output signal of the speed difference calculation circuit as an auxiliary reference signal to the speed reference signal with opposite polarity.