JPS6411092B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a temperature control device for an indirect heating furnace,
In particular, the present invention relates to a temperature control device that can obtain suitable temperature control characteristics even if there is an idle region within the operation input range that does not contribute to temperature control.

An indirect heating furnace that heat-treats an object to be heated through a partition wall heated by a burner is equipped with a predetermined operation input range (0 to 100%) as shown by the solid line in Figure 1, and the operation input When the neutral operation value N in the range is reached, the operation input value becomes that neutral operation value N.
an air amount adjusting device that increases the amount of air supplied to the burner as the distance from the burner increases; a fuel regulating device that supplies fuel to the burner at a predetermined ratio to
As shown between the neutral operation value N and the cut value C in the figure, the amount of operation input in the air amount adjustment device is the cut for supplying the minimum amount of air to the burner that can maintain a good combustion state. a fuel cutoff device that cuts off the fuel supplied to the burner when the value falls below the cut value C; and a fuel cutoff device that cuts off fuel supplied to the burner; A temperature control device is proposed that controls the atmospheric temperature in the heating furnace to match the target temperature by performing a cooling operation and setting the amount of operation input within a cooling control range smaller than the neutral operation position N. has been done.

However, in such a temperature control device,
Since the operation input range includes an idle range that does not contribute to temperature control, a delay in control response due to the idle range is unavoidable, resulting in the disadvantage that highly accurate temperature control characteristics cannot be obtained. That is,
In Fig. 1, for example, when the operating input amount falls below the cut value C from within the combustion control range and enters the idle range between the cut value C and the neutral operation value N, the fuel is cut off, but the air flow rate decreases. is further reduced and does not contribute to active cooling operations. Moreover, when the amount of operation input exceeds the neutral operation value N from within the cooling control range and enters the idle range, only the amount of air increases and the inside of the furnace is cooled, making no contribution to the active heating operation. Therefore, the time during which the operating input amount is in the idle range becomes a delay (dead time) in the control response, which increases the hunting of the atmospheric temperature in the heating furnace. In addition, such an idle range not only causes a delay in control response, but also
In the idle range, the amount of air is changed in the opposite direction to the temperature control direction, which also causes the ambient temperature to vary. Unlike direct-fired furnaces, indirect heating furnaces can easily control the atmosphere of the object to be heated, but on the other hand, the response time is inherently long when controlling the temperature of the atmosphere inside the heating furnace. In the zone, the disadvantages caused by the above idle range are noticeable.

The present invention has been made against the background of the above circumstances, and its object is to provide a temperature control device for an indirect heating furnace that can obtain highly accurate temperature control characteristics.

In order to achieve such an object, the temperature control device of the present invention includes at least a detection method for detecting that the amount of operation input exceeds the neutral operation value and that the amount of operation input falls below the cut value. means and
When the amount of operation input exceeds the neutral operation value from the cooling control range, the amount of operation input is immediately changed to a predetermined value greater than or equal to the cut value, and the amount of operation input is cut from the heating control range. The present invention is characterized in that it includes a manipulated variable changing means that immediately changes the manipulated input amount to a predetermined value that is less than or equal to the neutral value when the manipulated input amount falls below the neutral value.

In this way, when the amount of operation input exceeds the neutral operation value, it is immediately changed to a value greater than or equal to the cut value, and when the amount of operation input falls below the cut value, it is immediately changed to a value less than or equal to the neutral operation value. As a result, the amount of operation input is caused to skip the idle range, and it becomes as if the idle range in the operation input range does not exist. Therefore, delays in control response and variations in ambient temperature caused by the idle range are completely eliminated, and highly accurate temperature characteristics can be obtained.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below based on the drawings.

In FIG. 2, reference numeral 10 denotes an indirect heating furnace, and a radiant tube 14 serving as a partition wall is fixed to the furnace wall 12 with its end open to the outside of the furnace. A burner 16 is attached to one end of the radiant tube 14, and an air pipe 18 and a fuel pipe 20 are connected to the burner 16.
Air and fuel are supplied. A butterfly valve 22 as an air amount adjusting device is attached to the air pipe 18. As shown in FIGS. 1 and 3, this butterfly valve 22 has an operation input range (valve operation angle range) of ±90 degrees, and has a predetermined neutral operation position N (in this embodiment, the operation input is 50% , that is, the valve operation angle is 0 degrees), and the further the operation input amount is, the more the amount of air supplied to the burner 16 increases. The butterfly valve 22 is connected to a drive motor 24 by a connecting rod 26.
It is designed to be operated by 4. The fuel pipe 20 is provided in series with an electromagnetic valve 27 that allows fuel to flow through and shut off, and is also provided with a control valve 28 as a fuel control device. Control valve 28
is connected to a drive motor 30, and the drive motor 30 is connected to a flow rate sensor 32 provided in the air pipe 18.
It operates in accordance with a signal from a controller 34 that adjusts the flow of fuel at a constant ratio to the air flow rate represented by the output signal. Therefore, the fuel flowing through the fuel pipe 20 is adjusted at a predetermined ratio so as to obtain a desired air-fuel ratio with respect to the air flow rate flowing through the air pipe 18, as shown by the broken line in FIG. be.

On the other hand, a thermocouple 36 is attached to the furnace wall 12 to detect the atmospheric temperature within the furnace 10 .
The output signal of the thermocouple 36 is supplied to a recorder 38 to record the temperature inside the furnace 10 on recording paper, and is also supplied to a temperature converter 40 to be converted into a predetermined temperature signal. The temperature signal output from the temperature converter 40 is supplied to the arithmetic and control unit 44 via the A/D converter 42. The arithmetic and control unit 44 receives, for example, a fourth
Command signals representing target temperatures as shown in the figure are sequentially supplied according to a predetermined program. Also, a connecting rod 26 that drives the butterfly valve 22
is provided with a limit switch 48 as a detection means for detecting the moving position of the butterfly valve 22, that is, the amount of operation input, and the amount of operation input (operation angle) of the butterfly valve 22 is a neutral operation value N and a cut value C. A manipulated variable signal representing this is supplied from the limit switch 48 to the arithmetic and control unit 44.

The arithmetic and control device 44 is composed of a so-called digital computer, and processes temperature signals, command signals, and operation amount signals according to a pre-stored program, and as a result, turns ON/OFF to open/close the butterfly valve 22. - An open/close signal, which is an OFF signal, is supplied to the valve drive circuit 50 to drive the drive motor 24, and a cut signal is supplied to the solenoid valve 27 to cut off the fuel.

The operation of this embodiment will be explained below.

When a start operation is performed by an operation switch (not shown), the arithmetic and control unit 44 operates according to the flowchart shown in FIG.

First, step S1 is executed to set the cooling mode indicating that the amount of operation input to the butterfly valve 22 is within the cooling control range, and
Step S2 is executed to determine the mode setting state. In this state, since the cooling mode has already been set, step S3 is executed.
A temperature control operation is performed. That is, by reading the temperature signal and command signal,
The deviation between the ambient temperature in the furnace 10 and the target temperature is calculated, and the manipulated variable is calculated based on the deviation from arithmetic expressions for proportional, integral, and differential control so that the deviation becomes zero. A pulsed opening/closing signal having a time width corresponding to the angular amount is supplied to the valve drive circuit 50 so that the butterfly valve 22 is driven by the angular amount corresponding to the operation amount. Therefore, the drive motor 24 is connected to the butterfly valve 2.
2 is driven in a direction in which the amount of operation input approaches the neutral operation position N (50%) according to the opening/closing signal.

Next, step S4 is executed, and it is determined whether the opening degree of the butterfly valve 22 is fully closed, or in other words, whether the amount of operation input to the butterfly valve 22 has reached 50%. Before the amount of operation input to the butterfly valve 22 reaches 50%, steps S2 and S3 and step S of waiting for 1 second are performed.
15 is repeatedly executed to perform the temperature control operation, but when the amount of operation input to the butterfly valve 22 is 50
%, step S5 is executed and an opening/closing signal for continuously rotating the butterfly valve 22 in the normal direction is supplied to the valve drive circuit 50. That is, a constant voltage opening/closing signal is continuously supplied, and the amount of operation input to the butterfly valve 22 is rapidly increased.

In this state, by executing step S6, it is determined whether the operation input amount in the butterfly valve 22 has reached the cut value C according to the operation amount signal from the limit switch 48, and if it has reached the cut value C, step S7 is executed. executed. Step S
At step 7, the supply of the opening/closing signal is stopped, so that the drive of the butterfly valve 22 is stopped, and the output of the cut signal that had been supplied to the electromagnetic valve 27 is stopped, and the fuel is transferred to the burner 16.
and combusts the fuel within the radiant tube 14. At the same time, in step S7, the heating mode is set to indicate that the amount of operation input to the butterfly valve 22 is within the heating control range.

In this way, in steps S4 to S6,
As soon as the amount of operation input to the butterfly valve 22 exceeds the neutral operation position N from the cooling control range and enters the idle range, the amount of operation input is increased to the cut value C, so steps S4 to S6 operate the operation amount changing means. It is forming.

After starting combustion in step S7, step S
8 is executed and the engine is kept on standby for 5 seconds, which is the time corresponding to the combustion stabilization period. Thereafter, step S2 is executed again to determine the mode setting state. Since the heating mode has been set in step S7, the next step S9 is executed and temperature control operation is performed. That is, step S
Similarly to 3, by reading the temperature signal and the command signal, the deviation between the atmospheric temperature in the furnace 10 and the target temperature is calculated, and the deviation is adjusted so that the deviation becomes the atmosphere. Based on proportional, integral,
The manipulated variable is calculated from the arithmetic expression for differential control,
Butterfly valve 2 by the angle amount corresponding to the amount of operation.
A pulsed opening/closing signal having a time width corresponding to the angle amount is supplied to the valve drive circuit 50 so that the valve drive circuit 2 is driven.

Next, step S10 is executed, and it is determined whether the amount of operation input to the butterfly valve 22 has fallen below the cut value C or not. If the cut has not yet been lowered, steps S2, S9 and S15 are repeated to perform the temperature control operation, but if the cut has been lowered, step S11 is executed and a cut signal is supplied to the solenoid valve 27. While the fuel is cut off, an opening/closing signal is supplied to the valve drive circuit 50 to continuously reverse the butterfly valve 22 . In other words, the amount of operation input to the butterfly valve 22 is rapidly reduced.

By executing step S12 in this state, the amount of operation input to the butterfly valve 22 is below the neutral operation position N, and the valve opening is approximately 2%, according to the operation amount signal from the limit switch 48. It is determined whether or not a predetermined value L has been reached, and when the value L has been reached, step S13 is executed. In step S13, when the supply of the opening/closing signal is stopped, the drive of the butterfly valve 22 is stopped and the cooling mode is set.

In this way, in steps S10 to S13, when the amount of operation input to the butterfly valve 22 falls below the cut value C from the heating control range and enters the idle range, the amount of operation input immediately changes to the neutral operation value N.
Since the amount is changed to the following predetermined value L, steps S10 to S13 form a manipulated variable changing means.

After executing step S13, step S13 is executed.
After steps S14 and S15 are executed and put on standby, step S2 is executed again, and the above-described operations are repeated.

As described above, according to this embodiment, the amount of operation input (valve operation angle) of the butterfly valve 22 is in the idle range which not only does not contribute to temperature control but also has a characteristic in the opposite direction to the temperature control direction. When you enter,
The amount of operation input is immediately changed so that it is outside the idle range. That is, since the amount of operation input to the butterfly valve 22 is caused to skip the idle range,
It is as if the idle range has been removed from the operation input range, and delays in control response and variations in temperature control caused by the existence of the idle range are completely eliminated.
Highly accurate temperature control characteristics can be obtained. According to experiments conducted by the present inventor, in the conventional case without the above-mentioned operation variable changing means, the temperature variation of the heated object was ±15°C in the slow cooling zone, whereas By using the apparatus of this example, it was possible to achieve temperature control with a significantly high accuracy of ±3°C.

Although the embodiment of the present invention has been described above based on the drawings, the present invention can also be applied to other aspects.

For example, in the above embodiment, the value after changing the operating input amount of the butterfly valve 22 in order to skip the idle range is the cut value C in the heating mode, and the cut value C in the cooling mode. The predetermined value L may be predetermined at a value greater than or equal to the cut value C or less than the neutral position N.

In the embodiment described above, the control valve 28 is connected to the burner 1.
6 is operated by a regulator 34 and a drive motor 30 to supply fuel at a constant ratio to the amount of air provided to the connecting rod 26. It may also be configured to be operated by the user.

Further, it goes without saying that the drive motor 24 may be configured not only by an AC or DC servo motor but also by a pulse motor.

Further, the detection means for detecting the operating position of the connecting rod 26 continuously detects the operating input amount of the butterfly valve 22 using not only the limit switch 28 but also a position sensor such as a rotary encoder or a potentiometer. The amount of operation input to the butterfly valve 22 may be determined by comparing the detected neutral operation position N or cut value with the detected value. In this case, the position sensor and the comparator or decision program step form the detection means.

Furthermore, when changing the amount of operation input to the butterfly valve 22 to skip the idle range, the drive motor 24 may be driven at an increased speed. In such a case, there is an advantage that the skip time is further shortened.

Furthermore, in the characteristics of the butterfly valve 22, the neutral operation value N in the operation input range does not have to be 50%, and the air flow rate (valve opening degree) at the neutral operation value
It doesn't have to be an atmosphere. In short, it is sufficient to have a characteristic that the air flow rate increases as the amount of operation input moves away from the neutral operation value N.

The above-mentioned embodiment is merely one embodiment of the present invention, and various modifications may be made to the present invention without departing from the spirit thereof.

[Brief explanation of the drawing]

FIGS. 1 and 3 are diagrams showing the characteristics and structure of a butterfly valve used in an embodiment of the present invention. FIG. 2 is a block diagram illustrating the configuration of the embodiment shown in FIG. 1. FIG. 4 is a diagram showing the output characteristics of the temperature program setter shown in FIG. 2. FIG. 5 is a flowchart illustrating the operation of the embodiment shown in FIG. 10... Indirect heating furnace, 14... Radiant tube (partition wall), 16... Burner, 22... Butterfly valve (air conditioning device), 27... Solenoid valve (fuel cutoff device), 2
8... Regulating valve (fuel regulating device), 44... Arithmetic control device, 50... Valve drive circuit, 48... Limit switch (detection means).

Claims (1)

[Claims] 1. An indirect heating furnace that heat-treats an object to be heated through a partition wall heated by a burner, which is provided with a predetermined operation input range, and has a neutral operation value within the operation input range as a boundary. an air amount adjustment device that increases the amount of air supplied to the burner as the amount of operation input deviates from the neutral operation value; a fuel adjustment device for supplying a certain ratio of fuel to the burner; and a cut for supplying a minimum amount of air to the burner such that the operation input amount in the air amount adjustment device maintains a good combustion state. When it falls below the value,
a fuel cutoff device that cuts off the fuel supplied to the burner, and performs heating operation by setting the amount of operation input given to the air amount adjusting device within a heating control range larger than the cut value, and the amount of operation input A temperature control device that controls the atmospheric temperature in the heating furnace to match the target temperature by performing a cooling operation with the temperature within a cooling control range smaller than the neutral operation value, the temperature control device comprising: at least the amount of operation input; a detection means for detecting that the neutral operation value has been exceeded and that the operation input amount has fallen below the cut value; when the operation input amount exceeds the neutral operation value from the cooling control range; Immediately change the operating input amount to a predetermined value greater than or equal to the cut value, and when the operating input amount falls below the cut value from the heating control range, immediately change the operating input amount to a predetermined value equal to or higher than the neutral operating value. A temperature control device for an indirect heating furnace, comprising: a manipulated variable changing means for changing the value to a predetermined value.