JPH06193601A - Rod position control method for stepping cylinder - Google Patents

Abstract

PURPOSE:To improve the responsiveness by suppressing operation delay of an output rod caused by frictional resistance on the load side in the case of rod position controlling of a stepping cylinder. CONSTITUTION:Pressures P1, P2 on both sides of a stepping cylinder are supplied to a cylinder load estimator 25. A cylinder load is obtained in a relevant manner to the difference therebetween. Correction pulse having a pulse number corresponding to the result is generated by means of a pulse generator 28. When deviation is caused between the present rod position and an objective position, first, the correction pulse is added to a driving pulse which is generated by a pulse generator 23 correspondingly to the deviation. Then, the resultant pulse is transmitted to a driving circuit 80 which is a driving source of the stepping cylinder. After completion of the transmittance, the correction pulse only is supplied to the driving circuit 80 in a reverse direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, for example, when performing the level control of the molten metal surface inside a mold for continuous casting, the rod position of a stepping cylinder used as a means for adjusting the amount of molten metal poured into the mold is highly accurate. On how to control.

[0002]

2. Description of the Related Art At the time of operating a continuous casting facility, the level control of the molten metal in order to maintain the molten metal level in the mold at a predetermined target level stabilizes the cooling and solidification state of the molten steel in the mold, It is extremely important in order to improve the quality of the product slab and prevent the occurrence of various inconveniences such as breakouts that require the suspension of operation.

In this level control, the pouring nozzle for pouring the mold is provided with an opening / closing means such as a sliding nozzle and a stopper device, and the level inside the mold is sequentially detected. In order to eliminate the deviation from the target level, the opening degree of the opening / closing means is adjusted to adjust the amount of molten metal poured into the mold.

Conventionally, the opening degree of the opening / closing means is generally adjusted by a hydraulic servo system including a hydraulic servo cylinder and a servo valve. However, in this case, since a servo valve with poor heat resistance cannot be placed near the servo cylinder located directly above the mold, a long hydraulic pipe is required to connect the two, and there is also a gap between the servo cylinder and the servo valve. Since the flexible tube must be used as the hydraulic pipe in order to absorb the position fluctuation of the servo valve, the hydraulic pressure fed from the servo valve is used to expand the flexible tube and compress the accumulated oil inside the flexible tube, and There is a large time lag between the operation of the servo cylinder according to the operation of (1), that is, the time between the fluctuation of the molten metal surface and the actual operation of adjusting the molten metal surface, and there is a limit to improvement in responsiveness. However, there is a drawback that it is not possible to meet the recent demand for higher casting speed.

In order to solve this difficulty, in recent years,
Continuous casting equipment in which the opening degree is adjusted by a stepping cylinder is being put to practical use. The stepping cylinder is a direct-acting type actuator in which a piston of a hydraulic cylinder has a control spool built therein, and the rotation of the pulse motor is transmitted to the control spool so as to be displaced in the same direction as the piston. FIG. 4 is an operation explanatory diagram of the stepping cylinder.

As shown in the figure, in the stepping cylinder 7, a piston 71 is slidably inserted in the cylinder housing 70 in the axial direction, and an output rod 72 extending to one side of the piston 71 is provided outside the cylinder housing 70. While projecting, a spool chamber is formed inside the piston 71 coaxially therewith, and a control spool 73 is fitted in the spool chamber so as to be slidable in the axial direction, and the shaft of the control spool 73 is A screw shaft 74 screwed to the core is extended in the opposite direction to the output rod 72,
It is connected to the output end of the pulse motor 8 outside the cylinder housing 70.

That is, the piston 71 receives the internal pressure of the pressure chambers S ₁ and S ₂ divided on both sides thereof and moves in the axial direction, and this movement is taken out to the outside via the output rod 72. Further, the control spool 73 inside the piston 71 is displaced in the axial direction according to the rotation of the screw shaft 74 accompanying the rotation of the pulse motor 8, and the relative position with respect to the piston 71 causes a change in both A communication passage 75 communicating with _{one of} the pressure chambers S ₁ and S ₂ (the pressure chamber S ₂ on the right side in the figure).
Is selectively communicated with a high pressure port P connected to a hydraulic pressure source and a low pressure port T connected to an oil tank, the internal pressure of the pressure chamber S ₂ is regulated, and it is connected to the other pressure chamber S _1. Performs an operation that causes a pressure difference.

FIG. 4A shows a settling state, in which the high pressure port P and the low pressure port T of the piston 71 are opened by a predetermined amount by the control spool 73, and the pressure chamber S ₂
The internal pressure P _{2 of the above} is stopped at a position satisfying the following expression with respect to the internal pressure P ₁ of the pressure chamber S ₁ . In the formula, A ₁ and A ₂ are the pressure receiving areas of the piston 71 on the pressure chamber S ₁ and S ₂ sides, and F is the load in the pushing direction acting on the piston 71 via the output rod 72. It is the load. F = P ₂ · A ₂ −P ₁ · A ₁ (1)

When the applied load F fluctuates in the above settling state, the piston 71 moves to control the spool 73.
The relative position changes between, thereby opening the balance of the pump port P and tank port T is changed, the result the internal pressure P ₂ of the pressure chamber S ₂ is increased or decreased, the piston 71 is promptly stop position described above Return to and keep the position.

When the output rod 72 is moved back and forth, the pulse motor 8 is driven and the control spool 73 is displaced by the rotation of the screw shaft 74. FIG. 4B shows a transitional state in which the control spool 73 is being displaced rightward (toward the pressure chamber S ₂ ). At this time, as shown in the figure, the communication with the high pressure port P is cut off and the pressure chamber S 2 is closed. _{As a result} of the internal pressure P _{2 of 2} decreasing and the internal pressure P _{1 of} the other pressure chamber S ₁ relatively increasing,
The 71 moves rightward so as to follow the displacement of the control spool 73, and a new settling state as shown in FIG. 4A is newly formed and stopped at the position of the control spool 73 after the displacement is completed.

FIG. 4C shows a transitional state in which the control spool 73 is being displaced leftward (toward the pressure chamber S ₁ ). In this case, conversely, the communication with the low pressure port T is cut off. internal pressure P ₂ of the pressure chamber S ₂ rises Te, other pressure chamber S
_{Results 1} of pressure P ₁ is relatively low, the piston 71 moves to the left, and stops form a new settling conditions for the final position of the control spool 73.

As described above, in the stepping cylinder 7, the advancing / retreating position (rod position) of the output rod 72 connected to the piston 71 changes following the displacement of the control spool 73, while the displacement of the control spool 73 changes. Since the rotation position is generated according to the rotation of the pulse motor 8 which can be controlled with high accuracy, the rod position of the output rod 72 can be positioned with high accuracy. Therefore, when the stepping cylinder 7 is used as the means for adjusting the amount of molten metal poured into the mold, hydraulic piping is substantially unnecessary, and the precision and responsiveness of the molten metal level control are significantly improved. .

[0013]

In the molten metal level control using the stepping cylinder 7, the deviation between the detected value of the molten metal level inside the mold and the target level is obtained, and the pulse motor is used to eliminate this deviation. This is achieved by rotationally driving 8 and changing the rod position of the stepping cylinder 7, but a speed type command is required to drive the pulse motor 8. Therefore, in this type of molten metal level control, generally, the rod position of the stepping cylinder 7 is detected, and the deviation from the target position (position type command) given from the upper controller according to the level deviation is obtained. , A cylinder controller for issuing a drive pulse (speed type command) having a pulse number corresponding to the magnitude of this deviation and a direction corresponding to the direction (positive or negative) of this deviation is provided to the pulse motor 8. The method of giving is adopted.

FIG. 5 is a time chart showing the behavior of the control spool 73 and the output rod 72 of the stepping cylinder with respect to the drive pulse output from the cylinder control section. As is apparent from this figure, the control spool 73 which is directly driven by the rotation of the screw shaft 74 connected to the output end of the pulse motor 8 has a constant speed (tilt) corresponding to the transmission cycle of the drive pulse. The output rod 72, which operates following the control spool 73, has a load (sliding nozzle, stopper device, etc.) connected to its output end. There is a delay due to the effect of frictional resistance.

That is, the output rod 72 causes a predetermined time delay for resisting a large static friction resistance on the load side until the output rod 72 starts to move in response to the start of operation of the control spool 73 (see FIG. After that, the control spool 73 operates at a speed substantially equal to that of the control spool 73 against a comparatively small dynamic frictional resistance (area B in the figure), and after the position of the control spool 73 is settled, , The change in the opening state of the high pressure port P or the low pressure port T becomes gradual with the operation of the piston 71, and therefore, the behavior (C region in the figure) of settling to the target position while gradually decreasing the speed is shown.

The control spool 73 is capable of high-speed response of about 50 mm / sec to 100 mm / sec, which is substantially equal to that of the pulse motor 8. On the other hand, the opening change amount required for performing the molten metal level control, that is, the stepping cylinder 7 The maximum amount of rod position change is about ± 0.5 mm, so the total time required for area A and area B in Fig. 5 is 0.005 (0.5 / 100) to 0.01.
In contrast to (0.5 / 50) sec, the time required for the output rod 73 to reach the target position after the control spool 73 is settled, that is, the time required for the C region reaches 0.2 to 0.25 sec,
In the rod position control performed as described above, the required time in the C region is a factor that hinders improvement in responsiveness.

As is apparent from FIG. 5, the required time in the C area is shorter than that in the A area, and the control spool
This can be shortened by reducing the positional error between the output rod 72 and the control spool 73 at the stop of 73, that is, at the transition point from the B area to the C area, but the time required for the A area is
As described above, the output rod 73 resists the static friction force on the load side.
Is the time until the operation starts, that is, the time determined by the state of the load side, and this cannot be operated.

Further, the shortening of the time in the C region increases the amount of change in the opening area of the high pressure port P and the low pressure port T which is caused by the operation of the piston 71 after the control spool 73 is stopped,
It is also achieved by increasing the slope in the C region. However, in this case, since the internal pressure of the pressure oil chamber S ₂ suddenly changes due to a slight movement of the output rod 72, the output rod 72 vibrates before and after the target position, so-called hunting is caused, and the time required for settling is increased. Will rather increase.

The above-mentioned difficulties are not limited to the control of the molten metal level in the continuous casting equipment, but occur in the same manner in various applications in which the rod position control of the stepping cylinder is controlled according to the position type command.

The present invention has been made in view of the above circumstances, and shortens the time required for the output rod to settle to a predetermined target position, thereby enabling rod position control of a stepping cylinder in accordance with a position type command. It is an object of the present invention to provide a control method that is realized with the highest responsiveness.

[0021]

According to a rod position control method of a stepping cylinder according to the present invention, a rod position of a stepping cylinder that responds to a pressure difference generated on both sides of a piston due to displacement of a built-in spool accompanying rotation of a pulse motor is set to a predetermined value. In order to match the target position of, the drive pulse having the number of pulses corresponding to the deviation between the two positions is transmitted,
In a rod position control method for a stepping cylinder that rotationally drives the pulse motor, a pressure difference between both sides of the piston is detected, and a correction pulse having a pulse number corresponding to the detection result is added to the drive pulse in the same direction and transmitted. The correction pulse is transmitted in the reverse direction after the transmission of these signals is completed.

[0022]

According to the present invention, when a deviation between the current rod position of the stepping cylinder and the target position occurs, a correction pulse is added to the drive pulse having the number of pulses corresponding to this deviation, and the stepping cylinder is controlled. Timing when the output rod reaches the front and back of the target position by allowing the spool to settle to a position where the original target position has passed by a predetermined amount and making the operating position of the output rod close to the original target position when the control spool is stopped. Then, the correction pulse is emitted in the reverse direction to return the control spool to the target position, and the output rod is settled to this target position.

Further, the pulse number of the correction pulse is determined according to the load side state estimated from the pressure difference between both sides of the piston, and the initial overshoot amount of the control spool is the load side state at the start of operation, that is, , The output rod is set according to the load applied to the output rod, the time required until the output rod is settled is shortened regardless of the state of the load side, and the responsiveness is further improved.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments. FIG. 1 is a schematic diagram showing an implementation state in a molten metal level control of a continuous casting facility of a rod position control method for a stepping cylinder (hereinafter referred to as the method of the present invention) according to the present invention.

In the figure, T is a tundish in which the molten steel 3 is stored. A cylindrical mold M is disposed below the tundish T at an appropriate distance, and inside the mold M, a dipping nozzle 4 having a base end opened on the bottom surface of the tundish T is provided. Has been extended. Thus, the molten steel 3 in the tundish T is poured into the mold M through the immersion nozzle 4, cooled by contact with the inner wall of the mold M, and the slab 5 coated with the solidified shell 50 on the outside. Next to
It is continuously drawn below the mold M. Then, during the drawing, the product is further cooled, solidified to the inside, and then cut into an appropriate size to obtain a product slab which is a raw material in a post-process such as rolling.

In the middle of the immersion nozzle 4, the sliding movement of the gate plate 60 in a plane substantially orthogonal to the longitudinal direction of the immersion nozzle 4 opens and closes the immersion nozzle 4 to adjust the amount of molten metal poured into the mold M. 6 is fixed. The gate plate 60 of the sliding nozzle 6 is connected to the tip of the output rod 72 of the stepping cylinder 7 configured as described above, and the opening of the sliding nozzle 6 is caused by sliding of the gate plate 60 as the output rod 72 moves forward and backward. Adjustments are made so that the amount of molten metal poured into the mold M is adjusted. Further, reference numeral 9 in the drawing is a level detector 9 which is arranged so as to face the surface of the molten steel 3 staying in the mold M and detects a molten metal level inside the mold M.

In the molten metal level control in the continuous casting equipment having the above-mentioned structure, a drive command is given to the drive circuit 80 of the pulse motor 8 based on the result of the molten metal level detected by the level detector 9, and the output of the stepping cylinder 7 is output. This is performed by controlling the forward / backward position (rod position) of the rod 72.
The control device for performing this control includes an opening degree control unit 1 which is a higher position type controller, and a cylinder control unit 2 which is a lower speed type controller and operates according to the method of the present invention. .

A level detector 9 is provided in the upper opening control section 1.
The deviation between the current level of the molten metal in the mold M detected by and the preset target level is sequentially given,
The opening control unit 1 carries out a PID calculation using this deviation to obtain a target opening required to eliminate the deviation,
An operation of outputting the result to the cylinder control unit 2 as an opening degree command is performed.

The cylinder control unit 2 uses the position type opening command given from the opening control unit 1 to determine the rotation direction and the rotation amount of the pulse motor 8 required to realize this, and as a result, Is output to the drive circuit 80 of the pulse motor 8 as a speed type command, specifically, as a drive pulse for driving the pulse motor 8 in the forward rotation direction or the reverse rotation direction. The cylinder controller 2 also includes pressure detectors 76, 77 attached to the pressure chambers S ₁ , S ₂ of the stepping cylinder 7.
From the above, the detection results of the respective internal pressures P ₁ and P ₂ are given.

FIG. 2 is a block diagram showing the internal structure of the cylinder control unit 2. As shown in this figure, the cylinder control unit 2
Is an adder 20, 21, a divider 22, a first pulse generator 23,
And a drive pulse generator 2a including an integration counter 24, and a correction pulse generator 2b including a cylinder load estimator 25, an amplifier 26, a divider 27, and a pulse generator 28.

The opening command given from the opening controller 1 is
It is given to the adder 20 of the drive pulse generator 2a together with the current feedback signal of the rod position, which is obtained as the output of the integrating counter 25 as described later, and the adder 20 obtains the deviation X between the two, and the result is obtained. It is given to the adder 21. The deviation X is the opening change amount of the sliding nozzle 6, that is, the rod position change amount in the stepping cylinder 7, which is necessary to realize the above-described opening command, and the adder 21
Adds a fraction X ″ generated as described later to this position change amount X, and outputs the obtained correction change amount X ′ to the divider 22.

In the divider 22, the change amount of the rod position of the stepping cylinder 7, that is, the resolution n of the stepping cylinder 7, which is caused by the unit rotation of the pulse motor 8 according to one pulse output, is set. The device 22 divides the correction change amount X ′ given from the adder 21 by the resolution n and outputs the obtained quotient N to the pulse generator 23 and the pulse generator 28 in the correction pulse generator 2b. , The fraction X ″ generated as a result of the division is fed back to the adder 21.

In the above process, the absolute value of the quotient N output from the divider 22 is the number of pulses to be given to the pulse motor 8 to obtain the correction change amount X ', and the positive / negative of the quotient N is the pulse motor 8 Shows the rotation direction of. Pulse generator 23
Is the number of pulses corresponding to the absolute value of the quotient N and the quotient N
The drive pulse having a direction corresponding to the rotation direction of the pulse motor 8 determined by the positive or negative of is generated and output to the drive circuit 80 of the pulse motor 8 via the adder 29.

On the other hand, the internal pressures P ₁ and P ₂ of the pressure chambers S ₁ and S ₂ detected by the pressure detectors 76 and 77 are given to the cylinder load estimator 25 of the correction pulse generator 2b. The cylinder load estimator 25 estimates and calculates the load on the output rod 72 of the stepping cylinder 7 and outputs the result. For example, in this calculation, the detected values of the internal pressures P ₁ and P ₂ are (1). It is done by substituting it into an expression. In addition,
Since it is not necessary to exactly determine the load applied to the output rod 72, the cylinder load estimator 25 uses the detected internal pressure P
_It may be a simpler arithmetic unit such as obtaining the difference between ₁ and P ₂ .

The output of the cylinder load estimator 25 is the amplifier 26
Is multiplied by a predetermined gain K and is given to the divider 27 as a correction amount X ₀ . The resolution n of the stepping cylinder 7 is set in the divider 27 similarly to the divider 22 of the drive pulse generator 2a, and the divider 27 divides the correction amount X ₀ given from the amplifier 26 by the resolution n. , And outputs the obtained quotient N ₀ to the pulse generator 28. The pulse generator 28 also outputs the output N of the divider 22 in the drive pulse generator 2a.
And a signal indicating whether or not a drive pulse is generated in the pulse generator 23.

In the above process, the output N _{0 of the} divider 27
Is a value corresponding to the current cylinder load, and the pulse generator 28 first has the number of pulses corresponding to the output N _0, and the rotation of the pulse motor 8 determined by the sign of the input N from the divider 22. A correction pulse having a direction corresponding to the direction is generated, and after the output of the pulse generator 23 is finished and a predetermined delay time Δt described later elapses, a correction pulse having the same number of pulses is generated in the opposite direction. The former correction pulse is added to the drive pulse by the adder 29, and the latter correction pulse is directly applied to the drive circuit 80 of the pulse motor 8.

The output pulses of the pulse generators 23 and 28 are successively integrated by the integration counter 25 and added as a signal indicating the current rod position of the stepping cylinder 7, that is, the current opening of the sliding nozzle 6. It is being fed back to the vessel 20. The frequencies of the drive pulse and the correction pulse generated by the pulse generators 23 and 28 are the self-starting frequency of the pulse motor 8 in order to drive the pulse motor 8 at a speed as high as possible and improve the responsiveness. Has been adopted.

Further, since the division by the divider 22 is performed on the correction change amount X'which is obtained by adding the position change amount X which is the output of the adder 20 and the fraction X "generated by the previous division,
The fraction X ″ generated at each control opportunity is not discarded, and the opening command sequentially given from the opening control unit 1 is accurately realized.

With the above operation of the cylinder control unit 2, the pulse motor 8 first responds to the drive pulse having the number of pulses corresponding to the deviation between the current rod position and the target value according to the current cylinder load. Driven by a first pulse train, which is made by adding a correction pulse having a number of pulses,
Then, after the delay time Δt has elapsed, the second pulse train of the correction pulses is driven in the opposite direction.

FIG. 3 is a time chart showing the behavior of the control spool and the output rod of the stepping cylinder 7 when the pulse motor 8 is driven as described above, that is, when the method of the present invention is carried out. As is clear from this figure,
The control spool 73, which is directly driven by the rotation of the pulse motor 8, starts to move promptly when the output of the first pulse train is started, and is a regular target located at a position away from the current position by the correction change amount S '. After reaching a temporary target position that exceeds the position by a predetermined overshooting amount δ and stopping at that position for Δt, the second pulse train moves in the opposite direction,
Settle to the regular target position.

On the other hand, the output rod 72 of the stepping cylinder 7 is affected by the frictional resistance on the load side connected to the stepping cylinder 7, more specifically, the static frictional resistance on the gate plate 60 of the sliding nozzle 6, and thus the control rod 73 of the control spool 73 described above. Follow the movement with a delay. That is, there is a time delay for resisting the static friction resistance of the gate plate 60 until the output rod 72 starts to move with the start of the operation of the control spool according to the first pulse train (area A in the figure). ), After that, the gate plate 60 operates at a speed substantially equal to that of the control spool against the dynamic friction resistance (area B in the figure), and after the control spool 72 stops, the piston for the control spool 72 Since the propulsive force of the piston 71 weakens in accordance with the relative movement of the piston 71, the speed is reduced and the control spool 73 gradually approaches the stop position of the control spool 73 (C region in the figure).

As described above, since the stop position of the control spool due to the stop of transmission of the first pulse train is a position which is over the normal target position by δ, when the control spool 73 is stopped, as is apparent from FIG. That is, the position of the output rod 72 at the time of the transition from the B area to the C area is close to the normal target position, and thereafter, during the operation of the output rod 72 in the C area, the control spool 73 causes the second pulse train to move. Since the output is displaced in the opposite direction by the action and approaches the regular target position, the output rod 72 also moves following this, and deviates from the asymptote to the tentative target position indicated by the chain double-dashed line in the figure. The target position is gradually approached and settles to the target position.

At this time, the overshooting amount δ of the control spool 73 after the operation by the first pulse train is from the B area to the C area.
The rod position at the time of transition to the region is determined, but this overshooting amount δ is obtained by adding the correction pulse, and this correction pulse corresponds to the magnitude of the load load of the output rod 72 at the start of the operation. The number of pulses to do,
In other words, it has the number of pulses corresponding to the width of the delay region (A region) until the operation of the output rod 72 is started. Therefore,
The overshooting amount δ that is always adapted to the load side state at the start of operation is automatically obtained, and the rod position at the time of transition from the B region to the C region becomes slightly below the normal target position. The reverse movement of the control spool 73 that occurs after the delay time Δt causes the stepping cylinder 7 to move.
The time required for the output rod 72 to settle to the target position can be greatly shortened.

The overshoot amount δ is optimized by adjusting the gain of the amplifier 26 in the correction pulse generator 2b, and the delay time Δt is optimized by changing the setting of the delay timer also incorporated in the pulse generator 28. It is only necessary to perform each in the cold before the start of casting, and when the method of the present invention is carried out using the optimum value thus selected, as is apparent from the comparison between FIG. 3 and FIG. Time from the start of operation until the output rod settles to the target position, that is,
The time required for the A, B and C areas as a whole is significantly reduced,
The responsiveness of rod position control of the stepping cylinder 7 can be significantly improved.

In the present embodiment, the application example of the device of the present invention in controlling the level of the molten metal in the mold in the continuous casting equipment has been described. However, the application range of the device of the present invention is not limited to this, and the position type It is needless to say that it can be applied to any application that requires controlling the stepping cylinder according to the command.

[0046]

As described in detail above, in the method of the present invention, when a deviation between the current rod position of the stepping cylinder and the target position occurs, the pulse motor serving as the drive source of the stepping cylinder responds to the deviation. Driven by a pulse train in which a correction pulse is added to a drive pulse having a pulse number, the control spool of the stepping cylinder is settled at a position where the original target position has passed a predetermined amount.
The operating position of the output rod when the control spool is stopped is brought close to the original target position, and then the control spool is driven in the reverse direction only by the correction pulse to return the control spool to the target position, so the output rod is settled to the target position. It is possible to drastically reduce the time until the number of correction pulses is determined according to the load side condition estimated by the pressure difference between both sides of the piston. The amount is adapted to the load side state at the time, optimal control is performed according to the load side state, and rod position control of the stepping cylinder according to the position type control command can be realized with high responsiveness. The invention has excellent effects.

[Brief description of drawings]

FIG. 1 is a schematic view showing an implementation state of a method of the present invention in controlling a molten metal level in a continuous casting facility.

FIG. 2 is a block diagram showing an internal configuration of a cylinder control section that operates according to the method of the present invention.

FIG. 3 is a time chart showing the behavior of the control spool and the output rod when the method of the present invention is carried out.

FIG. 4 is an operation explanatory diagram of a stepping cylinder.

FIG. 5 is a time chart showing the behavior of the control spool and the output rod when the conventional rod position control method is executed.

[Explanation of symbols]

 1 Opening controller 2 Cylinder controller 2a Drive pulse generator 2b Correction pulse generator 6 Sliding nozzle 7 Stepping cylinder 8 Pulse motor 9 Level detector 23 Pulse generator 25 Cylinder load estimator 28 Pulse generator 71 Piston 72 Output rod 73 Control Spool M Mold T Tundish

Claims (1)

[Claims] 1. A pulse corresponding to a deviation between two positions of the stepping cylinder so that the rod position of the stepping cylinder responds to a pressure difference generated on both sides of the piston due to the displacement of the built-in spool accompanying the rotation of the pulse motor. In a rod position control method for a stepping cylinder that drives the pulse motor to rotate, the correction pulse having a pulse number corresponding to the detection result is detected. A rod position control method for a stepping cylinder, characterized in that the driving pulses are transmitted in the same direction, and the correction pulses are transmitted in the opposite direction after these transmissions are completed.