U.S. patent application number 12/866411 was filed with the patent office on 2010-12-23 for method and system for damping sloshing molten metal.
Invention is credited to Kazuhiro Ota, Makio Suzuki.
Application Number | 20100324719 12/866411 |
Document ID | / |
Family ID | 41319140 |
Filed Date | 2010-12-23 |
United States Patent
Application |
20100324719 |
Kind Code |
A1 |
Ota; Kazuhiro ; et
al. |
December 23, 2010 |
METHOD AND SYSTEM FOR DAMPING SLOSHING MOLTEN METAL
Abstract
The disclosed method is a control to suppress sloshing in a
ladle of a pouring device and a mold caused by their movements. A
plurality of flasks, each of which contains a conveyed mold, is
arranged linearly between an electric pusher-cylinder and an
electric cushion-cylinder. In the method, a first natural frequency
of the molten metal in the ladle is calculated based on a
predetermined relationship between the weight and the natural
frequency for the molten metal in the ladle, and the measured
weight of the molten metal in said ladle. Also, a second natural
frequency of the molten metal in said mold is calculated based on a
predetermined relationship between the weight and the natural
frequency for the molten metal in the mold, and the measured weight
of the molten metal in the mold. The first and second natural
frequencies are entered in a filtering circuit to modify a velocity
waveform of the movement of conveying the flasks such that the
modified velocity waveform does not include the first and second
natural frequencies. The electric pusher-cylinder and the electric
cushion-cylinder are driven such that the velocity waveform of the
movement of conveying the flasks is said modified velocity
waveform.
Inventors: |
Ota; Kazuhiro; ( Aichi,
JP) ; Suzuki; Makio; (Aichi, JP) |
Correspondence
Address: |
FINNEGAN, HENDERSON, FARABOW, GARRETT & DUNNER;LLP
901 NEW YORK AVENUE, NW
WASHINGTON
DC
20001-4413
US
|
Family ID: |
41319140 |
Appl. No.: |
12/866411 |
Filed: |
May 13, 2009 |
PCT Filed: |
May 13, 2009 |
PCT NO: |
PCT/JP2009/059233 |
371 Date: |
August 5, 2010 |
Current U.S.
Class: |
700/146 |
Current CPC
Class: |
B22D 47/02 20130101 |
Class at
Publication: |
700/146 |
International
Class: |
B22D 47/02 20060101
B22D047/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 16, 2008 |
JP |
2008-130073 |
Nov 11, 2008 |
JP |
2008-289028 |
Claims
1. A method of suppressing sloshing in a casting line, wherein said
casting line includes: a conveying line in which an electric
pusher-cylinder is located at one end of the conveying line for
intermittently pushing out a plurality of flasks, wherein each
flask contains a mold, one by one, and an electric cushion-cylinder
is located at the other end of said conveying line and opposed to
said electric pusher-cylinder to receive and cushion a group of
said pushed flasks such that said conveying line that conveys said
plurality of flasks is arranged linearly between said electric
pusher-cylinder and said electric cushion-cylinder; and an
automatic pouring device that has a ladle for containing molten
metal and that can be moved in synchronization with the flask on
the conveying line, to pour the molten metal into the mold by
tilting said ladle; said method controlling said electric
pusher-cylinder and said electric cushion-cylinder by using a
controller having filtering means such that the sloshing that
occurs in the molten metal is suppressed when said ladle and said
mold move by a distance corresponding to one flask, said method
comprising: calculating a first natural frequency of the molten
metal in said ladle based on a predetermined relationship between
the weight and the natural frequency for the molten metal in said
ladle, and the measured weight of the molten metal in said ladle,
and calculating a second natural frequency of the molten metal in
said mold based on a predetermined relationship between the weight
and the natural frequency for the molten metal in said mold, and
the measured weight of the molten metal in said mold; entering the
first and second natural frequencies in said filtering means to
modify a velocity waveform of the movement of conveying said flasks
such that the modified velocity waveform does not include the first
and second natural frequencies; driving said electric
pusher-cylinder and said electric cushion-cylinder such that the
velocity waveform of the movement of conveying said flasks is said
modified velocity waveform.
2. A system of suppressing sloshing in a casting line, wherein said
casting line includes: a conveying line in which an electric
pusher-cylinder is located at one end of the conveying line for
intermittently pushing out a plurality of flasks, wherein each
contains a mold, one by one, and an electric cushion-cylinder is
located at the other end of said conveying line and is opposed to
said electric pusher-cylinder to receive and cushion a group of
said pushed flasks such that said conveying line that conveys said
plurality of flasks is arranged linearly between said electric
pusher-cylinder and said electric cushion-cylinder; and an
automatic pouring device that has a ladle for containing molten
metal and that can be moved in synchronization with the flask on
the conveying line, to pour the molten metal into the mold by
tilting said ladle; wherein said system that controls said casting
line such that the sloshing that occurs in the molten metal in said
ladle and said mold is suppressed when said ladle and said mold
move by a distance corresponding to one flask; said system
comprising: a first weight-calculation means for calculating the
weight of the molten metal in said ladle; a second
weight-calculation means for calculating a second natural frequency
of the molten metal in said mold; a first natural
frequency-calculation means for calculating a first natural
frequency based on a predetermined relationship between the weight
and the natural frequency for the molten metal in said ladle, and
the calculated weight of the molten metal in said ladle by said
first weight-calculation means; a second natural
frequency-calculation means for calculating a second natural
frequency based on a predetermined relationship between the weight
and the natural frequency for the molten metal in said mold, and
the calculated weight of the molten metal in said mold by said
second weight-calculation means; filtering means for modifying a
velocity waveform of the movement of conveying of said flasks on
said conveying line such that the modified velocity waveform does
not include the first and second natural frequencies calculated by
said first and second natural frequency-calculation means; and
instructing means for providing operating instructions to said
electric pusher-cylinder, said electric cushion-cylinder, and said
automatic pouring device, based on said modified velocity
waveform.
3. A method of suppressing sloshing in a casting line, wherein said
casting line includes: a conveying line in which an electric
pusher-cylinder is located at one end of the conveying line for
intermittently pushing out a plurality of flasks, wherein each
flask contains a mold, one by one, and an electric cushion-cylinder
is located at the other end of said conveying line and is opposed
to said electric pusher-cylinder to receive and cushion a group of
said pushed flasks such that said conveying line conveys said
plurality of flasks and is arranged linearly between said electric
pusher-cylinder and said electric cushion-cylinder; an automatic
pouring device that has a ladle for containing molten metal and
that can be moved in synchronization with the flask on the
conveying line, to pour the molten metal into the mold by tilting
said ladle; driving means for driving said electric
pusher-cylinder, said electric cushion-cylinder, and said automatic
pouring device along a conveyed direction of said flasks;
controlling means for controlling said driving means; and
instructing means for providing operating instructions for said
electric pusher-cylinder, said electric cushion-cylinder, and said
automatic pouring device to said driving means through said
controlling means wherein; said method controls said casting line
using a controller having filtering means, based on a feedforward
control program such that the sloshing that occurs in the molten
metal is suppressed when said ladle and said mold move by a
distance corresponding to one flask, said method comprising:
calculating a first natural frequency of the molten metal in said
ladle based on a predetermined relationship between the weight and
the natural frequency for the molten metal in said ladle, and the
measured weight of the molten metal in said ladle, and calculating
a second natural frequency of the molten metal in said mold based
on a predetermined relationship between the weight and the natural
frequency for the molten metal in said mold, and the measured
weight of the molten metal in said mold; under the first natural
frequency, the second natural frequency, and the parameters of said
controlling means that are preliminarily calculated such that they
do not exceed the capacities of said driving means and are stored,
removing components that are located near the first and second
frequencies from the operating instructions, in which the maximum
value of at least one of a velocity of the movement, an
acceleration of the movement, and a jerk of the movement of said
ladle and said mold is restricted, by said filtering means using
said stored parameters, wherein said components to be removed are
decided based on a simulation using a model representing the
characteristics of said casting line to repeatedly calculate said
component by the following equation (1) or (2), y ( t ) = b 0 ( f )
x ( t ) + b 1 ( f ) x ( t - 1 ) + b 2 ( f ) x ( t - 2 ) + - a 1 ( f
) y ( t - 1 ) - a 2 ( f ) y ( t - 2 ) - y ( t ) = j = 0 m b j ( f )
x ( t - j ) - i = 1 n a 1 ( f ) y ( t - i ) ( 1 ) F ( S ) = Y ( S )
X ( S ) = b 0 ( f ) S 0 + b 1 ( f ) S 1 + b 2 ( f ) S 2 + a 0 ( f )
S 0 + a 1 ( f ) S 1 + a 2 ( f ) S 2 + = j = 0 m b j ( f ) S j i = 0
n a i ( f ) S i ( 2 ) ##EQU00007## while gradually varying
filtering parameters ai(f), bj(f) that are parameterized by a
resonance frequency f that are successively calculated from the
molten metal in said ladle and said mold, wherein y (t-i) is
time-series data that are output before i controlling cycles,
x(t-j) is time-series data that are input before j controlling
cycles, S is the Laplace operator, and equation (1) can be derived
by applying a Z transformation to the transfer function of the
filter that is expressed as equation (2); and entering the
operating instructions, in which said components that are located
near the first and second frequencies have been removed, in said
controlling means based on only said feedforward controlling
program, to operate said driving means based on only said
feedforward controlling program without using a feedback control
program.
4. A system for the suppression of sloshing in a casting line,
wherein said casting line includes: a conveying line in which an
electric pusher-cylinder is located at one end of the conveying
line for intermittently pushing out a plurality of flasks that each
contain a mold, one by one, and an electric cushion-cylinder is
located at the other end of said conveying line and is opposed to
said electric pusher-cylinder to receive and cushion a group of
said pushed flasks such that said conveying line conveys said
plurality of flasks and is arranged linearly between said electric
pusher-cylinder and said electric cushion-cylinder; an automatic
pouring device that has a ladle for containing molten metal and
that can be moved in synchronization with the flask on the
conveying line, to pour the molten metal into the mold by tilting
said ladle; driving means for driving said electric
pusher-cylinder, said electric cushion-cylinder, and said automatic
pouring device along a conveyed direction of said flasks; and
controlling means for controlling said driving means; wherein said
system controls said casting line to suppress the sloshing that
occurs in the molten metal in said ladle and the mold when said
ladle and said mold move by a distance corresponding to one flask,
said system comprising: a first weight-calculation means for
calculating the weight of the molten metal in said ladle; a second
weight-calculation means for calculating a second natural frequency
of the molten metal in said mold; a first natural
frequency-calculation means for calculating a first natural
frequency based on a predetermined relationship between the weight
and the natural frequency for the molten metal in said ladle, and
the calculated weight of the molten metal in said ladle by said
first weight-calculation means; a second natural
frequency-calculation means for calculating a second natural
frequency based on a predetermined relationship between the weight
and the natural frequency for the molten metal in said mold, and
the calculated weight of the molten metal in said mold by said
second weight-calculation means; instructing means for providing
operating instructions based on a feedforward program for
operations of said electric pusher-cylinder, said electric
cushion-cylinder, and said automatic pouring device, to said
driving means through said controlling means; parameter calculation
means for preliminarily calculating the parameters of said
controlling means such that the calculated parameters do not exceed
the capacity of said driving means; storing means for receiving and
storing the calculated parameters from said parameter calculation
means; restriction means for restricting a maximum value of at
least one of a velocity of the movement, an acceleration of the
movement, and a jerk of the movement of said automatic pouring
device and said mold; filtering means for receiving the first and
second resonance frequencies from said first and second
frequency-calculation means, and for removing components that are
located near the first and second frequencies from the operating
instructions, in which the maximum value is restricted by said
restriction means, using the stored parameters from the stored
means, wherein said components to be removed are decided based on a
simulation using a model representing the characteristics of said
casting line to repeatedly calculate said component, under said
stored parameters, by the following equation (1) or (2), y ( t ) =
b 0 ( f ) x ( t ) + b 1 ( f ) x ( t - 1 ) + b 2 ( f ) x ( t - 2 ) +
- a 1 ( f ) y ( t - 1 ) - a 2 ( f ) y ( t - 2 ) - y ( t ) = j = 0 m
b j ( f ) x ( t - j ) - i = 1 n a 1 ( f ) y ( t - i ) ( 1 ) F ( S )
= Y ( S ) X ( S ) = b 0 ( f ) S 0 + b 1 ( f ) S 1 + b 2 ( f ) S 2 +
a 0 ( f ) S 0 + a 1 ( f ) S 1 + a 2 ( f ) S 2 + = j = 0 m b j ( f )
S j i = 0 n a i ( f ) S i ( 2 ) ##EQU00008## while gradually
varying filtering parameters ai(f), bj(f) that are parameterized by
a resonance frequency f that are successively calculated from the
molten metal in said ladle and said mold, wherein y (t-i) is
time-series data that are output before i controlling cycles,
x(t-j) is time-series data that are input before j controlling
cycles, S is the Laplace operator, and equation (1) can be derived
by applying a 2 transformation to the transfer function of the
filter that is expressed as equation (2); and wherein said
instructing means provides said controlling means with operating
instructions in which said components that are located near the
first and second frequencies have been removed such that said
controlling means carries out the controls based on only said
feedforward controlling program without using a feedback control
program.
5. A computer readable media storing a computer program for the
suppression of sloshing in a casting line, wherein said casting
line includes: a conveying line in which an electric
pusher-cylinder is located at one end of the conveying line for
intermittently pushing out a plurality of flasks that each contain
a mold, one by one, and an electric cushion-cylinder is located at
the other end of said conveying line and is opposed to said
electric pusher-cylinder to receive and cushion a group of said
pushed flasks such that said conveying line conveys said plurality
of flasks and is arranged linearly between said electric
pusher-cylinder and said electric cushion-cylinder; and an
automatic pouring device that has a ladle for containing molten
metal and that can be moved in synchronization with the flask on
the conveying line, to pour the molten metal into the mold by
tilting said ladle; wherein said computer program causes a computer
having filter means to control said electric pusher-cylinder and
said electric cushion-cylinder such that the sloshing that occurs
in the molten metal is suppressed when said ladle and said mold
move by a distance corresponding to one flask, said computer
program comprising the steps to be executed by said computer of:
calculating a first natural frequency of the molten metal in said
ladle based on a predetermined relationship between the weight and
the natural frequency for the molten metal in said ladle, and the
measured weight of the molten metal in said ladle, and calculating
a second natural frequency of the molten metal in said mold based
on a predetermined relationship between the weight and the natural
frequency for the molten metal in said mold, and the measured
weight of the molten metal in said mold; entering the first and
second natural frequencies in said filtering means to modify a
velocity waveform of the movement of conveying of said flasks such
that the modified velocity waveform does not include the first and
second natural frequencies; and driving said electric
pusher-cylinder and said electric cushion-cylinder such that the
velocity waveform of the movement of conveying of said flasks is
said modified velocity waveform.
6. A computer readable media storing a computer program for the
suppression of sloshing in a casting line, wherein said casting
line includes: a conveying line in which an electric
pusher-cylinder is located at one end of the conveying line for
intermittently pushing out a plurality of flasks that each contain
a mold, one by one, and an electric cushion-cylinder is located at
the other end of said conveying line and is opposed to said
electric pusher-cylinder to receive and cushion a group of said
pushed flasks such that said conveying line that conveys said
plurality of flasks is arranged linearly between said electric
pusher-cylinder and said electric cushion-cylinder; an automatic
pouring device that has a ladle for containing molten metal and
that can be moved in synchronization with the flask on the
conveying line, to pour the molten metal into the mold by tilting
said ladle; driving means for driving said electric
pusher-cylinder, said electric cushion-cylinder, and said automatic
pouring device along a conveyed direction of said flasks;
controlling means for controlling said driving means; and
instructing means for providing operating instructions for said
electric pusher-cylinder, said electric cushion-cylinder, and said
automatic pouring device to said driving means through said
controlling means; wherein said computer program causes a computer
having filter means to control said electric pusher-cylinder and
said electric cushion-cylinder such that the sloshing that occurs
in the molten metal is suppressed when said ladle and said mold
move by a distance corresponding to one flask, said computer
program comprising the steps to be executed by said computer of:
calculating a first natural frequency of the molten metal in said
ladle based on a predetermined relationship between the weight and
the natural frequency for the molten metal in said ladle, and the
measured weight of the molten metal in said ladle, and calculating
a second natural frequency of the molten metal in said mold based
on a predetermined relationship between the weight and the natural
frequency for the molten metal in said mold, and the measured
weight of the molten metal in said mold; under the first natural
frequency, the second natural frequency, and parameters of said
controlling means that are preliminarily calculated such that they
do not exceed capacities of said driving means and are stored,
removing components that are located near the first and second
frequencies from the operating instructions, in which at least one
of a velocity of the movement, an acceleration of the movement, and
a jerk of the movement of said ladle and said mold, by said
filtering means using said stored parameters, wherein said
components to be removed are decided based on a simulation using a
model representing characteristics of said casting line to
repeatedly calculate said components by the following equation (1)
or (2), y ( t ) = b 0 ( f ) x ( t ) + b 1 ( f ) x ( t - 1 ) + b 2 (
f ) x ( t - 2 ) + - a 1 ( f ) y ( t - 1 ) - a 2 ( f ) y ( t - 2 ) -
y ( t ) = j = 0 m b j ( f ) x ( t - j ) - i = 1 n a 1 ( f ) y ( t -
i ) ( 1 ) F ( S ) = Y ( S ) X ( S ) = b 0 ( f ) S 0 + b 1 ( f ) S 1
+ b 2 ( f ) S 2 + a 0 ( f ) S 0 + a 1 ( f ) S 1 + a 2 ( f ) S 2 + =
j = 0 m b j ( f ) S j i = 0 n a i ( f ) S i ( 2 ) ##EQU00009##
while gradually varying filtering parameters ai(f), bj(f) that are
parameterized by a resonance frequency f that are successively
calculated from the molten metal in said ladle and said mold,
wherein y (t-i) is time-series data that are output before i
controlling cycles, x(t-j) is time-series data that are input
before j controlling cycles, S is the Laplace operator, and
equation (1) can be derived by applying a Z transformation to the
transfer function of the filter that is expressed as equation (2);
and entering the operating instructions, in which said components
located near the first and second frequencies have been removed, in
said controlling means based on only said feedforward controlling
program, to operate said driving means based on only said
feedforward controlling program without using a feedback control
program.
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to a control for a
casting line. In particular the present invention relates to a
method and a system for damping the sloshing that occurs in molten
metal in a ladle and a mold in the casting line.
BACKGROUND OF THE INVENTION
[0002] Patent publication 1, listed below, discloses one example of
the conventional casting line in which a conveying line for
conveying molds is provided with an encoder to detect the rate of
feeding a mold. Responding to the detection signal of the encoder,
a pouring device tracks, and synchronizes with the conveying mold,
such that the pouring device moves to the proper position, i.e.,
where a ladle of the pouring device pours molten metal into the
mold.
[0003] Reference of Prior-Art Document [0004] Patent Citation 1:
Japanese Patent No. 3113950 (Isuzu Manufacturing Co., Ltd.)
[0005] In such a conventional casting line, because cylinders push
out and thus convey a flask that contains the mold and the pouring
device, the velocity waveform of the flask or the pouring device
has a waveform that is generally trapezoidal when it is moved for
conveying. This involves sloshing the molten metal in the ladle of
the pouring device and the mold to cause the fluid level of the
molten metal to ripple. As a result, a casting piece may contain a
sand inclusion or a casting fin that adversely affects the quality
of the cast product.
[0006] Accordingly, there is a need for a method and a system for
damping sloshing that occurs in molten metal in a ladle and a mold
in a casting line where a process of pouring is automatic.
SUMMARY OF THE INVENTION
[0007] A first aspect of the present invention provides a method
and a system of suppressing sloshing in a casting line that
includes a conveying line in which an electric pusher-cylinder is
located at one end of the conveying line for intermittently pushing
out a plurality of flasks, each containing a mold, one by one. It
also includes an electric cushion-cylinder that is located at the
other end of the conveying line such that it is opposed to the
electric pusher-cylinder so as to receive and cushion a group of
the pushed flasks such that the conveying line conveys the
plurality of flasks, which are arranged linearly between the
electric pusher-cylinder and the electric cushion-cylinder; and an
automatic pouring device that has a ladle for containing molten
metal and that can be moved in synchronization with the flask on
the conveying line, to pour the molten metal into the mold by
tilting the ladle. The method and system control the electric
pusher-cylinder and the electric cushion-cylinder using a
controller having filtering means such that the sloshing that
occurs in the molten metal is suppressed when the ladle and the
mold move a distance that corresponds to one flask.
[0008] The method comprises: calculating a first natural frequency
of the molten metal in the ladle based on a predetermined
relationship between the weight and the natural frequency for the
molten metal in the ladle, and the measured weight of the molten
metal in the ladle, and calculating a second natural frequency of
the molten metal in the mold based on a predetermined relationship
between the weight and the natural frequency for the molten metal
in the mold, and the measured weight of the molten metal in the
mold; entering the first and second natural frequencies in the
filtering means to modify a velocity waveform of the movement of
conveying the flasks such that the modified velocity waveform does
not include the first and second natural frequencies; and driving
the electric pusher-cylinder and the electric cushion-cylinder such
that the velocity waveform of the movement of conveying the flasks
is the modified velocity waveform.
[0009] The system comprises: a first weight-calculation means for
calculating the weight of the molten metal in the ladle; a second
weight-calculation means for calculating a second natural frequency
of the molten metal in the mold; a first natural
frequency-calculation means for calculating a first natural
frequency based on a predetermined relationship between the weight
and the natural frequency for the molten metal in the ladle, and
the calculated weight of the molten metal in the ladle by the first
weight-calculation means; a second natural frequency-calculation
means for calculating a second natural frequency based on a
predetermined relationship between the weight and the natural
frequency for the molten metal in the mold, and the calculated
weight of the molten metal in the mold by the second
weight-calculation means; a filtering means for modifying a
velocity waveform of the movement of conveying the flasks on the
conveying line such that the modified velocity waveform does not
include the first and second natural frequencies calculated by the
first and second natural frequency-calculation means; and an
instructing means for providing operating instructions to the
electric pusher-cylinder, the electric cushion-cylinder, and the
automatic pouring device, based on the modified velocity
waveform.
[0010] A second aspect of the present invention provides a method
and a system of suppressing sloshing in a casting line, wherein the
casting line includes: a conveying line in which an electric
pusher-cylinder is located at one end of the conveying line for
intermittently pushing out a plurality of flasks that each contains
a mold, one by one, and an electric cushion-cylinder that is
located at the other end of the conveying line that is opposed to
the electric pusher-cylinder to receive and cushion a group of the
pushed flasks such that the conveying line conveys the plurality of
flasks that is arranged linearly between the electric
pusher-cylinder and the electric cushion-cylinder; an automatic
pouring device that has a ladle for containing molten metal and
that can be moved in synchronization with the flask on the
conveying line, to pour the molten metal into the mold by tilting
the ladle; driving means for driving the electric pusher-cylinder,
the electric cushion-cylinder, and the automatic pouring device
along the conveyed direction of the flasks; controlling means for
controlling the driving means; and instructing means for providing
operating instructions for the electric pusher-cylinder, the
electric cushion-cylinder, and the automatic pouring device to the
driving means through the controlling means.
[0011] The method and the system control the casting line using a
controller having filtering means, based on a feedforward control
program such that the sloshing that occurs in the molten metal is
suppressed when the ladle and the mold move a distance
corresponding to one flask.
[0012] The method of the second aspect comprises: calculating a
first natural frequency of the molten metal in the ladle based on a
predetermined relationship between the weight and the natural
frequency for the molten metal in the ladle, and the measured
weight of the molten metal in the ladle, and calculating a second
natural frequency of the molten metal in the mold based on a
predetermined relationship between the weight and the natural
frequency for the molten metal in the mold, and the measured weight
of the molten metal in the mold; under the first natural frequency,
the second natural frequency, and parameters on the controlling
means that are preliminarily calculated such that they do not
exceed the capacities of the driving means and that are stored,
removing components that are located near the first and second
frequencies from the operating instructions, in which the maximum
value of at least one of a velocity of the movement, an
acceleration of the movement, and a jerk of the ladle and the mold
is restricted, by the filtering means using the stored parameters,
wherein the components to be removed are decided based on a
simulation using a model representing the characteristics of the
casting line to repeatedly calculate the components by the
following equation (1) or (2), while gradually varying filtering
parameters ai(f), bj(f) that are parameterized by a resonance
frequency f that are successively calculated from the molten metal
in the ladle and the mold; and entering the operating instructions,
in which the components located near the first and second
frequencies have been removed, in the controlling means based on
only the feedforward controlling program, to operate the driving
means based on only the feedforward controlling program without
using a feedback control program.
[ Math . 1 ] y ( t ) = b 0 ( f ) x ( t ) + b 1 ( f ) x ( t - 1 ) +
b 2 ( f ) x ( t - 2 ) + - a 1 ( f ) y ( t - 1 ) - a 2 ( f ) y ( t -
2 ) - y ( t ) = j = 0 m b j ( f ) x ( t - j ) - i = 1 n a 1 ( f ) y
( t - i ) ( 1 ) ##EQU00001##
[0013] where x(t-j) is a time-series data that is input before j
controlling cycles, and y (t-i) are a time-series data that are
output before i controlling cycles.
[ Math . 2 ] F ( S ) = Y ( S ) X ( S ) = b 0 ( f ) S 0 + b 1 ( f )
S 1 + b 2 ( f ) S 2 + a 0 ( f ) S 0 + a 1 ( f ) S 1 + a 2 ( f ) S 2
+ = j = 0 m b j ( f ) S j i = 0 n a i ( f ) S i ( 2 )
##EQU00002##
[0014] where S is the Laplace operator, and equation (1) can be
derived by applying a Z transformation on the transfer function of
the filter that is expressed as equation (2).
[0015] As stated above, restricting the maximum value of at least
one of a velocity of the movement, an acceleration of the movement,
and a jerk of the movement, of the ladle and the mold can ensure
that the driving means of the casting line prevents an excess, in
particular, of the acceleration of the automatic pouring device and
the flasks. Further, removing the components of the resonance
frequencies by filtering the operating instructions to convey the
flasks can prevent the efficiency of the control means of the
driving means of the casting line from significant degradation,
even if the detected weights of the molten metal in the ladle and
the mold involves a detected error.
[0016] The system of the second aspect comprises: a first
weight-calculation means for calculating the weight of the molten
metal in the ladle; a second weight-calculation means for
calculating a second natural frequency of the molten metal in the
mold; a first natural frequency-calculation means for calculating a
first natural frequency based on a predetermined relationship
between the weight and the natural frequency for the molten metal
in the ladle, and the calculated weight of the molten metal in the
ladle by the first weight-calculation means; a second natural
frequency-calculation means for calculating a second natural
frequency based on a predetermined relationship between the weight
and the natural frequency for the molten metal in the mold, and the
calculated weight of the molten metal in the mold by the second
weight-calculation means; an instructing means for providing
operating instructions based on a feedforward program for
operations of the electric pusher-cylinder, the electric
cushion-cylinder, and the automatic pouring device, to the driving
means through the controlling means; a parameter calculation means
for preliminarily calculating the parameters of the controlling
means such that the calculated parameters do not exceed the
capacity of the driving means; a stored means for receiving and
storing the calculated parameters from the parameter calculation
means; a restriction means for restricting the maximum value of at
least one of a velocity of the movement, an acceleration of the
movement, and a jerk of the automatic pouring device and the mold;
a filtering means for receiving the first and second resonance
frequencies from the first and second frequency-calculation means,
and for removing components that are located near adjacent to the
first and second frequencies from the operating instructions, in
which the maximum value is restricted by the restriction means,
using the stored parameters from the stored means, wherein the
components to be removed are decided based on a simulation using a
model representing the characteristics of the casting line to
repeatedly calculate the components, under the stored parameters,
by the above equation (1) or (2), while gradually varying filtering
parameters ai(f), bj(f) that are parameterized by a resonance
frequency f that are successively calculated from the molten metal
in the ladle and the mold, and wherein the instructing means
provides the controlling means with the operating instructions in
which the components located near the first and second frequencies
are removed such that the controlling means carries out the
controls based on only the feedforward controlling program, without
using a feedback control program.
[0017] As used herein, the term "filtering means" refers to a
circuit or its partial configuration that includes a pair of an
input terminal and an output terminal with a transfer function
therebetween that has a frequency response.
[0018] As used herein, the term "feedforward control" refers to way
to control a manipulative variable to be applied to a controlled
object to a predetermined value such that output value is a target
value. The feedforward control may provide a highly efficient
control if an input-output relation and a disturbance, for example,
to the controlled object, are definite.
[0019] As used herein, the term "jerk" refers to a rate of
deviation in an acceleration relative to the time.
[0020] The forgoing and the other features and objects of the
present invention will also be obvious from the following
descriptions by referring to the accompanied drawing. Note that the
various embodiments of the present invention are not intended to be
limited to the illustrated arrangements and means.
BRIEF DESCRIPTION OF THE DRAWING
[0021] FIG. 1 is a schematic block diagram of one embodiment of the
casting equipment to which the present invention is applied.
EMBODIMENT OF THE INVENTION
The First Embodiment
[0022] FIG. 1 shows casting equipment to which the method and the
system of the present invention is applied. The casting equipment
includes a casting line in which a conveying line A conveys a
plurality of flasks. Each contains a mold Y to a conveyed direction
designated by an arrow X, arranged linearly, such that the casting
line carries out casting processes using the conveyed flasks. For
the ease of understanding the illustration, each flask is
schematically shown as a contour of the corresponding Y. Arranged
on the casting line are an electric pusher-cylinder B, an electric
cushion-cylinder C, and an automatic pouring device D. The electric
pusher-cylinder B is located at one end of the conveying line A for
the flasks to intermittently push out the plurality of flasks one
by one. The electric cushion-cylinder C is located at the other end
of the conveying line A that is opposed to the electric
pusher-cylinder B to receive and cushion a group of the pushed
flasks. The automatic pouring device D, which has a ladle Z for
containing molten metal, can be moved in the direction X in
synchronization with the flask on the conveying line A, to pour the
molten metal into the mold by tilting the ladle Z. The automatic
pouring device D is provided with a driving motor (driving means),
not shown, to move it in the direction X. Although the automatic
pouring device D is also provided with a plurality of motors (not
shown) to let the ladle Z move vertically, forward and backwards,
and tilt, explanations for these motors to move the ladle Z are
omitted. The casting equipment is also provided with a system to
control a controller having a filter circuit, using a program to
control the operations of the electric pusher-cylinder B, the
electric cushion-cylinder C, and the automatic pouring device D, in
the casting line.
[0023] On the electric pusher-cylinder B and the electric
cushion-cylinder C, induction motors (driving means) B1 and C1 for
driving the respective ball screws are mounted as driving motors to
move them in the direction X. The induction motors B1 and C1 are
electrically connected to a first servo controller (controlling
means) B3 and a second servo controller (controlling means) C3
through inverters B2 and C2 that can control the position by
entering data on a pulse string.
[0024] The control system includes, besides the first and second
servo controllers B3 and C3 described above, a control unit J for
the automatic pouring device D to control the X driving motor to
drive the automatic pouring device D in the X direction (and the
driving motors to drive the ladle Z) and a control device K for the
conveying line of the flasks to control the first and second servo
controllers B3 and C3. The control system also includes the
following functions: a first weight-calculating means for
calculating the weight of the molten metal in the ladle Z; a second
weight calculating means for calculating the weight of the molten
metal in the mold Y; a first natural frequency calculating means
for calculating the natural frequency (the first natural frequency)
of the molten metal in the ladle Z based on a predetermined
relationship between the weight and the natural frequency for the
molten metal in the ladle Z, and the calculated weight of the
molten metal in the ladle Z from the first weight-calculating
means; a second natural frequency calculating means for calculating
the natural frequency (the second natural frequency) of the molten
metal in the mold Y based on a predetermined relationship between
the weight and the natural frequency for the molten metal in the
mold Y, and the calculated weight of the molten metal in the mold Y
from the second weight-calculating means; an instructing means for
providing operating instructions to the electrical pusher-cylinder
B, the electrical cushion-cylinder C, and the automatic pouring
device D, based on the control program; and a filtering means for
modifying a velocity waveform of a conveying motion of the flask to
be targeted such that the casting line is operated by the modified
velocity waveform that does not include the calculated natural
frequencies of the molten metal in the ladle or in the mold from
the first and second weight-calculating means.
[0025] The first servo controller B3 may comprise a central
processing unit (CPU) B3a, a pulse output device B3b, I/O B3c, a
communication device B3d, a servo I/O B3e, and a counter B3f. The
second servo controller C3 may, like the first servo controller B3,
comprise a central processing unit (CPU) C3a, a pulse output device
C3b, I/O C3c, a communication device C3d, a servo I/O C3e, and a
counter C3f.
[0026] The first servo controller B3 and the second servo
controller C3 are connected to a communication device K2 of the
control device K of the conveying line through communication
devices B3d and C3d, which transmit and receive digital data, to
acquire data on the weights of the molten metal in the control unit
K for the conveying line.
[0027] The control unit J of the automatic pouring device is
electrically connected to the control device K of the conveying
line such that the control unit J transmits signals indicating the
weights of the molten metal in the ladle Z and mold Y to the
control device K through the link communication devices J3 and K3.
The control unit J also includes a programmable logic controller
(PLC) J4 to control the X driving motor of the automatic pouring
device D.
[0028] The first and the second servo controller B3 and C3 transmit
a positional command (a signal) of a pulse string to the inverters
B2 and C2 to drive the induction motors B1 and C1. Controlling the
torques, speeds, and positions of these motors, is carried out by
the inverters B2 and C2.
[0029] Attached to the automatic pouring device D is a load cell G
to measure the weight of the molten metal in the ladle Z. The load
cell G is electrically connected to an analog input unit J1 of the
control unit J of the automatic pouring device through an amplifier
H.
[0030] The function of the casting equipment constructed as
described above will now be explained. The weight of the molten
metal in the ladle Z is detected by the load cell G, and to measure
it, it is then input into the analog input unit J1 of the control
unit J of the automatic pouring device. The molten metal in the
ladle Z of the automatic pouring device D is then poured into the
mold Y. The measured weight of the molten metal in the ladle Z and
the reduced weight of the molten metal in the mold Y that is
calculated from the former are then provided in the control device
K of the conveying line, to retrieve the natural frequency (the
first natural frequency) of the molten metal in the ladle Z and the
natural frequency (the second natural frequency) of the molten
metal in the mold Y.
[0031] The electric cushion-cylinder C is positioned at a
predetermined set position in readiness. When the first and the
second servo controllers B3 and C3 detect a signal indicating that
the flask to be conveyed from the programmable logic controller
(PLC) K4 of the control device K of the conveying line, the
electric pusher-cylinder B is first extended at a low speed to
secure the group of the flasks on the conveying line entirely in
the sandwiched relation between the electric pusher-cylinder B and
the electrical cushion-cylinder C. Then the electric
pusher-cylinder B is extended, while the electric cushion-cylinder
C is contracted in the same velocity waveform of the electric
pusher-cylinder B, to convey the flasks such that the group of the
flasks moves in the X direction by a distance corresponding to one
flask. At the same time, the automatic pouring device D pours the
molten metal into the mold Y, while the automatic pouring device D
is moved in the X direction by the distance corresponding to one
flask. In such a rapid motion, a sloshing suppression control is
carried out to prevent the molten metal in the ladle Z and the mold
Y from the sloshing, as described below.
[0032] Both the calculated natural frequency of the molten metal in
the ladle Z and the calculated natural frequency of the molten
metal in the mold Y are input into the filtering means to modify
the velocity waveform of the conveying motion of the flasks on the
conveying line, to provide a version of it that is modified without
including these two natural frequencies. Both the electric
pusher-cylinder B and the electrical cushion-cylinder C are then
driven such that the velocity waveform of the conveying motion of
the flasks is in the modified version. Thus, the sloshing that
occurs in the molten metal in the ladle Z and the mold Y can be
accurately suppressed when the ladle Z and the flasks are moved by
a distance corresponding to one flask.
[0033] The control unit J of the automatic pouring device D causes
the second servo controller C3 to transmit the signals indicating
that the flasks are conveyed while the automatic pouring device D
pours the molten metal. The transmitted signal is input into the
counter J2 to be converted to positional data. The X driving motor
of the automatic pouring device D is then driven to follow the
positional command based on the converted positional data to move
the automatic pouring device D in the X direction such that it
follows the conveyed motion of the flasks.
[0034] Because the molten metal in the ladle Z and the mold Y has a
complicated shape and thus it is difficult to accurately calculate
the respective natural frequencies, a relationship between the
weights of the molten metal in the ladle Z and natural frequencies
that are derived based on a method to estimate the natural
frequencies, described below, is preliminarily established as
parameters. The method for determining the natural frequencies
includes, for example, a derivation based on fluid analysis
software, or an estimation based on the magnitude of the amplitude
of the vibrations when the molten metal is actually vibrated. This
derivation is made while the frequencies are varied. One example
that may be used as the fluid analysis software is
three-dimensional thermo-fluid analysis software that can calculate
with a high accuracy a complicated and unstable behavior of fluid
that involves nonlinear behavior or a large deformation
behavior.
[0035] Although, as described above, the inverter control of the
servo controllers in this embodiment is based on the positional
control by the output of the pulse string, such a control may be
carried out at the side of the servo controllers by configuring
control loops for velocities and positions. The induction motors
B1, C1 and the inverters B2, C2 may be replaced by servomotors and
servo amplifiers.
The Second Embodiment
[0036] The same as the first embodiment, the control system in the
second embodiment includes the first servo controller B3, the
second servo controller C3, the control unit J of the automatic
pouring device D, and the control device K of the conveying line,
as described above. The control system in the second embodiment
also includes an arrangement for controlling the suppression of
sloshing. This arrangement includes, the same as with the first
embodiment, a first weight-calculating means for calculating the
weight of the molten metal in the ladle Z; a second weight
calculating means for calculating a weight of molten metal in the
mold Y; a first natural frequency-calculation means for calculating
the natural frequency (the first natural frequency) of the molten
metal in the ladle Z based on a predetermined relationship between
the weight and the natural frequency for the molten metal in the
ladle Z, and the calculated weight of the molten metal in the ladle
Z from the first weight-calculating means; a second natural
frequency-calculation means for calculating the natural frequency
(the second natural frequency) of the molten metal in the mold Y
based on a predetermined relationship between the weight and the
natural frequency for the molten metal in the mold Y, and the
calculated weight of the molten metal in the mold Y from the second
weight-calculating means. However, the arrangement for controlling
the suppression of sloshing in the second embodiment, instead of
being that of the instructing means and the filtering means of the
first embodiment, includes the following instructing means,
parameter calculation means for calculating parameters, storing
means for storing parameters, restricting means for restricting the
maximal value, and filtering means. In this embodiment, the
instructing means provides operating instructions based on a
forward control program for the operation of the casting line. The
means to calculate parameters preliminarily calculates the
parameters of the controllers (i.e., the first servo controller B3,
the second servo controller C3, and the control unit J of the
automatic pouring device D) of the driving devices for the X
direction (i.e., the induction motor B1 of the electric
pusher-cylinder B, the induction motor C1 of the electric
cushion-cylinder C, and the X driving motor of the automatic
pouring device D) of the casting line such that the calculated
parameters do not exceed the capacities of these driving devices
for the X direction. The storing means receives the parameters from
the calculating means and stores them. In line with the stored
parameters given by the storing means, the restricting means limits
the maximum value in at least one of a velocity of the movement, an
acceleration of the movement, and a jerk of the movement of the
automatic pouring device and the flasks in the operating
instructions for the casting line from the instructing means. In
line with the stored parameters given by the storing means, the
filtering means receives data on the first and second resonance
frequencies from the first and second resonance
frequency-calculation means, and thus removes components located
near them from the operating instructions in which the maximum
value is restricted by the restricting means.
[0037] Removing the components located near the first and second
resonance frequencies is carried out using filtering parameters
that are preliminarily stored by simulating a model representing
the characteristics of the casting line to repeatedly calculate the
components by the following equation (1) or (2), while gradually
varying the filtering parameters ai(f), bj(f). Further, the
instructing means provides the operating instructions in which the
components located near the first and second resonance frequencies
are removed, by the filtering mean, to the driving devices for the
X direction through these controllers. These controllers drive the
driving devices for the X direction based on just the feedforward
control program, without the feedback program. The construction for
carrying out the control of suppression of sloshing can be
implemented by a computer.
[ Math . 3 ] y ( t ) = b 0 ( f ) x ( t ) + b 1 ( f ) x ( t - 1 ) +
b 2 ( f ) x ( t - 2 ) + - a 1 ( f ) y ( t - 1 ) - a 2 ( f ) y ( t -
2 ) - y ( t ) = j = 0 m b j ( f ) x ( t - j ) - i = 1 n a 1 ( f ) y
( t - i ) ( 1 ) ##EQU00003##
[0038] where ai(f), bj(f) are filtering parameters that are
parameterized from resonance frequencies f sequentially calculated
from the molten metal in the ladle and the mold, x(t-j) is
time-series data that is input before j controlling cycles, and y
(t-i) denotes time-series data that are output before i controlling
cycles.
[ Math . 4 ] F ( S ) = Y ( S ) X ( S ) = b 0 ( f ) S 0 + b 1 ( f )
S 1 + b 2 ( f ) S 2 + a 0 ( f ) S 0 + a 1 ( f ) S 1 + a 2 ( f ) S 2
+ = j = 0 m b j ( f ) S j i = 0 n a i ( f ) S i ( 2 )
##EQU00004##
[0039] where equation (1) can be derived by applying a Z
transformation to the transfer function of the filter that is
expressed as equation (2), and S is the Laplace operator.
[0040] In the second embodiment, the weight of the molten metal in
the ladle is entered in the first resonance frequency-calculation
means to calculate the resonance frequency of the molten metal in
the ladle, while the weight of the molten metal in the mold is
entered in the second resonance frequency-calculation means to
calculate the resonance frequency of the molten metal in the mold.
These two calculated resonance frequencies are entered in the
filter.
[0041] Meanwhile, the instructing means provides the operating
instructions to the restricting means. The restricting means then
reads out the stored parameters on the controllers of the driving
devices for the X direction in the casting line from the parameter
storing means, while the restricting means limits the maximum value
in at least one of the velocity of the movement, the acceleration
of the movement, and the jerk of the movement of the automatic
pouring device and the flasks in the operating instructions from
the instructing means such that the calculated parameters do not
exceed the capacities of these driving devices for the X direction.
The results are provided to the filter.
[0042] The filtering means reads out the stored parameters on the
controllers of the driving devices for the X direction in the
casting line that do not exceed the capacities of these driving
devices from the parameter storing means. The filtering means
filters the operating instructions to be provided to the driving
devices in the X direction in which the maximum value is restricted
in at least one of the velocity of the movement, the moving
acceleration, and the moving jerk of the automatic pouring device
and the flasks in line with the two resonance frequencies
sequentially calculated from the molten metal in the ladle and the
mold, to remove from the operating instructions the components
located near the first and second resonance frequencies. The
resulting filtering operating instructions are entered in the
driving devices for the X direction in the casting line through
their controllers. Thus, any sloshing that has occurred in the
molten metal in the ladle Z and the mold Y can be suppressed when
the ladle Z and the flasks are moved by a distance corresponding to
one flask.
[0043] The calculation by the filtering means is executed based on
the principle as discussed below. Namely, assuming that x (t) is
time-series data to be input in the filtering means, and y (t) is
time-series data output from the filtering means, a filter to be
applied to the time-series data is expressed by equation (1).
[ Math . 5 ] y ( t ) = b 0 ( f ) x ( t ) + b 1 ( f ) x ( t - 1 ) +
b 2 ( f ) x ( t - 2 ) + - a 1 ( f ) y ( t - 1 ) - a 2 ( f ) y ( t -
2 ) - y ( t ) = j = 0 m b j ( f ) x ( t - j ) - i = 1 n a 1 ( f ) y
( t - i ) ( 1 ) ##EQU00005##
[0044] where, ai(f), bj(f) are parameters that are parameterized
from two resonance frequencies f sequentially calculated from the
molten metal in the ladle Z and the mold Y.
[0045] Further, x(t-j) is time-series data that are input before j
controlling cycles, and y (t-i) is time-series data that are output
before i controlling cycles.
[0046] Although the number of items m and n can be appropriately
determined based on the construction of the filter, they should be
preliminary decided. For example, m=0 and n=1 if the filter is a
primary low-path filter, m=0 and n=1 if it is a secondary low-path
filter, and m=2 and n=2 if it is a notch filter, can be
preliminarily decided. These decided numbers of items m and n are
entered in the parameter storing means and the parameter
calculation means.
[0047] The parameters ai(f), bj(f) should be preliminary calculated
and decided using the parameter calculation means by simulations
using a model representing the characteristics of the casting line
to repeatedly calculate them, while their values are being
gradually varied.
[0048] To calculate these parameters, the constraining conditions
in the operating instructions to be provided to the driving devices
for the X direction in the casting line are as follows: the maximum
velocity in the operating instructions should not exceed the
maximum velocities of the electrical pusher-cylinder B and the
electrical cushion-cylinder C, each maximum value of the maximum
velocities of them should not exceed the restrictions on the
maximum value on the driving devices for the X direction, and the
time of the movements of the ladle Z and the flasks becomes the
shortest.
[0049] Equation (1) can be derived by applying a Z transformation
to the transfer function of the filter that is expressed as the
following equation (2).
[ Math . 6 ] F ( S ) = Y ( S ) X ( S ) = b 0 ( f ) S 0 + b 1 ( f )
S 1 + b 2 ( f ) S 2 + a 0 ( f ) S 0 + a 1 ( f ) S 1 + a 2 ( f ) S 2
+ = j = 0 m b j ( f ) S j i = 0 n a i ( f ) S i ( 2 )
##EQU00006##
[0050] where S is the Laplace operator.
[0051] In the second embodiment, the induction motors B1, C1 and
the inverters B2, C2 of the electric pusher-cylinder B and the
electric cushion-cylinder C may also be replaced by servomotors and
servo amplifiers.
[0052] The computer to use for the embodiments of the present
invention may include a central processing unit (CPU), an input
device, a display, a memory, and any other circuit that is able to
perform the functions described herein.
[0053] The computer also may include a storage device that may
include a hard disk drive, an optical disk drive, a floppy disk
drive, etc. The storage device may use other similar means to load
a computer program or other instructions to the computer.
[0054] The computer program, when loaded and executed, controls the
computer such that it carries out the methods described herein. A
computer readable storage media that stores the computer program
may include any volatile or non-volatile storage device.
[0055] Because the above embodiments are not intended to limit the
present invention to any specific embodiment, it will be
appreciated that various modifications and variations may be
embodied without departing from the spirit and the scope of the
present invention.
* * * * *