US 2011/0298146 A1 · Device and Method for Plasticization Control of Electric Injection Molding Machine

Abstract

The exact method with small time-lag of detecting screw back pressure for controlling the screw back pressure in the plasticizing process of an electric-motor driven injection molding machine without using a pressure detector has been asked for because the pressure detector is very expensive, necessitates troublesome works for mounting, an electric protection against noise and the works for zero-point and span adjustings and causes a complicate mechanical structure. The present invention uses a high-gain observer which contains the discrete-time arithmetic expressions derived from a mathematical model of a plasticizing mechanism in an electric-motor driven injection molding machine consisting of state equations and outputs an estimate of screw back pressure, which is one of the state variables of the above state equations, by using a screw position signal, a servomotor current demand signal or actual motor current signal and a screw revolution speed signal as inputs. The high-gain observer obtains the exact screw back pressure estimate with very small time-lag without using a pressure detector. Thus the estimate of screw back pressure fed by the high-gain observer can be adopted as a feedback signal of actual screw back pressure for controlling the screw back pressure in the plasticizing process.

Claims3

Dependent claims

An apparatus for controlling a plasticizing capability in an electric-motor driven injection molding machine having a plasticizing mechanism which consists of a screw revolution drive system where rotation of a servomotor for plasticization is transferred to rotation of a screw through a reduction gear and resin pellets fed through a hopper are melted by the rotation of said screw and a given amount of melted polymer is stored at the end of a barrel and a screw injection drive system where rotation of a servomotor for injection is transferred to rotation of a ball screw through a reduction gear and rotation of said ball screw is converted to a linear motion of a nut of said ball screw and said screw is moved back and forth through a moving part drived by a movement of said nut and pressure application to the melted polymer stored at the end of said barrel is realized by the movement of said screw and the pressure applied to the melted polymer is referred to as a screw back pressure,

comprising:
a high-gain observer operative to execute at a constant time interval discrete-time arithmetic expressions obtained by applying a standard method of forward rectangular rule to continuous-time calculation procedures which are derived from a continuous-time mathematical model representing motion equations of said plasticizing mechanism and consisting of state equations having three state variables of a screw position variable, a screw backward speed variable and a screw back pressure variable, two input variables of a motor current demand signal applied to said servomotor for injection or an actual motor current signal and a screw revolution speed signal and output variables of measured state variables;
a screw back pressure setting device operative to feed a screw back pressure command signal;
a subtracter operative to feed a difference signal between said screw back pressure command signal from said screw back pressure setting device and an estimate of screw back pressure which said high-gain observer outputs by using the input signals of a screw position signal detected by a rotary encoder mounted on said servomotor for injection, said motor current demand signal applied to said servomotor for injection or said actual motor current signal of said servomotor for injection and a screw revolution speed signal detected by a rotary encoder mounted on said servomotor for plasticization and a differentiator and by executing said discrete-time arithmetic expressions built in;
and
a pressure controller operative to derive said motor current demand signal for said servomotor for injection by using the output signal of said subtracter so that said estimate of screw back pressure follows said screw back pressure command signal.

3 more elements

A method for controlling a plasticizing capability in an electric-motor driven injection molding machine having a plasticizing mechanism which consists of a screw revolution drive system where rotation of a servomotor for plasticization is transferred to rotation of a screw through a reduction gear and resin pellets fed through a hopper are melted by the rotation of said screw and a given amount of melted polymer is stored at the end of a barrel and a screw injection drive system where rotation of a servomotor for injection is transferred to rotation of a ball screw through a reduction gear and rotation of said ball screw is converted to a linear motion of a nut of said ball screw and said screw is moved back and forth through a moving part drived by a movement of said nut and pressure application to the melted polymer stored at the end of said barrel is realized by the movement of said screw and the pressure applied to the melted polymer is referred to as a screw back pressure,

comprising:
deriving an estimate of screw back pressure {circumflex over (x)}3 and an estimate of a screw backward speed {circumflex over (x)}2 which a high-gain observer outputs by using the input signals of a screw position signal detected by a rotary encoder mounted on said servomotor for injection, a motor current demand signal applied to said servomotor for injection or actual motor current signal of said servomotor for injection and a screw revolution speed signal detected by a rotary encoder mounted on said servomotor for plasticization and by executing discrete-time arithmetic expressions represented by the following equation (118) in Math. 98 and the following equation (121) in Math. 99 derived from a mathematical model representing motion equations of said plasticizing mechanism represented by the following state equations in Math. 97;
deriving a difference signal between a screw back pressure command signal from a screw back pressure setting device and said estimate of screw back pressure from said high-gain observer by using a subtracter;
and
deriving a motor current demand signal applied to said servomotor for injection by using a pressure controller to which said difference signal is fed from said subtracter so that said estimate of screw back pressure follows said screw back pressure command signal by generating a motor torque of said servomotor for injection corresponding to said motor current demand signal and by realizing a given screw back pressure.
{
Math
.

97
}
x
.
=
Ax
+
[
0
χ
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(
x
2
)
+
cu
1
ψ
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(
x
,
u
2
)
]


A
=
[
0
a
0
0
0
b
0
0
0
]


x
=
[
x
1
x
2
x
3
]
(
115
)
y
=
[
1
0
0
]

x
(
116
)
χ
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(
x
2
)
=
x
2

x
2

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(
h
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
x
2

γ
+
p
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ψ
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x
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e
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x
1
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{
x
2
+
qf
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(
x
3
,
u
2
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}
(
117
)
where x1:
State variable of screw position dimensionless made by maximum stroke of screw backward movement, x2:
State variable of screw backward speed dimensionless made by maximum screw backward speed, x3:
State variable of screw back pressure dimensionless made by maximum screw back pressure, u1:
Input variable of motor current demand or actual motor current of a servomotor for injection dimensionless made by the motor current rating, u2:
Input variable of screw revolution speed dimensionless made by maximum screw revolution speed, y:
Dimensionless output variable expressing measurable state variable x1, a, b, c, d, e, h, p, q, γ:
Constants of a mathematical model of a plasticizing mechanism, χ(x2), ψ(x, u2):
Nonlinear functions of equation (117), ƒ(x3, u2):
Plasticizing rate function of dimensionless state variable x3 and dimensionless input variable u2 dimensionless made by maximum plasticizing rate.

{
Math
.

98
}
[
η
^
1
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(
k
+
1
)
η
^
2
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(
k
+
1
)
]
=
(
I
2
+
α


A
0
)

[
η
^
1
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(
k
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η
^
2
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(
k
)
]
+
α
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A
0
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K
0
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y
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(
k
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+
α
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[
ɛ
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(
k
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+
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2
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cu
1
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(
k
)
ɛ
3
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ψ
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(
k
)
]
(
118
)
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A
0
=
A
22
-
K
0
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A
12
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A
12
=
[
a
0
]
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A
22
=
[
0
b
0
0
]
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K
0
=
[
K
1
K
2
]

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α
=
Δ
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t
ɛ
(
119
)

χ
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(
k
)
=
x
^
2
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(
k
)

x
^
2

(
k
)


(
h
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
x
^
2
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(
k
)

γ
+
p
)



ψ

(
k
)
=
d
e
-
y

(
k
)

{
x
2

(
k
)
+
qf

(
x
3

(
k
)
,
u
2

(
k
)
)
}
(
120
)
where k:
Discrete variable representing a discrete-time tk (k=0, 1, 2, . . . ), {circumflex over (η)}1(k), {circumflex over (η)}2(k):
Estimates {circumflex over (η)}1(tk), {circumflex over (η)}2 (tk) of new state variables η1, η2 introduced for estimating state variables x2, x3 at a discrete-time tk, y(k), u1(k), u2(k):
Output variable y(tk) and input variables u1(tk), u2(tk) at a discrete-time tk, {circumflex over (x)}2(k), {circumflex over (x)}3(k):
Estimates {circumflex over (x)}2(tk), {circumflex over (x)}3(tk) of state variables x2, x3 at a discrete-time tk, χ(k), ψ(k):
χ(tk), ψ(tk) at a discrete-time tk, I2:
2×2 unit matrix, Δt:
Sampling period of a discrete-time high-gain observer, ε:
Positive parameter much smaller than 1 used in the high-gain observer, K1, K2:
Gain constants of the high-gain observer which are decided so that matrix A0 has conjugate complex eigenvalues with a negative real part.
{
Math
.

99
}
[
x
^
2

(
k
)
x
^
3

(
k
)
]
=
D
-
1

[
η
^
1

(
k
)
η
^
2

(
k
)
]
+
D
-
1

K
0

y

(
k
)


D
=
[
ɛ
0
0
ɛ
2
]
(
121
)
where {circumflex over (x)}2(k), {circumflex over (x)}3(k):
Estimates (tk), {circumflex over (x)}3(tk) of state variables x2, x3 at a discrete-time tk.

473 more elements

comprising:
deriving an estimate of screw back pressure {circumflex over (x)}3, an estimate of a screw backward speed {circumflex over (x)}2 and an estimate of a screw position {circumflex over (x)}1 which a high-gain observer outputs by using the input signals of a screw position signal, a screw backward speed signal (a revolution speed signal of said servomotor for injection) detected by a rotary encoder mounted on said servomotor for injection, a motor current demand signal applied to said servomotor for injection or actual motor current signal of said servomotor for injection and a screw revolution speed signal detected by a rotary encoder mounted on said servomotor for plasticization and by executing discrete-time arithmetic expressions represented by the following equation (125) in Math. 101 and the following equation (128) in Math. 102 derived from a mathematical model representing motion equations of said plasticizing mechanism represented by the following state equations in Math. 100;
deriving a difference signal between a screw back pressure command signal from a screw back pressure setting device and said estimate of screw back pressure from said high-gain observer by using a subtracter;
and
deriving a motor current demand signal applied to said servomotor for injection by using a pressure controller to which said difference signal is fed from said subtracter so that said estimate of screw back pressure follows said screw back pressure command signal by generating a motor torque of said servomotor for injection corresponding to said motor current demand signal and by realizing a given screw back pressure.
{
Math
.

100
}
x
.
=
Ax
+
[
0
χ

(
x
2
)
+
cu
1
ψ

(
x
,
u
2
)
]


A
=
[
0
a
0
0
0
b
0
0
0
]


x
=
[
x
1
x
2
x
3
]
(
122
)
y
=
[
y
1
y
2
]
=
[
x
1
x
2
]
=
Cx


C
=
[
1
0
0
0
1
0
]
(
123
)
χ

(
x
2
)
=
x
2

x
2


(
h


x
2

γ
+
p
)


ψ

(
x
,
u
2
)
=
d
e
-
x
1

{
x
2
+
qf

(
x
3
,
u
2
)
}
(
124
)
where x1:
State variable of screw position dimensionless made by maximum stroke of screw backward movement, x2:
State variable of screw backward speed dimensionless made by maximum screw backward speed, x3:
State variable of screw back pressure dimensionless made by maximum screw back pressure, u1:
Input variable of motor current demand or actual motor current of a servomotor for injection dimensionless made by the motor current rating, u2:
Input variable of screw revolution speed dimensionless made by maximum screw revolution speed, y1, y2:
Dimensionless output variables expressing measurable state variables x1, x2, respectively, a, b, c, d, e, h, p, q, γ:
Constants of a mathematical model of a plasticizing mechanism, χ(x2), ψ(x, u2):
Nonlinear functions of equation (124), ƒ(x3, u2):
Plasticizing rate function of dimensionless state variable x3 and dimensionless input variable u2 dimensionless made by maximum plasticizing rate.

{
Math
.

101
}
[
η
^
1

(
k
+
1
)
η
^
2

(
k
+
1
)
η
^
3

(
k
+
1
)
]
=
(
I
3
+
α


A
0
)

[
η
^
1

(
k
)
η
^
2

(
k
)
η
^
3

(
k
)
]
+
α


K
0

[
y
1

(
k
)
ɛ


y
2

(
k
)
]
+
α

[
0
ɛ
2

χ

(
k
)
+
ɛ
2

cu
1

(
k
)
ɛ
3

ψ

(
k
)
]
(
125
)

A
0
=
A
-
K
0

C


K
0
=
[
K
11
K
12
K
21
K
22
K
31
K
32
]


α
=
Δ


t
ɛ
(
126
)

χ

(
k
)
=
y
2

(
k
)

y
2

(
k
)


(
h


y
2

(
k
)

γ
+
p
)




ψ

(
k
)
=
d
e
-
y
1

(
k
)

{
y
2

(
k
)
+
qf

(
x
^
3

(
k
)
,
u
2

(
k
)
)
}
(
127
)
where k:
Discrete variable representing a discrete-time tk (k=0, 1, 2, . . . ), {circumflex over (η)}1(k), {circumflex over (η)}2(k), {circumflex over (η)}3(k):
Estimates {circumflex over (η)}1(tk), {circumflex over (η)}2(tk), {circumflex over (η)}3(tk) of new state variables η1, η2, η3 introduced for estimating state variables x1, x2, x3 at a discrete-time tk, y1(k), y2(k), u1(k), u2(k):
Output variables y1(tk), y2(tk) and input variables u1(tk), u2(tk) at a discrete-time tk, {circumflex over (x)}3 (k):
Estimates {circumflex over (x)}3 (tk) of state variable x3 at a discrete-time tk, χ(k), ψ(k):
χ(tk), ψ(tk) at a discrete-time tk, I3:
3×3 unit matrix, Δt:
Sampling period of a discrete-time high-gain observer, ε:
Positive parameter much smaller than 1 used in the high-gain observer, K0:
Gain matrix of the high-gain observer which is decided so that matrix A0 has conjugate complex eigenvalues with a negative real part and a negative real eigenvalue.
{
Math
.

102
}
[
x
^
1

(
k
)
x
^
2

(
k
)
x
^
3

(
k
)
]
=
D
-
1

[
η
^
1

(
k
)
η
^
2

(
k
)
η
^
3

(
k
)
]


D
=
[
1
0
0
0
ɛ
0
0
0
ɛ
2
]
(
128
)
where {circumflex over (x)}1(k), {circumflex over (x)}2(k), {circumflex over (x)}3(k) Estimates {circumflex over (x)}1(tk), {circumflex over (x)}2(tk), {circumflex over (x)}3(tk) of state variables x1, x2, x3 at a discrete-time tk.

509 more elements

Dependencies are inferred from the claim text.

Device and Method for Plasticization Control of Electric Injection Molding Machine

Life of this patent

Device and Method for Plasticization Control of Electric Injection Molding Machine

Life of this patent

Abstract

Claims3