US 8,119,044 B1 · Device and method for plasticization control of electric injection molding machine

Abstract

{Problem} 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. {Solution} 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 a state equation and an output equation and outputs an estimate of screw back pressure, which is one of the state variables of the above state equation, by using a screw backward velocity signal, a motor current demand signal applied to a servomotor for injection 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.

Claims2

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 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 a 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 a 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 and a screw revolution drive system where rotation of a servomotor for plasticization is transferred to rotation of said 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 said barrel, comprising:

a screw back pressure controller operative to provide a motor current demand signal for said servomotor for injection to external, which comprises
a high-gain observer operative to execute at a constant time interval a discrete-time expression of a time integration derived by applying a standard method of trapezoid rule to a continuous-time time integration equation representing a relational expression between a screw position and a screw backward velocity and operative to execute at a constant time interval discrete-time arithmetic expressions derived by applying a standard method of forward rectangular rule to a continuous-time mathematical model representing motion equations of said plasticizing mechanism and consisting of state equations having two state variables of a screw backward velocity variable and a screw back pressure variable and having three input variables of said motor current demand signal applied to said servomotor for injection or an actual motor current signal, a screw revolution speed signal and a screw position signal and an output equation having one output variable of a screw backward velocity signal as a measurable state variable,
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 a screw backward velocity signal detected by a rotary encoder mounted on said servomotor for injection axis and a differentiator, said motor current demand signal applied to said servomotor for injection or said actual motor current signal and a screw revolution speed signal detected in a motor controller for plasticization as inputs and by executing said discrete-time expression of a time integration and said discrete-time arithmetic expressions built in, and
a pressure controller operative to feed said motor current demand signal for said servomotor for injection by using said difference signal from said subtracter so that said estimate of screw back pressure follows said screw back pressure command signal;
a motor controller for injection fed said motor current demand signal from said screw back pressure controller;
and
a motor controller for plasticization controlling a revolution speed of said servomotor for plasticization.

5 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 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 a 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 a 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 and a screw revolution drive system where rotation of a servomotor for plasticization is transferred to rotation of said 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 said barrel, comprising:

deriving an estimate of screw back pressure {circumflex over (x)}3 which a high-gain observer outputs by using the input signals of a screw backward velocity signal detected by a rotary encoder mounted on said servomotor for injection and a differentiator in a motor controller 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 a motor controller for plasticization and by executing at a constant time interval a discrete-time expression of a time integration represented by the following equation (101) in Math. 79 derived by applying a standard method of trapezoid rule to a continuous-time time integration equation representing a relational expression between a screw position ys and a screw backward velocity y represented by the following equation (100) in Math. 78 and by executing at a constant time interval discrete-time arithmetic expressions represented by the following equation (103) in Math. 80 and the following equation (105) in Math. 81 derived by applying a standard method of forward rectangular rule to a continuous-time mathematical model representing motion equations of said plasticizing mechanism and consisting of a state equation represented by the following equation (97) in Math. 77 having two state variables of a screw backward velocity x2 and a screw back pressure x3 and having three input variables of a motor current demand signal applied to said servomotor for injection or an actual motor current signal u1, a screw revolution speed signal u2 and a screw position ys and an output equation represented by the following equation (98) in Math. 77 having one output variable y of a screw backward velocity x2 as a measurable state variable;
{
Math
.
⁢
77
}
[
x
.
2
x
.
3
]
=
[
0
b
0
0
]
⁡
[
x
2
x
3
]
+
[
χ
⁡
(
x
2
)
+
cu
1
ψ
⁡
(
x
2
,
x
3
,
u
2
,
y
s
)
]
(
97
)
y
=
[
1
0
]
⁡
[
x
2
x
3
]
(
98
)
χ
⁡
(
x
2
)
=
x
2

x
2

⁢
(
h
⁢

x
2

γ
+
p
)
(
99
)
ψ
⁡
(
x
2
,
x
3
,
u
2
,
y
s
)
=
d
e
-
y
s
⁢
{
x
2
+
qf
⁡
(
x
3
,
u
2
)
}
where x2:
State variable of screw backward velocity dimensionless made by maximum screw backward velocity, 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 x2, ys:
Input variable (dimensionless screw position) decided by an output variable y through the following equation (100) in Math. 78, b, c, d, e, h, p, q, γ:
Constants of a mathematical model of a plasticizing mechanism, χ(x2), ψ(x2, x3, u2, ys):
Nonlinear functions of equation (99), f(x3, u2):
Plasticizing rate function of dimensionless state variable x3 (screw back pressure) and dimensionless input variable u2 (screw revolution speed) dimensionless made by maximum plasticizing rate
{Math. 78}
ys=a∫ydt Initial value ys(t=0)=0 (100)
where a:
Constant of a mathematical model of a plasticizing mechanism, t:
Time variable
{Math. 79}
ys(k+1)=ys(k)+0.5 aαε{y(k)+y(k+1)} (101)
αε=Δt (102)
where k:
Discrete variable representing a discrete-time tk(k=0, 1, 2, . . . ), ys(k):
Value of input variable ys(tk) at a discrete-time tk, y(k):
Value of output variable y(tk) at a discrete-time tk, Δt:
Sampling period of a discrete-time high-gain observer, ε:
Positive parameter much smaller than 1 used in the high-gain observer
{Math. 80}
{circumflex over (η)}(k+1)=(1+αK1b){circumflex over (η)}(k)−αK12by(k)+αεK1χ(k)+αεK1cu1(k)+αε2ψ(k) (103)
χ
⁡
(
k
)
=
y
⁡
(
k
)

y
⁡
(
k
)

⁢
(
h
⁢

y
⁡
(
k
)

γ
+
p
)
ψ
⁡
(
k
)
=
d
e
-
y
s
⁡
(
k
)
⁢
{
y
⁡
(
k
)
+
qf
⁢
(
η
^
⁡
(
k
)
,
u
2
⁡
(
k
)
,
y
⁡
(
k
)
)
}
(
104
)
where {circumflex over (η)}(k):
Estimate {circumflex over (η)}(tk) at a discrete-time tk of new state variable η introduced for estimating state variable x3, u1(k):
Value of input variable u1(tk) at a discrete-time tk, u2(k):
Value of input variable u2(tk) at a discrete-time tk, χ(k), ψ(k):
Values of nonlinear functions χ(tk), ψ(tk) at a discrete-time tk, K1:
Parameter which decides a gain constant (K1/ε) of the high-gain observer, K1>0
{
Math
.
⁢
81
}
x
^
3
⁡
(
k
)
=
1
ɛ
⁢
{
η
^
⁡
(
k
)
-
K
1
⁢
y
⁡
(
k
)
}
(
105
)
where {circumflex over (x)}3(k) :
Estimate {circumflex over (x)}3(tk) of state variable x3 at a discrete-time tk 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;
deriving said motor current demand signal 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;
generating a motor torque of said servomotor for injection corresponding to said motor current demand signal by said motor controller for injection fed said motor current demand signal so that a screw back pressure equal to said screw back pressure command signal is realized.

292 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

Claims2