Apparatus and method for temperature control
Improved temperature control for melt distributing equipment for injection molding selects alternative set-point values according to occurrence of injection for heating devices controlled without measured temperature. The set-point values adapt operation of the heating devices to accommodate material heating resulting from flow of melt through the equipment into mold cavities. Occurrence of injection is advantageously determined from control of heating devices using measured temperature by detecting changes of heat producing operation of heating devices and or changes of values used for temperature control of heating devices where the changes are indicative of material heating resulting from flow. For electrical heaters energized by controlled connection to a power source, set-point values are adjusted to correct for variance of the power source voltage.
1 . Apparatus for temperature control for equipment for conveying melt to at least one mold cavity of a mold assembly in an injection molding machine, the apparatus comprising:
(a) a memory for storing first and second alternative proportioning set point values, the first alternative proportioning set point value defining the proportion of heat producing operation to be effective when melt is being injected into the mold cavities, the second alternative proportioning set point value defining the proportion of heat producing operation to be effective other than when melt is being injected into the mold cavities;
(b) a processor for producing a control signal for controlling a proportion of heat producing operation of a heating device in response to one of the first and second alternative proportioning set point values according to whether melt is being injected into the mold cavities.
2 . The apparatus according to claim 1 wherein the injection molding machine produces an injection signal representing the occurrence of injection of melt into the mold cavities and the processor is responsive to the injection signal for selecting the one of the first and second proportioning set point values to control the heating device.
3 . The apparatus according to claim 1 wherein the heating device is an electrical heater and the control signal is effective to control the proportion of electrical power deliverable by an interface device to be dissipated in the electrical heater.
4 . The apparatus according to claim 3 further comprising a sensor for measuring a value of one of electrical current delivered to the heater and electrical voltage of the source of electrical current and the processor adjusts the proportioning set-point values in response to the measured value differing from expected value.
5 . The apparatus according to claim 4 wherein the sensor measures electrical current delivered to the heater and the processor adjusts the proportioning set point in accordance with the following:
PS=PNOM*K ( I )
K ( I )= INOM/IACT
Where:
IACT is the measured value of electrical current delivered to the heater
INOM is the value of electrical current expected to be delivered to the heater
PS is the power proportioning set point
PSNOM is the power proportioning value for an electrical current equal to
INOM
* designates multiplication
/ designates division.
6 . The apparatus according to claim 4 wherein the sensor measures electrical voltage of the source of electrical current and the processor adjusts the proportioning set point in accordance with the following:
PS=PNOM*K ( V )
K ( V )= ENOM **2 /EACT **2
Where:
EACT is the measured value of electrical voltage delivered to the heater
ENOM is the value of electrical voltage expected to be delivered to the heater
PS is the power proportioning set point
PNOM is the power proportioning value for a source voltage equal to ENOM
* designates multiplication
** designates exponentiation
/ designates division.
7 . The apparatus according to claim 1 further comprising plural temperature control zones, each zone having associated therewith a controlled heating device for affecting temperature within the zone and at least one zone has associated therewith a sensor for measuring temperature, and the processor controls operation of the controlled heating device for the zone with the temperature measuring sensor according to an algorithm relating set point temperature and measured temperature.
8 . The apparatus according to claim 7 wherein the processor detects injection of melt into mold cavities from a reduction of heat producing operation of the controlled heating device in a zone controlled in accordance with an algorithm relating set point temperature and measured temperature, and the selection of a set point for a zone for which measured temperature is not available is made in accordance with the following:
IF P (1)− P (2)< LIMS ( P ), PS=PSA 1
IF P (1)− P (2))≧ LIMS ( P ), PS=PSA 2
Where:
LIMS(P) is a limit value of heat producing operation change over time associated with injection of melt into the mold cavities
P(1) is the value of the heat producing operation of the controlled heating device in a zone controlled in response to measured temperature at the beginning of a predetermined time interval ΔTP
P(2) is the value of the heat producing operation of the controlled heating device in the same zone at the end of a predetermined time interval ΔTP
PS is the proportioning set point for a zone controlled without measured temperature
PSA1 is the first alternative proportioning set point value
PSA2 is the second alternative proportioning set point value.
9 . The apparatus according to claim 8 wherein the controlled heating device is an electrical heater and the value of the heat producing operation is computed in accordance with:
P =( IACT **2)* R
Where
IACT is electrical current delivered to the heater
R is electrical resistance of the heater
* designates multiplication
** designates exponentiation.
10 . The apparatus according to claim 7 wherein the processor detects injection of melt into mold cavities from a reduction of heat producing operation of the controlled heating device in a zone controlled in accordance with an algorithm relating set point temperature and measured temperature, and the selection of a set point for a zone for which measured temperature is not available is made in accordance with the following:
IF V (1)− V (2)< LIMS ( V ), PS=PSA 1
IF V (1)− V (2)≧ LIMS ( V ), PS=PSA 2
Where:
LIMS(V) is a limit value of control variable change over time associated with injection of melt into the mold cavities
V(1) is the control variable value at the beginning of a predetermined time interval ΔTP for the zone controlled in response to measured temperature
V(2) is the control variable value at the end of a predetermined time interval ΔTP for the same zone
PS is the proportioning set point
PSA 1 is the first alternative proportioning set point value
PSA 2 is the second alternative proportioning set point value and the variable V is one of the proportional, integral and derivative terms of a control algorithm of the form:
POUT=VP+VI+VD
In which
POUT is a percentage of heat producing operation of a controlled heating device (0<POUT<100)
VP is the proportional term=KP*TE(t)
KP is the constant of proportionality of the proportional term
TE(t) is the difference between actual temperature and set-point temperature at time “t”
VI is the integral term=KI*S(t)
KI is the constant of proportionality of the integral term
S(i) is a sum at the “i th ” computation=S(i−1)+TE*(Δti)
S(i−1) is the value of S from the immediately preceding computation of S
Δti is the computational time interval of the integral term
VD is the derivative term=KD(TE(d)−TE(d−1))/(Δtd)
KD is the constant of proportionality of the derivative term
TE(d) is the difference between actual temperature and set-point temperature at the “d th ” computation of VD
TE(d−1) is the difference between actual temperature and set-point temperature at the immediately preceding computation of VD
Δtd is the computational time interval of the derivative term.
11 . Method for temperature control for equipment for conveying melt to at least one mold cavity of a mold assembly in an injection molding machine, the method comprising:
(a) storing first and second alternative proportioning set point values, the first alternative proportioning set point value defining the proportion of heat producing operation to be effective when melt is being injected into the mold cavities, the second alternative proportioning set point value defining the proportion of heat producing operation to be effective other than when melt is being injected into the mold cavities;
(b) producing a control signal for controlling a proportion of heat producing operation of a heating device in response to one of the first and second alternative proportioning set point values according to whether melt is being injected into the mold cavities.
12 . The method according to claim 11 wherein the injection molding machine produces an injection signal representing the occurrence of injection of melt into the mold cavities and the one of the first and second proportioning set point values is selected in response to the injection signal produced by the injection molding machine.
13 . The method according to claim 11 wherein the heating device is an electrical heater and the control signal is effective to control a proportion of electrical power deliverable by an interface device to be dissipated in the electrical heater.
14 . The method according to claim 13 wherein the value of one of the electrical current delivered to the heater and electrical voltage of the source of electrical current is measured and the proportioning set-point value is adjusted in response to the measured value differing from the expected value.
15 . The method according to claim 14 wherein the value of electrical current delivered to the load is measured and the proportioning set point is adjusted in accordance with the following:
PS=PNOM*K ( I )
K ( I )= INOM/IACT
Where:
IACT is the measured value of electrical current delivered to the heater
INOM is the value of electrical current expected to be delivered to the heater
PS is the power proportioning set point
PNOM is the power proportioning value for an electrical current equal to
I(NOM)
* designates multiplication
/ designates division.
16 . The method according to claim 14 wherein the value of the electrical voltage of the source of electrical current is measured and the proportioning set point is adjusted in accordance with the following:
PS=PNOM*K
K=ENOM **2 /EACT **2
Where:
EACT is the measured value of electrical voltage delivered to the heater
ENOM is the value of electrical voltage expected to be delivered to the heater
PS is the power proportioning set point
PNOM is the power proportioning value for a source voltage equal to ENOM
* designates multiplication
** designates exponentiation
/ designates division.
17 . The method according to claim 11 wherein temperature is controlled in plural zones, each zone having associated therewith a controlled heating device for affecting temperature within the zone and at least one zone has associated therewith a sensor for measuring temperature, and the operation of the controlled heating device for the zone with the temperature measuring sensor is controlled according to an algorithm relating set point temperature and measured temperature.
18 . The method according to claim 17 wherein the occurrence of injection of melt into mold cavities is detected from a reduction of heat producing operation of the controlled heating device in a zone controlled in accordance with an algorithm relating set point temperature and measured temperature, and the selection of a set point for a zone for which measured temperature is not available is made in accordance with the following:
IF P (1)− P (2)< LIMS ( P ), PS=PSA 1
IF P (1)− P (2)≧ LIMS ( P ), PS=PSA 2
Where:
LIMS(P) is a limit value of heat producing operation change over time associated with injection of melt into the mold cavities
P(1) is the value of the heat producing operation of the controlled heating device in a zone controlled in response to measured temperature at the beginning of a predetermined time interval ΔTP
P(2) is the value of the heat producing operation of the controlled heating device in the same zone at the end of a predetermined time interval ΔTP
PS is the proportioning set point for a zone controlled without measured temperature
PSA1 is the first alternative proportioning set point value
PSA2 is the second alternative proportioning set point value.
19 . The method according to claim 18 wherein the controlled heating device is an electrical heater and the value of the heat producing operation is computed in accordance with:
P= ( IACT **2) *R
Where
IACT is electrical current delivered to the heater
R is electrical resistance of the heater
* designates multiplication
** designates exponentiation.
20 . The method according to claim 17 wherein the occurrence of injection of melt into mold cavities is detected from a reduction of heat producing operation of the controlled heating device in a zone controlled in accordance with an algorithm relating set point temperature and measured temperature, and the selection of a set point for a zone for which measured temperature is not available is made in accordance with the following:
IF V (1)− V (2)< LIMS ( V ), PS=PSA 1
IF V (1)− V (2))> LIMS ( V ), PS=PSA 2
Where:
LIMS(V) is a limit value of control variable change over time associated with injection of melt into the mold cavities
V(1) is the control variable value at the beginning of a predetermined time interval ΔTP for the zone controlled in response to measured temperature
V(2) is the control variable value at the end of a predetermined time interval ΔTP for the same zone
PS is the proportioning set point
PSA1 is the first alternative proportioning set point value
PSA2 is the second alternative proportioning set point value and the variable V is one of the proportional, integral and derivative terms of a control algorithm of the form:
POUT=VP+VI+VD
In which
POUT is a percentage of heat producing operation of a controlled heating device (0≦SPOUT≦100)
VP is the proportional term=KP*TE(t)
KP is the constant of proportionality of the proportional term
TE(t) is the difference between actual temperature and set-point temperature at time “t”
VI is the integral term=KI*S(t)
KI is the constant of proportionality of the integral term
S(i) is a sum at the “i th ” computation=S(i−1)+TE*(Δti)
S(i−1) is the value of S from the immediately preceding computation of S
Δti is the computational time interval of the integral term
VD is the derivative term=KD(TE(d)−TE(d−1))/(Δtd)
KD is the constant of proportionality of the derivative term
TE(d) is the difference between actual temperature and set-point temperature at the “d th ” computation of VD
TE(d−1) is the difference between actual temperature and set-point temperature at the immediately preceding computation of VD
Δtd is the computational time interval of the derivative term.