U.S. patent application number 11/705884 was filed with the patent office on 2007-06-21 for two-wire layered heater system.
This patent application is currently assigned to Watlow Electric Manufacturing Company. Invention is credited to Kenneth F. Fennewald, William A. III McDowell, Kevin Ptasienski, Louis P. Steinhauser.
Application Number | 20070138166 11/705884 |
Document ID | / |
Family ID | 34591294 |
Filed Date | 2007-06-21 |
United States Patent
Application |
20070138166 |
Kind Code |
A1 |
Fennewald; Kenneth F. ; et
al. |
June 21, 2007 |
Two-wire layered heater system
Abstract
A heater is provided that includes a resistive layer formed by a
layered process (e.g., thick film, thin film, thermal spray, and
sol-gel) and two electrical lead wires connected to the resistive
layer. The resistive layer has sufficient temperature coefficient
of resistance characteristics such that the resistive layer is a
heater element and a sensor, and the resistive layer is in
communication with a two-wire controller through the two electrical
lead wires. Preferably, the sensor is a temperature sensor, and the
heater includes additional layers formed by layered processes.
Inventors: |
Fennewald; Kenneth F.;
(Maryland Heights, MO) ; McDowell; William A. III;
(Aurora, IL) ; Ptasienski; Kevin; (O'Fallon,
MO) ; Steinhauser; Louis P.; (St. Louis, MO) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 828
BLOOMFIELD HILLS
MI
48303
US
|
Assignee: |
Watlow Electric Manufacturing
Company
St. Louis
MO
|
Family ID: |
34591294 |
Appl. No.: |
11/705884 |
Filed: |
February 13, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10719327 |
Nov 21, 2003 |
7196295 |
|
|
11705884 |
Feb 13, 2007 |
|
|
|
Current U.S.
Class: |
219/542 ;
219/494 |
Current CPC
Class: |
H05B 2203/011 20130101;
H05B 1/023 20130101; H05B 3/42 20130101; H05B 2203/017 20130101;
H05B 2203/013 20130101; B29C 45/2737 20130101; H05B 3/26 20130101;
H05B 2203/002 20130101; H05B 3/46 20130101; B29C 2045/2745
20130101; B29C 2045/274 20130101; H05B 3/28 20130101; H05B 2203/035
20130101 |
Class at
Publication: |
219/542 ;
219/494 |
International
Class: |
H05B 3/06 20060101
H05B003/06; H05B 1/02 20060101 H05B001/02 |
Claims
1. A layered heater comprising: a substrate; a dielectric layer
disposed on the substrate; a resistive layer disposed on the
dielectric layer, the resistive layer having sufficient temperature
coefficient of resistance characteristics such that the resistive
layer is a heater element and a temperature sensor; a protective
layer disposed over the resistive layer; two electrical lead wires
connected to the resistive layer; and a two-wire controller
connected to the resistive layer through the two electrical lead
wires, wherein the two-wire controller determines temperature of
the layered heater using the resistance of the resistive layer and
controls heater temperature accordingly through the two electrical
lead wires.
2. The layered heater according to claim 1, wherein the two-wire
controller comprises a DC bias control for calculation of the
resistance of the resistive layer.
3. The layered heater according to claim 1, wherein the two-wire
controller comprises an AC bias control for calculation of the
resistance of the resistive layer.
4. The layered heater according to claim 1, wherein the two-wire
controller comprises high conduction angle firing.
5. The layered heater according to claim 1, wherein the two-wire
controller comprises a shunt resistor for calculation of the
resistance of the resistive layer.
6. The layered heater according to claim 1, wherein the two-wire
controller further comprises a microprocessor.
7. The layered heater according to claim 1, wherein the two-wire
controller further comprises firmware.
8. The layered heater according to claim 1, wherein the layered
heater is formed by a layered process selected from the group
consisting of thick film, thin film, thermal spray, and
sol-gel.
9. An apparatus comprising: a resistive layer formed by a layered
process selected from the group consisting of thick film, thin
film, thermal spray, and sol-gel; and two electrical lead wires
connected to the resistive layer, wherein the resistive layer has
sufficient temperature coefficient of resistance characteristics
such that the resistive layer is a heater element and a sensor, and
the resistive layer is in communication with a two-wire controller
through the two electrical lead wires.
10. The apparatus according to claim 9 further comprising a
substrate, wherein the resistive layer is formed on the
substrate.
11. The apparatus according to claim 9 further comprising a
dielectric layer, wherein the resistive layer is formed on the
dielectric layer.
12. The apparatus according to claim 11 further comprising a
substrate, wherein the dielectric layer is formed on the
substrate.
13. The apparatus according to claim 9, wherein the sensor is a
temperature sensor.
14. A heater comprising: a resistive layer formed by a layered
process selected from the group consisting of thick film, thin
film, thermal spray, and sol-gel, wherein the resistive layer has
sufficient temperature coefficient of resistance characteristics
such that the resistive layer is a heater element and a temperature
sensor, and the resistive layer is in communication with a two-wire
controller through two electrical lead wires.
15. The apparatus according to claim 14 further comprising a
substrate, wherein the resistive layer is formed on the
substrate.
16. The apparatus according to claim 14 further comprising a
dielectric, wherein the resistive layer is formed on the
dielectric.
17. A layered heater comprising a resistive layer formed by a
layered process selected from the group consisting of thick film,
thin film, thermal spray, and sol-gel, wherein the resistive layer
has sufficient temperature coefficient of resistance
characteristics such that the resistive layer is a heater element
and a sensor, and the resistive layer is in communication with a
two-wire controller through two electrical lead wires.
18. The apparatus according to claim 17 further comprising a
substrate, wherein the resistive layer is formed on the
substrate.
19. The apparatus according to claim 17 further comprising a
dielectric layer, wherein the resistive layer is formed on the
dielectric layer.
20. The apparatus according to claim 19 further comprising a
substrate, wherein the dielectric layer is formed on the
substrate.
21. The apparatus according to claim 19 further comprising a
protective layer formed over the resistive layer.
22. The apparatus according to claim 17, wherein the sensor is a
temperature sensor.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/719,327, filed on Nov. 21, 2003. The
disclosure of the above application is incorporated herein by
reference.
FIELD
[0002] The present disclosure relates generally to electrical
heaters and controllers and more particularly to layered
heaters.
BACKGROUND
[0003] The statements in this section merely provide background
information related to the present disclosure and may not
constitute prior art.
[0004] Layered heaters are typically used in applications where
space is limited, when heat output needs vary across a surface, or
in ultra-clean or aggressive chemical applications. A layered
heater generally comprises layers of different materials, namely, a
dielectric and a resistive material, which are applied to a
substrate. The dielectric material is applied first to the
substrate and provides electrical isolation between the substrate
and the resistive material and also minimizes current leakage
during operation. The resistive material is applied to the
dielectric material in a predetermined pattern and provides a
resistive heater circuit. The layered heater also includes leads
that connect the resistive heater circuit to a heater controller
and an over-mold material that protects the lead-to-resistive
circuit interface. Accordingly, layered heaters are highly
customizable for a variety of heating applications.
[0005] Layered heaters may be "thick" film, "thin" film, or
"thermally sprayed," among others, wherein the primary difference
between these types of layered heaters is the method in which the
layers are formed. For example, the layers for thick film heaters
are typically formed using processes such as screen printing, decal
application, or film printing heads, among others. The layers for
thin film heaters are typically formed using deposition processes
such as ion plating, sputtering, chemical vapor deposition (CVD),
and physical vapor deposition (PVD), among others. Yet another
process distinct from thin and thick film techniques is thermal
spraying, which may include by way of example flame spraying,
plasma spraying, wire arc spraying, and HVOF (High Velocity Oxygen
Fuel), among others.
[0006] Known systems that employ layered heaters typically include
a separate temperature sensor, which is connected to the controller
through another set of electrical leads in addition to the set of
leads for the resistive heater circuit. The temperature sensor is
often a thermocouple that is placed somewhere near the film heater
and/or the process in order to provide the controller with
temperature feedback for heater control. However, the thermocouple
is relatively bulky, requires additional electrical leads, and
fails relatively frequently. Alternately, an RTD (resistance
temperature detector) may be incorporated within the layered heater
as a separate layer in order to obtain more accurate temperature
readings and to reduce the amount of space required as compared
with a conventional thermocouple. Unfortunately, the RTD also
communicates with the controller through an additional set of
electrical leads. For systems that employ a large number of
temperature sensors, the number of associated electrical leads for
each sensor is substantial and results in added bulk and complexity
to the overall heater system.
[0007] For example, one such application where electrical leads add
bulk and complexity to a heater system is with injection molding
systems. Injection molding systems, and more specifically hot
runner systems, often include a large number of nozzles for higher
cavitation molding, where multiple parts are molded in a single
cycle, or shot. The nozzles are often heated to improve resin flow,
and thus for each nozzle in the system, an associated set of
electrical leads for a nozzle heater and a set of electrical leads
for at least one temperature sensor (e.g., thermocouple) placed
near the heater and/or the process must be routed from a control
system to each nozzle. The routing of electrical leads is typically
accomplished using an umbilical that runs from the control system
to a hot runner mold system. Further, wiring channels are typically
milled into plates of the mold system to route the leads to each
nozzle, and therefore, an increased number of electrical leads adds
cost and complexity to the hot runner mold system and adds bulk to
the overall injection molding system.
SUMMARY
[0008] In one form, the present disclosure provides a layered
heater comprising a substrate, a dielectric layer disposed on the
substrate, and a resistive layer disposed on the dielectric layer.
The resistive layer has sufficient temperature coefficient of
resistance characteristics such that the resistive layer is a
heater element and a temperature sensor. A protective layer is
disposed over the resistive layer, two electrical lead wires are
connected to the resistive layer, and a two-wire controller is
connected to the resistive layer through the two electrical lead
wires. The two-wire controller determines temperature of the
layered heater using the resistance of the resistive layer and
controls heater temperature accordingly through the two electrical
lead wires.
[0009] In another form, an apparatus is provided that comprises a
resistive layer formed by a layered process selected from the group
consisting of thick film, thin film, thermal spray, and sol-gel.
Two electrical lead wires are connected to the resistive layer, and
the resistive layer has sufficient temperature coefficient of
resistance characteristics such that the resistive layer is a
heater element and a sensor. Furthermore, the resistive layer is in
communication with a two-wire controller through the two electrical
lead wires. In one form, the sensor is a temperature sensor.
[0010] In yet another form, a heater is provided that comprises a
resistive layer formed by a layered process selected from the group
consisting of thick film, thin film, thermal spray, and sol-gel.
The resistive layer has sufficient temperature coefficient of
resistance characteristics such that the resistive layer is a
heater element and a temperature sensor, and the resistive layer is
in communication with a two-wire controller through two electrical
lead wires.
[0011] Additionally, the present disclosure provides a layered
heater comprising a resistive layer formed by a layered process
selected from the group consisting of thick film, thin film,
thermal spray, and sol-gel. The resistive layer has sufficient
temperature coefficient of resistance characteristics such that the
resistive layer is a heater element and a sensor, and the resistive
layer is in communication with a two-wire controller through two
electrical lead wires.
[0012] Further areas of applicability will become apparent from the
description provided herein. It should be understood that the
description and specific examples are intended for purposes of
illustration only and are not intended to limit the scope of the
present disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The drawings described herein are for illustration purposes
only and are not intended to limit the scope of the present
disclosure in any way.
[0014] FIG. 1 is a block diagram of a heater system in accordance
with the principles of the present disclosure;
[0015] FIG. 2 is an enlarged cross-sectional view of a layered
heater in accordance with the principles of the present
disclosure;
[0016] FIG. 3a is an enlarged cross-sectional view of a layered
heater comprising a resistive layer and a protective layer in
accordance with the principles of the present disclosure;
[0017] FIG. 3b is an enlarged cross-sectional view of a layered
heater comprising only a resistive layer in accordance with the
principles of the present disclosure;
[0018] FIG. 4a is a plan view of a resistive layer pattern
constructed in accordance with the teachings of the present
disclosure;
[0019] FIG. 4b is a plan view of a second resistive layer pattern
constructed in accordance with the principles of the present
disclosure;
[0020] FIG. 4c is a perspective view of a third resistive layer
pattern constructed in accordance with the principles of the
present disclosure;
[0021] FIG. 5 is a block diagram illustrating a two-wire control
system in accordance with the principles of the present
disclosure;
[0022] FIG. 6 is a simplified electrical schematic of a two-wire
control system constructed in accordance with the teachings of the
present disclosure;
[0023] FIG. 7 is a detailed electrical schematic of a two-wire
control system constructed in accordance with the teachings of the
present disclosure;
[0024] FIG. 8 is a perspective view of a high cavitation mold for
an injection molding system having a heater system with hot runner
nozzles and constructed in accordance with the teachings of the
present disclosure;
[0025] FIG. 9 is a side view of a hot runner nozzle heater system
constructed in accordance with the teachings of the present
disclosure;
[0026] FIG. 10 is a side cross-sectional view of the hot runner
nozzle heater system, taken along line A-A of FIG. 9, in accordance
with the principles of the present disclosure;
[0027] FIG. 11 is a side cross-sectional view of an alternate
embodiment of the hot runner nozzle heater system constructed in
accordance with the teachings of the present disclosure;
[0028] FIG. 12 is a schematic diagram of a modular heater system
for retrofit into existing systems in accordance with the
principles of the present disclosure; and
[0029] FIG. 13 is a block diagram of a heater system using a single
wire in accordance with the principles of the present
disclosure.
[0030] Corresponding reference numerals indicate corresponding
parts throughout the several views of the drawings.
DETAILED DESCRIPTION
[0031] The following description is merely exemplary in nature and
is in no way intended to limit the disclosure, its application, or
uses.
[0032] Referring to FIG. 1, a simplified heater system in block
diagram format in accordance with one form of the present
disclosure is illustrated and generally indicated by reference
numeral 10. The heater system 10 comprises a layered heater 12, a
two-wire controller 14, which is preferably microprocessor based,
and a power source 16 within or connected to the two-wire
controller 14. The layered heater 12 is connected to the two-wire
controller 14 as shown through a single set of electrical leads 18.
Power is provided to the layered heater 12 through the electrical
leads 18, and temperature information of the layered heater 12 is
provided on command to the two-wire controller 14 through the same
set of electrical leads 18. More specifically, the two-wire
controller 14 determines the temperature of the layered heater 12
based on a calculated resistance, one technique of which is
described in greater detail below. The two-wire controller 14 then
sends signals to the power source 16 to control the temperature of
the layered heater 12 accordingly. Therefore, only a single set of
electrical leads 18 is required rather than one set for the heater
and one set for a temperature sensor.
[0033] Referring now to FIG. 2, in one form the layered heater 12
comprises a number of layers disposed on a substrate 20, wherein
the substrate 20 may be a separate element disposed proximate the
part or device to be heated, or the part or device itself. As
shown, the layers preferably comprise a dielectric layer 22, a
resistive layer 24, and a protective layer 26. The dielectric layer
22 provides electrical isolation between the substrate 20 and the
resistive layer 24 and is disposed on the substrate 20 in a
thickness commensurate with the power output of the layered heater
12. The resistive layer 24 is disposed on the dielectric layer 22
and provides two primary functions in accordance with the present
disclosure. First, the resistive layer 24 is a resistive heater
circuit for the layered heater 12, thereby providing the heat to
the substrate 20. Second, the resistive layer 24 is also a
temperature sensor, wherein the resistance of the resistive layer
24 is used to determine the temperature of the layered heater 12 as
described in greater detail below. The protective layer 26 is
preferably an insulator, however other materials such as a
conductive material may also be employed according to the
requirements of a specific heating application while remaining
within the scope of the present disclosure.
[0034] As further shown, terminal pads 28 are disposed on the
dielectric layer 22 and are in contact with the resistive layer 24.
Accordingly, electrical leads 30 are in contact with the terminal
pads 28 and connect the resistive layer 24 to the two-wire
controller 14 (not shown) for power input and for transmission of
heater temperature information to the two-wire controller 14.
Further, the protective layer 26 is disposed over the resistive
layer 24 and is preferably a dielectric material for electrical
isolation and protection of the resistive layer 24 from the
operating environment. Since the resistive layer 24 functions as
both a heating element and a temperature sensor, only one set of
electrical leads 30, (e.g., two wires), are required for the heater
system 10, rather than one set for the layered heater 12 and
another set for a separate temperature sensor. Thus, the number of
electrical leads for any given heater system is reduced by 50%
through the use of the heater system 10 according to the present
disclosure. Additionally, since the entire resistive layer 24 is a
temperature sensor in addition to a heater element, temperature is
sensed throughout the entire heater element rather than at a single
point as with many conventional temperature sensors such as a
thermocouple.
[0035] In another form of the present disclosure as shown in FIG.
3a, the resistive layer 24 is disposed on the substrate 20 in the
case where the substrate 20 is not conductive and electrical
isolation is not required through a separate dielectric layer. As
shown, the protective layer 26 is disposed over the resistive layer
24 as previously described. In yet another form as shown in FIG.
3b, the resistive layer 24 is disposed on the substrate 20 with no
dielectric layer 22 and no protective layer 26. Accordingly, the
heater system 10 of the present disclosure is operable with at
least one layer, namely, the resistive layer 24, wherein the
resistive layer 24 is both a heating element and a temperature
sensor. Other combinations of functional layers not illustrated
herein may also be employed according to specific application
requirements while remaining within the scope of the present
disclosure.
[0036] Generally, the layered heater 12 is configured for operation
with any number of devices that require heating, one of which is
hot runner nozzles for injection molding systems as described in
greater detail below. Furthermore, the layered heater 12 is
preferably a thick film heater that is fabricated using a film
printing head in one form of the present disclosure. Fabrication of
the layers using this thick film process is shown and described in
U.S. Pat. No. 5,973,296, which is commonly assigned with the
present application and the contents of which are incorporated
herein by reference in their entirety. Additional thick film
processes may include, by way of example, screen printing,
spraying, rolling, and transfer printing, among others.
[0037] However, in another form, the layered heater 12 is a thin
film heater, wherein the layers are formed using thin film
processes such as ion plating, sputtering, chemical vapor
deposition (CVD), and physical vapor deposition (PVD), among
others. Thin film processes such as those disclosed in U.S. Pat.
Nos. 6,305,923, 6,341,954, and 6,575,729, which are incorporated
herein by reference in their entirety, may be employed with the
heater system 10 as described herein while remaining within the
scope of the present disclosure. In yet another form, the layered
heater 12 is a thermal sprayed heater, wherein the layers are
formed using thermal spraying processes such as flame spraying,
plasma spraying, wire arc spraying, and HVOF (High Velocity Oxygen
Fuel), among others. In still another form, the layered heater 12
is a "sol-gel" heater, wherein the layers are formed using sol-gel
materials. Generally, the sol-gel layers are formed using processes
such as dipping, spinning, or painting, among others. Thus, as used
herein, the term "layered heater" should be construed to
include,heaters that comprise at least one functional layer (e.g.,
resistive layer 24 only, resistive layer 24 and protective layer
26, dielectric layer 22 and resistive layer 24 and protective layer
26, among others), wherein the layer is formed through application
or accumulation of a material to a substrate or another layer using
processes associated with thick film, thin film, thermal spraying,
or sol-gel, among others. These processes are also referred to as
"layered processes" or "layered heater processes."
[0038] In order for the resistive layer 24 to serve both the
function of a temperature sensor in addition to a heater element,
the resistive layer 24 is preferably a material having a relatively
high temperature coefficient of resistance (TCR). As the resistance
of metals increases with temperature, the resistance at any
temperature t (.degree. C.) is: R=R.sub.0(1+.alpha.t) (Equation
1)
[0039] where: R.sub.0 is the resistance at some reference
temperature (often 0.degree. C.) and .alpha. is the temperature
coefficient of resistance (TCR). Thus, to determine the temperature
of the heater, a resistance of the heater is calculated by the
two-wire controller 14 as described in greater detail below. In one
form, the voltage across and the current through the heater is
measured using the two-wire controller 14, and a resistance is
calculated based on Ohm's law. Using Equation 1, or similar
equations known to those skilled in the art of temperature
measurement using Resistance Temperature Detectors (RTDs), and the
known TCR, temperature of the resistive layer 24 is then calculated
and used for heater control.
[0040] Therefore, in one form of the present disclosure, a
relatively high TCR is preferred such that a small temperature
change results in a large resistance change. Therefore,
formulations that include materials such as platinum (TCR=0.0039
.OMEGA./.OMEGA./.degree. C.), nickel (TCR=0.0041
.OMEGA./.OMEGA./.degree. C.), or copper (TCR=0.0039
.OMEGA./.OMEGA./.degree. C.), and alloys thereof, are preferred for
the resistive layer 24.
[0041] However, in other forms of the present disclosure, a
material for the resistive layer 24 need not necessarily have a
high TCR. For example, a negative TCR material, or a material
having a non-linear TCR, would also fall within the scope of the
present disclosure, as long as the TCR is predictable. If the TCR
of a given material is known, if it can be measured with the
necessary accuracy, and if it is repeatable or predictable, then
the material could be used to determine temperature of the heater
system 10. Such a TCR, including the relatively high TCR materials
as described, are hereinafter referred to as having sufficient TCR
characteristics. Accordingly, the materials described herein and
their related high TCRs should not be construed as limiting the
scope of the present disclosure. The relatively high TCR as
described herein are preferred in one form of the present
disclosure.
[0042] As another sufficient TCR characteristic, the material used
for the resistive layer 24 must not exhibit excessive "drift,"
which is a tendency of many resistive elements to change
characteristics, such as bulk resistivity or TCR, over time.
Therefore, the material for the resistive layer 24 is preferably
stable or predictable in terms of drift, however, the drift can be
compensated for over time through calibration of the two-wire
controller 14 that is described in greater detail below.
Additionally, drift can be reduced or eliminated through "burn-in"
of the heater to induce any resistance shift that would occur over
time. Accordingly, the resistive layer 24 is preferably a material
that has a relatively high temperature coefficient of resistance
and that is stable in terms of drift. However, if the drift is
predictable, the material may be used for the resistive layer while
remaining within the scope of the present disclosure.
[0043] In one form of the present disclosure, the resistive layer
24 is formed by printing a resistive material on the dielectric
layer 22 as previously set forth. More specifically, two (2)
resistive materials were tested for use in the present disclosure,
RI1 and RI2, wherein the TCR of RI1 was between approximately
0.0008 .OMEGA./.OMEGA./.degree. C. and approximately 0.0016
.OMEGA./.OMEGA./.degree. C., and the TCR of RI2 was between
approximately 0.0026 .OMEGA./.OMEGA./.degree. C. and approximately
0.0040 .OMEGA./.OMEGA./.degree. C. Additionally, temperature drift
was tested for RI1- and RI2, at various temperatures, and the drift
varied from approximately 3% for RI1 to approximately 10% for RI2.
With a "burn-in" as previously described, the drift was shown to
have been reduced to approximately 2% for RI1 to approximately 4%
for RI2. The materials for the resistive layer 24 and their
respective values for TCR and temperature drift as described herein
are exemplary in nature and should not be construed as limiting the
scope of the present disclosure. Any resistive material having
sufficient TCR characteristics as previously set forth can be
utilized for the resistive layer 24 while remaining within the
scope of the present disclosure.
[0044] Since a plurality of layered heaters having temperature
sensing capabilities are employed according to the present
disclosure, the two-wire controller 14 must be provided with
certain information about the heaters, and more specifically the
resistive layers 24, in order to properly calibrate the overall
heater system. Parameters that are necessary for such calibration
include the cold resistance, the temperature at which the cold
resistance value was measured, and certain TCR characteristics (TCR
at a temperature and/or over a temperature range) in order to
determine heater temperature from heater resistance calculations.
Preferably, the system automatically calculates the cold resistance
of each layered heater 12 based on the measured voltage and current
using the two-wire controller 14 as described in greater detail
below. Additionally, the TCR characteristics for each layered
heater 12 must be entered into the system, e.g. the two-wire
controller 14, using manual and/or electronic methods. Such values
may be entered individually or as a single value for all layered
heaters 12 depending on, for example, whether or not the material
for the resistive layer 24 came from a common manufacturing lot.
Regardless, the calibration data, namely, the cold resistance, cold
resistance temperature, and TCR of each layered heater 12 is
preferably entered into the two-wire controller 14 for more
accurate and controlled operation of the heater system 10.
[0045] A variety of methods of providing the TCR characteristics
and cold resistance data of each layered heater 12 to the two-wire
controller 14 may be employed while remaining within the scope of
the present disclosure. For example, each layered heater 12 may
include a bar-coded tag that would be scanned by an operator to
download the cold resistance data and TCR characteristics to the
two-wire controller 14. Alternately, a smart card chip or other
electronic means may be attached to each layered heater 12, which
would similarly be scanned by an operator to download the
calibration data to the two-wire controller 14. In yet another
form, the calibration data may be downloaded to the two-wire
controller 14 via the Internet, for example, through a supplier
website. Alternately, the TCR characteristics and cold resistance
data may be pre-programmed into the two-wire controller 14.
[0046] In addition to calibration for resistance data and TCR,
compensation for the resistance of electrical leads 30 is also
provided by the heater system 10 according to the present
disclosure. Since the electrical leads 30 add resistance to the
circuit, temperature errors would likely result if no compensation
for the increase in resistance were provided. Additionally, the
materials used for the electrical leads 30 may have a TCR higher
than that of the resistive layer 24, which results in the portion
of the electrical leads 30 that are exposed to higher temperatures
contributing more resistance. Therefore, the two-wire controller 14
also provides for calibration of lead wire resistance.
[0047] The two-wire controller 14 is preferably designed with
temperature calibration capabilities, which further reduces long
term temperature errors due to drift. One method of temperature
calibration is accomplished by using one or more pre-existing
thermocouples, or other pre-existing temperature sensors, to
ascertain both the temperature and the stability of the
temperature. The temperature data from the thermocouples is then
transmitted to the two-wire controller 14 for the resistance
calculations. Further, changes in the measured cold resistance of
the layered heater 12 may be used to calculate new TCR values as
appropriate. In another form for temperature calibration, the
two-wire controller 14 preferably comprises a calibration offset
feature that provides for input of a temperature offset parameter.
Such an offset is desirable when the location of the layered heater
12 is some distance away from the optimum location for sensing
temperature. Thus, the temperature offset parameter may be used
such that the heater system 10 provides a temperature that more
closely represents the actual temperature at the optimum
location.
[0048] Turning now to the construction of the layered heater 12 as
shown in FIGS. 4a-4c, the resistive layer 24 is preferably disposed
on the dielectric layer 22 in a pattern 40 that results in a
desired temperature profile for the given substrate or element
being heated. FIG. 4a shows a resistive layer 24a in a rectangular
pattern 40a based on the rectangular profile of the substrate 20a.
FIG. 4b shows a resistive layer 24b in a circular pattern 40b based
on the circular profile of the substrate 20b. FIG. 4c shows a
resistive layer 24c in a spiral pattern 40c based on a cylindrical
shape of the substrate 20c. Additionally, the width "W" and/or
pitch "P" of the patterns 40a-c may also be altered according to
the specific heating requirements of the heater system. Therefore,
the pattern of the resistive layer 24a is preferably customized for
each application of the heater system 10. The patterns illustrated
herein are exemplary only and are not intended to limit the scope
of the present disclosure.
[0049] The layered heater 12, including each of the layers and the
terminal pads 28 may also be constructed in accordance with U.S.
Pat. Nos. 6,410,894, 6,222,166, 6,037,574, 5,973,296, and
5,714,738, which are commonly assigned with the present disclosure
and the contents of which are incorporated herein in their
entirety, while remaining within the scope of the present
disclosure. Accordingly, additional specificity with regard to
further materials, manufacturing techniques, and construction
approaches are not included herein for purposes of clarity and
reference is thus made to the patents incorporated by reference
herein for such additional information.
[0050] Two-Wire Controller (14)
[0051] One form of the two-wire controller 14 is illustrated in
block diagram format in FIG. 5. As shown, the two-wire controller
14 generally comprises a power source 50, a voltage and current
measurement component 52, a power regulator component 54, and a
microprocessor 56 in communication with the layered heater 12. The
microprocessor 56 is also in communication with a communications
component 58, where certain output from the heater system 10 (e.g.,
temperature readings) is delivered and also where input (e.g.,
updated TCR values, calibration data, temperature set points,
resistance set points) may be provided to the heater system 10.
[0052] Referring now to FIG. 6, the voltage measurement component
52 of the two-wire controller 14 is illustrated in greater detail.
Generally, the two-wire controller 14 applies a DC bias, or low
level DC current, to the layered heater 12 during an AC power cycle
zero-cross interval so that the current value times a nominal
heater resistance results in a voltage that is higher than the full
wave voltage at the zero crossing for a time period on each side of
the zero value. During the time interval, the voltage of the
layered heater 12 is amplified and compared to a reference voltage,
and power to the layered heater 12 is then controlled as further
described herein. Application of the DC bias is further shown and
described in U.S. Pat. No. 4,736,091, which is commonly assigned
with the present application and the contents of which are
incorporated by reference in their entirety. In another form of the
present disclosure, an AC current may be used for the bias instead
of the DC bias to determine the resistance of the layered heater
12.
[0053] As shown, the two-wire controller 14 comprises a transistor
60, a diode 62, and a first resistor 64, wherein the first resistor
64 together with the layered heater 12 form a voltage divider. For
the DC bias, the transistor 60 is turned on for a short time
period, e.g., 200 .mu.s, during the zero cross interval and further
prevents current flow through the power source 50 (not shown)
during negative half cycles when the heater is receiving power.
Additionally, the diode 62 prevents current flow through the power
source 50 during positive half cycles when the layered heater 12 is
receiving power. The output of the layered heater 12 is then sent
through a second resistor 66 and into an opamp circuit 68 that
comprises an amplifier 70 and resistors 72, 74, and 76. The output
voltage of the amplifier 70 is thus used to calculate resistance
and determine the temperature of the layered heater 12, wherein the
output voltage of the amplifier 70 is read by an A/D converter
within the microprocessor 56. Further, during the DC bias time
period, conversion of the output voltage of the amplifier 70 from
an analog signal to a digital signal takes place, and a gating
pulse from a triac 80 is delivered to the layered heater 12 if the
calculated resistance, or layered heater 12 temperature, is such
that a control algorithm has determined a need for additional power
from the layered heater 12. As further shown, a field effect
transistor 82 clamps the input of the amplifier 70, thereby
preventing the amplifier 70 from being over driven during both
positive and negative half cycles when the heater is receiving line
power.
[0054] The microprocessor 56, which is described in greater detail
below, generally communicates with the circuit shown through an
output control 84, a bias control 86, and heater input 88.
Additionally, the microprocessor 56 further comprises firmware 90,
and/or software (not shown). The firmware 90 may be programmed for
a variety of functions, including but not limited to, allowing half
cycle delivery of power to improve controllability or full cycle
power in accordance with IEEE 519. As a further example, the
firmware 90 may include control algorithms to compensate for
thermal transient response and other calibration data as previously
described. Therefore, the microprocessor 56 is used in combination
with the DC bias circuitry to determine layered heater 12
temperature and to more efficiently control power to the layered
heater 12.
[0055] A further expansion of the two-wire controller 14 is now
shown in greater detail in FIG. 7. The power source 50 is
preferably non-isolated and capacitively coupled with a linear
regulator 100 as shown. The power source 50 thus regulates an
alternating current down to a specified value as required for
operation. As further shown, the sine wave for the zero-cross (DC
biasing) from the power source 50 is in communication with the
microprocessor 56. During the zero-cross interval, the DC bias is
applied through the transistor 102, diode 104, and resistor 106.
The voltage across the layered heater 12 is amplified and offset by
the amplifier 108, and the amplifier 110 is used as a reference for
the A/D converter within the microprocessor 56 for temperature
variances.
[0056] Measurement of the change in voltage across and current
through the layered heater 12 is accomplished using the dual
amplifiers 112 and 114 and analog switches 116 and 118, wherein the
change in voltage signal is through amplifier 112 and analog switch
116, and the change in current is through amplifier 114 and analog
switch 118. As further shown, the change in current is measured
using a shunt resistor 116. Additionally, the two-wire controller
14 comprises a triac 120 that is out of conduction at the
zero-cross and is conducting on each half cycle. During the DC
biasing interval, an A/D conversion takes place and the triac 120
delivers a pulse if the measured resistance is such that the
control algorithm has determined a need for additional power from
the layered heater 12. Therefore, two methods of calculating
resistance are provided by the circuit shown in FIG. 7, namely, the
DC bias circuit and the shunt resistor circuit. Additionally,
although the present disclosure preferably measures voltage and
current to determine resistance, alternate methods of determining
resistance such as a voltage gate or using a known current may also
be employed while remaining within the scope of the present
disclosure.
[0057] In yet another form, the triac 120 is preferably a random
fire triac such that the layered heater 12 is fired at high
conduction angles to reduce the amount of energy that is delivered
to the layered heater 12 during sampling. For example, firing the
layered heater 12 at conduction angles of 160.degree. and
340.degree. allows for sufficient sampling at 120 Hz with reduced
energy input to the layered heater 12. Alternately, sampling at
only 160.degree. or only 340.degree. would result in a sampling
rate of 60 Hz while reducing the energy input further in half.
Additionally, when using a random fire triac, any rate function may
be applied by delivering energy in smaller increments as the
temperature (or resistance in another form) approaches the set
point. Accordingly, the layered heater 12 is fired at higher and
higher conduction angles into a full line cycle.
[0058] As further shown, communications to and from the two-wire
controller 14 take place on the opposite side of the microprocessor
56. The communications component 58 comprises a series of
opto-isolators 122, 124, and 126, in addition to a line transceiver
128. Therefore, communications can be made through any number of
protocols, including by way of example, RS-485 communications as
illustrated herein. In addition to other functions, calibration
data can be entered utilizing this communications interface.
[0059] The firmware 90 is loaded into the microprocessor 56 using
the ISP (In-System Programming) connections as shown. Therefore,
certain modifications to the settings within the two-wire
controller 14, including entry of calibration data as previously
described, can be accomplished in an efficient manner.
[0060] The specific circuit components, along with the values and
configuration of the circuit components, (e.g., resistor values,
capacitor values, among others), as detailed in FIG. 7 are
exemplary of one form of the two-wire controller 14 and should not
be construed as limiting the scope of the present disclosure.
Accordingly, alternate circuit components, configurations, and
values, and resistance measuring circuit topologies may be
implemented in a two-wire configuration as defined herein while
remaining within the scope of the present disclosure.
[0061] Hot Runner Nozzle Application
[0062] One known application for the heater system 10 according to
the principles of the present disclosure is for hot runner nozzles
in injection molding systems as shown in FIG. 8. The hot runner
nozzles 150 are typically disposed within a hot runner mold system
152, which further comprises a plurality of mold wiring channels
154 that provide for routing of electrical leads (not shown) that
run from heaters (not shown) disposed proximate the hot runner
nozzles 150 to a two-wire controller (not shown) as described
herein. Since each heater serves as both a heating element and as a
temperature sensor, only one set of leads per heater is required
rather than one set of leads for the heater and one set of leads
for a temperature sensor. As a result, the amount of leads running
through the mold wiring channels 154 is reduced in half and the
related bulk and complexity is drastically reduced.
[0063] Additionally, injection molding equipment typically includes
an umbilical 164 that runs from the controller to the hot runner
mold system 152, wherein all of the leads and other related
electrical components are disposed. With the drastic reduction in
the number of leads provided by the present disclosure, the size
and bulk of the umbilical 164 is also drastically reduced.
Moreover, since the temperature is being sensed by the entire
resistive layer of the heater, the temperature is being sensed over
a length rather than at a point with a conventional
thermocouple.
[0064] Referring now to FIGS. 9 and 10, the heater system for a hot
runner nozzle 150' is illustrated in greater detail. The heater
system 200 comprises a layered heater 202 disposed around a body
203 of the hot runner nozzle 150', and a two-wire controller 204 in
communication with the layered heater 202 through a single set of
leads 205. The layered heater 202 further comprises a substrate
206, which is configured to fit around the geometry of the hot
runner nozzle 150' (shown as cylindrical). The layered heater 202
further comprises a dielectric layer 208 disposed on the substrate
206, a resistive layer 210 disposed on the dielectric layer 208,
and a protective layer 214 disposed on the resistive layer 210. As
further shown, terminal pads 216 are disposed on the dielectric
layer 208 and are in contact with the resistive layer 210.
Accordingly, the electrical leads 205 are in contact with the
terminal pads 216 and connect the resistive layer 210 to the
two-wire controller 204. As a result, only one set of electrical
leads 205 are required for the heater system 200, rather than one
set for the layered heater 202 and another set for a separate
temperature sensor.
[0065] As shown in FIG. 11, in an alternate form a layered heater
202' is disposed on an outer surface 220 of the hot runner nozzle
150' rather than on a separate substrate as previously described.
Similarly, the layered heater 202' comprises a dielectric layer
208' disposed on the outer surface 220, a resistive layer 210'
disposed on the dielectric layer 208', and a protective layer 214'
disposed on the resistive layer 210'. Terminal pads 216' are
similarly disposed on the dielectric layer 208' and are in contact
with the resistive layer 210'. As further shown, the single set of
leads 205' connect the heater 202' to the two-wire controller
204'.
[0066] In yet another form of the present disclosure, a modular
solution to retrofitting the heater system according to the present
disclosure with existing controllers that use separate temperature
sensors, e.g., thermocouples, RTDs, thermistors, is provided and
illustrated in FIG. 12. As shown, two-wire modules 230 are provided
between layered heaters 232 and an existing temperature controller
234. The temperature controller 234 comprises temperature sensor
inputs 236 and power outputs 238. The two-wire modules 230 thus
contain the two-wire resistance measuring circuit as previously
described, and the temperatures calculated within the two-wire
modules 230 are transmitted to the temperature sensor inputs 236 of
the existing temperature controller 234. Based on these temperature
inputs, the temperature controller 234 controls the layered heaters
232 through the power outputs 238. It should be understood that
power control may be a part of the temperature controller 234 or
may be a separate power controller 240 as shown while remaining
within the scope of the present disclosure. Accordingly, existing
temperature controllers can be retrofitted with the two-wire
modules 230 to implement the heater system of the present
disclosure without substantial rework and modification of existing
systems.
[0067] Referring now to FIG. 13, another form of a heater system
according the present disclosure that reduces the number of
electrical leads is illustrated and generally indicated by
reference numeral 300. The heater system 300 comprises a layered
heater 302 and a controller 304 that operate as previously
described wherein a resistive layer (not shown) of the layered
heater 302 is both a heating element and a temperature sensor. The
heater system 300 further comprises a power source 306, which is
preferably low voltage in one form of the present disclosure, that
provides power to the layered heater 302. The layered heater 302 is
connected to the controller 304 as shown through a single
electrical lead 308 and through the body or structure of a device
310 (e.g., hot runner nozzle system mold) designated as a common
return or neutral, wherein the common return device 310 provides an
electrical return to the controller 304 from the layered heater
302. The heater system 300 uses the electrically conductive nature
of the device 310 materials to complete the electrical circuit, and
thus a power source 306 is required to limit the current level
traveling through the device 310. Therefore, since the device
structure 310 is being used to connect the layered heater 302 to
the controller 304, another electrical lead is eliminated such that
the controller 304 is effectively a "single-wire controller."
[0068] The description of the disclosure is merely exemplary in
nature and, thus, variations that do not depart from the gist of
the disclosure are intended to be within the scope of the
disclosure. Such variations are not to be regarded as a departure
from the spirit and scope of the disclosure.
* * * * *