CA3072625A1 - Control module for a heat treatment apparatus - Google Patents

Abstract

A control module for a heat treatment apparatus is described. This control module includes a control module for a heat treatment apparatus. This control module includes a timer relay connected to a power input line supplying power to heating pads for the heat treatment apparatus. The timer relay receives power and starts timing when power is supplied to the heating pads. The timer relay resets when power is discontinued to the heating pads. The timer relay has at least one output that changes state when a time duration exceeds a pre-set time interval. The change in state causes a protection circuit to disrupt power from the power input line to the heating pads.

Description

TITLE
[0001] Control Module for a Heat Treatment Apparatus FIELD

[0002] There is described a control module for a heat treatment apparatus used for the heat treatment of a metal workpiece.
BACKGROUND

[0003] Heat treatment apparatus are used for preheating and post heating of a metal workpiece that is to be welded. Heating pads are placed on the metal workpiece with power delivered to the heating pads from a power source. A temperature controller selectively controls the power to the heating pads from the power source by energizing and de-energizing an electro-mechanical relay (EMR). In order to provide input regarding temperature to the temperature controller, a thermocouple is spot welded to the metal workpiece underneath one or more of the heating pads. Each heat treatment generally has "on" cycles involving an application of heat, followed by "off' cycles controlled at a rate based on the parameters set in the temperature controller and the feedback from the thermocouple. However, should operator error occur, the heat treatment apparatus malfunction or be installed incorrectly, a process control failure can occur resulting in the metal workpiece becoming over-heated and irreparable damage can occur.
SUMMARY

[0004]
According to one aspect there is provided a control module for a heat treatment apparatus. This control module includes a timer relay connected to a power input line supplying power to heating pads for the heat treatment apparatus. The timer relay receives power and starts timing when power is supplied to the heating pads. The timer relay resets when power is discontinued to the heating pads. The timer relay has at least one output that changes state when a time duration exceeds a pre-set time interval. The change in state causes a protection circuit to disrupt power from the power input line to the heating pads.

[0005] The control module, as will hereinafter be described, can be an addition to an existing heat treatment apparatus or can be built in to a heat treatment apparatus at the factor as a safety improvement. It prevents a metal workpiece from becoming overheated by disrupting the power to the heating pads, if the time duration of an "on"
cycle exceeds a pre-set time interval.

[0006] Although beneficial results may be obtained through the use of the control module, as briefly described above, even more beneficial results may be obtained when an alarm circuit is powered through the timer relay during a time of system failure. The alarm circuit provides an auditory, a visual alarm or both to alert personnel.

[0007] Further features and advantages of the control module will hereinafter be described.
BRIEF DESCRIPTION OF THE DRAWINGS

[0008] These and other features will become more apparent from the following description in which reference is made to the appended drawings, the drawings are for the purpose of illustration only and are not intended to be in any way limiting, wherein:

[0009] FIG. 1 is a wiring schematic of a control module for a heat treatment apparatus.

[0010] FIG. 2, labelled as PRIOR ART, is a wiring schematic for a heat treatment apparatus.

[0011] FIG. 3 is a block diagram of a control module for a heat treatment apparatus in accordance with the teachings of FIG. 1 with multiple branches.
DETAILED DESCRIPTION

[0012] A control module, generally identified by reference numeral 200, is described below with reference to FIG. 1 and FIG. 3. This control module was specifically designed for the control of a heat treatment apparatus. Encapsulated within control module 200 are prior art components. The prior art will first be described, to identify prior art components.

[0013] Referring to FIG. 2, prior art control components include one or more heating pads 102 (one has been illustrated). A power source (represented by power circuit 201) is used to deliver power to one or more heating pads 102. A thermocouple 106 is spot welded to a metal workpiece (not shown) underneath one or more of heating pads 102.
It will be understood that there are various devices that are equivalent to a thermocouple and which could be substituted. A thermocouple cable 108 connects thermocouple 106 to a temperature controller 110 which uses input from thermocouple 106 to selectively control the flow of power from the power source to heating pads 102. Temperature controller 110 has two outputs: output 1 (OP 1) and output 2 (OP 2). OP1 is an auxiliary output that can be used for various purposes. OP 1 is a miniature electro-mechanical relay that is energized by temperature controller 110. OP 2 is also a miniature electro-mechanical relay that energizes and de-energizes a larger electro-mechanical relay (EMR) 104 connecting heating pads 102 to the power source. EMR 104 is in a normally open position. Temperature controller 110 causes EMR 104 to close in order to supply power to heating pads 102.
Temperature controller 110 receives temperature feedback from thermocouple 106 to bring heating pads 102 up to a pre-selected temperature (135 C, for example). The temperature controller does algorithms based on what it's parameters have been set at (ie: set point and ramp rate) and the thermocouple feedback. Based on the result of these algorithms, the temperature controller causes multiple on and off heating cycles so that the temperature of the metal workpiece increases at the entered ramp rate before reaching the entered set point temperature without going over. This type of control is called PhD
(proportional-integral-derivative) control. A
power switch 112 is provided to switch power on and off to temperature controller 110.
Structure and Relationship of Parts:

[0014] The prior art components having been described, there will next be described the components of control module 200. Referring to FIG. 1, there is a power circuit 201.
Control module 200 includes a timer relay 202 connected by line 7 to a power input line 6 forming part of power circuit 201 which supplies power to one or more heating pads 102 (one has been illustrated) which are used for the heat treatment apparatus. It will be noted that timer relay 202 receives power and starts timing through a built in timing circuit when power is supplied along power input line 6 to heating pads 102. Timer relay 202 resets when power is discontinued to heating pads 102. When the heat treatment apparatus is operating properly, timer relay 202 is reacting to the cycles dictated by temperature controller, starting timing when power is supplied to start an "on" cycle and then resetting when power is discontinued to start an "off' cycle.

[0015] It is to be noted that timer relay 202 has a number of switches.
For the purpose of this description the switches are identified as switch 204 and switch 206.
Switch 204 is capable of connecting points 15 and 16 or in a different state of connecting points 15 and 18.
Switch 206 is capable of connecting points 25 and 26 or in a different state connecting points 25 and 28. Switch 204 and Switch 206 change state when a time duration of timer relay 202 exceeds a pre-set time interval (for example, 10 seconds). In the illustrated example, the change in state involves switch 204 changing from connecting points 15 and 16 to connecting points 15 and 18. In the illustrated example, the change in state involves switch 206 changing from connecting points 25 and 26 to connecting points 25 and 28.
This changes is state of timer relay 202, with switch 206 changing from connecting points 25 and 26 to connecting points 25 and 28, causes a protection circuit, generally indicated by reference numeral 208, to disrupt power passing along power input line 6 to heating pads 102.

[0016] Prior to tracing and describing protection circuit 208, an explanation is required regarding a change that has been made to electro-mechanical relay 104.
Referring to FIG. 2, the prior art had an electro-mechanical relay 104, which had a normally open position.
Temperature controller 110, when configured in accordance with the prior art, uses electro-mechanical relay 104 to control power to heating pads 102. With control module 200, power input line 6 also has an electro-mechanical relay EMR. This electro-mechanical relay differs from the prior art, in that it is maintained in a normally closed position. For that reason EMR has been identified by reference numeral 210 to differentiate this electro-mechanical relay from electro-mechanical relay 104 used in the prior art.
Control module 200 has a solid state relay SSR 212 that temperature controller 110 controls through a control circuit 214. Protection circuit 208 serves to disrupt power to a control circuit 214 for electro-mechanical relay 210, thereby causing electro-mechanical relay 210 to open.

[0017] When protection circuit 208 is energized power is supplied to relay R3 causing R3 relay contacts 216 and 218 associated with relay R3 to close. The closing of contacts 216 supplies power to relay R2, causing R2 relay contacts 220, 222 to open and 224 on control circuit 214 to close. The opening of contacts 220 positioned on line 15 of control circuit 214 causes EMR 210 to open. The opening of contacts 222 positioned on line 16 of control circuit 214 causes SSR 212 to open. Once EMR 210 is open there is no longer power going to heating pads 102. However, this means that there is also no power going to timer relay 202. Protection circuit 208 maintains EMR 210 in an open position. This is accomplished by R3 contacts 218 serving as holding contacts which close to maintain a path of power to R3 even if switch 206 changes back to its original state due to the power from line 6 to the timer relay 202 through line 7 being interrupted, thus latching the protection circuit.

[0018] Protection circuit 208 has a reset switch 226 with a status light 228. Reset switch 226 provides a means for resetting the system once the problem has been rectified. If the problem has not been rectified, timer relay 202 will trigger protection circuit 208 again after the passage of the pre-set time interval.

[0019] It is preferred that the control module includes an alarm circuit 230 for the purpose of alerting human operators. It is to be noted that the change in state of timer relay 202 with switch 204 changing from connecting points 15 and 16 to connecting points 15 and 18 results in alarm circuit 230 receiving power. There are a number of ways alarm circuit 230 can be configured. There has been illustrated an auditory alarm in the form of buzzer 232 positioned between wires 23 and 24. There has been illustrated a visual alarm in the form of a flashing alarm light 234 positioned between wires 19 and 21.

[0020] There is also a momentary silence button 236. Momentary silence button 236 is used to temporarily disable buzzer 232 while operators are examining the system.
Depressing momentary silence button closes contacts 25 and 26 and provides power to Relay RI. When relay R1 is energized it opens RI contacts 238 and closes contacts 240.
The opening of contact 238 silences buzzer 232. The flashing alarm light remains on until power is cut to the alarm circuit by switch 204 or contacts 224 - whichever one fed the alarm circuit in the first place.

[0021] In the description of FIG. 1 only one power input line has been illustrated. With many heat treatment apparatus the power input line has multiple branches.
Referring to FIG.
3, there are shown multiple branches 250, 252, 254. It will be understood that each of branches 250, 252, and 254 is supplying power to one or more heating pads.
Each of branches 250, 252, and 254 have their own power circuit, timer circuit, control circuits, and temperature controllers. There can, however, be a common alarm circuit 230.1iwuil

[0022]
Referring to FIG. 1, since OP 1 is available, it is preferred that OP 1 be connected to protection circuit 208. This enables auxiliary inputs to be received from temperature controller 110 to trigger protection circuit 208 and the alarm circuit 230.
For example, temperature controller 110 can use OP 1 to trigger protection circuit (and along with it alarm circuit 230) if thermocouple 106 indicates that the temperature of the workpiece underneath heating pads 102 has risen beyond a selected temperature threshold (for example, 150 degrees Celsius).

[0023]
Referring to FIG. 1, it is also preferred that a fuse indication circuit 260 be provided to give an indication as to when a fuse for the power circuit is intact and when it has blown. Fuse indication circuit 260 monitors fuse 262. Fuse indication circuit 260 also has a fuse 264 (not to be confused with fuse 262 which is being monitored) and a fuse indication light 266 which indicates status.

[0024] There are a few other optional features that are recommended. For example, it is preferred that a thermal switch 270 be provided to detect over heating of SSR
212.
Operation:

[0025]
During regular operation, temperature controller 110 cycles the heat on and off at a rate based on feedback from thermocouple 106 and on what the set point and ramp rate parameters within temperature controller 110 are set at. Thermocouple 106 would typically have 2-conductors, with each conductor spot welded to the metal workpiece underneath one or more flexible ceramic heating pads 102. Temperature controller 110 switches output 2 (OP 2) on and off which energizes and de-energizes the control portion of the solid state relay (SSR) 212 shown on control circuit 214 at points 17 and 18. When the control portion of SSR 212 is energized, power is allowed to pass through the SSR's 212 power terminals shown at points 2 and 6, to deliver power to heating pad 102. As described above, electrical mechanical relay EMR 210 becomes closed upon turning on temperature controller 110 and stays closed until it gets automatically opened in a circumstance where it needs to save the workpiece from being inadvertently overheated due to compromised field wiring or machine component failure, as will hereinafter be described.

[0026] An example of machine component failure could be power terminals 2 and 6 of SSR 212 becoming stuck in the closed position. In this abnormal operating condition, the power being delivered to heating pad 102, and thus the power to timer relay 202 through wire 7 would remain constant. When timer relay 202 receives power through wire 7, it starts timing. When the power through wire 7 ceases, timing relay resets and does not continue timing again until power is channelled through wire 7 again. Once the timer relay receives power for a pre-set amount of time, (say 10 seconds, for example), then the timer relay's contacts change their state. The continuity between points 25 and 26 would be broken and continuity between 25 and 28 would be established bringing power to protection circuit 208 energizing relay R3. Simultaneously, continuity between points 15 and 16 would be broken and continuity between points 15 and 18 would be made bringing power to alarm circuit 230 via wire 19/20.

[0027] The energization of R3 would cause R3's contacts to change their state. The R3 normally open contact 216 would close and allow R2 to become energized. Now R2's contacts would change their states and the following would happen: The control power to both SSR 212 and EMR 210 would be opened and EMR 210, and sequentially SSR
212, would be disabled, breaking the path to the heating pads 102 between points 6 and 7 resulting in saving the work piece from overheating. At this point the energy to timer relay 202 is taken away and therefor its contacts go back to their original state.
Despite this, R3 will remain energized because the R3 contact 218 shown just below timer relay 202 act as holding contacts. They became closed when R3 was originally energized and will remain closed, providing a continuous power to R3, until R3 is de-energized.

[0028] At this stage, alarm circuit 230 is in alarm with alarm light 234 is flashing and buzzer 232 is sounding. However, operators working on the equipment can push silence button 236 and buzzer 232 will stop, but alarm light 234 will continue to flash. Also, at this point light 228 on reset button 236 will be illuminated, indicating which branch/channel has the issue. Bear in mind that the schematic of FIG. 1 shows the wiring for one channel only.
A heating machine may have six channels, for example, and there for the wiring in the schematic would occur six times minus the alarm circuit. Only one alarm circuit is needed for a multi-channel machine. All six timer relays would be connected at the common point shown as point 18/19 on the schematic diagram so that they all could feed to the same alarm circuit. A form of a multi-channel machine with branches 250, 252 and 254 has been illustrated in FIG. 3 to show this type of configuration.

[0029] At this point if you were to press reset button 226 without rectifying the issue first, the power to R3 would become interrupted briefly which would cause the R3 holding contacts to open, causing R3 to become de-energized. With R3 becoming de-energized, R2 becomes de-energized, bringing its normally closed contacts back to their closed state. This in turn causes EMR 210 to close (at points 6 and 7) and the power to flow through to heating pad 102 again. The power would only flow through the heating pad for 10 seconds because, if the problem had not been rectified, timer relay 202 would time out again and bring you right back into the alarm condition with protective circuit 208 operational to disrupt power to heating pads 102 and alarm circuit 230 operational to warn operators.

[0030] If you were to rectify the issue by replacing SSR 212 and then press reset button 226, reset button 226 would become un-illuminated and everything would operate normally again.

[0031] Another situation that would cause control module 200 to spring into action and save the workpiece from being overheated is in a situation where the field wiring is compromised. Field wiring includes the power cables that deliver power to the heating pads and thermocouple cables 108, all of which go from the heating pad area 102 to where the temperature controller(s), control circuitry, and the rest of the power circuitry resides.. If, for example, a thermocouple cable 108 became shorted-out at a location away from heating pad 102, then the feedback temperature would be far less than the temperature of the workpiece underneath heating pad 102. For example, the shorted-out thermocouple cable 108 could be indicating a constant ambient temperature of 25 C. The temperature controller's set point could be at 135 C, for example. If this was the case, then the temperature controller would call for more and more aggressive "on-cycles" because it is programmed to get the workpiece temperature to 135 C, but thermocouple 106 keeps telling it that the temperature is only 25 C. Eventually, temperature controller 110 would make the power to the heating pad be 100% continuous. If this were to happen, control module 200 would go into the alarm state (which includes killing the power to heating pad 102) after the first on-cycle that reached 10 seconds in duration and stay in the alarm state until the problem is rectified and reset button 226 is pressed.

[0032] Another feature shown in this system is the "High Temperature Alarm". This is where OP 1 could be used from temperature controller 110. For example, you could set temperature controller 110 to trigger OP 1 as a high temperature alarm at 150 C. That means if the workpiece temperature was to inadvertently get to 150 C, then OP 1 would close, which would bring power to R2, which would cause the R2 contacts shown just below the alarm circuit, which would allow power to feed the alarm circuit. At this point normally closed R2 contacts would open, disabling SSR 212 and EMR 210 form delivering power to heating pad 102. A high temperature indication would be indicated on temperature controller 110 corresponding to the channel in trouble. When the workpiece temperature has recovered back down below 150 C, OP 1 will open automatically and everything resumes normal operation.

[0033] In this patent document, the word "comprising" is used in its non-limiting sense to mean that items following the word are included, but items not specifically mentioned are not excluded. A reference to an element by the indefinite article "a" does not exclude the possibility that more than one of the element is present, unless the context clearly requires that there be one and only one of the elements.

[0034] The scope of the claims should not be limited by the illustrated embodiments set forth as examples, but should be given the broadest interpretation consistent with a purposive construction of the claims in view of the description as a whole.

Claims (8)

What is Claimed is:

1. A control module for a heat treatment apparatus, comprising:
a timer relay connected to a power input line supplying power to heating pads for the heat treatment apparatus, the timer relay receiving power and starting timing when power is supplied to the heating pads, the timer relay resetting when power is discontinued to the heating pads, the timer relay having at least one output that changes state when a time duration exceeds a pre-set time interval, the change in state causes a protection circuit to disrupt power from the power input line to the heating pads.

2. The control module of Claim 1, wherein the power input line has at least one relay which is maintained in a closed position, the protection circuit serving to disrupt power to a control circuit for the at least one relay, thereby causing the at least one relay to open.

3. The control module of Claim 1, wherein an alarm circuit receiving power upon the change in state of the timer relay, the alarm circuit providing at least one of an auditory or a visual alarm.

4. The control module of Claim 3, wherein the power input line has multiple branches, with each of the branches supplying power to one or more heating pads, there is more than one timer relay with one timer relay and associated protection circuit for each of the branches.

5. The control module of Claim 4, wherein the protection circuit identifies which of the multiple branches is malfunctioning.

6. The control module of Claim 2, wherein one or more auxiliary inputs are received from a temperature controller to trigger the protection circuit and the alarm circuit.

7. The control module of Claim 2, wherein the protection circuit permits a latching function through holding contacts to maintain the action of the protection circuit after the power from the power line to the timer relay is interrupted.

8. The control module of Claim 1, wherein a fuse indication circuit gives an indication as to when a fuse for the power circuit is intact and when it has blown.