Title:
PRINTED CIRCUIT BOARD WITH INTEGRATED TEMPERATURE SENSING
Kind Code:
A1


Abstract:
An extruder for a three-dimension printer uses a printed circuit board (PCB) heating element with leads having temperature-sensitive resistance. The resulting circuit can be driven at high power to heat an extruder, or at a low power with a known current to measure a resistance from which temperature can be inferred. Thus a single circuit on a printed circuit board can be driven alternately in two modes to heat and sense temperature of an extruder.



Inventors:
Mulliken, Harry Elliot (Hamilton, NJ, US)
Application Number:
13/961972
Publication Date:
02/13/2014
Filing Date:
08/08/2013
Assignee:
MakerBot Industries, LLC (Brooklyn, NY, US)
Primary Class:
Other Classes:
425/113
International Classes:
B29C67/00
View Patent Images:



Primary Examiner:
PASCHALL, MARK H
Attorney, Agent or Firm:
STRATEGIC PATENTS P.C. (P.O. BOX 920629 NEEDHAM MA 02492)
Claims:
What is claimed is:

1. A device comprising: a printed circuit board; a hole in the printed circuit board; an extrusion nozzle passing through the hole; a heating element on the printed circuit board, the heating element positioned in thermal contact with the extrusion nozzle; and a conductive trace on the printed circuit board, the conductive trace having a first end coupled to a contact of the heating element, the conductive trace having a predetermined relationship of resistance to temperature.

2. The device of claim 1 wherein the conductive trace is a copper trace.

3. The device of claim 1 further comprising a second conductive trace on the printed circuit board electrically coupled to a second contact of the heating element.

4. The device of claim 1 further comprising a power supply electrically coupled to a second end of the conductive trace.

5. The device of claim 4 wherein the power supply operates in a first mode where high current is applied to the heating element to create heat in the heating element.

6. The device of claim 5 wherein the power supply operates in a second mode where a calibrated current is applied to the heating element and a voltage across the conductive trace is measured, thereby permitting a determination of the resistance of the conductive trace and, based upon the predetermined relationship of resistance to temperature, the temperature of the conductive trace.

7. The device of claim 1 further comprising processing circuitry configured to operate the power supply in a first mode where high current is applied to the heating element to create heat in the heating element.

8. The device of claim 7 wherein the power supply heats the heating element to at least one hundred degrees Centigrade.

9. The device of claim 7 wherein the processing circuitry is further configured to operate the power supply in a second mode where a calibrated current is applied to the heating element, the processing circuitry further configured to measure a voltage across the conductive trace.

10. The device of claim 9 wherein the processing circuitry is configured to calculate a temperature of the extrusion nozzle based upon the voltage.

11. The device of claim 1 wherein the heating element is a resistive element formed by a length of the conductive trace.

12. A method comprising: providing an assembly including a printed circuit board, an extrusion nozzle passing through a hole in the printed circuit board, a heating element mounted to the printed circuit board and thermally coupled to the extrusion nozzle, and a conductive trace on the printed circuit board electrically coupled to and in series with the heating element; determining a relationship of temperature to resistance for the conductive trace; powering the heating element through the conductive trace in a first mode to heat the heating element; powering the heating element through a conductive trace in a second mode with a known current and measuring a voltage across the conductive trace; and determining a temperature of the conductive trace based upon the voltage.

13. The method of claim 12 further comprising calculating a temperature of the extrusion nozzle based upon the temperature of the conductive trace.

14. The method of claim 12 wherein the conductive trace includes a first lead from a first contact of the heating element and a second lead from a second contact of the heating element.

15. The method of claim 14 further comprising determining a second voltage across the first contact and the second contact of the heating element and subtracting the second voltage from the voltage across the conductive trace.

16. The method of claim 12 wherein the conductive trace includes a copper trace.

17. A method comprising: fabricating a printed circuit board including a through-hole for an extrusion nozzle and a mounting location adjacent to the through-hole shaped for a heating element; adding a copper trace to the printed circuit board from a contact of the mounting location to a contact for a power supply; measuring a resistance of the copper trace; and modifying the copper trace to adjust the resistance toward a predetermined resistance.

18. The method of claim 17 wherein modifying the copper trace includes layering additional copper onto a pattern of the copper trace.

19. The method of claim 18 wherein modifying the copper trace includes maintaining a substantially constant temperature of the copper while layering additional copper and concurrently measuring the resistance.

20. The method of claim 17 wherein modifying the copper trace includes cutting the copper trace to a length corresponding to the predetermined resistance.

21. The method of claim 17 wherein the copper trace includes a plurality of traces, and wherein modifying the copper trace includes selectively coupling one or more of the plurality of traces having an aggregate resistance closest to the predetermined resistance to the contact of the mounting location and the contact for the power supply.

Description:

RELATED APPLICATION

This application claims the benefit of U.S. Prov. App. No. 61/680,989 filed on Aug. 8, 2012, the entire content of which is hereby incorporated by reference.

BACKGROUND

There remains a need for a printed circuit board that support heating and temperature sensing with a reduced part count.

SUMMARY

An extruder for a three-dimension printer uses a printed circuit board (PCB) heating element with leads having temperature-sensitive resistance. The resulting circuit can be driven at high power to heat an extruder, or at a low power with a known current to measure a resistance from which temperature can be inferred. Thus a single circuit on a printed circuit board can be driven alternately in two modes to heat and sense temperature of an extruder.

BRIEF DESCRIPTION OF THE FIGURES

The invention and the following detailed description of certain embodiments thereof may be understood by reference to the following figures:

FIG. 1 is a block diagram of a three-dimensional printer.

FIG. 2 shows a combined heater and temperature sensor integrated with a printed circuit board.

FIG. 3 shows a method for operating a printed circuit board with integrated temperature sensing.

FIG. 4 shows a method for fabricating conductive traces on a printed circuit board.

FIG. 5 shows a conductive trace forming a heating element.

DETAILED DESCRIPTION

All documents mentioned herein are hereby incorporated in their entirety by reference. References to items in the singular should be understood to include items in the plural, and vice versa, unless explicitly stated otherwise or clear from the text. Grammatical conjunctions are intended to express any and all disjunctive and conjunctive combinations of conjoined clauses, sentences, words, and the like, unless otherwise stated or clear from the context. Thus the term “or” should generally be understood to mean “and/or” and so forth.

The following description emphasizes three-dimensional printers using fused deposition modeling or similar techniques where a bead of material is extruded in a layered series of two dimensional patterns as “roads,” “paths” or the like to form a three-dimensional object from a digital model. It will be understood, however, that numerous additive fabrication techniques are known in the art including without limitation multijet printing, stereolithography, Digital Light Processor (“DLP”) three-dimensional printing, selective laser sintering, and so forth. Such techniques may benefit from the systems and methods described below, and all such printing technologies are intended to fall within the scope of this disclosure, and within the scope of terms such as “printer”, “three-dimensional printer”, “fabrication system”, and so forth, unless a more specific meaning is explicitly provided or otherwise clear from the context.

FIG. 1 is a block diagram of a three-dimensional printer. In general, the printer 100 may include a build platform 102, an extruder 106, an x-y-z positioning assembly 108, and a controller 110 that cooperate to fabricate an object 112 within a working volume 114 of the printer 100.

The build platform 102 may include a surface 116 that is rigid and substantially planar. The surface 116 may provide a fixed, dimensionally and positionally stable platform on which to build the object 112. The build platform 102 may include a thermal element 130 that controls the temperature of the build platform 102 through one or more active devices 132, such as resistive elements that convert electrical current into heat, Peltier effect devices that can create a heating or cooling affect, or any other thermoelectric heating and/or cooling devices. The thermal element 130 may be coupled in a communicating relationship with the controller 110 in order for the controller 110 to controllably impart heat to or remove heat from the surface 116 of the build platform 102.

The extruder 106 may include a chamber 122 in an interior thereof to receive a build material. The build material may, for example, include acrylonitrile butadiene styrene (“ABS”), high-density polyethylene (“HDPL”), polylactic acid (“PLA”), or any other suitable plastic, thermoplastic, or other material that can usefully be extruded to form a three-dimensional object. The extruder 106 may include an extrusion tip 124 or other opening that includes an exit port with a circular, oval, slotted or other cross-sectional profile that extrudes build material in a desired cross-sectional shape.

The extruder 106 may include a heater 126 (also referred to as a heating element) to melt thermoplastic or other meltable build materials within the chamber 122 for extrusion through an extrusion tip 124 in liquid form. While illustrated in block form, it will be understood that the heater 126 may include, e.g., coils of resistive wire wrapped about the extruder 106, one or more heating blocks with resistive elements to heat the extruder 106 with applied current, an inductive heater, or any other arrangement of heating elements suitable for creating heat within the chamber 122 sufficient to melt the build material for extrusion. The extruder 106 may also or instead include a motor 128 or the like to push the build material into the chamber 122 and/or through the extrusion tip 124.

In general operation (and by way of example rather than limitation), a build material such as ABS plastic in filament form may be fed into the chamber 122 from a spool or the like by the motor 128, melted by the heater 126, and extruded from the extrusion tip 124. By controlling a rate of the motor 128, the temperature of the heater 126, and/or other process parameters, the build material may be extruded at a controlled volumetric rate. It will be understood that a variety of techniques may also or instead be employed to deliver build material at a controlled volumetric rate, which may depend upon the type of build material, the volumetric rate desired, and any other factors. All such techniques that might be suitably adapted to delivery of build material for fabrication of a three-dimensional object are intended to fall within the scope of this disclosure.

The x-y-z positioning assembly 108 may generally be adapted to three-dimensionally position the extruder 106 and the extrusion tip 124 within the working volume 114. Thus by controlling the volumetric rate of delivery for the build material and the x, y, z position of the extrusion tip 124, the object 112 may be fabricated in three dimensions by depositing successive layers of material in two-dimensional patterns derived, for example, from cross-sections of a computer model or other computerized representation of the object 112. A variety of arrangements and techniques are known in the art to achieve controlled linear movement along one or more axes. The x-y-z positioning assembly 108 may, for example, include a number of stepper motors 109 to independently control a position of the extruder 106 within the working volume along each of an x-axis, a y-axis, and a z-axis. More generally, the x-y-z positioning assembly 108 may include without limitation various combinations of stepper motors, encoded DC motors, gears, belts, pulleys, worm gears, threads, and so forth. For example, in one aspect the build platform 102 may be coupled to one or more threaded rods by a threaded nut so that the threaded rods can be rotated to provide z-axis positioning of the build platform 102 relative to the extruder 106. This arrangement may advantageously simplify design and improve accuracy by permitting an x-y positioning mechanism for the extruder 106 to be fixed relative to a build volume. Any such arrangement suitable for controllably positioning the extruder 106 within the working volume 114 may be adapted to use with the printer 100 described herein.

In general, this may include moving the extruder 106, or moving the build platform 102, or some combination of these. Thus it will be appreciated that any reference to moving an extruder relative to a build platform, working volume, or object, is intended to include movement of the extruder or movement of the build platform, or both, unless a more specific meaning is explicitly provided or otherwise clear from the context. Still more generally, while an x, y, z coordinate system serves as a convenient basis for positioning within three dimensions, any other coordinate system or combination of coordinate systems may also or instead be employed, such as a positional controller and assembly that operates according to cylindrical or spherical coordinates.

The controller 110 may be electrically or otherwise coupled in a communicating relationship with the build platform 102, the x-y-z positioning assembly 108, and the other various components of the printer 100. In general, the controller 110 is operable to control the components of the printer 100, such as the build platform 102, the x-y-z positioning assembly 108, and any other components of the printer 100 described herein to fabricate the object 112 from the build material. The controller 110 may include any combination of software and/or processing circuitry suitable for controlling the various components of the printer 100 described herein including without limitation microprocessors, microcontrollers, application-specific integrated circuits, programmable gate arrays, and any other digital and/or analog components, as well as combinations of the foregoing, along with inputs and outputs for transceiving control signals, drive signals, power signals, sensor signals, and so forth. In one aspect, this may include circuitry directly and physically associated with the printer 100 such as an on-board processor. In another aspect, this may be a processor associated with a personal computer or other computing device coupled to the printer 100, e.g., through a wired or wireless connection. Similarly, various functions described herein may be allocated between an on-board processor for the printer 100 and a separate computer. All such computing devices and environments are intended to fall within the meaning of the term “controller” or “processor” as used herein, unless a different meaning is explicitly provided or otherwise clear from the context.

A variety of additional sensors and other components may be usefully incorporated into the printer 100 described above. These other components are generically depicted as other hardware 134 in FIG. 1, for which the positioning and mechanical/electrical interconnections with other elements of the printer 100 will be readily understood and appreciated by one of ordinary skill in the art. The other hardware 134 may include a temperature sensor positioned to sense a temperature of the surface of the build platform 102, the extruder 126, or any other system components. This may, for example, include a thermistor or the like embedded within or attached below the surface of the build platform 102. This may also or instead include an infrared detector or the like directed at the surface 116 of the build platform 102.

In another aspect, the other hardware 134 may include a sensor to detect a presence of the object 112 at a predetermined location. This may include an optical detector arranged in a beam-breaking configuration to sense the presence of the object 112 at a predetermined location. This may also or instead include an imaging device and image processing circuitry to capture an image of the working volume and to analyze the image to evaluate a position of the object 112. This sensor may be used for example to ensure that the object 112 is removed from the build platform 102 prior to beginning a new build on the working surface 116. Thus the sensor may be used to determine whether an object is present that should not be, or to detect when an object is absent. The feedback from this sensor may be used by the controller 110 to issue processing interrupts or otherwise control operation of the printer 100.

The other hardware 134 may also or instead include a heating element (instead of or in addition to the thermal element 130) to heat the working volume such as a radiant heater or forced hot air heater to maintain the object 112 at a fixed, elevated temperature throughout a build, or the other hardware 134 may include a cooling element to cool the working volume.

An extruder design of the printer 100 may use a printed circuit board (PCB) heating element that includes a through hole through which an extruder nozzle may pass. The PCB can be adhered to a metal plate that absorbs and transfers heat to the extruder nozzle. There may be one or more PCB copper traces that may be electrically coupled to the metal plate. The PCB copper traces may be manufactured to a tolerance such that their resistance changes predictably with temperature. With this known relationship, a calibrated current through the copper traces can provide a voltage indicative of the current temperature at the copper traces, from which other temperatures (metal plate, extruder nozzle) can be reliably inferred.

FIG. 2 shows a combined heater and temperature sensor integrated with a printed circuit board (PCB). As shown, an extrusion tool head 200 for a three-dimensional printer may generally include an extrusion nozzle 202, drive components 204 to drive a build material into and through the extrusion nozzle 202, and a PCB 206. The PCB 206 may include a hole 212 through which the extrusion nozzle 202 can pass, which may be filled after assembly with any suitable potting material or other thermal or electric insulator or conductor as desired. The PCB 206 may include a heating element 214 such as a resistive heating element that surrounds or is otherwise placed in close proximity to, and more specifically in thermal contact with, the extrusion nozzle 202 in order to create a hot zone to melt a build material in a chamber coupled to the extrusion nozzle 202 in order to extrude the build material through the extrusion nozzle 202. It will be appreciated that thermal contact may be achieved by direct physical contact or by contact through any suitable thermally conducting material(s).

The conductive traces 208 that may be formed of any suitably conductive material such as copper, aluminum, or the like. The conductive traces 208 may assume any suitable geometry within a plane of the PCB 206 such as spiral pattern or a series of adjacent linear runs. Where the PCB 206 has two or more layers, the conductive traces 208 may be on one or more such layers. In general, the use of longer, thinner traces provides greater resistance per unit of length and correspondingly more sensitive measurements, however no particular geometry or dimensions are required, provided that the relationship between temperature and resistance can be accurately characterized.

The heating element 214 may be electrically coupled to and driven through one or more conductive traces 208 on the PCB 206 that are manufactured to have a resistance that changes predictably with temperature. By applying a calibrated current to these conductive traces 208 and measuring the resulting voltage, the temperature of the traces (and by inference, the extrusion nozzle 202) can be determined. Each conductive trace 208 may have a first end 216 electrically coupled to the heating element 214 through a contact or the like, and have a predetermined relationship of resistance to temperature. Each conductive trace 208 may have a second end 218 electrically coupled to the power supply 210 through one or more wires. In general the heating element 214 may include one or more discrete heating element components coupled to or integrated into the PCB 206, such as resistive heating elements or the like. In another aspect, the heating element 214 may be a resistive heating element formed of a length of resistive material. This may advantageously be formed of a length of the conductive trace 208, eliminating the need for a separate, discrete heater.

Processing circuitry 220 may be coupled to the power supply 210 to control operation of the PCB 206, and more particularly to drive a heating circuit including the conductive traces 208 and the heating element 214 alternately in a heating mode and a temperature sensing mode as generally described herein. The processing circuitry 220 may also be coupled to a voltage sensing circuit 222 that provides a voltage differential across the conductive traces 208 or some portion thereof. It will be understood that while voltage sensing is depicted across the output of the power supply, voltage sensing may as a practical matter occur in a number of places. For example, voltage sensing may be performed across a single trace on the PCB 206 from a contact for the power supply 210 to a contact for the heating element 214. In another aspect the voltage sensing may be performed across the entire power circuit (e.g., from a positive to a negative contact of the power supply); however in this case, a load from the heating element might be independently measured, particularly where the load is known to be non-temperature sensitive, and calibrated out of a voltage sensing measurement across the conductive traces 208. In another aspect, the control circuitry 220 may selectively bypass the heating element 214 or otherwise isolate the lengths of conductive trace with a relay, switch or other low resistance coupling when in a temperature sensing mode in order to isolate a resistance measurement across the conductive traces 208, and then remove the bypass when returning to a heating mode. More generally, a variety of techniques may be used to isolate a voltage drop across some or all of the conductive traces 208 in order to measure resistance and calculate temperature thereof based upon the known, predetermined relationship between temperature and resistance for the conductive traces 208.

While FIG. 2 shows the PCB through hole approximately in the center of the PCB 206, it should be understood that the hole may be located at any location on the PCB 206 that allows for the placement of the extrusion tool head 200 components.

In this configuration, the traces 208 may be driven from a power supply 210 in two alternating modes. In one mode, high-current may be applied by the power supply 210 to heat the heating element 214. In a second mode, a calibrated, low-current signal may be applied by the power supply 210 to the traces 208 to determine the temperature of the heating element or the extrusion nozzle 202. In the second mode, the temperature may be determined by applying the calibrated current to the trace 208, measuring the voltage on the trace 208 that results from the calibrated current, and comparing the measured voltage to temperature data that is calibrated to the resistance of the traces 208. Additionally, there may be temperature data that relates the temperature or resistance of the traces 208 to the temperature of the heating element or extrusion nozzle 202. Therefore, once the resistance and temperature of the traces 208 is known, the temperature of the heating element or extruder nozzle may be determined.

In a non-limiting example of the trace and heating element configuration for temperature determination, two traces 208 may be connected in series with the heating element with a first trace 208 connected between the power supply 210 and a first heating element contact and a second trace 208 connected between a second heating element contact and the power supply 210. During the second mode of operation, while the calibrated current is applied, a first voltage across the two traces 208 and heating element may be determined as discussed above. Additionally, a second voltage may be measured across the first heating element contact and the second heating element contact to determine the voltage across the heating element. Then the second voltage can be subtracted from the first voltage to determine the voltage across only the traces 208. As stated above, once the voltage is determined for the traces 208, the temperature of the traces and heating element may be determined.

The high-current mode (or “heating mode”) and the low-current mode (or “sensing mode”) may usefully operate over a shared circuit to both heat the extrusion nozzle 202 and determine its temperature. In another aspect, the high-current mode and the low-current mode may be operated over parallel circuits—one coupled to the heating element 214 and one coupled to a conductive trace 208. Switching between modes may be performed periodically at any regular, varying, or random interval. In general, this approach advantageously reduces the number of wires and components required for concurrent temperature sensing and heating.

For meltable plastics such as PLA or ABS used in common extrusion-based three-dimensional printing, the power supply 210 may apply sufficient current to heat the extrusion nozzle 202 to at least one hundred degrees Centigrade. The amount of current required to achieve this temperature within the extruder may vary according to components used and the configuration of the physical arrangement of the heating element(s). Further, the desired operating temperature range may vary according to the build materials used in the extrusion process.

In the low-current mode, the processing circuitry 220 may control the power supply 210 to apply a calibrated current to the conductive traces 208. As described above, the processing circuitry 220 may be further configured to measure the voltage resulting from the applied current and, using Ohm's law and the predetermined relationship between temperature and resistance for the conductive traces 208, to calculate a temperature of the conductive traces 208. With this information, the temperature of the extrusion nozzle 202 may be inferred, or calculated directly from the measure voltage using a suitable mathematical model.

The processing circuitry 220 may also determine whether, based on a calculated temperature and a predetermined target temperature, additional heating is required, and the processing circuitry 220 may control the system in the high-current mode accordingly to move the calculated temperature for a subsequent measurement toward the target temperature.

FIG. 3 shows a method for operating a printed circuit board with integrated temperature sensing as described above.

The method 300 may begin with providing an assembly including the printed circuit board as shown in step 302. In general, the assembly may include the printed circuit board, an extrusion nozzle passing through a hole in the printed circuit board, a heating element mounted to the printed circuit board and thermally coupled to the extrusion nozzle, and a conductive trace on the printed circuit electrically coupled to and in series with the heating element, all as generally described above. In other embodiments, the conductive trace may be coupled in parallel with the heating element or otherwise arranged in a suitable electronic circuit on the printed circuit board with the power supply, heating element, voltage sensing circuitry, and processing circuitry. As described in the various embodiments above, the conductive trace used for measuring voltage may form a single length of trace, such as from a power supply terminal to a heating element terminal, or the conductive trace may include multiple segments completing a circuit between the positive and negative terminals of a power supply, such as by including a first lead from a first contact of the heating element and a second lead from a second contact of the heating element. More generally, any suitable circuit may be used provided that the trace has a known relationship between temperature and resistance. The conductive trace may be formed of copper, aluminum or any other suitable metal or other conductive material(s).

As shown in step 304, a relationship may be determined of the temperature to resistance for the conductive trace. While illustrated as occurring after the assembly is provided, it will be appreciated that this step may be performed at any time prior to calculating a temperature. For example, the relationship may be determined when the printed circuit board is fabricated, or after assembly into an extrusion system. In another aspect, the relationship may be measured using an onboard calibration circuit immediately prior to use. However determined, the relationship may be substituted into Ohm's law to permit calculation of temperature as a function of a known current and a measured voltage across the conductive trace.

As shown in step 306, the heating element may be powered through the conductive trace (from a power supply or the like) in a high-current or heating mode to heat the heating element.

As shown in step 308, the heating element may be powered through the conductive trace in a low-current or sensing mode with a known current and a voltage across the conductive trace may be measured. As noted above, the resistance of the heating element may be accounted for (either as a fixed or temperature-varying quantity), or the voltage may be measured only across the conductive trace. Accordingly, in one embodiment, the method may include determining a second voltage across a first contact and a second contact of the heating element and subtracting the second voltage from the voltage across a length of the conductive trace that includes two segments in series with the two terminals of the heating element. In other embodiments, the conductive trace may form an independent circuit in parallel with the heating element, and may be electrically isolated from or coupled to the power supply according to the desired mode. More generally, any technique for measuring voltage along a length of conductive trace that has a known relationship of temperature to resistance may be usefully employed in a temperature sensing measurement as contemplated herein.

As shown in step 310, the method 300 may include determining a temperature of the conductive trace based upon the voltage and the known, predetermined relationship between resistance and temperature for the conductive trace.

As shown in step 312, the method may include calculating a temperature of the extrusion nozzle based upon the temperature of the conductive trace. The relationship between the temperature of the conductive trace and the temperature of the extrusion nozzle may be empirically determined or estimated using physical modeling or the like based upon the structure of the extrusion nozzle, heater, circuit board, and so forth. It will be appreciated that, while illustrated as separate steps, the extrusion nozzle temperature may be calculated directly from the sensed voltage across the conductive trace using a suitably adapted mathematical model.

As shown in step 314, a control loop may be implemented by determining whether the temperature of the extrusion nozzle has reached a predetermined target value. If the temperature is at or above the target, then the method 300 may return to step 308 where the temperature may again be sensed. If the temperature is below the target, then the method 300 may return to step 306 where the heating element may be heated. The duration of heating in step 306 may be fixed, or may vary according to, e.g., a magnitude of the difference between the target temperature and the calculated temperature for the extrusion nozzle.

FIG. 4 shows a method for fabricating conductive traces on a printed circuit board. In the above techniques, it is generally advantageous to have conductive traces with known resistance/temperature characteristics. While the shape and/or amount of copper in the traces may be calculated for a desired temperature/resistance relationship based on physical properties of the copper, it may be impractical to manufacture such traces within a desired tolerance. In particular, in current manufacturing techniques the width of traces may vary significantly (e.g., 10-15%) in a manner that introduces excess variability into resulting resistance, thus making width a poor manufacturing parameter for controlling resistance; however, the height of a layer may be usefully controlled during fabrication to obtain calibrated traces notwithstanding variable width. These and similar techniques are described below for fabricating circuit boards with traces having temperature/resistance characteristics meeting desired specifications.

As shown in step 402, the method 400 may begin with fabricating a printed circuit board including a through-hole for an extrusion nozzle and a mounting location adjacent to the through-hole shaped for a heating element. The printed circuit board may be fabricated using any suitable techniques, the variety of which are well known to those of ordinary skill in the art, and may include one layer, two layer, or other multi-layer circuit board fabrication techniques.

As shown in step 404, the method 400 may include adding a copper trace to the printed circuit board extending from a contact of the mounting location (for the heating element) to a contact for a power supply, which would typically be off the printed circuit board for high-power heating applications, but is not necessarily so.

As shown in step 406, the method 400 may include measuring a resistance of the copper trace using any measurement circuitry amenable to use in a PCB fabrication environment.

As shown in step 308, the method 400 may include modifying the copper trace to adjust the resistance toward a predetermined resistance. A variety of techniques may be used to make such modifications. In one aspect, this may include layering additional copper onto a pattern of the copper trace in order to decrease resistance per unit length. By closely controlling the amount of copper added, the increased thickness and resulting change in resistance may be accurately estimated. In one aspect, this may include maintaining a substantially constant temperature—that is, a temperature that will not change in a manner that affects the resistance measurement or the resulting resistance per unit length, either within measurement limits of the testing circuitry or design limits of the resulting conductive trace—while layering additional copper. Similarly, the temperature may be varied within some range such as an intended operating range over which linear behavior is desired. By concurrently modifying the copper trace and measuring the resistance, suitable results may be achieved in a single, continuous fabrication step.

Other techniques may also or instead be employed. For example, modifying the copper trace may include cutting the copper trace to a length corresponding to the predetermined resistance. A suitable length for cutting may be determined, e.g., based on the aggregate resistance (as measured) and known length of the copper trace. In another aspect, the copper trace may include a number of traces having, e.g., different lengths or thicknesses, and modifying the copper trace may include selectively coupling one or more of the plurality of traces having an aggregate resistance closest to the predetermined resistance to the contact of the mounting location and the contact for the power supply. The traces may, e.g., be connected in series, in parallel, or in any combination of these to obtain a desired lump resistance parameter at a specific temperature.

As shown in step 410, after modifications the resistance of the copper trace may be measured again.

As shown in step 412, the measured resistance may be compared to a target resistance. While the relationship of resistance to temperature may be estimated or measured, this step may be simplified by comparing a single measurement at a single temperature to a discrete target. Once the scalar target is achieved, a more complete characterization may be performed as desired for accuracy of performance. If the measured resistance matches the target resistance within some predetermined tolerance, then the method 400 may proceed to step 414. If the measured resistance is outside the predetermined tolerance, then the method 400 may return to step 408 where the copper trace is once again modified to bring the actual resistance closer to the target resistance.

As shown in step 414, any number of finishing steps may be performed. This may for example include assembling components on the printed circuit board for use as intended. This may also include measuring or otherwise characterizing a temperature/resistance relationship over some range (such as an intended operating range for the finished product), and encoding the relationship into firmware or the like on the printed circuit board to support subsequent calibrated operation of the finished product. More generally, any additional steps for accurately capturing the temperature/resistance relationship of the copper traces, using the temperature sensing capabilities of the finished product, or otherwise shipping and deploying the finished product may be performed.

FIG. 5 shows a heating element formed of a conductive trace. As noted above, the heating element may advantageously be formed from the same conductive trace used to measure temperature. As shown in FIG. 5, this heating element 500 may be formed of a material such as copper on a printed circuit board. While depicted as an octagonal spiral, any suitable geometry may be employed. In general, a first end 502 may be coupled to a current source and a second end 504 may be coupled to a ground (or vice versa). The second end 504 may terminate in an opening for an extrusion nozzle to pass through. The second end 504 may also include a via to another layer of the printed circuit board for a return path to the power source. A similar spiral shape may also be provided in one or more other layers of the printed circuit board (not shown) including the other layer that provides the return path. This arrangement advantageously removes the need for a separate, discrete heating element and permits the conductive trace to serve as both a temperature sensing circuit and a heating circuit on the same printed circuit board.

The methods or processes described above, and steps thereof, may be realized in hardware, software, or any combination of these suitable for a particular application. The hardware may include a general-purpose computer and/or dedicated computing device. The processes may be realized in one or more microprocessors, microcontrollers, embedded microcontrollers, programmable digital signal processors, or other programmable device, along with internal and/or external memory. The processes may also, or instead, be embodied in an application specific integrated circuit, a programmable gate array, programmable array logic, or any other device or combination of devices that may be configured to process electronic signals. It will further be appreciated that one or more of the processes may be realized as computer executable code created using a structured programming language such as C, an object oriented programming language such as C++, or any other high-level or low-level programming language (including assembly languages, hardware description languages, and database programming languages and technologies) that may be stored, compiled or interpreted to run on one of the above devices, as well as heterogeneous combinations of processors, processor architectures, or combinations of different hardware and software.

Thus, in one aspect, each method described above and combinations thereof may be embodied in computer executable code that, when executing on one or more computing devices, performs the steps thereof. In another aspect, the methods may be embodied in systems that perform the steps thereof, and may be distributed across devices in a number of ways, or all of the functionality may be integrated into a dedicated, standalone device or other hardware. In another aspect, means for performing the steps associated with the processes described above may include any of the hardware and/or software described above. All such permutations and combinations are intended to fall within the scope of the present disclosure.

It should further be appreciated that the methods above are provided by way of example. Absent an explicit indication to the contrary, the disclosed steps may be modified, supplemented, omitted, and/or re-ordered without departing from the scope of this disclosure.

The method steps of the invention(s) described herein are intended to include any suitable method of causing such method steps to be performed, consistent with the patentability of the following claims, unless a different meaning is expressly provided or otherwise clear from the context. So for example performing the step of X includes any suitable method for causing another party such as a remote user or a remote processing resource (e.g., a server or cloud computer) to perform the step of X. Similarly, performing steps X, Y and Z may include any method of directing or controlling any combination of such other individuals or resources to perform steps X, Y and Z to obtain the benefit of such steps.

While particular embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that various changes and modifications in form and details may be made therein without departing from the spirit and scope of this disclosure and are intended to form a part of the invention as defined by the following claims, which are to be interpreted in the broadest sense allowable by law.