PRINTED CIRCUIT BOARD WITH INTEGRATED TEMPERATURE SENSING
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.
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.