System and method for control of plastic filament extruder

A method for control of a plastic filament extruder includes the steps of providing a plastic filament extruder; introducing a quantity of plastic chips to the extruder; activating a heater to heat a mold body of the extruder to a target temperature; activating an electric motor in response to the mold body reaching the target temperature, thereby causing an auger to drive plastic chips the mold body and out of an extrudate sizing die; monitoring the electric current draw of the electric motor; and upwardly adjusting the target temperature of the mold body in response to a threshold increase in the electric current draw of the electric motor. Steps may also include maintaining the mold body within a temperature range about the target temperature and of deactivating the electric motor in response to the target temperature exceeding a threshold deviation above the temperature of the mold body.

FIELD OF THE INVENTION

The present invention relates to home, or hobby, manufacturing. More particularly, the invention relates to a system and method for controlling the molding temperature of a plastic filament extruder of the type used by hobbyist to produce plastic filament for use in additive manufacturing processes, known also as “3-D printing.”

BACKGROUND OF THE INVENTION

The art of additive manufacturing, also known as “3-D printing.” has in recent times advanced dramatically such that 3-D printers are now widely available for use by hobbyist manufacturers. As the availability of such machines has increased, however, so too has the desire of the home manufacturer to produce his or her own plastic filament for use in the machine. To do so, the home user will typically obtain plastic material from any available source, such as, for example, recycled plastic products. The obtained plastic material is then chopped, ground, sliced or otherwise formed into small plastic chips, whereafter the plastic chips are fed into a heated extrusion mold adapted to form the plastic into plastic filament sized for use in the additive manufacturing device.

Unfortunately, this simple sounding process is fraught with difficulty owing in large part to the lack of manufacturing control generally implemented in the hobbyist environment. Of particular issue is the fact that the raw plastic material obtained by the hobbyist will often comprise a mixture of plastics and, in many cases, will be of a composition that is not fully known to the hobbyist. As a result, it is extraordinarily difficult for the hobbyist to establish and maintain the proper mold temperature for producing plastic filament of quality acceptable for use in the 3-D printer. To be sure, the only method available to the hobbyist beyond initial assessment of the raw plastic material for setting a likely melting temperature is for the hobbyist to examine the extrudate emanating from the mold and then making temperature adjustments based on perceived quality.

While to foregoing method is the state of the art, Applicant has found it less than satisfactory. In particular, it is noted that the foregoing method only allows adjustment to be made after the source plastic material has fully traversed the mold, resulting in wasted time and to material. Additionally, and especially to the extent that it is to be expected that the hobbyist obtained raw plastic material will be an inconsistent mixture of plastic types and sizes, the foregoing method required painstaking attention, and often difficult to achieve skill, to continuously monitor the extrudate and make necessary temperature adjustments.

Given these serious shortcomings of the prior art, it is an overriding object of the present invention to improve generally over the prior art by providing a system and method for control of a plastic filament extruder that includes an intrinsic means for indicating to the user that a temperature adjustment is necessary.

Additionally, it is an object of the present invention to provide such a system and method for control of a plastic filament extruder that may also be implemented in an autonomous or semi-autonomous mode.

Still further, it is an object of the present invention to provide such a system and method for control of a plastic filament extruder that is readily adaptable to, or capable of integration with, otherwise conventionally available home extruders.

Finally, it is an object of the present invention to provide such a system and method for control of a plastic filament extruder that is relatively simple and inexpensive to implement, thereby ensuring that the improvements of the present invention are widely available to hobbyist manufacturers.

SUMMARY OF THE INVENTION

In accordance with the foregoing objects, the present invention—a method for control of a plastic filament extruder—generally comprises the steps of providing a plastic filament extruder comprising:an auger body having an internal chamber for collecting a quantity of plastic chips and a hopper adapted to feed collected plastic chips into the internal chamber of the auger body;a mold having a body defining an internal chamber, a heater adapted to heat the body and its internal chamber, and an extrudate shaping die positioned in an outlet from the internal chamber;a conduit extending from an outlet from the internal chamber of the auger body to an inlet to the internal chamber of mold body;an auger extending from the internal chamber of the auger body, through the conduit and into the internal chamber of the mold body; andan electric motor operatively adapted to drive rotation of the auger,
and thereafter introducing a quantity of plastic chips into the internal chamber of the auger body; activating the heater to heat the mold body to a target temperature; activating the electric motor in response to the mold body reaching the target temperature, thereby causing the auger to drive plastic chips from the internal chamber of the auger body into the internal chamber of the mold body and, as the plastic chips are melted within the internal chamber of the mold body, through the die; monitoring the electric current draw of the electric motor; and upwardly adjusting the target temperature of the mold body in response to a threshold increase in the electric current draw of the electric motor.

The method for control of a plastic filament extruder also most preferably comprises the further steps of maintaining the body of the mold within a temperature range about the target temperature and of deactivating the electric motor in response to the target temperature exceeding a threshold deviation above the temperature of the mold body. In at least some preferred implementations of the present invention, the step of upwardly adjusting the target temperature of the mold body is conducted autonomously without user intervention beyond initially establishing operating parameters for the system for control of a plastic filament extruder in which the method is conducted.

Finally, many other features, objects and advantages of the present invention will be apparent to those of ordinary skill in the relevant arts, especially in light of the foregoing discussions and the following drawings, exemplary detailed description and appended claims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Although those of ordinary skill in the art will readily recognize many alternative embodiments, especially in light of the illustrations provided herein, this detailed description is exemplary of the preferred embodiment of the present invention, the scope of which is limited only by the claims appended hereto.

Referring now to the figures, and toFIG. 1in particular, the preferred implementation of the control system20of the present invention is shown to generally comprise a temperature control module21and an integrated or associated voltage and current meter37operatively adapted to control various aspects of an extruder43of the type typically utilized by hobbyists to produce plastic filament for use in home use additive manufacturing machines, commonly referred to as “3-D printers.” Referring now toFIGS. 2 and 3, in particular, such an extruder43generally comprises a base44or frame upon which is mounted an auger body45, a tubular conduit60extending from the auger body45and dependently supported a mold64, and an electric drive motor75adapted to rotate an auger55, which as particular depicted inFIGS. 4 through 6, is provided to run from the auger body45, through the tubular conduit60and into an internal chamber66defined by the preferably aluminum main body65of the mold64.

As shown inFIGS. 2 through 4, a drive shaft76from the electric motor75is operatively coupled to a drive shaft56of the auger55through provided drive gears77,57, respectively, or by any other substantially equivalent interconnection such as, for example, a sprocket and chain arrangement. In any case, as shown inFIGS. 4 and 5, the auger55is mounted generally within an internal chamber50of the auger body45with the screw58of the auger55extending through an outlet52from the internal chamber50leading to the conduit60, which is secured at its first, proximal end61within or about the outlet52from the internal chamber50. In order to fix the auger55operably in place, the auger body45is shown to comprise an axial through hole54or like bore though which the drive shaft56of the auger extends. Although, for clarity, not shown in the figures, those of ordinary skill in the art will readily recognize that other features should be and are implemented to promote smooth operation of the extruder20such as, for example, a thrust bearing fitted within a cylindrical shoulder53about the axial through hole54and drive shaft56adjacent to the internal chamber50.

To feed a supply of plastic chips into the internal chamber50of the auger body45, the auger body45also preferably comprises a hopper46having a chute47with open top48and terminating in an outlet49arranged atop and about an inlet51to the internal chamber50, as particularly depicted inFIGS. 4 and 5. As shown in the figures, the auger55and internal chamber internal chamber50of the auger body45are most preferably cooperatively adapted such that the screw58of the auger55substantially occupies the space defined by the internal chamber50.

Referring now toFIGS. 5 and 6, in particular, the second, distal end62of the tubular conduit60is shown to couple within or about an inlet69formed at a first end67of the main body65of the mold64and leading to the internal chamber66thereof. As also particularly shown inFIGS. 5 and 6, an extrudate shaping die71, which may preferably take the form of a selectively replaceable plug72, is affixed within an outlet70from the internal chamber66at a second end68of the main body65of the mold64. As shown inFIGS. 2 and 5, the die71comprises an axial through hole73, or aperture, therethrough which is sized as required to form the desired diameter plastic filament. In any case, as shown inFIG. 6, the auger is sized and positioned such that the distal end59of the screw58of the auger55(opposite the end of the auger55forming its drive shaft56) terminates just short of the die71. In this manner, the auger is adapted to force plastic through the through hole73of the die as the plastic chips, introduced through the hopper46and conveyed by the auger55through the conduit60and into the mold64, are melted with the body65of the mold64by a band or like heater74operably provided about the body65of the mold64.

In an inventive aspect of the present invention, Applicant has noted that when the temperature of the body65of the mold64is of insufficient temperature for adequate melting of plastic therein backpressure within the internal chamber66and about the screw58of the auger will immediately result in an increased draw of electric current by the drive motor75. It is Applicant's inventive discovery that this effect can be utilized to implement an intrinsic feedback mechanism for operably controlling the target temperature of the body65of the mold64such that substantially uniform and suitable quality plastic filament may be readily had. With this in mind,FIG. 1is again referred to as depicting additional details of the exemplary implemented control system20of the present invention.

As shown inFIG. 1, the implemented temperature control module21of the control system20comprises a temperature control circuit29(or equivalent logic) for monitoring and controlling the temperature of the body65of the mold64. To this end, the temperature control circuit29comprises a temperature transducer30associated with and adapted to obtain the temperature of the body65of the mold64and a heater relay31adapted to switch power from a heater power source32in selective activation and deactivation of the band heater74about the body65of the mold64, which activation and deactivation thus takes place under the control of the implemented temperature control module21.

Likewise, an auxiliary control circuit33(or equivalent logic) is implemented as part of the temperature control module21. As part of the auxiliary control circuit33, a motor relay34is provided in connection with the drive motor75and adapted to switch power from a motor power source35in selective activation and deactivation of the drive motor75, which activation and deactivation also takes place under the control of the implemented temperature control module21. As will be better understood further herein, this feature of the present invention enables automatic deactivation of the motor75during periods where the measured temperature of the body65of the mold64is insufficient to allow a determined minimal flow of extrudate through the die71.

Finally, the implemented temperature control module21is shown to also preferably comprise means for user input22and means for display26of temperature data. In particular, the user input22is shown to comprise a menu key23or like button for accessing programming functions of the temperature control module as may be necessary or desired and increment and decrement keys24,25, respectively, or like buttons for setting temperature values and/or other parameters accessed with the menu key23. In particular, the user input22is adapted for setting a target temperature for the heating of the body65of the mold64, which target temperature is preferably shown on the display26in a target value readout27. Likewise, the display26also preferably comprises a measured value readout28for showing the actual temperature of the body65of the mold64as monitored through the implemented temperature transducer30.

As also shown inFIG. 1, the combined voltage and current meter37of the control system20of the preferred implementation of the present invention comprises voltage and current transducer circuits41, which are operably interconnected with the power source35for the electric drive motor75. To this end, a current shunt42and other features are provided as necessary. In at least the most preferred implementations of the present invention, an amperage readout39is provided on an implemented display38for user monitoring of the electric current draw of the electric drive motor75. Although not critical for operation of the present invention, voltage transducer circuits and an associated voltage readout39are readily, and therefore desirably, implemented. As will be appreciated by those of ordinary skill in the art, the availability of voltage information may be very helpful in troubleshooting malfunctions and/or ensuring, for example, that an implemented constant voltage power source is not tasked beyond capacity.

In any case, as will be better appreciated further herein, the control system20of the present invention is adapted to enable a user to set initial operating parameters for the extruder43as well as to monitor the operation of the extruder43and/or adjust parameters during operation. That said, an exemplary mode of operation for the heretofore described control system20of the present invention is now described in detail with reference toFIGS. 7 through 11.

As shown inFIG. 7, the exemplary method of use of the control system20of the present invention generally begins with execution of a setup routine78, during which initial operating parameters may be set by the user and variables may be initialized. For example, upon beginning the routine (step79) as shown in the figure a needsAdjust variable, which, as will be better understood further herein is utilized to indicate that a low temperature condition exists at the body65of the mold64, is initially set to FALSE (step80) to indicate normal operating conditions. Likewise, the initial target temperature for the body65of the mold64may be set by the user (step81) based upon the user's evaluation of the material to be extruded. In cases where the control system20is adapted to autonomously adjust the target temperature of the body65of the mold64based upon the measured current draw of the electric drive motor75, the user may also set a expected nominal current draw (step82), which like the initial target temperature may be determined based upon the user's evaluation of the material to be extruded. In any case, the setup routine terminates with the calling (step83) of the establish temperature routine89.

Simultaneously with the beginning (step79) the setup routing78, however, the exemplary control system20is programmed to also begin (85) a watchdog type monitor auger routine85, which operates to continuously monitor the electric current drawn by the electric drive motor75to immediately identify a current increase indicative of a low temperature condition at the body65of the mold64. As shown inFIG. 8, the monitor auger routine85operates in a repeat loop86where the measured current draw of the electric drive motor75is constantly evaluated to determine whether it exceeds a threshold value greater than the expected nominal value (step87). If so, the needsAdjust variable is set to TRUE (step88) for handling by the other routines as appropriate; if not, however, the repeat loop86simply continues.

Turning then to the establish temperature routine89as depicted inFIG. 9, the routing is shown to begin90(step90) by first sending a signal (step91) to activate the heater relay31. With the heater relay31activated, and the band heater74thus bringing the body65of the mold64up to the initial target temperature, the establish temperature routine89enters a repeat loop92to monitor this progress. Under operation of the routine89, the measured temperature of the body65of the mold64is continuously evaluated against the target temperature (step93). Once the measured temperature of the body65of the mold64is found to exceed the target temperature, however, the routine89breaks out of the repeat loop92, sends a signal (step94) to activate the motor relay34, thereby turning on the electric drive motor75, and terminates by calling (step95) the monitor temperature routine96.

As shown inFIG. 10, the monitor temperature routine96begins (step97) by entering a repeat loop98wherein the monitor temperature routine96(a) ensures that the auger55does not run under circumstances likely to jam its operation or damage the electric drive motor75; (b) executes any adjustment of the target temperature indicated as necessary by the needsAdjust flag; and (c) attempts to maintain the actual (measured) temperature of the body65of the mold64within a range of temperatures established about the set target temperature.

In the first function of the monitor temperature routine96—ensuring that the auger55does not run under circumstances likely to jam its operation or damage the electric drive motor75—the monitor temperature routine96determines (step99) whether the currently set target temperature of temperature of the body65of the mold64exceeds the actual (measured) temperature of the body65of the mold64by greater than a maximum threshold value. As will be appreciated by those of ordinary skill in the art in light of this exemplary description, this condition will generally only result following an upward adjustment of the target temperature for the body65of the mold64, as will be described in greater detail further herein. If so, indicating that the body65of the mold64is likely at a temperature less than that required for readily producing extrudate, the monitor temperature routine96sends a signal (step100) to deactivate the motor relay34, thereby turning off the electric drive motor75; sets the needsAdjust flag to FALSE (step101), thereby ensuring that the flag is properly initialized to the expected condition upon a later restart of the electric drive motor75; and terminates by calling (step102) the establish temperature routine89to bring the body65of the mold64up to the target temperature.

If, on the other hand, it is determined (step99) that the currently set target temperature of temperature of the body65of the mold64does not exceed the actual (measured) temperature of the body65of the mold64by greater than the maximum threshold value, the monitor temperature routine96proceeds to check the state (step103) of the needsAdjust flag. If the flag is determined (step103) to be TRUE, indicating that the monitor auger routine85has found that the measured current draw of the electric drive motor75has exceeded the expected nominal value by an amount greater than the maximum allowable threshold, the monitor temperature routine96calls (step104) the adjust target temperature subroutine110to remedy the condition.

The adjust target temperature subroutine110begins (step111) by first determining (step112) an appropriate new target temperature for the body65of the mold64. While the new temperature may be a fixed or percentage value greater than the currently set target temperature; a value determined based on a formula whereby, for example, a more extreme, rapid or like deviation in current results in a greater increase in target temperature; or any equivalent calculation, it is noted that in autonomous implementations of this feature it is desired that the new temperature be a temperature sufficiently greater than the previously set target temperature as to cause the auger55to be deactivated (see step99). In any case, the target temperature is then set (step113) to the newly determined target temperature, which is automatically done by the temperature control module21in autonomous implementations or, in the case of manual intervention, by user action through the increment key24of the provided user input22. The needsAdjust flag is then reset (step114) to FALSE, accounting for a situation in which the new temperature is not a temperature sufficiently greater than the previously set target temperature as to cause the auger55to be deactivated, and the adjust target temperature subroutine110returns (step115) in place to the monitor temperature routine96where the repeat loop98continues.

If, on the other hand, the needsAdjust flag is determined (step103) to be FALSE, indicating that the measured current draw of the electric drive motor75appropriate near the expected nominal current, the monitor temperature routine96continues with steps to maintain the actual (measured) temperature of the body65of the mold64within a range of temperatures established about the set target temperature. At this juncture, it should be noted that any number of techniques or algorithms may be implemented in fulfillment of this requirement. For example, at one end of the spectrum, the upper and lower threshold values discussed below may simply be set at absolute value of percentage deviations from the target temperature value or, at the other end of the spectrum, advanced algorithms such as implemented in the well-known proportional-integer-derivative (“PID”) type controllers may be utilized. In any case, the following exemplary only discussion is intended to describe the integration of this feature with the extruder43according to the preferred methods of the present invention.

With the foregoing in mind, and recognizing that the following steps may to some extend be reordered, the exemplary implementation of the monitor temperature routine96continues by determining (step106) whether the actual (measured) temperature of the body65of the mold64exceeds and upper threshold value above the currently set target temperature of temperature of the body65of the mold64. If so, the monitor temperature routine96sends a signal (step107) to deactivate the heater relay31, thereby turning off the band heater74about the body65of the mold64, and the monitor temperature routine96continues with the repeat loop98. On the other hand, if the monitor temperature routine96determines (step106) that the actual (measured) temperature of the body65of the mold64does not exceed the upper threshold value above the currently set target temperature of temperature of the body65of the mold64, the monitor temperature routine96proceeds to determine (step108) whether the currently set target temperature of temperature of the body65of the mold64exceeds a lower threshold above the actual (measured) temperature of the body65of the mold64. If so, the monitor temperature routine96sends a signal (step109) to activate the heater relay31, thereby turning on the band heater74about the body65of the mold64, and the monitor temperature routine96simply continues with the repeat loop98. If not, the monitor temperature routine96continues with the repeat loop98.

While the foregoing description is exemplary of the preferred embodiment of the present invention, those of ordinary skill in the relevant arts will recognize the many variations, alterations, modifications, substitutions and the like as are readily possible, especially in light of this description, the accompanying drawings and claims drawn thereto. For example, those of ordinary skill in the art will recognize that the temperature control module21of the control system20of the present invention preferably comprises an isolated power source36separate from the other implemented power sources, thereby ensuring that inductance or the like from the motor75do not interfere with the operation of the implemented circuitry. In any case, because the scope of the present invention is much broader than any particular embodiment, the foregoing detailed description should not be construed as a limitation of the scope of the present invention, which is limited only by the claims appended hereto.