Abstract:
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.

Description:
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; and   an 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. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Although the scope of the present invention is much broader than any particular embodiment, a detailed description of the preferred embodiment follows together with illustrative figures, wherein like reference numerals refer to like components, and wherein: 
         FIG. 1  shows, in a schematic block diagram, a preferred implementation of the control system for use in connection with a plastic filament extruder of the present invention; 
         FIG. 2  shows, in a front isometric view, a plastic filament extruder as suitable for use of the control of system of  FIG. 1 ; 
         FIG. 3  shows, in a rear isometric view, the plastic filament extruder of  FIG. 2 ; 
         FIG. 4  shows, in a top plan view, the plastic filament extruder of  FIG. 2 ; 
         FIG. 5  shows, in a partially cut-away view taken through cut line  5 - 5  of  FIG. 4 , various details of the plastic filament extruder of  FIG. 2 , and wherein the auger and the die of the plastic filament extruder are not cut but rather shown in place in front elevational views; 
         FIG. 6  shows, in a partially cut-away detail view of the foremost positioned components of  FIG. 2 , various details of the conduit, auger and mold of the plastic filament extruder of  FIG. 2 ; and 
         FIGS. 7 through 11  show, in flowcharts, a preferred implementation of the method of operation in use of the control system for use in connection with a plastic filament extruder of the present invention, wherein: 
         FIG. 7  shows details of the implemented setup routine; 
         FIG. 8  shows details of the implemented monitor auger routine; 
         FIG. 9  shows details of the implemented establish temperature routine; 
         FIGS. 10A and 10B , which are to be taken together as a single figure and, collectively, are referred to herein as the single  FIG. 10 , show details of the implemented monitor temperature routine; and 
         FIG. 11  shows details of the implemented adjust target temperature subroutine. 
     
    
    
     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 to  FIG. 1  in particular, the preferred implementation of the control system  20  of the present invention is shown to generally comprise a temperature control module  21  and an integrated or associated voltage and current meter  37  operatively adapted to control various aspects of an extruder  43  of 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 to  FIGS. 2 and 3 , in particular, such an extruder  43  generally comprises a base  44  or frame upon which is mounted an auger body  45 , a tubular conduit  60  extending from the auger body  45  and dependently supported a mold  64 , and an electric drive motor  75  adapted to rotate an auger  55 , which as particular depicted in  FIGS. 4 through 6 , is provided to run from the auger body  45 , through the tubular conduit  60  and into an internal chamber  66  defined by the preferably aluminum main body  65  of the mold  64 . 
     As shown in  FIGS. 2 through 4 , a drive shaft  76  from the electric motor  75  is operatively coupled to a drive shaft  56  of the auger  55  through provided drive gears  77 ,  57 , respectively, or by any other substantially equivalent interconnection such as, for example, a sprocket and chain arrangement. In any case, as shown in  FIGS. 4 and 5 , the auger  55  is mounted generally within an internal chamber  50  of the auger body  45  with the screw  58  of the auger  55  extending through an outlet  52  from the internal chamber  50  leading to the conduit  60 , which is secured at its first, proximal end  61  within or about the outlet  52  from the internal chamber  50 . In order to fix the auger  55  operably in place, the auger body  45  is shown to comprise an axial through hole  54  or like bore though which the drive shaft  56  of 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 extruder  20  such as, for example, a thrust bearing fitted within a cylindrical shoulder  53  about the axial through hole  54  and drive shaft  56  adjacent to the internal chamber  50 . 
     To feed a supply of plastic chips into the internal chamber  50  of the auger body  45 , the auger body  45  also preferably comprises a hopper  46  having a chute  47  with open top  48  and terminating in an outlet  49  arranged atop and about an inlet  51  to the internal chamber  50 , as particularly depicted in  FIGS. 4 and 5 . As shown in the figures, the auger  55  and internal chamber internal chamber  50  of the auger body  45  are most preferably cooperatively adapted such that the screw  58  of the auger  55  substantially occupies the space defined by the internal chamber  50 . 
     Referring now to  FIGS. 5 and 6 , in particular, the second, distal end  62  of the tubular conduit  60  is shown to couple within or about an inlet  69  formed at a first end  67  of the main body  65  of the mold  64  and leading to the internal chamber  66  thereof. As also particularly shown in  FIGS. 5 and 6 , an extrudate shaping die  71 , which may preferably take the form of a selectively replaceable plug  72 , is affixed within an outlet  70  from the internal chamber  66  at a second end  68  of the main body  65  of the mold  64 . As shown in  FIGS. 2 and 5 , the die  71  comprises an axial through hole  73 , or aperture, therethrough which is sized as required to form the desired diameter plastic filament. In any case, as shown in  FIG. 6 , the auger is sized and positioned such that the distal end  59  of the screw  58  of the auger  55  (opposite the end of the auger  55  forming its drive shaft  56 ) terminates just short of the die  71 . In this manner, the auger is adapted to force plastic through the through hole  73  of the die as the plastic chips, introduced through the hopper  46  and conveyed by the auger  55  through the conduit  60  and into the mold  64 , are melted with the body  65  of the mold  64  by a band or like heater  74  operably provided about the body  65  of the mold  64 . 
     In an inventive aspect of the present invention, Applicant has noted that when the temperature of the body  65  of the mold  64  is of insufficient temperature for adequate melting of plastic therein backpressure within the internal chamber  66  and about the screw  58  of the auger will immediately result in an increased draw of electric current by the drive motor  75 . It is Applicant&#39;s inventive discovery that this effect can be utilized to implement an intrinsic feedback mechanism for operably controlling the target temperature of the body  65  of the mold  64  such that substantially uniform and suitable quality plastic filament may be readily had. With this in mind,  FIG. 1  is again referred to as depicting additional details of the exemplary implemented control system  20  of the present invention. 
     As shown in  FIG. 1 , the implemented temperature control module  21  of the control system  20  comprises a temperature control circuit  29  (or equivalent logic) for monitoring and controlling the temperature of the body  65  of the mold  64 . To this end, the temperature control circuit  29  comprises a temperature transducer  30  associated with and adapted to obtain the temperature of the body  65  of the mold  64  and a heater relay  31  adapted to switch power from a heater power source  32  in selective activation and deactivation of the band heater  74  about the body  65  of the mold  64 , which activation and deactivation thus takes place under the control of the implemented temperature control module  21 . 
     Likewise, an auxiliary control circuit  33  (or equivalent logic) is implemented as part of the temperature control module  21 . As part of the auxiliary control circuit  33 , a motor relay  34  is provided in connection with the drive motor  75  and adapted to switch power from a motor power source  35  in selective activation and deactivation of the drive motor  75 , which activation and deactivation also takes place under the control of the implemented temperature control module  21 . As will be better understood further herein, this feature of the present invention enables automatic deactivation of the motor  75  during periods where the measured temperature of the body  65  of the mold  64  is insufficient to allow a determined minimal flow of extrudate through the die  71 . 
     Finally, the implemented temperature control module  21  is shown to also preferably comprise means for user input  22  and means for display  26  of temperature data. In particular, the user input  22  is shown to comprise a menu key  23  or like button for accessing programming functions of the temperature control module as may be necessary or desired and increment and decrement keys  24 ,  25 , respectively, or like buttons for setting temperature values and/or other parameters accessed with the menu key  23 . In particular, the user input  22  is adapted for setting a target temperature for the heating of the body  65  of the mold  64 , which target temperature is preferably shown on the display  26  in a target value readout  27 . Likewise, the display  26  also preferably comprises a measured value readout  28  for showing the actual temperature of the body  65  of the mold  64  as monitored through the implemented temperature transducer  30 . 
     As also shown in  FIG. 1 , the combined voltage and current meter  37  of the control system  20  of the preferred implementation of the present invention comprises voltage and current transducer circuits  41 , which are operably interconnected with the power source  35  for the electric drive motor  75 . To this end, a current shunt  42  and other features are provided as necessary. In at least the most preferred implementations of the present invention, an amperage readout  39  is provided on an implemented display  38  for user monitoring of the electric current draw of the electric drive motor  75 . Although not critical for operation of the present invention, voltage transducer circuits and an associated voltage readout  39  are 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 system  20  of the present invention is adapted to enable a user to set initial operating parameters for the extruder  43  as well as to monitor the operation of the extruder  43  and/or adjust parameters during operation. That said, an exemplary mode of operation for the heretofore described control system  20  of the present invention is now described in detail with reference to  FIGS. 7 through 11 . 
     As shown in  FIG. 7 , the exemplary method of use of the control system  20  of the present invention generally begins with execution of a setup routine  78 , during which initial operating parameters may be set by the user and variables may be initialized. For example, upon beginning the routine (step  79 ) 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 body  65  of the mold  64 , is initially set to FALSE (step  80 ) to indicate normal operating conditions. Likewise, the initial target temperature for the body  65  of the mold  64  may be set by the user (step  81 ) based upon the user&#39;s evaluation of the material to be extruded. In cases where the control system  20  is adapted to autonomously adjust the target temperature of the body  65  of the mold  64  based upon the measured current draw of the electric drive motor  75 , the user may also set a expected nominal current draw (step  82 ), which like the initial target temperature may be determined based upon the user&#39;s evaluation of the material to be extruded. In any case, the setup routine terminates with the calling (step  83 ) of the establish temperature routine  89 . 
     Simultaneously with the beginning (step  79 ) the setup routing  78 , however, the exemplary control system  20  is programmed to also begin ( 85 ) a watchdog type monitor auger routine  85 , which operates to continuously monitor the electric current drawn by the electric drive motor  75  to immediately identify a current increase indicative of a low temperature condition at the body  65  of the mold  64 . As shown in  FIG. 8 , the monitor auger routine  85  operates in a repeat loop  86  where the measured current draw of the electric drive motor  75  is constantly evaluated to determine whether it exceeds a threshold value greater than the expected nominal value (step  87 ). If so, the needsAdjust variable is set to TRUE (step  88 ) for handling by the other routines as appropriate; if not, however, the repeat loop  86  simply continues. 
     Turning then to the establish temperature routine  89  as depicted in  FIG. 9 , the routing is shown to begin  90  (step  90 ) by first sending a signal (step  91 ) to activate the heater relay  31 . With the heater relay  31  activated, and the band heater  74  thus bringing the body  65  of the mold  64  up to the initial target temperature, the establish temperature routine  89  enters a repeat loop  92  to monitor this progress. Under operation of the routine  89 , the measured temperature of the body  65  of the mold  64  is continuously evaluated against the target temperature (step  93 ). Once the measured temperature of the body  65  of the mold  64  is found to exceed the target temperature, however, the routine  89  breaks out of the repeat loop  92 , sends a signal (step  94 ) to activate the motor relay  34 , thereby turning on the electric drive motor  75 , and terminates by calling (step  95 ) the monitor temperature routine  96 . 
     As shown in  FIG. 10 , the monitor temperature routine  96  begins (step  97 ) by entering a repeat loop  98  wherein the monitor temperature routine  96  ( a ) ensures that the auger  55  does not run under circumstances likely to jam its operation or damage the electric drive motor  75 ; (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 body  65  of the mold  64  within a range of temperatures established about the set target temperature. 
     In the first function of the monitor temperature routine  96 —ensuring that the auger  55  does not run under circumstances likely to jam its operation or damage the electric drive motor  75 —the monitor temperature routine  96  determines (step  99 ) whether the currently set target temperature of temperature of the body  65  of the mold  64  exceeds the actual (measured) temperature of the body  65  of the mold  64  by 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 body  65  of the mold  64 , as will be described in greater detail further herein. If so, indicating that the body  65  of the mold  64  is likely at a temperature less than that required for readily producing extrudate, the monitor temperature routine  96  sends a signal (step  100 ) to deactivate the motor relay  34 , thereby turning off the electric drive motor  75 ; sets the needsAdjust flag to FALSE (step  101 ), thereby ensuring that the flag is properly initialized to the expected condition upon a later restart of the electric drive motor  75 ; and terminates by calling (step  102 ) the establish temperature routine  89  to bring the body  65  of the mold  64  up to the target temperature. 
     If, on the other hand, it is determined (step  99 ) that the currently set target temperature of temperature of the body  65  of the mold  64  does not exceed the actual (measured) temperature of the body  65  of the mold  64  by greater than the maximum threshold value, the monitor temperature routine  96  proceeds to check the state (step  103 ) of the needsAdjust flag. If the flag is determined (step  103 ) to be TRUE, indicating that the monitor auger routine  85  has found that the measured current draw of the electric drive motor  75  has exceeded the expected nominal value by an amount greater than the maximum allowable threshold, the monitor temperature routine  96  calls (step  104 ) the adjust target temperature subroutine  110  to remedy the condition. 
     The adjust target temperature subroutine  110  begins (step  111 ) by first determining (step  112 ) an appropriate new target temperature for the body  65  of the mold  64 . 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 auger  55  to be deactivated (see step  99 ). In any case, the target temperature is then set (step  113 ) to the newly determined target temperature, which is automatically done by the temperature control module  21  in autonomous implementations or, in the case of manual intervention, by user action through the increment key  24  of the provided user input  22 . The needsAdjust flag is then reset (step  114 ) 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 auger  55  to be deactivated, and the adjust target temperature subroutine  110  returns (step  115 ) in place to the monitor temperature routine  96  where the repeat loop  98  continues. 
     If, on the other hand, the needsAdjust flag is determined (step  103 ) to be FALSE, indicating that the measured current draw of the electric drive motor  75  appropriate near the expected nominal current, the monitor temperature routine  96  continues with steps to maintain the actual (measured) temperature of the body  65  of the mold  64  within 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 extruder  43  according 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 routine  96  continues by determining (step  106 ) whether the actual (measured) temperature of the body  65  of the mold  64  exceeds and upper threshold value above the currently set target temperature of temperature of the body  65  of the mold  64 . If so, the monitor temperature routine  96  sends a signal (step  107 ) to deactivate the heater relay  31 , thereby turning off the band heater  74  about the body  65  of the mold  64 , and the monitor temperature routine  96  continues with the repeat loop  98 . On the other hand, if the monitor temperature routine  96  determines (step  106 ) that the actual (measured) temperature of the body  65  of the mold  64  does not exceed the upper threshold value above the currently set target temperature of temperature of the body  65  of the mold  64 , the monitor temperature routine  96  proceeds to determine (step  108 ) whether the currently set target temperature of temperature of the body  65  of the mold  64  exceeds a lower threshold above the actual (measured) temperature of the body  65  of the mold  64 . If so, the monitor temperature routine  96  sends a signal (step  109 ) to activate the heater relay  31 , thereby turning on the band heater  74  about the body  65  of the mold  64 , and the monitor temperature routine  96  simply continues with the repeat loop  98 . If not, the monitor temperature routine  96  continues with the repeat loop  98 . 
     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 module  21  of the control system  20  of the present invention preferably comprises an isolated power source  36  separate from the other implemented power sources, thereby ensuring that inductance or the like from the motor  75  do 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.