CN109465945B - Slurry extrusion device based on micro-flow extrusion process and control method thereof - Google Patents

Slurry extrusion device based on micro-flow extrusion process and control method thereof Download PDF

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Publication number
CN109465945B
CN109465945B CN201910006537.1A CN201910006537A CN109465945B CN 109465945 B CN109465945 B CN 109465945B CN 201910006537 A CN201910006537 A CN 201910006537A CN 109465945 B CN109465945 B CN 109465945B
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speed
extrusion
slurry
control module
pressure
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CN109465945A (en
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段国林
刘志鹏
周婧
蔡瑾
张静
夏晓光
王安邦
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Hebei University of Technology
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Hebei University of Technology
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B28—WORKING CEMENT, CLAY, OR STONE
    • B28B—SHAPING CLAY OR OTHER CERAMIC COMPOSITIONS; SHAPING SLAG; SHAPING MIXTURES CONTAINING CEMENTITIOUS MATERIAL, e.g. PLASTER
    • B28B1/00—Producing shaped prefabricated articles from the material
    • B28B1/001—Rapid manufacturing of 3D objects by additive depositing, agglomerating or laminating of material
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y10/00—Processes of additive manufacturing
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y30/00—Apparatus for additive manufacturing; Details thereof or accessories therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B33—ADDITIVE MANUFACTURING TECHNOLOGY
    • B33Y—ADDITIVE MANUFACTURING, i.e. MANUFACTURING OF THREE-DIMENSIONAL [3-D] OBJECTS BY ADDITIVE DEPOSITION, ADDITIVE AGGLOMERATION OR ADDITIVE LAYERING, e.g. BY 3-D PRINTING, STEREOLITHOGRAPHY OR SELECTIVE LASER SINTERING
    • B33Y50/00—Data acquisition or data processing for additive manufacturing
    • B33Y50/02—Data acquisition or data processing for additive manufacturing for controlling or regulating additive manufacturing processes

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Ceramic Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Feedback Control In General (AREA)
  • Coating Apparatus (AREA)

Abstract

The invention relates to a slurry extrusion device based on a micro-flow extrusion process and a control method thereof. The device comprises a base, a stepping electric cylinder, a pressure sensor and an injector; a stepping electric cylinder is fixed above the front surface of the base, and a pressure sensor is fixed at the bottom center of a push rod of the stepping electric cylinder through a buckle; the lower part of the base is fixed with a round clamping sleeve through a screw; the injector is fixed through a round cutting sleeve; the stepping electric cylinder push rod, the button-type pressure sensor and the injector are coaxial from top to bottom. According to the invention, the extrusion speed of the slurry and the scanning speed of the forming platform in the printing process can be matched on line according to the algorithm set forth in the extrusion speed/scanning speed matching mechanism control module, and meanwhile, the stable wire output speed in the extrusion printing process is ensured by utilizing the algorithm set forth in the pressure stability control module in the storage device, so that the printing forming precision is improved.

Description

Slurry extrusion device based on micro-flow extrusion process and control method thereof
Technical Field
The invention belongs to the technical field of additive manufacturing rapid prototyping manufacturing, and particularly relates to a control system of an additive manufacturing slurry extrusion device based on a microfluidic extrusion process.
Background
In the technical field of additive manufacturing rapid prototyping, printing materials have limited the development of new printing technologies. Common 3D printing manufacturing techniques include fused deposition, photo-curing, etc., and if small ceramic products such as ceramic dentures, ceramic parts, etc. are to be manufactured, zirconia ceramic slurries can be prepared, and the zirconia ceramic slurries are stacked layer by layer to form the final required 3D printed product. This process of extruding the slurry through a minute flow channel and stacking and forming the slurry layer by layer is called a micro-flow extrusion process. The additive manufacturing technology based on the micro-flow extrusion process is suitable for printing paste slurry, the molding principle is similar to that of the FDM process, materials are extruded through micro flow channels, and are piled and accumulated layer by layer on a X, Y plane, so that a target product is finally formed. In the extrusion molding control system at the present stage, the control module is mainly composed of a mechanical motion driving module, a pressure control module, a communication module, a display driving module, a data processing module based on Marlin firmware and the like, and in the system operation process, the mechanical motion driving module controls a mechanism to move, the pressure control module controls the internal pressure of the extrusion device, and all the control modules are relatively independent and do not perform cooperative control. In the additive manufacturing and forming process based on the micro-flow extrusion process, the extrusion speed of printing slurry often fluctuates, so that the phenomenon of unstable extrusion speed is caused; meanwhile, the sizing agent is often not continuously and continuously attached to the forming platform. If the scanning speed is far greater than the extrusion speed of the sizing agent, the sizing agent extruded by the extrusion device cannot be filled on the corresponding printing path in time, so that a wiredrawing phenomenon is caused; if the scanning speed is far less than the extrusion speed of the slurry, the slurry extruded by the extrusion device will tend to cause slurry accumulation in the X, Y plane direction, and the printing precision of the molded part is affected.
In summary, the problems in the prior art are: the slurry extrusion device cannot have stable extrusion speed, the scanning speed of the printing device cannot be matched with the extrusion speed of the extrusion device in time, fluctuation of slurry extrusion speed change cannot be avoided in the process of speed matching, so that a slurry extrusion device control system is urgently needed in additive manufacturing equipment based on a micro-flow extrusion process, the extrusion speed of the extrusion device is ensured to be stable, the extrusion speed of the slurry is automatically updated according to the scanning speed of a printer, and the slurry is extruded continuously and stably by the extrusion device in the process of speed matching update through cooperative adjustment of various control modules, and the ideal goal of avoiding large fluctuation of the slurry extrusion speed is finally achieved.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a control system of an additive manufacturing slurry extrusion device based on a micro-flow extrusion process. The slurry extrusion system mainly comprises a pressure stabilization control module in the storage device, an extrusion speed/scanning speed matching decision control module, a slurry extrusion initial speed setting module and an interrupt priority setting mechanism, wherein the pressure stabilization module in the storage device and the extrusion speed/scanning speed matching decision control module are core modules of the control system. The system introduces a slurry extrusion speed/printer scanning speed matching decision control module based on the traditional micro-flow extrusion process additive manufacturing equipment control system module, and the increase of the module makes up the problem that the current extrusion control system cannot match the slurry extrusion speed and the scanning speed in real time, and reduces the influence of the reduction of the precision of a formed part caused by material accumulation or wire drawing in the printing and forming process. The system optimizes the extruder pressure control module, so that the extrusion device pressure control module and the extrusion speed/scanning speed matching decision control module realize complementary adjustment, and the extrusion speed of the extrusion device is updated in the speed matching module, and then the internal pressure of the extrusion device is quickly adjusted to a stable state through the pressure control module.
The technical scheme of the invention is as follows:
the slurry extrusion device based on the micro-flow extrusion process comprises a base, a stepping electric cylinder, a pressure sensor and an injector;
a stepping electric cylinder is fixed above the front surface of the base, and a pressure sensor is fixed at the bottom center of a push rod of the stepping electric cylinder through a buckle; the lower part of the base is fixed with a round clamping sleeve through a screw; the injector is fixed through a round cutting sleeve; the stepping electric cylinder push rod, the button-type pressure sensor and the injector are coaxial from top to bottom.
The additive manufacturing device comprises a slurry extrusion device, a support column, a Z-axis sliding block, a Z-axis guide rail, a forming platform, an X-axis sliding block, an X-axis guide rail, a Y-axis double sliding block, a Y-axis double guide rail and a base;
the middle part of the rear side of the base is fixed with a supporting column, and the upper part of the supporting column is fixed with a Z-axis guide rail; a Z-axis sliding block is arranged on the Z-axis guide rail, and a slurry extrusion device is fixed on the Z-axis sliding block; the 2Y-axis guide rails are parallel and perpendicular to the bottom edge of the base; each Y-axis guide rail is provided with 1Y-axis sliding block; the lower parts of the two ends of the X-axis guide rail are respectively connected with 1Y-axis sliding block; an X-axis sliding block is arranged on the X-axis guide rail; a forming platform is arranged on the X-axis sliding block; the X-axis guide rail, the Y-axis double guide rail and the Z-axis guide rail are respectively provided with a driving motor; the base in the slurry extrusion device is fixed on the Z-axis sliding block.
The control method of the slurry extrusion device based on the micro-flow extrusion process comprises the following steps:
step 1: setting interrupt priority of each module, completing initialization of the interrupt priority, starting a slurry extrusion device, and immediately running the system;
wherein, the interrupt priority level is set from high to low as follows: the speed matching decision control module and the internal pressure stability control module of the storage device;
step 2: setting an extrusion feeding initial speed v (r/s), and driving a stepping electric cylinder to reach the initial speed v;
wherein, the initial extrusion speed of the paste is required to correspond to different initial rotation speeds of the stepping electric cylinder, and the target paste extrusion speed is v 0 ，v 0 According to the requirement of the user on the printing efficiency, according to the formula,
wherein A is 0 To the cross section of the extrusion headProduct (unit mm) 2 )；
A P Is the cross section area (unit mm) of the charging barrel 2 )；
P h Leads (unit mm/r) of stepping electric cylinders;
obtaining the initial rotation speed v of the stepping motor cylinder, and extruding the required target slurry at the speed v during operation 0 The ceramic slurry is configured to a PC, the PC automatically generates an initial rotating speed v (r/s) of the stepping electric cylinder according to a formula (1), the rotating speed of the stepping electric cylinder is driven to reach v by a stepping motor driver, and at the moment, a pushing rod of the stepping electric cylinder pushes a plunger pushing rod of the injector to extrude the ceramic slurry in the storage device;
Step 3: pushing a push rod of the storage device at the extrusion feeding initial speed set in the step 2, and enabling the pressure sensor to be in contact with the plunger push rod of the injector, so that the pressure born by the pressure sensor is approximately equivalent to the internal pressure of the storage device; the system collects the internal pressure information of the storage device in real time and feeds back, records the pressure deviation of the first 20 sampling periods, and numbers the pressure deviation as e 0 、e 1 、e 2 ...e 18 、e 19 The method comprises the steps of carrying out a first treatment on the surface of the The setting of the sampling period T is determined according to the required corresponding frequency, and the recommended sampling period is as follows:the sampling period T is set here to 100ms;
the slurry in the storage device is continuously extruded under positive pressure, the deviation of the pressure information data of the first 20 sampling periods stored in the memory is obtained, and the record is marked as e 0 、e 1 、e 2 ...e 18 、e 19 ，
Wherein e 0 ＝P 1 -P 0 、e 1 ＝P 2 -P 1 、e 2 ＝P 3 -P 2 ...e 19 ＝P 20 -P 19 (2)
Step 4: important judgment of sampling pressure deviation e 15 、e 16 、e 17 、e 18 、e 19 Whether within + -5;
comparing whether the pressure deviation is in the following orderWithin the set stable range + -5, and the sampling pressure deviation e is compared with the emphasis 15 、e 16 、e 17 、e 18 、e 19 Whether or not within + -5, and when the pressure deviation e 15 、e 16 、e 17 、e 18 、e 19 The pressure deviation is considered to be within a stable range within +/-5, and the slurry extrusion process is continued;
if the recorded pressure deviation value is not within + -5, and the pressure deviation e is sampled 15 、e 16 、e 17 、e 18 、e 19 If the voltage is more than 5, the phenomenon of blocking or wire breakage in the paste extrusion process is considered, the enabling pin of the stepping electric cylinder driving module is set to be low from high level, the operation of the stepping electric cylinder is interrupted, and the paste extrusion action is suspended; resetting the slurry extrusion speed, increasing the extrusion speed by 10r/s, comparing whether the sampling pressure real-time deviation e is within +/-5, and repeating the step 4; repeating for 2-3 times, and finishing the printing of the skirt edge at the stage; transferring to entity printing;
Step 5: the slurry extrusion device performs entity printing, extracts scanning speed information and judges whether the scanning speed of the printer is changed or not;
the translation of the G-code is carried out, firstly, the character F is identified, and the data after the character F is recorded as v 0 、v 1 、v k 、v k+1 Storing and realizing extraction of scanning speed information; judging whether the scanning speed of the front and back paths is changed, if so, the scanning speed v of the front path k Scan speed v not equal to the path of the next segment k+1 Then entering a speed matching decision control module, and then entering an internal pressure stabilizing control module of the storage device; if the scanning speed is unchanged, the scanning speed v of the previous path is higher than the scanning speed v k Equal to the scanning speed v of the next path k+1 Then the pressure stabilizing control module enters the internal of the storage device;
when entering the speed matching decision control module:
step (1): the scanning speed being changed (i.e. v k ≠v k+1 ) Speed matching decision control moduleOutputting an interrupt request;
the speed matching decision control module sends an interrupt request, the interrupt priority level of the speed matching decision control module is higher than that of the pressure stabilizing control module in the storage device, and the speed matching decision control module preferentially executes actions;
After the device to be processed enters the stable slurry extrusion process, the internal pressure stability control module of the storage device continuously maintains the internal pressure stability of the device to be processed, and when the scanning speed is changed within a stability threshold value + -5 as described below, the step (1) is executed, and at the moment, the operation executed by the internal pressure stability control module of the storage device is suspended;
step (2): the speed matching decision control module updates the slurry extrusion speed;
the speed matching decision control module extracts a new scanning speed in the memory and marks the new scanning speed as v k According to the formula
Wherein v is P ' is the linear feed rate (unit mm/s) of the slurry extrusion,
x P for stepping the electric cylinder push rod feed movement distance (unit mm),
t 0 for the time of the push rod movement of the stepping electric cylinder (unit s),
L 0 the distance (in mm) for the X, Y stepper motor,
A 0 is the cross-sectional area (unit mm) of the extrusion needle 2 )，
A 1 Is the cross-sectional area (unit mm) of the storage cylinder 2 )，
Updating the paste extrusion speed v P ', and v P ' store to memory;
step (3): according to the updated paste extrusion speed v P ' update and adjust the rotation speed v of the stepping electric cylinder, reassign the rotation speed v ' of the stepping electric cylinder to obtain updated rotation speed v ' of the stepping electric cylinder, and adjust the rotation speed;
wherein the rotating speed v' of the stepping electric cylinder is according to the formula
Wherein v' is the rotational speed (unit r/s) of the stepping electric cylinder,
v P ' is the linear feed rate (unit mm/s) of the slurry extrusion,
P h for a stepping motor cylinder lead (unit mm/r),
calculating, re-assigning the rotating speed v of the stepping electric cylinder to enable v=v', driving the stepping electric cylinder to adjust the rotating speed to reach a new target rotating speed v, and completing the step of speed matching;
step (4): finishing speed matching, jumping out of the speed matching decision control module, transferring to a pressure stabilization control module in the material forming device, and controlling the pressure in the material storage device to be stabilized within a recommended value +/-5 range;
when entering the internal pressure stability control module of the storage device:
step (1): the internal pressure stabilization control module of the storage device extracts pressure information and stores the pressure information in an internal cache;
the pressure stabilizing control module enters the storage device, at the moment, the pressure values before and after each sampling period are read and stored in a buffer memory, and the pressure values are recorded as P k And P k+1 。
Step (2): calculating internal pressure deviation e of storage device F (k) Variation Δe from internal pressure F (k)；
Internal pressure deviation e of storage device F (k)＝P k+1 -P k ，
Wherein P is k 、P k+1 Respectively measuring pressure data before and after a sampling period;
the pressure deviation variation in the storage device is represented by the formula delta e F (k)＝e F (k+1)-e F (k)，
Wherein e F (k)、e F (k+1) is the internal pressure obtained after each sampling period is completedForce bias.
Step (3): for internal pressure deviation e of storage device F (k) Variation Δe from internal pressure F (k) Carrying out fuzzification treatment;
wherein the blurring process is that let e F (k) And delta e F (k) Respectively multiplied by quantization factorsAnd->Obtaining e F (k) And delta e F (k) Fuzzy variables in the Fuzzy subsets respectively;
step (4): fuzzy reasoning is carried out to obtain fuzzy output variable delta K by reasoning P 、ΔK I 、ΔK D Performing defuzzification processing on the fuzzy output variable;
wherein, the fuzzy inference engine infers a corresponding fuzzy output variable delta K according to the fuzzy control parameter rule table and the fuzzy input variable P 、ΔK I 、ΔK D ；
Step (5): receiving actual output parameters DeltaK according to a conventional PID controller P 、ΔK I 、ΔK D Performing incremental PID control operation to obtain the output adjustment quantity delta u (k) of the fuzzy PID parameter from the setting pressure control module;
the traditional PID controller receives the actual variable delta K of the control parameter obtained in the last step (4) P 、ΔK I 、ΔK D And for initial control parameter K P 、K I 、K D Re-assigning the value of (C) to K P ＝K P +ΔK P ，K I ＝K I +ΔK I ，K D ＝K D +ΔK D ；
By utilizing the incremental PID control law,
Δu(k)＝q 0 e(k)+q 1 e(k-1)+q 2 e(k-2) (5)
wherein q 0 ＝K P (1+K I +K D )，
q 1 ＝-K P (1+2K D )，
q 2 ＝K P K D ，
e (k), e (k-1), e (k-2) are the pressure deviations stored in the memory,
obtaining a final fuzzy PID parameter self-tuning controller output variable Deltau (k);
Step (6): judging the positive and negative of a variable Deltau (k) output by the fuzzy PID parameter self-tuning control module, and if Deltau (k) is more than or equal to 0, increasing the rotating speed of the stepping electric cylinder of the slurry extrusion device; if Deltau is less than or equal to 0, the rotating speed of the stepping motor cylinder of the slurry extruding device is reduced;
step (7): judging the pressure deviation e in the next sampling period F (k+1) whether or not it is within a set threshold;
wherein the threshold is set within + -5 or + -10;
step 6: identifying a printing end mark character string in the G-code, and judging whether the printing process is ended or not;
if the character string is not recognized to appear, stopping slurry extrusion and closing each shaft stepping motor, returning to the step 5, and repeatedly executing the step 5; if the character string of 'stop paste extrusion and turn off each shaft stepping motor' is recognized, the stepping motor cylinder is disabled, the paste extrusion control system is jumped out, and the printing process is finished.
The beneficial effects of the invention are as follows:
in the control system of the additive manufacturing slurry extrusion device based on the micro-flow extrusion process, the system can carry out online matching on the extrusion speed of the slurry and the scanning speed (the moving speed in the X, Y direction) of the forming platform in the printing process according to the algorithm set forth in the extrusion speed/scanning speed matching control module. The speed matching decision control module judges whether the scanning speed changes in the printing process, if so, an interrupt request is sent, the speed matching module has higher interrupt priority and the matching of the extrusion speed/the scanning speed is preferentially carried out, the matching requirement is that the rotating speed of a stepping electric cylinder of the extrusion device is changed to a target value, an interrupt signal disappears after the operation is finished, the internal pressure of a charging barrel is perceived to change by the internal pressure control module of the storage device, the rotating speed of the stepping electric cylinder is regulated in a small range by the fuzzy PID parameter of the internal pressure control module of the storage device from the setting controller, so that the pressure of the charging barrel is stabilized in a new threshold value, and the extrusion speed of slurry is stabilized in an ideal threshold value of the target value again. The effect of the internal pressure stability control module of the storage device in the slurry extrusion control system is not only reflected in guaranteeing the internal pressure stability of the extrusion device, so that the extrusion speed of the slurry is stabilized within a reasonable threshold value, but also reflected in timely adjusting the internal pressure of the extrusion device when the speed is matched and updated, so that the internal pressure of the extrusion device is stabilized within a new threshold value, and the extrusion speed of the slurry is prevented from generating larger fluctuation. In the existing extrusion control system, only a mapping relation between a single extrusion speed and a scanning speed can be set, but in the actual printing process, the scanning speed of a printer is not always unchanged, (such as the scanning speed is changed when a peripheral outline is printed and an internal entity is filled), if the scanning speed of the peripheral outline is 2mm/s and the scanning speed of the internal filling is 4mm/s during solid model printing, the extrusion speed of slurry after the peripheral outline is printed cannot be matched with a target value corresponding to the internal filling scanning speed, and technological defects such as material accumulation, wire drawing, large diameter change of extruded wires and the like can occur, so that the precision of a printed molded part is reduced. According to the invention, the slurry extrusion control system maps different slurry extrusion speeds according to different scanning speeds, then obtains the corresponding stepping electric cylinder push rod feeding speed to control the extrusion of the slurry, and simultaneously ensures that the slurry extrusion speed is stabilized within a specific threshold value mapped by different scanning speeds in real time due to the existence of the pressure stabilizing control module in the storage device. In addition, the interrupt priority setting mechanism in the system ensures the cooperative operation of each module in the system, and the functions of the internal pressure stability control module of the storage device and the extrusion speed/scanning speed matching mechanism control module are cooperatively exerted, so that two mutually independent modules form internal connection, complement each other, mutually influence and regulate, and exert the maximum advantage of the microfluidic extrusion process.
Drawings
Fig. 1 is a schematic structural view of a slurry extrusion apparatus.
Fig. 2 is an overall block diagram of an additive manufacturing apparatus based on a microfluidic extrusion process.
Fig. 3 is a block diagram of the hardware architecture of an additive manufacturing device based on a microfluidic extrusion process.
Fig. 4 is a control flow diagram of an additive manufacturing apparatus based on a microfluidic extrusion process.
FIG. 5 is a control flow diagram of the internal pressure stabilization control module of the storage device.
FIG. 6 is a flow chart of the extrusion speed/scan speed matching decision control module control.
FIG. 7 is a schematic block diagram of fuzzy PID parameter self-tuning control in the present invention.
Fig. 8 is a force diagram of a slurry extrusion device.
Detailed Description
For a further understanding of the invention, its features and advantages, reference is now made to the following examples, which are illustrated in the accompanying drawings.
The structure of the present invention will be described in detail with reference to the accompanying drawings.
The device is mainly used for manufacturing ceramic parts formed by micro-flow extrusion, and particularly relates to an additive manufacturing device based on a micro-flow extrusion process and a slurry extrusion device thereof.
The additive manufacturing device based on the micro-flow extrusion process is shown in fig. 2, and comprises a slurry extrusion device 21, a support upright 22, a Z-axis sliding block 23, a Z-axis guide rail 24, a forming platform 25, an X-axis sliding block 26, an X-axis guide rail 27, a Y-axis double sliding block 28, a Y-axis double guide rail 29 and a base 2a;
A support upright post 22 is fixed in the middle of the rear side of the base 2a, and a Z-axis guide rail 24 is fixed at the upper part of the support upright post 22; a Z-axis sliding block 23 is arranged on the Z-axis guide rail 24, and a slurry extrusion device 21 is fixed on the Z-axis sliding block 23; the 2Y-axis guide rails 29 are parallel and perpendicular to the bottom edge of the base 2 a; each Y-axis guide rail 29 is provided with 1Y-axis sliding block 28; the lower parts of the two ends of the X-axis guide rail 27 are respectively connected with 1Y-axis sliding block 28; an X-axis sliding block 26 is arranged on the X-axis guide rail 27; the X-axis sliding block 26 is provided with a forming platform 25; the X-axis guide rail 27, the Y-axis double guide rail 29 and the Z-axis guide rail 24 are provided with a driving motor (namely an X-direction stepping motor, a Y-direction stepping motor and a Z-direction stepping motor);
the X-axis sliding block 26, the Y-axis double sliding block 28, the Z-axis sliding block 23, the X-axis guide rail 27, the Y-axis double guide rail 29 and the Z-axis guide rail 24 are all known devices, each axis guide rail consists of a base, an optical axis and a screw rod, flanges are arranged at two ends of the guide rail base, and the flanges are connected with a stepping motor through one side of the flanges; the stepping motor is connected with a screw rod fixed between flanges at two ends through a bearing through a coupler to complete mechanical transmission; each shaft guide rail is provided with two optical axes for connecting each shaft slide block, each shaft slide block is driven by a screw rod and the optical axes, and the upper part of each slide block is provided with a threaded hole for connecting a fixed guide rail base or a forming platform.
The slurry extruding device is shown in fig. 1, and comprises a base 12, a stepping electric cylinder 11, a pressure sensor 13 and a syringe 14;
the shape of the base 12 is a columnar cube, a stepping electric cylinder 11 is fixed above the front surface of the base 12, and a pressure sensor 13 is fixed at the bottom center of a push rod of the stepping electric cylinder 11 through a buckle; a round clamping sleeve is fixed at the lower part of the base 12 through a screw; the syringe 14 is secured by a circular ferrule; the stepping electric cylinder push rod, the button-type pressure sensor and the injector are coaxial from top to bottom.
The base 12 in the slurry extrusion device 21 is fixed on the Z-axis slide block 23 of the 3D printer; the Z-axis sliding block 23 drives the slurry extrusion device 21 to realize linear motion in the space Z direction of the slurry extrusion device; the Z-axis guide rail 24 consists of a guide rail base, an optical axis and a screw rod, wherein the lower end of the base is fixedly driven by a stepping motor through a flange and is connected with the screw rod through a coupler to complete mechanical transmission; the lower part of the supporting upright post 22 is fixedly connected with the base 2a, and the Z-axis guide rail is fixed on the front surface of the supporting upright post; two parallel Y-axis guide rails 29 are fixed above the base 2a and provided with sliding blocks to complete linear motion of the forming platform in the Y direction; the X-axis guide rail 27 is fixed on two sliding blocks of the Y-axis and provided with the sliding blocks, so that the linear motion of the forming platform in the X direction is completed; the forming platform 25 is fixed on the X-axis sliding block and can synchronously move along with the movement of the Y-axis sliding block, and finally, the linkage of the forming platform in the plane of the space X, Y is realized. The stepping motor cylinder 11 is arranged at the top of the slurry extrusion device clamp and is fixed by the clamp; the pressure sensor 13 is spliced with the clamp of the pressure sensor and then fixed at the bottom of the push rod of the stepping electric cylinder 11 of the slurry extrusion device; the syringe 14 is secured to the holder by a circular hole in the bottom of the slurry extrusion device holder. After the slurry extrusion device operates, the stepping electric cylinder push rod moves downwards with the pressure sensor, after the pressure sensor contacts with the injector plunger push rod, the pressure sensor is responsible for collecting and returning pressure data, the injector plunger push rod pushes the internal slurry to extrude the internal slurry from the extrusion head, and meanwhile, the forming platform moves in a X, Y plane to finish stacking of one layer; after one layer of the slurry is piled up, the slurry extruding device is lifted into a layer thickness unit in the Z direction to pile up the next layer, and therefore all the structures are matched through a control system to finish the printing and manufacturing of the micro-flow extrusion molding product.
As shown in fig. 3, the complete 3D printing and forming control system based on the micro-fluid extrusion process designed by the present invention mainly comprises a 3D printing control motherboard based on Marlin firmware and related hardware for completing a series of actions of 3D printing.
The 3D printing control main board is a common open source MKS MELZI main board in the market. The control main board is embedded with X, Y, Z stepping motor driving modules 31, 32 and 33 (recommended to use A4988 stepping motor driving), a display screen driving and touch driving module 36 (adopting ILI9341 liquid crystal display screen driving and XTP2046 touch driving), a serial port communication module 37 and a power module 38; in order to cooperate with the realization of the additive manufacturing of ceramic materials, the slurry extrusion device forming module for controlling the expansion of the main board mainly comprises a stepping motor cylinder driving module (A4988 stepping motor driving is recommended as well) 34 and a pressure detection module (ADC data acquisition module) 35. The control main board is connected with the relevant pins of the modules embedded on the main board through a certain circuit, and relevant hardware for finishing 3D printing action is connected with the whole system through the pins, wherein the X, Y, Z direction stepping motors 39, 3a and 3b are connected with X, Y, Z stepping motor drives 31, 32 and 33 through pulse output pins, so as to finish X, Y, Z movements in three directions and realize spatial movements of the 3D printer; the step electric cylinder 3c of the extrusion device is connected with the step electric cylinder drive 34 through a pulse output pin to finish the extrusion action of slurry; the pressure sensor 3d is connected with the pressure detection module 35 through a pulse input pin to complete the acquisition of pressure signals; the liquid crystal touch display screen 3e is connected with the liquid crystal display and touch driving module 36 through a data connecting wire to complete the display function; the upper computer (PC) 3f is connected to the serial port communication module 37 through a communication pin, and completes transmission of various data in the printing process, including transmission of pressure information, transmission of a stepping electric cylinder adjusting signal, transmission of printing path information, and the like.
As shown in fig. 4, the slurry extrusion control system according to the present invention, as a subsystem of the 3D printing control system, is mainly composed of 4 parts, including an interrupt priority setting mechanism 41, a slurry extrusion initial speed setting module 42, a speed matching decision control module 43, and a storage device internal pressure stabilization control module 44.
The control system of the slurry extrusion device based on the micro-flow extrusion process is nested in the 3D printing integral control system, the control system of the slurry extrusion device runs immediately after the 3D printing integral control system runs, the internal control module of the control system can send a corresponding interrupt request when running, and after receiving the interrupt request signal, the control system of the slurry extrusion device determines the running sequence of each control module according to the set interrupt priority, and finally ensures that each module in the control system of the slurry extrusion device runs stably in sequence, and the specific steps are as follows:
step 1: setting interrupt priority of each module, completing initialization of the interrupt priority, starting a slurry extrusion device, and immediately running the system;
wherein, the interrupt priority level is set from high to low as follows: the speed matching decision control module and the internal pressure stability control module of the storage device;
Step 2: setting an extrusion feeding initial speed v (r/s), and driving a stepping electric cylinder to reach the initial speed v;
wherein, the initial extrusion speed of the paste is required to correspond to different initial rotation speeds of the stepping electric cylinder, and the target paste extrusion speed is v 0 ，v 0 According to the requirement of the user on the printing efficiency, according to the formula,
wherein A is 0 Is the extrusion head cross-sectional area (unit mm 2 )；
A P Is the cross section area (unit mm) of the charging barrel 2 )；
P h Leads (unit mm/r) of stepping electric cylinders;
obtaining the initial rotation speed v of the stepping motor cylinder, and extruding the required target slurry at the speed v during operation 0 The ceramic slurry is configured to a PC, the PC automatically generates an initial rotating speed v (r/s) of the stepping electric cylinder according to a formula (1), the rotating speed of the stepping electric cylinder is driven to reach v by a stepping motor driver, and at the moment, a pushing rod of the stepping electric cylinder pushes a plunger pushing rod of the injector to extrude the ceramic slurry in the storage device;
step 3: pushing a push rod of the storage device at the extrusion feeding initial speed set in the step 2, and enabling the pressure sensor to be in contact with the plunger push rod of the injector, so that the pressure born by the pressure sensor is approximately equivalent to the internal pressure of the storage device; the system collects the internal pressure information of the storage device in real time and feeds back, records the pressure deviation of the first 20 sampling periods, and numbers the pressure deviation as e 0 、e 1 、e 2 ...e 18 、e 19 The method comprises the steps of carrying out a first treatment on the surface of the The sampling period T is determined according to the required response frequency, and the sampling period T is recommended:the sampling period T is set here to 100ms;
the slurry in the storage device is continuously extruded under positive pressure and storedThe pressure information data of the first 20 sampling periods stored in the memory is used for obtaining deviation, and recording is marked as e 0 、e 1 、e 2 ...e 18 、e 19 ，
Wherein e 0 ＝P 1 -P 0 、e 1 ＝P 2 -P 1 、e 2 ＝P 3 -P 2 ...e 19 ＝P 20 -P 19 (2)
The pressure sensor periodically collects pressure information, wherein the setting of the pressure sampling period T meets the requirement that T is larger than or equal to one response period of the control main board, the response frequency of a clock is set to be 72MHz in the Arduino control main board, and therefore the response period of the universal control main board is thatWhen the pressure sensor receives positive pressure, the pressure applied to the top end of the push rod of the injector is measured once every other sampling period, the numerical information of the pressure is recorded in the memory, the numerical quantity corresponding to the pressure information is obtained through conversion of a digital-to-analog (D/A) module, the numerical quantity can be displayed on a display screen, and the numerical quantity can also be fed back to an upper computer (PC) through a serial port, so that a user can observe the internal pressure of the slurry extrusion device conveniently;
step 4: important judgment of sampling pressure deviation e 15 、e 16 、e 17 、e 18 、e 19 Whether within + -5;
comparing whether the pressure deviation is within the set stable range + -0.5 in turn, and comparing the sampling pressure deviation e with emphasis 15 、e 16 、e 17 、e 18 、e 19 Whether or not within + -5, and when the pressure deviation e 15 、e 16 、e 17 、e 18 、e 19 The pressure deviation is considered to be within a stable range within +/-5, and the slurry extrusion process is continued;
if the recorded pressure deviation value is not within + -5, and the pressure deviation e is sampled 15 、e 16 、e 17 、e 18 、e 19 If the ratio is more than 5, the slurry extrusion process is considered to have the phenomenon of blocking or wire breakageThe enabling pin of the stepping motor cylinder driving module is set to be low level from high level to low level, the operation of the stepping motor cylinder is interrupted, and the slurry extrusion action is suspended; at this time, resetting the paste extrusion speed, increasing the extrusion speed by 10r/s, setting the extrusion speed according to the setting of the amplification to 10r/s, setting by experience recommendation, comparing whether the sampling pressure real-time deviation e is within a range of +/-5, and repeating the step 4; repeating for 3 times at most, and finishing the printing of the skirt edge at the stage; transferring to false tooth entity for printing;
the purpose of performing the operation of step 4 is to pre-print a circle of skirt before the actual entity is printed, the skirt is not part of the printed entity, but a layer of outer ring which is attempted to be printed is the final and unnecessary part; therefore, in the process of printing the skirt edge, the rotation speed of the stepping electric cylinder is adjusted to ensure that the paste extrusion wires are uniformly extruded, and the rotation speed is adjusted for at most three times, so that the skirt edge printing is completed, and the solid printing of the false tooth or a formed part is achieved.
Step 5: the paste extrusion device performs entity (false tooth) printing, extracts scanning speed information and judges whether the scanning speed of the printer is changed or not;
the scanning speed refers to the speed of the forming platform moving in the plane of the space X, Y, and in the process of printing the entity three-dimensionally, the printing of each layer of entity is divided into two parts: printing of the outer wall of the entity and filling of the inside of the entity. In order to ensure the entity forming precision, the scanning speed of a forming platform is relatively low when the outer wall of the entity is printed, and the scanning speed is usually 5-10 mm/s according to experience; in order to improve the processing efficiency, the scanning speed of the forming platform is higher when the solid is filled, and 8-12 mm/s is often taken according to experience. Because the scanning speeds of the two parts are different, whether the scanning speed is changed or not needs to be judged in printing, and the paste extrusion speed needs to be matched according to the scanning speed to ensure that the paste extrusion wire is just attached to the forming platform, which is the reason that the scanning speed is changed.
The translation of the G-code is carried out, firstly, the character F is identified, and the data after the character F is recorded as v 0 、v 1 、v k 、v k+1 Storing and realizing extraction of scanning speed information; judging front and rear sectionsWhether the scanning speed of the path changes or not, if the scanning speed v of the previous path is higher than the scanning speed v k Scan speed v not equal to the path of the next segment k+1 Then enters a speed matching decision control module 43 and then enters a pressure stabilizing control module 44 in the storage device; if the scanning speed is unchanged, the scanning speed v of the previous path is higher than the scanning speed v k Equal to the scanning speed v of the next path k+1 Then enter the internal pressure stabilization control module 44 of the storage device;
the G-code translation process described herein is similar to the translation of an execution machining instruction when a numerical control machine tool performs a cutting machining operation, except that the G-code instruction identified by the microfluidic extrusion process is simply a linear motion instruction and extraction of the feed rate, and the specific G-code translation process is available from document Li Qiushi. 3D printing control scheme design and implementation [ D ]. Hubei university of industry.2016:36-39.
When entering the speed matching decision control module 43:
step (1): the scanning speed being changed (i.e. v k ≠v k+1 ) The speed matching decision control module sends out an interrupt request;
the speed matching decision control module sends an interrupt request, the interrupt priority level of the speed matching decision control module is higher than that of the pressure stabilizing control module in the storage device, and the speed matching decision control module preferentially executes actions;
After the device to be processed enters the stable slurry extrusion process, the internal pressure stability control module of the storage device continuously maintains the internal pressure stability of the device to be processed, and when the scanning speed is changed within a stability threshold value + -5 as described below, the step (1) is executed, and at the moment, the operation executed by the internal pressure stability control module of the storage device is suspended;
step (2): the speed matching decision control module updates the slurry extrusion speed;
the speed matching decision control module extracts a new scanning speed in the memory and marks the new scanning speed as v k According to the formula
Wherein v is P ' is the linear feed rate (unit mm/s) of the slurry extrusion,
x P for stepping the electric cylinder push rod feed movement distance (unit mm),
t 0 for the time of the push rod movement of the stepping electric cylinder (unit s),
L 0 the distance (in mm) for the X, Y stepper motor,
A 0 is the cross-sectional area (unit mm) of the extrusion needle 2 )，
A 1 Is the cross-sectional area (unit mm) of the storage cylinder 2 )，
Updating the paste extrusion speed v P ', and v P ' store to memory;
step (3): according to the updated paste extrusion speed v P ' update and adjust the rotation speed v of the stepping electric cylinder, reassign the rotation speed v ' of the stepping electric cylinder to obtain updated rotation speed v ' of the stepping electric cylinder, and adjust the rotation speed;
wherein the rotating speed v' of the stepping electric cylinder is according to the formula
Wherein v' is the rotational speed (unit r/s) of the stepping electric cylinder,
v P ' is the linear feed rate (unit mm/s) of the slurry extrusion,
P h for a stepping motor cylinder lead (unit mm/r),
and (3) calculating, reassigning the rotating speed v of the stepping electric cylinder to enable v=v', driving the stepping electric cylinder to adjust the rotating speed to reach the new target rotating speed v, and completing the main step of speed matching.
Step (4): completing speed matching, jumping out of the speed matching decision control module, transferring to the internal pressure stability control module 44 of the material forming device, and controlling the internal pressure of the material storage device to be stable within a range of +/-5 of a recommended value described below;
the speed matching decision control module completes the matching work of extrusion speed/scanning speed, so that the slurry extrusion speed and the scanning speed of the printer are matched in real time, and the phenomena of material accumulation and wiredrawing caused by unmatched extrusion speed and scanning speed in the printing process are avoided. And after the speed matching decision control module is executed, or the scanning speed in the step 3 of the slurry extrusion control system is not changed, the slurry enters the pressure stabilizing control module in the storage device to perform pressure stabilizing control operation.
When entering the internal pressure stabilization control module 44 of the storage device:
Step (1): the internal pressure stabilization control module of the storage device extracts pressure information and stores the pressure information in an internal cache;
the pressure stabilizing control module enters the storage device, at the moment, the pressure values before and after each sampling period are read and stored in a buffer memory, and the pressure values are recorded as P k And P k+1 。
Step (2): calculating internal pressure deviation e of storage device F (k) Variation Δe from internal pressure F (k)；
Internal pressure deviation e of storage device F (k)＝P k+1 -P k ，
Wherein P is k 、P k+1 Respectively measuring pressure data before and after a sampling period;
pressure deviation change delta e in storage device F (k)＝e F (k+1)-e F (k)，
Wherein e F (k)、e F (k+1) is the internal pressure deviation obtained after the end of each sampling period, respectively.
Step (3): for internal pressure deviation e of storage device F (k) Variation Δe from internal pressure F (k) Carrying out fuzzification treatment;
wherein the blurring process is that let e F (k) And delta e F (k) Respectively multiplied by quantization factorsAnd->Obtaining e F (k) And delta e F (k) Fuzzy variables in the Fuzzy subsets respectively;
the quantization factor is determined by the error e=max (e F (k) Error change ec=max (Δe) F (k) A) the exact amount and the number of steps N divided after discretization (or quantization) of the continuously varying error; e. ec is determined according to the pressure control accuracy, and when high-accuracy control is performed, e=10, ec=5; e=20, ec=10 when low-precision control is performed; n is an integer, and the present control system selects n=7. In short, the blurring process is to obtain e F (k)、Δe F (k) Is the actual domain of theory [ -e, e]And [ -ec, ec]The quantization factors are processed and mapped to FuZZZy FuZZy subsets E= [ -3, -2, -1, 0, 1, 2 and 3]Corresponding e= [ NB, NM, NS, 0, PS, PM, PB]And ec= [ -3, -2, -1, 0, 1, 2, 3]Corresponding ec= [ NB, NM, NS, 0, PS, PM, PB]In (3) a process of (c).
Step (4): fuzzy reasoning is carried out to obtain fuzzy output variable delta K by reasoning P 、ΔK I 、ΔK D Performing defuzzification processing on the fuzzy output variable;
wherein, the fuzzy inference engine infers the corresponding fuzzy output variable delta K according to the fuzzy control parameter rule table and the fuzzy input variable provided in tables 1-3 P 、ΔK I 、ΔK D . The provided fuzzy control parameter rule table is summarized according to practical experience and research data and is widely applied to engineering practice. For example, if the input pressure deviation and the fuzzy value of the pressure deviation change are e=nb, ec=nm, respectively, the output variable Δk is P The blur value of (1) can be obtained as PB from Table 1, and the other two parameters ΔK I 、ΔK D The blur outputs of (2) are shown in tables 2 and 3, respectively.
Let fuzzy output variable delta K P 、ΔK I 、ΔK D Respectively multiplied by a scale factorObtaining fuzzy output variable delta K P 、ΔK I 、ΔK D The actual output variable corresponding to the actual argument. And the scale factor- >The actual variation range of the output variable u is calculated according to experience recommendation + -10 r/s, error and number N of steps divided after discretization (or quantization) of the error variation, wherein N is an integer, and the control system selects N=7 to determine.
Step (5): the conventional PID controller receives the actual output parameter DeltaK P 、ΔK I 、ΔK D Performing incremental PID control operation to obtain the output adjustment quantity delta u (k) of the fuzzy PID parameter from the setting pressure control module;
the traditional PID controller receives the actual variable delta K of the control parameter obtained in the last step (4) P 、ΔK I 、ΔK D And for initial control parameter K P 、K I 、K D Re-assigning the value of (C) to K P ＝K P +ΔK P ，K I ＝K I +ΔK I ，K D ＝K D +ΔK D 。
By utilizing the incremental PID control law,
Δu(k)＝q 0 e(k)+q 1 e(k-1)+q 2 e(k-2) (5)
wherein q 0 ＝K P (1+K I +K D )，
q 1 ＝-K P (1+2K D )，
q 2 ＝K P K D ，
e (k), e (k-1), e (k-2) are the pressure deviations stored in the memory,
and obtaining the final fuzzy PID parameter output variable Deltau (k) from the tuning controller.
Step (6): judging the positive and negative of a variable Deltau (k) output by the fuzzy PID parameter self-tuning control module, and if Deltau (k) is more than or equal to 0, increasing the rotating speed of the stepping electric cylinder of the slurry extrusion device; if Deltau is less than or equal to 0, the rotating speed of the stepping motor cylinder of the slurry extruding device is reduced;
the rotating speed adjusting quantity of the stepping motor cylinder of the extrusion device can be empirically set, and when high-precision adjustment is recommended, the rotating speed adjusting range of the stepping motor cylinder is set to be +/-10 rad/s; and (5) performing rapid adjustment, and setting the rotating speed adjustment range of the stepping motor cylinder to be +/-20 rad/s. Judging the conditions of the step, if Deltau is more than or equal to 0 and is high-precision adjustment, reassigning the rotating speed of the stepping electric cylinder by the system, wherein v=v+10; if Deltau is less than 0 and the rotation speed of the stepping motor cylinder is regulated with high precision, the system reassigns the rotation speed of the stepping motor cylinder, and v=v-10; if Deltau is more than or equal to 0 and is rapid adjustment, the system reassigns the rotating speed of the stepping electric cylinder, and v=v+20; if deltau is less than 0 and the speed of the stepping motor cylinder is regulated quickly, the system reassigns the rotating speed of the stepping motor cylinder, and v=v-20. After the rotating speed of the stepping motor cylinder is reassigned, the stepping motor cylinder driving module drives the stepping motor cylinder to act, so that the rotating speed of the stepping motor cylinder reaches the target value v, and the rotating speed adjustment of the stepping motor cylinder is finished.
Step (7): judging the pressure deviation e in the next sampling period F (k+1) whether or not it is within a set threshold;
the threshold value can be set according to experience recommendation by a user, and if the control precision is required to be higher, the threshold value can be set within +/-5; if control accuracy is generally required, the threshold value may be set within ±10.
If the internal pressure of the storage device deviates by e F (k+1) is not within the set threshold, i.e. |e F Returning to the step (1) of the internal pressure stability control module of the storage device for re-execution if (k+1) is more than 5; if the internal pressure of the storage device deviates by e F (k+1) is within a set threshold, i.e., -5.ltoreq.e F (k) And (3) not regulating the rotating speed of the stepping electric cylinder to be v, returning to the step (1), judging whether the pressure deviation is in a set range again, waiting to interrupt the corresponding process of interrupting the pressure stabilizing control module in the storage device, and switching to the step 6 of the slurry extrusion control system.
Step 6: identifying a printing end mark character string in the G-code, and judging whether the printing process is ended or not;
the specific implementation method is that the end G-code is read and translated, wherein the printing process control code M code indicates whether the printing process is ended or not. Such as M104S0; turn off extruder the stop of paste extrusion, M84; disable motors indicate turning off the stepper motors on each axis, stopping the printing operation.
If the character string M104S0 is identified; turn off extruder and M84; disable motors, disabling the stepping motor cylinder, ending the printing process, and jumping out of the slurry extrusion control system; if the character string M104S0 is not recognized; turn off extruder and M84; and (5) returning to the step (5) and repeatedly executing the step (5).
In the printing process, continuously searching a path with changed scanning speed, and matching corresponding paste extrusion speed according to the scanning speed; the pressure value inside the storage device is continuously fed back, the rotating speed of the stepping electric cylinder is regulated to enable the pressure to be stable, the slurry is uniformly discharged, and printing is finally completed through printing of the outer wall of the entity of the sheet layer, filling of the inner side of the entity and layer-by-layer stacking.
In the operation of the slurry extrusion system, the system sets the rotating speed of the stepping electric cylinder corresponding to the initial slurry extrusion speed, drives related hardware (the stepping electric cylinder) to operate, and the other control modules are in a standby state; the pressure sensor periodically collects pressure information and feeds back the pressure information; the internal pressure stability control module of the storage device continuously runs, related hardware (a stepping electric cylinder) is driven to run through an internal algorithm of the controller, and the internal pressure stability of the extruder is maintained by matching with the pressure detection device, so that the slurry is continuously and stably extruded, the extrusion system has stable extrusion speed, and whether a new interrupt request breaks the operation of the extrusion system is waited; the system judges whether the scanning speed of the printer needs to be changed according to the data transmitted by the upper computer, if so, the extrusion speed/scanning speed matching decision control module sends an interrupt request and interrupts the operation of the pressure stabilizing control module in the storage device, the new slurry extrusion speed is matched through an algorithm in the software control module, the extrusion speed is updated in real time, and the stepping electric cylinder is driven to enable the rotating speed to reach the vicinity of the target value; after the interrupt signal disappears, the internal pressure stabilizing control module of the storage device operates again, and as the rotating speed of the stepping motor cylinder changes, the internal pressure of the device also changes, and the internal pressure stabilizing control module of the storage device adjusts the rotating speed of the stepping motor cylinder within a small range again by using an internal algorithm, so that the internal pressure of the device is stabilized within a new threshold again. Therefore, the internal pressure stability control module of the storage device and the extrusion speed/scanning speed matching decision control module realize the mutual auxiliary and mutual regulation cooperative control, and the advantages of the microfluidic extrusion process are greatly exerted.
The interrupt priority setting mechanism is nested in the main control system of the 3D printer and is used for setting the interrupt priority of each control module, so that each module in the slurry extrusion system can be orderly operated, and the stable operation of the system is ensured. The mechanism ensures the cooperative operation of the pressure stability control module and the extrusion speed/scanning speed matching mechanism control module in the storage device, and can quickly and stably stabilize the updated slurry extrusion speed within a new threshold value when the slurry extrusion speed is updated.
TABLE 1 fuzzy control parameter K in the present invention P A control rule table.
TABLE 2 fuzzy control parameter K in the present invention I A control rule table.
TABLE 3 fuzzy control parameter K in the present invention D A control rule table.
The data provided in tables 1-3 provide decision making decisions for fuzzy PID parameters in the internal pressure stabilization control module of the storage device described above. Input variable e is received from input end of fuzzy PID parameter self-tuning control module F And Δe F (i.e., pressure deviation and pressure deviation variation), first go throughThe fuzzification interface changes the variable e F And Δe F The argument E= [ -3, -2, -1, 0, 1, 2, 3 mapped to Fuzzy]Corresponding fuzzy subset e= [ NB, NM, NS, ZO, PS, PM, PB ] ]In, e.g. e F And Δe F Mapping to-1 and 2 in the Fuzzy respectively, and respectively setting corresponding Fuzzy variables as NS and PM; the fuzzy parameter K is then provided in a fuzzy inference engine module according to tables 1-3 P 、K I 、K D The control rule obtains the output quantity delta K P 、ΔK I 、ΔK D Fuzzy variables of (e), e.g F And Δe F According to fuzzy parameter control rule table to obtain output variable delta K of fuzzy inference engine P 、ΔK I 、ΔK D Respectively NS, PS, NS; then the output variable delta K is subjected to the defuzzification interface P 、ΔK I 、ΔK D Mapping the real theory domain to a corresponding real theory domain and transmitting the real theory domain to a traditional PID controller for processing; finally, the actual output variable u of the fuzzy PID parameter self-tuning control module is obtained through the PID controller, so that the internal pressure of the extrusion device is quickly, efficiently and conveniently adjusted, and the continuous extrusion of the slurry and the stable and reliable extrusion speed are realized.
The foregoing description is only of the preferred embodiments of the present invention, and is not intended to limit the invention in any way, but any simple modification, equivalent variation and modification of the above embodiments according to the technical principles of the present invention are within the scope of the technical solutions of the present invention.
The invention is not a matter of the known technology.

Claims (2)

1. A control method of an additive manufacturing device with a slurry extrusion device based on a micro-fluid extrusion process is characterized in that
The additive manufacturing device with the slurry extrusion device based on the micro-flow extrusion process comprises the slurry extrusion device based on the micro-flow extrusion process, a supporting upright post, a Z-axis sliding block, a Z-axis guide rail, a forming platform, an X-axis sliding block, an X-axis guide rail, a Y-axis double sliding block, a Y-axis double guide rail and a base;
the middle part of the rear side of the base is fixed with a supporting column, and the upper part of the supporting column is fixed with a Z-axis guide rail; a Z-axis sliding block is arranged on the Z-axis guide rail, and a slurry extrusion device is fixed on the Z-axis sliding block; the 2Y-axis guide rails are parallel and perpendicular to the bottom edge of the base; each Y-axis guide rail is provided with 1Y-axis sliding block; the lower parts of the two ends of the X-axis guide rail are respectively connected with 1Y-axis sliding block; an X-axis sliding block is arranged on the X-axis guide rail; a forming platform is arranged on the X-axis sliding block; the X-axis guide rail, the Y-axis double guide rail and the Z-axis guide rail are respectively provided with a driving motor; the base in the slurry extrusion device is fixed on the Z-axis sliding block;
the slurry extrusion device based on the micro-flow extrusion process comprises a base, a stepping electric cylinder, a pressure sensor and an injector;
a stepping electric cylinder is fixed above the front surface of the base, and a pressure sensor is fixed at the bottom center of a push rod of the stepping electric cylinder through a buckle; the lower part of the base is fixed with a round clamping sleeve through a screw; the injector is fixed through a round cutting sleeve; the stepping electric cylinder push rod, the button-type pressure sensor and the injector are coaxial from top to bottom;
The control method comprises the following steps:
step 1: setting interrupt priority of each module, completing initialization of the interrupt priority, starting a slurry extrusion device, and immediately running the system;
wherein, the interrupt priority level is set from high to low as follows: the speed matching decision control module and the internal pressure stability control module of the storage device;
step 2: setting an extrusion feeding initial rotating speed v, and driving a stepping electric cylinder to reach the initial rotating speed v by a unit r/s;
wherein, the extrusion speed of the slurry is required to correspond to different initial rotation speeds of the stepping electric cylinder, and the extrusion speed of the target slurry is v 0 ，v 0 According to the requirement of the user on the printing efficiency, according to the formula,
units r/s; (1) Wherein,,A 0 in mm for extrusion head cross-sectional area 2 ；
A P Is the section area of the charging barrel, and the unit is mm 2 ；
P h The unit is mm/r for the lead of the stepping electric cylinder;
obtaining the initial rotation speed v of the stepping motor cylinder, and extruding the required target slurry at the speed v during operation 0 The ceramic slurry is configured to a PC, the PC automatically generates an initial rotating speed v of the stepping electric cylinder according to a formula (1), the unit r/s, the rotating speed of the stepping electric cylinder is driven to reach v through a stepping motor driver, and at the moment, a stepping electric cylinder push rod pushes an injector plunger push rod to extrude the ceramic slurry in the storage device;
Step 3: pushing a push rod of the storage device at the extrusion feeding initial rotating speed set in the step 2, and enabling the pressure sensor to be in contact with the plunger push rod of the injector, so that the pressure born by the pressure sensor is approximately equivalent to the internal pressure of the storage device; the system collects the internal pressure information of the storage device in real time and feeds back, records the pressure deviation of the first 20 sampling periods, and numbers the pressure deviation as e 0 、e 1 、e 2 ...e 18 、e 19 The method comprises the steps of carrying out a first treatment on the surface of the The setting of the sampling period T is determined according to the required response frequency, and the sampling period is as follows:s is a system clock; m is M HZ The frequency of the crystal oscillator is externally hung on the chip;
the slurry in the storage device is continuously extruded under positive pressure, the deviation of the pressure information data of the first 20 sampling periods stored in the memory is obtained, and the record is marked as e 0 、e 1 、e 2 ...e 18 、e 19 ，
Wherein e 0 ＝P 1 -P 0 、e 1 ＝P 2 -P 1 、e 2 ＝P 3 -P 2 ...e 19 ＝P 20 -P 19 (2)
Step 4: important judgment of sampling pressure deviation e 15 、e 16 、e 17 、e 18 、e 19 Whether or not within + -5；
Sequentially comparing whether the pressure deviation is within a set stable range + -5, and comparing the sampling pressure deviation e with emphasis 15 、e 16 、e 17 、e 18 、e 19 Whether or not within + -5, and when the pressure deviation e 15 、e 16 、e 17 、e 18 、e 19 The pressure deviation is considered to be within a stable range within +/-5, and the slurry extrusion process is continued;
if the recorded pressure deviation value is not within + -5, and the pressure deviation e is sampled 15 、e 16 、e 17 、e 18 、e 19 If the voltage is more than 5, the phenomenon of blocking or wire breakage in the paste extrusion process is considered, the enabling pin of the stepping electric cylinder driving module is set to be low from high level, the operation of the stepping electric cylinder is interrupted, and the paste extrusion action is suspended; resetting the slurry extrusion speed, increasing the extrusion speed by 10r/s, comparing whether the sampling pressure real-time deviation e is within +/-5, and repeating the step 4; repeating for 2-3 times, and finishing the printing of the skirt edge at the stage; transferring to entity printing;
Step 5: the slurry extrusion device performs entity printing, extracts scanning speed information and judges whether the scanning speed of the printer is changed or not;
the translation of the G-code is carried out, firstly, the character F is identified, and the data after the character F is recorded as v 0 、v 1 、v k 、v k+1 Storing and realizing extraction of scanning speed information; judging whether the scanning speed of the front and back paths is changed, if so, the scanning speed v of the front path k Scan speed v not equal to the path of the next segment k+1 Then entering a speed matching decision control module, and then entering an internal pressure stabilizing control module of the storage device; if the scanning speed is unchanged, the scanning speed v of the previous path is higher than the scanning speed v k Equal to the scanning speed v of the next path k+1 Then the pressure stabilizing control module enters the internal of the storage device;
when entering the speed matching decision control module:
step (1): the scanning speed being changed, i.e. v k ≠v k+1 The speed matching decision control module sends out an interrupt request;
the speed matching decision control module sends an interrupt request, the interrupt priority level of the speed matching decision control module is higher than that of the pressure stabilizing control module in the storage device, and the speed matching decision control module preferentially executes actions;
After the device to be processed enters a stable slurry extrusion process, the internal pressure stability control module of the storage device continuously maintains the internal pressure stability of the device to be processed, and when the scanning speed is changed within a stability threshold value + -5, the step (1) is executed, and at the moment, the operation executed by the internal pressure stability control module of the storage device is suspended;
step (2): the speed matching decision control module updates the slurry extrusion speed;
the speed matching decision control module extracts a new scanning speed in the memory and marks the new scanning speed as v k According to the formula
Wherein v is P ' is the linear feed speed of paste extrusion, unit mm/s,
x P the feeding movement distance of the push rod of the stepping electric cylinder is measured in mm,
t 0 for the movement time of the push rod of the stepping electric cylinder, the unit s,
L 0 the moving distance of the stepping motor in the X, Y direction is measured in mm,
A 0 to extrude the cross-sectional area of the needle in mm 2 ，
A 1 Is the section area of the storage cylinder, the unit is mm 2 ，
Updating the paste extrusion speed v P ', and v P ' store to memory;
step (3): according to the updated paste extrusion speed v P ' update and adjust the rotation speed v of the stepping electric cylinder, reassign the rotation speed v ' of the stepping electric cylinder to obtain updated rotation speed v ' of the stepping electric cylinder, and adjust the rotation speed;
wherein the rotating speed v' of the stepping electric cylinder is according to the formula
Wherein v' is the rotating speed of the stepping electric cylinder, the unit is r/s,
v P ' is the linear feed speed of paste extrusion, unit mm/s,
P h for stepping the electric cylinder lead, in mm/r,
calculating, re-assigning the rotating speed v of the stepping electric cylinder to enable v=v', driving the stepping electric cylinder to adjust the rotating speed to reach a new target rotating speed v, and completing the step of speed matching;
step (4): finishing speed matching, jumping out of the speed matching decision control module, transferring to the internal pressure stability control module of the material forming device, and controlling the internal pressure of the material storage device to be stable within a recommended value +/-5;
when entering the internal pressure stability control module of the storage device:
step (1): the internal pressure stabilization control module of the storage device extracts pressure information and stores the pressure information in an internal cache;
the pressure stabilizing control module enters the storage device, at the moment, the pressure values before and after each sampling period are read and stored in a buffer memory, and the pressure values are recorded as P k And P k+1 ；
Step (2): calculating internal pressure deviation e of storage device F (k) Variation Δe from internal pressure F (k)；
Internal pressure deviation e of storage device F (k)＝P k+1 -P k ，
Wherein P is k 、P k+1 Respectively measuring pressure data before and after a sampling period;
the pressure deviation variation in the storage device is represented by the formula delta e F (k)＝e F (k+1)-e F (k)，
Wherein e F (k)、e F (k+1) end for each sampling period respectivelyThe internal pressure deviation obtained later;
step (3): for internal pressure deviation e of storage device F (k) Variation Δe from internal pressure F (k) Carrying out fuzzification treatment;
wherein the blurring process is that let e F (k) And delta e F (k) Respectively multiplied by quantization factorsAnd->Obtaining e F (k) And delta e F (k) Fuzzy variables in the Fuzzy subsets respectively;
step (4): fuzzy reasoning is carried out to obtain fuzzy output variable delta K by reasoning P 、ΔK I 、ΔK D Performing defuzzification processing on the fuzzy output variable;
wherein, the fuzzy inference engine infers a corresponding fuzzy output variable delta K according to the fuzzy control parameter rule table and the fuzzy input variable P 、ΔK I 、ΔK D ；
Step (5): receiving actual output parameters DeltaK according to a conventional PID controller P 、ΔK I 、ΔK D Performing incremental PID control operation to obtain the output adjustment quantity delta u (k) of the fuzzy PID parameter from the setting pressure control module;
the traditional PID controller receives the actual variable delta K of the control parameter obtained in the last step (4) P 、ΔK I 、ΔK D And for initial control parameter K P 、K I 、K D Re-assigning the value of (C) to K P ＝K P +ΔK P ，K I ＝K I +ΔK I ，K D ＝K D +ΔK D ；
By utilizing the incremental PID control law,
Δu(k)＝q 0 e(k)+q 1 e(k-1)+q 2 e(k-2) (5)
wherein q 0 ＝K P (1+K I +K D )，
q 1 ＝-K P (1+2K D )，
q 2 ＝K P K D ，
e (k), e (k-1), e (k-2) are the pressure deviations stored in the memory,
obtaining a final fuzzy PID parameter self-tuning controller output variable Deltau (k);
Step (6): judging the positive and negative of a variable Deltau (k) output by the fuzzy PID parameter self-tuning control module, and if Deltau (k) is more than or equal to 0, increasing the rotating speed of the stepping electric cylinder of the slurry extrusion device; if Deltau (k) is less than 0, the rotating speed of the stepping motor cylinder of the slurry extrusion device is reduced;
step (7): judging the pressure deviation e in the next sampling period F (k+1) whether or not it is within a set threshold;
wherein the threshold is set within + -5 or + -10;
step 6: identifying a printing end mark character string in the G-code, and judging whether the printing process is ended or not;
if the character string is not recognized to appear, stopping slurry extrusion and closing each shaft stepping motor, returning to the step 5, and repeatedly executing the step 5; if the character string of 'stop paste extrusion and turn off each shaft stepping motor' is recognized, the stepping motor cylinder is disabled, the paste extrusion control system is jumped out, and the printing process is finished.
2. The method of controlling an additive manufacturing apparatus with a slurry extrusion apparatus based on a micro-fluid extrusion process according to claim 1, wherein the sampling period T in the step 3 is 100ms.
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