Injection molding machine and control method therefor

Abstract

An injection molding machine according to an embodiment of the present invention comprises: an injection device that injects material into a mold; and a control unit that controls the injection device and, on the basis of past velocity settings for injection velocity set in the past and past velocity detection results detected in the past by an injection-velocity-detecting velocity sensor in molding cycles performed in advance, controls the injection velocity at an injection step in which the injection device injects material into a mold.

Description

[Technical Field]

[0001] Embodiments of the present invention relate to an injection moldingmachine and a method of controlling the same.[Background Art]

[0002] In injection molding, low-pressure injection molding in whichpressure is not much applied to material such as melted resin is performedin some cases. One of known examples of the low-pressure injectionmolding is a method that switches from speed control to pressure controlhalfway through an injecting process. For example, at injection start,speed control is performed so that actual injection speed becomes equal toa set speed value. Thereafter, when actual injection pressure movestoward a set pressure value that is set to be low, pressure control isperformed so that the actual injection pressure does not exceed the setpressure value.

[0003] However, with the above-described molding method, the injectionspeed during pressure control potentially varies at each shot.Furthermore, due to such variance of the injection speed, the quality of anobtained molded product potentially differs for each shot.[Citation List][Patent Literature]

[0004] [Patent Literature 1] Japanese Patent Laid-open No. 2001-191383[Summary of Invention][Technical Problem]

[0005] It is intended to provide an injection molding machine that canimprove reproducibility of product quality and a method of controllingthe same.[Solution to Problem]

[0006] An injection molding machine according to the present embodimentincludes an injecting device configured to inject a material into a mold, anda controlling unit configured to control the injecting device and control,based on a past speed setting of an injection speed set in past and a pastspeed detection result in a molding cycle performed in advance, aninjection speed in an injecting process through which the injecting deviceinjects the material into the mold, the past speed detection result beingdetected in past by a speed sensor configured to detect the injection speed.[Brief Description of Drawings]

[0007] [Figure 1] Figure 1 is a block diagram illustrating an example of theconfiguration of an injection molding machine according to a firstembodiment.[Figure 2] Figure 2 is a block diagram illustrating an example of theconfiguration of a controlling device according to the first embodiment.[Figure 3] Figure 3 is a graph illustrating an exemplary speed waveformand an exemplary pressure waveform in pressure-controlled injection.[Figure 4] Figure 4 is a graph illustrating an exemplary speed waveformand an exemplary pressure waveform in injection molding with reference toa molding cycle in Figure 3.[Figure 5] Figure 5 is a flowchart illustrating an example of operation of theinjection molding machine according to the first embodiment.[Figure 6A] Figure 6A is a graph illustrating exemplary speed waveforms ina plurality of control methods.[Figure 6B] Figure 6B is a graph illustrating exemplary pressure waveformsin a plurality of control methods.[Figure 7] Figure 7 is a graph illustrating an exemplary speed waveformand an exemplary pressure waveform in laminar control.[Figure 8] Figure 8 is a block diagram illustrating the configuration of acontrolling device according to a second embodiment.[Figure 9] Figure 9 is a graph illustrating an example of change of a speedcommand by feedforward control.[Figure 10] Figure 10 is a graph illustrating an example of change of thespeed command by the feedforward control in a second process.[Description of Embodiments]

[0008] Embodiments of the present invention will be described below withreference to the accompanying drawings. The present embodiments donot limit the present invention. The drawings are schematic or conceptual,and the ratio of parts and the like are not necessarily identical to those inreality. In the specification and the drawings, the same element as thatalready described with reference to a drawing is denoted by the samereference sign, and detailed description thereof is omitted as appropriate.

[0009] (First embodiment)Figure 1 is a block diagram illustrating an example of theconfiguration of an injection molding machine 1 according to a firstembodiment. The injection molding machine 1 can repeatedly execute aseries of injection molding operations and repeats, for example, a cycleoperation in which a mold product is molded once. A cycle time is a timein which a series of cycle operations are executed.

[0010] The injection molding machine 1 includes a frame 2, a fixed board 3,a moving board 4, a tie bar 5, a clamp driving mechanism 6, an injectingdevice 7, a controlling device 8, an extruding mechanism 9, ahuman-machine interface 60, a storing device 110, an injection pressuresensor S1, and a screw position sensor S2.

[0011] The frame 2 is a base of the injection molding machine 1. The fixedboard 3 is fixed on the frame 2. A fixed mold 11 as a first mold is attachedto the fixed board 3. One end of the tie bar 5 is fixed to the fixed board 3,and the other end thereof is connected with a supporting board 10. Thetie bar 5 extends from the fixed board 3 to the supporting board 10 throughthe moving board 4.

[0012] The moving board 4 is placed on a linear guide, a slipping plate, aroller, or the like (not illustrated) provided to the frame 2. The movingboard 4 can be guided by the tie bar 5 or the linear guide and movetoward or away from the fixed board 3. A moving mold 12 as a secondmold is attached to the moving board 4. The moving mold 12 faces thefixed mold 11, moves toward the fixed mold 11 together with the movingboard 4, and becomes combined with the fixed mold 11. A spacecorresponding to a product shape is formed between the moving mold 12and the fixed mold 11 when the moving mold 12 and the fixed mold 11 arecombined in contact.

[0013] The clamp driving mechanism 6 includes a toggle mechanism 13 anda toggle mechanism driving unit 14. The toggle mechanism driving unit14 includes a clamping servomotor 21, a ball screw 22, and a transferringmechanism 23 to drive the toggle mechanism 13. A cross head 15 isattached to a leading end part of the ball screw 22. The cross head 15moves toward or away from the moving board 4 as the ball screw 22 rotates.The transferring mechanism 23 transfers rotation of the clampingservomotor 21 to the ball screw 22 to move the cross head 15.

[0014] The toggle mechanism 13 is actuated as the toggle mechanismdriving unit 14 moves the cross head 15. For example, as the cross head15 moves toward the moving board 4, the moving board 4 moves towardthe fixed board 3 and the molds 11 and 12 are clamped. Oppositely, as thecross head 15 moves away from the moving board 4, the moving board 4moves away from the fixed board 3 and the molds 11 and 12 are opened.

[0015] The extruding mechanism 9 includes an extruding servomotor 71, aball screw 72, a transferring mechanism 73, and an extruding pin 74 toremove a product from the moving mold 12 after molding. A leading endpart of the extruding pin 74 penetrates to the inner surface of the movingmold 12. As the ball screw 72 rotates, the extruding pin 74 extrudes theproduct adhering to the inner surface of the moving mold 12. Thetransferring mechanism 73 transfers rotation of the extruding servomotor71 to the ball screw 72 to move the extruding pin 74 in the right-leftdirection in Figure 1 as the ball screw 72 rotates.

[0016] The injecting device 7 includes a heating barrel (band heater) 41, ascrew 42, a measurement driving unit 43, and an injection driving unit 44.The heating barrel 41 includes a nozzle 41a through which resin beingmelted is injected into a cavity of the molds being clamped. The heatingbarrel 41 melts and stores resin from a hopper 45 by heating and ejects themelted resin through the nozzle. The screw 42 is provided to be able tomove while rotating or not rotating inside the heating barrel 41. In ameasurement process, the screw 42 rotates, melted resin is extruded to aleading end side of the heating barrel 41, and the screw 42 retracts beingpressed by the extruded melted resin. The amount of melted resin ejectedfrom the barrel 41 is measured and determined based on a travel distanceby which the screw 42 retracts. In an injecting process, the screw 42moves without rotating and ejects melted resin through the nozzle.

[0017] The measurement driving unit 43 includes a measuring servomotor46, and a transferring mechanism 47 configured to transfer rotation of themeasuring servomotor 46 to the screw 42. Resin is introduced from thehopper 45 into the heating barrel 41 as the measuring servomotor 46 isdriven and the screw 42 is rotated in the heating barrel 41. Theintroduced resin is transferred to the leading end side of the heating barrel41 while being heated and mixed. The resin is melted and stored at aleading end part of the heating barrel 41. The melted resin is ejected fromthe barrel 41 as the screw 42 is moved in a direction opposite to that inmeasurement. In this case, the screw 42 moves without rotating andextrudes the melted resin through the nozzle. Although melted resin isused as a molding material in the present embodiment, the moldingmaterial is not limited to melted resin but may be metal, glass, rubber,carbonized compound including carbon fiber, or the like.

[0018] The injection driving unit 44 includes an injecting servomotor 51, aball screw 52, and a transferring mechanism 53. The screw 42 in theheating barrel 41 moves in the right-left direction in Figure 1 as the ballscrew 52 rotates. The transferring mechanism 53 transfers rotation of theinjecting servomotor 51 to the ball screw 52. Accordingly, the screw 42moves as the injecting servomotor 51 rotates. As extruded through thenozzle 41a by the screw 42, melted resin stored at the leading end part ofthe heating barrel 41 is ejected from the nozzle 41a.

[0019] The injection pressure sensor S1 detects filling pressure when themolds are filled with melted resin from the barrel 41, and dwellpressure in a dwell process. In the injecting process, the injectionpressure sensor S1 detects injection pressure of melted resin material fromthe barrel 41 to the molds. In the dwell process, the injection pressuresensor S1 detects the dwell pressure of melted resin after dwell switchingfrom speed control to pressure control.

[0020] The screw position sensor S2 detects the position of the screw 42.Since the screw 42 moves along with rotation of the injecting servomotor51, the screw position sensor S2 may detect the position of the screw 42based on the rotation speed and angular position of the injectingservomotor 51. The speed and acceleration of the screw 42 can bedetermined by detecting the position of the screw 42 in eachpredetermined control period.

[0021] The human-machine interface (HM I / F) 60 displays various kinds ofinformation related to the injection molding machine 1. For example, theHM I / F 60 may include a display unit 100 and a keyboard or may be a touchpanel display. A user can input setting of commands and the like relatedto operation of the injection molding machine 1 through the HM I / F 60.For example, the injection molding machine 1 molds a product for eachexecution of a molding cycle through the injecting process of injectingmelted resin into the clamped molds, the dwell process of controlling thedwell pressure of the melted resin in the molds, and a cooling process ofcooling the melted resin in the molds.

[0022] The controlling device 8 monitors sensor information received fromvarious sensors (not illustrated) and controls the injecting device 7 basedon the sensor information. The controlling device 8 also controls thescrew 42 in accordance with the above-described setting values setthrough the HM I / F 60. In addition, the controlling device 8 causes thedisplay unit 100 to display necessary data.

[0023] The storing device 110 stores a plurality of pieces of operationinformation of the injection molding machine 1. The operationinformation is information indicating operation of the molds 11 and 12, theclamp driving mechanism 6, or the injecting device 7. The storing device110 may be provided inside the controlling device 8 or may beprovided outside the injection molding machine 1.

[0024] Figure 2 is a block diagram illustrating an example of theconfiguration of the controlling device 8 according to the first embodiment.

[0025] The controlling device 8 includes an interface 81, a position-speedconverting unit 82, a storage controlling unit 83, an injection speed settingunit 84, an injection controlling unit 85, an injection control servo amplifier86, an interface 87, an injection pressure controlling unit 88, and an alarm89. In the example illustrated in Figure 2, the storing device 110 isprovided inside the controlling device 8.

[0026] The position-speed converting unit 82 is connected with the screwposition sensor S2 through the interface 81. The screw position sensor S2is, for example, an encoder. In this case, the position-speed convertingunit 82 converts an encoder position into an injection speed. For example,the position-speed converting unit 82 counts a filling time (injection time)based on signals from a sequencer (not illustrated). For example, theposition-speed converting unit 82 outputs a waveform (temporal change)of the injection speed to the storing device 110 in a sampling mode inaccordance with the injection time.

[0027] The storing device 110 includes a data memory 111 and a referencewaveform memory 112.

[0028] The data memory 111 acquires the injection speed waveformtransferred from the position-speed converting unit 82 in each moldingcycle.

[0029] The reference waveform memory 112 as a storing unit stores a pastspeed setting and a past speed detection result in a molding cycleperformed in advance. The "past speed setting" is setting of an injectionspeed set in past in the molding cycle performed in advance. The speedsetting is also, for example, speed setting of the screw 42. The "pastspeed detection result" is a detection result detected in past in the moldingcycle performed in advance by a speed sensor configured to detect theinjection speed. The detection result of the injection speed is, forexample, the injection speed waveform of one molding cycle. The speedsensor is, for example, the screw position sensor S2. The position of thescrew 42 detected by the screw position sensor S2 is converted into theinjection speed by the position-speed converting unit 82 as describedabove.

[0030] The storage controlling unit 83 stores the past speed setting and thepast speed detection result in a molding cycle performed in advance in thestoring device 110 (reference waveform memory 112). More specifically,the storage controlling unit 83 stores the past speed setting and the pastspeed detection result in the reference waveform memory 112 based on anoperation of the user. The storage controlling unit 83 stores, in thereference waveform memory 112, for example, the injection speedwaveform stored in the data memory 111 through the HM I / F 60. Thestorage controlling unit 83 stores, in the reference waveform memory 112,for example, the past speed setting input in a past molding cycle throughthe HM I / F 60. The storage controlling unit 83 may store, in the referencewaveform memory 112, the past speed setting and the past speeddetection result from a storing unit provided outside the injection moldingmachine 1. The HM I / F 60 includes, for example, a key input device andreceives various kinds of operations from the user.

[0031] The injection speed setting unit 84 as a speed informationacquisition unit acquires the past speed setting and the past speeddetection result stored in the reference waveform memory 112 in advance.For example, the injection speed setting unit 84 automatically acquires thepast speed setting and the past speed detection result and transfers thepast speed setting and the past speed detection result to the injectioncontrolling unit 85. The injection speed setting unit 84 may acquire,based on an operation of the user, the past speed setting and the pastspeed detection result stored in the storing device 110 (data memory 111).

[0032] The injection controlling unit 85 as a controlling unit controls theinjecting device 7. The injection controlling unit 85 controls injection fromthe injecting device 7 by speed control and pressure control. The injectioncontrolling unit 85 converts, for example, the past speed setting and thepast speed detection result transferred from the injection speedsetting unit 84 into a speed command and transfers the speed command tothe injection control servo amplifier 86. Accordingly, the injectioncontrolling unit 85 can control movement of the screw 42 through theinjecting servomotor 51, thereby controlling injection from the injectingdevice 7. Details of the injection control by the injection controlling unit85 will be described later with reference to Figures 3 and 4.

[0033] The injection pressure controlling unit 88 is connected with theinjection pressure sensor S1 through the interface 87. The injectionpressure controlling unit 88 includes a pressure setting unit 881 and acomparing unit 882.

[0034] The pressure setting unit 881 sets an injection pressure setting Lpsand an upper limit change value of set pressure based on an operation ofthe user through the HM I / F 60 (refer to Figure 3). The sum of theinjection pressure setting Lps and the upper limit change value is referredto as an upper limit injection pressure setting Lps2 (refer to Figure 4). Thepressure setting unit 881 transfers the injection pressure setting Lps andhe upper limit change value to the injection controlling unit 85.Accordingly, the injection controlling unit 85 can control injection bypressure control. The injection controlling unit 85 performs, for example,such pressure control that the injection pressure does not exceed theinjection pressure setting Lps.

[0035] The comparing unit 882 compares a detected value (actualpressure) detected by the injection pressure sensor S1 with the upper limitinjection pressure setting Lps2. The comparing unit 882 transfers a signalto the alarm 89 when the actual pressure exceeds the upper limit injectionpressure setting Lps2.

[0036] The alarm 89 notifies that, for example, the actual pressure exceedsthe upper limit injection pressure setting Lps2.

[0037] The injection control by the injection controlling unit 85 will bedescribed below. The following description is made on injection control inthe injecting process.

[0038] Figure 3 is a graph illustrating an exemplary speed waveform and anexemplary pressure waveform in pressure-controlled injection. Thevertical axis represents the injection speed and the injection pressure.The horizontal axis represents time. An origin O corresponds to the startof the injecting process. Thus, the speed and the pressure aresubstantially zero at the origin O.

[0039] The reference sign Lvs denotes an injection speed setting and is, forexample, a setting value input to the injection speed setting unit 84. Thereference sign Lv denotes the actual speed and is, for example, theinjection speed obtained through conversion by the position-speedconverting unit 82. The reference sign Lps denotes the injection pressuresetting and is, for example, a setting value input to the pressure settingunit 881. The reference sign Lp denotes the actual pressure and is, forexample, the injection pressure detected by the injection pressure sensorS1.

[0040] The pressure-controlled injection is a low-pressure injectionmolding method in which the injection speed (actual speed Lv) is controlledwith the injection speed setting Lvs at beginning of the injecting processand pressure control is started halfway through the injecting process sothat the actual pressure Lp does not exceed the injection pressure settingLps as the upper limit value thereof. Thus, as illustrated in Figure 3, theinjecting process in the pressure-controlled injection is divided into a speedcontrol process and a pressure control process. A timing t of switchingbetween the speed control process and the pressure control process is, forexample, a timing at which the actual pressure Lp increases and reachesthe injection pressure setting Lps. The switching timing t may be thetiming at which the actual pressure Lp reaches a predetermined pressurerange including the injection pressure setting Lps.

[0041] In the pressure-controlled injection, molding is performed withoutapplying high pressure to melted resin. Thus, it is possible to preventdamage on the molds due to overfilling. Since the injection moldingmachine does not need to be able to perform high-pressure filling, cost ofthe device is low. Since filling operation is performed at low pressure,running cost of the injection molding machine is reduced. Sinceinjection is performed at low pressure, the sizes of the molds andperipheral instruments can be reduced, which also leads to reduction ofcost and running cost of the device. Moreover, residual stress on a moldedproduct can be reduced.

[0042] However, in the pressure-controlled injection, the injection speed inthe pressure control process varies at each shot in some cases. This isthought to be because resin behavior in the molds 11 and 12 changes dueto dependency of resin injection on pressure control. With the variance inthe injection speed, the filling time varies at each shot and appearancequality potentially becomes unstable. In other words, with the variance inthe injection speed, the quality of a molded product obtained at each shotdiffers in some cases. Thus, a non-defective product is not alwaysobtained.

[0043] Thus, the injection controlling unit 85 controls, based on the pastspeed setting of the injection speed set in past and the past speeddetection result in a molding cycle performed in advance, the injectionspeed in the injecting process through which the injecting device 7 injectsa material into the molds 11 and 12, the past speed detection result beingdetected in past by the speed sensor configured to detect the injectionspeed. First, as illustrated in Figure 3, sampling of a reference speedpattern is performed by the pressure-controlled injection executed inadvance. Thereafter, as illustrated in Figure 4, molding operation isperformed by using the past speed setting and the past speed detectionresult as the reference speed pattern. The injection controlling unit 85performs speed control in the entire injecting process, and thus thevariance in the injection speed at each shot can be reduced. As a result,reproducibility of the quality of a molded product in the low-pressureinjection molding improves.

[0044] More specifically, the injection controlling unit 85 controls theinjection speed in the injecting process based on the past speed setting andthe past speed detection result in a molding cycle in which a moldedproduct is a non-defective product among molding cycles performed inadvance. In other words, a reference molding cycle is a molding cycle inwhich a non-defective product is obtained by the pressure-controlledinjection.

[0045] (Speed pattern sampling by pressure-controlled injection)As illustrated in Figure 3, in a first process in a molding cycleperformed in advance, the injection controlling unit 85 controls theinjection speed based on the past speed setting until a pressure detectionresult of a pressure sensor configured to detect the injection pressurereaches a predetermined upper limit value after the start of the injectingprocess. The "first process" continues from the start of the injectingprocess to a halfway point thereof. The first process in thepressure-controlled injection is the speed control process. The pressuresensor is, for example, the injection pressure sensor S1. The"predetermined upper limit value" is the injection pressure setting Lps.The past speed setting is the injection speed setting Lvs. The injectionspeed setting Lvs illustrated in Figure 3 is a command value such as 100mm / sec and has a waveform of a step-like shape (rectangular shape).The injection speed setting Lvs illustrated in Figure 3 does not take intoaccount falling and falling of speed in an actual speed command to a motor.

[0046] In the speed control process, the actual speed Lv increases from thestart of the injecting process. The injection controlling unit 85 controlsthe injecting servomotor 51 to follow the injection speed setting Lvs.Feedback control, for example, such as PID control is used to control theinjecting servomotor 51. Thus, the actual speed Lv falls behind theinjection speed setting Lvs as an actual speed command. In the exampleillustrated in Figure 3, the actual speed Lv reaches the injection speedsetting Lvs at the end of the speed control process. The actual pressure Lpincreases with the actual speed Lv from the start of the injecting process.The timing at which the actual pressure Lp reaches the injection pressuresetting Lps is the switching timing t. Thereafter, the pressure controlprocess is performed.

[0047] The timing at which the actual speed Lv reaches the injection speedsetting Lvs is not limited to that in the example illustrated in Figure 3 butchanges depending on the increase speed of the actual pressure Lp in somecases. For example, when the increase speed of the actual pressure Lp isslow, the actual pressure Lp may reach the injection pressure settingLps after the actual speed Lv reaches the injection speed setting Lvs andsubstantially matches the injection speed setting Lvs for a predeterminedduration. The increase speed of the actual pressure Lp changesdepending on, for example, the cavity volume of the molds, the size of theinjection speed setting Lvs and the like.

[0048] In a second process in the molding cycle performed in advance, theinjection controlling unit 85 controls the injection pressure so that thepressure detection result is equal to or smaller than the predeterminedupper limit value. The "second process" is a process after the first processand continues from the halfway point of the injecting process to end thereof.The second process in the pressure-controlled injection is the pressurecontrol process. The start of the pressure control process corresponds tothe switching timing t. For example, the injection controlling unit 85decreases the injection speed when the actual pressure Lp has becomeequal to or larger than the injection pressure setting Lps. The actualpressure Lp would continue increasing if the injection speed right after thespeed control process is kept. Thus, the injection controlling unit 85largely decreases the injection speed by pressure control. As illustrated inFigure 3, the actual speed Lv abruptly decreases immediately afterswitching to the pressure control process. After the abrupt decelerationas well, the injection pressure increases due to continuation of injection.Thus, the actual speed Lv continues gradually decreasing so that the actualpressure Lp does not exceed the injection pressure setting Lps. In thepressure control process, the injection speed setting Lvs is ignored (refer toa dashed line in Figure 3). The end of the pressure control process (theend of the injecting process) is set by, for example, the position of thescrew 42. The dwell process is performed after the end of the pressurecontrol process.

[0049] For example, the user sets the molding cycle illustrated in Figure 3as a reference pressure-controlled injection cycle. In this case, thestorage controlling unit 83 stores the injection speed setting Lvs in thespeed control process and the actual speed Lv in the pressure controlprocess in the reference waveform memory 112.

[0050] (Molding operation using speed pattern)Figure 4 is a graph illustrating an exemplary speed waveform and anexemplary pressure waveform in injection molding with reference to themolding cycle in Figure 3.

[0051] The reference sign Lps2 denotes an upper limit injection pressuresetting. The upper limit injection pressure setting Lps2 is a value obtainedby adding the upper limit change value to the injection pressure setting Lpsas described above. Execution of pressure control with which the injectionspeed becomes unstable can be avoided by increasing an injection pressuresetting value related to switching to the pressure control process. Inother words, in molding operation after determination of the referencemolding cycle, speed control can be executed in the entire injecting process.The upper limit injection pressure setting Lps2 is set to be sufficientlyhigher than the injection pressure setting Lps.

[0052] The injection controlling unit 85 controls the injection speed basedon the past speed setting in the first process in the injecting process.More specifically, the first process includes the start of the injecting process.The same injection speed setting Lvs as the injection speed setting Lvs inthe reference pressure-controlled injection illustrated in Figure 3 is used inthe first process. Thus, the actual speed Lv illustrated in Figure 4substantially matches the actual speed Lv illustrated in Figure 3.Accordingly, the injection speed in the speed control process in thereference pressure-controlled injection can be substantially completelyreproduced.

[0053] In the second process after the first process in the injecting process,the injection controlling unit 85 controls the injection speed based on thepast speed detection result. Thus, in the second process, the actual speedLv in the reference pressure-controlled injection illustrated in Figure 3 isthe injection speed setting Lvs illustrated in Figure 4. In the referencepressure-controlled injection, the injection speed setting Lvs is ignored inthe pressure control process. Thus, the past speed detection result as theactual speed Lv in the pressure-controlled injection is used in speed control.Accordingly, injection molding can be executed by speed control so that thepressure control process in the reference pressure-controlled injection isreproduced. As a result, the variance in the injection speed ateach shot is reduced, and reproducibility of the quality of a molded productimproves.

[0054] More specifically, the injection controlling unit 85 controls theinjection speed in the injecting process by using the past speed setting andthe past speed detection result as a speed setting of the injection speed.Unlike the past speed setting, the "speed setting" is a setting of theinjection speed in a molding cycle being performed or to be performed.The past speed setting in the speed control process in thepressure-controlled injection is used for the speed setting in the firstprocess as described above. The past speed detection result in thepressure control process in the pressure-controlled injection is used for thespeed setting in the second process as described above. The injectioncontrolling unit 85 controls the injection speed in the injecting process sothat the injection speed follows the past speed setting and the past speeddetection result. The injection controlling unit 85 performs feedbackcontrol such as PID control.

[0055] A method of controlling the injection molding machine 1 will bedescribed below.

[0056] Figure 5 is a flowchart illustrating an example of operation of theinjection molding machine 1 according to the first embodiment.

[0057] First, the injection molding machine 1 executes thepressure-controlled injection, and the data memory 111 stores theinjection speed waveform of the pressure-controlled injection (S10).

[0058] Subsequently, the user determines whether or not a molded productis a non-defective product (S20). When the molded product is not anon-defective product (NO at S20), step S10 is executed again. Thus,steps S10 and S20 are repeatedly executed until a non-defective product isobtained. Steps S10 and S20 are executed, for example, in each moldingcycle.

[0059] When the molded product is a non-defective product (YES at S20),the storage controlling unit 83 stores the past speed setting andthe past speed detection result in the reference waveform memory 112(S30). For example, the user operates the storage controlling unit 83through an operation of the HM I / F 60 and stores, in the referencewaveform memory 112, the past speed setting set by the injection speedsetting unit 84 and the past speed detection result stored in the datamemory 111.

[0060] Subsequently, the injection speed setting unit 84 automatically setsthe injection speed (S40). The injection speed setting unit 84 acquiresand sets, as the speed setting in later molding operation, the past speedsetting and the past speed detection result stored in the referencewaveform memory 112.

[0061] Subsequently, the injection molding machine 1 starts moldingoperation based on the setting by the injection speed setting unit 84 (S50).

[0062] Subsequently, the user determines whether or not a molded productis a non-defective product (S60). When the molded product is not anon-defective product (NO at S60), the user corrects the injection speed(S70). In other words, the user adjusts the speed setting by the injectionspeed setting unit 84. Thereafter, step S50 is executed again. Thus,steps S50 to S70 are repeatedly executed until a non-defective product isobtained. Steps S50 to S70 are executed, for example, in each moldingcycle.

[0063] When the molded product is a non-defective product (YES at S60),the user continues operation without change. Accordingly, massproduction of the product is performed.

[0064] The pressure-controlled injection (step S10) and the moldingoperation (step S50) illustrated in Figure 5 do not necessarily need to beperformed through a series of operations. For example, thepressure-controlled injection may be separately performed before themolding operation, and the past speed setting and the past speed detectionresult obtained in the pressure-controlled injection may be used in themolding operation independently performed thereafter. Accordingly,when molds are frequently replaced along with change of moldedproducts in multi-kind small-lot production, the past speed setting and thepast speed detection result of the same molds can be reused. As a result,speed waveform sampling in the pressure-controlled injection can beomitted to improve manufacturing efficiency.

[0065] Figure 6A is a graph illustrating exemplary speed waveforms in aplurality of control methods. Figure 6B is a graph illustrating exemplarypressure waveforms in a plurality of control methods. The speed andpressure waveforms illustrated in Figures 6A and 6B are actual values.

[0066] The reference sign V1 denotes the actual speed in the referencepressure-controlled injection. The reference sign V2 denotes the actualspeed in the molding operation in the present embodiment. The referencesign V3 denotes the actual speed in laminar control as a comparativeexample. Like the actual speed Lv illustrated in Figures 3 and 4, the actualspeeds V1 to V3 illustrated in Figure 6A reach peaks and decreasethereafter.

[0067] The reference sign P1 denotes the actual pressure in the referencepressure-controlled injection. The reference sign P2 denotes the actualpressure in the molding operation in the present embodiment. Thereference sign P3 denotes the actual pressure in the laminar control as acomparative example. Like the actual pressure Lp illustrated in Figures 3and 4, the actual pressures P1 to P3 illustrated in Figure 6B increase andbecome substantially constant thereafter. As illustrated in Figure 6B, theactual pressures P1 to P3 gradually increase in some cases instead ofbecoming substantially constant.

[0068] The laminar control is a control method that controls the injectionspeed in the entire injecting process based on the past speed detectionresult in the pressure-controlled injection executed in advance. Thus, thepast speed setting is not used in the laminar control. Details of thelaminar control will be described later with reference to Figure 7.

[0069] As illustrated in Figure 6A, time until the actual speed V1 reacheshighest speed is 65 ms approximately. Time until the actual speed V2reaches highest speed is 64 ms approximately. These reachingtimes are close to each other. Thus, the actual speed V2 in the moldingoperation in the present embodiment undergoes temporal change similarto that of the actual speed V1 in the reference pressure-controlledinjection.

[0070] At 0 ms to 40 ms approximately, the actual speed V2 substantiallymatches the actual speed V1. At 40 ms approximately to 65 msapproximately, the actual speed V2 is lower than the actual speed V1.This is because such a control method is used that starts decelerationbefore the first process ends to prevent the actual speed behind the settingfrom exceeding (overshooting) the maximum value of the injection speedsetting. For example, when the first process ends after the actual speedLv substantially matches (is stable at) the injection speed setting Lvs for apredetermined duration, the actual speed V2 in the first processsubstantially matches the actual speed V1. Alternatively, a controlmethod that performs no deceleration in the first process may be used. Inthis case as well, the actual speed V2 in the first process substantiallymatches the actual speed V1.

[0071] At 65 ms approximately to 150 ms approximately, the actual speedV2 follows behind the actual speed V1. At 150 ms approximately or later,the actual speed V2 substantially matches the actual speed V1.

[0072] As illustrated in Figure 6B, the actual pressure P1 in the referencepressure-controlled injection reaches a peak at 77 ms approximately.Time until the actual pressure P2 reaches the peak pressure of the actualpressure P1 is 90 ms approximately. Thus, the actual pressure P2 in themolding operation in the present embodiment undergoes temporal changesimilar to that of the actual pressure P1 in the referencepressure-controlled injection.

[0073] Thus, in the molding operation in the present embodiment, injectionmolding can be executed at the injection speed and the injection pressureclose to those in the reference pressure-controlled injection.

[0074] As described above, according to the first embodiment, the injectioncontrolling unit 85 controls the injection speed in the injectingprocess based on the past speed setting and the past speed detection resultin a molding cycle performed in advance. Accordingly, the injectingprocess can be executed by speed control so that the injection speed andthe injection pressure in the reference pressure-controlled injection in apast molding cycle are reproduced. As a result, mold protection,low-pressure molding, and low-residual-stress molding can be achieved,and reproducibility of the quality of a molded product in low-pressureinjection molding can be improved by speed control.

[0075] Figure 7 is a graph illustrating an exemplary speed waveform and anexemplary pressure waveform in the laminar control.

[0076] As illustrated in Figure 7, in the laminar control, the actual speed Lvin the entire injecting process in the reference pressure-controlled injectionis set to the injection speed setting Lvs. Specifically, the laminar control isdifferent from the molding operation in the present embodiment illustratedin Figure 4 in that the past speed detection result is used for the speedsetting at the start of the injecting process as well and the past speedsetting is not used for the speed setting.

[0077] The actual speed Lv right after the start of the injecting processillustrated in Figure 7 is lower than the actual speed Lv illustrated in Figures3 and 4. This is because the actual speed in the referencepressure-controlled injection Lv is set to the injection speed setting Lvs inthe laminar control. Accordingly, the actual speed Lv illustrated in Figure7 is affected by double control delay behind the injection speed setting Lvsin the reference pressure-controlled injection illustrated in Figure 3. Inthe laminar control, since speed control is performed in the entire injectingprocess, reproducibility of the quality of a molded product at each shot isobtained as in the molding operation in the present embodiment. However,temporal change of the injection speed and the injection pressure in thelaminar control is largely different from that of the reference molding cyclein some cases. In such a case, a mold defect that does not occur in thereference molding cycle potentially occurs.

[0078] As illustrated in Figure 6A, time until the actual speed V3 reacheshighest speed is 95 ms approximately. The time 95 msapproximately is longer than 65 ms approximately and 64 msapproximately, which are the reaching times of the actual speeds V1 and V2.In other words, the actual speed V3 in the laminar control is largely behindthe actual speed V1 and the actual speed V2 at 0ms to 150 msapproximately.

[0079] As illustrated in Figure 6B, time until the actual pressure P3 reachesthe peak pressure of the actual pressure P1 is 117 ms approximately. Thetime 117 ms approximately is longer than 77 ms approximately and 90 msapproximately, which are the reaching times of the actual pressures P1 andP2. In other words, the actual pressure P3 in the laminar control is largelybehind the actual pressure P1 and the actual pressure P2 at 0ms to 150 msapproximately.

[0080] However, in the present embodiment, the past speed setting is usedin place of the past speed detection result for speed control in the firstprocess. Accordingly, the actual speed Lv and the actual pressure Lp inthe first process can be set to be substantially the same as those in thereference pressure-controlled injection. As a result, the actual speed Lvand the actual pressure Lp in the second process after the first process canbe set to be close to those in the reference pressure-controlled injection.Thus, the quality of a molded product such as appearance quality can beimproved as compared to the laminar control.

[0081] (Second embodiment)Figure 8 is a block diagram illustrating the configuration of thecontrolling device 8 according to a second embodiment. The secondembodiment is different from the first embodiment in that feedforwardcontrol (FF control) is used for control of the injection speed in the secondprocess.

[0082] In the molding operation of the first embodiment, the actual speedLv in the second process follows behind the injection speed setting Lvs dueto control delay as illustrated in Figure 4. Thus, when the injection speedsetting Lvs abruptly changes, for example, at the start of the secondprocess, the actual speed Lv potentially does not match the injection speedsetting Lvs. Thus, the actual speed Lv in the second process can be setcloser to the injection speed setting Lvs by reducing the control delay byusing the feedforward control. The feedforward control is not performedin the first process. Thus, the first process in the second embodiment isthe same as in the first embodiment.

[0083] The controlling device 8 further includes an integrator IN and acommand correcting unit C.

[0084] The injection controlling unit 85 generates a speed command of thescrew 42 based on the past speed detection result set by the injectionspeed setting unit 84.

[0085] The integrator IN as a command converting unit converts the speedcommand generated by the injection controlling unit 85 into a positioncommand by integrating the speed command. The integrator IN transfersthe position command obtained by the conversion to the injection controlservo amplifier 86.

[0086] The command correcting unit C corrects the position command ofthe screw 42 based on the speed command. More specifically, thecommand correcting unit C corrects the position command so that a speeddetection result detected by the speed sensor approaches the past speeddetection result. Unlike the past speed detection result, the "speeddetection result" is the detection result of the injection speed in a moldingcycle being performed or to be performed.

[0087] The command correcting unit C includes a feedforward controllingunit FC and an adder A.

[0088] The feedforward controlling unit FC calculates the product of thespeed command of the screw 42 based on the past speed detection resultand a predetermined value. The predetermined value is, for example, afeedforward control amount (FF amount) F illustrated in Figure 8. Forexample, the feedforward control amount F is constant.

[0089] The adder A corrects the position command by adding the product ofthe speed command of the screw 42 based on the past speed detectionresult and the feedforward control amount F to the position commandbased on the past speed detection result. The adder A transfers theposition command as the result of the addition to the injection control servoamplifier 86. Thus, the sum of the original position command and thefeedforward control amount F is transferred as a command to the injectioncontrol servo amplifier 86. Accordingly, speed response in the secondprocess improves and speed feedback delay due to control delay isreduced.

[0090] Figure 9 is a graph illustrating an example of change of the speedcommand by the feedforward control. The speed command is obtained bydifferentiating the position command with respect to time.

[0091] The reference sign L1 (dashed line) denotes temporal change of thespeed command when the feedforward control is not performed (when thefeedforward control amount F is zero). As time elapses, the temporalchange L1 increases, becomes constant, and decreases thereafter. Thereference sign L2 (solid line) denotes temporal change of the speedcommand when the feedforward control is performed.

[0092] As illustrated in Figure 9, the speed command when the feedforwardcontrol is performed has a speed waveform different from that of theoriginal command speed due to the addition of the feedforward controlamount F.

[0093] Figure 10 is a graph illustrating an example of change of the speedcommand by the feedforward control in the second process. Speedillustrated in Figure 10 is the outline of temporal change of the speedcommand.

[0094] The reference sign L1a (dashed line) denotes temporal change of thespeed command when the feedforward control is not performed. Thus,the temporal change L1a has the outline of the injection speed setting Lvsillustrated in Figure 4. The temporal change L1a takes into account risingof speed at the start of the injecting process. The reference sign L2a (solidline) denotes temporal change of the speed command when thefeedforward control is performed. Time of 150 ms to 300 ms illustratedin Figure 10 corresponds to time illustrated in Figure 6A.

[0095] In the example illustrated in Figure 10, the feedforward controlamount F in the first process is set to zero. Since the feedforward controlis not performed, L2a in the first process substantially matches L1a.

[0096] At a timing ta of switching between the first process and the secondprocess, setting of the feedforward control amount F is input and thefeedforward control is executed. Accordingly, L2a becomes smaller thanL1a. Thus, speed abruptly decreases right after the switching timing ta.Accordingly, control delay of speed feedback relative to the speedcommand is reduced, and for example, the actual speed Lv in the secondprocess in Figure 4 becomes closer to the injection speed setting Lvs.

[0097] At 150 ms, the difference between L1a and L2a decreases. This isbecause the value of the feedforward control amount F decreases. In thesecond process, setting of the feedforward control amount F may bechanged in accordance with the magnitude of feedback control delay, inother words, the magnitude of change of the speed command.

[0098] The feedforward control amount F is set to be substantially equal tothe deviation between the position command and the position feedback ofthe screw 42. The position feedback is, for example, the result ofdetection by the screw position sensor S2. Accordingly, feedback controldelay is compensated (reduced). For example, a desired value with whichfeedback delay is appropriately canceled is set for the feedforward controlamount F by the user in advance. For example, the user checks the actualspeed in performance check of the injection molding machine 1 anddetermines the value of the feedforward control amount F. Thefeedforward control amount F may be stored in a storing unit such as thereference waveform memory 112.

[0099] In Figure 10, the moving amount of the screw 42 is obtained byintegrating speed. In the example illustrated in Figure 10, the movingamount appears to be different between L1a and L2a. However, precisely,when the feedforward control is started, a speed command in a direction inwhich the moving amount difference between L1a and L2a iscompensated by an amount corresponding to one control scanning rightafter the start is generated. As a result, the moving amount issubstantially equal between L1a and L2a. With one control scanning only,the generated speed command hardly affects variation of speed feedback.

[0100] In this manner, delay of the injection speed in the second processcan be reduced by using the feedforward control. Not only delay of theinjection speed but also delay of the injection pressure can be reduced. Asa result, temporal changes of the actual speed Lv and the actual pressureLp can be made further closer to the values thereof in a molding cycle as areference (in non-defective product molding). Thus, the quality of amolded product can be further improved and made closer to quality inreference molding.

[0101] Any other configuration of the injection molding machine 1according to the second embodiment is the same as the correspondingconfiguration of the injection molding machine 1 according to the firstembodiment, and thus detailed description thereof is omitted.

[0102] The injection molding machine 1 according to the secondembodiment can obtain the same effects as in the first embodiment.

[0103] At least part of the injection molding machine 1 according to thepresent embodiment and the method of controlling the same may beconfigured as hardware or software. In a case of software configuration, acomputer program that achieves the function of at least part of theinjection molding machine 1 and the method of controlling the same maybe stored in a recording medium such as a flexible disk or a CD-ROM andmay be read and executed by a computer. The recording medium is notlimited to a detachable medium such as a magnetic disk or an optical diskbut may be a fixed recording medium such as a hard disk device or amemory. The computer program that achieves the function of at least partof the injection molding machine 1 and the method of controlling the samemay be distributed through a communication line (including wirelesscommunication) such as the Internet. Moreover, the computer program inan encrypted, modulated, or compressed state may be distributed througha wired or wireless line such as the Internet or may be stored in arecording medium and distributed.

[0104] While certain embodiments of the present invention have beendescribed, these embodiments have been presented by way of exampleonly, and are not intended to limit the scope of the invention. Theseembodiments may be embodied in a variety of other forms; furthermore,various omissions, substitutions and changes may be made withoutdeparting from the spirit of the invention. These embodiments and theirvariations are included in the scope and spirit of the invention, as well asincluded in the invention described in the claims and the scope of itsequivalents.

Claims

1. An injection molding machine comprising: an injecting device configured to inject a material into clamped molds; and a controlling unit configured to control the injecting device and control, based on a past speed setting of an injection speed set in past and a past speed detection result in a molding cycle performed in advance, an injection speed in an injecting process through which the injecting device injects the material into the molds, the past speed detection result being detected in past by a speed sensor configured to detect the injection speed.

2. The injection molding machine according to claim 1, wherein the controlling unit controls the injection speed based on the past speed setting in a first process in the injecting process, and controls the injection speed based on the past speed detection result in a second process after the first process in the injecting process.

3. The injection molding machine according to claim 2, wherein in the first process in a molding cycle performed in advance, the controlling unit controls the injection speed based on the past speed setting until a pressure detection result of a pressure sensor configured to detect injection pressure reaches a predetermined upper limit value since start of the injecting process, and in the second process in the molding cycle performed in advance, the controlling unit controls injection pressure so that the pressure detection result is equal to or smaller than the predetermined upper limit value.

4. The injection molding machine according to any one of claims 1 to 3, wherein the injecting device injects the material into the clamped molds by moving a screw in a barrel, the controlling unit generates a speed command of the screw based on the past speed detection result, and the injection molding machine further comprises a command correcting unit configured to correct a position command of the screw based on the speed command.

5. The injection molding machine according to claim 4, wherein the command correcting unit corrects the position command so that a speed detection result detected by the speed sensor approaches the past speed detection result.

6. The injection molding machine according to claim 4 or 5, wherein the command correcting unit corrects the position command by adding, to the position command based on the past speed detection result, a product of the speed command of the screw based on the past speed detection result and a predetermined value.

7. The injection molding machine according to claim 6, wherein the predetermined value is set to be substantially equal to a deviation between the position command and a position feedback of the screw.

8. The injection molding machine according to any one of claims 1 to 7, wherein the controlling unit controls the injection speed in the injecting process by setting the past speed setting and the past speed detection result as speed settings of the injection speed.

9. The injection molding machine according to any one of claims 1 to 8, wherein the controlling unit controls the injection speed in the injecting process so that the injection speed follows the past speed setting and the past speed detection result.

10. The injection molding machine according to any one of claims 1 to 9, wherein the controlling unit controls the injection speed in the injecting process based on the past speed setting and the past speed detection result in a molding cycle in which a molded product is a non-defective product among molding cycles performed in advance.

11. The injection molding machine according to any one of claims 1 to 10, further comprising a storage controlling unit configured to cause a storage unit to store the past speed setting and the past speed detection result in a molding cycle performed in advance.

12. A method of controlling an injection molding machine including an injecting device configured to inject a material into clamped molds and a controlling unit configured to control the injecting device, the method comprising controlling, by the controlling unit, based on a past speed setting of an injection speed set in past and a past speed detection result in a molding cycle performed in advance, an injection speed in an injecting process through which the injecting device injects the material into the molds, the past speed detection result being detected in past by a speed sensor configured to detect the injection speed.