Patent Publication Number: US-2007110841-A1

Title: Molding machine and molding method

Description:
TECHNICAL FIELD  
      The present invention relates to a molding machine and a molding method.  
     BACKGROUND ART  
      Conventionally, in a molding machine, such as an injection molding machine, having a drive apparatus which is operated by a hydraulic circuit, a resin which is heated and melted within a heating cylinder is injected at high pressure to fill the cavity of a mold apparatus, and is cooled and solidified inside the cavity to form a molded article.  
      For this purpose, the above-described injection molding machine has a mold-clamping apparatus and an injection apparatus, and the mold-clamping apparatus has a stationary platen and a movable platen. Closing, clamping, and opening of the mold apparatus are carried out by driving a mold-clamping cylinder and advancing and retracting the movable platen.  
      The above-described injection apparatus has a heating cylinder which heats and melts resin which is supplied thereto from a hopper, and an injection nozzle which injects the molten resin. A screw is disposed inside the heating cylinder so as to be able to rotate and so as to be able to advance and retract. If an injection cylinder is driven and the screw is advanced, resin is injected from the injection nozzle and fills the cavity.  
      A hydraulic circuit is provided for driving actuators such as the mold-clamping cylinder and the injection cylinder. In this hydraulic circuit, oil discharged from a hydraulic pump (hydraulic pressure source) upon drive thereof is supplied to an oil chamber of an actuator. In cases where a large amount of oil must be supplied to the oil chamber in order to drive the actuator, the amount of oil which is discharged from the hydraulic pump is inadequate. Therefore, an accumulator is disposed in the hydraulic circuit. Oil at a prescribed pressure; i.e., at a charge pressure, is stored within the accumulator, and when the actuator is driven, oil stored within the accumulator is supplied to the oil chamber.  
      Therefore, the hydraulic circuit includes a charge pressure sensor which senses the charge pressure, a logic valve which assumes an on-load position and an unload position in accordance with the charge pressure sensed by the charge pressure sensor; i.e., the sensed charge pressure, an on-load switching valve for switching the logic valve, and other components. When the sensed charge pressure falls below a preset lower limit, the logic valve is switched by the on-load switching valve and placed in its on-load position, and oil discharged from the hydraulic pump is stored in the accumulator. When the sensed charge pressure exceeds a preset upper limit, the logic valve is switched by the on-load switching valve and placed in its unload position, and oil discharged from the hydraulic pump is drained (see Patent Document 1, for example).  
      Patent Document 1: Japanese Patent Application Laid-Open (kokai) NO. H5-92462  
     DISCLOSURE OF THE INVENTION  
     Problem to be Solved by the Invention  
      In the above-described conventional accumulator, the lower limit and upper limit are fixed, so that when the actuators are driven at low pressure, oil at an unnecessarily high charge pressure is stored in the accumulator, the load applied to the hydraulic pump is increased by that amount, and the amount of energy which is consumed becomes large.  
      The object of the present invention is to solve the problems of the above-described conventional accumulator and to provide a molding machine and a molding method which can reduce the load which is applied to a hydraulic pressure source and reduce energy consumption.  
     MEANS FOR SOLVING THE PROBLEM  
      For this purpose, a molding machine of the present invention has an actuator which is driven by supplied oil, an accumulator which is disposed along an oil passage for supplying oil to the accumulator, a drive pressure sensing section which senses the drive pressure for driving the actuator, a charge pressure sensing section which senses the charge pressure of the accumulator, and a charge pressure setting processing means which sets the charge pressure in accordance with the sensed charge pressure and the sensed drive pressure.  
     EFFECTS OF THE INVENTION  
      According to the present invention, a molding machine has an actuator which is driven by supplied oil, an accumulator which is disposed along an oil passage for supplying oil to the actuator, a drive pressure sensing section which senses the drive pressure for driving the actuator, a charge pressure sensing section which senses the charge pressure of the accumulator, and a charge pressure setting processing means which sets the charge pressure on the basis of the sensed charge pressure and the sensed drive pressure.  
      In this case, the charge pressure is set on the basis of the sensed charge pressure and the sensed drive pressure, so that oil is not stored in the accumulator at an unnecessarily high charge pressure. Accordingly, the load which is applied to the hydraulic pressure source is reduced by that amount, and energy consumption can be reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram showing a control apparatus of a hydraulic circuit in an embodiment of the present invention.  
       FIG. 2  is a drawing showing the hydraulic circuit in the embodiment of the present invention.  
       FIG. 3  is a timing chart showing the operation of an accumulator in the embodiment of the present invention. 
    
    
     DESCRIPTIONS OF REFERENCE NUMERALS  
     
         
         
           
               11  Injection cylinder  
               19  Drive pressure sensor  
               31  Control section  
               35  Accumulator  
               36  Charge pressure sensor  
              L- 3  Oil passage  
           
         
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION  
      An embodiment of the present invention will now be described in detail while referring to the drawings. In this case, an injection cylinder disposed in an injection apparatus of an injection molding machine will be described as an actuator serving as a drive apparatus. However, the actuator may be a mold-clamping cylinder, an ejector cylinder for advancing and retracting an ejector pin in an ejector apparatus, or a plasticizing moving cylinder used in a plasticizing moving apparatus for advancing and retracting an injection apparatus with respect to a stationary mold. Further, the actuator serving as a drive apparatus may be a hydraulic cylinder or the like used in a mechanical apparatus.  
       FIG. 1  is a block diagram showing a control apparatus of a hydraulic circuit in an embodiment of the present invention,  FIG. 2  is a diagram showing the hydraulic circuit in the embodiment of the present invention, and  FIG. 3  is a timing chart showing the operation of an accumulator in the embodiment of the present invention.  
      In  FIG. 2 , reference numeral  11  denotes an injection cylinder. In an injection step, by driving this injection cylinder  11 , a screw which is disposed in an unillustrated heating cylinder is advanced and retracted, and a resin (molding material) can be injected and suck-back can be carried out. For this purpose, the injection cylinder  11  has a cylinder body  12 , a piston  13  which is advanced and retracted (moved leftward and rightward in  FIG. 2 ) within the cylinder body  12 , and a piston rod  14  which is formed so as to project forward (leftward in  FIG. 2 ) from the piston  13 . The piston rod  14  is linked to the screw. An oil chamber (first chamber)  15  is formed on the piston head side in the cylinder body  12 . An oil chamber (second chamber)  16  is formed on the side towards the piston rod  14 . By supplying oil to the oil chamber  15  and draining oil from the oil chamber  16 , the piston  13  can be advanced (moved to the left in  FIG. 2 ) to advance the screw, and by supplying oil to the oil chamber  16  and draining oil from the oil chamber  15 , the piston  13  can be retracted (moved to the right in  FIG. 2 ) to retract the screw.  
      For the injection cylinder  11 , there are provided a position sensor  18  for sensing the position of the piston  13 , and a drive pressure sensor (drive pressure sensing section)  19  for sensing the pressure of oil supplied to oil chamber  15 ; i.e., for sensing the drive pressure DP. A sensed drive pressure DPS signal, which indicates the drive pressure DP which is sensed by the drive pressure sensor  19 , is sent to a control section  31 . A hydraulic pump  21  is provided as an oil supply source for supplying oil to the injection cylinder  11 . In order to operate the hydraulic pump  21 , a motor (M) (drive source)  22  is connected to the hydraulic pump  21 . When the motor  22  is driven, the hydraulic pump  21  is operated, oil is sucked from an oil tank  23 , the oil is discharged into an oil passage L- 1 , and is supplied to a servo valve  25  through an oil passage L- 2 , a check valve  24 , and an oil passage L- 3 .  
      The servo valve  25  assumes a first position A, a second position B, and a third position N. By driving a solenoid (SOL)  32  on the basis of a solenoid signal SG 1  from the control section  31 , the servo valve is placed in the first through third positions A, B, and N and the flow rate of oil is adjusted. When the servo valve  25  is in the first position A, the oil passage L- 3  and an oil passage L- 4  are brought into mutual communication, and an oil passage L- 5  is brought into communication with the oil tank  23 . When the servo valve  25  is in the second position B, the oil passage L- 3  and the oil passage L- 5  are brought into mutual communication, and the oil passage L- 4  is brought into communication with the oil tank  23 . When the servo valve  25  is in the third position N, the oil passages L- 4  and L- 5  are brought into communication with the oil tank  23 .  
      Accordingly, an unillustrated injection processing means of the control section  31  carries out injection processing, and when the solenoid signal SG 1  is sent to the solenoid  32 , the servo valve  25  is disposed in the first position A, the oil passage L- 3  and the oil passage L- 4  are brought into mutual communication, and the oil passage L- 5  is brought into communication with the oil tank  23 . As a result, oil is supplied to the oil chamber  15 , oil is drained from the oil chamber  16 , the piston  13  is advanced, the screw is advanced, and resin is injected. By changing the value of the solenoid signal SG 1 , the degree of opening of the servo valve  25  is changed, and the speed of movement of the screw; i.e., the screw speed, can be changed. An unillustrated suck-back processing means of the control section  31  carries out suck-back processing, and when the solenoid signal SG 1  is turned off, the servo valve  25  is placed in the second position B, the oil passage L- 3  is brought into communication with the oil passage L- 5 , and the oil passage L- 4  is brought into communication with the oil tank  23 . As a result, oil is supplied to the oil chamber  16 , oil is drained from the oil chamber  15 , the piston  13  is retracted, the screw is retracted, and suck-back is carried out.  
      In order to advance the screw by driving the injection cylinder  11 , a large amount of oil must be supplied to the oil chamber  15 , and the amount of oil discharged from the hydraulic pump  21  is inadequate. Therefore, an accumulator  35  is disposed along the oil passage L- 3 , the accumulator  35  is filled with oil at a prescribed charge pressure CP, and when the injection cylinder  11  is driven, oil stored in the accumulator  35  is supplied to the oil chamber  15 .  
      For this purpose, a charge pressure sensor (charge pressure sensing section)  36  for sensing the charge pressure CP is disposed along the oil passage L- 3 . A sensed charge pressure CPS signal which indicates the charge pressure CP sensed by the charge pressure sensor  36  is sent to the control section  31 . A logic valve (filling oil adjusting apparatus)  37  which adjusts the amount of oil stored in the accumulator  35  is connected to an oil passage L- 8  which is formed so as to branch from the junction of the oil passages L- 1  and L- 2 . The logic valve  37  assumes an on-load position O and an unload position U. In the on-load position O, the logic valve cuts off communication between the oil passage L- 8  and an oil passage L- 9 , and in the unload position U, the logic valve brings the oil passage L- 8  and the oil passage L- 9  into communication with the oil tank  23 .  
      An oil passage M- 1  branches from the oil passage L- 3  between the check valve  24  and the connection between the accumulator  35  and the charge pressure sensor  36 . An on-load switching valve (signal oil pressure generating apparatus)  38  is connected to the oil passage M- 1 . The charge pressure CP is sent to the on-load switching valve  38  as a pilot oil pressure. The on-load switching valve  38  assumes a first position A and a second position B. The valve is placed in the first or second position A or B when a solenoid (SOL)  39  is driven on the basis of a solenoid signal SG 2  from the control section  31 . The on-load switching valve receives the pilot oil pressure and selectively sends the pilot oil pressure as a signal oil pressure to the logic valve  37  via an oil passage M- 2 . When the solenoid  39  is in the first position A, the oil passage M- 1  and the oil passage M- 2  are brought into mutual communication, and when the solenoid  39  is in the second position B, the oil passage M- 2  and an oil passage M- 3  are brought into communication with the oil tank  23 .  
      Accordingly, unillustrated pressure adjusting processing means of the control section  31  carries out pressure adjustment processing, reads the sensed charge pressure CPS from the charge pressure sensor  36 , operates the logic valve  37  on the basis of the sensed charge pressure CPS, and adjusts the charge pressure CP. Therefore, the pressure adjusting processing means determines whether the sensed charge pressure CPS is lower than a previously determined lower limit (first set value) CPL, and when the sensed charge pressure CPS is lower than the lower limit CPL, the pressure adjusting processing means turns the solenoid signal SG 2  on and drives the solenoid  39 .  
      As a result, the on-load switching valve  38  is placed in the first position A, the oil passage M- 1  and the oil passage M- 2  are brought into mutual communication, and a signal oil pressure is supplied to the logic valve  37 . The logic valve  37  is located in an on-load position O, and the oil passages L- 8  and L- 9  are cut off from each other, so that oil which is discharged into the oil passage L- 1  is sent through the check valve  24  to the oil passage L- 3 , and is stored in the accumulator  35 . In conjunction with this, the charge pressure CP gradually increases and the sensed charge pressure CPS increases, but the pressure adjusting processing means maintains the solenoid signal SG 2  on even when the sensed charge pressure CPS exceeds the lower limit CPL.  
      Then, the pressure adjusting processing means determines whether the sensed charge pressure CPS is higher than a previously determined upper limit (second set value) CPH. When the sensed charge pressure CPS is higher than the upper limit CPH, the solenoid signal SG 2  is turned off, and driving of solenoid  39  is stopped. In this manner, a hysteresis region is established between the lower limit CPL and the upper limit CPH.  
      As a result, the on-load switching valve  38  is placed in the second position B, the oil passage M- 2  and the oil passage M- 3  are brought into communication with the oil tank  23 , and a signal oil pressure is no longer supplied to the logic valve  37 . As a result, the logic valve  37  is placed in the unload position U, and the oil passages L- 8  and L- 9  are brought into mutual communication, so that oil which is discharged into oil passage L- 1  is drained through the oil passage L- 8 , the logic valve  37 , and the oil passage L- 9 . In conjunction with this, the oil pressure within oil passage L- 2  decreases, but the check valve  24  prevents oil within the oil passage L- 3  from flowing towards the oil passage L- 2 , so that the charge pressure CP is maintained constant.  
      In this manner, the charge pressure CP is adjusted on the basis of the sensed charge pressure CPS and the upper limit CPH and the lower limit CPL, and is maintained at the value of the upper limit CPH. At a prescribed timing, the injection processing means sends the solenoid signal SG 1  to the solenoid  32 , places the servo valve  25  in the first position A, establishes mutual communication between the oil passage L- 3  and the oil passage L- 4 , and establishes communication between the oil passage L- 5  and the oil tank  23 . As a result, oil is supplied to the oil chamber  15 , oil is drained from the oil chamber  16 , the piston  13  is advanced, the screw is advanced, and resin is injected.  
      At this time, the oil within the accumulator  35  is sent to the oil chamber  15  via the oil passage L- 3 , the servo valve  25 , and the oil passage L- 4 , and as a result, the charge pressure CP decreases.  
      If the lower limit CPL and the upper limit CPH are constant, when the injection cylinder  11  is driven at low pressure, oil at an unnecessarily high charge pressure CP is stored in the accumulator  35 , the load applied to the oil pressure pump  21  increases by that amount, and energy consumption ends up increasing.  
      In this embodiment, the lower limit CPL and the upper limit CPH are made variable, and the optimal required pressure is stored in the accumulator  35  as the charge pressure CP.  
      For this purpose, an unillustrated charge pressure setting processing means of the control section  31  carries out charge pressure setting processing. The charge pressure setting processing means operates the injection molding machine in accordance with previously set molding conditions, performs injection molding a number of times, and during this period, reads the sensed drive pressure DPS and the sensed charging CPS. On the basis of the sensed drive pressure DPS and the sensed charge pressure CPS, the charge pressure setting processing means sets the lower limit CPL and the upper limit CPH.  
      Therefore, an actual result obtaining processing means of the charge pressure setting pressure processing means carries out actual result obtaining processing, and obtains a maximum sensed drive pressure DPmax indicating the maximum value of the sensed drive pressure DPS and the minimum sensed charge pressure CPmin indicating the minimum value of the sensed charge pressure CPS. Then, the oil pressure determining means of the charge pressure setting processing means carries out oil pressure determination processing, reads the minimum sensed charge pressure CPmin and the maximum sensed drive pressure DPmax, calculates the differential pressure ΔP between the minimum sensed charge pressure CPmin and the maximum sensed drive pressure DPmax as ΔP=CPmin−DPmax, determines whether the differential pressure ΔP is higher than a previously set reference pressure α set for each molded article, and determines the pressure relationship between the charge pressure CP and the drive pressure DP.  
      When the differential pressure ΔP is higher than the reference pressure α, the charge pressure CP is determined to be unnecessarily high, so that the set pressure changing processing means of the charge pressure setting processing means carries out set pressure changing processing, and sets the upper limit CPH so that the differential pressure ΔP will become equal to the reference pressure α. Then, the set pressure changing processing means calculates and sets the lower limit CPL in consideration of the pressure gradient determined by the discharge ability of the oil pressure pump  21  and the capacity of the accumulator  35  and the molding conditions so that the sensed charge pressure CPS prior to the start of the injection step; i.e., when the servo valve  25  is in the first position A and before oil is supplied to oil chamber  15 , is made equal to the upper limit CPH.  
      In this manner, the upper limit CPH is lowered by just the amount by which the charge pressure CP is unnecessarily high, and at the same time, the lower limit CPL is lowered, so that, as shown in  FIG. 3 , the charge pressure CP can be changed from the conventional value denoted by line L 2  to the value denoted by line L 1 . In  FIG. 3 , line L 3  denotes the value of the drive pressure DP.  
      Accordingly, oil at an unnecessarily high charge pressure CP is not stored in the accumulator  35 , so that the load applied to the hydraulic pump  21  is lowered by this amount, and energy consumption can be decreased. An oil pressure control apparatus is constituted by the injection cylinder  11 , the accumulator  35 , the drive pressure sensor  19 , the charge pressure sensor  36 , the charge pressure setting processing means, and the like.  
      The upper limit CPH and the lower limit CPL can be set a plurality of times in one molding cycle.  
      The present invention is not limited to the above-described embodiments. Numerous modifications and variations of the present invention are possible in light of the spirit of the present invention, and they are not excluded from the scope of the present invention.  
     INDUSTRIAL APPLICABILITY  
      It can be applied to a molding machine having a drive apparatus operated by a hydraulic circuit.