JP5329318B2 - Control method of injection molding machine - Google Patents

Description

  The present invention is used to control an injection process including a filling process in which a screw is advanced to fill a mold with resin in a heating cylinder and a pressure-holding process in which pressure is applied to the resin filled in the mold. The present invention relates to a method for controlling a suitable injection molding machine.

  Conventionally, an injection molding machine that variably controls the rotational speed of a drive motor in a hydraulic pump, drives a hydraulic actuator such as an injection cylinder (hydraulic cylinder) based on this, and controls each operation step in a molding cycle. As for the control method, an injection molding machine control method disclosed in Patent Document 1 already proposed by the present applicant is known.

  The control method variably controls the rotational speed of the drive motor in the hydraulic pump, and uses a hydraulic pump capable of setting at least a plurality of fixed discharge flow rates as the hydraulic pump when performing control of each operation step in the molding cycle. The fixed discharge flow rate corresponding to each operation process is set based on a predetermined condition, and at the time of molding, the hydraulic pump is switched to the fixed discharge flow rate corresponding to each operation process, and the rotational speed of the drive motor is variably controlled. According to this control method, when viewed from the drive motor, the hydraulic pump can be used as at least a small-capacity type and a large-capacity type hydraulic pump. Increased energy savings, such as eliminating or reducing the need for separate measures for unstable areas where the motor speed is low It is possible to reduce running costs, reduce the overall initial cost including the servo circuit, etc. by realizing downsizing of the drive motor (servo motor), and further improve the moldability and molding quality by stabilizing the control. is there.

JP 2007-69500 A

  However, the above-described conventional injection molding machine control method still has the following problems to be solved.

  First, the operation process that requires a large flow rate in the molding cycle, specifically, the injection process (filling process, pressure holding process), etc. is completed in a relatively short time. When setting to a large flow rate (large capacity type), it is often the case that the drive motor is normally set to a high output (about 130% of the rated output) that does not cause a problem for a short time. In this case, there is no particular problem in normal operation. However, if an excessive load occurs due to some abnormality or the pressure holding process takes a long time, the drive motor stops due to overload (trip). Resulting in. Therefore, the molding cycle (molding operation) is interrupted, eventually resulting in a decrease in production efficiency and a decrease in molding quality and yield.

  Secondly, since a plurality of fixed discharge flow rates are set in units of operation processes such as a metering process, injection process (filling process, pressure holding process), etc., it cannot be said that they are necessarily in an optimal operation state (control state). Also occurs. For example, when the fixed discharge flow rate is switched during the transition period of operation, the control becomes unstable due to the time lag at the time of switching, or the fixed discharge flow rate is set for each operation process. From the standpoint of ensuring the stability of operation (control) and improving energy saving, such as the above-mentioned burden and increased energy consumption, it is not necessarily sufficient.

  An object of the present invention is to provide a method for controlling an injection molding machine that solves the problems existing in the background art.

  The control method of the injection molding machine M according to the present invention fills the mold 4 with a filling step Sic in which the screw 2 is advanced to fill the mold 4 with the resin in the heating cylinder 3 in order to solve the above-described problems. When controlling the injection process Si having the pressure-holding process Sip for applying pressure to the resin, the hydraulic pump 5 is supplied with at least a fixed flow rate Qm having a large flow rate and a fixed discharge flow rate Qs having a small flow rate smaller than the large flow rate. And a switching condition for switching the fixed discharge flow rates Qm and Qs in advance with respect to at least one physical quantity (Xs, Vs, Ps) associated with the operation of the injection process Si. As a physical quantity, one or more of the screw position Xs, the screw speed Vs, and the injection pressure Ps reach corresponding threshold values Xc, Vc, and Pc set in advance (first switching condition), and When the elapsed time Ts or the screw movement distance Ss, which is a physical quantity, reaches the preset setting values Tc and Sc or reaches the setting values Tc and Sc, the first switching condition is satisfied. A condition for satisfying (second switching condition) is set, and at the time of operation of the injection process Si, a large fixed flow rate Qm is set to control the injection process Si, and a physical quantity is monitored, and at least one If one or more physical quantities satisfy the corresponding second switching condition, the injection process Si is controlled by switching to a small fixed flow rate Qs.

  In this case, according to a preferred aspect of the invention, the hydraulic pump 5 may be a variable discharge hydraulic pump 5x that can set the fixed discharge flow rate Qm, Qs by changing the swash plate angle Rs, or the fixed discharge flow rate Qm. , Qs may be used, and a plurality of hydraulic pump units 5a, 5b may be used. The injection process Si can be controlled by variably controlling the rotational speed of the drive motor 6 that drives the hydraulic pump 5, and the drive motor 6 uses a servo motor 6s connected to the servo circuit 6sa. Can do. On the other hand, if the second switching condition is satisfied, predetermined abnormality processing including display processing can be performed.

  According to the control method of the injection molding machine M according to the present invention by such a method, the following remarkable effects are obtained.

  (1) During operation of the injection process Si, a large fixed flow rate Qm is set to control the injection process Si, and the physical quantity is monitored. At least one or more physical quantities corresponding to at least one physical quantity are monitored. If the switching condition is satisfied, the injection process Si is controlled by switching to the small fixed flow rate Qs, so that an excessive load occurs due to some abnormality or the process time of the injection process Si becomes longer. However, the stop (trip) of the drive motor 6 due to overload can be avoided. Therefore, since the production operation can be continued without interrupting the molding cycle (molding operation), the production efficiency can be improved and the molding quality and the yield can be improved.

  (2) Even in a normal operating state, it is not caught by the switching of the operating process or in the transition period of control, and from a large flow rate (fixed discharge flow rate Qm) at an optimal timing corresponding to the actual operating state (control state). Since the flow rate can be switched to a small flow rate (fixed discharge flow rate Qs), stability of operation (control) or energy saving can be further improved.

  (3) Since the switching condition includes that one or more of the screw position Xs, the screw speed Vs, and the injection pressure Ps reach the corresponding threshold values Xc, Vc, and Pc set in advance (first switching condition), The operating state of the screw in the injection process Si can be accurately detected, and the control method according to the present invention can be carried out easily and reliably.

  (4) As a switching condition, after the first switching condition is satisfied, the elapsed time Ts or the screw movement distance Ss reaches the preset set values Tc and Sc or reaches the set values Tc and Sc. Since one switching condition is satisfied (second switching condition), in addition to being able to accurately detect the operating state of the screw in the injection process Si, it is possible to avoid false detection and to further improve the reliability and reliability of detection. Can do.

  (5) According to a preferred embodiment, if a variable discharge hydraulic pump 5x capable of setting fixed discharge flow rates Qm and Qs by changing the swash plate angle Rs is used for the hydraulic pump 5, a single variable discharge hydraulic pump 5x can be used. Therefore, it is possible to smoothly switch between the fixed discharge flow rates Qm and Qs, and it is possible to contribute to the miniaturization of the entire hydraulic circuit used for carrying out the control method according to the present invention.

  (6) According to a preferred embodiment, if a plurality of hydraulic pump parts 5a and 5b capable of setting fixed discharge flow rates Qm and Qs are used for the hydraulic pump 5, a simple structure of the hydraulic pump parts 5a and 5b is combined. As a result, the overall cost can be reduced and control can be diversified.

  (7) According to a preferred embodiment, when the injection process Si is controlled, if the rotational speed of the drive motor 6 that drives the hydraulic pump 5 is variably controlled, the same effect (action) as in the inverter control can be saved. Energy property can be improved.

  (8) If the servo motor 6s connected to the servo circuit 3a is used as the drive motor 6 according to a preferred embodiment, the control method according to the present invention can be easily and reliably implemented, and the operational effects of the control method are more effective. Can enjoy.

  (9) According to a preferred aspect, if predetermined abnormality processing including display processing is performed when the second switching condition is satisfied, prompt countermeasures can be taken by rapid detection of abnormality. Can be minimized.

The flowchart which shows the process sequence of the control method of the injection molding machine which concerns on suitable embodiment of this invention, The block diagram including the hydraulic drive part of the injection molding machine used for implementation of the control method, Block circuit diagram of hydraulic drive unit in the same injection molding machine, Change characteristic diagram of each physical quantity versus time showing an example of operation in the injection process using the control method, Change characteristics diagram of each physical quantity versus time showing another example of operation in the injection process using the control method, Change characteristics diagram of each physical quantity versus time showing another example of operation in the injection process using the control method, Change characteristics diagram of each physical quantity versus time showing another example of operation in the injection process using the control method, Change characteristics diagram of each physical quantity versus time showing another example of operation in the injection process using the control method, Control state explanatory diagram of the molding cycle when the control method is implemented, The block diagram containing the hydraulic drive part of the injection molding machine used for implementation of the control method of the injection molding machine which concerns on the modified embodiment of this invention,

  Next, preferred embodiments according to the present invention will be given and described in detail with reference to the drawings.

  First, the configuration of an injection molding machine that can implement the control method according to the present embodiment will be described with reference to FIGS. 2 and 3.

  In FIG. 2, M is an injection molding machine, and includes an injection device Mi and a mold clamping device Mc. The injection molding machine M includes, as a hydraulic actuator (13a...), An injection cylinder 13a for moving the screw 2 built in the heating cylinder 3 in the injection device Mi and a metering motor (oil motor) 13b for rotating the screw 2. The mold clamping device Mc includes a mold clamping cylinder 13c that performs mold opening / closing and mold clamping with respect to the mold 4 and a projecting cylinder 13d (FIG. 3) that ejects a molded product from the mold 4 (ejector). In addition, an injection device moving cylinder 13e (FIG. 3) is provided to move the injection device Mi forward and backward to perform nozzle touch on the mold 4 or release thereof.

  On the other hand, 21 is a hydraulic drive unit, which includes a variable discharge hydraulic pump 5x (hydraulic pump 5) and a switching valve circuit 22 that serve as a hydraulic drive source. The variable discharge hydraulic pump 5x includes a pump unit 25 and a servo motor 6s (drive motor 6) that rotationally drives the pump unit 25, and can control the discharge flow rate by variably controlling the rotation speed of the servo motor 6s. Therefore, energy saving can be improved by the same effect (action) as the inverter control. In this case, an AC servo motor connected to a servo circuit (servo amplifier) 6sa is used as the servo motor 6s, and a rotary encoder 6se for detecting the rotation speed of the servo motor 6s is attached to the servo motor 6s. If a servo motor 6s connected to such a servo circuit 6sa is used as the drive motor 6, the control method according to the present invention can be easily and reliably implemented, and the effects of the control method can be more effectively enjoyed.

  Moreover, the pump part 25 incorporates the pump body 26 comprised with a swash plate type piston pump. Therefore, the pump unit 25 includes the swash plate 27. If the swash plate angle Rs, which is the inclination angle of the swash plate 27, is increased, the stroke of the pump piston in the pump body 26 increases, the discharge flow rate increases, and the swash plate angle Rs increases. If the plate angle Rs is reduced, the stroke of the pump piston is reduced and the discharge flow rate is reduced. Therefore, by setting the swash plate angle Rs to a predetermined angle, the fixed discharge flow rate Qm, Qs at which the discharge flow rate is fixed to a predetermined size, that is, a large fixed discharge flow rate Qm and smaller than this large flow rate. A small fixed flow rate Qs can be set. For this reason, the swash plate 27 is provided with a swash plate switching cylinder 28 and a return spring 29, and the swash plate switching cylinder 28 discharges the pump unit 25 (pump machine body 26) via a switching valve (electromagnetic valve) 30. Connect to the exit. Thus, the angle of the swash plate 27 can be switched by the swash plate switching cylinder 28. Furthermore, a pressure sensor 33 that detects the discharge pressure (load pressure) of the pump unit 25 is connected to the discharge port of the pump unit 25.

  Incidentally, since the variable discharge hydraulic pump 5x variably controls the rotation speed of the servo motor 6s to vary the discharge flow rate (discharge pressure), the fixed discharge flow rates Qm and Qs set by the swash plate angle Rs vary during control. On the other hand, it is necessary to switch the fixed discharge flow rate for a short period during non-control. For this reason, as described above, the swash plate switching cylinder 28 is connected to the discharge port of the pump unit 25 (pump machine body 26) via the switching valve 30, and the swash plate angle Rs is changed by the opening / closing control of the switching valve 30. In this case, the swash plate angle Rs that can be selected is two large and small angles. If such a variable discharge hydraulic pump 5x is used, it can be implemented by one variable discharge hydraulic pump 5x, so that the fixed discharge flow rate Qm and Qs can be switched smoothly and the control according to the present invention. There is an advantage that it is possible to contribute to miniaturization of the entire hydraulic circuit used for carrying out the method. Further, the hydraulic drive unit 21 can change the discharge flow rate and the discharge pressure of the variable discharge hydraulic pump 5x by variably controlling the rotation speed of the servo motor 6s, and based on this, each cylinder 13a described above can be changed. , 13c, 13d, 13e and the metering motor 13b can be controlled, and each operation process in the molding cycle can be controlled.

  On the other hand, the suction port of the pump unit 25 is connected to the oil tank 34, the discharge port of the pump unit 25 is connected to the primary side of the switching valve circuit 22, and the secondary side of the switching valve circuit 22 is As shown in FIG. 3, the injection cylinder 13a, the metering motor 13b, the clamping cylinder 13c, the protruding cylinder 13d, and the injection device moving cylinder 13e constituting the hydraulic actuator in the injection molding machine M are connected. Accordingly, the switching valve circuit 22 includes at least switching valves (electromagnetic valves) 22a, 22b, 22c, 22d connected to the injection cylinder 13a, the metering motor 13b, the clamping cylinder 13c, the protruding cylinder 13d, and the injection device moving cylinder 13e, respectively. And 22e. Each switching valve 22a is composed of one or two or more valve parts and necessary accessory hydraulic parts, and includes at least an injection cylinder 13a, a metering motor 13b, a mold clamping cylinder 13c, a protruding cylinder 13d, and an injection. It has a switching function related to supply, stop, and discharge of hydraulic oil to the device moving cylinder 13e.

  Reference numeral 41 denotes a molding machine controller. As shown in FIG. 3, a servo motor 6s is connected to the molding machine controller 41 via a servo circuit 6sa, and a rotary encoder 6se attached to the servo motor 6s includes: Connect to servo circuit 6sa. Further, the molding machine controller 41 is connected to each switching valve 22a, 22b, 22c, 22d, 22e and the switching valve 30 using electromagnetic valves. On the other hand, as shown in FIG. 2, the rear oil chamber of the injection cylinder 13a is provided with a pressure sensor 31 (injection pressure detecting means) for detecting the oil pressure of the rear oil chamber, that is, the injection pressure Ps, and the screw 2 A position sensor 32 (screw position detecting means) for detecting the position of the screw 2, that is, the screw position Xs, is attached to the rear end. The screw speed Vs can be obtained by differentiation of the screw position Xs. And the pressure sensor 31 and the position sensor 32 are connected to the molding machine controller 41, as shown in FIG. As a result, the physical quantities associated with the operation of the injection process Si (screw 2), that is, the injection pressure Ps, the screw position Xs, and the screw speed Vs can be detected at a position closer to the screw 2; High detection can be performed. Further, the pressure sensor 33 described above can be used instead of the pressure sensor 31. The molding machine controller 41 has a computing function for controlling the entire injection molding machine M, and executes control processing and arithmetic processing including various sequence controls, and in particular, for executing the control method according to the present invention. Stores control programs (processing programs).

  Next, the control method of the injection molding machine M according to the present embodiment will be specifically described with reference to FIGS.

  First, two different fixed discharge flow rates Qm and Qs, that is, a fixed flow rate Qm having a large flow rate and a fixed discharge flow rate Qs having a small flow rate smaller than the large flow rate are set in advance. Of the two fixed discharge flow rates Qm and Qs, the small fixed discharge flow rate Qs sets a standard discharge flow rate. Accordingly, the swash plate angle Rs is set to a relatively small angle (small capacity side). On the other hand, the fixed discharge flow rate Qm with a large flow rate can be set larger than the fixed discharge flow rate Qs with a small flow rate, specifically, about twice the fixed discharge flow rate Qs. Accordingly, the swash plate angle Rs is set to a relatively large angle (large capacity side). In particular, an operation process using a large fixed discharge flow rate Qm is often completed in a short time. Therefore, if the operation process is continued for a relatively long time, there is a possibility that the servo motor 6s may be adversely affected. In a relatively short time (several seconds), it is possible to set a discharge flow rate that hardly affects the servo motor 6s. Specifically, the output of the servo motor 6s is 130% of the rated output. It can be set on the large capacity side.

  Moreover, each operation process in the molding cycle to which each fixed discharge flow rate Qm, Qs is applied is set. In the following description, the large flow rate mode Fm is set to a large fixed flow rate Qm, and the small flow mode Fs is set to a small fixed flow rate Qs. As shown in FIG. 9, the operation process of the molding cycle includes main processes such as a metering process Sm, a filling process Sic, a pressure holding process Sip, a protruding process Se, and a mold clamping process Sc. FIG. 9 shows a large flow rate mode Fm for the metering step Sm, a large flow rate mode Fm for the filling step Sic, a small flow rate mode Fs for the pressure holding step Sip, a small flow rate mode Fs for the protruding step Se, and a large flow rate mode Fm for the clamping step Sc. An example of the mode switching pattern in which, is set is shown. Such a mode switching pattern is arbitrary. As in Patent Document 1 described above, in the filling process Si, the modes Fm and Fs to be applied are set differently depending on the magnitude of the injection speed, or in the pressure holding process Sip. The modes Fm and Fs to be applied can be set differently depending on the length of the pressure holding time.

  Further, since the filling step Sic and the pressure holding step Sip become the injection step Si, switching conditions are set for the injection step Si according to the present invention. That is, when the injection process Si (filling process Sic) is started in the large flow rate mode Fm (fixed discharge flow rate Qm), the switching conditions (first switching condition, second switching condition) for performing switching preferentially. ) Is set. Therefore, in the injection process Si in this case, control based on the above-described mode switching pattern is performed, but when the operation state satisfies the set switching condition, the operation in the large flow rate mode Fm (fixed discharge flow rate Qm). Even in the state, it is forcibly switched to the small flow rate mode Fs (fixed discharge flow rate Qs).

  In this case, the first switching condition is a threshold for each physical quantity associated with the operation of the injection process Si, specifically, screw position Xs [mm], screw speed Vs [%], and injection pressure Ps [%]. Xc [mm], Vc [%], and Pc [%] are set, and threshold values Xc, Vc, and Pc corresponding to at least one of the screw position Xs, screw speed Vs, and injection pressure Ps, which are these three physical quantities. On condition that Accordingly, the type (number) of threshold values Xc, Vc, and Pc to be applied and the sizes of the threshold values Xc, Vc, and Pc can be arbitrarily selected (set) in advance according to molding conditions, molded products, and the like. .

  Further, the second switching condition, after satisfying the first switching condition, reaches a set value Tc [second] in which the physical quantity accompanying the operation of the injection process Si, specifically, the elapsed time Ts [second] is set. On the condition. The second switching condition includes both a case where the elapsed time Ts only reaches the set value Tc and a case where the first switching condition is satisfied when the elapsed time Ts reaches the set value Tc. Is included. If necessary, the screw movement distance Ss [mm] may be used instead of the elapsed time Ts. In this case, a set value Sc [mm] corresponding to the screw movement distance Ss may be set.

  Table 1 shows setting examples of five specific switching conditions.

  Next, a specific processing procedure when the switching conditions of C1 to C5 in Table 1 are used will be described with reference to FIGS.

  First, the switching condition C1 sets a threshold value (limit pressure) Pc for the injection pressure Ps and a threshold value Xc for the screw position Xs as the first switching condition, and sets a set value Tc for the elapsed time Ts as the second switching condition. It is a thing. An example of a specific operation state when using the switching condition C1 is shown in FIG. This figure shows the change characteristics of the screw position Xs [mm], the screw speed Vs [%], and the injection pressure Ps [%] with respect to time [seconds] in the injection process Si (filling process Sic and pressure holding process Sip). By setting such a switching condition C1, the occurrence of an abnormality can be accurately detected. Therefore, the limit pressure Pc can be set in consideration of, for example, a magnitude that can prevent the servomotor 6s from stopping (tripping) due to overload. That is, when the load pressure at which the servo motor 6s stops due to overload is known, the limit pressure Pc can be set in consideration of a predetermined margin before this load pressure. Further, the threshold value Xc for the screw position Xs can be set by a deviation with respect to the position target value Xo. That is, it can be made a condition that the deviation between the detected screw position Xs and the position target value Xo is out of the allowable range (threshold value Xc).

  Hereinafter, the processing procedure when the switching condition C1 is used will be described with reference to the flowchart shown in FIG. Now, it is assumed that the injection molding machine M is in a molding operation and the molding cycle, in particular, the measuring step Sm in FIG. 9 is completed and the process proceeds to the injection step Si. In this case, the injection process Si starts from the large flow rate mode Fm according to a preset mode switching pattern (steps S1 and S2). That is, a predetermined switching signal is given to the switching valve 30 from the molding machine controller 41, and the swash plate angle Rs (large flow rate side) is switched. As a result, the variable discharge hydraulic pump 5x operates as a large-capacity hydraulic pump 5 that discharges a fixed discharge flow rate Qm that is a large flow rate.

  On the other hand, the molding machine controller 41 monitors the magnitude of the injection pressure Ps by the start of the injection process Si. Now, it is assumed that some abnormality occurs during the filling process Sic and the injection pressure Ps increases rapidly. In this case, the injection pressure Ps reaches the limit pressure Pc at time ts, which is earlier than the normal time. At the time ts when the limit pressure Pc is reached, the deviation between the screw position Xs and the position target value Xo is large, and this deviation is outside the allowable range (threshold value Xc). Therefore, the first switching condition is satisfied at time ts (step S3). Furthermore, time measurement is started from the time point ts that satisfies the first switching condition, and the molding machine controller 41 monitors whether or not the elapsed time Ts from the time point ts has reached the set value Tc. Then, it is determined again whether or not the first switching condition is maintained at the time point tc when the set value Tc is reached. At this time, the state where the injection pressure Ps reaches the limit pressure Pc is maintained even at the time point tc, and the state where the deviation between the screw position Xs and the position target value Xo is out of the allowable range (threshold value Xc) is maintained. In this case, the second switching condition is satisfied (step S4). Thereby, since the switching condition C1 consisting of the first switching condition and the second switching condition is satisfied at the time point tc, a predetermined switching signal is given from the molding machine controller 41 to the switching valve 30, and the swash plate 27 The angle is switched to a small swash plate angle Rs. That is, the large flow rate mode Fm is switched to the small flow rate mode Fs (step S5). As a result, the variable discharge hydraulic pump 5x operates as a small capacity hydraulic pump 5 that discharges a fixed discharge flow rate Qs that is a small flow rate.

  Thus, if the switching condition C1 is satisfied even in the middle of the filling step Sic, the switching condition C1 is given priority even in the operation state in the large flow rate mode Fm, and is forcibly switched to the small flow rate mode Fs. That is, even if the large flow rate mode Fm is set up to the VP switching position (end of the filling step Sic) by the mode switching pattern, the mode is switched to the small flow rate mode Fs before reaching the VP switching position. The control in the small flow rate mode Fs is performed at least until the end time te (FIG. 9) of the filling step Sic (step S6). Further, in the illustrated example, since the next pressure holding process Sip is also set to the small flow rate mode Fs, the pressure holding process Sip in the small flow rate mode Fs is performed as it is even after the filling step Sic is completed (steps S6 and S7). ). In the pressure holding step Sip, feedback control is performed on the pressure so that the target pressure is set in advance with respect to the pressure holding. In this case, the pressure control is performed by variably controlling the rotation speed of the servo motor 6s. During the control, the load pressure obtained from the pressure sensor 31 is applied to the molding machine controller 41.

  Furthermore, if a switching condition (first switching condition and second switching condition) C1 is satisfied, predetermined abnormality processing including display processing may be performed. As the abnormality processing, various types of abnormality processing such as display processing of error messages and warning lamps, alarm buzzer, notification by communication, and control associated with abnormality can be applied as necessary. By performing such an abnormality process, it is possible to take a quick countermeasure against the abnormality by quickly detecting the abnormality, and there is an advantage that the influence on the entire production can be minimized.

  When the above-described pressure holding process Sip ends, the entire injection process Si ends, and when the next molding cycle continues, another molding process (operation process) following the injection process Si is performed (step). S7, S8, S9). That is, according to the set mode switching pattern, the mold opening is performed, the protruding process Se is performed, and the mold clamping process Sc and the weighing process Sm are performed. In the case of the example, the control in the small flow rate mode Fs is performed in the protruding step Se, and the control in the large flow rate mode Fm is performed in the mold clamping step Sc and the measuring step Sm.

  The processing procedure in the case of using the switching condition C1 has been described above. Even in the case of the other switching conditions C2 to C5 in Table 1, the switching conditions to be set (first switching condition, second switching condition) Although the content of (condition) is different, basically, the processing by the same processing procedure as in the case of the switching condition C1 described above is performed.

  First, the switching condition C2 is a threshold (limit pressure) Pc for the injection pressure Ps, a threshold Xc for the screw position Xs, and a threshold Vc for the screw speed Vs, which are set as switching conditions (first switching conditions), respectively. Although the second switching condition is not set in the switching condition C2, the set value Tc for the elapsed time Ts can be set as the second switching condition if necessary. By setting such a switching condition C2, it is possible to accurately detect the occurrence of an abnormality as in the case of the switching condition C1. An example of a specific operation state when using the switching condition C2 is shown in FIG. This figure shows the change characteristics of the screw position Xs [mm], the screw speed Vs [%], and the injection pressure Ps [%] with respect to time [seconds] in the injection process Si (filling process Sic and pressure holding process Sip). In the case of FIG. 5, the threshold value Xc for the screw position Xs can be based on the condition that the deviation between the detected screw position Xs and the position target value Xo is outside the allowable range (threshold value Xc), and the screw speed. As the threshold value Vc for Vs, it can be a condition that the screw speed Vs falls within an allowable range (threshold value Vc) set near zero.

  When the switching condition C2 is used, the following processing is performed. In FIG. 5, the injection pressure Ps excluding the overshoot (transition period) reaches the limit pressure Pc at time tc. When the limit pressure Pc is reached, the deviation between the screw position Xs and the target position value Xo is large and is out of the permissible range (threshold value Xc), and the screw speed Vs is almost zero, and the permissible range (threshold value Vc). It enters the state. That is, the switching condition C2 is satisfied. In other words, although the screw 2 has not reached the target position, the screw 2 reaches the limit pressure Pc and the movement of the screw 2 is stopped. Therefore, in this case, since it is considered that an abnormality has occurred, the large flow rate mode Fm is switched to the small flow rate mode Fs at time tc.

  Further, the switching condition C3 is set as the first switching condition that the VP switching point (position) tr for switching from the filling process Sic to the pressure holding process Sip is set, and the screw speed Vs reaches about 0. The time Ts is set as the set value Tc (second switching condition). By setting such a switching condition C3, it is possible to optimize the switching timing at the normal time. An example of a specific operation state when the switching condition C3 is used is shown in FIG. This figure shows the change characteristics of the screw position Xs [mm], the screw speed Vs [%], and the injection pressure Ps [%] with respect to time [seconds] in the injection process Si (filling process Sic and pressure holding process Sip).

  When the switching condition C3 is used, the following processing is performed. In FIG. 6, when the screw 2 reaches the VP switching point tr, the first switching condition is satisfied, and therefore time measurement is started from this VP switching point tr. Then, at the time tc when the elapsed time Ts reaches the set value Tc, the large flow rate mode Fm is switched to the small flow rate mode Fs. In this case, since the speed control is canceled and the pressure control is switched at the VP switching point tr, the screw speed Vs rapidly decreases at the VP switching point tr, and the injection pressure Ps rapidly reaches the set pressure. It is a transitional period to transition. Therefore, an unstable transition period can be avoided by switching to the small flow rate mode Fs after the time corresponding to the set value Tc has elapsed from the VP switching point tr. As a result, the stability of the operation (control) can be improved, and the switching to the small flow rate mode Fs can be performed smoothly.

  Furthermore, the switching condition C4 sets the threshold value Pc for the injection pressure Ps and the threshold value Xc for the screw position Xs as the first switching condition, and sets the set value Tc for the elapsed time Ts as the second switching condition. . Similarly to the switching condition C3, the switching condition C4 can optimize the switching timing at the normal time. An example of a specific operation state when the switching condition C4 is used is shown in FIG. This figure shows the change characteristics of the screw position Xs [mm], the screw speed Vs [%], and the injection pressure Ps [%] with respect to time [seconds] in the injection process Si (filling process Sic and pressure holding process Sip). 7 is a special molding example in which speed control is not performed in the filling step Sic, unlike the cases of FIGS. 4 to 6, and the threshold value Pc is also greater than the threshold value (limit pressure) Pc of the switching conditions C1 and C2 described above. Set to a low value. Further, the threshold value Xc for the screw position Xs can set a position target value.

  When the switching condition C4 is used, the following processing is performed. In FIG. 7, when the injection pressure Ps reaches the limit pressure Pc at the time tm, the screw position Xs changes without reaching the threshold value Xc at the time tm, so that a normal operation is performed. Then, if the screw position Xs reaches the threshold value Xc (position target value) at the time point ts and the injection pressure Ps reaches the limit pressure Pc at the time point ts, the screw 2 is normally set to the position target value. Is considered to have reached. Further, since the first switching condition is satisfied at the time ts, time measurement is started from the time ts. Thereafter, if the elapsed time Ts reaches the set value Tc at the time point tc, the second switching condition is satisfied at the time point tc. Therefore, the large flow rate mode Fm is switched to the small flow rate mode Fs at the time point tc. In the example, when only the injection pressure Ps, that is, only a single physical quantity is monitored, there is a possibility of causing a malfunction and a molding defect may be caused. However, other physical quantities, that is, a plurality of screw positions Xs added. It is possible to avoid malfunction by monitoring the physical quantity. Further, by monitoring a plurality of physical quantities (injection pressure Ps and screw position Xs), it is possible to switch at an optimal timing, avoid a control transition period, and eliminate unnecessary energy consumption by the small flow rate mode Fs.

  Further, the switching condition C5 sets the threshold value Xc for the screw position Xs and the threshold value Vc for the screw speed Vs as the first switching condition without using the injection pressure Ps, and sets the set value Tc for the elapsed time Ts to the second value. This is set as a switching condition. As with the switching condition C4, the switching condition C5 can optimize the switching timing at the normal time. An example of a specific operation state when the switching condition C5 is used is shown in FIG. This figure shows the change characteristics of the screw position Xs [mm], the screw speed Vs [%], and the injection pressure Ps [%] with respect to time [seconds] in the injection process Si (filling process Sic and pressure holding process Sip).

  When the switching condition C5 is used, the following processing is performed. In FIG. 8, if the screw position Xs reaches the threshold value Xc at the time point tx, and then the screw speed Vs reaches the threshold value Vc at the time point tv, the first switching condition is satisfied at the time point tv, and the screw 2 It is considered that the position target value has been reached normally. Then, timing is started from the time point tv, and when the elapsed time Ts reaches the set value Tc at the time point tc, the second switching condition is satisfied at the time point tc, so that the large flow rate mode Fm is switched to the small flow rate mode Fs. The switching condition C5 differs from the switching condition C4 in the physical quantity to be monitored and the monitoring condition, but the monitoring target is the same. Therefore, FIG. 8 and FIG. 7 show the same operation state, and the time point tc in FIG. 8 is almost the same as the time point tc in FIG. That is, the basic principle is the same except that the injection pressure Ps and the screw position Xs are monitored under the switching condition C4, and the screw position Xs and the screw speed Vs are monitored under the switching condition C5. Even in the case of the switching condition C5, the optimum switching timing can be known by monitoring a plurality of physical quantities (injection pressure Ps and screw position Xs), so that it is possible to avoid the control transition period and wasteful consumption by the small flow rate mode Fs. Energy can be eliminated.

  Therefore, if such a control method is used, during the operation of the injection process Si, the fixed discharge flow rate Qm is set to a large flow rate to control the injection process Si, and the physical quantity is monitored, and at least one physical quantity is monitored. If at least one of the corresponding switching conditions is satisfied, the injection process Si is controlled by switching to a small fixed discharge flow rate Qs, so that an excessive load is generated due to some abnormality or the process of the injection process Si. Even when the time is long, the stop (trip) of the drive motor 6 due to overload can be avoided. Therefore, since the production operation can be continued without interrupting the molding cycle (molding operation), the production efficiency can be improved and the molding quality and the yield can be improved. In addition, even in a normal operation state, the flow rate is not changed from a large flow rate (fixed discharge flow rate Qm) to an optimum timing corresponding to the actual operation state (control state) without being caught by the switching of the operation process or the control transition period. Since the flow rate (fixed discharge flow rate Qs) can be switched, the stability of operation (control) or energy saving can be further improved.

  In this control method, the switching condition is that one or more of the screw position Xs, the screw speed Vs, and the injection pressure Ps reach the corresponding threshold values Xc, Vc, and Pc that are set in advance (first switching). In particular, the operating state of the screw in the injection process Si can be accurately detected, and the control method according to the present invention can be implemented easily and reliably. Furthermore, as the switching condition, after the first switching condition is satisfied, the first time when the elapsed time Ts or the screw moving distance Ss reaches the preset setting values Tc and Sc or reaches the setting values Tc and Sc. If the condition of satisfying the switching condition (second switching condition) is used, in addition to being able to accurately detect the operating state of the screw in the injection process Si, it is possible to avoid false detection, thereby ensuring the reliability and reliability of detection. Can be increased.

  On the other hand, FIG. 10 shows an injection molding machine M (control method) according to a modified embodiment of the present invention. 2 to 8 show the case where the variable discharge hydraulic pump 5x capable of setting the fixed discharge flow rates Qm and Qs by changing the swash plate angle Rs is used as the hydraulic pump 5, but FIG. 5 shows a case in which two hydraulic pump portions 5a and 5b capable of setting fixed discharge flow rates Qm and Qs, respectively, are used. Therefore, in the illustrated example, the fixed discharge flow rate Qm is set in the hydraulic pump unit 5a, and the fixed discharge flow rate Qs is set in the hydraulic pump unit 5b. The selection or merging of the hydraulic pump units 5a and 5b is performed by the switching valve circuit 22. The configuration of the hydraulic pump 5 shown in FIG. 10 shows a case where two variable discharge hydraulic pumps 5x shown in FIG. 2 are used. For this reason, it is possible to set the fixed discharge flow rate for each hydraulic pump unit 5a... By changing the swash plate angle Rs of each swash plate 27. Can be set. In FIG. 10, the same parts as those in FIG. 2 are denoted by the same reference numerals to clarify the configuration, and detailed description thereof is omitted. As described above, if a plurality of hydraulic pump portions 5a and 5b capable of setting the fixed discharge flow rates Qm and Qs are used as the hydraulic pump 5, it can be implemented by a combination of the hydraulic pump portions 5a and 5b having a simple structure. There are advantages that can contribute to cost reduction and diversification of control.

  Although the best embodiment has been described in detail above, the present invention is not limited to such an embodiment, and the detailed configuration, method, quantity, numerical value, and the like do not depart from the spirit of the present invention. It can be changed, added, or deleted arbitrarily. For example, the two hydraulic pump units 5a and 5b may have the same capacity or the same capacity. On the other hand, although the servo motor 6s is illustrated as the drive motor 6, another drive motor 6 having the same function may be used. Moreover, although the case where two fixed discharge flow rates Qm and Qs are set is illustrated, the case where three or more fixed discharge flow rates Qm... Are set is not excluded. Furthermore, although C1-C5 was illustrated as switching conditions, the switching conditions set by various conditions other than the illustration are applicable.

  The control method according to the present invention can be used in various injection molding machines that control the injection process in the molding cycle, and the type of the injection molding machine is not limited.

  2: hydraulic pump, 2x: variable discharge hydraulic pump, 5a: hydraulic pump section, 5b: hydraulic pump section, 3: drive motor, 6s: servo motor, 6sa: servo circuit, M: injection molding machine, Si: injection process , Xs: screw position (physical quantity), Vs: screw speed (physical quantity), Ps: injection pressure (physical quantity)

Claims (6)

  Control of an injection molding machine that controls an injection process including a filling process for filling a mold with resin in a heating cylinder by advancing a screw and a pressure-holding process for applying pressure to the resin filled in the mold. In the method, a hydraulic pump capable of setting a fixed discharge flow rate of at least a large flow rate and a fixed discharge flow rate of a small flow rate smaller than the large flow rate is used as the hydraulic pump, and at least one associated with the operation of the injection step in advance. As a switching condition for switching the fixed discharge flow rate for the above physical quantities, one or more of the screw position, screw speed, and injection pressure, which are the physical quantities, reach a preset threshold value (first switching Condition), and after satisfying the first switching condition, the elapsed time or screw movement distance, which becomes the physical quantity, reaches or reaches a preset set value. Is set to satisfy the first switching condition (second switching condition), and the injection process is controlled by setting the large flow rate to a fixed discharge flow rate during the operation of the injection process. The injection is characterized in that the physical quantity is monitored, and if at least one of the physical quantities satisfies the second switching condition, the injection process is controlled by switching to the small fixed flow rate. Control method of molding machine.   2. The method of controlling an injection molding machine according to claim 1, wherein the hydraulic pump is a variable discharge hydraulic pump capable of setting the fixed discharge flow rate by changing a swash plate angle.   2. The method of controlling an injection molding machine according to claim 1, wherein the hydraulic pump uses a plurality of hydraulic pump units each capable of setting the fixed discharge flow rate.   4. The method of controlling an injection molding machine according to claim 1, wherein the injection process is controlled by variably controlling the rotational speed of a drive motor that drives the hydraulic pump.   5. The method of controlling an injection molding machine according to claim 4, wherein a servo motor connected to a servo circuit is used as the drive motor.   2. The method of controlling an injection molding machine according to claim 1, wherein if the second switching condition is satisfied, predetermined abnormality processing including display processing is performed.

Images