Method for controlling mold clamping device

A predetermined speed control pattern A is set. In controlling mold opening, in the mold opening section Zm, mold opening control is performed at the mold opening speed Vm, and based on a current mold opening speed Vd and a current mold opening position Xd, which are both detected, a deceleration starting position Xmc of the deceleration section Zmd where a current mold opening speed Vd becomes a zero (O) at a virtual stop position Xso is sequentially forecasted at each predetermined time interval by calculation. Upon reaching the deceleration starting position Xmc the deceleration section Zmd is started, and in the deceleration section Zmd, based on the detected current mold opening position Xd, a speed command value Dm corresponding to the speed control pattern A is obtained sequentially by calculation, and according to the speed command value Dm deceleration control is performed. Upon reaching a last-transition speed Vc, a predetermined stop controlling processing is performed.

TECHNICAL FIELD

This invention relates to a method for controlling a mold clamping device which performs mold opening control by driving a mold clamping cylinder by a hydraulic pump.

BACKGROUND ART

Generally, a hydraulic-type injection molding machine has an aspect that it is difficult to precisely control a position and a speed compared to an electromotive-type injection molding machine. In other words, in the case of the hydraulic type, as it uses hydraulic oil and a hydraulic actuator, viscosity, volume, and the like of the hydraulic oil changes according to temperature, and an inertial force is generated in the hydraulic actuator. These physical behaviors directly affect the control precision and responsiveness. In the case where, as a hydraulic pump, a variable discharge type hydraulic pump capable of controlling a discharge flow rate by varying the number of revolutions of a drive motor is used, length of the hydraulic circuit from the hydraulic pump to the hydraulic actuator gets longer, thereby influence of changes in viscosity, volume, and the like of the hydraulic oil being larger. When supposing, as a hydraulic actuator, for example, a mold clamping cylinder equipped in a mold clamping device, even though feedback control is carried out for the positions, mold opening positions (mold opening stop positions) largely vary among shots, causing unnecessary overrun of the movable mold, furthermore a trouble such as breakage and damage from colliding a molded product taking-out device with a mold (three-plate mold). This problem is more serious, when a mold opening time period is accelerated to shorten a molding cycle time in order to increase productivity.

Meanwhile, hitherto, a control method which aims at obtaining a precise mold opening position in a mold clamping device is known. JP 09-222924 A (Patent literature 1) discloses a method for controlling a mold-opening completion position in a direct pressure-type mold clamping device in which, with allowing a mold open process, eventually a molding cycle, to be shortened, variation in stop positions at the times of mold opening completion of a movable platen is corrected thereby to reduce the variation range, and suppress and prevent product mischucking by a taking-out machine. This method for controlling a mold-opening completion position works as follows: in a direct pressure-type mold clamping device, when the mold opening speed is switched from a high-speed mold opening section to a low-speed mold opening section to complete the mold open process, the high-speed mold opening section is longer while the low-speed mold opening section is as short as possible, thereby shortening the mold open process; and a distance of the stop position of the movable platen from its reference position at the time of the mold opening completion is sampled successively plural times as the mold opening operation is repeated and, when the variation range of the sampled distances exceeds the permissible range of the target stop position precision of the movable platen, the switching position from the high-speed mold opening section to the low-speed mold opening section is corrected to hold the variation range within the permissible range.

SUMMARY OF INVENTION

Technical Problem

However, the abovementioned method for controlling a mold clamping device in the past (the method for controlling a mold-opening completion position in a direct pressure-type mold clamping device) has the following problems.

Firstly, since the basic technique thereof does not lessen variation of the stop positions by positively improving control precision of a stop position, the variation always occurs within the permissible range. Therefore, control precision higher than this permissible range cannot be secured, which imposes a limitation as a countermeasure for preventing product mischucking from occurring and the like.

Secondly, since variation of the stop positions is lessen by correcting the switching position from the high-speed mold opening section to the low-speed mold opening section, variation of the length of molding cycle time occurs. Consequently, this causes reduction in and variation of productivity, and possibly leads to significant influence on the production schedule such as delivery delay.

Solution to Problem

In order to solve the abovementioned problems, the method for controlling a mold clamping device1caccording to the present invention is characterized as follows: at the inception of performing mold opening control by driving a mold clamping cylinder3by a hydraulic pump2, preliminarily setting a predetermined speed control pattern A having, at least, a mold opening section Zm in which mold opening is performed at a predetermined mold opening speed Vm, a deceleration section Zmd in which the speed is gradually decelerated from an end point (Xmc) of the mold opening section Zm toward a virtual stop position Xso, and a last-transition section Zc for which a predetermined last-transition speed Vc is set before the virtual stop position Xso; in controlling mold opening, in the mold opening section Zm, performing mold opening control at the mold opening speed Vm, and sequentially forecasting, based on a current mold opening speed Vd and a current mold opening position Xd, which are both detected, a deceleration starting position Xmc of the deceleration section Zmd where a current mold opening speed Vd becomes a zero (O) at a virtual stop position Xso, at each predetermined time interval by calculation; starting the deceleration section Zmd upon reaching the deceleration starting position Xmc, and in the deceleration section Zmd, obtaining, based on a detected current mold opening position Xd, a speed command value Dm corresponding to the speed control pattern A sequentially by calculation, and according to the speed command value Dm, performing decelerated mold opening processing; and upon reaching a last-transition speed Vc, performing a predetermined stop controlling processing.

Advantageous Effects of Invention

The method for controlling a mold clamping device1caccording to the present invention exhibits the remarkable advantageous effects as follows.

(1) Even though viscosity, volume, and the like of the hydraulic oil in the hydraulic circuit are changed depending on temperature and an inertial force exists in the mold clamping cylinder3, in controlling mold opening, the mold opening control is so performed as to control according to a preliminarily-set speed control pattern A, thereby improving the control precision with respect to a mold opening position (stop positions Xso, Xe) and thus reducing variation in the mold opening positions of respective shots drastically. Consequently, unnecessary overrun of a mold (movable mold) and a trouble such as breakage and damage from colliding a molded product taking-out device with a mold (three-plate mold) can be avoided surely. And conditions can be determined more simply without restriction caused by such troubles.

(2) Since a precise mold opening position (stop positions Xso, Xe) can be achieved and variation in mold opening positions of respective shots is reduced, constant molding cycle time can be always secured and a molding cycle time can be accelerated. As a consequence, this makes it possible to avoid lowering and varying the productivity, thereby to smoothly and surely carry out the production schedule and increase productivity.

(3) According to a preferable mode of the invention, as a hydraulic pump2, a variable discharge type hydraulic pump2s, which is capable of controlling a discharge flow rate by varying the number of revolutions of the servomotor11, is used, thereby to inverter control the hydraulic pump2s, resulting in improvement in energy saving and a reduction in running costs. In addition, particularly, the control method according to the invention achieves a larger effect when it is applied to a mold clamping device1cequipped with such a variable discharge type hydraulic pump2s, which is largely affected by physical variation such as temperature in the hydraulic oil.

(4) According to a preferable mode of the invention, a sub-tank13is attached to the mold clamping cylinder3, and in the mold opening section Zm and the deceleration section Zmd, such control is performed that the sub-tank13is connected to a rear oil chamber3rof the mold clamping cylinder3so as for the hydraulic oil in the rear oil chamber3rto be flowed into the sub-tank13. Therefore, mold opening can be performed at higher speed and with higher responsiveness. Particularly, the control method according to the present invention is applied to such a mold clamping device1cin which mold opening can be performed at higher speed and with higher responsiveness, thereby to achieve a larger effect.

(5) According to a preferable mode of the invention, in the deceleration section Zmd, a time period Td required for the deceleration section Zmd is set, and then the time period between the deceleration starting position Xmc of the deceleration section Zmd and the virtual stop position Xso is so controlled as to be the fixed required time period Td. This provides more stable and precise position control with respect to the virtual stop position Xso.

(6) According to a preferable mode of the invention, in the stop control processing, control in which, at a stop position, any outflow and inflow of the hydraulic oil to the mold clamping cylinder3is cut, and operation of the hydraulic pump2is delayed for a predetermined time period and then stopped, is performed. This allows avoiding a malfunction in which a mold (movable mold) moves in a closing direction thereof by the pressure inside the hydraulic circuit being negative. As a result, the mold can be stably and surely stopped at the mold opening position (Xso).

(7) According to a preferable mode of the invention, as the stop control processing, control in accordance with a preliminarily-set last speed control pattern Ar is performed, and then upon reaching a final stop speed Ve, a predetermined final stop processing is performed. This makes it possible to stop at the mold opening stop position Xe more stably and precisely.

(8) According to a preferable mode of the invention, in a last deceleration section Zrd, a last time period Tr required for the last deceleration section Zrd is set, and then the time period between the deceleration starting position Xrc of the last deceleration section Zrd and the mold opening stop position Xe is so controlled as to be the fixed last required time period Tr. This provides more stable and precise position control with respect to the mold opening stop position Xe.

(9) According to a preferable mode of the invention, in the last mold opening section Zr and the last deceleration section Zrd, the mold clamping cylinder3is connected to the meter-out circuit14to perform meter-out control. This makes it possible to perform speed control in the last mold opening section Zr and the last deceleration section Zrd, which are relatively low speed sections, stably and precisely.

(10) According to a preferable mode of the invention, as the final stop processing, control in which, at a stop position, any outflow and inflow of the hydraulic oil to the mold clamping cylinder3is cut, and operation of the hydraulic pump2is delayed for a predetermined time period Te and then stopped, is performed. This allows avoiding a malfunction in which a mold (movable mold) moves in a closing direction thereof by the pressure inside the hydraulic circuit being negative. As a result, the mold can be stably and surely stopped at the mold opening stop position Xe.

(11) According to a preferable mode of the invention, before the mold opening section Zm, an initial mold opening section Zf in which mold opening is performed at an initial speed Vf lower than the mold opening speed Vm is set. This makes it possible to perform mold separating processing for separating the movable mold from the fixed mold smoothly and better at the beginning of mold opening.

(12) According to a preferable mode of the invention, in the initial mold opening section Zf, the mold clamping cylinder3is connected to the meter-out circuit14to perform meter-out control. This makes it possible to perform speed control in the initial mold opening section Zf, which is a relatively low speed section, stably and precisely.

DESCRIPTION OF EMBODIMENTS

The invention will now be described in greater detail with preferred embodiments of the invention and drawings attached. However, it should be appreciated that the drawings attached are given not to specify the invention, but to facilitate understanding of the invention. In addition, detail description of a well-known part of the invention is omitted to avoid that the invention becomes unclear.

Firstly, a configuration of a mold clamping device1carranged in an injection molding machine1, by which the control method according to this embodiment can be implemented, will be explained, with reference toFIG. 3.

InFIG. 3,1designates an injection molding machine, which is provided with an injection device1iand a mold clamping device1c. The mold clamping device1chas a fixed platen21which is fixed in a molding machine bed (not shown), and a plurality of tie bars22. . . which dispose from this fixed platen21to a pressure receiving platen (not shown), and a movable platen23which is slidably fitted to these tie bars22. . . . In addition, to the pressure receiving platen, a mold clamping cylinder3is fixed, and a piston24housed in the mold clamping cylinder3is coupled to the movable platen23. A fixed mold Cc is mounted to the fixed platen21, and a movable mold Cm is mounted to the movable platen23. The fixed mold Cc and the movable mold Cm constitute a mold C. This allows drive controlling the mold clamping cylinder3to move the movable platen23(movable die Cm) forward or backward, thereby closing (mold clamping) or opening the mold C. Besides, the injection device1ican inject and fill a melted resin in a cavity of the mold C by carrying out a nozzle touch with an injection nozzle1in on the mold C (fixed mold Cc).

Furthermore, the mold clamping device1cis provided with a hydraulic drive part31including the mold clamping cylinder3, and this hydraulic drive part31is controlled by a molding machine controller71. The hydraulic drive part31is provided with a variable discharge type hydraulic pump2s(hydraulic pump2), which serves as a hydraulic drive source, and a hydraulic circuit32. The hydraulic pump2shas a pump body33and a servomotor11s(drive motor11) for rotationally driving the pump body33. As the servomotor11s, an AC servomotor connected to an output port of the molding machine controller71is used. To the servomotor11s, a rotary encoder11efor detecting the number of revolutions of the servomotor11sis attached, and the rotary encoder11eis connected to an input port of the molding machine controller71.

Besides, the pump body33is composed of a swash plate type piston pump. Therefore, the pump body33has a swash plate35. When an inclination angle of the swash plate35(swash plate angle) is larger, a stroke of the pump piston in the pump body33is larger, and then the discharge flow rate increases. When a swash plate angle is smaller, a stroke of the pump piston therein is smaller, and then the discharge flow rate decreases. Thus, by setting the swash plate angle at a predetermined angle, a fixed discharge flow rate, which means that a discharge flow rate is fixed at a predetermined rate, can be set. Furthermore, to the swash plate35, a control cylinder36and a return spring37are attached. The control cylinder36is connected to a discharge port of the pump body33via a switching valve (solenoid valve) Mc, a throttle38, and a check valve39. This allows an angle of the swash plate35(swash plate angle) to be changed by controlling the control cylinder36. Incidentally,40designates a pump pressure sensor.

An inlet port of the pump body33is connected to an oil tank51and the discharge port of the pump body33is connected to the hydraulic circuit32. In this way, as a hydraulic pump2, a variable discharge type hydraulic pump2s, which is capable of controlling a discharge flow rate by varying the number of revolutions of the servomotor11s, is used, thereby to inverter control the hydraulic pump2s, resulting in improvement in energy saving and a reduction in running costs. In addition, particularly, the control method according to the invention achieves a larger effect when it is applied to a mold clamping device1cequipped with such a variable discharge type hydraulic pump2s, which is largely affected by physical variation such as temperature in the hydraulic oil.

The hydraulic circuit32, as shown inFIG. 3, is equipped with a pilot switching valve (solenoid valve) M1for switching the main operations, a direction switching valve M2, a direction switching valve (solenoid valve) M3in which a throttle is housed, a switching valve (solenoid valve) M4for switching a prefill valve Mp arranged in a sub-tank13, which will be mentioned later, a switching valve (solenoid valve) M5for switching the mold clamping operations, and a switching valve M6forming a safety circuit. The hydraulic circuit32is connected in such a way shown inFIG. 3, to configure a hydraulic system circuit. Incidentally,52,53,54designate check valves,55,56designate throttles, and57designates a cylinder pressure sensor. Besides, the mold clamping cylinder3is provided with a cylinder body61, and a piston24which is housed in the cylinder body61. The piston24also serves as a high-speed cylinder part62. A booster ram63forwardly projected from a rear end of the cylinder body61is inserted into the oil chamber of the high-speed cylinder part62. Furthermore, a sub-tank13is attached to the cylinder body61. Between the sub-tank13and a rear oil chamber3r, a prefill valve Mp for connecting and disconnecting the sub-tank13and rear oil chamber3ris arranged, and the sub-tank13is connected to an oil tank51via an oil cooler64. Thus, the mold clamping device1caccording to this embodiment forms a booster ram type mold clamping mechanism.

The hydraulic circuit32includes a differential circuit12and a meter-out circuit14. The direction switching valve M3mainly forms the meter-out circuit14and the direction switching valves M2, M3mainly form the differential circuit12. Each of the switching valves M1, M3, M4, M5. . . is connected to the output port of the molding machine controller71. This allows each of the switching valves M1. . . to be sequentially controlled by the molding machine controller71. Furthermore,66designates a position sensor for detecting a position (mold position) of the movable mold Cm, and the position sensor66is connected to an input port of the molding machine controller71.

Now, the control method according to this embodiment, which includes a mold opening operation of the mold clamping device1chaving such a configuration, will be explained according to the flow chart shown inFIG. 1, with reference toFIGS. 2 and 3.

Firstly, preliminarily, a speed control pattern A shown inFIG. 2is set (Step So). The speed control pattern A includes at least a mold opening section Zm in which mold opening is performed at a predetermined mold opening speed Vm, a deceleration section Zmd in which the speed is gradually decelerated from the end point (Xmc) of the mold opening section Zm toward a virtual stop position Xso, and a last-transition section Zc for which a predetermined last-transition speed Vc is set before the virtual stop position Xso. The illustrated speed control pattern A further includes an initial mold opening section Zf in which mold opening is performed at an initial speed Vf lower than the mold opening speed Vm, and a predetermined last speed control pattern Ar. In this case, the last speed control pattern Ar includes a last mold opening section Zr in which mold opening is performed at the last speed Vr set at a speed lower than the mold opening speed Vm, and a last deceleration section Zrd in which the speed is decelerated gradually from the end point (Xrc) of the last mold opening section Zr towards a mold opening stop position Xe, and a stop controlling section Ze for which a predetermined final stop speed Ve lower than the last speed Vr in the mold opening stop position Xe is set.

In the speed control pattern A, particularly, in the deceleration section Zmd, a time period Td required for the deceleration section Zmd is set and then a time period between the deceleration starting position Xmc of the deceleration section Zmd and the virtual stop position Xso is so controlled as to be the time period Td. Therefore, depending on an actual mold opening speed (current mold opening speed Vd), the end point position Xmc varies. Accordingly, in the case where the current mold opening speed Vd is higher than the set mold opening speed Vm, the end point position Xmc locates ahead of the end point position to be reached at the mold opening speed Vm, whereas in the case where the current mold opening speed Vd is lower than the mold opening speed Vm, the end point position Xmc locates behind the end position reached at the mold opening speed Vm. Thus, by controlling the time period between the deceleration starting position Xmc of the deceleration section Zmd and the virtual stop position Xso to be the fixed required time period Td, more stable and precise position control can be achieved with respect to the virtual stop position Xso. Likewise, in the last deceleration section Zrd, a time period Tr required for the last deceleration section Zrd is set and then a time period between the deceleration starting position Xrc of the last deceleration section Zrd and the mold opening stop position Xe is so controlled as to be the last required time period Tr. Therefore, depending on an actual last speed (current mold opening speed Vd), the end point position Xrc varies. Accordingly, in the case where the current mold opening speed Vd is higher than the set last speed Vr, the end point position Xrc locates ahead of the end point position to be reached at the last speed Vr, whereas in the case where the current mold opening speed Vd is lower than the last speed Vr, the end point position Xrc locates behind the end point position reached at the last speed Vr. Thus, by controlling the time period between the deceleration starting position Xrc of the last deceleration section Zrd and the mold opening stop position Xe to be the fixed last required time period Tr, more stable and precise position control can be achieved with respect to the mold opening stop position Xe.

Meanwhile, in the actual mold open process, the following mold opening control is performed. Firstly, at the inception of the mold open process, a current position of the movable mold Cm is determined. In other words, it is determined whether or not the current mold opening position Xd is 10 mm or less (Step S1). Incidentally, the starting position of the mold opening process is 0 mm. In this case, if the current mold opening position Xd is 10 mm or less, the mold C is in a completely closed state or nearly in that state. Then, mold opening control is performed in a normal mold opening mode. In the normal mode, firstly an initial mold opening processing is performed (Step S2). In the initial mold opening processing, as a speed command value, an initial speed Vf which is lower than the mold opening speed Vm to be mentioned later is used to perform mold opening control in the initial mold opening section Zf shown inFIG. 2. In this way, before the mold opening section Zm to be mentioned later, mold opening is performed at the initial speed Vf lower than the mold opening speed Vm. This makes it possible to perform mold separating processing for separating the movable mold Cm from the fixed mold Cc smoothly and better at the beginning of mold opening.

In this initial mold opening processing, in the hydraulic circuit32shown inFIG. 3, both the switching valves M1and M4are switched to symbol b. By switching the switching valve M1to symbol b, the switching valve M2is switched to symbol b. Meanwhile, other switching valves M3, M5, M6, Mc are maintained in the switching position shown inFIG. 3. According to this, the hydraulic oil of the hydraulic pump2is supplied to a front oil room3fof the mold clamping cylinder3via the switching valve M2, which moves the piston24backward thereby to open the mold. At this time, as the hydraulic oil of the hydraulic pump2is applied to the prefill valve Mp via the switching valve M4, the prefill valve Mp is opened, and then the hydraulic oil of the rear oil chamber3rof the mold clamping cylinder3is flown into the sub-tank13. Furthermore, the hydraulic oil flowing out from the high-speed cylinder part62flows into the switching valve M3via the switching valve M2, and then is returned to the oil tank51through the throttle in the switching valve M3. In other words, meter-out control is performed by means of the meter-out circuit14. With such a meter-out control being performed, speed control in the initial mold opening section Zf, which is a relatively low speed section, can be performed stably and precisely.

Then, as the initial mold opening section Zf ends and the starting position Xms of the mold opening section Zm is reached, high-speed mold opening processing is performed in the mold opening section Zm (Step S3, S4). In other words, as a speed command value, the high-speed mold opening speed Vm is used to perform mold opening control in the mold opening section Zm shown inFIG. 2. In the mold opening section Zm, the switching valve M3shown inFIG. 3is switched to symbol a. This releases the meter-out control. Accordingly, the hydraulic oil flowing out from the high-speed cylinder part62is joined into the hydraulic oil supplied from the hydraulic pump2via the switching valves M2, M3. In other words, the hydraulic oil joined by a function of the differential circuit12is supplied to the front oil chamber3f. Besides, since the prefill valve Mp is in an open state, when the piston24is retracted at high speed, the hydraulic oil of the rear oil chamber3rof the mold clamping cylinder3is escaped into the sub-tank13rapidly, thereby realizing a high-speed movement of the piston24. In this way, in the mold opening section Zm and the deceleration section Zmd mentioned later, the hydraulic oil in the rear oil chamber3rcan be flown into the sub-tank13. Therefore, mold opening can be performed at higher speed and with higher responsiveness. Particularly, the control method according to the present invention is applied to such a mold clamping device1cin which mold opening can be performed at higher speed and with higher responsiveness, to achieve a larger effect.

Furthermore, in the mold opening section Zm, based on a current mold opening speed Vd and a current mold opening position Xd, which are both detected, a deceleration starting position Xmc of the deceleration section Zmd where a current mold opening speed Vd becomes a zero (O) at a virtual stop position Xso is sequentially forecasted at each predetermined time interval by calculation and it is determined whether or not the deceleration starting position Xmc is reached. In other words, since the distance Lmd of the deceleration section Zmd is estimated to be Lmd=(Vd·Td)/2, when the condition of Xso−Lmd≦Xd is satisfied, it is determined that the deceleration starting position Xmc is reached, and then the deceleration section Zmd is started (Step S5). In the deceleration section Zmd, based on the detected current mold opening position Xd, a speed command value Dm corresponding to the deceleration section Zmd of the speed control pattern A is obtained sequentially by calculation. According to the speed command value Dm, decelerated mold opening processing is performed (Step S6). This decelerates the mold opening speed gradually. Incidentally, the speed command value Dm can be obtained by the following [Mathematical formula 1]. In [Math. 1], Vds is a current mold opening speed at the time of starting the deceleration section Zmd, Xrs is a starting position of the last mold opening section Zr (FIG. 2), which is after the set last-transition section Zc.

Then, deceleration control is performed in the deceleration section Zmd. When the current mold opening speed Vd is reached at the last-transition speed Vc, the predetermined stop processing is performed (Step S7). The last-transition speed Vc is set at a speed which is lower than the last speed Vr (for example about 0.5 to 0.8 times of the last speed Vr) in the last mold opening section Zr mentioned later. In addition, mold opening is performed at the last-transition speed Vc. When the starting position Xrs of the set last mold opening section Zr is reached and the last-transition section Zc ends, the last mold opening section Zr is started. In the last mold opening section Zr, the switching valve M3in the hydraulic circuit32is returned to the neutral position so that the same control as in the initial mold opening section Zf mentioned above is performed. Thus, meter-out control by means of the meter-out circuit14is performed, and speed control in the last mold opening section Zr and the last deceleration section Zrd to be mentioned later, which are relatively low speed sections, can be performed stably and precisely.

Meanwhile, it is possible that the mold opening is performed at the last-transition speed Vc and then, upon reaching the virtual stop position Xso, the final stop processing is performed. Accordingly, as the virtual stop position Xso, the actual mold opening stop position Xe may be set. In this case, as the final stop processing, the stop control processing in which, at a stop position, any outflow and inflow of the hydraulic oil to the mold clamping cylinder3is cut, and operation of the hydraulic pump2sis delayed for a predetermined time period and then stopped, can be performed. With such a stop control processing being performed, a malfunction in which a mold (movable mold Cm) moves in a closing direction thereof by the pressure inside the hydraulic circuit being negative can be avoided. As a result, the mold can be stably and surely stopped at the mold opening position (Xso).

On one hand, in the last mold opening section Zr, as a speed command value, the last speed Vr lower than the mold opening speed Vm is used, to perform mold opening control in the last mold opening section Zr shown inFIG. 2(Step S8). In the last mold opening section Zr, based on a current mold opening speed Vd and a current mold opening position Xd, which are both detected, a deceleration starting position Xrc of the last deceleration section Zrd, in which the mold is stopped at the mold opening stop position Xe, is sequentially forecasted at each predetermined time interval by calculation and it is determined whether or not the deceleration starting position Xrc is reached. In other words, since the distance Lrd of the last deceleration section Zrd is estimated to be Lrd=Vd·Tr·(Vr−Ve)/2, when the condition of Xe−Lrd≦Xd is satisfied, it is determined that the deceleration starting position Xrc is reached, and then the last deceleration section Zrd is started (Step S9). In the deceleration section Zrd, based on the detected current mold opening position Xd, a speed command value Dr corresponding to the last deceleration section Zrd of the last speed control pattern Ar is obtained sequentially by calculation. According to the speed command value Dr, decelerated mold opening processing is performed (Step S10). This decelerates the mold opening speed gradually. Incidentally, the speed command value Dr can be obtained by the following [Mathematical formula 2]. In [Math. 2], Vrs is a current mold opening speed at the time of starting the deceleration section Zrd.

Then, the deceleration control is performed in the deceleration section Zrd, and upon reaching the mold opening stop position Xe the predetermined final stop processing is started (Step S11). In the final stop processing, control in which, at a stop position, any outflow and inflow of the hydraulic oil to the mold clamping cylinder3is cut, and operation of the hydraulic pump2is delayed for a predetermined time period Te and then stopped is performed. In this case, upon reaching the mold opening stop position Xe, the predetermined time period Te is timed by a delay timer, and when the time is up, the operation of the hydraulic pump2is stopped (Step S12, S13, S14). This terminates the stop control section Ze. Incidentally, during timing by the delay timer, a speed for delaying the stop which is set as a speed command value is outputted, and pressure for delaying the stop which is set as a pressure command value is also outputted. With such a final stop control processing being performed, a malfunction in which a mold (movable mold Cm) moves in a closing direction thereof by the pressure inside the hydraulic circuit being negative can be avoided. As a result, the mold can be stably and surely stopped at the mold opening stop position Xe. In addition, as the stop control processing, control in accordance with a preliminarily set last speed control pattern Ar is performed, and then upon reaching the final stop speed Ve the predetermined final stop processing is performed. This makes it possible to stop at the mold opening stop position Xe more stably and precisely.

On the other hand, at the inception of mold opening process, the current position of the movable mold Cm is determined. In the case where the current mold opening position Xd exceeds 10 mm, the mold opening control is performed in the non-high-speed mold opening mode which starts from the abovementioned last mold opening section Zr (Step S1, S8. . . ). In other words, on starting the mold opening process, if the position of the movable mold Cm has already exceeded 10 mm, it is considered that the movable mold Cm was manually stopped at an arbitrary position for maintenance, testing or the like, that mold opening was emergency-stopped before its completion when a safety door was opened, and so on. In this case, the process is jumped to Step8to start mold opening control from the last mold opening section Zr, in which the operation is relatively slow.

FIG. 4shows the measurement data of mold opening stop positions Xe for respective shots when the control method according to this embodiment is used and the temperature of the hydraulic oil Eo (° C.) is intentionally changed for 20° C. during sequential operation of the mold clamping device1c(injection molding machine1). In this case, the variation range is almost 0.7 mm. For comparison purpose,FIG. 5shows the measurement data of mold opening stop positions Xer for respective shots when the control method according to this embodiment is not used, but normal feedback control is performed based on a preliminarily set speed command value and the temperature of the hydraulic oil Eor (° C.) is intentionally changed for 20° C. during the sequential operation. In this case, the variation range is almost 1.41 mm. Consequently, using the control method according to this embodiment allows the variation of the mold opening stop positions Xe to be reduced almost by half comparing to a related-art technique.

In addition,FIG. 6shows the measurement data of mold opening stop positions Xe for respective shots when the control method according to this embodiment is used and the mold opening speed Vm is changed with respect to the maximum speed in increments of 10% within a range of 10-100%. In this case, the variation range is almost 0.89 mm. For comparison purpose,FIG. 7shows the measurement data of mold opening stop positions Xe for respective shots when the control method according to this embodiment is not used, but normal feedback control is performed based on a preliminarily set speed command value and the mold opening speed Vm is changed with respect to the maximum speed in increments of 10% within a range of 10-100% during the sequential operation. In this case, the variation range is almost 21.46 mm. As a consequence, using the control method according to this embodiment allows the variation of the mold opening stop positions Xe to be reduced almost by 1/25 comparing to a related-art technique.

In this way, by performing the mold opening control by the control method according to this embodiment, even though viscosity, volume, and the like of the hydraulic oil in the hydraulic circuit are changed depending on temperature and an inertial force exists in the mold clamping cylinder3, the mold opening control is so performed as to control according to the preliminarily set speed control pattern A, thereby improving the control precision with respect to a mold opening position (stop positions Xso, Xe) and thus reducing variation in the mold opening positions of respective shots drastically. Consequently, unnecessary overrun of the mold (movable mold) and a trouble such as breakage and damage from colliding a molded product taking-out device with a mold (three-plate mold) can be avoided surely. In addition, conditions can be determined more simply without restriction caused by such troubles. And since a precise mold opening position (stop positions Xso, Xe) can be achieved and variation in mold opening positions of respective shots is reduced, constant molding cycle time can be always secured and a molding cycle time can be accelerated. As a consequence, this makes it possible to avoid lowering and varying the productivity, thereby to smoothly and surely carry out the production schedule and increase productivity.

While the preferable embodiment has been explained in detail, the present invention is not limited to such an embodiment, but in the detail of the hydraulic circuit configuration, techniques, numerical values and the like, any changes, additions, deletions may be made without departing from the spirit and scope of the inventions. For example, as a hydraulic pump2, a variable discharge type hydraulic pump2sis illustrated. However, this means that other types of hydraulic pumps2are not excluded. A speed control pattern A including the last speed control pattern Ar is not limited to the illustrated pattern, but various forms of patterns are applicable.

INDUSTRIAL APPLICABILITY

Although a mold clamping device1cof an injection molding machine1is illustrated, the control method according to the present invention can be also employed for a mold clamping device in various industrial machines which uses a die (generally, a mold), such as an extruder.

REFERENCE SIGNS LIST

CITATION LIST

Patent Literature 1JP 09-222924 A