JP4107309B2 - Hydraulic unit for injection molding machine - Google Patents

Description

  The present invention relates to a hydraulic unit for an injection molding machine that controls, for example, the flow rate and pressure of hydraulic oil supplied to an injection cylinder.

  Conventionally, as a hydraulic unit for an injection molding machine, a hydraulic pump that supplies hydraulic oil to an injection cylinder, a variable speed motor that drives the hydraulic pump, a pressure sensor that detects a discharge pressure of the hydraulic pump, and the variable speed Some include a controller that controls the discharge pressure and the discharge flow rate of the hydraulic pump by controlling the number of rotations of the motor (see JP 2003-172302 A).

  The pressure control of the hydraulic pump by the controller will be described. When the controller indicates that the pressure detected by the pressure sensor is a preset cutoff start pressure, the rotation of the motor Reduce the number.

  FIG. 5 shows the relationship between the pressure detected by the pressure sensor and time. More specifically, the operation start (injection start) time of the injection cylinder is set to 0, and the injection end time of the injection cylinder is set to t2. The cut-off start pressure is indicated by a one-dot chain line. Moreover, the full cutoff pressure shown by the dashed-two dotted line larger than this cutoff start pressure is set.

In all the steps of the injection cylinder, the controller sets the full cutoff pressure to a constant value p2. Further, the controller controls the forward speed of the injection cylinder to be constant, but pressure overshoot often occurs due to the initial resistance of injecting the resin material immediately after the start of forward movement. At this time, cut-off control, that is, control is performed so that the rotation speed of the motor starts to decrease at time t1 at the cut-off start pressure value p1, and the pressure does not increase excessively above the full cut-off pressure value p2. Is done.
JP 2003-172302 A

  However, as can be seen from FIG. 5, when the pressure exceeds p1, the rotation speed of the motor is reduced by the cut-off control of the controller, and the discharge flow rate of the hydraulic pump becomes smaller than the predetermined value q1. End up. If the amount of oil in the injection cylinder decreases at the start of injection, problems such as insufficient filling of the resin material into the mold occur, and the quality of the molded product deteriorates. Furthermore, due to poor quality of the molded product, the yield (acceptance rate) deteriorates and the molding cost increases.

  Accordingly, an object of the present invention is to provide a hydraulic unit for an injection molding machine capable of preventing deterioration of the quality of a molded product by preventing fluctuations in the forward speed of an injection cylinder even if pressure overshoot occurs. is there.

In order to solve the above problems, the hydraulic unit for an injection molding machine of the present invention is
A fixed displacement hydraulic pump that supplies hydraulic oil to the injection cylinder;
A variable speed motor that drives the hydraulic pump;
A pressure detector for detecting the discharge pressure of the hydraulic pump;
A cut-off control unit that reduces the rotational speed of the motor when the pressure detected by the pressure detection unit indicates a preset cut-off start pressure; and
A suppression unit that detects the start of operation of the injection cylinder and suppresses the operation of the cutoff control unit for a predetermined time; and
And a main control unit that controls the motor so that the discharge pressure or the discharge flow rate of the hydraulic pump becomes a predetermined value in response to the output of the cut-off control unit.

  According to the hydraulic unit for an injection molding machine of the present invention, the suppression unit detects the operation start of the injection cylinder and suppresses the operation of the cutoff control unit for a predetermined time. Even if a pressure overshoot occurs, the rotational speed of the motor does not decrease, and the discharge flow rate of the hydraulic pump does not decrease.

  In this way, even if pressure overshoot occurs after the operation of the injection cylinder is started, the forward speed of the injection cylinder does not fluctuate, and deterioration of the quality of the molded product can be prevented.

  In the injection molding machine hydraulic unit according to one embodiment, the predetermined time is a time until immediately before the pressure detected by the pressure detection unit becomes substantially constant.

  According to the hydraulic unit for injection molding machine of this embodiment, after the pressure detected by the pressure detection unit becomes substantially constant, the suppression unit does not work, and the process proceeds to the next step (pressure holding step). Return to the pressure setting.

  In one embodiment of the hydraulic unit for injection molding machine, the suppression unit corrects the cutoff start pressure higher than the maximum pressure detected by the pressure detection unit during the predetermined time. The operation of the cut-off control unit is suppressed.

  According to the hydraulic unit for injection molding machine of this embodiment, the suppression unit corrects the cutoff start pressure higher than the maximum pressure detected by the pressure detection unit for the predetermined time. Even if a pressure overshoot occurs during the predetermined time, the pressure detected by the pressure detection unit during the predetermined time does not reach the cutoff start pressure. For this reason, the rotation speed of the motor does not decrease during the predetermined time, and the discharge flow rate of the hydraulic pump does not decrease.

  Moreover, in the hydraulic unit for an injection molding machine according to an embodiment, the suppression unit stops the operation of the cutoff control unit for the predetermined time.

  According to the hydraulic unit for an injection molding machine of this embodiment, the suppression unit stops the operation of the cut-off control unit for the predetermined time, so even if a pressure overshoot occurs for the predetermined time. The rotational speed of the motor does not decrease, and the discharge flow rate of the hydraulic pump does not decrease.

  According to the hydraulic unit for an injection molding machine of the present invention, the suppression unit detects the operation start of the injection cylinder and suppresses the operation of the cutoff control unit for a predetermined time. In the meantime, even if a pressure overshoot occurs, the quality of the molded product can be prevented from deteriorating by preventing the forward speed of the injection cylinder from fluctuating.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

  FIG. 1 is a block diagram showing an embodiment of a hydraulic unit for an injection molding machine according to the present invention. The hydraulic unit 10 includes a fixed displacement hydraulic pump 11, a variable speed motor 12 that drives the hydraulic pump 11, a controller 15 that controls the rotation speed of the motor 12, and a discharge line 7 of the hydraulic pump 11. And a safety valve 14 connected to the discharge line 7 of the hydraulic pump 11. The discharge line 7 is connected to the injection cylinder 2 of the injection molding machine 1 through a three-position electromagnetic switching valve 5.

  The injection molding machine 1 heats a material such as rubber or resin with a screw or a heating cylinder and injects it with the injection cylinder 2. The hydraulic pump 11 supplies hydraulic oil to the injection cylinder 2.

  The motor 12 is, for example, a servo motor. The motor 12 is provided with an encoder 12a that measures the rotation speed of the motor.

  The pressure detector 13 is a pressure sensor, for example, and detects the discharge pressure of the hydraulic pump 11. The operation of the safety valve 14 will be described. When the controller 15 or the pressure detection unit 13 breaks down and the cut-off control unit 16 of the controller 15 does not work, the discharge line is formed at the stroke end of the injection cylinder 2. However, the safety valve 14 is activated to limit the excessive oil pressure and protect the machine.

  The controller 15 is, for example, a servo controller, controls the number of revolutions of the motor 12 to control the discharge pressure of the hydraulic pump 11 (hereinafter referred to as pressure control), and controls the number of revolutions of the motor 12. Thus, the discharge flow rate of the hydraulic pump 11 is controlled (hereinafter referred to as flow rate control).

  The controller 15 includes a cutoff control unit 16, a suppression unit 17, and a main control unit 18.

  The cut-off control unit 16 reduces the rotational speed of the motor 12 when the pressure detected by the pressure detection unit 13 indicates that the cut-off start pressure is set in advance.

  The suppression unit 17 detects the start of the operation of the injection cylinder 2 and suppresses the operation of the cutoff control unit 16 for a predetermined time. Specifically, the suppression unit 17 corrects the cutoff start pressure to be higher than the maximum pressure detected by the pressure detection unit 13 during the predetermined time, so that the cutoff control unit 16 Suppresses the operation.

  The main control unit 18 receives the output of the cut-off control unit 16 and controls the motor 12 so that the discharge pressure or the discharge flow rate of the hydraulic pump 11 becomes a predetermined value.

  First, the pressure control of the controller 15 will be described.

  FIG. 2 shows the relationship between the pressure detected by the pressure detector 13 and time. The time for starting the operation of the injection cylinder (starting injection) is set to 0, and the time for ending the injection of the injection cylinder is set to t2.

  The cutoff start pressure is indicated by a one-dot chain line. Moreover, the full cutoff pressure shown by the dashed-two dotted line higher than this cutoff start pressure is set. During a predetermined time after the start of injection (0 to t3), the cut-off start pressure is corrected by the suppression unit 17 to be higher by a predetermined value than the conventional example in FIG. The pressure is corrected to be higher by a predetermined value by the suppression unit 17 and becomes p4 (p3 <p4).

  Further, at least from the predetermined time to the end of injection (t3 to t2), the cut-off start pressure is a constant value p1 and the full cut-off pressure is a constant value p2 as in the conventional example of FIG. (P1 <p2).

  The discharge pressure of the hydraulic pump 11 indicated by the solid line is controlled by the main control unit 18 to be a predetermined value. When the discharge pressure of the hydraulic pump 11 reaches the cutoff start pressure, The cut-off control unit 16 reduces the rotation speed of the motor 12 and decreases the discharge flow rate of the hydraulic pump 11.

  The difference (p4-p3, p2-p1) between the full cut-off pressure and the cut-off start pressure is referred to as a cut-off pressure width, and this cut-off pressure width is a cut-off state (cut-off start and full cut-off). Is necessary to stabilize). For example, the full cut-off pressure p2 is 20 MPa, whereas the cut-off pressure width (p2-p1) is 1 MPa.

  The predetermined time t3 is a time until immediately before the pressure detected by the pressure detector 13 becomes substantially constant. For example, the predetermined time t3 is 0.2 seconds. From the predetermined time t3 to the end of injection t2, the forward speed of the injection cylinder 2 is substantially constant and the pressure detected by the pressure detector 13 is in a steady state.

  The cut-off start pressure p3, the full cut-off pressure p4, and the predetermined time t3 are input from the outside of the controller 15 or set inside the controller 15.

  Next, the flow control of the controller 15 will be described.

  FIG. 2 shows the relationship between the discharge flow rate of the hydraulic pump and time. The injection start time is 0, and the injection end time is t2. The main control unit 18 controls the rotation speed of the motor 12 so that the discharge flow rate of the hydraulic pump 11 indicated by a solid line maintains a constant value q1.

  The discharge flow rate of the hydraulic pump 11 is calculated from the number of rotations of the motor 12 measured by the encoder 12a in FIG. Instead of the encoder 12a, a flow meter may be connected to the discharge line 7 to directly determine the discharge flow rate of the hydraulic pump 11.

  According to the hydraulic unit for an injection molding machine having the above-described configuration, after the operation of the injection cylinder 2 is started by the suppressing unit 17, the cutoff start pressure p3 is set to the cutoff start pressure at the steady state for the predetermined time t3. Since the correction is made higher than p1 by a predetermined value, even if a pressure overshoot occurs during the predetermined time t3 after the start of the operation of the injection cylinder 2, the pressure detector 13 detects the pressure overshoot during the predetermined time t3. The pressure does not reach the cutoff start pressure p3. For this reason, the rotation speed of the motor 12 does not decrease during the predetermined time t3, and the discharge flow rate of the hydraulic pump 11 does not decrease.

  In this way, even if pressure overshoot occurs after the operation of the injection cylinder 2 is started, the forward speed of the injection cylinder 2 is not changed, and deterioration of the quality of the molded product can be prevented. As a result, the quality of the molded product by the injection cylinder 2 is stabilized, and the yield is improved.

  In the steady state after the predetermined time t3, the cut-off start pressure is p1, and the full cut-off pressure is the pressure setting p2 of the next process (pressure holding process).

  That is, after the predetermined time t3, as shown by the solid line in FIG. 3, the controller 15 gives the cutoff pressure width under the steady-state cutoff start pressure p1 and the full cutoff pressure p2, The discharge pressure and discharge flow rate of the hydraulic pump 11 are controlled. On the other hand, before the predetermined time t3, as shown by the broken line in FIG. 3, the controller 15 performs the hydraulic pump 11 under the cut-off start pressure p3 and the full cut-off pressure p4 which are temporarily corrected to be high. The discharge pressure and discharge flow rate are controlled.

  Next, FIG. 4 shows a flowchart of control at the start of the injection cylinder 2.

  The start of injection of the injection cylinder 2 is detected (S1), and it is determined whether or not a fixed time t3 has passed (S2).

  If the predetermined time t3 has not elapsed, the control unit 17 corrects the cutoff start pressure to a predetermined value (S3), and the controller 15 controls the pressure under the corrected cutoff start pressure. Or flow control is performed (S4).

  On the other hand, when the predetermined time t3 has elapsed, the controller 15 performs a normal process in which pressure control or flow rate control is performed under the normal normal cutoff start pressure that is not highly corrected (S5).

  In addition, this invention is not limited to the above-mentioned embodiment. For example, the suppression unit 17 may stop the operation of the cutoff control unit 16 during the certain time t3.

  Further, the safety valve 14 may be removed. In this case, a safety valve is usually installed in the hydraulic circuit of the injection molding machine. The motor 12 may be any motor as long as the rotation speed can be controlled by the controller 15.

It is a block diagram which shows one Embodiment of the hydraulic unit for injection molding machines of this invention. It is a graph which shows the relationship between the discharge pressure of a hydraulic pump, and time, and the graph which shows the relationship between the discharge flow rate of a hydraulic pump, and time. It is a graph which shows the relationship between the discharge flow rate and discharge pressure of a hydraulic pump. It is a flowchart which shows the control at the time of the start of an injection cylinder. It is a graph which shows the relationship between the discharge pressure of the conventional hydraulic pump, and time, and the graph which shows the relationship between the discharge flow rate of the conventional hydraulic pump, and time.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Injection molding machine 2 Injection cylinder 5 Switching valve 7 Discharge line 10 Hydraulic unit 11 Hydraulic pump 12 Motor 12a Encoder 13 Pressure detection part 14 Safety valve 15 Controller 16 Cut-off control part 17 Suppression part 18 Main control part 19 Tank

Claims (4)

A fixed displacement hydraulic pump (11) for supplying hydraulic oil to the injection cylinder (2);
A variable speed motor (12) for driving the hydraulic pump (11);
A pressure detector (13) for detecting the discharge pressure of the hydraulic pump (11);
When the pressure detected by the pressure detector (13) indicates a preset cut-off start pressure, a cut-off controller (16) that reduces the rotational speed of the motor (12). )When,
A suppression unit (17) that detects the operation start of the injection cylinder (2) and suppresses the operation of the cut-off control unit (16) for a predetermined time;
A main control unit (18) for receiving the output of the cut-off control unit (16) and controlling the motor (12) so that the discharge pressure or the discharge flow rate of the hydraulic pump (11) becomes a predetermined value; A hydraulic unit for an injection molding machine. In the hydraulic unit for injection molding machines according to claim 1,
The hydraulic unit for an injection molding machine, wherein the predetermined time is a time until immediately before the pressure detected by the pressure detector (13) becomes substantially constant. In the hydraulic unit for injection molding machines according to claim 1,
The suppression unit (17) corrects the cutoff start pressure to be higher than the maximum pressure detected by the pressure detection unit (13) during the predetermined time period, and the cutoff control unit (16 ) Is a hydraulic unit for injection molding machines. In the hydraulic unit for injection molding machines according to claim 1,
The said suppression part (17) stops the action | operation of the said cutoff control part (16) during the said predetermined time, The hydraulic unit for injection molding machines characterized by the above-mentioned.

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