JP4672044B2 - Pressure control device for injection molding machine - Google Patents

Description

  The present invention relates to a pressure control device for an injection molding machine that performs feedback control on hydraulic pressure based on a pressure detection value obtained from a pressure sensor.

  In general, a hydraulic injection molding machine is equipped with a pressure control device, and this pressure control device includes an injection cylinder that advances or retracts a screw in the injection device and a screw drive unit that has an oil motor that rotates the screw. The hydraulic drive unit for driving the screw drive unit is provided. In addition, it is equipped with back pressure control means that applies a predetermined back pressure to the screw during metering or suckback processing when the screw moves backward, and this back pressure control means is connected to the rear oil chamber of the injection cylinder. A pressure control valve is used. In this case, when applying the back pressure, the back pressure (hydraulic pressure) is detected by a pressure sensor, and the pressure connected to the rear oil chamber of the injection cylinder so that the detected back pressure becomes a preset back pressure target value. Feedback control of the control valve. Therefore, the molding machine controller includes a feedback control circuit that performs feedback control on such back pressure (see, for example, Patent Document 1).

By the way, since such feedback control is performed on the hydraulic pressure (back pressure), even if an oil temperature fluctuation that becomes a disturbance affecting the hydraulic pressure occurs, the hydraulic pressure matches the preset pressure command value. Controlled. However, it is difficult to completely avoid the effects of oil temperature fluctuations, and it also has a significant impact on actual molding quality. Conventionally, the influence of oil temperature fluctuations on operating conditions has been avoided. Patent Document 2 discloses a hydraulic circuit for the injection molding machine to perform a predetermined operation, an oil temperature sensor for detecting the oil temperature in the hydraulic circuit, and an execution value of the operating condition. An operating condition sensor, a computing means, a storage means, a setting means, and a control valve provided in the middle of the hydraulic circuit, and by sequentially changing the oil temperature in the hydraulic circuit, A deviation amount from the actual measurement value is detected in advance, a correction amount for the actual measurement value to coincide with the set value is calculated from the deviation amount, and a correction coefficient for each oil temperature unit is stored in the storage means. When the oil temperature change is detected by the oil temperature sensor, the stored correction coefficient is Operating condition setting method for an injection molding machine for controlling an output to the control valve by Zui signal is disclosed.
Japanese Patent No. 2665815 Japanese Patent Publication No. 6-43088

  However, the above-described conventional operating condition setting method for an injection molding machine has the following problems.

  First, since the positional relationship between the pressure sensor and the temperature sensor is not considered, a temperature difference is likely to occur between the hydraulic oil that detects pressure by the pressure sensor and the hydraulic oil that detects temperature by the temperature sensor. That is, the pressure detection surface of the pressure sensor is often provided at a recessed position where it does not directly receive the behavior of the hydraulic oil flow, and the temperature sensor is not restricted by such conditions, so the pressure of both is the same. Even so, a temperature difference tends to occur between the two. In particular, because the viscosity of the hydraulic fluid also changes due to changes in the oil temperature, even if control is performed so that the oil pressure matches the pressure command value, a good (normal) molded product may not actually be obtained. To do. Specifically, as shown in FIG. 7, a phenomenon occurs in which the molding quality amount decreases as the oil temperature increases, and this influence increases as the distance between the pressure sensor and the temperature sensor increases.

  Second, since feedback control is performed, the wiring distance of the signal line (closed loop control circuit) between the pressure sensor and the control unit or between the temperature sensor and the control unit tends to be long. Therefore, the influence of disturbance noise on the weak detection signal obtained from the pressure sensor or temperature sensor becomes an error factor that cannot be ignored. In particular, when detecting the back pressure generated in the rear oil chamber of the injection cylinder as the hydraulic pressure, the back pressure is usually a small pressure of about 0.5 [MPa], so that the output signal is greatly affected by disturbance noise. This is an important problem for molded products that are easy and require precision molding.

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

  In order to solve the above-described problems, the present invention provides a feedback to the hydraulic pressure based on the pressure sensor 2 for detecting the hydraulic pressure, the pressure detection value Spd obtained from the pressure sensor 2 and the pressure command value Spc set by the molding machine controller 3. In constructing the pressure control device 1 of the injection molding machine M including the feedback control circuit Cs for performing control, the oil temperature is set in the pressure detection surface 2d of the pressure sensor 2 or in the oil passage 4 facing the pressure detection surface 2d. The temperature sensor 5 for detecting To and the pressure detection value obtained from the pressure sensor 2 based on the detected oil temperature To are corrected to cancel the fluctuation of the pressure detection value due to the fluctuation of the oil temperature To, and the pressure detection after this correction Pressure detection means Fp for outputting the value Spd as a normal pressure detection value, and a pressure control system provided with a pressure sensor 2 and a feedback control circuit Cs. Characterized in that it comprises a valve Vs.

  In this case, according to a preferred aspect of the present invention, the pressure control valve Vs is provided with a separate connection port 7s that is blocked from the hydraulic oil inflow port 7i and the outflow port 7o, and the oil passage 4 that communicates with the connection port 7s. While facing the pressure sensor 2, at least the connection port 7 s and the rear oil chamber 6 r of the injection cylinder 6 can be connected via a predetermined oil distribution line 8. On the other hand, when the temperature sensor 5 is provided, the temperature sensor 5 may be disposed in the oil passage 4 located in the vicinity of the pressure detection surface 2d, or may be disposed on the pressure detection surface 2d of the pressure sensor 2 and on the surface 2df. May be provided, and the temperature detection element 13 of the temperature sensor 5 may be provided in an empty space on the surface 2df of the substrate 12. On the other hand, it is possible to use the hydraulic pump unit 17 that can variably control the rotation speed of the drive motor 16 and at least control the discharge flow rate.

  The pressure control device 1 for an injection molding machine according to the present invention having such a configuration has the following remarkable effects.

  (1) A temperature sensor 5 that is disposed in the pressure detection surface 2d of the pressure sensor 2 or in the oil passage 4 that the pressure detection surface 2d faces to detect the oil temperature To, and is obtained from the pressure sensor 2 by the detected oil temperature To. Since the pressure detection means Fp for correcting the pressure detection value to compensate for the fluctuation of the pressure detection value due to the fluctuation of the oil temperature To and outputting the pressure detection value Spd after the correction as a normal pressure detection value is provided. There is almost no temperature difference between the hydraulic oil whose pressure is detected by the sensor 2 and the hydraulic oil whose temperature is detected by the temperature sensor 5. Therefore, in addition to the basic effect that accurate and stable pressure control that is not affected by fluctuations in the oil temperature To (temperature drift) can be realized, when the pressure detection value Spd is corrected by the oil temperature To, the oil temperature To The substantial influence can be eliminated, the phenomenon that the mass of the molded product decreases as the oil temperature To becomes higher can be eliminated, and the molded product can be homogenized and further improved in quality.

  (2) In addition to being used for correcting the pressure detection value Spd, the temperature sensor 5 detects the oil temperature To, and therefore can also be used as a temperature sensor for acquiring the temperature detection value of hydraulic oil as data. .

  (3) Since the pressure control valve Vs provided with the pressure sensor 2 and the feedback control circuit Cs is provided, the signal line wiring distance between the pressure sensor 2 and the feedback control circuit Cs or between the temperature sensor 5 and the feedback control circuit Cs is short. Therefore, the influence of disturbance noise on the weak detection signal obtained from the pressure sensor 2 or the temperature sensor 5 can be ignored. Therefore, it is optimal for a molded product that requires precision molding.

  (4) According to a preferred embodiment, the pressure control valve Vs is provided with a separate connection port 7s blocked from the hydraulic oil inflow port 7i and the outflow port 7o, and the pressure sensor 2 is connected to the oil passage 4 communicating with the connection port 7s. And at least the connection port 7 s and the rear oil chamber 6 r of the injection cylinder 6 can be connected via a predetermined oil distribution line 8, the pressure sensor 2 allows the hydraulic pressure of the rear oil chamber 6 r in the injection cylinder 6 ( Back pressure) can be detected directly. Therefore, feedback control for back pressure can be performed with high accuracy and stability, and other pressure sensors attached to the injection cylinder 6 can be reduced.

  (5) According to a preferred embodiment, when the temperature sensor 5 is provided, the temperature sensor 5 is formed so as to face the inside of the pressure control valve Vs if it is disposed in the oil passage 4 located in the vicinity of the pressure detection surface 2d. The temperature sensor 5 can be easily provided using the oil path 4.

  (6) According to a preferred embodiment, when the temperature sensor 5 is provided, the pressure detection surface 2d of the pressure sensor 2 is provided with the substrate 12 in which the pressure detection elements 11 are formed on the surface 2df, and an empty space on the surface 2df of the substrate 12 In addition, if the temperature detection element 13 of the temperature sensor 5 is provided, the temperature detection element 13 can be formed together on the substrate 12 on which the pressure detection elements 11... Are formed. This can contribute to space saving and cost reduction, and can further facilitate implementation and contribute to the proximity of the pressure sensor 2 and the temperature sensor 5.

  (7) If the hydraulic pump unit 17 capable of variably controlling the rotational speed of the drive motor 16 and controlling at least the discharge flow rate is used according to a preferred embodiment, the pressure control device 1 according to the present invention can be implemented in an optimum form. In addition, it can be realized as a highly effective embodiment. Further, the inverter control for the pump body can improve the energy saving and reduce the running cost.

  (8) According to a preferred embodiment, the pressure control valve is based on the pressure detection value Spd given from the pressure control valve Vs to the molding machine controller 3 and the pressure command value (normal command value) Spci obtained from the molding machine controller 3. If the second feedback control circuit Cm for correcting the pressure command value Spc applied to Vs is provided, it is possible to eliminate an error generated between the normal command value Spci and the output command value Spc before correction. Therefore, accurate and stable pressure control can be realized even when the pressure command value Spc is small, regardless of the magnitude of the pressure command value Spc (hydraulic pressure) to be controlled.

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

  First, the configuration of the pressure control device 1 according to the present embodiment and the schematic configuration of an injection molding machine M including the pressure control device 1 will be described with reference to FIGS. 1 and 2.

  In FIG. 1, M is a hydraulic injection molding machine, and particularly shows an injection device Mi in which a mold clamping device is omitted. The injection device Mi includes a screw driving unit 14 disposed at the rear, and a heating cylinder 31 that is integrally assembled in front of the screw driving unit 14. The heating cylinder 31 has an injection nozzle 32 at the front end and a hopper 33 at the rear. The heating cylinder 31 incorporates a screw 30 having a ring valve (backflow prevention valve) 30v at the tip. The screw drive unit 14 includes an injection cylinder 6 and an oil motor 18 disposed at the rear end of the injection cylinder 6. The injection cylinder 6 includes a single rod type piston 6p, and a single rod portion 6pr protruding from the piston 6p protrudes forward from the front end of the cylinder body and is coupled to the rear end of the screw 30. Therefore, the inside of the injection cylinder 6 is partitioned into a front oil chamber 6f and a rear oil chamber 6r by the piston 6p. On the other hand, the drive shaft 18s of the oil motor 18 is splined to the rear end of the piston 6p. The oil motor 18 is of a type that can rotate in both the forward rotation and the reverse rotation. As a result, the injection cylinder 6 can pressurize the screw 30 in the forward or backward direction (movable), and the oil motor 18 can rotate the screw 30 forward or backward.

  On the other hand, the hydraulic drive unit 10 is connected to the screw drive unit 14. The hydraulic drive unit 10 includes a hydraulic circuit unit 15 and a hydraulic pump unit 17 connected to the hydraulic circuit unit 15, and the hydraulic circuit unit 15 and the hydraulic pump unit 17 are controlled by the molding machine controller 3. In this case, the molding machine controller 3 has a computing function for controlling the entire molding machine, executes various sequence control (process control) and communication control by the stored processing program 3p, and performs arithmetic processing and storage processing. A function for performing various data processing is provided. In FIG. 1, reference numeral 35 denotes a position sensor using a linear scale that directly detects the position of the screw 30 (screw position), and 19 denotes the rotation number or rotation angle when the oil motor 18 rotates forward and backward. The rotary encoder to detect is shown. The position sensor 35 and the rotary encoder 19 are attached to the molding machine controller 3 and are connected to input ports of the molding machine controller 3, respectively. The screw drive unit 14, the hydraulic drive unit 10 (hydraulic circuit unit 15, hydraulic pump unit 17) and the molding machine controller 3 constitute a hydraulic drive unit Mo, and this embodiment, which will be described later, is part of the hydraulic drive unit Mo. The pressure control apparatus 1 which concerns on is included. The hydraulic circuit unit 15 shown in FIG. 1 shows the pressure control valve Vs extracted, and the circuit part excluding the pressure control valve Vs from the hydraulic circuit unit 15 is shown by a hydraulic circuit body 15m.

  In FIG. 2, an example of the circuit diagram in the hydraulic system and control system which actualized the hydraulic drive unit Mo more is shown. In FIG. 2, the same components as those in FIG.

  First, a variable discharge hydraulic pump 17s serving as a hydraulic drive source is used for the hydraulic pump unit 17. The variable discharge hydraulic pump 17s includes a pump body 41 and a servomotor 16s (drive motor 16) that rotationally drives the pump body 41. The variable discharge hydraulic pump 17s can variably control the rotation speed of the servo motor 16s to control at least the discharge flow rate. As the servo motor 16s, an AC servo motor connected to the output port of the molding machine controller 3 is used. The servomotor 16s is provided with a rotary encoder 16e that detects the rotation speed of the servomotor 16s, and the rotary encoder 16e is connected to an input port of the molding machine controller 3. The pump body 41 is constituted by a swash plate type piston pump. Therefore, the pump body 41 includes a swash plate 42. If the inclination angle (swash plate angle) of the swash plate 42 is increased, the stroke of the pump piston in the pump body 41 increases, the discharge flow rate increases, and the swash plate 42 increases. If the plate angle is reduced, the stroke of the pump piston is reduced and the discharge flow rate is reduced. Therefore, by setting the swash plate angle to a predetermined angle, it is possible to set a fixed discharge flow rate at which the discharge flow rate is fixed to a predetermined size. Further, a control cylinder 43 and a return spring 44 are attached to the swash plate 42, and the control cylinder 43 is connected to a discharge port of the pump main body 41 via a switching valve (electromagnetic valve) Vc, a throttle 45 and a check valve 46. Connecting. Thereby, if the control cylinder 43 is controlled, the angle (swash plate angle) of the swash plate 42 can be changed. Reference numeral 47 denotes a pump pressure sensor. As described above, if the variable pump hydraulic pump 17s capable of controlling at least the discharge flow rate by variably controlling the rotation speed of the servo motor 16s is used for the hydraulic pump unit 17, the pressure control device 1 according to the present invention is optimal. It can be implemented depending on the form and can be realized as a highly effective embodiment. Moreover, there is an advantage that energy saving can be improved and running cost can be reduced by inverter control for the pump body. The suction port of the pump body 41 is connected to the oil tank 48, and the discharge port of the pump body 41 is connected to the hydraulic circuit unit 15.

  On the other hand, the hydraulic circuit unit 15 includes a first direction switching valve (electromagnetic valve) V1, a second direction switching valve (electromagnetic valve) V2, an additional switching valve (electromagnetic valve) V3, and a pressure control valve (back pressure control valve) Vs. The hydraulic circuit unit 15 is configured by connecting as shown in FIG. Reference numerals 51, 52 and 53 denote check valves, and 54 denotes a throttle. Therefore, the hydraulic circuit unit 15 is connected to the oil motor 18 and reversely rotates the oil motor 18 in addition to the two switching valves V1 and V2 that perform switching other than reversely rotating the oil motor 18. It has. If such a configuration is adopted, when the screw 30 in the hydraulic drive unit is reversely rotated, it is sufficient to add one switching valve. Therefore, there is an advantage that it can be easily realized with a relatively simple configuration. Further, the pressure control valve Vs is configured as a unit that performs back pressure control with respect to the backward movement of the screw 30 and can perform feedback control (closed loop control) of the minor loop with respect to the back pressure by having the pressure sensor 2. . Therefore, if such a pressure control valve Vs is used, a more accurate and stable metering process can be performed.

  Since the pressure control valve Vs includes the main part of the pressure control device 1 according to the present embodiment, the configurations and operations (functions) of the pressure control valve Vs and the pressure control device 1 will be described below with reference to FIGS. To explain.

  3, 4 and 5 show a specific structure of the pressure control valve Vs. The pressure control valve Vs includes a valve mechanism 60 that constitutes a basic control valve including a valve body 61 and an electromagnetic solenoid 62, and includes a pressure sensor 2, a temperature sensor 5, and a circuit box 64. The valve body 61 has a valve seat portion 61s formed therein, and incorporates a valve body 61m that can move forward and backward corresponding to the valve seat portion 61s. The valve body 61m is coupled to the armature 62s of the electromagnetic solenoid 62, and the valve seat portion 61s communicates with the hydraulic oil inflow port 7i on the upstream side and the hydraulic oil outflow port 7o on the downstream side. Reference numeral 66 denotes a spring for urging the valve body 61m in the returning direction.

  Further, the pressure sensor 2 is screwed on the outer surface of the valve body 61, and the pressure detection surface 2 d provided at the tip of the pressure sensor 2 faces the oil passage 4 provided inside the valve body 61. In this case, the pressure sensor 2 includes a substrate 12 as shown in FIG. 5A at the tip, and this substrate 12 constitutes the pressure detection surface 2d. The substrate 12 is formed as a printed circuit board, and a plurality of pressure detection elements 11... Using strain gauges are integrally arranged on the front surface 2 df. The pressure detection elements 11. .

  The illustrated oil passage 4 communicates with a third straight oil passage 4c facing the pressure detection surface 2d, a second straight oil passage 4b communicating with the third straight oil passage 4c, and the second straight oil passage 4b. The first straight oil passage 4 a is configured, and the outer end of the first straight oil passage 4 a serves as a connection port 7 s that opens to the outer surface of the valve body 61. Further, the openings of the second straight oil passage 4b and the third straight oil passage 4c facing the outer surface of the valve body 61 are closed by screwing closing caps 65b and 65c, respectively. In this case, the closing cap 65 c is also used as an attachment member for the temperature sensor 5. That is, when the temperature sensor 5 is attached through the center of the closing cap 65c and the closing cap 65c is screwed to the third linear oil passage 4c, the tip detection portion of the temperature sensor 5 is located inside the third linear oil passage 4c. Let us face you. Thereby, as shown in FIG. 3, the temperature sensor 5 is disposed in the oil passage 4 located in the vicinity of the pressure detection surface 2d, and can detect the temperature of the hydraulic oil close to the pressure detection surface 2d. That is, the temperature sensor 5 can be easily provided by using the oil passage 4 formed to allow the pressure sensor 2 to face the pressure control valve Vs.

  The temperature sensor 5 and the pressure sensor 2 are connected to the circuit box 64. The circuit box 64 includes an electric circuit shown in FIGS. 1 and 2, that is, a signal processing unit 71, a calculation unit 72, and an amplifier unit 73, and the temperature sensor 5 and the pressure sensor 2 are included in the signal processing unit 71. Are connected to form a minor loop feedback control circuit Cs. In this case, the signal processing unit 71 has a function of correcting the output signal of the pressure sensor 2 mainly corresponding to the detection result (oil temperature To) of the temperature sensor 5. That is, the signal processing unit 71 cancels the fluctuation of the pressure detection value due to the fluctuation of the oil temperature To with respect to the pressure detection value obtained from the pressure sensor 2 by the oil temperature To (temperature detection value) detected from the temperature sensor 5. The pressure detection means Fp that performs correction and outputs the corrected pressure detection value Spd as a normal pressure detection value is configured. Reference numeral 74 denotes a connector having an input terminal 74 a and an output terminal 74 b provided in the circuit box 64.

  The feedback control circuit Cs operates (functions) as follows. First, the output signal of the pressure sensor 2 and the output signal of the temperature sensor 5 are given to the signal processing unit 71. As a result, the signal processing unit 71 corrects the output signal of the pressure sensor 2 in accordance with the detection result (oil temperature To) of the temperature sensor 5. FIG. 8 shows input / output characteristics of the signal processing unit 71. In FIG. 8, Spdr indicated by a dotted line indicates a pressure detection value (output signal [mV]) from the pressure sensor 2 input to the signal processing unit 71, and when correction by the oil temperature To is not performed, the oil temperature To As the voltage rises, the output signal [mV] (pressure detection value Spdr) fluctuates in the increasing direction. However, by performing correction by the signal processing unit 71, the corrected pressure detection value Spd output from the signal processing unit 71 is substantially constant as shown by the solid line even if the oil temperature To varies. Then, the temperature-corrected pressure detection value Spd output from the signal processing unit 71 is input to the inverting input unit of the calculation unit 72.

  On the other hand, a command signal (pressure command value) Spc for back pressure is applied from the molding machine controller 3, and this pressure command value Spc is input to the non-inverting input unit of the calculation unit 72 via the input terminal 74a. Thereby, a control signal based on the deviation between the pressure command value Spc and the pressure detection value Spd is obtained from the output unit of the calculation unit 72, and this control signal is supplied to the electromagnetic solenoid 62 via the amplifier unit 73. Therefore, the minor position feedback control for the back pressure is performed so that the axial position of the valve body 61m is variably controlled by the control signal and the pressure detection value Spd matches the pressure command value Spc.

  As described above, when the pressure detection value Spd corrected by the oil temperature To detected by the temperature sensor 5 disposed in the vicinity of the pressure sensor 2 is used as the pressure detection value Spd, the hydraulic oil and the temperature at which the pressure sensor 2 detects the pressure. A temperature difference hardly occurs in the hydraulic oil whose temperature is detected by the sensor 5. Therefore, accurate and stable pressure control that is not affected by fluctuations in the oil temperature To (temperature drift) can be realized. In particular, when the pressure detection value Spd is corrected by the oil temperature To, the substantial influence of the oil temperature To can be eliminated. Therefore, the phenomenon that the mass of the molded product decreases as the oil temperature To becomes higher is caused. This can be eliminated, and can contribute to homogenization of the molded product and further quality improvement. In addition to being used for correcting the pressure detection value Spd, the temperature sensor 5 can also be used as a temperature sensor for acquiring the temperature detection value of hydraulic oil as data in order to detect the oil temperature To.

  Further, since the pressure control valve Vs provided with the pressure sensor 2 and the feedback control circuit Cs is used, the wiring distance of the signal line between the pressure sensor 2 and the feedback control circuit Cs or between the temperature sensor 5 and the feedback control circuit Cs is short. Thus, the influence of disturbance noise on the weak detection signals obtained from the pressure sensor 2 and the temperature sensor 5 can be ignored. Therefore, it is optimal for a molded product that requires precision molding.

  FIG. 9 shows changes in hydraulic pressure (back pressure) [MPa] when the molding operation is actually performed. When the signal processing unit 71 does not correct the detected pressure value Spd, the back pressure [MPa] decreases as the number of shots increases from the start of molding as in the distribution characteristic Pr. However, when the pressure detection value Spd is corrected by the signal processing unit 71, the back pressure molded product [MPa] hardly changes even when the number of shots is increased from the start of molding as in the distribution characteristic Pi. . 10 and 11 show the distribution characteristics of the molding quality amount [g] with respect to the oil temperature To [° C.]. When the signal processing unit 71 does not correct the pressure detection value Spd, as shown in the distribution characteristic Ur shown in FIG. 11, when the oil temperature To [° C.] varies by 20 to 50 [° C.], the oil As the temperature To [° C.] increases, the molding quality [g] decreases. However, when the signal processing unit 71 corrects the detected pressure value Spd, even if the oil temperature To [° C.] varies by 20 to 50 [° C.] as shown in the distribution characteristic Ui shown in FIG. Almost no change in distribution tendency.

  By the way, the pressure sensor 2 in the conventional pressure control valve Vs provided with the feedback control circuit Cs of a minor loop is normally assembled | attached so that the oil_pressure | hydraulic in the inflow port 7i can be detected. That is, the oil passage 4 described above has a structure that communicates with the inflow port 7 i without facing the outer surface of the valve body 61. However, in the pressure control valve Vs according to the present embodiment, the oil passage 4 and the inflow port 7i are shut off, and the tip of the oil passage 4 is used as the connection port 7s so that the external oil pressure can be detected. Therefore, in this embodiment, as shown in FIGS. 1 and 2, the connection port 7 s is connected to the rear oil chamber 6 r of the injection cylinder 6 via an external oil distribution line (oil distribution pipe) 8. Thereby, the pressure sensor 2 can directly detect the back pressure generated in the rear oil chamber 6r of the injection cylinder 6, and can perform the feedback control of the minor loop with respect to the back pressure with high accuracy and stability. Moreover, since the other pressure sensor attached to the injection cylinder 6 can also be used, other pressure sensors can be reduced. As is clear from FIG. 2, the pressure control valve Vs is normally connected to the downstream side of the first direction switching valve V <b> 1, and therefore the pressure control valve Vs having the built-in pressure sensor 2 is injected by the pressure sensor 2. It becomes difficult to directly detect the back pressure in the rear oil chamber 6r of the cylinder 6, and as a result, accurate back pressure control cannot be performed.

  On the other hand, even with such a pressure control valve Vs, if the inflow port 7i (or the outflow port 7o) and the connection port 7s are configured to be able to communicate with each other by a predetermined oil passage forming means (such as an optional oil distribution pipe), the pressure control valve It can also be used as a general type (conventional aspect) in which the pressure sensor 2 is built in the valve Vs and the hydraulic pressure of the hydraulic oil flowing through the pressure control valve Vs is directly detected. Therefore, if necessary, the usage mode according to the present embodiment or the conventional mode can be properly used in accordance with the difference in use.

  The pressure control valve Vs is provided with a second feedback control system (closed loop control system) for back pressure. That is, the temperature-corrected pressure detection value Spd output from the signal processing unit 71 in the pressure control valve Vs is given to the molding machine controller 3 via the output terminal 74b, and the pressure detection value Spd by the molding machine controller 3 is provided. The pressure command value Spc is corrected based on the magnitude of the pressure control value, and a second feedback control circuit Cm is provided in which the corrected pressure command value Spc is applied to the input terminal 74a of the pressure control valve Vs. FIG. 5 shows a functional block diagram of the second feedback control circuit Cm in the molding machine controller 3. In FIG. 5, 91 is a calculation unit for obtaining a deviation Ep between a pressure detection value Spd given from the pressure control valve Vs and a pressure command value (normal command value) Spci obtained from the inside of the molding machine controller 3, and 92 is a normalization of the deviation Ep. An adding unit 93 obtains a pressure command value (output command value) Spc to be added to the command value Spci and applied to the pressure control valve Vs, and 93 compensates the output command value Spc with a PID constant and outputs it to the pressure control valve Vs. Each of the PID compensation units is shown.

  This feedback control circuit Cm is provided for the following reason. As described above, since the molding machine controller 3 and the pressure control valve Vs are usually disposed in different installation environments that are separated from each other, the internal potential of an electric circuit provided in the pressure control valve Vs and the inside of the molding machine controller 3 are determined. There is a possibility that a slight potential difference (about several tens [mV]) is generated between the potentials. In this case, the injection pressure, mold clamping pressure, and the like are usually large pressures of about 15 [MPa]. Therefore, even if such a potential difference (offset level) occurs, there is almost no problem. Therefore, the occurrence of such an offset level becomes a non-negligible error factor. Therefore, the molding machine controller 3 is provided with a second feedback control circuit Cm for correcting the pressure command value Spc to be applied to the pressure control valve Vs based on the pressure detection value Spd and the normal command value Spci, and the normal command value Spci and the pressure An error generated between the command values Spc is excluded.

  The feedback control circuit Cm operates (functions) as follows. First, the pressure detection value Spd output from the pressure control valve Vs is given to the inverting input unit of the calculation unit 91, and the normal command value Spci obtained from the inside of the molding machine controller 3 is the non-inverting input unit of the calculation unit 91. To be granted. Thereby, a deviation Ep between the pressure detection value Spd and the normal command value Spci is obtained at the output unit of the calculation unit 91, and this deviation Ep is given to one input unit of the addition unit 92. Further, since the normal command value Spci is given to the other input unit of the adding unit 92, an output command value Spc obtained by adding the deviation Ep to the normal command value Spci is obtained from the output unit of the adding unit 92. The output command value Spc is compensated by the PID compensation unit 93 in which the PID constant is set, and the PID compensated output command value (pressure command value) Spc is applied to the pressure control valve Vs. Therefore, for example, when the pressure detection value Spd is smaller than the normal pressure command value Spci, the deviation Ep is added to the normal command value Spci, and the pressure command value (output command value) obtained from this is added. By giving Spc to the pressure control valve Vs, feedback control is performed so that the pressure detection value Spd always matches the normal pressure command value Spci.

  Therefore, by providing such a feedback control circuit Cm, the pressure command value Spc is accurate and stable even when the pressure command value Spc is small, regardless of the magnitude of the pressure command value Spc (hydraulic pressure) to be controlled. Pressure control can be realized. In particular, if the back pressure generated in the rear oil chamber 6r of the injection cylinder 6 when the screw 30 is retracted is applied, for example, even in the case of a relatively small back pressure, which is usually about 0.5 [MPa], it is accurate. Stable back pressure control can be realized. Further, the feedback control circuit Cm has an advantage that it can be implemented easily and at low cost by a relatively simple circuit configuration.

  Further, as shown in FIG. 3, the rotary encoder 19 is connected to the molding machine controller 3 to obtain the rotation speed (rotation speed detection value Rd) of the oil motor 18, so that the rotation speed detection value Rd is set in advance. A third feedback control circuit Cr is provided for variably controlling the rotation speed of the servo motor 16s based on the rotation speed setting value Rs. As a result, the rotational state of the screw 30 rotated by the oil motor 18 can be immediately reflected in the control of the hydraulic pump unit 17, so that the screw 30 can be quickly raised to the target rotational speed. Responsiveness when rotating can be improved. In particular, by combining with the above-described pressure control valve Vs, the back pressure control can be positively influenced, and the back pressure control can be performed stably and accurately.

  On the other hand, FIG. 5B shows a modified embodiment when the temperature sensor 5 is provided. 3 and 4 show the case where the temperature sensor 5 is provided in the oil passage 4 located in the vicinity of the pressure detection surface 2d. FIG. 5B shows the case where the temperature sensor 5 is provided. The temperature detection element 13 constituting the temperature sensor 5 is provided in an empty space on the surface 2df of the substrate 12 constituting the pressure detection surface 2d of the pressure sensor 2. In this case, for the temperature detection element 13, for example, a temperature-electric resistance conversion element can be used. According to such a modified embodiment, since the temperature detecting element 13 can be formed together on the substrate 12 on which the pressure detecting elements 11... Are formed, downsizing, space saving, and low cost when configuring the pressure control device 1. This can contribute to the realization of the sensor, and can further facilitate the implementation and contribute to the proximity of the pressure sensor 2 and the temperature sensor 5.

  Next, an overall operation (function) of the hydraulic drive device Mo including the pressure control device 1 according to the present embodiment, and an operation related to the pressure control valve Vs will be described with reference to each drawing.

  Assume that the weighing process is being performed. In this case, the switching valves V1 and V2 in the hydraulic circuit unit 15 in FIG. 2 are both switched to the symbol b, and the switching valve V3 is switched to the symbol a. The switching valve Vc maintains the position shown in FIG. Thus, the hydraulic oil of the variable discharge hydraulic pump 17s is measured by rotating the oil motor 18 forward, that is, rotating the screw 30 forward. In this case, the plasticized molten resin is measured and accumulated in front of the screw 30 inside the heating cylinder 31, and the screw 30 is retracted correspondingly. As the screw 30 moves backward, the hydraulic oil in the rear oil chamber 6r in the injection cylinder 6 is discharged, and the discharged hydraulic oil is returned to the oil tank 48 through the pressure control valve Vs. Therefore, the back pressure control by the pressure control valve Vs is performed with respect to the backward movement of the screw 30.

  For the back pressure, as described above, feedback control of the minor loop by the feedback control circuit Cs provided in the pressure control valve Vs and feedback by the second feedback control circuit Cm by the molding machine controller 3 attached to the pressure control valve Vs. Control (closed loop control) is performed. That is, the double feedback control system performs stable control with high accuracy against the back pressure. In addition, since the third feedback control circuit Cr attached to the servo motor 16s is provided, the back pressure control by the pressure control valve Vs is also performed stably and accurately.

  On the other hand, when the metering progresses and the screw 30 reaches the metering end position set, the switching valve V1 is switched to the neutral position to stop the rotation of the screw 30, and the switching valve V3 is switched to the symbol b to change the oil motor 18 And the pressurizing process for switching both the switching valves V1 and V3 to the symbol a and pressurizing the screw 30 in the forward direction are repeated at least once or preferably twice. As a result, the ring valve 30v of the screw 30 can be accurately closed even with a hydraulic drive unit, and variations in resin pressure and fluctuations in the measured amount of resin for each shot can be reduced. Accuracy can be secured.

  When the final pressurizing process is completed, the switching valve V1 is switched to the neutral position, and the switching valve V2 is switched to the symbol a to perform a suckback process for moving the screw 30 backward. In the suck back process, the screw 30 is moved backward by a preset stroke (for example, around 1 to 2 [mm]). In this case, the retreating speed of the screw 30 is determined by a retreating speed that is a relatively low speed at which the ring valve 30v does not open during retreating. As a result, it is possible to avoid the adverse effect that the retraction speed of the screw 30 is too fast and the ring valve 30v opens. This backward movement at low speed can be realized by controlling the pressure control valve Vs. Further, if the screw 30 is moved backward by the set stroke, the switching valve V2 is switched to the symbol b, and the standby state for the injection process is shifted. Thereafter, when it is time to start injection, an injection process is performed.

  Although the best embodiment has been described in detail above, the present invention is not limited to such an embodiment, and departs from the gist of the present invention in the detailed configuration, shape, quantity, numerical value, method, and the like. It can be changed, added, or deleted as long as it is not. For example, when the temperature sensor 5 is provided, the case where the temperature detection element 13 of the temperature sensor 5 is formed together with the empty space on the surface 2df of the substrate 12 is shown. However, the temperature sensor 5 is supported by the empty space. You may utilize as a support part to do. Furthermore, as the hydraulic drive unit 10, the hydraulic drive unit having the hydraulic pump unit 17 that can variably control the rotation speed of the drive motor 16 and control at least the discharge flow rate is illustrated, but a fixed discharge pump and a flow control valve are combined. Other hydraulic pump units such as a combined hydraulic pump unit may be used, and the hydraulic circuit unit 15 is not limited to the illustrated circuit configuration, and may be replaced by another circuit configuration that exhibits a similar function. May be.

The schematic block diagram of an injection molding machine provided with the pressure control apparatus which concerns on the best embodiment of this invention, Circuit diagram of hydraulic system and control system of the pressure control device, A partial cross-sectional side view of a pressure control valve used in the pressure control device, A plan view of the pressure control valve, A perspective view showing a pressure detection surface (a) of a pressure sensor used for the pressure control valve and a modified embodiment (b) in which a temperature sensor is formed on the pressure detection surface; A circuit diagram of a second feedback control circuit provided in the pressure control device, A graph showing the change in molding quality with oil temperature, A graph showing changes in the output signal of the pressure sensor and the output signal of the signal processing unit with respect to the oil temperature; A graph showing the change in hydraulic pressure (back pressure) with respect to the number of shots, A graph showing the change in molding quality with respect to oil temperature when corrected by the signal processing unit, A graph showing a change in the molding quality amount with respect to the oil temperature when not corrected by the signal processing unit,

Explanation of symbols

  1: pressure control device, 2: pressure sensor, 2d: pressure detection surface, 2df: substrate surface, 3: molding machine controller, 4: oil passage, 5: temperature sensor, 6: injection cylinder, 6r: after injection cylinder Oil chamber, 7i: Inflow port, 7o: Outflow port, 7s: Connection port, 8: Oil distribution line, 11 ...: Pressure detection element, 12: Substrate, 13: Temperature detection element, 16: Drive motor, 17: Hydraulic pump Part, Spd: pressure detection value, Spci: pressure command value, Spc: pressure command value, Cs: feedback control circuit, Cm: second feedback control circuit, M: injection molding machine, Fp: pressure detection means, Vs: pressure Control valve

Claims (5)

  In a pressure control device for an injection molding machine comprising a pressure sensor for detecting hydraulic pressure, and a feedback control circuit for performing feedback control on the hydraulic pressure based on a pressure detection value obtained from the pressure sensor and a pressure command value set by a molding machine controller A temperature sensor that is disposed in a pressure detection surface of the pressure sensor or an oil passage that the pressure detection surface faces to detect an oil temperature, and an oil temperature relative to a pressure detection value obtained from the pressure sensor by the detected oil temperature. And a pressure detection means for outputting the pressure detection value after the correction as a normal pressure detection value, and the pressure sensor and the feedback control circuit are provided. A pressure control device for an injection molding machine, comprising a pressure control valve.   The pressure control valve is provided with a separate connection port that is cut off from the inflow port and the outflow port for hydraulic oil, and the pressure sensor faces the oil passage communicating with the connection port, and at least the connection port and the injection cylinder 2. The pressure control device for an injection molding machine according to claim 1, wherein the rear oil chamber is connectable via a predetermined oil distribution line.   The pressure control device for an injection molding machine according to claim 2, wherein the temperature sensor is disposed in the oil passage located in the vicinity of the pressure detection surface.   The pressure detection surface of the pressure sensor has a substrate on which a pressure detection element is formed, and the temperature detection element of the temperature sensor is provided in an empty space on the surface of the substrate. Pressure control device for injection molding machines.   2. The pressure control device for an injection molding machine according to claim 1, further comprising a hydraulic pump unit capable of variably controlling the rotation speed of the drive motor to control at least the discharge flow rate.

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