JP2016168819A - Load sensing device of injection molding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a load sensing device of an injection molding machine which can correct temperature drift of a sensor used in a place added regular load with a simple method without arranging a temperature sensor separately.SOLUTION: On the basis of a detection value acquired in a state that load added to a first sensor is almost no load in a molding cycle, a detection value of a second sensor is corrected by estimating ambient temperature of an injection molding machine. The detection value of the second sensor can be corrected appropriately by acquiring the detection value in a state that the first sensor is no load, without arranging a temperature sensor separately, even in the absence of state of no load to the second sensor.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a load detection device used in an injection molding machine.

  In general, an injection molding machine and a mold incorporated in the injection molding machine are equipped with various sensors for actually measuring loads such as injection pressure, mold clamping force, bump output, and nozzle touch force. Then, during the molding cycle in which a series of processes consisting of mold closing, mold clamping, injection, holding pressure, weighing, cooling, mold opening, protrusion, etc. are repeatedly executed, the actual measured values of loads detected by these sensors are displayed on the screen. In order to display, use for evaluation of molding stability, or to generate a predetermined injection pressure, mold clamping force, bump output, and nozzle touch force, feedback control of detection values of these sensors is performed. Yes.

  As sensors for detecting pressure and force in injection molding machines such as injection pressure, mold clamping force, bump output, nozzle touch force, etc., strain gauges and load cells that convert the voltage of the strain gauge bridge circuit into pressure are used. ing. Specifically, the acting pressure load is measured from the potential difference of the bridge circuit caused by the resistance change of the strain gauge constituting the bridge circuit attached to the load cell body.

  As a load cell configuration, a strain gauge is provided at a plurality of positions to form a bridge circuit, and by using the output of the bridge circuit, a predetermined acting force is measured from a plurality of acting forces acting on the strain gauge. Conventionally, a temperature sensor for detecting the temperature of the strain gauge is provided to compensate for the output of the bridge circuit.

Patent Document 1 includes a plurality of pressure detectors, stores a correlation between the temperature of the pressure detector and an output value, and uses the temperature and correlation detected by the temperature detection unit to A technique for calculating a corrected pressure value by correcting an output value of a detector is disclosed.
Patent Document 2 has a strain sensor unit that detects the amount of strain of a component of a mold clamping device of an injection molding machine, and detects the mold clamping force by converting the amount of strain detected by the strain sensor into a mold clamping force. Thus, a technique for feeding back the clamping force is disclosed.

Patent Document 3 discloses a technique in which a distortion sensor is provided at a portion where distortion is detected in an injection molding machine, and the nozzle touch force is feedback-controlled by the detected value of the nozzle touch force and the distortion sensor.
In Patent Document 4, when detecting the internal pressure of a mold by a pressure sensor attached to the mold of an injection molding machine, the pressure detection value based on the output of the pressure sensor during the predetermined period is corrected in a predetermined period after the end of protrusion. A technique is disclosed in which a pressure detection value is corrected using a correction value stored as a value.

JP 2008-55714 A JP-A-9-187853 JP-A-2-45113 JP-A-7-76034

  It is known that a strain gauge and a load cell using the strain gauge generate a phenomenon called temperature drift in which an output value changes depending on an ambient temperature. When temperature drift occurs in this way, the pressure value may not be detected accurately. In order to solve this problem, in the technique disclosed in Patent Document 1, a temperature sensor for measuring the ambient temperature is provided, and the output value is corrected based on the actually measured temperature. Further, in the technique disclosed in Patent Document 4, it is noted that there is a period in which the mold internal pressure becomes zero after the end of the protrusion, and the detection value in this detection period is stored as a correction value, and in the subsequent detection It is used as a correction value for temperature drift.

  However, the technique disclosed in Patent Document 1 requires a separate temperature sensor for correcting the output value, which may lead to an increase in cost. The technique disclosed in Patent Document 4 does not require a temperature sensor, but requires a period during which the pressure becomes zero during the molding cycle. Therefore, there is a problem that it cannot be applied to temperature drift correction of a sensor used in a place where a load is constantly applied to the pressure sensor.

  Accordingly, the present invention provides a load detection device for an injection molding machine that can perform temperature drift correction of a sensor that is used in a place where a load is always applied by a simple method, without the need for a separate temperature sensor. Objective.

  In the invention according to claim 1 of the present application, an injection apparatus including a nozzle for injecting resin into a mold, a mold clamping apparatus for clamping the resin injected into the mold, and the mold clamping apparatus In the load detection device for an injection molding machine, comprising: a first sensor that detects a load in an injection molding machine that includes a projecting device that projects a molded product after mold clamping; and a second sensor. Based on the detection value acquisition means for acquiring the detection value of the first sensor when the load applied to the sensor is substantially unloaded, and the detection value acquired by the detection value acquisition means, the ambient temperature of the injection molding machine is determined. A load of an injection molding machine comprising temperature estimating means for estimating and detected value correcting means for correcting the detected value of the second sensor based on the ambient temperature estimated by the temperature estimating means A detection device is provided.

  In the invention according to claim 1, the detection value in the no-load state is acquired in the first sensor in which the no-load state exists, and the detection value of the second sensor is corrected based on the detection value. As a result, there is no need to provide a separate temperature sensor or the like for sensor correction, and even when the second sensor does not have a no-load state, the first sensor is in a no-load state. By acquiring the detected value, the detected value of the second sensor can be appropriately corrected.

In the invention according to claim 2 of the present application, the first sensor is either a mold clamping force sensor that detects a mold clamping force of the mold clamping device or a bump output sensor that detects a protruding force of the protruding device. A load detection device for an injection molding machine according to claim 1 is provided.
In the invention according to claim 3 of the present application, the second sensor is an injection pressure sensor that detects a resin pressure in the injection device or the nozzle, and a nozzle touch force that detects a contact force of the nozzle to the mold. The load detection device for an injection molding machine according to claim 1 or 2, wherein the load detection device is a sensor.

  According to the present invention, there is no need to provide a separate temperature sensor, and it is possible to provide a load detection device for an injection molding machine capable of correcting temperature drift of a sensor used in a place where a load is always applied in a simple manner. It becomes.

It is a figure which shows the structure of the injection molding machine in embodiment of this invention. It is the graph which showed the relationship between the detected value of the 1st sensor at the time of no load, and ambient temperature. It is the graph which showed the relationship between the correction value of the detected value of a 2nd sensor, and ambient temperature. It is the graph which showed the mode of correction of the 2nd sensor.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a configuration of an injection molding machine according to the present embodiment.
The injection molding machine includes an injection device and a mold clamping device on a machine base. The mold clamping device includes a movable platen 12 and a fixed platen 14, and the movable platen 12 and the fixed platen 14 are connected by a tie bar 15, and the movable platen 12 approaches the fixed platen 14 along the tie bar 15. It is possible to move in the direction away. A movable mold 16 is attached to the movable platen 12, and a fixed mold 18 is attached to the fixed platen 14.

The movable platen 12 moves along the tie bar 15 by the rotation of the mold clamping motor M1. Even after the movable side mold 16 and the fixed side mold 18 come into contact with each other, the mold clamping motor M1 can be further rotated to continue the mold clamping. The mold clamping force generated at that time is detected by a mold clamping force sensor S1.
After the mold clamping operation, the molded product is ejected by rotating the projecting motor M2 to drive the ejector (projecting device) 17. The bump output generated at that time is detected by the bump output sensor S2.

  The injection device includes a hopper 32 that mainly stores resin, an injection cylinder 34, a screw 36 provided in the injection cylinder 34, a nozzle 38 provided at the tip of the injection cylinder 34, an injection cylinder 34, and a nozzle 38. Is composed of a ball screw 39 for moving the tool in a direction approaching and moving away from the fixed mold 18. The resin stored in the hopper 32 is put into the injection cylinder 34. Then, while being heated by a heater (not shown), the screw 36 is rotated by the rotation of the screw rotation motor M4, and the resin is conveyed toward the tip of the injection cylinder 34 while being melted. The pressure inside the injection cylinder 34 at this time is detected by the injection pressure sensor S3.

Further, by rotating the nozzle back-and-forth motor M5, the injection cylinder 34 and the nozzle 38 provided at the tip thereof are moved back and forth along the ball screw 39. By moving the nozzle 38 forward in the direction of the fixed mold 18, the nozzle 38 contacts the fixed mold 18. The nozzle touch force generated at that time is detected by the nozzle touch force sensor S4.
After the nozzle 38 comes into contact with the fixed mold 18 and a predetermined nozzle touch force is generated, the molten resin in the injection cylinder 34 is injected into the fixed mold 18 by driving the injection motor M3. .

Each motor is connected to an amplifier for driving the motor, and as shown in FIG. 1, a servo amplifier 30a controls the mold clamping motor M1 and the protrusion motor M2. The servo amplifier 30b controls the screw rotation motor M4, and the servo amplifier 30c controls the injection motor M3 and the nozzle forward / reverse motor M5.
The servo CPU 20 is connected to a ROM 22 that stores a control program dedicated to servo control that performs processing of a position loop, a speed loop, and a current loop, and a RAM 21 that is used for temporary storage of data.

  The operation status of each motor is input to the servo CPU 20. The detection values of the mold clamping force sensor S1 and the bump output sensor S2 are input to the servo CPU 20 through the A / D converter 23a, and the detection values of the injection pressure sensor S3 and the nozzle touch force sensor S4 are A / D. The signal is input to the servo CPU 20 through the converter 23b.

  The PMC CPU 24 is connected to a ROM 26 storing a sequence program for controlling the sequence operation of the injection molding machine and a RAM 25 used for temporary storage of calculation data. Connected to the CNC CPU 27 are a ROM 29 storing an automatic operation program and the like for overall control of the injection molding machine, and a RAM 28 used for temporary storage of calculation data.

  An LCD / MDI (input device with a display device) 42 having a display device composed of a liquid crystal display device or the like is connected to the bus 26 via an LCD display circuit 41. Further, a molding data storage RAM 40 composed of a nonvolatile memory is also connected to the bus 26. The molding data storage RAM 40 stores molding conditions relating to injection molding work, various set values, parameters, macro variables, and the like.

  With the above configuration, the PMC CPU 24 controls the sequence operation of the entire injection molding machine, and the CNC CPU 27 distributes the movement command to each motor based on the operating program in the ROM 29 and the molding conditions stored in the molding data storage RAM 40. The servo CPU 20 performs so-called digital servo processing by performing servo control such as position loop control, speed loop control, and current loop control as in the prior art.

  Next, the operation of this embodiment will be described. First, out of a plurality of sensors attached to the injection molding machine, a sensor that may be almost unloaded during the molding cycle is extracted. In the injection molding machine, the mold clamping force is generated when the movable mold 16 and the fixed mold 18 are closed, but is not generated when both molds are open. For this reason, the mold clamping force sensor S1 is almost unloaded when both molds are open. Further, the projecting output sensor S2 that detects the projecting output generated when the ejector 17 is driven to project the molded product is substantially in a no-load state during the period when the projecting is not performed.

  Therefore, the mold clamping force sensor S1 and the bump output sensor S2 can be used as the first sensor. FIG. 2 is a graph showing the relationship between the detected value of the first sensor at no load and the ambient temperature in these first sensors. The relationship between the detected value and the ambient temperature can be obtained in advance by actual measurement, or can be obtained from the linear expansion coefficient of the metal resistor of the strain gauge of the first sensor or the linear expansion coefficient of the measured object of the strain gauge. You can also. In any case, there is a correlation between the detected value of the first sensor at no load and the ambient temperature, and the ambient temperature can be estimated by obtaining the detected value of the first sensor at no load. Is possible.

  Here, among the plurality of sensors attached to the injection molding machine, the injection pressure sensor S3 and the nozzle touch force sensor S4 are always loaded, so there is almost no unloaded state. If these sensors are the second sensors, no unloaded state can be created for each of the molding sensors for each molding cycle. FIG. 3 is a graph showing the relationship between the correction value of the detection value of the second sensor and the ambient temperature. These relationships can also be obtained in advance by actual measurement, or can be obtained from the linear expansion coefficient of the metal resistor of the strain gauge of the second sensor and the linear expansion coefficient of the measured object of the strain gauge.

Using these relationships, first, using the relationship of FIG. 2, the ambient temperature in the molding cycle is estimated from the detected value of the first sensor when there is no load, and then using the relationship of FIG. 3, Based on the estimated ambient temperature, a correction value of the sensor detection value of the second sensor in the molding cycle is obtained. As a result, as shown in FIG. 4, the detection value of the second sensor can be corrected based on the estimated value of the ambient temperature.
Here, since the temperature inside the injection molding machine is substantially the same, the ambient temperature value of the injection molding machine estimated based on the detection value of the first sensor is directly used as the correction value of the second sensor. However, if there is a difference in temperature depending on the location of the first sensor and the location of the second sensor, the relationship between the two is obtained in advance. It is also possible to obtain the correction value of the second sensor detection value based on the temperature correction value after correcting the ambient temperature estimated based on the detection value of the sensor.

  In this embodiment, after the ambient temperature is obtained from the detection value of the first sensor at no load, the detection value of the second sensor is further corrected from the ambient temperature. When the output characteristics of the sensor and the second sensor with respect to the strain gauge load are the same, the ambient temperature is estimated, and the process of correcting the detected value of the sensor from the estimated ambient temperature is omitted. The detection value of the first sensor may be directly used as the correction value of the second sensor.

  Further, the acquisition of the detection value of the first sensor and the correction of the detection value of the second sensor at the time of no load described above may be performed every molding cycle or every predetermined molding cycle. Alternatively, after the detection value of the first sensor at the time of no load is obtained over a predetermined molding cycle, the detection value of the second sensor can be corrected after averaging the acquired detection values.

  Further, in the present embodiment, the mold clamping force sensor S1 and the bump output sensor S2 are used as the first sensor, and the injection pressure sensor S3 and the nozzle touch force sensor S4 are used as the second sensor. As the first sensor, any other sensor can be used as long as it is in a state that is almost in the no load state during the molding cycle, and the no load state does not occur in the molding cycle as the second sensor. Other sensors can be used as the sensor.

DESCRIPTION OF SYMBOLS 12 Movable platen 14 Fixed platen 15 Tie bar 16 Movable side metal mold 17 Ejector 18 Fixed side metal mold M1 Mold clamping motor M2 Projection motor M3 Injection motor M4 Screw rotation motor M5 Nozzle back and forth motor S1 Mold clamping force sensor S2 Impact output sensor S3 Injection pressure sensor S4 Nozzle touch force sensor

Claims (3)

An injection device having a nozzle for injecting resin into the mold, a mold clamping device for clamping the resin injected into the mold, and a protrusion for projecting a molded product after clamping by the mold clamping device In a load detection device for an injection molding machine comprising a first sensor and a second sensor for detecting a load in an injection molding machine comprising an apparatus,
Detection value acquisition means for acquiring a detection value of the first sensor in a state in which the load applied to the first sensor is substantially unloaded;
Temperature estimation means for estimating the ambient temperature of the injection molding machine based on the detection value acquired by the detection value acquisition means;
A load detection device for an injection molding machine, comprising: a detection value correction unit that corrects a detection value of the second sensor based on an ambient temperature estimated by the temperature estimation unit.   2. The first sensor according to claim 1, wherein the first sensor is one of a mold clamping force sensor that detects a mold clamping force of the mold clamping device and a bump output sensor that detects a protruding force of the protruding device. Load detection device for injection molding machines.   The second sensor is either an injection pressure sensor that detects a resin pressure inside the injection device or the nozzle, or a nozzle touch force sensor that detects a contact force of the nozzle to the mold. The load detection device for an injection molding machine according to claim 1 or 2.