JP5144442B2 - Injection molding machine and method for determining closed state of backflow prevention valve - Google Patents

Description

  The present invention relates to an injection molding machine having a backflow prevention valve in a screw and a backflow prevention valve closed state determination method.

  2. Description of the Related Art Conventionally, an injection molding machine having an injection mechanism having a backflow prevention valve mechanism at a screw tip in order to prevent a backflow of resin at the time of injection, such as an inline screw type injection molding machine, has been used. FIG. 1 is an example of this check valve mechanism. On the main body side of the screw 1 of the reduced diameter portion provided between the screw head 2 provided at the tip of the screw 1 and the main body portion of the screw 1, the backflow prevention valve 3 is brought into contact and in close contact with the resin passage. A check sheet 4 to be closed is provided.

  The resin pellets supplied from the rear of the screw 1 are melted by shear heat generated by the rotation of the screw 1 and heat from a heater provided outside the cylinder in which the screw 1 is inserted. The molten resin raises the resin pressure behind the backflow prevention valve 3 and generates a force that pushes the backflow prevention valve 3 forward. When the backflow prevention valve 3 is pushed forward, the rear resin passes through the gap between the backflow prevention valve 3 and the reduced diameter portion and flows into the front of the backflow prevention valve 3 to increase the pressure in the cylinder in front of the screw head 2.

  When the pressure in front of the backflow prevention valve 3 exceeds a predetermined pressure (back pressure), the screw 1 is pushed backward, and the pressure in front of the backflow prevention valve 3 is reduced. Furthermore, since the pressure behind the backflow prevention valve 3 becomes higher than the pressure ahead of the backflow prevention valve 3 due to the rotation of the screw 1, the continuously melted resin is sent to the front of the backflow prevention valve 3, When the screw 1 moves backward to a predetermined amount, the screw rotation is stopped (metering step).

  Next, the injection process starts, but when the screw 1 moves forward to fill the resin, the resin pressure accumulated in front of the screw head 2 rises, so that the backflow prevention valve 3 moves backward and comes into close contact with the check sheet 4. The passage is closed and the molten resin is prevented from flowing backward in the screw retracting direction due to the filling pressure. If the backflow prevention valve 3 moves backward and the timing for closing the resin passage varies, the amount of resin to be filled also varies and molding becomes unstable.

  The backflow prevention valve mechanism at the time of injection is closed because the front pressure of the backflow prevention valve 3 becomes higher than the rear pressure by the advance of the screw 1, but the back of the backflow prevention valve mechanism immediately before the injection is between the flights 5. There is a residual pressure in the groove 6, and there is a problem that the closing timing varies due to the influence of this residual pressure. Since the back flow of the resin occurs from the front to the back of the back flow prevention valve from the start of injection to the back flow prevention valve closing, the change in the closing timing causes a change in the injection volume for each cycle, and the molded product to be molded. Affects the quality of the. Accordingly, a means for allowing the backflow prevention valve 3 to be closed at a stable timing every cycle is considered, and a method for monitoring the timing at which the backflow prevention valve 3 is actually closed has been proposed.

  For example, Patent Document 1 and Patent Document 2 are provided with a pressure sensor that detects the resin pressure in the cylinder at a position behind the backflow prevention valve, and based on the pressure change detected by the pressure sensor during screw advancement. A technique is disclosed in which the closing of the backflow prevention valve is detected, and the non-defective product is determined and the molding conditions are adjusted based on the detected backflow prevention valve closing position.

  In Patent Document 3, a conductive member is disposed behind the ring valve of the backflow prevention valve so as to face the ring valve, and a capacitance between the ring valve and the conductive member is detected to detect a ring. A technique for detecting the position of the valve, that is, when the resin flow path is closed by the ring valve is disclosed.

  Further, Patent Document 4 does not detect the closing timing of the backflow prevention valve during injection, but detects rotational torque acting on the screw at the time of injection. A technique for detecting an abnormality is disclosed.

  Further, in Patent Document 5, when injection is started with the screw being freely rotatable, the resin flows backward and the screw is rotated. However, when the backflow prevention valve is closed and the reverse flow of the resin is stopped, the rotation of the screw is stopped. The screw rotation stop is detected as the closing timing of the backflow prevention valve, and the injection speed switching position and the switching position to the holding pressure are corrected based on the detected backflow prevention valve closing position. Technology is disclosed.

  Patent Document 6 also provides a backflow prevention mechanism that shuts off the metering portion and the front of the screw head by rotating the screw in reverse after the measurement is completed. After the measurement is completed, the screw is rotated in reverse to prevent backflow. A technique is disclosed in which the metering unit and the front of the screw head are blocked by a mechanism, and then injection is started, and the quality of the molded product is determined based on the stroke position and amount at the time of injection.

  Further, in Patent Document 7, when a servo lock is performed to perform feedback control so as to keep the screw angle constant so that the screw does not rotate during the injection process, the peak point of the screw rotation angle is closed when the check valve is closed. The technology considered as the time is disclosed.

  Patent Document 8 discloses a technique that can detect the rotational force acting on the screw during the forward movement of the screw and can regard the peak point of the rotational force as the closing point of the check valve.

  Patent Document 9 discloses a technique for detecting a rotational force acting on a screw during screw advancement and determining a closed state of the check valve based on a waveform pattern of the rotational force.

JP-A-4-53720 JP-A-4-201225 JP-A-3-92321 JP-A-1-168421 JP 2004-216808 A JP 2006-69219 A JP 2008-126533 A JP 2008-155379 A JP 2008-195015 A

  The techniques disclosed in Patent Document 1 and Patent Document 2 described above detect pressure change in the cylinder to detect closing of the backflow prevention valve. In this technique, it is necessary to add a pressure sensor behind the check valve at a distance of at least the maximum injection stroke from the tip of the cylinder. For this reason, a difference occurs in the distance between the backflow prevention valve and the pressure sensor depending on the size of the injection stroke, and the detection accuracy is different. In addition, it is desirable that the inner wall surface of the cylinder has a smooth flow path without a step so as not to generate carbides or the like due to resin stagnation. Since it is unavoidable that a fine step portion is generated, adverse effects such as mixing of carbides due to resin retention into the molded product cannot be avoided. Further, in the pressure sensor that detects the pressure of the resin by indirectly detecting the strain of the cylinder without directly contacting the resin, the detection accuracy is sacrificed. In addition, any pressure sensor is expensive and complicated to handle, and there are many problems that require regular maintenance and calibration.

  In the technique disclosed in Patent Document 3 described above, a conductive member for detecting electrostatic capacity is arranged on a screw, a hole for passing a wire is processed at the center of the screw, and a measurement signal is further transmitted. It is necessary to add a means for measuring the electrostatic capacity such as arranging a slip ring for taking out the screw, and there is a disadvantage that the configuration becomes complicated.

  The technique disclosed in Patent Document 5 focuses on the component force Fθ (see FIG. 2) in the screw rotation direction of the force that the backflowed resin acts on the screw flight, and the rotation of the screw that can rotate during the injection is performed. It detects the stop and detects the closing of the check valve. This technology can accurately detect the closing point of the backflow prevention valve based on the stoppage of the screw rotation. However, when the screw that is made rotatable is rotated by the backflow resin, the screw rotation angle is held and controlled. In comparison, there is a problem that the reverse flow rate of the resin is greatly increased, and the amount of the resin filled by injection is reduced or becomes unstable.

  The technique disclosed in Patent Document 6 requires a backflow prevention mechanism of a type in which a screw is reversely rotated to shut off a metering portion and a screw head after measurement is completed, and an injection molding machine having a general backflow prevention mechanism There is a problem that cannot be applied.

  The technique disclosed in Patent Document 7 is a technique in which the peak occurrence time of the screw rotation angle is regarded as the closing time of the backflow prevention valve. However, in reality, even if the backflow prevention valve is not normally closed, A peak may occur. This is because the screw rotation angle is feedback-controlled, so even if the resin continues to flow back without closing the backflow prevention valve, the driving force that maintains the screw rotation angle causes the backflowed resin to rotate the screw. Since the screw rotation decelerates and stops when the force is exceeded, the screw rotation angle peaks when the screw rotation angle starts to return to the screw rotation angle at the start of injection by feedback control. It is.

  The technique disclosed in Patent Document 8 is a technique for detecting the rotational force acting on the screw during the forward movement of the screw, and regarding the peak point of the rotational force as the closing point of the backflow prevention valve. It does not detect that it did not close normally. Further, it is necessary to add a means for detecting the rotational force acting on the screw, and there is a problem that the configuration becomes complicated.

  The technique disclosed in Patent Document 9 is a technique for detecting the rotational force acting on the screw during the forward movement of the screw and determining the closed state of the backflow prevention valve based on the waveform pattern of the rotational force. It does not detect when the prevention valve is closed. Further, it is necessary to add a means for detecting the rotational force acting on the screw, and there is a problem that the configuration becomes complicated.

  Therefore, the object of the present invention is to solve the above problems, to detect the close timing of the backflow prevention valve more accurately without using a special mechanism, without increasing the backflow of the resin during injection, It is an object of the present invention to provide an injection molding machine that can reliably detect that a check valve has not been closed normally.

  The invention according to claim 1 of the present application includes a screw including a backflow prevention valve, a rotation driving unit that rotationally drives the screw, a rotation driving force detection unit that detects a rotation driving force of the screw rotation, and a rotation that detects a screw rotation angle. In an injection molding machine having an angle detection means, the screw rotation driving force and the screw rotation angle are detected while holding and controlling the screw rotation angle during the forward movement of the screw, and based on the detected screw rotation driving force and the screw rotation angle. A screw rotation angle estimation means for estimating an estimated screw rotation angle when the screw is rotatable, and a closing determination means for detecting the closing time of the backflow prevention valve using the estimated screw rotation angle estimated by the screw rotation angle estimation means And an injection molding machine.

According to a second aspect of the present invention, the screw rotation angle estimation means adds a value obtained by dividing a second-order integral value related to the time of the detected screw rotation driving force by a predetermined inertia value and the detected screw rotation angle. The injection molding machine according to claim 1, wherein the estimated screw rotation angle is calculated.
The invention according to claim 3 is characterized in that the closing determination means detects the closing time of the check valve by detecting the time when the estimated screw rotation angle is stopped. It is an injection molding machine as described in one.

  According to a fourth aspect of the present invention, the closure determining means calculates an estimated screw rotation speed by differentiating the estimated screw rotation angle with respect to time, and detects a time point when a peak occurs in the calculated estimated screw rotation speed. The injection molding machine according to any one of claims 1 and 2, wherein a closing time of the backflow prevention valve is detected.

The invention according to claim 5 is provided with means for detecting the amount of change in the estimated screw rotation angle from the start of screw advancement during screw advancement. This is an injection molding machine.
The invention according to claim 6 is the estimated screw rotation angle, the amount of change in the estimated screw rotation angle from the start of screw advancement, and the progress from the start of screw advancement, at the time of closing of the backflow prevention valve detected by the closing determination means. Physical quantity detection means for detecting at least one of time, screw position, screw position change from the start of screw advance, and resin pressure as a physical quantity at the time when the backflow prevention valve is closed, and a physical quantity detected by the physical quantity detection means The injection molding machine according to any one of claims 1 to 5, further comprising display means for displaying at least one of the two.

  The invention according to claim 7 is a screw provided with a backflow prevention valve, a rotational drive means for rotationally driving the screw, a rotational drive force detecting means for detecting the rotational drive force of the screw rotation, and a rotational angle detection for detecting the screw rotational angle. In the injection molding machine having the means and the display device, the screw rotation driving force and the screw rotation angle are detected at every predetermined sampling period while maintaining the screw rotation angle while the screw is moving forward, and the detected screw rotation driving force Based on the screw rotation angle, the estimated screw rotation angle when the screw is made rotatable is obtained every predetermined sampling period, the waveform pattern of the estimated screw rotation angle is displayed on the display screen of the display device, and the backflow prevention valve This is a check method for determining the closed state of the check valve that makes it possible to determine the closed state.

  The present invention makes it possible to increase the closing time of the backflow prevention valve without using a special mechanism, without increasing the backflow of resin during injection, and without being affected by the response characteristics of the control system that maintains the screw rotation angle. In addition, it is possible to accurately detect that the backflow prevention valve is not normally closed.

  In addition, since the present invention can more accurately detect the closing time of the check valve, the injection holding pressure switching position, the injection speed switching position, and the like are determined by various physical quantities at the detected closing time of the check valve. The molding conditions can be adjusted easily and accurately. Further, it is possible to more accurately determine the quality of the molded product based on various physical quantities at the time of closing the backflow prevention valve.

First, the screw operation from the end of the metering process to the end of the injection process and the movement of the backflow prevention valve will be described.
FIG. 3 (a) shows the screw position at the end of the metering process and the state of the backflow prevention valve mechanism. Molten resin is stored in the cylinder 7 at the tip of the screw head 2, and the screw 1 is in the retracted position. It is in. In the measuring step, the resin melted by the rotation of the screw 1 raises the resin pressure behind the backflow prevention valve 3 to generate a force for pushing the backflow prevention valve 3 forward, and the backflow prevention valve 3 is pushed forward. The molten resin flows through the gap between the backflow prevention valve 3 and the reduced diameter portion of the screw 1 and flows in front of the backflow prevention valve 3.
At the stage where the metering process is completed, as shown in FIG. 3A, the backflow prevention valve 3 is located in front and opens the passage of the molten resin.

  FIG. 3B shows a state after completion of suck back in which the screw 1 is moved backward by a predetermined amount after completion of measurement, and the pressure of the molten resin in the cylinder 7 at the tip of the screw head 2 is reduced by the suck back process. For this reason, the backflow prevention valve 3 remains open.

  FIG. 3C is a diagram illustrating a state in which injection is started and the backflow prevention valve 3 is closed, and a period from FIG. 3B to FIG. 3C is a section in which the resin flows back. is there. d represents the screw movement distance from the start of injection until the check valve 3 is closed. That is, when the screw 1 is moved forward from the state where the suck back in FIG. 3B is completed and the injection is performed, the pressure in front of the backflow prevention valve mechanism is present in the groove 6 between the rear flights 5 due to the filling pressure. When the pressure becomes higher than the pressure of the resin, the backflow prevention valve 3 moves rearward and comes into close contact with the check seat 4 to close the backflow prevention valve 3 and the resin passage is closed. When the backflow prevention valve is closed, there is no backflow of resin. FIG. 3D shows a state when the screw further moves forward and reaches the injection / holding pressure switching position.

  As described above, the backflow prevention valve 3 is closed during the injection process, but the injection amount, that is, the resin amount (weight) filled in the mold fluctuates due to the change in the closing timing of the backflow prevention valve 3. Therefore, it is necessary to accurately detect the closing timing of the check valve 3.

  Therefore, the principle of detecting the closing time of the check valve of the present invention will be described. The present invention detects the screw rotational driving force and the screw rotational angle while holding and controlling the screw rotational angle during the forward movement of the screw, and makes the screw rotatable based on the detected screw rotational driving force and the screw rotational angle. In this case, an estimated screw rotation angle is obtained, and the closing time of the check valve is detected using the obtained estimated screw rotation angle.

First, how to obtain the estimated screw rotation angle when the screw can be rotated will be described.
Let T be the screw rotation driving force for holding and controlling the screw rotation angle, D be the rotation force acting on the screw by the backflow resin, θ be the detected screw rotation angle, and I be the inertia of the screw rotation drive system. The inertia of the screw rotation drive system is known for each injection molding machine. Then, the equation of motion related to the screw rotation shown in Equation 1 is obtained. “” ”Added to“ θ ”means a second-order derivative with respect to time.

  The state in which the screw rotation angle is held and controlled means a state in which the screw rotation driving means is controlled to hold the screw rotation angle at the angle at the start of screw advancement. Specifically, for example, position feedback control may be performed on the axis of screw rotation, or speed feedback control having an integrator may be performed.

  The above equation 1 can be transformed into equation 2.

Next, when the estimated screw rotation angle when the screw rotation driving force T for holding and controlling the screw rotation does not act (in other words, when the screw is rotatable) is set to θ _free , the following equation is obtained. The equation of motion related to screw rotation. “” _” Added to“ θ _{free ”} means second-order differentiation with respect to time.

ここで、数３式を２階積分し、逆流樹脂によってスクリュに作用する回転力Ｄに数２式の関係式を用いて変形すると、数４式が得られる。数４式より、スクリュ回転駆動力Ｔが作用しなかった場合の推定スクリュ回転角度θ_freeは、前記検出したスクリュ回転駆動力Ｔの時間に関する２階積分値をスクリュ回転系のイナーシャＩで除算した値と、前記検出したスクリュ回転角度θとを加算することで推定できる。

Here, when Equation 3 is integrated twice and the rotational force D acting on the screw by the backflow resin is transformed using the Equation 2 Equation, Equation 4 is obtained. From the equation (4), the estimated screw rotation angle θ _free when the screw rotation driving force T is not applied is obtained by dividing the second-order integral value related to the time of the detected screw rotation driving force T by the inertia I of the screw rotation system. It can be estimated by adding the value and the detected screw rotation angle θ.

Equation 4 is an equation of motion for the case where the resin does not receive the viscous resistance of the resin when the screw is rotated. However, when the screw is rotated, the screw may actually receive the viscous resistance of the resin in the direction in which the screw rotation stops. . The viscosity resistance of the resin during screw rotation usually increases in proportion to the screw rotation speed. In addition, when the screw rotation stops, the viscous resistance of the resin disappears. Formula 5 takes into account the viscous resistance of the resin in Formula 4. When the screw receives the viscous resistance of the resin during the rotation of the screw, the screw rotation angle estimation means is a second-order integral value related to the time of the value obtained by removing the viscous resistance of the resin from the detected screw rotation driving force, as shown in Equation 5. The estimated screw rotation angle may be calculated by adding the value obtained by dividing the above by a predetermined inertia value and the detected screw rotation angle.
Here, α is the viscosity coefficient of the resin. As the value of α, a viscosity coefficient value may be set according to the type of resin used, or a standard viscosity coefficient value may be set in advance.

なお、数５式を変形したものが数６式である。数６式から明らかなように、数５式はθ_freeの時間に関する微分を含む微分方程式である。

Note that Formula 6 is obtained by modifying Formula 5. As is apparent from the equation (6), the equation (5) is a differential equation including a derivative with respect to the time of θ _free .

  Next, a method for detecting the closing time of the check valve in the present invention will be described with reference to FIGS. In the graphs shown in FIGS. 4 to 6, the horizontal axis represents time, and the vertical axis represents a screw rotation drive that drives the screw while maintaining and controlling the absolute value of the rotational force D acting on the screw by the backflow resin and the screw rotation. The absolute value of force T is shown. The absolute value is shown in order to compare the rotational force D acting on the screw with the backflow resin and the screw rotational driving force T. The origin of the graph represents the injection start point.

The injection is performed in a state where the screw rotation angle is held and controlled, the screw rotation angle θ and the screw rotation driving force T during injection are detected, and based on the detected screw rotation angle θ and the screw rotation driving force T, Formula 4 the calculated estimated screw rotation angle theta _free when made into a rotatable screw, is described to detect the time point at which the check ring closes based on the estimated screw rotation angle theta _free.

  FIG. 4 is a graph for explaining a state in which the check valve is normally closed. FIG. 4A is a graph showing the relationship between rotational force and time. FIG. 4B is a graph showing the relationship between the screw rotation angle and time.

The waveform of the alternate long and short dash line in FIG. 4A represents the rotational force D acting on the screw by the backflowed resin. The solid line waveform represents the screw rotation driving force T. In addition, although this invention does not require detecting the rotational force D which acts on a screw with backflow resin, the graph of the rotational force D which acts on a screw with backflow resin is represented here for description. A broken line connecting FIG. 4A and FIG. 4B indicates a point in time when the rotational force D acting on the screw by the backflow resin coincides with the screw rotation driving force T. The solid line waveform in FIG. 4B represents the detected screw rotation angle θ. The broken line waveform represents the estimated screw rotation angle θ _free estimated by the above-described equation (4).

  In the present invention, the screw rotation angle is controlled so that the screw rotation angle is maintained during the forward movement of the screw. Therefore, as shown in FIG. 4A, the screw rotation drive is performed so as to cancel the rotational force D acting on the screw by the backflow resin. The force T changes. In addition, with respect to the rotational force D acting on the screw, the screw rotational driving force T is delayed by a predetermined time due to the response speed of the control system.

Hereinafter, the relationship between the estimated screw rotation angle θ _free and the closing point of the backflow prevention valve when the backflow prevention valve is normally closed will be described with reference to FIGS. 3 and 4.
When injection is started with the backflow prevention valve opened as shown in FIG. 3B, the screw is reversely rotated by the rotational force D acting on the screw by the backflow resin, as shown in FIG. 4A. .
At this time, since the screw rotation angle is controlled so as to be maintained, a screw rotation driving force T that attempts to return the screw to the original rotation angle acts on the screw. Due to the response delay, the screw rotational driving force T is generated as shown in FIG. 4A behind the rotational force D acting on the screw by the backflow resin.
Therefore, it cannot be controlled so that the screw rotation angle does not change at all, and the detection screw rotation angle θ increases as shown in FIG. In addition, the estimated screw rotation angle θ _free calculated by Equation 4 also increases.

  Thereafter, as the screw advances, the backflow prevention valve moves to the closed state, so that the resin flow path is narrowed and the rotational force D acting on the screw by the backflow resin is reduced. At this time, since the screw rotation driving force T is controlled so as to maintain the screw rotation angle, if the screw rotation driving force T exceeds the rotation force D acting on the screw made of the backflow resin, the detection screw is slightly delayed. As shown in FIG. 4B, the rotation angle θ changes from an increasing tendency to a decreasing tendency, and a peak PA occurs at the detected screw rotation angle θ. In this way, a peak may occur in the detected screw rotation angle θ earlier than the check valve is closed.

On the other hand, since the estimated screw rotation angle θ _free in FIG. 4B is obtained by the equation (4), after the screw rotation driving force T exceeds the rotation force D acting on the screw made of the backflow resin, The estimated screw rotation angle θ _free continues to increase.

When the backflow prevention valve is completely closed, the rotational force D acting on the backflow resin screw disappears, and therefore the estimated screw rotation angle θ _free does not change at the time TA shown in FIG. 4B. This time TA can be regarded as a stop point of the estimated screw rotation angle θ. Therefore, the closing time point of the backflow prevention valve can be specified by detecting the stopping time point of the estimated screw rotation angle θ _free estimated by the equation (4).

  Next, the relationship between the estimated value of the screw rotation angle and the closing of the backflow prevention valve when the backflow prevention valve is not normally closed will be described with reference to FIGS. 3 and 5. FIG. 5 is a graph for explaining a state in which the backflow prevention valve is not normally closed. A broken line connecting FIG. 5A and FIG. 5B indicates a point in time when the rotational force D acting on the screw by the backflow resin coincides with the screw rotation driving force T.

As shown in FIG. 3 (b), when the injection is started with the backflow prevention valve opened, the screw is reversely rotated by the backflowed resin. Therefore, as shown in FIG. 5 (b), the detected screw rotation angle θ and Both the estimated screw rotation angle θ _free increases.
After that, even if the screw moves forward, the backflow prevention valve does not move in the closing direction, and the resin flow does not narrow, so that the backflow of the resin does not stop, so that it acts on the screw as shown in FIG. The rotational force D that is generated does not decrease. At this time, since the screw rotation driving force T is controlled so as to maintain the screw rotation angle, if the screw rotation driving force T exceeds the rotation force D acting on the screw by the backflow resin, FIG. As shown in FIG. 2, the detected screw rotation angle θ slightly shifts from an increasing tendency to a decreasing tendency, and a peak PA occurs at the detected screw rotating angle.
Thus, even if the peak PA occurs at the detection screw rotation angle θ, the backflow prevention valve may not be normally closed. Therefore, even when the peak PA occurs at the detection screw rotation angle θ, it cannot be determined that the backflow prevention valve is normally closed.

On the other hand, the estimated screw rotation angle θ _free is obtained by estimating the screw rotation angle by the equation (4). Therefore, even after the screw rotation driving force T exceeds the rotation force D acting on the screw, FIG. As shown in b), the estimated screw rotation angle θ _free continues to increase.
Then, if the backflow prevention valve does not close after that, the estimated screw rotation angle θ _free continues to increase.
Therefore, by detecting whether or not the estimated screw rotation angle θ _free has stopped (the estimated screw rotation angle θ _free does not change), it is possible to specify whether or not the backflow prevention valve has been normally closed.

Now, as described in the explanation related to FIG. 3, depending on the type of resin, even after the check valve is closed, it remains in the flight part of the screw for a while (see the groove part 6 between the flights, see FIG. 2). The screw may be rotated in reverse by the backflow resin. In this case, detection of the closing time of the check valve as the peak occurrence time of the estimated screw rotation speed θ ′ _free will be described with reference to FIG.

FIG. 6 is a graph for explaining a state in which the check valve is normally closed. FIG. 6A is a graph showing the relationship between rotational force and time. The dashed line in FIG. 6A represents the rotational force D acting on the screw by the backflow resin, and the solid line represents the screw rotational driving force T. FIG. 6B is a graph showing the relationship between the estimated screw rotation speed and the estimated screw rotation angle and time. A waveform indicated by a two-dot broken line in FIG. 6B represents the estimated screw rotation speed θ ′ _free . Moreover, the waveform of the broken line of FIG.6 (b) represents estimated screw rotation angle (theta) _free . A broken line connecting FIG. 6A and FIG. 6B indicates a point in time when the rotational force D acting on the screw by the backflow resin coincides with the screw rotation driving force T.

Here, the estimated screw rotation speed θ ′ _free is obtained by calculating the first derivative with respect to the time of the estimated screw rotation angle θ _free estimated by the equation (4). Alternatively, when the screw rotation speed is obtained by the speed detection means, as shown in Equation 7, the screw rotation speed V _θ detected by the speed detection means is set to 1 relating to the time of the detected screw rotation driving force T. You may calculate by adding the value which divided the floor integral value by the inertia I of the screw rotation system.

Hereinafter, the relationship between the estimated screw rotation speed θ ′ _free that is an estimated value of the screw rotation speed and the closing of the check valve when the check valve is normally closed will be described with reference to FIGS. 3 and 6.

Figure 3 when the check valve as shown in (b) is a state in starting the injection open, screw by the backflow resin is due to be rotated in reverse, the detected screw rotational angle theta and the estimated screw rotation angle theta _free increases both (See FIG. 4).
Thereafter, as the screw advances, the backflow prevention valve moves to the rear of the screw. Furthermore, when the backflow prevention valve is closed, the backflow of resin disappears. At this time, the screw may be reversely rotated by the backflow resin remaining in the groove 6 (see FIG. 2) during the flight even after the backflow prevention valve is closed.
In such a case, the estimated screw rotation angle θ _free obtained by the equation 4 is increased even after the check valve is closed. Therefore, there is a possibility that the stop time of the estimated screw rotation angle θ _free is delayed with respect to the actual closing time of the check valve, and does not exactly match.

On the other hand, as shown in FIG. 6B, the estimated screw rotation speed θ ′ _free tends to increase until the backflow prevention valve is closed, but the rotational force D acting on the screw when the backflow prevention valve is closed is reduced. When it gets smaller, it starts to decrease. Therefore, in such a case, the peak occurrence time of the estimated screw rotation angle θ _free substantially coincides with the closing time of the backflow prevention valve.
As described above, in the case where the screw is reversely rotated by the reverse flow resin remaining in the flight part of the screw for a while after the check valve is closed, when the estimated screw rotation speed θ ′ _free peak occurs You may make it identify the close time of a backflow prevention valve by detecting TB.

FIG. 7 is a principal block diagram of an embodiment of the present invention.
A nozzle 9 is attached to the tip of the cylinder 7 in which the screw 1 is inserted, and a hopper 15 for supplying resin pellets into the cylinder 7 is attached to the rear end of the cylinder 7. The tip of the screw 1 is provided with a backflow prevention mechanism including a backflow prevention valve 3 and a check sheet 4 (see FIG. 1).

  The screw 1 is rotationally driven by a measuring servo motor 10 via a transmission mechanism 12, and the screw 1 is linearly moved by the injection servo motor 11 to rotate the transmission mechanism 13 and ball screws / nuts. It is configured to be driven in the axial direction by a conversion mechanism 14 that converts the pressure into a pressure and to control injection and back pressure.

  Positioning / speed detectors 16 and 17 for detecting the rotational position and speed are attached to the measuring servo motor 10 and the injection servo motor 11, and the rotational angle of the screw 1 and the screw are detected by the position / speed detector. The rotational speed of 1, the position of the screw 1 (position in the screw axis direction), and the moving speed (injection speed) can be detected. Further, a pressure sensor 18 such as a load cell for detecting the pressure from the molten resin applied to the screw 1 is provided.

  A control device 20 for controlling the injection molding machine is connected to a CNC CPU 22 which is a numerical control microprocessor, a PMC CPU 21 which is a programmable machine controller microprocessor, and a servo CPU 25 which is a servo control microprocessor via a bus 36. ing.

  A ROM 26 storing a sequence program for controlling the sequence operation of the injection molding machine and a RAM 27 used for temporary storage of calculation data are connected to the PMC CPU 21, and an automatic operation program for overall control of the injection molding machine is connected to the CNC CPU 22. Are connected to a ROM 28 that stores the data and the like, and a RAM 29 that is used to temporarily store calculation data.

  The servo CPU 25 is connected to a ROM 31 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 32 that is used for temporary storage of data. Further, a servo amplifier 34 for driving the measuring servo motor 10 and a servo amplifier 35 for driving the injection servo motor 11 are connected to the servo CPU 25 based on a command from the CPU 25. Position / speed detectors 16 and 17 are attached to the servo motors 10 and 11, respectively, and outputs from the position / speed detectors 16 and 17 are fed back to the servo CPU 25.

The servo CPU 25 is positioned based on the movement command to each axis (the measuring servo motor 10 or the injection servo motor 11) commanded from the CNC CPU 22, the detection position fed back from the position / speed detectors 16 and 17, and the detection speed. In addition to performing speed feedback control, current feedback control is also executed to drive and control the servo motors 10 and 11 via the servo amplifiers 34 and 35, respectively. Further, a current position register for storing at least the rotation position of the measuring servo motor 10 fed back from the position / speed detector 16 is provided, and an angle in the rotation direction of the screw 1 (screw rotation) depending on the rotation position of the servo motor 10. Angle) can be detected.
The servo CPU 25 receives a detection resin pressure (resin pressure applied to the screw 1) obtained by converting the detection signal from the pressure sensor 18 into a digital signal by the A / D converter 33. A servo motor and servo amplifier for driving the mold closing mechanism and the ejector mechanism are also provided, but these are not directly related to the present invention and are therefore omitted in FIG. Yes.

  An input device 30 with a display device constituted by a liquid crystal display device or a CRT is connected to a bus 36 via a display circuit 24. Further, a molding data storage RAM 23 composed of a non-volatile memory is also connected to the bus 36, and the molding data storage RAM 23 stores molding conditions, various set values, parameters, macro variables, etc. relating to the injection molding operation.

  With the above-described configuration, the PMC CPU 21 controls the sequence operation of the entire injection molding machine, and the CNC CPU 22 instructs the servo motors for each axis to move based on the operating program in the ROM 28 and the molding conditions stored in the molding data storage RAM 23. The servo CPU 25 uses the movement command and position / speed detectors 16 and 17 distributed to each axis (servo motor of each drive axis such as the measuring servo motor 10 and the injection servo motor 11). Based on the detected position and speed feedback signals and the like, servo control such as position loop control, speed loop control, and current loop control is performed in the same manner as in the past, and so-called digital servo processing is executed. In the present embodiment, the screw rotation driving force T can be obtained based on the current of the motor that drives the rotation. Further, in the case of a hydraulic injection molding machine, it may be obtained based on the opening of a hydraulic device valve that drives rotation, or may be obtained based on a torque command value that drives rotation. The screw rotation driving force T and the screw rotation angle θ are detected at a predetermined sampling period during the injection process.

The configuration described above is the same as that of a conventional control unit for an electric injection molding machine. The difference from the conventional control device is that the screw is advanced after the metering process and the screw rotation angle is held and controlled while the screw is moving forward. The rotational driving force T and the screw rotational angle θ are detected, and based on the detected screw rotational driving force T and the screw rotational angle θ, an estimated screw rotational angle θ _free when the screw is rotatable is obtained and further estimated. A function for calculating the screw rotation speed θ ′ _free , a change amount of the estimated screw rotation angle from the start of injection, and a function for storing these in time series are added.

Further, based on the estimated screw rotation angle θ _free or the estimated screw rotation speed θ ′ _free , the closed position of the backflow prevention valve is identified or estimated from the start of screw advancement, which is derived from the closed position. Change amount of screw rotation angle, elapsed time from start of screw advancement, screw position, change amount of screw position from start of screw advancement, function to detect physical quantity such as resin pressure, these physical quantity and estimated screw rotation angle θ _free In addition, a function of displaying the estimated screw rotation speed θ ′ _free on the display device of the injection molding machine is also added.

When the back flow rate of the resin is large, the rotational force acting on the screw due to the back flowed resin increases, and the backflow time also increases, so the estimated screw rotation angle θ _free also increases. Therefore, a function of detecting the reverse flow rate of the resin from the amount of change in the estimated screw rotation angle θ _free from the start of injection may be provided. Further, a function of detecting the reverse flow rate of the resin based on the screw rotation angle up to the peak occurrence time of the estimated screw rotation speed θ ′ _free may be provided.
A function for judging pass / fail based on the detected reverse flow of the resin, a function for estimating the wear amount of the check valve based on the detected reverse flow of the resin, or an injection based on the detected reverse flow of the resin You may give the function which correct | amends the screw position set for process control.

By displaying the change in the estimated screw rotation angle θ _{free on} the screen of the display device as a waveform, when the backflow prevention valve is closed during the injection process based on the displayed waveform pattern, it was not closed until the end. The case can be judged. For example, as shown in FIG. 4B, in the case of a waveform pattern in which the estimated screw rotation angle increases until the middle of the injection process and does not change from the middle, it is determined that the check valve is closed during the injection process. it can. In the case of a waveform pattern in which the estimated screw rotation angle continues to increase from the beginning to the end of the injection process as shown in FIG. 5B, it can be determined that the backflow prevention valve has not been closed until the end of the injection process.

  FIG. 8 is a flowchart showing an algorithm of processing in one molding cycle according to the present invention (when it is determined that the backflow prevention valve is closed based on when the screw rotation angle is stopped). When a cycle start command for continuous molding is input, the PMCCPU 21 shown in FIG. 7 starts the processing shown in FIG. Hereinafter, it demonstrates according to each step.

  First, a mold closing servo motor (not shown) is driven and controlled to execute a mold closing process (step SA100). When the mold is closed until the set clamping force is generated, the injection / holding process is started, and the servo CPU 25 drives and controls the injection servo motor 11 via the servo amplifier 35 to advance the screw 1 (FIG. 7). The molten resin collected in front of the screw 1 in the cylinder 7 is injected into the mold (step SA101).

During the injection / holding step, the screw rotation driving force T and the screw rotation angle θ are detected and stored in the storage means while maintaining and controlling the screw rotation angle (step SA102). Using the screw rotation driving force T and the screw rotation angle θ detected in step SA102, the screw rotation angle when the screw is rotatable is estimated and stored in the storage means as the estimated screw rotation angle θ (n) _free. . The estimated screw rotation angle θ (n) _free is obtained for each predetermined sampling period based on the above-described equation 4 (step SA103). The estimated screw rotation angle θ (n) _free obtained in step SA103 is displayed on the display device as a waveform and a numerical value (step SA104). For the display device, display of only the plotted waveform, display of only the numerical value, or display of both may be selected as appropriate.

It is determined whether or not the estimated screw rotation angle θ (n) _free obtained in step SA103 is stopped. If stopped, the process proceeds to step SA106, and if not stopped, the process proceeds to step SA108 (step SA105). .
The estimated screw rotational angle θ (n) _free is stopped, since regarded as the check valve as described above were closed, the time of this estimated screw rotational angle theta of (n) _free stops, the check valve Displayed on the display device as the closing time (step SA106).

Next, the physical quantity at the time when the check valve is closed is acquired (step SA107). The physical quantity includes the estimated screw rotation angle θ _free , the amount of change in the estimated screw rotation angle θ _free from the start of screw advancement, the elapsed time from the start of screw advancement, the screw position, and the amount of change in the screw position from the start of screw advancement. It is at least one physical quantity among (moving distance) and resin pressure.

  Next, it is determined whether or not the injection has been completed. If the injection has not been completed, the process returns to step SA102 to continue the process. If completed, the process proceeds to step SA109 (step SA108). If it is determined in step SA108 that the injection is completed, it is determined whether or not the backflow prevention valve is closed during the injection. If the backflow prevention valve is closed during the injection, the process proceeds to step SA112. Shifts to step SA110 (step SA109), displays on the display device that the backflow prevention valve has not been closed (step SA110), outputs an alarm indicating that the result of pass / fail judgment is defective (step SA111), and measures Then, the mold opening and molded product take-out process is executed (step SA112), and this molding cycle is completed.

FIG. 9 is a flowchart showing an algorithm for processing in one molding cycle according to the present invention (when the closing of the check valve is determined based on the peak occurrence time of the estimated screw rotation speed θ ′ _free ). The difference between the flowchart shown in FIG. 9 and the flowchart shown in FIG. 8 will be described.

In step SB103, the estimated screw rotation angle θ (n) _free is estimated, and the estimated screw rotation speed θ ′ (n) _free is calculated from the estimated screw rotation angle θ (n) _free and stored in the storage means.
In step SB104, the estimated screw rotation speed θ ′ (n) _free calculated in step SB103 is displayed as a waveform and a numerical value. For the display device, display of only the plotted waveform, display of only the numerical value, or display of both may be selected as appropriate.
In step SB105, it is determined whether or not the estimated screw rotation angular velocity θ ′ (n) _free calculated in step SB103 is a peak occurrence time. If it is not a peak occurrence time, the process proceeds to step SB108. And the time point when the check valve is closed is displayed on the display device.
The other steps are the same as those described with reference to FIG.

Here, the flowcharts of FIGS. 8 and 9 will be supplementarily described.
After detecting the screw rotation driving force T and the screw rotation angle θ in step SA102 in FIG. 8, the screw rotation driving force T and the screw rotation angle θ detected are connected to the CNC CPU 22. It is stored in the RAM 29 as time series data for each sampling period. In step SA103, the estimated screw rotation angle θ (n) _free when the screw is rotatable is obtained, the estimated screw rotation angle θ (n) _free is stored in the RAM 29, and the aforementioned screw rotation driving force T and screw rotation angle θ are calculated. Store it in association.

In step SA105, whether or not the estimated screw rotation angle θ (n) _free has stopped is no longer increased from the time series data of the screw rotation angle θ _free when the screw estimated in step SA103 is made rotatable. Identify the time. The point of time when the increase no longer occurs can be determined, for example, by comparing the data obtained in the previous cycle with the data obtained in the current cycle.

  Further, the physical quantity is acquired in step SA107. The screw rotation angle at the injection start time, the time at the injection start time, and the screw position at the injection start time are respectively detected and stored in the RAM 23.

It is explanatory drawing of an example of the backflow prevention valve mechanism provided in the screw front-end | tip. It is explanatory drawing of the force applied to a screw when the back flow of resin generate | occur | produces during screw advance. It is operation | movement state explanatory drawing of a backflow prevention valve mechanism when performing an injection process after a measurement process. It is a graph which shows the relationship between rotational force and time, and a rotation angle, and time when a backflow prevention valve closes normally. It is a graph which shows the relationship between rotational force and time when a backflow prevention valve does not close normally, rotation angle, and time. It is a graph which shows the relationship between the rotational force and time, rotational speed, rotational angle, and time when the backflow prevention valve is normally closed. It is a principal part block diagram of embodiment of this invention. It is a flowchart which shows the algorithm of the process of 1 shaping | molding cycle in this invention (when closing of a backflow prevention valve is determined by the time of screw rotation stopping). It is a flowchart which shows the algorithm of the process of 1 shaping | molding cycle in this invention (when closing of a backflow prevention valve is determined by the peak generation time of an estimated screw rotational speed).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Screw 2 Screw head 3 Backflow prevention valve 4 Check sheet 5 Flight 6 Groove part 7 Cylinder 20 Control apparatus

Claims (7)

In an injection molding machine having a screw including a backflow prevention valve, a rotation driving means for rotating the screw, a rotation driving force detecting means for detecting a rotation driving force of the screw rotation, and a rotation angle detecting means for detecting a screw rotation angle ,
Estimated screw rotation when the screw rotation driving force and screw rotation angle are detected while holding the screw rotation angle while the screw is moving forward, and the screw is made rotatable based on the detected screw rotation driving force and screw rotation angle. A screw rotation angle estimating means for estimating an angle;
Closure determination means for detecting the closing time of the check valve using the estimated screw rotation angle estimated by the screw rotation angle estimation means,
An injection molding machine characterized by comprising:   The screw rotation angle estimation means adds the value obtained by dividing the second-order integral value related to the detected screw rotation driving force time by a predetermined inertia value and the detected screw rotation angle, thereby calculating the estimated screw rotation angle. The injection molding machine according to claim 1, wherein the injection molding machine is calculated.   3. The injection molding machine according to claim 1, wherein the closing determination unit detects a closing time of the check valve by detecting a time when the estimated screw rotation angle is stopped. .   The closing determination means calculates the estimated screw rotation speed by differentiating the estimated screw rotation angle with respect to time, and detects the closing time of the check valve by detecting the time point when the calculated estimated screw rotation speed has occurred. The injection molding machine according to any one of claims 1 and 2.   The injection molding machine according to any one of claims 1 to 4, further comprising means for detecting a change amount of the estimated screw rotation angle from the start of screw advancement during screw advancement. The estimated screw rotation angle, the amount of change in the estimated screw rotation angle from the start of screw advancement, the elapsed time from the start of screw advancement, the screw position, and the start of screw advancement when the backflow prevention valve detected by the closing determination means is closed A physical quantity detecting means for detecting at least one of the change amount of the screw position from the resin pressure and the physical quantity at the time when the backflow prevention valve is closed;
The injection molding machine according to any one of claims 1 to 5, further comprising display means for displaying at least one of the physical quantities detected by the physical quantity detection means. A screw having a backflow prevention valve, a rotational drive means for rotationally driving the screw, a rotational drive force detecting means for detecting the rotational drive force of the screw rotation, a rotational angle detecting means for detecting the screw rotational angle, and an injection having a display device In the molding machine,
While maintaining the screw rotation angle during screw advancement, the screw rotation driving force and the screw rotation angle are detected every predetermined sampling period.
Obtaining an estimated screw rotation angle for each predetermined sampling period when the screw is rotatable based on the detected screw rotation driving force and screw rotation angle;
A backflow prevention valve closed state determination method for displaying a waveform pattern of the estimated screw rotation angle on a display screen of the display device, and making it possible to determine a closed state of the backflow prevention valve.

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