Method and apparatus for detecting mold gap of toggle-type injection molding machine

Abstract

This apparatus includes: a strain sensor unit 5 attached to a peripheral surface 4f of a tie bar 4 provided on a toggle-link mold clamping mechanism 2 for slidably supporting a movable platen 3 to which a movable mold Cm is attached; and a molding machine controller 10 for obtaining an elongation L of the tie bar 4 corresponding to a mold gap Lm by a prescribed arithmetic expression in accordance with detection data De of the strain sensor unit 5 and obtaining the size of the corresponding mold gap Lm on the basis of the obtained magnitude of the elongation L of the tie bar 4. The mold gap Lm is obtained with high accuracy on the basis of the elongation L of the tie bar 4.

Description

Toggle-type injection molding machine mold gap detection method and device

[0001] The present invention relates to a mold gap detection method and device for a toggle-type injection molding machine that detects the mold gap between the movable mold and the fixed mold of a mold that performs mold clamping by a toggle link type clamping mechanism.

[0002] Conventionally, as a mold gap detection device that performs mold clamping by a toggle link type clamping mechanism and detects the mold gap (parting opening amount) between the movable mold and the fixed mold of the mold, the mold gap detection device described in the injection molding machine of Patent Document 1 is known.

[0003] In the same Document 1, when configuring a waveform monitoring device for an injection molding machine that monitors at least the operation waveform during molding by mounting it on an injection molding machine that performs molding by a specific molding method, parting opening amount detection means for detecting change data of the parting opening amount with respect to time during molding, and change data detected by the parting opening amount detection means from at least after the start of resin filling into the mold until the end of the mold cooling time are provided. It is configured with an operation waveform display means for displaying on the waveform display section of the screen of the display attached to the molding machine controller. In particular, as the parting opening amount detection means, a position detector for detecting the relative position of the movable mold and the fixed mold by attaching it to the mold is used. Thereby, more accurate monitoring can be performed by superimposing the change data of the injection pressure with respect to time during molding on the change data of the parting opening amount, and fine adjustment for optimizing the molding conditions can be easily performed.

[0004] Japanese Patent Application Laid-Open No. 2013-22842

[0005] However, the conventional mold gap detection device provided in the above-described injection molding machine also had the following problems to be solved.

[0006] That is, since the conventional mold gap detection device is directly attached to the side surfaces of the movable mold and the fixed mold of the mold and mainly uses a position sensor using an eddy current sensor or the like, when the mold is small, the mounting area and mounting position are restricted, and the mounting becomes difficult. In addition, when the position sensor is vulnerable to high heat, it cannot be used, and there is a problem that the detection accuracy is adversely affected.

[0007] On the other hand, in toggle-type injection molding machines equipped with a toggle-link clamping mechanism, a detection method has been proposed that determines the clamping force by detecting the expansion and contraction of the tie bar. However, from the perspective of detecting changes in the mold gap, there are drawbacks such as the inability to monitor accurately and precisely, making it difficult to obtain the desired change data.

[0008] The present invention aims to provide a method and apparatus for detecting the mold gap of a toggle-type injection molding machine that solves the problems present in the background technology described above.

[0009] The mold gap detection method for a toggle-type injection molding machine M according to the present invention solves the above-mentioned problems by detecting the mold gap Lm between the movable mold Cm and the fixed mold Cc of a mold C clamped by a toggle-link clamping mechanism 2. This method involves attaching a strain sensor unit 5 to the circumferential surface 4f of a tie bar 4 provided on the toggle-link clamping mechanism 2, which slidably supports the movable platen 3 to which the movable mold Cm is attached. The method uses the detection data De from the strain sensor unit 5 to determine the elongation L of the tie bar 4 corresponding to the mold gap Lm using a predetermined calculation formula, and then uses the obtained elongation L of the tie bar 4 to determine the corresponding mold gap Lm.

[0010] In this case, according to a preferred embodiment of the invention, when a strain sensor unit 5 is placed on the circumferential surface 4mf of the main body portion 4m, which has the largest diameter, the elongation L [μm] of the tie bar 4 can be calculated by L = Lt - Tc + Td - Ls + [Ls × (St / Ss) × Ew] ... [Calculation formula 1], where Lt [mm] is the effective tie bar length, Tc [mm] is the maximum mold thickness, Td [mm] is the mold thickness, Ls [mm] is the constriction length, St [square mm] is the tie bar cross-sectional area, Ss [square mm] is the constriction cross-sectional area, and Ew [με] is the output value of the strain sensor unit 5. Furthermore, when a strain sensor unit 5 is placed on the circumferential surface 4sf of the constricted portion 4s, which has a smaller diameter than the main body portion 4m of the tie bar 4, the elongation L [μm] of the tie bar 4 can be calculated by L = Lt - Tc + Td + [Ls × (St / Ss) × Ew] ... [Calculation formula 2], where Lt [mm] is the effective tie bar length, Tc [mm] is the maximum mold thickness, Td [mm] is the mold thickness, Ls [mm] is the constriction length, St [square mm] is the tie bar cross-sectional area, Ss [square mm] is the constriction cross-sectional area, and Ew [με] is the output value of the strain sensor unit 5. In addition, the strain sensor unit 5 can be used by connecting four strain gauges 5a, 5b, 5c, and 5d in a full bridge configuration, or by connecting two strain gauges 5a, 5d and two resistive elements Rb, Rc in a full bridge configuration. Furthermore, the detection data De from the strain sensor unit 5 can be the increase from the detection result immediately before the injection process starts, and the mold thickness Td can be calculated from the output of the encoder 7e in the mold thickness adjustment motor 7 provided in the mold thickness adjustment mechanism 6.

[0011] On the other hand, the mold gap detection device 1 for the toggle-type injection molding machine M according to the present invention, in order to solve the above-mentioned problems, is configured as a mold gap detection device that detects the mold gap Lm between the movable mold Cm and the fixed mold Cc of a mold C that is clamped by a toggle-link clamping mechanism 2, and is characterized by comprising: a strain sensor unit 5 attached to the circumferential surface 4f of a tie bar 4 provided on the toggle-link clamping mechanism 2 that slidably supports the movable platen 3 to which the movable mold Cm is attached; and a molding machine controller 10 that uses the detection data De of the strain sensor unit 5 to determine the elongation L of the tie bar 4 corresponding to the mold gap Lm using a predetermined calculation formula, and determines the size of the corresponding mold gap Lm based on the obtained elongation L of the tie bar 4.

[0012] In this case, according to a preferred embodiment of the invention, the strain sensor unit 5 can be arranged at two mounting positions X1 and X2 on the circumferential surface 4f of the tie bar 4 that are at least 180° opposite each other. Furthermore, at one of the locations on the tie bar 4 where the strain sensor unit 5 is installed, two strain gauges 5a, 5b… can be arranged in a positional relationship of orthogonality. In this case, the strain sensor unit 5 can be installed on the circumferential surface 4mf of the main body portion 4m, which has the largest diameter, or on the constricted portion 4s of the tie bar 4, which has a smaller diameter than the main body portion 4m. In addition, the size of the mold gap Lm can be graphically displayed on a display 11 attached to the molding machine controller 10. Alternatively, a position sensor 15 that directly detects the mold gap Lm of the mold C can be provided, and the molding machine controller 10 can be provided with an input selection means Fs that can switch between preliminary detection data Des obtained from the position sensor 15 and detection data De obtained from the strain sensor unit 5.

[0013] The following remarkable effects are achieved by the toggle-type injection molding machine M mold gap detection method and apparatus 1 according to the present invention.

[0014] (1) A strain sensor unit 5 is attached to the circumferential surface 4f of a tie bar 4 provided on a toggle link clamping mechanism 2 that slidesly supports a movable platen 3 to which a movable mold Cm is attached. The elongation L of the tie bar 4 corresponding to the mold gap Lm is determined by a predetermined calculation formula based on the detected data De of the strain sensor unit 5, and control is performed on the mold gap Lm based on the obtained size of the mold gap Lm. As a result, the size of the mold gap Lm can be detected by the amount of expansion and contraction of the tie bar 4, that is, the mold gap Lm can be determined with high accuracy by the elongation L of the tie bar 4. This makes it possible to obtain the desired accurate change data from the viewpoint of monitoring change data of the mold gap Lm.

[0015] (2) In a preferred embodiment, when implementing the mold gap detection method, if the strain sensor unit 5 is placed on the circumferential surface 4mf of the main body portion 4m, which has the largest diameter in the tie bar 4, the elongation L [μm] of the tie bar 4 is determined by [Calculation Formula 1], it can be installed using the main body portion 4m, which has the largest diameter in the tie bar 4, and can therefore be universally attached to various models from large to small machines.

[0016] (3) In a preferred embodiment, when implementing the mold gap detection method, if the strain sensor unit 5 is placed on the circumferential surface 4sf of the constricted portion 4s of the tie bar 4, which has a smaller diameter than the main body portion 4m, the elongation L [μm] of the tie bar 4 is determined by [Calculation formula 2], so that it can be placed on the small diameter portion of the tie bar 4, it can be detected with high sensitivity and the detection accuracy can be further improved.

[0017] (4) In a preferred embodiment, when implementing the mold gap detection method, if the strain sensor unit 5 uses four strain gauges 5a, 5b, 5c, and 5d in a full bridge connection, the detection results of the four strain gauges 5a, 5b, 5c, and 5d can be used on average, thereby obtaining highly accurate detection results and further reducing variability.

[0018] (5) In a preferred embodiment, when implementing the mold gap detection method, if the strain sensor unit 5 is connected in a full bridge configuration with two strain gauges 5a and 5d and two resistive elements Rb and Rc, detection can be reliably performed even when there are constraints such as insufficient mounting space for the strain gauges 5a and 5d, and the method can be easily implemented while suppressing detection accuracy and variability.

[0019] (6) In a preferred embodiment, when implementing the mold gap detection method, if the increase in the detection data De of the strain sensor unit 5 from the detection result immediately before the start of the injection process is used, the starting point of the elongation L of the tie bar 4 can be set accurately, thereby ensuring reliable detection of the elongation L related to the tie bar 4.

[0020] (7) In a preferred embodiment, when implementing the mold gap detection method, if the mold thickness Td is calculated from the output of the encoder 7e of the mold thickness adjustment motor 7 provided in the mold thickness adjustment mechanism 6, it can be easily determined by directly using the existing mold thickness adjustment mechanism 6, and the mold thickness Td can be determined accurately in real time while eliminating errors such as temperature fluctuations.

[0021] (8) In a preferred embodiment, when configuring the mold gap detection device 1, if the strain sensor unit 5 is placed at two mounting positions X1 and X2 on the circumferential surface 4f of the tie bar 4 that are at least 180° opposite each other, detection results can be obtained at two 180° opposite points, thereby canceling out unnecessary stress and obtaining accurate detection results.

[0022] (9) In a preferred embodiment, when configuring the mold gap detection device 1, if the strain sensor unit 5 is arranged on the tie bar 4 and two strain gauges 5a, 5b... are placed in orthogonal positions, the detection results from the two strain gauges 5a, 5b... placed in orthogonal positions can be used, thereby obtaining detection results with higher accuracy and less variation.

[0023] (10) In a preferred embodiment, when configuring the mold gap detection device 1, if the strain sensor unit 5 is placed on the circumferential surface 4mf of the main body portion 4m which has the largest diameter in the tie bar 4, it can be installed using the main body portion 4m which has the largest diameter in the tie bar 4, and can therefore be universally attached to various models from large to small machines.

[0024] (11) In a preferred embodiment, when configuring the mold gap detection device 1, if the strain sensor unit 5 is placed in the constricted portion 4s of the tie bar 4 which has a smaller diameter than the main body portion 4m, it can be placed in the small-diameter portion of the tie bar 4, thus enabling detection with high sensitivity and further improving detection accuracy.

[0025] (12) In a preferred embodiment, when the mold gap detection device 1 is configured, if the size of the mold gap Lm is graphically displayed on the display 11 attached to the molding machine controller 10, the change over time can be displayed, so that the size and change state of the mold gap Lm can be grasped visually and intuitively in comparison with various molding conditions, i.e., change data such as injection pressure and clamping force, and fine adjustments to optimize the molding conditions can be easily made.

[0026] (13) In a preferred embodiment, when configuring the mold gap detection device 1, a position sensor 15 is provided to directly detect the mold gap Lm of the mold C, and the molding machine controller 10 is provided with an input selection means Fs that can switch between preliminary detection data Des obtained from the position sensor 15 and detection data De obtained from the strain sensor unit 5. This makes it possible to compare the two different data De and Des, so that abnormalities and molding conditions can be easily and reliably grasped.

[0027] A diagram of the configuration of a toggle-type injection molding machine equipped with a mold gap detection device according to a preferred embodiment of the present invention; a side view showing the strain sensor unit of the mold gap detection device attached to the main body of the tie bar; a side view showing the strain sensor unit of the mold gap detection device attached to the constricted part of the tie bar; a plan view of the strain sensor unit of the mold gap detection device; a side view showing the position sensor attached to the mold of the toggle-type injection molding machine; a circuit diagram of the strain sensor unit of the mold gap detection device; a circuit diagram relating to an example of a modification of the strain sensor unit of the mold gap detection device; a display screen diagram of a display attached to the molding machine controller equipped in the toggle-type injection molding machine; a characteristic diagram of the change in gas pressure inside the mold cavity with respect to the number of shots of the toggle-type injection molding machine; a characteristic diagram of the change in mold gap with respect to time of the strain sensor unit and position sensor of the mold gap detection device.

[0028] 1: Mold gap detection device, 2: Toggle link clamping mechanism, 3: Movable platen, 4: Tie bar, 4f: Tie bar surface, 4m: Main body, 4mf: Main body surface, 4s: Constriction, 4sf: Constriction surface, 5: Strain sensor unit, 5a: Strain gauge, 5b: Strain gauge, 5c: Strain gauge, 5d: Strain gauge, 10: Molding machine controller, 11: Display, 15: Position sensor, M: Toggle injection molding machine, C: Mold, Cm: Movable mold, Cc: Fixed mold, Lm: Mold gap, De: Detection data, Des: Preliminary detection data, Rb: Resistor element, Rc: Resistor element, Fs: Input selection means, X1: Mounting position, X2: Mounting position

[0029] Next, the best embodiment of the present invention will be described in detail with reference to the drawings.

[0030] First, the overall configuration of the toggle-type injection molding machine M equipped with the mold gap detection device 1 according to this embodiment will be described with reference to Figure 1.

[0031] In Figure 1, the toggle-type injection molding machine indicated by M comprises a toggle-link type clamping device Mc and an injection device Mi. The clamping device Mc includes a spaced-apart fixed platen 21 and a pressure receiving platen 22. The fixed platen 21 is fixed to a machine base (not shown), and the pressure receiving platen 22 is supported on the machine base so as to be able to move back and forth.

[0032] Furthermore, four tie bars 4 are installed between the fixed platen 21 and the pressure receiving platen 22. In this case, the front end of each tie bar 4 is fixedly attached to the fixed platen 21, and the rear end of each tie bar 4 is slidably attached to the pressure receiving platen 22.

[0033] Furthermore, a movable platen 3 is slidably mounted on top of the tie bar 4. A movable mold Cm is attached to the movable platen 3, and a fixed mold Cc is attached to the fixed platen 21. The mold C is formed by this movable mold Cm and fixed mold Cc.

[0034] Meanwhile, a toggle link mechanism 23 is provided between the pressure receiving plate 22 and the movable plate 3. The toggle link mechanism 23 has a pair of first links 23a, 23a pivotally supported on the pressure receiving plate 22, a pair of output links 23c, 23c pivotally supported on the movable plate 3, and a pair of second links 23b, 23b connected to the support shafts of the first links 23a, 23a and the output links 23c, 23c, and these second links 23b, 23b are pivotally supported on the crosshead 23h.

[0035] On the other hand, an electric drive unit 24 is provided on the pressure receiving plate 22. The electric drive unit 24 includes a ball screw mechanism 25 that moves the crosshead 23h of the toggle link mechanism 23 forward and backward, and a rotation drive unit 26 that inputs rotation to the ball screw mechanism 25. The ball screw mechanism 25 includes a ball screw portion 25s that is rotatably supported on the pressure receiving plate 22, and a ball nut portion 25n that is screwed onto the ball screw portion 25s and integrally provided on the crosshead 23h. The rotation drive unit 26 includes a servo motor 26s and a rotation transmission mechanism 27 that transmits the rotation of the servo motor 26s to the ball screw portion 25s. 26e indicates a rotary encoder attached to the servo motor 26s for detecting the rotation speed.

[0036] In this configuration, the rotational output of the servo motor 26s is transmitted to the ball screw portion 25s, causing the crosshead 23h, which is integrated with the ball nut portion 25n, to move back and forth. As a result, the toggle link mechanism 23 bends or extends, causing the movable platen 3 to move back and forth in the mold opening direction (retraction direction) or the mold closing direction (clamping direction).

[0037] Furthermore, a mold thickness adjustment mechanism 6 is attached to the pressure receiving plate 22. The mold thickness adjustment mechanism 6 is constructed by forming threaded portions 32 on the rear ends of four tie bars 4, screwing adjustment nuts 33 onto each threaded portion 32, and attaching a mold thickness adjustment motor (geared motor) 7, which moves the pressure receiving plate 22, to the side of the pressure receiving plate 22. These adjustment nuts 33 also serve as stoppers for the pressure receiving plate 22.

[0038] Furthermore, a rotary encoder 7e for detecting the rotational speed of the motor shaft is attached to the output shaft of the mold thickness adjustment motor 7. This rotary encoder 7e utilizes an incremental encoder, and the absolute position can be detected by the number of encoder pulses generated relative to a reference position.

[0039] A drive gear is attached to the output shaft of the mold thickness adjustment motor 7, and a small gear is integrally attached to each adjustment nut 33..., and a large gear 34 is provided that meshes with each small gear and the drive gear. As a result, when the mold thickness adjustment motor 7 is operated, rotation is transmitted in the order of the output shaft of the mold thickness adjustment motor 7 → drive gear → large gear 34 → each small gear, and each adjustment nut 33... which rotates integrally with each small gear, moves back and forth along the threaded portion 32... of the tie bar 4..., causing the pressure receiving plate 22 to also move back and forth, and its front-to-back position is adjusted.

[0040] On the other hand, the injection device Mi includes a heating cylinder 41 having an injection nozzle 41n at its tip, and a screw 42 that is inserted into the heating cylinder 41, the rear end of which is connected to a screw drive unit (not shown). In this way, the injection device Mi receives molding material from a hopper (not shown) located at the rear of the heating cylinder 41 into the heating cylinder 41. The molding material is then plasticized and melted by the rotation of the screw 42, and the molten resin is injected and filled into the cavity of the mold C by the forward movement of the screw 42.

[0041] Further, the toggle-type injection molding machine M includes a molding machine controller 10 that controls the entire toggle-type injection molding machine M. A display 11 is attached to the molding machine controller 10, and this display 11 includes a display body 11d and a touch panel 11t attached to the display body 11d. This touch panel 11t constitutes an operation unit (input unit) and can perform various setting operations, selection operations, and the like. The servo motor 26s and the mold thickness adjustment motor 7 described above are connected to a motor driver built in the molding machine controller 10, and each rotary encoder 26e and 7e is connected to an input port of the molding machine controller 10.

[0042] The molding machine controller 10 includes a molding machine controller main body 50 that incorporates hardware such as a CPU and an internal memory and has a computer function for storing various software. Therefore, the internal memory includes a program writing area for installing a processing program for executing various arithmetic processes and control processes (sequence control) and a data writing area for writing various data (databases).

[0043] Further, a strain sensor amplifier 55 that processes the detection data De of the strain sensor unit 5 described later, that is, a strain sensor amplifier 55 having an arithmetic process for obtaining the elongation L of the tie bar 4 corresponding to the mold gap Lm from the detection data De by a predetermined arithmetic formula, is provided, and a position sensor amplifier 56 that processes the detection data (preliminary detection data Des) of the position sensor 15 described later is provided. The strain sensor amplifier 55 and the position sensor amplifier 56 are connected to an input unit of the molding machine controller main body 50.

[0044] Next, the configuration of the mold gap detection device 1 according to the present embodiment provided in such a toggle-type injection molding machine M will be described with reference to FIGS. 1 to 7.

[0045] As shown in FIG. 1, the mold gap detection device 1 includes a strain sensor unit 5 attached to the peripheral surface 4f of at least one tie bar 4.

[0046] Figures 2 and 3 show a strain sensor unit 5 attached to the peripheral surface 4f of the tire 4. Figure 2 shows the case where it is disposed on the peripheral surface 4mf of the main body portion 4m having the largest diameter in the tire 4, and Figure 3 shows the case where it is disposed on the peripheral surface 4sf of the constricted portion 4s having a smaller diameter than the main body portion 4m in the tire 4.

[0047] The tire 4 is usually formed by a main body portion 4m having the largest diameter and a constricted portion 4s formed at an end of the main body portion 4m and having a smaller diameter than the main body portion 4m, as shown in Figures 2 and 3. The tire 4 is attached to the fixed plate 21 by inserting the constricted portion 4s of the tire 4 into the mounting hole of the fixed plate 21 and fixing it with a fixing member 51.

[0048] Figure 2 shows the case where the strain sensor unit 5 is attached to the peripheral surface 4mf of the main body portion 4m. In this case, the strain sensor unit 5 uses two units, namely, a first unit 5u and a second unit 5v, and is attached to at least two attachment positions X1 and X2 that are opposed to each other by at least 180° on the peripheral surface 4f of the tire 4. That is, the first unit 5u is disposed on the upper end surface 4mu, and the second unit 5v is disposed on the lower end surface 4md and fixed with a fixing band 52. In this way, if the strain sensor unit 5 is disposed at at least two attachment positions X1 and X2 that are opposed to each other by at least 180° on the peripheral surface 4f of the tire 4, detection results at two points opposed by 180° can be obtained, so that useless stress can be canceled out and accurate detection results can be obtained.

[0049] At this time, when configuring one unit, for example, the first unit 5u, as shown in Figure 4, two strain gauges 5a and 5b are arranged on the upper end surface 4mu. Specifically, as shown in the figure, two strain gauges 5a and 5b are arranged at the attachment position X1 in an orthogonal positional relationship. That is, one strain gauge 5a is arranged parallel to the tire 4, and the other strain gauge 5b is arranged perpendicular to the strain gauge 5a. Such a first unit 5u is usually configured as a unit part in which two strain gauges 5a and 5b are integrated in an orthogonal positional relationship.

[0050] Figure 4 shows the case where the strain gauge is positioned at mounting position X1, which is the upper end surface 4mu of the main body 4m. However, it can be similarly positioned at mounting position X2, which is the lower end surface 4md of the main body 4m. In this case, one strain gauge 5c at mounting position X2 is positioned parallel to the tie bar 4, and the other strain gauge 5d is positioned perpendicular to the strain gauge 5c.

[0051] In this way, by arranging two strain gauges 5a, 5b... in an orthogonal positional relationship at one location on the tie bar 4 where the strain sensor unit 5 is installed, the detection results from the two orthogonal positional strain gauges 5a, 5b... can be used, thus enabling the acquisition of detection results with higher accuracy and less variation.

[0052] The four strain gauges 5a, 5b, 5c, and 5d that constitute the strain sensor unit 5 are connected in a full bridge configuration, as shown in Figure 6, and connected to the input of the strain sensor amplifier 55 shown in Figure 1 (Figure 6). By using the four strain gauges 5a, 5b, 5c, and 5d in a full bridge configuration in this way, the detection results of the four strain gauges 5a, 5b, 5c, and 5d can be used on average, thereby obtaining highly accurate detection results and further reducing variability.

[0053] Furthermore, the strain sensor amplifier 55 calculates the elongation L of the tie bar 4 corresponding to the mold gap Lm based on the detection data De from the strain sensor unit 5 using a predetermined calculation formula. As shown in Figure 2, when the strain sensor unit 5 is placed on the circumferential surface 4mf of the main body portion 4m, which has the largest diameter in the tie bar 4, the elongation L [μm] of the tie bar 4 can be calculated using the following [Calculation Formula 1], where Lt [mm] is the effective tie bar length, Tc [mm] is the maximum mold thickness, Td [mm] is the mold thickness, Ls [mm] is the constriction length, St [square mm] is the tie bar cross-sectional area, Ss [square mm] is the constriction cross-sectional area, and Ew [με] is the output value of the strain sensor unit 5. L = Lt - Tc + Td - Ls + [Ls × (St / Ss) × Ew] ... [Calculation Formula 1]

[0054] The effective tie bar length Lt is the tie bar length when the maximum possible mold thickness is installed. The mold thickness Td can be determined from the mold thickness adjustment mechanism 6 described above.

[0055] As a result, the mold gap Lm can be determined from (elongation of the tie bar 4 after injection starts) - (elongation of the tie bar 4 at the start of injection). In this way, by using the increase from the detection result immediately before the start of the injection process in the detection data De of the strain sensor unit 5, the starting point of the accurate elongation L of the tie bar 4 can be set, thereby ensuring reliable detection of the elongation L related to the tie bar 4. Furthermore, by calculating the mold thickness Td from the output of the encoder 7e of the mold thickness adjustment motor 7 provided in the mold thickness adjustment mechanism 6, it can be easily determined by directly utilizing the existing mold thickness adjustment mechanism 6, and an accurate mold thickness Td can be determined in real time while eliminating errors such as temperature fluctuations.

[0056] Furthermore, if the elongation L [μm] of the tie bar 4 when the strain sensor unit 5 is installed on the circumferential surface 4mf of the main body portion 4m, which has the largest diameter in the tie bar 4, is determined by [Calculation Formula 1], then it can be installed using the main body portion 4m, which has the largest diameter in the tie bar 4, and thus can be universally attached to various models from large to small machines.

[0057] On the other hand, Figure 3 shows the case where the strain sensor unit 5 is installed in a constricted portion 4s of the tie bar 4 that has a smaller diameter than the main body portion 4m. Specifically, it shows a state in which two strain gauges 5a and 5b are placed on the upper end surface and two strain gauges 5c and 5d are placed on the lower end surface and fixed with a fixing band 62.

[0058] In this case, if the strain sensor unit 5 is placed on the circumferential surface 4sf of the constricted portion 4s of the tie bar 4, which has a smaller diameter than the main body portion 4m, the elongation L [μm] of the tie bar 4 can be calculated using the following [Calculation Formula 2]: L = Lt - Tc + Td + [Ls × (St / Ss) × Ew] ... [Calculation Formula 2]

[0059] Thus, by determining the elongation L [μm] of the tie bar 4 when the strain sensor unit 5 is placed on the circumferential surface 4sf of the constricted portion 4s, which has a smaller diameter than the main body portion 4m of the tie bar 4, using [Calculation Formula 2], the unit can be placed on the smaller diameter portion of the tie bar 4, enabling detection with high sensitivity and further improving detection accuracy.

[0060] Furthermore, Figure 3 allows for more accurate measurements than Figure 2. On the other hand, if it is necessary to make the strain sensor unit 5 smaller, such as in models with a small mold C, it is also possible to measure using two strain gauges 5a and 5d as shown in Figure 7. In this case, it is also possible to add resistive elements Rb and Rc to the two strain gauges 5a and 5d, that is, connect resistive element Rb instead of strain gauge 5b and resistive element Rc instead of strain gauge 5c and measure in the same way.

[0061] In this way, by connecting the strain sensor unit 5 with two strain gauges 5a and 5d and two resistive elements Rb and Rc in a full bridge connection, reliable detection can be performed even when there are constraints such as insufficient mounting space for the strain gauges 5a and 5d, and the system can be easily implemented while suppressing detection accuracy and variability.

[0062] Next, the method of use and function of the gap detection device 1 according to this embodiment will be described with reference to Figures 1 to 10.

[0063] Figure 8 shows the display screen 11d of the display 11 attached to the molding machine controller 10. This display screen 11d shows the injection and metering screen, as well as the process monitoring screen and waveform screen. Therefore, the display screen 11d includes a graphic screen V1 relating to change data with time displayed on the horizontal axis as a waveform screen, a graphic screen V2 relating to change data with position displayed on the horizontal axis, and a mold gap screen Vs relating to the mold gap detection device 1 displayed in a window.

[0064] Furthermore, the example mold gap screen Vs displays a switching key 61 related to the input selection means Fs. By turning this switching key 61 ON, the output of the strain sensor unit 5 can be used, and by turning the switching key 61 OFF, the output of the position sensor 15 can be used, allowing the user to select the sensing means to be used.

[0065] In other words, as shown in Figure 1, a position sensor 15 for detecting the mold gap Lm is provided on the side of the mold C. As shown in Figure 5, this position sensor 15 has a conductive plate 15r installed on the side of one fixed mold Cc and an eddy current displacement sensor 15m installed on the side of the other movable mold Cm, and the output data Des changes depending on the position where the eddy current displacement sensor 15m approaches or moves away from the conductive plate 15r. As a result, when the aforementioned switching key 61 is turned ON, the output of the strain sensor unit 5 can be used, and when the switching key 61 is turned OFF, the output of the position sensor 15 can be used.

[0066] Figure 10 shows the change data over time for the mold gap Lmi using the output of the strain sensor unit 5 and the mold gap Lmr using the output of the position sensor 15. If corrections are made as necessary, the data can be used as almost identical change data.

[0067] Thus, by providing a position sensor 15 that directly detects the mold gap Lm of the mold C, and by providing an input selection means Fs in the molding machine controller 10 that can switch between preliminary detection data Des obtained from the position sensor 15 and detection data De obtained from the strain sensor unit 5, it becomes possible to compare the two different data, De and Des, making it easy and reliable to grasp abnormalities, molding conditions, etc.

[0068] Next, as an example of a molding method, we will describe a case where a low-pressure clamping force is set and the molding process is performed.

[0069] Now, let's assume that the molding conditions are set to a low-pressure clamping force Pc (see Figure 8), and that molten resin is injected and filled into the cavity of mold C at a predetermined injection pressure Pi.

[0070] In this case, as the injection filling of molten resin progresses and the internal pressure of the cavity increases, the mold gap Lm gradually increases. That is, as the internal pressure increases, the parting surface of the mold C gradually opens, and the mold gap Lm increases. This allows for degassing from within the cavity.

[0071] Figure 9 shows the gas pressure [MPa] inside the cavity of mold C. The change characteristic Qi shows the case where clamping is performed with a low clamping force as in the embodiment, while the change characteristic Qr shows the case of a general method, i.e., when a high clamping force Pc is set so that no mold gap Lm occurs.

[0072] In this way, by setting the mold gap Lm to an appropriate level and monitoring it, appropriate degassing can be performed.

[0073] On the other hand, the detection data De detected from the strain sensor unit 5 is provided to the strain sensor amplifier 55, and the elongation L [μm] of the tie bar 4 is determined by the calculation processing of this strain sensor amplifier 55 using the aforementioned [Calculation Formula 1] or [Calculation Formula 2].

[0074] As a result, the corresponding mold gap Lm is calculated and displayed on the graphic screens V1 and V2 of the display 11 shown in Figure 8. By graphically displaying the size of the mold gap Lm on the display 11 attached to the molding machine controller 10, the change over time can be displayed. This allows for a visual and intuitive understanding of the size and change state of the mold gap Lm by comparing it with various molding conditions, i.e., change data such as injection pressure and clamping force, and facilitates fine-tuning to optimize the molding conditions. Furthermore, necessary control processing is performed, i.e., the molding machine controller main unit 50 controls the clamping force, injection pressure, etc., based on the obtained mold gap Lm.

[0075] Therefore, according to the mold gap detection device 1 (mold gap detection method) according to this embodiment, the basic configuration includes a strain sensor unit 5 attached to the circumferential surface 4f of a tie bar 4 provided on a toggle link clamping mechanism 2 that slidably supports a movable platen 3 to which a movable mold Cm is attached, and a molding machine controller 10 that uses the detection data De of the strain sensor unit 5 to determine the elongation L of the tie bar 4 corresponding to the mold gap Lm using a predetermined calculation formula, i.e., [Calculation Formula 1] or [Calculation Formula 2], and determines the size of the corresponding mold gap Lm based on the obtained elongation L of the tie bar 4. As a result, the size of the mold gap Lm can be detected by the amount of expansion and contraction of the tie bar 4, that is, the mold gap Lm can be determined with high accuracy by the elongation L of the tie bar 4. Thus, from the viewpoint of monitoring change data of the mold gap Lm, the desired accurate change data can be obtained.

[0076] Although the best embodiment (including modifications) has been described in detail above, the present invention is not limited to such embodiments, and the details of the configuration, shape, materials, quantity, method, etc., can be arbitrarily changed, added, or deleted without departing from the spirit of the present invention.

[0077] For example, the elongation L [μm] of the tie bar 4 is preferably determined using [Calculation Formula 1] or [Calculation Formula 2], but this is not necessarily a mandatory requirement. Furthermore, while it is preferable for the strain sensor unit 5 to be a full bridge connection of four strain gauges 5a, 5b, 5c, 5d, or a full bridge connection of two strain gauges 5a, 5d and two resistive elements Rb, Rc, this does not preclude the use of a single strain gauge 5a or detection using more than four strain gauges 5a.... In addition, the detection data De of the strain sensor unit 5 is shown as the increase from the detection result immediately before the start of the injection process, or as the mold thickness Td calculated from the output of the encoder 7e of the mold thickness adjustment motor 7 provided in the mold thickness adjustment mechanism 6, but these are not mandatory configuration requirements. On the other hand, the size of the mold gap Lm is preferably graphically displayed on the display 11 attached to the molding machine controller 10, but other management computer systems or display means such as smartphones may also be used. Furthermore, a position sensor 15 that directly detects the mold gap Lm of the mold C can be provided, and the molding machine controller 10 can be provided with an input selection means Fs that can switch between preliminary detection data Des obtained from the position sensor 15 and detection data De obtained from the strain sensor unit 5, but whether or not to provide it is optional.

[0078] The mold gap detection method and apparatus according to the present invention can be used in various toggle-type injection molding machines that require detection of the mold gap between the movable mold and the fixed mold of a mold clamped by a toggle-link clamping mechanism.

Claims

1. A method for detecting the mold gap between a movable mold and a fixed mold of a mold clamped by a toggle link clamping mechanism, characterized in that a strain sensor unit is attached to the circumferential surface of a tie bar provided on the toggle link clamping mechanism that slidably supports a movable platen to which the movable mold is attached, the elongation of the tie bar corresponding to the mold gap is determined by a predetermined calculation formula based on the detection data of the strain sensor unit, and the size of the corresponding mold gap is determined based on the obtained magnitude of the tie bar elongation.

2. The method for detecting the mold gap of a toggle-type injection molding machine according to claim 1, characterized in that the elongation L [μm] of the tie bar when the strain sensor unit is placed on the circumferential surface of the main body portion having the largest diameter is determined by [Calculation Formula 1], where the effective tie bar length is Lt [mm], the maximum mold thickness is Tc [mm], the mold thickness is Td [mm], the constriction length is Ls [mm], the tie bar cross-sectional area is St [square mm], the constriction cross-sectional area is Ss [square mm], and the output value of the strain sensor unit is Ew [με].

3. The method for detecting the mold gap of a toggle-type injection molding machine according to claim 1, characterized in that the elongation L [μm] of the tie bar when the strain sensor unit is placed on the circumferential surface of the constricted portion of the tie bar which has a smaller diameter than the main body portion is determined by [Calculation Formula 2], where the effective tie bar length is Lt [mm], the maximum mold thickness is Tc [mm], the mold thickness is Td [mm], the constriction length is Ls [mm], the tie bar cross-sectional area is St [square mm], the constriction cross-sectional area is Ss [square mm], and the output value of the strain sensor unit is Ew [με].

4. The method for detecting the mold gap of a toggle-type injection molding machine according to claim 1, characterized in that the strain sensor unit uses four strain gauges connected in a full bridge configuration.

5. The method for detecting the mold gap of a toggle-type injection molding machine according to claim 1, characterized in that the strain sensor unit uses two strain gauges and two resistive elements connected in a full bridge configuration.

6. The method for detecting the mold gap of a toggle-type injection molding machine according to claim 1, characterized in that the detection data of the strain sensor unit is the increase from the detection result immediately before the start of the injection process.

7. The mold gap detection method for a toggle-type injection molding machine according to claim 1, characterized in that the mold thickness is calculated from the encoder output of a mold thickness adjustment motor provided in the mold thickness adjustment mechanism.

8. A mold gap detection device for a toggle-type injection molding machine that detects the mold gap between a movable mold and a fixed mold of a mold clamped by a toggle-link clamping mechanism, characterized by comprising: a strain sensor unit attached to the circumferential surface of a tie bar provided on the toggle-link clamping mechanism that slidably supports a movable platen to which the movable mold is attached; and a molding machine controller that uses the detection data from the strain sensor unit to determine the elongation of the tie bar corresponding to the mold gap using a predetermined calculation formula, and determines the corresponding size of the mold gap based on the obtained magnitude of the tie bar elongation.

9. The mold gap detection device for a toggle-type injection molding machine according to claim 8, characterized in that the strain sensor unit is disposed at two positions on the circumferential surface of the tie bar that are at least 180° opposite each other.

10. The mold gap detection device for a toggle-type injection molding machine according to claim 9, characterized in that the strain sensor unit has two strain gauges arranged in an orthogonal positional relationship at one location on the tie bar.

11. The mold gap detection device for a toggle-type injection molding machine according to claim 8, characterized in that the strain sensor unit is disposed on the circumferential surface of the main body portion having the largest diameter in the tie bar.

12. The mold gap detection device for a toggle-type injection molding machine according to claim 8, characterized in that the strain sensor unit is disposed in a constricted portion of the tie bar that has a smaller diameter than the main body portion.

13. The mold gap detection device for a toggle-type injection molding machine according to claim 8, characterized in that the size of the mold gap is graphically displayed on a display attached to the molding machine controller.

14. The mold gap detection device for a toggle-type injection molding machine according to claim 8, characterized in that the molding machine controller is provided with input selection means capable of switching between preliminary detection data obtained from the position sensor and detection data obtained from the strain sensor unit, by providing a position sensor that directly detects the mold gap of the mold.

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