Control method for injection molding machine and motor

Abstract

In injection molding machines, vibration generation is suppressed while maintaining production efficiency. [Solution] The control device 100 sets the gain of the servo motor 16 so that the temporal change in the acceleration of the crosshead 12 is slower than predetermined, while keeping the opening and closing cycle time of the movable platen 6 constant, according to the position of the crosshead 12.

Description

Technical Field

[0001] The present disclosure relates to an injection molding machine and a motor control method in an injection molding machine.

Background Art

[0002] Japanese Unexamined Patent Application Publication No. 2020-69758 (Patent Document 1) discloses a technology related to a mold opening and closing method for an injection molding machine equipped with a toggle mechanism. In an injection molding machine equipped with a toggle mechanism, a ball screw is rotated by driving a servo motor, and a ball nut fixed to a crosshead moves in the axial direction together with the crosshead, whereby a movable platen is driven to perform mold opening and closing.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of Invention

Problems to be Solved by the Invention

[0004] In an injection molding machine, vibration may occur when the movable platen accelerates or decelerates. Such vibration is generated by the action of inertial force during acceleration or deceleration in a section where the acceleration of the movable platen, which is a particularly heavy component among the movable parts of the injection molding machine, changes significantly. However, in an injection molding machine, if the acceleration and deceleration of the movable platen is suppressed to reduce vibration, the cycle time will be prolonged, which may rather lower the efficiency of injection molding in some cases.

[0005] An object of the present disclosure is to suppress the occurrence of vibration while maintaining production efficiency in an injection molding machine.

Means for Solving the Problems

[0006] The injection molding machine of this disclosure comprises a fixed platen, a clamping housing, a movable platen, a toggle mechanism, a motor, and a control device. The clamping housing is connected to the fixed platen. The movable platen is provided between the fixed platen and the clamping housing. The toggle mechanism is provided between the clamping housing and the movable platen and includes a crosshead, which is driven to operate the movable platen. The motor drives the crosshead. The control device sets the motor gain according to the position of the crosshead, while keeping the opening and closing cycle time of the movable platen constant, so that the temporal change in the acceleration of the crosshead is slower than predetermined. [Effects of the Invention]

[0007] According to this disclosure, the motor gain is set so that the temporal change in the acceleration of the crosshead becomes slower than predetermined while keeping the opening and closing cycle time of the movable platen constant, depending on the position of the crosshead. This makes it possible to suppress the generation of vibrations while maintaining production efficiency. [Brief explanation of the drawing]

[0008] [Figure 1] This is a diagram illustrating the configuration of an injection molding machine. [Figure 2] This is a block diagram showing the configuration of the control device. [Figure 3] This graph shows the ratio of the velocity of the movable platen to the velocity of the crosshead at the position of the crosshead, the time change of the velocity of the crosshead, and the time change of the acceleration of the crosshead. [Figure 4] This graph shows the ratio of the speed of the movable platen to the speed of the crosshead at the crosshead position, and the relationship between acceleration and motor gain with respect to the crosshead position. [Figure 5] This is a flowchart showing the motor control process. [Modes for carrying out the invention]

[0009] The embodiments of this disclosure will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0010] Figure 1 is a diagram illustrating the configuration of the injection molding machine 1. For the sake of explanation, the floor on which the injection molding machine 1 is placed is defined as the XY plane, and the direction perpendicular to this floor is defined as the Z axis. The positive direction of the Z axis may be referred to as the top side or upward, and the negative direction as the bottom side or downward. The diagram shown in the YZ plane of Figure 1 is a front view of the injection molding machine 1. Although the injection molding machine 1 is shown as a horizontal injection molding machine, it is not limited to a horizontal type and may also be a vertical injection molding machine.

[0011] Referring to Figure 1, the injection molding machine 1 includes a clamping device 3 for clamping the mold, an injection device 2 for melting and injecting the injection material, an operation panel 130, a servo amplifier 160, and a control device 100. In Figure 1, the clamping device 3 is located on the negative side of the X-axis relative to the injection device 2.

[0012] The clamping device 3 includes a bed 111, a fixed platen 5, a clamping housing 7, a movable platen 6, a tie bar 9, a clamping mechanism 11, a servo motor 16, a geared motor 20, and gears 18 and 19. The bed 111 is positioned on the floor surface, and the fixed platen 5, clamping housing 7, and movable platen 6 are mounted on its upper surface. The clamping mechanism 11 includes a crosshead 12, a ball nut 13, and a ball screw 14.

[0013] The fixed platen 5 is fixed to the end of the bed 111 on the side closer to the injection unit 2 (i.e., in the positive direction of the X-axis). The clamping housing 7 is located at the end of the bed 111 in the negative direction of the X-axis. The fixed platen 5 and the clamping housing 7 are connected by tie bars 9, which include multiple bars. The clamping housing 7 is movable in the X-axis direction on the bed 111. The movable platen 6 is located on the bed 111 between the fixed platen 5 and the clamping housing 7. The movable platen 6 is configured to be movable in the X-axis direction. The clamping housing 7 and the movable platen 6 are connected by a clamping mechanism 11.

[0014] The clamping mechanism 11 is a toggle mechanism comprising a ball screw 14 rotationally driven by a servo motor 16 and a crosshead 12 that moves in conjunction with the rotation of the ball screw 14. A ball nut 13 is fixed to the crosshead 12. The ball screw 14 is screwed into the ball nut 13. The clamping mechanism 11 can move the movable platen 6 relative to the clamping housing 7 in the X-axis direction by driving the servo motor 16, which is located in the clamping housing 7, to rotate the ball screw 14. The toggle mechanism is a link mechanism in which two links (arms) are driven by the movement of the crosshead 12, and a large output can be obtained from a small input.

[0015] Gear 18 is fixed by a tie bar nut (not shown). Gear 18 is engaged with gear 19. The clamping device 3 is driven by a geared motor 20, which causes the tie bar nuts to rotate synchronously via gears 18 and 19. The clamping device 3 moves the clamping housing 7 by the rotation of the tie bar nuts. The clamping device 3 adjusts the distance between the movable platen 6 and the fixed platen 5 by the movement of the clamping housing 7.

[0016] A mold member 23 is positioned on the movable platen 6. A mold member 22 is positioned on the fixed platen 5. The mold member 23 and the mold member 22 are positioned facing each other between the movable platen 6 and the fixed platen 5. A single mold is formed by moving the movable platen 6, to which the mold member 23 is attached, relative to the fixed platen 5, to which the mold member 22 is attached.

[0017] By moving the mold member 23 in the X-axis direction using the mold clamping mechanism 11, the mold member 23 and the mold member 22 can be brought into close contact, or the mold member 23 can be separated from the mold member 22. The dimensions of the mold when the mold member 23 and the mold member 22 are in contact and become one are called the mold thickness. The position where the mold member 23 and the mold member 22 come into contact is called the mold touch position. In the following explanation, the process of transitioning from a state where the mold member 23 and the mold member 22 are separated to a state where they are in close contact is called the "mold closing" process. From the mold closed state, the process of tightening the mold with a large force to prevent it from opening due to the pressure during injection is called the "mold clamping" process. The process of transitioning from a state where the mold member 23 and the mold member 22 are in close contact to a state where they are separated is called the "mold opening" process.

[0018] The movable platen 6 is equipped with an ejector device (not shown) and a servo motor 152 that operates the ejector device's ejection mechanism. With the mold member 23 and mold member 22 tightened together in the mold clamping process, molten material (resin) is filled into the mold and cooled to solidify, thereby forming a product of the desired shape. After the product is formed, with the mold member 23 separated from the mold member 22 in the mold opening process, the servo motor 152 located on the movable platen 6 is driven. This activates the ejector device's ejection mechanism, allowing the molded product (also called a molded product) to be ejected from the mold member 23. The process of removing the product using the ejector device is called the "ejection" process.

[0019] The injection device 2 includes a base 121, a heating cylinder 122, a drive device 124, a hopper 125, an injection moving device 127, and a temperature sensor 128. The base 121 is disposed on the floor surface on the positive direction side of the X-axis of the bed 111, and the drive device 124 is mounted on the upper surface thereof. Servo motors 153 and 154 are disposed in the drive device 124.

[0020] The drive device 124 is provided with the heating cylinder 122 extending in the X-axis direction. The heating cylinder 122 includes a heater (not shown) for heating the interior, a screw 123, and an injection nozzle 126. The screw 123 is driven by the servo motor 153 in the drive device 124, and is configured to be rotatable about the X-axis direction as the rotation axis. Further, the screw 123 is configured to be movable in the X-axis direction by the servo motor 154. The injection nozzle 126 is disposed at the end portion of the heating cylinder 122 on the side of the mold clamping device 3 (that is, the end portion in the negative direction of the X-axis). The heating cylinder 122 heats and melts the bead-shaped resin material charged from the hopper 125, and kneads it using the screw 123 to generate a molten material. In this way, the step of melting the resin material is referred to as a "plasticization" step.

[0021] The injection moving device 127 is constituted by, for example, a mechanism using a hydraulic cylinder or a mechanism using a ball screw, and connects the drive device 124 and the fixed platen 5 of the mold clamping device 3. When the injection moving device 127 is constituted by a mechanism using a ball screw, the injection moving device 127 is driven by a drive device to move the drive device 124 and the heating cylinder 122 in the X-axis direction. By the injection moving device 127, the injection nozzle 126 is brought into contact with the sprue bush of the mold member 22 in the mold clamping device 3, and the molten material is injected from the injection nozzle 126, so that the cavities of the mold members 22 and 23 (molds) are filled with the molten material. The servo motor 154 applies pressure to the molten material by moving the screw 123 in the heating cylinder 122 in the negative direction of the X-axis, injects the molten material into the mold, and keeps the pressure of the molten material after injection constant.

[0022] The process of injecting molten material into mold members 22 and 23 is called the "injection" process. After the injection process, the process of maintaining the molten material filled into mold members 22 and 23 at a constant pressure to adjust the amount of shrinkage is called the "holding pressure" process. After the holding pressure process is completed, a cooling process is carried out in parallel to allow the molten material to solidify in the mold, and a plasticization process is carried out in parallel to melt, knead, and weigh the material for the next injection.

[0023] The temperature sensors 128 are located at several points from the base of the heating cylinder 122 to the injection nozzle 126 (only one is shown in the figure). The temperature sensors 128 detect the temperature of the heating cylinder 122 and output the result to the control device 100. The control device 100 controls the heater based on the values ​​detected by the temperature sensors 128 to adjust the heating cylinder 122 to the desired temperature.

[0024] Once the cooling and plasticizing processes are complete, the mold opening and ejection processes are performed to remove the molded product. The injection molding machine 1 can continuously form products by cyclically repeating the mold closing, clamping, injection, holding pressure, cooling and plasticizing, mold opening, and ejection processes.

[0025] The control panel mounted on the base 121 houses a control device 100 and a servo amplifier 160 for driving servo motors 16, 152-154. The control device 100 includes a CPU (Central Processing Unit) 101 and memory 102. The control device 100 acquires detection values ​​from various sensors placed on the injection molding machine 1 and comprehensively controls the injection molding machine 1.

[0026] The clamping device 3 is equipped with a sensor 25 for detecting the clamping force. The sensor 25 is, for example, a strain sensor and is placed on the tie bar 9. The sensor 25 detects the elastic deformation of the tie bar 9. The control device 100 calculates the clamping force based on the signal from the sensor 25. The control device 100 drives a servo motor 16 to adjust the clamping force.

[0027] A position sensor 26 (for example, an optical encoder) is installed on the servo motor 16 to detect the rotation angle of the servo motor 16. A position sensor 27 (for example, an optical encoder) is installed on the geared motor 20 to detect the rotation angle of the geared motor 20. The detection signals from the position sensors 26 and 27 are output to the control device 100. The control device 100 can detect the position of the crosshead 12 based on the detection signal from the position sensor 26. The control device 100 can detect the position of the clamping housing 7 based on the detection signal from the position sensor 27. The control device 100 adjusts the distance between the clamping housing 7 and the fixed platen 5 by driving the geared motor 20.

[0028] Next, the details of the control device 100 will be described. Figure 2 is a block diagram showing the configuration of the control device 100. It includes a CPU 101 and a memory 102. The CPU 101 functions as an arithmetic processing unit and, as an example, includes a position detection unit 103 and a motor drive unit 104. The memory 102 functions as a storage device that stores various data, control programs, etc., and, as an example, stores motor gain data 106. Motor gain is a numerical value that adjusts the responsiveness of the rotational speed of the servo motor 16 to speed commands. Details of the data will be described later.

[0029] The detection signals from position sensors 26 and 27 are output to the control device 100. The position detection unit 103 calculates the position of the crosshead 12 from the detection signal of position sensor 26 and the position of the clamping housing 7 from the detection signal of position sensor 27 by performing calculation processing. The motor drive unit 104 transmits a command value corresponding to the motor gain data 106 to the servo motor 16.

[0030] In the injection molding machine 1, vibrations may occur when the movable disc 6 accelerates or decelerates. Such vibrations occur because of the inertial force acting on the movable disc 6, which is particularly heavy among the movable parts of the injection molding machine 1, when it accelerates or decelerates in sections where its acceleration changes significantly. However, in the injection molding machine 1, if the acceleration and deceleration of the movable disc 6 are suppressed in order to reduce vibrations, the cycle time will increase, which may actually decrease the efficiency of injection molding. Therefore, it is desirable to suppress the generation of vibrations while maintaining production efficiency.

[0031] The clamping mechanism 11 of the injection molding machine 1 of this disclosure is a toggle mechanism. The toggle mechanism is a mechanism in which a link is driven by the movement of the crosshead 12, and a movable platen 6 connected to one end of the link moves relative to the clamping housing 7 connected to the other end. In other words, the toggle mechanism is a mechanism in which the movable platen 6 moves in conjunction with the movement of the crosshead 12. Because the shape of the arms constituting the link changes depending on the position of the crosshead 12, for example, in the mold opening and closing stroke, depending on the positional relationship between the crosshead 12 and the movable platen 6, the amount of movement of the movable platen 6 may be greater than the amount of movement of the crosshead 12. In such regions, the movable platen 6 will accelerate even if the crosshead 12 is moving at a constant speed, so when the crosshead 12 accelerates or decelerates, the acceleration of the movable platen 6 may change abruptly.

[0032] Since changes in the acceleration of the movable platen 6 cause vibration of the movable platen 6, it is necessary to suppress the acceleration and deceleration of the crosshead 12 in order to suppress vibration by suppressing the acceleration and deceleration of the movable platen 6. Therefore, in this embodiment, a configuration is adopted in which the motor gain setting of the servo motor 16 that operates the crosshead 12 is changed according to the position of the crosshead 12.

[0033] Specifically, the injection molding machine 1 of this disclosure sets the gain of the servo motor 16 so that the temporal change in the acceleration of the crosshead 12 becomes slower than predetermined, while keeping the opening and closing cycle time of the movable platen 6 constant so as not to increase the cycle time. The setting of the servo motor 16 is performed by calculation processing of the CPU 101 using various data. The injection molding machine 1 and the motor control method in the injection molding machine 1 will be described in detail.

[0034] Figure 3 is a graph showing the ratio of the speed of the movable disc 6 to the speed of the crosshead 12 at the position of the crosshead 12, the time change of the speed of the crosshead 12, and the time change of the acceleration of the crosshead 12. Figure 3(A) is a graph showing the ratio (increase rate) of the speed of the movable disc 6 to the speed of the crosshead 12 at each position of the crosshead 12 when the crosshead 12 is moved at a constant speed. The injection molding machine 1 is a toggle mechanism as described above. Therefore, the increase rate of the speed of the movable disc 6 to the speed of the crosshead 12 changes depending on the position of the crosshead 12, as shown in Figure 3(A), even when the crosshead 12 is moved at a constant speed. In the following explanation, the increase rate of the speed of the movable disc 6 to the speed of the crosshead 12 shown in Figure 3(A) will also be simply referred to as the "speed increase rate".

[0035] In Figure 3(A), the range where the rate of increase in speed is 1 or greater corresponds to the range where the speed of the movable platen 6 is greater than the speed of the crosshead 12. On the other hand, the range where the rate of increase in speed is less than 1 corresponds to the range where the speed of the movable platen 6 is smaller than the speed of the crosshead 12. Thus, the speed of the crosshead 12 and the speed of the movable platen 6 are not synchronized, and even if the speed of the crosshead 12 is constant, the speed of the movable platen 6 changes according to the position of the crosshead 12.

[0036] Figure 3(B) is a graph showing the time evolution of the velocity of the crosshead 12 in the range where the rate of velocity increase is less than 1. Figure 3(C) is a graph showing the time evolution of the acceleration of the crosshead 12 in the range where the rate of velocity increase is less than 1. Figure 3(D) is a graph showing the time evolution of the velocity of the crosshead 12 in the range where the rate of velocity increase is greater than 1. Figure 3(E) is a graph showing the time evolution of the acceleration of the crosshead 12 in the range where the rate of velocity increase is greater than 1. Figures 3(B) to (E) show the velocity and acceleration of the crosshead 12 at the start of the mold closing stroke.

[0037] In injection molding machine 1, as shown in Figure 3(A), the position of the crosshead 12 corresponding to the mold closing position near the origin of the graph is approximately 200 mm. In injection molding machine 1, the rate of increase of the speed of the movable platen 6 relative to the speed of the crosshead 12 increases from the mold closing position to approximately 700 mm in the mold opening direction. In other words, as the crosshead 12 approaches a position of approximately 700 mm from the mold closing position to the mold opening position, the amount of movement of the movable platen 6 gradually increases relative to the amount of movement of the crosshead 12.

[0038] Furthermore, in injection molding machine 1, the rate of increase of the speed of the movable platen 6 relative to the speed of the crosshead 12 decreases from a position of approximately 700 mm to a position of 1200 mm corresponding to the mold open position. In other words, as the position of the crosshead 12 approaches the mold open position from a position of approximately 700 mm, the degree to which the amount of movement of the movable platen 6 is relative to the amount of movement of the crosshead 12 gradually decreases. However, the amount of movement of the movable platen 6 remains greater than the amount of movement of the crosshead 12.

[0039] As shown in Figure 3(A), the rate of increase of the speed of the movable platen 6 relative to the speed of the crosshead 12 exceeds the specified value of 1 after the position of the crosshead 12 reaches approximately 400 mm, up to the mold open position. Therefore, from the position of the crosshead 12 at approximately 400 mm to the mold open position at approximately 1200 mm, the amount of movement of the movable platen 6 is larger than the amount of movement of the crosshead 12, and the speed of the movable platen 6 becomes faster than the speed of the crosshead 12. Consequently, in this section, the movable platen 6 accelerates even if the crosshead 12 is moving at a constant speed. In particular, if the crosshead 12 is accelerated or decelerated in this section, the acceleration or deceleration of the movable platen 6 may change abruptly, potentially causing vibrations from the movable platen 6.

[0040] As shown in Figure 3(B), consider a control that accelerates the speed of the crosshead 12 from 0 mm / s to 50 mm / s during period T0, when the position of the crosshead 12 is approximately 300 mm, as an example of a range where the rate of increase is smaller than the specified value. When the speed of the crosshead 12 is changed as shown in Figure 3(B), as shown in Figure 3(C), the acceleration of the crosshead 12 increases during period T11, becomes constant during period T12, and decreases during period T13. Periods T11, T12, and T13 combined are the same as period T0. The speed waveform and acceleration waveform of the crosshead 12 during acceleration in such a range smaller than the specified value are called the "reference waveform". In a range where the rate of increase is smaller than the specified value, if the crosshead 12 is accelerated according to the reference waveform, the change in acceleration of the movable platen 6 will be smaller than that of the crosshead 12, and therefore no vibration will occur due to the movable platen 6.

[0041] On the other hand, if the crosshead 12 is operated with the reference waveform in a range where the rate of increase is greater than the specified value, the acceleration change of the movable disc 6 will be greater than that of the crosshead 12. As a result, the acceleration of the movable disc 6 will change abruptly during periods T11 and T13, shown by the dashed lines in Figure 3(E), which may cause vibrations to occur due to the movable disc 6. Therefore, in the injection molding machine 1, the acceleration of the crosshead 12 is changed by changing the motor gain of the servo motor 16 that drives the crosshead 12, as shown by the solid line in Figure 3(E), thereby suppressing the generation of vibrations due to the movable disc 6.

[0042] As shown in Figure 3(E), the acceleration of the crosshead 12 is set to increase during period T1, which is longer than period T11, to remain constant during period T2, which is shorter than period T12, and to decrease during period T3, which is longer than period T13. In other words, when the rate of increase of velocity is 1 or greater, the acceleration waveform of the crosshead 12 has a gentler slope during period T1, which is the period of acceleration increase, compared to when the rate of increase of velocity is less than 1, and the acceleration increases over a longer period than the reference waveform.

[0043] Furthermore, during period T3, which is the period of acceleration reduction, the acceleration waveform of the crosshead 12 is set to have a gentler slope than when the rate of increase in velocity is less than 1, and the acceleration decreases over a longer period than the reference waveform. As a result, in order to make the acceleration period of the crosshead 12 the same as T0, the period T2 during which the acceleration is set to be constant must be shorter than the period T12 when the rate of increase in velocity is less than 1. Therefore, the maximum value of the acceleration of the crosshead 12 during period T2 of the acceleration period is set to be greater than when the rate of increase in velocity is less than 1.

[0044] When the motor gain is set to produce the acceleration waveform shown in Figure 3(E), the graph of speed change is smoother in the case of Figure 3(D), where the rate of increase in speed is greater than the specified value, compared to the case of Figure 3(B), where the rate of increase in speed is less than the specified value.

[0045] In the injection molding machine 1 of this embodiment, as shown in Figures 3(D) and 3(E), the gain of the servo motor 16 is set so that the change in acceleration of the crosshead 12 is more gradual than the reference waveform in the range where the acceleration of the movable disc 6 may change abruptly, where the rate of increase in speed is 1 or more. By changing the gain of the servo motor 16, the change in acceleration of the movable disc 6 can be reduced.

[0046] Since the crosshead 12 and the movable platen 6 are connected by a toggle mechanism link, the acceleration of the crosshead 12 can be set to vary according to the position of the crosshead 12, thereby suppressing the sudden change in the acceleration of the movable platen 6 at the start of the mold closing stroke. As shown in Figure 3(E), the injection molding machine 1 can prevent the generation of vibrations by the movable platen 6 while keeping the start time of the mold closing stroke constant, by setting the gain of the servo motor 16 to an acceleration waveform in which the change in acceleration over time becomes gradual, within a range where the rate of increase in speed is above a specified value.

[0047] Furthermore, the injection molding machine 1 can prevent vibrations caused by the movable platen 6 while keeping the time at the end of the mold closing process constant, by setting the acceleration of the movable platen 6 at the end of the mold closing process in the same way as at the start of the mold closing process. As a result, the injection molding machine 1 can prevent vibrations caused by excessive changes in the acceleration of the movable platen 6 while keeping the time of the entire mold opening process constant.

[0048] Next, we will explain the acceleration and motor gain at each position of the crosshead 12 using Figure 4. By setting the motor gain of the servo motor 16 that drives the crosshead 12, the acceleration of the movable platen 6, which is connected to the crosshead 12 by a toggle mechanism, can be set. Figure 4(A) is a graph showing the ratio of the speed of the movable platen 6 to the speed of the crosshead 12 at the position of the crosshead 12. Figure 4(B) is a diagram showing the acceleration and motor gain at each position of the crosshead 12. Since Figure 4(A) is the same graph as Figure 3(A) described above, we will omit its explanation. Of the data in the graph of Figure 4(B), the data showing the relationship between the motor gain and the position of the crosshead 12 is stored in memory 102 as motor gain data 106.

[0049] In Figure 4(B), the dashed line shows the change in acceleration of the crosshead 12 with respect to the position of the crosshead 12, and the solid line shows the change in motor gain of the crosshead 12 with respect to the position of the crosshead 12. As shown in Figure 4(B), in the range where the increase rate is less than 1, the motor gain is controlled to be constant regardless of the position of the crosshead 12. In contrast, in the range where the position of the crosshead 12 is approximately 400 mm or more, and the increase rate of the speed of the movable platen 6 with respect to the speed of the crosshead 12 is 1 or more, control is performed to reduce the motor gain compared to the case where the speed increase rate is less than 1.

[0050] By reducing the motor gain of the crosshead 12, as shown in Figure 3(E), the acceleration can be gradually changed during the acceleration increase period and the acceleration decrease period while keeping the acceleration period constant. On the other hand, as shown in Figure 4(B), the maximum value of the acceleration of the crosshead 12 increases compared to when the motor gain is constant. However, as shown in Figure 4(B), the period during which the acceleration of the crosshead 12 is maximum is a period during which the acceleration is constant, so there is no sudden change in the acceleration of the movable platen 6, and the influence of the movable platen 6 on vibrations is small.

[0051] In the range where the rate of increase in speed is 1 or greater, the acceleration of the crosshead 12 can be changed gradually by implementing control that reduces the motor gain compared to the range where the rate of increase in speed is less than 1. This allows the acceleration of the movable platen 6 to be changed gradually. On the other hand, in response to the extension of the acceleration increase / decrease period, the maximum value of the acceleration can be increased, and the period during which the acceleration remains constant at the maximum value can be shortened, thereby keeping the opening and closing cycle time of the movable platen 6 constant. Therefore, vibration generation in the movable platen 6 can be suppressed while maintaining production efficiency.

[0052] Next, the specific control details of the injection molding machine 1 will be explained. Figure 5 is a flowchart showing the control details of the motor gain setting control in the mold closing stroke, which is performed by the control device 100 (CPU 101). In Figure 5, the control device 100 detects the position of the crosshead 12 in step S (hereinafter simply referred to as "S") 1. The control device 100 detects the position of the crosshead 12 based on the detection signal of the position sensor 26, which functions as a detection device.

[0053] Next, the control device 100 sets the gain of the servo motor 16 corresponding to the position of the crosshead 12 using the motor gain data 106 shown in Figure 4(B) (S2). Next, the control device 100 determines the speed command waveform of the crosshead 12 according to the set gain of the servo motor 16 (S3). Specifically, in S3, the control device 100 determines the speed command waveform as shown in Figures 3(B) and (D). Next, the control device 100 drives the servo motor 16 according to the speed command waveform and starts the mold closing stroke (S4).

[0054] The control device 100 applies the same processing to the mold opening stroke as shown in Figure 5 for the mold closing stroke. This allows the control device 100 to prevent vibrations caused by the movable platen 6 in the section where the acceleration of the crosshead 12 increases or decreases during the mold opening and closing stroke, regardless of the position of the crosshead 12.

[0055] As described above, the control device 100 sets the gain of the servo motor 16 so that the temporal change in the acceleration of the crosshead 12 becomes slower than predetermined, while keeping the opening and closing cycle time of the movable platen 6 constant, according to the position of the crosshead 12. This makes it possible to suppress the generation of vibrations in the movable platen 6 while maintaining production efficiency.

[0056] The embodiments disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of this disclosure is indicated by the claims rather than by the description of the embodiments above, and all modifications within the meaning and scope equivalent to the claims are intended to be included. [Explanation of symbols]

[0057] 1 Injection molding machine, 2 Injection device, 3 Clamping device, 5 Fixed platen, 6 Movable platen, 7 Clamping housing, 9 Tie bar, 11 Clamping mechanism, 12 Crosshead, 13 Ball nut, 14 Ball screw, 16, 152, 153, 154 Servo motor, 18, 19 Gear, 20 Geared motor, 22, 23 Mold components, 25 Sensor, 26, 27 Position sensor, 100 Control device, 102 Memory, 111 Bed, 121 Base, 122 Heating cylinder, 123 Screw, 124 Drive device, 125 Hopper, 126 Injection nozzle, 127 Injection transfer device, 128 Temperature sensor, 130 Control panel, 160 Servo amplifier.

Claims

1. Injection molding machines including the following: Fixed plate; Clamping housing connected to the aforementioned fixed plate; A movable plate provided between the fixed plate and the clamping housing; A toggle mechanism provided between the clamping housing and the movable platen, comprising a crosshead, which operates the movable platen when the crosshead is driven, thereby performing mold opening and closing; A motor that drives the crosshead; and Control device; The control device sets the motor gain such that the temporal change in the acceleration of the crosshead becomes slower than predetermined, while keeping the opening and closing cycle time of the movable platen constant, according to the position of the crosshead.

2. The injection molding machine according to claim 1, further comprising the following: A detection device for detecting the position of the crosshead, Here, the position of the crosshead is detected by the detection device.

3. The injection molding machine according to claim 1 or claim 2, further comprising the following: A memory device that stores the relationship between the position of the crosshead and the gain of the motor.

4. The injection molding machine according to claim 1 or claim 2, Here, The control device sets the motor gain such that the temporal change in the acceleration of the crosshead becomes slower than predetermined, while keeping the opening and closing cycle time of the movable platen constant, within a range where the rate of increase of the speed of the movable platen relative to the speed of the crosshead at each position of the crosshead is greater than or equal to a predetermined value.

5. A motor control method in an injection molding apparatus, including the following: Fixed plate; Clamping housing connected to the aforementioned fixed plate; A movable plate provided between the fixed plate and the clamping housing; A toggle mechanism provided between the clamping housing and the movable platen, comprising a crosshead, which operates the movable platen and performs mold opening and closing when the crosshead is driven; and A motor that drives the crosshead; The motor control method includes the following steps: (a) A step of obtaining the position of the crosshead, (b) A step of setting the gain of the motor such that the temporal change in the acceleration of the crosshead becomes slower than predetermined, while keeping the opening and closing cycle time of the movable platen constant, according to the position of the crosshead.

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