Method and control device for controlling the opening and closing speeds of the injection mold in an injection molding machine

Abstract

Method for controlling the opening and closing speeds of the injection mold in an injection molding machine (M), wherein the injection molding machine (M) has a toggle clamping unit (Mc) for opening and closing operations of the movable mounting plate (30) by moving a crosshead (34) forward and backward and thereby extending and shortening a toggle mechanism (36), wherein the method comprises the steps: Specifying a velocity (Vc) for each position of the crosshead (34); Determining a total moment (Pm) of the movable mounting plate (30) and the injection mold for each transverse head position (Pc) based on the specified transverse head velocities (Vc), a velocity increase of the toggle lever mechanism (36), the mass (Mm) of the movable mounting plate (30) and the mass (Ma) of the injection mold; Determining a section (B) in which the determined total moment (Pm) of the movable mounting plate (30) and the injection mold exceeds the preset total moment (PL) of the movable mounting plate (30) and the injection mold; Determine the transverse main velocity (Vc) for each transverse main position (Pc) in the determined section (B) such that the total moment (Pm) of the movable mounting plate (30) and the injection mold equals the preset total moment (PL) of the movable mounting plate (30) and the injection mold, based on the velocity increase (G), the preset total moment (PL), and the mass (Mm) of the movable mounting plate (30) and the mass (Ma) of the injection mold, and Moving the movable mounting plate (30) for opening and closing operations of the movable mounting plate (30) according to the transverse main velocity (Vc) determined for each transverse main position (Pc) in the determined section (B) and moving the movable mounting plate (30) for opening and closing operations according to the specified transverse main velocities (Vc) at transverse main positions (Pc) outside the section.

Description

Background of the invention 1. Field of the invention

[0001] The present invention relates to a method and a control device for controlling the opening and closing speeds of the injection mold in an injection molding machine. 2. Description of the state of the art

[0002] A toggle clamping unit for an injection mold moves a movable platen back and forth by moving a crosshead back and forth, thereby extending and contracting a toggle joint. Because the moving speed of the movable platen is amplified by the toggle mechanism, the movable platen accelerates even when the crosshead is moved at a constant speed. The movable platen alternates between acceleration and deceleration at a predetermined position (see, for example, JP 2004-155063 A). At such an acceleration-deceleration transition point, the movable platen is subjected to mechanical shock and generates vibration and noise.

[0003] The technique disclosed in JP 2004-155063 A suppresses the above-mentioned shocks due to the characteristics of the movable platen by controlling the deceleration according to the crosshead position when the movable platen is stopped. However, this technique does not take measures against the shocks that occur when the movable platen is accelerated and then decelerated while the crosshead is moving at a constant speed.

[0004] On the other hand, the technique disclosed in JP 2010-111021A effectively determines the acceleration rate at which the movable platen accelerates from its rest position, taking into account the aforementioned characteristics of the movable platen. However, like the technique in the aforementioned JP 2004-155063A, this technique also offers no measures against the shocks that occur when the movable platen transitions from acceleration to deceleration while the crosshead moves at a constant speed.

[0005] In the technique disclosed in JP S63-112136 A, the positions and speeds of the movable platen are preset, and the crosshead is controlled so that the movable platen moves at the preset positions at the predetermined speeds. The technique disclosed in this document controls the speed of the movable platen so that it is always maintained at the predetermined values ​​and can prevent the movable platen from abruptly changing from acceleration to deceleration. However, there is a problem with this technique in which the speed of the movable platen is controlled to always be maintained at the predetermined value: some presettings limit the speed of the crosshead at positions where shock does not occur, preventing the original performance of the machine from being achieved.

[0006] In an injection mold clamping unit with a toggle mechanism, even if the crosshead is moved forward and backward at a constant speed to contract and extend the toggle mechanism to move the movable platen, the movable platen is accelerated and decelerated by the speed-increasing action mechanism of the toggle. A sudden change from acceleration to deceleration causes a shock to occur. Traditionally, this shock was reduced by uniformly reducing the moving speeds of the crosshead to reduce the speed of the movable platen and thus suppress its acceleration. However, a uniform reduction in speed increases the opening and closing time of the injection mold and consequently lengthens the entire injection molding cycle, leading to a reduction in productivity.

[0007] Document DE 10 2006 041 579 A1 also discloses a method for controlling and / or regulating an injection molding machine having a toggle lever mechanism with a crosshead. Restriction variables for the movement of the movable mold clamping plate and restriction variables for the movement of the crosshead are defined, and a time-optimal movement trajectory is numerically calculated and stored. Summary of the invention

[0008] It is an object of the present invention to provide a method and a control device for controlling the opening and closing speed of the injection mold by controlling the crosshead of a toggle mechanism of a toggle clamping unit such that a movable platen in an injection molding machine does not suddenly change from an acceleration to a deceleration in which the movable platen is opened and closed by means of a toggle mechanism.

[0009] In a method for controlling the opening and closing speeds of an injection mold in an injection molding machine according to a general example, the injection molding machine includes a toggle clamping unit for the injection mold for moving a movable platen for opening and closing operations of the injection mold by moving a crosshead forward and backward, thereby extending and shortening a toggle mechanism. The method includes the steps of: specifying a speed for each position of the crosshead; determining a speed of the movable platen for each position of the crosshead based on the specified crosshead speeds and a speed increment of the toggle mechanism;Determining a section having those crosshead positions at which the detected speed of the movable platen exceeds a predetermined speed for the movable platen; determining a crosshead speed for each crosshead position in the determined section such that the speed of the movable platen becomes equal to the predetermined speed of the movable platen, based on the speed increment and the predetermined speed of the movable platen, and moving the movable platen for opening and closing operations of the movable platen according to the crosshead speed determined for each crosshead position in the determined section and moving the movable platen for opening and closing operations according to the predetermined crosshead speeds at crosshead positions outside the section;

[0010] In the method for controlling the opening and closing speeds of an injection mold in an injection molding machine according to a first embodiment of the present invention, the injection molding machine includes a toggle clamping unit for the injection mold for moving a movable platen during opening and closing operations of the injection mold by moving a crosshead of a toggle mechanism forward and backward, thereby extending and shortening it. The method comprises the steps of: specifying a speed for each position of the crosshead; determining a total momentum of the movable platen and the injection mold for each crosshead position based on the specified crosshead speeds, a speed increment of the toggle mechanism, the mass of the movable platen, and the mass of the injection mold;Determining a section in which the determined total impulse of the movable platen and the injection mold exceeds the preset total impulse of the movable platen and the injection mold;Determining the crosshead speed for each crosshead position in the determined section such that the total momentum of the moving platen and the injection mold is equal to the preset total momentum of the moving platen and the injection mold, based on the speed increment, the preset total momentum, and the mass of the moving platen and the mass of the injection mold, and moving the moving platen for opening and closing operations of the moving platen according to the crosshead speed determined for each crosshead position in the determined section and moving the moving platen for opening and closing operations according to the preset crosshead speeds at crosshead positions outside the section;

[0011] In a control device for controlling opening and closing speeds of the injection mold in an injection molding machine according to another general example, the injection molding machine has a toggle clamping unit for the injection mold for moving a movable platen during opening and closing operations of the injection mold by moving a crosshead of a toggle mechanism forward and backward, thereby extending and shortening it. The control device comprises: a setting unit for setting a crosshead speed for each crosshead position; a movable platen speed calculation unit for determining the speed of the movable platen for each crosshead position based on the set crosshead speeds and a speed increment of the toggle mechanism; a section calculation unit for determining a section containing crosshead positions,where the detected speed of the movable platen exceeds a predetermined speed for the movable platen, and a crosshead speed calculation unit for determining the crosshead speed at each crosshead position in the detected section so that the movable platen moves at the predetermined speed for the movable platen based on the speed increase and the predetermined speed of the movable platen. The movable platen for opening and closing operations of the injection mold is moved according to the crosshead speed determined for each crosshead position in the detected section, and the movable platen for opening and closing operations is moved according to the predetermined crosshead speeds at crosshead positions outside the detected section.

[0012] In a control device for controlling opening and closing speeds of the injection mold in an injection molding machine according to a second embodiment of the present invention, the injection molding machine has a toggle clamping unit for the injection mold for moving a movable platen during opening and closing operations of the injection mold by moving a crosshead of a toggle mechanism forward and backward, thereby extending and shortening it. The control device comprises: a setting unit for setting a crosshead speed for each position of the crosshead; a total momentum calculation unit for determining a total momentum of the movable platens and the injection mold for each crosshead position based on the set crosshead speeds, a speed increase of the toggle mechanism,the mass of the movable platen and the mass of the injection mold; a section calculation unit for determining a section in which the determined total momentum of the movable platen and the injection mold exceeds the preset total momentum of the movable platen and the injection mold, and a crosshead speed calculation unit for determining the crosshead speed at each crosshead position in the determined section so that the total momentum of the movable platens and the injection mold equals the preset total momentum of the movable platen and the injection mold, based on the speed increase, the preset total momentum, the mass of the movable platen, and the mass of the injection mold. The movable platen for opening and closing operations of the injection mold is moved according to the crosshead speed.which has been determined for each crosshead position in the determined section, and the movable clamping plate is moved for opening and closing operations of the injection mold according to the preset crosshead speeds at crosshead positions outside the determined section.

[0013] The present invention can provide a method and a control apparatus for controlling opening and closing speeds of the injection mold by controlling a crosshead in a toggle mechanism such that a movable platen does not suddenly change between acceleration and deceleration in an injection molding machine in which the movable platen is opened and closed by a toggle mechanism. Short description of the drawings Fig. 1 is a block diagram of an injection molding machine in which the method and control apparatus of the present invention are applied. Fig. 2A and Fig. 2B shows an example of user presets for the speeds for a closing state of an injection mold. Fig. 3A and Fig. 3B show crosshead velocities at given crosshead positions. Fig. Figure 4 is a graphical representation showing the relationships between crosshead positions and speed increments, crosshead speeds and moving platen speeds. Fig. Figure 5 illustrates the crosshead velocities according to the present invention. Fig. Figure 6 shows an example of speed limits. Detailed description of preferred embodiments

[0014] Fig. 1 is a block diagram of an injection molding machine to which the method and control apparatus for controlling opening and closing speeds of the injection mold of the present invention are applied.

[0015] An injection molding machine M includes a mold clamping unit Mc and an injection unit Mi on a machine frame (not shown). The injection unit Mi heats and melts a plastic material (pellets) and injects the molten plastic into the cavity of an injection mold 40. The mold clamping unit Mc primarily serves to open and close the injection mold 40, which has a mold half 40a on the movable side and a mold half 40b on the stationary side.

[0016] First, the injection unit Mi is described. An injection cylinder 1 has a nozzle 2 attached to one end and a screw 3 extending therethrough. The screw 3 is equipped with a plastic pressure sensor 5, which uses, for example, a pressure cell, for measuring a plastic pressure resulting from the pressure applied by the screw 3. An output signal of the plastic pressure sensor 5 is converted into a digital signal by an analog-to-digital (A / D) converter 16 and applied to a servo CPU 15.

[0017] The worm shaft 3 is rotated by a servomotor M2 for worm drive via a transmission gear 6 with pulleys, belts, etc. The worm shaft 3 is driven and axially driven by a servomotor M1 for moving the worm shaft back and forth via a transmission drive 7, which includes a mechanism for converting rotary motion into linear motion, such as a pulley, belt, drive screw / nut mechanism, and the like. Reference symbol P1 denotes a position and speed detector for detecting the axial positions and speeds of the worm 3 by detecting the positions and speeds of the servomotor M1 for moving the worm shaft 3 back and forth.Reference numeral P2 denotes a position and speed detector for detecting the positions and speeds of axial rotation of the screw shaft 3 by detecting the positions and speeds of the servo motor M2. Reference numeral 4 denotes a hopper for supplying plastic into the injection cylinder 1.

[0018] Next, the injection mold clamping unit Mc will be described. The injection mold clamping unit Mc includes a movable platen 30, a platen drive motor M3 for moving the movable platen 30 back and forth, a rear end platen 31, an ejector drive motor M4 for moving an ejector pin forward and backward to expel the finished molded part from the injection mold, guide rails 32, a fixed platen 33, a crosshead 34, an ejector mechanism 35, and a toggle mechanism 36 having a plurality of interconnected toggle links. The rear end platen 31 and the fixed platen 33 are interconnected by a plurality of guide rails 32. The movable platen 30 is disposed between the rear end platen 31 and the fixed platen 33 and is guided by the guide rails 32.The movable injection mold half or tool half 40a of the injection mold or tool 40 is attached to the movable platen 30, while the other injection mold half or tool half 40b is fixed on the fixed side to the fixed platen 33. To open the injection mold or tool, the toggle mechanism 36 moves back the crosshead 34 attached to the drive spindle 38, which is actuated by the drive motor M3 for the back and forth movement of the movable platen 30 (in . Fig. 1 to the left). To close the injection mold, the crosshead 34 is moved forward (in Fig. 1 to the right) to advance the movable clamping plate 30. After the movable mold half 40a has been brought into contact with the fixed mold half 40b, the crosshead 34 is advanced further until the toggle mechanism 36 is fully extended to build up the clamping force for the injection mold.

[0019] On the rear end plate 31, a motor M5 for adjusting the closing position of the injection mold is provided. A drive gear (not shown) is mounted on the rotating shaft of the motor M5 for adjusting the closing position of the injection mold. A guide post nut (not shown) is screwed onto the threaded portion 37 of each guide post 32. The rotating force of the drive gear is transmitted to the gears of all the guide post nuts via another gear (not shown). The rotating force of the drive train is transmitted to all the guide post nuts via another gear (not shown). When the injection mold closing position adjusting motor M5 is rotated in a certain direction, this drive mechanism synchronously rotates all the guide post nuts screwed onto the threaded portions 37 of the guide post 32.When the injection mold closing position adjusting motor M5 is rotated a predetermined number of times in a predetermined direction, the rear end plate 31 is moved forward or backward by a predetermined distance. The injection mold closing position adjusting motor M5, which is preferably a servo motor as shown in this figure, is equipped with a position detector P5 for measuring the rotational (angular) positions. The detected rotational position signals of the injection mold closing position adjusting motor M5, which are detected by the position detector P5, are input to the servo CPU 15.

[0020] A control device 100 for the injection molding machine M includes a CNC CPU 20 as a numerical control microprocessor, a PMC CPU 17 as a programmable machine control microprocessor, and a servo CPU 15 as a servo control microprocessor. These microprocessors are configured to exchange information between them via a bus 26 by mutually selecting their inputs and outputs.

[0021] A ROM 13 in which servo control programs for position, speed, and loop processing are stored, as well as a RAM 14 as a temporary data storage are connected to the servo CPU 15. The servo CPU can detect pressure signals from the plastic pressure sensor 5 provided in the main frame of the injection molding machine M via the A / D converter 16. Servo amplifiers 11 and 12 are also connected to the servo CPU 15, which drive an injection servo motor M1 connected to the injection shaft and the screw drive servo motor M2 connected to the screw drive shaft according to the instructions of the servo CPU, so that the output signals of the position and speed detectors P1 and P2 connected to the servo motors M1 and M2 are fed back to the servo CPU 15. The rotational positions of the servo motors M1 and M2 are determined by the CPU 15 based on the fed back signals.The position signals reported back from the detectors P1 and P2 for position and speed are calculated and updated and stored in memory registers for the current position.

[0022] Servo amplifiers 8 and 9 are connected to servo motor M3 for actuating a mold closing shaft for closing the mold and the injection mold, respectively, and to servo motor M4 for actuating an ejection shaft for expelling the injection-molded articles from the mold. Output signals from the position / speed detectors P3 and P4 mounted on servo motors M3 and M4 are fed back to servo CPU 15. The rotational positions of servo motors M3 and M4 are calculated and updated by the servo CPU based on the position signals fed back from position / speed detectors P3 and P4, and stored in the current position memory registers.

[0023] A ROM 18 storing a sequence program for controlling the operation steps of the injection molding machine and a RAM 19 as a temporary storage for arithmetic data are connected to the PMC-CPU 17. A ROM 21 storing various programs such as automatic operation programs for controlling the entire operation of the injection molding machine and control programs for controlling the opening and closing operations of the injection mold related to the present invention and a RAM 22 as a temporary storage for arithmetic data are connected to the CNC-CPU 22. A RAM 23 for storing injection molding data is a non-volatile memory for storing the injection molding conditions, various settings, parameters, macro variables, etc. related to an injection molding job.A display device / MDI (manual data entry device) 25 is connected to bus 26 via an interface (I / F) and enables selection of a function menu and various data entry operations. Numeric keys for entering numeric data, as well as various function keys, are also provided. An LCD (liquid crystal display), a cathode ray tube monitor (CRT), or other display device can also be used as a display device.

[0024] The PMC CPU 17 generally controls the operation sequences of the thus constructed injection molding machine M. The CNC CPU 20 distributes motion commands to the servomotors connected to the shafts according to the operation program stored in the ROM 21 and the injection molding conditions stored in the injection molding data memory RAM 23. The servo CPU 15 controls the drive of the servomotors M1, M2, M3, M4, and M5 by executing digital servo processing based on the motion commands issued to each axis and the position and speed feedback signals detected by the position and speed detectors P1, P2, P3, P4, and P5.

[0025] An injection molding process performed using the above-described injection molding machine M will now be described. When the drive motor M3 for moving the movable platen 30 back and forth is rotated in the positive direction, the drive screw 38 rotates in the positive direction and moves the crosshead 34, which is in screw engagement with the drive screw 38, forward, thereby actuating the toggle mechanism 36 to move the movable platen 30 in the forward direction (i.e., toward the fixed platen 33).

[0026] When the movable half 40a of the injection mold attached to the movable platen 30 is brought into contact with the fixed half 40b of the injection mold, the process proceeds to the injection mold closing operation. During the injection mold closing operation, the movable platen is further driven in the positive direction by the forward / reverse drive motor M3 to stretch the toggle mechanism 36, thereby exerting a mold closing force on the mold 40. Then, the forward / reverse screw drive motor M1 provided on the injection unit Mi is driven to drive the screw shaft 3 forward in the axial direction, so that the cavity volume in the injection mold is filled with molten resin.

[0027] To open the injection mold, the drive motor M3 for moving the movable platen 30 back and forth is rotated in the opposite direction to drive the drive spindle 38 in the opposite direction and move back the crosshead 34, which is in screw engagement with the drive spindle 38, and thereby open the toggle mechanism 36 and move the movable platen 30 back (ie, toward the rear end plate 31).

[0028] When the injection mold opening operation is completed, the ejector drive motor M4 is driven for the forward and backward movement of the ejector to extend the ejector pin and push the molded article out of the movable half 40a of the injection mold. The ejector pin (not shown) is extended through the inner surface of the movable mold half 40a and ejects the molded article from the movable half 40a of the injection mold.

[0029] Next, the opening and closing operations of the movable platen 30 for the injection mold 40 according to the present invention will be described.

[0030] Since the movable platen 30 is moved by the movable platen drive motor M3 via the toggle mechanism 36, the movement speed and acceleration of the movable platen 30 are not proportional to the speed and acceleration of the movable platen drive motor M3. To close, compress, and open the injection mold 40, it is necessary to control the position, speed, and acceleration of the movable platen 30, on which the mold half 40a of the injection mold 40 is mounted.

[0031] Since the movable platen 30 is actuated by the movable platen reciprocating drive motor M3, the position, speed, and acceleration of the movable platen 30 are controlled by controlling the position, speed, and acceleration of the movable platen reciprocating drive motor M3. However, the speed and acceleration of the movable platen 30 vary with the position of the movable platen reciprocating drive motor M3 even when the movable platen reciprocating drive motor M3 is rotated at a constant speed because the position, speed, and acceleration of the movable platen reciprocating drive motor M3 are not proportional to the position, speed, and acceleration of the movable platen 30.On the other hand, the position, speed, and acceleration of the drive motor M3 for moving the movable platen forward and backward are in a predetermined proportional relationship to the position, speed, and acceleration of the crosshead 34. Once the position, speed, and acceleration of the crosshead 34 are determined, the position, speed, and acceleration of the drive motor M3 for moving the movable platen forward and backward are also determined. The method for controlling the motor speeds with the acceleration rates according to the speeds is known.

[0032] First, the positions of the crosshead 34, which are referred to below as “crosshead positions”, and the speeds of the crosshead 34 corresponding to these positions, which are referred to below as “crosshead speeds”, are measured during an opening and closing process of the injection mold for the Fig. 1 shown injection molding machine M preset, as shown in the example in Fig. 2B, using an input device in conjunction with a display device / MDI 25. The crosshead position and speed presets are displayed on the display device / MDI 25 screen in the form of the Fig. 2A is displayed.

[0033] Then, the control device 100 for the injection molding machine M calculates the speed of the movable platen (hereinafter referred to as "platen speed") corresponding to all crosshead positions based on the above-mentioned preset crosshead speed and the speed increment of the toggle mechanism 36 that performs the opening and closing operations of the injection mold. When the calculated speed of the movable platen is equal to or greater than the preset maximum speed limit, the crosshead speed at the current crosshead position is calculated based on the speed increment to reduce the speed of the movable platen to the predetermined maximum speed limit, and the crosshead is moved at the calculated crosshead speed.

[0034] The speed Vm(Pc) of the moving platen can be described by the following equation (1): Vm(Pc)=Vc(Pc)×G(Pc) where Vm / Pc) is the speed of the movable platen at the crosshead position Pc, Vc(Pc) is the crosshead speed at the crosshead position Pc and G(Pc) is the speed increase of the toggle mechanism.

[0035] As is well known, the speed increase G(Pc) is a function of the crosshead position Pc (see, for example, Japanese Laid-Open Patent Application No. 2009-251804).

[0036] When the crosshead position Pc and the corresponding crosshead speeds Vc(Pc) are displayed on the display screen of the display unit / MDI 25 for the injection molding machine M (see Fig. 2A) are preset as described above, the control device 100 reads from the speed presets the crosshead speed Vc(Pc) for each given crosshead position Pc (see Fig. 3A and Fig. 3B) and stores the relationship between the crosshead position Pc and the crosshead speeds Vc(Pc) in memory (e.g., RAM 22). Next, for each crosshead position Pc stored in memory, a speed Vm(Pc) of the movable platen is determined using the above equation (1).

[0037] If equation (1) yields a value for a moving platen speed Vm(Pc) that is equal to or greater than the preset maximum speed limit VL for a crosshead position Pc (i.e., Vm(Pc) ≥ VL), equation (1) is solved assuming Vm(Pc) = VL to determine the crosshead speed Vc(Pc) for this crosshead position Pc, and this determined crosshead speed Vc(Pc) is used as the preset crosshead speed. Specifically, the following equation (1') is solved to determine the crosshead speed Vc(Pc) at the crosshead position Pc: Vm(Pc)=VL / G(Pc)

[0038] Here, the maximum speed limit VL can be preset based on the vibration and noise levels determined in previously conducted tests on each machine type and size. On the other hand, if equation (1) results in a speed Vm(Pc) for the moving platen that does not exceed the preset maximum speed limit VL for the crosshead position Pc (i.e., Vm(Pc) < VL), this crosshead speed Vc(Pc) is used as the preset crosshead speed.

[0039] In the above-described embodiment, the moving platen speed Vm(Pc) is obtained for each crosshead position (Pc) stored in the memory, and the moving platen speed Vm(Pc) among the obtained moving platen speeds that is greater than PL at the crosshead position (Pc) is used as PL. Since the relationship between the crosshead position Pc and the moving platen speeds Vm(Pc) is as shown in Fig. 4, two crosshead positions can be determined at which the speeds of the movable clamping plate Vm(Pc) exceed the maximum speed limit VL (see Fig. 5) intersect, and the crosshead velocities Vc(Pc) can be determined such that Vm(Pc) becomes equal to PL in the section between these two positions. More specifically, two intersection points at which a curve given by equation (1) describing the relationship between the crosshead velocity Vc(Pc) and the moving platen velocities Vm(Pc) - the straight line Vm(Pc) = VL - passes are first determined. Then, the moving platen velocities Vm(Pc) for the given crosshead positions Pc between these two points are determined, and the crosshead velocity Vc(Pc) satisfying the condition Vm(Pc) = VL is determined using equation (1') as described above.Note that section B contains crosshead positions where the speed of the moving platen 30 exceeds the specified speed of the moving platen (maximum speed limit VL of the moving platen 30), while sections A and C contain crosshead positions where the speed of the moving platen does not exceed the specified speed of the moving platen.

[0040] The inertial force of the moving platen 30 is determined from the total mass of the moving platen 30 and the injection mold (only the moving mold half 40a) attached to the moving platen 30. A larger inertial force due to the larger mass generates a larger shock when the moving platen 30 changes from acceleration to deceleration. Since the mass of the injection mold varies with it, the maximum speed limit VL should be corrected taking the mass of the injection mold into account. The maximum speed limit VL at which vibration and noise are generated within the tolerable range can be determined in advance using a reference injection mold and then corrected using Equation (2) given below based on the ratio of the actual mass of the mold to the mass of the reference injection mold. VLa=VLb×(Mb+Mm) / (Ma+Mm) with Ma: Mass of the current injection mold Mb: Mass of the reference injection mold Mm: Mass of the movable clamping plate VLa: maximum speed limit for the current injection mold VLb: maximum speed limit for the reference injection mold

[0041] The inertial mass of the reference injection mold and the inertial mass of the currently used injection mold can be preset by the operator on the screen of the injection molding machine or can be determined using the following equation (3) by measuring the acceleration of the moving platen using an acceleration sensor and also by measuring the motor torque with which the moving platen is driven while the moving platen is accelerated during the currently occurring opening and closing operations of the injection mold. Ma+Mm(or Mb+Mm)=Fm / A

[0042] They mean: A: The currently measured acceleration of the moving clamping plate Fm: The impact force of the movable clamping plate is calculated from the torque of the motor for opening and closing the movable clamping plate.

[0043] According to the method described above, the preset maximum speed limit for the movable platen is set based on a calculation or input on the screen of the display device for the injection molding machine. Alternatively, instead of the maximum speed limit VL, the maximum impulse limit of the movable platen (including the injection mold (half)) can be preset to control the crosshead speed Vc(Pc) so that the impulse of the movable platen does not exceed its maximum limit. In this case, the impulse of the movable platen 34 for the crosshead position Pc is first calculated using the following equation (4). Pm(Pc)=(Ma+Mm)×Vm(Pc) with Pm: the momentum of the moving platen (including the injection mold) at the crosshead position.

[0044] In equation (4), (Ma + Mm), the total mass of the moving platen plus the injection mold, is constant regardless of the position of the crosshead. Therefore, the moving platen velocity Vm(Pc) is equivalent to the moving platen momentum Pm(Pc).

[0045] When the momentum of the moving platen Pm(Pc) reaches or exceeds the preset maximum momentum limit PL (i.e., Pm(Pc) ≥ PL), the velocity Vm(Pc) of the moving platen at the crosshead position Pc is determined by solving equation (4) assuming Pm(Pc) = PL. This means that Vm(Pc) is determined by the following equation (4'). Vm(Pc)=(Ma+Mm) / PL

[0046] Then, the moving platen speed Vm(Pc) just determined is substituted into equation (1) to obtain Vc(Pc), which is to be used as the preset crosshead speed Vc(Pc). Here, measures can be taken to enable the operator to preset the maximum pulse limit PL on the screen for the injection molding machine to an optimal value by judging the vibration and noise of the machine, or to preset it according to a value specific to the machine type or size as the maximum pulse limit PL. On the other hand, when Pm(Pc) < PL, the preset crosshead speed Vc(Pc) stored in the memory is used as the preset crosshead speed Vc(Pc).

[0047] Since the relationship between the momentum of the movable platen Pm(Pc) and the crosshead position Pc can be represented in the form of a graph - like the one in Fig. 4 - the momentum of the moving platen Pm(Pc), the crosshead position Pc and two intersection points of equation (4), which are the relational expression for the relationship between the speed of the moving platen Vm(Pc) and the momentum of the moving platen Pm(Pc), with Pm(Pc) = PL, can be determined and then the momentum Pm(Pc) can be obtained for each of the predetermined crosshead positions between these two points to determine the crosshead speed Vc(Pc), at which Pm(Pc) becomes equal to the value PL, as is the case for the case described above.

[0048] As described above, the crosshead speed is controlled by presetting the maximum speed limit for the moving platen and the maximum impulse limit to prevent the moving platen speed from suddenly changing from acceleration to deceleration. According to the present invention, it is possible to suppress shocks with minimal impact on the cycle time because the crosshead speed is reduced only in the section where shocks may occur.

Claims

[1] A method for controlling the opening and closing speeds of the injection mold in an injection molding machine (M), wherein the injection molding machine (M) has a toggle clamping unit (Mc) for opening and closing operations of the movable platen (30) by moving a crosshead (34) back and forth and thereby stretching and shortening a toggle mechanism (36), the method comprising the steps of: Presetting a speed (Vc) for each position of the crosshead (34); Determining a total moment (Pm) of the movable platen (30) and the injection mold for each crosshead position (Pc) based on the predetermined crosshead speeds (Vc), a speed increase of the toggle mechanism (36), the mass (Mm) of the movable platen (30) and the mass (Ma) of the injection mold; Determining a section (B) in which the determined total moment (Pm) of the movable clamping plate (30) and the injection mold exceeds the preset total moment (PL) of the movable clamping plate (30) and the injection mold; Determining the crosshead speed (Vc) for each crosshead position (Pc) in the determined section (B) such that the total moment (Pm) of the movable platen (30) and the injection mold is equal to the preset total moment (PL) of the movable platen (30) and the injection mold, based on the speed increase (G), the preset total moment (PL) and the mass (Mm) of the movable platen (30) and the mass (Ma) of the injection mold, and Moving the movable clamping plate (30) for opening and closing operations of the movable clamping plate (30) according to the crosshead speed (Vc) determined for each crosshead position (Pc) in the determined section (B) and moving the movable clamping plate (30) for opening and closing operations according to the predetermined crosshead speeds (Vc) at crosshead positions (Pc) outside the section. [2] A control device for controlling the opening and closing speeds of an injection mold in an injection molding machine (M), wherein the injection molding machine (M) has a toggle clamping unit (Mc) for opening and closing operations of the movable platen (30) by moving a crosshead (34) forwards and backwards and thereby stretching and shortening a toggle mechanism (36), wherein the control device comprises: a setting unit for setting a crosshead speed (Vc) for each position (Pc) of the crosshead (34); a total moment calculating unit for calculating a total moment (Pm) of the movable platens (30) and the injection mold for each crosshead position (Pc) based on the predetermined crosshead speeds (Vc), a speed increase (G) of the toggle mechanism (36), the mass (Mm) of the movable platen (30) and the mass (Ma) of the injection mold; a section calculation unit for determining a section (B) in which the determined total moment (Pm) of the movable clamping plate (30) and the injection mold exceeds the preset total moment (PL) of the movable clamping plate (30) and the injection mold, and a crosshead speed calculation unit (Vc) for calculating the crosshead speed (Vc) at each crosshead position (Pc) in the determined section (B) such that the total moment (Pm) of the movable platens (30) and the injection mold equals the preset total moment (PL) of the movable platen (30) and the injection mold, based on the speed gain (G), the preset total moment (PL), the mass (Mm) of the movable platen (30) and the mass (Ma) of the injection mold; wherein the movable clamping plate (30) for opening and closing operations of the injection mold is moved according to the crosshead speed (Vc) determined for each crosshead position (Pc) in the determined section (B), and the movable clamping plate (30) for opening and closing operations of the injection mold is moved according to the preset crosshead speeds (Vc) at crosshead positions (Pc) outside the determined section (B).

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