JP3583071B2 - Injection molding machine weighing method - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a weighing method for an injection molding machine that performs weighing by rotating a screw by a drive mechanism.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a measurement processing method of an injection molding machine that performs measurement by rotating a screw by a driving mechanism unit using a servomotor, a suckback control method of the injection molding machine disclosed in Japanese Patent Publication No. 7-41652 is known. ing.
[0003]
In the method disclosed in the publication, a pressure sensor provided between a movable member that is moved by a moving driving device and an injection screw that is moved with respect to a heating cylinder by the movable member is applied to the injection screw at the time of suckback. The pressure sensor detects the pressure and sucks back the injection screw at the suckback speed determined according to the suckback position of the injection screw so that the suckback speed of the injection screw decreases gradually or continuously. The suck back of the injection screw is stopped when the relationship between the detected pressure and the preset target value of the pressure becomes a predetermined relationship.
[0004]
[Problems to be solved by the invention]
By the way, as shown in FIG. 4, in the conventional weighing method including the suck-back control method described above, the screw is rotated at a predetermined rotation speed Vrr [rpm], and the screw is weighed. Is moved backward by a predetermined distance Lsr [mm], the back pressure (resin pressure) Pbr [MPa] against the screw can be temporarily reduced to zero.
[0005]
However, the suck-back process is for preventing a so-called drooling phenomenon in which the resin drips from the injection nozzle, and this dripping phenomenon occurs due to a pressure difference between before and after the screw check valve and the inertia of the resin. Therefore, in consideration of the principle of the occurrence, even if the resin pressure Pbr once becomes 0 by the suck-back process, the resin pressure Pbr slightly increases again with the passage of time. The rise in resin pressure after such a suck-back process was relatively small, and in the past it was not so much noticed, but it increased with the passage of time, and the degree of contact of the molten resin with the air even if the resin did not drip Because of the increase, there is a problem that cannot be ignored in realizing a high quality and a high degree of homogeneity with respect to a molded product, and there is a problem that it cannot sufficiently cope with diversifying resin grades.
[0006]
In addition, it is conceivable to lengthen the retreat distance of the screw at the time of suckback processing, or to perform the operation stepwise as described in Japanese Patent Publication No. Hei 7-41652, but the former causes air to be entrained, and the latter causes Since the suckback process is only improved, the above problem cannot be drastically solved in consideration of the generation principle of the drooping phenomenon. In FIG. 4, Vbr [mm / s] is the screw retreat movement speed, Xar [mm] is the suckback start position, Xbr [mm] is the suckback end position, and Vsr [mm / s] is the suckback time. The backward movement speed of the screw is shown.
[0007]
The present invention has solved the problems existing in such conventional techniques, and in particular, can realize a high quality and a high degree of homogeneity with respect to a molded article, and sufficiently cope with diversifying resin grades. It is an object of the present invention to provide a measuring method for an injection molding machine that can perform the measurement.
[0008]
Means and Embodiments for Solving the Problems
According to the measuring method of the injection molding machine M according to the present invention, when the screw 3 is rotated by the drive mechanism unit 2 to perform the metering, the screw 3 is set in advance with the retreat movement characteristic to offset the increase in the resin pressure Pb. Is rotated to perform weighing, then the screw 3 is moved backward by a predetermined distance Ls [mm] to perform a suck-back process, and thereafter, the resin pressure Pb [MPa] generated after the suck-back process is increased. And a resin pressure offsetting process of retreating the screw 3 in accordance with the retreating characteristic so as to cancel out.
[0009]
【Example】
Next, preferred embodiments according to the present invention will be described in detail with reference to the drawings.
[0010]
First, a configuration of an injection molding machine M that can execute the measurement processing method according to the present embodiment will be described with reference to FIG.
[0011]
The injection molding machine M shown in FIG. 2 shows only the injection device Mi without the mold clamping device. The injection device Mi includes an injection table 11 and a drive table 12 which are separated from each other. The front end of the injection table 11 supports the rear end of the heating cylinder 13. The heating cylinder 13 has an injection nozzle 14 at the front end, a hopper 15 for supplying a molding material to the inside of the heating cylinder 13 at a rear part, and the screw 3 is inserted into the heating cylinder 13. On the other hand, four tie bars 17 are provided between the injection table 11 and the drive table 12, and a slide block 18 is slidably mounted on the tie bars 17. A rotary block 20 integrally having a driven pulley 19 is rotatably supported at the front end of the slide block 18, and the rear end of the screw 3 is coupled to the center of the rotary block 20. Further, a measuring servomotor 22 provided with a rotary encoder 21 is attached to a side surface of the slide block 18. An endless timing belt 24 is provided between a driven pulley 23 fixed to a rotating shaft of the measuring servomotor 22 and the driven pulley 19. To form the drive mechanism 2 for measurement.
[0012]
On the other hand, a nut portion 26 is coaxially and integrally provided at the rear portion of the slide block 18, and a ball screw portion 27 rotatably supported by the drive base 12 is screwed into the nut portion 26 so that the ball is screwed into the nut portion 26. The screw mechanism 25 is configured. Further, a driven pulley 28 is attached to the rear end of the ball screw portion 27 projecting rearward from the drive base 12, and an injection servomotor 30 provided with a rotary encoder 29 is mounted on a support plate 12s attached to the drive base 12. And a timing belt 32 is stretched between a driven pulley 31 and a driven pulley 28 fixed to a rotating shaft of the servomotor 30 for injection to form a drive mechanism 33 for injection. By controlling the drive of the injection servomotor 30, a suck-back process and a resin pressure offset process in a measuring process described later can be performed.
[0013]
S is a control system, which includes a control unit 35. The control unit 35 has various control functions for executing basic molding steps such as an injection step and a weighing step in a molding cycle, and has a built-in sequence controller to execute the weighing method according to the present embodiment. it can. The control unit 35 is connected to a setting unit 36 that can set various conditions such as speed and time, and has a resin pressure sensor 37 attached to the injection nozzle 14 for detecting the internal resin pressure Pb [MPa]. Connecting. Further, a servo circuit 38 for measurement and a servo circuit 39 for injection are connected to the control unit 35. The measuring servo circuit 38 is connected to the measuring servo motor 22 and the rotary encoder 21, and the injection servo circuit 39 is connected to the measuring servo motor 30 and the rotary encoder 29.
[0014]
Next, a weighing method according to the present embodiment will be described with reference to FIGS. 2 and 3 and according to the flowchart shown in FIG.
[0015]
First, in the measuring step, the measuring servomotor 22 is operated, and the screw 3 is rotated at a preset rotation speed Vr [rpm]. Thereby, the resin plasticized and melted in the heating cylinder 13 moves to the front of the screw 3 and is metered and accumulated. On the other hand, the screw 3 gradually moves backward from the measurement start position (the screw most forward position) at the backward movement speed Vb [mm / s] (step S1). Then, when the screw 3 reaches the metering end position, suckback processing is executed (step S2). In the suck-back process, the control unit 35 controls the driving of the injection servomotor 30 and executes control to move the injection servomotor 30 backward by a predetermined distance Ls [mm] at a preset backward movement speed Vs (step S3). Note that the predetermined distance Ls can be set by distance, time, or position. As a result, the pressure in the heating cylinder 13 is released, and the resin pressure (back pressure) Pb becomes zero.
[0016]
Next, a resin pressure offset process is executed upon completion of the suck back process (step S4). In the resin pressure canceling process, the control unit 35 controls the driving of the injection servomotor 30 and performs control to move the screw 3 backward so as to offset the increase in the resin pressure Pb generated after the suck back process (step S5). .
[0017]
As a specific control method, the retreating movement characteristic of the screw 3 for offsetting the increase in the resin pressure Pb is obtained in advance by actual trial molding or the like, and the retreating movement characteristic is registered and according to the registered retreating movement characteristic. The screw 3 is moved backward, that is, the screw 3 is moved backward by open loop control.
[0018]
On the other hand, as another control method in the resin pressure offset processing, the resin pressure Pb is detected by the resin pressure sensor 37, a target value for the resin pressure Pb is set to 0, and the control unit 35 cancels the resin pressure Pb. It is also possible to perform feedback control (closed loop control) on the rotation of the servo motor 22 for measurement. Note that, instead of the resin pressure Pb detected by the resin pressure sensor 37, a resin pressure (back pressure) Pb detected by a load cell 41 interposed between the slide block 18 and the rotary block 20 shown in FIG. Is also possible.
[0019]
By executing such a resin pressure offset process, the resin pressure Pb can be maintained at 0 even after the suck back process. Then, when the termination condition of the resin pressure offset processing, for example, immediately before the injection step is performed, the resin pressure offset processing is terminated (step S6). Thereby, all the measuring steps are completed, and the process shifts to the next step, the injection step (step S7). In FIG. 3, Xa [mm] is the suck back start position, Xb [mm] is the suck back end position, Vs [mm / s] is the retreat movement speed of the screw 3 during suck back processing, and Xc [mm] is The end positions of the resin pressure offset processing are respectively shown.
[0020]
According to the weighing method according to the present embodiment, after the screw 3 is rotated and weighed, the screw 3 is moved backward by the predetermined distance Ls to perform the suck-back process. Since the screw 3 is moved backward so as to offset the increase in the resin pressure Pb generated after the suck-back process by the resin-pressure canceling process, the resin-pressure canceling process complements the suck-back process and provides a high degree of precision for molded products. It can realize high quality and high homogeneity, and can sufficiently cope with diversifying resin grades.
[0021]
Although the embodiments have been described in detail above, the present invention is not limited to such embodiments, and arbitrarily changes and additions can be made in the details of the configuration, shape, method, and the like without departing from the gist of the present invention. , Can be deleted. For example, an electric injection molding machine has been exemplified, but the invention can be similarly applied to a hydraulic injection molding machine.
[0022]
【The invention's effect】
As described above, according to the present invention, the screw retreating characteristic for canceling the increase in the resin pressure is set in advance, the screw is rotated to perform the measurement, and then the screw is retracted a predetermined distance to perform the suck-back process. At the same time, after that, the resin pressure offset processing of moving the screw backward according to the backward movement characteristic so as to offset the increase in the resin pressure occurring after the suck back processing is performed. It has a remarkable effect that it can realize homogeneity and can sufficiently cope with diversifying resin grades.
[Brief description of the drawings]
FIG. 1 is a flowchart for sequentially explaining a weighing method of an injection molding machine according to a preferred embodiment of the present invention;
FIG. 2 is a configuration diagram of an injection molding machine capable of performing the same measurement processing method;
FIG. 3 is a profile characteristic diagram of a screw rotation speed, a screw retreat movement speed, and a resin pressure (back pressure) with respect to a screw position when the weighing method is performed.
FIG. 4 is a profile characteristic diagram of a screw rotation speed, a screw retreat movement speed, and a resin pressure (back pressure) with respect to a screw position when a weighing method according to the related art is performed;
[Explanation of symbols]
2 Drive mechanism 3 Screw M Injection molding machine Ls Predetermined distance Pb Resin pressure

Claims (1)

In a weighing method for an injection molding machine that performs measurement by rotating a screw by a drive mechanism, a retreating movement characteristic of a screw that cancels the increase in the resin pressure is set in advance, and the screw is rotated to perform measurement. A resin that moves the screw backward by a predetermined distance to perform a suck-back process, and thereafter, a resin that moves the screw backward according to the backward-moving characteristic so as to offset an increase in resin pressure generated after the suck-back process. A weighing method for an injection molding machine, comprising performing a pressure offset processing.

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