JP2537725B2 - Control method of injection molding machine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling an injection molding machine in which a hydraulic circuit drives and controls a multistage hydraulic cylinder.

[0002]

2. Description of the Related Art Conventionally, an injection molding machine equipped with a multi-stage hydraulic cylinder is known from Japanese Utility Model Laid-Open No. 2-146017 and Japanese Patent Publication No. 59-15295, and the former injection molding machine is a screw type. Multiple pairs of single hydraulic cylinders, which are arranged in parallel at positions symmetrical with respect to the axis, are connected to the screw.The latter injection molding machine has several different diameters in stages. The rams are connected in the order of increasing diameter, and the working chamber composed of this ram and the cylinder is formed into a cylindrical shape.At the same time, an oil inflow pipe is connected to each working chamber to guide it to the directional control valve. Oil is press-fitted into the working chambers at the same time or with a time difference between the working chambers to operate the hydraulic cylinders.

By the way, usually, in the injection process of filling the resin into the mold cavity, the speed of the screw is controlled, and the magnitude of the speed is controlled based on the variable injection pressure. On the other hand, the resin that has flowed into the mold cavity is cured more rapidly toward the outside (skin layer), and the resin flow state in the mold cavity is not constant. For this reason, the magnitude of the injection pressure varies depending on the flow state of the resin, and the molding quality is greatly influenced. That is, the residual stress on the resin changes according to the flow state of the resin,
This causes molding defects such as warpage and distortion.

However, in the conventional control method in the injection molding machine which employs the multi-stage hydraulic cylinder, the pressure change is stepped, so that the pressure control cannot be performed with high accuracy and stability, and the molding quality is improved. There was a limit.

The present invention has solved the problems existing in the prior art as described above. Even when a multi-stage hydraulic cylinder is used, it is possible to perform pressure control with high accuracy and stability to improve molding quality. In addition, since the pressure control is shared by the meter-in circuit and the meter-out circuit, it is an object of the present invention to provide a control method for an injection molding machine that can simplify the entire hydraulic circuit.

[0006]

A control method for an injection molding machine according to the present invention is a switching valve V1 forming a meter-in circuit 12 of a hydraulic circuit 10 when a hydraulic circuit 10 drives and controls a multi-stage hydraulic cylinder 2. , V2, V3, V4, V
By controlling 5, V6, V7, one or more of the plurality of oil chambers Ca, Cb, Cc, Cd in the multistage hydraulic cylinder 2 is selected to supply the pressure oil, and the magnitude of the injection pressure P is increased. From the hydraulic cylinder 2
The return oil pressure control valve constituting the meter-out circuit 11 of a hydraulic circuit 10 for varying the pressure of 11p, by controlling the 11m, continuously variable size of each injection pressure P is switched by the meter circuit 12 Linearity of injection pressure
It is characterized in that control is performed .

[0007]

According to the control method of the injection molding machine of the present invention,
On the meter-in circuit 12 side of the hydraulic circuit 10, the switching valve V
By controlling 1, V2, V3, V4, V5, V6, V7, one or more of the plurality of oil chambers Ca, Cb, Cc, Cd in the multi-stage hydraulic cylinder 2 is selected to supply the pressure oil. Therefore, the injection pressure P, that is, the magnitude of the output F [kg] with respect to the screw can be changed stepwise.

For example, a first oil chamber Ca having a pressure receiving area Sa [cm ² ], a second oil chamber Cb having a pressure receiving area Sb [cm ² ] and a third oil having a pressure receiving area Sc [cm ² ]. There is a chamber Cc and a fourth oil chamber Cd that has a pressure receiving area Sd [cm ² ] and generates a reverse pressure, and the relationship between them is Sd <Sa <Sb <Sc, and the pressure receiving area Sa [ cm ² ] and the hydraulic pressure Pi of the hydraulic circuit 10 [kg / c
m ² ] product is Fa [kg], pressure receiving area Sb [cm ² ] and hydraulic pressure Pi [kg / cm ² ] product is Fb [kg], pressure receiving area Sc [cm ² ] and hydraulic pressure Pi [kg / cm ^2] ] Of Fc
[Kg], pressure receiving area Sd [cm ² ] and hydraulic pressure Pi [kg /
If the product of cm ² ] is Fd [kg], the output to the screw 3 is F1 = Fa−Fd, F2 = Fa, F3.
= Fb-Fd, F4 = Fb, F5 = Fa + Fb-Fd,
F6 = Fa + Fb, F7 = Fc−Fd, F8 = Fc, F
9 = Fa + Fc−Fd, F10 = Fa + Fc, F11 =
Fb + Fc-Fd, F12 = Fb + Fc, F13 = Fa
It is possible to select fourteen different sizes of + Fb + Fc-Fd and F14 = Fa + Fb + Fc, in other words, fourteen different injection pressures.

On the other hand, the meter-out circuit 1 of the hydraulic circuit 10
On the 1st side, the pressure of the return oil can be controlled by controlling the pressure control valves 11p and 11m, whereby the output F1 ... (Injection pressure P) switched by the meter-in circuit 12 can be continuously varied in magnitude. it can. That is, back pressure control is possible at each output F1 ... (Injection pressure P), and continuous linearity control is performed for each output F1 ... (Injection pressure P) even if the pressure on the meter-in circuit 12 side is constant. You can

[0010]

Next, preferred embodiments according to the present invention will be described in detail with reference to the drawings.

First, the structure of an injection molding machine capable of implementing the control method according to the present invention will be described with reference to FIG.

In the figure, reference numeral 1 is an injection molding machine, and in particular,
A part of an injection device is shown. Reference numeral 3 denotes a screw, the front end side of which is inserted into a heating cylinder (not shown), and the rear end of the screw 3 is supported by a screw drive mechanism E. The screw drive mechanism E includes a tubular casing block 21, and the rear end of the casing block 21 is closed by an oil motor support block 22. The casing block 2
The rear part of 1 constitutes a multistage hydraulic cylinder 2.

Reference numeral 8 denotes an outer cylinder portion, and an inner cylinder portion 9 is coaxially arranged inside the outer cylinder portion 8 via a gap G2. The rear end of the inner cylinder portion 9 is integrally formed with the oil motor support block 22, so that the rear portion 8n of the outer cylinder portion 8 and the rear portion 9n of the inner cylinder portion 9 are configured as a coupled cylinder block 7.

On the other hand, 6 is a cylindrical outer piston portion, and the inner piston portion 5 is coaxially arranged inside the outer piston portion 6 with a gap G1. The front part 6t of the outer piston part 6 has bearings 23, 2 with respect to the front part 5t of the inner piston part 5.
It is rotatably coupled via 4 and thereby constitutes the piston block 4. The inner cylinder portion 9 has a gap G.
1 and the outer piston portion 6 is inserted into the gap G2.

With the above construction, the first oil chamber Ca is located behind the inner piston part 5, the second oil chamber Cb is located in front of the inner cylinder part 9, and the third oil chamber Cb is located behind the outer piston part 6. Oil chamber C
A fourth oil chamber Cd for applying a pressure in the opposite direction is provided between the outer piston portion 6 and the outer cylinder portion 8 in front of the outer piston portion main body 6u. In this case, the pressure receiving area Sa of the oil chamber Ca, the pressure receiving area Sb of the oil chamber Cb, the oil chamber C
The pressure receiving area Sc of c and the pressure receiving area Sd of the oil chamber Cd have a relationship of Sd <Sa <Sb <Sc, and desirably Sa: Sd = 2: 1, Sb: Sd = 4: 1, Sc. :
It is selected so that Sd = 8: 1.

The piston block 4 projects forward from the front end 8f of the outer cylinder portion 8, and the rear end of the screw 3 is connected to the front end 5f of the inner piston portion 5. On the other hand, the oil motor 25 is provided on the rear end surface of the oil motor support block 22.
The rotation shaft 25 of the motor 25
s penetrates the center of the oil motor support block 22,
Further, the rear end 5r of the inner piston portion 5 is passed through the oil chamber Ca.
Is connected by a spline mechanism 26.

Therefore, if the hydraulic cylinder 2 constituting the injection drive system is operated and controlled, the screw 3 can be moved forward and backward, and if the oil motor 25 constituting the metering drive system is operated and controlled, the screw 3 is rotationally controlled. it can.

On the other hand, a hydraulic circuit 10 is connected to each oil chamber Ca, Cb, Cc and Cd. In this case, oil chambers Ca, C
The meter-in circuit 12 is connected to b and Cc, and the meter-out circuit 11 is connected to the oil chamber Cd. The meter-in circuit 12 side includes a hydraulic pump 31, an oil tank 32, four-port switching valves V1, V2, V3, V4, V6, V7, a three-port switching valve V5, relief valves 33, 34, and the meter-out circuit 11 side. Is provided with a main relief valve (pressure control valve) 11m and a pilot relief valve (electromagnetic proportional pressure control valve) 11p, which are connected as shown in FIG.

Further, the meter-out circuit 11 is provided with an arithmetic processing unit 35, and an oil pressure sensor 36 and a setting unit 37 connected to the discharge line of the hydraulic pump 31 are connected to the input side of the arithmetic processing unit 35, and the arithmetic processing is performed. The output side of the portion 35 is connected to the control input side of the pilot relief valve 11p via the amplifier 38. In this case, if the setting unit 37 sets the injection pressure P, the arithmetic processing unit 35 outputs a switching valve control command to control switching of the switching valves V1 to V7, and
A pressure control command is output to variably control the pilot relief valve 11p of the meter-out circuit 11.

Next, the overall operation of the injection molding machine 1 including the control method according to the present invention will be described.

First, by the hydraulic circuit 10, each oil chamber Ca,
If one or more of Cb, Cc and Cd are selected and pressure oil is supplied, the output to the screw 3 is F1 = Fa−
Fd, F2 = Fa, F3 = Fb−Fd, F4 = Fb, F
5 = Fa + Fb−Fd, F6 = Fa + Fb, F7 = Fc
-Fd, F8 = Fc, F9 = Fa + Fc-Fd, F10
= Fa + Fc, F11 = Fb + Fc-Fd, F12 = F
b + Fc, F13 = Fa + Fb + Fc-Fd, F14 =
Fourteen sizes of Fa + Fb + Fc can be selected. In this case, the magnitude of the output Fa is the product of the pressure receiving area Sa of the oil chamber Ca and the hydraulic pressure Pi of the hydraulic circuit 10 (Sa × Pi), and the output Fb.
Is the product of the pressure receiving area Sb of the oil chamber Cb and the oil pressure Pi (S
b × Pi), the size of the output Fc is the pressure receiving area S of the oil chamber Cc
The product of c and the oil pressure Pi (Sc × Pi), and the magnitude of the output Fd is the product of the pressure receiving area Sd of the oil chamber Cd and the oil pressure Pi (Sd × Pi).
And Fd is generated in the negative direction.

FIG. 2 is a control matrix of the switching valves V1 to V7 that are switched and controlled when selecting the outputs F1 to F14, and the circles indicate the switching valves V1 to V7 in FIG. This means switching to the b side. As an example, when the output F1 is selected, the switching valve V1 is on the symbol a side, the switching valve V2 is on the symbol b side, the switching valve V3 is on the symbol b side, and the switching valve V4 is on the symbol b side. V5 is switched to the symbol b side, switching valve V6 is switched to the symbol a side, and switching valve V7 is switched to the symbol b side. In the other output modes, the switching valves V1 to V7 are similarly switched and controlled according to the control matrix shown in FIG.

On the other hand, in FIG. 3, the vertical axis represents the injection pressure P [kg / c
m ² ], a horizontal axis is an output F [kg] with respect to the screw 3, and is a characteristic diagram showing the magnitude of the output F corresponding to the injection pressure P. That is, if the switching valves V1 to V7 are switch-controlled in accordance with the control matrix shown in FIG. 2, the output F changes stepwise as shown in FIG. As an example, if the injection pressure P6 is specified, the output F6 is output, and at this time, the switching valves V1 to V7 corresponding to F6 in FIG.
Are switched and controlled. The magnitude of the injection pressure P6 is F6.
/ Ss (Ss: heating cylinder cross-sectional area) and other injection pressure P
1 and the like are set in advance in the setting unit 37 so as to be designated or selectable.

The main relief valve 11m and the pilot relief valve 11p which constitute the meter-out circuit 11 are also provided.
Thus, by controlling the back pressure of the return oil, it is possible to perform continuous linearity control with respect to the injection pressure P. The linear function characteristic expressed in a straight line in FIG. 3 is a case where such control is performed. That is, as an example, the injection pressure P shown in FIG.
If x is designated, the switching valve control command is output from the arithmetic processing unit 35, and the switching valves V1 to V1 corresponding to F6 in FIG.
V7 is switch-controlled. On the other hand, the arithmetic processing unit 35 calculates the back pressure of the return oil in the meter-out circuit 11 according to the linear function characteristic shown in FIG. 3, and gives a corresponding pressure control command to the pilot relief valve 11p via the amplifier 37. The relief valve 11P is variably controlled. This allows
The magnitude of the output to the screw 3 is Fx. Thus, since the back pressure control is also used for each selected output F, continuous linearity control with respect to the injection pressure P can be easily performed.

The embodiment has been described in detail above.
The present invention is not limited to such an embodiment.
For example, the multi-stage hydraulic cylinder is not limited to the example, and can be applied to any multi-stage hydraulic cylinder configured in another form. In addition, the detailed configuration, shape, and the like can be arbitrarily changed without departing from the scope of the present invention.

[0026]

As described above, the control method for the injection molding machine according to the present invention controls one or more of the plurality of oil chambers in the multi-stage hydraulic cylinder by controlling the switching valve forming the meter-in circuit of the hydraulic circuit. Select two or more to supply pressure oil,
The injection pressure can be changed stepwise and the hydraulic pressure
By controlling the pressure control valve that constitutes the meter-out circuit of the hydraulic circuit that varies the pressure of the return oil from the Linda, the magnitude of each injection pressure switched in the meter-in circuit can be continuously varied to Since linearity control is performed , even if a multi-stage hydraulic cylinder is used, high-precision and stable pressure control can be performed to improve molding quality, and pressure control is shared by the meter-in circuit and meter-out circuit. The remarkable effect that the entire hydraulic circuit can be simplified.

[Brief description of drawings]

FIG. 1 is a partial configuration diagram including a partial cross section of an injection molding machine that implements a control method according to the present invention;

FIG. 2 is a control matrix diagram of each switching valve with respect to output,

FIG. 3 is a characteristic diagram showing the relationship between output and injection pressure,

[Explanation of symbols]

 2 hydraulic cylinder 10 hydraulic circuit 11 meter-out circuit 11p pressure control valve 11m pressure control valve 12 meter-in circuit V1 ... switching valve Ca ... oil chamber

Claims (1)

(57) [Claims] 1. A method for controlling an injection molding machine in which a hydraulic circuit drives and controls a multi-stage hydraulic cylinder, wherein a plurality of oils in the multi-stage hydraulic cylinder are controlled by controlling a switching valve that constitutes a meter-in circuit of the hydraulic circuit. Select one or more chambers to supply pressure oil, change the injection pressure stepwise, and return from the hydraulic cylinder.
By controlling the pressure control valve that constitutes the meter-out circuit of the hydraulic circuit that changes the oil pressure, the injection pressure switched by the meter-in circuit can be continuously changed in magnitude and injected.
A method for controlling an injection molding machine, characterized in that linearity control of the entire pressure is performed .