JPH03213320A - Injection device for motorized injection molding machine - Google Patents

Abstract

PURPOSE:To eliminate the necessity of a large injection servo motor and reduce the cost by disposing a variable reduction gear between the servo motor and an injection mechanism and driving the injection mechanism by the servo motor through the variable reduction gear. CONSTITUTION:At the starting time of injection, injection pressure is not controlled, and the ratio of a variable reduction gear 4 is set small, while an injection mechanism 3 driven at high speed and a screw 1 is moved at the set speed. When the screw 1 reaches the switchover position for dwelling, a speed reduction ratio changing signal of the variable reduction gear 4 is output through an output circuit 108 by a CPU 102 for PAC, and said signal is converted from a digital signal to an analog signal by a D/A converter 6 and input into the variable reduction gear to get the speed reduction ratio of the variable reduction gear 4 of a large value. After that, when the dwelling process is completed, the speed reduction ratio of the variable reduction gear 4 of is restored to the original by CPU 102 through the output circuit 108 and the D/A converter 6 to restore the speed reduction ratio of the variable reduction gear 4 and discontinue the output of a pressure switchover of signal. As a result, the speed reduction gear ratio of the variable reduction gear 4 gets small and an injection pressure circuit in a servo circuit 104 is switched over to the opened loop control.

Description

[Detailed description of the invention] Industrial applications The present invention relates to an injection device for an electric injection molding machine.

The conventional technology screw is driven by a servo motor through an injection mechanism,
In an electric injection molding machine that performs injection, the injection pressure is controlled by controlling the output torque of the servo motor for injection.

In the case of this injection pressure control, an open loop control method (for example, Japanese Patent Laid-Open No. 1-288419) controls the injection pressure by limiting the output torque of the injection servo motor;
A method is known that detects the pressure applied to the resin and performs closed-loop control so that the detected pressure matches the command injection pressure (for example, Japanese Patent Laid-Open No. 62-97818, Japanese Patent Laid-Open No. 64-18619, etc.). ).

However, in any case, these injection pressure control systems control the injection pressure by controlling the output torque of the injection servo motor.

Problems to be Solved by the Invention In the injection process, a large injection pressure is required during the pressure holding stage. Also, a high injection speed is required until the pressure holding stage is reached. Therefore, the injection servo motor requires a large motor that can rotate at high speed and output large torque, which causes an increase in the cost of the electric injection molding machine.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an injection device that does not require a large injection servo motor.

Means for Solving the Problems The present invention solves the above problems by disposing a variable speed reducer between the servo motor and the injection mechanism, and driving the injection mechanism with the servo motor via the variable speed reducer. did.

In the injection process, in the injection speed control section, the reduction ratio of the variable reducer is reduced to enable the screw to move at high speed, and the injection speed is controlled. On the other hand, in the holding pressure section,
The reduction ratio is increased, the moving speed of the screw is decreased, the force applied to the resin is increased, and the injection pressure (holding pressure) is controlled by controlling the reduction ratio of the variable reducer.

Example Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a block diagram showing an electric injection molding machine according to an embodiment of the present invention and the main parts of the control system of the injection molding machine, in which reference numeral 1 is a screw, numeral 2 is a heating cylinder, and numeral 3 is a block diagram showing rotational motion in a straight line. This is an injection mechanism that converts the motion into motion and drives the screw 1 in the axial direction, and a pressure sensor 5 is installed inside the injection mechanism 3 to detect the pressure from the resin applied in the axial direction of the screw 1. Reference numeral 4 denotes a variable speed reducer whose speed reduction ratio changes depending on the input voltage, which slows down the output rotation of the injection servo motor M1 and transmits it to the injection mechanism. Also,
Pl is a pulse coder attached to the injection servo motor M1 for detecting the current position of the screw 1.

Reference numeral 100 denotes a numerical control device (hereinafter referred to as an NC device) that controls the injection molding machine, and the NC device 100 includes a microprocessor for NC (hereinafter referred to as a CPU) 101 and a programmable machine controller (hereinafter referred to as a PMC).
The PMC CPU 102 includes a ROM 112 that stores sequence programs, etc. for controlling sequence operations of the injection molding machine, and a PMC RAM.
109 is connected, and the NC CPU 10I has a ROMI that stores a management program that controls the entire injection molding machine.
11 and for injection, clamping, screw rotation,
A servo circuit 104 that drives and controls a servo motor for each axis, such as for an ejector, is connected via a servo interface 110.

In FIG. 1, only the injection servo motor M1 and the servo circuit 104 of the injection servo motor M1 are shown.

106 is a non-volatile shared RAM composed of bubble memory or CMOS memory, and includes a memory section that stores NC programs, etc. that control each operation of the injection molding machine, and stores various setting values, parameters, macro variables, etc. and a setting memory section.

103 is a bus arbiter controller (hereinafter referred to as BAC), and the BAC 103 includes an NC CPU 101 and a PMC CPU 102 . Shared RAM 106, input circuit 1
07. Each bus of the output circuit 108 is connected, and the BAC1
03 controls the bus to be used.

114 is a CRTR7 display purchase manual data input device (referred to as CRT/MDI) connected to the BAC 103 via the operator panel controller 113, and is provided with a CR7 display screen as a graphic display.
The molding condition setting screen is displayed on this display screen, and various setting data can be input by operating various operation keys (software, numeric keypad, etc.).
A RAM 105 is connected to the NC CPU 10I via a bus and is used for temporary storage of data.

An injection servo motor M1 is connected to the servo circuit 104, and the output of the pulse coder P1 is input to the servo circuit 104. Further, the output of the pressure sensor 5 is input to a servo circuit 104. Further, a torque command value for controlling the output torque of the injection servo motor M1 and a switching command for injection pressure control are output from the output circuit 108 to the servo circuit 104. , the aforementioned Japanese Patent Publication No. 62-97
It has a circuit that switches injection pressure control between closed-loop control and oven-loop control, as described in Publication No. 818, and in the case of open-loop control, the output is output from the output circuit 108. The torque command value acts as a torque limit value, and the injection servo motor M1
The output torque will be limited to the command torque limit value, and the injection pressure will be controlled in an open manner. On the other hand, the output circuit 10
When a switching command is output from 8 and closed loop control is performed, the command injection pressure output from the output circuit 108 and the actual pressure applied to the resin are compared, and the pressure applied to the resin is adjusted to the command injection pressure. Feedback control will be performed so that

The open-loop control and closed-loop control of this injection pressure control are described in the above-mentioned Japanese Patent Application Laid-Open No. 62-9781.
Since it is well known from Publication No. 8, etc., detailed explanation will be omitted.

On the other hand, the output circuit 108 is further connected to the D/A converter 6 and controls the input voltage of the variable reducer 4 via the D/A converter 6 to control the reduction ratio of the variable reducer 4. It looks like this.

The setting memory section of the shared RAM 106 is loaded.

Various molding conditions such as holding pressure, metering, and cylinder temperature are stored as parameters, and the NC device 1100 has a shared RAM 1.0.
While the 2MC CPU 102 performs sequence control based on the NC program stored in the 6, the various molding conditions described above, and the sequence program stored in the ROM 112, the NC CPU 01 controls each axis of the injection molding machine. Pulses are distributed to the servo circuit via the servo motor interface 110 to control the injection molding machine.

Since these hardware configurations are similar to those of a conventional electric injection molding machine, the details will be omitted, and the injection pressure control method of the present invention will be explained with reference to the operation flowchart of FIG. 2.

First, when setting the molding conditions, the screw position for switching the injection pressure, the injection pressure of each stage, the pressure holding time during pressure holding, etc. are set. In this embodiment, injection pressure control is not performed from the start of injection to the pressure holding start screw position, and the torque limit value is set to the maximum torque value of the injection servo motor. As a result, open loop control is performed in which the torque command value is the maximum torque value.

Further, this embodiment employs an example in which the pressure holding process is performed in four stages, and the pressure in each stage and the pressure holding time in each stage are set.

The 2MC CPU 102 repeatedly executes one cycle of injection molding shown in FIG. 2, and first performs a mold closing process (step Sl). This mold closing process is the same as before, and the NC CPU U 1.01 performs the same process based on the NC program.
The CPU 10 for 2MC distributes pulses to the servo circuit that controls the servo motor of the mold clamping mechanism to control mold closing.
2 performs various controls. Then, when the mold closing is completed, P
CPL1102 for MC outputs the injection start command and BAC
When the NC CPU 10I receives this command via the IO3 and the shared RAM 106, the NC CPU 101 starts distributing pulses to the surf circuit 104 via the servo interface 110, and drives the injection servo motor M1 (step S2). At the start of injection, that is, in the injection speed control section, the injection pressure is not controlled and the variable reducer 4
The reduction ratio of the injection servo motor M is set small, and the pressure is controlled in an open loop with no pressure control switching signal input to the servo circuit 104.
The maximum torque value of 1 is output.

In this way, in the injection speed control section, the variable reducer 4
Since the reduction ratio of is small, the injection mechanism 3 is driven at high speed,
The screw 1 will move at the set speed.

On the other hand, the output pulse of the pulse coder P1 is transmitted to the servo circuit 10.
4 to the current value register of the servo interface 110 to determine the current value SA of the screw. N
The C CPUl0I reads this current value SA and sets the BAC
103 to the screw current value storage section of the shared RAM 106, and the PMC CPtJ102 writes the screw current value S written to this screw current value storage section.
A is read (step S3), and it is determined whether the screw position has reached the pressure holding switching value 1isT set in the shared RAM 106 (step S4).

Since the point at which the screw 1 reaches the tip of the heating cylinder 2 is set as the origin, it is determined whether the read current screw position SA is below the set holding pressure switching position ST, and it must be below. For example, steps S3 and 8
4 is repeated and when the screw 1 reaches the pressure holding switching position ST, the PMC CPU 102 outputs a reduction ratio change signal for the variable speed reducer 4 via the output circuit 108, and the D/A converter 6 converts the digital signal into an analog signal and inputs it to the variable reducer. In this way, the variable speed reducer 4
The reduction ratio of is set to a large value (step S5).

Next, a pressure control switching signal is output from the output circuit 108 to the servo circuit 104, and the injection pressure is switched to be controlled in a closed loop (step S6). And share R
Pressure command 1 of the first stage of holding pressure set in AM106,
The pressure command 1 is output to the servo circuit 104 via the output circuit 108, and closed loop control is performed so that the pressure value of the pressure command 1 and the pressure detected by the pressure sensor 5 match. The process is performed (step S7).

Further, the read pressure holding time of the first stage of holding pressure is set in the timer T1 and started, and the timer T1 is waited for to time out (step 38.S9).

When the timer T1 times up, the pressure command 2. of the second stage of holding pressure is sent from the shared RAM 106. The pressure holding time is read out and this pressure holding command 2 is sent to the servo circuit 104 via the output circuit 108.
At the same time, the timer T2 is set to this pressure holding time and started, and waits for the timer T2 to time up (steps 810 to 512).

When the timer T2 times up, the pressure holding command 3. of the third stage of holding pressure is issued from the shared RAM 106. The pressure holding time is read out, the pressure holding time is set and started in the timer T3, and pressure holding control is performed using the third stage pressure holding command 3 until the timer T3 times out (steps 313 to 515). Timer T3
When the time-up occurs, the holding pressure command of the fourth stage of holding pressure 4. The holding pressure time is read from the shared RAM 106, and this fourth holding pressure time is also read out from the shared RAM 106.
Pressure holding control of the stage is performed for a set time (step S1
6-518).

In this way, the pressure is held so that it matches the time set for each stage and the set pressure command value according to the pressure command of each holding pressure stage (1st to 4th stage) set in the shared RAM 106 and the holding pressure time. will be controlled in a closed loop.

In this way, when the pressure holding process is completed, the PMC CPU 10
2 is an output circuit 108. Via the D/A converter 6, the reduction ratio of the variable speed reducer 4 is returned to its original value and the output of the pressure control switching signal is stopped (step S19.520). As a result, the reduction ratio of the variable speed reducer 4 becomes smaller, and thus the servo circuit 10
The injection pressure control circuit in 4 is switched to open loop control.

Then, a weighing process (step 521) and a mold opening process (step 522) are performed as in the conventional case, and one cycle of the injection molding process is completed. When the mold opening process is completed, the process starts again from step S1.

In the above embodiment, the reduction ratio of the variable reducer 4 is switched to two stages, one for injection speed control and one for pressure holding control, and the holding pressure during pressure holding control is changed by controlling the output torque of the injection servo motor. However, during pressure holding control, the output torque of the injection servo motor may be kept constant and the reduction ratio of the variable speed reducer 4 may be controlled to control the holding pressure.

Effects of the Invention In the present invention, the injection mechanism that drives the screw is driven by an injection servo motor via a variable speed reducer.
During injection speed control that requires a high injection speed, the reduction ratio of the variable reducer is reduced to enable high-speed movement of the screw, and during pressure holding control, etc., where high-speed movement of the screw is not required, the variable reduction gear is used. By increasing the reduction ratio of the machine and using the variable reduction gear, the output torque of the injection servo motor is amplified and transmitted to the screw, increasing the injection pressure (holding pressure).
Since the injection servo motor is controlled, a high output motor is not required as the injection servo motor, and an injection servo motor with a smaller output than the conventional injection servo motor can be used.

Furthermore, the injection pressure can be controlled using two factors: the output torque (motor current) of the injection servo motor and the reduction ratio of the variable speed reducer, increasing the degree of freedom in pressure control.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the main parts of an electric injection molding machine according to an embodiment of the present invention, and FIG. 2 is a flow chart of the injection molding operation performed by the embodiment. 1...Screw, 2...Heating cylinder, 3...
Injection mechanism, 4... variable reducer, 5... pressure sensor,
6... D/A converter, Ml... injection servo motor,
Pl... Pulse coder, 100... Numerical control device (
NC device).

Claims (1)

[Claims] In an electric injection molding machine in which the injection mechanism is driven by a servo motor and the screw is moved in the axial direction to perform injection, a variable reducer is disposed between the servo motor and the injection mechanism to variable reduce the speed of the injection mechanism. An injection device for an electric injection molding machine that is driven by a servo motor through the machine.