JPH0813485B2 - Holding pressure control method for electric injection molding machine - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding machine, and more particularly to a pressure holding control method for an electric injection molding machine.

2. Description of the Related Art In an electric injection molding machine that is controlled by a numerical control device that moves a screw in the axial direction by a servo motor to inject and hold pressure, the servo motor is used to apply a predetermined holding pressure during the pressure holding process. A torque limit must be applied to limit the output torque to a torque corresponding to the holding pressure, and a screw forward command to move the screw forward in order to maintain the holding pressure must be commanded. With this screw forward command, it is necessary to command the final target position and feed rate, but the screw forward position (the position where the minimum cushion amount remains in the heating cylinder at the pressure holding is normally set to "0"). The maximum forward position of the screw is commanded as the final target position, and the feed rate is maintained when the feed rate of the holding pressure is low. The reason why the rising of the forward command in the pressure process is delayed and the rising of the holding pressure is delayed, and in order to complete the distribution of the holding pressure movement command as quickly as possible, conventionally, the feeding speed of the holding pressure is Was commanding maximum speed.

Problems to be Solved by the Invention Pulse distribution is performed on the injection shaft based on the screw forward command, and the screw moves forward according to the distributed pulse amount, but the position corresponding to this distributed pulse amount. The difference between the current value of the screw and the current value of the screw occurs as the position deviation amount of the screw, and feedback control is performed so that this position deviation amount becomes zero. How to increase will also be faster. In the pressure-holding process, the torque of the servomotor is limited to a torque corresponding to the set pressure-holding pressure, so the speed at which the screw follows the screw forward command is slowed down. At the highest speed, the position deviation amount of the screw becomes excessive depending on molding conditions, an alarm is generated, and there is a high possibility that the injection molding operation is stopped.

Therefore, an object of the present invention is to provide a holding pressure control method capable of issuing a holding pressure screw advance command at an optimum feeding speed by making it possible to set the holding pressure feed speed.

Means for Solving the Problems The present invention uses a servomotor as a drive source for axially moving a screw to inject and maintain pressure, and feedback-controls the position of the screw by a numerical controller.
In an electric injection molding machine that controls the screw moving speed and the holding pressure, the screw moving speed command in the command block of the pressure holding process in the NC program is programmed with a macro variable, and the macro variable of the screw moving speed command in the holding pressure is programmed. On the other hand, by solving the above problem, the screw moving speed command at the time of pressure holding can be selected by setting the screw moving speed at the time of pressure holding.

The feed rate command of the screw movement command in the pressure holding process is programmed by a macro variable and any feed rate can be set for this macro variable. Therefore, the feed rate set in the macro variable according to the molding conditions. Just by changing, the position deviation amount becomes excessive and the optimum feed rate that does not generate an alarm can be set.
Continuous molding can be performed without stopping the injection molding operation due to excessive positional deviation.

Embodiment FIG. 1 is a block diagram of an essential part of an electric injection molding machine for carrying out an embodiment of the present invention, in which 1 is a screw and 2 is the screw 1 driven in an axial direction via a transmission device (not shown). The injection shaft servo motor 3 is a position detector that is attached to the motor shaft of the servo motor 2 and detects the position of the screw 1 from the rotational position of the servo motor 2. Further, 10 is a numerical control (NC) device, and the NC device 10 has a microprocessor 11 for NC (hereinafter referred to as CPU) 11 and a CPU 12 for a programmable machine controller (hereinafter referred to as PMC) for PMC. The CPU 12 is connected to the ROM 15 that stores a sequence program or the like for controlling the sequence operation of the injection molding machine, and is also connected to the RAM 22 that is used for temporary storage of data or the like. The NC CPU 11 has a ROM 14 that stores a management program that controls the injection molding machine as a whole, and an injection
A servo circuit for driving and controlling a servo motor for each axis for clamping, screw rotation, ejector, etc. is connected via a servo interface 16, and the position of the screw is feedback-controlled by the servo circuit, and the screw The moving speed and the holding pressure are controlled. In the figure, injection servo motor 2 and servo circuit are shown.
Only 17 is shown.

18 is a non-volatile shared RAM composed of bubble memory and CMOS memory, which controls each operation of the injection molding machine.
It has a memory unit for storing programs and the like, and a memory unit for macro variables for storing various set values and parameters in macro variables. Reference numeral 13 is a bus arbiter controller (hereinafter referred to as BAC), and the BAC 13 includes an NC CPU 11 and a PMC CPU 12, and a shared R.
Each bus of AM18, input circuit 19, output circuit 20 is connected,
It is designed to control the bus used by C13. Reference numeral 24 is a manual data input device with a CRT display device (hereinafter referred to as CRT / MDI) connected to the BAC 13 via an operator panel controller 23. 21 is the CPU 11 for NC
It is used for temporary storage of data in RAM connected to the bus.

Therefore, the parameters of the injection conditions are set to the address positions of the macro variables that specify the parameters via the CRT / MD 124. At this time, the optimum holding pressure feed rate according to the molding condition is also set and stored in the address position of the predetermined macro variable. Set the macro variable that sets the feed speed during this pressure holding to #
Assuming NNN, the block of the NC program of the pressure holding process is programmed as follows.

N210 G90 G01Xx ₁ F # NNN M13; In the pressure-holding process block, N210 is a sequence number, G90 is an absolute command code, G01 is a cutting feed (linear catch) G code, and X is an injection axis. ,
It means a movement command to the servo motor 2 that moves the screw 1 in the axial direction, and the most advanced position x ₁ of the screw ₁ (usually this most advanced position x ₁ is "0" with this point as the origin)
Is programmed. Further, F means a screw forward feed speed command at the time of holding pressure, and a macro variable #NNN in which the feeding speed of holding pressure is set is programmed. Note that M13 is an M code.

As described above, the NC program for the pressure-holding process is programmed, the injection molding machine starts operating in accordance with the NC program, the pressure-holding process is started, and when the block of the sequence number N210 is read, the NC CPU 11 executes the macro. The feeding speed of the holding pressure set in the variable #NNN is read from the shared RAM 18 via the BAC 13, and the pulse distribution is started to the screw forward position of the movement command position x ₁ according to the feeding speed of the holding pressure, and the servo interface 16, The servo motor 2 is driven via the servo circuit 17 to move the screw 1 forward.

In addition, the CPU 11 for NC uses the M code M13 designated by the block of the sequence number N210 through the BAC 13 to share the RAM 18
When the PMC CPU 12 detects that the M13 code has been written in the shared RAM 18, the holding pressure torque limit value set and stored in the shared RAM 18 is transferred to the servo circuit 17 via the BAC 13 and the output circuit 20. Output to the internal torque limit circuit,
The output torque of the servo motor 2 is limited to the torque corresponding to the set holding pressure.

Thus, the screw is driven with the torque corresponding to the set holding pressure and at the feed rate set in the macro variable #NNN to move forward. In this case, the feed pressure of the holding pressure set in macro variable #NNN is set to the optimum feed rate according to the molding conditions, so the position deviation amount does not become excessive and an alarm is generated There is no stopping the molding operation.

If the position deviation amount is excessive and an alarm occurs, the feed rate set in macro variable #NNN is set to CRT / MDI24.
Change the settings further to set a high feed rate that does not cause an alarm for excessive position deviation.

As described above, in the present invention, the screw forward speed during pressure holding can be set to an arbitrary value, and the optimum feed rate during pressure holding is established according to the molding conditions. NC that controls the injection molding when the position deviation amount becomes too large and the alarm is issued when the pressure is maintained according to the conditions.
There is no need to re-execute the program, simply changing the screw movement speed setting value for holding pressure set by the macro variable to obtain the optimum screw movement speed setting value for holding pressure. It is possible to perform the optimal pressure holding control in which the alarm for the excessive deviation amount does not occur and the rising of the pressure holding pressure is made as fast as possible.

[Brief description of drawings]

FIG. 1 is a block diagram of an essential part of an injection molding machine that embodies an embodiment of the present invention. 1 ... screw, 2 ... servo motor, 3 ... position detector, 10 ... numerical control device (NC device).

Claims (1)

[Claims] 1. A servomotor is used as a drive source for injecting and holding a screw by moving the screw in the axial direction, and the position of the screw is feedback-controlled by a numerical controller.
In an electric injection molding machine that controls the screw moving speed and the holding pressure, the screw moving speed command in the command block of the pressure holding process in the NC program is programmed with a macro variable, and the macro variable of the screw moving speed command in the holding pressure is programmed. On the other hand, a pressure holding control method for an electric injection molding machine in which a screw moving speed command during pressure holding can be selected by setting a screw moving speed during pressure holding.