JPH0446215B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an injection motor control method for an injection molding machine, and more particularly to an injection motor control method that prevents the injection motor from overheating.

BACKGROUND OF THE INVENTION It is known that a synchronous motor (hereinafter referred to as a motor) is used as a drive source for an injection device in an injection molding machine.

The injection motor as the drive source of this injection device is
This device performs back pressure during injection, pressure holding, and metering, but since the output torque is small during injection operation and back pressure application, an extremely small drive current flows through the injection motor, and the output torque must be increased during pressure holding. Therefore, an extremely large drive current flows. On the other hand, injection motors are selected taking various design conditions such as economic efficiency into consideration, and therefore, large-capacity motors whose motor current does not exceed the continuous rated current are not generally used as injection motors. The injection motor drive current during pressure holding greatly exceeds the continuous rated current of the motor, and the average value of the drive current flowing through the injection motor during one injection molding cycle may also exceed the continuous rated current. In such a case, since the amount of heat generated by the injection motor is proportional to the square of the drive current, problems such as overheating of the injection motor occur.

Problems to be Solved by the Invention The present invention solves the drawbacks of conventional injection motor control in that the average injection motor current exceeds the continuous rated current and tends to overheat, and improves the specifications of the injection motor and injection molding machine. It is an object of the present invention to provide an injection motor control method for an injection molding machine that can take measures against overheating of the injection motor without making any changes.

Means for Solving the Problems The injection motor control method for an injection molding machine of the present invention includes:
It is determined whether or not an overheating condition has been established in which the integral value of the calorific value due to the injection motor drive current over one injection molding cycle exceeds the allowable integral value of the calorific value when a continuous rated current flows, and the overheating condition is determined. The configuration is such that a predetermined avoidance action is performed when the situation is established.

Effect: An overheating state is established in which the integral value of the amount of heat generated by the injection motor drive current over one injection molding cycle exceeds the allowable integral value of the amount of heat generated when the rated current is passed through the injection motor continuously over one injection molding cycle. It is determined whether or not. When the overheating condition is established, a predetermined avoidance operation is performed to eliminate the condition, and for example, the next injection molding cycle is executed after a pause period corresponding to the difference between the integral value of the calorific value and the allowable integral value has elapsed. The actual calorific value integral value is prevented from exceeding the allowable integral value, or the operation of the injection molding machine is stopped along with an alarm operation.

Embodiment FIG. 3 shows the main part configuration of an injection molding machine to which the injection motor control method of the present invention is applied.
(referred to as a device) 1 controls the drive of servo motors for each axis such as injection, clamp, screw rotation, and ejector, and various actuators (only the injection motor 3 that drives the screw 2 in the injection direction is shown). The NC device 1 includes a numerical control microphone processor (hereinafter referred to as NC CPU) 10 and a program controller microprocessor (hereinafter referred to as PC CPU) 20.

The NC CPU 10 includes a ROM 11 that stores a management program that controls the entire injection molding machine, and a ROM 11 that stores a management program that controls the injection molding machine as a whole and a ROM 11 that stores data temporarily during various calculation processes.
The RAM 12 is also connected to the servo circuit for each axis (only the servo circuit 14 for the injection motor 3 is shown) via the servo interface 13. On the other hand, the CPU 20 for the PC is connected to the sequence control for the injection molding machine. A ROM 21 storing programs and the like is connected. Furthermore, both CPU1
A bus arbiter controller (hereinafter referred to as BAC) 31 connected to terminals 0 and 20 has a backup power source and stores control programs for controlling various operations of the injection molding machine and various setting values described below. Non-volatile shared RAM32, MDI/CRT
An operator panel controller 34 to which 33 is connected, an input circuit 35 and an output circuit 36 are connected to each other via a bus. Although not shown, various actuators and the like are connected to both the circuits 35 and 36.

Injection motor control executed in the injection molding machine configured as described above will be explained below with reference to FIGS. 1 and 2.

First, the concept of injection motor control according to an embodiment of the present invention will be explained with reference to FIG. When an injection device using a motor as a drive source in an injection molding machine performs pressure holding, metering, and kneading processes following injection of molten resin, the injection motor has an output during injection, metering, and kneading, as shown in Figure 2. Since the torque is small, an extremely small drive current flows, and when the pressure is held, the output torque is large, so an extremely large drive current flows. Therefore, the integral value of the amount of heat generated by the drive current flowing to the injection motor during one injection molding cycle is calculated during pressure holding. It can be approximated by the integral value of the amount of heat generated by the drive current that flows through the pump, and the drive current value during holding pressure can be approximated by the set holding pressure, and since the amount of heat generated is proportional to the square of the current,
The integral value of the amount of heat generated during one cycle can be obtained by integrating the square of the set holding pressure over the holding pressure time.

This example focuses on the above point, and determines whether or not an overheating state exists in which the integral value of the heat generation amount due to the drive current during one injection molding cycle exceeds the allowable integral value when continuous rated current flows. In order to do this, the product value CT・(MP) ² of the detected injection molding cycle time CT and the square of the generated pressure MP at the time of maximum output torque output of the injection motor, and the set holding pressure at each holding pressure stage of the injection molding cycle. HPi (i=1
-3) squared and the set pressure holding time HTi, the sum Σ(HPi) Ratio of ²・HTi (={Σ
(HPi) ² ·HTi}/{MP) ² ·CT)} and determines whether the ratio R exceeds a predetermined allowable ratio Rmax. Then, when the overheating state is established, execution of the next injection molding cycle is delayed for a required rest period DW, and the ratio R is set to a ratio R′(={Σ(HPi) ²・HTi}/{(MP) ²・(CT+
DW)}). Here, the ratio
In order to set R' to a value equal to or smaller than the predetermined allowable ratio Rmax, it is sufficient to make the following formula (1) hold.

{{Σ(HPi) ²・HTi}/{(MP) ²・(CT+DW)}≦Rmax That is, DW≧[{Σ(HPi) ²・HPi)/{(MP) ²・Rmax}]−CT… (1) FIG. 1 shows a control program executed by both CPUs 10 and 20 for injection motor control according to an embodiment of the present invention. First, in step 101, the PC CPU 20 calculates the injection molding cycle time by software. Measurement timer (hereinafter referred to as CT)
(referred to as a timer) is reset and started.
Next, various servo motors and actuators are controlled by the NC CPU 10 and the PC CPU 20, and one injection molding cycle, that is, injection by the injection device, pressure holding, measuring/kneading process, mold clamping by the mold clamping device, mold opening process, and eject device. The process of ejecting the molded product using the machine and the process of ejecting the product using the product take-out device are carried out (step
102). In addition, both CPUs in the injection molding cycle
Since the contents of control by 10 and 20 are not directly related to the present invention, their explanation will be omitted.

When one injection molding cycle is completed,
The CT timer is stopped by the PC CPU 20 (step 103), and the timer value CT and MDI/CRT are
Setting holding pressure Pi (in this embodiment, i
= 1, 2, 3), the set pressure holding time HTi, the generated pressure MP at the time of maximum output torque output of the injection motor, and the predetermined ratio Rmax are read out (step 104). Next, based on these measured values and set values, the following formula (2)
The pause period DW is calculated from (step 105).

DW=[{Σ(HPi) ²・HTi}/ {(MP) ²・Rmax}]−CT…(2) Then, in step 106, the calculated pause period is
Determine whether DW is a positive value or not, and if the calculated value is positive
The PC CPU 20 sets a software pause timer to the calculated value DW, and starts the timer (steps 107 and 108). Then, after delaying the start of the next injection molding cycle until the pause timer times out (step 109), the above steps are performed.
Return to 101. On the other hand, if it is determined in step 106 that the value DW is negative or zero, the step is immediately executed.
Move to 101.

Next, an injection motor control method according to another embodiment of the present invention will be described. In this embodiment, when an overheating state occurs, the next injection molding cycle is executed after a pause period corresponding to the difference between the integral value of the heat generation amount due to the drive current of the injection motor during the injection molding cycle and the allowable integral value. Unlike the above-mentioned embodiment, when an overheating state is established, an alarm is activated and the operation of the injection molding machine is stopped. For this reason, the same processing as Steps 101 to 106 in FIG. 1 is performed to determine whether or not the calculated suspension period DW is a positive value, and if the calculated value is positive, an alarm operation is performed using a conventionally known method. , the operation of the injection molding machine is stopped; on the other hand, if it is negative or zero, the next injection molding cycle is started without issuing an alarm.

In addition, when an alarm is issued and operation is stopped, the operating times for mold opening, mold closing, etc. are reset to prevent the injection motor from overheating.

Effects of the Invention As described above, according to the present invention, an overheating state is established in which the integral value of the amount of heat generated by the injection motor drive current over one injection molding cycle exceeds the allowable integral value when a continuous rated current flows. Since the system determines whether or not the overheating condition is present and performs a predetermined avoidance operation when the overheating condition is established, the overheating condition of the injection motor can be resolved.In other words, the average injection motor current exceeds the continuous rated current and the injection motor overheats. This eliminates the disadvantage of conventional injection motor control that the injection motor is easy to control, and prevents the injection motor from overheating without changing the specifications of the injection motor and injection molding machine.

[Brief explanation of the drawing]

FIG. 1 is a flowchart of a control program for implementing an injection motor control method according to an embodiment of the present invention, FIG. 2 is a diagram for explaining the concept of injection motor control according to the embodiment, and FIG. 1 is a diagram illustrating a main part of an injection molding machine to which the control method of the same embodiment is applied. 1... Numerical control device, 2... Screw, 3...
Injection motor, 10... Numerical control microprocessor, 11... ROM, 12... RAM, 13...
... Servo interface, 14 ... Servo circuit, 20 ... Microprocessor for program controller, 21 ... ROM, 31 ... Bus arbiter controller, 32 ... Shared RAM, 33 ...
...MDI/CRT, CT...Detection injection molding cycle time, MP...Maximum pressure generated by the injection motor MP,
HPi...Setting holding pressure, HTi...Setting holding pressure time, R,
R′...Ratio, Rmax...Predetermined allowable ratio, DW...
hiatus period.

Claims (1)

[Claims] 1. Whether or not an overheating state has been established in which the integral value of the calorific value due to the injection motor drive current over one injection molding cycle exceeds the allowable integral value of the calorific value when a continuous rated current flows. An injection motor control method for an injection molding machine that performs a predetermined avoidance operation when the overheating state is established. 2. An injection motor control method for an injection molding machine according to claim 1, wherein, as the avoidance operation, the next injection molding cycle is executed after a pause period corresponding to the difference between the integral value of the calorific value and the allowable integral value has elapsed. . 3 Detect the injection molding cycle time, and calculate the product value of the detected injection molding cycle time and the square of the pressure generated at the maximum torque output of the injection motor, and the set pressure holding time at each pressure holding stage of the injection molding cycle. When the ratio of the sum of the product values and the value obtained by squaring the set pressure holding time exceeds a predetermined allowable ratio, it is determined that the overheating state has been established, and the sum is divided into the value obtained by squaring the maximum generated pressure and the sum of the products. The injection motor of an injection molding machine according to claim 2, wherein the pause period is set to a value greater than or equal to a value obtained by subtracting the detected injection molding cycle time from a value obtained by dividing by a product value with a predetermined allowable ratio. Control method. 4. The injection motor control method for an injection molding machine according to claim 1, wherein an alarm operation is performed as the avoidance operation and the operation of the injection molding machine is stopped.