JPH0419118A - Detecting device for abnormality of motor-driven injection molding machine - Google Patents

Abstract

PURPOSE:To detect easily an abnormality at the time of positional control, speed control and torque control, by providing an abnormality monitoring timer putting out an alarm signal when a signal outside of a range is kept applying to an electric current value discriminator of an electric motor for an established period. CONSTITUTION:When an electric current detected signal put out by an electric current detecting instrument 9 for detecting an electric current of a servomotor 1 is applied to an electric current discriminator 10, the electric current discriminator 10 monitors a size of the electric current detected signal and when the signal is larger than a upper limit established value of a monitoring reference value or smaller than a lower limit established value, the signal outside of a range is put out. When the signal outside of the range is kept applying to an abnormality monitoring timer 11 for a period established beforehand, since the timer 11 puts out an alarm signal, a central controller 7 suspends operating of an injection molding machine.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an abnormality detection device for an electric injection molding machine.

[Conventional technology]

The abnormality detection force formula for electric injection molding machines that perform injection molding using an electric motor as the drive source for mold clamping, injection, etc. is a value in which the magnitude of the difference between the command value and the actual measured value during position control is set in advance. It was a method and device that considered it abnormal when it was larger than .

[Problem that the invention seeks to solve]

Due to the characteristics of the control device, this device that detects the difference between the command value and the actual measured value during position control cannot detect belt breakage in machines where the electric motor is equipped with a position detector such as an encoder. There was a problem. Further, abnormality could not be detected during speed control such as the number of revolutions of the screwdriver or pressure control such as injection holding pressure control.

An object of the present invention is to provide a new device capable of solving the above-mentioned problems of an abnormality detection device for an injection molding machine using an electric motor as a drive source.

[Means for solving problems]

The features of the present invention according to the above object include, in an electric injection molding machine that performs injection molding using an electric motor as a drive source, a current detector that detects the electric current of the electric motor and outputs a current detection signal according to the magnitude of the electric current; The magnitude of the current detection signal of the current detector is monitored, and it is determined whether the current value of the motor is outside or outside the range of the monitoring reference value set at the front, and depending on the determination result, an in-range signal or a range A current value discriminator outputs an outside signal, and the current value discriminator is reset by an in-range signal or an OFF signal of an out-of-range signal, and time measurement is started by the out-of-range signal, and the out-of-range signal is maintained for a set time. It also includes an abnormality monitoring timer that outputs an alarm signal if input continues.

[For production]

The current value of the electric motor when performing mold opening/closing, injection, screw rotation, molded product ejection, or nozzle movement using position control, speed control, torque control, etc. changes depending on the setting value or load condition, but all equipment If it is normal and the load condition is the same, each molding cycle will be the same during automatic operation. Therefore, by monitoring the current of the motor, it is possible to detect abnormalities in the machine or changes in the load.

During transitional periods of operation, such as when starting the motor, changing speed, or switching from speed control to torque control, the motor current changes significantly, and in some cases, the maximum torque limit value may change for a short period of time. It may be a current value, or it may be a current with the opposite polarity. The setting time of the abnormality monitoring timer is set to be somewhat longer than the time required for the transition period until the current value of the motor stabilizes.

During normal machine operation when there is no mechanical failure and when the actual measured values of position, speed, or torque are not in a transitional period where they are almost equal to the set values, the torque A current with a certain range of magnitude commensurate with the load smaller than the limit value flows through the motor.A value smaller than the torque limit value and larger than the normal current value is set as the upper limit of the monitoring reference value of the current value discriminator. When a malfunction such as a mechanical failure occurs, the load increases and the current value of the motor becomes larger than normal and becomes larger than the upper limit set value.In other words, it falls outside the range of the monitoring reference value.

Furthermore, in the event of a belt breakage failure, the load on the load side after the belt becomes 0, resulting in a low current value. A value that is thicker than this low current value (and slightly smaller than the current value at the lowest load in normal times without failure) is set as the lower limit setting value of the monitoring reference value of the above current value discriminator.When a belt breakage occurs, the electric motor The current value becomes smaller than the lower limit set value, that is, outside the range of the monitoring reference value.

In this way, when an abnormality occurs in the electric injection molding machine, the current value of the electric motor becomes larger than the upper limit set value and falls outside the range of the monitoring reference value, or becomes smaller than the lower limit set value and exceeds the monitoring reference value. is outside the range, and the current value discriminator outputs an out-of-range signal. Further, as described above, even if the machine is normal, the current value may change significantly for a short time, and at that time, the current value discriminator may output an out-of-range signal, albeit for a short time. The abnormality monitoring timer starts counting when an out-of-range signal is detected, but since the out-of-range signal disappears or it is reset by an in-range signal, the motor current value changes before the set time of the abnormality monitoring timer elapses. returns to its normal value.If there is no abnormality in the machine, no alarm signal will be output.If the out-of-range signal continues to be input during a machine abnormality, the abnormality monitoring timer will continue to measure time without being reset during timing. After the set time has elapsed, an alarm signal is output and an abnormality in the machine can be detected.

As described above, since the abnormality detection device of the present invention is a device that monitors the current of the electric motor, it is possible to easily detect an abnormality in any of the position control, speed control, and torque control.

〔Example〕

Embodiments of the present invention will be described in detail below based on the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention, which relates to a mold clamping device, and the injection mechanism, molded product ejecting mechanism, etc. are omitted. Further, the illustrated mold clamping device uses a servo motor 1 as an electric motor, and the servo motor 1
It is equipped with a transmission mechanism that transmits the rotational motion of the screw to the screw nut 4 threadedly engaged with the screw shaft 5 through the interposition of the ball 4a through the pulleys 2, 2 and the belt 3, and converts it into linear motion of the screw shaft 5. The movable platen 6 moves together with the mold 6a to open and close the mold by the linear movement of the screw shaft 5. The mold opening/closing servo motor 1 is placed under the control of a servo controller 8 according to commands from a central controller 7 that controls the injection molding machine, and the mold opening/closing operation is performed.

A current detector 9 for detecting the current of the servo motor 1 is provided between the servo motor 1 and the servo controller 8 . The current detection signal output by the current detector 9 is converted into a signal proportional to the magnitude of the current, which is independent of the direction of flow, and is input to the current value discriminator 10. The current value discriminator 10 monitors the magnitude of the input current detection signal and determines whether the servo motor 1
The current value is the upper limit setting value of the monitoring reference value (I upper
) (Illustrations and detailed explanations of the upper limit setter, comparator, etc. are omitted) or when it is smaller than the lower limit set value (I under ) (lower limit setter and comparator not shown), an out-of-range signal is output. , is equal to the upper limit setting value or the lower limit setting value, or outputs an in-range signal when it is between the upper limit setting value and the lower limit setting value.

The upper limit setting value Iupper is set to a value slightly larger than the current value flowing at the highest load in normal conditions, and the lower limit setting value Iupper
under is set to a value that is larger than the current value when there is no load after the belt 3 when the belt 3 is broken and is smaller than the current value when there is no load after the belt 3 and when there is no fault and the current value is the lowest load.

The clock is reset by the in-range signal and started by the out-of-range signal, and the preset time (
An abnormality monitoring timer II is provided which outputs an alarm signal if the above-mentioned out-of-range signal continues to be input during the timer setter (not shown). In response to the alarm signal from the abnormality monitoring timer 11, the central controller 7 performs predetermined processing in the event of a machine abnormality, such as stopping operation of the injection molding machine.

FIG. 2 is an example of a measurement record of the normal speed and current measured in the mold opening process of the mold clamping device, with the vertical axis representing the servo motor speed and the servo motor current, and the horizontal axis representing time.

The section (3) is an acceleration section at the start of mold opening, and the highest current value of the torque limit value is generated at that moment.

The section (2) is a slow mold opening section for demolding, and is in a stable state with an approximately constant current value.

The section (2) is a high-speed mold opening section, and during acceleration, a peak current is generated as in (2).

In the section ①, during the slow mold opening process before the mold opening stop process, during deceleration until the speed stabilizes at a low speed, the polarity is opposite to that during acceleration, and the current up to the torque limit value is recorded. .

The section (3) is a deceleration section for stopping the mold opening, and the peak current flows again.

Figure 3 shows that the output of the current value discriminator 10 is an out-of-range signal.
This is an example of an operating circuit of the abnormality monitoring timer 11a in the case of only the 10FF signal.

Between the out-of-range signal output circuit, which is the output circuit of the current value discriminator IO, and the reset input circuit of the abnormality monitoring timer 11a,
An OT logic element 12 is inserted.

When the out-of-range signal is turned off, the in-range signal is turned on.
, the same operation as described above can be performed.

To explain the abnormality detection operation during mold opening with reference to FIGS. 1 and 2, the setting time of the abnormality monitoring timer 11 is somewhat longer than the time required for speed acceleration or deceleration as illustrated in FIG. The time is set. In the section (■) when the mold opens, the current exceeds the monitoring reference value l upper, the current value discriminator 10 outputs an out-of-range signal, and the abnormality monitoring timer 11 starts timing, but the timer setting The current value before the time is the monitoring reference value l u
pper or less, and the abnormality monitoring timer It is reset before it times up due to the in-range signal.
No alarm output occurs. The same applies to the following sections (■ to ■), and no alarm signal is output under normal conditions.

However, if belt 3 breaks during the mold opening process, there is no load after belt 3, so the current value becomes less than the lower limit set value ■under, and the current value discriminator IO continues to output an out-of-range signal and monitors the abnormality. The timer 11 outputs an alarm signal when the timer continues counting and times out. Also, if there is an abnormality in the direction of increasing the load, the current value will change to Iup.
PER becomes abnormal and falls outside the range of the monitoring reference value, so an alarm signal is output in the same manner as described above.

In the above example, the explanation was given during the mold opening process, but the same applies to the mold closing process. It goes without saying that the same method can be applied to injection, screw rotation, nozzle movement, molded product ejection, etc.

〔Effect of the invention〕

As explained above, the present invention is (1) an abnormality detection device that can be used for all control methods used in injection molding machines, such as position control, speed control, and pressure control.

■ Failures that result in light loads, such as belt breaks, can be detected early.
Belt breakage can also be easily detected in an injection molding machine having a mold opening/closing position control device in which an encoder is attached to an electric motor.

(3) Although the setting time of the alarm timer is somewhat longer than the response time of the servo motor, it can be set to 0.1 to 0.5 seconds, allowing for abnormality detection in a short time and preventing serious failures. .

(4) The current detector can also be used for servo motor control, allowing the abnormality detection device to be manufactured at low cost.

It is highly effective as an abnormality detection device for electric injection molding machines.

[Brief explanation of the drawing]

The drawings illustrate the abnormality detection device of the present invention.
The figure is a block diagram, the second figure is a measurement record of the servo motor speed and servo motor current in the mold opening process, and the third figure
The figure shows another operating circuit of the abnormality monitoring timer. 1... River... Servo motor 2...
・Pulley 3...Belt 4・
......Screw nut 5...Screw shaft 6...Movable platen 7...
... Central controller 8 ... Servo motor controller 9 ... Current detector 10 ... Current discriminator 11, lla ... ...Abnormality monitoring timer 1st
figure

Claims (1)

[Claims] In an electric injection molding machine that performs injection molding using an electric motor as a drive source, there is a current detector that detects the electric current of the electric motor and outputs a current detection signal according to the magnitude of the current, and a current detection signal of the current detector. A current value discriminator that monitors the size, determines whether the current value of the motor is outside or outside a preset monitoring reference value range, and outputs an in-range signal or an out-of-range signal according to the determination result. Then, it is reset by the OFF signal of the in-range signal or out-of-range signal of the current value discriminator, starts time measurement by the out-of-range signal, and outputs an alarm signal if the above-mentioned out-of-range signal continues to be input for a set time. An abnormality detection device for an electric injection molding machine, comprising an abnormality monitoring timer.