JPH0567410B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an injection control method for an injection device driven by an electric motor.

[Conventional technology]

This type of injection control method is described in JP-A-59-156726 and JP-A-59-224324. In those prior technologies, in addition to setting the injection speed value and the upper limit torque value, the injection speed is controlled in a closed loop so that the injection speed becomes the set value by feeding back the speed value that is electrically detected by the speed sensor. The injection speed or injection pressure is controlled based on the relationship between the speed and torque settings and the load acting on the drive source, and the injection pressure is controlled in an open loop. Torque value (motor current upper limit value)
The electric motor is driven by setting . In addition, when the injection plunger or injection screw is moving forward and the inertial force of the rotor of the electric motor is acting, if you switch from controlling the injection speed to controlling the injection pressure, the inertial energy will cause the set injection pressure to increase. Because of the problem of overfilling the mold with resin due to the injection pressure acting on the machine, the speed is controlled using closed-loop control from the start of injection until the mold is almost filled with material. In order to reduce the influence of the inertial force of the motor rotor, etc., after braking control that decelerates the injection speed almost linearly, injection pressure control is performed by changing the setting of the torque value (the upper current limit value of the motor). It was being migrated.

[Problems to be solved by the invention]

A disadvantage in the characteristics of electric motors is that even if the drive current value of the electric motor is constant, the output torque fluctuates due to changes in the temperature of the electric motor. Therefore, when a motor is controlled using open-loop control, this characteristic will appear as is, and even if the drive current value is constant as the temperature of the motor changes due to changes in outside temperature or the heat generated by the motor itself, the actual As the output torque generated by the mold fluctuates and the pressure applied to the resin filled in the mold fluctuates, there is a problem of molding defects due to overfilling or underfilling of the molded product. As the actual force applied to the resin changes due to the influence of physical transmission efficiency, etc., the injection pressure control accuracy for the set value is poor, and some molded products may not be able to be molded to meet the required quality. It was hot. In addition, if braking control is performed gradually to remove the influence of inertia force when switching from injection speed control to injection pressure control, the screw speed will decrease and it will take time to switch control, but during that time, However, as the cooling of the resin in the mold cavity progresses, the stress in the molded product tends to become uneven, and in some cases, especially when molding thin-walled molded products, complete filling is not possible. The inventors believe that the effects of such changes in output torque and mechanical transmission efficiency due to temperature changes can be eliminated by using feedback control to control the set value and actual value to match. Therefore, the injection speed was controlled using the injection speed detection value as the feedback signal, and the injection pressure was controlled using the injection pressure detection signal detected by the injection pressure detector as the feedback signal. An attempt was made to achieve this by feedback control of the injection pressure, which directly controls the drive current of the motor. However, even in such a case, if control is performed by simply switching between the injection speed feedback circuit and the injection pressure feedback circuit, fluctuations in the actual value relative to the set value can be suppressed, but injection will still occur under the influence of inertial force. When switching from speed control to injection pressure control, the electric motor is driven forward until the injection pressure feedback value exceeds the set value, so inertia force and forward force from the electric motor act on the injection plunger or screw. As a result, an injection pressure higher than the set pressure was generated, causing a problem of overfilling. On the other hand, pressure detectors using strain gauges have a structure that allows pressure to be detected only when strain occurs due to pressure, and there is a distance between the injection pressure source and the pressure detector. The response is poor because it takes time to transmit the injection pressure, and when the gain of the injection pressure control circuit is increased, large pressure fluctuations occur when switching from injection speed control to injection pressure control, or when switching injection speed or injection pressure. In order to prevent this, the gain has to be lowered at the expense of responsiveness.When the gain is lowered, due to the characteristics of feedback control, when the set value and the actual value are close to each other during injection pressure control, there is almost no deviation, so the electric motor Since almost no current is supplied and the torque decreases, the injection plunger or screw is pushed back by the resin pressure, causing pressure fluctuations.

[Means to solve the problem]

An object of the present invention is to provide feedback for controlling injection speed and injection pressure (holding pressure) using a speed sensor and a pressure detector (sensor for detecting injection pressure) in an injection device that uses an electric motor as a drive source. It is an object of the present invention to provide a new injection control method that does not cause the above-mentioned problems, although it is controlled with high precision. The feature of the present invention for the above-mentioned purpose is that, in an injection control method of an electric injection device using an electric motor as a drive source of an injection mechanism, the filling process of filling a material into a mold cavity is performed by a speed command of an injection plunger or an injection screw. The difference signal generated by comparing the signal and the speed detection signal from the motor side with an adder is used as a current command signal, and current detection is obtained by detecting the current command signal and the input current of the motor with a current detector. This is performed by a speed feedback control circuit that drives the motor based on the voltage difference from the signal, and the compression and pressure holding processes are performed using a strain gauge that electrically detects the injection pressure from the strain caused by the reaction force during injection as an injection pressure sensor. A pressure control signal obtained by comparing the pressure detection signal detected by the injection pressure sensor with the injection pressure command signal set in the injection pressure setting device is supplied to the adder in exchange for the speed command signal. However, the switching between the speed command signal V1 and the pressure control signal is performed by a pressure feedback control circuit equipped with the speed feedback control circuit, and the switching between the speed command signal V1 and the pressure control signal is performed so that the amount of material filled by the speed feedback control reaches a preset value. This is done using a signal switch that activates when the target is reached.

[Effect]

In the above configuration, injection speed control is performed by a speed feedback control circuit based on an injection speed command signal and an injection speed detection signal, and when it is detected that the amount of material filled has reached a preset value, the injection speed is Instead of the injection speed command signal input to the speed control circuit, a pressure control signal based on the deviation between the injection pressure command signal and the injection pressure detection signal is input,
The pressure control signal is further compared with the speed detection signal and amplified to supply armature current to the motor. In other words, during injection pressure control, a pressure feedback control circuit is constructed in which the speed feedback control circuit works as a minor loop, and as a result, the pressure control signal is compared with the speed detection signal, amplified, and becomes a command signal, and is also used with the current detection signal. Comparison operation, amplification and supply to power converter. The motor is then controlled by the armature current output from the power converter.

【Example】

The present invention will be explained in detail below using illustrated examples. The injection device has an injection heating cylinder 2 in which an injection member formed by a screw 1 is housed, and a housing 4 on a machine base 3 which also serves to hold the injection heating cylinder. Inside the housing 4 is a screw movable member 6 connected via a rotation shaft 5 connected to the rear end of the screw 1.
As shown in FIG. 3, there are support shafts 7, 7 on both sides extending parallel to the rotation shaft 5 and spanning the front and rear walls 4a, 4b of the housing. is attached by penetrating both ends so that it can slide freely in the front-back direction. A small-diameter extension shaft 5a having a gear 8 for rotating the screw is protruded from the rear end of the rotation shaft 5.
The screw movable member 6 is connected to the end of the extension shaft 5a via a thrust bearing 9. The central part of the screw movable member 6 is cylindrical, and a screw receiving member 10 having a screw threaded on the inner peripheral surface is fitted into the rear end of the central part. , is screwed in concentrically with the screw 1. The rear end of this screw shaft 11 is a shaft portion 11a rotatably held on the housing rear wall 4b with a thrust bearing 12, and a gear 13 is attached to the shaft portion 11a. The gears 8 and 13 mesh with gears 17 and 18, which are attached to a transmission shaft 14 on the lower side inside the housing 4 with clutches 15 and 116, respectively, and are connected to the transmission shaft 14 and the lower surface of the housing 4. The drive shafts of the DC electric servo motors 19 are connected via a drive belt 20, and the servo motors 19
The screw 1 can be rotated and moved in the axial direction using the screw 1 as a driving source. Reference numeral 21 denotes a strain gauge for measuring the amount of deformation of the rear wall 4b of the housing, and is attached to a portion of the wall that receives the reaction force when the screw 1 moves forward with injection, that is, a portion of the wall that holds the shaft portion 11a. Note that 22 is a brake device that controls the rotational force of the screw 1 via the shaft portion 11a. The strain gauge 21 is commercially available as a molded strain gauge, and consists of a strain gauge molded inside a plastic case, which is fixed using screws. Screw 1 in the electric injection device with the above structure
The rotational retraction (material charge) of the screw 1 takes place via gears 17, 8, and the injection advance of the screw 1 takes place via gears 18, 13. That is, as the gear 13 rotates, the screw shaft 11 also rotates, and this rotational force is converted into thrust by the screw receiving member 10 on the side of the screw movable member whose rotation is prevented. Then, the screw 1 moves forward together with the screw movable member 6, and the molten resin in the injection heating cylinder 2, which is charged in front of the screw, is injected from the nozzle. This forward force is the injection pressure, and an equivalent backward force is generated in the screw shaft 11 as a reaction force. This backward force is applied to the housing rear wall 4 through the thrust bearing 12.
As a result, stress is applied to the rear wall 4b, and the portion where the strain gauge 21 is attached also undergoes slight deformation in response to the injection pressure, and the amount of deformation is determined by the strain gauge 21. It is measured electrically and further detected as injection pressure. When the bridge power source from the strain amplifier 23 is input to the strain meter 21, an output corresponding to the amount of deformation of the rear wall 4b is generated (see FIG. 1 below). This output is applied as a voltage signal to the distortion amplifier 23.
The pressure detection signal V5 corresponding to the injection pressure is amplified by the recorder 23a and the adder 2 described later.
4 and the comparator 25. The pressure detection signal V5' inputted from the strain amplifier 23 to the comparator 25 is sent to the setting device 26 where the pressure for switching the injection speed control to the injection pressure control is set.
It is compared with the setting value of V7, and is constantly inputted to the signal switch 27 as a switching signal V7. This signal switch 27 is a speed setting device (figure omitted)
This is a switch for switching between the speed command signal V1 and the pressure control signal ΔV4, and switching the control to either injection speed control or injection pressure control. The pressure control signal ΔV4 is a pressure command signal V set by an injection pressure setting device (not shown).
4 and the measured injection pressure detection signal V5 are input to the adder 24, and the difference signal therebetween is calculated and outputted. The difference signal ΔV obtained by adding the speed command signal V1 and the speed detection signal V6 detected by the tachometer generator 29 to the adder 28 is amplified by the amplifier 30 to become the current command signal V2. A difference voltage ΔV2 obtained by adding the current detection signal V3 fed back to the adder 31 is amplified by an amplifier 32 and then supplied to a power converter 33. The power converter 33 is configured with an ignition control circuit using a thyristor or a pulse wide control circuit using a transistor, and an armature current Ia flows to the servo motor 19 according to an input signal. Further, in order to detect the armature current Ia, a current detector 34 is provided in the circuit between the power converter 33 and the servo motor 19, and a current detection signal V3 corresponding to the detected current is fed back to the adder 31. At the start of injection, the signal switch 27 is switched so that the speed command signal V1 is added to the adder 28, and the speed command signal V1 is switched between the speed command signal V1 and the speed detection signal V6 of the tachometer generator 29 of the servo motor 19. Drive control of the servo motor 19 is performed based on the difference signal ΔV, and feedback control is performed so that the screw advance speed becomes the injection speed setting value, and the screw 1 moves forward. Therefore, in the filling process of filling the material into the mold cavity, the speed command signal V1 of the injection screw (plunger) and the speed detection signal V6 from the electric motor side are compared and calculated by the adder 28, and the resulting The difference signal ΔV is set as the current command signal V2, and the speed at which the motor is driven is determined based on the difference voltage ΔV2 between the current command signal V2 and the current detection signal V3 obtained by detecting the input current of the motor with the current detector 34. This will be done by the feedback control circuit. Next, as the screw 1 moves forward, the mold (not shown) is filled with molten resin from the nozzle, and the load increases, so that the injection pressure detected by the strain gauge 21 is adjusted by the setting device 26. When the value exceeds a preset value, the comparator 25 operates and outputs the switching signal V7 to the signal switching device 27. By inputting this switching signal V7, the signal switching device 27
switches from injection speed control (solid line) to injection pressure control (dashed line). As a result, the difference signal ΔV4 between the injection pressure detection signal V5 calculated by the adder 24 and the pressure command signal V4 from the pressure setting device (not shown) replaces the speed command signal V1 and serves as the pressure control signal ΔV4. input to adder 28; In this adder 28, the pressure control signal ΔV4 is added to the speed detection signal V6 in the same way as the speed command signal V1, and the difference signal ΔV is amplified, so that the pressure control signal ΔV4 is converted into the current command signal V2. It will be output. As a result, the speed feedback control circuit in the filling process works as a minor loop of the pressure feedback control circuit, and the pressure control signal ΔV4
is compared with the speed detection signal V6 and amplified, thereby driving the servo motor 19 and controlling the injection pressure to match a preset value through force feedback control. Furthermore, during pressure control, the inside of the mold cavity is already filled with resin and the screw hardly moves, so even if the pressure control signal ΔV4 is small, the value of the speed detection signal V6 will also be small, so the difference signal ΔV will be Since it is amplified by the amplifier 30 with a large gain in a state that is almost unchanged from the control signal ΔV4 and is supplied to the motor as a large current command signal V2, the small pressure control signal ΔV4 is directly transmitted without going through a minor speed loop. Compared to the case where the motor current is controlled by the current command signal V2, the current supplied to the motor is larger and the output torque of the motor is also larger, so the time required to reach the predetermined pressure is shorter and the response is extremely high. This allows for better control of performance. In addition, when the screw is moving forward and the inertia of the rotor of the electric motor is acting, the pressure control is started, and when the value of the pressure detection signal V5 is smaller than the value of the pressure command signal V4, the pressure control signal ΔV4 is Even when input to the adder 28, since the speed detection signal V6 is moving and large, the difference signal ΔV has a polarity opposite to that of the pressure control signal ΔV4, and an armature current that drives the motor in the opposite direction is supplied. As a result, the screw is braked rapidly and there is no possibility of overfilling. Although a DC servo motor is used in the above embodiment, the electric motor may be a brushless DC servo motor, an AC servo motor, or the like.

【Effect of the invention】

As described above, this invention performs injection speed control using a speed feedback control circuit based on an injection speed command signal and an injection speed detection signal, and detects that the amount of material filled has reached a preset value. Since the speed feedback control circuit is controlled by switching to injection pressure control by the pressure feedback control circuit acting as a minor loop, the injection speed and injection pressure are each controlled by feedback control so as to always match the command signal, Stable control is possible because the output torque does not fluctuate due to changes in motor temperature or mechanical transmission efficiency of the drive system, unlike in conventional open-loop control. In addition, since the speed feedback control circuit acts as a minor loop during injection pressure control, even if the pressure control signal ΔV4 is small, the amplifier 3
Since the current command signal V2 can be increased by the action of 0, the responsiveness during injection pressure control is improved, making it possible to mold a higher quality molded product. Furthermore, when switching from injection speed control to injection pressure control, braking action is automatically generated without the need for special braking control to remove the influence of inertia force, so the control condition can be maintained without overfilling. This makes it possible to quickly fill and mold high-quality molded products. Therefore, even if the drive source is an electric motor, the injection process can be divided into an injection speed control process and an injection pressure control process, making it easier to perform feedback control of speed and pressure than before. have Furthermore, since a strain gauge that electrically detects the injection pressure from the strain caused by the reaction force during injection is used as the injection pressure sensor 21, the injection pressure can be directly detected, thereby causing temperature changes in the motor. It also has the advantage of being able to perform injection control with higher precision than conventional methods, such as by being able to reduce the effects of fluctuations in the output torque caused by the mechanical transmission of the drive system and the mechanical transmission efficiency of the drive system.

[Brief explanation of drawings]

The drawings illustrate an injection control device for an electric injection device according to the present invention, and FIG. 1 is a block diagram of the injection control device, FIG. 2 is a partially cutaway side view of the injection device, and FIG. 3 is a side view of the injection device. Figure 2 - Line sectional view, 4th
The figure is a rear view of the injection device with a portion cut away. V1...Speed command signal, V2...Current command signal, V3...Current detection signal, V4...Pressure command signal, V5, V5'...Injection pressure detection signal, V6...
...Speed detection signal, V7...Switching signal, ΔV...Difference signal, ΔV2...Difference signal, ΔV4...Pressure control signal, 1...Injection screw, 21...Strain gauge, 1
9... Servo motor, 23... Strain amplifier, 2
4... Adder, 25... Comparator, 26... Setting device, 27... Signal switcher, 28... Adder, 29
... Tachometer generator, 30, 32 ... Amplifier, 31 ... Adder, 32 ... Power converter.

Claims (1)

[Claims] 1. In an injection control method for an electric injection device using an electric motor as a drive source of an injection mechanism, the filling step of filling a material into a mold cavity is performed using a speed command signal V1 of an injection plunger or an injection screw. and speed detection signal V6 from the motor side.
The difference signal ΔV generated by comparing and calculating with the adder 28 is set as the current command signal V2, and the difference between the current command signal V2 and the current detection signal V3 obtained by detecting the input current of the motor with the current detector 34. The compression and pressure holding steps are performed by a speed feedback control circuit that drives the electric motor based on the voltage ΔV2, and a strain gauge that electrically detects the injection pressure from the strain caused by the reaction force during injection is used as the injection pressure sensor 21 for the compression and pressure holding steps. The pressure control signal ΔV4 obtained by comparing the pressure detection signal V5 detected by the injection pressure sensor and the injection pressure command signal V4 set in the injection pressure setting device is converted into the speed command signal V1 by the adder. 28, and is performed by a pressure feedback control circuit equipped with the speed feedback control circuit, and switching between the speed command signal V1 and the pressure control signal ΔV4 is performed so that the filling amount of material by the speed feedback control is set in advance. An injection control method for an electric injection device, characterized in that the injection control method is carried out by a signal switching device 27 that is activated when a specified value is reached.