JPH0815751B2 - Feedback control device for injection molding machine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a feedback control device for an injection molding machine, in which an injection speed and the like are feedback-controlled, and particularly, without providing a dedicated analog feedback control circuit. The present invention relates to a feedback control device for an injection molding machine in which feedback control is performed by software.

[Prior Art] In an injection molding machine, an injection speed condition is an important factor in molding a non-defective product, and an injection molding machine in which the injection speed is feedback-controlled is known.

In a conventional injection molding machine having a feedback control function of this kind, a dedicated analog feedback control circuit was attached to control a servo valve for controlling injection cylinder (hydraulic cylinder) drive as an injection drive source. . Before shipment of the machine, adjust the feedback constant (zero, gain, span, etc.) of the feedback control circuit to a safe value (maximum common divisor) that can handle all molding conditions by adjusting the volume. It was supposed to be fixed.

[Problems to be Solved by the Invention] As described above, in the conventional injection molding machine, the feedback constant is adjusted at the shipping stage of the machine. However, this feedback control circuit must be adjusted by a skilled worker. In addition, since the individual adjusting elements are often associated with each other, it is complicated and time-consuming.
Further, the adjusted / fixed feedback constant is a safe value having general versatility, and therefore, it cannot be said that it is always the optimum value for each molding condition. That is, for example, in a molded product such as a thin-walled molded product in which a sharp increase in the injection speed is desired, the gain is insufficient, and the responsiveness of the feedback control system tends to be too slow for the molding conditions of such a molded product. However, or when molding an optical component such as a lens with an acrylic resin in order to raise the injection speed extremely slowly, there is a problem that the response of the feedback control system tends to be too sharp. It was

On the other hand, it has been considered to perform feedback control by software (a program for feedback control) without providing a dedicated analog feedback control circuit, but the response of the hydraulic circuit is slower than the process control of the program. Since no method was found to measure the injection speed with high speed and high accuracy, which is faster than the response of this hydraulic pressure, it was the current situation that effective feedback control by software could not be realized.

Therefore, the technical problem to be solved by the present invention is to solve the above-mentioned problems of the conventional technique. The purpose thereof is to measure the injection speed at high speed and with high accuracy and perform feedback control by software. With the realization,
An object of the present invention is to provide a feedback control device for an injection molding machine in which the optimum response characteristic of the feedback control system can be set for each individual molded product (each individual molding condition).

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention measures at least the injection speed and compares the measured value with a set command value so that the measured value matches the set command value. In a feedback control device for an injection molding machine that performs feedback control of injection speed, a microcomputer (hereinafter referred to as a microcomputer) that controls molding conditions, and a high speed that drives and controls a hydraulic drive source for injection according to a command from the microcomputer. A proportional solenoid valve, an injection stroke sensor including an encoder for detecting the position of the drive unit of the hydraulic drive source for injection, and a programmable timer module that is integrated into the microcomputer and counts a clock. , The microcomputer also measures the time from the count contents of the programmable timer module. In addition, the actual injection speed is measured from this measurement time and the output of the injection stroke sensor, and the high-speed proportional solenoid valve is feedback-controlled so that the measured actual injection speed value matches the set command value. To be done.

[Operation] For example, the counter in the programmable timer module to which the clock of 2MHz is input counts the time in 0.5μsec unit, and the operation part of the microcomputer subtracts the count value sampled at the front from the current count value. By doing so, the time for each predetermined sampling period is
Measure with ~ 5 significant digits. On the other hand, the microcomputer measures the stroke value in the same sampling period with, for example, three significant digits from the count value of the output from the injection stroke sensor including a pulse encoder having a high resolution (for example, a resolution of about 0.003 mm). . Then, the microcomputer calculates and recognizes the injection speed with an accuracy of three significant digits by dividing the stroke value obtained for each predetermined sampling cycle by time. By adopting such a velocity measuring method, even at the maximum injection velocity, the injection velocity can be measured in a short time of about 1.6 msec and with an accuracy of 3 significant digits.

Then, the microcomputer compares the actual injection speed value measured at every predetermined sampling cycle with the preset setting command value and executes feedback control based on PID (proportional / integral / derivative) operation to perform the actual injection. The high-speed proportional solenoid valve is drive-controlled so that the speed matches the set command value.

If feedback control is performed by such software, the response characteristics are discriminated by a microcomputer that constantly compares the set command value and the measured value, and if the measured characteristic is not stable, If it is determined that an unsuitable feedback constant is set for the currently operating molding conditions by referring to the stored data of the optimum response characteristics that was previously case-studied for each molded product (for each of many molding conditions), It is possible to execute a calculation process for calculating a correction value such that the currently set feedback constant satisfies the most preferable response characteristic, and based on this, a process for changing the feedback constant can be executed.

[Embodiment] Hereinafter, the present invention will be described with reference to an embodiment shown in FIGS. 1 to 4.

FIG. 1 is an explanatory diagram showing an outline of a feedback control device of an injection molding machine.

In the figure, 1 is a heating cylinder, 2 is a screw arranged in the heating cylinder 1 so as to be able to move forward and backward, and 3 is a hopper for supplying raw materials, 4 is a screw rotation in which the rear end of the screw 2 is connected. Driving motors 5 are injection cylinders (hydraulic cylinders) that are hydraulic drive sources for injection. In the illustrated example, the casing of the motor 4 is fixed to the tip of the piston rod 5a of the injection cylinder 5,
As the piston rod 5a moves forward and backward, the screw 2 moves forward and backward together with the motor 4. As is known in the above configuration, the resin material supplied from the hopper 3 is transferred to the tip end side of the screw 2 while being kneaded and plasticized by the rotation of the screw 2 driven by the motor 4 and the molten resin. As the screw 2 is stored on the side, the screw 2 moves backward while controlling the back pressure, and when one shot of molten resin is stored on the tip side of the screw 2, the screw rotation is stopped. Then, after the elapse of a predetermined time, when the injection start timing is reached,
The screw 2 is driven forward by the injection cylinder 2 so that the molten resin is injected and filled in the cavity of a mold (not shown). In the present embodiment, the injection speed during the forward movement process (injection stroke) of the screw 2 described above is feedback-controlled by a programmed process by the microcomputer 10 as described later.

Reference numeral 6 denotes a rack body that moves forward and backward integrally with the piston rod 5a of the injection cylinder 5, and an injection stroke composed of an optical encoder so as to rotate in synchronization with a gear (not shown) gear-coupled to the rack body 6. The rotating part of the sensor 7 is connected to the gear. Therefore, piston rod 5a
When the (screw 2) moves forward and backward, the injection stroke sensor 7 outputs a number of detection pulses commensurate with this, and the detection pulses are sent to the microcomputer 10 described later. In the present embodiment, the injection stroke sensor 7 is adapted to generate a detection signal of 1 pulse per stroke 0.003 mm of the piston rod 5a (screw 2).

10 is a microcomputer that controls the entire injection molding machine.
It has an I / O interface, a ROM that stores the main control program and various fixed data, a RAM that reads and writes various flags and measurement data, a CPU (microprocessor) that controls the overall control, and so on. Although various processes are executed according to the various programs described above, in the present embodiment, for convenience of explanation, the counter 11, the programmable timer module (hereinafter referred to as PTM) 12, the arithmetic processing unit 1
3, molding condition setting storage unit 14, feedback control unit 15,
The following description will be made on the assumption that the molding sequence control unit 16 and the output processing unit 17 are provided.

The detection pulse of the injection stroke sensor 7 is input to the counter 11, and the counter 11 counts by adding or subtracting it. A 2 MHz clock is input to the clock input terminal of the PTM12, and an internal counter adds (or subtracts) this clock to count the time in 0.5 μsec units.

Arithmetic processing unit 13 has a predetermined sampling time (cycle)
Then, the count value of the counter 11 and the count value of the PTM12 are read, and the screw stroke Sn in the sampling period is measured as Sn = (previous count value of counter 11) − (current count value of counter 11). , And the time Tn within the sampling period
Is calculated as Tn = (previous count value of PTM12) − (current count value of PTM12), and based on this, the injection speed Vn within the sampling period is calculated as Vn = Sn / Tn.

The sampling time by the arithmetic processing unit 13 is preset to be automatically shortened at high speed and automatically lengthened at low speed in order to improve measurement accuracy.
In this embodiment, for example, the sampling time is about 3 to about 30.
An appropriate value within msec is selected. Also, in order to maintain the measurement accuracy at the same accuracy, it is possible to add a predetermined number of screw strokes and time and calculate the injection speed V as V = (ΣSn) / (ΣTn). It has become. In any case, in this embodiment, the injection speed is calculated by three significant digits, and Sn or ΣSn is the value of three significant digits, and Tn or ΣTn is four or five digits. The injection speed is calculated using the values of the above significant digits. By adopting such a velocity measuring method, it becomes possible to measure the injection velocity at a maximum injection velocity in a short time of about 1.6 msec and with an accuracy of three significant digits.

The molding condition setting storage unit 14 stores various known molding condition values in a rewritable form. The molding conditions are, for example, the relationship between the screw position and the screw rotation speed and the back pressure during the charging process, suck back control conditions, and subdivision from the injection start point (position) to the holding pressure switching point (position). Injection speed conditions, subdivided secondary injection pressure (holding pressure) from the holding pressure switching time to the holding pressure end time
Conditions, band heater temperature of each part, mold closing stroke and speed, mold clamping force, mold opening stroke and speed, eject control conditions, and the like are mentioned, but the description thereof is omitted here except the injection speed condition.

FIG. 2 is an explanatory diagram showing an example of injection speed conditions set / stored in the molding condition setting storage unit 14, and as shown in FIG. 2, the charging completion point (position) to the holding pressure switching point (position). The injection speed up to is set according to the screw forward position.

The molding casing control unit 16 is based on a molding process control program created in advance and setting condition values stored in the molding condition setting storage unit 14, and measurement information from a sensor (not shown) arranged in each part of the machine and The output processing unit while referring to the timing information from the clock means built in the microcomputer 10.
A sequence control signal is sent via 17 to drive and control a large number of drive sources including the injection cylinder 5 to execute a series of molding steps.

The feedback control unit 15 includes the actual injection speed value calculated by the arithmetic processing unit 13 and the molding condition setting storage unit 14
The set injection speed value at the corresponding position stored in is compared in real time, and when the actual injection speed value deviates from the set injection speed value, the actual injection speed value is made to match the set injection speed value. Is calculated, and a speed control signal based on the calculated correction value is generated and output by the output processing unit 17. The output of the output processing unit 17 is sent to a high-speed proportional solenoid valve (DFP valve) 20 for driving and controlling the injection cylinder 5 via a D / A converter 18 and a driver circuit 19, whereby the injection cylinder 5 is driven. The injection speed is controlled so as to match the set command value.

The arithmetic control process performed by the feedback control unit 15 is based on a so-called PID (comparison / integration / derivative) operation. In the P operation, the output is a size K times larger than the unit step input, and in the I operation the unit step. It is assumed that the output is linearly increased / decreased by the integral action with respect to the input, the time advance is caused by the differential action in the D action, and these P, I, D actions are performed simultaneously, thereby performing the feedback control. ing. When such PID control is performed, feedback control can be performed with anticipation (coverage) of the hydraulic response delay, overshoot and oscillation due to too sharp rising can be suppressed as much as possible, and rising too sharp. It is possible to eliminate the delay in the arrival time to the target due to, and it is possible to obtain a suitable rising characteristic.

In addition, the microcomputer 10 compares the set command value (set injection speed pattern) with the actual injection speed pattern to determine the response characteristics, and when the measurement characteristics are not stable, or when a large number of molded products Refer to the stored data of the optimum response characteristics that was previously case-study
When it is determined that a feedback constant that is unsuitable for the molding conditions currently in operation is set, a correction value is calculated so that the feedback constant currently set satisfies the most suitable response characteristic. The calculation processing is executed and the feedback constant is changed based on the calculation processing. For example, the process of changing the feedback constant so that the measurement pattern causing oscillation as shown in FIG. 3 (a) becomes a stable pattern as shown in FIG. 3 (b), or FIG. It is possible to change the feedback constant so that the measurement pattern as shown in) is the most suitable pattern according to the molding conditions (molded product). It is obvious to those skilled in the art that such a feedback constant changing process can be easily realized by a feedback constant changing process program created in advance.

As described above, in the present embodiment, the injection speed can be measured at high speed and high accuracy, and the feedback control programmed by the microcomputer 10 can be realized based on the measurement. It does not require the complicated work of adjusting feedback constants,
Further, an abnormal situation such as overshoot or oscillation can be easily detected and suppressed as much as possible, and the feedback constant can be changed easily and easily.

In the above-described embodiment, the feedback control of the injection speed is taken as an example, but the present invention can be applied to other feedback control such as the mold opening / closing speed, the eject speed, the charge rotation speed, and the like. is there.

[Advantages of the Invention] As described above, according to the present invention, it is possible to measure the injection speed with high speed and high accuracy and to realize feedback control of the injection speed by software, and also for each molded product (for each molding condition). It is possible to provide a feedback control device for an injection molding machine in which the optimum response characteristic of the feedback control system can be set, and in this kind of injection molding machine, its industrial value is great.

[Brief description of drawings]

Each of the drawings relates to one embodiment of the present invention, FIG. 1 is an explanatory diagram showing an outline of a feedback control device of an injection molding machine, and FIG. 2 is an explanatory diagram showing one example of injection speed conditions set / stored. 3 and 4 are explanatory views showing the relationship between the injection speed pattern before the feedback constant is changed and the injection speed pattern after the feedback constant is changed. 1 ... Heating cylinder, 2 ... Screw, 3 ... Hopper, 4 ... Motor, 5 ... Injection cylinder (hydraulic cylinder), 5a ... Piston rod, 7 ... Injection stroke sensor, 10 ... Microcomputer ( Microcomputer), 11 ...
… Counter, 12 …… Programmable timer module (PTM), 13 …… Calculation processing unit, 14 …… Molding condition setting storage unit, 15 …… Feedback control unit, 16 …… Molding sequence control unit, 17 …… Output processing unit , 18 …… D / A converter, 19…
… Driver circuit, 20… High-speed proportional solenoid valve.

Claims (2)

[Claims] 1. An injection molding machine which measures at least an injection speed, compares the measured value with a set command value, and feedback-controls at least the injection speed so that the measured value matches the set command value. From a microcomputer that controls the conditions, a high-speed proportional solenoid valve that drives and controls a hydraulic drive source for injection according to a command from the microcomputer, and an encoder that detects the position of the drive unit of the hydraulic drive source for injection. Injection stroke sensor
A programmable timer module that is integrally incorporated in the microcomputer to count a clock, the microcomputer measures time from the count content of the programmable timer module, and the measured time and the injection stroke sensor A feedback control device for an injection molding machine, characterized in that the actual injection speed is measured from the output, and the high-speed proportional solenoid valve is feedback-controlled so that the measured actual injection speed value matches the set command value. . 2. The feedback control device for an injection molding machine according to claim 1, wherein the microcomputer performs feedback control by proportional / integral / derivative (PID) operation.