JP3158143B2 - Method of controlling parison length of blow molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for controlling a parison length of a blow molding machine.

[0002]

2. Description of the Related Art As a conventional technique for keeping the parison length constant, there is Japanese Patent Application No. 3-358178 filed by the present applicant.

[0003] This conventional example is used when a parison in a molten state is extruded by rotating a screw of an extruder, the end is closed by clamping means, the parison is cut, and air is blown to form a hollow. This is a method for controlling a blow molding machine that controls the number of revolutions of a screw of the extruder to keep the parison length constant.

In this conventional example, a test molding step is provided before the ordinary molding step, and the length of the parison of the resin to be used is detected by one photoelectric tube, and the relationship between the parison length and the screw rotation speed of the extruder is obtained in advance. In the normal molding process, the current parison length is detected by the phototube, and the parison length difference between the current parison length and the target parison length is obtained.
The target parison length was obtained by controlling the screw rotation speed of the extruder according to the difference in the parison length from the relationship between the parison length and the screw rotation speed of the extruder determined in advance.

[0005]

However, the method of controlling the parison length of a blow molding machine according to the above-mentioned conventional technique has the following problems. (1) When the molded product is changed, the position of the photoelectric sensor must be adjusted according to the height of the product. Such an adjustment of the position must be performed while observing the relationship with the molding cycle, and it is very difficult and time-consuming to set the conditions. (2) In order to adjust the position of the photoelectric sensor, a control constant representing the relationship between the parison length and the screw rotation speed of the extruder could not be automatically set.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a method for controlling the length of a parison of a blow molding machine for easily stabilizing product quality. It is in.

[0007]

In order to achieve the above object, a method for controlling the parison length of a blow molding machine according to the present invention comprises:
The screw of the extruder is rotated to extrude the molten parison, the parison is clamped by mold clamping means, the end is closed, the parison is cut with a parison cutting cutter, and a blow pin is driven into the parison, In the method of controlling the parison length of a hollow molding machine for performing blow molding by blowing air from the blow pin, first, a test molding process is performed.
Then, the extruded parison is passed through a plurality of photoelectric sensors arranged in the direction in which the parison is extruded, and the extruded parison is moved from a command for cutting the parison to a time when the mold clamping unit goes to clamp the parison. The last photoelectric sensor that detects the position of the parison is used as the reference photoelectric sensor, and then the time from when the parison is cut off to when the parison shields the reference photoelectric sensor is measured a plurality of times, and the average time is calculated. , A reference time corresponding to the reference parison length, and then extruding the parison by changing the screw rotation speed by at least two from the current value by a predetermined rotation speed, and from the parison cutting command, the parison receives the reference photoelectric. Measure the time until the sensor is shielded several times,
Next, the average time is obtained for each of the screw rotation speeds, and a control constant is determined from the at least two changed screw rotation speeds and the average time until the parison shields the reference photoelectric sensor from light at that time. set, then in the normal molding process, measures the time from the disconnection command of the parison until the parison to shield the reference photoelectric sensor, the time until the light-shielding, screw
-Parison is a reference photoelectric sensor that does not correct rotation speed
If the time until the light is shielded is out of the range, the control
Using a constant, the screw rotation speed according to the reference time
The correction amount is calculated, and the screw rotation speed is controlled to make the parison length constant.

In the method for controlling the length of a parison of a blow molding machine according to the present invention, a plurality of photoelectric sensors are arranged and arranged in the direction in which the parison is extruded. By using the last photoelectric sensor that detects the position of the parison that was extruded until the pinch is sandwiched as the reference photoelectric sensor for detecting the parison length, the photoelectric sensor in the event that the molded product changes, etc. Adjustment of the position of is unnecessary.

The control for keeping the parison length constant controls the relationship between the screw rotation speed of the extruder and the time from when the parison is cut off to when the parison shields the reference photoelectric sensor in the test molding process by at least two screw rotation speeds. keep in determined for the change in the normal molding process, measures the time from the disconnection command of the parison until the parison is to shield the reference photoelectric sensor, when until the light shielding
In the meantime, a parison that does not correct the screw rotation speed
When the time until the reference photoelectric sensor is shielded is out of the range
The control constant, the screw according to the reference time
Calculate the amount of rotation speed correction to control the screw rotation speed.
Made by us.

In the present invention, by eliminating the need to adjust the position of the photoelectric sensor, the control constant in the control of the parison length, which indicates the relationship between the screw rotation speed and the time until the parison shields the reference photoelectric sensor, is reduced. It enables automatic installation and facilitates control to keep the parison length constant.

[0011]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a diagram showing a configuration example of a parison length control (PLC) system for realizing the method for controlling the parison length of the present invention in a blow molding machine.

In FIG. 1, reference numeral 1 denotes a hollow molding machine having an extruder 1a, and 2 denotes an extruder driving inverter motor (hereinafter referred to as "motor") for rotating a screw (not shown) of the extruder of the hollow molding machine 1. ) 3 is a screw rotation detector that detects the rotation of the screw of the extruder with a pulse, and 4 is the rotation of the motor 2 so that the rotation of the screw reaches a specified rotation speed by feeding back the detection pulse of the screw rotation detector 3. An inverter driver for controlling the speed, 5 is a molten tube-shaped parison made of a thermoplastic resin extruded by rotation of an extruder screw, and 6 is a parison cutting cutter. Reference numeral 7 denotes a photoelectric sensor for detecting the length of the parison, which comprises, for example, a plurality of photoelectric sensors 7-1, 7-2, 7-3, 7-4, and 7-5 as shown in FIG. Reference numeral 8 denotes a controller constituted by a programmable controller or the like for instructing the inverter driver 4 to correct the screw rotation speed so that the parison length becomes constant using the photoelectric sensor 7. This controller 8
The molding cycle time from the closing of the mold to the cooling process consisting of blowing and discharging (discharging) of air through the lowering of the blow pin for driving the blow pin into the parison from the mold open command is made constant in a feed-forward manner by correction. It also has functions.

FIG. 2 is a diagram showing an example of the arrangement of the photoelectric sensor 7 used when the parison length is made constant. Reference numeral 1b denotes a head of a hollow molding machine for pushing the parison 5 vertically downward, and a parison cutting cutter 6 is disposed near the lower end of the head 1b. Each photoelectric sensor 7 includes a pair of a light emitter (PHD) and a light receiver (PHS). In the present system example, five photoelectric sensors 7-1 (PHD1 and PHS) are provided.
S1), 7-2 (PHD2 and PHS2), 7-3 (PH
D3 and PHS3), 7-4 (PHD4 and PHS4), 7
-5 (PHD5 and PHS5) are arranged in the hanging (extrusion) direction of the parison 5 at regular intervals at a predetermined pitch from a predetermined position, with the cutting position of the parison cutting cutter 6 as the 0 position.

In the above configuration, the blow molding machine 1 extrudes a thermoplastic resin in a molten state from the extruder 1a and causes the tubular parison 5 to hang down. The parison 5 is clamped by a molding die (not shown) having a mold clamping means, thereby closing the lower end of the parison 5 and cutting the parison 5 with a parison cutting cutter 6, and driving a blow pin or the like into the closed parison 5, Air is blown from this blow pin or the like to expand the parison 5 until it matches the cavity of the molding die, and then cooled to obtain a hollow molded product.

The outline of the control method for keeping the parison length constant according to the present invention is as follows.

First, a test molding step is provided before the normal molding step. In this test molding step, one reference photoelectric sensor is set from among the plurality of photoelectric sensors 7. Based on this reference photoelectric sensor, the time until the extruded parison shields the reference photoelectric sensor is measured a plurality of times, and the average value is calculated to be the reference time corresponding to the reference parison length.

By changing the screw rotation speed at least two times from the current value to the predetermined rotation speed, the time from the cutter command (parison cutting command to the parison cutting cutter 6) to the time when the parison shields the reference photoelectric sensor from light is determined. At the same time, a proportional constant is determined from the inversely proportional relationship between the screw rotation speed and the time required for the parison to shield the reference photoelectric sensor from light, and is used as a control constant.

Next, in the normal molding process, determine the time until the parison to shield the reference photoelectric sensor, the light-shielding
Time until you, Do not multiplied by the correction to the screw rotation speed
The time it takes for a parison to block the reference photoelectric sensor
If the width deviates, the control time is used to determine the reference time.
Depending was then calculates a correction amount of the screw rotational speed, and controls the scan click <br/> Liu rotational speed to obtain a parison length of the target.

An embodiment of the present invention will be described in detail with reference to FIGS. 4, 5 and 6.

FIGS. 4 and 5 are flowcharts showing the operation executed by the controller 8 in the test molding process.

In FIG. 2, a certain photoelectric sensor 7 is set as a reference photoelectric sensor. The controller 8 obtains, for example, a timing of a cutter command (a command of cutting the parison 5 to the parison cutting cutter 6) by a timer or the like as a timing means, and a timing until the parison 5 shields the reference photoelectric sensor from light. Is determined, and this time t is used as a value corresponding to the parison length (current parison length) at the mold clamping timing of the parison 5. After the automatic molding condition setting is completed, the reference photoelectric sensor performs an automatic operation as a test molding step, and determines one of the plurality of photoelectric sensors 7 as a reference photoelectric sensor.

The test molding process is started by, for example, pressing the reference value setting key 4b (the confirmation lamp is lit) on the monitor panel 4a of the controller shown in FIG. 7 and pressing the start key 4c.

That is, first, as shown in the timing chart of FIG. 3, a cutter command (parison cutting cutter 6) is issued.
The parison 5 detects, for example, five times the last photoelectric sensor 7 that is shielded from light until the slide instruction to the molding die is input, and detects the photoelectric sensor 7 that has been continuously shielded five times from the last time until the slide instruction to the molding die is input. The photoelectric sensor is a reference photoelectric sensor.
In the example of FIG. 3, the photoelectric sensor 7-4 is a reference photoelectric sensor.

Next, a reference time corresponding to a reference parison length is obtained using the reference photoelectric sensor. That is, the time from when the parison is cut off to the cutter 6 until the parison shields the reference photoelectric sensor is measured ten times, and the average time is used as the reference time for obtaining the target parison length in the normal molding process. In parallel with the determination of the reference time, a range of (maximum value−minimum value) × 0.7 in the ten times is set as a dead zone. The parison, which does not correct the screw rotation speed N in the normal molding process, blocks the reference photoelectric sensor in order to eliminate the cause of hunting by ignoring fine variations due to the cut shape at the cutter 6 and shaking of the parison. This is for setting the width of the time t until the operation is performed.

Next, in the test molding process, the relationship between the screw speed of the extruder and the parison length equivalent value (time t until the parison shields the reference photoelectric sensor from light) is determined . When the push extruder screw rotation speed to N, N is known to be proportional to the inverse 1 / t of the time t. Therefore, when the proportional constant (hereinafter, referred to as a control constant) is a, it can be expressed as N = a × (1 / t). The following is this a
This is the procedure for asking.

The stops automatic operation cycle, the screw rotation speed of the extruder 1a to N _1, the parison cutting cutter (Hot Cutter: HC) power is kept is ON. When the parison 5 is detected by the photoelectric sensor 7-5 at the lowest position and 1.0 second has elapsed, the parison cutting cutter 6 is operated. The molding process screw rotation speed N is repeated until the N _1. Next, screw rotation speed N is reached to N _1, reference photoelectric sensor by the parison 5 from the cut command to cutter 6 measures the time until the light-shielding. The lowermost photoelectric sensor 7-5 detects parison 5 and detects
After a lapse of sec, the parison cutting cutter 6 is operated.
The above measurement is performed 10 times to calculate an average value, and the average value t
₁ as a reference value during rotation at the rotational speed N _1.

Next, in the same manner as described above, the reference value t ₂ of the time until the parison shields the reference photoelectric sensor when the screw rotation speed of the extruder 1 a is N ₂ is determined.
That is, the cutter 6 is operated when the parison 5 is detected by the photoelectric sensor 7-5 at the lowest position and 1.0 sec has elapsed. The molding process screw rotation speed N is repeated until the N _2. When the screw rotation speed N becomes N ₂ , the time from the cutting command to the cutter 6 until the reference photoelectric sensor is shielded from light by the parison 5 is measured. The lowermost photoelectric sensor 7-5 detects the parison 5 and activates the cutter 6 1.0 seconds later. The measurement to calculate the ten rows not mean, and the average value t ₂ with the reference value at the time of rotation at the rotational speed N _2. After the above measurement is completed, the extruder 1a is stopped, the power of the parison cutting cutter (HC) is turned off, the control constant a is obtained, the reference value setting key lamp is turned off, and the process ends.

Here, the control constant a can be obtained as follows. As described above, the reciprocal of time t is 1
/ T and the screw rotation speed N are in a proportional relationship, and it is recognized that the target parison length can be secured by changing the screw rotation speed by ΔN with respect to the shift amount Δt of the time t. Therefore, the control constant a can be determined by the following equation using the times t ₁ and t ₂ until the parison corresponding to at least two screw rotation speeds N ₁ and N ₂ shields the reference photoelectric sensor. .

That is, two points (1 / t ₁ , N ₁ ), (1 /
t ₂ , N ₂ ) into the general formula of a straight line N = a (1 / t) + b, N ₁ = a × (1 / t ₁ ) + b, N ₂ = a × (1 /
t ₂ ) + b, and as a result, the control constant a is obtained by the following equation.

A = t ₁ × t ₂ × (N ₁ −N ₂ ) / (t ₂ −t ₁ ) The control constant a is usually determined by 1 when the resin is changed.
You just need to do it twice.

When the test molding process described above is completed, the normal molding process for obtaining an actual product can be started. Here, the controller 8 executes the operation shown in the flowchart of FIG.

In the normal molding step, first, the time t until the parison at the time of the current molding shields the reference photoelectric sensor from light is measured. Then, the time t is measured four times so that the screw rotation speed is not corrected for the sudden fluctuation, and the average time is calculated. When the average time is out of the dead zone, the correction amount of the screw speed of the extruder according to the parison length difference x = 1 / t−1 / t ₀ using the above-mentioned control constant a determined in advance. Calculate ΔN. Here, as the reference time, the control constant a, and the dead zone, values obtained in the test molding process and stored in a data memory or the like are used.

The controller 8 drives and controls the extruder screw motor 2 using the inverter driver 4 and corrects the screw rotation speed by feedback from the screw rotation detector 3 to obtain the target parison length. . When the screw rotation speed N is corrected, when α = ax exceeds the correction rotation speed (upper limit), the correction is performed using the corrected rotation speed. When α = ax does not exceed the correction rotation speed, ΔN = − if α> 0. The speed is reduced as | α |, and if α <0, the acceleration is performed as ΔN = | α | to correct the screw rotation speed.

[0035]

As is apparent from the above description, according to the method for controlling the parison length of the blow molding machine of the present invention, the photoelectric sensor for detecting the position of the parison when the shape of the molded product changes. It is not necessary to adjust the position while watching the balance with the molding cycle, and it is possible to automatically set the control constants and the like for controlling the parison length to be constant. These make it easy to set the molding conditions in the test molding process,
The time required for the setting can be greatly reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a system configuration for realizing an embodiment of the present invention;

FIG. 2 is a diagram showing an example of the arrangement of photoelectric sensors in the embodiment.

FIG. 3 is a timing chart illustrating a method for determining a reference photoelectric sensor in the embodiment.

FIG. 4 is a flowchart showing an operation of a test molding process in the embodiment (part 1).

FIG. 5 is a flowchart showing an operation of a test molding step in the embodiment (part 2).

FIG. 6 is a flowchart showing an operation of a normal molding process in the embodiment.

FIG. 7 is a diagram showing an example of a monitor panel of a controller according to the embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Blow molding machine 2 ... Extruder drive inverter motor 3 ... Screw rotation detector 4 ... Inverter driver 5 ... Parison 6 ... Parison cutting cutter 7, 7-1, 7-2, 7-3, 7-4, 7 -5 ... Photoelectric sensor 8 ... Controller

Claims (1)

(57) [Claims] 1. A screw in an extruder is rotated to extrude a parison in a molten state, the parison is sandwiched by mold clamping means to close an end thereof, and the parison is cut by a parison cutting cutter. Into the blow pin,
In the method of controlling the length of a parison of a hollow molding machine that blows air from the blow pin to form a hollow, first, in a test molding step, the extruded parison passes through a plurality of photoelectric sensors arranged in the direction in which the parison is extruded. At the same time, the last photoelectric sensor for detecting the position of the extruded parison is used as a reference photoelectric sensor during a period from the parison cutting command to the clamping by the mold clamping means to pinch the parison. From the above, the time until the parison shields the reference photoelectric sensor is measured a plurality of times, and the average time is calculated as a reference time corresponding to the length of the reference parison. The parison is extruded by changing at least two by a predetermined rotation speed from the parison, and the parison receives the reference light from the parison cutting command. The time until the sensor is shielded from light is measured a plurality of times. Next, the average time is obtained for each of the screw rotation speeds, and the at least two changed screw rotation speeds and the parison at that time are the reference values. A control constant is set based on the average time until the photoelectric sensor is shielded from light, and then, in the normal molding process, the time from when the parison is cut off to when the parison shields the reference photoelectric sensor from the parison cutting command is measured. Time until is corrected to screw rotation speed
Until the parison that does not apply light shields the reference photoelectric sensor
If the time is out of range, the control constants are used to
Calculate the screw rotation speed correction amount according to the quasi-time
And controlling the parison length of the blow molding machine by controlling the screw rotation speed to keep the parison length constant.