JP3101483B2 - Control method of molding cycle time of blow molding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a molding cycle time of a blow molding machine.

[0002]

[Prior art] Conventional parison length technology and
Therefore, Japanese Patent Application No. 3-358178 filed by the present applicants is
is there. In this conventional example, the screw of the extruder is rotated
Extrude the parison in the molten state, hold it with
Close the part and cut the parison, blow the air and hollow
When molding, controlling the screw rotation speed of the extruder
Control method for blow molding machine to keep the parison length constant
It is. In this conventional example, test formation is usually performed before the molding process.
The molding process is set, and the parison length of the resin used is
Parison length and extruder screw speed detected by the electric tube
The relationship between the current
The parison length is detected by the photocell, and the current parison length and eye
The parison length difference from the standard parison length was calculated and found in advance.
From the relationship between the parison length and the screw speed of the extruder,
Of screw speed of extruder according to parison length difference
Calculating the positive amount to control the screw speed of the extruder
To obtain the target parison length.

[0003]

However, the above-described conventional method for controlling a blow molding machine has the following problems.

The molding cycle time on the molding machine side is expected to be constant, and is not corrected. However, the actual molding speed of the blow molding machine is changed, for example, the operating speed fluctuates due to a change in oil temperature like a hydraulic mechanism. Have irregularities in the operation time, and the unstable molding cycle time has been a factor of unstable product quality.

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 a molding cycle time of a hollow molding machine for easily stabilizing product quality. is there.

[0008]

In order to achieve the above object, according to the present invention, a parison in a molten state is extruded by rotating a screw of an extruder, and the parison is clamped by mold clamping means to close an end. At the same time, the parison is cut with a parison cutting cutter, and a blow pin is driven into the parison,
In the method of controlling a molding cycle time of a hollow molding machine for performing blow molding by blowing air from the blow pin, first, from a die opening command to a molding die to a start of driving of the blow pin into a parison in the molding die. Measure the operating time, then
A value obtained by subtracting the operation time from the set molding cycle time is defined as a cooling time, and then the cooling time is allocated to a blowing time and a discharging time, and the fluctuation of the operating time is adjusted by increasing or decreasing the discharging time. It is characterized by.

Alternatively, the screw of the extruder is rotated to extrude the parison in a molten state, the parison is sandwiched by mold clamping means, the end is closed, and the parison is cut by a parison cutting cutter. In the method of controlling the molding cycle time of a blow molding machine that blows air into the blow pin and blows air from the blow pin to perform blow molding.
First, the operation time from the mold opening command to the molding die to the start of the driving of the blow pin into the parison in the molding die was measured, and then the operation time was subtracted from the set molding cycle time. The value is defined as the cooling time, and then the cooling time is allocated to the blowing time and the discharging time, and the fluctuation of the operating time is adjusted by increasing or decreasing the discharging time, and the parison length is controlled by controlling the screw rotation speed. Is constant. Alternatively, in the step of controlling the screw rotation speed and keeping the parison length constant, first, in the test molding step, the extruded parison is passed through a plurality of photoelectric sensors arranged in the direction of extrusion of the parison, 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 instruction to the clamping means going to clamp the parison. Measures the time until the reference photoelectric sensor is shielded a plurality of times, calculates the average time, sets it as a reference time corresponding to the reference parison length, and then sets the screw rotation speed to a predetermined value from the current value. The parison is extruded by changing at least two rotation speeds, and the parison shields the reference photoelectric sensor from the parison cutting command. And measured a plurality of times the time in,
Next, the average time is determined for each of the screw rotation speeds, and a control constant is determined from the average rotation time at which the at least two changed screw rotation speeds and the parison at that time shield the reference photoelectric sensor from light. Set,
Next, in the normal molding process, the time from the parison cutting command to the light blocking of the reference photoelectric sensor by the parison is measured, and the time until the light blocking is measured by the screw rotation.
A parison that does not correct the rotation speed blocks the reference photoelectric sensor
If the time before disconnection is out of the range, the control constant
Of screw rotation speed according to the reference time using
Calculate the amount and control the screw rotation speed to control the parison
It is characterized by keeping the length constant.

[0011]

According to the method of controlling the molding cycle time of the blow molding machine of the present invention, the operation time from the mold opening command to the blow molding machine to the start of the driving of the blow pin into the parison is always measured. The value obtained by subtracting the operation time from the above is taken as the cooling time, and this cooling time is distributed to the blowing time and the discharging time, and the variation of the operating time is adjusted each time on the discharging time side, so that the blow molding machine is set at a predetermined constant value. Operate in molding cycle time. As a result, the molding cycle time is made constant every time, and the variation in product quality is reduced and stabilized. In addition, by controlling the screw rotation speed of the extruder to keep the parison length constant, product quality is further stabilized.

[0012]

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 implementing a method of controlling a molding cycle time of a blow molding machine according to the present invention. In this system, a parison of a fixed length formed of a molten resin is sandwiched between molding dies, and air is blown into the molding. Control of the molding cycle time is performed by a mold opening command (molding command). This is to control the time from the slide command for the mold) to the end of cooling to be constant. First, the configuration of the present system will be described. In FIG. 1, 1 is an extruder 1
a, an extruder driving inverter motor (hereinafter abbreviated as “motor”) for rotating an extruder screw (not shown) of the extruder of the hollow molding machine 1; A screw rotation detector 4 for detecting rotation by a pulse; an inverter driver 4 for feeding back a detection pulse of the screw rotation detector 3 to control the rotation speed of the motor 2 so that the rotation of the screw becomes a specified rotation speed; A molten tubular parison made of a thermoplastic resin extruded by the rotation of a screw of the extruder, and 6 is a parison cutting cutter. Numeral 7 denotes a photoelectric sensor for detecting a parison length. As shown in FIG. 3, for example, a plurality of photoelectric sensors 7-1, 7-2, 7-3,
7-4 and 7-5. 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. The controller 8 corrects a molding cycle time from a mold closing command to a cooling process consisting of blowing and discharging (discharging) of air through lowering of the blow pin for driving the blow pin into the parison from the mold opening command, thereby correcting the molding cycle time in a feedforward manner. It has a function to make it constant.

FIG. 3 is a diagram showing an example of the arrangement of the photoelectric sensor 7 used when the parison length is made constant. 1
Reference numeral b denotes a head of a hollow molding machine that pushes 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 projector (PHD) and a light receiver (PHS). In this system example, five photoelectric sensors 7-1 (PHD1 and PHS1), 7-2 (PHD2 and PHS2), 7 -3
(PHD3 and PHS3), 7-4 (PHD4 and PHS)
4), 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 being 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. Next, an embodiment of a control method for keeping the molding cycle time constant in the normal molding step of the present invention will be described with reference to the flowchart of FIG. First, pre-input and set a predetermined molding cycle time T ₀ to the controller 8 to start the forming operation. When molding is started, the controller 8 measures the operation time T _1. Here, the operation time is a time from the mold opening command to the start of the driving of the blow pin into the parison. The operation time T ₁ is an average time of three times calculated by the controller 8 after adding the operation time measured twice in the past to the current operation time after the automatic operation is started. The automatic operation before start operation time until the operation time T ₁ is determined, the operation time in the preceding molding operation time T _1. Next, Hesi the operation time T ₁ from the molding cycle time T ₀ set, calculates the cooling time T _2. Cooling time = molding cycle time setting - operating time = T ₀ -
T ₁ = T ₂ Subsequently, the determined cooling time T ₂ is distributed to the blowing time T ₃ and the discharging time T ₄ at a predetermined ratio, for example, 8: 2. Cooling time _{× 0.8 = T 2 × 0.8 =} T 3 ( blow time) cooling time _{× 0.2 = T 2 × 0.2 =} T 4 ( release time) Subsequently, in the normal molding (currently) Operation The time T ₁ ′ is measured, and the (current) cooling time T ₂ ′ is calculated by subtracting the (current) operation time T ₁ ′ from the molding cycle time T ₀ . Cooling time = molding cycle time setting - operating time = T ₀ -
T ₁ ′ = T ₂ ′ Further, the blowing time T ₃ distributed from the (current) cooling time T ₂ ′
To calculate the (current) release time T ₄ ′. Release time = Cooling time−Blowing time = T ₂ ′ −T ₃ = T ₄ ′ After that, the (current) discharging time is maintained while the variation of the (current) operating time T ₁ ′ in the normal molding is maintained without changing the blowing time T _3. Correct every time by adjusting T ₄ ′. Thus, the molding cycle time is always controlled to the set molding cycle time. Next, a control method for keeping the length of the parison 5 constant will be described. This method is performed by controlling the rotation speed of a screw that extrudes the extruder 1a. The outline of the method for controlling the screw rotation speed is as follows. A test molding process is provided before the normal molding process. In this test molding process , a plurality of photoelectric sensors are used.
One of which is the reference photoelectric sensor, and the parison length of the resin used
Equivalent value , in other words, the parison blocks the reference photoelectric sensor.
Calculate the reference time by measuring the time until the
Control constant based on the relation between quasi-time and screw speed of extruder
The parison cutting finger is usually used in the molding process.
From the date the parison shuts off the reference photoelectric sensor.
Measure the time at. The time to shut off
The parison that does not correct the Liu rotation speed
If the time for shutting down the sensor is out of the range,
Using the control constant, and calculates a correction amount of screw rotation speed corresponding to the reference time, obtain a parison length of <br/> targets by controlling the screw rotation speed. Also, the following method may be used as a method for controlling the screw rotation speed. A test molding process is provided before the normal molding process, and in this test molding process,
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 at least two screw rotation speeds from a current value to a predetermined rotation speed, a time from a cutter command (a parison cutting command to the parison cutting cutter 6) until the parison shields the reference photoelectric sensor is obtained. A proportional constant is obtained from an inversely proportional relationship between the screw rotation speed and the time until the parison shields the reference photoelectric sensor, and is used as a control constant. Then, in the normal molding process, determine the time until the parison to shield the reference photoelectric sensor, the time until the light-shielding, screw
-A parison that does not correct the rotation speed
If the time before the light is blocked out of the
Screw rotation speed according to reference time using control constant
Calculate the correction amount of and control the screw rotation speed,
Get the target parison.

The controller 8 executes an operation as shown in the flowcharts of FIGS. 5 and 6 in the test molding process.

In FIG. 3, 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 is determined by performing an automatic operation as a test molding step. The test molding step 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. 8 and pressing the start key 4c. That is, first, as shown in the timing chart of FIG. 4, the parison 5 shields light from a cutter command (a parison cutting command to the parison cutting cutter 6) to a slide command to the molding die. For example, the last photoelectric sensor 7 is detected five times, and the photoelectric sensor 7 that has been shielded from light five times in succession is set as a reference photoelectric sensor as the last photoelectric sensor. In the example of FIG. 4, 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 step, a relationship between the screw speed of the extruder and a parison length equivalent value (time t until the parison shields the reference photoelectric sensor from light) is determined. Assuming that the extruder screw rotation speed is N, it is known that N is proportional to the reciprocal 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, a 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, a 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. Then, the controller 8 drives and controls the motor 2 of the extruder screw 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, if α = ax exceeds the correction rotation speed (upper limit value), the correction is performed using the corrected rotation speed.
The speed is reduced as N = − | α |, and if α <0, the speed is increased as ΔN = | α | to correct the screw rotation speed.

[0031]

As is apparent from the above description, according to the method for controlling the molding cycle time of the blow molding machine of the present invention, the variation of the operating time of the blow molding machine can be automatically corrected to reduce the molding cycle time. Since the molding is made constant,
Factors of unstable product quality are eliminated, and a product of good quality can be obtained. In addition, since the length of the parison is made constant by adding the control of the screw rotation speed to the control of the molding cycle time, the product can be molded stably, and a product with stable quality can be obtained.

[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 flowchart showing an embodiment of the present invention.

FIG. 3 is a diagram showing an example of arrangement of photoelectric sensors in the above system configuration example.

FIG. 4 is a timing chart for explaining a method for determining a reference photoelectric sensor in the above system configuration example.

FIG. 5 is a flowchart showing an operation of a test molding process in the above system configuration example (part 1).

FIG. 6 is a flowchart showing an operation of a test molding process in the above system configuration example (part 2).

FIG. 7 is a flowchart showing the operation of a normal molding process in the above system configuration example.

FIG. 8 is a diagram showing an example of a monitor panel of a controller in the above system configuration example.

[Description of Signs] 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 (3)

(57) [Claims] 1. Rotating the screw of the extruder to melt
Extruded parison, and clamp the parison with mold clamping means
And close the end with a parison cutting cutter.
Cut the lisson, drive a blow pin into the parison,
A blow molding is performed by blowing air from the blow pin.
In a method of controlling a molding cycle time of a molding machine, first, a pariso in the molding die is issued from a mold opening command to the molding die.
Measures the operation time until the start of the blow pin driving down
And  Next, the operation time is calculated from the set molding cycle time.
The subtracted value is used as the cooling time,  Next, this cooling time is allocated to the blowing time and the discharging time,
Adjust the fluctuation of the operating time by increasing or decreasing the release time That
A method for controlling a molding cycle time of a hollow molding machine. 2. A parison in a molten state is extruded by rotating a screw of an extruder, and the parison is sandwiched by mold clamping means to close an end, and the parison is cut by a parison cutting cutter. Into the blow pin,
In a method of controlling a molding cycle time of a hollow molding machine that blows air from the blow pin to perform hollow molding, first, from a die opening command to a molding die to a start of driving down of a blow pin into a parison in the molding die. The operation time is measured, and then a value obtained by subtracting the operation time from the set molding cycle time is defined as a cooling time.Then, the cooling time is allocated to the blowing time and the discharging time, and the fluctuation of the operation time is calculated. A method for controlling a molding cycle time of a blow molding machine, characterized in that, in addition to adjusting the release time, the screw rotation speed is controlled to keep the parison length constant. 3. In the step of controlling the screw rotation speed to keep the parison length constant, first, in a test forming step, the extruded parison is transferred to a plurality of photoelectric sensors arranged in the direction in which the parison is extruded. While passing, the last photoelectric sensor for detecting the position of the extruded parison is used as a reference photoelectric sensor during a period from the command for cutting the parison to the time when the mold clamping means goes to clamp the parison. From the command, 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 reference parison length. The parison is extruded by changing at least two by a predetermined rotation speed from the value, and the parison is driven by the reference photoelectric sensor based on a cutting instruction of the parison. The time until the light is shielded 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 photoelectric sensor. Then, a control constant is set based on the average time until the light is shielded, and then, in the normal molding process, the time from the parison cutting instruction to the light blocking of the reference photoelectric sensor by the parison is measured. Time corrected to screw rotation speed
Before the parison shuts off 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
Control the screw rotation speed to keep the parison length constant
Control method for a molding cycle time of a blow molding machine according to claim 2, characterized in that the.