DE2947916A1 - CONTROL UNIT FOR A TUBE FILM EXTRUDER - Google Patents

Description

U.S. Ser. No. 964,983 November 23, 1979 Filed: November 30, 1978 10688 Dr.v.B / E

Gloucester Engineering Co., Inc. Blackburn Industrial Park, Gloucester , Mass. , V.St.A.

Control device for a tubular film extruder

The present invention relates to a control device according to the preamble of claim 1, in particular a control device for a Schiauchfolienblasanlage operating with internal cooling, in which the flow rate of the continuously flowing internal cooling air is directly dependent on the deviation of the position of the tube wall through optical devices is made.

In the case of tubular film biasing systems for the production of plastic bags and the like. A melted plastic tube is made from a ring-shaped nozzle or shape and then stretched while enlarging its diameter and reducing its thickness by means of squeegee rollers arranged above and by generating an overpressure inside the tube and expands. When the film is to be rolled up, the annular nozzle or the overhead nip rollers are slowly rotated to distribute any irregularities in the thickness of the film which may pass through Imperfections of the nozzle. To control the scope of the finished tube, it is generally necessary to measure the volume of the Control air trapped between the annular nozzle and the overhead nip rollers. It is common to use the volume of the trapped air through valves in the small air supply or inflation line that communicates with the interior of the tube. Normally, these valves are controlled by a two-point control depending on

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is controlled by the hose size that is being measured. With some of these Control devices, the hose size is measured by optical radiation blinds, which run tangential to the hose and are detected by a photocell. From US-PS 39 32 080 it is known, for example, to define the upper limit and the lower limit of the size of the hose with one photocell. One photocell opens a shut-off valve in the air supply, if the associated light beam can fall on them past the hose, what corresponds to a correspondingly small hose size. The other photocell Opens a shut-off valve in a vacuum or exhaust air line if the associated light beam is interrupted when the hose size has increased accordingly will. From US-PS 31 59 698 a working with photocells two-point control is known.

It is also known to use mechanical sensors for control purposes of the enclosed air volume with a two-point control. For example, in a rule known from US Pat. No. 3,700,370, the voltage difference between the output signals of potentiometers occurs the sensors are used to control a thyristor. A positive differential voltage, which corresponds to a too small dimension of the film tube, causes the thyristor to close a shut-off valve in the air supply to open. Generate fluctuations in the hose without changing its size no differential voltage and therefore do not cause any actuation of the solenoid valve. However, the use of mechanical sensors has the disadvantage that. the film is deformed.

In the case of blow molding machines, it is known to increase the production speed by an uninterrupted flow of cooling air Insert the cannula inside the nozzle, against the inner wall of the tube to be directed and allowed to flow off again through channels in the nozzle. It is known in such nozzles to dynamically regulate the air flow rate use a mechanical probe that follows the wall of the hose. From US-PS 39 80 418, for example, such a rule is known, which contains a single sensor, mechanically linked to a pneumatic one

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Control valve is connected, which via a pneumatic cylinder Controls the flap valve in the inner air supply line proportionally. As with all mechanical sensors, however, deformations occur as a result in the slide and there is necessarily a certain inaccuracy, that the film must first exert a certain pressure on the sensor before it reacts. In addition, the size of the hose with such sensors must be be carried out behind the area of the hose, while it is still in the molten state, in order to avoid impermissible deformations of the To prevent the hose wall from being caused by the cooling effects of the sensor. However, if you take the measurement in the pull-off direction of the film behind the melted area performs delays in the control system and the accuracy suffers.

The present invention is based on the object of a simple control device for keeping constant the circumference of an internally cooled, indicate blown film that works without contact and allows smaller tolerances to be adhered to.

This object is achieved according to the invention by a rule device of the type mentioned with the characterizing features of claim 1 solved.

Further developments and advantageous refinements of the invention are the subject of subclaims.

In the rule device according to the invention, the throughput a continuous flow of internal cooling air depending on the output signal of at least one specially designed optical position sensor controlled. The optical position sensor supplies an output signal that is based on the deviation of the position of a part or area of the hose wall in a position range on both sides of a predetermined set point (target position) depends directly and is preferably proportional to this deviation.

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Because of the fact that for these proportional measurements the Hose size does not use a mechanical but an optical position or position sensor, the measurement can be taken at or even below carry out the solidification limit, which separates the melted and solidified part of the hose, so that errors due to the delay are avoided which occurs when the measuring point is further down in the withdrawal direction of the solidified hose. The optical measurements are also more accurate than measurements made with mechanical sensors because there are no problems with the inertia of the feeler arm and the flexibility of the hose wall.

In particularly advantageous, preferred embodiments arrangements are provided to generate an electrical output signal, the 1m position or control range is linearly proportional to the position deviation of the wall; each optical probe contains an optical transmitter that is effective projecting a broad beam of radiation substantially tangential to the hose; the location or position of the hose wall is based on the percentage * set of coverage of the bundle width measured; a mask with an opening or a diaphragm is used to give the bundle a uniform appearance To give energy incrementally across its width, so that the linearity between the position of the hose wall and the output signal of the sensor is guaranteed; Coupled brackets are provided for the sensors, see above that the sensors can be adjusted in the radial direction, e.g. inwards, in order to to be able to set a desired hose target size, furthermore are the The sensor can be adjusted together in the longitudinal direction of the hose in order to to be able to determine on which the hose is measured; two or more optical sensors and theirs are arranged around the circumference of the hose Output signals are electrically combined to improve the accuracy of measuring the circumference of the hose and it is a control circuit provided to the air valve as a function of both the output signal of a valve position transmitter and the output signals of the optical To adjust sensors, with an internal feedback or control loop is provided, which ensures stable and rapid control of the air flow.

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The following is an advantageous embodiment of the invention explained in more detail with reference to the drawing.

Show it:

1 shows a schematic side view of a film blown film blower operating with internal cooling with a device according to the invention for regulating the tube circumference;

FIG. 2 shows a cross-sectional view in a plane 2-2 of FIGS. 1, 1n of the hose wall position sensors;

Fig. 3 is a vertical cross-sectional view in a plane 3-3 of Fig. F1g. 2, 1n which shows a height adjustment mechanism;

Flg. 4 is a vertical cross section 1n of a plane 4-4 of FIG. 2, 1n which shows the transmitter and receiver of a position sensor, a mounting arm for the sensor and an associated swivel mechanism for the mounting arm ;

Fig. 5 is a vertical section in a plane 5-5 of F1g. 4, 1n which the transmitter is shown;

6 is a vertical section in a plane 6-6 of FIG. 4 showing the receiver;

7a, 7b, 7c and 7d are schematic top views of the sensors for four different states of the hose, with 1st through the shading in small squares the fraction of a realtib wide optical Radiation beam that is covered or under the respective conditions blocked 1st, shown;

Fig. 8 is a circuit diagram of a control device;

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FIg. 9 shows a vertical section of the extruder nozzle and the internal hose cooling device of the system according to FIG. 1 on an enlarged scale, and FIG

Fig. 10 is a block diagram of the control device in which the Control device and the blow molding system are represented by function blocks.

In Fig. 1 is a film blowing system for the production of high quality plastic bags or plastic rolls shown. the The system contains an extruder 10 charged with plastic granulate via a feed hopper, in which the plastic granulate is melted and through a shape or nozzle 12 with an annular cross-section is extruded as a molten plastic tube 14. The hose is made by nip rollers pulled upwards, which stretch and lay him flat. The hose laid flat is fed through further rollers to a take-up roll (not shown). In order to evenly distribute azimuthal (calculated along the circumference) irregularities in the thickness of the hose wall, which are caused by irregularities in the nozzle opening 12, the nozzle 11 slowly rotated around its vertical axis Y, e.g. at a speed of approx 1 rpm.

After exiting the nozzle opening 12, the tube, which is still in the molten state, is in an area 18 from the diameter of the nozzle (e.g. 300 mm) to a desired final diameter expanded, which is typically between about two and three times the nozzle diameter. In the expansion area 18 is both of an outer and an inner cooling air ring 13 and 15 cooling air directed against the hose. The inner cooling air is supplied to the inner cooling air ring 15 through channels in the nozzle. The stale, warmed air is through a chamber 20 and through an outlet 19 and a pipe 21 through Channels 1n of the DUse removed. The air channels in the DUse are shown in more detail in Fig. 9. The hose solidifies at a so-called frost or Solidification line at a level L and has almost reached its final diameter there.

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The final diameter of the hose is controlled by changing the flow rate at which the internal cooling air is supplied will. By increasing the feed speed, i.e. the throughput of the supplied cooling air, the internal pressure in the hose and that in the The volume of air trapped in the tube increases and the tube is expanded more as a result. The speed at which the hose passes through the Squeeze rollers 16 is withdrawn, also affects the shape of the expansion area 18 and the height of the level L of the solidification line.

The final diameter is measured by two diametrically opposed optical sensor assemblies 22 (Fig. 2) which are just below each other are above the level L, where the final diameter is reached for the first time. The sensor assemblies 22 are supported by curved support arms 30 which are hinged to a lower ring 24. In the present embodiment, the ring 24 is suspended by shafts 34, 36 from an upper platform 37 which rests on supports 39. In the case of retrofitting, a such upper platform generally already exist.

The vertical .. adjustment of the lower ring 24 and the or the sensor holder arms 30 attached to it are carried out by turning a crank 42 which is fastened to the shaft 34, see FIGS. 1 and 2. When turning the hand crank 42, the shafts 34 and 36 are both in the same direction turned. The shafts are each provided with a thread at their lower ends, which is fastened into a corresponding thread on the ring 24 Guide blocks 23 is screwed so that the ring 24 can be raised or lowered by rotating the shafts. That at the same time * and Rotation of the shafts 34 and 36 in the same direction is effected by sprockets 40 attached to the upper ends of the shafts and by an upper one Chain 38 are coupled, which is guided around the upper platform 37. To guide the upper chain 38 guide wheels 43 are provided on a seat upper ring 41.

Fig. 2 shows that a transmitter 44, which delivers a broad beam of light 32, and a receiver 46 for the light

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Bundles 32 are arranged. The bracket arms are connected to each other by tine lower chain 28 coupled, which engage in sprocket elements 27, the are attached to pivot shafts 26 (Fig. 4) of the respective sensor mounting arms 30. The pivot shafts are supported by bearings in blocks 25, which are attached to a lower ring 24. The lower chain 28 is in places which are at a distance of 90 ° from the shafts 26 by means of bearing surfaces 31 of the frame (Flg. 3) out. By turning a crank 29, dl · on one Square can be plugged into one of the pivot shafts 26, can be dl Bracket arms 30 with the sensor assemblies in the same direction in the direction of swivel the hose towards or away from it.

As can be seen from Figures 4 and 5, each contains Transmitter 44 comprises a housing 82 in which an incandescent lamp 74 is arranged with a single vertical filament 75 which is parallel to the vertical axis · Y of the hose and the walls of the hose. The filament 75 Is placed at the focal point of a Fresnel lens 76. An dl Frcsnci-Lins 76 adjoins a nose plate or screen 84 with a specially shaped one Opening 84 and these two components are held behind a round opening 87 provided in the front of the housing 82 (Fig. 5). On the rear wall of the housing 82, a photocell 80 is arranged to the Measure the intensity of the light emitted by the light bulb 74 and they by means of a control circuit (not shown) at a constant value to keep. The position of the light bulb 74 can be adjusted by means of a screw 89. The light bulb 74 is operated at half its rated power, to increase the service life and reliability. The interior of the housing 82 is provided with a light-absorbing cover to ensure that that no light is reflected from the inner walls to the Fresnel lens 76.

The radiation receiver 46, which is shown in more detail in FIGS. 4 and 6, contains a housing 86 in which a photocell 78 mounted on the rear wall of the housing is located. An example is advantageous passivated silicon photodiode measuring 9.25 mm square (Type e.g. Optical Coating Labs P / N 110PL-1). The front wall

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The front wall of the housing 86 has an opening 91, behind which a window

85 and an infrared filter 88 are mounted. In the distance behind the arrangement A diffuser plate 90 and a polarizing filter 92 are arranged out of the window and the filter and in front of the photocell 78. The inside of the case

86 Is covered with a light-absorbing layer to prevent internal reflections to prevent.

As FIGS. 1 and 8 show, the electrical output signals of the opto-electrical converters or radiation receivers 46 Inputs 48 of amplifiers 50 in a control unit 51 are supplied. The output signals of the amplifiers 50 are summed by an amplifier 54 and filtered. The amplified and filtered photocell output signal or the output signal can be from a manually adjustable potentiometer 72 Via a switch 70 optionally fed to the input of an amplifier 55, in which the selected output signal with a valve position feedback signal or valve position actual value signal from a valve position transmitter 64 (e.g. type Pickering RVDT P / N 23330) is compared by the amplifier 55 generated error signal is further amplified by a power amplifier 66, whose output signal a valve servomotor 68 (type e.g. Electrocraft E-660), which in turn drives the valve 58 in the direction of the inner cooling ring 15 leading air supply line adjusted. The valve 58 can have a circular flap-shaped or wing-shaped shut-off member. The amplifiers 56 and 52 are operational amplifiers. In Fig. 8 are appropriate resistance and capacitance values entered for the circuit shown as an example.

F1g. 10 shows a block diagram of the control device. By The sensor 22 is the circumference error CL by calculating the difference between the target circumference Cp (which is given by the position of the feeler arms 30) and can be set) and the actual circumference C ^ of the film tube is calculated. The sensors also introduce a gain K- (2 V / cm). To simplify the block diagram, the sensors 22 are shown only in the form of a single subtracter and block; the amplifier hold 1m Control device that ko **> 1n1ert the output signals of the two position sensors, 1st

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on the other hand omitted. The signal at the output 100 of the sensors is processed by a low-pass filter 102 with a transfer factor or gain factor K. (1.0 V / V) and a time constant T ₁ (Vt ₁ = 50 rad / sec) (which is formed by the amplifier 54) ). The switch 70 can be used to set either the signal at the output 104 of the filter or a manually adjustable input signal H as a valve position command or valve position setpoint signal P _£ . In the amplifier 55, the difference between the setpoint signal Pp and the valve position feedback signal or valve pitch actual value signal Pp is calculated. This difference, the error signal Pp, is passed through a low-pass filter 110 with the gain factor K- (0.15 V / V) and a time constant τ _? (1 / τ ₂ = 1200 rad / sec) processed. The output amplifier 66 (an adjusting device) with the gain _{factor K 0} (10 V / V) converts the output signal of the filter 110 into an electrical signal suitable for driving the motor 68.

The motor 68 (K _n = 3.3 rad / V-sec) behaves like an integrator when converting the electrical output signal of the power amplifier 66 1n to the actual valve graduation P ^ (rad). The reason for this is that the angular speed of the motor is proportional to its electrical input signal and the valve position is the integral of the angular speed of the motor. The high-frequency response of the motor is determined by two first-order delays with the time constants τ and τ. The mechanical delay due to the rotational inertia and damping of the notor as well as its load is represented by a limit frequency of the value 1 / τ _Μ « 100 rad / sec . The inductance of the motor results in a cutoff frequency of 1 / τ * 280 rad / sec.

The valve position indicator 64 (transmission factor or amplification factor of 3.1 V / rad) generates an electrical RUckflihrungssignai accordance with the valve ISTS pitch P ^, which then is formed by a portion of the amplifier 55 through a DI Kompensationsfliter 114 (and Signalvor- or . lag compensated) 1n converted the valve control feedback signal Pp. The compensation filter has a D or lead time

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constant τ-, = τ, whereby the frequency response of the motor due to the

J 111

Compensation of its first cutoff frequency 1 / τ is extended. This enables a higher degree of amplification of the inner control loop and thus a higher degree of accuracy without endangering the stability. The I or lag cutoff frequency \ / x. of the compensation filter is 1000 rad / sec.

The remaining blocks in FIG. 10 describe the dynamic behavior of the hose and the air flow introduced into it. The effect of the valve 58 is by a constant gain factor Ky between the valve position P. and the cooling air flow Q approximated.

The relationship between the air flow Q introduced into the film tube and the actual circumference C. of the tube is approximated by blocks 116 and 118. The block 116 is an integrator with the gain or transfer rate Kp and represents the relationship between the air throughput (flow rate) and the hose circumference or its change. The integrating behavior results from the fact that the circumference of the hose is proportional to the volume of the in a first approximation Air trapped in the tube, which in turn depends on the integral of the flow rate of the air introduced into the tube. The block 118 then shows the dynamic behavior of the hose, including a standing wave resonance with a frequency of 1.3 Hz and fluctuations or flutter vibrations with a frequency of roughly 20 Hz. The block diagram is completed by a feedback branch 120, which is the actual -Couple scope C _A with sensors 22. The overall gain KyKp is about 300 mm / sec / rad (12 in / sec / rad).

Mode of operation : When the system is in operation, the circumference of the hose 14 is kept at the target value with narrow tolerances by controlling the throughput of the air stirred into the interior of the hose proportionally to the circumferential error determined. The flow rate or the throughput is adjusted by turning the flap or wing valve 58. The normal adjustment range of the valve is t 30 ° with respect to a normal rest position in which the valve flap forms an angle of 30 ° with the direction of flow. Normally only small changes in angle are required after

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which the system automatically returns to the set value or point has stabilized. A change in the hose diameter of 2.5 mi, for example, causes an initial change in the angle of attack of the valve flap by about 2 °, resulting in the nominal flow rate of about 17 m / min (600 cfm) is changed by about 0.226 m (8cfm). After a short tent span (a few Seconds), this change in the angle of attack falls back to zero, see above that the valve then resumes its initial setting with an angle of attack of 30 °.

When the film blower is started, the switch 70 Switched to the "manual mode" (M) position and the nominal diameter of the Hose is made by adjusting the position of the probe support arms 30 adjusted so that the vertical distance between the centers of the radiation bundles 32 is equal to the sol diameter of the tube. Then the set by a fan not shown discharged air flow so that when setting the valve 58 in the rest position with the angle of attack of 30 ° an air flow enters the hose interior, which is at least approximately results in the desired hose size. The potentiometer 72 can instead of the Sensor 22 can be used to adjust the valve 58 and / or the blower and thus the hose size.

To switch to the automatic regulation of the hose size, the switch 70 is switched to the automatic position. If the The hose circumference measured by sensor 22 is not correct, is displayed at the input of the Amplifier 55 generates a valve position command signal. This signal is through the amplifier 55, the power amplifier 66, the valve servomotor 68 and the feedback from the transmitter 64 in a corrective adjustment of the flap valve 58 converted. This will make the air flow automatic increased or decreased proportionally to the determined error of the hose circumference.

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29Λ7916

Changes in the circumference of the hose are determined or measured by processing the output signals of the sensors 22. Every feeler measures the position of the part or area of the wall of the hose leading from the The beam path of the relevant bundle 32 is cut. The position or attitude measurement is carried out by measuring the amount of the radiation receiver 46 reaching light. In the undisturbed state, each wall area should advantageously block approximately 50% of the width of the bundle 32 concerned or shade. If the wall area in question moves radially inward, a larger part of the bundle reaches the radiation receiver 46, with an outward movement, more of the bundle becomes covered.

As Fig. 4 shows, the width of the light beam tapers 32 from about 63.5 mm for the transmitter 44 to about 9.5 mm for the radiation receiver 46 and the bundles are at the point where they cut the hose wall, relatively wide, in the present case about 32 mm, so that correspondingly large changes in the position of the hose wall can be detected de * given example changes in a range of about 32 mm.

As can be seen from FIG. 7, the measurement of the hose circumference by calculating the sum of the optically generated output signals of the position sensors 46 is independent of fluctuations in the hose. 7a shows the situation when the hose circumference is too small; on both radiation receivers fills more than 50% of the relevant radiation beam 32 and the sum is therefore greater than 100%, which causes an increase in the cooling air supply. Id the 1n Flg. 7b, if the hose circumference is correct and the hose is not shifted laterally; 50% of the associated bundle 32 therefore falls on both recipients and the total is 100 t. In FIG. 7c, the hose circumference is also correct, but the hose is offset to the right by a fluctuation; the toads receiver fall more than 50% of the bundle 32 and on the right receiver less than 5OX, however, the sum is constant 100t, so that neither dnc increase or a reduction is effected of the air supply. In F1g.7d finally the tube circumference 1st too large, so that WE on both receivers

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Less than 5OZ of the associated bundle falls and the SuiMe less than 100X which indicates and causes a decrease in the air supply. Among other things at Use of this Sunmatic technique an independence of the comprehensive measurement of To achieve lateral displacements or fluctuations of the hose, the Output signals from the detectors or radiation receivers 46, or an electrically processed version of these output signals, is substantially linear proportional to the positional deviation of each wall area or wall part.

In order to achieve this linearity without additional electrical signal processing, the radiation bundles 32 are formed in such a way that each Incrementally, i.e. each vertical strip of a given width along the horizontal width direction of the bundle contains the same radiant energy. This homogeneity of the radiation beam in the width direction is at the described Ausrührungsbeispiel achieved that nan the opening 85 of the aperture 84 of each optical transmitter 44 has a curved shape, in particular a curved upper and / or lower edge of the otherwise substantially rectangular aperture (see Fig. 5), so that the natural horizontal Non-linearity produced by the light bulb 74 and the Fresnel lens 76 Energy distribution is compensated for when there is a perfect lens, be it one Fresnei lens or another type of lens, and the correct focal distances or Brennwelten are used, the curved shape becomes that of an hourglass correspond, whereby the height of the radiation beam in the middle is smaller 1st than on the lateral margins. Such a shape simply corrects that known cosine square drop in light intensity in the direction of the Edge of a lens. In the case of the embodiment used for the described embodiment, special Fresnel lens increases the light intensity towards the edges. so that an aperture with an approximately barrel-shaped aperture is used will, as they 1n Flg. 5 shown 1st.

In order to make the circumferential measurement independent of fluctuations or displacements of the tube, which run parallel to the direction of the bundles, the directions in which the two parallel bundles of radiation taper are opposite to one another, to that bti

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Emigration of the hose parallel to the bundle axes creates one bundle stronger and the other bundle is shaded accordingly less strongly. Fluctuations of the hose in the direction of the bundle therefore change the Total shading is not.

The difference between the positional deviations of the two diametrically opposite wall areas results in the change in the hose diameter, which is proportional to the circumference for a circular cross-section (the same applies to non-circular cross-sections if the Shape as such is retained with the size changes.) The difference between the positional deviations is in the described embodiment calculated according to the invention by forming the analog sum of the output signals of the sensors 46. This sum gives the difference due to the polarity of the Output signals from the sensors, as the latter deliver a larger signal when the wall area in question moves radially inward. the Sum is calculated by amplifier 54 in an analogous manner.

The light bundles 32 enter the respective radiation receiver 46 through the window 85 and the infrared filter 88. The filter retains infrared radiation so that it appears more opaque, since it generally has a higher transmission capacity for infrared light. Before that If the bundle falls on the photocell 78, it passes through the diffuser plate 90 and the polarizing filter 92. The diffuser plate 90 distributes the received Light beam over the entire receiving surface of the photocell, so that a maximum response for the changes in the received light results. The polarization filter 92 holds back light of the polarization direction which is let through by the hose. The polarization filter, like the infrared filter, makes the tube appear more opaque.

The electrical output signals of the photocells 78 pass through the feedback control circuit shown in FIG. 8 to control the flow of the To change the internal cooling air in the sense of a correction of the hose diameter. The summer 52 summarizes the output signals of the two photocells, according to

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to which they have been amplified by the amplifier SO and the summed signal, 12 volts are added to produce a difference signal which is representative of the deviation from the nominal circumference of the hose (i.e. the difference signal is equal to zero when the sum of the transmission percentages is on the receivers 46 is equal to 1002). The difference signal is passed through a first-order low-pass filter (cut-off frequency about 8 Kz) at the amplifier 54 in order to filter out the 20 Hz natural fluttering vibrations in the hose wall layer, which are generated by the external cooling air flow. The filtered difference signal (or the output signal of the manually adjustable potentiometer 72) is then fed to the amplifier 50 via the switch 70.

The input signal of the amplifier 55 acts as a valve position command signal and is converted into a rotation of the flap valve 58 by the Amplifier 55, the power amplifier 66 and the motor 68 converted and generated via the position transmitter 64 a corresponding valve 11 position actual value signal. The difference between the command or Sol 1 value signal and the The feedback actual value signal, that is to say the error signal, controls the power amplifier 66, which in turn drives the valve servomotor 68.

Aer in the automatic regulation of the flow InnenkUhlluft by the just described system is the inner control loop, by the! Is returned position, the grip handle, essential for the maintenance of a stable tube diameter and decisive. The inner feedback loop eliminates the integrator relation between the signal fed to the servomotor and the valve position.

The gain factors and the compensation of the inner feedback loop are advantageously chosen so that the gain factor f (0 dB} for the open loop results at around f0 Hz (65 rad / sec). This causes the bandwidth of the closed inner rule to be skewed ft (3 dB attenuation) also f0 Hz. Which is sufficiently large not to slow down the response of the external control loop regulating the hose circumference.

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In addition, the open loop gain is low enough to allow to prevent the delays (τ urdx) of the actuating devices in

III C

Cause stability. The gain factor Kp and / or K. are selected so that the desired gain factor of the open loop results. The reciprocal of the product of K ₃ and K _$ (0.08 rad / V) determines the gain of the closed loop or the proportionality or wet bar factor between the valve position and the command signal Pp.

After the Inner Loop address has been determined 1st, the gain of the outer loop is adjusted so that a bandwidth (or an open loop gain of 1) of about 0.6 Hz results. The bandwidth is chosen so that it is about 50X the standing wave resonance frequency of the hose in order to ensure a large safety factor for stability and at the same time to ensure a sufficiently quick response to precisely adhere to the desired hose circumference. A faster response can be achieved by increasing the Reinforcement of the outer loop (by adjusting the potentiometer 71) can be achieved, but this reduces the margin of safety. With a « Foil tube with a length of 6.1 m, a width of about 0.9 m and a thickness of 25 μm, which was under a tension of about 13.5 g / 25.4 cm-25.4 μm (0.03 1b / 1n-mi1), a resonance frequency (a standing UeIIe in the film) of 1.3 Hz determined.

With the feedback of the valve position in the inner control loop, the system is stable, i.e. a small disturbance does not generate an increasing vibration.

Without the inner control loop, an unstable oscillation can occur as a result of phase shifts that are introduced by the two integrators, the valve motor and the flow integration and through the inherent negative feedback of the actual circumference of the hose. Without the inner rule loop, the effect would occur that an oscillation that initially occurs somewhere in the outer control loop would immediately be replaced by equal

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phase signals that have traversed the loop is amplified. Since the If the gain in the outer loop is greater than 1 in order to be able to regulate the hose size effectively, such an initial disturbance would itself amplify and generate strong fluctuations in the hose circumference.

The stability also depends on the vertical position of the sensor assemblies 22 with respect to the solidification line or limit. if If the sensors are positioned too far above the solidification limit, a delay is introduced because changes to the hose circumference at the solidification limit require a certain amount of time before they move up to the position sensors. long. This delay contributes to the phase shift, as does the integration behavior of the valve servomotor and the flow integration.

On the other hand, the position sensor arrangements 22 should normally not be in the frustoconical area below the solidification limit because in this case changes in the shape of this area (e.g. a steepening of the cone angle) are wrongly considered changes in the Hose circumference could be interpreted. In addition, the solidification limit often moves vertically during operation. One of those considerations The compromise that takes into account is to arrange the position sensors at or slightly above the solidification limit.

The specific embodiment of the invention described can be modified in some respects. E.g. less or more arranged as two sensor assemblies along the circumference of the hose will. If fewer than two position sensors are used, fluctuations in the position of the hose are included in the circumference measurement. By the use of more than two position sensors, on the other hand, one can better take into account a situation in which the hose assumes a non-circular cross-section, but maintains the circumference. In this case there would be no correction the air flow is desirable, since the width of the hose laid flat does not change. Another possible modification of the one described Execution example would consist, for example, in the use of other types of optical position

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lead to use, including laser scanning devices, instead of the preferred optical transmitters or radiation beam sources described.

The upper bracket assembly shown in Fig. 1 is preferably omitted if such a support frame is not already available in the system. The upper construction would then be replaced by a corresponding Replaces bracket assembly that is supported on the outer cooling air ring 13 or the carriage or support that carries this ring.

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Read 11 e

Claims (13)

Claims Typically, a tubular film extruder is used to maintain a predetermined target circumference in a longitudinal direction extending, thin-walled, expanded plastic hose, which is made of an annular nozzle is extruded, with an internal cooling device, which is in communication with the interior of the hose and introduces a continuous flow of cooling air into the hose interior, an outlet device through which the heated air flows out of the hose interior, a valve arrangement for adjusting the flow of cooling air and an optical position sensor device which is responsive to changes in the position of the wall of the inflated plastic tube, characterized in that a) the optical position sensor device has at least two optical position sensors (22) and an arrangement for generating a variable electrical Contains output signal for each sensed wall area, which in a given position range from the deviation of the position of the wall in question 030025/0606 mOncbjbn nm. «ti 4 ·· μμ · Bank account ιιυγοιιανη μΓνγηκν uii.k tuomnmoi κ το. μ »μ ·« τ · τη »throw κ · γ ro na mm ORIGINAL INSPECTED area depends directly on a predetermined target position and a large number can assume different values that correspond to different positional deviations; b) a control device (54) is provided which is derived from the electrical output signals a difference signal is calculated which represents the deviation of the circumference of the hose from the nominal circumference; c) that formed by the position sensor device and the control device System is designed so that the difference signal is insensitive to transverse movements of the hose is if this does not affect the hose circumference and d) the valve arrangement (58) is a device responsive to the differential signal which contains the continuous introduced into the Sch! Air flow in the sense of a reduction in the amount of the difference signal and thus in the sense of returning the circumference of the hose to the target value adjusted. 2. Control device according to claim 1, characterized in that to eliminate the influence of transverse movements or fluctuations of the plastic hose on the difference signal, an arrangement (76, 84, 85) which each of the electrical output signals 1m substantially linearly proportional to the deviation in the position of each wall part is provided in a certain position range of a predetermined set and the control device contains an arrangement (54) which calculates the difference signal as a function of the relative distances between the wall parts. 3. Control device according to claim 1 or 2, characterized in that each optical position sensor (22) has an optical transmitter (44) for generating a radiation beam (32) which extends 1m substantially tangential to the sensed wall area of the 1n longitudinally extending tube and in Radial direction of the hose has a cross section of such a size that it extends over a certain area on both sides of a certain position and thereby the location area 030025/0606 the wall area in question is defined, and a radiation sensor (46), which detects the radiation beam (32) at a location beyond the tangent wall area, each of the many electrical The output values of the position sensor correspond to a different percentage of the shading of the bundle by the relevant wall area and the control device (54) calculates the difference signal by adding up the electrical output signals. 4. rule device according to claim 3, characterized in that each optical transmitter (44) has an arrangement (76, 84, 85) for incrementally projecting a bundle of uniform beam energy in the transverse direction and each optical radiation sensor contains a photocell array (78) which generates the electrical output signal from the incident beam. 5. Control device according to claim 4, characterized in that the optical transmitter has a light source (74), a lens (76) and a diaphragm or masking device (84, 85) for changing the height of the light beam in a direction parallel to the longitudinal axis of the Hose In zones that are transversely outside its center, contains to To correct irregularities in the light beam generated by the light source, in particular its filament, and the lens in the transverse direction. 6. Control device according to one of the preceding claims, characterized in that the control device (54) supplies the difference signal in the form of an analog value and that the valve arrangement contains a device (55, 64, 66, 68) which adjusts the air flow proportionally to this analog signal. 7. rule device according to claim 2 or claim 2 and one of claims 3 to 6, characterized in that the position sensor device (22) senses two wall areas which are arranged diametrically opposite on opposite sides of the hose; 030025/0608 29A7916 that each light beam has a tapered, tapered cross-section along the length of the bundle, the direction of the bundles sensing the two wall portions being opposite to each other such that If the tube migrates in the longitudinal direction, the bundles are covered more and the other less; that the control device (54) forms the difference between the electrical output signals of the two areas as a difference signal, which accordingly is independent of a fluctuation in a direction parallel to the direction of the bundles. 8. Control device according to one of the preceding claims, characterized in that the system for detecting deviations has a number of brackets (30) which each carry an optical position sensor arrangement and can be adjusted as a function of a plurality of different radial positions with respect to the hose wall, in order to be able to set different Sol! layers for hoses of different dimensions. 9. rule device according to claim 8, characterized in that that the brackets (30) contain pivotable arms which are pivotable in planes extending transversely to the hose, and that a coupling arrangement (27, 28) is provided, the simultaneous pivoting of the arms and thus an adjustment of the transverse position of all optical Allow sensor arrangements with respect to the wall of the hose by a single adjustment process of the pivotable arms coupled to one another. 10. Control device according to claim 8 or 9, characterized in that each optical sensor arrangement has an optical transmitter (44) for generating an optical radiation beam which is substantially tangential to the wall of the longitudinally extending hose, the area in which the radiation beam is tangent to the wall, which corresponds to the respective position sensor associated wall portion, and an optical radiation sensor (46) for converting the 030025/0608 incident radiation beam in an electrical output signal which is linearly proportional to the percentage up to which the respective radiation beam is shaded by the associated wall area; and that the control device (54) contains an arrangement for summing the electrical output signals with calculation of the difference signal, the mountings (30) being adjustable so that the radiation beams are partially shaded by the wall parts in the tangential areas when the hose is at its desired circumference and that changes in the sum of the percentages of coverage of the bundles are representative of changes in scope. 11. rule device according to claim 8, 9 or 10, characterized in that a device for adjusting the longitudinal position of the optical sensor assemblies is provided along the hose, which includes a support ring (24) surrounding the hose; that the brackets extend away from points which are spaced apart in the circumferential direction of the support ring and that a device (23, 34, 38, 40, 42) is provided for longitudinal movement or adjustment of the support ring. 12. Control device according to one of the preceding claims, characterized by a valve position transmitter (64) which supplies a valve actual position signal dependent on the actual position of the valve arrangement (58); that the actual valve position signal is fed to an arrangement (55) which generates an _{error signal (P E} ) dependent on the difference between these signals from the difference signal (P-) and the actual valve position signal (P.); that an actuating arrangement (66, 68) controlled by the error signal is provided which supplies a control signal for controlling the valve arrangement (58) in order to adjust the air flow, the valve position transmitter (64), the arrangement (55) processing the signals Actuating arrangement (66, 68) and the valve arrangement (58) form an inner feedback loop which reports the valve position back to the arrangement processing the signals and this inner feedback or control loop enables the control device to correct deviations in the circumference of the hose quickly and stably. 030025/0606 13. Control device according to claim 12, characterized by a second processing arrangement (54) which on the difference signal is responsive and provides a signal to the first-mentioned arrangement (55), the gain factors of the first and second Signal processing arrangement is chosen so that the frequency at which the total loop gain of the device is equal to 1, sufficiently far below the Standing wave resonance of the hose and stable operation is guaranteed. 030025/0606