US 3628025 A
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United States Patent inventor Franz Kieierle Well am Rhein, Germany Appl. No. 4,583 Filed Jan. 21, 1970 Patented Dec. 14, 1971 Assignee Lonza Ltd.
Basel, Switzerland Priority Jan. 24, 1969 Switzerland 1041 PHOTOELECTRIC CONTROL DEVICE 5 Claims, 2 Drawing Figs.
US. Cl ...250/2 19 LG, 250/220. 250/222 lnt.Cl ..G0ln 21/30 Field of Search 250/208,
209, 221, 222, 231 P. 229, 206, 43.5 L, 219 WD, 219 LG, 220, 224, 219QA; 315/159  References Cited UNITED STATES PATENTS 3,123.217 3/1964 McMillan 250/222 X 3,375,377 3/1968 Barrows 250/23l P Primary Examiner-Archie R. Borchelt Assistant Examiner-D. C. Nelms Atlorney Brady. OBoyle & Gates ABSTRACT: A photoelectric control device in a tube inflating device comprises a light source directed to a series of photoelectric elements each associated with a trigger. Each trigger, except that of the element at one end of the series has a blocking device arranged in response to response of its trigger darkening of its photoelectric element. to operate the trigger of the next photoelectric element in the direction of said end.
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FRANZ K/EFERLE y ATTORNEYS Patented Dec. 14, 1971 3,628,025
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ATTORNEYS PHOTOELECTRIC CONTROL DEVICE This invention relates to a photoelectric control device for controlling the position of one limit of a dark zone having two limits which always lie between the limits of a distance which also represents the range of control.
Photoelectric control devices, e.g., for level control, are known wherein a photoelectric scanning device (light box) follows one edge of a dark zone whose other edge lies outside the range of control.
Previously proposed devices of this type have a follower wherein the beam from a light source follows the movements of one limit of the dark zone. If the other limit of the dark zone lies within the control range, this previously proposed follower arrangement cannot be used, since the follower device is uncertain when the light box is outside the dark zone.
The present invention provides a photoelectric control device for controlling the position of one limit of a dark zone having two limits which always lie within the limits of a distance which also represents the range of control, the device also having means to measure this position, wherein photoelectric elements are disposed in a series along the distance forming the range of control at a mutual spacing such that at least one of the photoelectric elements always lies in the dark zone, and each photoelectric element has a respective trigger responsive to darkening of its photoelectric element, thereof, the triggers each having an output current which assumes a constant value, and the output jointly fonning the measurement value, each trigger, with the exception of the trigger of the photoelectric element at one end of the series, controls a respective blocking circuit which on response of its controlling trigger also operates the trigger of the next photoelectric device in the direction of said end of the series in the same manner as a darkening of said next photoelectric device, so that the triggers of all the photoelectric devices following a darkened photoelectric device in the said direction also respond.
This control device can be designed for instance as a twopoint or multipoint controller, or as a continuous controller for controlling a constant or for program control.
This control device is preferably used in a device for inflating tubes of sheet material, especially thermoplastic material, in order to control the tube diameter by affecting the inflating air inlet and/or outlet.
The present photoelectric device may be included in a tube inflation device with the series of photoelectric devices and a light source directed towards them so disposed that, in use, the inflated tube protrudes into a divergent light beam projected by the light source towards the series of photoelectric devices, and an adjustment motor actuated by the photoelectric control device for adjusting a control valve in the inlet and/or outlet air feed to the tubular foil.
The light absorption of the transparent and extremely thinwalled tube may be so slight that all the light beams which pass through the sheet material along the chords of the tube cross section, i.e., which pass through the sheet material twice, are hardly weakened. In this case, there is only a very narrow zone of darkness in the region wherein the light beams immediately adjacent a tangent to the tubular foil undergo total internal reflection into the foil. The photoelectric control device responds to changes in the position of this narrow band of darkness (whose two boundaries lie between the ends of the series of photoelectric elements) caused by changes in the diameter of the tube, and adjusts the adjustment motor for the control valve in the inlet and/or outlet air feed to the tube in order to keep the tube diameter constant.
One embodiment of the photoelectric control device provided by the invention will now be described in detail, by way of example only, with reference to the accompanying diagrammatic drawings, in which:
FIG. 1 is a partial layout of photoelectric means for controlling the tube diameter by acting on the inflating air inlet and outlet, for instance through the inflation head, in a device for inflating tubes; and
FIG. 2 shows details of the electrical circuiting of the device of F K]. 1.
As shown in FIG. 1, an air feed blower 1 is provided for forcing fresh air into a pipe 2 which contains a control valve 3 and which can be brought by a normally closed valve 4 into communication with the external atmosphere and through an inflation head 5 into the interior of the tube 6 of sheet material (shown in cross section) in order to inflate this tube. The device for inflating tubes also has an extractor fan 7 which draws air out of an exhaust conduit 8 leading from the interior of tube 6 at the inflation head 5, in order to extract vapors (e.g., of plasticizer and lubricant) from inside the tube. The exhaust conduit 8 contains a manually adjustable exhaust valve 9 and can be brought into communication with the external atmosphere by a normally closed valve 10. The control valve 3 is adjusted by an adjustment motor 11 in the photoelectric control device to be described in detail below.
The photoelectric control device has in this instance 16 photodiodes 12a-12p disposed, in a series corresponding to the control range in a transverse plane of the tube 6, opposite an illumination device 13 which emits a divergent beam 14 towards the photodiodes l2a-12p. As will be seen, the photodiodes 12a-12p and the illumination device 13 are disposed so that the inflated tube 6 projects into the light beam 14.
An appreciable light loss due to the tube 6 only occurs with rays which enter the tube immediately adjacent a tangent to the tube cross section. Only a correspondingly narrow (acuteangled) part of the beam 14 is appreciably weakened.
The distance between the photodiodes 12a-12p is such that at any moment at least one of them lies in the dark zone corresponding to the weakened part of the light beam. This is possible, in spite of the weakened part of the light beam near the tube tangent being very narrow, since the beam 14 is divergent, so that the dark zone is broader in the region of the series ofphotodiodes 12a-l2p than in the region of tube 6.
The illumination device 13 comprises a point-source lamp 15 in front of which rotates a disc 17 formed with a ring of holes and driven by a synchronous motor 16, in order to produce intennittent light with a frequency of 400 cycles per second, which enables AC amplifiers to be used for the photocurrent from the photodiodes l2a-l2p, and whereby the influence of extraneous light can be excluded. Each photodiode -121; is provided with a cylindrical hood 18 in the form of a tube directed towards the lamp 15. This ensures that each photodiode 12a-12p responds only to light coming directly from the lamp l5, and the difficulties are avoided which could occur if light reflected at the tube 6 were to fall on one or more of the photodiodes 12a-l2p.
Each of the photodiodes l2a-l2p is connected to an AC amplifier 19a-l9p, for 400 cycles/sec, whose output feeds a trigger 20a-20p and is also connected to one pole of a six-pole switch 21, which by means of a voltmeter 22 permits a check to determine which of the photodiodes are illuminated and which are not illuminated, i.e., are lying in the dark zone, at any moment, using corresponding amplifiers. Flg. 2 shows only the amplifiers 19a, 19b, 19c, 19p and triggers 20a, 20b, 20c, 20p of the first, second, third and sixteenth photodiodes 1211,1217, 12c, and 12p.
Each trigger responds to darkening of its corresponding photodiodes by delivering a constant output current when the intensity of the light falling on the respective diode has not reached a predetermined threshold value. The total of these output currents of the triggers 20a-20p constitutes the control value which, as further described below, is used to produce an adjustment setting signal.
With the exception of trigger 200 which corresponds to the first photodiode 12a, each of the triggers 20b-20p controls a respective blocking circuit 23b-23p which on response of its perspective trigger also operates the trigger of the photodiode which is next in the series. For example, the trigger 20c controls the blocking circuit 230 so that when photodiode 12c of the trigger 20c is darkened, the constant output current of the trigger 20c is applied to the blocking circuit 23c, which in turn causes the trigger 20b to respond. The blocking circuit 20b then, in the same way, causes the trigger 20a to respond. This ensures that when e.g., the photodiode 12c is darkened, not only its own trigger c but also the triggers 20a and 20b of all the photodiodes 12a, 12b between the photodiode 12c, and the start of the series also respond. The effect is thus as if the zone of darkness extended to the start of the series or beyond.
As shown by the example of trigger 20b in FIG. 2, each trigger comprises a monostable multivibrator with two transistors 24b and 25b and is controlled by a full-wave rectifier 27b (not shown in FIG. 1) supplied from the output 26!: of the corresponding amplifier 1917. As shown by the example of blocking circuits 23b and 23c in FIG. 2 each blocking circuit has an amplifier stage with a transistor 28b, 28c, and a zener diode 31b, 32b, or 31c, 32c in the input 29b, 29c and in the output b, 30c. The input 29!) of blocking circuit 23b is connected to the output 33b of trigger 20b, and the input 29c of paralysis circuit 23c is connected to the output of trigger 200. The additional input 34b is connected to the base of the second transistor 25b the monostable multivibrator of trigger 20b, and in the blocking function converts this transistor into the conductive condition, which corresponds to darkening of the respective photodiode 12b. The output 30b of the blocking circuit 23b is connected to a blocking input of the trigger 20a (FIG. 1) corresponding to the additional input 3412.
As FIG, 1 shows, the outputs of all the triggers 20a20p are jointly connected to a comparison circuit 35 wherein the sum of the trigger output currents which forms the electrical control value, is compared with an electrical value, adjustable to equal the desired control value, producing an output potential whose magnitude and polarity depend on the difference between these values. This control difference can be read oil on a meter 36 and fed to a Pl-controller 37 which provides at its output an adjustment signal which is partly proportional to the control difference and partly proportional to the time integral of the control difference. A Pl-controller is a proportional and integral action controller, that is, a combination of a proportional action controller with an integral action controller, known in the art as disclosed in the book Brockhaus der Naturwissenschaften und der Technik, Wiesbaden l960, page 459.
A switch 38 feeds the output potential of the Pl-controller 37, which forms the adjustment signal, or else a potential taken from a potentiometer 40 supplied from a DC-source 39 and used for manual control, to a control valve 41 which controls the motor 11 to adjust the valve 3 in accordance with the adjustment signal.
In order to pennit smooth transition from automatic to manual control, a voltmeter 42 with a switch 43 is provided, whereby either the output potential of the Pl-controller 37 (adjustment signal) or the output potential of the manual controller 40 (potentiometer) can be measured, in order gradually to match the latter to the former manually before the switch 38 is changed from automatic to manual control or vice versa. When manual control is used, the information is taken from meter 36 by observation by the operator and is used to guide manual control.
The exeiter coil of valve 4 is connected to the trigger (not shown) of the fourteenth photodiode 12n. If for any reason the diameter of the tubular foil 6 increases so greatly that one or more of 'the photodiodes l2n, 12o, 12p are obscured, the trigger 20n of photodiode 12n responds and also opens to affect the adjustment signal of valve 4, so that the air blown by the input blower 1 largely escapes into the atmosphere, and in general air is only withdrawn from tube 6 by the extractor fan '7, the tube diameter rapidly decreases, and bursting of the more air from the tube 6, while the air feed blower 1 injects more air into the tube which is therefore inflated faster and prevented from collapsing.
1. Apparatus for controlling the diameter of an inflated tubular film 6, comprising a plurality of photoelectric devices 12a-l2p disposed on one side of the tubular film 6 in a line extending laterally of the tubular film,
a light source 13 arranged on the opposite side of said tubular film 6 to direct a light beam 14 to said line of photoelectric devices l2a-12p,
said tubular film 6 positioned to project partially into said light beam 14 in a direction from one end (end at 12a) to the other end (end at 12p) of said line of said plurality of photoelectric devices (120, 12p),
said photoelectric devices (12a-12p being arranged close together in said line so that at least one thereof is assigned to the sector of the said light beam 14 which strikes on the tubular film 6 immediately adjacent a tangent thereof,
a plurality of trigger circuits 20a-20p each assigned to one of said photoelectric devices 12a-12p and responsive thereto, said trigger circuits having blocking inputs 34b,
a plurality of blocking circuits 23b-23p each connected to two of said trigger circuits which trigger circuits are each assigned to one of two adjacent photoelectric devices in said line of photoelectric devices 12a-12p and having an input 29b, 29c and an output 30b, 30c,
said input 29):, 290 being connected to the output of one trigger circuit 20b, 20c of the said two trigger circuits, which is assigned to that one photoelectric device 12b, 12c of the said two photoelectric devices which is a greater distance than the other 12a, 1212 from said one end (end at 12a) of said line of photoelectric devices -12, 12b
said output 30b, 30c being connected to a said blocking input 34b of the other 20a, 20b of said two trigger circuits which is assigned to the other 12a, 12b of said two photoelectric devices,
each of said blocking circuits 23b23p being operable upon the control of said one trigger circuit 20b, 200 of the two trigger circuits assigned thereto when the output signal thereof corresponds to a darkened state of the assigned said one photoelectric device 12b, 12c to affect said other trigger circuit 20a, 20b in a manner corresponding to a darkened state of the photoelectric device 12a, assigned to said other trigger circuit 20a, 20b,
and a control circuit 35, 37 having an input connected to the output of each of said trigger circuits 20a-20p,
inflating means 5 having pressure control means 1-4, 7-10,
11, 41 to extrude the blown tubular film,
and said control circuit 35, 37 connected to said pressure control means to control the pressure within said blown tubular film 6 whereby a predetermined diameter is maintained throughout the blow tubular film.
2. Apparatus for controlling the diameter of an inflated tubular film as set forth in claim 1, in which said pressure control means includes air pressure inlet means 3. Apparatus as set forth in claim 1 in which said one end 120 of said line of said plurality of photoelectric devices 120-12 is positioned adjacent said inflating means and said other end 12p of said line of photoelectric devices is positioned a greater distance from said extruding means.
4. Apparatus for controlling the diameter of an inflated tubular film as set forth in claim 2, including airflow restriction means 4,10 in at least one of the air pressure inlet means 1,2 and an air pressure outlet means 7,8 to rapidly change the flow of air therethrough in communication with said tubular film, and said airflow restriction means connected to selected ones 20n,20c of said trigger circuits 20a-20p for control thereby.
5. Apparatus for controlling the diameter of an inflated tubular film as set forth in claim 4 in which a first airflow restriction means 4 is connected in said air pressure inlet means 1,2
for control by a selected one 20n of said trigger circuits as signed to a photoelectric device 12n positioned adjacent the said other end of said line of photoelectric devices, and a second airflow restriction means is connected in said air pressure outlet means 7.8 for control by a selected one 200 of 5 said trigger circuits assigned to a photoelectric device 12c positioned adjacent the said one end of said line of photoelectric devices.
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