US2392229A - Control apparatus for coating machines - Google Patents

Description

Jan. 1, 1946. co E 2,392,229

CONTROL APPARATUS FOR COATING MACHINES Filed Jan. 26, 1943 3 Sheets-Sheet 2 X R g e adore A [0% e22 INVENTOR,

BYJM/UM 1, 4 T. A. COHEN I CONTRO L APPARATUS FOR COATING MACHINES Filed Jan. 26, 1943 3 Sheets-Sheet 3 o 77;cadareAL IM E TOR,

JM Z M Art aw m fi m W Y Patented Jan. 1, 1946 umrso STATES PATENT OFFICE Theodore A. Cohen, Chicago, 111., minor, by meme assignments, to Wheelco Instruments Coarpany, Chicago, 11]., a corporation of lilino 7 Application January 28, 1943, Serial No. 474,042 2: Claims. (01. 91-18) g This invention relates to control apparatus and more particularly to a control apparatus for antomatically controlling the admission and recession of a liquid vehicle for fluorescent powder, commonly used for coating the interior of fluorescent tubes, to and from the tubes.

One of the objects of my invention is to provide an apparatus for efficiently effecting and controlling the application of a liquid vehicle for fluorescent powders, such as above referred to, to the interior of the tubes to sharply and effectively stop the rising of the liquid in the tubes when it has reached a predetermined point therein and thereafter cause the recession of the liquid from the tubes to complete an application cycle. Other and further objects of my invention will be apparent as the same becomes better understood from an examination of the specification and claims in conjunction with the accompanying drawings wherein:

' Figure 1 represents a schematic view of anal!- paratus embodying my invention;

Figure 2 is a diagrammatic view of the same;

Figure 3 is an enlarged, fragmentary, detail, elevational view, partly in section and with parts removed, showing the portion 01' the apparatus for mounting the fluorescent tubes to be coated by the powder carried by the liquid vehicle to be introduced into and withdrawn from them Figure 4 is a side elevation of same;

Figure 5 is an enlarged section at the line II! of Figure 3;

Ic'ligure 6 is a modified form of pick up clip, an

Figure 7 is a section taken at the line 1-1 of Figure 6.

Referring to the drawings more particularly, reference character I designates a liquid container carrying a liquid vehicle 2 for fluorescent powder commonly used for coating the interior of fluorescent tubes, such as tubes I8, "II, lab

4 and Itc are intended to be when completed.

A tube 3 connects container I with a manifold 4 having longitudinally spaced output tubes 5, 8,

I and 8.

A three way air valve 0. having an operating solenoid I0, is connected by a tube I3 to deliver air to the top of container I to cause pressure, as desired, on top of the liquid 2 therein. A soiu'ce of air II, or connecting tube from same, and a separate exhaust pipe I2 to atmosphere is connected to valve 9.

A push button It is connected to arelay I4 to energize same through oscillator controlled contacts l2 andcperatevalveltoadmitairtocontainer I to cause the rising oi liquid 2 in the tubes I8, etc. When the liquid has risen to the point desired in said tubes an impedance change device I! operates as will be hereinafter described to aifect an oscillator apparatus I6 to open contacts 82 to cause deenergization of relay I4 to thereby deenergize valve 9 and exhaust air from container I to atmosphere.

The liquid is then permitted to recede in the tubes II etc., coating the interiorof said tubes, as it recedes, with substance capable of rendering the tubes fluorescent when energized in the customary manner.

The details of the aforementioned parts" "and functions will now be described more particularly.

The tubes l8, IBa, I8!) and I80 desired to be coated with fluorescent powder are mounted in holders I 9, 20, 2I and 22, respectively, in which they may be readily inserted to be treated and thereafter removed to be replaced by other tubes when the process of coating their interiors has been completed.

The details of the mounting for the tubes I8, etc., being treated are shown more particularly in Figures 3 and 4, wherein holders I9, etc., are

mounted upon a plate 28. Each holder I8, etc., is recessed to provide a rubber gasket 28 apertured to receive the upper end of the corresponding manifold tube such as 5, and seal the lower end of the corresponding tube to be treated, such as I8, in said holder. ii flanged and apertured closure 30 surrounds the lower end of the tube It and holds the gasket 28 in position.

Yieldably and vertically movable top cap 28, 23a, 23b and 22c are provided for the upper ends of the tubes I8, etc., whereby these tubes may be readily inserted or removed from the holders I9, etc., as desired. These caps 23, 23a, 23b and 220 are each mounted upon the lower end of a stem or plunger 25 which extends through abearing plate 21 and a bearing 26, each plunger being provided with an integral knob III and a spring 24 holding the cap down against the top of the corresponding tube to removably hold same in its corresponding holder. The bearln8 plate 27 is vertically and adjustably supported on vertical rods 32 and 33 attached to and extending up from plate 28. The rods 32 and 32 extend through bosses or bearings 34 and 25 on opposlte ends of bearing plate 21 and are provided with adjustable set screws 36 so that adjustment may be made to accommodate tubes of different lengths.

The impedance change device II comprises a pair of metal plates 31 and 38 (Fig. 2) s ared annotated to at laterally-spaced positions on the tube I8 at the a justable vertical position thereon at which it is desired to commence the coating of the interior thereof with the subplates.

The plates 31 and 38 are connected to a self contained grid tank unit 39 for the oscillator it. This unit 39 is mounted in a suitable housing to and comprises an inductance coil M and condenser t2 and together with the plates 31 and 38 forms a resonating circuit with said plates connected to opposte ends of said coil and said condenser connected to one end of said coil. A pair of male plugs t3 and M are connected respectively to one end of coil 41! and the condenser $2.

The male plugs 43 and 4c are adapted to connect with female connector elements 35 and 56 respectively, at one end of a concentric conductor cable 61 insulated'from ground by an external rubber sheath or cover (not shown). The cable 4! comprises an inner conductor 98, separa-' tors 49 and an outer conducting sheath 50. The end of the cable opposite to the connector 53-56 is provided with a connector Ma similar thereto for connection to the input of an oscillator circuit l6 hereinafter described.

The concentricco-axial conductor cable M is constructed in well known manner with its core conductor fixedly and concentrically positioned within the conducting sheath. By properly choosing the values of the capacitive and inductive components of the resonating circuit in enclosure so, the cable is properly terminated so that minimum power losses are obtained in the system due to the cable for any substantial length thereof. In this manner the remote control assembly Just described may control the oscillator apparatus 16 hereinafter described without fear of transmission losses which otherwise would reduce the sensitivity of the apparatus if not actually prevent its operation.

asoaaao ing negative or non-conducting portion of A. C.

cycle. Transformer secondary winding ll is connected to filaments 59 and H to heat cathodes 5B and I0, respectively, by wires X-X not completed. The grid bias for effectingproper operation of the repeater tube 61 is obtained by connecting the grid or control electrode 58 to one end of the load resistor is, the remaining portion of this circuit extending from the' cathode 1o to the secondary transformer winding 16, the conductor 18a to the opposite end of the load resistor it. It will be apparent that the voltage across the winding 16 is opposite to and thus compensates for a portion of the voltage drop across the load impedance i3 and accordingly when the oscillator tube isin oscillatory condition so that a plate current of low value flows through the load impedance 13, a minimum negative bias ,equal to the difference between the voltage of the winding 18 and the voltage drop across the load across the load impedance is is impressed on the grid 58. Under these conditions, and with proper The oscillator circuit includes a vacuum tube 55 connected to a plate tank comprising an inductance B0, variable condenser SI for tuning to resonance, as will hereinafter be described, and grid bias resistor or grid leak 12 for said tube.

Alternating current voltages are obtained from a multi-winding transformer having a primary winding 66, connected to a suitable source of alternating current 65, and having a plurality of secondary windings 66. i5, i8 and ii arranged to supply suitable voltages to the tube circuits. The tube 55 and repeater tube 81, hereinafter described,"are self rectifying and therefore the operation will be described only with respect to the positive half cycles of the alternating current voltages.

The output section of the tube 55 may be traced from the left-=hand terminal of the secondary winding 65 through the plate tank circuit so, of, the anode or plate 5?, the cathode 58, thesecondary winding it, conductor its, a load impedance or resistor 13 and thence to the right hand terminal of secondary winding 68. By-pass con densers 82 and is are connected as shown and prevent the fiow of high frequency oscillatory currents through the transformer windings and through the load impedance it. 'The total voltage impressed across the anode circuit of tube '55 is the sum of the voltages of the secondary windings 66 and I8.

voltages, the tube constants, and the value of the load resistance all so pre-chosen to provide a low negative grid bias, a high repeater plate current is obtained for proper operation of the relay.

A regenerative coupling is provided betweenv the grid circuit of the tube 55 and the output of the repeater tube 67, as shown. The grid circuit for the oscillator tube 55 extends from the cathode 58, the transformer winding 16, the lower end of relay winding it, the tap B0 and the grid bias resistor or grid leak E2 to the grid 55.

A fixed grid bias is applied, by the above circuit, to the grid 56 which is equal to the voltage drop across the relay winding is to tap 80 and is so chosen that with maximum current fiowing in the output circuit of the amplifier or repeater tube 6? the maximum desired negative bias is applied to the grid 56.

The plate tank is tuned to predetermined resonance with condenser 6| so as to energize relay 18 when liquid in tube 18 is below the predetercrease in current through the relay 19 causes adecrease in the negative grldbias applied to the grid of the oscillator tube 55, which tends to furrelay 19 to release air from container 1 as will 'be hereinafter more particularly described."

In order to initiate a coating cycle a clean tube i8 is placed in position as described. The oscillator circuit being in resonance because of the low capacity between plates 3l-38 maintains the relay contact 82 closed. The push button I5 is now depressed energizing the relay it through I5 and B2. The armature Ma pulls down closingccnt-act 83 to energize valve iii to allow air pressure to chamber 5. The contact 34 closes to lock the relay M in closed position. The push button i5 may now be released. As the liquid rises in it, due to air pressure in chamber I, it will eventually reach the prechosen level whereupon thecontacttt will open to deenergize locked up relay M. The contact 83 will open to deenergize valve Ill releasing the air pressure in chamber i to atmosphere whereupon the liquid in tube IE will recede to leave tube coated. The contact 35 will close energizing the indicator 86 to indicate that a coating cycle has been completed. A new tube may then be placed in the holder.

when anew and clean tube is is placed in apparatus again after removal of coated tube the oscillator circuit is retuned and oscillator .plate current drops, decreasing the drop across resistor 13, which decreases the negative bias on the amplifier tube 61; the plate current of the amplifier increases, increasing the drop across the relay 13, which increases the negative bias on the grid of the oscillator 55, aiding in dropping the oscillator plate current, which further tends-t0 decrease the bias upon the amplifier 61, etc., with the result that the final positioning of the plate current of amplifier 61 is at saturation. By the judicious choosing of load resistance 13, of the resistance of the relay winding 79 and the proper apportioning of bias voltages as shown, the valuesof plate current between cut-off and saturation may be fixed at any desired value. The result is that large, abrupt, and rapid plate current changes are always ob-' tained. The result obtainable is comparable to the triggering off of a Thyratron type hot cathode grid control rectifier without. the necesv sity of using gasfilled tubes.

Study of the circuit arrangement will also bring out that the system is self compensating for changes in line voltage which prevents shiftage of the control point if the line voltage should change.

It is not necessary that the apparatus be limited to the use of separate vacuum tubes, each containing separate triode elements, since these separate tubes have been chosen only as a matter of convenience. Dual purpose tubes having triode elements in a common envelope may be operated in the same manner. Direct current voltages may also be used.

It will be noted that the plate supply for tubes 55 and l! are obtained from windings 86 and II, respectively, in series with 16. Should the line voltage fall the supply voltage from 15 would reduce and therefore the plate current flow in plate circuit of tube 61 would tend to decrease. However, since winding 66 supplies the plate circuit of tube 55 and since the negative bias on grid 68 is obtained from drop across resistor 13 due to plate current flow in plat circuit of tube 85, the plate current of tube'ii is also reduced with reduction o voltage from 66. Therefore negative bias on grid .68 is reduced keeping the plate current flow in plate circuit of tube 61 substan' tially constant. The reverse result is obtained with rise in line voltage. This self compensating feature is important in electronic control apparatus since it prevents shift of the control point or level upon changes in line voltage.

Aging of tubes is also compensated for in the same manner in conjunction with the regenera tive connection between tap Maud resistor 12.

In summary, the advantages of this circuit are manifest, inasmuch as a. relay with a high throwout percentage is not necessary, since the plate current changes through said relay are very rapid and very large. It is impossible to lose control of the oscillator, since, because of the fact that it is self-rectified, oscillations, no matter how minute, will always reoccur. Other variaticns of this'circuit will readily occur to those versed in the art, such as the use of a common power supply, with a self-rectified circuit, instead of separate voltages as shown. Such circuits have been designed and are entirely feasible. The one shown being one of a family of such circuits and being chosen as the most descriptive of the aboveexplained operation.

As shown in cross section in Figure 5, the plates 31 and 38, symbolically shown in Figure 2,. each partially circumscribes the tube i8 and are mounted upon a non-conducting portion fitia of the enclosure of Figure 2.

In the previous embodiment two capacitorplates were used with the liquid acting as a dielectric to change the capacity between said plates as in Figure 5. In Figure 7 a single plate We is used to partly circumscribe tube 58 which acts as one plate of the condenser while a ground connection at 2a in Figure 2 makes the liquid itself the other plate of the condenser since the liquid itself may be partly conducting.

I am aware that many changes may be made and details varied without departing from the principles of my invention and I therefore do not wish to be limited to the details shown or described.

I claim:

1. In combination, an apparatus adapted to perform an operation cycle having means for per forming the first part of the cycle and, upon reversal of said means, for performing the second part of the cycle, an impedance change device responsive to the operation cycle, an oscillator circuit adapted to have its tuning changed by said device at the end of the first part of the cycle and means controlled by the oscillator, upon the change in tuning thereof, to reverse said means for performing the second part of the cycle of operation.

2. In combination, an apparatus adapted to 69 perform an operation cycle having means upon being initiated, for performing the first part of the cycle and. upon reversal of said means. for performin the second part of the cycle, an impedance change device responsive to the condition of the cycle, an oscillator circuit adapted to have its tuning changed by said device upon the attainment of the condition of said cycle at the end of the first part thereof, and means controlled by the oscillator, upon the change in tun- 70 ing thereof, for reversing the first means to cause the performance of the second part of the cycle and retuning of the oscillator, said last means including initiating means interposed between said oscillator and first means for initiating the letreturned from again affecting the first means until the initiating means has been operated.

3. In combination, an apparatus for applying a substance to the interior of tubes by the introductlon and withdrawal of a vehicle carrying the substance to and from the tube, means for introducing said vehicle and, upon reversal, for withdrawing the vehicle and applying the substance to the interior of the tubes, an impedance change device responsive to the position of the vehicle within one of the tubes, an oscillator circuit adapted to have its tuning changed by said device when said vehicle has been introduced a predetermined amount into the tube and means controlled by the oscillator, upon the change in tuning thereof, to reverse said means for causing the withdrawal of said vehicle and the application of said substance to the interior of the tubes.

4. In combination, an apparatus for applying a fluorescent substance to the interior of tubes, means in said apparatus, upon being initiated, for introducing a vehicle into the tube carrying said substance and, upon reversal, for withdrawing from the tube and applying the substance thereto, an impedance change device responsive to the position of the vehicle within the tube, an oscillator circuit adapted to have its tuning changed by said device upon said vehicle being introduced perform an operation cycle having means upon being initiated, for performing the first part of the cycle and, upon reversal of said means, for performing the second part of the cycle, an impedance change device response to the condition of the cycle, an oscillator circuit adapted to have its tuningchanged by said device upon the attainment of the condition of said cycle at the end of the first part thereof, and means con-' trolled by the oscillator, upon the change in tuning thereof, for reversing the first means to cause the performance of the second part of the cycle and rctuning of the oscillator.

6. In combination, an apparatus for applying a substance to the interior of tubes, means in said apparatus; upon being initiated, for introducing a vehicle into the tube carrying said substance and, upon reversal, for withdrawing from the tube and applying the substance thereto, an impedance change device responsive to themsition of the vehicle within the tube, an oscillator circuit adapted to have its tuning changed by said device upon said vehicle being introduced a predetermined amount into the tube and means controlled by the oscillator, upon the change in tuning thereof, for reversing the first means to cause the withdrawal of the vehicle to apply said substance to the tube and retune'the oscillator.

'7. In combination, an apparatus adapted to perform an operation cycle having means for performing the first part of the cycle and, upon reversal of said means, for performing the second part of the cycle, an impedance change device responsive to the operation cycle, on oscillator circuit adapted to have its tuning changed byaaiddeviceattheendotthefirstpartoifthe change device response to the condition of the cycle and retuned during the second part of the cycle, means controlled by the oscillator, upon the tuning change thereof, to reverse said first means, and means for initiating the first means when the oscillator is retuned and preventing the first means from being affected by the retuning of the oscillator unless the initiating means is operated.

8. In combination, an apparatus adapted to vice at the end of the one part of the cycle and means controlled by the oscillator, upon the change in thereof, to reverse said means for performing the other part of the cycle of operation.

9. In combination, an apparatus adapted to perform an operation cycle having means upon being initiated, for performing one part of the cycle and, upon reversal of said means, for per forming another part of the cycle, an impedance change device responsive tothe condition of the cycle, an oscillator circuit adapted to have its tuning changed by said device upon the attainment of the condition of said cycle at the end of one part thereof, and relay means controlled by the oscillator, upon the change in tuning thereof, for reversing the first means to cause the performance of the other, part of the cycle and retuning of the oscillator, a second relay and a push button therefor interposed between said oscillator relay and first means for initiating the latter and for preventing theosclllator upon being returned from again affecting the first means until the push button has been operated.

10. In combination, an apparatus adapted to perform an operation cycle having means for performing one of the cycle and, upon reversal of said means, for performing another part of the cycle, an impedance change device responsive to theoperation cycie, an oscillator circuit adapted to have its tuning changed by said device at the end of the one part of the cycle and retuned during the other part of the cycle, means controlled by the oscillator, upon the change in tuning to reverse said first means,

and means for initiating the first means when the oscillator is retuned and preventing the first means from being affected by the retuning of the oscillator unless the initiating means is operated.

11. In combination, an apparatus adapted to perform an operation cycle having means up being initiated, for performing one part of the cycle and, upon reversal of said means, for performing another part of the cycle, an impedance cycle, an oscillator circuit adapted to have its tuning changed by said device upon the attainment of the condition of said cycle at the end of the one part thereof, and means controlled by the oscillator, upon the change in tuning thereof, for reversing the first means to cause the performance of the other 'part of the cycle and retuning of the oscillator. Y

12. In combination, an apparatus adapted to perform an operation cycle having means upon being initiated, for performing the first part of the cycle and, upon reversal 0! said means, for performing the second part oi the cycle, an impedance chance device responsive to the condi- 13,899,929 'tion of the cycle, an oscillator circuit adapted to have its tuning changed by said device upon the attainment of the condition of said cycle at the end of the first part thereof, and relay means controlled by the oscillator, upon the change in tuning thereof,- for reversing the first means to cause the performance of the second p rt of the cycle and retuning of the oscillator, a second relay and a push button therefor interposed between said oscillator relay and first means for 'initiatingthe latter and for preventing the osvice responsive to the operation cycle, on oscillator circuit adapted to have its tuning changed "by said device at the end of the first part of the cycle andretuned during the second part of the cycle, relay means controlled by the oscillator,

upon the change in tuning thereof, to reverse said means and second relay means for initiating the first means when the oscillator is retuned and preventing the first means from being affected by the retuning of the oscillator unless the initiating means is operated.

14. In combination, an apparatus adapted to perform an operation cycle having means, upon being initiated, for performing one part of the cycle and, upon reversal'of said means, for performing the other part of the cycle, an impedance change device responsive to the condition of the cycle, an oscillator circuit adapted to have its tuning changed by said device upon the attainment of the condition of said cycle at the end of the one part thereof, and means controlled by the oscillator, upon the change in tuning thereof, for reversing the first means to cause the performance of the other part of the cycle and retuning of the oscillator, said last means including initiating means interposed between said oscillator and first means for initiating the latter and for preventing the oscillator, upon being retuned, from again affecting the first means until the initiating means has been operated.

15. In combination, an apparatus adapted to Perform an operation cycle having means for performing one part of the cycle and, upon reversal of said means, for performing another part of .the cycle, an impedance change device responsive to the operation cycle, an oscillator circuit adapted to have its tuning changed by said device at the end of the one part of the cycle and retuned during the other part of the cycle, relay means controlled by the oscillator, upon the change in tuning thereof, .to reverse said means. and second relay means for initiating the first means when the oscillator is retuned and preventing the first means from being aflected bythe retuning of the oscillator unless the initiating means is operated.

1 6. In combination, an apparatus adapted to .perform an operation cycle upon a physical medium and having means for performing the first part of the cycle and, upon reversal of said means, for performing the second part of the cycle, an impedance change device responsive to the op-. eration cycle and situated in proximity to a predetermined point with respect to said medium, an oscillator circuit adapted to have its tuning ond Part of the cycle, an impedance change depart of the cycle and means controlled by the oscillator, upon the change in tuning thereof, to reverse said means for performing the second part of the cycle of operation, said means acting to perform the first part of the cycle from a predetermined starting point with respect to said medium spaced from the predetermined point in proximity to said device and, upon reversal, to perform the second part of the cycle from the last mentioned point back to said starting point. 1

17. In combination, an apparatus adapted to perform an operation cycle upon a physical medium and having means for performing the first part of the cycle and, upon reversal of said means, for performing the second part of the cycle, a pair of capacitor plates and an oscillating circuit responsive to'the operation cycle and situated in proximity to a predetermined point with respect to said medium, an oscillator circuit adapted to have its tuning changed by said plates and connected to said first circuit and means controlled by the oscillator, upon change in tuning thereof, to reverse said means for performing the second part of the cycle of operation, said means acting to perform the first part of the cycle from a predetermined starting point with respect to said medium spacedfrom the predetermined point in proximity to said plates and to perform the second part of the cycle from said last point back to said starting point. I

18. In combination, an apparatus adapted to perform an operation cycle upon a physical medium and having means. for performing the first part of the cycle .and, upon reversal of said means,

for performing the secondpart of the cycle, a pair of capacitor plates and situated inproximity to a predetermined point with respect to said medium and an oscillating circuit, an oscillator circuit tuned to predetermined resonance with and including said oscillating circuit, a concentric from the predetermined point in proximity to said plates and to perform the second part of the cycle from said last mentioned point back, upon reversal, to said starting point.

' 19. In combination, an apparatus adapted to perform an operationcycle upon a physical medium and having means for performing the first part of the cycle and, upon reversal of said means, for performing the second part of the cycle, an impedance change device responsive to the operation cycle and situated in proximity to a predetermined point with respect to said medium.

an electronic circuit adapted to be operated at the end of the first part of the cycle by said 'device and means controlled by said circuit, upon the operation thereof, to reverse said first means for performing the second part of the cycle of operation, said means acting to perform the first part of the cycle from a predetermined startin point with respect to said medium spaced from the predetermined point in proximity to said device and to perform the second part of the cycle from said last mentioned point back to said startin point.

changed by said device at the end' of the first 7 20. In combination, an apparatus adapted to perform an operation cycle upon a physical medium and having a valve, a pneumatic means controlled thereby for performing the first part of the cycle, and, upon reversal of said valve, for performing the second part of the cycle, an impedance change device responsive to the operation cycle and situated in proximity to a predetermined point with respect to said medium, an oscillator circuit adapted to have its tuning changed by said levice at the end of the first part of the cycle and means controlled by the oscillator, upon the change in tuning thereof, to reverse said valve for performing the second part .of the cycle oi! operation, said pneumatic means acting to perform the first part of the cycle from a predetermined starting point with respect to said medium spaced from the predetermined point in proximity to said device and, upon reversal, to perform the second part of the cycle from said last mentioned point back to said starting point.

21. In combination, an apparatus adapted to perform an operation cycle having means for performing the first part of the cycle and, upon reversal of said means,. for performing the secstarting point to the attainment of said level and from the lowering of said level back to said starting point.

22. In combination, an apparatus for applying a substance to the interior of tubes by the introduction and withdrawal of a vehicle carrying the substance to and from the tubes, means for introducing said vehicle and, upon reversal, for withdrawing the vehicle and applying the substance to the interior of the tubes, an impedance change device responsive to the position of the vehicle within one of the tubes, an oscillator circuit adapted to have its tuning changed by said device when said vehicle has been introduced a predetermined amount into the tube and means controlled by the oscillator, upon the change in tuning thereof, to reverse said means for causin the withdrawal of said vehicle and the application of said substance to the interior of the .tubes, and a stand for said tubes provided with a plurality of supports for the lower ends of tubes and a plurality of yieldably held caps for the upper ends of said tubes.

23. In'combination, an apparatus for applying a substance to tubes by applying a vehicle carrying the substance longitudinally to the tube, means for moving the vehicle longitudinally of the tube and, upon reversal, for moving said vehicle in the other direction, an impedance change device responsive to the position of the vehicle with respect to the tubes, an oscillator circuit adapted to have its tuning changed by said device when said vehicle has attained a predetermined position with respect to the tube, and means controlled by the oscillator, upon a change in tuning thereof, to reverse said means for causing the opposite movement of said vehicle.

mononn A. COHEN.

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