US2251277A - Control apparatus for electrostatic drying - Google Patents

Description

Aug. 5, 1941. G. "r. HART, JR., ETAL 2,251,277

CONTROL APPARATUS FOR ELECTROSTATIC DRYING Filed Jan. 24, 1939 FRE QU ENCY OSCILLATOR Patented Aug. 5, 1941 CONTROL APPARATUS FOR ELECTRO- STATIC DRYING George T.

Lynn, Masa, ery Corporation,

Hart, Jr., and Erastus E. Winkley,

assignors to United Shoe Machln- Borough of Flemington, -N. 1.,

a corporation of New Jersey Application January 24, 1939, Serial No. 252,605

Claims.

This invention relates to the control of an apparatus arranged to produce an electrostatic field for drying or otherwise treating a series of articles, in order that the output of the apparatus which produces the field may be varied in response to changes in the demands of the load.

The use of a high frequency electrostatic field for the purpose of drying articles is well understood and when such an apparatus is employed commercially it follows that it will be utilized commonly for a large number of articles which frequently are not presented simultaneously to the fleld but are added one after another. Such an apparatus is employed for drying shoes, for example, and then the load will vary as successive shoes are presented to the field and the resultant changes in the load will depend not only upon the number of articles presented but also on the quantity of moisture in the various articles, which, in the case of shoes being bottomed, is located principally in their outsoles. The quantity of moisture in turn will depend partly upon the sizes of the shoes being treated and partly upon the quality of the material, because of the diiierent absorptive powers of different types of leather, as well as upon the way the shoes are put together and other factors. The demand for power created by these various factors will for convenience be termed the shoeor work-load. In considering the problem, it will be convenient to think of the various articles as included in a single electrostatic field, that is to say, a field produced merely by one pair of electrodes. The problem is, however, not substantially diiferent where pairs of electrodes are provided for single articles and a plurality of these electrodes are joined in parallel and connected to a single source of supply, such as a high frequency oscillator.

In one physical embodiment of an apparatus for. this purpose, cars of a conveyor are provided for supporting pairs of shoes and each car has electrodes associated with the respective shoes, these electrodes being joined to a single oscillator by means of a trolley and live rail arrangement. There will further be no substantial diiTerence in the problem of control of output if the shoe supports are mounted in fixed positions, or, if electrodes are provided for association with shoes positioned upon the ordinary shoe racks so commonly used in shoe factories.

It will be understood that, in designing a conveyor for drying articles, the number of cars pmvided is more than sufificient to take care of the regular run of work during an interval such as ..the' various articles is to be kept substantially constant so that they may be removed from the cars returning along the lower run of the conveyor as these cars reach the loading station. As moist articles are presented to the system, the

load increases; as theydry out, the load is correspondingly reduced. At any particular settin of the oscillator, an electrostatic field of certain intensity is produced and if this field is shared by a plurality of wet articles, the active power in each article will be less than would be the case if a lesser number of articles were within the field and the oscillator must be adjusted to meet the needs of the greater load.

One important object of the invention is to provide a control organization for use with a high frequency source whereby the action of the field on the articles, such as shoes, is substantially unaflected by variations in the load as determined by the various factors mentioned above.

To this end, and in accordance with a feature of the invention, automatic means is provided which is responsive to changes in the demands of the load and is arranged to vary the output of the oscillator to meet its demands.

Other features of the invention reside in employment of apparatus which is responsive to changes of the output current of the oscillator which supplies the electrodes, these changes operating to regulate the voltage applied so that the efliciency of the field will be maintained and the drying time will be substantially uniform.

Still another object of the invention is to devise an improved method of drying articles by means of an electrostatic field in accordance with which the drying time for the various articles is rendered substantially constant by automatically varying the effectiveness of the field as the load changes.

In another aspect, the novel method consists in applying the field to a changing number oi! articles and in automatically maintaining the effectiveness of the field as the load imposed by the articles changes.

The way in which this method may be carried out'and an illustrative apparatus which may be employed, will now be described in the i'ollowing specifiecation taken in connection with the drawing.

lnthesinglefla'iireoithisdrawingtypical control apparatus has been shown a cally There, a high frequency oscillator I90 of any well-known construction receives power from wires I52 leading from a source of alternatingcurrent power of ordinary commercial frequency and delivers high frequency current to live rails 60 and H4 typiiying the electrodes in association with which the articles are positioned for treatment. It will be assumed, tor the sake of illustration, that the oscillator I is of the sellexcited type and involves vacuum tubes of wellknown construction, the filaments of which are supplied with power through leads I64.

In our arrangement for automatically controlling the output of the oscillator in accordance with the shoe or work-load present between the electrodes, an ammeter IE6 is inserted in the circuit between the oscillator and one of the live rails and, hence, is responsive to the varying load. This ammeter I60, indicating changes in output current, is provided with a mirror I60 mounted to be tilted as the needle oi the ammeter moves, thereby to vary the angle of reflection of a beam of light received from a lamp I10 focused by a lens system "2 on a small area of the mirror and reflected therefrom through a V-slot I14 in a plate I10 for reception by the cathode I18 of a photoelectric tube I00 having the usual anode I19. It will be seen that the slot I14 is wider at the top than at the bottom and as the current in the ammeter decreases, the mirror will be tilted counterclockwise to pass the beam of light through the upper part of the slot thereby throwing more light on the cathode and causing a greater current to flow through the tube I80. Current passing through the photoelectric tube I00 is amplified by a thermionic tube I02 in the usual manner. The plate currents for the photoelectric tube I00 and the amplifier tube I02 are supplied from the transformer secondary winding I84, one end of which is connected to the direct current winding I90 oi the saturable reactance I92 and thence to the anodes of the tubes I00 and I82, the other end being connected to the mid point of the filament transformer I94 and to one end of the potentiometer I96. The other end of the potentiometer is connected back to a tap in the transformer winding I94. Adjustment of the potentiometer determines the voltage impressed on the anode of the photoelectric tube I80. Because of the rectiiying action of the tubes, it is obvious that pulsating direct current flows in the winding I90 0! the saturable reactance I92.

The alternating current coil 200 of the saturable reactance is supplied with power from another transiormer secondary 202. A condenser 204 and a non-inductive resistance 200 are in series with the reactance coil 200 and the primary of a grid transformer 2I0 is connected between a mid point of the secondary coll 202 and a point between the condenser 204 and the resistance 206 in the circuit of the coil 200 of the saturable reactance. It will be understood that the saturable reactance I92, in a well understood fashion, responds to small changes in the current flowing through the direct current coil I90, thereby producing large changes in the current delivered to the grid transformer 2I0. The secondary oi the grid transformer 2I0 is connected to the grids of a pair of thyratron tubes 2I2, the filaments of which are supplied from a transformer secondary 2. These tubes act to supplymore orless current from a transformer secondary 220 to the input circuit 222 of the oscillator I00. To this end, the terminals of the secondary 220 are connected to the plates of the thyrat-ron tubes 2I2 and the input circuit 222 derives its power in a well-understood fashion by reason of connections to a mid point 224 in the secondary 220 and a point 228 in a lead connecting the filaments of the thyratron tubes. A switch I40 is in series with this input circuit of the oscillator.

It will be understood, however, that the particular control circuits herein shown by way of illustration are not the only ones which may be used and that other well-known arrangements may be substituted for enabling variations in load to control the output of the oscillator. For example, in oscillators where the load imposed requires a smaller output, the thyratron tubes together with their transformers could be dispensed with and the alternating current windings 200 01 the saturable reactance I92 be connected directly to the input terminals 222 of the oscillator I60 by connecting together the points a, a and also connectlng the points I), b, thus accomplishing the same result in the smaller power range, Any preferred arrangement which provides for automatically increasing the output power of the oscillator as the work load increases and corresponding- 1y decreasing the output power as the work load decreases, comes within the scope of this invention.

It is found that, where the greater part of the electrical capacity in the output circuit of the oscillator is formed by the electrical capacities of the articles, then the frequency of the current delivered by the oscillator will be continually upset because of the change in the electrical capacities of the articles as they dry. It has been found desirable, therefore, especially in the case of a self -excited oscillator, to provide a stabilizing condenser 230 bridged across the output side of the oscillator which will have a suillcient capacity so that the capacity provided by the articles, such as shoes, is a small part of the total of the electrical capacity of the output circuit of the oscillator, As a consequence, changes in the capacities provided by the articles as they dry will not unbalance the oscillator and cause it to operate inefliciently. The stabilizing condenser 230 is shov-n diagrammatically as comprising a pair of plates, one of which may be moved with respect to the other by rotating it about a supporting pin 232. This adjustment is required chiefly during the setting up of the apparatus.

The action of the control apparatus will now be explained. As articles, such as shoes, are inserted between the electrodes, the effect on an oscillator circuit having a fixed input power is to increase the output voltage drop and consequently to reduce the output amperage. This would lengthen the drying time since there would be less power per article. In the illustrated method of regulating the output power so that drying is accomplished in a uniform time regardless of changes in the work load, it is elected to adjust the power supplied to the input circuit of the oscillator. The ammeter I60, responding to changes of current in the output circuit, reflects more light to the photoelectric tube I as the work-load increases by adding wet articles, thus temporarily causing a decreased output current or less light as the load decreases during the progress of the dryingout process. The electrical response of the photoelectric tube Hill to the changing values of impinging light, amplified by the tube I82, will cause a controlled, pulsating, direct current to flow in the coil I90 the saturable reactance.

In this reactance I92, the construction is such that with no direct current fiowing in coils I50, the large amount of iron in the core offers a high impedance to the alternating current in coils 200 and so but little current can fiow. As direct current is admitted to cells I90, a flux will be created that tends to saturate the iron, decreasing the impedance of the alternating current coils 2M and, since the impedance drop is inversely proportional to the total saturation of the iron, more alternating current will flow. As the direct current required is only a fraction of one per cent of the alternating current controlled, the necessary amount is readily supplied by the small currents in the photoelectric tube I80 stepped up by the amplifier tube I82. Utilizing a well-understood principle of phase shifting, changes in the amount of current in the circuit which includes the inductance 200, the capacitance 204, the resistance 2%, the primary of the grid transformer 2H! and the transformer secondary 202, are effective to change the phase of the grid currents with respect to the plate. currents in the thyratron tubes 212. As the phase of the grid current in the thyratrons aids or opposes the electron emission in those tubes, they will act as a rheostat and more or less power will be supplied to the input circult 222 of the oscillator Hill. This will result in energy at higher terminal voltages being impressed on the live rails 68 and H4 as wet articles are added to the field and in a reduction of that voltage as the drying process proceeds toward completion. Inasmuch as the change in the alternating current flowing through the coil 200 of the saturable reactance is not a straightline change, the sides of the slot I14 in the plate "6 are not straight but have been curved arbitrarily to compensate for the characteristics oi the saturable reactance I92.

Having thus described our invention, what we claim as new and desire to secure by Letters Patent of the United States is:

1. In an apparatus for treating articles, electrodes between which such articles may be positioned, an oscillator for supplying high frequency current to said electrodes to produce an electrostatic field passing through the articles, and automatic means responsive to changes in the demands of the load and arranged to vary the output of the oscillator to meet those de mands.

2. In an apparatus for treating articles, elec- 6 trodes in association with which articles may be positioned, an oscillator for supplying high frequency current to said electrodes to produce an electrostatic field passing through the articles, means for indicating changes in the output of the oscillator, means for supplying current to the oscillator, and means, including a photoelectric cell, responsive to changes in said inditating device and arranged to contfol the input to the oscillator.

3-. In an apparatus for treating articles electrically, means for producing an electrostatic field within which a plurality of articlg may be positioned, and a device, responsive to a current which is proportional to the output of said fieldproducing means, for regulating the amount of power delivered by said field-producing means.

4. In an apparatus for treating articles, electrodes in association with which articles may be positioned, means including an oscillator for de livering high frequency current to said electrodes, a device responsive to changes in the output current of the oscillator as the load changes, means for delivering power to the oscillator, and means controlled by said device for varying the amount of power delivered to said electrodes as the output current is varied, thereby to keep the efi'ectiveness of the electrostatic field substantially constant.

5. That method of drying articles by means of an electrostatic field which consists in treating a plurality of articles in such a held, and in rendering the drying time for the various articles substantially constant by automatically increasing the effectiveness of, the field as the load increases.

6. That method of drying articles by mean of an electrostatic field which consists in treating a plurality of articles in such a field, indicating changes in a current flow as the article load changes, and automatically adjusting the power supplied to the electrostatic field to maintain that current substantially constant.

'7. That method of drying articles by means of an electrostatic field, which consists in applying the field to a changing number of articles and automatically maintaining the efiectiveness of the field as the load imposed by the articles changes.

8. That method of drying articles by means of an electrostatic field, which consists in treating a plurality of articles in such a field and in automatically adjusting the field in response to the changing load provided by the articles to dry the various articles in a substantially uniterm time.

9. That method of drying articles by means of an electrostatic field, which consists in applying the field successively to a plurality of articles which are wet and removing some of the articles which have become dry, and automatically adjusting the field in response to the changing load provided by the articles to keep the efliciency of the field substantially constant independent of the number of articles under treatment.

10'. That method of drying articles by means of an electrostatic field, the power for which 0 is supplied by an oscillator, which consists in progressively applying the field to additional articles which are wet, removing articles which have become dry, and automatically varying the output 0! the oscillator in response to the changing load provided by the articles.

GEORGE T. HART. JR. ERASTUS E. WINKLEY.

. CERTIFICATE OF comcuori. Patent No. 2,251,277. August 5, 19141.

- GEORGE '1'. HART, .m., ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page}, second column, lines Shand 55, claim 9, strike out the words "in response to the changing load providedby the articles"; and that the said Letters Patout should be read with this correction therein that the same may conform to the record ofthe cesin the Patent Office.

Signed and sealed this mm day October, A. D. 19t

Henry Van Arsdale;

(Seal) Acting Commissioner of Patents

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