US2927255A - Electrostatic controls - Google Patents

Description

March 1, 1960 J. w. DIESEL Y 2,927,255

ELECTROSTATIC CONTROLS Filed July 2, 1954 5 Sheets-Sheet 1 INVENTOR. fj JOHN W.D|ESEL 10: 3M JIM?! March 1, 1960 J. w. DIESEL 2,927,255

ELECTROSTATIC CONTROLS Filed July 2, 1954 5 Sheets-Sheet 2 INVENTOR. JOHN W. DIESEL BY Mw/JM March 1, 1960 J. w. DIESEL 7 2,927,255

ELECTROSTATIC CONTROLS I Filed July 2, 1954 $Sheets-Sheet 3 FIG. 8

INVEN TOR.

.JOHN W. DIESEL BY .iWM/M United States Patent ELECTROSTATIC CONTROLS John Diesel, Maplewood, Mo., assignor to Erdco, Inc., Maplewood, Mo., a corporation of Missouri Application July 2, 1954, Serial No. 441,057 12 Claims. (Cl. 3 17144 This invention relates generally to electrostatics and more particularly to electrostatic controls, such as relays.

It has been known for many years that an attractive force is developed between two bodies when they bear opposite electric charges, but the commercial applications of this principle have been few. Indeed, the electrostatic controls heretofore proposed have been largely laboratory curiosities of erratic performance and considerable complexity. Accordingly, it is an object of the invention to simplify the construction and improve the operation of electrostatic controls. More specifically, the invention provides electrostatic controls that are comparable in function to electromagnetic and electronic devices, but which can be operated with better efiiciency, manufactured at substantially less cost, made considerably more compact, and more conveniently connected and assembled in multiple-component apparatus.

The construction of an electrostatic relay has presented serious problems to those skilled in the art. The electrostatic or actuating forces are quite weak and are extremely sensitive to plate spacing, with the result that the performance is erratic and considerable precision is required in manufacture. If the plate spacing were slightly greater than intended, the plates would fail to attract, and if too close, they would readily be actuated by extraneous secondary effects, such as might result from leakage.

Attempts to resolve these difiiculties by the use of high voltage and close spacing of the plates have not been too successful, because they, lead to a considerable problem in preventing discharge between the plates, such discharge resulting in loss of the electrostatic force. It has, therefore, been suggested that the plates be protected against discharge with an intervening layer of solid insulation, but this expedient has led to even more serious difiiculties. The introduction of solid insulation necessitates an increase in the distance between the conductive surfaces of the plates, which consequently weakens the electrostatic force, and the insulation, if not of considerable thickness, is subject to breakdown under high voltage stresses. More important, however, are the problems that arise from dielectric absorption and the property of the insulation to collect asurface charge, these factors causing the plates to stick and otherwise misbehave. In some instances, the plates will fail to release upon removal of the exciting voltage, and in other instances, the plates will move in a direction opposite to that intended when excitation is applied.

There follows a brief description of some of the features of construction and methods of operation utilized in solving these. difliculties. The plate excitation is at rather high voltage, at least a thousand volts, but the exciting current is limited to very low values. For example, in the case of a relay of a type suitable for use in a computer, the plate excitation might be at two thousand volts and the current limited to one tenth of a milliamp, although lower exciting voltages may be employed at the price of greater exactitude in construction "ice (the plates being more closely spaced) or higher voltages may be used if physical size is not too important.

While the plate excitation is at rather high voltage, the plate spacing is very small. in the case of a relay having an effective plate area of about one square inch, the spacing of the plates might be one sixty-fourth inch, but may be increased, especially with a corresponding increase in the plate excitation. Generally speaking, the spacing of the plates will otherwise be determined by the size of the signal which the contacts are required to interrupt.

In this respect, the invention contemplates that the signals carried by the secondary or contact circuit will also be at high voltage, at least a thousand volts and low current, and that the contacts will operate in an ionizable gas, such as air. With such a relay, closed or open circuit conditions are determined more by the distance between the contacts rather than by actual engagement, and the behavior is more analogous to that of a gas-filled tube than that of a solenoid relay. Such high voltages (which in the case of a multi-component apparatus would be of the same order of magnitude as those used to excite the plates) permit the establishment of a closed circuit condition, even though the contacts are not in perfect engagement, a feature which greatly facilitates manufacturing procedures and improves reliability. Low current signals are desired, especially when the contacts are small, in order to prevent heating to an extent such that an injurious arc eflEect is esablished by burning, melting or vaporization of the contacts. High-voltage low-current signals have additional advantages when the circuit components are formed by printed circuit techniques.

As pointed out, one of the fundamental concepts of this invention is the use of high voltage and close spacing of the plates, features which have heretofore been impractical, but for the introduction of a solid intervening insulator for preventing discharge between the plates, which insulator, in turn, has resulted in additional dithculties of an even more serious nature. The invention contemplates, in a preferred embodiment, that there will be no such solid insulator, but that neutralizing discharge between the plates will be controlled by high resistance within the control itself. Preferably, one of the plates is formed, at least in part, of high resistance material, and discharge is localized over certain areas of the plates, thc arrangement being such that other areas of the plates will be maintained at difierent potential, despite the presence of a charge transfer. This arrangement serves to prevent the uncontrolled accumulation of charges of a type that would produce malfunctioning of the control, and also permits very close spacing of the plates.

Additionally, the invention contemplates the provision of a high resistance shorting connection between the plates, the arrangement being such as to permit adequate accumulation of charges on the plates in response to plate excitation and yet quick removal of such charges in response to the withdrawal of the exciting voltage. This shorting connection or release circuit has the additional function of discriminating between true exciting signals and extraneous charges resulting from leakage, which if permitted to accumulate, might result in false actuation of the control.

While the above principles might be utilized in a1 wide variety of structures of diiiering application, the invention further provides an improved relay structure especially adapted for multi-component apparatus. Briefly, such a relay comprises a plurality of'overlying panels of insulating material, upon which panels the plates, circuit parameters and leads are formed as conductive coatings by printed circuit techniques. One of the panels may be a relatively fixed rigid member, whereas an opposite panel may be mounted to flex toward and t) away from the fixed panel in response to the presence and absence of plate excitation. The plates are formed on opposed faces of these panels as areas of the order of a square inch, contacts being actuated by relative movement of the panels.

in one embodiment, the movable panel includes a flap, the free end of which is normally spaced from the fixed panel so that the inherent resilience thereof supplies the bias for opening the contacts and separating the plates. This flap is enclosed in a fixed frame-like cer and is limited in outward movement by a fixed overr ing shielding panel. A movable contact is secured at the free end of the flap for cooperation with a fixed contact mounted over the other panel, a low-resistance plate being formed by silver paint on the flap and a high-resistance coating being formed on the other fixed panel v. .h carbon paint, With this arrangement, the free end portion of the movable plate is prevented from engaging the highresistance fixed plate, although the plates may engage one another in their center portions. The exciting circuit lead for the high-resistance plate then extends therefrom adjacent the free end of the flap. Leads for the movable contact and plate may extend on opposite faces of the flap to the fixed end thereof; and a high-resistance release circuit is provided for shorting the plates.

The terminals for the plates and contacts are brought out at the sides and ends of the unit; and these terminals may extend across the edges of the unit in order to make connection with similar units stacked one upon the other or with a suitable base upon which units are secured. It will be observed that this laminar panel construction simplifies manufacturing operations inasmuch as such panels may be readily die cut, printed and assembled with automatic machinery.

It may also be noted that the electrostatic controls of this invention are adapted for use as signal or information storage devices and other applications, which will be subsequently described in detail.

Other features of the invention will be in part apparent from and in part pointed out in the following detail description taken in connection with the accompanying drawings, in which:

Fig. 1 is a circuit diagram of a relay that embodies features of the invention, parts being shown in position prior to excitation;

Fig. 2 is a more detailed cross-sectional view, showing the relay arm in its actuated position;

Fig. 3 is an exploded view of certain insulating panels Which are assembled to form a relay;

Fig. 4 is a view similar to that of Fig. 3, but showing the reverse faces of the insulating panels;

Fig. 5 is a cross-sectional view of an assembled relay taken on the line 55 of Fig. 6;

Fig. 6 is a cross-sectional view taken on the line 66 of Fig. 5;

Fig. 7 is a cross-sectional view taken on the line 77 of Fig. 5;

Fig. 8 is a top plan view of a bottom panel illustrating an alternative embodiment of the high-resistance plate;

Fig. 9 is a top plan view of a relay-arm panel showing a construction for use where a relay is to control a large number of secondary circuits;

Fig. 10 is a simplified circuit diagram of a valve type of control;

Fig. 11 is a View similar to that of Fig. 10 but showing a control for introducing a time-delay in the passage of a signal;

Fig. 12 is a circuit diagram of a control suitable for short-term temporary storage;

Fig. 13 is a view similar to that of Fig. 12, but showing a control that might be used for comparatively longterm temporary storage;

Fig. 14 is a circuit diagram of a control wherein the relay arm is electrically biased in either direction of movement; and

Fig. 15 is a detail sectional view somewhat similar to Fig. 2, but illustrating an arrangement for use in a double-throw relay.

Initially, it should be understood that in the field of electrical controls, such as relays, one has been limited for practical purposes to a selection between electromagnetic and electronic devices. In many applications, particaularly multiple-component apparatus, neither type of device is entirely satisfactory. For example, an electromagnetic control is expensive (the cost of a reliable solenoid relay being of the order of one dollar), bulky (the practical size being not less than one cubic inch), and ofttimes not too reliable (because of failure at the contacts from dust or corrosion). Moreover, a solenoid draws a significant exciting current.

Electronic controls are faster, principally because they have only to deal with the insignificant mass or inertia of an electron as compared with the substantial Weight of an iron armature in a magnetic device. On the other hand, electronic components are also expensive and space consuming. In addition, an electronic device of the thermionic emission type requires a substantial filament heating current, and when such components are used in large numbers, they not only consume considerable power, put generate appreciable heat.

These factors are especially important when the components are assembled to form apparatus of the type used for such purposes as internal storage, addressing, data switching and arithmetic computations. In this area, a given piece of equipment will include a large number of components, hence the components should not only be inexpensive, small and operate with little power, but they also should be convenient to assemble and con nect together. In relation to the last point, printed circuits offer great promise, but are not easily connected to solenoid relays or vacuum tubes. Also, printed circuits frequently have a significant amount of resistance and are therefore not adapted to carry the substantial exciting current of a solenoid or filament-heating current of a vacuum tube.

Furthermore, since solenoids operate with relatively low-voltage high-current signals, diificulties are frequently encountered from imperfect closure of the contacts. A small particle of dust or slight corrosion at the contacts may prevent relay of the signal, a matter which is especially serious in computer applications because error is introduced in the output information and because it is extremely difiicult to locate the cause of the trouble. On the other hand, electronic 'or vacuum tube components suffer from the serious limitation of controlling only one circuit at a time, a. fact which leads to considerable expense in some applications, 'such as digital computers.

For these reasons, it is customaryin the digital computer field to use motor-driven gear devices when cost and size are important and speed unimportant, or to use vacuum tube devices where speed is the primary consideration and where cost, size and complexity are of nominal concern. Between these two types of machines, there lies a wide area in which there has not been much success in applying solenoid or electronic components. Perhaps some experimenters have considered electrostatic controls, but the difficulty is that while the principles are of some antiquity, the structures heretofore proposed have not been comparable'in a practical sense with more familiar electromagnetic or electronic controls.

Various proposals are found in the art, among which may be noted the use of rigid m'etal electrodes separated by an air gap (Patent No. 749,775), conductive plates separated by a solid resilient dielectric (Patent No. 1,834,786), spaced metal electrodes coated with insulation and hermetically sealed (Patent No. 2,175,354), piezoelectric crystals (Patent No. 2,182,340), and liquid dielectrics'(Pate'nts No. 2,419,111 and No. 2,417,850).

The simplest type of control-consistsof two relativelymovablerigidmetal plates which are separated by an air fruitful. -device wherein slight movement of the relay arm is caused to trigger other mechanism, which actually closes athe contacts, but such a tripping device is complicated :and must be reset after each operation. The other tack gap. The difiic'ulty with thisarrangentent isthat the plates must not only be initially spaced to prevent loss of potential by discharge between the plates, but they must be prevented from approaching one another to an extent that they would so discharge. If the distance between the plates is large, however, the electrostatic attractive force is very weak. It is of no help to increase theexciting voltage, because a corresponding increase in plate separation is necessary in order to prevent inadvertent discharge, and the electrostatic force falls off rapidly with an increase in the plate spacing.

Consequently, it is not surprising that resort has been made to the use of a solid dielectric between the plates, but this approach has also proved unsatisfactory. Thin dielectrics are subject to breakdown, and a thick dielectric increases the spacing and limits movement of the plates. The'dielectric has a further serious disadvantage in that secondary charges collect on the surface, and such extraneous charges cause the plates to stick and otherwise misbehave. For example, when a positive plate moves against or even near an insulated surface, a positive charge is transferred to the insulation. When the electrodes are again excited at a later time, this positive charge upon the insulation may well cause the positive electrode to move away rather than toward the negative electrode. It may be noted that the problem of dealing with secondary extraneous charges is much more serious than is generally recognized, especially when attempt is made to build a device of small size.

Finally, there is the problem presented by the secondary circuit of a relay type of control. Inasmuch as the mechanical forces are weak and the electrode spacing rather critical, particularly in prior devices, the art has been faced with a problem of imperfect closure and inadequate separation at the contacts. This difliculty has led the art in two paths, neither of which has been very One approach involves the use of a tripping taken makes use of contacts that are initially separated ;a very slight amount so that the least possible motion is required to close the circuit. The difliculty here is that only signals of very low voltage can be handled by the contacts.

Referring now to the drawings,.Fig. l illustrates certain electrical aspects of an electrostatic relay having a relatively fixed conductive plate 1 and a fixed contact 3. A movable relay arm 5 overlies the fixed plate, and this arm carries a conductive plate 7 on its lower surface opposite the fixed plate 1. A movable contactv 9 is mounted at the free end of the relay arm opposite the fixed contact 3 and in insulated relationship from the plate 7. The relay arm may be fixed at its other end 11 and is normally biased away from the fixed plate, but this bias is adapted to be overcome by the attractive force developed electrostatically between the plates. Connections to the'movable plate 7 and movable contact 9 may then be made at the fixed end of the relay arm on opposite faces thereof.

Referring to Fig. 2, the fixed plate 1 is secured to the upper face of. a relatively rigid insulating member 13, and

the movable plate 7 is a flexible conductive coating on the relayarm 5, which is formed of resilient insulating material. The member 5 is biased outwardly, as by a wedge member 15adjacent the fixed end 11, so that the plates 1 and 7 and contacts 3 and 9 are normally spaced apart. The plate is sufiiciently flexible, however, so that the arm bends resiliently over the wedge 15 to close the contacts when voltage is applied across the plates. The intervening portion may also bend so that the movable plate7 engages the fixed plate 1 at locus X. A flexible conductor 17 leads from the plate at the fixed end thereof,

i overly weakattractiveforce and the incorporation of a 6 while aflexible conductor 19 leads from the movable contact 9 over the upper surface of the relay arm to the fixed end thereof. This fixed end may be secured by an overlying member 21.

In addition, the relay includes an insulating member 23 located above the relay arm 5 to limit its outward movement. The lower face of this-insulating member 23 may carry a conductor 25 which is coextensive with the contact conductor 19, and the upper face may carry a plate 27 which is generally coextensive with the plates 1 and 7.

Returning to Fig. l, the plates are shown to be connected by an exciting circuit EC to a DC. power supply designated by the box V. The positive terminal of this power supply is connected through a switch S to the movable plate 7, whereas the negative terminal andfixed plate 1 are connected to one another and may be grounded. 1

The invention contemplates'that the plate excitation will be at high voltage and of low current, an output of two thousand volts being suggested for relay controls of-the type described herein. The current output of this source may be relatively low, adequate safety being achieved by limiting the current output to a few milliamps., as by using a power supply having high internal resistance IR.

The exciting current is-chiefly limited by the resistance or impedance of the control itself, and indeed, satisfactory relay controls have been operated on currents as low as one-tenth of a milliamp, although this does not exclude even smaller operating currents. This impedance is in part in series with and in part in parallel with the plates. The series resistance, in turn, may be in part or entirely internal with the plates, such internal resistance being represented by the legend PR.

As indicated previously, the movable plate 7 bends to approach or -even engage the fixed plate 1. In the absence of an intervening dielectric or vacuum, a transfer of charge would occur when the relay arm is in its actuated position, and such a transfer would tend to result in discharge of the plates, especially when both plates are formed of metalor other high conductivity material. If the plates discharge, the relay arm is released, and when it swings outwardly, the discharge path is interrupted and the plates would recharge until the relay arm is again actuated. Such a fluttering of the relay arm is not desired, and for that reason, it has generallybeen deemedv necessary to prevent plate discharge by-use of a solid dielectric or bylarge plate separation. Neither of these approaches; is considered satisfactory,- however, inasmuch as-a large separation of the plates results in an dielectric leads to difficulties from stray charges collected on or in the'dielectric.

The present invention recognizes-that such discharge need not be completely prevented and that a conductive condition is indeed necessary if undesired accumulation of charges is to be prevented. In contrast with prior practices, there is provision fora transfer of charges between the plates, but it is controlled, as to rate, direction and location. The arrangement is such that a voltage differential is maintained over some portions of the plates despite the flow of charge and loss of potential at other portions, such as at locus X. This may be accomplished in various ways, one of which involves mounting the relay arm, as shown in Fig. 2, so that a portion of the movable plate at the free end of the relay arm is prevented from" approaching the fixed plate as nearly as the center portion X. The exciting circuit is then connected to the fixed plate 1 at an adjacent point so that when charge flow develops at the locus X, it will pass through a portion of the negative plate in a direction primarily parallel to its surface toward the free end of the relay arm. Finally, the fixed plate is designed to provide considerable resistance PR between mamas 7 the locus X and the end portion, where the plate is connected to the exciting circuit. I

In the absence of a transfer of charge directly between the plates, the full output of the supply V would appear uniformly across the plates. When a flow does develop at X. a voltage gradient occurs across the plates from the locus X to the end portion of the plates, and the resulting electric field is sufficient to maintain the relay arm in its actuated position.

The internal plate resistance PR can be conveniently supplied by forming the fixed plate -1 of high resistance material, such as a suspension of carbon granules in a suitable binder. A rather high resistance is desired; for example, the resistance between the point X and the terminal connection 29 might be thirty megohms; in which event, the plate current would be less than one'tenth of a milliamp. If additional series resistance is desired. it may be supplied by extending the high-resistance negative plate 1 beyond the positive plate 7, as will be apparent hereinafter to provide a resistance DR. For relays of the type to be described in detail, a total series resistance of thirty to forty megohms seems to be satis factory, but these values obviously can be varied considerably.

If the series resistance is too high, however, the control may become unreliable. Also, the plates may not charge at an adequate rate. On the other hand, too low a resistance will result in excessive sparking at the plate surfaces and burning of the plates. While the highresistance plate may be formed in various ways, a suspension of conductive granules in a body having dielectric properties may have special advantages, which are not as yet entirely understood.

In the past, it has been customary to assume that when the switch S is closed, the full voltage of the source V is immediately impressed across the plates, thereby causing an attraction of the plates. Actually, closure of the switch S merely establishes a circuit which permits a charge to accumulate on the plates. The amount of charge is determined by the exciting voltage and the capacitance CP of the plates, although this capacitance varies as the plates move together. When the switch S is opened and the excitation removed, it has similarly been assumed that the plates immediately swing apart. With the control herein described, at least, such an assumption is not entirely justified. Indeed, it is necessary to clear all of the accumulated charges, if the plates are to release upon removal of the plate voltage and if other malfunctions due to these residual charges are-to be prevented. In order to prevent these difficulties, the invention contemplates the provision of a release or shorting connection between the plates to remove the charges accumulated in the conductive portions thereof. Charges that otherwise might tend to collect in or on a dielectric are carried away through the resistance of conductive granules of the fixed plate.

In the illustrated embodiment, this shorting connection is a release circuit RC connected in parallel with the plates in the exciting circuit. As such, the circuit RC also acts as a short across the power supply V, hence a resistor RR is connected in the release circuit to minimize the drain effect of the release circuit and insure a potential difierence at the plates. The magnitude of the resistance RR should not be too high, however, it it is to be effective in quickly releasing the plates. a typical relay, the parallel resistance RR might be of the same order of magnitude as the series resistance PR. described previously.

The release circuit RC has an additional important function in that it largely eliminates, difliculties that would otherwise be encountered from general leakage throughout the system. Such leakage is almost impossible to avoid in a device that is not hermetically sealed or otherwise protected against high humidity conditions,

and it is especially troublesome with electrostatic devices.

With the present invention, leakage will not result inadvertent actuation of the relay under normal conditions. Insofar as extraneous secondary positive charges tend inadvertently to build up on the positive plate 7, they will be withdrawn through the release circuit RC before they can accumulate to an extent that would result in false actuation of the control.

While the resistance of the release circuit is substantial and interferes with rapid transfer of such charges, generally speaking, leakage is a relatively slow process. Consequently, the release circuit might be said to have the function of discriminating between true signals (which involve relatively large currents, and fallacious signals resulting from leakage through the system (which are generally of very low current values).

it may also be desirable to provide an inductor RL in the release circuit as part of the parallel impedance. The inductor functions to prevent an excessive drain through the release circuit RC when the switch is first closed and the exciting current is initially high. In other words, the inductor RL increases the eifective impedance of the release circuit when the plates are initially excited. After some delay (determined by the amount of inductance and resistance in series with the inductor), the eifect of RL fades and the release circuit draws a larger current. This is permissible, however, because the plates will have been substantially charged in the interval. The inductor RL may also serve to increase the release speed of the relay upon the de-excitation of the plates.

A somewhat similar effect could be obtained by connecting a capacitor in series with the plates, the capacitor being by-passed by a high resistance element or having some leakage.

It may additionally be desirable to provide a capacitor C in the exciting circuit across the voltage supply V when the supply has considerable internal resistance IR. The significance of the capacitor C is that a substantial current is initially required to charge the plate, but once charged, the current requirements are relatively low, being only that resulting from discharge between the plates and drain through the release circuit RC. The capacitor C is a storage device, which will supply the initially heavy charging current without overloading the voltage source when the switch S is first closed.

Referring now to the contact or secondary circuit CC, the invention contemplates that the signals carried by this circuit will be of a sufliciently high voltage to permit establishment of a closed circuit condition, even though the contacts are not in perfect engagement, the high voltage tending to cause the signal to jump a slight gap between the contacts or overcome contact impedance that would otherwise interfere with passage of the signal. With this arrangement, the open and closed circuit conditions are determined by the distance separating the contacts rather than by actual physical engagement of the contacts. In using this principle, it is necessary to have an ionizable atmosphere, and for that reason, there should not be a high vacuum condition at the contacts. On the other hand, the current of these signals should be low enough to prevent contact heating such that an arc discharge occurs between the contacts. The behavior of the device, in this respect, is comparable to a gaseous-discharge vacuum tube, but with the difference that the circuit is opened by increasing separation of the contacts rather than by an inverse plate voltage.

In computer applications involving a series of electro- Static l h si a carried y e s ondary c rcu uld, be of h s me olt g an c r-ren these required to actuate the plates. It may be noted that the contact problem, while always important, is critical in the case of computers and the like, because failureat even a single contact point cannot be tolerated. It might be said that in a computing apparatus, thev contacts should be eager to carry a signal (as in the disclosed device) rather than reluctant (as in solenoid relays).

Utilizing the above principles, it is possible in an electrostatic relay to have (1) a lightweight sensitive relay arm, (2) close spacing of the conductors, (3) close spacing of the plates, and (4) a compact arrangement of a series of relays, these being features which are of prime importance in many applications. Heretofore, the first three conditions or features have been impractical to achieve because of interference or leakage between the parts of a given control unit. The fourth abovementioned feature also tends to cause interference when units are stacked close together, as they normally would be in multiple component apparatus.

For instance, a positive relay arm may be undesirably attracted by the negative plate of a relay located immediately above. If the outer case of the relay is at ground potential and in close proximity to the relay arm, the arm might even be attracted by the case when excited positively. This difficulty is herein overcome by reflecting the charge on the relay arm in a plane opposite the fixed electrode. Referring to Figs. 1 and 2, the plate area 27 on the member 23 is connected, in. parallel with the positive plate 7 so that both of the elements 7 and 27 are positively charged upon closure of the switch. To some extent, the relay arm is thereby repelled by the plate 27, although in another sense, the plate 27 serves merely as a shield between stacked relays.

; A similar undesired effect may be caused by the contact lead 19, and is herein prevented by the conductive strip' 25 on the member 23. This conductive strip 25 is connected in parallel with the strip 19 so that a charge differential will not develop therebetween. Also, the contacts themselves should be of small area in comparison with the plate areas, so that the attractive force between opposed contacts is at a minimum. Large contacts are not required in the described relay, inasmuch as the contact currents are relatively low and have an insignificant heating effect.

Reference is now made to Figs. 3-7 for a description of a specific structure which might be used as a relay in a digital computer and other multi-component apparatus. The device comprises a plurality of flat, generally rectangular insulating members for carrying the conductive elements. In a device for controlling ten secondary'circuits, the panels measure approximately three inches in width and length, and are of varying thickness and composition. A bottom panel 101 and top panel 109 are .010 inch Vinylite (polymerized vinyl chloride resin), a relay-arm panel 105 is .005 inch Vinylite, a contact member 103 is .020 inch Vinylite, and a spacer frame 107 is .060 inch laminated phenolic or styrene resin. Such insula'ting members would be die cut from sheet stock, the conductive elements being formed thereon using printed circuit techniques. sembled in stacked overlying relationship and are secured together, as by bolts 111 through corner apertures 113.

The panel 101 constitutes the base of the device and serves as a support for the fixed plate, which is formed as a coating 115 of conductive paint. Conductive paints being known in the art, they are not described other than to note that they customarily comprise a suspension of conductive granules in a suitable binder. The resistance of the paint and resulting co'ating is to some extent controlled by the proportions and character of the ingredients, silver granules being generally used where high conductivity or low resistance is desired, and carbon granules being utilized for high resistance paint.

In the disclosed embodiment, the fixed plate 115 is formed as a high resistance coating measuring one and three-eighths inches in width and one and three-fourths inches in length. The paint is of a type providing approximately one hundred seventy-five megohms per square inch, this being a term of art indicating that a coating one inch in width and length normally has a resistance of the stated value between opposite edges.

The coated members are then as-' 10 The plate area extends close to an end 117 of the device and a high conductivity lead is formed as a strip 119 to extend across that end of the plate to an adjacent corner aperture 113. A connection to ground and to the negative terminal of the exciting source is then made through the associated bolt 111 (Figs. 5-7).

It may be observed at this point that the terms high resistance and high conductivity (or low resistance) are used in a relative sense inasmuch as printed leads formed with silver paint will have appreciable resistance. It is only intended that the voltage drop in the leads are nominal in relation to the drop at a resistive plate or across one of the resistances referred to. Also, a distinction is made between resistive material, such as carbon paint, anda semi-conductive dielectric, such as stone or organic membranes, the latter having only a very slight leakage usually aided by absorbed moisture. Semiconductive dielectrics are considered impractical because of their very high volume resistivity, if such materials can really be considered to have a resistance.

The plate 115 may in part extend beneath a thin piece 121 of insulating material, which is located at the end 117 of the device to minimize leakage between the fixed plate and fixed contacts. This covered portion of the plate 115 serves as the series resistor DR referred to earlier. The resistor RR of the release circuit is a relatively narrow strip 123 of high-resistance conductive paint extending over the panel 101 outwardly of the plate 115 and inwardly of the side edge 125 of the device, and a lead 127 extends therefrom to the side 129 of the device. The width and length of this strip, as well as the character of the paint, determine the resistance in the release circuit, which would be approximately thirty megohms in the described embodiment.

The contact member 103 has a central opening for accommodating the relay arm of the device, and up-. wardly-facing contacts 131 are mounted along the margin of this opening and high-conductivity leads 133 extend to the adjacent end 117 of the device. Although conductive paints may not be entirely satisfactory for contact purposes, there are other techniques known in the art which may be utilized in forming a lightweight contact which will withstand the slight heating to be ex-' pected from sparking. Although some degree of uniformity is desired when there are several contacts, the problem is not what it is in conventional devices where wiping engagement is generally necessary to establish a closed circuit condition and where contact rebound is a matter for concern.

The'relay-arm panel 105 is out about the margins 117, j

125 and 129 to form a resilient flap 135, the free end ofwhich extends over the fixed contacts 131 as a relay arm. The movable plate is a high-conductivity coating 137 over the lower face of the flap, the plate extending from a point short of the free end to the other end 139 of the device, where it is connected to a strip 141 of highconductivity paint. The conductor 141 extends over the fixed marginal portion of the panel to the side 129, so

as ultimately to make a connection with the lead 127 of the releasecircuit.

Movable contacts 143 are mounted on the free end of theflap for cooperation with the fixed contacts, and leadforming strips 145 of high-conductivity paint extend over the upper face of the flap to the end 139 of the device.

Inasmuch as the flap is fixed during use, it may be desirable to incorporate a plasticizer in the conductive paint forming the coatings 137 and 145. In assembly, a narrow piece 147 of insulating material is sandwiched between the flap and the bottom panel' 101 adjacent the fixed or hinged end so as to urge the relay arm 135 upwardly. Movement of the relay arm is accommodated by the surrounding frame-like spacer 107 and is limited by engagement with the overlying top panel .109. When several devices are to be. stacked one upon are assembled together.

the other, the panel 109 may be coated to shield the several devices against electrical interference with one another. Conductive strips 149 on the lower face of the panel 109 extend over the contact leads 145 and are electrically connected thereto at the end 139 of the device, whereas a conductive shield 151 on the upper face of this panel is connected to the movable plate by a lead 153 at the side 129 of the device.

It will be noted that the free end portion of the flap 135 is projected through the contact member 103 and also curled outwardly somewhat, the latter being desirable in that it permits relatively close spacing of the plates 115 and 137 with rather wide spacing at the contacts. Contact closure is achieved both by downward movement of the flap and by a tendency of the flap to straighten under the electrostatic forces applied across the plates. The contact member 193 prevents the plates from coming into physical engagement over their entire surfaces, however. The inherent resiliency of the flap supplies the bias for otherwise opening the contacts and separating the plates, the wedging strip 147 being adjustable to vary the amount of bias, but in the finished device, this wedging strip is secured so that the device may be operated in any position.

The disclosed arrangement also provides for connection of the electrical elements merely by assembly of the panels. To that end, connecting elements of high-conductivity paint are formed on the several insulating members to extend across the edges thereof and partially over the margins. Connecting elements 155 provided at the side 129 are aligned so that the leads 127, 141, and 153 become connected with one another when the members Connecting elements 157 are provided at the end 117 in alignment with the leads 133 for the fixed contacts. Similar connecting elements 159 located at the other end serve to connect the leads 145 for the movable contacts and the overlying coextensive shielding strips 149. This arrangement is not only desirable in facilitating the construction of a single unit but also facilitates the assembly and connection of several units, whether they be stacked one upon the other or mounted on a panel previously ruled with conductive strips adapted to register with the connecting elements 155, 157 and 159.

Whereas the negative plate 115 in the embodiment of Figs. 3-7 is shown to be formed as a coating of uniform resistance, different arrangements are possible. For example, as shown in Fig. 8, the coating on a bottom panel 201 may be constituted by contiguous strips 215 of highresistance paint, the strips being of varying width and being formed from high-resistance paints of differing resistance values. Similarly, the release circuit may be of a different arrangement. For example, the movable plate may extend at its fixed end into direct overlapping engagement with the high-resistance fixed plate, so that the latter provides the high-resistance for the shorting connection.

Fig. 9 illustrates an alternative arrangement which might be used where a rather wide relay arm is required to accommodate a large number of secondary circuits 245. In this instance, one or more slots 263 is cut in the center of the flap 235 to relieve buckling and facilitate escape of the air cushion between the plates as the relay arm is actuated. While there are not theoretical limits to the size of the relay arm, present experience seems to indicate that a relay arm one-eighth inch in width and one-half inch in length is about the smallest practical size, and a relay arm three inches in width and two inches in length is about the largest useful size. These figures are, given merely in the nature of suggestion, however, and should not be taken as limiting inasmuch as further development work may extend the range considerably.

Fig. 9 also illustrates an arrangement wherein the free end of the relay arm is slit at 265 to provide resilient contact fingers 267 carrying the movable contacts. It has been found that this type ofrelay arm is especially de- 1'2 sirable when a large number of secondary circuits are carried on the relay arm.

The arrangement shown in Fig. 1 is a simple control for relaying a signal from the source V to a load L upon closure of the switch S, but there are many other applications of the invention. In Fig. 10, there is shown a valve type of control which is adapted to pass a signal from the terminals T-l to the terminals T-Z while preventing passage of a signal in the reverse direction. In such case, the movable contact MC is normally spaced from the fixed contact FC and is connected to the movable plate MP, so that the open contacts block transfer of charge from the terminals T-2 to the plates, but permit charging of the plates MP and PP from the terminals T-1.

Fig. 11 illustrates a similar device which is adapted to introduce a delay in the passage of a signal from the input terminals T-1 to the terminals T-2. In this embodiment, a resistor R1 is connected between one of the input terminals T-1 and the movable plate MP. The resistor R-1 serves to delay charging of the plates so that the contacts MC and FC do not immediately close upon application of a signal to the input terminal T-l. The plate capacitance PC is rather low, hence the resistance R-l should be of a very high value.

Referring to Fig. 12, there is shown a hold type of control which might be used for storing information'over a short period of time. Input terminals T-1 are connected to the movable and fixed plates MP and FF, whereas the contacts MC and PC are connected to output terminals T-2. In this instance, the release circuit RC includes a normally open switch S-1 and may or may not have a series resistor RR. An input pulse results in attraction of the plates and closure of the contacts. The plates remain actuated upon discontinuance of the input, immediate discharge being prevented by the open switch 8-1 in the release circuit. The closed condition of the contacts hence serves to indicate the prior existence of a pulse received at the input terminals, although such pulse is of a transient character. This control would be used for short-term storage because leakage between the plates would utimately result in their release. Otherwise, release is achieved by closing the switch S-1.

Fig. 13 illustrates a hold circuit which might be used for storage over longer periods of time. As before, input terminals T1 are connected to the respective plates and output terminals T-2 are connected to a first set of contacts MC-l and FC-1. A second movable contact MC-2 is connected to the movable plate and an associated fixed contact FC-2 is connected through a switch 8-2 to the positive terminal of a voltage source V-l. This voltage source is otherwise connected to the fixed plate FF. In operation, a pulse applied to the input terminals results in actuation of the plates and closure of both sets of contacts. The second set of contacts then establishes a charging circuit from the voltage source V-l across the plates so that they will be held in their actuated position upon discontinuance of the input at T-l. The contacts will remain closed until the switch 8-2 is opened to permit discharge of the plates through the release circuit RC.

Fig. 14 discloses a further embodiment which might be employed where it is desired to have little, if any. mechanical bias on the movable plate MP. As in Fig. l, the positive terminal of an exciting source V is connected through a switch S to the movable plate, and the negative terminal is connected to a fixed plate FP-l, a high resistance release circuit RC being connected across these plates. A second fixed plate FP-Z is mounted over the movable plate and is permanently connected to the positive terminal of the exciting source V. It will be understood that the movable plate MP has conductive surfaces which face both upwardly and downwardly for cooperation respectively with the plates FP2 and FP-1. Also, the plate FP-Z, as well as the plate FP-l, would be formed of high-resistance paint.

When the switch 8 is open, there is little, if any, volt age diflerential between the movable plate MP and the lower fixed plate FP-l, but there exists a substantial voltage difference between the movable plate and the upper fixed plate FP-2, which difference causes the movable plate to be drawn upwardly. When the switch S is closed, the plates MP and FP-2 lose their potential dif' ference and a voltage differential appears between MP and FP-l, thereby causing the movable plate to be drawn downwardly.

It will additionally be apparent that normally-closed or double-throw relays may be designed in accordance with the principles of this invention. For example, Fig. 15 illustrates a possible arrangement for a double-throw relay. In this instance, the relay arm 305 has upper and lower movable plate areas 307. Movable contacts 309 are mounted at the end of the arm, but the lead 319 therefor is embedded in the relay arm in insulated relationship from the plates 307, as by using a laminated type of construction. A pair of fixed contacts 303 are spaced on opposite sides of the movable contact 309, and resilient biasing fingers 304 project inwardly from the fixed contacts so that the relay arm is normally biased to a center position clear of the fixed plates 301 and fixed contacts 303.

From the foregoing, it will be apparent that the invention provides a control that can be manufactured at small expense in comparison to present devices used for equivalent purposes. The insulating members or panels can be die cut and coated at high rates of production, and it is possible that conventional printing machinery may be used for this purpose. Assembly of the panels is obviously a very simple operation, and the assembled units may be readily stacked or mounted upon panels to form multiple-component apparatus. The block-like shape and the small size of the units also permits a very compact arrangement.

Efiiciency is also excellent, as a unit of the type described draws on the order of one-tenth of a milliamp when the input is approximately two thousand volts, the power consumption being only one fifth of a watt. Inasmuch as the currents are of such low values, the high voltage signals are practically harmless.

Generally speaking, it will be desirable to hold the plate spacing to as small a distanceas possible, bearing in mind the voltage that must be interrupted by the contacts. At the present time, plate spacing of the order of one sixty-fourth inch is found practical, particularly when the relay arm is curved slightly as shown in Fig. 5'

so as to be flattened by the pull between the plates when excited. The contact separation could also be increased by extending the relay arm or by using other well-knownprinciples. There being no necessity for the contacts to be tightly pressed together, the relay arm and other parts may be made of lightweight thin material. This feature of construction and the absence of series inductance permits a high-speed operation, as compared with solenoid relays which have relatively heavy armatures and considerable series inductance.

Additionally, it is to be observed that the relay arm is entirely enclosed in the devicev illustrated and described in connection with Figs. 3-7, and it will be apparent that the chamber containing the relay arm may be hermetically sealed to provide a controlled atmosphere.

Such an arrangement may be desired when high relative humidity produces leakage in excess of that which can be adequately handled by the device. A sealed condition is readily achieved by compressing the insulating panels or by coating the outer surface of the device with lacquer.

As has beenindicated, relays of the character disclosed herein are particularly useful in digital computers, business machines and the like. In contrast to present business machines which make use of magnetic tape or punched cards, it is contemplated that the input information for a machine using components of the type decr herein o d .b um .li. d.. sra a s sn s? '14 tape marked'rnerely with a lead pencil or conductive inle, this practice being permissible because the signals used can be conducted by this marking or other type of mark ing which would not be suiiiciently conductive for solenoid or tube controls.

A typical card might have indicia boxes arranged in ten rows (to accommodate numerals zero through nine) and a number of columns corresponding to the number of digits to be handled. At other points, the card would be marked to indicate to the machine What type of operation is required. The cards would then be conveniently read, as by being fed against a drum on which a plurality of paired contacts would register with the various boxes on a card. Where a box has been marked with a con.- ductive material, a circuit would be established thereby, through the paired drum contacts for that box. One of the advantages connected with this practice is that the cards could be marked manually.

From the foregoing description, it is apparent that those skilled in the art will understand the structure, function, and mode of operation of the invention herein disclosed, and appreciate the advantages thereof. Although several embodiments have been disclosed in detail, it is to be understood that the invention is not limited thereto, but the drawings and description thereof are to be understood as being merely illustrative. It is realized that many modifications and variations will present themselves to those skilled in the art without departing from the spirit of this invention or the scope thereof as set forth in the appendedclaims. I

It will be understood that the term fully conductive is used in describing the plates as being conductive over their entire effective opposed surfaces, so that no stray charges can accumulate thereon, even at limited areas. The plates are conductive in the sense that stray charges cannot accumulate, although the degree of conduction may be low-in fact, the resistance of the plate circuit is quite high and at least one of the plates is preferably formed of high resistance material.

Having thus described the invention, What is claimed and desired to be secured by Letters Patent is:

1. Electrostatic relay apparatus comprising a pair of opposed fully conductive plates mounted for relative movement toward and away from one another, a pair of,

cooperating contacts at least one of which is mechani-' cally actuated by relative movement of the plates, an

ionizable gas between the plates and contacts, said plateshaving conductive surfaces in opposed relationship free of an intervening solid dielectric barrier, thereby to prevent accumulation of stray charge between the plates, a power source adapted to be connected to and disconnected from the plates and having a high-voltage output of no less than about one thousand volts, resistance means of at least one megohm in series with the plates and power supply, and means permitting limited conduction while preventing complete discharge between the plates upon relative movement toward one another,

thereby to hold the plates by electrostatic force while tric barrier on which stray charge rriight accumulate, a power source adapted to be connected to and disconnected from the plates and having a predetermined highvoltage output of no less than about one thousand volts," resistance means of at least one megohm in series with the plates and power supply, and means preventing thess. and f th mo b e gfirqm ,ar r es i s hgs hc plate so closely as to permit conduction between said end areas at said predetermined voltage while permitting limited conduction between other areas of the plates, thereby permitting electrostatic force to hold the plates together while said power source is connected thereto, and means effecting relative movement of the plates away from one another upon removal of the applied voltage.

3. Electrostatic relay apparatus comprising a pair of opposed fully conductive plates mounted for relative movement toward and away from one another, a pair of cooperating contacts at least one of which is mechanically actuated by relative movement of the plates, said plates havint conductive surfaces in opposed relationship free of an intervening dielectric barrier on which stray charge might accumulate and so that a condition of conduction may develop between the plates, a high-voltage power source adaptedto be connected to and disconnected from the plates, a first resistive element of at least one megohm connected in series with the plates and power source, and a second resistive element of at least one megohm connected in parallel with the power source and plates, said two resistive elements being arranged to limit the current fiow between the plates both when the power supply is connected thereto and when the power supply is disconnected therefrom, thereby to prevent the plates from being actuated by stray leakage but permit actuation of the plates when the power source is con nected and disconnected.

4. Electrostatic relay apparatus comprising a pair of opposed fully conductive plates mounted for relative movement toward one another from a predetermined released to a predetermined actuated position, said relay apparatus having contacts mechanically actuated by relative movement of the plates, said conductive plates being in opposed relationship without an intervening dielectric barrier on which stray charge may accumulate, means permitting predetermined areas of the plates to approach one another more closely than other areas, a power source associated with said plates and having an output voltage sufiiciently high to permit conduction between the relatively closely spaced areas of plates in their actuated position, and at least one of the plates having resistance material to maintain a voltage drop at said relatively widely spaced areas of the plates relative to said closely spaced conducting areas, thereby to hold the plates in the actuated position upon conduction between said relatively closely spaced areas.

5. Electrostatic relay apparatus comprising a pair of opposed conductive plates mounted for relative movernent toward and away from one another from a released to an actuated position, said relay apparatus having relatively movable contacts actuated from a predetermined normally-open position to a predetermined normally-closed position by relative plate movement, an ionizable gas between the plates and contacts, the closing force on said contacts being that developed by electrostatic attraction between the plates, and a high-vole age power source of at least one thousand volts associated with said contacts, the voltage of said power source being sufficiently low to prevent conduction between the contacts when in their relative normally-open position andresistive means of at least one megohm in series with said contacts to limit current flow between the contacts.

6. In an electrostatic control of the character set forth wherein a pair of conductive plates are mounted for relative electrostatic attraction; the improvement that comprises one of said plates being of a resistive character such as to have a high resistance in the direction parallel to the surface thereof, said resistive plate being in part conductively cooperable with said other plate at a predetermined locus spaced inwardly from one margin of said resistive plate, and exciting means connected to said resistive plate outwardly of said locus of conduction and to said other plate, thereby to cause current flow through the resistive plate to be substantially parallel to the surface thereof and to produce a voltage drop across the surface of the resistive plate, the space between the plates being free of a solid dielectric barrier.

7. In an electrostaticcontrol of the character set forth wherein a pair of conductive plates are mounted for relative electrostatic attraction; the improvement that comprises one of said plates being relatively rigid and of a resistive character and said other plate being relatively movable and being hinged along one margin thereof for movement toward and away from said rigid resistive plate, means preventing said opposite margin of the movable plate from contacting the fixed plate, and plate exciting means connected to the movable plate at its hinged margin and to the rigid resistive plate along the margin thereof which is most remote from said hinged margin of the movable plate, the space between the plates being free of a solid dielectric barrier.

8. In an electrostatic control of the character set forth wherein a pair of conductive plates are mounted in spaced relationship for relative movement toward one another in response to the application of an electrical potential thereto; the improvement that comprises one of said plates being relatively fixed and the other plate being mounted opposite said fixed plate with its center area movable toward said fixed plate into conductive relationship therewith, plate exciting means connected to end portions of said respective plates at points remote from said center areas, and at least one of said plates being formed of resistive material so as to develop a voltage drop between the center and end areas thereof when the plates move into conductive relationship with one another, the space between the plates being free of a solid dielectric barrier.

9. Electrostatic control apparatus comprising a pair of relatively fixed plates mounted in opposed spaced relationship from one another, relatively movable plate means extending therebetween and having opposed conductive surfaces conductively cooperable with the respective fixed plates, at least one of each pair of conductively cooperable surfaces having means preventing complete discharge therebetween but the plates being free of an intervening solid dielectric barrier, cooperating contacts mounted for actuation by the movable plate, a DC.

' power supply having one terminal relatively permanently connected to one of said fixed plates and another terminal relatively permanently connected to the other fixed plate so that the fixed plates are at opposite potentials, and a circuit including a switch means for intermittently connecting the movable plate to one of the two terminals of the power supply and a circuit including resistance means of at least one megohm permanently connecting the movable plate to the other terminal of the power supply.

10. Electrostatic relay apparatus comprising a pair of fixed plates mounted in opposed spaced relationship and a relatively movable plate means extending therebetween, but the plates being free of an intervening solid dielectric barrier, cooperating contacts mounted for actuation by the movable plate, means preventing complete discharge directly between the plates, a power supply of at least one thousand volts having one terminal relatively permanently connected to one fixed plate and another terminal relatively permanently connected to the other fixed plate, a control circuit including switch means for intermittently connecting one of the terminals of the power supply to the movable plate, and a release circuit including resistance means of at least one megohm relatively permanently connecting the movable plate to the other terminal of said power supply.

11. An electrostatic valve device comprising a fixed conductive plate and a relatively movable conductive plate mounted opposite said fixed plate, said plates being free of an intervening dielectric barrier, a movable contact carried by and forming a conductively-associated part of said movable plate, a cooperating relatively fixed contact mounted opposite the movable contact and clear of the fixed plate for conductive engagement by the movable contact, a power supply, an input circuit including switch means connecting one pole of the power supply to the movable plate, and an output circuit leading from said fixed contact to said other pole of the power supply, said other pole also being connected to said fixed plate, and a resistive current permanently connected in parallel with the two plates, and means preventing complete discharge directly between the plates as the movable plate moves toward the fixed plate.

12. An electrostatic memory device for short-term storage of information comprising a pair of opposed conductive plates mounted for relative movement toward and away from one another, said plates being free of an intervening dielectric barrier, a pair of relatively movable contacts actuated by relative movement of the plates and at least one of which is electrically insulated therefrom, a power supply, an input circuit including switch means connecting the poles of the power supply to the plates, a release-clear circuit including normally open switch means connected in parallel with said plates and the power supply to discharge the plates, and means otherwise preventing complete discharge directly between the plates as they move toward one another.

References Cited in the file of this patent UNITED STATES PATENTS 749,775 Lacour Jan. 19, 1904 1,446,748 Johnsen Feb. 27, 1923 1,605,911 Banneitz Nov. 9, 1926 1,834,786 Kacser Dec. 1, 1931 2,066,211 McCreary Dec. 29, 1936 2,175,354 Lewin Oct. 10, 1939 2,201,879 Blattner May 21, 1940 2,269,442 Dench Jan. 13, 1942 2,365,738 Williams Dec. 24, 1944 2,419,111 Bostwick Apr. 15, 1947 2,466,053 Shaper Apr. 5, 1949 2,786,111 Reed Mar. 19, 1957 FOREIGN PATENTS 201,679 Great Britain Aug. 9, 1923

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