DE2164202A1 - Pressure actuation sensitive signaling device - Google Patents

Description

Western Electric Company, Incorporated Sessler 10-36-10

Pressure actuation sensitive signaling device

The invention relates to signaling apparatus, and more particularly a pressure actuation sensitive key selector. Fundamental demands placed on improved pressure actuation selectors are in the simplification of their mechanical construction, the elimination of metal contacts and improving reliability. Furthermore, the dimensions should be reduced, improves sensitivity, reduces manufacturing costs, and enables an output signal to be generated that can be used without additional monitoring or processing.

A large number of signaling operations require the generation of voltage pulses or tone signals after one prescribed code. For example, voter arrangements are used in the known telephones which actuated metal contacts to interrupt a power source when poles of binary pulses are formed will. Modern telephones use push button selectors that mechanically form circuits that control the Trigger the formation of multi-tone signals. Pushbutton switches are of additional importance as input devices.

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gene for electronic calculating machines and the like.

As with all mechanical switch designs, ohmic contacts occasionally become contaminated and fail then. More importantly, mechanical assemblies are relatively heavy and bulky, have high inertia and contribute significantly to the total cost of the signaling arrangement because of the precision required for their manufacture.

In order to avoid the difficulties inherent in mechanical dial or push-button selectors, a variety of alternative switch designs, such as crosspoint matrices and magnetic and electrostatic units, have been developed. For example, the spring element of an actuating member can be replaced by a single layer of flexible material which covers a matrix arrangement of conductors. When the flexible cover layer is pressed at defined points, a corresponding ^{ohmic 1} shear contact is established by bringing the conductors underneath into contact with one another. Similarly constructed signaling devices with pressure actuation sensitive electrostatic elements, such as those described in US Pat. No. 3,281,541, avoid a number of difficulties inherent in mechanical units.

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In a typical electrostatic unit, a change in capacitance between pressure actuation, plate and a reference electrode, which as a result of the touchdown a finger is generated on the plate, scanned and used to generate a further processable signal used. Such units using electrostatic and film-like membranes, while compact, require however, auxiliary power for the excitation and scanning and signal generating devices for generating suitable ones Switching signals.

The disadvantages of the known devices are according to the invention by using the special properties of a charged thin-film membrane overcome. Such a charged slide is called "electret" and, if the slide with a thin conductive coating provided on one of their surfaces, commonly called "metal foil electret" or known simply as "metallized electret". Electets have a permanent charge and develop when they are in transducer-like structure can be used, output signals measurable in the event of displacement.

In a typical pressure actuated signaling device in accordance with the invention, a plurality of mutually separated conductive members are in a desired pattern arranged in an insulating body. All of these components are made of a thin, metallized electret film

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or a multitude of such films, which are kept at a short distance from the components and from one another are. A front cover provided with openings the size of a finger, for example, is in alignment with the held by the metallic, conductive components. When the film is mechanically relative to one of the conductive components is shifted, a signal pulse is generated in a connected output circuit. There is no auxiliary detector necessary. The signal is sufficient to operate auxiliary oscillators, switch elements, and amplifiers or the like. the end. The push actuation selector of the present invention can be modified in various ways to suit special applications. So for example, an uncharged auxiliary foil between the metal foil electret and the one provided with openings Cover can be arranged to protect the electret against environmental influences or damage from manual operation or to protect against other damage. Furthermore, pushbuttons can act as an interface between an operator and the electret sheet can be used. If desired, different metallized electret foils can be inserted between the apertured plate or the protective membrane and the counter electrodes are placed one above the other to Generate pulse trains of positive and negative polarity. Such pulse trains can be used to address logic circuits used by connection devices will.

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Regardless of the arrangement of the components used, the electret pressure actuation selector device according to the invention is extremely compact, easy to add and reliable. In a typical unit intended for use as a push-button dial for a telephone in place of the usual disk dialer, a voltage of more than 8 V was generated in a load resistance of 10, the unit having an overall thickness of less than 0.65 cm and the force applied was on the order of 5 χ 10 ⁴ dynes.

The invention is in the following description several Embodiments explained in more detail in conjunction with the drawing. In the drawing shows:

Fig. 1 is an exploded view of the basic components a pressure-actuation-sensitive selection device according to the invention j

2 shows a sectional view of the basic structure of a call dialing device according to the invention, in which a protective sheet and push button guide members are used;

Fig. 3 shows an embodiment according to the invention, at which a plurality of individual metal foil electrets for generating coded Pulse trains of different polarities are used;

4 shows a trapezoidal displacement of the film of an electret selection device according to the invention and the resulting tension

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pulse of the unit for two different time constants; and

Fig. 5 shows the tension of a unit of one according to the invention pressure sensitive Electret selector as a function the force exerted for various terminal resistances.

Fig. 1 shows in an exploded view for explanatory purposes the main components of a pressure sensitive selector switch device according to the invention. The selection device has a plurality of conductive counter-electrodes 11 _a ... H _n , which are embedded in an insulating mounting component 12. The counter electrodes 11 are preferably set back by a small amount behind the front surface of the holding component 12. In a typical embodiment used in practice, each counter electrode 11 has a diameter of approximately 1.6 cm and the holding component 12 is made of an insulating plastic material. In this exemplary embodiment, the counter electrodes are set back into the insulator by about 50 μm.

If desired, the individual counter electrodes can be designed as conductive surfaces printed on a circuit board be. When the conductive portions are applied to the surface of the circuit board, one with Apertured insulating layer is used to form the required dislocations. On the other hand, the

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tend counter electrodes also in recesses in the circuit board to be deposited.

A sheet of metallized electret material 13 is placed over the counter electrodes and essentially rests on the surface of the support member 12. In a practical example, an electret sheet was used from a single 51 µm thin film of polyfluoroethylene propylene plastic material (commercially available under the trademark "Teflon FEP") with a 1,000 8 thick Metal layer 13c (Fig. 2) made on one of its surfaces. After polarization, such an electret

-8 2 film usually has a charge of about 10 ~ "C / cm.

The metal foil electret 13 is covered by a thin cover plate 14 with a plurality of the conductive counter electrodes 11 .... 11 in the holder 12 in alignment Openings 15 .... 15 held in place. In this configuration, the metal layer points on the foil

13 to the cover plate 14. If desired, the cover plate

14 can be made of conductive material to provide additional electrical shielding for the unit. The cover plate is attached, for example, to a conductive housing 16 which is the insulating support component 12 encloses. Each counter electrode 11 is on a led through the unit and exposed for external connections.

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connected to terminal 17_ .... 17_. The other (not

a. Room

electrical connection (shown) takes place at the metal layer 13c on the foil 13. If the cover plate 14 is conductive, and if no further auxiliary layers are used, the connection can be made to the cover plate 14. Apparently other types of brackets can also be used.

The voter mechanism is activated by briefly pressing one of the exposed film sections through one of the openings 15 actuated in the cover plate 14. After the film is released, it reverses due to its tension and stiffness back to their rest position. As a result of this mode of operation, the film electret 13 and the one opposite to it act Counter electrode as an electromechanical converter - im Unlike an electroacoustic transducer - and generate a voltage pulse v (t) at one between the metallic Surface 13c of the electret 13 and the counter electrode terminal 17 switched impedance.

The generated voltage pulse can be described by one of the following two relationships:

v (t) = s (t) h (t) (1)

v (t) = s (t) a (t) (2)

Here s (t) means the mean (spatial) displacement of the film electret, s (t) the derivative of s (t) according to the

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Time and h (t) and a (t) are the ^- Einheitsimpuls- or unit step responses to the shift. The selection device can therefore be viewed as a circuit which comprises a series connection of the capacitance C of one of the electret transducers (foil 13 and counter electrode 11), a connection resistor R (not shown) and a voltage source which is responsible for the voltage generated by the electret transducer. This circuit is characterized by!

hit) -Ai (t) - ~ e " ^{t / RC} fort ^ .0 (3) = 0 t <0

a (t) = Ae ~ ^{t / RC for} tio (4)

= 0 t <0

Here £ (t) is the Diracse S function and A is the ratio of the voltage generated by the voltage source to the mean displacement of the film electret. So A is given by:

A = eD / (D + gd) e _o . (5)

In equation (5), & is the effective surface charge density of the electret on its non-metallic surface, D and d are the thicknesses of the electret or the air layer between the electret 13 and the counter electrode 11, ε. is the dielectric constant of the electret material and _{£ o} is the dielectric constant of the free space. Equation (5) applies when the displacement s (t) is considerably smaller than the gap d.

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As an example, the voltage is v (t) for the trapezoidal Shift function according to Fig. 4a given by

s (t) = (s / ^ t) (t _o + t) for -t _o <t <-t _y .

O Δ - ■ 2. 1

s (t) = s _rt -t. <t <; t "

° Ii ₍₆₃

s (t) = (s Mt) (t _o -t) t. <t <; t _o

set) = ο t ₅ <| t I

Here, At = t ₂ - t ^ is equal to the rise time of the shift function

time shift.

Shift function and s the (spatially averaged) maximum

Using equations (2) and (4), the voltage is v (t) across R

- ^fc - (tX) / RC ,.

v (t) = A 1 S (X) e ^a \ (7)

J '

'2

By calculating s from equation (6) and substituting the obtained value in equation (7), we get

le " ^{(t + t} 2 ^{) / RC}

t _a <t <t ₂

-t / RC - - ^t 2 ^{/ RC} -t _a / RC t _a / RC t ₂ / RC 5 £. — e + e + e —e J

t (8)

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The function v (t) / As _Q is plotted for RC = 0.1 t ₂ and RC = 10 t ₂ in FIGS. 4b and 4c, respectively. It was assumed that ^ β 0.9 t. in both cases. The figure shows that for RC <£ t? the system response is a distorted ("differentiated") representation of the displacement consisting of two needle pulses, while for RC ^ ξ> t _? a response similar to the shift function is obtained.

In summary, it can be said that with a trapezoidal displacement of the metal foil electret the electrical Output signal at a connection resistor a pair of needle pulses of opposite polarity with durations comparable to the time constant of the system exists if the time constant is less than the shift duration is. For time constants that are larger, the electrical output voltage is approximately equal to that Shift. As the output voltage of the unit from the product of the field in the air gap between the foil and the counter electrode and of the displacement of the foil into the Air gap is dependent, the size of the air gap should, for example, by the depth of the recess in the Bracket component 12 is given, selected depending on the film parameters and the expected displacement will. If the recess is too large, the field is small; if the recess is too small, the displacement is limited. It has been found that a recess depth in the order of magnitude of the film thickness is suitable.

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For an electret with a charge density of 10 ~ ⁸ C / cm ² , pulse amplitudes due to pressure actuation in the order of 0.3 to over 20 V were measured, these values depending on the connection resistance and the force exerted. The output voltage developed in a typical unit is plotted in Figure 5 as a function of the force exerted. Although the output voltage increases with the force at low force levels, it becomes independent of the force at higher force levels. This is due to _k that the rise time of the displacement function At becomes considerably smaller than the time constant of the system as the force level is increased. Equation (8) shows that for At significantly smaller than RC, the amplitude of the voltage generated is essentially independent of Δ t.

Signal voltages of this type can be recorded directly without further recording and often used without additional processing. The generated signal can for example be direct P can be applied to an amplifier circuit with a suitably high input impedance. It has been found that a single stage field effect transistor amplifier is a suitable input circuit element. Alternatively, the output signals be amplified in each bipolar transistor amplifier, for example to achieve the required Input impedance a multi-stage amplifier with negative feedback can be used.

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An alternative embodiment used in the manufacture of a selector switch according to the invention is shown schematically in FIG. The one here in the Cross-section shown structure largely corresponds to the device of FIG. 1, with the exception that a uncharged thin and resilient auxiliary foil 18 between the foil electret 13 and the one provided with openings Cover plate 14 is inserted. It is often desirable to have such an auxiliary layer to protect the foil electret against environmental influences or other damage and to ensure maintenance-free operation. The foil 18 is preferably connected to the housing 16 (FIG. 1) in order to achieve maximum protection for the voter unit .

Sometimes it may also be desirable to use shaped pushbuttons ord.dgl. to use to facilitate operation of the unit. Since push buttons are commonly used, they give the unit a more conventional look. It is more important, however, that pushbuttons or other mechanical actuators are used to ensure a more uniform displacement of the electret. In the drawing, the push buttons 19 have a concave surface shape and are held in openings in the plate 14. The push-button or push-button shape and its dimensions is only a question of the design chosen. If they are depressed ^be they act the necessary displacements of the electron

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steps 13 relative to the counter electrode 11 and generate an output signal. By appropriately adjusting the length of the through the openings protruding pushbutton shaft a stop effect is secured, which is a possible physical Destruction of the foils is prevented. The compliant films are generally elastic enough to to return the pushbuttons to their inoperative position, but it may be desirable to use auxiliary springs for this purpose to use. If necessary, auxiliary devices (not shown) can be used to indicate that contact takes place. For example, the finger openings or the push buttons can be illuminated when Contact has been made or an audible or other visual indication that the operator has made contact, is provided. Such indicator elements are known to those skilled in the art and include elements such as buzzer, cricket "Devices and analog or digital display windows. For this purpose, suitably arranged electrical contacts between a section of a pushbutton, e.g. 19, and connections of a printed circuit on the auxiliary foil 18 or in isolated channels of the cover plate 14 can be used.

As a further aid, which a desired switching sequence Appropriate identification tags can be used in conjunction with any selector switch position. For example, suitable position indicators can be displayed

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printed or individually attached to the outward-facing surface of the film at the location of each opening be. If the auxiliary protective film is used, are the identification marks are preferably arranged under the protective layer. If pushbuttons are used, the position identifier is preferably arranged in the usual way in the key body.

A further exemplary embodiment is schematically shown in FIG. 3 the invention shown in which multiple sheets of electret material to generate a pulse train positive or negative polarity are used on each shift. In the drawing there are two foils 13 and 20 arranged over each individual counter-electrode 11, the two metal layers 13c and 20c from the electrode point away. A small air gap 21 is created between the film layers, for example by means of insulating spacers 22 maintained. The spacers 22 can may be in the form of individual insulators, but may also have a lattice-like configuration or an apertured one Plate made of insulating material are used, the openings of which are aligned with the counter electrodes 11. To the conductive surfaces 13c and 20c of the foils 13 and 20 and on the connections 17 electrical connection extensions are provided. Preferably the conductive layer of the outer foil, e.g. 20c, is kept at ground potential in order to provide a to ensure electrostatic shielding of the unit. The various signals generated by the foils are

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supplied directly to the summation device 23, while the signal generated by the electrode 11 at the terminal 17 via a delay device 24 and then to the summation device 23 is performed. The delay interval d of the unit 24 is selected so that there is the desired spacing between the pulses of the resulting pulse train.

In this multi-layer configuration, two or more capacitive switching elements are effectively connected in series. Thus, the electret film 20 acts with the conductive layer 13c of the film 13 as a holding element and the electret 13 in cooperation with the counter electrode 11 as a further switching element. The slides are heading towards the counter electrode 11 is depressed and between the electret sheet 20 and the conductive layer 13c, which is associated with it Counter electrode acts, an initial output signal is developed. This via the summation device The signal provided by 23 represents the first pulse of the foI-ge. If the foils are pressed down further, a second signal is generated when the foil 13 is displaced relative to the counter electrode 11 * This signal is shown in the delay device 24 is delayed so that it is shifted to a time period d relative to the first pulse Time occurs. In the present example it is assumed that both foils have the same polarity, so that two positive pulses are generated. When the fo-

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If both are negatively or both positively polarized, time-shifted pulses of the same polarity are generated. If one foil is positive and the other negative, pulses of opposite polarity are generated. Alternatively, the delay device 24 for example in the film 20 with the summation device 23 connecting connecting line be arranged. In this solution, this can happen between the film 13 and the counter electrode 11 developed signal before the between the film 20 and the conductive layer of the film 13 generated signal occur. Obviously, by suitable choice of the polarities of the foil electret layer th and generated by the arrangement and the number of delay units any desired pulse train configuration will. If desired, this can be between one foil electret and the conductive layer of the other electret generated signal can be fed to an output circuit that is independent of the output circuit that the of a foil electret and the associated counter electrode receives the signal developed at the same point.

Since an electret film can be polarized in opposite directions at individual points that are separate from one another, the can the respective actuation point arranged portion of the electret film either positively or negatively polarized be. The signal developed at each actuation point is therefore coded according to its polarity. at

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Use of multiple foil electrets, be it with or without a counter electrode, similar polarity codes can be used at each actuation point. The from the different electret layers at a single actuation point generated signals of different polarity can be used in different Verarbextungsschaltungen are performed, which are determined independently of the delayed signals to pick up from this actuation position Circuits are.

Further application possibilities are obtained when the metal layers on selected electret poles in the area each actuation point in separate individual areas be divided, and if the metal surfaces of these foils can be independently connected to external circuits. Known methods can be used to produce such individual surfaces be used. Regardless of the way in which the signals are generated or combined into a composite signal, they are usually sent to a processing device, e.g., an amplifier.

While the invention has been described with reference to a number of specific embodiments, it is for those skilled in the art will recognize that a variety of combinations of the foregoing features, if desired can be used. For example, the embodiment according to FIG. 1 provided with openings can have a plurality can be supplemented by electret foils as shown in FIG

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and in addition, a protective film of the type shown in FIG. 2 can be provided. Similarly, at the push button arrangement of FIG. 2, a single electret film can be used instead of the embodiment shown with a film and a protective film. Also multiple electrets can be used in this construction. Suffice it to say that the presented Refinements only stand for example for a variety of alternatives.

As from the detailed description of the various exemplary embodiments of the pressure actuation selector device according to the invention As can be seen, the structure is extremely simple and critical dimensions do not arise. As a result With modern thin-film technology, the entire unit can be made extremely thin so that it is in can be used in a wide variety of applications. Obviously, individual voter units, i.e. a Arrangements in which an actuation point with a counter electrode is used can be applied in single display applications are present. This means that it is not necessary in the manner according to the invention to use the entire arrangement of actuation points, although such a procedure is economically advantageous Brings results. The actuation points can be in any desired configuration, e.g. circular, in Row or the like. Be arranged.

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In practice it has been shown that the pressure actuation sensitive Selector is not adversely affected by frequent actuation. In experimental trials the output voltage changed one of the in Pig. I shown Unit similar unit cannot be measured after more than 400,000 automatic presses. The actuations were made by means of a motor-driven plunger that acts directly on the metal layer of the electret polie carried out. Nevertheless, it is desirable, in the manner shown in FIG. 2, to have an additional plastic film for protection to be provided against damage during manual operation. In addition, it has been shown that the electoral elements are against Are relatively insensitive to airborne sound. Generated a pistol fired approximately three feet away a signal that was more than 70 dB weaker than the signal generated when the button was pressed. For actuation the selector must therefore use a mechanical pushing force and not an acoustic force, i.e. the Dialing device must be pressed to operate and can not by shouting or the like. to be triggered. If the Circuitry was dropped from a height of about 3 feet, the generated signal was 30-50 db weaker than the signal generated by the push operation. In an embodiment designed to be suitable for finger actuation the cross coupling generated in neighboring units was 40 db weaker than that caused by pressing the unit generated signal.

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Claims (9)

Claims A pressure-actuation-sensitive signal would give a device, in which a conductive counterelectrode is opposed to a component at a distance and the electrical properties of the conductive counter electrode and the component relative to one another as a result of the application of a pressure on the Component can be changed, characterized, that the component has a conductive membrane with at least a metal layer (13c) on a charged electret film (13), the parameters of the component (13) and the distance between the component and the counter electrode (11) are coordinated so that the device is insensitive to forces other than pressure actuation, and that facilities (e.g. 15 and 19) for applying external Pressure actuation forces for moving the electret film relative to the counter electrode (11) are provided. 2. Apparatus according to claim 1, characterized through devices (e.g. 15} 19) to localize the possibility of applying the external pushing force. 3. Apparatus according to claim 2, characterized that the limiting devices have an opening (15), the electret film (13) 209829/1105 2Ί64202 " covering cover plate (14), the opening of which is essentially aligned with the counter electrode (11). 4. Apparatus according to claim 2, characterized in that the limiting devices one essentially aligned with the counter electrode (11) Have push button (19). 5. Device according to one of claims 1 to 4, d a k characterized in that the component (13) is a covering, uncharged and resilient Has protective film (18). 6. Device according to one of claims 1 to 5, in which several components and associated counter electrodes are provided, characterized in that that the electret (13j 20) at discrete, essentially with the associated counter electrode (11) aligned points one of the two polarities is polarized. 7. Apparatus according to claim 6, characterized in that two superimposed electret foils (20, 13) with metallized, from the counter electrodes ( ¹ Il) pointing away surface sections (20c, 13c) and connecting devices for forwarding the individual displacement of each of the electret foils changed electrical properties to an external circuit (23,24, 25) are provided. 209829/1105 '■ "''" ^{μ υ} * 8. Apparatus according to claim 7, characterized in that the connection devices Have delay units (24) for delayed forwarding of the individual signals. 9. Apparatus according to claim 8, characterized that summation devices (23) for combining the delayed signals of certain components are provided with the other signals to generate a composite signal 2 09829/1105