US2201879A - Delay type piezoelectric relay - Google Patents

Description

Mayvzl, 1940- D. G. BLATTNER El AL 79 DELAY TYPE PI'EZOELECTRIC REL Filed Sept. 5, 193a R TRANSLA TING R DEV/CE I 2 E A f Ca,

L I /7 l8 NON L INEAR IMPEDANCE TRANSLA TING DEV/CE TRANSLA TING DEV/CE B LM ATTORNEY Patented May 21, i940 UNITED. STATES PATENT OFFICE DELAY TYPE PIEZOELEGTRIC RELAY New York Application September 3, 1938, Serial No. 228,357

9 Claims.

This invention relates to delay type relays mm the piezoelectric e e Over a P w c ploying piezoelectric-actuated members.

An object of the invention is to provide means for determining the time required for a piezoelectric relay to operate after application of the actuating electromotive force to its circuit.

Another object is to provide means for determining the time required for piezoelectric relay to release after withdrawal of the actuating electromotive force from its circuit.

An additional object of the invention is to pro-- vide means for obtaining any desired operating many very desirable features.

time for a piezoelectric relay without interfering with its desired delay time in releasing and vice versa. I

I A further object of the invention is to enable the practicable range of ratio between the operating time and the release time of a piezoelectric relay to be substantially extended with respect to those hitherto attainable.

Piezoelectric relay structures and operating circuits suitable for such relays are disclosed in the U. S. Patent of W. P. Mason, No. 2,166,763 granted July 18, 1939, for Piezoelectric apparatus and circuits, Such relays may be characterized as electrostatic in that they are essentially capacity elements and they operate in response to a charge impressed .upon their input terminals. They remain operated without further application of energy to the relay until such charge has been withdrawn or such an interval has elapsed that the charge has dissipated. Such relays present Finite amounts of power are required to operate them but no power is required to hold them in the operated position. They may, moreover, be operated with moderate electromotive forces over circuits of extremely high impedance ranging in some cases in the order of megohms. This enables the use of such devices for remote control apparatus over long lines and in high resistance circuits.

Inasmuch as the piezoelectric relays are essentially capacitance elements the problem of their operation and release is fundamentally that of charging and discharging a condenser. It is, therefore, possible to so coordinate the relay with the charging and discharging circuit as to obtain various desirable operating characteristics and it is with such aspects of the piezoelectric relay problem that the present invention is concerned.

In accordance with this invention the charging source which m be at a point both geographicallyand electrically remote fromthe-mezoelec- Y tric relay is connected through the input ter- .minals of the relay to the capacity electrodes of clude a charge regulating impedance. This impedance is such that in conjunction with the capacity of the relay, supplemented in some instances by an auxiliary capacity element, the time within which the source will bring the potential across the relay to the necessary operating magnitude may be predetermined. In'order to permit the relay to release at some desired interval after the-source has been disconnected a discharge regulating impedance element of suitable type and magnitude is provided to cause the voltage across the relay to drop'to' its releasing value in a definite time interval.

The discharge path is naturally a shunt path across the line leading to the relay. If the charge regulating impedance be connected between the discharge regulating impedance and the relay, the discharge current must traverse the charging impedance and the discharging impedance in series provided the charge and discharge regulating impedances are symmetrical with respect to direction and magnitude of current. This imposes rather severe limitations in that for a given charge, the rate of discharge must always be less than the rate of charge and, therefore, the range of release times that can be had is limited. This disadvantage may be avoided by resort to a discharge path connected between the charge regulating resistance and the relay thereby making the release time independent of the operate time. This feature of the invention is not without a certain disadvantage in that during the charging operation the two impedances act as a poten-. tiometer between the source and the relay and thus require a higher voltage source. As an alternative method of overcoming the release time limitation an additional feature of the present invention is provided in which the path including the charge regulating impedance is of an asymmetric character and is so designed as to have the proper impedance for charging current but a negligible or different impedance for discharge current.

Additional aspects and features of the invention will be apparent from a consideration of the detailed specification taken in connection with the accompanying drawing in which Fig. 1 illustrates a piezoelectric relay circuit ior permitting the magnitudes of the charging and discharging paths to be substantially independent of each other.

Fig. 2 illustrates a modification of the circuit in which an asymmetric impedance element is pedance element employing a saturated core inductance.

Referring to Fig. 1 there is illustrated a circuit including a source I of charging current of an electromotlve force Ec, switch or circuit closer 2, a line 3 leading to a remote piezoelectric relay 4 having input terminals 5 and 6. The relay is illustrated'diagrammatically as of the bilame or twoplate type disclosed in Mason Patent No. 2,166,763. As is explained in the specification of that patent, the plates 1 and 8 may be cut from Rochelle salt or other suitable piezoelectric material and may be glued or clamped to an intervening common electrode 9 which comprises a metallic or other conducting coating applied to each plate or to both. The two oppositely located outer faces of the piezoelectric plates are similarly conducting electrodes I0 and are electrically connected to terminal 5, the inner electrode 9 being connected to terminal 6. The plates 1 and 8 may be clamped or held firmly in contact'at their lower ends by any suitable means to constitute a unitary assemblage.

The plates I and 8 are so cut that an electromotive force of proper polarity impressed between terminals 5 and 6 causes one plate to lengthen and the other to contract thus causing the assemblage to flex laterally to one side to carry-the attached insulated contact element I2 into engagement with a stationary adjustable contact element l3 to close the circuit of local source It through the motor or other translating device l5.

Associated with the line 3 are the series charge controlling resistance l6 of magnitude R1 and the shunt discharge resistance I! of magnitude R2. There may also be connected across the terminals 5-5, an auxiliary or shunt capacity element IS, the magnitude of the capacity of which is C5. The auxiliary capacity may be dispensed with in instances where the electrostatic capacity of the piezoelectric device between electrodes 9 and I0 is sumciently large. Mason has also shown in his patent, No. 2,166,763, that under certain conditions it may be advantageous to connect an auxiliary capacity in series with the piezoelectric element as is illustrated in Fig. 11 of that application.

The operating time required after closure of the switch 2 to enable the relay 4 to close the contacts of its local circuit is determined by the time necessary to charge the capacitance of the piezoelectric relay up to its operating potential. Neglecting the potential drop in the line 3. the voltage across the relay t seconds after the switch 2 is closed is Where C represents the combined capacity of the condenser Ca and of the piezoelectric relay, Q is where it: is the current flowing into capacity 0.

By Kirchhofis electric circuit laws:

and

Substituting the values of i2 and ie in (5) 5 and substituting the value of 51 from Equation (6) and of i: from Equation (2) in Equation (4) which may be rewritten as:

which may be solved for Q by multiplying both members by an integrating factor e The left-hand member of Equation (10) is the same as fic e) so that (10) may be written as 11 e'= o =ke Integrating gives 12 =e +A where A is a constant of integration to be evaluated later.

It A Q= Substituting the values of k and K' in (13) EJ? C A (14) Q= T n.

-RlRIC R1+R| 15 1 RlRic When E,R,C' t-O Q-O and A R1+Rz Substituting in (15) E.,R,c E.R,c '1j%i (16) IFE Ran or Rl+m --z 17 RIRIG When t is very large this voltage across the relay approaches the limiting value (19) E R,+R. If the operating potential at which the piezoelectric relay flexes suiliciently to close the circuit with its contacts I2 and I3 be E0 (a value less than E'R then To, the time required to cause the relay to operate after closure of the switch 2 is obtained by substituting E0 for EH2 in Equation (18). Thus When the switch 2 is opened the discharge circuit consists simply of condenser C discharging through resistance R2. The condenser has a po-' tential ER given by Equation (18) and since E0 is the potential across the condenser or across R: at which the relay will release the time of release Tr is the time required for the potential to drop from Ea to E0. This relation between potential and time is well known. (See, for example, The Engineers Manual by R. G. Hudson, 1st edition, page 207, section 879, John Wiley 8: Sons, Inc.,

copyright, 1917.) It is given by 25 E,=E,.,.e

Fig. 2 discloses an alternative method of obtaining the advantage of Fig. 1 without its disadvantage. In this case the charge regulating impedance Z consisting of a resistance element I 6 and an asymmetrical element III, e. g., a copper oxide rectifier, is connected between the element I1 and the relay 4. The element I9 is so designed and poled that its impedance to charging currents is large in comparison with the impedance of I6 or in comparison with its own impedance to discharge currents. This enables relay 4 to be charged through element I6 from source I but to discharge through I9 and II. The impedance of the discharge path may be of any desired value without regard to the impedance of the charging path and yet the full potential of source I is effective in charging which is to say the final steady state of potential across the capacity element I8 and the piezoelectric relay 4 is substantially equal to the charging electromotive force of source I. Accordingly, through the use of this circuit the electromotive force of source I may be considerably reduced with respect to that required for the circuit of Fig. 1. This circuit, therefore, has the advantage which circuit I possesses of enabling the discharge or release time of the relay to be entirely independent of the operate time without the disadvantage of the high charging electromotive force for source I which the circuit of Fig. 1 entails. The circuit of Fig. 2 offers the additional possibility of employing a non-linear function of the magnitude of the discharge current. Such a non-linear impedance may comprise impedance element, the resistance of which is a a thyrite element 20 in series with the copper oxide rectifier I9. If the resistance of the element 20 be made an inverse function of the current, the discharging rate will be decreased as the steady state condition is approached and the release interval will be increased over that which 7 may be obtained with a fixed resistance. In a similar manner the charging time may be increased by making the charge regulating resistance It also of thyrite.

The circuit of Fig. 3 is similar to that of Fig. 2

with the modification that the resistance and there is no energy required from the charging current for setting up flux in the impedance coil 2| and the coil therefore reacts as a negligible or at most very low impedance. Conversely, the flux produced by the charging current tends to oppose the polarizing flux and, accordingly, to increase the impedance of the coil2I. For very short intervals such as those involved in relay operation the impedance element may serve eff ectively as an asymmetric conductor.

It is evident, of course, that in both circuits 2 and 3 the effects of the asymmetric paths with respect to charging and discharging currents are reversible.

What is claimed is:

1. A piezoelectric relay, a charging source therefor, a charging circuit connecting the source to the input terminals of the relay and including a. charge regulating impedance cooperating with the electrostatic capacity of the relay to determine the operating time of the relay, 9. discharging circuit including a discharge regulating impedance and means connecting the discharging circuit to the relay input terminals to determine the time for release of the relay after withdrawal of the charging electromotive force said time being substantially independent of the magnitude of the charge regulating impedance.

2. A piezoelectric relay system including a charging circuit comprising a source of charging electromotive force, a charge regulating impedance and the input terminals of a piezoelectric relay all in series to determine the time for the relay to respond after application of the charging electromotive force, and a discharge path connected between the input terminals of the relay and including a discharge regulating impedance to determine the interval between the withdrawal of the charging electromotive force and the re lease of the relay, said interval being substantially independent of the magnitude of the charge regulating impedance.

3. A circuit for determining the operating and release periods of a piezoelectric relay comprising in series asource of electromotive force, a circuit closer, a first resistance element and the input terminals of the piezoelectric relay, a second resistance element connected in shunt discharge which is an inverse function of the current wheret by the time required for the relay to be charged up to an actuating potential is increased over that which would be required were the impedance constant.

Sa -A piezoelectric relay, a discharge circuit therefor including a current regulating impedance having an effective value which is an 'inverse function of the discharging current to increase the time required for the deenergization of the relay after withdrawal of the source of actuating electromotive force.

6. A piezoelectric relay system comprising a piezoelectric relay having contacts operable into and out of engagement with each other, input terminals upon which actuating potentials may be impressed, a circuit including in series a source ,charge impressed upon the input terminals may discharge over the asymmetric current path and the shunt impedance.

7. A piezoelectric device having input terminals, charging and discharging paths connected thereto and including in common an element which is.

asymmetrically conducting for transient currents of opposite polarity, the charging path including a source of charging electromotive force, the discharging path including a resistance element to determine the period for' deenergization of the device after the charging electromotive force is withdrawn.

8. A piezoelectric relay system comprising a source of actuating electromotive force, a ferromagnetic impedance element and the input terminals of a piezoelectric relay all connected in series, a discharge path connected in shunt across the system at a point between the source and the impedance element, and means for establishing a polarizing magnetic field in the region of the impedance element whereby the element behaves in an asymmetric fashion in differentiating betwen sudden charging and discharging currents.

9. In a series circuit, a piezoelectric electromechanical device, a source of electromotive force, an asymmetric impedance element and a charging resistance element in shunt to the impedance element, a path in shunt to the electromechanical device including a discharging resistance element whereby a predetermined operating period and a predetermined release period for the electromechanical device may be provided.

DAVID G. BLA'ITNER. LEONARD VIETH.

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