US2926293A - Electrical actuator - Google Patents

Description

Feb. 23, 1960 DC POWER 4 SUPPLY J. c. CAMM ETAL 2,926,293

ELECTRICAL ACTUATOR Filed June 24, 1957 FIG.3

POWER SUPPLY IN V E N TO R S J.C. CAMM R.K.LEE R. SILVER PM BY 7 ATTO R N E'Y 2,926,293 Patented Feb. 23, 1966 ice ELECTRICAL ACTUATQR Application June 24, laa'l, Serial No. 667,536

3 Claims. (Cl. 3l8117) The present invention relates to an electrical actuator which translates an electrical signal into a mechanical motion. The most widely used electrical actuator is the electromagnetic relay. The electromagnetic relay is a fast-acting device which requires a weighty armature in order to exert a substantial mechanical force. Another well-known electrical actuator is the bimetallic strip which, in most instances, does not exert a substantial mechanical force.

The principal object of the present invention is to provide a flash-responsive electrical actuator which can translate an electrical signal into a substantial mechanical force within a very short period of time of the order of one to one thousand microseconds.

Another object of the present invention is to provide a flash-responsive mechanical actuator which is extremely light relative to the mechanical force it can exert.

The electrical actuator in accordance with the present invention comprises a mechanical spring. Energy is stored in this spring which is restrained by a wire made of a metal having a high coeflicient of resistance and a high coeflicient of expansion. This wire is connected to an electrical power source which is controlled by a flash-responsive thyratron. When the thyratron is closed, electrical energy from the power supply passes through the wire causing it to heat and expand rapidly. The expansion oi the wire releases the energy stored in the spring, causing a mechanical motion which may be used to actuate a mechanical device.

Other and incidental objects of the present invention will be apparent to those skilled in the art from a reading of the following specification and an inspection of the accompanying drawing in which:

Figure l is a circuit diagram illustrating an embodimerit of the present invention, and

Figures 2 and 3 illustrate an application of another embodiment of the electrical actuator in accordance with the present invention.

Reference is now made to Figure 1 which shows an electrical actuator in accordance with the present invention designed to perform a mechanical function upon the detection of a flash of light. The flash detector comprises a photoe ectric cell 37 which is connected in series with a resistor 39 between the terminals 41 and 43 of a direct current power supply 45. The junction 47 of photoelectric cell 37 and resistor 39 is connected through a differentiating network 49 and a resistor 51 to the control grid 53 of a thyratron 55. A voltage source 56 supplies a negative biasing voltage to the control grid 53. The anode 57 of the thyratron is connected to a terminal 41 of the power supply 45 through a resistor 58 and to the other terminal 43 of the power supply 45 through a large storage capacitor 59. The cathode 61 of thyratron 55 is electrically connected to terminal 43 through a piece of heat-resistant Wire 63 made of an alloy such as Nichrome. The wire 63 is held fast mechanically at point 65 and has its end 67 mechanically connected to one end of a spring 69 the other end of which is held fast mechanically at point 71. The spring 69 is under tension. The end 67 of wire 63 is mechanically connected through a link 73 to a mechanical device 75 which is to be actuated.

The operation of the electrical actuator of Figure 1 is as follows: the photocell 37 and the resistor 39 form a potential divider connected between the power supply terminals. The potential at junction 47 thus varies with the resistance of photocell 37 and consequently with the amount of radiant energy impinging upon photocell 37. A negative biasing voltage from the voltage source 56 is applied to the control grid 53 of the thyratron 55 which is thus normally held in a non-conductive state. The junction 47 is coupled to the control grid 53 of thyratron 55 through the differentiating circuit 49. The time constant of the differentiating circuit 49 is so chosen that it will pass a positive pulse of suflicient mag nitude to overcome the negative bias on the grid 53 of thyratron 55 only when the rate of change of potential at junction 47 corresponds to the rate of change of illumination of the flash to be detected. When the bias on tliyratron 55 is overcome and it fires, capacitor 59, which was previously charged through resistor 58, discharges through thyratron 55 and wire 63 to ground. The passing of current through wire 63 causes it to heat and expand rapidly. When wire 63 expands, the spring 69 (which is under tension) contracts and the link 73 moves in the direction of the arrow 77, thereby actuating the mechanical device 75.

Reference is now made to Figures 2 and 3 which illustrate an application of the electrical actuator in accordance with the present invention. in this application use is made of goggles designed to protect the eyes of combat personnel such as aircraft pilots in the event or" the occurrence of a sudden flash of light such as may be caused by the explosion of an atomic bomb. Each eyepiece of the goggle includes two plates, each plate having grid lines thereon. 'v 'hen the grid lines coincide the user may see through the two superimposed plates. When one plate is moved the distance of one grid line with respect to the other, the grid lines do not coincide and shut off the users field of view. In this application the problem is to move one plate with respect to the other in an extremely short interval of time upon the dctcction of a bright flash of light.

The movable plate 79 has one end mechanically connected to one end of the spring 81, the other end of which is held fast mechanically at point 83. The other end of plate 79 is mechanically connected to a set of metal strips which are interleaved with another set of metal strips 87, which latter strip is held fast mechanically at point 89. The spring 81 is under tension and the interleaved metal strips '85 and 87 are pressed together between two plates '91 and 93 by means of a block 95 which is pulled ti ht in the direction of the arrow 96 by means of a piece of heat-resistant wire 97. The wire 97 is electrically connected as shown in the circuit of Figure 2 for the wire 63.

Upon the occurrence of a bright flash of light which is detected by the circuit of Figure 2, current passes through the wire 97 which expands. This releases the pressure exerted by block 95 and which presses together the interleaved strips 85 and 87. When this occurs the spring 81 moves the plate 79 in the direction of the arrow 161.

We claim:

1. A flash responsive electrical actuator comprising a mechanical spring, means to impress a force upon said spring so as to store energy therein, said means including a metallic wire having a high electrical resistance and a high coefiicient of expansion, and means to pass an electrical current through said wire to actuate said actuator, said last named means comprising a normally non-con- 3 ductive thyratron connected in series with said wire, and a flash detector connected to render said thyratron conductive upon detection of a flash.

2. A flash responsive electrical actuator comprising a mechanical spring, means to restrain said spring so as 'to store energy therein, said means comprising a metallic wire having a high coefiicicnt of electrical resistance and a high coefiicient of expansion, and means to pass an electrical current through said Wire to actuate said actuator, said last named means comprising a normally non-conductive thyratron connected in series with said Wire, and a flash detector connected to render said thyratron conductive upon detection of a flash. t

3. A flash responsive electrical actuator comprising a mechanical spring, means to store mechanical energy in said spring comprising a wire under mechanical tension, said wire being made of a metal having a high coefficient of electrical resistance and a high coefficient of expansion,

and means to release the mechanical energy stared in said spring, said last named means comprising means to pass an electrical current through said Wire, said last named means comprising a normally non-conductive thyratron 5 connected in series with said wire, and a flash detector connected to render said thyratron conductive upon detecticn of a flash.

References Cited in the file of this patent UNITED STATES PATENTS l,22,105 Sheonberg Jan. 21, 1919 2,555,882 Guajardo June 5, 1951 2,588,908 Crane Mar. 11, 1952

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