Conducting fluid inertia type switch with linearly movable conductive plunger contact

[57] ABSTRACT

A switch which is closed or opened by an external force applied thereto. A weight resiliently suspended in the switch casing and an electrically conductive liquid in the casing are alternatively caused by an external force applied thereto to move thereby to establish electrical connection between the two switch terminals.

Claims, 10 Drawing Figures

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Patented June 19, 1973

3,740,503

Sheets-Sheet 1

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Patented June 19, 1973

3,740,503

Sheets-Sheet 2

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Patented June 19, 1973

3,740,503

Sheets-Sheet 3

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Patented June 19, 1973 3,740,503

Sheets-Sheet 4

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3,740,503

CONDUCTING FLUID INERTIA TYPE SWITCH WITH LINEARLY MOVABLE CONDUCTIVE PLUNGER CONTACT bore of the weight, so that the resiliency of the spring urges the weight downwardly. One end of the lower coil spring is secured to the lower terminal member and the other end thereof is borne against a contact disk provided in the axial through bore of the weight, so that the resiliency of the spring urges the weight upwardly. The resiliency of the upper spring and the mass of the weight balances the resiliency of the lower spring so that the weight is held in suspension inside the casing.

The switch is held in a vertical position with the axes of the terminal members in vertical alignment with each other and secured to a suitable support. Under the condition, the weight remains stationary. Suppose that a force or impact is applied to the switch in the horizontal direction. The weight more or less swings in the horizontal direction but is never moved in the vertical direction. However, the conductive liquid in the casing produces a reactive force against the horizontal force. This reactive force.causes the liquid to move inside the casing, so that the surface of the liquid which was horizontal under the normal condition now becomes inclined or aslant. The angle of this inclination is proportional to the magnitude of the force that has been applied. When the force exceeds a predetermined magnitude and the inclination of the liquid surface exceeds a predetermined angle, the liquid surface contacts a lower portion of the weight, thereby establishing an electrical connection between the weight and the liquid. As previously described, the upper coil spring is in contact with the weight and the lower coil spring, with the liquid and the two coil springs, with the upper and lower terminal members, respectively, so that the two terminal members have now been electrically connected. This means that the switch has now been closed. A moment after the liquid surface is restored to its original horizontal level, whereupon the contact between the weight and the liquid is broken, so that the switch is now opened.

When a force is applied vertically to the switch, the is hot enough to establish any contact between the weight and the liquid. However, since the weight is resiliently held inside the casing, the vertical force causes the weight to be moved in the opposite direction to that of into contact with the liquid. Oil the contrary, if it is moved upwardly, the contact disk inside the axial bore of the weight comes into contact with the lower end of the upper terminal member. Since the lower coil spring is always in contact with the contact disk, the upper nected, so that the switch is closed. At the next moment the weight is restored to the original position, thereby opening the switch.

When vibration is applied to the switch, the same operation as mentioned above is effected regardless of the direction in which the vibration occurs.

It is understood from the above description that the switch is instantaneously closed upon application of an external force thereto and a moment thereafter it is again opened. Therefore, if it is required to continuously supply electric energy to a load through the switch, the above arrangement of the switch is not suffi. cient. To meet the requirement, the signal obtained upon closure of the switch may be used to actuate a different circuit to produce a continuous output to be supplied to the load. As such a circuit a monostable circuit

This invention relates to a switch which is opened or closed through mechanical motion of an interior movable component caused by application of an exterior force thereto.

There are known several types of switches that are operated by an external force applied thereto. However, in any of them, it is the force applied in a single predetermined direction alone that enables their operation. For example, one prior art switch is so designed as to operate only when a horizontal force is applied thereto. The switch can not be operated by a vertical force applied thereto. At least two such switches are required in order to be able to operate in response to both vertical and horizontal forces.

The primary object of the invention is therefore to provide a switch operable in response to a force externally applied thereto regardless of the direction in which the force is applied.

Another object of the invention is to provide a switch which can exactly operate in response to both horizontal and vertical forces.

Another object of the invention is to provide a switch which operates when the force applied thereto exceeds a predetermined magnitude, regardless of the direction in which the force is applied.

Another object of the invention is to provide a switch ³⁰in which it is possible to selectively determine the magnitude of the force that effects operation of the switch.

Still another object of the invention is to provide an apparatus which comprises such a switch as aforesaid and a circuit operable in response to the operation of ³³the switch to provide an output to be applied to a load, the switch and the circuit being enclosed in a single housing.

Still another object of the invention is to provide such .. .

an apparatus as aforesaid in which the output from said ⁴⁰ liquid may splash to touch the weight, but the splash i circuit continues a predetermined period of time.

The switch of the invention chiefly comprises a hollow cylindrical casing made Of an electrically insulating ί _ _ .....

conductive liquid material such as mercury, and a material such as glass and containing an electrically . -----conductive liquid material such as mercury, and a the force. If the weight is moved downwardly, it comes weight of an electrically conductive material resiliently suspended in the space of the casing. Normally, the weight is held above and out of contact with the surface of the conductive liquid. However, the weight is resil- ₍iently held there so that it is vertically movable relative 1 . .

lar terminal members are secured to the upper and lower sides of the casing. Each terminal member serves as a guide for the weight as the latter moves vertically , inside the casing, and also as a pipe through which the inside space of the casing is evacuated. After evacuation the opening of each tubular terminal member is tightly closed by crushing a part of the tube. The weight is formed with an axial through bore, into the opposite ₆₀ends of which the two terminal members are inserted as far as the inner ends thereof are positioned in the bore with a predetermined gap therebetween.

In order to resiliently support the weight inside the casing, a coil spring is provided encircling each of the terminal members. One end of the upper coil spring is secured to the upper terminal member while the other end is borne against the inner surface Of the through to the surface of the conductive liquid. A pair of tubu- and lower terminal members are thus electrically con3,74 3 may be used. A bistable circuit may also serve the purpose if a reset signal is provided by a different suitable circuit. Preferably, such a circuit is provided in the form of a printed circuit having necessary circuit elements such as transistors, resistors, etc. printed on a base. The printed circuit together with the switch may conveniently be enclosed in a single casing.

The invention will be described in further detail with reference to the accompanying drawings wherein;

FIG. 1 is a vertical section of a preferred embodiment of the invention, the switch being shown in its normal, open condition;

FIG. 2 is a view similar to FIG. 1 but showing the switch in a transient, closed condition as a horizontal force is applied thereto from the right-hand side in the figure;

FIG. 3 is a view similar to FIG. 1 but showing the switch in a transient, closed condition as a vertically downward force is applied thereto;

FIG. 4 is a view similar to FIG. 1 but showing the switch in a transient, closed condition as a vertically upward force is applied thereto;

FIG. 5 is a vertical section of an apparatus comprising the switch and a circuit to be actuated thereby enclosed in a single casing;

FIG. 6 is a top plan view of FIG. 5, with the casing partially cut away to ishow the interior elements;

FIG. 7 is a diagram of the circuit used in FIGS. 5 and 6;

FIG. 8 is a waveform diagram to explain the operation of the circuit of FIG. 7;

FIG. 9 is a diagram Of another form of the circuit used in FIGS. 5 and 6; and

FIG. 10 is a waveform diagram to explain the operation of the circuit of FIG. 9.

In FIG. 1 there is shown a generally cylindrical casing 10 made of electrically insulating transparent glass. A pair of terminal members 11 and 12 pierce through the upper and lower end walls of the casing 10, respectively, to be fluid-tightly secured thereto in axial alignment with each other and the axis of the casing. Each terminal member comprises a tube of an electrically conductive material with its opposite ends initially open. Inside the casing there is provided a weight 14 made of an electrically conductive material and having an axial through bore 15. The weight is resiliently suspended in the casing 10 so that the bore 15 is aligned with the axis of the casing, as will be described later in detail. The inner end portions of the terminals 11 and 12 are inserted into the opposite ends of the through bore 15 of the weight 14 so that a gap is provided between the opposing ends of the terminals inside the bore 15. The portion of each terminal projecting outside the casing 10 is used for electrical connection to an external circuit.

Spirally encircling the upper terminal 11 inside the casing 10 there is provided a coil spring 16 made of an electrically conductive material. The spring has its upper end held in contact with the upper terminal member 11 and its lower end borne against a shoulder 24 formed in the through bore 15 of the weight so that the spring resiliently biases the weight downwardly. In this manner an electrical connection is established between the upper terminal 11 and the weight 14 through the coil spring 16. In a similar manner, a lower coil spring 18 spirally encircles the lower terminal member 12 inside the casing 10. The spring 18 has its lower end

0,503 held in contact with the lower terminal 12 and its upper end borne against a contact disk 20 secured in the through bore 15 of the weight 14 axially spaced from the shoulder 24, so that the spring 18 resiliently biases 5 the weight upwardly. Thus, the mass of the weight and the resiliency of the upper spring 16 balances the resiliency of the lower spring 18 thereby to hold the weight in suspension.

The contact disk 20 is electrically separated from the 10 weight by means of an insulating sleeve 22 inserted into the lower half of the through bore 15. This sleeve also electrically separates the lower coil spring 18 and the lower terminal 12 from the weight. The disk 20 need not be mechanically fixed to the sleeve but may simply 15 be placed on a shoulder 23 formed in the upper end of the sleeve since the lower coil spring holds the disk there. A tiny hole 21 may advantageously be formed in the disk 20 to decrease the fluid resistivity thereof upon vertical movement of the weight, as will be described 20 later.

Inside the casing 10 there is contained a predetermined amount of electrically conductive liquid 26 such as mercury and also preferably hydrogen gas to improve the fluidity of the mercury. The mercury is al25 ways in contact with the lower coil spring 18.

In the actual manufacturing process of the switch of the design shown and described, it is advisable to initially produce two halves of the casing formed by dividing the casing by a plane perpendicular to the axis ³θ thereof and fix the necessary parts and elements to each of the halves and then put them together into a complete casing, with the weight held in suspension therein as previously described. One of the tubular terminal members, say, 11 is then closed, and through the ³⁵ other terminal opening the casing is evacuated, and mercury and hydrogen are introduced into the casing and then the opening of this tubular terminal 12 is closed. The amount of hydrogen is preferably such as to keep the inside pressure twice atmosphere.

⁴⁰ The switch is secured to a suitable frame or base in the vertical position as shown in FIG. 1. The base with the switch thereon is put on a place where external forces are applied to the switch.

Suppose that as shown in FIG. 2 an external force has ⁴⁵ been applied to the switch form right to left in the horizontal direction of an arrow 31. Despite the shock, the casing 10 is not moved in the direction since it is fixed to the base. Nor is the weight vertically displaced by the θ horizontal force since the weight is movable only verti^υ cally. However, since the mercury 26 in the casing is free to move, the force applied causes the mercury to move so that the right-hand portion of the mercury rises, that is to say, the surface thereof is inclined up55 wardly to the right relative to the horizontal line, as shown in FIG. 2. The angle of inclination is proportional to the magnitude of the force applied.

Suppose that a sufficient force has been applied to cause the level of the mercury to be sufficiently inclined to touch the lower right-hand corner of the weight 14. An electrical connection is then established between the upper and lower terminals through the upper coil spring 16, the weight 14 and the mercury 26. In other words, the switch has now been closed. A moment after, the mercury is displaced in the opposite direction to decrease the angle of inclination of the surface and then again in the direction to increase the angle of inclination. At this time, however, the surface

3,740,503 does not rise as high as the previous level. The surface swings in this manner till it is returned to the original horizontal level after a short time.

If a force is applied to the switch in the opposite direction to the arrow 31, that is horizontally from the left-hand side, or perpendicular to the plane of the drawing sheet, the same operation as mentioned above is effected to close the switch except that the direction of inclination of the surface of the mercury differs depending upon the direction in which the force is applied to the switch. Thus, the switch is closed by a force applied thereto horizontally in whichever direction it may be perpendicular to the axis of the casing.

As previously mentioned, the angle of inclination of the surface of the mercury 26 is proportional to the magnitude of the force applied thereto. Therefore, the mass of the mercury 26 and the vertical position of the weight as it normally stands determines the magnitude of the force required to cause closure of the switch. In other words, in order to determine the magnitude of the force required, the amount of mercury and the normal position of the weight may accordingly be determined.

The periphery of the lower end of the weight may be tapered as at 28, so that by changing the angle of the tapered edge 28 it is possible to vary the magnitude of the force required to cause the surface of the mercury to be inclined into contact with the tapered edge of the weight.

Now turning to FIG. 3, suppose that a force has been applied to the switch in the direction on an arrow 32, that is, vertically downwardly. The weight 14 is instantaneously moved downwardly to compress the lower coil spring 18. At the next moment the resilient energy stored in the coil spring 18 causes the weight to move upward as far as the contact disk 20 moving together with the weight comes into contact with the lower end of the upper terminal 11 as shown in FIG. 3, whereupon the upper and lower terminals 11 and 12 are electrically connected through the contact disk 20, the spring 18 and the mercury 26. This means that the switch has now been closed. After a moment the weight moves downward and then again upward. The vertical reciprocal movement or vibration continues with the amplitude decreasing until the weight comes to a standstill at the position of FIG. 1.

Turning to FIG. 4, suppose that a vertical force has been applied to the switch in the deirection of an arrow 33, that is, upwardly in the figure. The weight 14 is then instantaneously displaced vertically upwardly. At the next moment the resilient force stored in the upper coil spring by the upward movement of the weight causes the weight to move downwardly as far as it comes into contact with the mercury at the bottom of the casing 10, thereby establishing an electrical connection between the upper and lower terminals 11 and 12 through the upper coil spring 16, the weight 14 and the mercury 26. This means that the switch has now been closed. In this case, too, it is possible to set the force required for operation of the switch to a desired magnitude by appropriately selecting the amount of the mercury 26, the mass of the weight 14 and the resiliency of the springs 16 and 18.

In the above explanation, the force is applied to the switch in the form of a shock or impact. The same course of events occurs if it is applied in the form of vibration and also if the casing 10 is tilted instead of a force being applied thereto.

As can be understood from the above description, the switch of this invention is closed upon application 5 of a force thereto and a moment after that it is again opened. Therefore, in order to continue power supply to a load for a certain period of time, some other circuit is required, which may advantageously be a monostable circuit. Practically it is convenient to have such a cir10 cuit and the switch together enclosed in a single housing so as to be dealt with as a single device. FIG. 5 shows an example of such an arrangement. A housing 41 made of a suitable synthetic resin encloses the switch of FIG. 1 designated here by 1 and such a mono15 stable circuit as mentioned above in the form of a printed circuit. The casing 10 of the switch is preferably enclosed in a protective cover 43 made of, preferably, a shrinkable plastic tube. The housing 41 has a base 44, which is fixed by means of screws to a member 20 to which external forces are applied. The switch 1 is placed on a base 45 and secured to the housing 41, with the peripheral wall of the casing 10 of the switch 1 in contact with the adjacent two walls of the housing 41, so that the force applied to the housing is directly trans25 mitted to the switch 1. Leads 60 connects the terminals 11 and 12 to the printed circuit, which comprises a base 42 and a monostable circuit printed thereon. The circuit comprizes transistors 47, a condenser 48, resistors 49, etc. If necessary, a heat-radiating plate 50 is ad³⁰ ditionally provided, which supports a transistor 51 and other necessary elements.

The monostible circuit may be of any suitable design provided that when the switch is closed the circuit produces an output continuing for a predetermined period ³³ of time. Examples of the monostable circuit are illustrated in FIGS. 7 and 9. In FIG. 7 a monostable circuit 70 chiefly comprises a pair of transistors 71 and 72, a resistor 73 and a condenser 74 for deteermining the time constant of the circuit. The switch 1 is connected ⁴θ across the transistor 72. A load 76 is connected to a switching transistor 75. With a voltage E being applied to source terminal 77, the transistor 71 is “on” and the transistor 72, “off” and the transistor 75, “off” so that no power is supplied to the load 76. The circuit is at this time in the stable condition. The condenser 74, however, is charged with the base current of the transistor 71 to the level E at the polarity shown in FIG· 7.

Under the condition, when the switch 1 is closed, an inverted input is applied between the emitter and col⁵θ lector of the transistor 72, so that the potential at pent A becomes E as shown in FIG. 8α. As a result, the transistor 75 is turned on and the resulting amplified current flows through the load 76. On the other hand, the ₅₅ instant the switch 1 has been closed, the condenser 74 is short-circuited, so that the potential at point B transiently becomes about + 2E as shown in FIG. 8fe. As a result, the transistor 71 is counter-biased between the base and the emitter thereof, so that the transistor 71 ₆₀ is turned off. The moment the switch is again opened, a base current flows through the transistor 72, which is then turned on, so that the condenser 74 is continuously discharged through the resistor 73 until the opotential at B decreases to a level enough to turn on the ₆₅ transistor 71.

During this course of events the operative conditions of the transistors 71, 72 and 75 are kept as they are, so that the output of the transistor 75 is continuously ap3,740,503 plied to the load 76 for a period of time t. The time t is determined by the time constant of a delay circuit composed of the condenser 74 and the resistor 73.

As the condenser 74 is discharged, the potential at point B is reduced to the operating voltage level E of the transistor 71, whereupon a current flows through the base of the transistor 71 to restore it to the “on” condition. Then the condenser 74 is beginning to be charged again. Simultaneously, the transistors 72 and 75 are turned off again, so that the power supply to the load 76 is stopped. The whole circuit has now been restored to its original condition.

The arrangement of FIG. 7 is such that normally no current is supplied to the load and when the switch is closed, the current supply is started. In FIG. 9, however, normally current is supplied to the load and when the switch is closed the current supply is stopped for a predetermined period of time. Here, the switch 1 is connected between the base and emitter of the transistor 72.

With a voltage E impressed on the source terminals 77, the transistors 71,72 and 75 are all in the “on” condition, and the circuit remains stable. The output of the transistor 75 keeps the load 76 operative and the condenser 74 is charged to the potential +E with the collectorcurrent of the transistor 72. Of course the switch is kept opened at this time.

Under the condition, when the switch is closed, an inverted input is applied to the transistor 72 between the base and emitter thereof, so that the voltage at point A is reduced to zero as shown in FIG. 10α. As a result, the potential at point B becomes lower by E-volt than the potential at A as shown in FIG. 10b, so that the transistor 71 is turned off. On the other hand, due to the potential at A having become O volt, the transistor 75 also is turned off, so that the current supply to the load 76 is stopped.

After a moment the switch 1 is opened, but the potential at B is kept negative, so that the then operative conditions of the transistors 71, 72 and 75 remain unchanged. During the course of events, the condenser 74 is continuously discharged through the resistor 73. Upon lapse of a predetermined period of time t the potential at B becomes O volt, whereupon the transistor 71 is turned on and the base current flows through the transistor 72 to turn it on. The transistor 75 is turned on by the collector current of the transistor 72, so that the current supply to the load 76 and the charging of the condenser 74 are resumed. Thus the whole circuit has now been restored to its original condition. Needless to say, the holding time t is determined by the time constant of the delay circuit consisting of the condenser 74 and the resistor 73.

A bistable circuit may be used instead of the monostable circuit, provided that a reset signal is provided by means of a different circuit.

Such an arrangement is obvious to those skilled in the art so that no description thereof will be necessary.