US3172016A - Highly sensitive electrical switch - Google Patents

Description

F. J. KENLINE Filed April 2'7, 1960 AMPLIFIER HIGHLY SENSITIVE ELECTRICAL SWITCH SWITC u March 2, 1965 4 @AJ 441' 2Z1: BY X W IZ TOFA/FXS United States Patent 3,172,016 HIGHLY SENSITIVE ELECTRICAL SWITCH Frederick J. Kenline, Buffalo, N.Y., assignor, by mesne assignments, to Patterson Industries, Inc., East Liverpool, Ohio, a corporation of Ohio Filed Apr. 27, 1960, Ser. No. 24,933 4 Claims. (Cl. 317132) This invention relates to a highly sensitive electrical switch and more particularly to such a switch which is operative at relatively high temperatures, say, in the order of 300 to 400 F.

Electrical switches operable under such temperatures and having a high degree of sensitivity, such as operating within a fraction of a thousandth of an inch, and of such ability as to give many exact repetitions in operation are not commercially available.

It is the principal object of the present invention to provide an electrical switch which will operate under the above prescribed high temperature conditions in response to movement of its probe or actuating part which is in order of a fraction of a thousandth of an inch and which is stable or free from drift and will give an exact repetition of its action under conditions of rapid or slow repetitive use.

Another object of the invention is to provide such a switch which is extremely simple and rugged i-n construction, this simplicity, in fact, largely contributing to its high degree of accuracy which is obtained in part by eliminating the clearances for movable parts contained in commercially available switches.

Another object of the invention is to provide such a highly sensitive switch which is easily set to operate within the required range of movement and will stand up under conditions of severe and constant use without getting out of repair or changing its operating characteristics.

Another object is to provide such a switch which does not require any unusual or costly materials, the principal parts of the switch being desirably fabricated from a suitable plastic sheet and the contacts being of brass or any other metal.

Other objects and advantages of the invention will be apparent from the following description and drawings in which:

FIG. 1 is a vertical section taken on line 11, FIG. 2 through a highly sensitive switch embodying the present invention, with a part of the body broken away.

FIG. 2 is a top plan view thereof.

FIG. 3 is a schematic drawing showing the electronic switching relay used in conjunction with the switch.

An important feature of the present invention is that the operating parts of the switch are essentially contained within a body part 5 having one or more covers 6 made of a plastic which is resistant to heat both in not being subject to deterioration under high temperature and also being dimensionally stable under constant application of these temperatures. The present switch was particularly designed to operate in a temperature range of 300 to 400 F., although the invention is not limited to any particular operating temperature range. For operating in this range the body and covers of the switch can be made of a synthetic tar-acid resin or impregnated body a resin satisfactory for this purpose being commercially known as grade AAA spauldite such synthetic tar and resin can be obtained by the condensation of a tar acid or a mixture of tar acids by dilute mineral acid. The body 5 is shown as being of simple rectangular form and as having a through cavity 8, the opposite sides of which are closed by the two covers 6, which can be secured by corner screws 9. Prefer-ably the housing and cover are provided with registering mounting holes 10 at their opposite ends by means of which the switch can be secured in position.

At one end of the cavity 8, the housing 5 is formed to provide a mount 11 for a switch arm 12. To this end the mount 11 is formed to provide a V-shaped notch 13 in its top extending transversely of the housing, preferably the full width thereof. This V-shaped notch 13 receives and supports a downwardly projecting knife edge 14 of the switch arm 12 and which knife edge 14 is formed integrally with the switch arm to provide with the notch 13 a knife edge bearing. An important feature of the invention is that the switch arm is made of a heat resistant plastic so as not to be subject to deterioration or dimensional changes under relatively high temperatures. As with the body and its covers, a synthetic tar acid resin such as grade AAA spauldite has been found to be a satisfactory material for this purpose within an operating range of from 300 to 400 F.

The outboard end of the switch arm 12 has a contact 15 on its underside. This contact can be of brass of any suitable form, but is shown as being in the form of a vertical screw extending above the top of the switch arm 12 and having a nut 16 at its upper end by means of which a wire 19 can connect this contact screw 15 with a binding post in the form of a screw 20 extending through the top wall of the body 5. This binding post can have a nut 21 at its lower end by means of which the wire 19 can be connected, and can have a nut 22 at its upper end by means of which connection can be made to a low energy switching unit as hereinafter described.

The movable contact 15 is held in permanent engagement or contact with the rounding upper head 24 of a fixed contact 25. This is shown as being in the form of a screw, which can be made of brass, extending through the bottom of the body 5 and held by a pair of nuts 26, 27, the lower one of which can serve to connect the switch with a low energy switching unit as hereinafter described.

The pressure contact between the contacts 15, 25 can be provided by helical compression spring 28 operatively interposed between the top of the switch arm 12 near its center and the top of the cavity 8. This helical compression spring can be held in position by any suitable means, such as by the heads of screws 29, 30 in the body and switch arm, respectively. p

The sensitive part of the switch is in the form of a longitudinally extensible probe, indicated generally at 32, slidingly mounted in the bottom of the body 5 which opposes the movable contact 15. This probe consists of an internally threaded tubular pin 33 having an enlarged head 34 within the cavity 8 which is of conical form to provide an apex 35 having substantially point contact with the underside of the flat head 36 of a pin 38 fixed in the arm 12 as by a tap fit. This tubular pin 33 is slidingly mounted in a metal bushing 39 and pro vides a slideway for this pin. Screwed into the outer or lower end of the tubular pin 33 is an externally threaded pin 40 which has a lock nut 41 tightening against the outer end of the tubular pin 33 so that the pins can be set in different axial relations to each other and thereby provide a composite pin or probe which is longitudinally extensible.

The switch is shown as being actuated by a part 42 which can be maintained at a high temperature and which moves only a fraction of a one thousandth of an inch in opening and closing the switch.

The switch contacts are connected in the low voltage, low amperage end of the low energy switching unit, and the variation in the contact resistance of its contacts 15, 25 varies the drive signal on the low energy switching unit corresponding to changes in the pressure between the contacts. The signal is amplified and then employed to actuate a relay which supplies current at standard voltage to the electrical control component being served. This component in turn operates to return the part 42 to the desired position.

For this purpose the binding post is shown as connected to one side 45 of a low voltage, low amperage line the other side 46 of which is connected to the input of an amplifier 48. The other input terminal of this amplifier 48 is connected by a line 49 to the other binding post of the switch. The output of the amplifier 48 is connected by lines 50, 51 to the input of a relay 52 and is supplied with available power current through power lines 53 and 54. The output lines 55 and 56 from the relay to connections with the electrical component which the switch is designed to serve and which operates to return the part 42 to the desired level.

In the operation of the switch, the head 34 of the extensible actuating pin or probe 32, when seated on the bottom of the cavity 8, allows contacts 15, 25 to be closed. This contract is maintained by the helical compression spring 28. Under this condition a corresponding microcurrent at a voltage of, say, six volts, passes through the switch and through the input of the amplifier 48. A corresponding amplified current is supplied to the relay 52 and can hold this relay either open or closed depending upon whether the switch is operated as a normally open or a normally closed switch.

It is assumed that the part 42 which controls the switch rises in temperature to a high value, say 300 to 400 F. and that during this rise the operating characteristics of the switch must remain constant and free from drift and that at this elevated temperature the parts of the switch must not be subject to deterioration. For this purpose the body 5 and arm 12 of the switch are made of plastic, such as grade AAA sp auldite, which is stable dimensionally and against deterioration at these elevated temperatures. It is also assumed that the switch must be opened and closed with movement of a fraction of a one thousandth of an inch of the part 4-2 and for this purpose the switch arm 12 has a knife edge bearing connection 13, 14 with the body 5 and also the switch operates essentially through change in contact resistance between the contacts 15, 25 rather than through physical separation of the surfaces, only because this change in resistance takes place first.

Thus with the switch operating as above described, when the part 42 rises the assumed fraction of a one thousandth of an inch it elevates the composite probe 32 which moves upwardly in the slideway provided in the bearing bushing 39. Its head 34 has substantially point contact 35 with the bottom of the enlarged head 36 of the pin 38 carried by the synthetic plastic switch arm 12 and hence this small movement of the part 42 elevates the outboard end of this arm 12, this arm fulcru-rning about its knife bearing 13, 14. V

This slight movement of the outboard end of the synthetic plastic arm 12 is sufficient to relieve the contact pressure between the contacts 15, 25 and this increases the contact resistance between these contacts. Thus this contact resistance can be increased from, say, zero ohms while closed to, say, forty thousand ohms or so, at the time the switch operates. Accordingly the relay parts are shifted from one position to the other either cutting off or supplying current to the electrical component to be served, depending upon whether the switch is norm-ally open or normally closed. This reverses the movement of the part 42 thereby to withdraw the composite probe 32 and permit the pressure between the contacts 15, 25 to increase to its original value at which their contact resistance is restored to the assumed zero chm-s. Through the amplifier 48, this restores the relay 52 to its original condition for a repetition of the signal.

As previously indicated the switch of the present invenprimary circuit including the input to an amplifier, and a secondary circuit including the output of said amplifier and a relay responsive to 'a predetermined range of change in value of the characteristics of the current flowing through said secondary circuit; the combination therewith of a switch highly sensitive to a very small relative movement between two parts, comprising a fixed contact connected to one side of said primary circuit and being fast to one of said parts, a movable contact connected to the other side of said primary circuit and being in engagement with said fixed contact, means biasing said movable contact into contact pressure with said fixed contact, and means actuated by the other of said parts to actuate said movable contact to vary and at the same time maintain contact pressure between said contacts thereby to vary the contact resistance to current flowing between these contacts and efiect a corresponding change in value, through said predetermined range, of the characteristic of the current flowing through said secondary circuit,

2. In a circuit having a low voltage, low amperage primary circuit including the input to Ian amplifier, and a secondary circuit including the output of said amplifier and a. relay responsive to a predetermined range of change in value of the characteristics of the current flowing through said secondary circuit; the combination therewith of a switch highly sensitive to a very small relative movement between two parts, comprising a fixed contact connected to one side of said primary circuit and being fast to one of said parts, a movable contact connected to the other side of said primary circuit and being in engagement with said fixed contact, means biasing said movable contact into contact pressure with said fixed contact, a stop limiting the position of said movable contact to a maximum contact pressure between said contacts, and means actuated by the other of parts to actuate said movable contact to vary and at the same time maintain said contact pressure between said contacts thereby to vary the contact resistance to current flowing between these contacts and effect a corresponding change in the value, through said predetermined range, of the characteristics of the current flowing through said secondary circuit.

3. In a circuit having a low voltage, low amperage primary circuit including the input to an amplifier, and a secondary circuit including the output of said amplifier and a relay responsive to a predetermined range of change in value of the characteristics of the current flowing through said secondary circuit; the combination therewith of a switch adapted-tor use in a high temperature environment and sensitive to a very small relative movement between said parts, comprising a hollow body part made of a plastic resistive to heat and fixed to one of said parts, a fulcrum in one end of said body, a switch arm made of a plastic resistive to heat and having a knife edge bearing at one end seated in said fulcrum and having a movable contact at the outer end of said switch arm and connected to one side of said primary circuit, a contact connected to the other side out said primary circuit and fixed to said body in line to be engaged by said movable contact, p g means interposed between said body and switch arm and biasing said movable contact to have contact pressure with said fixed contact, a stop mounted on said body and limiting the position of said movable contact to a maximum contact pressure between said contacts, and means actuated by the other of said parts to move said stop to actuate said switch arm to vary and at the same time maintain contact pressure between said contacts thereby to vary the Contact resistance to current flowing between these nontaots and effect a corresponding change in the value, through said predetermined range, of the characteristics of the current flowing through said secondary circuit.

4. The combination set forth in claim 3 wherein the body and switch mm are made of a plastic which is thermally stable over a wide range of temperatures.

References Cited in the file of this patent UNITED STATES PATENTS Sohaelchlin Dec. 26, 1939 Lamb Feb. 10, 1942 Kelleigh Mar. 4, 1958 Saint-Amour Sept. 2, 1958 Altier-i Oot. 21, 1958 Henley Apr. 5, 1960

Claims (1)

1. 3. IN A CIRCUIT HAVING A LOW VOLTAGE, LOW AMPERAGE PRIMARY CIRCUIT INCLUDING THE INPUT TO AN AMPLIFIER, AND A SECONDARY CIRCUIT INCLUDING THE OUTPUT OF SAID AMPLIFIER AND A RELAY RESPONSIVE TO A PREDETERMINED RANGE OF CHANGE IN VALUE OF THE CHARACTERISTICS OF THE CURRENT FLOWING THROUGH SAID SECONDARY CIRCUIT; THE COMBINATION THEREWITH OF A SWITCH ADAPTED FOR USE IN A HIGH TEMPERATURE ENVIRONMENT AND SENSITIVE TO A VERY SMALL RELATIVE MOVEMENT BETWEEN SAID PARTS, COMPRISING A HOLLOW BODY PART MADE OF A PLASTIC RESISTIVE TO HEAT AND FIXED TO ONE OF SAID PARTS, A FULCRUM IN ONE END OF SAID BODY, A SWITCH ARM MADE OF A PLASTIC RESISTIVE TO HEAT AND HAVING A KNIGE EDGE BEARING AT ONE END SEATED IN SAID FULCRUM AND HAVING A MOVABLE CONTACT AT THE OUTER END OF SAID SWITCH ARM AND CONNECTED TO ONE SIDE OF SAID PRIMARY CIRCUIT, A CONTACT CONNECTED TO THE OTHER SIDE OF SAID PRIMARY CIRCUIT AND FIXED TO SAID BODY IN LINE TO BE ENGAGED BY SAID MOVABLE CON-

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