US3334320A

US3334320A - Magnetic reed switches having minimum contact bounce

Info

Publication number: US3334320A
Application number: US493657A
Authority: US
Inventors: Gerald F Frank
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1965-10-07
Filing date: 1965-10-07
Publication date: 1967-08-01
Anticipated expiration: 1984-08-01
Also published as: GB1129357A; JPS44258B1; FR1498721A; CH460126A; NL6614174A; DE1640179A1

Description

1, 96 G. F. FRANK 3,334,320

MAGNETIC REED SWITCHES HAVING MINIMUM CONTACT BOUNCE Filed Oct. 7, 1965 INVENTOR. I GERALD F/ fiA/VK A TTORNE Y United States Patent 3,334,320 MAGNETIC REED SWITCHES HAVING MINIMUM CONTACT BOUNCE Gerald F. Frank, Normal, Ill., assignor to General Electric Company, a corporation of New York Filed Oct. 7, 1965, Ser. No. 493,657 11 Claims. (Cl. 335-454) This invention relates to magnetic reed switches and has particular relation to sealed magnetic reed switches with provision for minimizing contact bounce.

One type of reed switch commonly employed is a single throw reed switch comprising a sealed tube mounting therewithin a pair of deflectable electrically and magnetically conductive reeds which overlap in spaced relation. The reeds are moved into engagement in response to application of a suitable magnetic field thereto. Such a reed switch is disclosed in U.S. Patent 2,289,830. Reed switches of the double throw type are also in commercial use and include a sealed tube containing a pair of fixed electrically and magnetically conductive contacts and netically conductive reed having a contact portion located between and overlapping the fixed contacts. A permanent magnet is provided to control movement of the reed relative to the fixed contacts, and application of a suitable additional magnetic flux source eflects movement of the reed into engagement with a selected one of the fixed contacts. A very desirable switch of this type is disclosed in U.S. Patent 3,117,202.

When the contacts of reed switches are actuated into engagement, they experience what is commonly known as contact bounce which is very disadvantageous in that it results in poor electrical contact and also can result in undesirable arcing between the contacts and deterioration of the contact making surfaces. The contact bounce problem is present in both single throw and double throw reed switches.

It is therefore a primary object of the present invention to provide a magnetic reed switch having novel and improved means for minimizing contact bounce.

It is another object of the invention to provide a double throw magnetic reed switch having two fixed contacts and a novel and improved deflectable reed assembly for minimizing contact bounce between the reed assembly and each of the fixed contacts.

In carrying out the invention in one preferred form, a sealed magnetic reed switch is provided including a sealed t-ube mounting at one end a magnetically and electrically conductive electrode having a terminal part outside the tube and a contact part within the tube for co-operation with an electrically and magnetically conductive deflectable reed assembly mounted by the tube at the other end thereof. The electrode may be deflectable or rigid as desired. The reed assembly includes a terminal part outside the tube and a contact part within the tube which is deflectable relative to the electrode in directions toward and away from the electrode. The reed assembly is split from its free end along a plane which is perpendicular to the direction of deflection of the reed assembly to form a pair of reeds of substantially equal length and having substantially the same natural frequency of vibration. The free ends of the two reeds are spaced from each other in the direction of deflection of the reed assembly and are in overlapping relation with the contact part of the electrode. When a magnetic field is applied to the switch, the reed assembly is deflected toward the contact part of the electrode so that one of the reeds engages the contact part. It has been observed that the two reeds cooperate during a contact making operation to substantially eliminate contact bounce between the one reed and the contact part of the electrode.

a deflectable electrically and mag-,

Other objects and advantages of the invention will become apparent from the following description taken in conjunction with the accompanying drawing in which:

FIGURE 1 is a view with parts broken away and with parts shOWn in section of a sealed double throw reed switch constructed in accordance with the present invention showing the reed assembly in engagement with one fixed contact part; and

FIGURE 2 is a View similar to FIGURE 1 showing the reed assembly in engagement with the other fixed contact part of the switch.

The present invention is applicable to single throw reed switches as well as double throw reed switches, and for purpose of illustration the invention will be described in connection with a double throw reed switch of the type shown in FIGURE 7 of the aforementioned U.S. Patent 3,117,202.

Referring now to the drawings, there is illustrated in FIGURE 1 a sealed magnetic reed switch of the double throw type constructed according to the present invention. The switch includes a generally cylindrical elongated tube 10 preferably formed of glass and sealed at its opposite ends to support and enclose parts of the switch mechanism. At the left hand end of the tube 10 as viewed in FIGURE 1 is mounted a pair of electrodes formed of electrically and magnetically conductive material, such as a nickel-iron alloy, and designated generally by the numerals 11 and 12. The electrodes 11 and 12 in the illustrated embodiment are rigidly mounted and are adapted for selective engagement by a defiectable magnetic reed assembly 13 of unique construction described hereinafter.

In the illustrated embodiment the electrode 11 is of two part construction including a flattened contact part 14 within the tube and having a flattened section 15 outside the tube. The part 14 includes an intermediate cylindrical section which is sealed to the tube by any suitable glass to metal sealing process. The section 15 supports a permanent magnet 16 which in turn supports the terminal part 17 of the electrode 11. The part 17 may be secured to the magnet 16 and the magnet 16 may be secured to the section 15 as by welding. The magnet 16 is preferably of cylindrical configuration having a high coercive force and may be formed of any suitable magnetic material, such as Alnico. The magnet 16 is shown positioned externally of the tube 10 so that when magnetized its north and south poles designated N and S respectively are spaced longitudinally of the tube. If desired, the magnet 16 may be located within the tube as in the switch shown in FIGURE 1 of Patent 3,117,202.

The electrode 12 is of one piece construction including a flattened contact part 18 within the tube and a cylindrical terminal part 19 extending outside the tube. The electrode 12 is sealed to the tube by any suitable glass to metal sealing process. The

contact parts

14 and 18 are spaced transversely of the longitudinal axis of the tube 10 to cooperate with the reed assembly 13.

The magnet 16 and the reed assembly 13 are included in series in a magnetic circuit which provides a path for magnetic flux emanating from the magnet 16. The magnetic flux from magnet 16 is effective to attract the reed assembly 13 to the contact part 14 as shown in FIGURE 1. To eiIect movement of the reed assembly 13 along its path of deflection between the

contact parts

14 and 18 there is provided a suitable additional magnetic field source illustrated in the form of a winding 20 surrounding the tube 10. It is understood that the additional field source may comprise other means such as a permanent magnet. Energization of winding 20 by current flowing in the direction of the arrows associated therewith establishes magnetic flux etfective to transfer the reed assembly 13 out of engagement with the contact part 14 and '2 J into engagement with the contact part 18. The reed assembly will remain in engagement with the contact part 18 until the winding is deenergized at which time the reed assembly will return into engagement with the contact part 14.

When the deflectable reed of a reed switch is moved into engagement with an associated contact, it experiences contact bounce, that is, it vibrates relative to the associated contact to dissipate its kinetic energy. Such vibration of the reed produces a poor electrical contact between the contacts and may also result in arcing which contributes to the deterioration of the contact surfaces. The extent of the undesirable contact bounce varies depending upon the design of the particular reed switch but is present to a greater or lesser degree in all reed switch designs.

In accord with the present invention the reed assembly 13 is of split construction which is found to minimize bouncing of the reed assembly as it engages either of the

contact parts

14 or 18. In the illustrated embodiment of the invention, the reed assembly 13 is split through a substantial portion of its length along a plane which is generally perpendicular to the path of deflection of the reed assembly and to the direction of spacing of the

contact parts

14 and 18. Such splitting of the reed assembly forms two reeds of substantially equal length with substantially the same natural frequency of vibration which cooperates to minimize contact bounce.

In the preferred embodiment of the invention the split reed assembly comprises a first main deflectable reed 21 formed of electrically and magnetically conductive material and having a free end 22 within the tube and a terminal end 23 located externally of the tube. The reed 21 is supported by the tube at the right hand end thereof as viewed in FIGURE 1 and extends longitudinally of the tube with the free end 22 between and in overlapping relation with the

contact parts

14 and 18 and adjacent the contact part 14. The reed assembly includes further a second short deflectable reed 24 also formed of electrically and magnetically conductive material and secured at one end in any suitable manner to the underside of the reed 21 at an area spaced from the free end of reed 21 so that the

reeds

21 and 24 are in vertical alignment as viewed in FIGURE 1. The reed 24 extends from its attached end 25 toward the

contact parts

14 and 18 with its free end 26 spaced from the free end 22 of the reed 21 in overlapping relation with and between the

contact parts

14 and 18 and adjacent the contact part 18. The reed 24 is preferably attached to the reed 21 by welding and lies tangent to the elastic curve of the reed 21 at the point of attachment thereto when the reed 21 engages the contact part 14. Prior to magnetization of the magnet 16 the two

reeds

21 and 24 extend midway between the

contact parts

14 and 18 in spaced relation thereto with a slight spacing between the

free ends

22 and 26 of the reeds. The

reeds

21 and 24 are deflectable relative to each other and the spacing between the free ends of the reeds increases slightly after magnetization of the magnet 16 and attraction of the reed 21 to the contact part 14.

Operation of the improved switch will now be described according to the present understanding thereof. With the switch parts in positions shown in FIGURE 1, when the coil 20 is energized by current of sufficient magnitude flowing in the direction of the arrows associated therewith, a magnetic flux is produced in such a direction and of such magnitude as to reduce the magnetic fiux at the contact part 14 and the free end 22 of the reed 21 resulting from the magnet 16 so that the spring force stored in the reed 21 is sufficient to disengage the reed 21 and the contact part 14. Flux produced by such ener-gization of winding 20 also attracts the reed assembly toward the contact part 18 causing deflection of the reed 21 and movement of reed 24 so that the free end 26 of reed 24 engages the contact part 18. At the time of initial contact engagement as shown in FIG- URE 2, the entire reed assembly 13 has certain kinetic energy which must be dissipated. At this time the reed 24 constitutes a beam which is simply supported at its free end by the contact part 18 and which may be considered to be clamped at its attached end to' the reed 21. Also, the portion of reed 21 from its point of attachment to reed 24 to its free end constitutes a clamped cantilever beam. Therefore, the reed 24 will vibrate considerably faster than the portion of the reed 21 from its area of attachment to its free end 22. After engagement of reed 24 and contact part 18, the reed 21 continues to move downwardly as viewed in FIGURE 1 due to its kinetic energy and thus applies an additional force to the reed 24 in the direction to increase the contact pressure. Vibrations of the reed 24 are very quickly damped by engagement of the free end 22 of reed 21 with the free end 26 of reed 24. A great part of the kinetic energy of the reed assembly is expended by such contact between the two reeds to thereby minimize contact bounce. Since the reed assembly is symmetrical, the same action will take place when it is moved away from the contact part 18 toward the contact part 14.

Although the invention has been described with reference to certain specific embodiments thereof, numerous modifications are possible and it is desired to cover all modifications falling within the spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A reed switch comprising an electrically and magnetically conductive electrode having a terminal part and having a contact part, and an electrically and magnetically conductive deflectable reed assembly having a common terminal part, said reed assembly being deflectable along a path toward and away from said contact part, said reed assembly having only first and second reeds of substantially equal length, said first and second reeds having terminal ends supported in abutting relationship by said common terminal part, said first and second reeds extending from said common terminal part and overlying each other in a direction generally parallel to said path of deflection, said two reeds being deflectable relative to each other and having free contact ends spaced from each other in a direction generally parallel to said path of deflection and in overlapping relation with said contact part, said free contact end of said first'one of said reeds being moved into engagement with said contact part in response to deflection of said reed assembly toward said contact part resulting from application of an external magnetic field, said free contact end of said second one of said reeds being thereafter moved into engagement with said free contact end of said first reed, whereby the kinetic energiesof said first and second reeds are expended by the engagement, such that the bouncing of said first reed relative to said contact part resulting from engagement thereof is minimized.

2. A switch as defined in claim 1 wherein said reeds have substantially the same natural frequency of vibration.

3. A switch as defined in claim 1 wherein said terminal end of said second reed is attached to said first reed at an area spaced from the free end of said first reed.

4. A switch as defined in claim 3 wherein said reeds have substantially the same natural frequency of vibration.

5. A reed switch comprising a sealed tube, a pair of electrically and magnetically conductive electrodes mounted by said tube having terminal parts outside the tube and having contact parts within the tube in spaced relation, an electrically and magnetically conductive deflectable reed assembly mounted Within said tube and having a common terminal part extending outside the tube, said reed assembly extending longitudinally of the tube between and in overlapping relation with the contact parts of said electrodes for deflection into and out of engagement with the contact parts, said reed assembly within said tube having only first and second reeds of substantially equal length, said first and second reeds having terminal ends supported in abutting relationship by said common terminal part, said first and second reeds extending from said common terminal part and overlying each other in a direction which is generally parallel to the direction of spacing of said contact parts, said two reeds being deflectable relative to each other and relative to said contact parts and having free contact ends spaced from each other in a direction parallel to the direction of spacing of said contact parts, a permanent magnet for attracting said reed assembly toward the contact part of one of said electrodes so that said first reed engages the contact part of said one electrode, said second reed being moved into engagement with the contact part of the other electrode in response to defiection of the reed assembly away from the contact part of said one electrode resulting from application of an external magnetic field, whereby when said free contact end of one of said reeds engages the contact part of one of said electrodes said free end of the other of said reeds is thereafter moved into engagement with said free contact end of said one reed and the kinetic energies of said first and second reeds are expended by the engagement such that the bouncing of said one reed relative to said contact part resulting from engagement thereof is minimized.

6. A switch as defined in claim 5 wherein said magnet is mounted outside said tube by said one electrode with the poles of the magnet being spaced longitudinally of said tube.

7. A switch as defined in claim. 5 wherein said reeds have substantially the same natural frequency of vibration.

8. A reed switch comprising a sealed tube, a pair of electrically and magnetically conductive electrodes mounted by said tube having terminal parts outside the tube and having contact parts within the tube in spaced relation, an electrically and magnetically conductive defiectable reed assembly mounted in said tube and having a terminal part outside the tube, said reed assembly extending longitudinally of the tube between and in overlapping relation with the contact parts of said electrodes for deflection into and out of engagement with the contact parts, said reed assembly having only a first reed mounted by said tube, and a second reed secured at one end to said first reed at an area spaced from the free end of said first reed, Said second reed being substantially tangent to the elastic curve of said first reed at the area where secured when said first reed engages its associated contact part, said first and second reeds being of substantially equal length and overlying each other in a direction which is generally parallel to the direction of spacing of said contact parts, said two reeds being deflectable relative to each other and relative to said contact parts and having free contact ends spaced from each other in a direction parallel to the direction of spacing of said contact parts, a permanent magnet for attracting said reed assembly toward the contact part of one of said electrodes so that said first reed engages the contact part of said one electrode, said second reed being moved into engagement with the contact part of the other electrode in response to deflection of the reed assembly away from the contact part of said one electrode resulting from application of an external magnetic field, whereby when said free contact end of one of said reed engages the contact part of one of said electrodes said free end of the other of said reeds is thereafter moved into engagement with said free contact end of said one reed and the kinetic energies of said first and second reeds are expended by the engagement such that the bouncing of said one reed relative to said contact part resulting from engagement thereof is minimized.

9. A switch as defined in claim 8 have substantially the same natural bration.

10. A reed switch comprising an electrically and magnetically conductive electrode having a terminal part and having a contact part, and an electrically and magnetically conductive deflectable reed assembly having a terminal part, said reed assembly being deflectable along a path toward and away from said contact part, said reed assembly having only first and second reeds of substantially equal length and overlying each other in a direction generally parallel to said path of deflection, said reed assembly terminal part and said first reed being integrally formed, and said second reed being secured to said first reed at an area spaced from said terminal part, said second reed being substantially tangent to the elastic curve of said first reed at the area where secured when said first reed engages its associated contact part, said two reeds being deflectable relative to each other and having free contact ends spaced from each other in a direction generally parallel to said path of deflection and in overlapping relation with said contact part, said free contact end of said first one of said reeds being moved into engagement with said contact part in response to deflection of said reed assembly toward said contact part resulting from application of an external magnetic field, said free contact end of said second one of said reeds being thereafter moved into engagement with said free contact end of said first reed, whereby the kinetic energies of said first and second reeds are expended by the engagement, such that the bouncing of said first reed relative to said contact part resulting from engagement thereof is minimized.

11. A reed switch comprising a sealed tube, a pair of electrically and magnetically conductive electrodes mounted by said tube having terminal parts outside the tube and having contact parts within the tube in spaced relation, an electrically and magnetically conductive deflectable reed assembly mounted in said tube and having a terminal part outside the tube, said reed assembly extending longitudinally of the tube between and in overlapping relation With the contact parts of said electrodes for deflection into and out of engagement with the contact parts, said reed assembly having only first and second reeds of substantially equal length and overlying each other in a direction which is generally parallel to the direction of spacing of said contact parts, said reed assembly terminal part and said first reed being integrally formed, and said second reed being secured to said first reed at an area spaced from said terminal part, said second reed being substantially tangent to the elastic curve of said first reed at the area where secured when said first reed engages its associated contact part, said two reeds being deflectable relative to each other and relative to said contact parts and having free contact ends spaced from each other in a direction parallel to the direction of spacing of said contact parts, a permanent magnet for attracting said reed assembly toward the contact part of one of said electrodes so that said first reed engages the contact part of said one electrode, said second reed being moved into engagement with the contact part of the other electrode in response to defiection of the reed assembly away from the contact part of said one electrode resulting from application of an external magnetic field, whereby when said free contact end of one of said reeds engages the contact part of one of said electrodes said free end of the other of said reeds is thereafter moved into engagement with said free contact end of said one reed and the kinetic energies of said first and second reeds are expended by the engagement such that the bouncing of said one reed wherein said reeds frequency of virelative t6 said contact part resulting from engagement thereof is minimized.

References Cited UNITED STATES PATENTS 2,929,895 3/1960 Shebanow 335-454 v 3,117,202 1/1964 Werts 200-457 OTHER REFERENCES 5 German printed application, Gunther, 1,085,944, July Mathes ZOO-87 28, 1960. Brown 200-87 Hastings ZOO-87 BERNARD HEANY, Przmary Exammer.

Riley ZOO-87 X R. N. ENVALL, JR., B. DOBECK, Assistant Examiners.

Claims

1. A REED SWITCH COMPRISING AN ELECTRICALLY AND MAGNETICALLY CONDUCTIVE ELECTRODE HAVING A TERMINAL PART AND HAVING A CONTACT PART, AND AN ELECTRICALLY AND MAGNETICALLY CONDUCTIVE DEFLECTABLE REED ASSEMBLY HAVING A COMMON TERMINAL PART, SAID REED ASSEMBLY BEING DEFLECTABLE ALONG A PATH TOWARD AND AWAY FROM SAID CONTACT PART, SAID REED ASSEMBLY HAVING ONLY FIRST AND SECOND REEDS OF SUBSTANTIALLY EQUAL LENGTH, SAID FIRST AND SECOND REEDS HAVING TERMINAL ENDS SUPPORTED IN ABUTTING RELATIONSHIP BY SAID COMMON TERMINAL PART, SAID FIRST AND SECOND REEDS EXTENDING FROM SAID COMMON TERMINAL PART AND OVERLYING EACH OTHER IN A DIRECTION GENERALLY PARALLEL TO SAID PATH OF DEFLECTION, SAID TWO REEDS BEING DEFLECTABLE RELATIVE TO EACH OTHER AND HAVING FREE CONTACT ENDS SPACED FROM EACH OTHER IN A DIRECTION GENERALLY PARALLEL TO SAID PATH OF DEFLECTION AND IN OVERLAPPING RELATION WITH SAID CONTACT PART, SAID FREE CONTACT END OF SAID FIRST ONE OF SAID REEDS BEING MOVED INTO ENGAGEMENT WITH SAID CONTACT PART IN RESPONSE TO DEFLECTION OF SAID REED ASSEMBLY TOWARD SAID CONTACT PART INSULTING FROM APPLICATION OF AN EXTERNAL MAGNETIC FIELD, SAID FREE CONTACT END OF SAID SECOND ONE OF SAID REEDS BEING THEREAFTER MOVED INTO ENGAGEMENT WITH SAID FREE CONTACT END OF SAID FIRST REED, WHEREBY THE KINETIC ENERGIES OF SAID FIRST AND SECOND REEDS ARE EXPENDED BY THE ENGAGEMENT, SUCH THAT THE BOUNCING OF SAID FIRST REED RELATIVE TO SAID CONTACT PART RESULTING FROM ENGAGEMENT THEREOF IS MINIMIZED.