US 3873957 A
A pushbutton switch producing a snap-action pulse from a Hall element. A snap magnet is held in a rest position and then released to follow the movement of a control magnet thereby applying a magnetic field to the Hall element.
Claims available in
Description (OCR text may contain errors)
United States Patent Wiirscher et al.
PUSH BUTTON Inventors: Horst Wiirscher; Rolf Blass; Oskar Becker, all of Eiserfeld/Sieg,
Germany Assignee: U.S. Philips Corporation, New
Filed: Sept. 28, 1973 Appl. No.: 401,718
Foreign Application Priority Data Oct. 20, I972 Germany 2251530 U.S. Cl 338/32 H, 323/94 H, 335/205,
335/207, 338/32 R Int. Cl H016 7/16 Field of Search 338/32 H, 32 R; 335/1,
335/205, 207; 340/365 L; 323/94 H; 197/98; 324/45, 46; 3l0/DIG. 3
'[ Mar. 25, 1975 Primary E.\aminerC. L. Albritton Attorney, Agent, or Firm-Frank R. Trifari  ABSTRACT A pushbutton switch producing a snap-action pulse from a Hall element. A snap magnet is held in a rest position and then released to follow the movement of a control magnet thereby applying a magnetic field to the Hall element,
3 Claims, 5 Drawing Figures PATENTEUHARZSIQYS 3,873,957
sum 1 9 5 P/UENTEB 1873.957
saw u qlf 5 PUSH BUTTON This invention relates to a pushbutton comprising a Hallelement and magnets which are movable with respect thereto in order to generate pulses.
The generation of a Hall voltage by magnets, in particular by permanent magnets, is known. The use of such a device for pushbuttons in keyboards of typewriters, calculating machines and bookkeeping machines always gives riseto problems because only a comparatively short stroke of the button is available for the control ofthe Hall element. Moreover, with such pushbuttons the snap-action inherent to buttons with spring contacts would be lacking.
In purely mechanically operating pushbuttons a pawl or lever is cocked and the tensioned lever is suddenly released after having passed a pressure threshold (point of maximum accumulated pressure energy). The contact to be operated is then closed, independent of the further movement of the button shaft. A snapaction (shoot-through effect is thus achieved. After the cocking of the pawl, the operator is sure that the contact has been operated. The closing and the opening of the contact takes places quickly, even if the pawl is only slowly cocked. The depressed button is mechanically returned to the starting position after a pulse has been given, i.e., after the closing of the contact.
These pushbuttons are generally comparatively expensive and attempts have been made to perform the operation purely electrically, using as few contacts with the required functions as possible, the aim being to imitate the described snap-action as well as possible.
For example, a pushbutton with reed contacts is known in which different permanent magnets are used (US. Pat. specification No. 3,283,274). A pressure threshold or tensile force threshold is obtained in that in the rest position a permanent magnet which is arranged about the reed contact and which is rigidly connected to the button shaft must be pulled loose from a fixed permanent magnet. If desired, a third permanent magnet can be present'which either keeps the button shaft in the working position or returns it to the rest po sition by opposed polarization as soon as the button is released. The use of a reset spring is then superfluous.
These buttons give an indication to the operator, due to the disappearance of the button pressure, that the pressure threshold has been exceeded and that the contact operation by the permanent magnet to be moved can now be effected, but they do not give an indication that this'has indeed take place. This is because the permanent magnet can still be returned prior to the switching of the contact. Consequently, the button shaft of these pushbuttons must always be completely pushed through for the operator to be sure that the contact has indeed been made. Another drawback of these pushbuttons with reed contacts is that the contacts are liable to bounce, which can be particularly annoying when they are used in calculating and bookkeeping machines.
The invention has for its object to provide a pushbutton which incorporates a pressure threshold, which offers guaranteed switching after having overcome the threshold (pressure point and which operates in a contactless manner. Use is made of the so-called Hall effect, according to which a voltage is generated if the Hall element is moved with respect to a magnetic field.
In a pushbutton according to the invention the Hall element is arranged between two magnets, one of which (control magnet) is rigidly connected to the slidable button shaft and the other (snap magnet) is freely movable in the longitudinal direction of the button shaft, the magnetizations being directed such that, the movement of the snap magnet is determined by the position change of the control magnet after the release from a given rest position. In the rest position of the button the Hall element is situated outside the field, for example, between similar poles of the two magnets. In the switching position the Hall element and is situated in the magnetic field in the switching, i.e., between dissimilar poles of the two magnets.
In a preferred embodiment a threshold (the pressure point) is provided because the snap magnet is magnetically held in the non-depressed position of the button shaft and can be released from this rest position by the button shaft only after the control magnet has completed partof its traject.
The invention will be described in detail with reference to the drawing in which:
FIGS. 1 to 4 are front views, partially in section, of a pushbutton according to the invention in the rest position, the pressure point position, the switching position, and the furthest depressed position, respectively, and
FIG. 5 is a front view, partially in section, ofa modification of a pushbutton according to FIG. I. v
The button which is chosen by way of example and which can be integrated in a keyboard consists of the button housing 1 which is closed at its top by the housing lid 2 which simultaneously serves for guiding the button shaft 3. A carrier plate 7 on which a Hall element 8 is provided is rigidly arranged at the bottom of the button housing 1. The button shaft 3 is provided with an extension 9 which serves as a carrier for the control magnet 4. In a preferred embodiment, this control magnet 4 is a permanent magnet and its magnetiza tion direction extends transverse to the button shaft 3. The button shaft is held by the reset spring 13 in the rest position shown in FIG. 1.
The button shaft 3 also comprises a pin 10 on which a mandril 11 is provided, the diameter of which is smaller than that of the pin 10. The mandril 11 fits loosely in an annular snap magnet which is preferably formed by a permanent magnet whose magnetization direction corresponds to the movement direction of the button shaft. Provided on the free end of the mandril 11 is a safety plate 12 which serves to return the snap magnet 5 to the rest position shown in FIG. 1, in the case of failures.
The snap magnet 5 is freely movable in a guide sleeve 14 of the button housing 1. The stroke of this snap magnet 5 is limited in the upward direction by a magnetic metal ring 6 whose opening is so large that the pin 10 freely slides through this metal ring and can engage the head face of the snap magnet 5.
The arrangement is such that in the rest position shown in FIG. 1 no magnetic flux of the two magnets 4 and 5 is present in the Hall element 8, or the flux present therein is so small that no Hall voltage is generated. In the embodiment shown, this is the result of the special dissimilar polarization of the two permanent magnets 4 and 5.
If the button shaft 3 is moved downwards, it first assumes the pressure point position shown in FIG. 2. In this position the control magnet 4 has already been shifted downwards over part of its stroke. However, the
snap magnet remains in the rest position during this button movement, i.e., it is retained by the metal ring 6. Hardly any magnetic flux flows through the Hall element 8 in this pressure point position.
If the button shaft 3 is moved further downwards, the snap magnet 5 is taken along and is pulled loose from the metal ring 6. At the same time, the control magnet 4 is moved further downwards. As soon as the snap magnet 5 has been magnetically separated from the metal ring 6, which takes place after a comparatively short movement, the button pressure quickly decreases. The snap magnet is then pulled further downwards by the control magnet 4, independent of further movement of the button shaft, until a magnetically stable position between the two magnets 4 and 5 is reached. This free movement of the snap magnet 5 which is determined exclusively by the control magnet 4 is independent of whether the movement of thebutton shaft 3 is arbitrarily stopped after the pressure point of the button shaft 3 has been overcome or the shaft is further moved downwards. In any case, the magnetic flux between the north pole of the control magnet 4 and the south pole of the snap magnet 5 now flows through the Hall element, and a Hall voltage pulse is generated. The location of the safety plate 12 can be chosen such that the downward movement of the snap magnet is limited, without the strength of the magnetic field through the Hall element 8 being influenced thereby. This safety plate also serves then to reduce or prevent oscillation of the snap magnet 5 about the magnetically stable position. The safety plate 12 is not absolutely necessary in this respect because the oscillations of the snap magnet 5 do not necessarily have an adverse effect on the generation of the pulse.
If the button is moved further downwards by the operator, the lower position shown in FIG. 4 is finally reached. The full magnetic flux between the two magnets flows through the Hall element 8 also in this position.
The invention is not restricted to the shape and the arrangement of the magnets as in the embodiment shown in the FIGS. 1 to 4. For example, a magnetically neutral zone can be present between the poles of the snap magnet 5. The essence of the invention is that as a result of the button movement first one of the two magnets is displaced over a short distance, the second magnet being moved, after the pressure point has been overcome, only by the magnetic forces prevailing be tween the two magnets. It is another aspect of the invention that the variation of the magnetic flux between the two magnets is controlled such that no or only a slight magnetic flux between the two magnets 4 and 5 is present in the Hall element 8 in the rest position of the pushbutton (FIG. 1), and that this magnetic flux is suddenly fed through the Hall element by the downward movementof the snap magnet 5 after the pressure point has been overcome. Consequently, only comparatively short trajects are required for generating a pulse.
It is alternatively possible to modify the structural arrangement of the pushbutton. For example, an anvil 11 with the safety plate 12 can be simply dispensed with. The mandril l1 and the plate 12 serve merely to ensure the resetting of the snap magnet to the rest position in the case of failures. The same function is performed by the springs 15 and 16 which are shown in FIG. 5 instead of the mandril 11 and the plate 12. The resilience of the spring 15 is slightly less than that of the spring 16. However, the two springs 15 and 16 may not be so strong that they impede the free movement of the snap magnet 5 which is effected by the drive magnet 4.
What is claimed is:
.1. A pushbutton of the type having a Hall element and magnets which are movable with respect thereto for generating pulses, comprising a housing, a button shaft slidably mounted in said housing for movement in a longitudinal direction between a non-depressed position and a switching position, a control magnet rigidly connected to said button shaft, a snap magnet, means for mounting said snap magnet in said housing for freely sliding movement parallel to said longitudinal direction, means for holding said snap magnet in a rest position when said button shaft is in the non-depressed position and for releasing said snap magnet upon move ment of said button shaft to the switching position, a Hall element, means for fixing said Hall'element in position between said magnets, the magnetization of the magnets being directed such that when the button shaft is in the non-depressed position the Hall element is outside the field, while when the button shaft is in a switching position the Hall element is in the field between the two magnets and the longitudinal movement of the snap magnet is determined only by the position change of the button shaft and the control magnet.
2. A pushbutton as claimed in claim 2, wherein the snap magnet is magnetically held in the rest position, while the snap magnet is released by said releasing means only after the button shaft has moved from a rest position to a switching position.
3. A pushbutton as claimed in claim 2, wherein the magnetization of the snap magnet is directed parallel to the longitudinal direction, and the magnetization of the control magnet is directed perpendicular to the longitu- UNITED sTATEs PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3873957 DATED March 25, 1975 lN\/ ENTOR(S) HORST WURSCHER; ROLF BLASS; OSKAR BECKER It is certified that error appears in the ab0ve-identified patent and that said Letters Patent are hereby corrected as shown below:
column 4, line 5, "trajects" should be strokes-- column 4, Claim 2, line 1, "claim 2" should be -claim 1-- En'gncd and Scaled this Arrest:
RUTH C. MASON C. MARSHALL DANN Arresting Officer ('ummr'ssiuner ofParenrs and Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3873957 DATED March 25, 1975 |NVENTOR(S) I HORST WURSCHER; ROLF BLASS; OSKAR BECKER It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
"trajects" column 4, line 5, should be strokescolumn 4, Claim 2, line 1, "claim 2" should be claim 1-- Engnecl and Sealed this twenty-fourth Day Of February 1976 [SEAL] Attest.
RUTH C. MASON Arresting Officer