Abstract:
An electrical key switch provides a sensing of inserted keys and an ejector mechanism preventing parking of the key in a partially inserted position within the key switch.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to electrical switches and in particular to an electrical switch having a key lock and suitable for certain override applications. 
   In certain applications, for example, those which provide manual override of machine guard features, it is desirable to have an override switch that may be locked against use by all but a single individual using a key or the like. 
   With any key switch, there is a risk that the key will be left in the lock eliminating its security. 
   BRIEF SUMMARY OF THE INVENTION 
   The present invention provides an electrical key switch that may sense the presence of a key within the switch. A key ejector, incorporated into the switch, prevents defeating of the key sensor; that is, “parking” the key or partially inserting the key into the key slot enough to hold the key in place but not to activate the sensing switch is avoided. 
   Specifically, in one embodiment, the invention provides an electrical key switch having a housing attachable to a support, and a key mechanism receiving a key within a key slot to allow rotation of the key mechanism with respect to the housing. At least one electrical switch element communicates with the key mechanism to switch state with rotation with the key mechanism and an ejector ejects the key from the key slot absent a countervailing pressure on the key holding the key within the key slot. 
   Thus it is one object of at least one embodiment of the invention to provide an electrical switch which reduces the possibility of the key being forgotten or “parked” in the lock. 
   The electrical key switch may provide a second electrical switch element communicating with the key mechanism to change state when a key is inserted in the key slot. 
   It is thus another object of at least one embodiment of the invention to provide a method of electrically sensing the key in the key slot so as to respond appropriately when the key is left in the key slot for too great a length of time. 
   The ejector may be a shaft passing along the key slot to be displaced by a key inserted into the key slot to activate the second electrical element. 
   It is thus another object of at least one embodiment of the invention to provide a simple mechanism that serves both as a sensor and ejector of the key. 
   The shaft may be hardened steel. 
   It is thus another object of at least one embodiment of the invention to use a simple shape that may be easily fabricated out of hardened steel or other similar material providing stiffness and strength. 
   The shaft may be positioned along an axis of rotation of a key mechanism to maintain constant axial alignment with respect to the housing during rotation of the key mechanism. 
   It is thus another object of at least one embodiment of the invention to provide an ejector that may remain substantially aligned with a non-rotating electrical switch element to activate the electrical switch element at a variety of different rotary positions. 
   The shaft may extend rearwardly from the key slot with respect to an opening of the key slot through which the key is inserted to activate the electrical switch element. 
   It is thus another object of at least one embodiment of the invention to provide a mechanism in which the key-sensing switch element may be aligned with the key slot to provide a narrow profile switch element fitting in a standard panel area. 
   The second electrical switch element may be a set of contacts with a travel less than a length of the key slot and further include a spacer block spacing the contacts away from the key slot by an amount at least equal to a difference of the length of the key slot and the travel of the contacts. 
   Thus it is another object of at least one embodiment of the invention to provide a simple mechanical interface between the ejector shaft which must travel the full length of the key slot to fully eject the key, and the switch which may have a relatively short operator throw. 
   The housing may include releasable fittings allowing assembly of different combinations of modular contact blocks to the key mechanism including at least one contact block aligned with an axis of rotation of the key mechanism and the spacer may be received by the releasable fitting. 
   Thus it is one object of at least one embodiment of the invention to provide a mechanism that may be easily integrated with standard multi-application key switches that are assembled out of standard modular blocks. 
   The ejector shaft may have a coaxial helical extension spring biasing the shaft into the key slot. 
   It is thus another object of at least one embodiment of the invention to provide an extremely compact mechanism for ejecting the key. 
   The ejector may provide an average ejecting force on a key inserted into the key of a key slot of at least one half pound. 
   Thus it is another object of at least one embodiment of the invention to provide a large ejection force to reduce the chance of a key remaining inadvertently in the key slot. 
   The key mechanism may include a blocking structure allowing insertion of the key into or removal of the key from the slot only when the key mechanism is in a first rotative position and the key mechanism may rotate to a second position when the key is in the key slot. 
   Thus it is an object of at least one embodiment of the invention to provide an option for the key to be retained in the key slot when in use to prevent the user from having to hold the key when the switch is being activated. 
   The key mechanism may be spring biased to return to the first rotative position. Alternatively, the key mechanism may not be spring biased so that it remains stably in either the first or second rotative position. 
   Thus it is another object of at least one embodiment of the invention to provide a variety of different modes of operation of the key switch. 
   The key mechanism may be a pin tumbler/cylinder lock. 
   Thus it is another object of at least one embodiment of the invention to provide a simple mechanism that works with standard and readily available lock assemblies. 
   These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a modular electric key switch providing one embodiment of the present invention showing the rotative positions of the cylinder and rear-attached modular contact assemblies; 
       FIG. 2  is a cross-sectional view along  2 — 2  of  FIG. 1  showing an internal ejector shaft within the cylinder of the key switch as may move rearward to close contacts indicating a key has been inserted in the key switch; 
       FIG. 3  is cross-sectional view along lines  3 — 3  of  FIG. 1  showing an internal cam mechanism for activating modular contact assemblies with rotation of the key; 
       FIG. 4  is a partial, fragmentary perspective view of a rearward portion of the lock cylinder showing its engagement with a helical extension spring used with the ejector shaft; and 
       FIG. 5  is a cross sectional view along line  5 — 5  of  FIG. 1  showing the retention of the key by tumblers when the key switch is activated and showing an optional return spring. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring now to  FIG. 1 , an electrical key switch  10  of the present invention provides a front housing  12  having an escutcheon  14  surrounding a lock cylinder  16  extending along a cylinder axis  20  from a front face of the front housing  12 . The front housing  12  may be attached to a panel or the like (not shown), for example, captured between a front face of the housing  12  and the escutcheon  14  as is generally understood in the art. 
   The lock cylinder  16  includes a key slot  18  extending along the cylinder axis  20 . A blade  22  of a key  24  may be inserted into the key slot  18  when the cylinder  16  is in an insertion orientation as shown in  FIG. 1 . Once the key  24  is inserted, the key  24  may be rotated to the right or to the left about the cylinder axis  20  to activation positions. As will be described further below, turning the key  24  in the key slot  18  activates contact blocks  26  and  28  positioned at left and right edges of a rear face of the housing  12 . The contact blocks  26  and  28  contain contacts (not shown in  FIG. 1 ) which change state (i.e., open or close) depending on the rotative position on the key  24 . 
   A spacer block  32  positioned between the contact blocks  26  and  28 , centered on rear face of the housing  12 , supports a third contact block  30 . 
   Referring also now to  FIG. 2 , the lock cylinder  16  may rotate within a hull  34  about the cylinder axis  20 . A series of radial bores  37  pass through the cylinder  16  and hull  34  to align when the cylinder  16  is in the insertion position allowing movement within the bores  37  of lower key pins  36  and upper drive pins  38  under the influence of compression springs  40  held in the hull  34 . The structure is that of a standard pin-tumbler cylinder lock well known in the art. 
   As will be understood to one of ordinary skill in the art when a blade  22  of the key  24  is inserted in the key slot  18 , notches  42  in the upper edge of the blade  22  cause the lower key pins  36  and upper drive pins  38  to move up and down so as to align their interfaces along a shear surface  44  between the cylinder  16  and the hull  34 . This alignment allows the cylinder  16  to rotate under the influence of the key  24  with respect to the hull  34  to the activation positions. 
   In the present invention, the key slot  18  receives an ejector shaft  48  extending along axis  20  through a rear of the cylinder  16  opposite the front of the cylinder  16  through which the blade  22  is inserted in the key slot  18 . The shaft  48  is preferably hardened steel to ensure that the shaft  48  will resist deformation by the softer brass blade  22  of the key  24 . By using a simple cylindrical shaft  48 , complex machining operations on hardened steel are not required. 
   The shaft  48 , prior to insertion of the blade  22  of the key  24  occupies the full length of the key slot  18  along axis  20 . In this state, the shaft  48  continues through the rear of the cylinder  16  into the housing  12  terminating at a rear button  50  approximately even with the rear surface of the housing  12 . 
   Referring now to  FIGS. 2 and 4 , the shaft  48  is free to move along axis  20  through a journal  56  formed by the rear face of the cylinder  16 , but is biased into the key slot  18  by a helical extension spring  52 . The cylinder  16  and journal  56  may be of brass or other easily machinable material that provides for a natural bearing surface for the hardened and polished steel shaft  48 . The outer circumference of the journal  56  has threads  58  of a pitch and diameter suitable to receive the wire end of the helical extension spring  52  threaded thereon. Likewise the rear button  50  of the shaft  48  has threads  60  similarly receiving the opposite end of the helical extension spring  52 . In this manner, the helical extension spring  52  is retained coaxially about the shaft  48  to occupy very little additional space. It will be recognized, however, that other methods of biasing the shaft  48 , including leaf springs and or the springs associated with electrical contacts of the third contact block  30 , described below, may also be used. 
   Referring again to  FIG. 2 , each of the contact blocks  26  and  28  and the spacer block  32  have opposed snap hooks  62  extending forward along axis  20  from upper and lower edges of their front faces. These snap hooks  62  may be received by corresponding hook holds  64  formed in the abutting rear face of the housing  12 . Thus, contact blocks  26  and  28  may be snapped to the rear face of the front housing  12 . Spacer block  32  includes corresponding hook holds  66  in its rear face that may receive the snap hooks  62  of the contact block  30 . In this way, contact block  30  may be snapped to spacer block  32  which may be snapped to the rear of housing  12  so that contact block  30  is spaced away from the housing  12  by the width of the spacer block  32 . 
   The snap hooks  62  are preferably molded as part of the housing of the contact blocks  26 ,  28 , and  30  and spacer block  32  to flex outward and then to engage the holds  66  to firmly retain the assembled parts together. Modular switches of this design providing contact blocks  26 ,  28 , and  30 , but not spacer block  32  are commercially available from the Rockwell Automation Company. 
   Contact block  30  like contact blocks  26  and  28  includes an axially extending operator  68  activated by pressing of the operator  68  inward along axis  20  by a operator activation distance  70 . The operator  68  connects to a movable contact set  72  which, with motion of the operators  68  by activation distance  70 , causes the movable contact set  72  to bridge a stationary contact set  74  against the returning bias of compressing spring  78 . The stationary contact set  74  may be connected through terminals or the like to external wiring  75  as shown in  FIG. 1 . As shown, the contact set  72  and contact set  74  are normally open, however, it will be understood to those of ordinary skill in the art that normally closed contacts may also be used. In an alternative embodiment, the contact sets  72  and  74  may be replaced with other equivalent switch elements including proximity detectors, Hall effect switches, and the like. 
   Referring to  FIG. 3 , when the key  24  is fully inserted with its blade  22  extending a full length  19  of the key slot  18 , the tip of the blade  22  presses the shaft  48  rearward through the journal  56  to pass through a hollow bore within the spacer block  32  so that the rear button  50  of the shaft  48  compresses the operator  68  of the contact block  30  by the activation distance  70 . While the full length  19  of the key slot  18  is greater than the activation distance  70 , the spacer block  32  absorbs the extra distance of the movement of the shaft  48  providing compatibility between the desires of moving the operator  68  and activation distance  70  without significant over travel and having the key  24  stay in contact with the shaft  48  as it travels the full length  19  of the key slot  18 . 
   The helical extension spring  52  provides, when the shaft  48  is fully rearward in the key slot  18 , a spring force of as much as one pound. Thus an average ejection force of about a half-pound is provided to the key  24  as it is inserted 
   This force is sufficient to move the key  24  against the friction of the key slot  18  and the lower key pins  36  and fully eject the key  24  out of the key slot  18  when the key  24  is released. 
   Referring still to  FIG. 3 , when the cylinder  16  is rotated to either activation position from the insertion position, the shaft  48 , as aligned with axis  20 , remains aligned with the operator  68  of the stationary contact block  30 . 
   The rotation of the cylinder  16  from the insertion position to either activation position moves a cam disk  46  and cam surfaces  80  which may selectively compress the operator  68  of contact block  26  or contact block  28  depending on the direction of rotation of the key. Optional follower blocks (not shown) riding on the cam disk  46  may be interposed between the operators  68  and the cam surfaces  80 . Switches of this type having cam disks  46  are well known in the art. The contact block  26  or  28  provide signals indicating key rotation, independent from a signal produced by contact blocks  30 , the latter which indicates the presence of the key  24  in the electrical key switch  10  regardless of position of the cylinder  16 . 
   Referring now to  FIG. 5  when the blade  22  of the key  24  is fully inserted in the key slot  18  of the cylinder  16  and rotated to a first activation position, the lower key pins  36  are trapped beneath the shear surface  44  thus pinning the blade  22  within the key slot  18  preventing its ejection under the influence of the shaft  48 . In this manner, after rotation of the cylinder  16 , ejection of the key  24  is prevented and activation of the electrical key switch  10  does not require continued holding of the key  24 . 
   Optionally and alternatively, the cylinder  16  may be subject to rotational bias by a spring  86  to cause it to naturally rotate back to the insertion position  89  from one or either activation position  88  in either a counter clockwise or clockwise direction. When such a spring  86  is provided, the operator must retain a grasp on the key  24  or it is ejected as the cylinder  16  returns to the insertion position  89 . 
   It is specifically intended that the present invention not be limited to the embodiments and illustrations contained herein, but include modified forms of those embodiments including portions of the embodiments and combinations of elements of different embodiments as come within the scope of the following claims.