Abstract:
A mounting arrangement includes a first mounting that is attachable to a first support structure and configured to cooperate with one of a safety switch and a safety switch actuator and a second mounting configured to cooperate with the other of the safety switch and the safety switch actuator. The first and second mountings provide variable guided interaction between the first and second mountings and thereby provided variable guided interaction between the safety switch and the safety switch actuator.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to Great Britain patent application 0700146.4 filed on Jan. 5, 2007 and the disclosure of which is incorporated herein. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a mounting arrangement for a safety switch and a safety switch actuator. 
     Safety switches are well known, and are typically used to prevent access to, for example, electromechanical machinery when that machinery is in operation. In a conventional arrangement, the safety switch is mounted on a door post of a machinery guard, and an actuator for the safety switch is mounted on a corresponding door. When the door is closed, the actuator engages with the safety switch, which in turn closes a set of electrical contacts which allow power to be supplied to the machinery. This arrangement ensures that power can only be supplied to the machinery when the guard door is shut. When the guard door is opened, the actuator disengages from the safety switch, thereby opening the electrical contacts and cutting off the supply of power to the machinery. 
     A typical safety switch comprises a housing, in which is provided a set of contacts that are generally fixed in position relative to the housing. An axially slideable plunger is mounted inside the housing, and is moveable relative to the housing. The plunger is provided with another set of contacts. The plunger is biased towards a cam arrangement by a spring. The actuator mentioned above is arranged to engage with the cam arrangement. 
     In many safety switches, if the actuator is not engaged with the cam arrangement (i.e. if the actuator is not engaged with the safety switch), the cam arrangement is arranged to prevent the contacts on the plunger coming into contact with the contacts of the housing by preventing movement of the plunger (i.e. the plunger is kept in a first plunger position). By preventing the contacts from contacting one another, the switch cannot conduct electricity while the actuator is not engaged with the cam arrangement. 
     Bringing the actuator into engagement with the cam arrangement causes the cam arrangement to rotate, which in turn causes the plunger (which is biased toward the cam arrangement) to move into a notch provided in the cam arrangement. Such a configuration provides a plunger that is moveable between the first plunger position and a second plunger position. When the plunger moves into the notch, the contacts on the plunger are brought into contact with the contacts of the housing, allowing electricity to flow through the safety switch. 
     In order to ensure that the actuator is brought into engagement with the cam arrangement, the actuator must be directed through an opening in the housing of the safety switch. If for some reason the actuator is misaligned with the opening, when the door to the machinery guard is closed the actuator may not pass through the opening in the housing, but hit the housing. If the actuator hits the housing, one or both of the housing and the actuator may become damaged. Alignment of the actuator with respect to the opening of the housing can be made even more difficult if the door post to which the safety switch is mounted is vibrating, or if the door to which the actuator is mounted is vibrating. Misalignment of the actuator with the opening in the housing may also occur due to wear and tear of the door of the machinery guard. For example, the weight of the door to the machinery guard may cause the door to, over time, move in a vertical direction causing misalignment of the actuator relative to the opening in the housing. 
     Even when the actuator is satisfactorily aligned with the opening of the housing, and the actuator is brought into engagement with the cam arrangement of the safety switch, problems can still be encountered. Problems can occur if there is relative movement between the door to which the actuator is mounted and the door post to which the safety switch is mounted. For example, if the door moves vertically relative to the safety switch, the actuator may become bent, and/or the safety switch may be damaged or removed from the door post. In another example, if the door moves away from the door post due to vibrations caused by operating machinery, the actuator may be disengaged from the cam arrangement of the safety switch. Disengagement of the actuator from the safety switch causes the safety switch to turn off the supply of power to the machinery within the machinery guard. It is possible that, due to vibrations, this process of cutting off the supply of power to the machinery may be repetitious, i.e. following the cycle of the vibrations (e.g. the power supply to the machinery may ‘flutter’). Even if the supply of power to the machinery is not interrupted, the movement of the actuator may cause wear on the cam arrangement, and other parts of the safety switch. 
     It is therefore desired to provide a reliable safety switch mechanism that has generally repeatable operating conditions and which overcomes one or more of these or other disadvantages. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention, there is provided a mounting arrangement for use with a safety switch and a safety switch actuator. The mounting arrangement includes a first mounting attachable to a first support structure and arranged to be located adjacent to or attached to the safety switch. The first mounting is provided with a tapered aperture which tapers inwardly toward a channel located in the first mounting. The mounting arrangement includes a second mounting that includes an elongate guiding element configured to be received in the channel of the first mounting. A surface on which the safety switch actuator is attachable, such that the actuator and elongate guiding element extend in the same direction, parallel to one another and away from the mounting. The mounting arrangement includes a resilient member which attaches the second mounting to a second support structure. 
     Preferably, an end of the elongate guiding element that is to be received by the channel tapers inward. Preferably, the resilient member is a spring. Preferably, the spring is a helical spring. 
     Preferably, the mounting arrangement includes a catch mechanism. More preferably, the catch mechanism includes a snap-fit arrangement. Preferably, a catch is provided on the elongate guiding element. Preferably, a catch receiving portion is provided in a surface that defines a channel for receiving the catch of the elongate guiding element. Alternatively, a catch may be provided in the channel. In this alternative, the guiding element may include a catch receiving portion for receiving the catch in the channel. In either alternative, preferably the catch comprises a biasing element. Preferably, the catch further comprises a catching member connected to the biasing element. The catching member maybe a ball. Preferably, the catch receiving portion is a groove. 
     Preferably, the first mounting and second mounting are shaped such that, when the safety switch actuator is brought into engagement with the safety switch, the first mounting comes into contact with the second mounting. 
     The second mounting may be provided with a safety switch actuator. 
     The first support structure may be one of a group that includes a door post, a gate post, and a fence post. The second support structure may be one of a group including a door and a gate. 
     Alternatively, the second support structure may be one of a door post, a gate post, or a fence post. The first support structure may be one of a door or a gate. 
     According to a second aspect of the present invention, there is provided a mounting arrangement for use with a safety switch and a safety switch actuator. The mounting arrangement includes a first mounting and a second mounting. The first mounting is attachable to a first support structure and is arranged to be located adjacent to, or attached to, the safety switch. The first mounting is provided with an elongate guiding element that extends away from the first mounting. The second mounting includes a tapered aperture which tapers inwardly toward a channel located in the second mounting. The channel is configured to receive the elongate guiding element of the first mounting. The safety switch actuator is attachable on a surface such that the actuator and elongate guiding element extend in the same direction, parallel to one another and away from the mounting. The second mounting is attachable to a second support via a resilient member. 
     Preferably, an end of the elongate guiding element that is to be received by the channel tapers inwardly. Preferably, the resilient member is a spring. Preferably, the spring is a helical spring. 
     Preferably, the mounting arrangement includes a catch mechanism. Preferably, the catch mechanism is a snap-fit arrangement. Preferably, a catch is provided on the elongate guiding element. Preferably, a catch receiving portion is provided in a surface that defines the channel, for receiving the catch of the elongate guiding element. Alternatively, a catch may be provided in the channel. In this alternative, a catch receiving portion may be provided in the guiding element, for receiving the catch in the channel. In either alternative, preferably the catch comprises a biasing element. Preferably, the catch further comprises a catching member connected to the biasing element. The catching member may be a ball. Preferably, the catch receiving portion is a groove. 
     Preferably, the first mounting and second mounting are shaped such that, when the safety switch actuator is brought into engagement with the safety switch, the first mounting comes into contact with the second mounting. The second mounting may be provided with a safety switch actuator. One of the first support structure and the second support structure may be one of a door post, a gate post, and a fence post. The other of the first support structure and the second support structure may be one of a door and a gate. 
     These and other aspects and advantages of the present invention will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following description, while indicating preferred embodiments of the present invention, is given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
         FIG. 1  depicts a safety switch for use with the mountings of the present invention; 
         FIGS. 2   a  and  2   b  depict a cam arrangement of the safety switch of  FIG. 1 ; 
         FIG. 3  depicts operating principles of the safety switch of  FIG. 1 ; 
         FIGS. 4   a  and  4   b  depict use of the safety switch of  FIG. 1 ; and 
         FIGS. 5 ,  6  and  7  depict mountings according to embodiments of the present invention, for use with a safety switch, and use of those mountings. 
     
    
    
     In describing the preferred embodiment of the invention which is illustrated in the drawings, specific terminology will be resorted to for the sake of clarity. However, it is not intended that the invention be limited to the specific terms so selected and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. For example, the word connected, attached, or terms similar thereto are often used. They are not limited to direct connection but include connection through other elements where such connection is recognized as being equivalent by those skilled in the art. 
     DETAILED DESCRIPTION 
       FIG. 1  depicts a plan view of a prior art safety switch. The safety switch comprises a two-part housing. One part of the housing defines a main body  1  of the safety switch. Mounted within the body  1  are electrical contacts which are fixed in position relative to the body  1 . The contacts consist of two fixed safety contacts  2  and a fixed auxiliary contact  3 . Also mounted within the body  1  is a plunger  4  which is slideable relative to the body  1  in an axial direction. The plunger  4  is provided with a plurality of contacts which extend through the plunger and which are moveable relative to the plunger  4 . The moveable contacts include two moveable safety contacts  2   a  and a moveable auxiliary contact  3   a . By moving the plunger  4 , the moveable contacts  3   a ,  4   a  can be brought into contact (and thus electrical connection) with the fixed contacts  3 ,  4  of the safety switch. The plunger  4  is also provided with a moveable insulating barrier  11  which serves to provide additional electrical insulation for some of the moveable safety contacts  2   a.    
     The plunger  4  is biased by a spring  5  towards a second part of the housing, which forms a head  6  of the safety switch. The head  6  of the safety switch is provided with a rotatable cam arrangement  7 . The cam arrangement  7  is arranged to receive and engage with an actuator  10  ( FIGS. 2   a  and  2   b ). Engagement or disengagement of the actuator with the cam arrangement  7  causes the cam arrangement  7  to rotate, which in turn causes axial movement of the plunger  4  within the body  1  of the safety switch. 
       FIGS. 2   a  and  2   b  illustrate the interaction between the cam arrangement  7  and the plunger  4  in more detail.  FIG. 2   a  shows that the cam arrangement  7  defines a cam surface  8 . The cam surface  8  is provided with an indentation  8   a  which is (upon rotation of the cam arrangement  7 ) arranged to receive the plunger  4 . The cam arrangement  7  is also provided with a notch  9  for receiving and engaging with an actuator. It can be seen from  FIG. 2   a  that, when no actuator is brought into engagement with the cam arrangement  7 , the cam arrangement pushes back against the plunger  4  (which is biased toward the cam arrangement  7  by the spring  5 ) and prevents the plunger  4  from moving towards the cam arrangement  7 . The plunger  4  is said to be in a first plunger position  12 . 
     It can be seen from  FIG. 1  (in combination with  FIG. 2   a ) that when no actuator is brought into engagement with the cam arrangement  7  all of the fixed safety contacts  2  of the body  1  of the safety switch are kept apart from all of the moveable safety contacts  2   a  of the plunger  4 . Thus, when no actuator is engaged with the cam arrangement  7 , the safety contacts  2 ,  2   a  are not in electrical connection with each other, which prevents the safety switch from conducting electricity (to, for example, electrically powered machinery with a machine guard). When no actuator is engaged, the auxiliary contacts  3 ,  3   a  are in contact with each other, which may allow an auxiliary power supply to be supplied to the switch (for example, to power a light which indicates that no actuator has been engaged with the switch). 
       FIG. 2   b  depicts an actuator  10  that has been brought into engagement with the cam arrangement  7 . It can be seen from  FIG. 2   b  that when the actuator  10  has been brought into engagement with the cam arrangement  7 , the cam arrangement  7  and therefore cam surface  8  is arranged to rotate in a clockwise direction. Rotation of the cam arrangement  7  causes the indentation  8   a  in the cam surface  8  to be brought into alignment with the plunger  4 . As the indentation  8   a  moves into alignment with the plunger  4 , which is biased by the spring  5 , the plunger  4  moves towards the right of  FIG. 2   b . The plunger  4  is said to be in a second plunger position  14 . 
       FIG. 3  shows the safety switch with an end cap  6   a  enclosing the head  6  of the safety switch. The end cap  6   a  protects the cam arrangement  7  from damage, dust etc. and makes the safety switch appear more aesthetically pleasing. It can be seen from  FIG. 3  that when the actuator  10  is brought into engagement with the cam arrangement  7 , the plunger  4  moves towards the right of  FIG. 3 . When the plunger  4  moves to the right, all of the moveable safety contacts  2   a  are brought into electrical connection with the fixed safety contacts  2  of the body  1  of the safety switch. When all of the safety contacts  2 ,  2   a  are brought into electrical connection with each other, the switch is capable of conducting electricity (to, for example, electrically powered machinery with a machine guard). The safety switch is configured such that if one or more of the safety contacts  2 ,  2   a  are not in electrical connection with each other, the switch is incapable of conducting electricity. 
       FIG. 4   a  illustrates the safety switch of  FIG. 1  mounted to a door post  20  of a machinery guard. The actuator  10  of  FIGS. 2 and 3  is shown mounted on a door  21  of the machinery guard. The end cap  6   a  of the safety switch is provided with an opening  6   b  (e.g. a slot), through which the actuator  10  may pass and engage with the cam arrangement located within the end cap  6   a . For clarity, the cam arrangement is not shown in this Figure. The actuator  10  is mounted on the door  21  in direct alignment with the opening  6   b  of the safety switch. When the door  21  to the machinery guard is closed, a protruding part  10   a  of the actuator  10  passes through the opening  6   b  of a safety switch, and into engagement with the cam arrangement to allow the safety switch to conduct electricity. 
       FIG. 4   b  shows the door  21  in a closed position. It can be seen that the protruding part  10   a  of the actuator  10  has passed through the opening  6   b  and into engagement with the cam arrangement of the safety switch  1 . 
     There are a number of problems with the arrangement illustrated in  FIGS. 4   a  and  4   b . For example, if the actuator  10  is not correctly aligned with the opening  6   b  of the safety switch, the actuator  10  will hit the housing  1  of the safety switch when the door  21  to the machinery guard is closed. The protruding part  10   a  of the actuator  10  may damage the housing of the safety switch, or even the internal workings of the safety switch (for example, the cam arrangement). Actuator  10  may also become damaged. Even if the actuator  10  is only slightly misaligned with the centre of the opening  6   b , such that the actuator  10  can still be brought into engagement with the cam arrangement of the safety switch, the slight misalignment may nevertheless cause repetitive wear of the housing  1  of the safety switch, or even its internal workings. 
     Even if the actuator  10  is correctly aligned with the opening  6   b  of the safety switch, there may still be problems with the mounting arrangement shown in  FIGS. 4   a  and  4   b . For example, if the door  21  to the machine guard is closed with sufficient force, parts of the door  21 , or even the actuator  10 , can hit the safety switch  1  and damage the safety switch. If the actuator  10  has been brought into engagement with the cam arrangement of the safety switch, the actuator  10  can become damaged (e.g. bent) if the door  21  of the machinery guard moves in a vertical or horizontal direction. If there is relative movement between the actuator  10  and the safety switch, for example due to vibrations of the door  21 , the actuator  10  may repeatedly hit or move the cam arrangement or housing  1  of the safety switch, which can cause damage to these features. It is possible that even slight movement of the actuator  10  towards and away from the safety switch (caused, for example, by vibration of the door  21 ) can cause the cam arrangement to move, which may cause the contacts within the safety switch to undesirably open or close. If the contacts open and close repeatedly (for example, due to vibration of the actuator), the power supply to the machinery within the machinery guard will be interrupted repeatedly. Such repetitious interruption of the power supply may damage the machinery and/or cause the machinery to operate in a non-continuous, and likely undesirable, manner. 
       FIGS. 5   a  to  5   c  illustrate a safety switch and actuator arrangement according to an embodiment of the present invention.  FIG. 5   a  illustrates a safety switch  1  and actuator  10  constructed generally in accordance with the description provided above. However, in contrast to the arrangement of  FIGS. 4   a  and  4   b , the safety switch and actuator  10  are not attached directly to the door post  20  and door  21  respectively, but instead attached to the door post  20  and door  21  via mountings  30 ,  40 . The safety switch  1  is attached to the door post  20  via a first mounting  30  (hereinafter referred to as “the safety switch mounting  30 ”). The actuator  10  is attached to the door  21  via a second mounting  40  (hereinafter referred to as “the actuator mounting  40 ”). 
     The safety switch mounting  30  is substantially L-shaped. The safety switch mounting  30  is shaped to accommodate a safety switch, which sits in a corner formed by the L-shaped safety switch mounting  30 . The back-side of the L-shaped safety switch mounting  30  is attached to the door post  20 , and is thinner than the bottom of the L-shaped safety switch mounting  30 . The bottom of the L-shaped safety switch mounting  30  is provided with a tapered aperture  31 . The tapered aperture  31  tapers inwards towards a channel  32 . The channel  32  extends away from the tapered aperture  31  towards the back-side of the L-shaped safety switch mounting  30 . At an end of the channel  32 , near the back of the L-shaped safety switch mounting  30  (i.e. away from the tapered aperture  31 ), there is provided an annular groove  33  which extends about the circumference of the channel  32 . The lower part, or base, of the L-shaped safety switch mounting  30  is dimensioned such that it is approximately equal to the depth of the safety switch  1  (i.e. the distance which the safety switch  1  extends away from the door post  20 ), or such that it slightly exceeds the depth of the safety switch  1 . 
     The safety switch mounting  30  may be made from any appropriate materials. For example, the safety switch mounting  30  may be made from metal, plastic or any durable material. 
     The actuator mounting  40  comprises a first part  41  which is connected to a second part  42  by a helical spring  43  and a steel cable  50  which extends through the helical spring  43 . The second part  42  of the actuator mounting  40  is attached to the door  21 , such that the first part  41  of the actuator mounting  40  extends towards the safety switch mounting  30 . The first part  41  of the actuator mounting  40  is provided with an elongate guiding element  44 . The elongate guiding element  44  is shaped to conform to the inner surfaces of the tapered aperture  31  and channel  32  of the safety switch mounting  30 . An end of the elongate guiding element  44  is shaped to taper to a point, to aid engagement with the tapered aperture  31  of the safety switch mounting (described in more detail below). The elongate guiding element  44  is also provided with a catch  45  which is positioned and shaped to engage with the groove  33  of the safety switch mounting  30 . It can be seen from  FIG. 5   a  that a section of the first part  41  of the actuator mounting  40  extends perpendicularly away from the elongate guiding element  44 . Attached to this section is the actuator  10 , the actuator  10  being positioned such that the actuator  10  and elongate guiding element  44  both extend parallel to one another and towards the safety switch mounting  30 . The elongate guiding element  44  extends further away from the first part  41  than does the actuator  10 . 
     The first part  41  and second part  42  of the actuator mounting  40  may be made from any suitable material. For example, the first part  41  and second part  42  of the actuator mounting  40  may be made from metal, plastic or any durable material. 
     In order to bring the actuator  10  into engagement with the safety switch  1 , the door  21  is moved towards the safety switch  1  in the actions shown by the arrow  51 .  FIG. 5   b  depicts the situation when the actuator  10  has been brought into engagement with the safety switch  1 . It can be seen that not only is the actuator  10  engaged with the safety switch  1 , but also that the elongate guiding element  44  is engaged with the channel  32  and tapered aperture  31  of the safety switch mounting  30 . As shown, the separation of the actuator  10  and the elongate guiding element  44  is chosen such that if the elongate guiding element  44  is received by the guide or channel  32  and tapered aperture  31  of the safety switch mounting  30 , the actuator  10  of the actuator mounting  40  will also be received by the opening  6   b  in the safety switch  1 . Since the elongate guiding element  44  extends further away from the first part  41  than does the actuator  10 , if the elongate guiding element  44  is brought into engagement with the channel  32  and the tapered aperture  31  of the safety switch mounting  30 , the actuator  10  of the actuator mounting  40  will also be brought into engagement with the opening  6   b  in the safety switch  1 . This is described in more detail below. 
     If for some reason the actuator  10  is not accurately aligned with the opening  6   b  in the safety switch  1  before the door  21  to the machinery guard is closed, the actuator would, in prior art arrangements, hit the body of the safety switch  1 . However, using the arrangement of the present invention, this situation is avoided. When arranged according to embodiments of the present invention, if the actuator  10  is slightly misaligned with the opening  6   b , the elongate guiding element  44  will also be slightly misaligned with respect to the channel  32 . It can be seen from  FIGS. 5   a  and  5   b  that the elongate guiding element  44  extends further in the direction of the safety switch mounting  30  than does the actuator  10 . The elongate guiding element  44  is therefore brought into engagement with the tapered aperture  31  and channel  32  of the safety switch mounting  30  before the actuator  10  has had a chance to hit the safety switch  1  (or alternatively, before the actuator  10  has been brought into engagement with the safety switch  1 ). If the actuator  10  and therefore elongate guiding element  44  are slightly misaligned, the elongate guiding element  44  will be guided into the channel  32  by the tapered aperture  31 , which will in turn cause the actuator  10  to be accurately aligned and brought into engagement with the opening  6   b  in the safety switch  1 . The spring  43  of the actuator mounting  40  allows movement of the first part  41  of the actuator mounting  40 , and therefore movement of the actuator  10  and elongate guiding element  44 . 
     If the door  21  to the machinery guard is closed with excessive force, it can be seen from  FIG. 5   b  that this force will be dissipated through the actuator mounting  40  and safety switch mounting  30 . This is because the safety switch  1  is accommodated in the L-shaped safety switch mounting  30 , where the lower part of the L-shaped safety switch mounting  30  extends beyond the depth of the safety switch  1 . Therefore, when the door  21  to the machinery guard is closed, the actuator mounting  40  will come into contact with the lower part of the safety switch mounting  30 , and not the safety switch  1  itself. 
     In prior art arrangements, if the door to the machinery guard moves in a vertical direction, the actuator and/or safety switch may become damaged (e.g. the actuator may bend). This is not the case with the arrangement in accordance with embodiments of the present invention. As can be seen in  FIG. 5   c , if the door  21  to the machinery guard moves in a vertical direction, this vertical movement is taken up by the spring  43 , which prevents the actuator  10  from bending. If vertical movement of the door  21  is temporary, the spring  43  will return to its original shape when the door  21  moves to its original position. If movement of the door  21  in the vertical direction is permanent, the actuator  10  can still be accurately brought into engagement with the safety switch due to the nature of the tapered aperture  31  of the safety switch mounting  30 , as described in relation to  FIG. 5   b  above. 
     In prior art arrangements, if the door to the machinery guard moves towards and away from the safety switch, the safety switch and/or the actuator may become damaged, or alternatively the power supply to the machinery within the machine guard may be repeatedly interrupted. This is not the case with the arrangement according to embodiments of the present invention. In some prior art safety switches, two set of contacts are employed and are monitored by monitoring apparatus. If one of the sets of contacts fails (e.g. short circuits, or becomes welded together) the monitoring apparatus detects this, and prevents the safety switch from conducting electricity until, for example, the switch is inspected and possible reset or fixed. In prior art safety switches, movement of the door to the machinery guard towards and away from the safety switch can cause one or both of the contacts to move at different times. The monitoring apparatus may deem this to be a fault in one or both contacts, and prevent the safety switch from conducting electricity. This is sometimes referred to as false-tripping of the safety switch. This scenario is avoided using the arrangement according to embodiments of the present invention. Referring to  FIG. 6   a , if the door  21  repeatedly moves towards and away from the safety switch  1 , this movement will be taken up by the spring  43 , and will not cause movement of the actuator  10 . As can be seen in  FIG. 6   b , only when sufficient force is applied to the door  21  to overcome the catch  45  is the elongate guiding element  44  removed from the channel  32 , and also the actuator  10  disengaged from the safety switch  1 . Therefore, the actuator  10  may not be slightly disengaged from the safety switch  1 , or repeatedly engaged and disengaged, but can be only be disengaged in a single quick, sharp motion when sufficient force is applied to the door  21  to overcome the catch  45 . 
     The steel cable  50  shown in the Figures may act in co-operation with the spring  43 , or as a backup to the spring  43 . If the spring  43  is not sufficiently stiff (i.e. if the spring is not strong enough, for example due to wear and tear), movement of the door  21  away from the door post  20  may not cause the elongate guiding element  44  to be removed from the channel  32 . Instead, the spring  43  may become stretched. However, even if this happens, the steel cable  50  will, when pulled taught, remove the elongate guiding element  44  from the channel  32 , and also disengage the actuator  10  from the safety switch  1 , in a single quick, sharp motion. Similarly, even if the spring  43  should break (e.g., from wear and tear), the steel cable  50  ensures that the elongate guiding element  44  may be removed from the channel  32 , and the actuator  10  disengaged from the safety switch  1 . In summary, the optional steel cable  50  increases the surety that, by opening the door  21  to a sufficient extent and with sufficient force to overcome the catch  45 , the actuator  10  can be withdrawn from the safety switch  1 . If a cable (or any other suitable connector) is employed, it may be made from any suitable material. Preferably the material is relatively inelastic when subject to tensile forces along its length. Preferably, the connector may change shape as the spring  43  expands and contracts, for example coiling or uncoiling. 
     In the embodiments describe above, the elongate guiding element  44  has been described as being part of the actuator mounting  40 , and the channel  32  and tapered aperture  31  as being part of the safety switch mounting  30 . Understandably, and the elongate guiding element  44  could be part of the actuator mounting  34 , and the channel  32  and tapered aperture  31  be part of the actuator mounting  40 . This alternative embodiment is shown in  FIG. 7 . The arrangement shown in  FIG. 7  may have all the features (and variations on those features) described above and below. 
     In the embodiments describe above, the helical spring  43  has been described as the element which allows movement of the first part  41  of the actuator mounting  40 . Understandably, a spring and a coil spring, are only examples of a suitable resilient member. For example, in some situations a body of rubber may be sufficiently malleable and elastic to be a suitable replacement for the spring  43 . 
     In the embodiments describe above, the elongate guiding element  44  is kept in the channel  32  during, for example, vibration of the door  21 , due to the incorporation of the catch  45  and groove  33  arrangement. It will be appreciated that this arrangement can be any suitable catching arrangement. For example, the catch  45  may comprise one or more sprung balls which can be moved out of the groove  33  and into the elongate guiding element  44  by subjecting the elongate guiding element  44  to a sufficient force. Preferably, the catching arrangement is arranged such that, when overcome, the elongate guiding element  44  is readily removable from the channel  32 . The catching arrangement is either engaged or disengaged, so that the elongate guiding element  44  can only be removed from the channel in a quick, snap like action such as a catch arrangement that is a snap fit. A catch may be provided on a surface defining the channel, with a catch receiving portion being provided on the elongate guiding element  44 , or vice versa. However, it may be more practical to provide the catch receiving portion (e.g. a groove) inside the channel than it would be to provide a catch (e.g. a biased mechanism of some kind). For example, it may be more difficult to manufacture a mounting having a channel with a catch as compared to a guiding element with a catch. 
     In the embodiments describe above, the safety switch mounting  30  is described as being L-shaped. This allows the safety switch  1  to be attached to the mounting  30 , and the mounting then attached to the door post  20 . This also allows the length or base or bottom of the L-shaped mounting to be dimensioned to extend beyond the depth of the switch, and therefore absorb impacts from the door  21  or the actuator mounting  40 . Understandably, such a construction is merely exemplary and other configurations are readily appreciated. The safety switch mounting  30  may just be a channel  32 , or elongate guiding element  44 , located adjacent to the safety switch  1 . The safety switch mounting  30  may not be attached to the safety switch  1 . Instead of a part of the safety switch mounting  30  extending beyond the depth of the safety switch  1  to absorb impacts from the door  21  (etc.), the actuator mounting  40  and safety switch mounting  30  may, together, be arranged to ensure that the safety switch  1  is not impacted. For example, a part of the actuator mounting  40  may extend further towards the safety switch  1  than is shown in the Figures, therefore negating the need for a part of the safety switch mounting  30  to extend up to or beyond the depth of the safety switch  1 . 
     In the embodiments described above, the L-shaped safety switch mounting  30  is provided with a tapered aperture  31 . The tapered aperture  31  tapers inward towards the channel  32 . If there has been no rotation between the safety switch mounting  30  and the actuator mounting  40 , the tapered aperture  31  guides the elongate guiding element  44  into the channel  32 , which causes the actuator  10  to be brought into engagement with the safety switch. However, it will be appreciated that in some situations, the safety switch mounting  30  and the actuator mounting  40  may be rotated relative to one another. If this happens, the actuator  10  may not be brought into engagement with the safety switch  1  even if the tapered aperture  31  guides the elongate guiding element  44  into the channel  32 —i.e. the actuator  10  may have been rotated out of alignment with the opening  6   b  of the safety switch  1 . Therefore, the elongate guiding element  44  and/or the channel  32  may be shaped to co-operate such that, when engaged with one another, the actuator is (if applicable) rotated into alignment with the opening  6   b  of the safety switch  1 . For example, one or both of the channel  32  and the elongate guiding element  44  may be provided with indexes or channels and/or elongate protrusions which urges the (or a part of the) actuator mounting  40  to rotate to the correct position for engagement with the opening  6   b  of the safety switch  1 . Any suitable arrangement may be used. For example a channel and guide arrangement may be used. Alternatively, the elongate guiding element  44  and channel  32  may be elliptical in cross-section, such that the axes of the ellipses are urged to align when the elongate guiding element  44  is brought into engagement with the channel  32 . Alignment of the elliptical axes will cause the rotation of the actuator mounting to bring the actuator into alignment with the opening of the safety switch  1 . 
     In the embodiments described above, the tapered aperture  31  is described as tapering inwardly toward a channel  32 . The channel shown in the Figures is substantially elongate and straight. It is appreciated that the channel  32  may be any appropriate shape. For example, the channel  32  may also be tapered. The angle at which the channel  32  tapers may match that of the tapered aperture  31 . 
     In the embodiments described above, the safety switch mounting  30  is described as being attached to a door post  20 , and the actuator mounting  40  described as being attached to a door  21 . It is appreciated that, instead, the safety switch mounting  30  maybe attached to the door  21 , and the actuator mounting  40  attached to the door post  20 . Similarly, the safety switch mounting  30  and actuator mounting  40  maybe attached to any suitable support structure. For example, the safety switch mounting  30  and actuator mounting  40  may be attached to any one of a door post, a gate post, a fence post, a door or a gate. The mountings  30 ,  40  may be attached directly to access points on machines or vehicles, or windows in enclosures or buildings. 
     The mounting arrangements discussed above have been described with reference to a safety switch comprising, amongst other elements, a cam arrangement, a plunger, and an elongate key-like actuator engageable with the cam arrangement. It will be appreciated that the mounting arrangements may be used with many other types of safety switches and other switches. For example, the switch may be a non-contact switch. The actuator maybe a magnet or a light source, for example. The present invention is still applicable to such switches. For example, the present invention allows accurate alignment of the actuators, as discussed above. 
     As described above the present invention may be particularly suited to switches which utilise and monitor multiple sets of contacts (e.g. two sets of contacts). The use a mounting arrangement as described above reduces or eliminates the possibility of false-tripping (as described above) occurring. The reduction or elimination of false-tripping may save users of the switches the inconvenience and time of having to repeatedly check and reset the switches. 
     In the embodiments described above, a plurality of safety contacts has been described. However, it will be appreciated that any suitable configuration of safety contacts (and even auxiliary contacts) may be employed. For example, a plunger may be provided with only a single safety contact, and not two as shown in the Figures. 
     It will be understood by the skilled person that a contact is a conductor which may be shaped at each of its ends, i.e. to define contact points. In the above described embodiments, the moveable safety and auxiliary contacts are conductors which extend transversely through the plunger, and protrude from both sides of the plunger. The fixed contacts are conductors fixed in position relative to the housing of the safety switch. 
     The plunger of the present invention has been described in relation to a safety switch having a fixed set of contacts located and fixed in position in the housing of the safety switch. The fixed contacts of the housing may be individually fixed or integral to the housing, or may form part of a safety switch contact block. The safety switch contact block is a structure that is provided with the fixed contacts (or conductors). The safety switch contact block as a whole is fixed in position into the housing. So, the fixed safety contacts (conductors) may be formed integrally with the housing, individually fixed in position in the housing, or form part of a contact block which is itself fixed in position in the housing. 
     It will be appreciated by a person skilled in the art that the invention is not limited to the embodiments described above, and that various modifications may be made to those and other embodiments without departing from the invention, which is defined by the claims which follow.