Abstract:
A safety switch assembly having a handle pivotably attached to a casing to allow selective operation of an electrical contact assembly. The handle is attached to the casing with a movable pivot such that excessive grip pressure renders the safety switch inoperable until the safety switch is reset. The handle is moveable responsive to grip pressures that range from no actuation to a first grip pressure. Actuation of the handle in this range controls operation of the electrical contact assembly. Gripping of the switch with a grip pressure greater than the first grip pressure moves the pivot such that the safety switch is rendered inoperable, or non-conductive, until manipulation of a reset actuator returns the pivot to a pivot position associated with the first operating zone. Such a construction provides a safety switch that can be rendered inoperable and reset to allow subsequent operation.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a United States patent application that claims priority to Great Britain Patent Application number 0606154.3 filed Mar. 28, 2006, the disclosure of which is incorporated herein. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to a safety switch. 
         [0003]    In a variety of environments, including for example industrial environments, there is a need for systems that are capable of preventing access to one or more pieces of equipment or machinery whilst that equipment or machinery is operating, in a manner that is highly reliable. In some circumstances, this may be achieved by the use of a safety switch. 
         [0004]    Electrically operated machinery, for example, may be located within an enclosure. The enclosure may be a room, a cage, a specific area etc. When a person enters the enclosure, for example by opening a gate, the safety switch disconnects, grounds or otherwise isolates the electrical machinery from one or more power sources in a predictable, reliable manner. Thus, when a user enters the enclosure the chances of him/her suffering injury from the machinery are reduced or eliminated. In some circumstances, the machinery is not able to be restarted until the user has left the enclosure and reset the safety switch. While this is a useful safety feature, it is not very flexible. 
         [0005]    In some circumstances it is conceivable that the user, while inside the enclosure, may still require the machinery to be operating in, for example a special mode (e.g. low speed or incremental movement mode), or, at the very least have control over its operation. For example, the user may wish to have electrical power maintained to the machinery within the enclosure so that he may test the equipment or clean the equipment. If the equipment within the enclosure is of a robotic nature, the user may wish to maintain power to the equipment so that he may teach the robot what to do. In this case, the robot must have some power to learn. 
         [0006]    With prior art safety switches and enclosures, power is in general not supplied to the equipment while a user is in the enclosure. However, safety switches are known which do allow the supply of electrical power to machinery when in the enclosure. The safety switch is connected to the machinery and operable from within the enclosure. An example of such a safety switch has a handle moveable to three positions. In the first position, where no pressure is applied to the handle, the switch does not conduct electricity and no power is supplied to the machinery. When a certain amount of pressure is applied to the handle, electrical contacts within the switch are closed and the switch conducts electricity so that power is supplied to the machinery. If the handle is depressed further, for example due to the user reacting to a dangerous situation, the supply of electrical power to the machinery is cut-off and is not restored until the handle is moved to the second position. 
         [0007]    Thus, it is an object of the present invention to provide a novel safety switch. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0008]    According to a first aspect of the present invention there is provided a safety switch having a body; at least one electrical component for controlling the conduction of electricity by the safety switch; and a handle pivotably attached to the body and pivotable about a pivot point. The handle is pivotable between a first operating zone, a second operating zone and a third operating zone. The first operating zone corresponds to a situation where the handle is not depressed and the electrical component is arranged such that the safety switch cannot conduct electricity. The second operating zone corresponds to a situation where the handle is depressed to a first extent and the electrical component is arranged such that the safety switch is able to conduct electricity. The third operating zone corresponds to the situation where the handle is depressed to a further, second extent, and the electrical component is arranged such that the safety switch cannot conduct electricity, wherein the pivot point is moveable from a first position to a second position when the handle is depressed to the third operating zone, the second position of the pivot point being arranged such that the electrical component is arranged such that the safety switch cannot conduct electricity, irrespective of whether the handle is subsequently moved to the first or second operating zones. 
         [0009]    According to a second aspect of the present invention, there is provided a powered piece of equipment and a safety switch arranged to allow the control of the supply of power to the equipment. The safety switch comprising a body, at least one electrical component for controlling the conduction of electricity by the safety switch, and a handle pivotably attached to the body and pivotable about a pivot point. The handle is pivotable between a first operating zone, a second operating zone and a third operating zone. The first operating zone corresponds to a situation where the handle is not depressed and the electrical component is arranged, such that the safety switch cannot conduct electricity. The second operating zone corresponds to a situation where the handle is depressed to a first extent and the electrical component is arranged such that the safety switch is able to conduct electricity. The third operating zone corresponds to the situation where the handle is depressed to a further, second extent, and the electrical component is arranged such that the safety switch cannot conduct electricity. The pivot point is moveable from a first position to a second position when the handle is depressed to the third operating zone. The second position of the pivot point is arranged such that the electrical component is arranged such that the safety switch cannot conduct electricity, irrespective of whether the handle is subsequently moved to the first or second operating zones. 
         [0010]    According to a third aspect of the present invention, there is provided a safety switch comprising: a body; at least one electrical component for controlling the conduction of electricity by the safety switch; and a handle attached to the body. The handle is moveable between a first operating zone, a second operating zone, and a third operating zone wherein the first operating zone corresponds to a situation where the handle is not depressed and the electrical component is arranged such that the safety switch cannot conduct electricity. The second operating zone corresponds to a situation where the handle is depressed to a first extent and the electrical component is arranged such that the safety switch is able to conduct electricity and the third operating zone corresponds to the situation where the handle is depressed to a further, second extent, and the electrical component is arranged such that the safety switch cannot conduct electricity. The safety switch further comprises a reset actuator which is arranged such that upon moving the handle to the third operating zone, the electrical component is maintained in an arrangement such that the safety switch cannot conduct electricity, until the reset actuator has been activated. 
         [0011]    The safety switch has the advantage that it avoids power accidentally being provided to machinery by a user unintentionally moving the handle to the second operating zone (for example if the user relaxes his or her grip on the safety switch) after reacting to a dangerous situation and moving the handle to the third operating zone (for example if the user is startled). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, in which: 
           [0013]      FIG. 1  is a schematic representation of an enclosure equipped with a safety switch according to the present invention; and 
           [0014]      FIGS. 2   a  to  2   g  depict a safety switch according to an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0015]      FIG. 1  shows a perspective view of an enclosure  1  that encloses electrically operated machinery  2 . Access to the enclosure  1  is gained via a gate  3 , which is provided with a safety switch  4 . To open the gate  3 , the safety switch  4  must be activated. By activating the safety switch  4 , the supply of electrical power to the machinery  2  is interrupted. Electrical power to the machinery  2  can only be re-established by the user leaving the enclosure  1  and re-setting the safety switch  4 . 
         [0016]    It will be appreciated that different safety switches, or different operating principles for a given safety switch may be used. For example, opening the gate  3  may automatically cut the power supply, negating the need to consciously activate the switch  4 . Alternatively, the gate  3  may only be opened, and the power to the machinery  2  cut off, when an actuator (e.g. a key) is inserted into the safety switch  4 . The safety switch  4  could even comprise a light gate, whereby when a beam of light is broken the power to the machinery  2  is cut-off. 
         [0017]    It may be desirable to supply power to the machinery  2  even when the user is in the enclosure  1 . However, if a simple on-off switch is provided, the safety measures provided by the safety switch  4  are circumvented, which re-introduces the possibility of the user suffering injury from the machinery  2 . 
         [0018]      FIG. 2   a  illustrates a safety switch in accordance with an embodiment of the present invention. The safety switch comprises a casing  10 , in which is pivotally mounted a handle  11 . The handle  11  is free to pivot about a moveable pivot point  12 . The handle  11  is connected to a set of contacts  13   a ,  13   b  by way of a post  14 . 
         [0019]      FIG. 2   a  shows the handle  11  with no force applied by a user (not shown), i.e. the handle  11  is in a first operating zone. While in the first operating zone, the pivot point  12  is maintained in position by a biasing member  15 . Springs  16  located about the post  14  and contacts  13   a ,  13   b  keep the handle  11  in the first operating zone when no force is applied by the user, whereby the contacts  13   a ,  13   b  are kept open so that no electrical power can flow through the switch. The handle  11  is provided with a fulcrum  1  a which extends perpendicular to the length of the handle  11 . The safety switch is also provided with a reset actuator  17 , which is biased by a spring  17   a , and a further spring  18 , the significances of which are described in more detail later. 
         [0020]    The safety switch may be formed using any suitable materials. For example, the handle  11  and casing  10  of the safety switch can be formed from a durable plastic, or any material that can electrically insulate the contacts  13   a ,  13   b  from the user. 
         [0021]    The safety switch of the present invention differs from those of the prior art in that the pivot point  12  of the safety switch of the present invention is moveable, and that the safety switch of the present invention is provided with a reset actuator  17 . 
         [0022]    In use, the contacts  13   a ,  13   b  may be connected between a power supply and equipment to be powered by the power supply (not shown in the figures). The safety switch itself may be carried around by the user while in an enclosure. 
         [0023]      FIG. 2   b  illustrates the safety switch when the handle  11  has been depressed to such an extent as to close the electrical contacts  13   a  and  13   b  such that electrical power may be supplied to the machinery. When the handle  11  is in this position, it is in a second operating zone, i.e. the safety switch is able to conduct electricity. It can be seen that the pivot point  12  has not changed position, and that it is still held in position by the biasing member  15 . The fulcrum  11  a makes contact with a surface of the casing  10  when the handle  11  is in the second operating zone. 
         [0024]    If the user reduces the pressure applied to the handle  11  (for example, by dropping the safety switch), the handle  11  will be pushed from the second operating zone to the first operating zone by the springs  16 . At the same time, the electrical contacts  13   a ,  13   b  are opened such that the supply of electrical power to the machinery is interrupted. Thus, if the user of the safety switch loses grip on the handle  11  (for example due to an incident involving the machinery), power to the machinery will be cut-off so that the chance of injury to the user is reduced. 
         [0025]    Instead of the user of the safety switch losing grip of or dropping the safety switch, it is possible that due to a reaction to a dangerous situation the user may actually increase his/her grip on the safety switch and handle  11 . If the pressure on the handle  11  exceeds a predetermined amount, it is desirable that power to the machinery is cut off. For example, if the user is startled, it may be safer to cut off power to the machinery than to have a startled user in close proximity to dangerous machinery in operation. This safety measure is particularly important if the user is electrocuted, because a sudden increase in grip is associated with electrocution. If the machinery on which the user is operating causes the user to be electrocuted, the user&#39;s grip on the safety switch will increase and cut-off the supply of electricity to the machinery. 
         [0026]      FIG. 2   c  illustrates the handle  11  in a third operating zone, whereby the pressure applied to the handle  11  is greater than that illustrated in  FIG. 2   b . It can be seen that since the fulcrum  11   a  is now in contact with an inner surface of the casing  10 , the handle  11  now pivots about the fulcrum  11   a . It can be seen that the pivot point  12  about which the handle  11  pivots in  FIGS. 2   a  and  2   b  (i.e. when the handle  11  is in the first or second operating zone) has now moved, since the force applied to the handle  11  has caused the pivot point  12  to overcome the biasing member  15 . In overcoming the biasing member  15 , the pivot point  12  has moved from a first position to a second position. As the pivot point  12  has moved, so has the post  14  which is connected to the contacts  13   a ,  13   b . Consequently, the contacts  13   a ,  13   b  are opened. The pivot point  12  is kept in the second position by the further spring  18 . 
         [0027]    It can be seen from  FIG. 2   d  that when the handle  11  is released and returned to the first operating zone by the springs  16 , the electrical contacts  13   a ,  13   b  remain open. The electrical contacts  13   a ,  13   b  remain open even when the handle  11  is depressed until the fulcrum  1  la once again comes into contact with the surface of the casing  10 , as illustrated in  FIG. 2   e.    
         [0028]      FIG. 2   f  corresponds to  FIG. 2   d  , and illustrates that after the handle has been moved to the third operating zone, so that the pivot point  12  moves and the electrical contacts  13   a  and  13   b  are opened, electrical power cannot be supplied to the machinery simply by moving the handle  11 . The contacts  13   a ,  13   b  can only be closed, and electrical power restored to the machinery by activation of the reset actuator  17 , which will move the pivot point  12  back to its original position. 
         [0029]      FIG. 2   g  shows that in order to reset the safety switch, the reset actuator  17  is depressed. The reset actuator  17  pushes the pivot point  12  against the further spring  18 , and moves the pivot point  12  from the pivot point&#39;s second position to the pivot point&#39;s first (and initial) position. When pressure is removed from the reset actuator  17  the spring  17   a  pushes the reset actuator  17  away from the casing  10  such that the safety switch is returned to its initial settings as illustrated in  FIG. 2   a . Electrical power can now be re-supplied to the machinery by depressing the handle  11  to the position as shown and described with reference to  FIG. 2   b.    
         [0030]    Provision of the reset actuator  17  ensures that if the user is startled or electrocuted (for example), thereby increasing the pressure on the handle  11 , power to the machinery cannot be restored without a deliberate action. This provides an additional safety measure, beyond the non-conducting state of the safety switch when the handle  11  is in the first or third operating zone. 
         [0031]    It will be appreciated that the handle  11  and casing  10  may be of any suitable shape. For example, the handle  11  and casing  10  may be of a certain ergonomic design. The handle  11  may not be mounted within the casing  10 , but may be attached to any suitable body. 
         [0032]    Pressure applied to the handle  11  need not be applied by the hands of a user. For example, the handle  11  may be operated by the foot or feet of a user, or even by the mouth or chin of a user. Such a method of operation leaves both hands of the user free to use tools, equipment etc. 
         [0033]    The safety switch may be used with a power supply and machinery or equipment powered by that power supply. The safety switch of the present invention may also be used in conjunction with other safety switches which may be used to control the power supplied to machinery within an enclosure as described above, so that a user may enter an enclosure and operate on machinery safely. 
         [0034]    The springs and biasing members referred to above may be coil springs, leave springs or any suitable biasing element. 
         [0035]    It will be appreciated that the above embodiment has been described by way of example only, and that the various modifications may be made thereto without departing from the invention as defined by the claims, which follow. 
         [0036]    The use of electrical contacts is not essential. In some circumstances a variable power supply (as opposed to a simple on-off arrangement) may be desirable. Movement of the handle between the first operating zone and the second operating zone may be used to control a variable power supply to the machinery, for example to control the speed of operation of the machinery. In this case, movement of the handle may be used to control the resistance of a variable resistor, or any other apparatus suitable for varying the supply of electrical power to the machinery. In short, any electrical circuit components may be used to implement the desired supply of electrical power to the machinery. The circuit components may be, for example, electrical contacts, a variable resistor, etc. The electrical contacts may be arranged to open to prevent the switch from conducting electricity, and arranged to close to allow the switch to conduct electricity. 
         [0037]    Most preferably, when the handle is moved from the second operating zone to the third operating zone, the electrical power to the machinery is switched off immediately, i.e. a simple on-off arrangement is employed. Such an arrangement ensures that should the user be startled and depress the handle to the third operating zone, the power supply to the machinery is cut-off immediately (as opposed to gradually), so that the time over which the startled user is exposed to operating machinery is minimised. 
         [0038]    It will be appreciated that the handle need not be pivotably attached to the body. For example, the handle may be slidably mounted within the body, and moveable between the first, second and third operating zones. In the case where pivotable attachment of the handle to the body is not essential, the handle may be attached to the body in any suitable manner.