Abstract:
Disclosed herein is a simplified EMO linkage circuit that enables add-on equipment without retrofit, and eliminates the need for multi-contact EMO switches.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to electrical circuits for system safety controls, and in particular to an emergency machine off for shutdown of equipment. 
       BACKGROUND 
       [0002]    In many environments such as industrial environments, multiple pieces of equipment are utilized which may share energy or power hazards. Under these circumstances it is important for safety purposes to incorporate EMO (Emergency Off) initiated from any piece of equipment which will shut off all the equipment if a hazardous condition occurs. An example of a patented EMO feature is illustrated in US Patent Publication US 2009/0066502, published Mar. 12, 2009. 
         [0003]    A possible straightforward design of EMO linkage utilizes N EMO switches each having N contacts, where N is the number of pieces of equipment in a test cell. An example of a test cell in a manufacturing environment might include: a puncher; a presser; a packager; and a handler. The various pieces of equipment in a test cell may cover a large physical area, but EMO connectivity must be maintained between all the pieces of equipment.  FIG. 1  illustrates an example of the aforementioned EMO linkage design. In this example, four pieces of equipment  100 ,  105 ,  110 , and  115  share hazard conditions. Each piece of equipment includes a 4-contact EMO switch  120 . Four power loops  125 ,  130 ,  135 , and  140  are connected through each EMO switch, and a local EMO control circuit  145  is included in each power loop. If the power loop is closed, the local shut-down features are not activated. However, when any one of the EMO switches  120  are depressed, contacts  150  are broken for each power loop, thereby opening all four power loops. In this case, local EMO control circuits  145  are activated, shutting down all four pieces of equipment. 
         [0004]    A problem with this aforementioned straightforward design is the difficulty in changing the equipment configuration, e.g., adding a new piece of equipment. Each time new equipment is added, an extra link in the chain (i.e. the power loops) is added, and one more contact must be added to the EMO switches for each piece of equipment in the cell. This makes field retrofit difficult, and may require design modification. 
       SUMMARY OF THE INVENTION 
       [0005]    Disclosed herein is a simplified EMO linkage circuit that enables add-on equipment without retrofit, and eliminates the need for multi-contact EMO switches. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  illustrates a traditional EMO linkage design. 
           [0007]      FIG. 2  illustrates an embodiment of the inventive EMO linkage design. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]      FIG. 2  illustrates an embodiment of an inventive simplified EMO linkage circuit design. Each piece of equipment is associated with an identical EMO module  200 . The EMO modules for different equipment are daisy-chained in series into a complete circuit. Additional modules can be added very easily, as will be shown hereinafter. Power supplies  205  (e.g., +24 VDC) have their outputs  210  connected through optional diodes  215  to V+bus  220 , which is connected to the EMO switches  225  of all equipment modules. V+bus  220  provides power to the entire series of EMO modules through series linkage of all EMO switches  225 , which are connected as follows: Jumper  230  from V+bus  220  to EMO switch series circuit  235  connects V+bus  220  to a first contact  240  of the first EMO switch  225 . This contact is termed “EMO switch in”. Second contact  245  of the first EMO switch  225  is termed “EMO switch out”, and is linked to EMO switch in  240  of the second EMO switch  225 . The EMO switches are connected in the same way up through the last equipment, termed “Equipment N”. The EMO switch out for equipment N is jumped to EMO relay power bus  250  with jumper  255 . Assuming the circuit remains closed, EMO relay power bus  250  powers relay coils  260  in each module. Within each equipment module, EMO relay coil  260  is connected to EMO relay power bus  250 . When the EMO circuit is closed and EMO relay power bus  250  is powered, relay coils  260  are also powered. The powered relay coils  260  close contacts  270  which are in series with local EMO control circuits  275  in each EMO module. When contacts  270  are closed, local EMO control maintains power to the local equipment. However, if any of EMO switches  225  are activated, the EMO circuit is opened, EMO relay power  250  to each relay coil  260  is lost, and contacts  270  are opened. In this case, the local EMO control circuits  275  turn off the associated equipment under EMO mode. The serial module aspect of the inventive circuitry enables simple addition of new equipment. It may be accomplished by removing jumper  255  from Equipment N, adding an additional module  200  in series after module N, and repositioning jumper  255  after the new module. Alternatively, a new module can be inserted between two existing modules by breaking the original connections, then re-connecting to the inserted module. In either of these cases, no modification is necessary within the modules, as is necessary with the traditional circuitry. 
         [0009]    Optional diodes  215  act as blocking diodes which prevent false EMO shutdowns if one of the power supplies  205  are off. Auxiliary contacts  280 , also controlled by relay coils  260 , may be used for controlling any equipment that does not have the inventive simplified EMO linkage designed in during EMO linkage integration. Power supply return bus  285  closes the circuit, i.e., is the return to all power supplies  210 . 
         [0010]    The inventive EMO linkage circuit design provides simplification of test cells comprising equipment that shares energy or power hazards. The inventive EMO design utilizing equipment modules connected in series in a daisy-chain mode enables addition or movement of equipment simply, without requiring modifications within modules. Regardless of how many pieces of equipment are linked, only five signal paths are required for the EMO linkage: 1) EMO switch in; 2)EMO switch out; 3) EMO relay power; 4) power return; and 5) V+Bus. In addition, only one-contact EMO switches are needed, eliminating the need for costly and difficult-to-obtain multi-contact EMO switches, which would need to be modified if additional equipment were added. 
         [0011]    It is not expected that the invention be restricted to the exact embodiments disclosed herein. Those skilled in the art will recognize that changes and modifications can be made without departing from the inventive concept. By way of example, details of the exact circuitry within each module may be different, while maintaining the serial modular aspects of the inventive design. The scope of the invention should be construed in view of the claims.