Patent Publication Number: US-6215204-B1

Title: Emergency stop system employing modular relays

Description:
FIELD OF THE INVENTION 
     This invention relates generally as indicated to a modular emergency stop device and system and more particularly to an emergency stop device and system having a switch unit and a control unit that may be coupled/uncoupled in a modular manner. 
     BACKGROUND OF THE INVENTION 
     A machine is typically powered by an electrical power source and typically has an on/off switch for use during normal operating conditions. For safety reasons, a machine will usually also include an emergency stop device for terminating electrical power to the machine in an emergency situation. While the design of an emergency stop device may vary greatly, the device will generally include a switch which converts from a normal state to an emergency state when an emergency stop is necessary and a controller which controls the power source for the motor or machine. The switch and controller typically are enclosed in a housing or casing to protect them against weather, dust, explosive situations, or other hazards presented by the environment of the particular machine. 
     In a more sophisticated emergency stop device, the switch will include a circuit board including, among other things, a series of contacts that are either normally closed or normally open contacts. The controller in a sophisticated emergency stop device will usually include a microprocessor for appropriating controlling the machine&#39;s power source in an emergency situation. The switch, and specifically its contacts, are usually considered component most vulnerable to damage and deterioration. However, in view of the criticality of the switch in the operation of the emergency stop device, a faulty contact must be replaced or else the machine will not run until the relays are replaced. For this same reason, the ability to periodically inspect and/or test switch components could be a very important part of a preventive maintenance plan but such inspection/testing is not always possible or at least not practical. 
     Accordingly, the inventor appreciated that a need remains for an emergency stop device which allows efficient and convenient replacement, inspection and/or testing of the switch components. 
     SUMMARY OF THE INVENTION 
     The present invention provides an emergency stop device wherein the switch and the controller are contained in separate modular units. This modular construction allows the switch to be conveniently removed from the controller and then replaced, inspected and/or tested. 
     More particularly, the present invention provides a modular emergency stop device comprising a switch unit and a control unit. The switch unit includes a switch which converts from a normal state to an emergency state when an emergency stop is necessary and a housing for the switch. The control unit includes a controller which controls a power source for a machine and a housing for the controller. The switch unit&#39;s housing and the control unit&#39;s housing are adapted to be selectively coupled/uncoupled relative to each other. When the housings are coupled together, the switch is operably coupled to the controller, whereby the controller may appropriately control the machine&#39;s power source when the switch is converted to the emergency state. Preferably, the housings include a quick-release coupling arrangement therebetween. 
     The switch may comprise a circuit arrangement necessary to convert the switch to the emergency state if an emergency stop is necessary. The circuit may include, among other things, contact pins which are usually the component most vulnerable to damage and deterioration in the emergency stop device. To replace the switch, the switch unit&#39;s housing is uncoupled from the control unit&#39;s housing to remove the switch unit and a new switch unit is coupled to the controller&#39;s housing. Likewise, to test the switch, the switch unit&#39;s housing is uncoupled from the control unit&#39;s housing to remove the switch unit, the uncoupled switch unit is tested, and the tested switch unit is recoupled to the controller unit if testing reveals that the switch is still acceptable. Preferably, the switch unit&#39;s housing includes a plurality of housing sections latched together to form a casing for the switch and/or the control unit&#39;s housing includes a plurality of housing sections latched together to form a casing for the controller. For example, the switch&#39;s housing may include a front housing section and rear housing section and the controller&#39;s housing may include a front housing section and a rear housing section. In this manner, the switch and/or controller may be easily accessed from its respective housing by unlatching the housing sections. 
     An emergency stop system may be compiled by interconnecting directly (or substantially directly) a plurality of modular emergency stop devices via connectors which eliminates field wiring therebetween and improves system reliability. Additionally or alternatively, diagnostics or other functions could be provided by the additional control units. To this end, each of the controllers would preferably include a network interconnection base and the control units&#39; housings would each include a window for this base to facilitate the interconnection of various modules. 
     As indicated above, the modular coupling between the switch unit and the control unit provides many advantages over traditional single unit emergency stop devices in the areas of replacement, testing, and/or repair. A further manufacturing advantage is that the controller may be programmed to be compatible with a plurality of different switch units for different machines and/or different emergency stop conditions. The appropriate type of switch unit for the machine and/or the desired emergency stop conditions could then be selected and the controller provided with the selected switch unit. 
     These and other features of the invention are fully described and particularly pointed out in the claims. The following descriptive annexed drawings set forth in detail certain illustrative embodiments, these embodiments being indicative of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a modular emergency stop device according to the present invention, the device including a switch unit and a control unit which are shown coupled together in a modular manner. 
     FIG. 2 is another perspective view of the modular emergency stop device, the switch unit and the control unit being shown uncoupled from each other. 
     FIG. 3 is an exploded perspective view of the switch unit. 
     FIG. 4 is a top perspective view of a switch of the switch unit. 
     FIG. 5 is an exploded perspective view of the control unit. 
     FIG. 6 is a schematic view of a network arrangement of a plurality of modular emergency stop devices. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings in detail, and initially to FIGS. 1 and 2, an emergency stop device  100  according to the present invention is shown. The emergency stop device  100  is designed to stop the motor of a machine in an emergency situation. As is explained in more detail below, the device  100  has a modular construction that provides the ability to periodically inspect and/or test certain components, as well as other networking and/or manufacturing advantages. 
     The emergency stop device  100  comprises a switch unit  200  and a control unit  300  which can be selectively coupled together in a modular manner. The switch unit  200  includes a switch  202  which converts from a normal state to an emergency state when an emergency stop is necessary and a housing  204  for the switch  202 . The control unit  300  includes a controller  302  which controls a power source for the machine and a housing  304  for the controller  302 . 
     When the modular units  200  and  300  are coupled together, such as is shown in FIG. 1, the switch  202  is operably coupled to the controller  302  whereby the controller  302  may appropriately control the power source when the switch  202  is converted to the emergency state. Additionally, the units  200  and  300  may be selectively uncoupled from each other to inspect, replace, and/or repair one of the units independent of the other. Typically, the switch unit  200  would be the unit removed since it contains components (e.g. contact pins  208  introduced below) usually more prone to damage and/or deterioration than the components of the control unit  300 . 
     The switch unit  200  is illustrated isolated from the control unit  300  in FIG.  3  and the switch  202  is illustrated isolated from the housing  204  in FIG.  4 . The illustrated switch  202  includes a circuit board  206  having the electrical circuitry necessary to convert the switch  202  to the emergency state if an emergency stop is necessary. In the illustrated exemplary embodiment, the electrical circuitry includes contact pins  208 , male connectors  210  for mating with the control unit  300 , capacitors  212 , and LEDs  214 . However, it should be noted that the electrical circuitry may vary depending on the desired circuit functions. Protective covers  216  and/or  218  may be provided for the contact pins  208  and/or male connections  210 . The bottom surface of the circuit board  206  may be provided with spacers  220  to insure proper positioning relative to the switch unit&#39;s housing  204 . 
     The switch unit&#39;s housing  204  preferably includes a plurality of housing sections  240  and  242  latched together to form a casing for the switch  202 . In this manner, once the switch unit  200  is uncoupled from the control unit  300 , the housing sections  240  and  242  may be unlatched for inspection and/or repair of the switch  202 . In any event, the housing  204  is designed to protect the switch  202  against weather, dust, explosive situations, or other hazards presented by the environment in which the machine operates. 
     In the illustrated embodiment, the housing section  240  is a front housing section and the housing section  242  is a rear housing section. The front and rear housing sections  240  and  242  together form a roughly rectangular casing for the switch  202 . The front housing section  240  includes side walls  252 , top and bottom walls  253 , and a front wall  254 . The front portions of the walls  252  and  253 , and the top and bottom portions of the front wall  254  are shaped to form concavely rounded cut-off corners  256  to accommodate the front cut-off corners of the circuit board  204 . The front wall  254  includes a series of windows  258  for the LEDs  214 . The top/bottom walls  254  each include a rectangular slot  260  for coordination with a latching component of the rear housing section  242  (namely a latching tab  272  introduced below). Although not visible in the illustrated orientation, the front housing section  240  may include rails and/or bars (similar to rails  274  and bars  276  introduced below in connection with the rear housing section  242 ) to insure proper positioning of the circuit board  206 . 
     The rear housing section  242  includes side walls  266 , top and bottom walls  267 , and a rear wall  268 . The front edges of the walls  266 - 268  are shaped to form an inward lip  272  and a sloped latching tab  272  extends outwardly from the top and bottom sections of the lip  270 . The top and bottom walls  267  include rails  274  extending inwardly therefrom and one of the side walls  266  (the left-hand wall in FIG. 3) includes spacer bars  276  extending inwardly therefrom. In the assembled housing  204 , the rear edges of the walls  252  and  253  of the front housing section  240  fit over the lip  272  and the latching tab  272  is snap fit into the slot  260  to secure the housing sections together. The rails  274  and bars  276  assure proper positioning of the circuit board  206  relative to the housing  204 . Although not visible in the illustrated orientation, the rear wall  268  includes a rectangular window through which the male connectors  208  and the cover  218  extend. 
     The rear housing section  242  further includes coupling members  280  for selectively coupling the switch unit  200  to the control unit  300 . In the illustrated switch unit  200 , one coupling member  280  is attached to each the top and bottom walls of the rear housing section  242 . Each coupling member  280  includes a resilient arm  282  attached to the top/bottom wall  253  by an elbow  284 . The arm  282  includes a ramp  286  and a distal push tab  288 . When selectively coupling the switch unit  200  to the control unit  300 , the push tab  288  is pushed inward to allow the resilient arm to slide into or out of a groove (namely groove  360  introduced below) in the control unit  300 . 
     Referring now to FIG. 5, the control unit  300  is illustrated isolated from the switch unit  200 . The controller  302  comprises circuit boards  306  and  308  containing the components necessary to control the power source for the machine. In the illustrated embodiment, these components include a female connector base  310 , stepped terminal blocks  312 , a microprocessor  314 , connectors  316  from the female connector base  310 , and a network connector base  318 . The circuit board  306  includes rectangular edge slots  320  arranged to correspond with latching components of the control housing  304  (namely latching tabs  352  introduced below). The circuit board  308  includes similar rectangular edge slots  322  except that they include expanded rectangular corners. The circuit board  308  additionally includes semi-circular slots  324  positioned on either side of the network connectors  318 . 
     The controller housing  304  also preferably comprises a plurality of housing sections  330  and  332  latched together to form a casing for the controller  302 . In this manner, the controller  302  may be easily accessed by unlatching the sections  330  and  332  once the switch unit  200  is uncoupled therefrom and typically once the control unit  300  is uncoupled from the machine. In any event, the housing  304  is designed to protect the controller  302  against weather, dust, heat, explosive situations, or other hazards presented by the environment of the particular machine. 
     In the illustrated embodiment, the housing section  330  is a front housing section and the housing section  332  is a rear housing section which together form a roughly C-shaped casing for the controller  302 . The front housing section  330  includes side walls  340 , top and bottom walls  341  and a rear wall  342 . The walls  340  and  341  are shaped to form stepped corners  344  that accommodate the stepped terminal blocks  312  and to this end have windows  346  for access to the screws and/or wire openings of the terminal blocks. The rear wall  342  of the housing section  330  includes a rectangular window  348  to accommodate the female connector base  310 . The side walls  340  each include a central rectangular tab  350  which together with the rear housing section  332  forms a window for the network connector base  318 . 
     The front housing section  330  additionally comprises a plurality of latching tabs  352  which are used to latch the housing sections  330  and  332  together. In the illustrated housing section  330 , the latching tabs  352  extend outwardly from the rear edges of the side walls  340  and the top/bottom walls  341 . The tabs  352  are rectangular in shape and each includes a rectangular slot  354 . 
     The front housing section  330  further comprises a rectangular recess  356  defined by the rear wall  342  and the stepped corners  344  and giving the housing section  330  its C-shape. Preferably, the surfaces of the stepped corners  344  defining the ends of the recess  356  include a rectangular groove  358  and a further rectangular groove  360 . As is explained in more detail, this recess  356  and these grooves  358  and  360  provide interfacing and/or latching surfaces for the switch unit&#39;s housing  204  when selectively coupling/uncoupling the units  200  and  300  in a modular manner. 
     The rear housing section  332  comprises side walls  370 , top/bottom walls  371 , and a rear wall  372  which together form a roughly rectangular casing. The side walls  370  each include a central rectangular slot  374  which together with the tabs  350  of the front housing section  330  form a window for the network connector base  318 . Stacking bars  376  are positioned on the side, top and bottom walls  370  and  371  to fit within the expanded corners of the rectangular edge slots  322  and the semicircular slots  324  of the circuit board  308 . When the circuit board  308  is inserted into the rear housing section  332 , it will slide past the stacking bars  376  while the circuit board  306  (which does not include the expanded corners and/or semicircular slots) will rest upon the top of the stacking bars  376 . The rear wall  372  may also include spacing bars  378  to properly position the circuit board  308  relative thereto. 
     At least some of the stacking bars  376  are preferably also positioned to correspond to the latching tabs  352  of the front housing section  330 . In the assembled housing  302 , the latching tabs  352  are inserted between the appropriate stacking bar pairs to secure the housing sections  330  and  332  together. Ramps  380  are positioned between the pairs of stacking bars  376  for engagement with the tab&#39;s latching slots  354 . 
     As was indicated above, the front housing section  330  interfaces with the switch unit&#39;s rear housing section  242  to allow selectively coupling/uncoupling of the switch unit  200  and the control unit  300 . Specifically, when the switch unit  200  is modularly received within the rectangular recess  356 , the male connector base  210  of the switch unit&#39;s circuit board  206  (which projects through the window in the switch unit&#39;s rear wall  268 ) mates with the female connector base  310  of the controller  302  (which projects through the window in the control unit&#39;s rear wall  342 ). In this manner, the switch  202  is operably coupled to the controller  302  whereby the controller  302  may appropriately control the power source when the switch  202  is converted to the emergency state. 
     Preferably, the emergency stop device  100  has a quick release coupling arrangement between the modular units  200  and  300 . In the illustrated embodiment, this quick release arrangement is accomplished by the coupling members  280  of the switch unit  200  and the rectangular recess  356  of the control unit  300 . Specifically, the push tabs  288  are pushed inward as the switch unit  200  is slid into the grooves  358  of the control unit  300  and released so that the resilient arm  282  is locked within the grooves  360 . To uncouple the switch unit  200  from the control unit  300 , the procedure is repeated in reverse. 
     As was indicated above, the control unit  300  includes a network connector base  318  that projects through a window in the controller housing  304 . This allows the operable interconnection of a series of devices  100  as may be necessary in more sophisticated equipment, such as is shown in FIG.  6 . The system of FIG. 6 advantageously provides for the integration of multiple emergency stop devices or emergency stop modules into a single unit and thereby eliminates any field wiring therebetween. Perhaps the best way to fully appreciate the advantageous features associated with the present invention is to briefly describe and highlight the disadvantages associated with conventional emergency stop systems. 
     Conventionally, an emergency stop is a monolithic structure or device having one or more outputs associated therewith that couple to machine safety switches via wiring. If, however, a particular machine has a greater number of peripherals to stop than the number of outputs available on the monolithic structure or device, a second monolithic expander structure or device is added and wired to the first or “master” emergency stop device. In addition, the expander outputs are wired to the additional machine peripherals which need to stop in an emergency. 
     The conventional emergency stop system configuration has a number of disadvantages. First, wiring an expander module to the master module takes two of the master emergency stop outputs. Therefore, for example, if the master emergency stop has eight outputs and the expander has eight outputs, wiring the expander to the master results in fourteen (14) total outputs instead of sixteen (16), as might otherwise be expected. In addition, if a second expander is added, the resulting system has twenty (20) total available outputs instead of twenty-four (24) since another two outputs are needed to wire in the additional expander. Clearly then, the conventional wiring configuration results in an inefficient utilization of emergency stop outputs and thereby negatively increases the emergency stop system cost. 
     Another disadvantage associated with conventional emergency stop system configurations is the wiring necessary to electrically connect the various separate, monolithic devices together. It is estimated that the wiring needed to interconnect the various monolithic emergency stop devices comprises about 20% of the total system wiring. Such an extensive amount of wiring is expensive and further adds to the total cost of the emergency stop system. In addition, the significant amount of wiring adds to the complexity and cost of servicing the emergency stop system. For example, a technician must navigate the maze of wiring between the various emergency stop devices when debugging system level errors or when running manual diagnostics. 
     In addition, the wiring interconnect methodology of conventional emergency stop systems creates a latent reliability problem and may provide a potential false sense of security. That is, the manner in which various monolithic expanders are wired to the master is often a function of the particular control methodology being employed and consequently must be wired in a particular fashion. If wired improperly, the error will not necessarily prohibit the machine or machines associated therewith from operating. Instead, the machine or machines may continue to operate and if an emergency condition arises and a safety switch is manually activated, the machine power may not be cut off, thus creating a safety hazard. Consequently, to ensure that such conditions do not occur, technicians must check and re-check the wiring interconnections in order to ensure reliability. Such redundancy takes a substantial amount of time and labor, and thereby further increases the cost of the conventional emergency stop system. 
     In stark contrast to conventional wired systems, the emergency stop system of the present invention utilizes modules  100  having connectors such as the network connector base  318  which are operable to couple the various modules together directly or substantially directly. The term “substantially directly” is used because the coupling of the modules  100  of the present invention contemplates any physical interconnection of the modules that eliminates the field wiring therebetween. For example, the modules may be directly connected together via the network connector bases  318 , wherein one module  100  has a male-type connector and the neighboring module  100  has a female-type connector. Alternatively, the network connector bases  318  of neighboring modules  100  may be electrically connected together through an interface adaptor or the like. In either case, however, the modules are interconnected without the use of field wiring therebetween. 
     The coupling of the modules  100  in a direct or a substantially direct manner via, for example, the network connector bases  318  associated therewith, as illustrated in FIG. 6, advantageously provides for the integration of multiple emergency stop modules into a single unit. Further, use of the network connector bases  318  permit the various modules  100  to operatively engage one another in a side-to-side manner, as illustrated in FIG. 6, thereby providing for a minimal emergency stop system form factor. As a direct result, many of the significant disadvantages associated with the conventional wired interconnect systems are eliminated. For example, all the available outputs associated with the master control module and any expander modules are available for connecting to machine safety switches, thus substantially improving the output usage efficiency of the system. In addition, all the cost, complexity and reliability issues associated with the wiring of the master control module and various other modules is eliminated, since each module  100  may be directly coupled together via the network connector bases  318 . Consequently, the entire system may be plugged into a din rail (not shown) as a single integrated unit and the only wiring necessary is for incoming power and the wiring associated with wiring the machine safety switches to the various outputs. 
     According to another aspect of the present invention, additional modules  100  that are not expanders may also be added to the system to provide various forms of functionality, as may be desired. For example, a power converter type module may be added to the system. In such a case, the power converter couples to the master control emergency stop module via connectors, for example, the network connector base  318  associated with each module. Preferably, the power converter receives a first power signal provided at the din rail, for example, 110 VAC line voltage, and converts the signal to a second power signal, for example, ±24 VDC for use by the master control module and the other modules. Use of the power converter advantageously eliminates the wiring interconnection between a monolithic power transformer and the monolithic master emergency stop device in conventional systems. In addition, further cost is eliminated by the system configuration of the present invention since each unit would otherwise require its own power supply. 
     According to another aspect of the present invention, the system of FIG. 6 may further include a communications module. The communications module is operable to interface with the master control emergency stop module in accordance with a first data format protocol, for example, DeviceNet, etc., and then convert the data received from the master control emergency stop module into a second data format protocol, for example, Ethernet, RS-232, etc. The communication module is further operable to transmit the data in the converted data format to accommodate the second communication protocol along a communication link. Such a link may be, for example, a coaxial cable, wireless RF, etc. 
     The operation of an exemplary emergency stop system of the present is as follows. A power converter module receives 110 VAC or 220 VAC line voltage and converts the line voltage to ±24 VDC for use in the control system. A master control emergency stop module is coupled to the power converter module directly or substantially directly through a connector, for example, the network connector base  318 . On the other side of the master control emergency stop module is an expander module which provides a greater number of outputs for machine safety switches associated with one or more machines for which the system provides protection. 
     The ±24 VDC power is provided to the master control emergency stop module which taps onto the ±24 VDC on the circuit board  308  for powering the various circuits, etc. The ±24 VDC is also passed through to the expander module through the network connector base  318  on the other side of the module and the expander module uses the ±24 VDC in the same manner as the master control emergency stop module. Note that via use of the network connector bases  318 , power is easily supplied to all modules without field wiring therebetween. In addition, although ±24 VDC is the preferred power level used in the preferred embodiment of the present invention, it should be understood that the present invention may use other voltage levels based on system requirements and/or needs and such variations are contemplated as falling within the scope of the present invention. 
     The master control emergency stop module also contains additional control circuitry on the circuit board  308  which provides system control based on varying user needs. For example, the control circuitry may be configured for E-stop control, two-hand control, etc., and configured for differing control interfaces for the outputs such as instantaneous off control or time-delay off control, etc. According to a preferred embodiment of the present invention, such control is hardware based relay control logic, and thus varying types of master control emergency stop modules may be selected by the user based on the various differing system control needs. Since all the control logic preferably is hardware based on the circuit board  308 , the user does not have to execute a complicated wiring scheme between different monolithic blocks, and thus the present invention greatly reduces the time, money and complexity of control system set-up and further improves the system reliability. For example, the user simply orders the desired modules and plugs the modules together via, for example, the network connector bases  318 . The user then only needs to wire the machine safety switches to the outputs, thus greatly simplifying the set-up process. 
     Although hardware based relay control logic is preferred, the present invention also contemplates a more sophisticated programmable controller on the circuit board  308  which allows different control configurations to be programmed therein, either by the manufacturer based on the user&#39;s system request, or at the system location by the user. In any event, the control portion  300  of the master control emergency stop module provides the necessary control circuitry to effectuate system control and the network connector base configuration allows for any easy interconnection to an expander without field wiring or the possibility of wiring the control circuitry to the expander improperly. 
     On the other side of the last expander module, a jumper preferably is coupled to the exposed network connector base  318  to close the circuit, as may be desired. As discussed supra, other modules may be easily integrated into the system based on the various system needs, for example, a communications module. Interface control between such modules and the master control emergency stop module is provided through the control circuitry on the circuit board  308  of the master control emergency stop device. 
     According to yet another aspect of the present invention, a method of configuring an emergency stop system is disclosed. Initially, the method contemplates the identification of the emergency stop system requirements. For example, determining the required number of outputs, whether a power converter is necessary, whether a two-hand type control or other type control is required, whether or not the output instantaneously shut off a safety switch or instead are on a timer, etc. Upon identifying the system requirements, the appropriate emergency stop system modules necessary to effectuate the system requirements are identified. 
     According to the present invention, the modules have connectors thereon, for example, the network base connectors  318 , and are operable to directly connect or substantially directly connect together. The identified modules are then coupled together via the connectors preferably in a side-to-side orientation which provides a small form factor and eliminates field wiring therebetween. The coupling methodology also prevents the possibility of an incorrect wiring connection and thus improves system reliability. The emergency stop system then forms a single integral unit and may be easily plugged into a din rail or the like. Alternatively, the modules may be separately plugged into the din rail and then slid laterally to interconnect the various modules. 
     According to another aspect of the present invention, a diagnostics system for the emergency stop system is disclosed. The diagnostics system allows a user to obtain a quick status of each of the various modules within the system without having to disassemble the system and perform individual diagnostic tests thereon. In prior art emergency stop systems, no manner of automatically diagnosing the system existed. Instead, when a user became aware that a problem existed (either the machine was shut off without an emergency condition, or an emergency condition occurred and the machine was not properly shut off) the system had to be disassembled to identify the system failure. That is, each monolithic structure had to have its field wiring removed and then had to be taken apart to identify whether a problem existed. Alternatively, the complex field wiring had to be tediously examined to determine whether the system was wired together properly. 
     According to the present invention, a microprocessor is provided on the circuit board  308  of each module control unit  300  and each is programmed to carry out one or more diagnostic routines to ensure the proper operation of the respective module. Since the microprocessor is resident on the control unit  300 , damage to the switch unit  200  associated therewith does not result in a costly failure. Instead, the modular switch unit  200  is merely replaced with a new switch unit  200  and the system is again operational. Further, since each control unit  300  diagnoses its own module, any failure or defect that occurs can be specifically identified. That is, both the nature of the failure and the module experiencing the failure is identified. Consequently, a user can quickly identify what is wrong with the system with particularity and replace that identified portion immediately, without having to analyze each module manually as in the prior art control systems. 
     The microprocessor on each of the modules, particularly the master control emergency stop module and the expander modules, is operable to analyze a variety of different status conditions of the module. For example, if a short circuit is detected within one of the modules, for example, where the ±24 VDC power terminals are shorted together due to some type of failure condition, the microprocessor will detect that condition and communicate it to the master control emergency stop module for appropriate action. 
     Other types of module diagnostics include, but are not limited to, an open contact detection routine, wherein the microprocessor determines whether a contact in the switch unit  200 , upon being triggered to an open condition, properly resets back to a closed condition upon the removal of the emergency condition. In addition, the microprocessor may evaluate a reset push button (if one exists with the system) to determine whether the reset button is either stuck or otherwise being artificially held open or closed. Obviously, any other module condition that may be worthy of note may be monitored by the resident microprocessor and any such diagnostic routines to monitor such conditions are contemplated as falling within the scope of the present invention. 
     Diagnostic data collected by the microprocessor of each module is then transmitted through the system to the master control emergency stop module. According to a preferred embodiment of the present invention, if a status condition of one of the modules indicates a failure, the master control module shuts down the entire system, that is, the one or more machine associated therewith and provides a user indication regarding the nature of the failure and the module experiencing the failure condition. Such an indication can be provided, for example, locally at the system via a display and communications module electrically coupled thereto, or remotely via a communications module and a communication link. A user, upon receiving the failure indication, can then quickly replace the switch unit  200  associated with the failure and be operational again. 
     The diagnostic data is transmitted by the microprocessor of each module through the connectors, for example, the network connector bases  318 , to the master control module. In one embodiment, each piece of status data can be transmitted as a single status bit on individual pins. In such a case, the control module receives a serial data string for each pin, wherein the string contains a plurality of data packets that provide a particular type of status information for each respective module in the system (i.e., first packet has data for expander #1, second packet contains data for expander #2, etc.) Alternatively, the microprocessor may use a plurality of pins to represent a status of a particular module. Any manner of communicating the diagnostic data through the connectors may be implemented and is contemplated as falling within the scope of the present invention. 
     In summary, with or without a networking arrangement, the modular coupling between the switch unit  200  and the control unit  300  provides many advantages over traditional single unit emergency stop systems. For example, in the event of a faulty switch, the switch unit  200  is simply disconnected from the control unit  300  and replaced with a new switch unit. The replaced switch unit could be sent to a facility for testing and/or repair. Additionally, this arrangement allows an efficient preventive maintenance program. Specifically, a switch unit  200  could be uncoupled from the control unit  300 , tested by an appropriate electrical testing device, and then recoupled to the control unit  300  if the testing reveals that the switch was still suitable. Alternatively, the present invention allows an inventory of back-up switch units to be available for easy replacement, thereby eliminating the need for a technician to fix failed switch units. A further advantage is that the control unit  300  could be made compatible with a plurality of different types of switch units  200 , thereby streamlining manufacturing procedures and/or inventory requirements. Still another advantage of the present invention is that replacing the switch unit  200  does not require any rewiring of the control unit  300 . Yet another advantage of the present invention is that diagnostic data can be sent via the network connector base  318  for network communications, thereby allowing service technicians, etc. an easy way to identify the status of the various switch units. 
     One may now appreciate that the present invention provides an emergency stop device  100  wherein the switch  202  and the controller  302  are contained in separate modular units  200  and  300  thereby allowing the switch  202  to be readily replaced without replacement and/or reinstallment of the controller  302 . Although the invention has been and described with respect to certain preferred embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon a reading and understanding of this specification. The present invention includes all such equivalent alterations and modifications. It should also be noted that the directional terms and modifiers, such as front, rear, side, top, bottom, etc. used to describe the device  100  correspond to the illustrated orientation. These directional terms have been used only for convenience and ease in explanation with respect to the illustrated embodiment of emergency stop device  100 . They are not intended to, and do not, limit the device  100  to any particular orientation or direction.