Abstract:
A machine guarding system generally includes a switch mat in electrical communication with a machine being guarded. The switch mat is adapted to be placed on a floor adjacent the machine being guarded and includes a pressure actuated switch mechanism which causes power to the machine to be terminated when a pressure is applied to the switch mat. The switch mat further includes a status indicator display disposed on a surface of the switch mat which is illuminated based on a status of the machine being guarded. In a preferred embodiment, the machine guarding system further includes a machine control unit for controlling power to the machine being guarded. The switch mat is in electrical communication with the machine control unit, wherein the switch mechanism causes the machine control unit to terminate power to the machine when a pressure is applied to the switch mat. The machine control unit also illuminates the indicator display based on a status of the machine being guarded.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates generally to safety systems to protect persons from injury from industrial machines, and more particularly, to a system for terminating power and indicating an active condition of a machine. 
   It is known in the art to provide safety systems for dangerous machinery and industrial apparatus to protect persons from injury from such equipment. Such dangerous equipment includes welding machines, robotic assembly devices, metal cutting equipment and the like, all of which may be self-operating or person-operated. Generally, safety systems for such machinery typically involve some form of means for preventing personnel from inadvertently approaching the dangerous equipment or involve some form of alarm or power cut-off to the machine which is activated upon a dangerous condition, such as when a person gets too close to the dangerous equipment. Examples of such safety systems include dual hand operated controls which forces an operator to keep both hands on the controls, presence sensing devices incorporating light beams and receivers and electric switch mats connected to a machine controller for terminating power to the machine if someone steps on or off the mat. 
   Various types of electrical switch mats are known in the art. Electrical switch mats have been designed for use in many different applications including use in floor mats for security, safety or other purposes to detect movement of objects or pedestrian traffic thereover. Generally, electrical switch mats include one or more pressure-actuated switches incorporated within a floor mat material which protects the switch against wear. For example, normally open and normally closed pressure-sensitive electrical ribbon switches have been incorporated into numerous designs for electrical switch mats. Open and closed pressure-sensitive ribbon switches generally include a pair of either spaced or closed conductors respectively supported in an insulative jacket. Generally, relatively light pressure on the jacket will close the space in an open switch and open the conductors in a close switch thereby activating the switch. Thus, someone stepping on or off an electrical switch mat having a ribbon switch incorporated therein will activate the switch. 
   Electrical switch mats as described above have been extremely useful in detecting and responding to the presence, or absence, of the operator or others anywhere on its sensing surface, wherein the sensing surface is defined as the area covered by a single mat or a plurality of mats in combination. In one typical application, one or more sensing mats are placed directly in front of a piece of machinery, wherein the machine operator stands on the mat during operation of the machinery. If the operator steps off the mat, or if someone else steps on the mat, the switch mat is activated to terminate power to the machine. 
   In another application, the dangerous equipment may be surrounded by a plurality of switch mats to define a danger zone, wherein a person entering the danger zone will step on a mat, thereby activating a switch to terminate power to the equipment. Alternatively, the dangerous equipment may be substantially surrounded by a protective barrier, such as a guard cage or fence, to define a danger zone and a switch mat is placed at the only entrance into the danger zone. Similarly, anyone entering the danger zone will step on the switch mat to terminate power to the dangerous equipment. 
   While such switch mat based safety systems are effective in terminating power to a piece of dangerous equipment upon a change in status within the danger zone, it is often difficult for persons approaching such a danger zone to ascertain the present status within the danger zone. In particular, a person having a need to enter the danger zone may not be able to easily determine if it is indeed safe to enter (e.g., the dangerous machinery is already turned off), or whether the zone is in a danger status (e.g. the machinery is operating). 
   Accordingly, it would be desirable to provide a machine guarding safety system that can readily indicate a present status of a danger zone surrounding the dangerous machinery. It would be further desirable to provide a machine guarding safety system utilizing a switch mat having a visual status indicator incorporated directly in the switch mat to display an active status of the danger zone to those approaching the switch mat. 
   SUMMARY OF THE INVENTION 
   The present invention is a machine guarding system that generally includes a switch mat in electrical communication with a machine being guarded. The switch mat is adapted to be placed on a floor adjacent the machine being guarded and includes a pressure actuated switch mechanism which causes power to the machine to be terminated when a pressure is applied to the switch mat. The switch mat further includes a status indicator display disposed on a surface of the switch mat which is illuminated based on a status of the machine being guarded. 
   In a preferred embodiment, the machine guarding system further includes a machine control unit for controlling power to the machine being guarded. The switch mat is in electrical communication with the machine control unit, wherein the switch mechanism causes the machine control unit to terminate power to the machine when a pressure is applied to the switch mat. The machine control unit also illuminates the indicator display based on a status of the machine being guarded. 
   Preferably, the status indicator display is made up of a plurality of first and second color light emitting diodes (LEDs). The first color is illuminated by the machine control unit to indicate a safe condition of the machine being guarded and the second color is illuminated by the machine control unit to indicate a dangerous condition of the machine being guarded. Also, the switch mechanism causes the machine control unit to illuminate the first color when pressure is applied to the switch mat and when power is terminated to the machine being guarded to indicate the safe condition. 
   The machine control unit preferably includes a flasher, a timer and a switch for activating the timer. The flasher alternately illuminates the first and second colors to indicate an interim condition of the machine being guarded. The timer initiates a timing sequence when activated by the switch, wherein the flasher alternately illuminates the first and second color light emitting diodes. The timer then ends the timing sequence after a pre-determined amount of time, wherein the machine control unit provides power to the machine being guarded and illuminates the second color to indicate the dangerous condition of the machine being guarded. 
   In one embodiment, the machine guarding system further includes a guard cage substantially surrounding the machine being guarded. The guard cage defines a machine work area and an entrance to the machine work area. The switch mat is placed at the entrance to the machine work area to detect intrusion into the work area. Alternatively, a plurality of switch mats surrounding the machine being guarded is provided, wherein the switch mats are electrically connected to each other to define the machine work area. 
   The switch mat of the present invention preferably includes a support frame, a flexible plate member supported in the support frame, a pressure actuated switch mechanism disposed between the support frame and the plate member and a status indicator display disposed on a surface of one of the support frame or the plate member. Pressure applied to the plate member actuates the switch mechanism illuminates the status indicator display. The support frame of the switch mat further preferably includes a ramp portion and the status indicator display is disposed on a top surface of the ramp portion. 
   The present invention further involves a method for guarding a machine work area against intrusion. The method generally includes the step of providing a switch mat on a floor adjacent the machine work area being guarded. The switch mat includes a pressure actuated switch mechanism and a status indicator display. The method according to the present invention further includes the steps of terminating power to a machine in the machine work area when a pressure is applied to the switch mechanism of the switch mat and illuminating the indicator display of the switch mat based on a status of the machine work area. 
   In a preferred embodiment, the step of illuminating the indicator display of the switch mat is achieved by illuminating a plurality of first and second color light emitting diodes (LEDs). The first color light emitting diode is illuminated to indicate a safe condition of the machine work area and the second color is illuminated to indicate a dangerous condition of the machine work area. The first color light emitting diode is also illuminated when a pressure is applied to the switch mechanism and power is terminated to the machine in the work area to indicate the safe condition. 
   Also, the first and second color light emitting diodes are further preferably illuminating in an alternating fashion to indicate an interim condition of the machine work area. In this regard, the method of the present invention further preferably includes the steps of initiating a timing sequence to begin the step of alternately illuminating the first and second color light emitting diodes, ending the timing sequence after a pre-determined amount of time, illuminating the second color light emitting diode to indicate the dangerous condition of the machine work area after the timing sequence has ended and providing power to the machine in the machine work area after the timing sequence has ended. 
   As a result of the present invention, a safety system is provided to visually indicate an interactive status between persons and machines, equipment and other dangerous devices. Status indicator lights incorporated in a sensing mat of the safety system serve to indicate, enhance or draw attention to the current status of a potential danger zone surrounding a machine or other industrial equipment. 
   These and other objects, features, and advantages of this invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic drawing of the machine guarding system formed in accordance with the present invention. 
       FIG. 2  is a schematic drawing of an alternative embodiment of the machine guarding system formed in accordance with the present invention. 
       FIG. 3  is a schematic wiring diagram of the machine guarding system shown in  FIG. 1 . 
       FIG. 4  is a top perspective view of a sensing mat with status indicator lights formed in accordance with the present invention. 
       FIG. 5  is a cross-sectional view of the sensing mat shown in  FIG. 4  taken along the line  5 — 5 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring first to  FIG. 1 , a machine guarding system  10  formed in accordance with the present invention generally includes an electrical switch mat  12  having status indicator lights  14  incorporated therein and a control unit  16  electrically connected to the switch mat. A switch mat or sensing mat as used herein is also defined as encompassing sensing edges, sensing bumpers and ribbon switches. 
   The control unit  16  is electrically connected to a machine  18  or other piece of dangerous equipment for controlling power to the machine based on activation of the switch mat  12 . The guarding system arrangement shown in  FIG. 1  includes a hard guarding cage  20  substantially surrounding the machine  18  to define a danger zone  22  having an entrance  24 . In this arrangement, the switch mat  12  is located at the entrance  24  to the danger zone  22  so that anyone entering the danger zone will necessarily step on the switch mat. 
   As described above, however, a plurality of switch mats  12  may be utilized instead of the hard cage  20  to define the danger zone  22 , as shown in  FIG. 2 . In this embodiment, each switch mat  12  is electrically connected in series to adjacent switch mats to form a continuous sensing barrier. Thus, someone stepping on any one switch mat  12  of the sensing barrier will trigger the system as described in further detail below. 
   Referring additionally to  FIG. 3 , the switch mat  12  preferably includes light emitting diode (LED) indicator lights  14  of at least two contrasting colors disposed around a substantial portion of the periphery of the mat. Preferably, the switch mat  12  includes red LEDs  14   a  interspersed with green LEDs  14   b  along the peripheral edge of the mat. As will be discussed in further detail below, the control unit  16  alternately illuminates the red LEDs  14   a  and the green LEDs  14   b  depending on the active status of the danger zone  22 . 
   The control unit  16  preferably includes a machine controller  26 , a normally open momentary switch  28 , a 115VAC timer  30  with 0.5 to 10 second adjustability, a 115 VAC DPDT relay K 1  having a coil  32 , a 12VDC DPDT relay K 2  having a coil  34 , and a 12 VDC flasher  36 . The control voltages used are an externally supplied 115VAC and 12 VDC, which can be externally or internally supplied to the control unit  16 . The machine controller  26  also preferably includes its own status indicator lights in the form of a red “MACHINE POWER” LED  38   a , an amber “RESET” LED  38   b , a green “SENSOR CLEAR” LED  38   c  and a green “OUTPUT”, the operation of which will be described in further detail below. One suitable machine controller  26  for use with the present invention is Guardstar Model No. PSSU/3 manufactured and distributed by Tapeswitch Corporation, 100 Schmitt Boulevard, Farmingdale, N.Y. Other control unit types, however, may also be used. 
   When the danger zone  22  is in a safe or static condition (i.e., the machine  18  is turned off and not operating), the red “MACHINE POWER” status indicator LED  38   a  of the controller  26  is off, the yellow “RESET” status indicator LED  38   b  is off, the green “SENSOR CLEAR” status indicator LED  38   c  is on and the “OUTPUT” status indicator LED  38   d  is off. In this condition, the control unit  16  also illuminates the green LEDs  14   b  on the switch mat  12  to indicate a safe condition within the danger zone  22 , wherein entry can be made without danger. 
   When it is desired to power-up the machine  18 , the normally open momentary initiation switch  28  is pressed and released to start the timer  30 . The timer  30  energizes the 115 VAC coil  32  of the relay K 1 , making the relay contacts of pins  2  and  7  change state from normally closed to normally open. +12 VDC is then applied from the relay K 1 , pin  6  to energize the coil  34  of the 12 VDC relay K 2  making the relay contacts of pins A and B change state from normally closed to normally open. +12 VDC is also applied thru the contacts of pin  3  of the relay K 1 , to the 12 VDC flasher  36 , which in turn alternately illuminates or “flashes” the red and green LEDs  14   a  and  14   b  of the switch mat  12 . Preferably, +12 VDC is applied to the green LED  14   b  of the switch mat  12  through an N/C (pin  9 ) portion of a reset circuit  40  in the machine controller  26 . Also, in a preferred embodiment, pin  6  of the relay K 2  is supplied pulses from the flasher  36 , which causes both the red and green LEDs  14   a  and  14   b  of the switch mat  12  to alternately flash on and off at about 1 second intervals. Moreover, pins  4  and  7  of the relay K 2  preferably act like a momentary switch to the reset input of the reset circuit  40  of the machine controller  26 . 
   The LEDs  14   a  and  14   b  of the switch mat  12  thus illuminated in a flashing green and red pattern indicate that the machine area  22  is now in a condition that a change is about to occur. Specifically, the flashing red and green LEDs  14   a  and  14   b  of the switch mat  12  indicate an imminent change from a safe condition to a potentially dangerous condition. In this regard, the LEDs on the controller  26  may also be illuminated in a particular pattern to indicate this condition. In particular, the red “MACHINE POWER” status indicator LED  38   a  of the controller  26  will still be off, but the yellow “RESET” status indicator LED  38   b  will now be turned on, while the green “SENSOR CLEAR” status indicator LED  38   c  is on and the “OUTPUT” status indicator LED  38   d  is off. 
   Once the timer  30  has timed out, voltage is removed from pin  2  of the relay K 1  and the relay contacts return to their normally closed position. This action causes the applied voltage from pin  6  of the relay K 1  to pin A of the relay K 2  to stop, thereby de-energizing relay K 2 . The pulses from the 12 VDC flasher  36  are no longer present because pin  6  of the relay K 2  has returned to it normally open position causing the pulses going to both the red and green LEDs  14   a  and  14   b  of the switch mat  12  to stop. Pin  1  of the relay K 2 , now normally closed, allows pin  4  of the relay K 2  to be normally open. This action causes the reset input of the controller reset circuit  40  to make the reset circuit change from normally closed to normally open, switching +12VDC thru pin  7  of the controller  26  to energize the red LED  14   a  of the switch mat  12  and de-energize the green LED  14   b  of the switch mat. With the red LED  14   b  of the switch mat  12  now steadily illuminated, the switch mat indicates that the machine area  22  is now in a dangerous condition making it unsafe to enter. 
   Similarly, in an unsafe status condition, the controller LEDs are illuminated accordingly. Specifically, the red “MACHINE POWER” status indicator LED  38   a  of the controller  26  will now be on, while the yellow “RESET” status indicator LED  38   b  will now be turned off. The green “SENSOR CLEAR” status indicator LED  38   c  is on and the “OUTPUT” status indicator LED  38   d  is off. 
   If there is any entry into the machine area danger zone  22 , the switch mat  12  will detect such entry and cause power to the machine  18  to be terminated. In particular, when the switch mat  12  is activated, the internal switch mechanism of the mat changes from a normally open to a closed condition, as will be described in further detail below. This causes the controller  26  to open an output circuit to the machine controls, thereby shutting the machine off. The reset circuit  40  in the controller  26  changes from normally open to normally closed, whereby the +12VDC is removed from between pin  7  of the controller and the red LED  14   a  of the switch mat  12 , thereby turning the red LED off. On the other hand, +12VDC is now applied thru pin  9  of the controller  26 , thereby turning on the green LED  14   b  of the switch mat  12 . Thus, the green LEDs  14   b  of the switch mat  12  are again steadily illuminated to indicate that the machine area  22  is now safe to enter. In the same manner, the red “MACHINE POWER” status indicator LED  38   a  of the controller  26  will now be off and the yellow “RESET” status indicator LED  38   b  will be off, but the green “SENSOR CLEAR” status indicator LED  38   c  will now be turned off and the “OUTPUT” status indicator LED  38   d  will be off. 
   Once the sensing mat  12  is cleared, the machine control system  10  returns to its static condition, as described above. Specifically, the green LEDs  14   b  of the switch mat  12  are steadily illuminated until the initiation sequence is begun by pressing and releasing the normally open momentary initiation switch  28  to start the timer  30 . Once the timer  30  times out, power is restored to the machine  18 . 
   As mentioned above, various types of switch mats may be used with the present invention. However, in a preferred embodiment, the present invention utilizes a switch mat as described in commonly owned U.S. Pat. No. 6,054,658, the specification of which is incorporated herein by reference. In particular and as shown in  FIGS. 4 and 5 , the electrical switch mat  12  of the preferred embodiment generally includes a semi-rigid support frame  42  a flexible plate member  44  and at least one switch mechanism  46  disposed between the support frame and the plate member. Preferably, the switch mat  12  further includes a plurality of elastic members  48  and a plurality of plate member supports  50  for helping support the plate member  44  within the frame support  42 . 
   The switch mechanism  46  is operable under pressure between a closed condition and an open condition and is maintained, in this case, in the opened condition in the absence of pressure. The switch mechanism  46  can be a conventional open-style ribbon switch, as described above, which generally includes a pair of vertically spaced electrical conductors  52  enclosed in an insulative jacket  54 . Compression applied to the plate member  44  transfers pressure to the insulative jacket  54  causing the pair of electrical conductors  52  to move into electrical engagement. Alternatively, the switch mechanism  46  can be a closed-type ribbon switch wherein pressure applied to the switch interrupts the electrical engagement of the contacts. 
   Each switch mechanism  46  is supported within a respective protective receiving space  56  of the support frame  42  which extends across the surface area of the plate member  44 . The switch mechanisms  46  can be electrically connected to each other in a conventional manner with wire leads to maintain electrical conductivity between electrical conductors of the intermittent-sections of the switch mechanisms. An external wire lead  57  electrically connects the plurality of switching mechanisms  46  to the control unit  16 . 
   The support frame  42  is preferably made from a plurality of aluminum frame members that can be sized to fit the particular needs of the electric mat user. For example,  FIGS. 1 and 4  show rectangular electrical switch mats  12 , but other shapes and configurations are contemplated, such as semi-circular shaped switch mats, as shown in  FIG. 2 . The plate member  44 , which may also be made from aluminum, is sized to fit within the two-dimensional area defined by the support frame  42  and may also be covered with a flooring material  58 . The plate member  44  is supported by a plurality of plate-member supports  50  attached to the bottom of the plate member, as shown in  FIG. 5 . The plate-member supports  50  are sized to insure that in the presence of pressure, the plate member  44  can freely deflect to transmit activating compression to the switch mechanisms  46 . However, once the switch mechanism has been activated, the plate-member supports  50  prevent further deflection of the plate member. The plate member  44  is further preferably supported by a plurality of open cell foam elastic members  48  for biasing the plate member with respect to the support frame  42 . 
   As shown in  FIG. 5 , the support frame  42  includes a ramp portion  60  to facilitate pedestrian traffic and objects which are rolled across the electric switch mat  12 . The ramp portion  60  includes a plurality of ramp support members  62  extending from a bottom surface thereof for reinforcement of the ramp portion and a skid resistant dust cover  64  disposed over a top surface thereof. Furthermore, in order to seal the bottom of the electrical switch mat  12 , a dust barrier  66  is preferably provided. The dust barrier  66  can be formed from a plastic fabric and is attached at the base of the support frame  42 . 
   However, unlike conventional switch mats, the switch mat  12  of the present invention includes status indicator lights  14  incorporated on a surface thereof. In a preferred embodiment, the status indicator lights  14  of the present invention are in the form of one or more light strips  68  having alternating red and green LEDs  14   a  and  14   b  disposed thereon. The strips  68  are received in correspondingly sized slots  70  or recesses formed in a top surface  72  of the ramp portion  60  of the support frame  42 . The LED strips  68  may be adhered or otherwise fastened within the receiving slots  70  of the support frame so that the strips are disposed flush with the top surface  72  of the ramp portion. The strips  68  preferably extend around the entire periphery of the switch mat  12  so that the indicator LEDs can be seen from any direction. 
   While the present invention has been described herein with respect to a sensing mat or a sensing edge, it is conceivable that the status indicator lights can also be incorporated in treadles, interlocks and light curtains. For example, another possible application of the present invention is in a transit bus treadle, wherein the LED status indicator lights will indicate to passengers a “safe” mode when green so that passengers may enter or exit the bus, a “warning” mode when flashing green and red to indicate that the bus doors will close shortly and a “danger” mode when red to indicate that the doors are closed or when somebody is already on the treadle. Other possible applications of the present invention include assembly line applications, commercial car wash facilities, powered door applications, amusement parks and point of purchase advertising. 
   Although illustrative embodiments of the present invention have been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various other changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention.