Abstract:
An apparatus and method of disabling a drive system of a passenger conveying system is provided. The passenger conveying system is monitored with switches each arranged to detect a respective malfunction of the passenger conveying system. A shutdown signal is produced by a respective one of the switches detecting the respective malfunction and is coupled to a corresponding shutdown contact and to a controller. The corresponding shutdown contact operates to interrupt a drive enabling signal of the drive system in response to receipt of the shutdown signal. The controller monitors the shutdown signals from the switches and the drive enabling signal. The controller sends a signal to open a redundant contact to interrupt the drive enabling signal if the shutdown signal is detected and the drive system remains enabled.

Description:
BACKGROUND OF THE INVENTION 
   Escalators are provided with safety systems, each one of which is operable to stop movement of the escalator in the event that an unsafe operating condition is detected. Examples of such unsafe operating conditions include: a missing step or a detached step on the escalator; a handrail which is moving at an improper speed; something becoming caught between adjacent steps or between the steps and the side skirts; a foreign object becoming lodged between the step treads and the comb plate at the escalator exit landing; or the like. The safety system components used to detect unsafe escalator operating conditions include proximity sensors, switches, pressure sensors, or the like, which are able to detect unsafe escalator-operating conditions so long as the sensors and their associated circuitry remain operative. 
   U.S. Pat. No. 5,601,178 describes a method and apparatus for checking escalator safety circuit components to confirm circuit operability prior to start up of motion of the escalator. A start up check relay is energized whenever escalator motor motive power is interrupted. The start up check relay checks speed and non-speed-dependent safety circuit components to determine whether these safety circuit components have all come to an escalator start up state. When the start up condition of these safety circuit components has been verified the circuit allows power to be applied to the escalator motor. When power is applied to the escalator motor, a start up delay timer is energized and the start up check relay is de-energized. When speed-dependent components of the escalator have come to operating speeds, the start up delay timer will be de-energized, and the escalator will continue movement in its normal operating mode provided that all safety circuits are fully operational. 
   U.S. Pat. No. 6,230,871 describes a device for monitoring functional units on escalators and moving walkways, comprising several processors which monitor predetermined parameters of a particular functional unit independently of each other. The processors are connected to devices for immediately shutting down the escalator or moving walkway and interact with at least one other processor which is provided for controlling and/or diagnosing functions which are not relevant to safety. 
   U.S. Pat. No. 6,758,319 describes a method and a system for disconnecting passenger transport systems, especially escalators and moving walkways. Functional units of a passenger transport system monitor for malfunctions of the passenger transport systems by using switching elements and the signals of the functional units are combined to form a security chain. The signals of the functional units and signals from a drive monitoring unit are supplied to at least one pilot unit. Subsequently, a disconnecting signal is provided to a respective disconnecting contact as a result of a malfunction detected by the functional units and/or the drive monitoring system. 
   Current safety systems require large amounts of wiring and switches. Also, there is no mechanism provided for determining the operability of the safety system detectors or their circuitry. There is a need for a cost effective solution that addresses these problems. 
   SUMMARY OF THE INVENTION 
   In an exemplary embodiment of the invention, a safety circuit for a passenger conveyor having a drive system is provided. The safety circuit comprises a plurality of controllable switches, each switch of the first plurality of controllable switches being responsive to a functional unit associated with the passenger conveyor to produce a first switch output signal having a first state if the functional unit is operating properly and a second state if the functional unit is malfunctioning; a controller apparatus including: a plurality of input terminals each coupled to a respective one of the switches for receiving the respective switch output signals; a plurality of interrupt switches, each interrupt switch being arranged in electrical series to conduct a drive enabling signal for the drive system when all of the interrupt switches are in a closed state, each interrupt switch being coupled to a respective one of the input terminals and being opened in response to a respective first switch output signal having the second state to interrupt the drive enabling signal to stop operation of the drive system; a redundant interrupt switch arranged in electrical series with the plurality of interrupt switches, wherein the series connection of the redundant interrupt switch and the plurality of interrupt switches has an output producing a second output signal having a first state if all of the interrupt switches and the redundant interrupt switch are closed and a second a state if any one of the interrupt switches and the redundant interrupt switch is open; and a controller arranged to monitor the state of the first switch output signals of the plurality of controllable switches and to monitor the state of the second output signal, the controller sending a signal to open the redundant interrupt switch when the signal state of the any one of the first switch output signals has the second output state and the second output signal has the first signal state. 
   In another embodiment of the invention, a method of disabling a drive system of a passenger conveying system is provided. The method comprises monitoring the passenger conveying system with switches each arranged to detect a malfunction of the passenger conveying system; providing a shutdown signal from a respective one of the switches detecting a malfunction to a corresponding shutdown contact and to a controller; operating the corresponding shutdown contact to interrupt a drive enabling signal of the drive system in response to receipt of the shutdown signal from one of the switches; monitoring the shutdown signals from the switches and the drive enabling signal with the controller; sending a signal from the controller to open a redundant contact to interrupt the drive enabling signal if the shutdown signal is detected and the drive system remains enabled. 
   In another embodiment of the invention, a method comprises monitoring a passenger conveying system with functional units, each functional unit having a switch; providing a shutdown signal from a respective switch for the functional unit to a controller and to a corresponding shutdown contact when a fault with the passenger conveying system is detected by the functional unit; detecting with the controller if the shutdown contact opens; sending a signal from the controller to open a redundant contact if the shutdown contact does not open. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of a circuit according to an embodiment of the invention; and 
       FIG. 2  is a schematic diagram of a circuit according to an exemplary embodiment of the invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1  illustrates an exemplary embodiment of a safety circuit according to the invention. The safety circuit may be used for stopping operation of passenger conveying systems, such as escalators, moving walkways, travelators, etc. The safety circuit includes a number of switches S 1 -SN that are associated with and controlled by respective functional units F 1 -F N , for example handrail intake monitoring, step intake monitoring, chain brake monitoring, etc. Switches S 1 -SN are normally closed during operation, although for purposes of illustration they are all shown in the open state. The switches S 1 -SN may be activated when a fault in a corresponding functional unit of the passenger conveying system is detected. The switches S 1 -SN may be connected in parallel with each other. One contact  11  of each respective switch S 1 -SN is connected to a signal line  30 . A voltage may be applied to the signal line  30 . The other contact  12  of each switch S 1 -SN is connected to a respective input A 1 -AN on a controller board  32 . 
   The controller board  32  may be arranged at a distance from the switches S 1 -SN, sometimes hundreds of feet. In embodiments of the invention, an individual wire  13   1 - 13   N  from a respective switch S 1 -SN to the controller board  32  may couple the switches S 1 -SN to the controller board  32 . This structure and accompanying method may eliminate the need for two or more wires from the switches to the controller board  32 , for example, as shown in U.S. Pat. No. 6,758,319, and provide a significant savings in material and labor. 
   A plurality of interrupt switches may be coupled, respectively, to inputs A 1 -AN on the controller board  32 . The inputs A 1 -AN may be coupled to corresponding switches S 1 -SN to receive switch output signals. The interrupt switches may be arranged in electrical series to conduct a drive enable signal for the drive system  5  of the passenger conveying system. The interrupt switches may comprise electrical switches, electromechanical switches, and/or mechanical switches. 
   For example, the interrupt switches may comprise relays including coils  14   1 - 14   N  and corresponding contacts  20   1 - 20   N . The contacts  20   1 - 20   N  are closed during operation of the drive system  5 . The coils  14   1 - 14   N  may be coupled, respectively, to inputs A 1 -AN on the controller board  32 . The contacts  20   1 - 20   N  may be arranged in electrical series. The series connection of contacts  20   1 - 20   N  conducts the drive enable signal for the drive system  5  of the passenger conveying system. 
   When a switch S 1 -SN is opened, a signal is sent to open corresponding interrupt switch to interrupt the drive enable signal and stop operation of the passenger conveying system. For example, opening one of switches S 1 -SN interrupts current flow through the corresponding coil  14   1 - 14   N , causing the corresponding contacts  20   1 - 20   N  to open. Opening any one of contacts  20   1 - 20   N  interrupts the drive enable signal for the passenger conveying system. Operation of the safety circuit to stop operation of the passenger conveying system is discussed in more detail below. 
   A redundant interrupt switch may be provided. The redundant interrupt switch may be arranged in series with the interrupt switches to conduct the drive enable signal. The redundant interrupt switch should be independent from the switches S 1 -SN, that is, the redundant interrupt switch should not be controlled by switches S 1 -SN. The redundant interrupt switch may be used to interrupt the drive enable signal if there is a failure in opening any of interrupt switches. The redundant interrupt switch may comprise electrical switches, electro-mechanical switches, and/or mechanical switches. 
   For example, the redundant interrupt switch may comprises a redundant relay including coil  25  and contacts  26 . The redundant relay should be independent from the switches S 1 -SN, that is, the redundant relay should not be controlled by switches S 1 -SN. The redundant relay may have its contacts  26  arranged in series with contacts  20   1 - 20   N  to conduct the drive enable signal. Current flow through the coil  25  may be controlled by a controller, such as microprocessor  34 . The redundant relay may be used to interrupt the drive enable signal if there is a failure in opening any of contacts  20   1 - 20   N . 
   When the switches S 1 -SN close and open, the switch output signals take a first state and a second state corresponding to a logic level high and logic level low, respectively. The logic level high and logic level low is present at the inputs A 1 -AN. Microprocessor  34  may monitor the logic levels at the inputs A 1 -AN and an output SAFE_OUT of the series arrangement of contacts. Sense circuits SE 1 -SE N  may detect the logic high or logic low at inputs A 1 -AN. A separate sense circuit SE 1 -SE N  should be provided for each switch S 1 -SN. The sense circuits SE 1 -SE N  may be coupled to microprocessor  34  for monitoring the logic level at inputs A 1 -AN. A sense circuit  50  may also be coupled to the output SAFE_OUT. The microprocessor  34  may monitor SAFE_OUT via the sense circuit  50 . The microprocessor  34  may send a signal to open one or more of the contacts  20   1 - 20   N  and/or  26  based on the logic levels at the inputs A 1 -AN and SAFE_OUT. 
   In operation of the safety circuit, a respective switch S 1 -SN is opened when a fault in the passenger conveying system is detected. In the embodiment shown, opening a switch S 1 -SN interrupts current flow through that switch S 1 -SN and causes a logic low at the corresponding input A 1 -AN. A logic low at any one of inputs A 1 -AN should cause interruption of the drive enable signal. Interruption of the drive enable signal may be done in several ways. The opening of any one of the switches S 1 -SN interrupts current flow through the corresponding coil  14   1 - 14   N , causing the corresponding contact  20   1 - 20   N  to open. Opening any one of the contacts  20   1 - 20   N  interrupts the drive enable signal to stop operation of the passenger conveying system. Opening any one of the contacts  20   1 - 20   N  also causes a logic low at SAFE_OUT. 
   The logic level at the inputs A 1 -AN is detected and compared with the logic level at the output SAFE_OUT by the microprocessor  34  to ensure proper operation of the safety circuit. If a logic low is detected at any one of the inputs A 1 -AN, but a logic high is present at SAFE_OUT, an error has occurred. For example, the contacts of a relay may be welded shut, maintaining the logic high at SAFE_OUT. 
   In such a case, microprocessor  34  may send a signal to stop operation of the passenger conveying system device. For example, the microprocessor  34  may send a signal to open redundant relay contacts  26  via coil  25 . If the signal to the redundant relay does not interrupt the drive enable signal, the microprocessor  34  may send a signal to open additional ones or all of the relay contacts  20   1 - 20   N . The microprocessor  34  may also generate fault codes to indicate where an error occurred, for example, which contacts failed to open. 
     FIG. 2  illustrates a more detailed example of the safety circuit. In the embodiment illustrated in  FIG. 2 , the sense circuits SE 1 -SE N  comprise opto-isolators  9   1 - 9   N . Each opto-isolator includes a light emitting diode  54  and a photo-transistor  56 . Each switch S 1 -SN is coupled to a respective relay  12   1 - 12   N  and to an opto-isolator  9 , although only the relay  12  associated with switch S 1  on the left side of the drawing is illustrated. An opto-isolator  9  should be associated with each switch S 1 -SN. An output of each opto-isolator  9   1 - 9   N  is provided to the microprocessor  34 . Based on the information received from the opto-isolator  9 , the microprocessor  34  can determine whether a switch S 1 -SN is open or closed. 
   Referring to relays  12   1 - 12   N , diode  18  may be coupled to the coils  14   1 - 14   N  and contacts  20   1    20   N . In addition, each coil  14   1 - 14   N  may be respectively connected in series with a transistor  38  to control the flow of current through the coil. The transistors  38  may be controlled by a signal from the microprocessor  34 . For example, a control electrode  40  of the transistors  38  may receive a control signal from the microprocessor  34 . The microprocessor  34  provides the control signal to the control electrode  40  to turn on or turn off the transistor  38 , allowing or disabling current flow through the respective relay coil  14   1 - 14   N . A capacitor  16  may also be provided as will be understood by those skilled in the art. 
   Redundant relay  13  may include diode  19  coupled to the coil  25  and contacts  26 . In addition, coil  25  may be connected in series with a transistor  39  to control the flow of current through the coil  25 . The transistor  39  may be controlled by a signal from the microprocessor  34 . For example, microprocessor  34  provides the control signal to turn on or turn off the transistor  39 , allowing or disabling current flow through the coil  26 . Capacitor  17  may also be provided 
   The microprocessor  34  on the controller board  32  may be in communication with a main controller  42 . The main controller  42  controls the operation of the passenger conveying system. 
   A method of operating an exemplary embodiment of a safety circuit, such as the safety circuit described above is now described. When a switch S 1 -SN opens, for example due to a fault in a corresponding functional unit, the corresponding coil  14   1 - 14   N  de-energizes, causing corresponding contacts  20   1 - 20   N  to open. The drive enable signal is interrupted and the output SAFE_OUT should be a logic low. At the same time, a logic low is present at the corresponding input A 1 -AN on the controller board  32 . The microprocessor  34  monitors the output SAFE_OUT and the output of the switches S 1 -SN at inputs A 1 -AN. When operating properly, SAFE_OUT is a logic low when any one of the inputs A 1 -AN is a logic low. If this is not the case, an error is detected. 
   For example, if the microprocessor  34  detects that the logic level at input A 1  is low, but the output SAFE_OUT is high, an error is detected. This may occur, for example, if the relay contacts  20   1  become welded shut. An error code for coil  14   1  and contacts  20   1  may the be generated. When such an error is detected, the microprocessor  34  may send a signal to open redundant relay contacts  26 . This may be done by causing transistor  39  to turn off, interrupting current flow through the redundant relay coil  25 , which, in turn, opens relay contacts  26 , interrupting the drive enable signal and causing the passenger conveying system to stop. 
   It is possible that an error may occur in opening relay contacts  26 . Therefore, the microprocessor  34  may continue to monitor the output SAFE_OUT after sending the signal to open redundant relay contacts  26 . If the redundant relay contacts  26  fail to interrupt the drive enable signal and to cause the output SAFE_OUT to go low, the microprocessor  34  detects the error. The microprocessor  34  may then send a signal to open one or more of relays contacts  20   1 - 20   N  to interrupt the drive enable signal, for example via transistors  38 , thereby providing another level of redundancy. 
   It is further possible that an error may occur with the microprocessor  34 . The main controller  42  may monitor the microprocessor  34  to ensure that the microprocessor  34  is operational. For example, messages may be intermittently exchanged between the microprocessor  34  and main controller  42 . If the main controller  42  does not receive an expected message from the microprocessor  34  and/or an expected acknowledgement, the main controller  42  may determine that the microprocessor  34  is not operational. In such a case, the main controller  42  may send a signal to de-energize the motor and brake contactors of the passenger conveying system. 
   Additionally, after a fault with the passenger conveying system is detected and a switch S 1 -SN opened, the safety circuit is set to a “not ready” mode. In order to change to a “ready” mode, the main controller  42  requires a test of the safety circuit. Each of the switches S 1 -SN and relays should be tested before a change to the “ready” mode is allowed. During the test, the microprocessor  34  may send a signal to open each relay contact  20   1 - 20   N  and  26  to check if the output SAFE_OUT is a logic low when the signal to open that particular relay is sent. If the output SAFE_OUT does not go low, an error is detected for that relay. For any errors, a fault report indicating the relay(s) which had the error may be generated. 
   The embodiments illustrated and discussed in this specification are intended only to teach those skilled in the art the best way known to the inventors to make and use the invention. Nothing in this specification should be considered as limiting the scope of the present invention. The above-described embodiments of the invention may be modified or varied, and elements added or omitted, without departing from the invention, as appreciated by those skilled in the art in light of the above teachings. It is therefore to be understood that, within the scope of the claims and their equivalents, the invention may be practiced otherwise than as specifically described.