Abstract:
An elevator safety circuit includes a plurality of relays; safety logic for monitoring status of the plurality of relays, the safety logic generating an output signal in response to the status of the plurality of relays; and a processor controlling operation of an elevator drive in response to the output signal; wherein at least one of the relays is a forced guided relay and at least one of the relays is other than a forced guided relay.

Description:
FIELD OF INVENTION 
       [0001]    The subject matter disclosed herein relates generally to the field of elevator systems, and more particularly, to a safety circuit for an elevator system. 
       BACKGROUND 
       [0002]    Elevator systems may include safety circuits to control operation of the elevator systems in a predefined manner. U.S. Pat. No. 5,407,028 discloses an exemplary elevator safety circuit that employs a number of relays to provide power to an elevator brake and elevator motor. Existing safety circuits employ forced guided relays to apply or interrupt power to elevator components, such as a brake or motor. Forced guided relays have contacts that are mechanically linked, so that all contacts are ensured to move together. Forced guided relays are typically more expensive than other relays lacking a mechanical connection between relay contacts. Also, forced guided relays are typically larger than other relays lacking a mechanical connection between relay contacts. 
       BRIEF SUMMARY 
       [0003]    According to an exemplary embodiment, an elevator safety circuit includes a plurality of relays; safety logic for monitoring status of the plurality of relays, the safety logic generating an output signal in response to the status of the plurality of relays; and a processor controlling operation of an elevator drive in response to the output signal; wherein at least one of the relays is a forced guided relay and at least one of the relays is other than a forced guided relay. 
         [0004]    Other aspects, features, and techniques of embodiments of the invention will become more apparent from the following description taken in conjunction with the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    Referring now to the drawings wherein like elements are numbered alike in the FIGURES: 
           [0006]      FIG. 1  depicts an elevator safety circuit in a standstill condition in an exemplary embodiment; and 
           [0007]      FIG. 2  depicts a drive unit including the safety circuit of  FIG. 1  in an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0008]      FIG. 1  depicts an elevator safety circuit  10  in an exemplary embodiment. Elevator safety circuit  10  applies or interrupts power to an elevator brake  12  (e.g., on an elevator car or drive unit) and an elevator drive  14 . Elevator drive  14  provides power (e.g., 3 phase power) to elevator motor  16  to impart motion to an elevator car. 
         [0009]    Elevator safety circuit  10  includes a brake relay  20  that applies or interrupts power to brake  12 . Brake relay  20  is other than a forced guided relay. Elevator safety circuit  10  includes a drive relay  30  that applies or interrupts power to drive  14 . Drive relay  30  is other than a forced guided relay. Elevator safety circuit  10  includes a safety relay  40 . Safety relay  40  includes three contacts,  42 ,  44  and  46 , connections to which are described in further detail herein. Safety relay  40  is a forced guided relay, meaning that contacts  42 ,  44  and  46  are mechanically linked to move together. 
         [0010]    Brake relay  20  includes a contact  22  connected to a first contact  42  of safety relay  40 . Power to the brake  12  is applied through contact  22  and first contact  42 . Drive relay  30  includes a contact  32  connected to a second contact  44  of safety relay  40 . Power to the drive  14  is applied through contact  32  and second contact  44 . Third contact  46  of safety relay  40  is connected to a reference voltage V 1 , which may be a ground, logic one (e.g., 5 volts), etc. 
         [0011]    The states of brake relay  20 , drive relay  30  and safety relay  40  are monitored in order to determine if the system is in a proper state to operate an elevator car. Safety logic  50  receives monitoring signals from each of the brake relay  20 , drive relay  30  and safety relay  40 . A connection  24  is provided from a location in brake relay  20  to safety logic  50 . The connection  24  may include a coupler  26 , convert the voltage of a brake relay monitoring signal from brake relay  20  (e.g., 48 volts) to a level suitable for safety logic  50  (e.g., 5 volts). Coupler  26  may be an opto-coupler or other known type of device. In operation, when contact  22  is closed, the brake relay monitoring signal will indicate this state to the safety logic  50  (e.g., a 5 volt signal is provided to safety logic  50 ). When contact  22  is open, the brake relay monitoring signal is not provided to safety logic  50 . 
         [0012]    A connection  34  is provided from a location in drive relay  30  to safety logic  50 . The connection  34  may include a coupler  36 , convert the voltage of a drive relay monitoring signal from drive relay  30  (e.g., 22 volts) to a level suitable for safety logic  50  (e.g., 5 volts). Coupler  36  may be an opto-coupler or other known type of device. In operation, when contact  32  is closed, the drive relay monitoring signal will indicate this state to the safety logic  50  (e.g., a 5 volt signal is provided to safety logic  50 ). When contact  32  is open, the drive relay monitoring signal is not provided to safety logic  50 . 
         [0013]    A connection  48  is provided from a location in safety relay  40  to safety logic  50 . At standstill, when contact  46  is closed, a safety relay monitoring signal will indicate this state to the safety logic  50  (e.g., a reference voltage V 1  signal is provided to safety logic  50 ). This indicates that contact  42  and  44  are opened. When contact  46  is open, the safety relay monitoring signal is not provided to safety logic  50 . 
         [0014]    Safety logic  50  receives the brake relay monitoring signal, drive relay monitoring signal and safety relay monitoring signal and generates an output signal. The safety logic  50  may include logic gates (e.g., AND, OR, NOR) to generate a three-bit output signal that is provided to a processor  60 . Processor  60  controls operation of the elevator system based on the output signal from the safety logic  50 . For example, processor  60  may prevent starting of motor  16  if one of brake relay  20 , drive relay  30  or safety relay  40  has not closed. Further, processor  60  may prevent starting of motor  16  if one of brake relay  20 , drive relay  30  or safety relay  40  has not opened after an elevator run. 
         [0015]    Safety logic  50  may also be placed into a test mode so that test signals may be applied to the safety logic  50 , and the resultant output signal monitored.  FIG. 1  depicts test signals  70  applied to safety logic  50 . The output of the safety logic  50  can then be checked to ensure proper operation. This may be performed periodically (e.g., once a year) as part of an inspection process. 
         [0016]      FIG. 2  depicts a drive unit  100  including the safety circuit  10  of  FIG. 1  in an exemplary embodiment. Drive unit  100  includes a power board  102  and a control board  104 . Power board  102  includes drive  14  that controls a converter  106 . Converter  106  includes switches that convert DC power from battery  108  to AC power to drive motor  16  in motoring mode. Conversely, converter  106  converts AC power from motor  16  to DC power to charge battery  108  in regenerative mode. 
         [0017]    Safety circuit  10  is located on control board  104 . Brake relay  20 , drive relay  30  and safety relay  40  are represented as a safety chain on control board  104 . Safety logic  50  is also positioned on control board  104 , along with couplers  26  and  36 . Brake relay contact  22 , drive relay contact  32 , and safety relay contacts  42 ,  44  and  46  are also on control board  104 . As described above with reference to  FIG. 1 , safety logic  50  uses the brake relay monitoring signal, drive relay monitoring signal and safety relay monitoring signal to enable and disable operation of the drive unit  100 . 
         [0018]    Several advantages are provided by using relays other than forced guided relays. Brake relay  20  and drive relay  30  are smaller in physical size than safety relay  40 , reducing the overall size of the safety circuit  10 , as compared to safety circuits employing all forced guided relays. Brake relay  20  and drive relay  30  may be surface mount devices. Further, the cost of safety circuit  10  is reduced, as compared to using all forced guided relays. 
         [0019]    The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. While the description of the present invention has been presented for purposes of illustration and description, it is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications, variations, alterations, substitutions, or equivalent arrangement not hereto described will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. Additionally, while the various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as being limited by the foregoing description, but is only limited by the scope of the appended claims. Features shown with one embodiment may be used with any other embodiment even if not described with the other embodiments.