Redundant multidrop communication system for elevators

Abstract

An elevator system comprises a plurality of cars, and a group controller. A pair of multidrop communication links are connected with the cars such that, absent a communication break, a datagram transmitted by any car controller onto either link may be received by any or all of the remaining car controllers. Each car controller includes means for designating a primary link for each of the remaining cars, and means for rebroadcasting datagrams intended for another car on the primary link only when the datagram is received on a link other than the primary link. Preferably, each controller includes a means to determine when communications with another car, over the primary link, have been disrupted, and to switch the designation of primary link accordingly. In the preferred embodiment, a timer means is associated with each car, which is reset each time the car receives a datagram originating from that car. If the timer expires, and subsequently the car receives a datagram from such car over another link, it resets the primary link. The group controller may be a separate component of the system, but preferably all the car controllers have group controller software.

Dependencies are inferred from the claim text.