Embodiments of the invention relate to elevators, and in particular to the vibration-based wear and life monitoring of elevator tension members.
Elevator systems typically utilize tension members, such as ropes, belts, bands, or cables, to propel an elevator car along a hoistway. One type of tension member is a coated steel belt which may be made up of multiple wires located within a jacket material. During normal elevator operation, tension members are subjected to a large number of bending cycles as the tension member travels over drive sheaves and deflector sheaves of the elevator system. In addition, over time, the weight of the elevator car on the tension member may result in stretching of the tension member, which may result in fatigue, such as the creation of micro-cracks in the tension member. Such fatigue is a major contributor to reduction in service life of the tension member. While the service life of tension members can be estimated through calculation, a more accurate estimation of remaining life of the coated steel tension member is often obtained by utilizing a life-monitoring system.
One such system is called resistance-based inspection (RBI). An RBI system monitors an electrical resistance of each cord in the tension member. Some cord configurations, however, do not exhibit a significant, measurable change in resistance which can be correlated to a number of bending cycles or cord degradation. In such cases, assessment of tension member condition based upon changes in electrical resistance of the cords is difficult due to the small magnitude of change in electrical resistance of the cords as the cords wear.