Active position measurement method for ropeless linear motor elevators
Gürbüz, Çağrı (2010) Active position measurement method for ropeless linear motor elevators. [Thesis]
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Elevators in modern high-rise buildings face two main difficulties: physical limitation of the traction cable that actuates the elevator car because of stretch, and loss of floor-space because numerous elevator hoistways are required to keep passenger waiting time low. Ropeless elevators where the elevator car is propelled by a linear motor that spans the whole hoistway is one strong solution candidate. They eliminate the traction cable and enable several elevator cars to travel independently in one hoistway. For freedom of movement, however, no cables must be attached to the traveling elevator car. Although the traction can be designed to satisfy this requirement, measurement of the position of the elevator car for the purpose of motor drive using the conventional techniques requires a linear encoder, which must have an electrical connection. In this thesis we propose LinearMotor Active PositionMeasurement Method (LIMAP) which is based on the principle of linear variable differential transformer. It utilizes the coils of the motor just ahead of the elevator car that are not used for traction and a magnetic shunt fixed at a known distance from the elevator car, for position measurement. The position can be determined by exciting one of the coils under the shunt while measuring the mutual inductance with the neighboring coils. Our second contribution is a design method based on finite element methods that can be used to determine the best size magnetic shunt to meet the design criteria. The third important contribution is a position search algorithm that can work under the nonlinear characteristics of the sensor in real-time. Results based on the finite element simulations of an existing motor are given, followed by actual experiments on a real motor. The results agree well to demonstrate the validity of the proposed approach.
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