AP9.7 Building elevators are limited to about 800 meters.

Above that height, elevator cables become too thick and too heavy for practical use. One solution is to eliminate the cable. The key to the cordless elevator is the linear motor technology now being applied to the development of magnetically levitated rail trans

portation systems. Under consideration is a linear syn

chronous motor that propels a passenger car along the track like guideway running the length of the elevator shaft. The motor works by the interaction of an elec

tromagnetic field from electric coils on the guideway with magnets on the car [28].

If we assume that the motor has negligible fric

tion, the system may be represented by the model shown in Figure AP9.7. Determine K so that the phase margin of the system is P M. . = 60°. For the gain K selected, determine the system bandwidth.

Also calculate the maximum value of the output for a unit step disturbance for the selected gain.

Controller R(s) Desired K(s+4) elevator FIGURE AP9.7 position Elevator position control. Ta(s) Disturbance Elevator and linear motor 112 Y(s) Elevator position