14. Internal Transport

While it is hoped that many of the daily journeys aboard the station could be accomplished on foot, the fact remains that in an environment the size of DaedalusaL4 and with the added difficulty of ‘vertical’ journeys through varying gravity levels, a certain amount of transport infrastructure must be provided for in the design. The simplest and easiest way to do this is clearly in the form of elevators.

As the elevators will be required to move both horizontally and vertically through various g-levels, the standard hydraulic elevators found in many building today are not practical. As such a linear-motor driven transport system has been chosen for DaedalusaL4. Such a system has several advantages over conventional roped elevators

·         The cab runs without the use of ropes, thus allowing for the accommodation of multiple cabs in one shaft. Mass transportation can be achieved without increasing the shaft space.

·         The self-driven cab is allowed to operate in a vertical, horizontal, curved or branched path. Cabs would also be able to pass each other.

One of the major advantages of a linear motor driven system is its flexibility. Not only can cabs move in many directions but the number of cabs can also be varied. This allows for an increase in the number of elevator cabs at peak times so as to ensure a satisfactory service is maintained.

As well as purely technical issues, several physiological and psychological issues have to be addressed.  The elevator industry has developed the following physiological limits which standing elevator riders can tolerate without discomfort (ref. 56).

Vertical acceleration/deceleration

< 1.0-1.5 ms-2

Jerk rates

< 2.5ms-3


< 50 dB

Horizontal sway

15-20 mg

Ear-pressure change

< 2 kPa

All of these design parameters can be easily regulated by proper equipment design.  The only real psychological concern is waiting times. Current research suggests that waiting times should not exceed 25-28 seconds. If they were to exceed this, then it would be desirable to provide audio-visual screens showing short films to minimise the boredom of the wait.

14.1      Linear Motors

Linear motors (ref. 57) can be divided into two categories:

·         A linear induction motor (LIM).

·         A linear synchronous motor (LSM).

The LSM can be further divided into two types:

·         A permanent magnet type.

·         A super conductive electromagnet.

Considering the requirements and practical use, a permanent magnet-type LSM was adopted with a permanent magnet mover on the cab and armatures on the track. As with conventional rotational motors, a LSM consists of armatures which generate a shifting field for drive, and permanent magnets which generate a field on the moving body. The energised armature generates a shifting field in the air gap, which creates a motive force on the permanent magnetic field on the cab. As a result, the cab travels at synchronous speed with the shifting field.

In order to reduce the size and weight of the magnet, a neodymium rare-earth magnet (maximum energy product 255kJ/m3), with more than six times the magnetic force of a ferrite magnet, was chosen for the permanent magnet. The magnet makes the installation of power supply equipment to the cab unnecessary, resulting in substantial weight reduction and energy savings when compared with other types of elevators.

The armature consists of a coil and a core.  The armature is set at the track side, positioned to hold the magnetic mover between, thus adopting a double-sided arrangement. This offsets the magnetic attraction force acting between the permanent magnetic mover and the armature. The linear motor is driven by a sine-wave pulse width modulation inverter with insulated gate bipolar transistors, which have low audible noise levels.

The armature and permanent magnet are matched to each other in magnetic pole pitch and thrust is controlled by allowing current to flow through the armature coil. To detect the speed and position of the magnetic mover, a slotted plate is provided on the cab with a photo switch on the track. Speed feedback is accomplished through the use of speed detection signals.

As a countermeasure against power failure, armature coil circuits may be automatically shunted by external resistors. The resistors use power to apply dynamic braking. This prevents free-fall of the cab, allowing it to ‘descend’ at a stable, if slow speed even if all safety-monitoring functions fail.