1985 Mitsubishi DC-GL Elevators - Bangunan Yayasan Negeri Sembilan, Malaysia

Here is a set of 3 really nice Mitsubishi DC Gearless Elevators installed in the mid 1980s. In this video, I will joyride these lifts. In the second part, I shall showcase footage of the lift machine room.

These are equipped with TLCM controllers, Mitsubishi’s 3rd generation of Thyristor Leonard Systems. Unlike the first generation of Thyristor Leonard controllers which were controlled using relays and ICs (SMN/SMH), the 2nd (SHM/SHH) and 3rd (TLCM/TLCH) generations of Thyristor Leonard Systems incorporated microprocessors into both the individual car controllers and group controllers (or supervisory systems). And unlike older Ward Leonard systems, the use of a Thyristor convertor has allowed the elimination of Motor-Generator Sets.

The first generation of Mitsubishi’s Thyristor Leonard Systems still relied on mechanical floor selectors, with Mitsubishi’s DMSH selectors being employed to perform deceleration control. However, the introduction of microprocessor control has allowed the mechanical floor selector to be digitised with the use of a DC tachometer generator and plates in the shaft to determine the position of the car in the lift shaft. The DC tachometer generator measures the angular velocity of the motor, and the product of the angular velocity and the radius of the main sheave gives the linear velocity. As the integral of velocity is displacement, from any fixed reference point determined the shaft plates, the position of the lift car can be derived by integrating the velocity with respect to the time after the car has passed by a shaft plate. For example, suppose the up direction is defined as the positive direction, and there is a shaft plate installed around 20m above the lowest landing. If a car is travelling at 3m/s in the downwards direction, 1 second after passing the shaft plate, the DC tachometer generator can detect that the lift car has moved approximately 3 metres in the negative direction. The position of the lift car can then be derived by subtracting 3m from 20m, which means that the height of the car is approximately 17m. From there, the controllers can accurately perform acceleration and deceleration control. Microprocessors in the controller generate the speed reference (a signal that represents the “ideal” speed at any given moment), and the speed reference is compared with the actual speed signal given by the DC tachometer generator. According to the difference, the thyristors are adjusted to vary the DC voltage supplied to the motors.

The digitised floor selector also had a greater degree of accuracy compared to mechanical floor selectors, as mechanical floor selectors which were used to reconstruct the lift car’s position in the shaft had to be scaled down by a factor of around 1:100 (as with Mitsubishi’s DMS and DMSH selectors) in order to fit inside the machine room. The lack of accuracy meant that lift cars could not rely on the velocity regulating system of the mechanical floor selectors to perform deceleration control when the cars were within a short distance of stopping at the landing. To ensure precise levelling, elevator cars had to switch to a position regulating system right before stopping, and this inevitably led to a creeping phase.

The use of microprocessors has not only allowed for smoother acceleration and deceleration control, but has also significantly reduced creeping time. Running characteristics for these lifts are excellent: acceleration and deceleration are stepless, creep time is next to none, the elevator car has a soft landing so one can scarcely feel the brake set, and running open or pre-opening operation (where the door starts to open while the car platform is still levelling) saves time by allowing passengers to board and alight earlier. Even for partial speed operation where the travel distance is insufficient for the lift car to accelerate to the rated speed, rather than having pre set fixed top speeds (eg. 1m/s for single floor travel, 1.5m/s for double floor travel and so on) as with some other manufacturers, the lift cars accelerate as much as permissible given the travel distance before decelerating to a stop, leading to reduced floor-to-floor travel time.