There is hardly any other product with the same life expectancy as a lift. Even after many years, a lift system is capable of continuing to give good service if carefully maintained. On average, wearing parts do require replacing around once every 3 years.
However, experience has shown that the lift itself frequently still continues to do its job without cause for complaint. One of the reasons for this is that elevator gearboxes used to be designed to include generous reserves, which provided they were regularly serviced, allowed them to achieve an extremely long service life.
As well as maximum safety and a high degree of availability, today’s lift user demands extreme stopping accuracy and low energy consumption, alongside low noise emissions.
Many of these requirements can be addressed and major improvements achieved simply by retrofitting a frequency inverter. Even if the original drive system is retained, this can offer a number of substantial advantages, including
- Shorter travel times and consequently greater lift availability, due in particular to optimized timing of the landing approach.
- Constant speeds in the upward and downward direction with a loaded or unloaded car.
- Good positioning accuracy within a tolerance of less than ± 1 mm irrespective of load.
- Energy savings of more than 50% compared with pole-changing motors.
- Gentle-action running characteristics relieving stress on the mechanical components.
Standard solutions are now available permitting the integration of new frequency converters into existing control systems which are reasonable in cost and quick and easy to implement.
A frequently more complicated procedure is mounting an incremental encoder on the existing lift. As the pole-changing motor can continue to be used, there is no preparation in place either for integration of the encoder in the motor shaft or for mounting the necessary torque support in the housing. This is why it often makes sense when modernizing an existing system to operate the motor without an encoder. This is generally termed encoderless or open-loop operation.
Encoderless operation calls for a high-grade frequency converter which is capable of using a precise integrated mathematical motor model to calculate the function and response of the motor in advance and use this information for precise motor control. For the installer on site, simple converter parameterization is of decisive importance.