Issue 5/2006
09/02/06
The perfect drive
Elevator drives with efficiency exceeding 90 per cent
Theodor Helmle (Director Elevator, alpha getriebebau GmbH)
Experience gathered in the manufacture of high-quality servo drives destined for use in mechanical engineering, aviation, medical technology and other industries has been successfully applied in devising new system technology for elevators. The central component in this development by alpha getriebebau GmbH is a low-play planetary drive distinguished by superb dynamics and torque transmission and great precision, as well.
Category: Issue 5/2006
Posted by: Editor
Taking a look at the advantages offered here, in comparison with a gearless drive, is certainly worthwhile. The efficiency level achieved by a high-quality gearless drive is the equivalent of that for a planetary elevator drive. The disadvantage of gearless drives is found, however, in the fact that they have only a 35 per cent duty cycle. Modern lift equipment should, however, achieve a 60 per cent duty cycle. The high-quality planetary gear systems engineered by alpha getriebebau are persuasive due to their overall efficiency of more than 90 per cent and their capacity for up to 240 motor starts per hour.
Developing economical elevator technology is just as much in line with current trends as are other energy-saving measures. That’s hardly a surprise since, due to drastic price increases in the energy sector, greater emphasis is being placed on the total efficiency of elevator systems.
A high-torque featherweight
The idea behind this innovative lift technology is as simple as it is effective. The combination of a synchronous motor and two-stage planetary gearing lends the elevator drive high torque which cannot be achieved by a comparable gearless drive.
Thanks to the compact design of the planetary gear the drive (without the drive sheave) for an elevator generating 630 kg of lifting power weights less than 100 kg. A comparable gearless drive will weight in at 600 to 680 kg.
The gearless drives available on the market today have a duty cycle of about 35 per cent. It has been demonstrated in practical testing that these drives can move the cars within the hoistway for a maximum of 21 minutes in continuous duty. If a gearless drive with a higher duty cycle (at the same lifting load) is required, then a larger gearless drive with the appropriate output data, power consumption and purchase costs will have to be used.
Unequalled in efficiency, even in continuous duty
In short: The limited duty cycle of the gearless drive, when compared to a planetary drive using a synchronous drive, results from the drive’s high heat generation level. One of the results of this heating is that the motor’s inductance changes and, if the inverter is not large enough, this can lead to unsatisfactory ride quality. Elevator machinery with planetary drives is engineered for 240 motor starts per hour and have no limits to their output in continuous operation, something often required in hospitals, for instance.
Customer requirements satisfied – Quieter, faster, more reliable
The customers‘ very understandable desire for the quietest possible drive is also achieved with a high-quality combination of motor and gearing, provided that maximum manufacturing precision is paired with good engineering design. Ride quality can be further enhanced by using inverters with a clock frequency of 16 kHz at the output. In order to shave costs, a clock rate of 12 kHz or even less is often used so as to be able to use smaller IGBTs, modules and less expensive heat sinks. But regulators which use a clock rate of 12 kHz or less generate – in conjunction with the drive – noises which are perceived by the human ear as unpleasant.
Proven in testing: Maximum, zero-defect quality
To examine its own quality achievement the company has had quality testing carried out at the Central Technical College for Elevator Technology at Rosswein. Among the tests carried out there were emergency stop trials in which loads and stresses were generated far beyond normal requirements in elevator engineering.
Test 1: Emergency stop tests, power outage simulation:
Test 2: Emergency stop testing, loading tests when the safeties engage during an overspeed condition:
During these tests acceleration values > 6 g were achieved.
Even after several trials the drive was still 100 % functional.
Test 3: Bouncing counterweight, car travelling to contact with various bumper systems to generate counterweight bounce at differing loading states and car speeds:
Test 4: Determining system stiffness, varying stiffness by removing the sprung suspension at the car and the counterweight:
Changing system stiffness, i.e. removing the spring elements at the car and counterweight, makes it possible to determine the frequency change to be expected but no increase in the moments which might occur. The spring elements or spring buffers have no influence on the forces or acceleration which appear.
Result
The test results have demonstrated convincingly that the planetary gearing used in the drive can withstand the load levels encountered in lifts to an above-average extent.
Utilization options
The combination of compactness and weight savings opens up entirely new solution options for the engineer. On the one hand it is possible to realize a “roomless” system for new installations in which the machine can ride on the car without creating any problems. This give the engineer the option of building a self-propelled car featuring an integral drive unit. In order to complete integration, the manufacturer is offering in addition a suitably modified control and regulation package.
On the other hand, the ECD machinery offers undreamed-of options for rehabilitation work. Its low weight makes it easy to move it to even the most difficult installation locations. Thanks to its compact dimensions it will fi t into any available space.
In summary
The product description, augmented by testing and the installation options which derive from that, prove that this “perfect” drive is absolutely uncompromising in its quality and utility.
5/2006
