automation4me - Drive Tech

Tank rotators are equipment, which are used to rotate large jobs under fabrication in workshops so that welding, cutting and other processes can be carried out by the operator.

As shown in fig., each rotator consists of two wheels, which are mechanically coupled and are driven by an electrical motor through a reduction gearbox. The job is placed on these wheels and positioned by the operator as desired. As the rotator can be used with jobs of varying diameters, weights and lengths, speed control is desired, so that the operator can set the speed as per his requirement. Typical job weights can range from 100 tons to 1000 tons with lengths upto 20 metres. Precision welding and other machining operations can be performed by the operator while standing inside the job.

Earlier, D.C motors with thyristorised D.C drives were being used for speed control of the rotators. However, because of the maintenance problems associated with D.C motors, the trend is shifting towards use of standard squirrel cage induction motors. Typical ratings vary from 3.7 KW to 18.5 KW depending on the load to be rotated. The motors are with 1500 rpm base speed with reduction upto 50 rpm or less through the drive units. As these motors run at low speeds continuously for long periods of time, separate cooling is normally provided.

Depending on the budget of end-user and accuracy desired , either open loop vector or closed loop flux vector options can be offered.

If the job length is very long, then a single rotator is not sufficient. In this case, multiple rotators are used along the length of the job as shown below.

All these inverters are fed by a common speed reference. For flux vector configurations even Master Slaving or Droop Control could be thought of for better synchronisation. The user benefits would be:

	Use of standard squirrel cage induction motor which is mechanically more robust, instead of D.C motor which requires regular maintenance of brushes and commutators.
	Smaller physical size of the drive panel and motor. This is important, as the rotators have to be frequently moved in the shop floor from job to job. Tank rotators are used in almost all medium and large fabrication shops. L&T AUTOMATION has expertise in this area with Yaskawa inverters.