The drive system can be set in three different operating modes:
- control of the torque (speed depends on the load)
- control of the speed (torque depends on the load)
- control of the position
The first operating mode is the easiest one and it can be utilised in all those cases requiring to control a force (winding up / unwinding machines, textile and belt processing machinery, etc.).
Usually, the torque control is very stable (stability does not depend on the load) and quick (pass-band >300Hz), but not so precise ( 10%).
In the multi-axis applications with very quick and modern CN or with adapter control or at variable parameters, it is well worth to set the torque control drive and allocate the closing of the other rings to the CN.
For the torque control, the drive adjusts the current of the motor; as a consequence the motor will act also as transducer. No external sensors are necessary. The sensor on the motor can be simplified to the Hall system for the commuting only.
In the multi-axis applications (electronic cam, automatic production machinery) where an axis or a transmission chain are eliminated and replaced by synchronized servomotors, a simple and smart systems theory approach must be allocated to the CN, to the PLC, or to the industrial PC fitted with multi-axis board, and the operation of seek and speed sensors by programming the drives as simple torque controllers.
Since the torque control does not depend on the load, in such a solution the drives do not need for any personalization or setting and therefore they are intrinsically interchangeable. The encoders are operated directly by the PC which in-records all the programming parameters of the system for all the axis. The only control signal is the current reference, which has a more restricted dynamics and it is not affected by the disturbance of the traditional voltage reference.
Such a simple and smart approach avoids the need for any complicated and expensive field buses, which are in any case limited in speed and have few axis. The disadvantage lies in the high speed required by the axis board and in handling the encoders which can probe to be quite difficult in an industrial PC at high resolutions.
The speed control is the most traditional one.
The position or space control is carried out by the digital drives (AX-V). In this way the running error is limited to few calculations of the sensor equivalent, in case of an encoder at 4096 impulses / revolution, to 1/16000 of revolution.
According to this operating mode, it is also possible to synchronize more axis (electric axis, electric cam).