By using high-energy magnetic materials it is possible to design small diameter disk motors. For this reason and due to a carefully optimized technical construction of the rotor, the motors have a low moment of inertia. The stability of the magnetic material and the design of the magnetic field in the face of demagnetisation allow maximum currents of up to 3 - 4 times the rated current.

The high acceleration capacity of the low-inertia three-phase AC servo drives is the result of this. Through the excitation of the permanent magnets, no heat losses due to current occur in the rotor. With the three-phase AC-servomotors AC-G heat losses due to current occur only in the stator, which then can be directly drawn off.

These favorable cooling conditions allow high-capacity windings. Since all the current heat losses are drawn off directly via the surface, the motors are designed at low cost with the enclosure type providing protection in accordance with IP xx and they are thus very resistant to liquids and dirt. The resolver is built into the B-side bearing bracket. The signals of this integrated measuring system for the actual speed value, the rotor position and the indirect position are taken at the motor over a 12-pin connector.

Synchronous three-phase AC servo drives have a series of advantages over the DC drives:

• • no electromechanical parts to wear out, therefore "maintenance-free".
  • a low moment of inertia of the rotor due to power density, therefore high acceleration capacity.
  • no commutation limit curve, therefore high acceleration moments, also in higher speed ranges.
  • no losses in the rotor of the motor, therefore favorable thermic qualities and a high degree of protection due to the closed construction.

Three-phase AC servomotors built in the way described, are specifically more efficient (higher rated torque) than DC servomotors and also have a small moment of inertia. The size necessary for an application will, for this reason, be smaller with three-phase AC servos than with DC servos.