Mattke Servo Motors

Brushless (electronically commutated) motors have a rotor equipped with permanent magnets. This rotor is moved by a rotating field which is excited in the stator winding and controlled by the amplifier; there is no electrical connection between rotor and stator. The advantages of these motors are the good heat dissipation, the high overload capacity (full torque at standstill for an almost indefinite time) and the little maintenance required. The only wearing parts are the ball bearings of the motor shaft. This motor is especially suitable for continuous operation with high torques at speeds over 100rpm with a feedback of the rotor encoder signals by hall sensors (rotor encoder). If the feedback of the rotor position is effected by a resolver, the motor can be used as a highly dynamic element; even in the case of low speed the motor does not jerk on account of torque ripple.

To the brushless motors

Compared with the above mentioned types of motors, the bar-armature motor is equipped with a ferrous armature and conventional wire windings. By using different materials for the permanent magnets (ferrite, alnico, samarium-cobalt), similar powers can be achieved with different sizes. Moreover the line of products, which is equipped with samarium-cobalt magnets (series RS), is characterised by a low volume, a very small moment of inertia of the rotor and thus a high dynamic.

Bar-armature motors have a relatively high moment of inertia. Armature inductance is high compared to that of the motor types described above, i.e. in most cases, chokes are not needed.

In order to avoid commutator sparking and the resulting risks for the amplifier and the motor, the bar-armature motors must be operated according to their commutation curve.

To the bar-armature motors

The bell-type armature motor (moving coil) is a non-ferrous motor. It is equipped with a permanent internal magnet which is balanced symmetrically around the motor shaft. The armature, which is wound in the shape of a bell, is fitted over this magnet. Commutation is effected by means of brushes and collectors. The advantages of this motor are, high power despite low weight, linearity between voltage and speed as well as between current and torque, an extremely low accelerating voltage and great efficiency. On account of the mechanically complicated construction, this motor is only manufactured for powers of up to 100W. As far as inductance is concerned, the same characteristics as for the disk-armature motors apply.

To the bell-type armature motors

The disk-armature motors are non-ferrous motors. The disk can be manufactured by various methods. It can be wound from copper wire and cast in a plastic mould for stability. The wire ends are then attached to a disk commutator. The alternative method of manufacturing disk-armatures involves punching out tracks from copper foils to form a continuous wave-winding. These solid-copper conductors form both winding and commutator. In the case of the second version the current supply is effected directly to the conductors via carbon brushes. Due to an especially good commutation and the great number of "conductors", pole gaps do not occur and the motor runs quietly and evenly even at very low speed. No matter how the disk is produced, rotating mass and thus the motor's moment of inertia is very small. This motor type is therefore ideal for drives which require a high level of dynamic control because it can be braked down to the desired speed or the direction of rotation can be changed within milliseconds. The minimum load inductance that is necessary for p.w.m. amplifiers is achieved by connecting chokes between amplifier and motor.

To the disk-armature motors