The present invention relates to an electric machine having a first machine part, which comprises a rotary actuator, and having a second machine part, which comprises a linear actuator.
Electric machines of the type mentioned at the beginning are used, in particular, as drive devices in machine tools or as roller drive devices, for example in printing machines. Such machines principally require high dynamics, for example when a tool such as a milling machine is to be moved both in a rotary fashion and in a linear one. The aim here is to implement a linear movement in addition to a rotary one, in particular without switching gear and at high feed rates and with high precision.
By way of example, use is made for such an application of electric machines that both have a rotary actuator for converting a rotary driving movement, and have a linear actuator for converting a linear driving movement. Use is made for this purpose of, for example, electric machines that have appropriate different machine parts. For example, a first machine part includes a stator element and a rotor element that, by interacting with the stator element, ensures a rotary drive oft for example, a tool fastened on the rotor element. The stator element is accommodated in a stator of the electric machine that is at rest mechanically. A rotor, by contrast, includes the rotor element that is, in particular, fastened on a rotating shaft. The stator is generally designed as a hollow cylinder in whose interior the rotor is accommodated as a solid cylinder. The stator element of the stator includes the stator windings that, when flowed through by current, produce the main magnetic field, which interacts with the exciting field produced by the rotor windings or by permanent magnets in the rotor element.
Such a first machine part designed as rotary actuator is connected to a second machine part that, as linear actuator, ensures a linear movement of the shaft fastened to the rotor element of the first machine part. The second machine part comprises, in particular, a primary part with electrical windings that produce the main field, and a secondary part, which is, for example, fitted with permanent magnets, for producing the exciting field. The individual phases of the windings of the primary part are energized with the aid of three current profile curves resembling sinusoidal ones, and give rise to a so-called moving field leading to a linear movement of the secondary part.
The primary part of such a second machine part is generally designed as a hollow cylinder, in a way similar to the stator element of a rotary electric machine, while the secondary part, in a way similar to the rotor element of a rotary electric machine, is designed as a solid cylinder that is arranged in the interior of the hollow cylinder of the primary part. Owing to the restricted installation conditions in a machine tool, for example, and to the implementation of high feed forces, the efficiency of the linear motors used therein is generally already greatly exploited. The result of this is that known linear motors are capable of implementing high feed forces only to a limited extent, because of a limited linear force.