Research On PM Ring Torque Motor And Its Control Strategy Used In Direct Drive NC Table

Numerical control (NC) table is one of the most important assemblies in multiaxial linkage NC machine. It is acknowledged that the elastic distortion, friction, backlash , and any other problems resulting from mechanical drive chain are shown on the traditional drive NC table. The direct drive NC table not only resolves the above problems but also has many advantages, such as high torque, quick response ability, high position precision, and so on. In recent years, the direct drive NC table assembly is the research hot spot in multiaxial linkage high-grade NC machine field. Therefore, taking permanent magnet (PM) ring torque motor and its control strategy used in direct drive NC table as subjects, the key technologie of subjects is dicussed in this dissertation.To satisfy the drive motor requirements of low torque ripple and high torque density, used in the NC table, the similar pole and slot number outer-rotor PM ring torque motor with unequal teeth tips width and alternate winding is researched and designed based on the design theory of multipolar fractional-slot motor. The structure of similar pole and slot number can increase the winding pitch coefficient, and reduce cogging torque ripple effectively with the reasonable combination of pole number and slot number. The alternate winding and unequal teeth tips width structure optimize the stator teeth flux linkage and winding coefficient, as a result, the torque density is increased. Furthermore, the influences of unequal teeth tips width and alternate winding structure on the harmonic torque and cogging torque are analyzed.In order to increase the output torque ability of table motor further, combining the special requirements of direct drive NC table mechanical structure, the dual-synchronous dual-rotor PM ring torque motor with series connection structure is researched. The new dual-rotor table motor structure with better ability of heat dissipation, resolves the heat dissipation problem of high torque table motor to some extent and increases the torque density. And it also resolves the synchronous control and power distribution problems between the two independent motors of traditional double-drive mode.Based on dual-rotor PM ring torque motor structure characteristics, the generating rule of dual-rotor motor cogging torque is researched further. On the basis of this analysis, the reduction principle of dual-rotor motor cogging torque with phase-shifting technology is studied, and the reduction principle of cogging torque by combination of inner and outer slot notch width is also analysed. The optimal phase-shifting angle calculation formulas both in equal teeth tips motor and unequal teeth tips motor are obtained by analytic calculation method. And the dual-rotor PM ring torque methmatical model is also established.In the aspect of control strategy, aiming at the periodic input signal tracking problem of the PM ring torque motor, a plug-in type repetitive controller is designed. On this basis, in order to improve the robustness against load disturbances and parameter variations, the control method of repetitive control combining withμ(structured singular value) theory is researched. The robust repetitive control problem is transformed into H∞optimal control problem using linear fractional transformation(LFT). The D-K iteration is used to design the robust repetitive controller, which realized the stability, the robustness and improved the tracking precision of the servo system.In the end, the outer-rotor PM ring torque motor with unequal teeth tips width and alternate winding structure is produced, and the direct drive NC table combining reasonable mechanical structure design is also produced. Consequently, the many prototype experiments are completed, such as noload torque ripple experiment, load torque performance experiment. The table experiment system is established using digital signal processor TMS320LF2407A. The position tracking experiments are completed under the conditions of noload, load disturbance, and rotational inertia parameter variations repectively. All the experiments results prove that the motor design scheme and control strategy are reasonable and correct.