Xiaoyou Zhang

Compensation of rotor imbalance for precision rotation of a planar magnetic bearing rotor

Magnetic bearings provide an alternative for achieving precision rotation. But the rotational accuracy is sensitive to rotor imbalance. The system we study is a planar rotor supported by aerostatic suspension and positioned by a radial magnetic bearing of nanometer precision. We present compensation designs and experiment results for precision rotation about the geometric center and the mass center, respectively. In the former case, the base harmonic component at each sensor output is removed by explicit trigonometric compensation signals that are constructed in real time. In the latter case, a new double-loop compensation design is given. Each compensation loop is similar to that in the former case. The compensation, aided by a variable rotational speed that is changed up and down repeatedly, is shown to push the rotational center to approach the mass center. Once the mass center is reached, the rotor remains to rotate about the mass center at variable rotational speed without transient. Compared with the existing methods, which find the mass center or inertial axis at a fixed rotational speed and rely on exact values of plant parameters, our method may locate the mass center more accurately. Experiment data indicate that the mass center is located with an error of tens of nanometers.

Precision Control of Radial Magnetic Bearing

The aim of the research is to realize a radial magnetic bearing with the rotational accuracy of several nanometers. In this paper, a partial bias current method for driving electromagnets is introduced. The heat generation by the method is smaller than that by a conventional bias current method. Furthermore, the method has higher force-slew-rate than a zero bias current one at the zero force point. Then a repetitive controller is applied to eliminate the periodic runout caused by the unbalance and the profile error of the spindle. The experimental results show that the partial bias current method has the merits of precision positioning capability, low heat generation and low rotational electromagnetic damping. The repetitive controller can eliminate the periodic runout and achieve the rotational accuracy of 15.1nm at 1500min −1 .

Development of a 5-DOF Controlled, Wide-Bandwidth, High-Precision Maglev Actuator for Micro Electrical Discharge Machining

This paper describes a five degrees of freedom (5-DOF) controlled, wide-bandwidth, high-precision maglev local actuator to maintain a suitable distance between an electrode and the workpiece for micro electrical discharge machining (EDM). The actuator is sufficiently compact to be attached to conventional electrical discharge machines. The maglev actuator possesses a positioning resolution of the order of sub-micrometer and micro-radian, a bandwidth greater than 100 Hz in the 5-DOF directions, and a positioning stroke of 2 mm in the thrust direction. The maglev actuator can be levitated stably and positioned precisely, even under electrical discharge conditions. The use of the maglev actuator could increase the machining speed for Phi 1 mm holes by 21.8%, compared with the conventional EDM.