The cogging force disturbance of linear motor is one of the main factors affecting the positioning accuracy of ultraprecision moving platform. And this drawback could not be completely overcome by improving the design of motor body, such as location modification of permanent magnet array, or optimization design of the shape of teeth-slot. So the active compensation algorithms become prevalent in cogging force rejection area. This paper proposed a control structure based on internal mode principle to attenuate the cogging force of linear motor which deteriorated the accuracy of position, and this structure could make tracking and anti-disturbing performance of close-loop designed respectively. In the first place, the cogging force was seen as the intrinsic property of linear motor and its model constituting controlled object with motor ontology model was obtained by data driven recursive identification method. Then, a control structure was designed to accommodate tracking and anti-interference ability separately by using internal model principle. Finally, the proposed method was verified in a long stroke moving platform driven by linear motor. The experiment results show that, by employing this control strategy, the positioning error caused by cogging force was decreased by 70%.
In order to improve the throughput of lithography machine, a new type of lithography machine began to adopt double wafer stages which make the exposure and measurement work simultaneously. But at the same time, this structure also increases the risk greatly, the wafer stage collision for instance. Therefore, a corresponding safety protection system is necessary to protect the whole double wafer stages system and to improve the throughput on the premise of safety. In this paper, a passive safety protection strategy for double-stages lithography machine is proposed based on analysis of its working conditions. The design principle of safety needle is elaborated, and then needle distribution is determined correspondingly. The simulation results show that, the proposed passive protection method carried out by safety needles could avoid damages of sensitive apparatus.