Positioning system and lithographic projection apparatus

A lithographic apparatus has a positioning system for positioning an object table, said positioning system comprising a planar motor having a stator (10) and a translator (20), one of said stator and said translator comprising a periodic magnet structure (13-15) and the other of said stator and said translator comprising a plurality of energizable coils (21-24). The phase relationship between stator and translator of the planar motor is determined by: energizing a plurality of said energizable coils in turn with an oscillating signal sufficient to cause vibrations of said translator having an amplitude less than the period of said periodic magnet structure; measuring said vibrations of said translator; and determining the phase relationship between said translator and said stator on the basis of said measured vibrations. Alternatively, the relationship between stator and translator is be determined by detecting means detecting distinct optical marks on the periodic magnet array. Control means determine the relationship between said translator and said stator on the basis of detected distinct optical marks

Positioning system and lithographic projection apparatus

A lithographic apparatus has a positioning system for positioning an object table, said positioning system comprising a planar motor having a stator (10) and a translator (20), one of said stator and said translator comprising a periodic magnet structure (13-15) and the other of said stator and said translator comprising a plurality of energizable coils (21-24). The phase relationship between stator and translator of the planar motor is determined by: energizing a plurality of said energizable coils in turn with an oscillating signal sufficient to cause vibrations of said translator having an amplitude less than the period of said periodic magnet structure; measuring said vibrations of said translator; and determining the phase relationship between said translator and said stator on the basis of said measured vibrations. Alternatively, the relationship between stator and translator is be determined by detecting means detecting distinct optical marks on the periodic magnet array. Control means determine the relationship between said translator and said stator on the basis of detected distinct optical marks

Force analysis of linear induction motor for magnetic levitation system

This paper presents the analyses of thrust and normal forces of linear induction motor (LIM) segments which are implemented in a rotating ring system. To obtain magnetic levitation in a cost effective and sustainable way, decoupled control of thrust and normal forces is required. This study includes the design of a static test setup from which the measurement results are compared and verified with the derived analytical methods and finite element simulations. The comparison shows significant correlation of the thrust and normal forces as function of the slip frequency

Modeling of a Linear PM Machine Including Magnetic Saturation and End Effects: Maximum Force-to-Current Ratio

Abstract-The use of linear permanent-magnet (PM) actuators increases in a wide variety of applications because of their high force density, robustness, and accuracy. These linear PM motors are often heavily loaded during short intervals of high acceleration, so that magnetic saturation occurs. This paper models saturation and end effects in linear PM motors using magnetic circuit models. The saturating parts of the magnetic circuit are modeled as nonlinear reluctances. Magnetomotive forces represent the currents and the magnets. This paper shows that when saturated, a negative -axis current increases the force developed by the motor. Although the increase is not large, it is nevertheless useful, because a negative -axis current also results in a decrease in the amplifier rating. Further, the trajectory for the maximum force-to-current ratio is derived. The correlation between the calculated and the measured force justifies the model. Index Terms-Linear actuator, magnetic circuit modeling, maximum force-to-current ratio, permanent-magnet (PM) motor, saturation

Epidemiology, pathophysiology, diagnosis, and management of intracranial artery dissection

Spontaneous intracranial artery dissection is an uncommon and probably underdiagnosed cause of stroke that is defined by the occurrence of a haematoma in the wall of an intracranial artery. Patients can present with headache, ischaemic stroke, subarachnoid haemorrhage, or symptoms associated with mass effect, mostly on the brainstem. Although intracranial artery dissection is less common than cervical artery dissection in adults of European ethnic origin, intracranial artery dissection is reportedly more common in children and in Asian populations. Risk factors and mechanisms are poorly understood, and diagnosis is challenging because characteristic imaging features can be difficult to detect in view of the small size of intracranial arteries. Therefore, multimodal follow-up imaging is often needed to confirm the diagnosis. Treatment of intracranial artery dissections is empirical in the absence of data from randomised controlled trials. Most patients with subarachnoid haemorrhage undergo surgical or endovascular treatment to prevent rebleeding, whereas patients with intracranial artery dissection and cerebral ischaemia are treated with antithrombotics. Prognosis seems worse in patients with subarachnoid haemorrhage than in those without