Electricity: electrical systems and devices – Control circuits for electromagnetic devices – Systems for magnetizing – demagnetizing – or controlling the...
Patent
1991-03-04
1993-09-07
Gaffin, Jeffrey A.
Electricity: electrical systems and devices
Control circuits for electromagnetic devices
Systems for magnetizing, demagnetizing, or controlling the...
361146, 32420712, H02N 1500
Patent
active
052434915
ABSTRACT:
A device for positioning a body (5) by means of at least two electromagnets (13, 15). A position sensor (29) measures the size of an air gap (23) between one of the electromagnets (13, 15) and a guide beam (1). An output signal of the position sensor (29) is applied to a linear electronic control unit (35) which passes a control current through the electromagnets (13, 15) in dependence on a difference between the measured and a desired size of the air gap (23). An electronic root extractor (37) is connected between the control unit (35) and the two electromagnets (13, 15). An output signal of the root extractor (37) has a value equal to the square root of a control signal coming from the control unit (35). In this way a force exerted by the electromagnets (13, 15) on the guide beam (1) is proportional to the value of the control signal, so that a control is obtained with the linear control unit ( 35) in which the stiffness and bandwidth are independent of the value of the control current.
Since the electrical resistance losses in the electromagnets (13, 15) in such a device are low, the device is particularly suitable for use as an electromagnetic bearing in an optical lithographical device for the irradiation of semiconductor substrates, or in other precision machines.
REFERENCES:
patent: 4795927 (1989-01-01), Morii et al.
patent: 5013987 (1991-05-01), Wakui
patent: 5066879 (1991-11-01), Yamamura
patent: 5093754 (1992-03-01), Kawashima
E. M. H. Kamerbeek, "Magnetic Bearings", Philips Technical Review, vol. 41, No. 11/12, 1983/84, pp. 348-361.
Beekman Henricus E.
Cox Hendrikus H. M.
Van Eijk Jan
Gaffin Jeffrey A.
Miller Paul R.
U.S. Philips Corporation
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