Linear motors and control circuitry therefor

Details Linear motors and control circuitry therefor Linear motors and control circuitry therefor

H - Electricity

02

K

318/1, 341/97

H02K 41/02 (2006.01) G05B 19/39 (2006.01)

Patent

CA 1197550

ABSTRACT OF THE DISCLOSURE IMPROVEMENTS IN OR RELATING TO LINEAR MOTORS AND CONTROL CIRCUITRY THEREFOR The relative position of the armature and stator of a linear motor is controlled using the outputs of two optical transducers 14 and 15 in phase quadrature from an optical graticule disposed along the length of the stator. An analogue, velocity-indicating signal is derived from the output of the photoelectric devices 14 and 15 which are also digitised and used to cycle an up/down counter 317 which produces as an output a ten-bit digital word representing the armature position. The outputs of this counter 317 are used as the ten higher order bits of the twelve-bit digital word representing the armature position which is compared by means of a comparator 316 with a demanded armature position. The two lower order bits of the actual-position word are derived directly from the digitised outputs of the devices 14 and 15 so as to eliminate the effect of variation in the exact position at which the counter 317 is reset to zero by a position-detecting switch 340. While the positional error is large, the motor is servoed in accordance with a predetermined velocity profile and, when the higher order bits of the position error word are zero, the circuitry switches over to a position-servo mode using as the actual position signal, the analogue output of one of the two photoelectric devices 14 and 15. The commutation of the motor coils 415 and 416 is controlled in accordance with the seventh and eighth bits of the output of counter 317, the graticule spacing being chosen so that it equals the commutation spacing divided by 2 raised to an integral power. The polarities of the drive signals to the motor coils 415 and 416 is additionally controlled in the position servo-mode in accordance with the slope of the analogue output of the selected photoelectric device 14, 15 so as to achieve the correct, negative feedback action.

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