Abstract: A linear motor comprises a stator 1 and an armature 2 provided, respectively, with a set of spaced apart permanent magnets and a set of drive coils (not shown). The permanent magnets produce a radial magnetic field whose strength varies periodically along the length of the stator 1. The field strength is to derive speed and position signals by means of detectors constituted by field coils 4 (FIG. 1) and Hall Effect sensors 10 (FIG. 5). The periodic variation of the field strength is compensated for in the case of the field coils 4 by staggering their phases along the length of the armature and selectively combining their outputs; in the case of the Hall Effect sensors, the periodical variation is used to derive positional information.

Abstract: The relative position of the armature and stator of a linear motor is controlled using the outputs of two optical transducers in phase quadrature from an optical graticule disposed along the length of the stator. An analog, velocity-indicating signal is derived from the output of the optical transducers. The optical transducers are digitized and cycle an up/down counter which produces an output of a ten-bit digital word representing the armature position. The outputs of the up/down counter are used as the ten higher order bits of the twelve-bit digital word representing the armature position which is compared by a comparator with a demanded armature position. The two lower order bits of the actual-position word are derived directly from the digitized outputs of the optical transducers to eliminate the effect of variation in the exact position at which the counter is reset to zero by a position-detecting switch.

Abstract: A linear motor comprises an armature and a stator each adapted to provide a sequence of North and South poles along the length of the motor. The pole pitch of the stator magnets is different from that of the armature coils such that with appropriate energization of the coils this difference in pole pitch and stator can result in a net thrust of the armature relative to the stator in a desired direction at any location within a range of relative longitudinal positions of the armature and stator. The motor may be subject to closed loop velocity--and/or positional control and means are disclosed to achieve this. Several variations in pole configurations and means of controlling the coil energization are disclosed.

Abstract: In order to ensure correct registration of printing, a printing device is provided with a transducer arrangement which scans the printing platen to detect one of the edges of the stationary or, in the case of continuous feed stationery, pre-printed markings on the stationery. The scanning may take place in the vertical and/or horizontal directions according to the direction in which precise registration is desired. The transducer arrangement is provided with an associated light source and to avoid errors arising, e.g. from variations in ambient lighting level, the transducer arrangement comprises two sensors which are spaced apart in the direction of scanning and an associated circuit forms a difference signal from the outputs of the sensors, which is discriminated with respect to a predetermined threshold level to produce a signal representative of the edge or marking.