Linear motor

Claim 2

A linear motor comprising an armature and a stator each adapted to provide a sequence of north and south poles along the length of the motor, at least one of the armature and stator having at least two coils to produce the poles thereof, and means to enable the energisation of said coils, the pole pitches of the stator and the armature being different from one another such that with appropriate energisation of said coils by said means the difference in pole pitch of the armature and stator can result, in use, 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.

Claim 3

2 A motor according to claim 1 wherein said means is arranged to energise said coils such that a number of longitudinally spaced detent positions are defined so that a stepper function may be achieved.

Claim 4

A motor according to claim 1 or 2 wherein the stator comprises a plurality of substantially coaxial regularly mutually spaced permanent magnets, and the armature comprises two or more coils coaxially surrounding the magnets and which have a mutual spacing different from that of the magnets.

Claim 5

A motor according to claim 3 wherein a ferromagnetic shroud is located around the coils and magnets and provides a tubular air gap along which the coils may move.

Claim 6

A motor according to any one of the preceding claims, wherein a position detector is provided to detect the relative position of the armature and stator and the coil energisation means is arranged to respond to the output of the position detector to appropriately energise the coils to effect a desired relative movement of the armature and stator.

Claim 7

A motor according to claim 5 and including control circuitry for controlling in closed loop fashion the relative velocity and/ br position of the armature and stator, the control circuitry including said coil energisation means.

Claim 8

A motor according to claim 6 wherein the closed loop velocity or positional control is carried out using the position detector for feedback.

Claim 9

A motor according to claim 5, 6 or 7 wherein the position detector includes an optical graticule on one of the armature and stator and at least one photoresponsive element on the other of the armature and stator.

Claim 10

A motor according to any one of claims 5 to 8 wherein, in use, a weighting factor derived from the output of the position detector is applied to the corresponding coil current(s) to improve linearity of thrust imparted by the armature.

Claim 11

A motor according to any one of the preceding claims wherein said means is arranged to control the energisation of the coils so that a desired thrust/position or thrust/time profile is achieved.

Claim 12

A motor according to any one of the preceding claims wherein said means is arranged to energise the coils with D.C. currents which, in use, are appropriately controlled by electronic or electromechanical means as the relative position of the armature and stator varies, to maintain the desired direction of thrust.

Claim 13

1 2. A motor according to claims 10 and 11 wherein said means is arranged to apply to the coils pulses having appropriate duration, and whose pulse rate and/or amplitude may be appropriately modulated to achieve a desired thrust characteristic.

Claim 14

1 3. A motor according to any one of claims 1 to 1 2 wherein one of the stator and armature is provided with coils to provide the poles thereof and the other of the stator and armature has permanent magnets to provide the poles thereof, the permanent magnets being arranged in a N S.S N N S. . sequence.

Claim 15

A motor according to claim 13 wherein the permanent magnets are spaced from one another along the lengths of the motor by distances substantially equal to their pole pitch and the coils are arranged in two sets, coils of the two sets alternating along the length of the motor, the pitch of adjacent coils being substantially equal to the pole pitch of the permanent magnets. 1 5. A motor according to any one of claims 1 to 10 wherein the fields of the stator and armature are provided by coils supplied with alternating current and said means is arranged to appropriately vary the phase relationship between the currents to the coils of the armature and stator as the relative positions of the stator and armature change to obtain thrust in a desired direction. 1 6. A motor according to any one of claims 1 to 1 2 wherein to produce the poles thereof the armature has two sets of coils, coils of the two sets being of substantially equal length and arranged in alternation along the length of the motor, the coils of different sets being mutually spaced apart by substantially one half of the pole pitch of the stator. 1 7. A linear motor constructed and ar ranged to operate substantially as hereinbe fore described with reference to and as illus trated in the accompanying drawings.