Patent GB-1399273-A (GB)
Title: Positioning apparatus
IPC: B43L13/02
Filed: 1972-06-28
Abstract: 1399273 Slides and carriages XYNETICS Inc 28 June 1972 [19 July 1971] 30328/72 Heading B3B [Also in Divisions H2 and G1] Positioning apparatus, e.g. for positioning a cutting tool or stylus 22, comprises a plurality of spaced parallel tracks 10, a beam 18 transversely spanning the tracks, a plurality of first linear motors 14, 16 each of which has a stator extending along a corresponding one of the tracks and a moving part attached to the beam, means for energizing the first linear motors concurrently with periodic signals to move the beam along the tracks, a movable member 20 movable along the beam 18, a second linear motor having a stator extending along the beam and moving part attached to the movable member, and means for energizing the second linear motor with a periodic signal to move the member 20 along the beam 18, each moving part of the first and second linear motors being adjacent to but spaced from the corresponding stator and being constructed to create a driving reaction force to move the beam along the tracks and the member 20 along the beam when the motors are energized by the periodic signals. The linear motors may be fluid motors or induction or hysteresis motors, or as described, are reluctance linear motors (Figs. 2-4a, not shown) wherein, e.g. a track is formed of regularly spaced magnetic "teeth" spaced apart by air gaps, or by such gaps filled with a non-magnetic solid, e.g. plastics material. Spaced from the track is held the movable motor part, e.g. supporting one end of the beam 18, which comprises two sets of electromagnets having polepieces offset linearly relative to each other and which co-operate with the track to cause movement. Control signals are fed to the two sets of electromagnets in phased relationship, e.g. sine and cosine phased signals to cause movement. The distance the beam or head moves can be controlled by feeding a predetermined number of pulses which have a fixed relationship to the pitch of the magnetic "teeth" in the track. Alternatively magnetic pick-offs may be mounted on the moving part to produce pulses as it moves relative to the track. The moving part may be spaced from the track by an air bearing (Fig. 4a, not shown). In an alternative embodiment (Figs. 5-7, not shown) four tracks are provided along which the beam carrying the operating member is moved, each track having a drive means. During movement of the beam stresses are caused, and these are minimized by providing strain gauges at nodal points of zero stress (Fig. 8, not shown) which operate through a control servosystem (Fig. 9, not shown) to control the force applied by the driving means on each track. Alternatively, a laser beam, metal take, load measuring devices; or accelerometers, may be used to monitor the load and/or deflections along the beam. In a further embodiment (Figs. 10 and 11, not shown) the operating member is carried at the intersection of two beams that cross at right angles and are driven by a track and drive means at each end of the beams. Drive means in both orthogonal directions is provided at the intersection of the beams by means of tracks provided on each beam. The apparatus may be used for polar or spherical co-ordinates.