DISPLAY OR INDICATING DEVICE

Abstract: In a display or indicating device, an electromag­ netically-actuated rotatable display or indicating element (12, 38, 40) uses low coercivity magnetic cores (26) and/or permanent magnet assemblies (44), which have pole pieces (52, 54) short circuited at one end by low coercivity material (50), to minimise the power required to switch the element between first (display) and second (obscured) limiting posi­ tions. Additionally, or alternatively, the starting torque ap­ plied to the element upon switching between the limiting positions is optimised by selected an angle or rotation for the element in the range 125°-150°. The ability to achieve such an angle of rotation is enhanced by the support (16, 18, 20) for the element having an inner extent perpendicular to the base plate (10) and an outer extent which is at an angle to the inner extent, the direction of slope of the outer extent being in the direction or rotation of the element from the first to the second limiting position.

Description: This invention relates to a display or indicating device having at least one display or indicating element. The device may have one such element or several such elements which are selectively operable to make letters or figures. The invention in its commonest usage, will be used for the same purposes as prior U.S. Patent 4,223,464 dated September 23, 1980 and assigned to Ferranti-Packard Limited. However, the invention described herein is not limited to uses described in the patent above. The display device in Patent 4,223,464 has a display or indicating element having permanent magnets rotating at opposed ends of a pair of magnetic cores. The cores as described in the patent are of high coercivity material. These high coercivity cores have the advantage that their polarity may be switched, or ′set′, by a pulse of short duration shorter than and of duration independent of the time for the display element to move from one limiting position to the other. The display elements if accidentially displaced from their ′set′ position will tend to return to it. However they have the disadvantage that the high coercivity requires a relatively high increase in switching power, i.e. energizing coil current, to produce a relatively low increase in switching torque. Thus, when ′sticking′ of the display element in its set position is a problem, it is difficult and expensive to raise the switching power to a level sufficient to overcome a sticking of the element. It is therefore an object of this invention to provide a display or indicating device having the general physical configuration of that shown in U.S. Patent 4,223,464 but using soft iron or low coercivity cores. The result is a switchable display element wherein the increase in driving torque to switch the element from one position to the other is closely related to the increase in switching power applied. A tendency for an element to stick can thus be relatively easily avoided by increase of the coil energizing current. The duration of the switching pulse is increased and the element does not necessarily return to its ′set′ position after accidentical deflection, but rather magnetically latches in whichever of the limiting position it comes to rest. However in many applications the ability to conveniently increase switching power to avoid sticking outweighs the disadvantages. "The viewing direction" referred to herein is the approximate centre of the solid angle defined by the limits of directions in which it is intended that the display device will be viewed. "Outward" herein refers to the direction from the device toward the viewing direction and "inward" is in the opposite direction. (It will be appreciated that the element has a display position and an obscured position and "inward" and "outward" on the element have reference to its attitude in the display position). By "display position" we mean a first limiting position in which the "display surface" (that is the contrasting surface) of the element is displayed in the viewing direction and by "obscured position" we mean a second limiting position in which the display surface is obscured in the viewing direction. By "flag" we mean a member having a display surface which member is separable from and attachable to the element. The element uses two permanent magnets usually circular and coaxial with the rotation axis of the element and located opposite the free ends of the magnetic cores, which permanent magnets are locally magnetizable to form diametrically opposed north and south poles facing respective cores. Each of such poles has a complementary pole at the side of the permanent magnet remote from the cores. It is found that the strength of such magnets are increased if a soft iron bridge is provided on the side of the magnet remote from the cores to complete the magnetic circuit between the complementary locally magnetized poles. It is therefore an object of the invention to provide an element having a permanent magnet magnetized axially on diametrically opposed sides with a bridging soft iron member, as described in the previous paragraph. In preferred embodiments of the invention, the display surface of the element is an elongate surface or flag having its longitudinal axis extending parallel to the rotational axis of the element. In the display position, the display surface is displayed in the viewing direction and is coloured to contrast with its background. In the obscured position, the element is rotated so that the display surface is obscured in the viewing direction. The greater the angle of rotation beyond 90° the wider the angle through which the element may be viewed without seeing the display surface in the obscured position. The closer the angle of rotation approaches 180°, the more serious the reduction in the starting torque applied to the element upon switching between the first and second limiting positions. The compromise between these requirements is to choose an angle of rotation of about 135° and in any event between 125°-150°. To attach the support for the element to a base plate, it is easier to design a support which projects from the base plate in a direction parallel to the viewing direction. In order, then, to obtain 135° rotation it is easier to slope the outer extent of the support, which is preferably a pillar, in the direction of rotation of the element from the display position toward the obscured position. This slope, which is at an angle of at least 35° and preferably is at an angle equal to the difference between the desired rotation and 90°, provides a convenient ′underhang′ to receive the display surface in the obscured position. Where the desired rotation is 135°, the angle of the slope of the outer extent to the inner extent of the pillar is therefore 45°. It is an object of this facet of the invention, therefore, to provide, in combination with a base plate facing in the viewing direction, a support for an element, preferably in the form of a pillar, with an inner extent extending from the base plate and perpendicular thereto, and an outer extent sloping at an angle to the inner extent in a direction corresponding to the direction of rotation of the element from the display position to the obscured position. In this respect, acknowledgement is made to DE 27 35 254 A1 which discloses a pillar extending at an oblique angle from a base plate, but which pillar does not incorporate inner and outer extents at an angle to one another in the manner of the preferred embodiment of the invention. Other objects and advantages will be apparent from the description of the preferred embodiment to follow. In drawings which illustrate a preferred embodiment of the invention: Fig. 1 is an illustration viewed from the viewing direction of a display device comprising seven display elements in accord with the invention; Fig. 2 is an exploded perspective view showing the construction of one element and its respective support and the base plate, the element being in the first limiting or display position; Figure 3 is a perspective view of the element and its support, the element being in the second limiting or obscured position; Figure 4 is a section showing the element and its support along a plane through the rotational axis and parallel to the viewing direction; Figure 4a is a view of a magnet assembly; Figure 5 is a partially schematic view showing the movement of the rotor between the display and obscured positions; and Figures 6 and 7 schematically indicate the operation of the device. In the drawings Figure 1 shows a base plate 10 facing in the viewing direction ′V′ in (Figure 5) and mounting seven display elements arranged to provide, by selective switching of the display elements, the digits 0 to 9. In Figure 1, the upper left and lower right display elements are in their obscured positions, showing the backs of the flags 12 which backs correspond in colouring to the background, while the remaining elements are in their display positions with the display surfaces of the flags 12 contrasting with the background so that the number ′2′ is shown. Figure 2 shows the base plate 10 with a square aperture 14 in which the support, in the form of a pillar, for an element may be clipped. The pillar comprises opposed side plates 16 having an inner straight extent perpendicular to the base plate 10 and an outer straight extent sloping at 45° to the inner extent in what will turn out to be the direction of rotation of the element from its display position towards its obscured position. Inner and outer end walls 18 and 20 join the edges of opposed side walls to form a square in transverse section through the pillar. The end walls 18 and 20 stop a short distance outward of the beginning of the slope in the pillar. The pillar is attached to the plate 10 by resiliently inwardly deflectable dogs 22 inwardly projecting from end walls 18 and 20 and having outwardly facing shoulders 24 which, after such inward deflection insertion and release, engage the inner surface of the plate 10 to retain the pillar in position. The side walls are provided with inwardly diverging supports 27 which abuttingly meet the outer surface of the plate 10 to help maintain the pillar rigid. It will be readily appreciated that, if desired, the dogs 22 may be positioned on the side walls and the supports 24 on the end walls. The side walls and end walls may be attached by adhesive or by other means as desired. Towards the outer end of the pillar a pair of low coercivity or soft iron cores 26 extend longitudinally and parallel between the side walls 16. Energizing coils 28 surround the cores 26 and are supplied with current from a source, not shown. Halfway between the cores 26, side walls 16 mount aligned outwardly projecting stub shafts 30 on which the element is to be mounted for rotation between the first and second limiting positions. Alternatively the two stub shafts are replaced by a single central shaft extending between the side walls and projecting therefrom The outer edges of the side walls are provided with an rounded arc 32 over which the element may rotate and are shaped to provide, at each end a shoulder (34 and 36 respectively) which limits the movement of the element in its display and obscured positions, respectively. The element preferably comprises a rectilinear outer wall or crossbar 38 with a pair of opposed legs 40 extending inwardly therefrom at a spacing such that such legs may extend (and rotate) on each side of the pillar adjacent opposed side walls 16. Opposed circular apertures 42 are provided in the legs 40 of a size to receive generally cylindrical permanent magnets assemblies 44. The magnet assemblies are preferably slightly tapered to allow easy insertion in the apertures 42. In place, the magnet assemblies are held in place by adhesive or any other desired means. The magnetic assemblies are centrally apertured at 46 to rotatably to receive the stub shafts 30. The central apertures are preferably lined with low frication bearing material. The magnet assembly comprises a cylindrical high remanence high coercivity thicker portion 48, preferably nearer the free ends of cores 26 and a cylindrical low coercivity or soft iron thinner portion 50 farther from the free ends of cores. The high coercivity portion of each magnet assembly is locally magnetized at 52 and 54 parallel to the rotational axis to provide respectively diametrically opposed N and S poles nearer the coil free ends as best shown in Figure 4a. Since the magnetization is in the axial direction the N pole shown requires a complement south pole (not lettered) at the low coercivity layer 50; and the S pole shown requires a complement north pole (not lettered) at the low coercivity layer. The low coercivity layer 50 thus provides a short circuiting of the magnetic circuit between the complement poles. It is found that this arrangement greatly improves the flux density at the core -adjacent poles N and S, and the operation of the display element is thereby improved. The size of the magnet assembly is chosen so that the locally magnetized poles N and S are at each side of the pillar directly opposite the free ends of core 26. The inward ends of legs 40 are provided with axially projection abutments 56 and these are provided with axially open bores 58. These bores will be sized, larger or smaller as required, to balance the element, including the flag 12 about its rotational axis. The surfaces of cross bar 38 of the element are designed to act, in cooperation with the stop surfaces 34 and 36, to define the display position and obscured position, respectively. Thus the inward surface 62 of the cross bar 38 contacts surface 34 at the display position and the edge 64 of the cross bar 38 contacts the surface 36 at the obscured position. The axially directed edges of cross bar 38 each form three axially directed projections being arranged to be disposed from each other in a direction generally transverse to the rotational axis and parallel to the display surface thereon. Central projection 66 is notched on its inward surface and outer projections 68 are notched on their upper surface to allow nesting of a resilient wire 70. The wire is provided with arms 72 and 74 extending transversely on each side of the element in a shallow, outwardly directed v. The unstressed attitude of the wire is such that it must be flexed to slightly narrow the v to fit into the notches of the projections 66, 68. Thus, the wires 70 are stressed when supported in the notches and will ′stand′ on the rotor so stressed, for insertion of the flag 12. The outer ends of the v arms are reversed turned in the outward direction through about 135° to receive the edges of the flag 12. The flags 12 shaped as any one of those shown in Figure 1 are elongate and are preferably parallel sided and designed to extend longitudinally on each side of the element. The flag 12 is constructed of resilient plastic or metal and alone at rest is designed to assume a concavo-convex shape slightly wider from edge to edge than the hooked ends of the v arms. The concave surface of the flag 12 is the ′display surface′ and is coloured (here with a light colour) to contrast with the background of the plate 10 and is displayed in the viewing direction on the display position of the element. (The solid line position of Figure 2). The convex surface of the flag 12 is coloured to correspond to the background, (and to those parts of the element and pillar exposed in the obscured position in Figure 5). The flag 12 is attached to the wires 70 as they ′stand′ on the rotor by flexing the flag 12 to increase its concavity and placing its opposed longitudinal edges in the exposed wire hooks. The flag 12 then unbends resiliently along its length and bears on the inside of the wire hooks and is securely retained in position. It will be noted that the extra stress provided on the wire hooks by the flag 70 increases the flexure pressure of the wire hooks on the projections, making the connection between the wire and the element more secure. In other applications than the 7 bar module of Figure 1, the flag 12 may have any other shape with edges suitable for coupling to the wires 70. Two terminals 25 are attached to the molding side walls and are connected to the respective coils 28 which are connected in series. The coil winding and connection is such that adjacent outer ends of cores 28 are of opposite polarity and switchable by the pulses of coil current. Inward ends 29 of terminals 25 are connected to a source (not shown) of the current pulses. The operation is described through the schematics of Figure 6 and 7 with reference also to Figure 5. Figures 6 and 7 show the magnetism of the ends of the cores 26 at the end viewed in Figure 5. Figure 6 shows the rear ends of cores 26 magnetized to polarities S′ and N′ to attract the poles 52 and 54 of magnet 48 to the display position of the element as shown in the solid line position of Figure 5. The opposite ends of the cores 26 are each oppositely magnetized but the corresponding magnet 48 is oriented to produce identical magnetic torque to that shown. When it is desired to rotate the element to the dotted line position of Figure 5, the coils 28 are pulsed to reverse the polarity of the cores 26 so that, with reference to Figure 5, the new N′ and S′ magnetized core ends attract the S and N poles 54 and 52 to swing the rotor 135° to the dotted line position of Figure 5. In connection with the magnetic drive, it will be noted that the magnetic axis of the ends of the cores 26 is offset from the magnetic axis of the permanent magnet 48 by 180 - 135 2 = 22 1/2° at each end, giving a good starting torque when the polarity of the cores 26 is reversed. The remote end of the element and cores 26 will of course provide the same torque and in the same sense. When the cores 26 are switched, because they are of soft iron, the switching pulse in coils 28 must be maintained until the permanent magnet poles have latched to the respectively adjacent cores 26 in the new position.

Claims: 1. Display or indicating device defining a viewing direction (V) comprising: a support (16, 18, 20), a display or indicating element (12, 38, 40) rotatably mounted on said support (16, 18, 20) to rotate on an axis of rotation relative thereto, a display surface on said element (12, 38, 40) designed to contrast with the background when displayed in the viewing direction (V), means (34, 36) limiting rotation of said element (12, 38, 40) to rotation through a predetermined angle between a first limiting position where said display surface is displayed in the viewing direction (V) and a second limiting position where said display surface is not visible in the viewing direction (V), a pair of substantially parallel longitudinally extending low coercivity iron cores (26) or soft iron cores (26) extending generally parallel to said rotation axis and between first and second free ends, an electrical energizing coil (28) corresponding to each core (26) for magnetizing the latter for the duration of current in said coil (28), first and second permanent magnets (44) mounted on and rotatable with said element (12, 38, 40), each defining a polar axis with a component perpendicular to the axis of rotation, the pair of first free ends and the pair of second free ends each being designed, when each pair is of mutually opposite magnetic polarity, to define between each pair of ends a magnetic flux path of reversible polarity, each said flux paths including the locus of one of said permanent magnets (44) over said rotational range and being arranged so that, for a given polarity across said path, the field associated with said path exerts a torque in one sense over the range of movement, between the two limiting positions, on the corresponding permanent magnet (44) and so that said torque is in the same sense for both magnets (44). 2. A device as claimed in claim 1, wherein each said permanent magnet (44) comprises a layer of permanently magnetized high remanence material (48) on the side nearest the core ends and magnetized to provide north and south poles (52, 54) radially displaced from the centre of rotation and angularly displaced from each other and a layer of soft iron or low remanence material (50) on the side farthest from the core ends. 3. A device as claimed in claim 2 wherein said high remanence material (50) is magnetized to provide on the side nearest the core ends with a north pole (52) at one radially outer location and a south pole (54) diametrically opposed thereto and on the side remote from the core ends opposite poles axially disposed from those referred to. 4. A device as claimed in any one of claims 1 to 3, wherein said device further comprises a base plate (10) facing and extending transverse to the viewing direction (V), said support (16, 18, 20) being mounted on said base plate (10) and having an inner extent projecting from said base plate (10) in the viewing direction (V) and an outer extent extending at an angle of at least 35° to said inner extent in the direction of movement of said display surface from said first to said second limiting position. 5. A device as claimed in claim 4, wherein said angle is approximately 45°. 6. A device as claimed in any one of claims 1 to 5, wherein said display surface is formed on the concave side of a concave-convex elongate member (12) of resilient material, and wherein said device further comprises means (66, 68) on said element (12, 38, 40) mounting at least two pairs of diverging arms (72, 74), each pair of diverging arms (72, 74) being resilient, terminating in curved hook ends extending through about 135° and adapted to receive an edge of said member (12), the attitude of each pair of diverging arms (72, 74) before attachment of said member (12) being such that the curvature of said member (12) must be increased to allow the edges thereof to be slid within said four hook ends to be held thereby. 7. A device as claimed in claim 6, wherein said arms (72, 74) are mounted by providing three axial projections (66, 68) on each axial facing side of said display element (12, 38, 40), said three axial projections (66, 68) being arranged to be disposed from each other in a direction generally transverse to the rotation axis and parallel to the display surface thereon and being designed to retain a flexed resilient wire (70) passing on one side of the two outer projections (66), wherein said one side is toward said member (12) and wherein said arms (72, 74) are formed at each end of a single resilient extent of wire (70) designed to be resiliently flexed when attached to said element (12, 38, 40).

Inventors: BROWNE, JOHN, WALES, THOMAS
Applicants: NEI CANADA LIMITED
Application year: 1987
Main classification: G09F9
IPC codes: G09F9