IMPROVEMENTS TO INFORMATION DISPLAY DEVICES

Abstract: A display device of the matrix type utilises coincident cur­ rent selection of display elements by the provision of row con­ ductors (R) activating row electromagnets (D) and column con­ ductors (C) activating column electromagnets (H). Each display element includes a rotatable vane (S) which is stable in open and closed positions and a permanent magnet (M) co-operates with the electromagnet (D) to urge the vane (S) into the appro­ priate position. Bar (L) extending from the vane (S) contacts the pole face of electromagnet (H) which, when activated, serves to inhibit movement of the vane irrespective of activation of the row electromagnet (D). Thus by pulsing the display row-by-row, the state of the display elements can be set by selective inhibit­ ing of movement in coincident manner of the appropriate vanes (S) by pulsing the respective column conductors.

Description: Improvements to Information Display Devices This invention relates to information display devices of the type in which each display element in the complete display includes a movable member and an electromagnet for actuating it. Displays of this type include those described in. U.S. Patent Nos. 4,163,332 and 3,140,553 which specifically relate to displays including a matrix of display elements. Another known display matrix using a technique known as Coincident Current selection is described in U.S. Patent No. 3,469,258. With this arrangement, there is provided a single winding conductor for. each row of the matrix and similarly one for each column. Writing on the matrix can be carried out row-by-row or column by-column. With row-by-row writing, for example, each row conductor is energised in turn to select the row, and coincidentally selected column conductors are energised, corresponding to the required pattern of dots to be written onto the row. Since only oneWrow is energised at a time, the main drive power for altering the display elements is in the column drives. For many patterns, all or nearly-all the columns must b driven simultaneously. In the arrangement in U.S. Patent No. 3,469,258, each column conductor must be driven so as to apply to each of its associated display elements one half of the power needed to alter the state of the display element. The arrangment actuates each display element by the use of an individual electromagnet having a core of square loop magnetic material that is permanently magnet isable. It therefore requires a large amount of power to actuate the matrix, since for a change of element state, the magnetisation must be reversed along the square hysteresis loop. An object of the present invention is to reduce the number and total cost of the drive circuits required to energise the electromagnets. Another object is to provide a simple, low-cost scheme for winding the electromagnets. A further object is to reduce the power required to actuate the display. The present invention provides a display device including a plurality of display elements, each display element including a member movable between first and second positions in which said display element presents contrasting appearances, first electromagnet means having a core of ferromagnetic material and being arranged to urge said member to move from one to the other of said positions, and second electromagnet means having a core of ferromagnetic material and being arranged to inhibit movement of said member between said positions urged by said first electromagnet means, whereby said display elements may be selectively set by activating their corresponding first electromagnet means and simultaneously activating particular ones of their corresponding second electromagnet means so as to allow movement of only selected members. The preferred embodiment of the invention has the advantage that the electromagnet for actuating the display element uses a core of soft ferromagnetic material and requires less than a quarter of the power that would otherwise be needed if it were of square loop material. This is because the permeability of the soft core material is appreciably greater than that of the square loop material, resulting in less ampere-turns being needed to produce the same magnetic flux. Also the drive power applied through a column conductor to each of its display elements can, with suitable design, be made less than one fifteenth of the power needed to alter the state of the display element. Taking the two factors into account, the column drive power is reduced by a factor of 30 compared to the previous arrangement described in U.S. Patent No. 3, 469,258. The very low column drive power requirement is achieved in the preferred embodiment by using a simple but very sensitive inhibitor arrangement in each display element, actuated by the column current. Another advantage of the preferred embodiment of the present invention compared to the arrangement of US. Patent No. 3,469,258 is that only the row currents have to be bidirectional, instead of'both the row and column currents. There is therefore a considerable saving in the number of switching circuits, as well as in their power handling requirements. Yet another advantage of the present arrangement is that, unlike the arrangement of U.S. Patent No. 3,469,258, the amplitudes of the row and column currents can be considerably larger than their nominal design values without resulting in misoperation. This makes the display less sensitive to the net effects of changes in power supply voltage, changes of coil resistance due to temperature variations, and variations of characteristics due to manufacturing tolerances. U.S. Patent Nos. 3,775,881 and 3,562,938 describe other display matrices with coincident current selection. These require much more power than do matrices according to the present invention, partly because they lack electromagnet cores for guiding flux from the windings to the display element armatures. They also have the disadvantage that the array of display elements is buried within the windings making access to the display elements for maintenance difficult. Because of the reduction of column power, the present invention enables matrices to be constructed having 30 times more rows without increasing the cost of column drivers relative to known arrangements. This facilitates the economical construction of large display matrices capable of displaying pictures with fine detail. In order that the present invention may be more readily understood, embodiments thereof will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows a front perspective view of part of a matrix display in accordance with one embodiment of the invention; Figure 2 shows the wiring scheme of the coils of the display shown in Figure 1; Figure 3 shows adjacent display elements of a second embodiment of the invention Figure 4 shows a manner of assembly of a display element part; Figure 5 shows a modification of the display element part shown in Figure 4; and Figure 6 shows one display element of a further embodiment of the invention. Referring to Figure 1, there is shown a portion of a display matrix, the portion having two rows and two columns of display elements. Associated with each row there is a row conductor R and with each column a column conductor C. These designations are followed by a number to indicate the row and column positions. The display elements share a common opaque base plate 1 having apertures A therein and are optically of the type described in U.S. Patent No. 4,163,332 from which further constructional details may be derived. Each element includes a vane S mounted with the aid of hinge brackets B attached to base plate 1 to rotate about a horizontal axis between a first stable position in which it covers aperture A and a second position in which it uncovers the aperture, for example so as to allow light from a source, not shown, behind panel 1 to pass through to the viewer, as illustrated for vane S12 in row 1, column 2. Alternatively, or in addition to the light source, the opposite faces of each vane may present contrasting appearances, such as different colours. Each vane S carries a permanent magnet M having a magnetic axis normal to the plane of the vane and a bar L of magnetic material of low remanence protruding out beyond an edge of the vane. Each display element also includes a first electromagnet pole D placed near to the zone of the magnet M and a second electromagnet pole H mounted so as to be in contact with or very close to the tip of the protruding portion of bar L, when the vane covers the aperture. The polarity of magnet M is chosen so that when pole D is energised by current in the direction of arrow E, the vane is urged into the aperture covering position. As shown in Figure 2, for each row, conductor R is wound round each pole D in the row in turn and, for each column, conductor C is wound round each pole H in the column in turn. A method of operating this matrix is as follows. Firstly, the matrix is blanked by pulsing all rows H simultaneously with currents in the direction of arrow E. The apertures are thus all covered. Next, each row conductor R in turn is pulsed with current in the direction of arrow W. At the same time as a row conductor is pulsed, column conductors C are pulsed for those column positions where it is required that the display elements in the row remain light blocking. The effect of pulsing a row conductor R in the direction of arrow W is to urge the vanes S into the aperture exposing position. The current in each selected column conductor C is made sufficiently large to ensure that the vane S is held closed with a torque greater than that induced in the vane by energising its electromagnet D. With the arrangement in Figure 1 suppression of rotation of vanes S is possible for both blanking and writing, since for both vane positions bar element L is in contact with a pole H. This feature is useful under certain conditions, for example when the matrix is used to show the time of day digitally. In this case those digits that change from minute to minute are blanked prior to updating the time. The remaining digits are left undisturbed. Figure 3 illustrates how the arrangement of Figure 1 can be modified so that poles H can hold the vanes only when they are in the aperture covering position. The holding poles H for each row are placed lower than half way between the hinge axis of the row and that of the next row down, and bar L is placed on the vane S so that it protrudes sideways. With the vane in the aperture exposing position, bar L is spaced away from pole H. With this modified arrangement, it is possible to blank the matrix row by roz and to write on each row, i.ev expose selected apertures, as the row below it is being blanked. In the arrangements of Figures 1 and 3, bar L is preferably arranged so that its portion that comes in contact with pole H is free to move to a limited extent relative to the vane S in a direction normal to that of the vane surface. This is to ensure that when the vane is in the aperture blocking position it is in contact at its top with base plate 1 and at the same time bar L is-in contact with pole H, regardless of small variations in the dimensions of the parts. A way of achieving the desired limited degree of movement is illustrated in Figure 4, which is a cross-sectional view of a portion of vane S with the section taken through the longitudinal axis of bar L. Holes Q are provided in vane S. Bar L is initially Ulshaped as indicated by the dotted lines and is inserted through holes Q prior to bending in the directions indicated by arrows Z. The lengths of the short portions sliding in apertures Q are chosen to give the desired freedom of motion. Figure 5 shows a modified arrangement of bar L in which the end portion T is bifurcated. Because of the loose mounting of bar L through holes Q, bar L is free to rotate slightly about its longitudinal axis. Thus, a small portion of grit lodged between one of the prongs of end portion T and the face of pole H will not prevent contact between bar L and pole H, as the other prong is free to come into contact. Figure 6 shows another arrangement of vane S and holding bar L. Bar L is pressed out of soft iron or nickel-iron permalloy and is formed to have two bearing eyelets El, E2. Vane S is also provided with bearing eyelets E3, E4 Brackets BI, B2 attached to base plate 1 have further eyelets E5, E6. A bearing rod N is threaded through all six eyelets and it may be common to several display elements in a row. Vane s includes an angle bracket portion F that retains bar L in position on vane S but allows it to rotate slightly relative to the vane, about the same axis as the vane itself rotates. Tip portion T of bar L can come into contact with holding pole H and is arranged to be flared out so that it presents to pole H a contact surface of large area. This results in a strong attraction between the two when pole H is magnetised, even if there are particles of grit trapped between tip T and pole H.

Claims: CLAIMS 1. A display device including display elements arranged in a number of groups, each display element within one of said groups forming a set together with corresponding display elements of the other groups, each said display element including a member movable between first and second positions in which said display element has different appearances, a permanent magnet coupled to said movable member, a part of ferromagnetic material associated with said movable member, first electromagnet means arranged when energised to act upon said permanent magnet to urge said member to move from one to the other of said positions, second electromagnet means operable when energised to exert force upon said part, said part being arranged in response to predetermined excitation of said second electromagnet means to inhibit motion of said movable member when said member is in one of said positions, means connecting said first electromagnet means in a said group so that they can be energised together and means connecting said second electromagnet means in a said set so that they can be energised together whereby display elements may be selectively set. 2. A display device as claimed in claim 1, wherein said permanent magnet is attached to said movable member. 3. A display device as claimed in claim 1, wherein said part is mounted on said movable member. 4. A display device as claimed in claim 3, wherein said part is loosely attached for limited relative movement to said movable member. 5. A disp ] ay device as claimed in claim 1, wherein said movable member is pivoted. 6. A display device as claimed in claim 1, wherein said part is pivoted. 7. A display device as claimed in claim 6, wherein said movable member and said part are pivoted along the same axis. 8. A display device as claimed in claim 1, wherein a said part and said second electromagnet means are arranged to inhibit movement of a said movable member in only one of said positions. 9. A display device as claimed in claim 1, wherein a said part and said second electromagnet means are arranged to inhibit movement of a said movable member in both of said positions. 10. A display device as claimed in claim 1, wherein each of said first and second electromagnet means includes a core of ferromagnetic material of low remanence. 11. A display device as claimed in claim 1, wherein for one of said positions each said display element appears as a bright area to the observer, said area being bounded by a rectangle having vertical and horizontal sides, said second electromagnet means including a magnetisable pole tip placed close to a corner of said rectanglular area. 12. A display device as claimed in claim 1, wherein said first electromagnet means in a said group are connected in series and said second electromagnet means in a said set are connected in series. 13. A display device as claimed in claim 1, wherein selected display elements within a said group are switched from said first to said second positions and at the same time all the display elements of a different said group are switched from said second to said first positions. 14. A display device includingaplurality of display elements, each display element including a member movable between first and second positions in which said display element presents contrasting appearances, first electromagnet means having a core of ferromagnetic material and being arranged to urge said member to move from one to the other of said positions and second electromagnet means having a core of ferromagnetic material and being arranged to inhibit movement of said member between said positions urged by said first electromagnet means, whereby said display elements may be selectively set by activating their corresponding first electromagnet means and simultaneously activating particular ones of their corresponding second electromagnet means so as to allow movement of only selected members.

Inventors: SALAM, HASSAN PADDY ABDEL
Applicants: UNISPLAY S.A.
Application year: 1983
Main classification: G09F9
IPC codes: G09F9, G09F11