Blanking circuit for electromagnetic display

#This invention relates to electro-magnetic displays wherein an array of rotatably mounted display elements, each designed to selectively display one of two contrastingly colored faces so that information may be displayed or "written" by the array, by the combined visual effects of the faces displayed by the individual elements.

#Such rotatably mounted elements carry magnets and their orientation is controlled by a magnetizable member the sense of whose magnetization is determined by a winding and whose magnetic field controls the orientation of the corresponding element in accord with the sense of magnetization.

#Electromagnetic elements of the type referred to are shown in U.S. Pat. Nos. 3,140,553 dated July 14, 1964; 3,283,427 dated Nov. 8, 1966; 3,295,238 dated Jan. 3, 1967; 3,365,824 dated Jan. 30, 1968; and 3,303,494 dated Feb. 7, 1967. Arrays of such elements are shown in U.S. Pat. Nos. 3,303,494; 3,295,238; 283,427; 3,140,553 listed above although the wiring for "writing" such arrays is somewhat different from the wiring described herein.

#In drawings which illustrate a preferred embodiment of the invention:

#FIG. 1 shows a display element of the type with which the invention may be used;

#FIG. 2 shows the arrangement of a group of 35 of the display elements in FIG. 1 in 7 rows and 5 columns energized to write the letter "T" as part of an array;

#FIG. 1 shows one of a number of electromagnetically operated rotatably mounted elements which may be used. In all such elements a generally flat rotatable element, such as disc 40 has a magnet 42 rotatable therewith. Although the magnet is physically circular in the drawing it is constructed of a material defining a magnetic axis perpendicular to the axis of rotation and here perpendicular to the plane of disc 40. The disc 40 is, as shown, rotatably mounted on brackets 41. The disc 40 is provided with contrastingly on colored faces on opposite sides so that a group of such disc selectively displaying their contrasting faces collectively provide a part of information as demonstrated by FIG. 2, and a number of such groups in an array provides the complete information. A magnetizable member, here polepiece 44 is mounted exterior to the disc 40 but located so that the magnetic field of pole piece 44 will affect magnet 42 throughout the locus of movement of the latter. The polepiece 44 may be of any desired material which under selectively reversible magnetizations will (in the absence of an applied field) produce sufficient remanence flux, and will have sufficient coercivity to retain the element in its desired orientation on return it thereto if displaced. By the term "reversibly permanently magnetizable" herein in relation to the pole piece 44 or other equivalent member is meant a pole piece being reversible in magnetization but capable of having sufficient remanence flux and having sufficient coercivity to retain the orientation of the element with no sustaining current in the polepiece winding. A winding 46 about pole piece 44 is energized by electric current pulses to magnetize the pole piece in the sense desired. The magnetization of the pole piece 44 determines which contrasting face of the disc 40 is displayed and the magnetized pole piece 44 will hold the element in the selected position until the winding 46 is pulsed in a direction to alter the magnetization. It will be obvious that so far as this invention is concerned the pole piece may be replaced by a U-shaped arrangement with uprights of the U forming a pair of pole pieces both located near the magnet locus and with the winding 46 about the crossbar of the U. (such as that shown in U.S. Pat. No. 3,518,664 issued June 30, 1970, or U.S. Pat. No. 3,295,238 issued June 3, 1967). Instead of placing the magnet 42 at the end of the rotatable element as shown it may be located in or on the disc itself as, for example, is shown in U.S. Pat. No. 3,295,238.

#In this application a winding is said to be "energized" to "magnetize" the magnetizable member to display a particular color, (say black). Since the operation of the elements involves the energization of a winding to display one color even though it is already that color, the terms "energization" and "magnetization" include the situation where the magnetization was previously in the desired sense.

#FIG. 2 shows the arrangement of a group of 35 of the elements of FIG. 1 in 7 rows and 5 columns in the customary arrangement for forming letters and numbers, the elements are shown forming a "T". In the preferred form of display, such a group of 7 .times. 5 units form part of a larger array. The ends of winding 46 are arranged in sub-groups with the first sub groups corresponding to one end of each winding differing from the second sub groups corresponding to the other end of each winding and arranged so that the combination of a first and a second sub group is unique for each winding. Thus one end of all the windings in a first sub-group may be energized simultaneously along with selected second sub groups energize selected windings. On the preferred embodiment, the first sub groups are windings in the same row of the rectangular array and the second sub groups are windings in the same column of the array. In the group, as in the remainder of the array, an element (here disc 40) is "operated" or switched to a desired state of displaying the selected one of the light or dark sides by energizing a lead characteristic of the row of the element and a lead characteristic of its column. The number of rows and columns in the array as a whole or the number of rows and columns in a group (such as the 7 .times. 5 arrangement) is not essential to the invention. The invention is, however, principally concerned with displays where the elements are arranged in rows and columns and energized in accord with a row and a column selection.