US2943313A

US2943313A - Electromagnetic indicator

Info

Publication number: US2943313A
Application number: US641932A
Authority: US
Inventors: Bernard M Gordon; Hector R Durocher; Sico Americo
Original assignee: Epsco Inc
Current assignee: Epsco Inc
Priority date: 1957-02-25
Filing date: 1957-02-25
Publication date: 1960-06-28
Anticipated expiration: 1977-06-28
Also published as: DE1146412B

Description

B. M. GORDON ETAL 2,943,313 ELECTROMAGNETIC INDICATOR 3 Sheets-Sheet 1 INVENTORS BERNARD M. GORDON HECTOR R. DUROCHER AMERICO SICO June 28, 1960 Filed Feb. 25, 1957 FIG.4

2 U G I F.

4 & if? I M will 5 1 F v 1 n H 1 w w m m a a B June 28, 1960 B. M. GORDON EIAL 2,943,313

ELECTROMAGNETIC INDICATOR Filed Feb. 25, 1957 3 $heets-$heet 2 INVENTORS BERNARD M. GO N HECTOR R. DUR ER AMERICO SICO A TZDRNE) n q (0 9 w l-L Ll.

June 28, 1960 B. M. GORDON ETAL 2,943,313

ELECTROMAGNETIC INDICATOR Filed Feb. 25, 1957 5 Sheets-Sheet 3 FIG. 3

/ N VE N T0193 BERNARD M. GORDON HECTOR R. DUROCHER AMERICO SICO r97 ATTORNEY United States Patent 2,943,313 ELECTROMAGNETIC INDICATOR Bernard M. Gordon, Newton, Mass., Hector R. Duroeher, Nashua, N.H., and America Sico, Revere, Mass., assignors to Epsco, Incorporated, Boston, Mass, a corporatlon of Massachusetts Filed Feb. 25, 1957, Ser..No. 641,932

13 Claims. (Cl. 340-378) The present invention relates in general -to an electromagnetic data display system, and more particularly concerns novel, compact and relatively low cost apparatus responsive to external electrical excitation for reliably indicating any one of a plurality of preselected characters or indicia.

Within the broad subject classification of data display devices, virtually innumerable mechanical, electromagnetic and electronic techniques have been described in the literature, and a comparatively large number of specific instrument types are commercially available at the present time. Perhaps the most successful of the prior electromagnetic character display units is dependent upon the multiposition stepping relay; which while quite satisfactory for such applications as stock quotation boards, is relatively costly, noisy, slow in operation and mechanically complex. Further, its weight precludes use in airborne systems, and wear problems attendant pawl and rachet mechanisms severely limit the reliability which may be anticipated.

Recent innovations in electronic tubes have resulted in novel glow-tube discharge indicators, an example being an elongated neon tube having a plurality of axially spaced filamentary cathodes, each having the configuration of the character to be displayed. These devices are eminently eifective in darkened surroundings andmay be operated at high speed, but are subject to disadvantages such as complete inflexibility with respect to character selection and the poor reliability and high failure expectancies of gas discharge tubes.

The present invention contemplates and has as a primary object the provision of an electromagnetic data display device of novel, simplified design and construction offering positive, unambiguous, high speed character selection and presentation wholly without complex pawl and rachet linkages, electronic circuits and components, which is particularly adaptable to low cost mass production techniques. This invention represents an extension of the principles of the copending application of Bernard M. Gordon and Randall L. Gibson, entitled Indicating Device, Serial No. 584,803, filed May 14, 1956.

Broadly speaking, the present invention utilizes a character bearing member in association with an electromagnetic structure selectively energizable to produce any one of a plurality of discrete magnetic field orientations. A magnetic device whose motion is controlled by the selected field controls the displacement of the character member, and a viewing window is provided for visual observation of the chosen character. In accordance with the principles of this invention, for each inscribed figure to be displayed, two closely adjacent, magnetically determined stable positions are available for the character bearing member, one fixed by the electromagnetic structure when electrical excitation is applied thereto, and the other by an independent static magnetizable member which coacts with the magnetic device associated with the character bearing member in the absence of electrical excitation. This permits precise, unambiguous centering of each of the characters to be displayed, provides a restraining torque which precludes drift of the character bearing member due to environmental disturbances such as vibration, and of special significance, yields a magnetic circuit without dead-spots or conditions of magnetic equilibrium which would otherwise tend to prevent the development of displacement forces upon the character member despite the applied excitation.

More specifically, in one aspect of the present invention, the data indicating device comprises a stator having a symmetrical, circular configuration of electromagnets capable of establishing a discrete number of magnetic field orientations in response to the selective application of current to the coils thereof. The characters to be displayed are inscribed upon the outer cylindrical surface of a light weight, low inertia rotor which is activated by an attached salient pole permanent magnet whose angular orientation is initially controlled by the stator field.

A symmetrical array of static magnetizable elements is fixed in the space between the rotor permanent magnet and the stator, and arranged to provide, by mutual magnetic attraction, a number of discrete orientations for the rotor magnet, equal to the number available from the stator electromagnets but slightly displaced therefrom. In other words, when the appropriate current is applied to the stator electromagnets, the rotor magnet immediately assumes the angular orientation of the magnetic field thus established, which is completely independent of the presence of the static magnetizable elements. Upon the interruption of this current, however, the attractive force between the respective, slightly displaced static element and the rotor magnet controls, and the rotor is accordingly displaced angularly and locked into .a new position in proximity with the static element. By precisely positioning the magnetizable elements, it is possible to fix with a corresponding degree of accuracy, the display position of each of the characters to be viewed through the window provided therefor.

As will become apparent as the discussion proceeds, numerous novel mechanical concepts are combined with the objective of achieving manufacturing simplicity and cost reduction while enhancing flexibility and utility. Thus, a simplified toroidal stator structure is used which eliminates the tedious machining and assembly required for a salient pole design, and further permits incapsulation into a unitary, trouble free package. The housing is arranged so that a multiplicity of like indicating units maybe joined together in an integral compact package allowing numbers or codes of any order to be displayed. While be ing of minimum inertia to permit rapid angular adjustment, the rotor is nevertheless arranged so that viscous fluid damping may be added to enhance its transient response to applied signals, and a single cover plate simultaneously affords both shielding from stray magnetic fields and magnetic damping.

Ease of final assembly is another object of this invention, and the simplified assembly technique allows rapid initial adjustment to insure accurate display. Adjustments once made will be retained for the life of the device.

Other objects and advantages will best be understood from the following detailed specification when read in connection with the accompanying drawing in which:

Fig. l is a fragmentary front view of a panel illustrating the manner in which an assembly of indicating units embodying this invention may be mounted to furnish a multidigit data display;

Fig. 2 is a perspective view of one of the data indicating units embodying the principles of this invention;

Fig. 3 is an axially exploded perspective view which illustrates the key components of the data indicating unit illustrated in Fig. 2;

Fig. 4 is a top view, partly in cross-section, of an assembled indicating unit, the cross-sectional area being taken along a diameter of the device indicated in Fig. 2;

Fig. 5 is a schematic circuit diagram illustrating the electrical interconnection of the electromagnets within the indicating device of Fig. 2 and the mode of actuation thereof;

Fig. 6A andFig. 6B are respectively end and front views of the indicating device and serve to illustrate the relative angular orientation of several of the components under a particular electrical condition; and

Fig. 7A and Fig. 7B are respectively end and front views of the indicating device and illustrate the orientation of these components for an electrical condition other than that shown in Fig. 6.

Throughout the several views of the drawing, like reference numerals will be used to designate like components. I

With reference now to the drawing and more particularly to Fig. 1 thereof, there is shown a portion of a panel 11 formed with an elongated rectangular opening 12 through which are visible the character display portions of a mechanically cascaded group of identical indicator units 13, each of which embodies the principles of this invention. As will become more apparent from the description which follows, any selected indicia may be displayed by the respective indicating units 13 as a function of applied electrical excitation. The indicia chosen will, of course, be a function of the specific application; for example, assuming each indicator as eapable of displaying all ten decimal digits, the apparatus disclosed in Fig. 1 may readily be used to furnish a visual output of a five decade electronic counter. On the other hand, it is unnecessary that the display be digital in character, and any or all of the devices may be employed to display alphabetic or special symbols associated with the apparatus into which the indicators are incorporated.

Figs. 2 to 7 inclusive disclose the specific mechanical and the electrical details, including the mode of operation, of one of the devices 13 shown in Fig. 1. By viritue of the fact that the bulk of the applications for indicators having these general specifications relate to the presentation of the ten decimal digits, an indicator so designed has been chosen for detailed illustration and discussion herein. It will be understood, however, that by relatively simple design changes, the principles of this invention may be extended to indicators capable of displaying greater or fewer digits, letters or symbols.

Fig. 2 is a perspective view which generally illustrates the external physical characteristics of the indicator of this invention. All electrical and mechanical elements of the device are completely enclosed within a thin cylindrical housing 14, formed with a single rectangular window 15, through which the digits inscribed upon the outer cylindrical surface of a coaxial rotor 16, may be viewed.

A multiplicity of wires 18 extend out of the indicator for connection to an external circuit for electrical control of the digit presentation.

With the physical appearance of the indicating device 13 in view, reference is now made simultaneously to Figs. 3 and 4 which disclose the mechanical details of each of the key components both individually and as assembled.

More specifically, housing 14 is seen to comprise a relatively short cylinder closed at one end by a circular end wall. The edges of window 15 may be beveled to emphasize the outline thereof and to generally improve its appearance in a display. An annular ridge 25 is formed onthe closed end of housing 14 and is beveled at 26, as best illustrated in Fig. 4, to provide a circular edge which will mate exactly with the circular edge 27 of another of the indicating devices 13. In this manner the array shown in Fig. l, or any larger or smaller group of devices, may be built up as a rigid integrated structure. The inner edge of ridge 25 confines a circular region which is adapted to receive a disc-shaped magnetic end plate 31 having a central opening 32 and three symmetrically positioned countersunk holes 33. A central opening 34 in the side Wall of housing 14 is aligned axially with opening 32 and three arcuate slots 35 are aligned with openings 33. The thickness of end plate 31 corresponds exactly to the depth of the recess formed within circular ridge 25; consequently, when the plate is appropriately inserted and the fiat-

head screws

36 and 37 passed through the respective counter-sunk openings, a smooth external surface is presented, as best illustrated in Fig. 4.

Returning to the details of housing 14, a slot 41 is provided in the end wall which extends to a small notch 42 in the cylindrical surface thereof. As best illustrated in Fig. 4, this arrangement permits withdrawal of the wires 18 without interference with the seating of end plate 31 in the recess provided by ridge 25.

Turning now to rotor 16, this component is seen. to comprise a central hub 43 which diverges into an integral substantially circular side wall 44 which in turn supports the thin integral character bearing cylindrical surface 17.

Returning momentarily to Fig. 2, it will be observed that the circular end wall of rotor 16 contains a plurality of relatively large perforations 21 which advantageously function to minimize the inertia of the rotor and as a consequence enhance the speed of response to external signals.

A key 45 is fitted in mating keyways provided in hub 43 and in a permanent magnet 46, the latter having ogival or similar sharply pointed magnetic poles. When assembled as shown in Fig. 4, magnet 46 and rotor 16 rotate as a unit.

An arbor 51 rotatably supports rotor 16 within a cylindrical housing 14. As shown, arbor 51 is provided with a threaded axial opening 52 which on assembly is engaged by screw 36. Annular ridge 53 forms a seat to firmly position arbor 51 against the inner wall of housing 14. Cylindrical surface 54 accepts ball bearing 55, which on assembly as shown in Fig. 4, rotatably supports rotor 16 in housing 14. A saucer-shaped cover 56, secured in place by snap ring 57, keeps the rotating elements dust and dirt free.

An electrotmagnetic stator 61 is symmetrically and co axially disposed within housing 14 and the manner in which this component is constructed is best seen by simultaneous reference to Figs. 3, 4 and 6A. The magnetic component of this assembly is a toroid 62 formed of a plurality of stacked iron laminations. With particular reference to Fig. 6A, each of the magnetic core laminations comprises a flat circular stamping of magnetic material which is formed with a relatively narrow slit 63. In assembling the magnetic structure 61 the requisite number of laminations, for example, five as shown in the drawing, are placed one upon the other with the slits 63 in transverse alignment. At this point the laminations as a group are bent open, forming a helical core, and for the decimal indicator under discussion, ten coil forms 64, each wound with a respective solenoid type coil 65, are slipped on to the magnetic structure. As best shown in Fig. 6A, coil forms 64 are so dimensioned as to abut one another along the inner circular edge thereof when in position. This arrangement makes it unnecessary to use spacers or other means to assure a reasonably symmetrical distribution of coils 65 about laminations 62.

With the coils in place, the laminar core structure is allowed to spring back to its normal circular form, and to avoid an abrupt air gap, a screwdri er or like implement is used to rotate each of the laminations with reference to the others so that the respective slits 63 are symmetrically distributed. For example, when using five laminations, each of the circular elements may be shifted approximately seventy-two degrees with reference to the others. Under the circumstances the effect of the individual air gaps 63 is negligible. The number of turns in each of the solenoidal coils 65 will be determined by design factors, such as applied voltage, but for general application may consist of several thousand turns of relatively fine wire.

Fig. is a schematic diagram illustrating the wiring symmetry of the circular array of coils 65 about the mag netic core (not shown in this figure). Conventional dot notation has been used to indicate winding direction and it is seen that the dotted end of each coil is joined to the undotted end of the next adjacent coil. Insofar as the magnetic field is concerned, this is effectively the equivalent of Winding a tapped, continuous toroidal winding upon core 62.

Wires 18 which are used for external actuation extend from the junctions between each two adjacent coils. The wires interconnecting the adjacent coils 65 are not shown in Fig. 6A but the group of output wires 18 has been illustrated in both Figs. 4 and 6A. Evidently the number of output wires 18 is exactly equal to the number of coils used upon the toroidal magnetic core 62, and for a decimal display device this number of course is ten.

With coils 65 appropriately disposed upon the magnetic core structure, and the output leads 18 suitably attached, the array of electromagnets is inserted into a stamped or molded open toroidal shell 66 of non-magnetic material. Thereafter the coil structure is potted or encased in a plastic compound 67 which not only rigidly secures the coil structure relative to shell 66, but permanently seals the electrical components against moisture. During the incapsulation process, three symmetrical threaded holes maybe formed in the region between coils, these being aligned properly for engagement by screws 37 to secure the electromagnetic stator 61 to the inner surface of the end wall of housing 14.

A relatively thin non-magnetic cylinder 71 is positioned in the space between magnet 46 and the inner surface of stator 61. This element, as is best illustrated in Figs. 3 and 6A, is formed with small rectangular slots 72 equal in number to the stator electromagnets 65, and according- -ly equal in number to the digits to be displayed. Slots 72. As shown in Fig. 6A the cross-section of these magnetizable elements is such that each exactly fills the space provided therefor in the cylindrical member 71.

Fig. '4 demonstrates the manner in which the components individually pictured in Fig. 3 are assembled into an indicating unit of the type illustrated in Fig. 2. The exact order of assembly is not too critical; typically however, circular end plate 31 may be placed in the recess provided therefor, and stator 61 then secured by screws 37 (a loose fit pending final adjustment). Cylindrical member 71 is preferably press-fitted or cemented to the inner surface of shell 66, and this composite unit is rotatable about the inwardly facing circular ridge 75 provided on the inner side wall of housing '14. The angular relationship of the magnetic elements 73 and the coil assembly will be more fuily considered below. The subassembly of arbor'51, ball bearing 55, dust cover 56, clamp ring 57, magnet 46 and rotor 16 are fastened in the position shown by the single screw 36.

Returning now to Fig. 5, the manner in which the indicator unit is actuated will be discussed briefly. Each of the wires 18, which may be color-coded for convenience current I which divides equally between opposite symmetrical semi-circles of the coils 65. The net elfect of both currents U2 is to establish a diametrical magnetic field designated by the vector B.

Vector B is one of the ten possible discrete diametrical magnetic fields which may be created by rotation of

switch arms

79 and 80. Each of these fields, which has the effect of displaying a respective digit, will be separated from adjacent fields by the angular separation of adjacent coils 65. For the decimal indicator this is thirty-six degrees, however some variation in this distribution may be expected because, as noted earlier, a high degree of precision was not a primary requirement in mounting coils 65 on the supporting core.

Although rotation of

opposed switch arms

79 and 80 is effective in rotating vector B, it should be apparent that this is not the only means by'which a desired field orientation may be established. For example, if an indicator unit is used as a computer output device, all ten wires 18'may be directly coupled to the computer, and energization of any two opposite wires will set up a field and select a digit for display.

Reference is now made to Figs. 6A and 7A for illustration of the relative orientation of certain of the key components in the assembled indicator, and for a discussion of the significance and utility of the magnetic elements 73. Line 81 has been drawn for reference purposes from the center through a point midway between two adjacent coil forms 64. The purpose of this line is to define the position of one of the ten discrete magnetic field vectors B, such as the one shown upon the circuit diagram, Fig. 5.

Thus, these figures show that cylinder 71 is fixed within the stator and oriented within housing 14 so as to provide a substantially uniform angular separation, designated on the drawing as 0, between the individual magnetic elements 73 and the respective mid-points between adjacent electromagnets.

With current flowing as in Fig. 5, and assuming that the device is in perfect adjustment, salient pole-magnet 46 will rapidly rotate and align itself with the field vector B, Fig. 6A; the sharply defined N and S poles falling along line 81. Assuming further, that with power thus applied, the selected character is digit 5; the manner in which the 5 appears in the viewing window is shown in Fig. 6B. Thus, note that the 5 is off-centered by a small amount. If now the current I is cut off, the magnetic field designated by vector B disappears, with the result that the force of attraction between each of the salient poles of magnet 46 and the immediately adjacent magnetic element 73 will cause angular rotation of the magnet, and the attached rotor, to the rest position shown in Fig. 7A. Displacement through angle 0 will now bring digit 5 into the symmetrical, centered position within window 15 shown in Fig. 7B.

Thus, speaking generally, for each of the ten discrete orientations of the magnetic field vector B in the decimal device being considered, there exists a fixed, stable angular position for magnet 46. In addition, in the region of each of these ten discrete orientations, there exists a second stable position for magnet 46 which is defined, as in Fig. 7A, by the respective magnetic. element 73. Stated otherwise, when power is applied to a particular opposite set of input terminals, rotor 16 is brought to a first stableposition where it remains until power is cut off; immediately thereafter, the rotor is pulled through the slight angle 0 by magnetic forces to the second stable position.

The specific advantages of this magnetic configuration may be best demonstrated by an example. The excitationfshown in Fig. 5 was assumed to be that which would bring the character 5 into the viewing window. With the decimal digits to 9 uniformly marked upon the periphery of cylindricalsurface 17, the digit 0 is brought into view by reversing the polarity of current through the same input wires which brought digit into view. If now the angular orientationshown in Fig. 6A were the rest position for viewing digit 5, reversal of field vector B would in fact develop no rotational torque on magnet 46, other than that which might be generated due to inherent imperfections and inaccuracies in manufacturing the device. Effectiv ly, for a situation which demanded a 180 reversal or the rotor, a condition of unbalanced or unstable equilibrium would exist which would result either in no'inotion whatsoever or exceedingly slow initial rotation due to the negligible torque resulting from machining and alignment errors. I

on the other hand, Figs. 6A and 7A demonstrate that the application of power is used to efiiect an approximate alignment and that immediately after power cut-off, a definite displacement from the original aligning field is accomplished in reaching the correct position. Thereafter, this displacement will permit the development of substantial rotational torque even if a digit 180 displaced from the digit under observation is selected by the external source. Y

Further advantages of the device are apparent from an examination of Figs. 6A and 7B. Obviously precision angular separation of the multiplicity of electromagnets wound on core 64 would be difiicult, and perhaps an extraordinarily expensive task. If alignment of each of the digits to be viewed within the viewing window 15 were to be dependent upon the establishment of ten magnetic field vectors each precisely thirty-six degrees apart, an exceptional degree of care in the winding and mounting of each of the coils would be required. As disclosed in the drawing, however, the stator electromagnets serve primarily to position the rotor close to the rest position, while the exact determination of the position of the digit in the viewing window is made by the ten magnetic elements 73 supported by cylinder 71. Obviously, it is a relatively simple task to space these magnetic elements thirty-six degrees apart, whereby each of the ten digits will be precisely centered within the viewing window as illustrated in Fig. 7B.

Of interest however, is the fact that the magnetizable elements 73 perform still another vital function, perhaps best illustrated with reference to Fig. 7A; namely, that of providing a restraining torque which tends to keep the rotor 16 in the selected position notwithstanding vibration, shock or other environmental interference. It is especially significant to note that a minimum of spacing exists between the salient poles of magnet 46 and the inner surface of cylinder 71. Thus a modest amount of torque would be required to displace magnet 46 from the position shown in Fig. 7A unless power is applied to the input wires of the device.

Previous discussio'n assumed precise initial adjustment of the indicator to obtain the operating results discussed in connection with Figs. 6 and 7. Referring to Figs. 3 and 6A, it may be seen that the angular relationship specified for the assembly including the stator electromagnets and the magnetizable elements 73 may be obtained during assembly by angular adjustment of the entire stator structure 61 relative to the housing 14 through the aid of the arcuate openings 35. When this relative magnetic orientation is accomplished, all four

screws

36 and 37 may be tightened, and further adjustment will not be required.

Magnet 46 has been described as having ogival shaped, salient poles, the latter being formed either by molding or grinding. In the manufacture of permanent magnets it is not infrequent that the magnetic poles are not pre- 8 cisely apart. The effect of such inherent defect upon the'present indicator is best demonstrated in Fig. 7A where point 87 is for discussion purposes assumed to represent the true magnetic pole. Although this is not precisely at the physical extremity of the magnet, the effect of this displacement will be negligible since the sharp taper places the displaced magnetic pole sufliciently inward radially from the pointed end, that the latter will, in fact, be determinative of angular position when at rest as shown in Fig. 7A.

Disc 31, as disclosed earlier, performs the dual function of shielding the interior of the display unit from stray magnetic fields and offering a degree of magnetic damping to rotation of magnet 46. While treating the subject of damping, it should be observed that it is also possible, if desired, to add a degree of viscous damping through the use of a fluid in ball bearing 55. For this purpose it is preferably that a customary ball retainer type hearing (not shown) he used. The fluid which may be of silicone base, and retained by capillary action is sufiicicnt to provide the necessary transient damping. The region 91 shown in the assembly Fig. 4 may, through capillary action, also be used to retain a modest amount of damping fluid if desired. The close proximity of rotor and arbor surfaces will preclude fluid leakage irrespective of mounting position of the indicator.

Special note should be taken of the nature of the electrical signal required to achieve the results illustrated in Figs. 6 and 7. When power is applied for the purpose of changing digits the torque developed upon rotor 16 by field vector B causes rapid acceleration to the new position. Obviously, if the power is cut off before this new position is reached, the rotor will spin free, and though it will ultimately come to rest due to the attraction of some magnetic element 73, there remains a high probability of an erroneous reading. It is therefore necessary to apply power for a sufficient time to insure a correct orientation of rotor 16. It is, in fact, desirable to utilize some safety factor in the current pulse to preclude erroneous reading if for any reason the mechanism should behave in a sluggish manner.

Although the preceding discussion has assumed that the power is turned off shortly after the rotor arrives at the position defined by the magnetic field, it is possible to utilize the device shown under conditions in which the power is on throughout the display period of a char-' acter. Under such operating conditions, adjustment would be made so that the characters were symmetrically disposed in the viewing window 15 during periods of energrzatiou. The static magnetizable elements 73 would still function to create an unbalanced torque condition in the event that a selected digit fell diametrically opposite the one previously indicated. The advantage of operating the device with the power on throughout the period of character display of course is that the residual or retaining torque is much higher than that achieved under the conditions previously described in connection with Fig. 7A. On the other hand the disadvantage is larger power consumption and a dependence upon power even if a particular reading were to be retained for an extensive period of time.

Certain comments are now in order concerning the choice of materials for fabrication of the device. For the purpose of minimizing weight, particularly for airborne applications, it is highly desirable that both housing 14 and rotor 16 be made of dimensionally stable plastics, which may either be machined or die molded to the configuration shown depending upon the economics of the situation. Cylinder 71 may be either molded or extruded of plastic, but may also be made of a non-magnetic metal such as aluminum.

The size of the device, of course, may be scaled to meet ounces have been successfully operated as high speed decimal indicators for the output of computing machinery. The maximum time required to achieve a digit change w'as'0.6 second, and speedier response was achieved by increasing input power.

Of course, many modifications of this device may now become apparent to those skilled in the art. Consequently, the spirit and scope of this invention should not be considered as defined by the foregoing disclosure, but by the appended claims.

What is claimed is:

1. Indicating apparatus for displaying a predetermined plurality of discrete indicia associated with a rotatable magnet comprising, electrically energizable means for selectively providing a magnetic field in the region of said magnet having one of a like plurality of discrete orientations angularly separated about a common center, and a corresponding plurality of static magnetic elements disposed about said magnet respectively associated with and angularly offset relative to each said discrete orientation, whereby in each of said orientations two stable and distinctive display positions are provided for the respective one of said indicia, one of said display positions being determined by said rotatable magnet and said electrically generated magnetic field substantially independently of said static magnetic elements, the other being determined solely by said rotatable magnet and said static magnetic elements in the absence of electrical energization.

2. Indicating apparatus as in claim 1 wherein said electrically energizable means comprises a substantially circular configuration of electromagnets and wherein said static magnetic elements comprise a corresponding configuration of sharply-defined magnetizable members.

3. A character indicating device comprising a character bearing member, a configuration of electromagnets selectively energizable to furnish any one of a plurality of discrete magnetic field orientations, a like configuration of sharply-defined static magnetizable elements, and a magnet having a pair of sharply-defined diametrically opposite poles associated with said character bearing member and coacting with said static magnetizable elements whereby the orientation of said character bearing member is controlled exclusively by said static elements in the absence of electrical energization of said electromagnets.

4. A character indicating device comprising a character bearing member, a configuration of electromagnets selectively energizable to furnish any one of a plurality of discrete magnetic field orientations angularly separated about a common center, a like configuration of sharply-defined static magnetizable elements, each of said elements being angularly ofiset from a respective magnetic field orientation, and a magnetic member having sharply-defined diametrically opposite poles associated with said character bearing element and arranged for angular movement under control of the discrete magnetic field selectively established by energization of said electromagnets and for angular movement exclusively under control of the respective magnetizable element in the absence of energization of said electromagnets.

5. A character indicating device comprising, a generally cylindrical housing, a circular array of electromagnets forming a stator disposed within and affixed to said housing, arotor including a hub for supporting a salient pole magnet rotatable within said array of electromagnets and a character bearing member aflixed to and extending outwardly of said hub and having a cylindrical surface rotatable in the region between said electromagnets and said housing, a circular array of sharply-defined magnetic elements equal in number to said electromagnets disposed in the region between said salient pole magnet and said electromagnets, and a window in said cylindrical housing for displaying a portion of said character bearing member.

6. A character indicating device comprising, a housing having a generally hollow cylindrical portion terminated by at least one circular end wall, an arbor extending into said cylindrical portion and substantially centrally aifixed to said end wall, a stator structure formed of a plurality of electrically energizable coils symmetrically and concentrically distributed about said arbor and afiixed to the inner surface of said end wall, a rotor structure including a hub rotatably supported upon said arbor, said rotor structure further including a circular portion extending ities of said salient pole magnet, and a window in said cylindrical portion of said housing for displaying an area of the outer surface of said cylindrical character bearing portion of said rotor structure.

7. A character indicating device comprising, a housing having a generally hollow cylindrical portion terminated by at least one circular end wall, an arbor extending into said cylindrical portion and substantially centrally atfixed to said end wall, a stator structure including a substantially circular magnetic core bearing a plurality of symmetrically distributed coils thereon, said stator structure being concentrically affixed to the inner surface of said circular end wall and arranged for angular adjustment about said arbor, the ends of each of said coils being electrically connected to the ends of the coils immediately adjacent thereto, lead wires extending from each of said coil connections through an aperture in said housing, a rotor structure including a hub rotatably supported upon said arbor, said rotor structure further including a circular portion extending radially outward of said hub opposite said end wall and terminating in a generally cylindrical reentrant character bearing portion rotatable in the region between said stator structure and the inner surface of said cylindrical portion of said housing, a salient pole permanent magnet rigidly secured to said hub and rotatable therewith within the circular region defined by said coils, sharply-defined staticv magnetic elements equal in number to said coils and symmetrically distributed about and aflixed to said stator structure in the region between said coils and the extremities of said salient pole magnet, and a window in said cylindrical portion of said housing for displaying an area of the outer surface of said cylindrical character bearing portion of said rotor structure.

8. A character indicating device comprising, a housing having a generally hollow cylindrical portion terminated by at least one circular end wall, an arbor extending into said cylindrical portion and substantially centrally afiixed to said end wall, a stator structure including a substantially circular magnetic core bearing a plurality of symmetrically distributed coils thereon, said stator structure being concentrically aflixed to the inner surface of said circular end wall and arranged for angular adjustment about said arbor, the ends of each of said coils being electrically connected to the ends of the coils immediately adjacent thereto, lead wires extending from each of said coil connections through an aperture in said housing, a rotor structure including a hub rotatably supported upon said arbor, said rotor structure further including a circular portion extending radially outward of said hub opposite said end wall and terminating in a generally cylindrical reentrant character bearing portion rotatable in the region between said stator structure and the inner surface of said cylindrical portion of said housing, a permanent magnet having a pair of diametrically opposed ogival shaped salient poles and a central opening adapted to fit over said hub, said magnet being rigidly aflixed to said rotor structure and rotatable therewith within the circular region defined by said coils, a cylindrical member for symmetrically supporting magnetic elements equal in number to said coils, said cylindrical member being afiixed to said stator structure in the region between said coils and the pointed extremities of said salient poles, and a window in said cylindrical portion of said housing for displaying an area of the outer surface of said cylindrical character bearing portion of said rotor structure.

9. Character indicating apparatus asin claim 8 wherein the inner surface of said circular end wall of said housing is formed with an inwardly facing circular ridge rotatably supporting said magnetic element supporting cylinder and said stator structure affixed thereto.

10. Character indicating apparatus as in claim 6 where in the outer surface of said circular end wall of said housing is formed with a circular recess, and a circular plate of magnetic material equal in dimensions and secured within said recess for magnetically shielding said apparatus and magnetically damping rotation of said permanent magnet affixed to said rotor structure.

11. Character indicating apparatus as in claim 10 wherein said hub and said arbor confine a region having a capillary clearance to permit rotation therebetween and adapted to enclose a viscous damping fluid substantially without leakage.

12. Character indicating apparatus as in claim 8 wherein said magnetic elements are angularly oliset about the axis of said arbor in relation to the angularly separated discrete magnetic fields generated by electrically energizing diametrically opposite coil connections, whereby motion of said permanent magnet and rotor structure is controlled by the magnetic field generated by said coils when energized and by said magnetic elements when deenergized.

13. Character indicating apparatus as in claim 12 and including indicia inscribed on said outer surface of said character bearing portion of said rotor, said indicia being arranged thereon to be centrally disposed in said viewing window in said housing when the angular position of said rotor structure is fixed by interaction of said permanent magnet and the respective magnetic elements in the absence of energization of said coils.

References Cited in the file of this patent UNITED STATES PATENTS 594,979 Barrett Dec. 7, 1897 1,058,545 Caldwell Apr. 8, 1913 2,649,559 Wargo Aug. 18, 1953 FOREIGN PATENTS 137,255 Great Britain Jan. 8, 1920