US3028588A

US3028588A - Parity bit generator

Info

Publication number: US3028588A
Application number: US828319A
Authority: US
Inventors: Jean H Veldkamp
Original assignee: Thales Nederland BV
Current assignee: Thales Nederland BV
Priority date: 1958-07-21
Filing date: 1959-07-20
Publication date: 1962-04-03
Anticipated expiration: 1979-04-03

Description

April 3, 1962 J. H. VELDKAMP 3,028,588

PARITY BIT GENERATOR Filed July 20, 1959 2 Sheets-Sheet 1 i 28 INVENTOR. A MP 3 HG H JEAN H VELD A lax WWW ATTORNIYJ April 1962 J. H. VELDKAMP 3,028,588

PARITY BIT GENERATOR Filed July 20, 1959 2 Sheets-Sheet 2 FIG. 8

FIG. I2

MEAN H. VEL DKAMP m BY United States Patent 3,028,588 PARITY BIT GENERATOR Jean H. Veldkamp, Hengelo (Overijsel), Netherlands, as-

siguor to N.V. Hollandse Signaalapparaten, Hengelo (Overijsel), Netherlands Filed July 20, 1959, Ser. No. 828,319 Claims priority, application Great Britain July 21, 1958 17 Claims. (Cl. 340-345) This invention relates to an electro-magnetic step-bystep mechanism, and in particular to such a mechanism which drives a display unit, a memory system or a similar system.

It is an object of the invention to increase the speed of operation of such a mechanism as well as to reduce its volume. It permits such a reduction of the crosssection of a display unit that a large number of such units may be housed in a small display board. The width of a practical embodiment of a display unit according to the invention was only so that 25 units of this type, each of them showing a letter or a figure, can be mounted on a line having a length of 1 ft. only. The height of the said unit was so that, allowing for supporting plates between the units, 20 lines can be housed in a panel with a height of 1 ft. The setting speed of the said unit was, moreover, high. It has been used at speeds of 120 steps per second, and speeds of 50 to 60 steps per second could be obtained for a very substantial period of useful life.

- In the step-by-step mechanism according to the invention the plunger core of the driving electro-magnet drives a rotatable drum by means of a resilient drawing pawl and a resilient pushing pawl, the driven end of each pawl being fixedly mounted to an element connected to or forming part of the plunger core, which pawls cooperate with at least one ratchet wheel with inside teeth, countersunk into the said rotatable drum. 7

Preferably the pawls are made from resilient wire, such as steel wire.

In a preferred formof the step-by-step mechanism according to the invention the drum is provided with two countersunk ratchet wheels, one at each end, each pawl cooperating with its own ratchet wheel.

Furthermore, in a preferred form of the step-by-step mechanism according to the invention, the drum is provided with pins or sprockets,by means of which it drives an endless belt.

In a suitably built magnetic system with a slideable core it is possible to obtain a high ratio of the mechanical energy supplied by the system to the volume of the system, as well as a high ratio of said mechanical energy'to the weight of the system whereas the force exerted on the armature, i.e. on the slideable core, shows only relatively small variations due to the change in position of this core during its stroke. This permits a small magnetic driving system to be used for driving the step-by-step mecharusm.

The ratchet wheel or wheels being countersunk into the rotatable drum, no part of the length of the drum need be reserved for the ratchet or ratchets, and this permits the application of a drum with a length not larger than is necessary for carrying the signs to be displayed or for driving and supporting the belt to be driven. The application of resilient pawls, especially of pawls made of resilient wire, permits the building of a unit the dimension of which in the direction of the axis of the rotatable drum is only slightly larger than the length of this drum. The application of fixedly mounted resilient pawls makes hinges or rotatable connections for the pawls which, as a rule, are subject to serious wear in such small and rapidly operating apparatus, superfluous.

Recapitulating, it can be stated that the invention per- 3,028,588 Patented Apr. 3, 1962 'ice mits the building of light and small step-by-step mechanisms which, because of the small weight and inertia of the moving parts, can be used at very high stepping speeds.

In one form of the mechanism a single energizing coil is wound on a spool consisting of a non-magnetic tubular element and two flanges of soft iron mounted on the tubular element. An outside yoke connects these flanges. The movable plunger core enters the tubular element at one end, whilst a fixed core enters it from the other end. Preferably one of the cores has a conical end at the side facing the other core which possesses a correspondingly shaped conical recess. A spring acts on the plunger core, causing it to rest against a stop in a position in which it has the greatest distance from the fixed core. If the coil is excited the plunger is pulled into the tubular element until it reaches another stop restricting the motion to such an extent that a small air gap remains between the plunger and the fixed core.

In another form of the invention the driving magnet system possesses two windings wound on separate coaxial spools which are adjacently mounted in a direct line, each of them consisting of a non-magnetic tubular element and two soft iron flanges connected by an outside yoke. Preferably both spools possess a common tubular element and one common flange at the adjacent ends. Fixed cores enter the tubular element or elements at the non-adjacent ends, and the movable core is situated in between these fixed cores. The ends of the cores facing each other are preferably conically shaped as described in the case of the first embodiment. No springs act on the movable core, this core being shifted in the one or the other direction by energizing the one or the other coil. In a preferred form of this driving magnet the core is coupled by means of a rod passing through a bore in one of the fixed cores to the element to which the pawls are fixedly mounted.

The two pawls are preferably made of resilient wire and are fixedly mounted to the part carryingv them and owing to their elasticity are able to swing.

If the drum driven by the pawls is the last driven object and the step-by-step mechanism is used as a dis play unit, this drum carries the signs to be displayed. If the drum drives a belt and the mechanism is used as a display unit, the signs to be displayed are represented on this belt. In certain embodiments the two pawls co-' operate with the opposite halves of a single ratchet wheel, but if high requirements as to operating speed and small dimensions must be met, two ratchet wheels are used. Preferably these ratchet wheels are relatively displaced through an angle which may be equal to half the cir-. cular pitch or nearly that value, each pawl cooperating with its own ratchet. It will be shown below that in this case the stresses in the pawls can remain smaller.

In various applications of the step-by-step mechanism it is desirable for the position of the element driven by the magnet to be signalled back. The number of pulses applied to the magnet coil is not an infallible measure for the position reached, because a step-by-step mechanism may get out of step. Consequently certainty as to the position reached can only be obtained by signalling back. A certain amount of space is, however, required for the mounting of the elements controlling the signalling back and the volume of the step-by-step mechanism is reduced to such an extent by the application of the invention, that this space cannot be found without special measures. According to a special form of the invention these measures consist in mounting the said elements controlling the signalling back circuits in the space enclosed by the belt.

In one embodiment according to the invention the belt driven by the drum possesses for this purpose at least one track passing under a set of brushes mounted in the space enclosed by the belt by means of which brushes electrical circuits can be closed in various permutations through suitable openings or recesses in the track, for the purpose of signalling back the position reached by the stepping mechanism. The brushes are mounted in a line so as to rest on the track of the belt, whilst electrical contact is established between a brush and a contact strip or between a brush and one contact element out of a set of contact elements mounted in a line at the opposite side of the belt, if an opening or recess in the track of the belt has reached the position between the said brush and the contact strip or the contact element. The openings or recesses in the belt are situated in such a way that they permit the contact between a brush and a contact element whilst the stepping mechanism is in one of its positions of rest. If the stepping mechanism is a display unit a sign is displayed in such a position of rest. The recesses or openings in the belt are arranged so as to form a shifting code, indicating the position reached and the sign shown by the display unit. In normal use the stepping motor is fed by a pulse generator until a suitable control circuit establishes that signalling-back circuits in a desired code combination are closed by the brushes. Then the circuit between the stepping mechanism and the pulse generator is broken, causing the belt to remain at rest in the desired position.

The stepping mechanism can also be used as a memory which can be read out by means of the circuits through the various brushes. If two tracks provided with recesses or openings, cooperating with a set of brushes are present, the step-by-step mechanism can be applied as a code converter.

In another embodiment according to the invention, perinitting the use of signalling back contacts, the belt possesses at least one track on which a feeler or a set of feelers, mounted in the space enclosed by the belt, rests. Such a track is provided either with projections or with openings or recesses, causing the positions of the feelers to be dependent on the position of the belt. The feelers close or open electrical contacts in signalling back circuits, depending on the positions reached by them under the control of the belt.

This embodiment can also be applied as a memory mechanism or as code converter.

The way of mounting the contact devices for signalling back described above, permitting these devices to be confined in the small space available, requires the use of a shifting code. A shifting code can, however, not be made self-checking by the simple means applied for this purpose Withother codes, such as arranging the code so as to make the number of elements of one type always even or always uneven. Nevertheless the application of such a code is desirable in order to prevent imperfect contacts in the signalling back circuits from producing mutilated signals. According to a special form of the invention the application of a self-checking code is made possible by mounting a special contact device in the space enclosed by the belt, resting on a separate track of the belt in which such openings, recesses, or projections are present that the code furnished by all contact devices becomes selfchecking.

Step-by-step mechanisms according to the invention, applied in display units according to the invention, will now be described with reference to the drawings.

FIG. 1 shows a cross section of a driving magnet system of a step-by-s'tep mechanism, and

FIG. 2 partly a front view and partly a cross section according to the line I-I in FIG. 1 of this magnet system.

FIG. 3 shows a step-by-step motor according to the invention. v

FIG. 4 shows the step-by-step motor according to FIG. 3 seen from the opposite side.

FIG. 5 shows a detail of the step-by-step motor of FIG. 3.

FIG. 6 shows the cooperation of the pawls and ratchet wheels.

FIGS. 7 and 8 show a complete display unit according to the invention.

FIGS. 9 and 10 show the brushes and contacts of a display unit.

FIG. 11 shows a belt for the display unit.

FIG. 12 shows a driving magnet system with two coils.

FIGS. 13 and 14 show the cooperation of a belt and a set of feeler arms for the purpose of signalling back.

FIG. 1 shows the cross section of the driving magnet system of a step-by-step mechanism according to the invention. The winding 2 of the driving magnet of this system is wound on a spool consisting of a non-magnetic tubular element 20, provided with soft-

iron flanges

3 and 17. The tubular element may be provided with a longitudinal slot in order to avoid eddy currents, but if the magnet is fed by direct current pulses with frequencies up to c./s. such a slot is not absolutely necessary. A fixed soft iron .core 18 of suitable cylindrical shape, provided with a conical end 19, is mounted in the tubular element 20, and a movable cylindrical core 21 can be shifted longitudinally in the tubular element and possesses a conical recess 22, the shape of which corresponds to the shape of the cone 19. The core 18 can be shifted longitudinally in the tubular element from the purpose of adjusting the air gap between the cores in the position of rest. It is fixed by a clamping screw (not shown in the figure). The cylindrical part of the movable core glides this core during its motion in the tubular element and should be of at least such a length that jamming and wear of the core is avoided. The object of the conical parts is to reduce the magnetic resistance of the air gap and, by making the recess in the movable core instead of in the fixed core, the weight of the movable core is reduced without reducing the length of the guiding surface. This is important because it permits the core to move at a higher frequency with the same inertia resistance. The magnetic circuit of the coil 2, which passes through the flange 3, the movable core 21, the fixed core 18, and the flange 17, is closed through flat iron yoke parts 1 and 16, which are screwed to the

flanges

3 and 17. The coil 2, the flange 3, and the yoke elements 1 and 16 may also beseen in FIGS. 3 and 4, to which the following description also refers. A U-shaped frame element with the arms 9 and 14 is mounted onto the flange 3 by means of screws such as 15 and spacers such as 4. A square frame 5, preferably made of material with low rate of wear, such as nylon or a similar polyam-ide, is screwed to the outer end of the movable core 21. The central part of the U-shaped frame, which is parallel to the flange 3 of the coil, passes through the opening of this square frame. A spring 6 is mounted between the right hand side of the square frame and the central part of the U-shaped frame, which spring is kept in place by cylindrical stubs such as 25, which are present on the right hand part of the square frame and on the centralpart of the U-shaped frame. The force exerted by this spring 6 causes the core 21 to be moved to the right to such an extent that the left hand side of the square frame rests against the central part of the U-shaped frame. If the coil 2 of the step-by-step mechanism is excited, the movable core 21 is moved to the left against the pressure of the spring 6, causing the length of the air gap between the conical parts of the fixed and the movable core to be reduced to a few hundredths of a millimeter. The motion of the core is restricted by the square frame when this frame reaches the flange 3. The inside surface of the tubular element 20 is smooth, and in order to reduce wear the movable core 21 is covered by a thin layer of nylon or a similar polyamide or by a thin layer consisting of a mixture of such a polyamide and a small percentage of molybdenum di-sulfide (e.g. molycote). This layer is made by dipping the heated core into a container containing fine nylon or a similar polyamide powder, or a mixture of fine nylon or a similar polyamide powder and fine molybdenum di-sulfide powder, this powder or mixture being kept in motion, more or less in suspension, by a stream of compressed air. In order to promote the adherence of the polyamide to the core the core possesses a rough surface. A shaft 12 is mounted in the U-shaped' frame and carries a sprocket wheel in the shape of a drum 11, preferably made of nylon or a similar polyamide, and which is freely rotatable around the said shaft. This dnlrn carries at both sides .a ratchet wheel. In order to reduce the axial length of the drum required for a given width of the belt to be driven by it, the ratchet wheels possess inside teeth and are counten sunk in the drum, such as shown for the ratchet wheel in FIG. 3. The square frame 5 carries two

pawls

8 and 13, which are made out of one piece of steel wire and fixed to the square frame 5. It would be possible to fix the pawls to the frame by means of screws, but in the example shown that part of the steel wire of the pawls which is to be fixed, is directly bedded in the polyamide. In this embodiment the free parts of the pawls are for a substantial part situated in cylindrical recesses 7 in the square frame, in which recesses they are free to swing, so that the length of the pawl required in connection with the amplitude of the traversely swinging pawl motion, may be housed in a shorter unit. The

pawls

8 and 13 are bent at their ends, so as to possess end parts which are parallel to the shaft 12. The pawl 13 rests on the inside toothing of the ratchet wheel 10, whilst the end of the pawl 8 rests on the inside toothing of the other ratchet wheel 23. As may be derived from FIG. 3 and FIG. 4, the pawl 13 rests on the lower half of its ratchet wheel, whilst the pawl 8 rests on the upper half of its ratchet wheel. The ratchet wheels are so shaped that they drive the drum 11 in an anticlockwise direction. The cooperation of the two pawls and the two internal ratchet wheels may be derived from FIG. 6, in which the front ratchet 10 and the back ratchet 23 as well as the front pawl 13 and the back pawl 8 are schematically shown. It is assumed that the two ratchet wheels are coupled so as to rotate together. When the movable core is drawn to the left by the magnetic field, the back pawl 8, operating as a drawing pawl and cooperating with the steep side of a tooth of the back ratchet wheel 23, causes this ratchet wheel and the front ratchet wheel 10 to rotate. The stroke of the core and the pawls corresponds to a rotation of the ratchet wheels through an angle which is half or about half the angle of rotation of the ratchet wheels caused by one complete to and fro motion of the core, i.e about half the circular pitch of the ratchet wheels. The ratchet wheels shown possess six teeth, so that the stroke of the core must correspond to about 30 ratchet wheel motion.

It is desirable to restrict the swinging motion of the driving pawls, because at the high frequency of this motion fatigue fractures at the root of these pawls may very well occur. The amplitude of this swinging motion is determined by the extreme positions of the end of the pawl, cooperating with the ratchet occurring during its complete to and fro motion. Depending on the positions of the points of reversal of this motion, extreme positions of the free end of the pawl may occur at various points of the path of the end of the pawl. These points are:

(1) The point where the said end of the pawl is in the plane of symmetry through the axis of rotation of .the ratchet wheel perpendicular to the direction of motion of the core of the magnet and where it rests on the full depth circle of the ratchet wheel (point A in FIG.

6). The said end of the pawl can only be in this point when it passes, or at any rate reaches this symmetry plane during its motion.

(2) The point where the end of the pawl reaches the full depth circle after having fallen from the tip of a tooth only in the case, however, of the said end not reaching or passing the said symmetry plane.

(3) The point where the end of the pawl passes over the tip of a tooth (point B in FIG. 6).

(4) The point C where the end of the pawl reverses its motion after having driven the ratchet wheel. This may be a point where an extreme position occurs, but, as a rule, it is not.

(5) The point which presents itself when the end of the pawl, whilst moving over a non steep face of a tooth, is lifted higher than it is at the moment at which it passes over the tip of that tooth. It is, however, undesirable to lift the pawl higher than is necessary for passing the tip of the tooth because bending stresses and pawl pressure increase when the pawl is lifted, and high pawl pressures cause wear. Consequently it is desirable to shape the non steep face of the tooth in such a way as to lift the pawl no higher than is necessary for passing the tip. Such a shape is feasible in practically any case. If the points of reversal of the motion of the driving end of the pawl are situated on both sides of the symmetry plane mentioned above, then at any rate the pawl end will pass through the point A, where in this case it will occupy an extreme position. The other extreme position will either be situated in the point B or in the point C. In practical forms of the step-bystep motor according to the invention the number of teeth of the ratchet wheel will not be less than five, because otherwise the amplitude of the motion of the pawl will become too large. In the form described the ratchet wheel has six teeth, in which case every one of the two pawls drives its ratchet through an angle of 30". In these cases the pawl will be lifted less high when its end is at point C than when the end is at point B, if the teeth are high enough to cooperate with a pawl of sufficient strength, e.g. with a diameter of at least 0.6 mm., even if the stroke during which the pawl drives the ratchet wheel starts in the said symmetry plane. In the practical embodiment described the diameter of the full depth-circle of the ratchet wheel is 9 or 10 millimeters and the depth of the teeth 1 mm, the number of teeth being six. It can then easily be shown that the end of the pawl is lifted less high at point C than at point B. If the points of reversal of the motion of the end of the pawl are situated on both sides of the symmetry plane, the lower extreme position remains A, but the pawl must be lifted higher to pass over the tip of the tooth, the position in which this takes place being the position B, for instance. It is, therefore, clear that in order to reduce the amplitude of the swinging motion of the pawl the motion of its end should be preferably performed at that side of the symmetry plane where the driving stroke ends, the pawl passing over the teeth at the point of reversal nearest to the symmetry plane. If however the end of the pawl passes the symmetry plane during the driving stroke, but only a small part of the stroke is performed before this end reaches the said symmetry plane, this will have no serious consequences. Even if the stroke is situated symmetrically with respect to the said symmetry plane the swing of the pawls is only increased by 10%, but the bending stresses in the root of the pawl increase rapidly if a larger part of the stroke is performed before the end of the pawl passes the symmetry plane, reaching in the embodiment described of the stress occurring during the most favourably situated stroke if the driving stroke is completed before the symmetry plane is reached. If, in the case of a ratchet with six teeth, the driving stroke of the end of the pawl begins in the symmetry plane, the pawl will, during the return stroke, be lifted by the face of the tooth in order to reach the height required for passing over the tip of the tooth. As a rule this is undesirable, because at the very high operating speed this lifting operation causes relatively large forces to be ex- 'full depth circle.

:straight line.

the pushing pawl as well as for the drawing pawl. One

7 erted on the face of the tooth. The point B at which the pawl passes over the tip of the tooth may, however, be situated at the same height as the point C, reached 'at the end of the active stroke. For this purpose the end of the pawl should never pass the said symmetry plane and should start its active stroke not in, but at a small distance from this plane. In the case of e.g. a wheel with an outercircle diameter of 9 mm. and six teeth with a depth of 1 mm. the bending'of the pawl is the same when its end is in the points C and B if theleft hand reversal point of the motion is situated at 9 or 10 from the symmetry plane. It has been mentioned above that the shape of the non steep face of the tooth must be such that it does not lift the pawl higher during its motion over this face than near its tip. This may be approximately realised by using teeth the non steep face of Whichis cylindrically shaped with a diameter which is slightly larger than the diameter of the In the example shown for instance, this face of the tooth is a cylindrical surface with a the pawl end passes over the tip of a tooth is situated ,at 10 from the symmetry plane the return-motion of theend of the pawl is practically a motion along a The above considerations hold true for of the pawls is a drawing pawl and the other one a pushing pawl, and if the pushing pawl operates in a sector corresponding to half the circular pitch on the one side of the symmetry plane the drawing pawl must operate in a corresponding sector on the other side of the symmetry plane and diametrically situated with re- :spect to the other sector. in turn. In order to obtain the smallest bending stresses "the drivingshould start at two points which are on the Both ratchets must be driven same diameter. The driving must be continued through 'half the circular pitch. Consequently the smallest stresses will result if both ratchets are relatively displaced through an angle of about half the circular pitch of the ratchet wheels. The length of the pawls must ditfer to such an extent that when one of the pawls has reached the end of its operative stroke the other pawl has reached the position in which it passes over the tip of a tooth. The

'completeunit willnow be described with'reference to the FIGURES 7, 8, 9, and 10. The unit is housed in a sheet steel U-shaped housing 31, in which the stepby-step motor with its winding 2 is mounted by means of counter sunk screws, screwed in the

flanges

3 and 17. A brush support of insulating material indicated by the

reference numbers

27 and 42 is fixed in a similar way in the said housing. It possesses a middle part of reduced cross section on which, by means of screws such as 33, a brush plate 29 is fixed. This carries six brushes 30 at the one side of the part of insulating material and 37. The piece of plate material is mounted on a tubu-.

lar element 36 which is supported in a cylindrical opening in the part of insulating material 42. The tubular element contains a spring 34 which keeps the belt 20 taut in all conditions. The direction of the shaft 39 is determined by a slot in the part of insulating material 42, in which slot the part of plate material 37 narrowly fits. A part of the belt is shown in FIG. 11. Suitable signs such as letters or figures are printed between the openings 60. When the belt is driven by the step-by-step motor it slides 'under the brushes of the "brush holder.

"strip. -In this channel the wire is situated betweenthe strip and the channel shaped housing. In this;way--the "strip of insulating material 40 prevents damage to the -belt by the said wire should it become dislodged.

'In' the trajectory of these brushes near both edges of the belt, suitable recesses such as '58 and 59 are present. If the step-by-step motor is at rest the position of the belt is'such that either a recess or a tooth of the belt will be situated under each brush of the brush holder, causing electric circuits through these brushes and contacts, such as 46, to be closed or opened. The recesses and thete'eth controlling the circuits through the siX brushes 30 are situated so as to form a six bit shifting code denoting the sign situated on the pulley 38, and shown through the top opening of the unit. A suitable construction'of the contacts may be derived from the FIGURES 7 and 10. A plate of insulating material 43 is mounted in the housing by means of counter sunk screws such as 45 and 55. This partpossesses a recess 54 permitting the passage of the sprockets 24 of the drum 11. It possesses, moreover, a channel 48, provided with a row of openings, such as 47, which are situated between and at both sides of the brushes 30 when the strip of insulating material is mounted in the housing. Small strips of contact material to which a thin insulated wire is soldered, are bent around the dams of insulating material between the said openings 47 so as to form contacts 46 able to co-operate with the brushes. In a similarway a contact '56 is mounted in order to cooperate with the single brush 32at the other side of the belt. The seven wires leading to the said contacts pass through the channel 48 and through the flat channel at the right hand side-of the step-by-step motor to a contactiplug 52 provided 'Wlth contact pins 53 mounted in the bottom side of the housing. Each of said wires and also each of the wires feeding coil 2 is soldered to a contact pin in said plug. The

brush plate 21 is connected toa contact pin 48 by means of a wire which passes through an opening in the strip of insulating material 40 and through a channel in this The setting of the unit is performed in the following way. A code indication of the sign to-be shown is received in a suitable register. After the reception of this indication a comparison system comparing the code circuits closed by the brushes 30 with the code indication received is made operative. If these indications are not the same a pulse circuit for the driving motor is closed, causing the belt 28-to be driven and the comparison system to be made inoperative. Between-stepping pulses the comparison system is temporarily caused to be operative, and'as soon as the'code indication given by the circuits through'the brushes and caused by the recesses and teeth of the belt, which code indication denotes the sign shown, is the same as the code indication received by the register, the step-by-step'circuit for the step-by-step motor is broken bythe comparison system; afterwhich the unit remains at rest. The number of brushes 30 is determined by the number of signs for which the unit can be used. In the example described the belt carries 40 signs, for which a six bit binary code is mounted, it is necessary to take into account the pos sibility that the contact between a brush and its contact may not be established when a recess is under this brush,

because of dirt either on the brush or on the contact.

This may result either in the showing of a Wrong sign or in continuous running of the unit. As continuous running shows the unit to be defective no false indication will result from it, butin most cases the failure of a brush to contact its contact-element will result in a wrong sign being-shown by the unit. This may be conbe mounted at the other side of the brush holder.

sidered as highly undesirable. It might be prevented by using a self-checking code e.g. a code in which the number of elements of one type is always even or always uneven. As the code provided by the brushes 30 is necessarily a shifting code it is impossible or at any rate requires a large number of brushes to arrange this code in such a way that it is self-checking. According to the invention, however, a self-checking code may be obtained by mounting one single brush in such a way that it rests on the belt on a second track, for instance near the other edge, because the element provided by this brush is completely independent of the shifting code and may for instance, always be selected in such a way that it makes the total number of elements of the type taken into consideration for the self-checking, either even or uneven as required.

The housing of the unit is closed by a lid 61 (FIG. 8) which narrowly fits between the edges of the channel shaped housing and is fixed to the unit by means of counter sunk screws, two of them passing through the

openings

26 and 44 to opening provided with screw thread in the back wall of the channel shaped housing and two screwed in the openings 51 and 50 in the flanges of the coil of the step-by-step unit. A plate of insulating material 41 is situated under the lid.

The speed of operation being high, in some cases the belt may show a tendency to run on as a result of the inertia of the various moving parts such as the drum and the pulley after the step-by-step motor has finished its operation. This is undesirable because it results in the showing of a mutilated sign. If a unit is to be used at very high speeds special measures according to the invention are taken in order to prevent this prolonged rotation. For this purpose a stop for one of the pawls is arranged which causes this pawl to be pressed against the ratchet when it has reached the position of rest. FIG. shows an example of such a stop. It consists of a lip 57 on the supporting arm 14- of the U-shaped frame which causes the pawl to be pressed in an outward direction when it has reached its position of rest. Such a support for the pawl can only be arranged for that pawl which has completed its active stroke when the core reaches its position of rest and which, consequently, does not pass over the tip of a tooth at the end of this stroke. If this pawl is lifted by the ratchet during its nonoperative stroke, as has been described above for a certain situation of the position of rest, the stop must not be extended in the direction of the magnet so as to permit this lifting. If the situation of the position of rest is such that the pawl is not lifted during its return stroke there are no restrictions for this stop. In this case it may consist of an extended central hub of the sprocket drum. The pawl wire must then, as a rule, be bent near its end so that it can rest against the hub in the position of rest of the pawl, as shown by dotted lines in FIG. 6.

The mechanism according to the invention can also be used as a mechanical memory for a code indication. In this case the application of a self-checking code is important in order to ensure a faultless operation.

Instead of one brush a larger number of brushes can A second complete set of brushes, able to give a code indication can even be applied, in which case the unit can be used as a code converter. On the other hand, if no self-checking code is required, a single set of brushes, resting on one side of the belt, suffices.

A driving magnet system with two coils will now be described with reference to FIG. 12. The two coils, 63 and 68, are Wound on a spool with three flanges. This spool consists of a non-magnetic tubular element 64, two soft

iron end flanges

62 and 71, and one central flange made of soft iron, 66. Fixed

iron cores

78 and 69 enter the tubular element, one at each end. Both cores are provided with conical ends. A slideable soft iron core 65, provided with recesses corresponding to the conical ends of the fixed cores, is situated between these fixed cores. The magnetic circuits for both coils, each of them passing through an end flange, a fixed core, a part of the movable core, and the central flange, are closed by soft iron yoke elements, such as 67 and 77, screwed to the flanges. If coil 63 is energized, the slideable core is shifted to the left, if coil 68 is energized, the movable core is shifted to the right. The movable core is mounted on a slender rod 70 of small diameter, for instance by means of screw thread cut in a central part of this rod, which has a slightly larger diameter. This rod passes through bores in the fixed cores. It carries adjustable stop elements such as

nuts

76 and 79 and lock nuts. Such a stop limits the motion of the core by abutting against a fixed core. By means of a nut 74 a small bar 72 is screwed to the rod 70 :and, consequently, moves with the core. The bar 72 is situated diagonally in the housing of the stepby-step mechanism so that it cannot rotate around the axis of the rod 70. Wire pawls 73 and 75, preferably made out of one single piece of steel wire, are bedded in the bar 72. Preferably the fixed

cores

69 and 78 are so arranged that they can be shifted or screwed (by means of screwthread in the flanges and on a part which has a slightly larger diameter) inwardly and outwardly in the

flanges

71 and 62 in order to adjust the space available for, and the situation of the stroke of the movable core 65. After the fixed cores have been adjusted and fixed, for instance by means of set screws in the flanges, the minimum length of the two air gaps is adjusted by means of the

stops

76 and 79. It is an advantage of this magnet system that no spring is required, so that no space need be reserved for the spring, and the magnet system need not furnish the force for compressing this spring. Consequently it is possible for the magnetic field to be weaker, causing the magnetomotive force required for the air gap as well as the leakage to be diminished so that the number of windings per spool can be substantially smaller than in the magnet system shown in FIG. 3. The two coils can be alternatively fed through oppositely directed rectifiers by one single source of alternating current. On the other hand it is a disadvantage of this two coil driving magnet system that it has no definite position of rest, because it remains in the position which it reached under the influence of the coil which has been excited last.

It would be possible to apply a driving magnet system according to FIG. 12 in such a way that it possesses two positions of rest, the driven belt or drum changing the sign shown when the core is shifted to the left as well as when the core is shifted to the right.

The contacts in the signalling-back circuits closed by means of the brushes 30 described with reference to FIG. 7 have a tendency to be unsafe as a result of dirt settling on the brushes or on the contacts. The signalling-back contacts of the type shown in the FIGURES 13 and 14 are in this respect to be preferred. In FIG. 13 part 79 is the belt, provided with recesses such as 86. Lever shaped feelers rest on this belt on the track in which the recesses are present. Two of these feelers, namely the feeler 80 and the feeler 85, are shown in FIG. 13. The feeler 80 is a lever which is rotatable around a shaft 8 1 and is situated between two bars 87 and 88- Which, in

this construction, replace the central part of the insulating

brush carrier

27, 42 of FIG. 7. The upper end of the lever moves between two

pins

82 and 84. These pins are used as contact elements. A blade spring 83 is mounted to the lever and rests on the contact element 84-,

. tending to rotate the lever in an anti-clockwise direction.

The lever can nevertheless not reach the contact member 82 as long as the lower end of the lever rests on the belt, as shown in the case of the lever 80. As soon, however, as a recess such as 86 in the belt is situated under the lower end of the lever, the blade spring rotates the lever to such an extent that the upper end contacts belt flexible.

1 1 the contact element 82, causing a signalling-back circuit to be closed through the contact element 84, the blade spring 83, the lever 80 and the contact element'8'2. The position then reached by the lever is shown in the figure in the case of lever 85. The right hand side of FIG. 13 shows a lever as seen in the longitudinal direction of the belt. Levers, contacts and supports are centrally situated in the unit in order to reduce the volume, but the tracks on which the levers must rest are situated near the edge of the belt so that the levers have to have the special zig-zag shape shown in the right hand side of the figure.

It is a disadvantage of the contact construction accord ing to FIG. 13 as well as of the contact construction according to FIGS. 7 and 10 that recesses or openings must be made in the belt, causing the strength of this belt to be reduced. No such openings are required in the case of the construction shown in FIG. 14. In this construction similar contact levers are applied as feelers,

but insteadof recesses or openings in the belt, projections are made on the belt, which are able to lift the lower extremity of such a lever. A lever of this type opens its contact if it rests on a projection of the belt and closes this contact if no projection is present under its lower end. As the belt must remain flexible, the dimensions of For this purpose, in

the projections are divided into separate parts, the dimensions of which are sufliciently small to keep the In another embodiment of a contact system in astep-by-stepmechanism according to the invention only one sui'liciently small projection is used for every position of rest, in which a feeler should be lifted. This should not, however, influence the length of the route along which the belt can travel without .changing the position of a lever resting on one of its projections.

The levers are, therefore, provided with feeler parts, which are parallel to the surface of the belt whilst this part is resting on a projection and the length of this part is such that the lever remains in a position shown in FIG. 14 in the case of the right hand lever "during a displacement of the belt corresponding to about one complete to and fro motion of the magnet armature.

What I claim is:

1. An electromagnetic mechanism comprising a driving electromagnet with a winding enclosing a non-magnetic tubular element carrying two ferro-magnetic end flanges connected by an external ferro-rnagnetic yoke system, a fixed ferro-magnetic core mounted in the said tubular element so as to be partly in the opening enclosing the tubular element in one of the end flanges, a ferro-magnetic plunger core slidable in the tubular element, a supporting element fixedly connected to said plunger core, two driving pawls, a drawing pawl and a pushing pawl, both -made of resilient material and each of them fixedly supported at one end by the said supporting element, a rotatable drum situated in line with the driving magnet and with its axis of rotation traverse to the axis of said magnet,

. an endless belt, carried around and in driving connection protruding into the countersunk ratchet wheel with which the pawl cooperates and resting by the pawls o-wn elastic force on the toothing of said wheel, either near one edge or near both edges of the belt, a longitudinal track provided with different parts following each other in the longitudinal direction of the track and some of which have one given material thickness and others of which have another given material thickness which may be a zero, a contact mechanism controlled by the belt situated-in the space enclosed by the endless belt, a number 12 of contact devices-in said mechanism eachprovided with a part cooperating with a longitudinal trackof the belt, at least one electrical contact in such a contact device openedand closed by the device depending on the material thickness of the belt in the track on the spot Where the said part of the contact device cooperates with the track.

2. An electromagnetic mechanism comprising a driving electromagnet with a winding enclosing a non-magnetic tubular element carryingtwo ferro-magnetic end flanges connected by an external ferromagnetic yoke system, a fixed ferro-magnetic core situated in thesaid-tubularelement so as to be partly in the opening enclosing the tubular part in one of the end flanges, a ferro-magnetic plunger core slidable in the tubular element, a supporting element fixedly connected to said plunger core, two driving pawls, a drawing pawl-and a pushing pawl, both made of resilient material and each of them fixedly supported at one end by the said supporting element,

a rotatable drum situated in direct line with the driving magnet and with its axis of rotation traverse to the axis of said magnet, an endless belt, carried around and in driving connection with said drum and with straight parts having substantially the same direction as the-axis of the driving magnet, a countersunk ratchet wheel with inside teeth in each ofthe two ends of the drum, each ratchet wheel cooperating with a separate driving pawl, apart at the free end of each driving pawl with a direction substantially traverse to the longitudinal directionof said pawl, protruding into the countersunkratchet wheel with which the pawl cooperates and resting by the pawls own elastic-force on the toothing of said wheel, either near 'one edge, or near both edges of the belt a longitudinal track provided with different parts following each other in the longitudinal direction of the track and some of which have one given material thickness and others of which have another given material thickness, whichqmay be zero, a contact mechanism situated in the space'enclosed by the endless belt, a number of contact devices in said mechanism each provided with a part cooperating with a longitudinal track of the belt, at least one electrical contact in such a contact'device opened or closed by the device dependingon the material thickness -of-the belt in the track'on the spot wheresthe said part of the contact device cooperates with the track.

3. An electromagnetic mechanism comprising a driving electromagnet with a winding enclosing a nonmagnetic tubular elementcarrying two term-magnetic end flanges connected byan external 'ferro-magnetic yoke system, a fixed ferro-magnetic core situated in the said tubular element so as to be partly in the opening enclos-' ing the tubular part in one of the-end flanges, a ferromagnetic plunger core slidable in the tubular element, a supporting element fixedly connected to said plunger core, two driving pawls, a drawing pawl and a pushing pawl, both made of resilient material and each of them fixedly supported at one end by the saidsupporting element,-a rotatable drum situated in line with the driving magnet, and with its axis of rotation traverse to the axis of said magnet, an endless belt with straightyparts having substantially the same direction asthe axis-ofsthe driving magnet, and carried around the drum and in driving connection with this drum by means of'pins or sprockets on the surface of the drum cooperating with'openings in the belt, a countersunk ratchet wheel with inside teeth in at least one of the two ends of the drum, a part at the free end of each driving pawl with a direction substantially traverse to the longitudinal; direction of said :pawl, protruding into the countersunk ratchet wheel with which the pawl cooperates and resting 'by its own elastic. force on the toothing of said wheel, either near one edgeor near both edges of the belt a longitudinal track provided with different parts following each other in the longitudinal direction of the track, and some of which have one-given material thickness and others of which. have .7 r 13 another given material thickness which may be zero, a contact mechanism situated in the space enclosed by the endless belt, a number of contact devices in said mechanism each provided with a part cooperating with a longitudinal track of the belt, at least one electrical contact in such a contact device opened or closed by the device depending on the material thickness of the belt in the track on the spot where the said part of the device cooperates with the track.

4. An electromagnetic mechanism comprising a driving electromagnet with a winding enclosing a nonmagnetic tubular element carrying two ferro-magnetic end flanges connected by an external ferro-magnetic yoke system, a fixed ferro-magnetic core situated in the said tubular element so as to be partly in the opening enclosing the tubular part in one of the end flanges, a ferro-magnetic plunger core slidable in the tubular element, a supporting element fixedly connected to said plunger core, two driving pawls, a drawing pawl and a pushing pawl, both made of resilient material and each of them fixedly supported at one end by the said supporting element, a rotatable drum situated in line with the driving magnet and with its axis of rotation traverse to the axis of said magnet, an endless belt with straight parts having substantially'the same direction as the axis of the driving magnet, and carried around the drum and in driving connection with said drum by means of pins or sprockets on the surface of the drum cooperating with openings in the said belt, a countersunk ratchet wheel with inside teeth in each of the two ends of the drum, each ratchet wheel cooperating with a separate driving pawl, a part at the free end of each driving pawl with a direction substantially traverse to the longitudinal direction of said pawl, protruding into the countersunk ratchet wheel with which the pawl cooperates and resting by the pawls own elastic force on the toothing of said wheel, either near one edge or near both edges of the belt a longitudinal track provided with difiere'nt parts following each other in the longitudinal direction of the track and some of which have. one given material thickness and others of which haveanother given material thickness which maybe Zero, a contact mechanism situated in the space enclosed by the endless belt, a number of contact devices in 'said mechanism each provided with a part cooperating with a longitudinal track of the belt, at least one electrical contact in such a contact device opened or closed by the device depending on the material thickness of the belt in the track on the spot where the said part of the device cooperates with the track.

5. An electromagnetic mechanism comprising a driving electromagnet with a winding, enclosing a non-magnetic tubular element carrying two ferro-magnetic end flanges connected by an external ferro-magnetic yoke system, a fixed ferro-magnetic core situated in the said tubular element so as to be partly in the opening enclosing the tubular element in one of the end flanges, a terro-magnetic plunger core slidable in the tubular element, a supporting element fixedly connected to said plunger core, two driving pawls, a drawing pawl and a pushing pawl, both made of resilient material and each of them fixedlysupported at one end by the said supporting element, a rotatable drum situated in line with the driving magnet and with its axis of rotation traverse to the axis of said magnet. an endless belt, carried around and in driving connection with said drum and with straight parts having substantially the same direction as the axis of the driving magnet, a countersunk ratchet wheel with inside teeth in at least one of the two ends of the drum, a part at the free end of each driving pawl with a direction substantially. traverse to the longitudinal direction of said pawl, protruding into the countersunk ratchet wheel with which the pawl cooperates. and resting by the pawls own elastic force on the toothing of said wheel, a longitudinal track near both edges of the belt, each provided with difierent parts following each other in the longitudinal direction of the tracks and some of which have one given material thickness and others another given material thickness which may be zero, a contact mechanism situated in the space enclosed by the endless belt, in said contact mechanism a number of contact devices arranged in a line, each provided with a part cooperating with the track near one edge of the belt and one contact device with a part cooperating with the track near the other end of the belt, at least one electrical contact in each contact device opened or closed by this device depending upon the material thickness of the belt in the track on the spot where the said part of the contact device cooperates with the track, the parts with different thickness in both tracks being arranged so as to cause the contact devices arranged in a line to close and open their contacts according to a shifting binary code indicating the position reached by the belt, and the other contact mechanism to close or open its contact so as to add such an element to the code produced by the other device, that either the total number of code-elements of one type is always even, or the total number of elements of one type is always odd.

6. An electromagnetic mechanism comprising a driving electromagnet with a winding enclosing a non-magnetic tubular element carrynig two ferro-magnetic end flanges connected by an external ferro-magnetic yoke system, a fixed ferro-magnetic core situated in the said tubular element so as to be partly in the opening enclosing the tubular part in one of the end flanges, a ferro-magnetic plunger core slidable in the tubular element, a supporting element fixedly connected to said plunger core,

two driving pawls, a drawing pawl and a pushing pawl,

magnet, an endless belt, carried around and in driving connection with said drum and with straight parts having substantially the same direction as the axis of the driving magnet, a countersunk ratchet wheel with inside teeth in each of the two ends of the drum, each ratchet wheel cooperating with a separate driving pawl, a part at the free end of each driving pa-wl with a direction substantially traverse to the longitudinal direction of said pawl, protruding into the countersunk ratchet wheel with which the pawl cooperates and resting by the pawls own elastic force on the toothing of said wheel, a longitudinal track near both edges of the belt, each provided with different parts following each other in the longitudinal direction of the tracks and some of which have one given material thickness and others another given material thickness which may be zero, a contact mechanism situated in the space enclosed by the endless belt, in said contact mechanism a number of contact devices arranged in a line, each provided with a part cooperating with the track near one edge of the belt and one contact device with a part cooperating with the track near the other edge of the belt, at least one electrical contact device opened or closed by this device depending upon the material thickness of the belt in the track on the spot where the said part of the contact device cooperates with the track, the parts with different thickness in both tracks being arranged so as to cause the contact devices arranged in a line to close and open their contacts according to a shifting binary code indicating the position reached by the belt and the other contact mechanism to close or open its contacts so as to add such an element to the code produced by the other devices, that either the total number of code-elements of one type is always even, or the total number of elements of one type is always odd.

7. An electromagnetic mechanism comprising a driving electromagnet with a winding enclosing a non-mag- -lar element so as to be partly in the opening enclosing the tubular part in one of the end flanges, a ferro-magnetic plunger core slidable in the tubular element, a supporting element fixedly connected to said plunger core, two driving pawls, a drawing pawl and a pushing pawl, both made of resilient material and each of them fixedly supported at one end by the said supporting element, a rotatable drum situated in line with the driving magnet .and with its axis of rotation traverse to the axis of said magnet, an endless belt with straight parts having substantially the same direction as the axis of the driving vmagnet, and carried around the drum and in driving connection with this drum by means of pins or sprockets on the surface of the drum cooperating with openings in the .belt, a countersunk ratchet wheel with inside teeth in at least one of the two ends of the drum, a part at the free ,end of each driving pawl with a direction substantially traverse to the longitudinal direction of said pawl, protruding into the countersunk ratchet wheel with which the pawl cooperates and resting by the pawls own elastic force on the toothing of said wheel, a longitudinal track near both edges of the belt, each provided with difierent parts following each other in the longitudinal direction of the tracks and some-of which have one given material thickness and others another given material thickness which may be zero, a contact mechanism situated in the .space enclosed by the endless belt, in said contact mechanism a number of contact devices arranged in'a line, each provided with a part cooperating with the track near one edge of the belt and one contact device with apart cooperating with the track near the other edge of the belt, at least one electrical contact in each contact device opened or closed by this device depending upon the material thickness of the belt in the track on the spot where the said part of the contact device cooperates with the track, the parts with different thickness in both tracks being arranged so as to cause the contact devices arranged in a line to close and open their contacts according to a shifting binary code indicating the position reached by the belt, and the other contact mechanism to close or open its contacts so as to add such an element to the system, a fixed ferro-magnetic core situated in the said tubular element so as to be partly in the opening, enclosing the tubular part in one of the end flanges, a ferromagnetic plunger core slidable in the tubular element, a

supporting element fixedly connected to said plunger core, two driving pawls, a drawing pawl and a pushing pawl, both made of resilient material and each of them fixedly supported at one end by the said supporting element, a rotatable drum situated in line with the driving magnet and with its axis of rotation traverse to the axis of said magnet, an endless belt with straight parts having substantially the same direction as the axis of said driving magnet, and carried around the drum and in driving connection with said drum by means of pins or sprockets on the surface of the drum cooperating with openings in the said belt, a countersunk ratchet wheel with inside teeth in each of the two ends of the drum, each ratchet wheel cooperating with a separate driving pawl, a part at the free end of each driving pawl with a direction substantially traverse to the longitudinal direction of said pawl, protruding into the countersunk ratchet wheel with which the pawl cooperates and resting by the pawls own elastic force on the toothing of said wheel, a longitudinal track near both edges of the belt, each provided with diiferent parts following each other in the longitudinal direction of the tracks and some of which have one given material thickness and others another given material thickness which may be zero, a contact mechanism situated in the space enclosed by the endless belt, in said contact mechanism anumber of contact devices arranged in a line, each provided with a part cooperating with the track nearone edge of the belt and one contact device with a part cooperating with the track near the other end of the belt, at least one electrical contact in each contact device opened or closed by this device depending upon the material thickness of the belt in the track on the spot where the said part of the contact device cooperates with the track, the parts with different thickness in both tracks being arranged so as to cause the contact a brush with its free end on a track of the belt and a contact strip arranged at the side of the belt opposite to the brushesin such a position, that a brush establishes electrical contact with the strip if a part of the track in which the material thickness iszero is under the brush.

10. In an electro-magnetic mechanism according to claim 1, in each contact device inthe contact mechanism a brush with its free end on "a track ofthe belt and at the side of the belt opposite to the brushes, opposite to each brush a contact piece in such a position that said brush establishes an electrical contact with the said con- .tact piece it a part of the track in which the material thickness is zero is under the brush.

11. In an electro-magnetic mechanism according to claim 1 in each contact device a lever, rotatable around an axis and an elastic elementexerting a force on said lever so asto cause one end of the lever to rest against the material of the track, and at least one contact element arranged in the contact device in such a position in the vicinity of thelever, that this lever establishes electrical contact with such a contact element in one of the two positions in which it can'bebrought by the track of the belt.

vl,'Z. Electro-magnetic mechanism according to claim 1, in which each drivingpawl remains atone sideof the symmetry plane through the axis of rotation of the drum and perpendicular to the direction of motion of the pawls whilst performing its stroke, the stroke during which the drum is driven by a pawl beginning at that end of the stroke which is nearest to the said symmetry plane.

13. In an electro-magnetic mechanism according to claim 1, further comprising a stop for a driving pawl arranged to press the said pawl into the toothing of the ratchet at the end of the stroke during which the pawl drives the ratchet.

14. In an electro-magnetic mechanism according to claim 1, further comprising a lengthenedhub arranged on the drum in a countersunk ratchet wheel and a bent part of a pawl cooperating with said ratchet wheel arranged to run against the lengthened hub at the end of the stroke during which the pawl drives the ratchet wheel thereby causing the pawl to be pressed in the toothing of the ratchet wheel.

15. In an electro-magnetic mechanism according to claim 1, further comprising two recesses in the supporting element, and two driving pawls each of them fixedly supported at one end by the said supporting element at the end of a recess away from the rotatable drum. and passing through and being able .to switch freely in the said recess.

16. In an electro-magnetic mechanism according to claim 1, further comprising a second fixed core situated in the tubular element so as to be partly in theopening amuse v 17 1'3 enclosing the tubular element in the secondlend flange, References Cited in the fileof this patent a ferro-magnetic plunger core slidable 'in the tubular element between the two fixed cores and a connecting ele- UNITED STATES PATENTS ment connecting the plunger core with the supporting 615,418 Wilkinson Dec. 6, 1898 element running through a bore of one of the fixed cores. 5

17. In an eiectro-magnetic element according to claim FOREIGN PATENTS 1, further comprising a layer of polyamide covering the slidable com 372,535 Germany Mar. 29, 1923