Electromagnetic Motion Imparting Means And Transportor System Embodying The Same

Abstract

An electromagnetic device producing a mechanical action, as in a transporter system comprising a suspended car, or in an electric motor, includes a magnetizing assembly and a magnetized assembly adapted to move one with respect to the other. The magnetizing assembly comprises at least one magnetic circuit defining an air gap and provided with at least one inductor winding, the magnetized assembly, subjected to the action of the magnetizing assembly comprising at least one magnetic portion associated with at least one non-magnetic portion and being in part housed in the air gap of said magnetizing assembly. This latter comprises at least two electromagnetic units each comprising an air gap and disposed in line whereas said magnetized assembly comprises a number of separate magnetic sections at least equal to two, the pitch of which is different from that of the electromagnetic units of said magnetizing assembly, said magnetic sections being coupled together mechanically, separated by non-magnetic sections and constituting a series in line. The windings of said electromagnetic units are connected to a switch adapted to ensure their energization following a predetermined sequence, guiding means being provided so as to permit the displacement of the magnetic sections of said magnetized assembly in the air gaps of said electromagnetic units in a transverse direction relative to the lines of force in said air gap.

Parent Case Text

This application is a division of copending application Ser. No. 697,089, filed Jan. 11, 1968, now abandoned.

Description

The present invention relates to an electromagnetic device capable of producing a mechanical action, as in transporter systems comprising suspended cars, or in electric motors, or the like.

This device is of the kind comprising a magnetizing unit and a magnetized unit which are movable one with respect to the other, the magnetizing unit comprising at least one magnetic circuit defining an air gap and provided with at least one field winding, while the magnetized unit which is subjected to the action of the magnetizing unit comprises at least one magnetic section associated with at least one non-magnetic section, and it is housed in part in the air gap of the magnetizing unit.

In particular, one of the units may be fixed, in which case the other may be associated with any device for receiving mechanical power.

Linear or rotary electric motors are already known which utilize polyphase electric current and work by conversion of electro-magnetic energy to mechanical energy, and more precisely by the effect of magnetic induction generated by the field assembly in the armature assembly.

The practical construction of linear motors of this type has serious inadequacies: the controls of speed, acceleration and braking are not satisfactory, the armature has a considerable mass and its conductivity must be high, which necessitates the use, whenever the armature is long, of large quantities of copper or aluminum which are particularly expensive metals. Finally, the existence of a relative slip between the field and the armature aggravates the problem presented by the control of movement, and prevents the development of a large force at low translation speeds.

Certain forms of linear electric induction motors permit the armature to be supported with respect to the field or vice-versa and constitute an electromagnetic suspension, but this necessitates a power per unit of weight which is too high to be utilizable in practice.

Another type of linear electric motor already described comprises a succession of cylindrical windings surrounding a magnetized assembly sliding along the axis of the unit: however, the movement generated can then only be transmitted by the extremity, which limits the possibilities of application. The power/weight ratio is low and the unit power is limited. The control of the movement and speed necessitates complicated and expensive switching and relay arrangements, since the air-gap is not precisely defined; the force varies considerably with the position of the magnetic cores and the impulses received by the moving system are not well defined in time and in space.

Finally, amongst the rotary induction motors, the polyphase asynchronous machines can only operate in a narrow range of speeds of rotation, and only have a moderate starting torque, contrary to the requirements of numerous applications. Rotary direct-current motors do actually comply with the requirements, but these are of expensive construction since the field and the armature must both be wound. Furthermore, the rotor cannot be fixed in a pre-determined position.

The foregoing machines employ two well-known physical laws:

The so-called electrodynamic machines utilize the action of a field on a current;

in the others, the displacement of the moving system is parallel to the field lines, and following the law of magnetic attraction, the force variation is inversely proportional to the square of the displacement.

The devices which form the object of the present invention make use of a different physical law, namely the fact that if there is established in a first element an electromagnetic circuit supplied at constant current and closed by an air-gap in which is arranged a second element comprising a magnetic tooth, the edges of which are arranged transversely with respect to the flux, the attraction is very low when the tooth is out of the air-gap, but increases abruptly at the moment when the edge of the tooth passes into the air-gap, and then remains substantially constant, in spite of the displacement, until the converse phenomenon takes place. Under these conditions, the attraction is in fact substantially proportional to the variation of magnetic permeance per unit displacement.

The present invention thus employs this particular law of force in order to overcome the abovementioned difficulties and disadvantages, for the purpose of constructing machines in which the force, the displacement, the speed and the acceleration of the magnetized unit with respect to the magnetizing unit can be controlled in an accurate manner, whether the speed is increasing or decreasing. Another object of the invention is to obtain a particularly low mass for one of the two units, which is particularly advantageous in the case of linear electric traction motors, in which the fixed portion is long, and of rotary motors with high speeds of rotation, in which the rotor must be capable of withstanding large centrifugal forces.

Another object of the invention is to obtain rotary motors with high starting torques and variable speed of rotation over a wide range, these motors having furthermore a low production cost.

According to the invention, the electromagnetic device of the kind defined above is characterized in that the magnetizing assembly comprises at least two electromagnetic units, each comprising an air-gap and arranged in line, in that the magnetized assembly comprises a number of separate magnetic sections at least equal to two, the pitch of which is different from that of the electromagnetic units of the magnetizing assembly, these sections being mechanically coupled together, separated by non-magnetic sections and forming a line; in that the windings of the electromagnetic units are connected to a commutator ensuring their excitation following a predetermined sequence; and in that guiding means are provided to permit the displacement of the magnetic sections of the magnetized assembly in the air-gaps of the electromagnetic units in a transverse direction relative to the lines of force in the said air-gap.

A device of this kind has appreciable advantages. In particular, one of the two parts, the magnetized assembly, has a low weight and a high power/weight ratio and its cost is small since it is not bulky and is made of cheap magnetic material. The starting force is very high. The controls of the position of the moving system, of its speed and acceleration, positive or negative, are easily effected by acting on the electric impulse switch.

The pitch of the electromagnetic units of the magnetizing assembly, measured along the axis of relative displacement of the two assemblies is preferably constant, but is different from the also constant pitch of the magnetic sections of the magnetized assembly. In particular, the axial length corresponding to N pitches of one of the assemblies, and especially of the magnetizing assembly, may be equal to the length of (N + 1) pitches of the other assembly, where N is a whole number.

This arrangement produces a uniform driving effort.

Depending on the applications, the magnetizing assembly and the magnetized assembly may extend in parallel rectilinear or coaxial circular directions, or finally along any curvilinear directions, the moving system being then constituted by an in-line series of articulated elements.

According to an advantageous feature of the invention, the device comprises means for regulating the starting and end instants of the electric impulse supplying an electromagnetic unit, these means being operated as a function of at least one of the following parameters: position, speed, acceleration of the moving system with respect to the fixed system.

In particular, the device may advantageously comprise a detector of the relative position of a magnetic section and an electromagnetic unit which cooperates therewith, this detector being itself preferably adjustable in position with respect to the assembly on which it is carried enabling the electric impulse to be initiated or interrupted at an adjustable pre-determined position. This detector may be advantageously combined with a device introducing, with a variable phase according to the desired conditions of operation, this detection signal in a device which modulates the electric impulses. This combination of regulating means having very great flexibility, makes it possible to ensure precise control of the movement, the force, the speeds and the accelerations, and furthermore ensures optimal efficiency.

According to another outstanding aspect of the invention, provision is made to utilize the device in question as an effective system of electromagnetic suspension of one of the assemblies with respect to the other. A suspension of this kind represents a considerable economy of means per unit of lifting force, with respect to other known suspensions. In fact, when an electromagnetic circuit is excited by an electric impulse, a slight relative displacement of the magnetizing and magnetized assemblies in a direction which is simultaneously normal to the direction of movement and to that of the lines of force in the air-gap (namely a vertical downward direction) creates a large restoring force on the magnetic section in the air-gap (namely an upward force), and this does not involve a considerable consumption of additional energy.

The industrial constructions which will now be described show that, depending on the application, the force applied by the magnetizing assembly may only cause a small displacement of the moving assembly, such as is the case in machines producing a vibratory movement. The device may also produce a resultant movement of medium amplitude (as is the case for pumps and compressors) or a movement of large amplitude (the case especially of conveyors of any kind: industrial conveyors, trains, etc.).

In applications for which a large travel is required, it may be advantageous to provide a fixed magnetized assembly and a moving magnetizing assembly, and conversely for applications requiring a small travel. The various forms of construction of the invention vary between two extreme cases: a machine in which the magnetized assembly comprises two magnetic sections successively attracted into the air-gaps of a large number of electromagnetic circuits, and conversely a machine in which a large number of magnetic sections forming the magnetized assembly are attracted successively into the air-gaps of two consecutive electromagnetic units. In the long-travel machines, if a small number of electromagnetic units is employed, a large number of magnetic sections is necessary for the magnetized assembly and vice-versa.

A remarkable special case of the long-travel construction is that in which the movement is rotating and there is thus obtained a rotary motor having the advantageous characteristics specified above, and in particular a great aptitude for operation at high torque, at variable speed and at high speed of rotation.

The electromagnetic device in accordance with the invention constitutes a driving machine which can be used over a large field of applications and especially in the case of the following apparatus:

Devices for lifting, or braking during lowering, with a linear movement, for lifts, lifting trucks, extraction of boring rods, pile-driving equipment;

Sliding control devices, especially for doors, shuttles, machine carriages;

Propulsion and braking devices for transport or handling means for passengers, goods or equipment, comprising guided vehicles such as: trains, trolleys, launching catapults for aircraft or rockets, toys;

Actuating motors giving considerable power, for example for driving tools for cold-forging metals by percussion or broaching tools;

Driving motors for alternating machines at relatively low speed and large travel, such as pumps and compressors;

Driving motors for devices of the chain type for caterpillar tractors, conveyors, bucket dredgers, etc.;

Driving motors for rotating machines such as crane-driving tables or drilling platforms, vehicle wheels and more generally rotary machines requiring a high torque at low speeds, accurate control, a very wide range of speeds and a rotor having a low weight and low inertia;

Torque or force limiting or transmitting devices; clutches;

Transmission to a distance of angles of rotation or linear displacements, remote recording, remote synchronization, servo-controls.

Further particular characteristics of the invention will be brought out in the description which follows below.

In the accompanying drawings, given by way of non-limitative examples, there have been shown various industrial constructions according to the invention.

FIG. 1 is a general perspective diagram of the device according to the invention.

FIG. 2 is a view in cross-section taken along the line II--II of FIG. 3, of a first industrial construction relating to an actuating device.

FIG. 3 shows a cross-section taken along the line III--III of FIG. 2.

FIG. 4 is a cross-section taken along the line IV--IV of FIG. 2.

FIG. 5 shows to a larger scale a detail of the cross-section along the line V--V of FIG. 2.

FIG. 6 shows diagrammatically an immobilizing device for the moving element of the first construction.

FIG. 7 is a transverse section of an alternative form of the first construction, constituting an electromagnetic suspension.

FIG. 8 is a plan view from above of a magnetizing assembly forming a conveyor.

FIG. 9 is a view to a larger scale of the above conveyor in cross-section along the line IX--IX of FIG. 8.

FIG. 10 is a side view of the magnetized assembly assumed to be isolated.

FIG. 11 is a transverse section of a lifting device for a vehicle.

FIG. 12 is a diagram of an electronic switching system of impulses utilizable for the previous constructions.

FIG. 13 is a view in side elevation taken along the section XIII--XIII of FIG. 14, showing an industrial construction intended for vehicle traction.

FIG. 14 is a cross-section taken along the line XIV--XIV of FIG. 13.

FIG.15 is a section taken along the line XV--XV of FIG. 13.

FIG. 16 shows the diagram of the electrical supply for the device of FIGS. 13 to 15.

FIG. 17 is a transverse section along the line XVII--XVII of FIG. 18, showing an alternative form of the previous construction applied to wall-effect vehicles.

FIG. 18 is a cross-section taken along the line SVIII--XVIII of FIG. 17.

FIG. 19 shows a detail of the cross-section XIX--XIX of FIG. 18.

FIG. 20 is a view in longitudinal section taken along the line XX--XX of FIG. 21, of a motor with a reciprocating movement.

FIGS. 21 and 22 are views in cross-section along the line XXI--XXI and XXII--XXII of FIG. 20.

FIG. 23 is a view in elevation of the cross-section XXIII--XXIII of FIG. 24, showing another industrial construction intended for driving a member in rotation.

FIG. 24 is a cross-section taken along the line XXIV--XXIV of FIG. 23.

FIG. 25 shows diagrammatically the method of supplying the windings of the device of FIGS. 23 and 24.

FIG. 26 is a cross-section along the line XXVI--XXVI of FIG. 27, showing the application of the invention to the construction of a micro-motor.

FIG. 27 is an axial cross-section along the line XXVII--XXVII of FIG. 26.

FIGS. 28 and 29 are detail explanatory diagrams concerning the starting system.

FIGS. 30 and 31 are diagrams of electrical supply devices.

FIG. 32 is a partial view of an alternative form of construction of the magnetized assembly of the above micro-motor, following the section XXXII--XXXII of FIG. 33.

FIG. 33 is a partial view in transverse section of an alternative form of construction of the magnetizing circuit.

FIG. 34 is a diagrammatic view in cross-section along the line XXXIV--XXXIV of FIG. 35 of a motor with mechanical self-commutation.

FIG. 35 is a cross-section along the line XXXV--XXXV of FIG. 34.

FIG. 36 shows an alternative form with electrical self-commutation, taken along the line XXXVI--XXXVI of FIG. 37.

FIG. 37 is a cross-section along the line XXXVII--XXXVII of FIG. 36.

FIG. 38 is a diagram showing the electric switching device of the construction of FIGS. 36 and 37.

FIG. 39 is an explanatory diagram.

FIG. 40 is a diagram of a supply circuit.

There will first be described, with reference to FIG. 1 of the accompanying drawings, a simplified construction of the device according to the invention.

This device is intended to produce a mechanical action (development of a driving or static force) and comprises essentially a magnetizing assembly 1 including at least two electromagnetic units 2 forming a series. Each unit 2 comprises a magnetic circuit 3 having an air-gap 4 and carrying a magnetizing winding 5 which creates a magnetic flux in the said air-gap.

The device further comprises a magnetized assembly 6 including at least two sections 7 of magnetic material (that is to say having a magnetic permeability greater than 1). The sections 7, the number of which is furthermore different from that of the electromagnetic units 2, are coupled mechanically to each other, arranged in line and separated by non-magnetic sections 8 (for example of air).

The relative mechanical couplings of the assemblies 1 and 6 are such that a relative displacement may take place between them, this displacement being effected in the air-gaps 4, in a substantially transverse direction with respect to the lines of force of the magnetic flux created in these air-gaps.

The windings 5 of the electromagnetic units 2 are supplied from a source 13 of electrical impulses through a commutator 14 which distributes these impulses cyclically between the various windings 5.

The device may also comprise a system 15 for modulating the impulses, acting on the commutator 14 and controlled in turn simultaneously by the orders and operating data inscribed in a recording system 12, and by a unit 9 connected to a detector 10 of the position of the magnetized assembly 6.

Means may further be provided for determining a preferential direction of displacement of the magnetized assembly 6.

In operation, the windings 5 of the magnetizing assembly 1 receive successive electric impulses through the commutator 14 in such manner that the magnetic flux is established in at least one of the air-gaps 4 at the moment when one of the magnetic sections 7 of the magnetized assembly 6 has reached the entrance of this air-gap. The section 7 is thus attracted and tends to take up the position of minimum reluctance in the air-gap 4. When this condition is reached, or during the course of the previous movement, a new circuit 3 is excited and attracts another section 7 at the moment or time when this latter also reaches the entrance of its air-gap, and so on.

Apart from special geometric relations which may be established between the pitches of the air-gap 4 and those of the sections 7 in order that one of these sections may be at the entry of an air-gap 4 when the other section is located in this air-gap, for the purpose of permitting the systematic and sequential development of a driving attraction, the invention provides means for acting on the amplitude, the duration and the phase of the impulses from the commutator 14 in order to provide a regulation, especially of the acceleration or the speed of the magnetized assembly 6.

The general features which have been specified above will now be detailed and illustrated with reference to the description of the particular applications of the invention.

The first particular construction of the invention illustrated in FIGS. 2 to 5 relates to a linear actuating device constituting a semi-static driving machine with controlled displacement. This device comprises a frame 21, on which is mounted the magnetizing assembly formed by a succession of electromagnetic units 22, five in number in the case selected. Each unit 22 comprises a magnetic circuit 23 formed by an assembly of magnetic laminated sheets, stamped out to the shape of a C. The interrupted arm thus forms a parallelepiped air-gap 24, between the two poles 25.

The circuits 23 are retained by a transverse bar 32 arranged in their central portion and fixed to the frame 21 by screws 33. The bar 32, of non-magnetic metal has a U-shaped section as shown in FIG. 5, and it is bordered by lugs 26 slotted with a bevel at the level of the poles 25 similar to a rack, which ensures an absolutely firm fixing of the units 22.

On each of the lateral branches of the circuits 23 are mounted the magnetizing windings 28 which, for the same unit, are supplied in phase from a source of direct-current 36, through a switch 39, a potentiometer 39a. and a rotary switch 37, the rotating contact 38 of which is driven by a motor 301 with two directions of rotation and variable speed regulated by the operator. This device could furthermore be replaced by a manually-operated crank-handle.

Each winding 28 of the electromagnetic unit 22 is connected to one of the terminals 37a, 37b, 37c, 37d and 37e of the rotary switch 37. The rotating contact 38 simultaneously establishes contact with several of the said terminals, as will be described later. The potentiometer 39a provides a regulation for the power of the impulses and therefore of the force applied on the moving element.

The magnetized assembly 27 is composed of a flat strip of magnetic material having a substantially parallelepiped shape, adapted to the air-gaps 24 and to the free space provided between the lugs 26 of the bar 32. The assembly 27 has a succession of magnetic sections formed by teeth 30 produced by cutting-out and forming a toothed rack. The non-magnetic sections arranged between the teeth 30 are constituted by blocks 31, of plastic material for example, which restore the parallelepiped shape of the strip and ensure the continuity of the guiding surface.

The assembly 27 thus constituted is slidably mounted axially on the bar 32 between the poles 25 of the electromagnetic units 22.

The clearance between the magnetized assembly and the poles remains practically constant over the greater part of the travel, due to the fact that the magnetic fields in the air-gaps 24 are transverse with respect to the movement. The magnetized assembly 27 is guided in its displacement by the lugs 26 of the bar 32, the play in this guiding action being substantially twice as small as that existing between the elements 27 and the poles 25. The element 27 is coupled to the utilization device by a crank-arm 34 by means of an articulation shaft 35. The friction of the element 27 with the bar 32 and the lugs 26 can be reduced by employing self-lubricating materials 303 for the parts in contact (plastic material, non-magnetic alloy, for example) -- (see FIG. 5).

In order to ensure the effective operation of the actuating device, the following particular relations are preferably provided for the assemblies 22 and 27:

The parallelepiped shape of the air-gap 24 is such that its section perpendicular to the flux approximates to that of a square, the side of which is larger than the thickness of the air-gap in the direction of the flux.

The axial length of the non-magnetic sections 31 is slightly greater than the length of the poles 25 relative to the direction of the movement L or M, and their height is slightly greater than that of the poles 25.

The axial length of the magnetizing assembly corresponding to N pitches (the pitch being the axial length of a pole plus the distance separating two poles) is equal to that of (N + 1) pitches of the magnetized assembly.

The number of electromagnetic units is odd. Thus, in the present embodiment, 5 pitches of the electromagnetic units 22 occupy the same axial length as 6 pitches of the magnetic sections 30.

This value of the pitch makes it possible to obtain a high proportion of electromagnetic units 22 which are active at any particular moment, while at the same time having an attraction in the opposite direction with respect to the desired direction of movement having a value as small as possible on the magnetized assembly 27. To the same end, it is provided that the axial length of the non-magnetic sections 31 of the magnetized assembly 27 is greater than that of the magnetic sections 30 in the proportion of 5 to 50 percent. The spacing between the electromagnetic units is thus fixed by all the foregoing points.

To the magnetized element 27 there may advantageously be added a solenoid-brake 40 (FIG. 6) intended to prevent any relative movement between the magnetizing assembly 22 and the magnetized assembly 27 when none of the windings 28 is excited. When stationary, the magnetized assembly 27 is gripped by two mechanical jaws 41 by the action of springs 42 applying a force in opposition to that of release electromagnets 43, the sliding cores 302 of which are fixed to the jaws 41. When the switch 39 is closed, the jaws 41 move away from the element 27 due to he attraction effect of the electromagnets 43 on the cores 302.

The differential spacing of the electromagnetic units 22 and the magnetic sections 30 of the magnetized assembly 27 provides the following operation: when one of the magnetic sections 30a is exactly between the poles 25 of one of the electromagnetic units 22a, another magnetic section 30b of the magnetized assembly is partially between the poles of the following electromagnetic unit 22b, while the magnetic section 30c is ready to pass into the electromagnetic unit 22c and the magnetic section 30d is half-way between the units 22c and 22d.

The rotary switch 37 is arranged with respect to the fixed contacts 37a, 37b, . . . 37e, in such manner that for this position of the element 27, the electromagnetic unit 22b is excited, so that the magnetic section 30b is attracted in the direction L between the poles of this section. At the end of this movement, the section 30c is partially engaged in the electromagnetic unit 22c, and the electromagnet unit 22c is then excited instead of the electromagnetic unit 22b, so that the movement of the magnetized assembly 27 in the direction L may continue.

Thus, the excitation in sequence of the electromagnetic units 22 produces a movement of the magnetized assembly in the same direction as the order in which these units are excited. Under these conditions however, it will be observed that only one of the electromagnetic units is excited at a given instant, so that the power/weight ratio of the system does not have its maximum value. In order to remedy this, the invention provides for the simultaneous excitation of a second electromagnetic unit 22 as follows:

The rotating contact 38 of the switch 37 is arranged in such manner as to connect continuously two of the terminals such as 37a and 37b to the source 36, and to establish contact with a fresh terminal 37c at the exact moment when it breaks the contact with the terminal 37a which it leaves behind.

Under these conditions, the magnetized element 27 being in the position shown in FIG. 3, the unit 22a which supplies no driving force is not excited, whereas the units 22b and 22c are excited simultaneously. When the section 30b has come into the air-gap 24 of the unit 22b, the corresponding winding 28 is de-excited in turn to the benefit of the winding of the following unit, and so on. A reverse order of switching is utilized in order to obtain a movement of the magnetized assembly 27 in the opposite direction.

Rotation of the contact 38 thus controls the position, the direction, the movement and the acceleration of the moving magnetized element 27. The potentiometer 39a permits the regulation of the force applied in the axial direction by this magnetized assembly 27 which, by means of the crank-arm 34 communicates the movement and the force of the actuating device to the member which is to be driven. This latter may equally well be a sliding door, a control device for a machine-tool, or an aircraft control device. The device considered can also be employed in place of rotary electric motors with reduction gearing and worm-screws or toothed racks.

In certain applications of this embodiment, it is essential that the movement under load of the magnetized assembly should be particularly uniform. It is then provided that the variation of the total permeance of the various circuits is proportional to the travel for an excitation current which is maintained constant. This can be effected by various means, such as: magnetic sections having a sinusoidal profile, magnetic sections having a slightly variable thickness and a permeability less than that of the circuit, lamination of this latter perpendicular to the movement, air-gap with a lightly variable thickness, switching de-phased with respect to the passage into and out of the air-gap, and more generally by any means controlling the increase of flux at the beginning of the introduction of a magnetic section 30 into the air-gap. There is thus obtained simultaneously an optimum efficiency and an easier control of the movement.

By way of an alternative form, the present invention provides an actuating device of the foregoing type to ensure at the same time the propulsion and also the lifting of a driven element. This embodiment is illustrated in FIG. 7, in which there is seen at 45 the driven element which is to be simultaneously displaced and held in suspension. To this end, the element 45 is attached by slings 46 to the magnetized assembly 27 similar to that described above, but which is in this case located below the units 22 of the magnetizing assembly, itself fixed to the lower part of a fixed support 47 such as a ceiling or framework. The weight of the element 45 tends to pull the magnetized assembly 27 downwards and to pull the magnetic sections 30 out of the air-gaps 24, which creates restoring forces increasing rapidly with the vertical displacement. These forces finally counterbalance the weight of the element 45. An additional lifting force may be obtained by joining together the magnetic sections 30 by a transverse magnetic piece 48.

In order that the lift forces may be well distributed over the length of the magnetized assembly 27, it is provided to employ at least two magnetizing assemblies, adequately spaced apart. The lift force is proportional to the axial length of the magnetic sections or teeth 30, while the propulsion force is proportional to the height of these teeth. Flanges or angle-iron sections 49, continuous over the whole length of the device and located below the element 27, prevent the latter from falling in the event of a failure of current supply.

In the foregoing devices, the switch 37 and the potentiometer 39a provide a precise control of the actuating device and especially of its position, of the direction of movement, of the speed and the acceleration of the driven element. The driving force for starting-up is large. The moving system may be held stopped in any position, even on load. The direct transmission of electromagnetic energy to the magnetized assembly 27 serving as an actuating slide results in a very simple unit having no intermediate transmission element. The bulk of the magnetized assembly 27 is small and its construction of magnetic metal results in a very low cost. By virtue of a magnetic play, substantially greater than the mechanical play and practically constant, and due to the rules for dimensioning and switching indicated above, the force on the moving magnetized element can be made practically constant for a given current. The displacement is thus effected without appreciable shocks and there is no sticking effect on the poles.

A prototype machine in accordance with FIGS. 2 to 5 has been built and tested. Its characteristics are as follows:

Axial length of poles 19 mm. Distance between poles 30 mm. Height of poles 15 mm. Axial length of magnetized sections 19 mm. Axial length of non-magnetic sections 22 mm. Axial length of magnetic assembly 600 mm. Number of electromagnetic units 5 Total weight of magnetizing assembly 2.5 kg. Supply voltage 12 volts Power absorbed 100 watts Resistance of each winding 1.40 ohms Number of turns 2 .times. 210 Average force 2.5 kg. Mechanical commutator.

The following operational results were obtained during the tests:

Maximum linear speed 2 m./sec. Pulsation speed obtained with alternating current for a travel of 100 mm 2 cm./sec. Maximum slope climbed by the magnetizing assembly forming a trolley 80% Maximum force of magnetic lift: 3,700 g.: 100 = 37g./watt.

An alternative form of construction of the conveyor device of FIG. 7, intended to permit of movement over a curve, is shown in FIGS. 8 to 10. In this embodiment two magnetized assemblies 27a, 27b are provided, each constituted by an articulated assembly of magnetic sections 260 forming successive castellations in which are interleaved non-magnetic sections 261, also in the form of castellations which have an arrangement reversed with respect to the preceding. The sections 260 and 261 form in pairs substantially rectangular plates joined to each other by hinges through which pass the pivotal shafts 262. On each of these plates are provided guiding shoes 263. The assemblies 27a, 27b each carry a supporting rod 46a, 46b, and these two suspension rods are coupled together by a swing-bar 264 which carries a lifting hook 265.

The magnetizing assembly constitutes a continuous supporting track with a curvilinear outline (FIG. 8) formed by a succession of electromagnetic units 22 each comprising a C-shaped circuit 23, as in the case of FIG. 7, fixed to the support 47, and in the air-gap 24 of which can circulate the magnetized assemblies 27a, 27b. In this case it is provided however to mount the magnetizing windings 28 on the horizontal limbs of the circuits 23 and in the vicinity of the air-gaps 24. Above the pole-pieces 25 are arranged continuous friction bands 266 with which the shoes 263 are in contact. At the lower part of these pole-pieces are arranged guiding and safety angle-irons 49, by which the lower shoes 263 are supported. The articulation axes 262 permit the assemblies 27a, 27b to follow the curves.

The units 22 are supplied with current in pairs, the corresponding windings of the same pair being separated by a distance which corresponds to that separating the homologous sections 260 of the assemblies 27a, 27b.

The actuating device provided thus constitutes a particularly simple electromagnetic suspension having a high power/weight ratio and low friction, the trajectory of which may have any desired form in space.

In the constructions which have just been described, the magnetized assembly is moving and the magnetizing assembly is fixed, but this arrangement may be reversed without departing from the scope of the invention, especially in the cases where, for reasons of practical construction, it is preferable to keep the magnetized assembly stationary and to cause the magnetizing assembly to move by attaching the driven element 45 to this latter.

A version of this kind is shown diagrammatically in FIG. 11. The conveyor comprises a magnetized assembly 250 fixed to the lower part of the support 47 and which comprises, as previously, a succession of magnetic and non-magnetic sections, such as 251. The magnetizing assembly 252 comprises a series of electromagnetic units 253 in line, fixed to the upper part of a vehicle 254 and playing simultaneously the parts of lifting and propulsion motors. Each unit 253 comprises in particular two windings 267 located in the vicinity of the poles 268. As previously, supporting angle-irons 269 prevent the fall of the vehicle 254 in case of interruption of the current by coming to rest on a widened portion of the magnetized assembly 250.

The rotary switch 37 of FIG. 3, intended to ensure the sequential switching of the current supply to the electromagnetic units 22 may, according to a preferred embodiment of the invention shown in FIG. 12, be replaced by a static electronic device, in particular with thyristors.

More precisely, this device comprises a thyristor 51 assigned to each winding 28. The thyristor 51 is connected between the conductor 50a coupled to the negative pole of the source 36 and one of the terminals of the winding 28 concerned, the other terminal of which is connected to the positive pole of the source 36 by the conductor 50b.

The trigger of each thyristor 51 is controlled by an electronic gate 52 of the "AND" type, of which one of the inputs is connected to an impulse generator 53 and the other input to a routeing contact 54. The fixed studs of the contact 54 terminate respectively at the output circuit of the preceding thyristor 51 and of the following thyristor 51.

It can thus be seen that the control gate 52b of the thyristor 51b is connected to the contact 54b, the fixed studs of which terminate respectively at the outputs of the thyristor 51a and of the thyristor 51c.

Condensers 55 are connected between the corresponding conductors of the windings 28, two by two, following a circular permutation, and diodes 56 are connected in parallel with each winding 28, their cathode being coupled to the positive pole of the source 36 in order to prevent voltage surges in the windings 28 when these latter are de-energized.

The operation is as follows: if the displacement takes place in the direction L, the contacts 54 are connected as shown in FIG. 12. Assuming that the windings 28a and 28b are excited, the excitation of the following winding 28c is determined by the striking of the thyristor 51c which is triggered by the gate 52c. This release occurs when the generator 53 delivers an impulse and the preceding winding 28b is excited simultaneously. The striking of the thyristor 51c short-circuits the condenser 55a and thus creates a reverse potential at the terminals of the thyristor 51a which becomes blocked. The winding 28a of the unit 22a is no longer excited, while the winding 28c is put into circuit. At the following impulse, the thyristor 51d strikes and the thyristor 51b becomes blocked and so on, the successive excitation of the electromagnetic units 22 being effected in the direction L. In order to reverse the direction of movement, that is to say to effect it in the direction M, it is only necessary to modify the position of the switch 54 which changes the sequence of excitation of the second input of the gates 52. The diodes 56 protect the thyristors 51 against voltage surges which may occur during the break of the corresponding circuit.

This electronic switch enables high powers to be controlled with accuracy and avoids the problems presented by mechanical switches, especially the arcs due to voltage surges on interruption of inductive circuits.

The checking of the control impulses can readily be made automatic in order to ensure that the moving system has a movement at constant speed or at progressive acceleration, depending on the applications. For this purpose, it is only necessary to control the impulse generator 53 in dependence on an appropriate parameter.

The electromagnetic device contemplated by the invention may, following another industrial application, be employed for the propulsion of vehicles guided by a track for handling, transport of goods or passengers. In particular, this device may equip railway vehicles, monorails or ground-effect vehicles.

In these applications, the magnetized assembly is preferably stationary and follows the outline of the track. The electromagnetic units which form the magnetizing assembly are mounted on the vehicle and are supplied with electric current derived from any known means.

While in certain cases, especially of conveyors, it is necessary to provide control means external to the vehicle, as in the machines which have been described in the preceding embodiments, in the present case the control and in consequence the switching of the electromagnetic units is effected directly from the interior of the vehicle.

In the construction shown in FIGS. 13 to 16, there is indicated diagrammatically at 60 the frame of a vehicle fitted with wheels 61 and moving along a normal railway track 62. The fixed magnetized assembly 63 which constitutes a rail and follows the outline of the track is arranged at equal distances from the two rails 62. The upper part of the magnetized assembly 63 comprises a succession of teeth 64, separated by non-magnetic sections 65, produced very economically by simple cutting-out. A suitable magnetized assembly may be made from a normal carbon steel of good quality.

The driving section is preferably constituted by several magnetizing assemblies distributed amongst the vehicles of a train. There is thus obtained a moving assembly having a small mass, which more readily follows the irregularities of profile of the magnetized assembly 63. Furthermore, this multiplication of the driving units results in a better utilization of the magnetized assembly, permits of manufacture on a larger scale and at low cost of small light driving units which are readily housable in and removable from all the vehicles of a train, and provides an installed power proportional to the size of the train.

In the particular construction described, the magnetizing assembly provided for a vehicle 60 comprises four electromagnetic units 67 fixed on a frame 66 mounted elastically in the lower part of the vehicle 60. Each unit 67 comprises a circuit 68 made from magnetic sheet, and two windings 69 mounted on poles 71 defining an air-gap and arranged in such manner that the teeth 64 of the magnetized assembly 63 may pass in line through the abovementioned air-gap, perpendicular to the lines of force between the poles 71, when the windings 69 are excited. The magnetic circuits 68 which are of C-shape are laminated in the plane of this latter and are arranged at right angles to the direction O or N of the movement.

The non-magnetic frame 66 comprises enclosing flanges 70 and re-entrant flanges 72, which provide a housing for the circuits 68. This mounting reinforces the transverse rigidity of the assembly and offers remarkable resistance to the forces of attraction of the poles between each other. In particular, the flanges 70 which surround the base of the poles 71 of each magnetic circuit 68, preventing the bending of the sheets of this latter due to the effect of the attraction force acting on the magnetic teeth 64.

The frame 66 is fixed to the lower part of the vehicle 60 by means of crank-arms 73, mounted between elastic articulations 311, 312 (see FIG. 15). The thrust or traction efforts of the magnetizing assembly are transmitted to the vehicle 60 by at least one elastic coupling 74 which damps out the variations and the shocks of these efforts.

The guiding of the frame 66 with respect to the rail 63 is ensured by two pairs of rollers 75 mounted in opposition on each side of the magnetized rail 63, at the front and at the rear of the frame. The rollers 75 run just beneath notched portions 65 of the rail 63, and the mechanical play is regulated in such manner that the distance between the poles 71 and the magnetic teeth 64 is greater than at least twice the value of the mechanical play. Thus, the attraction forces of the poles are balanced and the residual lateral force is negligible. A sticking effect of the poles on the magnetized assembly is a fortio i made impossible. These mechanical and magnetic clearances and the wheel base of the rollers 75 are determined in such manner that in curves of short radius, the pole surfaces 71 remain sufficiently distant from the magnetized assembly 63.

According to an improvement, the magnetized rail 63 also serves as a third rail for supplying current. For this purpose, it is insulated from the track by a non-conductive sole-plate 77. The current is taken-off by one or more collector shoes (not shown) supported on the lateral surface of the rail.

According to a further special feature of the invention, it is provided that the four electromagnetic units of the driving assembly are associated in pairs, 67a, 67c on the one hand and 67b, 67d on the other, in such manner that in each pair (FIG. 39) when one of the electromagnetic units 67a comes opposite a magnetic section 64 of the magnetized assembly 63, the other unit 67c is facing a non-magnetic section 65. In addition, the distance between the pairs of associated units 67a, 67c is such that when the poles of one pair are located respectively opposite a magnetic section 64 and a non-magnetic section 65, the poles of the other pair are situated opposite the half of a magnetic section 64 and the half of a non-magnetic space 65.

The supply of current to the windings 69a . . . 69d associated in pairs is effected as shown in FIG. 16 by means of a two-phase current source 79 of variable frequency, such as a Diesel electric generating set carried by the train. The conductors 313a of the same phase supply two associated windings 69a, 69c, by means of two power diodes 78 connected in opposition so that one of the associated windings is supplied at each half-wave. The same arrangement is adopted for the second phase (conductors 313b). The source 79, associated if necessary with a phase-shifting system, is furthermore arranged in such manner that the phase-shift between the phase conductors 313a, 313b is 90.degree..

Thus, the four electromagnetic units 67 of the magnetizing assembly begin to be excited respectively at 90.degree., 180.degree., 270.degree. and 360.degree. of the cycle, and each one of them ceases its operation 180.degree. later.

In addition, if the electromagnetic units 67 are excited following the sequence a, b, c, d, the vehicle 60 will be propelled in the direction 0. If the excitation sequence is a, d, c, b, the movement will take place in the opposite direction N.

No other means for controlling the direction of displacement is necessary, since if the first electromagnetic unit excited tends to cause the movement to start in the wrong direction (the case, for example, of the unit d, whereas the movement is desired in the direction 0), the subsequent windings (b, c, d, a, etc. . . ) will correct this tendency and the movement will continue in the desired direction. The control of speed can be effected by varying the frequency of the source 79, and especially by increasing it as the train gathers speed.

According to another alternative form shown in FIG. 40, the determination of the direction of the speed is effected by means of a feeler 76 such as a magnetic or capacitive detector which controls the triggers of the thyratrons 401 or of the thyristors forming part of the electronic switching device 402 of the electromagnetic units 67, when the latter are supplied, for example, in accordance with FIG. 12.

The control is regulated in such manner that the release impulse is produced at a suitable moment with respect to the relative forward movement of the tooth 64 nearest the magnetized assembly 63. When an acceleration is necessary, the release of the thyratrons or thyristors referred to above can be effected in phase advance. This variation of phase can be obtained by any means known per se and forming part of the electronic triggering system (and especially by a phase-shift stage 403), or by mechanically displacing the feeler 76 with respect to the chassis 66. The deceleration of the vehicle is effected in a similar manner by a phase delay. This deceleration is independent of the adhesion of the wheels. For this reason, the braking of the vehicle can be made very effective, flexible and silent, and gives a greater degree of safety.

Due to the high inductive impedance of the circuits, the increase and decrease of the current in the magnetizing windings 69 is delayed with respect to the beginning and the end of the electric impulse delivered by the generator 79.

In order to compensate for the effects of this delay at high speeds, the invention provides for increasing with the speed the advance of the setting of the instants of the beginning and end of the driving electric impulse with respect to the relative positions of the poles 71 and the teeth 64 of the magnetized assembly.

This advance makes it possible to prevent the subsistence of a magnetizing field in the air-gap at the moment when the poles 71 are about to pass beyond the tooth 64 considered of the magnetized assembly 63. In an arrangement of this kind, the feeler 76 may operate as a speed-detection device and may permit the frequency modulation of a signal which is employed for the regulation of the phase between the impulse periods and the instants when the magnetizing and magnetized assemblies occupy pre-determined relative positions.

The reluctance of the magnetic circuit of the units 67 varies according to the displacement of the magnetizing assembly. According to a further particular feature of the invention, it is then provided to adapt this law of variation to the most probable speed of the vehicle in the section of track considered. The modifications of this law of variation may be obtained by acting on the longitudinal profile of the magnetic sections 64, on their thickness and on their magnetic characteristics.

In particular, provision is preferably made on the portions of track intended for high speeds, for the formation of teeth such as 64a (FIG. 13) of which at least the leading edge forms an acute angle with the direction of movement, and the mean length of which is greater than for low speeds, while the permeability and thickness are reduced.

These arrangements considerably reduce shocks and vibrations, and increase the effort developed.

The method of propulsion of guided vehicles thus provided by the invention may be advantageously applied to wall-effect vehicles and especially to those of the air-cushion type. An application of this type, shown in FIGS. 17 to 19, is advantageous since vehicles of the kind considered have no physical contact with the wall, so that it is difficult for them to utilize the adhesion effect with the wall for acceleration or braking.

In this embodiment, the vehicle 80 is supported above an area 81 serving as a track by the ground effect resulting from air cushions 82 supplied by distribution channels 83. The vehicle is guided by a vertical rib 84 which forms the magnetized assembly with the magnetic sections 85 and the non-magnetic sections 86 uniformly spaced apart. The magnetic sections 85 are in this case constituted by parallelepiped blocks of magnetic material embedded in the guiding rib 84 of a non-magnetic material such as concrete. There is thus formed a low-cost magnetized assembly which furthermore plays an essential part in guiding the vehicle along the track.

The magnetizing assembly 87 comprises, in this example, four electromagnetic units each comprising a magnetic circuit 88 in the form of a C, which has an air-gap defined by the poles 91.

The windings 89 are mounted in pairs on each magnetic circuit 88 close to he poles 91, in order to concentrate the magnetizing field in the air-gap, to reduce the leakage flux and to have the maximum driving force on each magnetic section for a given magneto-motive force.

The guiding of the magnetizing assembly 87 is effected by the wall effect resulting from air cushions 94 created between the rib 84 and the said assembly. The cushions 94 are supplied through channels 93, depending on the size of the vehicle.

The magnetizing assembly 87 is preferably mounted on a separate frame 316 coupled to the vehicle 80 by suspension and thrust arms 317. The guiding of the vehicle 80 is effected by other air cushions 321 created by discharge nozzles 322 which produce a wall effect with the rib 84. The independent guiding provided for the magnetizing assembly 87 makes it possible for this latter, by reason of its low weight, to follow faithfully the profile of the magnetized assembly while facilitating its oscillations and its relative movements with respect to the vehicle. The air cushion follows the law of compression of gases, which gives a law of force as a function of the lateral displacement which is particularly well suited to compensate the law of the magnetic disturbing force, since the two laws give representative curves of the same form. In this case, it is therefore no longer necessary to provide guiding rollers.

The electric motor proposed avoids the use of air propellers, propulsion wheels, braking shoes and other means ill-suited to this type of vehicle, especially by reason of the noise during operation and of the numerous degrees of freedom of the system.

The invention enables a direct, progressive and silent driving force to be applied to the vehicle, together with a large braking effort and complete control of the speed.

Within the framework of systems comprising a relative rectilinear displacement between the magnetizing assembly and the magnetized assembly, it is also contemplated by the invention to produce driving machines with a reciprocating motion of low frequency and large travel, such as liquid pumps, compressors, mud pumps, pile-driving devices, etc.

For the construction of these machines, the invention provides for the use of an assembly of electromagnetic units with sequential switching, so as to produce a linear movement of one of the two halves of the machine as previously, but the switching means are so arranged that the movement changes direction when one of the moving parts of the machine reaches the extremity of its specified travel. This generates a uniform alternating movement between the two limits of the travel. A regulating device for the switching system may be added to the machine in order to provide for a variable travel, when so desired.

The construction of a machine of this kind is shown in FIGS. 20 to 22 for driving a single-acting pump 230 comprising a cylinder 231 provided with suction valves 232 and delivery valves 233 and with a piston 234 having a reciprocating motion.

The piston 234 is rigidly fixed to a piston rod 235 which slides in the end 325 of a non-magnetic frame belonging to the magnetizing assembly of the driving system. On the rod 235 are stacked alternately magnetic sections 237 and non-magnetic blocks 326 both having an annular volume. The magnetized assembly 236 thus constituted, of cylindrical form, moves in the air-gaps of a certain number of electromagnetic units 238 of the magnetizing assembly 239, which comprises excitation windings 240 mounted on a magnetic circuit 241 in the form of a double C (FIG. 21), and the air-gap 242 of which is defined by the poles 241a having cylindrical pole surfaces.

The electromagnetic units 238 are separated by non-magnetic spacers 243 comprising a central arm 327 in which is formed a bore 244 serving to guide the magnetized assembly 236. In order to facilitate this guiding action while avoiding any contact between the fixed and moving magnetic parts, it is provided that the diameter of the bores 244 should correspond to that of the blocks 326, while the diameter of the poles 241a is slightly greater than that of the magnetic sections 237 of the magnetized assembly.

The magnetized assembly 239 is fixed by long bolts 246 which clamp together the various fixed parts.

The cylindrical shape of the magnetized assembly 236 has the advantage of permitting free rotation of the moving system, piston, rod and magnetic cores, and thus to distribute the wear equally.

The rules of differential spacing of the poles 241a and the moving magnetic sections 237 are of course the same as in the previous embodiments. It should however be indicated that the shorter magnetized assembly must in this case be constructed with greater care and with metals having superior magnetic characteristics, or alternatively by means of a stack of magnetic sheets, as provided in FIG. 20.

As previously, a switching system 247 controls the order in which the successive electromagnetic units 238 are excited. The system 247 also controls the speed at which the first and then those following are excited and the phase of the impulses relative to the position of the magnetic sections 237. This determines the frequency of oscillation and the change of speed and acceleration throughout the cycle. For each successive unit, it is thus possible to provide for the setting of the beginning and the end of the impulse, which ensures maximum energy transfer.

The switching system 247 is piloted by a mechanical feeler 248 excited by grooves 330 formed in the rod 235. This simple and robust feeler is very well suited for low frequencies of oscillation of a pump of large size. The reversal of the direction of running is controlled by a reversing rocker device 249, provided with a reciprocating sliding actuation finger 328 which is alternately displaced by a stop 329 located at the end of the rod 235, and by the cheek 331 on the edge of the last magnetic section 237.

The feeler 248 may also be employed to interrupt the electric supply to the electromagnetic units in the case where the stroke exceeds a pre-determined value.

A second group of industrial applications of the invention concerns the construction of machines with a curvilinear movement and in particular a movement of rotation. These applications will now be described.

In particular, the trajectory of the magnetized assembly and the structure of this latter may be curved, while the electromagnetic units of the magnetizing assembly are arranged on each side of this trajectory.

A first construction of this kind is shown in FIGS. 23 to 25, and relates to the drive at slow speed of a rotating plate such as a crane platform, on which is mounted the magnetized assembly which forms a closed ring of large diameter.

The moving platform 110 of the crane is rotatably mounted about the axis X--X in a base-plate 111 by means of a bearing ring 112 with frusto-conical rollers, carrying the weight of this platform and ensuring its peripheral guiding.

The driving portion is constituted by two magnetizing assemblies 113, diametrically opposite and housed in a circular groove 332 of the base-plate 111. Each magnetizing assembly 113 comprises three electromagnetic units 119 which each include a magnetic circuit 114 of C-shape, interrupted by an air-gap 115 defined by the poles 116. On the non-interrupted limb of each magnetic circuit is mounted a winding 118 which receives electric impulses from a generator (not shown).

The magnetized assembly 120 is formed by a circular ring 333 fixed under the moving platform 110 of the crane which it drives in its movement of rotation. The ring 333 comprises trapezoidal magnetic sections 121, uniformly spaced apart, and non-magnetic sections 122 obtained by cutting-out. The angle at the center of two magnetic sections 121 is shown at a.

In order to correspond to the circular shape of the magnetized assembly 120, the electromagnetic units 119 are arranged radially and spaced apart from each other by an angle b at the center. The polar surfaces of the poles 116 are of respectively concave and convex cylindrical form so as to be adapted to the circular form of the magnetized assembly 120, with a residual play which is as small as possible, but is at least twice as great as the mechanical play, so as to avoid any risk of sticking between the sections 121 and the poles 116.

The two magnetizing assemblies 113 provide a high rotational torque, at the same time having a small number of electromagnetic units. For machines of larger size, the number of magnetizing assemblies may be increased so as to increase the torque.

The diametrically opposite electromagnetic units 119 are energized simultaneously so as to apply a couple of equal, parallel and opposite forces, namely 119a with 119d, 119b with 119e, and 119c with 119f (FIG. 24).

As in the previous embodiments, a differential spacing is provided between the electromagnetic units 119 and the magnetic sections 121 of the magnetized assembly 120. More precisely, for a number N of electromagnetic units 119 of the magnetizing assembly 113, there is provided an arrangement of these electromagnetic units and of the magnetic sections 121 of the magnetized assembly 120, such that for N angular spacings b of the electromagnetic units 119 there are (N + 1) angular spacings a of the magnetic sections 121. In addition, the total number of the magnetic sections 121 must be a whole multiple of the number of magnetizing assemblies 113 in order that the latter may work simultaneously, as it was intended.

The differential switching of the electromagnetic units can be ensured by the same means as previously, and will not require any further description.

The arrangement of the magnetized assembly 120 in a ring with the magnetic sections 121 parallel to the axis of rotation X--X, permits of accurate guiding of the magnetized assembly 120 which has a good resistance to the forces of attraction of the poles. In addition, this arrangement is not liable to deformation due to the bending stresses of the crane under load.

The trapezoidal shape given to the magnetic sections 121, the leading edge of which is thus inclined to the vertical, produces a slower variation of the permeance during the entry of such a magnetic section 121 into the air-gap. This reduces the shocks and vibrations which could result from the rectangular shape.

In the case where a still more uniform movement would be necessary, it is even provided to construct magnetic sections 121 having teeth with a profile approximating to that of a sine curve, in such manner that irrespective of the suddenness with which the excitation current is sent into the winding 118, the force of attraction applied to a tooth 121 by a corresponding electromagnetic unit increases progressively.

In the case of industrial applications in which the movement of rotation is slow and continuous (for example for the rotating tables of drilling equipment), the electric switching must be synchronized with the passage of the magnetic sections and it must be controlled in dependence on the speed of rotation. The invention then provides means for varying the relative excitation of an electromagnetic unit with respect to the adjacent unit, in order to enable the operator to bring the moving platform 110 into any desired position with very great accuracy.

FIG. 25 shows one particular form of embodiment of these means. The electromagnetic units 119 are supplied through the intermediary of a group 125 of circular rheostats 126, the number of which is equal to that of the pairs of diametrically-opposite units of the magnetizing assemblies.

More precisely, the windings 118 of the associated units 119a, 119d are supplied in series from the terminal 335 of a direct-current source 336 and are connected to the slider 127a of a circular rheostat 126a, of which the ring winding is connected at one of its extremities to the second terminal 337 of the source 336. The rheostats 126b and 126c are connected in a similar manner.

A knob 128 controls the rotation of the sliders 127 of the three rheostats 126, these three sliders being set at 120.degree. from each other. The current intake is effected at a point on the resistance of the rheostat.

In this particular switching arrangement, the windings 118 of the units 119 are practically always excited, but depending on the position of the sliders 127, the value of the current which passes through each winding is more or less great and this is also true for the force of attraction of the corresponding electromagnetic unit.

The operation is as follows: the sliders 127 being in the position shown in FIG. 25, the units 119b and 119e are excited to a maximum by the slider 127b of the rheostat 126b, whereas the units 119a and 119d, 119c and 119f are feebly excited, since the sliders 127a and 127c are distant from the intake point of the current.

If the knob 128 is turned in the direction P, the resistance of the rheostat 126c is reduced, which increases the current and therefore the force of attraction applied by the units 119c and 119f. On the other hand, the increase of resistance of the rheostats 126a and 126b causes a reduction of the current in the units 119a, 119d on the one hand, and 119b, 119e on the other.

The corresponding variation of the forces of attraction on the magnetic sections 121 drives the platform 110 in the direction P.sub.1. The progressive variation of current in each unit gives a rotation which is also progressive and a uniform movement to the said platform.

By a differential excitation of the windings, it is thus possible to position the moving system with great accuracy, which represents an important advantage for a handling device.

A machine of this kind can be employed whenever the rotation of the driven mechanism is continuous and at relatively-low speed, such as is the case, for example, for the driving table of a petroleum drilling equipment, or for the driving wheels of vehicles. A further field of application is that in which the rotation is intermittent with frequent changes of direction, especially when precise control of the speed or position is essential. This is the case in particular for the rotation tables of certain machine-tools or the platforms or drums of machines for Public Works, handling and industrial treatments (washing machines, rotary dryers, etc.).

In all these cases, the movement is produced directly by the action of the electromagnetic units on the magnetic sections of the magnetized assembly without it being necessary to provide complicated and costly reduction gears at several stages, with their bearings and safety and lubrication systems which are generally required when conventional electric motors are employed. The invention thus permits of the elimination of a large number of parts of the assembly, which is thus moderate in cost and much more reliable.

Another field of application of the invention to rotary motors concerns the construction of small single-phase synchronous motors intended to drive the timing systems of electrical apparatus, clocks, illuminated signs, servo-control systems and the like.

In this embodiment, illustrated by FIGS. 26 to 33, the magnetizied assembly is formed by a disc 130 inset on a rotating shaft 131 between two packing pieces 132. The periphery of the disc 130 comprises a series of magnetic sections formed by teeth 133 alternating with non-magnetic sections 134, these latter being simply obtained by punching-out slots. The profile of the teeth 133 is substantially sinusoidal. The disc 130 is made from a magnetic material with good saturation induction and high resistivity such as ferro-silicon steel sheet. Its very low inertia facilitates instantaneous starting.

The magnetizing assembly is constituted by two diametrically-opposite electromagnetic units 135 which necessitates an odd number of magnetic sections 133, in order that one of the electromagnetic units 135 may be opposite a magnetic section 133 when the other is opposite a non-magnetic section 134. Each electromagnetic unit 135 comprises a U-shaped magnetic circuit 136 made of sintered magnetic metal which is embedded in a groove of a frame 137 of cast non-magnetic material, such as an aluminium-base alloy.

The magnetic circuit 136 is extended by an armature 138 of sintered metal, which is inserted in a cover 139 of a material preferably identical to that of the body 137 on which it is fixed by screws 140. The armature 138 carries a salient pole 142.

The complete magnetic circuit 136 and 138 is interrupted by an air-gap 141 defined by the poles 142, and through which passes the periphery of the disc 130. On the inner limb of the magnetic circuit 136 is mounted an excitation winding 144. A self-lubricating ring 145 of sintered material or of polytetra-fluoro-ethylene ensures the centering and guiding of the disc 130 in the air-gap by means of a shoulder 405 on the shaft 131 and one of the packing pieces 132, so that the residual play of the disc 130 in the air-gap 141 may be equally distributed between the two poles 142.

This assembly of simple and cheap construction is supplied with alternating single-phase current through a simple electronic switching device shown diagrammatically in FIG. 30.

Each winding 144 of the two electromagnetic units 135 is supplied with alternating current from a source 341, but with the interposition of a diode 146, in such manner that the winding of the electromagnetic unit 135a has its diode 146a reversed with respect to the diode 146b of the unit 135b. Upon closure of the switch 147, each of the windings 144 receives an electric impulse corresponding to a half-period of the alternating current, and the attraction of the magnetic sections 133 is produced in synchronism with the alternating current of the supply mains. As the profile of the teeth is substantially sinusoidal, the movement of the rotor is very regular.

In order to ensure the starting-up of the disc 130 in the correct direction, a magnetic asymmetry is created on one of the electromagnetic units 135b by means of slots 148 made on the same side of the pole faces of the magnetic circuit as shown in FIG. 28, or alternatively by an inclination 149 of the whole pole surface, as shown in FIG. 29.

Under these conditions, the lines of flux have a tendency to be concentrated at the narrower extremity of the air-gap, and if the poles of the unit 135b are arranged astride between two teeth 133, the movement of the disc 130 necessarily takes place in the direction R.

There may further be provided, as shown in FIG. 31, an additional starting device comprising a switch 150 with three contact studs 150a, 150b, 150c. The moving contact 342 can simultaneously connect two of these studs, the connection of which is as follows: 150c: stop -- 150a: winding of the electromagnetic unit 135a alone excited -- 150b: both windings excited.

When the contact 342 connects the single contact stud 150a, the unit 135a is excited, attracts the nearest magnetic section 133 and brings it into its air-gap.

When the contact studs 150a, 150b are connected, the arrangement corresponds to that of FIG. 30 and ensures operation at full speed, as above. This simple electrical system improves the starting-up of the disc 130.

It is observed that at each period, a magnetic section 133 comes into the air-gap 141 of the electromagnetic units 135 and the angular speed in number of revolutions per second of the disc 130 is therefore equal to the ratio of the frequency of the supply mains to the number of sections 133 carried by the disc 130.

Thus if there is a large number of magnetic sections on the disc, the latter rotates at a relatively-slow speed, which is advantageous in the case of cyclic timing devices and avoids the use of reduction gears which are always expensive in these small sizes.

If it is desired to build a motor of this type for a very slow speed, the rotor can be constructed according to the method of execution shown in FIGS. 32 and 33. The magnetized assembly 151 is in this case formed by a disc of magnetic sheet from which there has been uniformly punched out along a circular track, a succession of oblong holes 152 which thus form the non-magnetic sections, the magnetic sections 153 of the magnetized assembly being constituted by the radial strips separating the holes 152.

As shown in FIG. 33, the electromagnetic unit 157 comprises a magnetic circuit formed by a stack of magnetic sheets 154 and non-magnetic sheets 155, and on which is wound the exciting winding 156. The thicknesses of these magnetic sheets 154 or non-magnetic sheets 155 correspond respectively to the width of the magnetic sections 153 and of the holes 152, so that all the magnetic sheets 154 are located opposite the magnetic sections at the same time, as shown in FIG. 33.

The construction of the magnetic circuit may also be effected by sintered magnetic metal with slots on the pole faces, these slots being sufficiently deep to separate the lines of flux into narrow bands facing the magnetic sections of the magnetized assembly.

As previously, the magnetizing assembly comprises two electromagnetic units mounted in such manner that they are displaced with respect to each other by a magnetic section. The supply and the starting of the disc 151 may be effected by following the system of connections of FIGS. 30 or 31.

Each electromagnetic unit thus behaves like a group of magnetic circuits working in phase.

The advantage of this solution is that, for identical inertia and overall size, it comprises a very large number of teeth or magnetic sections, and in consequence it has a very slow speed of rotation, thus dispensing with a reduction gear.

There will now be described with reference to FIGS. 34 and 35 the application of the invention to the construction of motors of much greater power.

This rotary motor running at average speed, can be supplied with direct-current or single-phase alternating current.

The stator 170 carries the magnetizing assembly 171 made-up of magnetic sheets stamped to the shape of a C and stacked so as to form two poles 172 on which are wound the excitation windings 174. The packets of steel sheets are separated by non-magnetic and rigid intermediate packing pieces 173.

Inside the stator 170 is adapted to rotate a rotor 175 forming the magnetized assembly and constituted by a certain number of magnetic sections 180 formed by a stack of stamped magnetic sheets separated by non-magnetic sheets and embedded in a non-magnetic and feebly conductive material 177 which forms the non-magnetic sections. The rotor is keyed on the shaft 178. This latter carries a rotary commutator 181 constituted by a conductive ring 182 comprising radial contact strips 183, the whole being inserted in an insulating block 184. The magnetic and non-magnetic sections form projections which pass into the air-gaps formed between the poles 172 (FIG. 35) of each electromagnetic circuit.

In the example described, the windings 174 are divided into three phases, each comprising four pairs of poles 172. The connections of the windings 174 have been shown on FIG. 34 with a different outline from two supply conductors 185a, 185b connected to a source of direct or single-phase current 343. Each of the phases comprises two adjacent poles and the two diametrically-opposite poles, the windings of which are supplied in series from the conductors 185a, 185b, the connection between the two categories of windings being effected by brushes 186 held in contact with the commutator 181 by springs 192 and with which the strips 183 of the rotary switch 181 come successively into contact.

The motor is closed by two end-plates 187 and 188 supporting the shaft 178 through the intermediary of bearings 189 and 190. On the end-pate 188 are fixed the brush-carriers 191 of non-conductive material, which contain the springs 192. The fixing of the whole system is effected by tie-rods 193 clamping together the end-plates 187, 188 and the stator 170.

In the position shown in FIG. 34, the current circulates through the conductor 185a into the diametrically-opposite windings 174a and 174b, into the brush 186a, into the switch 181, into the brush 186b, into the windings 174c and 174d, diametrically-opposite but adjacent to the preceding. The return of the current is made by the conductor 185b. The poles corresponding to the windings 174a, 174b, 174c and 174d attract the magnetic sections 180a, 180b, 180c and 180d of the rotor 175 which come opposite these poles. This drives the rotor 175 in rotation in the direction S. A slight rotation of the rotor 175, and therefore of the commutator 181 puts the windings 174e and 174f into circuit through the brush 186c which makes contact with a strip 183 of the commutator 181 and interrupts the windings 174a and 174b when the magnetic sections 180a and 180b are opposite the corresponding poles, and so on.

The interposition of non-magnetic sheets between the magnetic sheets of the rotor ensures that the magnetic parts of the rotor become saturated before the magnetic circuits of the stator, thus improving the efficiency and the power/weight ratio.

It will be noted that the diametrically-opposite windings are energized in series, which creates a couple of forces having no action on the bearings, and that a fresh pair of windings 174 is energized before the interruption of the pair which has just fully attracted the magnetic sections.

In order to reverse the rotation of the rotor in the direction T, it is only necessary to shift the brushes 186 through a certain angle so as to bring them into a position such as that shown in broken lines 194 in FIG. 34. This may be effected by rotation of the brush-carriers 191 on the end-plate 188.

The construction of this motor of stacked magnetic sheets and the rotary commutator permit of its direct operation on single-phase alternating current or on direct current. The same means are applicable to the construction of a three-phase machine by connecting the three input and output conductors respectively to the three phases.

This type of motor has a very high starting torque without substantial surge of current, which may be advantageous in the applications where the rotor is held blocked during operation. Contrary to what takes place with a conventional motor, such a blocking is not liable to result in excessive rise of temperature.

The embodiment of FIGS. 36 and 37 relates on the contrary to a rotating motor with high speed and electronic switching.

In this example, the magnetizing assembly 200 comprises three electromagnetic units 201 and forms the stator of the motor. Each electromagnetic unit 201 comprises a magnetic circuit 202 of magnetic sheets cut-out in the shape of a C, on the limbs of which are wound two windings 203 and 204. These units are fixed by bolts 206 on three segmental supports 205, of cast non-magnetic material for example, which comprise widened radial portions 345 clamping the steel sheets of the circuits 202 at the edges of the poles of these circuits, so as to prevent deformation of the sheets by the effect of the forces of attraction.

The magnetized assembly 207 forms the rotor and comprises two magnetic sections 208 and 209, of which the projecting cylindrical faces 208a, 209a pass between the poles of the magnetic circuits. The magnetic sections 208 and 209 are separated by a non-magnetic core 500 which supports these latter and which is mounted on a shaft 210 of non-magnetic material which pivots on the two bearings 211 and 212 of the end-plates 213 and 214, fixed by screws 215 on the segmental supports 205.

On one of the supports 205c is mounted a magnetic detector 216, the point 346 of which is located close to a cylindrical belt 217 of the magnetized assembly 207, and in which are pierced spaced-apart holes 218. The magnetic detector 216 is connected (see FIG. 38) to the input of an amplifier 222. The output of this amplifier is connected to two electronic units 223 and 224 of the monostable multivibrator type with variable and adjustable delay, and mounted in series, of which each output controls, through the intermediary of power amplifiers 225 and 226, an electronic thyristor switch 220, similar to that of FIG. 12, which is connected to each of the winding 201 through a mechanical switch 221 with manual control, enabling the direction of rotation of the rotor to be reversed, for example, by reversing the connections of the windings.

When the motor is rotating, the magnetic detector 216 gives electric signals at the passage of each hole 218 in front of its point 346. These signals are amplified and shaped by the amplifier 222 which delivers electric impulses. These impulses are first retarded by the multivibrator 223, the output impulse of which controls the striking of the thyristors of the electronic switch 220 through the intermediary of the amplifier 225, and are retarded a second time by the multivibrator 224, the output impulse of which controls the blocking of the thyristors of the switch 220 through the intermediary of the amplifier 226.

This rotor has neither windings nor brushes, and can thus rotate at very high speeds of rotation. The electronic switching is very well adapted to high frequencies and permits of easy regulation of the torque and the speed of rotation by the addition of an electronic speed-control device.

The control of the speed may be ensured by an electronic device 228 of the frequency-comparator type, connected on the one hand to the detector 216 and on the other to a manual operation device 227. The device 228 compares the frequency of rotation measured by the detector 216 with a frequency corresponding to the speed set on the control 227. The result of this comparison acts through the intermediary of a coupling stage 229 connected to the multivibrators 223, 224, to modify the phase and the duration of the magnetizing impulses, until the real speed corresponds to that displayed.

It is clear that the invention is not limited to the foregoing embodiments, given simply by way of examples, and that alternative forms of construction may be given to these embodiments. In particular, the means described may be combined in different ways and, for example, the position detector of the magnetized assembly described in connection with a given construction could equally well be employed within the scope of another construction, this remark being also especially valid for the supply and switching systems and for the particular structures of the magnetizing and magnetized assemblies.

Claims

Having described our invention, we claim:

1. A transporter system comprising at least one beam serving as a track, at least one car suspended from and movable along said track and provided with drive means for imparting motion thereto, said drive means comprising a magnetizing assembly and and a magnetized assembly adapted to move one with respect to the other and mounted one on said beam and the other on said car, the magnetizing assembly comprising a plurality of electromagnetic units disposed in line and each said unit comprising one magnetic circuit having two oppositely facing pole faces defining an air gap therebetween and having at least one inductor winding, the magnetized assembly projecting into said air gap in the magnetic field of the magnetizing assembly and comprising a plurality of magnetic sections disposed in line in alternate relation with non-magnetic sections, each said magnetic section comprising at least a pair of oppositely facing surfaces, at least a pair of said section surfaces facing respectively two of the said pole faces of a said magnetic circuit so that the magnetic flux generated by said inductor winding and acting upon said magnetic section enters one of said section surfaces and leaves the opposite surface of said magnetic section, the pitch of said magnetic sections being different from that of the electromagnetic units of said magnetizing assembly, switching means for supplying current pulses to the windings of said electromagnetic units according to a predetermined sequence, each pulse of the sequence being supplied at about the time when one of the magnetic sections reaches the entrance of the corresponding air gap, means for guiding the relative displacement of the said magnetized assembly through the air gaps of said electromagnetic units in a direction crossing the lines of force within said air gaps, the direction of said lines of force being substantially the same in said air gaps and in said magnetic sections of said magnetized assembly, sensing means for detecting a parameter of that assembly which is moving with respect to the other assembly, and means controlled by said sensing means for controlling the current pulses supplied to said windings.

2. A system as claimed in claim 1, said sensing means detecting the position of said moving assembly.

3. A system as claimed in claim 1, said sensing means detecting the speed of said moving assembly.

4. A system as claimed in claim 1, said sensing means detecting the direction of movement of said moving assembly.

5. A system as claimed in claim 1, said controlling means controlling the beginning of the current pulses.

6. A system as claimed in claim 1, said controlling means controlling the end of said current pulses.

7. A system as claimed in claim 6, said means controlling the end of the current pulses effecting the interruption of a current pulse fed to an electromagnetic unit before the corresponding magnetic section reaches a central position in the corresponding air gap.

8. A system as claimed in claim 1, said controlling means controlling the order in which said current pulses are supplied to said windings.

9. A system as claimed in claim 1, the line in which said electromagnetic units are disposed being a straight line.

10. A system as claimed in claim 1, the line in which said electromagnetic units are disposed being a curved line.

11. A system as claimed in claim 1, the amount by which the pitch of said magnetic sections is different from that of the electromagnetic units of said magnetizing assembly being such that the axial length of N pitches of one said assembly is equal to the length of (N+1) pitches of the other assembly, N being a whole number.

12. A system as claimed in claim 1, said guiding means being so arranged that the mechanical play of said magnetized assembly in a direction parallel to the lines of force within the air gaps of said electromagnetic units is substantially less than the value of the residual air gap between the pole faces of said units and the oppositely facing surfaces of the magnetic sections of said magnetized assembly when the latter are in the position of minimum reluctance.

13. A transporter system comprising at least one member serving as a track, at least one member movable along said track and provided with driving means for imparting motion thereto, said driving means comprising a magnetizing assembly and a magnetized assembly, one of said assemblies being carried by one of said members and the other of said assemblies being carried by the other of said members, the magnetizing assembly comprising a plurality of electromagnetic units disposed in line and each said unit comprising one magnetic circuit having two oppositely facing pole faces defining an air gap therebetween and having at least one inductor winding, the magnetized assembly projecting into said air gap in the magnetic field of the magnetizing assembly and comprising a plurality of magnetic sections disposed in line in alternate relation with non-magnetic sections, each said magnetic section comprising at least a pair of oppositely facing surfaces, at least a pair of said section surfaces facing respectively two of the said pole faces of a said magnetic circuit so that the magnetic flux generated by said inductor winding and acting upon said magnetic section enters one of said section surfaces and leaves the opposite surface of said magnetic section, the pitch of said magnetic sections being different from that of the electromagnetic units of said magnetizing assembly, switching means for supplying current pulses to the windings of said electromagnetic units according to a predetermined sequence, each pulse of the sequence being supplied at about the time when one of the magnetic sections reaches the entrance of the corresponding air gap, means for guiding the relative displacement of the said magnetized assembly through the air gaps of said electromagnetic units in a direction crossing the lines of force within said air gaps, the direction of said lines of force being substantially the same in said air gaps and in said magnetic sections of said magnetized assembly, sensing means for detecting a parameter of that assembly which is moving with respect to the other assembly, and means controlled by said sensing means for controlling the current pulses supplied to said windings.

14. A system as claimed in claim 13, said sensing means detecting the position of said moving assembly.

15. A system as claimed in claim 13, said sensing means detecting the speed of said moving assembly.

16. A system as claimed in claim 13, said sensing means detecting the direction of movement of said moving assembly.

17. A system as claimed in claim 13, said controlling means controlling the beginning of the current pulses.

18. A system as claimed in claim 13, said controlling means controlling the end of said current pulses.

19. A system as claimed in claim 18, said means controlling the end of the current pulses effecting the interruption of a current pulse fed to an electromagnetic unit before the corresponding magnetic section reaches a central position in the corresponding air gap.

20. A system as claimed in claim 13, said controlling means controlling the order in which said current pulses are supplied to said windings.

21. A system as claimed in claim 13, the line in which said electromagnetic units are disposed being a straight line.

22. A system as claimed in claim 13, the line in which said electromagnetic units are disposed being a curved line.

23. A system as claimed in claim 13, the amount by which the pitch of said magnetic sections is different from that of the electromagnetic units of said magnetizing assembly being such that the axial length of N pitches of one said assembly is equal to the length of (N+1) pitches of the other assembly, N being a whole number.

24. A system as claimed in claim 13, said guiding means being so arranged that the mechanical play of said magnetized assembly in a direction parallel to the lines of force within the air gaps of said electromagnetic units is substantially less than the value of the residual air gap between the pole faces of said units and the oppositely facing surfaces of the magnetic sections of said magnetized assembly when the latter are in the position of minimum reluctance.

25. A system comprising guide means, means movable on said guide means, drive means for imparting motion to said movable means on said guide means, said motion-imparting means comprising an electromagnetic device producing a mechanical action and comprising a magnetizing assembly and a magnetized assembly adapted to move one with respect to the other, one of said assemblies being carried by said guide means and the other of said assemblies being carried by said movable means, the magnetizing assembly comprising a plurality of electromagnetic units disposed in line and each said unit comprising one magnetic circuit having two oppositely facing pole faces defining an air gap therebetween and having at least one inductor winding, the magnetized assembly projecting into said air gap in the magnetic field of the magnetizing assembly and comprising a plurality of magnetic sections disposed in line in alternate relation with non-magnetic sections, each said magnetic section comprising at least a pair of oppositely facing surfaces, at least a pair of said section surfaces facing respectively two of the said pole faces of a said magnetic circuit so that the magnetic flux generated by said inductor winding and acting upon said magnetic section enters one of said section surfaces and leaves the opposite surface of said magnetic section, the pitch of said magnetic sections being different from that of the electromagnetic units of said magnetizing assembly, switching means for supplying current pulses to the windings of said electromagnetic units according to a predetermined sequence, each pulse of the sequence being supplied at about the time when one of the magnetic sections reaches the entrance of the corresponding air gap, said guide means guiding the relative displacement of the said magnetized assembly through the air gaps of said electromagnetic units in a direction crossing the lines of force within said air gaps, the direction of said lines of force being substantially the same in said air gaps and in said magnetic sections of said magnetized assembly, sensing means for detecting a parameter of that assembly which is moving with respect to the other assembly, and means controlled by said sensing means for controlling the current pulses supplied to said windings.

26. A system as claimed in claim 25, said sensing means detecting the position of said moving assembly.

27. A system as claimed in claim 25, said sensing means detecting the speed of said moving assembly.

28. A system as claimed in claim 25, said sensing means detecting the direction of movement of said moving assembly.

29. A system as claimed in claim 25, said controlling means controlling the beginning of the current pulses.

30. A system as claimed in claim 25, said controlling means controlling the end of said current pulses.

31. A system as claimed in claim 30, said means controlling the end of the current pulses effecting the interruption of a current pulse fed to an electromagnetic unit before the corresponding magnetic section reaches a central position in the corresponding air gap.

32. A system as claimed in claim 25, said controlling means controlling the order in which said current pulses are supplied to said windings.

33. A system as claimed in claim 23, in which the residual air gap between the pole faces of said electromagnetic units and the oppositely facing surfaces of the magnetic sections of said magnetized assembly is at least equal to twice the maximum mechanical play of said magnetized assembly in a direction parallel to the lines of force within the air gaps of said electromagnetic units.

34. A system as claimed in claim 25, in which the section of passage of the magnetic flux in the magnetic circuits of said electromagnetic units and in the magnetic sections of said magnetized assembly is determined in such a way that said magnetic sections are saturated before said magnetic circuits reach saturation.

35. A system as claimed in claim 25, in which the moving assembly is mounted below the fixed assembly and is suspended by magnetic attraction, retention means being further provided for preventing said moving assembly from falling in case of interruption of current supply to said magnetized assembly.

36. A system as claimed in claim 25, in which said electromagnetic units of the magnetizing assembly are connected in parallel to a single source of electrical energy through means for differential regulation of the voltage across the terminals of the windings of said electromagnetic units, said means comprising synchronized sliders and means for controlling the displacement of said sliders in dependence of the desired position of the moving assembly.

37. A system as claimed in claim 25, the line in which said electromagnetic units are disposed being a straight line.

38. A system as claimed in claim 25, the line in which said electromagnetic units are disposed being a curved line.

39. A system as claimed in claim 25, the amount by which the pitch of said magnetic sections is different from that of the electromagnetic units of said magnetizing assembly being such that the axial length of N pitches of one said assembly is equal to the length of (N+1) pitches of the other assembly, N being a whole number.

40. A system as claimed in claim 25, said guiding means being so arranged that the mechanical play of said magnetized assembly in a direction parallel to the lines of force within the air gaps of said electromagnetic units is substantially less than the value of the residual air gap between the pole faces of said units and the oppositely facing surfaces of the magnetic sections of said magnetized assembly when the latter are in the position of minimum reluctance.