US3587797A

US3587797A - Dual speed clutches with brake

Info

Publication number: US3587797A
Application number: US824454A
Authority: US
Inventors: Laszlo Szekely; Claude Pigache; Michel Lafaye
Original assignee: Engins Matra SA
Current assignee: Engins Matra SA
Priority date: 1968-05-24
Filing date: 1969-05-14
Publication date: 1971-06-28
Anticipated expiration: 1988-06-28
Also published as: DE6920850U; DE1926398B2; LU58454A1; FR1577456A; ES367654A1; NL142226B; DE1926398A1; NL6907942A; DE1926398C3; GB1230941A; BE731794A

Abstract

A DEVICE FOR DRIVING AND STOPPING A MACHINE, MORE PARTICULARLY A SEWING MACHINE. BETWEEN AND ELECTRIC DRIVING MOTOR AND AN OUTPUT PULLEY OR THE LIKE CONNECTED TO THE MACHINE, THERE IS PROVIDED A SPEED-REDUCING TRAIN AND AN ELECTROMAGNETIC-CLUTCHING AND -BRAKING DEVICE. THE LATTER COMPRISES TWO COAXIAL COILS, ONE OF WHICH CONTROLS THE CLUTCHING BY CAUSING, UPON EXICITATION, THE MOVEMENT OF AN ASSEMBLY INTEGRAL WITH A CLUTCH-COUPLING MEMBER AND THE OTHER ONE OF WHICH CONTROL THE BRAKING BY APPLICATION OF A FRACTION PACKING HOUSED IN A SUPPORT OF SAID ELECTROMAGNETIC DEVICE AGAINST A PLATE INTEGRAL WITH THE MOVEABLE ASSEMBLY.

Description

United States Patent Inventors DUAL SPEED CLUTCHES WITH BRAKE 9 Claims, 11 Drawing Figs.

U.S. Cl 192/18, 188/161, 192/9, 192/48.2, 112/219, 317/157, 192/142 lnt.Cl Fl6d 67/06 Field of Search ..192/9, 12.2, 18.2

Primary Examiner- Benjamin W. Wyche Attorney-limestF. Marmorek ABSTRACT: A device for driving and stopping a machine, more particularly a sewing machine. Between an electric driving motor and an output pulley or the like connected to the machine, there is provided a speed-reducing train and an electromagnetic-clutching and -braking device. The latter comprises two coaxial coils, one of which controls the clutching by causing, upon excitation, the movement of an assembly integral with a clutch-coupling member and the other one of which controls the braking by application of a friction packing housed in a support of said electromagnetic device against a plate integral with the movable assembly.

PATENIEU JUN28 I971.

3587.797 sum 1 0r 6 F E. mm on mm K2 2 a PATENTEU JUN28 19m SHEET 2 OF 6 PATENTED JUN28 197i SHEET U, [1F 6 v/zi 227 n 1 WW DUAL SPEED CLUTCIIES WITII BRAKE FIELD OF THE INVENTION The invention relates to a driving and stopping device of a machine, more especially of a sewing machine comprising, between an electric driving motor and an output pulley or the like connected to the machine, a speed-reducing train and an electromagnetic-clutching and braking device.

SUMMARY OF THE INVENTION It is an object of the invention to supply such a device which is of simple construction, of reliable function and practically devoid of breakdowns.

According to the invention, this object is achieved in that the electromagnetic device comprises, in a sliding support, two coaxial coils, one of which controls the uncoupling by sliding displacement of a movable assembly integral with a coupling member and the other of which brings about the braking by application of a friction packing, housed in said support, against a plate integral with said assembly.

In one embodiment, the device comprises means for ensuring the stoppage of the machine in a predetermined position.

Advantageously, these means supply a current impulse at each rotation of a member forming part of the machine, said impulse having a width the wider as the member rotates more slowly and being used for the control of an electronic threshold member controlling the putting into action of the braking. When used on a sewing machine, the device according to the invention permits driving at all the speed conditions desired from a maximum speed down to a minimum speed and, inversely, also permits the stoppage of the machine to be obtained in a very short time, the needle of the sewing machine being for the effective stoppage always in the same position, for example the lower position.

The device according to the invention also permits, from the last-mentioned position, the machine to be conducted automatically into another predetermined position, for example that which corresponds to the upper position of the needle.

The device in accordance with the invention therefore permits, in conjunction with a sewing machine, the work of sewing to be facilitated and speeded up.

The invention will be understood from the description which follows, given by way of example, and with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial view in longitudinal section and with parts broken away of a device in accordance with the invention, for a first embodiment;

FIG. 2 is a partial view in longitudinal section'and with parts broken away, but for another part of the device;

FIG. 3 is a view, partly in longitudinal section, partly in elevation with parts broken away, on a smaller scale and for a modification;

FIG. 4 is a longitudinal sectional view of a device provided for the automatic performance of the operation of a machine provided with a driving device in accordance with one or other of the preceding embodiments;

FIG.-5 is a sectional view along line 5-5 in FIG. 4;

FIG. 6 is an electrical diagram;

FIGS. 7 to 11 are diagrams.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference is first made to FIGS. 1 and 2. The device comprises an electric motor 10, which can be of the conventional type having a single speed, for example of the order of 3,000 r.p.m., as usual. Keyed on the shaft 11 of the electric motor, near the outlet of the case or housing 12 of the motor proper, is a wheel 13 of small diameter, having a toothed rim 14, with which cooperates a notched belt 15 which also cooperates with a wheel 16 of large diameter, having a toothed rim 17. The wheel 16 is integral, by its hub 18, with an intermediate shaft 19, which rests, by means of a collar 20, in a bearing 21 forming part of a first case body 22 of the device. Keyed on the intermediate shaft 19 there is, in addition, a second wheel 23, of small diameter, having a toothed rim, with which cooperates a notched belt 25 which also cooperates with the toothed rim 26 of a wheel 27 of large diameter. The wheel 27 rests, for rotation, by a ball bearing 28, on a boss 29 forming part of the second case body 30.

Keyed on the shaft 11, by its hub 31, is a flywheel 32, which thus rotates at the speed of the electric motor. The shaft 11 is supported by an annular boss 33 of the case 22 with insertion of a ball bearing 34. A collar 35 is interposed between said bearing and the wheel 13 and a washer 36 ensures the holding of the flywheel 32. The circlips" 37 and 38 locate the ball bearing 34.

In the boss 29 is slidingly mounted, with interposition of a sleeve from which there projects a guiding finger 51, a socket 52 having a groove 53 cooperating with the finger 51. The socket 52 forms part of a sliding assembly 54 which comprises a rotary shaft 55 whose axis is aligned with that of the shaft 11 of the electric motor, the shaft 55 being mounted for rotation in the socket 52 with interposition of a ball bearing 56. The bearing 56 is framed by a thrust part 57 on the one hand and a shoulder 58 of the shaft 55 on the other hand. Fixed by means of screws 60 on a shoulder 59 of larger diameter is a plate 61 which carries, on its

opposite faces

62 and 63,

friction packing

64 and 65 respectively.

The thrust part 57 has, besides its front face 66 cooperating with the ball bearing 56, a flange 67 with which is integral an annular plate 68. A cheek 69 integral with the case body 30 carries by their feet pins 70, for example three in number, which are housed in bores 71 of a coil support or yoke 72. The latter is of a general disc shape, and has an external annular housing 73 and an internal annular housing 74 which respectively receive a first annular coil 75 and a second annular coil 76. The external front face 77 of the yoke 72 is immediately facing the internal front face 79 of the plate 68. Springs 72a, housed in bores of the yoke 72 and resting on the other hand on the cheek 69, pull the coil support 72 away from said check.

In the central bore 79 of the body 72 passes freely a tubular strut 80 surrounding the shaft 55 and integral with the latter. Said strut abuts at its external end against the thrust part 57 and at its internal end against a ball bearing 81 interposed between the shaft 55 and a sleeve 82. The latter has a port 83 in which there is engaged a swivel 84 which forms the end of a lever 85 mounted for rotation about a spindle 86 carried by the frame of the machine; the lever 85 has a branch 87 terminating in the swivel 84 and which is continued by a branch 88 substantially at a right angle, the end of which has a hole 89 where can engage a chain or the like solicited by a pedal, which, when one presses on it, exerts a pull in the direction marked by thearrow f. The arm 88 comprises a tubular body 103' inside which there is housed an arm 105 mounted for articulation about a spindle 106 which is carried by the lever, in its connecting zone between the

branches

87 and 88. It is on said arm 105 that there is provided the hole 89 of the chain. On arm 105, there is exerted, by means ofa seat 106 which it possesses, the action of a spring 107, resting on the other hand on the interior face of the body 103' and which thus tends to urge the control button 108 of a microswitch 109 carried by the arm 105 against a fixed stop 110 of adjustable position, carried by body 103'.

An annular cap 90 is integral with the sleeve 82 through screws 78 and its internal rim 91 butts against the ball bearing 81; its external rim 92 can slide against a rim 93 of the cover 94 of the case of the device comprising a tubular projection 94' in which the sleeve 82 is mounted slidingly. The cover 94 has bores 95 in which are housed spiral springs 96 which are braced on the other hand against the cap 90. One or more screws 97, mounted in tapped holes of the cover 94, can cooperate with the internal face 98 of the body 72.

Means are provided to feed the coil 75 and the coil 76 with electrical current.

The operation is as follows:

In the condition of rest, the sliding assembly 54 is in its right-hand end position, as shown in FIG. 1 and FIG. 2, under the action of the springs 96. In this position, the plate 61 is in its position for which the packing 65 can cooperate with the wheel 27. When, through bearing on the pedal, one exerts a slight pull on the arm 105, this latter pivots about the spindle 106 against the action of the spring 107; the projection of the button 108 of the microswitch 109 interrupts the current in the coil 76 so that the packing 102, carried by a packing carrier 103, is moved away from the annular plate 68, ensuring the debraking in rotation of the sliding assembly 54. The packing 65 of the plate 61 cooperates with the wheel 27, driven by the electric motor at a comparatively low speed, by virtue of the double reduction introduced on the one hand by the pair of wheels 13- 16 and on the other hand by the pair of wheels 23- -27. The machine is driven at a low speed, by means of the pulley 100 keyed on the shaft 55 with which the plate 61 is integral.

When the pull exerted on the arm 105 becomes stronger, it is the whole of the lever 85 which pivots about the axis 86; the sliding assembly 54, comprising the sleeve 82, the cap 90, the ball bearing 81, the tubular strut 80, the stop piece 57, the ball bearing 56, the socket 52, the plate 61 and the shaft 55, is driven from right to left by the action of the swivel 84, exerting on the sleeve 82 against the action of the springs 96, the packing 65 draws away from the wheel 27 driven at a low speed and the packing 64 cooperates with the internal front face 101 of the flywheel 32 the latter, keyed directly on the shaft 11 of the electric motor, rotates at the high speed. Fol lowing the more or less deep sinking of the pedal, the pressure exerted by the packing 64 against the front face 101 is more or less great for a highly sunken position of the pedal, the pressure is sufficient for the plate 61 to rotate at the speed of the flywheel 32; the pulley 100 is then driven at the maximum high speed; if the pedal is less sunken, there is produced a sliding between the packing 64 and the face 101 of the flywheel 32; the speed of the pulley 100, as well as that of the machine, diminish. One can thus regulate in a progressive manner the speed of the machine between the maximum high speed and the low speed.

To stop the machine, the operator ceases to exert pressure on the pedal, so that the machine is driven at a low speed, and the braking drive is triggered by feeding the coils 75 and 76. Through the feed of coil 75, the bobbin support 72, initially in contact by its face 98 with the ends of the screws 97, under the action of the springs 72a, is attracted magnetically by the cheek 69, so that there is produced, by cooperation of the said support 72 with the plate 68, a sliding of the sliding assembly 54 from the right towards the left (in FIG. 1), which draws the packing 65 away from the wheel 27 and thus ensures the uncoupling of the shaft 55 and of the members rotating with it with regard to the driving device. The abutment of the coil support 72 against the cheek 69 interrupts the slide of the assembly 54 before the packing 64 of the plate 61 can cooperate with the flywheel 32.

The feed of the coil 76 creates a magnetic field which ensures an application under strong pressure of a packing 102, carried by a packing carrier 103 closing the annular housing 74 of the nonrotary coil support 72 in which is housed the winding 76, against the plate 68 of the rotating assembly 54, so that there results a strong braking of the latter, therefore of the pulley 100 and of the members connected to the same.

The application force of the packing 102 against the plate 68, which gives rise to the braking, has a predetermined value resulting both from the characteristics of the coil 76 and from those of the springs 96 and the braking action is exerted on a rotating assembly disconnected from the motor, so that when it rotates at a predetermined speed, the stoppage is obtained in a well-determined position in relation to that in which the stopping process of the machine has been initiated.

When the machine is stopped, if one interrupts the feed of the coils 75 and 76, one can resume the normal operation of the machine, either at a low speed, or at a high speed.

Reference is now made to FIG. 3, relating to a modification. In this modification, the coil support or yoke comprises an external annular housing 121 whose opening is turned towards the internal side of the machine (opposed to that of the electric motor) and which receives the declutching coil 122; the second internal annular housing 123 has its orifice turned towards the external side of the machine; it receives the braking coil 124. In the coil support 120 are also provided bores 125 in which are housed springs 126 resting on the one hand on a cheek 127 ofthe case of the machine. The coil 122 is opposite a ring 128 made of magnetic material fixed by screws 129 on the cover 94.

The functioning of this modification is identical to that of the embodiment previously described as regards obtaining the various speeds of the machine in the conditions of the high speeds and also that of the low speed. However, during operation the coil 122 is fed permanently, so that the magnetic actions developed by said coil apply the coil support 120 against the ring of magnetic material 128 as shown in FIG. 3, against the action of the springs 126. When the sleeve 82 is not actuated by the swivel joint 84, i.e. for the high position of the pedal, the springs 96, exerting their action on the cap 92, keep the sliding assembly 54 in the right-hand end position, i.e. for which the packing 65 cooperates with the wheel 27; this is the low speed of the machine. When the sleeve 82 is actuated by means of the lever 85 in the direction of the arrow marked in the FIG., i.e. from right to left, then it is the packing 64 of the plate 61 which cooperates with the face 101 of the inertia flywheel 32 and one obtains the various high speeds in accordance with the degree of driving-in of the pedal, the maximum high speed being obtained when the plate 61 rotates at the speed of the flywheel 32. Both for the high speeds and for the low speed, the contact between the plate 68 of the sliding and rotating assembly 54 and the coil support 120 is not established.

For the braking, which is caused solely when the machine is in the low speed condition, i.e. as shown in FIG. 3, the feeding current of the coil 122 is interrupted. The magnetic action which was exerted by the coil 122 disappearing, the springs 126 urge the coil support 120 from right to left into abutment of the external front face 129 of the coil support against the bearing face 130 of the cheek 131. In the course of this movement, the support 120 has, by its shoulder 132, brought about the driving in the same direction, by cooperation with the plate 68, of the sliding and rotating assembly 54, which draws the packing 65 away from the wheel 27; the limitation of the movement gives the assurance that the packing 64 remains at a distance from the inertia flywheel 32; the sliding and rotating assembly 54 is therefore disconnected from the motor. For the braking also, the feed of the coil 124 is established and the magnetic action which it develops applies the fixed support 120 under pressure against the plate 68, with interposition of the friction packing 102, so that one effects the braking in the same conditions as for the embodiment previously described.

In this modification, a current breakdown, by interrupting the feed of the coil 122, automatically brings the machine into its declutched condition. The result is, if the machine is in the course of working, a more rapid stoppage of the latter, the in ertia of the flywheel and of the electric motor then being without any influence.

In this modification, likewise, if a current breakdown occurs when, the machine being at a standstill, one is effecting some maneuver on this latter which obliges the operator to put his fingers into contact with a part of the machine, the machine stays at a standstill, even if the motor is rotating at the moment of the breakdown, so that this latter has no annoying consequence.

Reference is now made to FIGS. 4 and 5, relating to a device for the automatic performance of an operation process of a machine, more especially a sewing machine provided with the driving device as described.

This device comprises a rotor 200 and a stator 201. The rotor 200 is keyed on a shaft actuated by the general movement of the machine, for example the main shaft 202 of the sewing machine. To this end, the rotor comprises a dish 203 slipped on said shaft, secured to the shaft by screws 204 traversing the dish. The dish 203 is followed by a tubular extension 205, which serves for revolubly mounting the rotor on the stator by means of a ball bearing 206. The stator 291 has the general shape of an annular disc 207, with an internal rim 208, integral with the fixed cage of the ball bearing 206, and an external rim 209, on which is placed a protective cap 210. The stator 201 is extended by a tail 223, which passes between the

resilient branches

224 and 225 of a clip, thus enabling to angularly adjust the position of the stator about the axis of rotation 226 of shaft 202.

The rotor 202 also comprises a hub 211, integral with the dish 203 by a screwing of the tail 212 of the hub in the tubular projection 205. The hub has a rim 213, presenting two parallel

elongated housings

214 and 215, diametrically opposed and perpendicular to their common diameter, one of which receives a magnetized rectilinear bar 216 and the other one of which receives a bar 217, not magnetized, but balancing the bar 216.

On the stator disc 207, fixed on the edge of the internal rim 208, is placed a first switch support 218 and a second switch support 219, said supports being mounted so as to be able to be angularly adjusted one with regard to the other, by means of a circular slide 220 and immobilized by

screws

221 and 222. The support 218 and the support 219 carry magnetosensitive electrical switches, 227 and 228 respectively, at a distance from the axis 226 which is substantially that of the

bars

216 and 217.

The magnetosensitive switches 227 and 228 are advantageously flexible blade switches of a known type, respectively lLS,, 1LS (HO. 6), the contacts of which are shown respectively at 229230 and 231-232, said contacts cooperating with one another when the switch is placed in a magnetic field and being on the contrary separated from one another by the elasticity effect of the blades, respectively 233- -234 and 235-236, in the absence of a magnetic field. An electric control source 237 has its negative pole 258 earthed and its other pole 239 is connected by a conductor 240, on which there is a switch 1,, to the input A of a circuit 242. The switch l is, for example, controlled from the lever 85, so as to be closed only when the lever is in the position shown in FIG. 1, i.e. when the operator is not pressing on the pedal, and is open for as long as the pedal is depressed, even slightly.

On the conductor 243 of the circuit 242 connected to the input A is provided a switch 1 which, according to its position, puts the conductor 243 into electrical relation with a first conductor 244 or a second conductor 245. The conductor 244 is connected to an input 246 of the switch lLS,, whose output 247 is connected, by a conductor 248, to the output D of the circuit 242. A branch 249 of the conductor 244 is connected to a second output B of the circuit 242, connected to the anode 250 of a controlled diode T, the gate 251 of which is connected to the common point 252 of two resistances R and R interposed between the output D and earth. A condenser C has its plate 253 connected to the point 252 and its other plate 254 connected to earth. The cathode 255 of the controlled diode T is connected to the winding 256 ofa relay RY, whose armature 257, when the relay is excited, cooperates with a contact 258 to close a feed circuit of the winding controlling the braking, which is the winding 76 in the first embodiment and the winding 124 in the second.

The mounting of the second blade switch [LS is similar to that of the first, but a switch I, is inserted between the terminal 259 of said switch and the conductor 245. The moving member 260 of switch I, cooperates with the

contacts

261 and 262, to effect the feed of the switch lLS only when the relay RY is not fed. The terminal 259 is connected to the output B by a branch 263 which comprises a diode D An autofeed circuit 264 is inserted between the conductor 243 and the terminal 259 and comprises a switch 1 having a moving member 265 and fixed

contacts

266 and 267.

The operation is as follows:

For as long as the pedal is depressed, the machine is at its condition of high speed, its speed being at the maximum that for which the pulley rotates at the speed of the inertia flywheel 32, and being able to adopt lower values if, as a function of the pressure exerted on the pedal, the application force of the packing 64 against the inertia flywheel permits slip between the two members. For as long as the pedal is not returned to its high position, by means of resilient means which are not shown, the switch'l is open, so that the controlling device ofthe braking cannot be fed. When the pedal is in its top position, the switch I is closed, so that the controlling device of the braking can be fed by the source 237.

The device according to the invention is such that, in the course of the decreasing speed of the machine from a high speed, the braking is effectively actuated only when the speed of the machine reaches, when decreasing, a predetermined value, which is advantageously that of the low speed, i.e. that at which the machine rotates when the clutch between the packing 65 and the wheel 67 is effective.

The diagram of FIG. 7 shows the values of the potential at the output D as a function of the time for high speeds of the machine, the width of the rectangular pulses 268 being comparatively very slight.

The diagram of FIG. 8 is representative of the value of the potential of the gate 251, which is that of the plate 253 of the condenser C. The maximum value 269 of said potential is lower than the triggering tension of the controlled diode T, shown by the line U of the diagram.

As the machine slows down, the width of the rectangular pulses 268 increases and the maximum value of the potential of the gate 251 increases, as shown by the diagrams of FIGS. 9 and 10. When this maximum value reaches the value U the diode T suddenly becomes conductive. The potential of the gate 251 then varies as shown in FIG. 11.

Upon the triggering of the controlled diode T, the relay RY, which was not traversed by any current, becomes fed by connection of its winding 256 to the source 237, by means of a circuit which comprises: the controlled diode T, the conductor 270 as far as the output B, the conductor 249, the conductor 244, the switch 1 the conductor 243, the switch 1,, as far as the pole 239 of the source 237. The pedal not being sunk in, the machine is disconnected from the electric motor; the rotating mass has a very determined inertia. The triggering of diode T is obtained when the magnetized bar 216 passes in front of the switch 1LS,, therefore for a well determined angular position of the rotor, i.e. of the rotating assembly which then has exactly the predetermined angular speed. The kinetic energy of the rotating mass thus has a predetermined value so that, by application of the determined braking force resulting from the excitation of the winding 76 or of the winding 124, one ends up with the stoppage for a constant angular position of the machine, which can be a predetermined position for the needle of the sewing machine, for example the bottom position or the top position. An initial adjustment can be obtained by angular shifting of the stator about the axis 226.

When the moving member 271 of the switch l cooperates with the contact 272, it is the switch ILS which is operative and the stoppage takes place, for example for the bottom position of the needle, by the process which has been defined above.

When, on the other hand, the moving member 271 cooperates with the other fixed contact 273, the switch 1LS,, is inoperative and, on the other hand, it is the switch lLS which becomes operative. The stoppage takes place in the angular position determined by the location of said switch 1LS The angular shifting of the first position of stoppage and of the second position of stoppage can be modified initially at will, by displacing the first stator support 218 with regard to the second support 219.

The passage of the moving member 271 from its position of cooperation with the contact 272 to its position of cooperation with the contact 273 can take place by pressing on a special button on the machine. There is provided for example that, without any load, it is the contact 272 which is operative,

so that upon the braking the machine stops with its needle in the lower position. If, simultaneously with letting go of the pedal, the operator presses the button making the contact 273 operative, then, upon the braking, the machine stops with its needle in the upper position.

One can also obtain the storage of the machine with its needle in the bottom position, then, by a subsequent action, make it pass to the upper position.

We claim:

1. A driving and stopping device of a machine, particularly a sewing machine comprising, between an electric driving motor and an output pulley or the like connected to the machine, a speed reducing train and an electromagnetic clutch and brake device having a longitudinally sliding support, two coaxial coils means in said support, a slidingly movable assembly integral with the coupling member of said clutch device and adapted to be slidingly displaced upon excitation of one said coil means, and a friction packing, housed in said support, adapted to be applied against a plate integral with said assembly upon excitation of said other coil means for the braking of the machine.

2. A device as claimed in claim I, wherein the excitation of the electromagnetic device results in the attraction of the coil means support by a fixed check of the housing of the device, the limitation of the sliding movement of said support being obtained by abutment of the same against said cheek.

3. A device as claimed in claim 2, further comprising elastic means urging said support away from said cheek and stop means comprising screws housed in a cover of the housing for limiting the action of said elastic means.

4. A device as claimed in claim 2, further comprising spring means housed in the device housing urging said sliding assembly towards its position in which the coupling member cooperates with the output wheel of the speed reducing train, for the drive at low speed.

5. A device as claimed in claim 4, further comprising, for the drive at high speed, a control lever, connected to a pedal or the like, to displace the sliding assembly against the action of said spring means.

6. A device as claimed in claim 1, further comprising means supplying a current pulse at each revolution of a member forming a part of the machine, said pulse having a width all the greater as said member turns more slowly and electronic threshold means controlled by said pulse for initiating the braking action in view of stopping the machine in a predetermined position.

7. A device as claimed in claim 6, wherein said rotating member is a disc integral with the main shaft of the machine, said disc carrying a magnetized bar which cooperates with a flexible blades switch to supply said current pulse.

8. A device as claimed in claim 7, wherein said switch is carried by a stator of adjustable position about the axis of the shaft ofthe machine.

9. A device as claimed in claim 7, wherein said stator carries several switches having flexible blades separately operative in view of controlling the stoppage of the machine in one of several predetermined positions.