GB2135345A

GB2135345A - Motor-driven sewing machine

Info

Publication number: GB2135345A
Application number: GB08320138A
Authority: GB
Inventors: Hiroshi Kumatani
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1981-11-30
Filing date: 1982-11-29
Publication date: 1984-08-30
Also published as: GB8320138D0; KR860000399B1; DE3249227T1; GB2135345B; WO1983001967A1; KR840002477A

Abstract

Motor-driven sewing machine which rotatably drives a sewing shaft (11) by a motor (14) so as to drive a sewing needle (1) reciprocatingly. In a sewing machine having the sewing shaft (11) driving the needle (1), a sewing frame (10) rotatably journaling the shaft (11) and the motor (14) driving the shaft (11), the rotor (40) of the motor is mounted on the shaft (11) and the stator (38) of the motor is mounted in the frame (10). Thus, the parts such as a belt or pulleys which have previously been necessary to transmit power between the motor (14) and the shaft (11) at the side of the frame (10) can be omitted, the structure of the entire machine can be simplified and the cost of the machine can be reduced.

Description

SPECIFICATION Electric sewing machine This invention relates to electric sewing machines, and more particularlyto an electric sewing machine in which a sewing shaft for reciprocating a sewing needle is driven by an electric motor.

In general, an electric sewing machine comprises: a sewing mechanism including a sewing arm shaft for reciprocating a sewing needle and a sewing machine frame pivotallysupporting the arm shaft; an electric motorfor driving the sewing mechanism; and a position detectorfor detecting the position of the sewing needle'. The rotation output ofthe output shaft which is coupled directly orthroug h a clutch to the shaft of the motor istransmitted through a motor's pulley, a transmission belt and a sewing machine's pulley to the sewing arm shaft. In the case where the motor is an induction motor, it has no braking effect, and therefore an electromagnetic brake is provided to brake the sewing arm shaft.Furthermore, control means for controlling the brake and the motor according to the detection output ofthe aforementioned position detector, so thatthesewing needle can be stopped at predetermined positions. The motor and the brake means are controlled through control means by switch means. The switch means is for instance a foot switch.

In the above-described conventional electric sewing machine, the sewing mechanism and the motor are separately provided. The motor is an independent component which is made up of a frame, stator, shaft and rotor, and is coupled to the sewing mechanism through coupling means such as the above-described two pulleys and belt or a coupling.Accordingly, in a conventional electric sewing machine ofthis type, the ratio ofthe number of parts required for coupling the motorto the sewing mechanism to the remaining parts ofthe sewing machine is relatively large, which makes it rather difficult to simplify the construction of the sewing machine, to make the sewing machine compact and to reducethe manufacturing cost The fact itself thatthe sewing mechanism and the motor are separately provided is not always reason ableforsimplifyingtheconstruction ofthesewing machine, making the sewing machine compact and reducing the manufacturing cost.

An electric:sewing machine of thins type needs position detecting means in order to control the stop position of the sewing needle. In the conventional electric sewing machine, the position detecting means is provided on the coupling unit between the motor and the sewing mechanism. Accordingly, the coupling unit is intricate.

In view ofthe foregoing, an object of this invention is to providean electric sewing machine in which the numberofpartssuch aspulleys,a beltand a coupling required forcoupling the motor to the sewing mechanism is reduced, and the sewing mechanism and the motor are considerably simple in construction and IQW in manufacturing cost.

The foregoing object of the invention has been achieved by the provision of an electric sewing motor comprising a sewing shaft for reciprocating a sewing needle, a frame pivotally supporting the sewing shaft and an electric motor for driving the sewing shaft, in which, according to the invention,the rotor ofthe motor is mounted on the sewing shaft and the stator of the motor is mounted on theframe.

Fig. lisa diagram outlining an electric sewing machine according to this invention. Fig. 2 is a diagram showing the entire arrangement of one preferred embodimentofthe invention. Fig.3 is an explanatory diagram showing the detailed arrangement of a pedal detecting circuit in Fig. 2. Fig. 4 is an explanatory diagram showing the detailed arrangement of a sewing machine control circuit in Fig. 2. Fig.

5 is an explanatory diagram showing the detailed arrangement of a low speed detecting circuit in Fig. 4.

Fig. 6 is an explanatory diagram showing waveforms atvarious points in the low speed detecting circuit in Fig. 5. Fig. 7 isan explanatory diagram showing a motor speed control circuit in Fig. 2 in detail. Fig. 8 is an explanatory diagram showing relations between various waveforms and speeds of rotation in a fixed position stop device in the sewing machine. Fig. 9 is a diagram showing the entire arrangement of another preferred embodiment of the invention. Fig. loins an explanatory diagram showing a motor speed control circuit in Fig. 9 in detail.

Priorto providing a description of preferred embodiments ofthis invention, the entire arrange mentofan electric sewing machine according to the invention will be described.

Fig. lisa diagram outlining the entire arrangement ofthe electric sewing machine according to the invention. The sewing machine comprises: a sewing mechanism having an arm shaft 11 for reciprocating a sewing needle 1 and a sewing machine frame 10 pivotally supporting the arm shaft 11; an induction motor 14; position detecting means, namely, a position detector 24 for detecting the position of the sewing needle; and braking means, namely, an electromagnetic brake 18. The motor 14 has no independent frame. Therefore, the stator 38 is mounted on the frame 10 of the sewing mechanism.

On the other hand, the rotor40 and the position detector 24 are mounted directly on the arm shaft 11 on the side ofthe sewing mechanism. Accordingly, the motor 14 has no independent shaft; that is, it uses the arm shaft 1 as its shaft. The motorl4andthe position detector 24 are mounted on the arm shaft 11 as described above. In addition, the electromagnetic brake 18 is also mounted on the arm shaft 11.

Accordingly, almostall the parts such as pulleys and transmission belts for coupling the motor 1 4to the sewing mechanism can be eliminated, which makes it possible to considerably simplify the construction of the electric sewing machine and therefore to decrease the manufacturing cost. Furthermore, the motor 14 itselfisgreatlysimplified in construction, when compared with a conventional electric sewing motor in which the motor is provided independently. Since the position detector 24, the electromagnetic brake 18, etc. are collectively mounted on the arm shaft 11,the numberof partsformounting them on the shaft and the time required for doing so are greatly reduced, which makes it possible to provide a compact electric sewing machine and to further decrease the manufac turing cost.In Fig. 1, reference numeral 12 designates control means, 28 switch means.

The embodiment of the invention will be described in detail. In Figs. 2through 8, reference numeral 10 designates a sewing machine frame, 14 an AC induction motorfor driving a sewing machine arm shaft 11,24 a position detector mounted on the arm shaft 11,38the stator, and 40 the rotor. These parts are the same as those which have been described with referenceto Fig. 1.

A motor speed control circuit32 including a variable voltage frequency inverter circuit causes the arm shaft 11 to perform variable speed operation and fixed position stop with the aid ofthe motor 14.

A pedal detecting circuit 30 coupled to a foot pedal 28 which is one example of the switch means is as shown in Fig. 3 in detail. The arrangement of the circuit 30 will be described.

The detecting circuit 30, as shown in Fig. 3, comprises: a photo sensor unit 50 which includes photo interrupters 42 and 44, a shield plate 46 moving through the gaps in the photo interrupters and a resistor 48; and a magnetic sensor unit which includes a magnet 52 cooperating with the shield plate 46, a Hall element 54 magnetically coupling to the magnet 52to provide a speed command during sewing, a resistor 56 connected to the Hall element 54, and an emplifier 58 for amplifying the speed command provided bythe Hall element 54for applying a speed command signal VC to the control circuit 32. The shield plate46 and the magnet 52 is operated in association withthefoot pedal 28.

As the foot pedal 28 is,depressed, the degree of magnetic coupling between the magnet 52 and the Hall element 54 is changed and accordingly a speed command signal VC is also changed. As the shield plate 46 is moved downwardly, the outputs ofthe photo interrupters 42 and 44 are set to "0" and "1 " and are applied, as operation command signals S1 and S2 representing the fact that the sewing machine is in operation, to the control circuit 32, respectively.When the foot pedal 28 is in neutral state as shown in Fig.3, the operation command signals Sa and S2 are both at "0"; that is, the factthatthe foot pedal is in neutral state is detected by the control circuit 32 from the fact thatthe signals S, and S2 are both at "0". When the foot pedal 38 is kicked back, i.e., when it isturned in the opposite direction, the thread is cut off and the shield plate 46 is moved upwardly, so that the operation command signals S1 and S2aresetto "1" and "0", respectively.Thus, when the foot pedal is in "kicked back" state is detected by the control circuit 32 from thefactthatthe signals Sa and 52 are at"1" and "0", respectively.

The position detector 24 outputs a needle upper position signal UP and a needle lower position signal DN which indicate positions of the needle 1. The outputs ofthe position detector 24 and the pedal detecting circuit30areappliedto a sewing machine control circuit 34 adapted to control the speed of the motor 14 and to control various solenoids (not shown) ofthe sewing machine.

The sewing machine control circuit 34, as shown in Fig. 4, comprises operation signal memory circuits 62 and 64 like flip-flop circuits (hereinafter referred to as "FFcircuits 62 and 64", when applicable) to which the operation command signals Si and S2 ofthe pedal detecting circuit 30 are applied. The positive output of the FF circuit 62 is applied to an OR circuit 66. The output of the OR circuit 66 is supplied, as a start signal SRT,to the speed control circuit 32, and itisfurther applied through a brake one shot circuit 68, as a brake signal BK, to the speed control circuit 32.Thus, when the operation command signal Si is raised to "1" and the affirmative output of the FF circuit 62 is raised to "1 ", the speed control circuit32 controls the drive of the arm shaft 11 according to the speed command signal VC.

The affirmative output ofthe FF circuit 64 is applied, as a low speed command signal LLKD,tothespeed control circuit 32 and it its further applied to the OR circuit 66 and a sewing machine control circuit 70. The FF circuit 64 operates when the foot pedal 28 is in "kicked back" state, i.e., when the thread is cut off after the sewing machine has been stopped. When the speed command signal S2 is raised to "1" and the affirmative output of the FF circuit 64 is also raised to "1 ",the low speed command signal LLKD is supplied to the speed control circu it 32, so that the needle 1 is lifted. Then, the control circuit 70 controls a thread cutting solenoid IS and a thread wiping wiper WP.

Finally, the needle 1 is stopped atthe upper position.

When the needle 1 is not atthe upper position, in order to stop the needle 1 atthe upper position the upper position signal UP is supplied through a NAND circuit 72 to the resetinputterminal ofthe FF circuit 64. In orderto preventthe occurrence of a trouble even when, in this case,thefoot pedal 28 is erroneously depressed, the affirmative output ofthe FF circuit 62 is applied through an inverter74to the other input terminal ofthe NAND circuit 72.

The brake one shot circuit68 isto supplythe brake signal BKto the speed control circuit32 for a predetermined period oftime afterthe affirmative outputs of the FF circuits 62 and 64 are setto "1" and "0", respectively, thereby to immediately stop the sewing machine arm shaft 11.

The sewing machine control circuit 34further comprises a low speed detecting circuit76 to which the upper position detection signal UP and the lower position detection signal DN.Thecircuit76 operates to detect it from the period ofthe lower position detection signal DN when the speed of rotation ofthe sewing machine 10 reaches a lowvalue, therebyto output a low speed detection signal LDN to resetthe FF circuit62. The circuit34 is shown in Fig. in detail.

The circuit 34 comprises: a flip-flop circuit78 to the set terminal Sand the reset terminal R of which the upper position detection signal UP and the lower position detection signal DN ofthe position detector 24 are applied, respectively; a time constant circuit 86 connected to the affirmative output terminal Qthereof, the circuit 86 having a fixed resistor 80, a variable resistor 82 and a charging capacitor 84; an inverter 88 to which the capacitor charge voltage of the circuit 86 is applied; and a NOR circuit 90to which the affirmative output ofthe fl i p-flop circuit 78 and the output ofthe inverter 88 are applied. In Fig. 5, reference numeral 92 designates a diodefor quickly discharging the capacitor 84.

The affirmative outputoftheflip-fiop circuit78 is raised to "1" in response to the upper position detection signal UP and set to "0" in response to the lower position detection signal DN as shown in the partA of Fig. 6. Accordingly, the charge voltage ofthe capacitor84is gradually increased while the affirmative output is at "1", and it is abruptly decreased while the affirmative output is at "0", as shown in the part B of Fig. 6. This operation is repeatedly carried out. If this period of repetition T is increased (i.e., if the speed of rotation of the arm shaft 11 is decreased), the charge voltage exceeds a reference value, whereupon the output ofthe inverter 88 is changed to "0" from "1 " as indicated in the part C of Fig. 6.Accordingly, the NOR circuit 90 outputs the low speed detection signal LDN representing the fact that the low speed has been reached, thus resetting the FF circuit 62.

The motor speed control circuit 32 which receives the outputs ofthe sewing machine control circuit 34 and the speed command signal VC ofthe pedal detecting circuit 30 to drive the motor 14, will be described with reference to Fig. 7.

The circuit 32 comprises: a command circuit 92 which receives the speed command signal VC from the magnetic sensor unit 60 in the pedal detecting circuit and a stop preparation command signal INCO and the low speed command signal LLKO from the sewing machine control circuit 34; a voltage control circuit 94 and a frequency control circuit 96to which a voltage command signal and a frequency command signal are applied by the command circuit 92, respectively; a transistor drive circuit 98 which receives the outputs of these circuits 94 and 96 and the start signal SRTfrom the control circuit 34; a transistor inverter power circuit 100 to which the outputTD of the drive circuit 98 is applied; a rectifier circuit 102 for rectifying three-phase alternate currents; a smoothing circuit 104 connected between the rectifier circuit 102 and the transistor inverter power circuit 100; and a brake circuit 106 to which an output of the command circuit 92 and the brake signal BKofthe control circuit 34 is supplied. The output of the circuit 100 is supplied to the motor 14to drive the latter 14, while the output of the brake circuit 106 controls the electromagnetic brake 18. The smoothing circuit 104 is provided with a protective circuit 108 for detecting abnormal current.

The abnormal current detection output of the circuit 108 stopsthetransistor drive circuit 98to stop the motor 14. The voltage control circuit 94, being connected through a transformer 101 to the output of the inverter power circuit 100, is stabilized by voltage feedback.

With the aid ofthe start signal SRTfrom the sewing machine control circuit 34 and the outputs ofthe command circuit 92 provided in response to the speed command signals LLKD, IMCO and VC,thevoltage and frequency are adjusted respectively in the voltage control circuit 94 and the frequency control circuit 96, so thatthe speed of rotation ofthe motor 14 is maintained in the range of predetermined value. The output ofthe brake circuit 106 excites the electromagnetic brake 18 to stop the needle at a predetermined position.

The operation ofthe electric sewing machine thus constructed will be described.

To start a sewing operation, the foot pedal 28 is depressed, so thatthe magnet 52 is broughtcloseto the Hall element 58. As a result, the magnetic sensor unit 60 applies the sewing speed command signal VC to the motor speed control circuit 32, while the photo interrupter 44 applies the operation signal S1 which is at "1 ", to the control circuit 34. Accordingly, the sewing machine control circuit 34 applies the start signal SRTwhich is at "1 " to the speed control circuit 32, so that a drive output POWER is supplied to the motor 1 4to start driving the latter 14.In the speed control circuit32, the voltage control circuit 94 and the frequency control circuit 96 adjustthe voltage and the frequency in agreement with the specified speed, so thatthe motor 14 is rotated art a predetermined speed and the arm shaft 11 is rotated.

When it is required to decrease the speed during sewing, the foot pedal is returned, so that the value of the sewing speed command signal VC is decreased and the transistor drive circuit 98 is changed into an electric brake circuit. As a result, the speed is decreased quickly to the required value.

When it is required to change the sewing direction during sewing with the needle 1 piercing the cloth or with the needle held atthe lower position, the foot pedal 28 is set backto its "neutral" position. As a result, the pedal detecting circuit 30 applies the operation command signal S1 which is at "0" to the FF circuit 62 in the sewing machine control circuit 34. The FF circuit 62 applies the start signal SRTwhich is at "1" to the speed control circuit 32 until preparation for stop has been accomplished. Accordingly, the speed of rotation of the motor 14 is maintained at a predeterminedvaluewhich is smallerthan the ordinarysewing speed as shown in Fig. 8.

During the stop preparation period, in the low speed detecting circuit76, the capacitor 84 is charged according to the upper position detection signal UP and the lower position detection signal DN from the position detecting circuit 24 onlyfora period of time thatthe affirmative output oftheflip-flop circuit78 is at "1 ",as described before. And the inverter 88 applies an output signal, which is at "0", to the NOR circuit 90 onlyfora period oftimethatthe charge voltage of the capacitor 84 is larger than a predetermined value Vth because the speed of the motor is decreased and the period of repetition T is increased.Accordingly, at the time instantwhenthe affirmative outputofthe flip4lop circuit 78 is set to "0", the NOR circuit 90 provides the reset signal LDN for the FF circuit 62.

Thus, the direction changing conditions thatthe speed of rotation ofthe motor 14 has reached the low value and the sewing needle is at the lower position are satisfied. Therefore, atthistime instant, the brake one shot circuit 68 provides the brake signal BKwhich is at "1". The signal BK is applied through the brake circuit 106 in the speed control circuit 32 to the motor 14to stop the latter 14.

When it is required to cut the thread after sewing, the foot pedal 28 is kicked back, so that the photo interrupter 42 applies theth read cutting signal S2, which is at "1", to the FF circuit 64 in the sewing machine control circuit. In response to the signal, the FF circuit 64 applies the startsignal SRTwhich is at "1" and the low speed signal LLKO (or a middle speed signal IMCO when necessary) to the speed control circuit 32. And the sewing machine control circuit 70 is operated to control the thread cutting orwiping operation. The FF circuit 64 is reset by the upper position detection signal UP which is at "1", and the motor 14 is stopped with the needle 1 at the upper position.

Figs. 9 and 10 shows a second preferred embodi ment ofthe invention. In these figures, those compo nents which have been already described with refer ence to the first embodiment in Figs. 2 through 8 are accordingly designated by the same reference numerals or characters. In the Figures, reference numeral 26 designates a speed detector mounted on the sewing machine arm shaft 11, fordetecting the speed of the sewing machine, and 32 a motor speed control circuit which receives outputs ofthe sewing machine control circuit 34 and the speed command signal VC of the pedal detecting circuit 30.

More specifically, the circuit 32 comprises: a command circuit 92 which receives the speed signal VC from the magnetic sensor unit 60 in the pedal detecting circuit 30 and the start signal SRT, stop preparation command signal IMCO and low speed command signal LLKO from the sewing machine control circuit 34; a voltage control circuit 94 and a slip correction frequency control circuit 109 to which a voltage command signal and afrequencycommand signal are supplied by the command circuit 92, respectively; a thyristor converter 110 which receives the output ofthevoltage control circuit 94 as a firing control signal,to convert three phase AC voltages into a DC voltage; a thyristor inverter power circuit 112 which is connected through a smoothing circuit 111 in series to the output of the converter 10 and receives the output of the slip correction frequency control circuit 109 as a firing control signal; and a brake circuit 106 which receives the output ofthe command circuit 92 and the brake signal BK ofthe sewing machine control circuit34. The output ofthe inverter power circuit 112 is applied to the motor 14to drive the latter 14, and the electromagnetic brake 18 is controlled by the output ofthe brake circuit 106.

The slip correction frequency control circuit 109 is servo-controlled receiving a detection signal FG from the speed detector 26. The voltage control circuit 94, being connected through a transformer 101 to the output ofthe inverter power circuit 112, is stabilized through voltage feedback. An abnormal current detecting currenttransformer 113 is connected between the smoothing circuit and the inverter power circuit 112. 1 2. The detection output of the transformer 113 is supplied to the voltage control circuit94, to interrupt the converter drive current, to stop the motor 14.

The operation ofthe second embodiment of the invention,which is organized as described above, will be described.

In starting a sewing operation,thefoot pedal 28 is depressed to causethe magnet 52 to come close to the Hall element 58, so that the magnetic sensor unit 60 applies the sewing speed command signal VCto the motor speed control circuit 32, and the photo interrup ter44 applies the operation signal S1, which is at "1", to the sewing machine control circuit 34. Thereupon, the control circuit 34 supplies the start signal SRT, which is at "1", to the speed control circuit 32, to start driving the motor 14. In the speed control circuit32, the voltage control circuit 94 and the frequency control circuit 96 adjust the voltage and the frequency in agreement with the specified speed, so that the motor 14 is rotated at a predetermined speed.

In orderto decrease the speed during sewing, the foot pedal 28 is returned. Thereupon,the value ofthe sewing speed command signal VC is decreased.

Accordingly, with the aid of the voltage control circuit 94 and the frequency control circuit 96, the converter ll0andtheinverter ll2arechanged into an inverter and a converter, respectively, so that generative braking is carried aut with the motor 14 as a generator.

Thus, the speed is quickly decreased to a desired intermediate speedcorrnspondingto the degree of depression of the foot pedal.

When it is required to changethesewing direction during sewing with the needle piercing the cloth, i.e., with the needle at the lower position,thefoot pedal 28 is returned to the "neutral" position, so thatthe pedal detecting circuit 30 applies the operation command signal S1, which is at "0", to the FF circuit 62 in the sewing machine control circuit 34. As the FFcircuit 62 supplies the start signal SRT, which is at "1", to the speed control circuit 32 until preparation forstop is accomplished, similarly as in the case of Fig. 7 the speed of rotation of the motor 14 is maintained at a predetermined value lowerthan the ordinary sewing speed.

During the stop preparation period, in the low speed detecting circuit 76, the capacitor 84 is charged according to the upper position detection signal UP and the lower position detection signal DN from the position detecting circuit 24 only for a period of time that the affirmative output of the flip-flop circuit78 is at "1 ", as described above. And the inverter 88 applies an output signal, which is at "0", to the NOR circuit 90 only for a period oftimethatthe charge voltage ofthe capacitor84 is largerthan a predetermined value Vth because the speed of the motor is decreased and the period of repetition T is increased.Accordingly, atthe same time instant when the affirmative output of the flipJlop circuit 78 is setto "0", the NOR circuit 90 provides the reset signal LDN forthe FF circuit 62.

Thus,the direction changing conditionsthatthe speed -of rotation ofthe motor 14 has reached the low value and the sewing needle is atthe lower position are satisfied. Therefore, atthis time-instant,the brake one shot circuit 68 provides the brake signal BKwhich is at "1 ". The signal BK is appliedthrough the brake circuit 106 in the speed control circuit 32 to the motor 1 4to stop the latter 14.

When it is required to cutthethread aftersewing, the foot pedal 28 is kicked back, so that the photo interrupter 42 applies the thread cutting signal S2, which is at "1", to the FFcircuit 64 in the sewing machine control circuit. In response to the signal, the FF circuit 64 applies the start signal SRTwhich is at "1" and the low speed signal LLKO (or a middle speed signal IMCO when necessary) to the speed control circuit 32. And the sewing machine control circuit 70 its operated to control the thread cutting orwiping operation. The FF circuit 64 is reset by the upper position detection signal UP which is at "1", and the motor 14 is stopped with the needle 1 at the upper position.

In the above-described two preferred embodiments, the speed command and the operation command are controlled by operating the foot pedal; however, they may be controlled external operation switch signals.

Another embodiment ofthe invention will be briefly described. In a sewing machine with an arm shaft, the above-described motor rotor 40, position detector 24 and electro-magnetic brake 18 are mounted on the arm shaft. An electric motor such as a DC motor, induction motor or pulse motor which has a stator and a rotor and is suitable for driving a sewing machine can be employed. If a motor such as a pulse motor having a braking effect is employed, then the abovedescribed brake may be eliminated. In the abovedescribed embodiments, the position detector 24 is provided on the prolongation ofthe arm shaft 11 and outside the sewing machine frame 10, while the motor stator38 and rotor 40 are provided inside the frame 10; however, the invention is not limited thereto or thereby. For instance all of them may be provided inside the sewing machine frame 10, or may be provided outside the frame 10.

The speed detector 26 may be utilized as the position detector 24. If a speed detecting means which is differentfrom the speed detector is mounted on the arm shaft 11, then it can be utilized for controlling the speed of rotation ofthe motor 14orthe like.

As is apparentfrom the above description, in the electric sewing machine according to the invention, the number of components required for coupling the motor to the sewing mechanism is greatly reduced.

Accordingly, the sewing machine is considerably simple and compact in construction and is low in manufacturing cost.

Claims

1. An electric sewing machine comprising: a sewing shaft for reciprocating a sewing needle; a sewing machine frame pivotally supporting said sewing shaft; and an electric motorfor driving said sewing shaft, CHARACTERIZED in that the rotor of said electric motor is mounted on said sewing shaft, and the stator of said electric motor is mounted on said sewing machine frame.

2. An electric sewing machine as claimed in claim 1, CHARACTERIZED in that said electric motor is an induction motor.

3. An electric sewing machine comprising: a sewing shaft for reciprocating a sewing needle; a sewing machine frame pivotally supporting said sewing shaft; an electric motorfordriving said sewing shaft; position detecting means for detecting a position of said sewing needle and applying a detection output to operation control means for said electric motor, CHARACTERIZED in that the stator of said motor is mounted on said sewing machine frame, the rotor of said motor and said position detecting means are mounted on said sewing shaft.

4. An electric sewing machine as claimed in claim 3, CHARACTERIZED in that said electric motor is an induction motor.

5. An electric sewing machine as claimed in claim 3, CHARACTERIZED in that the stator of said electric motor is arranged inside said sewing machine'frame, and said position detecting means is arranged outside of said sewing machine frame.

6. An electric sewing machine, CHARACTERIZED by comprising: a sewing shaft for reciprocating a sewing needle; frame pivotally supporting said sewing shaft; an electric motorfordriving said sewing shaft; position detecting means for detecting a position of said sewing needle and applying a detection outputto operation control meansforsaid electric motor; switch meansforapplying desired operation commands to said operation control means; and brake means controlled by said operation control means according to said detection output from said position detector, for braking said sewing shaft, said brake meanstogetherwith said motor's rotor and said position detecting means being mounted on said sewing shaft.

7. An electric sewing machine as claimed in claim 6, CHARACTERIZED in that said electric motor is an induction motor.

8. An electric sewing machine as claimed in claim 6, CHARACTERIZED in that said motor's stator is arranged inside said sewing machineframe, and said position detecting means is arranged outside said sewing machine frame.

9. An electric sewing machine as claimed in claim 6, CHARACTERIZED in that said switch means include a pedal switch.

10. An electric sewing machine as claimed in claim 6, CHARACTERIZED in that said brake means is an electromagnetic brake which is provided inside said sewing machine frame.