Sewing Machine

Abstract

A sewing machine includes an electric driving system which moves a reciprocable needle to sew a work fabric pressed by a presser foot. The foot is automatically lifted after the needle is stopped at a predetermined position by the operation of a treadle, a time delay compensating for continued needle operation due to inertia of the mechanism.

Description

The present invention relates to sewing machines and more particularly to motor-driven sewing machines of the type provided with a presser foot for keeping a work fabric in place thereon and a needle positioning device for stopping a reciprocable needle in a predetermined position. Generally, with such a motor-driven sewing machine as mentioned above, the fast depression of a treadle causes the driving mechanism of said machine including a rotary shaft mounted on a frame for vertically reciprocating a needle to be coupled through a clutch with a high speed motor with the resultant reciprocation of said needle. When the necessary and required sewing is completed the treadle is released, the driving mechanism thereof is changed from a high speed to a low speed motor and at the same time a needle positioning device is actuated to stop the needle at predetermined position.

With the prior art sewing machine of such type, a treadle for actuating both the driving mechanism and needle positioning device was disposed independently of a means for working a presser foot, for example, a knee lever so that to complete one cycle of sewing operation, the machine operation had to take two steps of stopping the driving mechanism and subsequently to working the knee lever as to lift the presser foot. This not only interfered with sewing efficiency, but also resulted in the increased fatigue of the operator.

A sewing machine of the present invention is provided with electrical control device which allows a presser foot to be worked also by a treadle for stopping the movement of a needle, eliminating the necessity of hand operating the presser foot independently of the driving of the needle. Moreover, the lifting of the presser foot is commenced only after the movement of the needle has fully stopped, so that there is no possibility of the presser foot being lifted too early which might lead to the rise or displacement of a work fabric and the loosening of the upper thread.

In the drawings:

FIG. 1 is a perspective view of a sewing machine according to an embodiment of the present invention;

FIG. 2 is an enlarged perspective view of the members fitted to the frame of the machine illustrative of their movements;

FIGS. 3A and 3B are schematic side views of the driving mechanisms of said members; FIG. 3A shows the driving mechanism of a presser foot and that of cutter means and FIG. 3B indicates a clutch means involved in the driving mechanism of a rotary shaft;

FIG. 4 is an elevation of the synchronizing means of the machine, particularly showing the manner in which there are jointly used the slip rings and brushes of said means;

FIG. 5 is a diagram showing the relative timing in which there are used said slip rings; and

FIGS. 6 to 15 are circuit diagrams of an electrical control device for controlling the needle positioning device and means for working the presser foot; FIG. 6 shows the sewing operation; FIGS. 7 to 10 present the operation of stopping the needle at a low position and lifting the presser foot; and FIGS. 11 to 15 indicate the operation of cutting threads.

There will now be described by reference to the appended drawings a sewing machine according to an embodiment of the present invention. Referring to FIG. 1 illustrating the whole of said embodiment, numeral 10 is a table supported by a stand 11. To said table 10 is fitted a machine frame 12. At one end of the machine frame 12 are disposed a needle 13 and a presser foot 14 and immediately under the needle 13 is positioned a stitch forming means 15 (see FIG. 2). Below the table 10 are arranged a high speed motor 16, auxiliary low speed motor 17, knee lever 19 rotatably pivoted by means of a pin 18 so as to be operable by the knee, a microswitch 20 operable by said lever 19 for actuating the later described thread cutting means, the later described electrical control device 21 and a main switching control device 22. Across the bottom parts of the legs of the stand 11 is stretched a beam 23. To said beam is rotatably pivoted a treadle 24. To the free end of the treadle 24 is connected one end of an assembly of a pair of connection rods 25, the other end of said assembly being connected to the free end of a clutch changing lever 26. Numeral 27 is a spring means for normally holding the clutch changing lever 26 in the direction in which a driving pulley 28 is released from said high speed motor 16. As shown particularly in FIGS. 3A and 3B, there is stretched a belt 31 across the driving pulley 28 and another pulley 30 disposed near one end of a main rotary shaft 29 fitted to the frame 12. At the aforesaid end of the main rotary shaft 29 is positioned the later described synchronizing means 32 operable by said shaft. Numeral 33 denotes a treadle switch (a microswitch) so operated by the clutch changing lever 26 as to open the contact when the treadle is depressed and close the contact when the depressing force on the treadle is removed.

The motor assembly 34 provided with a clutch comprises said high speed motor 16 and auxiliary low speed motor 17. The high speed motor 16 consists of a stator 35 and rotor 36. At one end of a first rotary shaft 37 fitted to the rotor 36 is positioned a cooling fan 38, and to the other end thereof is fixed a flywheel 40 leaving an annular rib 39 formed at the front part. In the housing 48 is slidably set a second rotary shaft 42 by the well known means (not shown). To the one end of said second rotary shaft 42 is fixed a connection disc 41 in a manner to face the annular rib 39 of the flywheel and at the other end thereof is located a movable bearing 43 allowing said second shaft 42 to be shifted in its axial direction. To said bearing 43 is connected the free end of the clutch changing lever 26. Said lever 26 is allowed to rotate at the intermediate pivot point 45 of one half portion thereof by a support strip 44 projecting from one end of the frame 48. Numeral 46 is a worm wheel slidably disposed in the axial direction. Ahead of said worm wheel 46 is positioned an annular rib 47 in a manner to contact the connection disc 41. When the force on the depressed treadle 24 is released said connection disc 41 is urged to contact the annular rib 47 of a worm wheel. The worm wheel 46 is made rotatable about the axis of the second rotary shaft 42, and is received in the housing 48 so as not to be shifted in position depending on the extent of the axial movement of said rotary shaft 42. With the worm wheel 46 meshes a worm 49 which is fitted to the furthest end of a rotary shaft 50 of the auxiliary low speed motor 17.

The machine driving mechanism involving the aforementioned clutch-fitted motor 34 is operated in the following manner. There is thrown a master switch (not shown) to bring the high speed motor 16 to an operable state and then the treadle is depressed, allowing the clutch changing lever 26 to swing about the aforesaid pivot point 45 in the direction of the indicated arrow 51. Accordingly the movable bearing 43 is carried along with the second rotary shaft 42 in its axial direction to cause the connection disc 41 to contact the annular rib 39 of the flywheel 40. This frictional contact allows the rotating motion of the high speed motor 16 to be transmitted to the rotary shaft 42 and then to the main rotary shaft 29 fitted to the machine frame 12 through the driving pulley 28, belt 31 and pulley 30, with the resultant vertical reciprocation of the needle 13. Next where the depression of the treadle 24 is released to change the driving mechanism from the high speed to the low speed motor in preparation to stop the machine operation, the clutch changing lever 26 is brought back to its original position by the connection disc 41 so as to allow the connection disc 41 to leave the annular rib 39 of the flywheel 40 and contact the annular rib 47 of the worm wheel 46. Accordingly, the rotation of the auxiliary low speed motor 17 is decreased in speed by a reduction gear mechanism consisting of the worm 49 and worm wheel 46, said reduction being transmitted to the main rotary shaft 29 through the connection disc 41, second rotary shaft 42, driving pulley 28, belt 31 and pulley 30, in the order mentioned, later allowing the needle 13 to be stopped at a predetermined position by an electrical control device 21. At the first depression of said treadle 24 said treadle switch 33 is turned off through the clutch changing lever 26 to permit the presser foot 14 to be lowered. At the second depression thereof, the connection disc 41 is permitted to be connected with the fly wheel 40, thereby causing the rotary shaft 29 to be rotated at high speed.

As shown in FIG. 2, the main rotary shaft 29 for vertically reciprocating the needle 13 has a bevel gear 52 formed at an intermediate point. Perpendicular to said main rotary shaft 29 is positioned another rotary shaft 54 provided at one end also with a bevel gear 53 which meshes with the first mentioned bevel gear 52. At the other end of the latter rotary shaft 54 is formed another bevel gear 55, to which is associated still another rotary shaft 57 through a bevel gear 56 paired with the aforesaid bevel gear 55. Accordingly, when the main rotary shaft 29 rotates in the direction of the indicated arrow, the last mentioned rotary shaft 57 is allowed to rotate in the opposite direction. To the other end of said rotary shaft 57 is fitted the known stitch forming means 15, which is designed to sew a work fabric in cooperation with the needle 13.

There will now be described the driving mechanism of the presser foot 14 particularly with reference to FIG. 2 or 3A. On the upper surface of the pressor foot 14 is positioned an upwardly projecting presser bar 58, the upper end of which is connected to the free end of the rotary arm 59 of a rotary shaft 60. Further, this presser bar 58 is always urged downward by a coil spring 61 fitted somewhere along its length. The aforementioned rotary shaft 60 is rotatably supported in the machine frame 12, both ends of said shaft 60 being fitted with the aforesaid rotary arm 59 and a separate rotary arm 62. To the free end of the latter rotary arm 62 is pivoted the top end of a work rod 63 disposed in the frame in a manner to move vertically or in the axial direction. The lower end of said work rod 63 is operably connected with one end of an L-shaped lever 65 rotatable about a fulcrum 64. The other end of said L-shaped lever 65 is connected to the piston 68 of an air cylinder 67 controlled by an electromagnetic valve 66. This valve 66 is so arranged that its work rod is always pressed in one direction by a coil spring 69 and brings the piston 68 to the position shown in FIG. 3A when an electromagnetic coil 70 is excited. Numeral 71 denotes a compressor for supplying air to the air cylinder 67 of the presser foot 14 and the later described air cylinder of the thread cutting means.

There will now be described a thread cutting means 72. The thread cutting means is so provided in the frame 12 as to be positioned near the stitch forming means 15. The thread cutting means 72 consists of a stationary blade 73 and movable blade 74, which are paired with each other. The movable blade can rotate horizontally in conjunction with a rotary shaft 75 about the central axis thereof. The rotary shaft 75 is connected to the piston 76 of a cylinder 77, so that when said shaft 75 rotates due to the reciprocating movement of the piston 76 the movable blade 74 catches the upper thread (not shown) inserted into the needle 13 to cut it in cooperation with the stationary blade 73. The cylinder 77 is so designed that the switching of an electromagnetic valve 80 having electromagnetic coils 78 and 79 allows compressed air to be introduced into the cylinder 77 in varying directions and the piston 76 to be shifted in position according to said directions.

The synchronizing means 32 consists of, as shown in FIG. 4, four slip rings 81, 82, 83 and 84 prepared by forming the later described conductive layer or region and nonconductive layer or region on the peripheral surface of a cylindrical member of electrically insulating material fixed to the main rotary shaft 29 and four stationary brushes 85, 86, 87 and 88 slidably fitted to said sliprings. The first slipring 81 has a conductive layer or region A.sub.1 formed at a part corresponding to the timing of cutting threads and a nonconductive layer or region B.sub.1 at the remaining part. The second slipring 82 whose entire region consists of a conductive region A.sub.2 is for common use. On the other hand, the third and fourth sliprings 83 and 84 are electrically connected to the second ring 82. The third ring 83 has a nonconductive region B.sub.3 formed at that part of its entire region which corresponds to the timing of allowing the needle 13 to assume an upper position and a conductive layer A.sub.3 at the remaining part thereof. The fourth ring 84 has a nonconductive layer B.sub.4 formed at that part its entire region which corresponds to the timing of allowing the needle 13 to assume a lower position and a conductive region A.sub.4 at the remaining part thereof. These third and fourth rings are used in defining the upper and lower positions respectively, at which the needle 13 is to be stopped. Of course, the exact position of the conductive layer of each slipring is determined by the relationship of desired upper and lower stop positions of the needle with respect to the fixed positions of the brushes. FIG. 5 presents on the periphery of the same circle the relative positions of the conductive and nonconductive regions of each of said sliprings or the overall relative positions thereof in terms of angular values. The numerals used in FIG. 5 represent the same layers as shown in FIG. 4.

There will now be described by reference to FIG. 6 an electrical control system 89 consisting of the electrical control device 21, switch 20, treadle switch 33 and synchronizing means 32, said system being used in controlling the operation of the needle positioning mechanism, presser foot working mechanism and automatic thread cutting means. Numeral 90 denotes one of the source lines connected through the treadle switch 33 to the positive terminal 91 of a DC source (not shown), and numeral 92 represents the other source line connected to the negative terminal 93 of said DC source. Between these source lines 90 and 92 are connected a relay R.sub.1 and the aforesaid switch 20 in series. Parallel to said switch 20 is connected a normally open contact R.sub.11. Accordingly, the relay R.sub.1 is energized by the make of the switch 20 and holds itself by the break of said normally open contact r.sub.11. Between the source lines 90 and 92 there are also connected a relay R.sub.2 and condenser 95 arranged in series. Parallel to the condenser 95 is connected a high resistor 94 for discharges. Thus when current flows through the source lines 90 and 92, the relay R.sub.2 for lifting the presser foot is actuated only for a specified length of time. Also between the source lines 90 and 92 are connected the normally closed contact r.sub.21 of the relay R.sub.2, the normally closed contact r.sub.31 of the later described relay R.sub.3 and the electromagnetic coil 70 of the electromagnetic valve 66 for working the presser foot which are all arranged in series. Numerals 81s, 83s and 84s represent in the form of contacts the electrical switching operations performed between the brushes 85, 87 and 88 and the corresponding sliprings 81, 83 and 84. These contacts are hereinafter referred to as equivalent contacts. Between the source lines 90 and 92 there is also connected a branch formed by serially connecting the normally closed contact r.sub.12 of the relay R.sub.1, equivalent contact 84s and relay R.sub.3. Parallel to said normally closed contact r.sub.12 and equivalent contact 84s are connected the normally open contact r.sub.13 of the relay R.sub.1, diode 96 and equivalent contact 83s. Between the anode terminal of said diode 96 and the source line 92 are connected another diode 97, equivalent contact 81s and relay R.sub.4 in series relation. These two diodes 96 and 97 are connected in the normal direction as shown. Between the source lines 90 and 92 are further connected three branches. To the first branch are connected in series the normally open contact r.sub.32 of the relay R.sub.3 and another relay R.sub.5 for controlling the auxiliary low speed motor 17. Parallel to said relay R.sub.5 is connected a condenser 98. To the second branch are connected in series the normally open contact r .sub.41 of the relay R.sub.4 and electromagnetic coil 78 for drawing out the movable blade of the electromagnetic valve 80. To the third branch are connected in series the normally closed contact r.sub.42 of the relay R.sub.4 and the electromagnetic coil 79 for retracting the movable blade.

Numeral 17a of FIG. 6 denotes the rotor winding of the auxiliary low speed motor 17. Said winding 17a is connected in series to the normally open contact r.sub.34 of the relay R.sub.3, field winding 17f and normally open contact r.sub.51 of the relay R.sub.5. Across the winding 17a and normally open contact r.sub.51 flow direct current through DC source terminals 99 and 100. Parallel to said rotor winding 17a is connected the normally closed contact r.sub.33 of the relay R.sub.3, the make of said contact r.sub.33 forming a short circuit for dynamic braking. Parallel to the normally open contact r.sub.34 of the relay R.sub.3 is connected a resistor 101 for restricting the field current when power generation is braked, and parallel to the field winding 17f is connected a diode 102 in the opposite direction for controlling an inverse electromotive force. Parallel to the normally closed contact r.sub.33, normally open contact r.sub.34 and normally open contact r.sub.51 are connected CR circuits 103, 104 and 105 respectively for extinguishing contact sparks, each of which consists of a resistor and condenser arranged in series.

Numeral 32 of FIG. 6 is an equivalent representation of the aforementioned synchronizing means. The same numerals as those of FIG. 4 denote the same elements.

There will now be described with reference to FIGS. 6 to 15 the operation of the aforesaid electrical control system 89.

SEWING OPERATION (refer to FIG. 6)

When the main switching control device is operated, then the electrical control device 21 is turned on, initiating the rotation of the high speed motor 16. Simultaneously therewith, the electrical control system 89 is energized. FIG. 15 shows the state of a circuit diagram, assumed when the sewing machine is stopped. In such stage, the energization of the coil 70 of the electromagnetic valve 66 through the treadle switch 33, contact r.sub.21 and contact r.sub.31 causes the presser foot 14 to be raised as shown in FIG. 3A. When the depression of the treadle 24 is initiated subsequent to supplying the work fabric at the stitching point under the undersurface of the presser foot 14, the treadle switch 33 is turned off, causing the coil 70 to be deenergized. Then, the presser foot is lowered under the force of the spring 61, pressing the work fabric down to the bed surface. At the next stage when the treadle is again depressed, the clutch changing lever 26 is turned counterclockwise in FIG. 3A, causing the connecting disc 41 to be operatively engaged with the high speed motor 16 now rotated at a high speed, thereby rotating the drive shaft 29, at the high speed, through the belt 31. This puts the associated operative mechanisms in operation for stitch formation. During the operation of the sewing machine the electrical control system 89 remains inoperative, since the treadle switch 33 is turned on.

The presser foot presses the work fabric down to a prescribed position at the first stage of depression. If the depression is not sufficient, the pedal switch 33 is again turned on by releasing the treadle, thereby causing the presser foot to be again raised. Thus, the position of the work fabric can be corrected.

Operation of stopping the needle at the

lower position and automatically lifting

the presser foot (refer to FIGS. 7 to 10)

As already set forth above, the stitch formation is effected during the time the treadle is depressed. After the completion of a required stitch formation, when it is desired to effect the thread cutting and then to detach the work fabric from the sewing machine, or it is desired to turn the stitching direction, said treadle is released, thereby bringing the needle down to the lower position. This process is effected in the following sequence:

Where the depression of the treadle 24 is released when the brushes 87, 88 and 85 and sliprings 83, 84 and 81 of the synchronizing means 32 are in the state of FIG. 7, that is, the brush 87 is positioned on the conductive region A.sub.3, the brush 88 on the conductive region A.sub.4 the brush 85 on the nonconductive region B.sub.1, then the treadle switch 33 is closed and the driving mechanism of the needle is changed from the high speed motor 16 to the auxiliary low speed motor 17. On the other hand, the make of said switch 33 causes the relay R.sub.3 to be excited through the normally closed contact r.sub.12 and equivalent contact 84s for defining the lower stop position of the needle, thereby closing the normally open contacts r.sub.32 and r.sub.34 and opening the normally closed contacts r .sub.31 and r.sub.33 . Then the relay R.sub.5 is excited through the normally open contact r.sub.32 to close the normally open contact r.sub.51. Accordingly, direct current flows from one DC source terminal 99 to the other DC source terminal 100 through the rotor winding 17a of the auxiliary low speed motor 17, normally open contact r.sub.34, field winding 17f, and normally open contact r.sub.51, allowing said auxiliary low speed motor 17 to be rotated and in consequence the needle to be driven or vertically reciprocated at a slow speed through the main rotary shaft 29 of the machine.

The make of the treadle switch 33 causes the relay R.sub.2 to be excited through the condenser 95 only until the 5 is fully stopped at the lower position, allowing the normally closed contact r.sub.21 to be opened in the meantime. Accordingly, the coil 70 of the electromagnetic valve 66 serially connected to said contact r.sub.21 is not excited, so that the presser foot 14 still remains in a downwardly urged state, namely, in a state of keeping a work fabric in place on the table.

When the brush 87 is brought, as shown in FIG. 8, on the nonconductive region B.sub.3 of the slip ring 83, the equivalent contact 84s for defining the lower stop position of the needle is opened to deenergize the relay R.sub.3. This causes the normally open contacts r.sub.32 and r.sub.34 and normally closed contacts r.sub.31 and r.sub.33 to be brought back to their original positions. However, the relay R.sub.5 serially connected to the contact r.sub.32 still continues to be excited, though for a short time, by the discharge current of the condenser 98 even after the aforesaid contact r.sub.32 is opened, and the normally open contact r.sub.51 of said relay R.sub.5 remains closed. For a short time after the return of the relay R.sub.3 to its original position, the field winding 17 f is excited by the current flowing from one DC source terminal 99 to the other DC source terminal 100 through the normally closed contact r.sub.33, resistor 101, field winding 17f and normally open contact r.sub.51. At this time the rotor winding 17a is shorted with the normally closed contact r.sub.33 due to its make, so that the auxiliary low speed motor 17 is dynamically braked to be instantly stopped. If the foregoing operation fails to fully stop said motor, repetition of the same cycle of operation will be able to fully stop it. During the aforesaid operation of stopping the needle at the lower position, the relay R.sub.2 still continues to be excited through the condenser 95 to keep the electromagnetic coil 70 deenergized, so that the presser foot 14 is maintained in a downwardly urged position. Upon completion of the discharge of the condenser 98 after a certain length of time, current ceases to run through the relay R.sub.5, allowing it to be brought back to its original position, so that as shown in FIG. 9, the normally open contact r.sub.51 of said relay R.sub.5 is opened to break the energizing circuit of the auxiliary low speed motor 17. After the needle is fully stopped at the lower position, the relay R.sub.2 is returned, as shown in FIG. 10, to its original position, because the condenser 95 serially connected to said relay R.sub.2 is charged fully to its capacity, thus bringing said relay R.sub.1 to a state cut off from current. As a result the normally closed contact r.sub.21 which was opened up to this time is now closed, allowing the coil 70 of the electromagnetic valve 66 to be excited through the normally closed contacts r.sub.21 and r.sub.31, thereby immediately lifting the presser foot 14. Namely, said presser foot 14 is detached from a work fabric only after the needle is fully stopped at a predetermined lower position. At such time the needle is stopped at the lower position and the presser foot is raised, if it is desired to detach the work fabric from the sewing machine the thread cutting operation may be operated as will be described later; and if it is desired to turn the stitching direction, the operator may suitably rotate the work fabric with the needle, stopped at the lower position, as a center. Thereafter, when the depression of the treadle is further continued as before, the stitching is effected continuously from that seam portion of the work fabric which the stitching has been effected.

Thread Cutting Operation (refer to FIGS. 11 to 15)

When the brushes 87, 88 and 85 are in the positions shown in FIG. 11, namely, the brush 87 is brought on the conductive region A.sub.3 of the slip ring 83, the brush 88 on the conductive region A.sub.4 of the slip ring 84 and the brush 85 on the nonconductive region B.sub.1 of the slip ring 81, then the make of the treadle switch 20 by operating the knee lever 19 with the knee after release of the depressed treadle 24 causes the relay R.sub.1 to be excited and brought to a self-holding state due to the make of its normally open contact r.sub.11. At this time, the relay R.sub.1 is excited to open its normally closed contact r.sub.12 and close its normally open contact r.sub.13. thereby bringing the control circuit to a "upper stop" position. Accordingly, the relay R.sub.3 is excited through the diode 96 and the equivalent contact 83s for defining the upper stop position of the needle. Then the relay R.sub.5 is excited as in the operation of the stopping the needle at the lower position, bringing the electrical circuit to a state shown in FIG. 11. The aforementioned operation causes the auxiliary low speed motor 17 to be energized and driven by the voltage prevailing across the DC source terminals 99 and 100.

When, as shown in FIG. 12, the rotation of said auxiliary low speed motor 17 advances to bring the thread cutting brush 85 to the conductive region A.sub.1 of the slipring 81, namely, while the end of the needle 13 is rising toward the table top, the relay R.sub.4 is excited through the normally open contact r.sub.13, diode 97 and thread cutting equivalent contact 81s to close the normally open contact r.sub.41 and open the normally closed contact r.sub.42. As a result, the electromagnetic coil 78 for drawing out the movable blade is excited to allow said blade 74 to rotate and catch the sewing thread extending out of a work fabric.

Later when the rotation of the auxiliary low speed motor 17 further advances to allow, as shown in FIG. 13, the brush 85 to be removed from the conductive region A.sub.1, of the slip ring 81, then the thread cutting equivalent contact 81s is opened to return the relay R.sub.4 to its original position and in consequence allow its normally closed contact 42 to be closed, so that the electromagnetic coil 79 for retracting the movable blade 74 is excited to bring it back to its original position. The thread caught by the movable blade 74 while it is drawn out and retracted is cut off by the joint action of said movable blade 74 and stationary blade 73.

FIG. 14 represents the circuit condition where the needle is brought to an upper position, namely, the brush 88 is carried on to the nonconductive region B.sub.4 of the slip ring 84. This condition shows that the auxiliary low speed motor 17 is braked for the same reason as given in connection with the circuit condition of FIG. 8. Thus the relay R.sub.3 is brought back to its original position to close its normally closed contact r.sub.31 and in consequence the coil 70 of the electromagnetic valve 66 is excited to lift the presser foot 14.

FIG. 15 shows the circuit condition where the auxiliary low speed motor 17 is stopped, namely, where the needle 13 is brought to rest at an upper position.

When the treadle 24 is depressed after the stop of the needle at a predetermined position and the lifting of the presser foot to restart sewing operation, then the treadle switch 33 is opened and the circuit is brought to a state shown in FIG. 6.

As already set forth above, the thread cutting operation is effected, only after the needle is stopped at the predetermined lower position. After the release of the treadle and before the stopping of the needle to the predetermined lower position, of the knee lever 19 is operated, then the thread cutting operation is effected, immediately subsequent to the required stitch formation, without the needle being stopped to the lower position. Thereafter, the presser foot is raised and the work fabric can be withdrawn. Such operation can be effected by the skilled operator without any troublesomeness. Thus, the operational efficiency is enhanced.

As apparent from the description given above, the presser foot is automatically urged upward or downward, offering great convenience in operation. What is more important is that said presser foot begins to be lifted only after the needle has been fully stopped, thus preventing the rise or displacement of a work fabric and the loosening of the upper thread.

Claims

What I claim is:

1. A sewing machine comprising a frame; a rotatable shaft fitted to said frame; a reciprocable needle supported by said frame and operably connected with said shaft; stitch forming means mounted on said frame to cooperate with said needle; a presser foot movably supported on said frame; means for moving said presser foot downwardly to a fabric holding position and upwardly to a position released therefrom; and a control system, the control system including drive means for said sewing machine, machine with with said drive means and disengaging it therefrom, an operator actuating member movable between operable and inoperable positions, said member operating said coupling means so as to engage said sewing machine with said drive means upon movement of said member from said inoperable position to said operable position and also operating said coupling means so as to disengage said sewing machine from said drive means upon movement of said member from said operable position to said inoperable position, needle positioning means for stopping said needle in a predetermined position, electrical operating means for operating said needle positioning means and said presser foot moving means, an electrical control circuit for energizing said electrical operating means, said control circuit being energized by said operator actuating means when said member is operated from said operable position to said inoperable position, and time setting means provided in said circuit for holding said presser foot in a fabric holding position until said needle is stopped in a predetermined position by said needle positioning means, whereby said presser foot is automatically raised, to said released position after said needle is stopped in said predetermined position.

2. A sewing machine comprising a frame; a rotatable shaft fitted to said frame; a reciprocable needle supported by said frame and operably connected with said shaft; stitch forming means mounted on said frame to cooperate with said needle; a presser foot movably supported on said frame; means for moving said presser foot downwardly to a fabric holding position and upwardly to a position released therefrom; and a control system, said control system including drive means for said sewing machine, coupling means for engaging said sewing machine with said driving means and disengaging it therefrom; an operator actuating member movable between operable and inoperable positions, said member operating said coupling means so as to engage said sewing machine with said drive means upon movement of said member from said inoperable position to said operable position and also operating said coupling means so as to disengage said sewing machine from said drive means upon movement of said member from said operable position to said inoperable position, needle positioning means for stopping said needle in a predetermined position, a first electrical operating means for operating said positioning means, a first electrical control circuit for energizing said first electrical operating means; a second electrical operating means for operating said presser foot moving means, a second electrical control circuit for energizing said second electrical operating means, said first and second electrical control circuits being energized by said operator actuating means upon its movement from said operable position to said inoperable position, said second electrical control circuit comprising a first switch operated in response to the stop of said needle in a predetermined position by said needle positioning means and a second switch operated after the lapse of time required in stopping said reciprocable needle in a predetermined position, said first and second electrical control circuits being already brought to an operable state by the working of said operator actuating means said second electrical control circuit operating said second electrical operating means only when both first and second switches are operated, whereby said presser foot is automatically raised to said released position after said needle is stopped in said predetermined position.

3. A sewing machine according to claim 2 wherein said first and second switches are connected in series.

4. A sewing machine comprising a frame; a rotatable shaft fitted to said frame; a reciprocable needle supported by said frame and operably connected with said shaft; stitch forming means mounted on said frame to cooperate with said needle; a presser foot movably supported on said frame; means for moving said presser foot downwardly to a fabric holding position and upwardly to a position released therefrom; and a control system, said control system including drive means for operating said sewing machine at a high speed, coupling means for engaging said sewing machine with said drive means and disengaging it therefrom, a treadle movable between an operable position and inoperable position, said treadle operating said coupling means so as to engage said sewing machine with said drive means upon movement of said treadle from said inoperable position to said operable position and also operating said coupling means so as to disengage said sewing machine from said drive means upon movement of said treadle from said operable position to said inoperable position, needle positioning means for stopping said needle in a predetermined position, said needle positioning means comprising a supplementary drive means for driving said sewing machine at a slow speed; position detecting means responsively actuated when the rotatable shaft of said sewing machine driven by said supplementary drive means is brought to a predetermined angular position and brake means for stopping the operation of said supplementary drive means when the position of said needle is detected by the responsive actuation of said position detecting means, a first electrical operating means for operating said needle positioning means, a first electrical control circuit for energizing said first electrical operating means, a second electrical operating means for operating said presser foot moving means, a second control circuit for energizing said second electrical operating means, said first and second electrical control circuits being energized by said operator actuating means upon its movement from said operable position to said inoperable position, said second electrical control circuit comprising a first switch operated by position detecting signals from said position detecting means and a second switch operated after the lapse of time required in stopping said needle in a predetermined position after said first and second electrical circuits are already brought to an operable state by the working of said operator actuating means, said second electrical operating means being operated only when both first and second switches are operated, whereby said presser foot is automatically raised to said released position after said needle is stopped in said predetermined position.

5. A sewing machine including a frame; a rotatable shaft fitted to said frame; a reciprocable needle supported by said frame and operably connected with said shaft; stitch forming means mounted on said frame to cooperate with said needle; a presser foot movably supported on said frame, means for moving said presser foot downwardly to a fabric holding position and upwardly to a position released therefrom; and a control system, said control system including drive means for said sewing machine, coupling means for engaging said sewing machine with said drive means and disengaging it therefrom, an operator actuating means movable between an operable position and inoperable position, said member operating said coupling means so as to engage said sewing machine with said drive means upon its movement from said inoperable position to said operable position and also operating said coupling means so as to disengage said sewing machine from said drive means upon its movement from said operable position to said inoperable position, needle positioning means for stopping said needle in a predetermined position, electrical operating means for operating said needle positioning means and presser foot moving means, an electrical control circuit for energizing said electrical operating means normally closed switch means provided in said control circuit for energizing the same to move said presser foot upwardly and also to operate said needle positioning means said normally closed switch means being opened to move said presser foot downwardly upon movement of said operator actuating means from said inoperable position to said operable position, time setting means disposed said electrical control circuit so as to move said presser foot to a fabric holding position until said needle is stopped in a predetermined position by said needle positioning means, whereby said presser foot is automatically raised to said released position after said needle is stopped in said predetermined position.

6. A sewing machine comprising a needle plate; a frame to be provided with said needle plate on a fabric holding plane; a rotatable shaft fitted to said frame; a reciprocable needle supported by said frame and operably connected with said rotatable shaft; loop taker means mounted on said frame to cooperate with said needle, a presser foot movably supported by said frame; means for moving the presser foot downwardly to a fabric holding position and upwardly to a position released therefrom; thread cutting means operably disposed between said needle plate; loop taker means and said means for operating said thread cutting means; and a control system, said control system including main drive means for said sewing machine, coupling means for engaging said sewing machine with said main drive means and disengaging it therefrom, a first operator actuating means movable between an operable position and inoperative position, said operator actuating means operating said coupling means so as to engage said sewing machine with said main drive means upon movement of said operator actuating means from said inoperable position to said operable position and also operating said coupling means so as to disengage said sewing machine from said main drive means upon movement of said operator actuating means from said operable position to said inoperable position, needle positioning means for stopping said needle in a predetermined position, said needle positioning means comprising a supplementary drive means for driving said sewing machine at a slow speed, position detecting means responsibly actuated when the rotatable shaft of the sewing machine driven by the supplementary drive means is brought to a position adapted to stop said needle in predetermined high and low positions and also to operate said thread cutting means, and brake means for stopping the operation of said supplementary drive means and bring said needle to rest in a predetermined position when the predetermined high and low positions of said needle are detected upon responsive actuation of said position detecting means, a second operator actuating means for operating said thread cutting means, a first electrical operating means for operating said needle positioning means and means for actuating said thread cutting means, a first control circuit for energizing said first electrical operating means, said first electrical control circuit comprising a switching means for normally bringing said position detecting means to a state capable of detecting the predetermined low position of said needle and, upon the working of said second operator actuating means, bringing said position detecting means to a state capable of detecting the predetermined high position of said needle and the thread cutting position and also bringing said supplementary drive means to an operable state, a second electrical operating means for operating said presser foot moving means, a second electrical control circuit for energizing said second electrical operating means, said first and second electrical control circuits operated by said first operator actuating means upon its movement from said operable position to said inoperable position, said second electrical control circuit comprising a first switch operated by signals from said position detecting means for detecting the predetermined high and low positions of said needle and a second switch operated after the lapse of time required in stopping said needle in a predetermined low position after said first and second electrical control circuits are already brought to an operable state by said first operator actuating switch, said second electrical operating means being operable only upon actuation of both first and second switches so as to allow said presser foot to be automatically raised to said released position after said needle is stopped in a predetermined position, said second operator actuating means operated after the stop of said needle in a predetermined low position, whereby the similar cycle of operation as described above is repeated, namely, the operation of said switching means causes said first switch to be actuated again so as to move again the presser foot downwardly to a fabric holding position, said thread cutting means to be energized when said needle is raised up to said needle plate by said supplementary drive means and said presser foot to be again automatically raised when said needle is stopped in a predetermined high position.

7. A sewing machine according to claim 1, wherein said time setting means comprises; a relay energized upon movement of said operator actuating member from said operable position to said inoperable position; a condenser connected in series with said relay; and a discharge resistor for said condenser connected in parallel with said condenser.

8. A sewing machine comprising; a frame; a rotatable shaft fitted to said frame; a reciprocable needle supported by said frame and operably connected with said shaft; stitch forming means mounted on said frame to cooperate with said needle; a presser foot movably supported on said frame; means for moving said presser foot downwardly to a fabric holding position and upwardly to a position released therefrom; and a control system; said control system including; main drive means for operating said sewing machine at a high speed; coupling means for engaging said sewing machine with said main drive means and disengaging it therefrom; an operator actuating member movable between an operable position and inoperable position; said member operating said coupling so as to engage said sewing machine with said main drive means upon movement of said member from said inoperable position to said operable position and also operating said coupling means so as to disengage said sewing machine from said drive means upon movement of said member from said operable position to said inoperable position; needle positioning means for stopping said needle in a predetermined position; said needle positioning means comprising supplementary drive means for driving said sewing machine at a slow speed, position detecting means responsively actuated when the rotatable shaft of said sewing machine driven by said supplementary drive means is brought to a predetermined angular position and brake means for stopping the operation of said supplementary drive means when the position of said needle is detected by the responsive actuation of said position detecting means; first electrical operating means for operating said needle positioning means; second electrical operating means for operating said presser foot moving means; and an electrical control circuit for energizing said first and second electrical operating means; said electrical control circuit comprising; switch means for energizing the control circuit upon movement of said operator actuating member from said operable position to said inoperable position; a first exciting circuit for said first electrical operating means; a first relay for controlling the first exciting circuit to operate the supplementary drive means when said relay is energized through the closing of said switch means upon movement of said operator actuating member from said operable position to said inoperable actuating member from said operable position to said inoperable position and to operate the brake means when said relay is deenergized through the detection of said needle position by said detecting means; a second exciting circuit for said second electrical operating means; time setting means for holding said presser foot in a fabric holding position until said needle is stopped in a predetermined position; said time setting means including a second relay energized upon the closing of said switch means, a condenser connected in series with said relay and a discharge resistor for said condenser connected in parallel with said condenser; said second exciting circuit including a normally closed contact of said first relay and a normally closed contact of said second relay connected in series; capacity of said condenser being set to prevent the exciting of said second exciting circuit until said needle is stopped in a predetermined position by said needle positioning means, whereby, said presser foot is automatically raised to said released position after said needle is stopped in said predetermined position.