US3810438A

US3810438A - Fixed point stop mechanism for sewing needle in sewing machine

Info

Publication number: US3810438A
Application number: US00086692A
Authority: US
Inventors: M Yokoyama; T Kobayashi
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1970-11-04
Filing date: 1970-11-04
Publication date: 1974-05-14
Anticipated expiration: 1991-05-14

Abstract

A fixed point stop mechanism for selectively stopping an output member, such as a sewing needle in a sewing machine in one of a plurality of predetermined positions comprises a position sensing means for sensing the sewing needle being at a selected one of predetermined positions, means for driving the sewing machine at a low speed sufficient to render the position sensing device operative, a first relay connected in series to said position sensing device, and a second relay energized upon operation of the first relay thereby to cause a set position, in which the sewing needle is to be selectively stopped, to be changed over from one to another of the predetermined positions without stopping the rotation of the sewing machine.

Description

United States Patent [191 Yokoyama et a1. Y

[451 May 14, 1974 FIXED POINT STOP MECHANISM FOR SEWING NEEDLE IN SEWING MACHINE [75] Inventors: Masahiro Yokoyama; Takanori Kobayashi, both of Nagoya, Japan [73] Assignee: Mitsubishi Denki Kabushiki Kaisha,

Tokyo, Japan [22] Filed: Nov. 4, 1970 [21] Appl. No.: 86,692

[52] US. Cl 112/219 A [51] Int. Cl...' D05b 69/22 [58] Field ofSearch 112/219 A,2l9 B,2l9 R, 112/220, 67, 87

[56] References Cited 7 UNITED STATES PATENTS 3,174,450 3/1965 Becker et al 112/219 A 3,590,969 7/1971 Kajitani 112/219 A X 3,596,743 8/1971 Yokoyama 112/219 A X' 8/1955 Frankel 112/219 A 3,352,396 ll/l967 Moseley 112/219 A X Primary Examiner-H. Hampton Hunter Attorney, Agent, or FirmRobert E. Burns; Emmanuel J. Lobato [5 7] ABSTRACT A fixed point stop mechanism for selectively stopping an output member, such as a sewing needle in a sewing machine in one of a plurality of predetermined positions comprises a position sensing means for sensing the sewing needle being at a selected one of predetermined positions, means for driving the sewing machine at a low speed sufficient to render the position sensing device operative, a first relay connected in series to said position sensing device, and a second relay energized upon operation of the first relay thereby to cause a set position, in which the sewing needle is to 1 be selectively stopped, to be changed over from one to 7 another of the predetermined positions without stopping the rotation of the sewing machine.

9 Claims, 2 Drawing Figures OPERATORACTUATABLE MEMBER PATENTEI] In 14 um I OPERATOR-ACTUATABLE FIG.

NUMBER OF ROTATION BACKGROUND OF THE INVENTION This invention relates in general to a fixed point stop mechanism selectively stopping an output member such as a sewing needle at a selected one of its predetermined positions and more particularly to a control system therefor.

' In general, when it is desired to stop an output member such as a a sewing needle at a selected one of its predetermined positions, a sewing machine being ina normal operation is firstly decelerated-to be put in sustained rotation at a predetermined low speed to allow a position sensing means to sense the sewing needle being at the selected one of the predeterminedpositions and thereafter stopped when the needle has reached its selected position.

With a conventional fixed point stop mechanism of the type described above, however, in effecting the stoppage of the sewing needle at its predetermined position, it would often occur that a position of the sewing needle, at a time point whenthe speed of rotation of the sewing machine just reaches the aforesaid predetermined low speed, changes each time such a fixed point stop operation is effected. This causes the sewing needle to be accidentally positioned at its predetermined position at that time point, i.e., the sewing machine is unexpectedly stopped without passing through the sustained stage of rotation at the predetermined low speed. Such a lack of uniformity in positional conditions of the sewing needle at the aforesaid time point is accompanied by a larger amount of scatter in the stop-positions of the sewing needle.

Accordingly, in a case where it is desired to stop the sewing needle at the selected one of its predetermined positions with high accuracy such, as the upper end of its stroke, a machine operatoris required to effect a stopping operation in such a manner as consisting of preparatorily stopping the sewing needle at one of the predetermined positions, i.e., the lower end of the stroke, and thereafter manually putting the sewing machine in the sustained rotation of the low speed to permit the sewing needle to be stopped at the desired one, i.e., the upper end of the needle stroke. In addition, the aforesaid stopping operation is not only effective for stopping the sewing needle at the predetermined position with high accuracy but also is required of a sewing machine of the type that includes an automatic thread cutter. As will be apparent, such a stopping operation is complicated in procedure and includes a dead time that is a pause interval of time during the preparatory stoppage of the sewing machine. This has an unfavorable effect on promoting sewing efficiency and labor saving.

SUMMARY OF THE INVENTION 2 the operation of said mechanism in sensing the sewing needle being at another of said predetermined positions and a third element electrically connected to either said first or second element, a first relay electrically connected to said third element, and a second relay adapted to operate to be energized responsive to an energization of the first relay, said second relay cooperating with a first and second relay switches so that upon the energization of the second relay the first relay switch is automatically changed-over from electrical connection with the first element into an electrical connection with the second element and that upon the energization of the second relay the second relay switch is closed thereby to self-hold the second relay.

Itis therefore an object of the invention to provide a fixed point stop mechanism for an output member such as a sewing needle of the type described in which the second relay automatically switches its first relay switch from the first element to the secondelement of the position sensing means to bring the position sensing means from one condition sensing the sewing needle being at one position into another condition sensing the sewing needle being at another position thereby to enable the sewing needle to stop automatically at another position after its passage through one position without stopping the rotation of the sewing machine when the sewing needle passes through its one position.

It is another object of the invention to provide a fixed point stop mechanism of the type described wherein the first relay switch of the second relay is automatically switched from the first to the second element with a time delay after the second relay is energized thereby to adapt the fixed point stop mechanism for a sewing machine with an automatic thread cutter.

BRIEF DESCRIPTION OFTHE DRAWING DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing and FIG. 1 in particular, a source of alternating current generally designated by the reference numeral 1 is shown connected to a full-wave rectifier 2 to supply a flow of current to a control circuit as will be described hereinafter. One terminal of the rectifier 2 is electrically connected to a switch S1 cooperating with an operator-actuatable member such as a foot pedal, which switch is adapted to be connected when the operator treads the foot pedal to effect a normal high-speed operation of the sewing machine, to a circuit including a time-delay relay RAI as described hereinafter and, when the operator ceases the treading of the foot pedal to stop the rotation of the sewing machine, to another circuit including relays RA2 and RA3 as described hereinafter. As well known in the art, a resistor 3 and a condensor 4 connected in series with each other and in parallel to the time-delay relay RAI serve to form a timer for setting a period of a time delay in deenergization of the relay RAl when the current flowing from the source 1 through the relay RAl is shut off by ceasing the treading of the foot pedal. The time delay in deenergization of the relay RAl is so adjusted as to maintain the relay RAl not to be deenergized until the sewing machine is decelerated into sustained rotation at the predetermined low speed.

A needle-position sensing device generally designated by the reference numeral SN may be mounted on the end portion of an arm shaft (not shown) extending beyond a trunk portion (not shown) of the sewing machine and comprises a rotary member 8 secured in electrically insulated relation to the arm shaft to rotate in synchronism with the sewing machine, and a set of position sensing elements or brushes 5, 6 and 7 of any suitable electrically conductive material such as carbon disposed in contact with the rotary member 8. The rotary member 8 comprises a first circular annulus including an annular segment 9a of any suitable electrically conductive material such as copper and an annular segment 91? of any suitable electrically insulating material such as mica plate, which insulating segment 9b corresponds in position to one of predetermined positions, i.e., the upper end on a stroke for the sewing needle. The first annulus consisting of the segments 9a and 9b is rotated by the arm shaft while contacting with the first brush 5. The rotary member 8 further comprises a similar circular annulus including a conductive annular segment 10a and an insulating annular semgment 10h corresponding in position to another of the predetermined positions, i.e., the lower end on the stroke for the sewing needle, the segments 10a and 10h being rotated in alternating contact with the second brush 6, and a conductive surface portion 11 rotated in contact with the third brush 7. It is therefore understood that each of the first and second brushes 5, 6 cooperates with the third brush 7 so that a flow of current therethrough is shut off only when each ofthe first and second brushes 5, 6 comes in contact with the respective 'insulating portion 91) or 1012 and is established when each ofthe brushes 5, 6 comes in contact with the respective conductive portion 9a or 10a. In this example, the insulating portions 9b and 1012 are arranged in substantially diametrically opposite relation with each other while the brushes 5 and 6 are angularly spaced away from each other by an angle of less than I80", so that the current is not simultaneously conducted through the brushes 5 and 6.

As seen from FIG. I, the brushes 5 and 6 are electrically connected respectively to one of a pair of break contacts and one of a pair of make contacts of a relay switch RA3] driven by a second relay RA3 as described hereinafter. Therefore. when the relay RA3 is rendered operative, the make contacts are closed and the break contacts are opened to bring the position sensing device SN into such a condition capable of sensing the sewing needle being at the lower end of its stroke. On the other hand, when the relay RA3 is rendered inoperative, the make contacts are opened and the break contacts are closed to bring the positioned sensing device SN into such a condition capable of sensing the sewing needle being at the upper end of its stroke. Thus, upon operation of the relay RA3, the change-over of the stopping position at which the sewing needle is to be stopped can be effected automatically.

The brush 7 is electrically connected to a first relay RA2 which is deenergized when the position sensing device SN senses the sewing needle being at the lower or upper end of its stroke, i.e., when the brush 5 or 6 comes in contact with the insulating segment 9b or 10]). Connected across the position sensing device SN is a pair of make contacts RAll which operate to close when the relay RA! is rendered operative. It is therefore understood that the relay RA2 is short-circuitted by the relay contacts RA] 1, so that even when the position sensing device SN senses the sewing needle being at one of the predetermined positions the relay RA2 remains energized so far as the contacts RAl I are closed, i.e., the relay RAI remains energized. A switch S2 connected in series with the relay RA3 is adapted to be closed by the operator when he back treads the pedal after ceasing the normal treading of the foot pedal or when there is a force tending to close the switch S2.

It is to be noted that the switch S2 may be removed in case where it is necessary to stop the sewing needle only in one predetermined position.

A pair of break contacts RA2] is connected in series with the switch S2 and closes when the relay RA2 is deenergized. The time-delay relay RA3 connected in series with the break contacts RA2] operates to close a pair of make contacts RA32 with a time delay after it is energized. A period of such a time delay can be suitably adjusted by a variable resistor 12 connected in series with the relay RA3 and a condensor 13 connected across the relay RA3. Thus, the resistor 12 and the condensor 13 form a timing device. The make contacts RA32 are connected across the switch S2 as well as the relay contacts RA2I so that even if the switch S2 and the break contacts RA2] are opened the time-delay relay RA3 can be self-held through the closing of the make contacts RA32.

Generally designated by the reference numeral 14 is a source of alternating current for exciting an auxiliary drive means such as an electric motor SM for driving the sewing machine at the sustained low speed sufficient to allow the position sensing device to sense the sewing needle being at its predetermined position. The electric motor SM is electrically connected in series with a pair of make contacts RA22 of the relay RA2 while a braking device MB for stopping the sustained rotation of the sewing machine is electrically connected in series with a pair of break contacts RA23 of the relay RA2. In the braking device circuit, there is disposed in series a switch S11 cooperating with the switch S1. The switch S1 is closed when the operator treads the foot pedal as was described hereinbefore, but the switch S11 is closed when the operator ceases the treading of the foot pedal.

The operation of the invention, comprising the construction as described above will now be described in conjunction with FIGS. 1 and 2.

A mode of stopping operation of the sewing machine is shown in FIG. 2 wherein the axis of ordinate represents the number of rotations of the sewing machine and the axis of abscissa represents time in seconds.

First, the operation in the case where the sewing needle is to be stopped only at one predetermined position will be described as follows. When the operator treads the foot pedal to sew cloth, the sewing machine is driven by a main driving device (not shown) at the high speed as shown at a straight line a in FIG. 2. At this time, the switch S1 closes the RAl relay circuit while the switch S11 opens the braking device circuit and therefore the current from the source 1 flows only through the break contacts of the switch S1, the relay RAH, the resistor 3 and the condensor 4,-but not the position sensing'device circuit.

Upon completion of one cycle of the desired sewing work, the operator ceases the treading of the foot pedal at a time point shown at b in FIG. 2, causing the switch S1 to close the position sensing device circuit and the switch S11 to close the braking device circuit. Under such a condition, although the RAl relay circuit is rendered open, the relay RAl continues to be excited by the condensor 4 for a time period tl after the RAl relay circuit isopened. In the meantime, the number of rotations in unit time of the sewing machine is decreased in a manner as shown at a sloping line c to predetermined low speed level as shown at e. Such a time delay in deenergization of the relay RAl causes the relay contacts RAM to be closed to short-circuit the position sensing device so that the relay RA2 continues to be energized even if the position sensing device SN senses the sewing needle being at the predetermined position during the deceleration stage c of rotation of the sewing machine. It is to be noted that the delay time :1 of the relay RAl is defined by the timing device to wait until the sewing machine has put in the sustained rotation at the predetermined low speed as shownat e, i.e., the delay time [1 terminates at a time point d during the sustained rotation of the sewing machine. After the lapse of the delay time t1, the contacts RA ll opens and the position sensing device SN is rendered operative. i

Furthermore, the sewing machine continues to rotate at vthe sustained low' speed until the sewing needle reaches the selected one ofits predetermined positions, i.e., the lower end of its stroke. This position corresponds to a time point as shown atfand to that angular position of the insulating segment 9b where it contacts the first brush 5. The contacting of the brush 5 with the insulating segment 91) causes the relay RA2 to be deenergized, whereby the contacts RA22 are rendered open to deenergize the driving motor SM while at the same time the contacts RA23 are closed to energize the braking device MB, resulting in the abrupt stoppage of the sewing needle at the predetermined lower end ofits stroke.

From the foregoing, it will be readily understood that, according to the invention, the sewing needle is always stopped at the selected one of its predetermined positions during the sustained rotation of the sewing machine at the low speed e, unlike the conventional sewing machine in which the sewing needle would be often stopped during the deceleration stage c of the sewing machine. In this manner, the sewing needle of the invention is stopped under the constant rotational condition of the sewing machine, with the result that the sewing needle can be stopped at the predetermined position with high accuracy.

Secondly, the mode of operation for stopping the sewing needle, after its passage through one of the predetermined positions, at another of the predetermined positions will be described as follows: with the fixed point stop mechanism including in a circuit the aforesaid switch S2, upon the completion of one cycle of the desired sewing work, the operator back treads the foot pedal to render all the switches S1, S2 and S11 to be closed; whereby the number of rotations in unit time of 6 the sewing machine is decreased in the aforesaid manner to the predetermined low speedlevel e and thereafter the sewing needle comes into its one predetermined position corresponding tothe'time point f. At this time that the position sensing device SN just senses the sewing needle being at the positionf, the relay RA2 is deenergized to close the contacts RA21 and consequently the relay RA3 is energized as the switch S2 has already been closed. This causes the contacts RA31 to be brought out of electrical connection with the brush 5 but into electrical connection with the brush 6. Thus. the position sensing device SN is prepared for the sensing of the sewing needle being at the other position, i.e., the upper end of the needle stroke. Under such conditions, the brush6 is not yet in contact with the insulating segment 10b so that the relay RA2 is energized again to close the contacts RA22 to energize the driving motor SM while opening the contacts RA23 to deenergize the braking device MB. Therefore, the sewing machine is allowed again to increase in speed and its speed reaches a predetermined low speed level It substantially equal to the aforesaid level e. The sewing machine continues to be driven at such a low speed h until the insulating segment 10b comes in contact with the brush 6 as shown at a time point i in FIG. 2. By the contacting of the brush 6 with the insulating segment 10b, the relay RA2 is again deenergized to open the contacts RA22 thereby stopping the rotation of the driving motor SM and to close the contacts RA23 whereby the brake is applied to the motor SM by the braking device MB, resulting in the stoppage of the sewing needle at the'predetermined upper end of its stroke corresponding to the time point i. When it is desired to initiate a next cycle of the desired sewing work, the operator is required merely to actuate the foot pedal, whereupon the switch S1 opens the position sensing device circuit and the relay RA3 is deenergized to cause the contacts RA31 to be brought into electrical connection with the brush 5. Thus, the fixed point stop mechanism is prepared for a next stopping operation.

With the conventional fixed point stop mechanism, when it is desired to stop the sewing needle at the selected one of the predetermined positions after its passage through the other position during the sustained rotation of the sewing machine at the relatively low speed, the stoppage of the sewing needle at the selected one position is effected in such a manner that, when the position sensing device senses the sewing needle being in the other position corresponding to the time 'pointf, the sewing machine is decreased in speed to zero, stopping once at the other position and thereafter driven again to be put in the sustained rotation at the relatively low speed to permit of the sewing needle being stopped at the selected one of the predetermined positions. Therefore, it will be understood that a time during the sewing needle stays in the other positionfis a dead time for the sewing work by the conventional sewing. machine. In contrast, with the fixed pointstop mechanism of the invention, after the position sensing device senses the sewing needle being at the other position, the position sensing device is automatically set in a condition capable of sensing the sewing needle being at the selected one of the predetermined positions. Thus, the stoppage of the sewing needle at the desired position can be effected automatically with ease.

In addition, in case where the sewing machine is equipped with an automatic thread cutter, it is preferable that the make contacts of the relay switch RA3l close with a suitable time delay 12 after the relay RA3 is energized. During the period of the time delay, the thread cutting operation is accomplished automatically and the period of the time delay can be so adjusted by the timer consisting of the resistor 12 and the condensor 13 as to have a minimum magnitude to be required to effect the thread cutting operation, resulting in savings in the working hours and in a high operating efficiency of the sewing machine. For example, the time delay may be adjusted to have a relatively short time as shown between the time pointfand a time point g on the solid curve depicted in FIG. 2 or may be adjusted to have a relatively long time as shown between the time pointfand a time point g. In the latter case, the sewing needle is stopped at the predetermined upper end of its stroke corresponding to a time point 1" shown on a dotted curve.

What we claim is:

l. A fixed point stop mechanism for a sewing needle in a sewing machine comprising: a source of electrical energy; a position sensing device for sensing when a sewing needle is at any one of a plurality of predetermined positions; an auxiliary motor connectable to said source for driving the sewing machine at a low speed sufficient to allow said position sensing device to sense the sewing needle when same is at a selected one of said predetermined positions; brake means or braking and stopping rotation of said auxiliary motor after said selected position of the sewing needle is sensed by said position sensing device; a first relay having make and brake contacts and connected in series with said position sensing device defining a series circuit; switching means co-acting with an operator actuatable member of the sewing machine and movable to one switching position in response to cessation of actuating of the member to effect energization of said first relay thereby effecting energization of said auxiliary motor to enable said position sensing device to sense the sewing needle being at said selected position; means responsive to the sensing of the needle at said selected position for effecting deenergization of said first relay accompanied by deenergization of said auxiliary motor and at the same time energizing said brake means for breaking said auxiliary motor and stopping same to stop the sewing needle at said selected position; said position sensing device including first circuit means for sensing a lower and an upper position of the sewing needle, and a second relay having make and brake contacts and connected to be energized through second circuit means comprising another series circuit including a switch connected to break contacts of said first relay, said second series circuit connected in parallel with make contacts of said second relay, whereby energization of said second relay enables said circuit means to sense the upper needle position.

2. A fixed point stop mechanism according to claim I, wherein said position sensing device comprises a first delay circuit means comprising a variable resistor having a movable arm and connected between said second relay and said second circuit means, and a condensor connected to said arm of said resistor and connected in parallel with said second relay whereby the time at which said second relay is energized after said second switch is closed is variable.

3. A fixed point stop mechanism according to claim 1, including a third relay having make and break contacts and connected to said switching means and energized when the member is actuated and deenergized when the actuation of the member is ceased, delay circuit means comprising a resistor and a condensor connected in series and the two connected in parallel with said third relay. make contacts of said third relay connected in parallel with said position sensing device and in series with said first relay for delaying deenergization of said third relay and effecting energization of said first relay independently of the sensing of said selected needle position by said position sensing device, and wherein said delay circuit means delay deenergization of said third relay for a predetermined time period equal to the time from which the actuation of the member is ceased to the time the speed of rotation of the sewing machine is allowed to decrease to said low speed.

4. In a sewing machine having a movable sewing needle, a fixed point stop mechanism for selectively stopping said sewing needle in one of a plurality of predetermined stop positions comprising: drive means for driving said sewing needle at a first speed; auxiliary drive means for driving said sewing needle at a second speed which is substantially less than said first speed; selecting means for alternatively selecting one of said drive means and auxiliary drive means to drive said sewing needle; position sensing means operative when said sewing needle is driven at said second speed for sensing one of a plurality of predetermined stop positions wherein said sewing needle is to be selectively stopped and developing a corresponding output signal and including means for selecting a predetermined one of said stop positions, a switch having two switching states, a relay connected to said switch deenergized when said switch is in one switching state and energized when said switch is in another switching state, said relay being operative when energized to render said position sensing means effective to sense the selected position of said sewing needle and operative when deenergized to render said position sensing means ineffective to sense the selected position of said sewing needle, and delay circuit means connected to said relay for delaying the deenergization of said relay for a predetermined delay time after said switch is in said one switching state to enable said sewing needle to be driven at said second speed before said position sensing means is rendered effective; and braking means responsive to the output signal for braking said sewing needle and stopping same at the selected predetermined stop position.

5. In a sewing machine having a movable sewing needle, a fixed point stop mechanism for selectively stopping said sewing needle sequentially in at least two predetermined stop positions comprising: drive means for driving said sewing needle at a first speed; auxiliary drive means for driving said sewing needle at a second speed which is substantially less than said first speed; selecting means for alternatively selecting one of said drive means and auxiliary drive means to drive said sewing needle; position sensing means operative when said sewing needle is driven at said second speed for sensing sequentially said at least two predetermined stop positions wherein said sewing needle is to be selectively stopped and developing corresponding first and second output signals; braking means co-acting with said auxiliary drive means and responsive to the first output signal for braking said sewing needle and stopping same in one of said at least two stop positions for a preselected time after which time said auxiliary drive means resumes driving said sewing needle and responsive to the second output signal for braking said sewing needle and stopping same in the other of said at least two stop positions.

6. A sewing machine according to claim wherein said position sensing means comprises a. switch having two switching states, a relay connected to said switch deenergized when said switch is in one switching state and energized when said switch is in another switching state said relay operative when energized to render said position sensing means effective to sense the selected position of said sewing needle and operative when deenergized to render said position sensing means ineffective to sense the selected position of said sewing needle, and delay circuit means connected to said relay for delaying the deenergization of said relay for a predetermined delay time after said switch is in said one switching state to enable said sewing needle to be driven at said second speed before said position sensing 10 means is rendered effective.

7. A sewing machine according to claim 5, wherein said position sensing means comprises circuit means for sequentially sensing two predetermined stop positions and comprising a switch having two switching states. a relay connected to said switch energized when said switch is in one switching state and deenergized when said switch is in another-switching state, said relay operative when energized to render said position sensing means effective to sense one position of said sewing needle and operative when de-energized to render said position sensing means effective to sense another position of said sewing needle and delay circuit means connected to said relay for delaying for a predetermined time the energization of said relay after said switch is in said one switching state.

8. A sewing machine according to claim 7, wherein said delay circuit means includes means for selectively varying the delay time.

9. A fixed point stop mechanism according to claim 1, wherein said operator-actuated member comprises a treadle pedal.

Claims

1. A fixed point stop mechanism for a sewing needle in a sewing machine comprising: a source of electrical energy; a position sensing device for sensing when a sewing needle is at any one of a plurality of predetermined positions; an auxiliary motor connectable to said source for driving the sewing machine at a low speed sufficient to allow said position sensing device to sense the sewing needle when same is at a selected one of said predetermined positions; brake means or braking and stopping rotation of said auxiliary motor after said selected position of the sewing needle is sensed by said position sensIng device; a first relay having make and brake contacts and connected in series with said position sensing device defining a series circuit; switching means co-acting with an operator actuatable member of the sewing machine and movable to one switching position in response to cessation of actuating of the member to effect energization of said first relay thereby effecting energization of said auxiliary motor to enable said position sensing device to sense the sewing needle being at said selected position; means responsive to the sensing of the needle at said selected position for effecting deenergization of said first relay accompanied by deenergization of said auxiliary motor and at the same time energizing said brake means for breaking said auxiliary motor and stopping same to stop the sewing needle at said selected position; said position sensing device including first circuit means for sensing a lower and an upper position of the sewing needle, and a second relay having make and brake contacts and connected to be energized through second circuit means comprising another series circuit including a switch connected to break contacts of said first relay, said second series circuit connected in parallel with make contacts of said second relay, whereby energization of said second relay enables said circuit means to sense the upper needle position.

2. A fixed point stop mechanism according to claim 1, wherein said position sensing device comprises a first delay circuit means comprising a variable resistor having a movable arm and connected between said second relay and said second circuit means, and a condensor connected to said arm of said resistor and connected in parallel with said second relay whereby the time at which said second relay is energized after said second switch is closed is variable.

3. A fixed point stop mechanism according to claim 1, including a third relay having make and break contacts and connected to said switching means and energized when the member is actuated and deenergized when the actuation of the member is ceased, delay circuit means comprising a resistor and a condensor connected in series and the two connected in parallel with said third relay, make contacts of said third relay connected in parallel with said position sensing device and in series with said first relay for delaying deenergization of said third relay and effecting energization of said first relay independently of the sensing of said selected needle position by said position sensing device, and wherein said delay circuit means delay deenergization of said third relay for a predetermined time period equal to the time from which the actuation of the member is ceased to the time the speed of rotation of the sewing machine is allowed to decrease to said low speed.

6. A sewing machine according to claim 5; wherein said position sensing means comprises a switch having two switching states, a relay connected to said switch deenergized when said switch is in one switching state and energized when said switch is in another switching state said relay operative when energized to render said position sensing means effective to sense the selected position of said sewing needle and operative when deenergized to render said position sensing means ineffective to sense the selected position of said sewing needle, and delay circuit means connected to said relay for delaying the deenergization of said relay for a predetermined delay time after said switch is in said one switching state to enable said sewing needle to be driven at said second speed before said position sensing means is rendered effective.

7. A sewing machine according to claim 5, wherein said position sensing means comprises circuit means for sequentially sensing two predetermined stop positions and comprising a switch having two switching states, a relay connected to said switch energized when said switch is in one switching state and deenergized when said switch is in another switching state, said relay operative when energized to render said position sensing means effective to sense one position of said sewing needle and operative when de-energized to render said position sensing means effective to sense another position of said sewing needle and delay circuit means connected to said relay for delaying for a predetermined time the energization of said relay after said switch is in said one switching state.