US3347194A

US3347194A - Power assist mechanism for sewing machines

Info

Publication number: US3347194A
Application number: US515867A
Authority: US
Inventors: Arthur N Hale; James J Matias
Original assignee: Union Special Machine Co
Current assignee: Union Special Machine Co
Priority date: 1965-12-23
Filing date: 1965-12-23
Publication date: 1967-10-17
Anticipated expiration: 1984-10-17
Also published as: DE1685070A1; FR1506066A

Description

OC- 17, 1967 A, N. HALE ETAL POWER ASSIST MECHNISM FOR SEWING MACHINES 4 Sheets-Sheet l Filed Dec. 25, 1965 O O i? x C- W, 1967 A. N. HALE ETAL POWER ASSIST MECHANISM FOR SEWING MACHINES Filed Dec. 23, 1965 FIGZ..

CCL 17, 1967 A. N. HALE ETAL POWER ASSIST MECHANSM FOR SEWING MACHINES 4 Sheets-Sheet 5 Y Filed Deo. 23, 1965 FIG.

F-iC.

Oct. 17, 1967 A. N. HALE ETAL POWER ASSIST MECHANISM FOR SEWING MCHINES 4 Sheets-Sheet 4 Filed DeC.

United States Patent Office 3,347,194 PWER ASSIST MECHANISM FOR SEWING MACHINES Arthur N. Hale, Park Ridge, and James J. Matias, Hodman Estates, ill., assiguors to Union Special Machine Company, Chicago, lll., a corporation of Illinois Filed Dec. 23, 1965, Ser. No. 515,867 18 Claims. (Cl. i12- 237) This invention relates to high-speed sewing machines of the industrial type. It is concerned with reducing the amount of effort required by the operator of the machine, in the course of its operation, to perform stitching operations on a relatively large number of workpieces.

In the course of operating a sewing machine there are a number of devices which normally require manual operation by the operator in order to complete the desired stitch-ing and other work on each workpiece. These include a presser foot which must be lifted and lowered upon dealing with each workpiece to be stitched upon certain machines, work clamping and releasing mechanism which must be similarly operated on other types of machines, thread cutting or edge trimming mechanism on certain machines, and other devices requiring manual control in performing other operations on a succession of workpieces. The term manual operation as used herein is to be understood as referring to devices normally operated either by han-d or by connections from a treadle or a knee press member for imparting the force or energy needed to perform the desired function. These manual operations have heretofore called upon the operator to expend a substantial amount of effort during a day to keep-up with the work load.

An important purpose of the present invention has been to reduce as far as possible the amount of energy or effort required to be used by the operator in bringing about the proper functioning of the manually operated devices that must be frequently brought into action in dealing with a large stack of work-pieces.

While, as stated above, the invention is adapted for use in the periodic operation of any of a number of different manually controlled devices, it will be described hereinafter as used in connection with the presser foot lifting mechanism of a sewing machine. In modern high speed sewing machines it is necessary to apply a substantial spring force to the presser foot carrying member in order to insure its proper action in holding the work against the work supporting surface of the machine. If the spring force is not adequate, it has been found that during high speed operation of the machine the frequent upward movement of the work and presser foot, resulting `from the upward movement of the feed dog, will cause the presser foot to oat and not come down quickly enough to hold the work against the support surface and the feed dog. This results in improper stitch formation. Accordingly the spring pressure applied to the presser foot must be quite high, and the amount of effort which the operator is required to expend, to lift the presser foot and enable the introduction and removal of successive workpieces, is fatiguing.

Under the present invention only a small force, not exceeding about 4.5 lbs., is required to be applied by the operator to a foot treadle or knee press to overcome a much greater force that is need to lift a presser foot away from the work. This is accomplished by enabling the operator to shift a spring urged valve from its normally closed position into an open or active position, with only a small force and under a readily sensed condition, to bring into action a pneumatically operated piston to supply the necessary force to lift the presser foot a desired distance for the proper manipulation of the work.

Toward the foregoing end, the invention contemplates the provision of a single assembly having an air operated piston connected with the presser foot operating mechanism for lifting and then permitting the lowering of the same under spring action, and a valve axially slidable within the piston for variably and accurately controlling the introduction of air into a cylinder surrounding the piston and for controlling the discharge of air from the cylinder, to bring about the desired up and down movements of the presser foot. The arrangement is such that a small force applied to a treadle or knee press, to overcome the force of a relatively light spring urging such manually operated member into a normal position, will operate the valve to place the cylinder in communication with the source of supply of air under pressure. As such air is introduced into the cylinder it urges the piston downwardly in the same direction that the valve has been shifted. However the compressed air acting on the piston supplies a much greater force to a connecting linkage from the piston to a presser foot than the force applied by the operator to the valve. This extra force is adequate to lift the presser foot against the action of the rather strong spring needed to urge the presser foot toward the work support in order to insure proper and uniform stitch formation.

As the piston moves downwardly in the manner explained, its relationship to t-he valve tends to be restored to that normally maintained, so that if the operator Wishes to have the presser foot lifted to a somewhat greater extent the relatively small force must continue to be applied by the operator to the treadle or knee press or the like to cause the valve to be shifted still further downwardly and thus maintain the cylinder in communication with the source of air under pressure. Once the desired elevation of the presser foot has been achieved, the valve and piston will be shifted slightly relative to each other to assume a relative position, in which no further air will be delivered to the cylinder; but both the valve and piston will be at a lower point within the cylinder, thus retaining the presser foot in its raised position. When the particular workpiece being manipulated by the operator has been properly dealt with, the downward force applied to the valve member is released so that the spring which urges the valve member upwardly will do so, thus restoring it to its normal position in relation to the piston. This will then place the compressed air in the cylinder in communication with .passages extending outwardly to the atmosphere, thereby again placing the presser foot under the downward force of its relatively strong spring so that the machine may be set into operation for the Seaming of the new workpiece that will have been introduced by the operator.

As will Abe explained in connection with the detailed description of a preferred embodiment of the pneumatic assist mechanism of the invention, a rather precise relationship is provided between various parts of the structure, and means are also provided for accurately adjusting `certain parts of the `device to achieve the smoothest possible operation of the unit. These are important aspects of the invention, since they minimize the production of objectionable noise and vibration in the use of the mechanism.

With the foregoing general explanation as to the nature of the invention, a preferred embodiment of the same, with provisions for control either from a foot treadle or a knee press, will now be described in detail in relation to the accompanying drawings of which:

FIG. 1 is a front elevational view of a sewing unit comprising a supporting table, with a sewing machine mounted on the top thereof and with an electric transmitter together with various devices incorporated in the present Patented ct. 17, 1967i invention mounted beneath the table top, parts of the structure being broken away and shown in section;

FIG. `2 is an elevational view of the pneumatic power unit of the present invention connected with a treadle for controlling the operation or" the same;

FIGsZa is a detail view showing a portion of the unit disclosed in FIG. 2, as seen from the left of the latter;

FIG. 3 is a cross-sectional view through the vpower unit, with a .portion of the valve member shown in section and another portion thereof in elevation;

FIG. 4a is an elevational view of the piston element of the unit as seen from the front in FIG. 3;

FIG. 4b is an elevational view of the piston element as seen from the right in FIG. 3;

FIG. 4c is a top plan view of the piston element;

FIG. 5 .is a detail view showing the valve element in elevation;

FIG. 5a is a top plan view of the Valve element;

FIG. 6 is a detail view showing in elevation a portion of the means by which the power unit is mounted on the supporting structure of the work table;

FIG. 6a is an elevational view of the parts shown in FIG. 6, as seen from the left of the latter;`

FIG. 7 is a front elevational view of a power unit and a form of control mechanism therefor arranged for control by a knee press member, certain elements being shown in section; and

FIG. 8 is a top plan view of the construction shown in FIG. 7, and includes the knee press control member.

Turning now to the drawings, there is illustrated in FIG. 1 a sewing machine table structure Lhaving a top member 10 secured to the upper ends of leg members 11. Each of the latter is formed of two telescopically arranged parts to enable lengthening or shortening of them to adjust the elevation of the top 10 to suit the particular requirements of the operator of the sewing machine. Horizontally disposed members 11a and 11b and angularly disposed brace members 11C serve to give the table structure the desired rigidity and strength. Mounted on table top 10 is a sewing machine 12 which may be of any of a variety of different types of construction. It may, for example, be of the type shown in the Covert Patent No. 2,977,910, dated Apr. 4, 1961. It will ybe understood Athat the table has a suitable opening therein through which the base portion of the -frame of the sewing machine may extend, while a work supporting member of the sewing machine frame structure rests upon the top of the table 10. The sewing machine has suitable stitch-forming devices, not shown, which may be of any of a number of different forms and which have no bearing upon the present invention. Also the machine embodies work feeding mechanism of the four-motion feed dog type, such as that illustrated in the above-mentioned Covert patent, but which likewise does not enter into the present invention except in so far as it necessitates the use of a relatively strong spring for urging the presser foot downwardly, for t-he reasons mentioned above.

Since the embodiment of the invention to be described in detail herein is concerned with the provision of a pneumatic assist arrangement for relieving the operator of the necessity of expending substantial effort in bringing about the lifting of the presser foot, this has lbeen shown at 14 and is secured to the lower end of a presser bar 13 mounted for vertical movement within a bearing sleeve 13a carried by the head of the overhanging arm of the machine frame. A coil spring 15 has its lower end disposed about the upper end of the presser bar 13 and exerts a downward force against an arm 13b carried by the presser bar. At its upper end the spring 15 surrounds the stem of a screw-threaded element 15a which may be turned by a knurled head 15b to adjust the height of this member and thus the amount of force that is exerted by the spring 15. For lifting the presser foot there is rockably mounted within the overhanging arm of the frame structure of the machine a lever 16. This is rockable about a pivot 16a and has its forward end connected by a linkv pneumatic power means of the present invention, in the manner to be explained in detail. As conventional, the sewing machine is provided with a combined handwheel and pulley 18 secured to thek main drive shaft of the ma.- chine, and which is connected by a lbelt 19 with a pulley 2t! adapted to be driven -by an electric motor forming part of a transmitter or drive unit 21. Current is delivered to the motor from a power source through a line 22. Whenever the machine is to be put into operation to form a line of stitching, the pulley 20 which forms a part of a clutch and brake arrangement included in the transmitter unit is put into operation by suitable connections under the control of the operator. Such connections include a lever 23 rockably mounted on theframe of the transmitter and having an upwardly extending arm arranged to.

bring about engagement of the clutch which drives the pulley 26. The lever 23 is provided With a series of openings 23a which may be selectively connected by a screw 23h with an extensible rod 24. The latter is formed in two sections which are clamped together by a collar 25 and set screw 25a. Thus the overall length of the rod 24 may be varied in accordance with the height of the table top and the like. At its lower end the rod 24 has a hook that is connected with an arm 26 secured to the rear end of a treadle 27 that is rockable by the foot of an operator about a supporting rod 28. Also rockably supported by the rod 28 is another treadle 29 which is adapted to lbe operated by the foot of the operator to bring about the lifting of the presser foot. As best shown in FIG. 2, the treadle 29 has a rearwardly extending arm 29a to which is .pivotally connected a coupling member 30 having screw-threaded engagement with the lower end of a rod 31 which has its upper end in screw-threaded engagement with another coupling element 32 which is pivotally connected by a screw or ybolt 32a with a block 33 having screw-threaded engagement with a downwardly extending hollow stem or sleeve 34 forming part of the valve to be hereinafter described in some detail.

Downward movement of the rod 31, block 33 and the stem 34 throws into action the power assist means indicated generally at 35 and this power assist unit is iixedly secured to the table structure carrying the sewing machine, but it is adapted for adjustment and setting in various positions in relation to the table structure to locate it most conveniently in relation tothe operator and the part to be driven. A spring 36 having its lower end connected with the arm 29a of treadle 29 has its upper end connected by a screw 36a (FIG. 2a) to a stationary part of the power assist unit. Thus the rod 31 is urged upwardly into a position which may -be characterized as the normal position in which the power assist unit is inactive. As will be explained hereinafter, the downward movement of the rod 31 under the action of the foot treadle operates a valve forming part of the unit 35 to bring into action a power piston which has connected with it an upwardly extending rod 38 carrying a coupling member 39 which is in turn connected by a screw or bolt 39a with the lower end of a rod 40 that has its upper end connected with the free end of the lever 16 by means of a screw or bolt 41, as shown in FIG. 1.

The power assist unit designated generally as 35 comprises various components which are of simple form and readily assembled. It includes a cylinder 42 havin-g a sufcient wall thickness to withstand the pressure of the air utilized in the operation of the device. At thetop of the cylinder 42 there is a closure member 43 having an outwardly extending ange portion cooperating with the top surface of the cylinder and an inwardly extending portion snugly fitting within the bore of the cylinder. For retaining the top closure rmly on the cylinder there is provided a plate 44 having a central opening therein adapted to tit snugly about the ange portion of the closure 43 and cooperating with a shoulder of the latter to retain the closure firmly against the top of the cylinder. Member 44 also has four downwardly turned, semi-circular lian-ge portions 44a (FIGS. 3 and 7) forming part of the supporting structure for the power assist unit. At the -bottom of the cylinder there'is provided a member 45 similar to member 44 but in inverted position, arranged to cooperate with shoulders at the lower end of the cylinder. It is provided with upwardly extending, semi-circular flange portions 45a. The two

members

44 and 45 are firmly secured to the opposite ends of the cylinder by a plurality of bolts 46 extending throughout the length of the cylinder and having nuts 47 at their lower ends for securing the parts in firmly assembled relation. As shown in FIGS. 6 and 6a, there is provided a U-shaped frame structure 48 having a base wall 49 and parallel walls 49a and 4917 extending outwardly from the base. Frame structure 48 is secured to a rigid support plate 50 'by means of screws 51. The shanks of the latter cooperate with

arcuate grooves

52 and 53 in the Wall 49 and thus the latter with its

side walls

49a and 49b may be turned through a suitable angle in relation to the support .plate 50. The latter has tubular members S4 and 55 rigidly connected with it, and these tubular members are arranged to cooperate with circular openings in a support 56 rigidly secured to the leg structure 11 of the table by means of `

brackets

57 and 58. The support member 56 may have a plurality of spaced circular openings to receive the

tubular elements

54 and 55 at different elevations, and the latter are secured in their selected positions by set-screws 59.

Within the cylinder 42 there is mounted a piston 60 (FIGS. 3, 4a, 4b and 4c) which has a close sliding fit in relation to the inner wall of the cylinder. This piston has an axially extending bore 61 of a predetermined diameter in the major portion of its length. At the upper and lower ends of the passage provided by the bore the latter is slightly enlarged in its internal diameter, and that portion 60d of the .piston at the lower end thereof, which carries the enlarged diameter passage, has a slightly smaller outside diameter than that of the remainder of the piston. This is to provide a passage for the escape of air between the inner wall of the cylinder and the outer wall of the portion 60d of the piston in the manner to be later eX- plained. The inner wall of the portion 60d is provided with screw threads to receive the threaded portion of a member 62. This arrangement is such that the extent to which member `62 is introduced into the lower end of the piston may be adjusted slightly. To facilitate such adjustment t-he number 62 is provided with an enlarged head portion 62a which is knurled, as shown in FIGS. 2 and 7. The lower portion of member 62 has an opening through which the stem 34 extends and in which the latter is axially slidable to a limited extent. The rest of the opening through member 62 is slightly larger so as to provide an annular recess 62b for the pocketing of air around the stern 34. The extent to which the stem 34 is urged upwardly is predetermined by a nut 62C having screwthreaded engagement with the stem to enable it to be adjusted to a certain extent in relation to the stem. The spring 36 will normally urge the stem upwardly until the upper surface of nut 62e engages the lower face of member 62.

In the upper end of the piston, the slightly, enlarged internal diameter thereof has a snug fitting engagement in relation 4to a radially enlarged bottom portion 38a of the connecting rod 38. This enlarged lower portion of the connecting rod is held firmly in fixed position within the piston by a snap ring -63 which cooperates with a suitable groove in the inner Wall of the piston and rests lupon the upper surface of the enlarged portion 38a of the connecting rod. Preferably this enlarged lower end is provided with a groove adapted to receive a seal 64 cooperating with the inner wall of the piston to prevent any appreciable movement ofair between the piston and said enlarged portion of the connecting rod. The main portion of the connecting rod 38 extends upwardly through the top closure member 43 of the cylinder and cooperates with a sealing element 65 fitted within a groove in the upward extension of member 43.

Slida'ble within the bore 61 of the piston 60 is a valve member 66 integrally connected with the stem or sleeve 34. As best shown in FIGS. 3 and 5 the upper end of the valve has spaced surfaces 66a and l'66b providing a groove 66e adapted to receive a sealing element 67 cooperating with the inner surface of the piston. Another annular groove 66d below portion 66h provides a channel Ifor the delivery of air under pressure in the manner to be described. Below this channel is a further surface 66e, of somewhat greater axial extent than the

surfaces

66a and 66h, for close cooperation with the inner wall of the piston in a certain region. The valve member, with its hollow stem 34 as well as the various portions just described above, is provided with a longitudinally extending bore 66g which is open at its lower end for communication with a source of air in a manner to be explained. This bore is open up to the top of groove 66d, but above that groove it is closed off by a plug 66j (FIG. 3). Radial passages 66h serve to connect therbore 66g with the groove 66d.

In the normal position of the piston and valve member, as shown in FIG. 3, the groove 66d is slightly above a pair of passages 60h extending through the wall of the piston. These openings 60h communicate with longitudinally extending grooves 60g provided in the outer su-rface of the piston. This arrangement is such that when the Valve member is lowered to carry the groove 66d into alinement with the openings 60h the air under pressure will be delivered to the grooves `60g and thence to a compartment or pocket 72 at the top of the cylinder, above the bottom portion 38a of the connecting rod. In this way a downward force will be applied to the piston and its connecting rod 63 which will in turn be imparted to the lever 16 for lifting the presser foot.

Returning to the normal position of the valve in relation to lthe piston it will =be seen that the bottom surface of portion 66e of the valve is slightly above the lower edges of a pair of openings 601 extending through the piston wall adjacent the lower end of the grooves 60g. Accordingly when the parts are in this normal position any air which has previously been accumulated in the pocket 72 will be discharged through grooves 60g, openings 601' and between the reduced diameter portion of valve 66 and the inner surface of bore 61 of piston 60 down to openings 60]', extending through the wall of the piston, and then will be discharged to the outside atmosphere through an outlet passage provided between the cylinder and the reduced diameter portion 60d of the piston. Therefore when the parts are in this normal position the presser foot will be urged by the full force of its spring toward the work. However when the valve is shifted downwardly, as -mentioned above, to bring the groove 66d into alinement with passages 60h to deliver air -under pressure into pocket 72, the portion 66e of the valve will close off the passages 601'.

For the most effective functioning of the valve it has been found desirable to form the passages 60h and 601' at a slight angle, preferably about 2, to a plane at right angles to the longitudinal axis of the passage through the piston. So also it has been found desirable to make the passages 601' of slightly greater dimension in an axial direction than the passages 60h. These particular features of vthe construction serve to improve the smoothness of operation of the device.

Now turning to the condition in which the valve has been lowered to cause introduction of air under pressure into pocket 72, this will naturally cause downward movement of the piston so that if the valve were not lowered still further the delivery of air under pressure would be very quickly cut-off. Therefore when it is desired to lift the presser foot to a greater extent than would be achieved in this short interval of time, the operator must continue to apply about the same force to the foot treadle to cause the valve to move downwardly along with the piston. Once the presser foot has been lifted tothe desired extent the operator simply needs to hold the treadle in the particular postion it has reached until the removal of one piece of work and the introduction of the next piece has been completed. Then the treadle may be released to permit the presser foot to descend into its active position under the force of spring 15. It Will be appreciated that once the treadle has -been rocked sufficiently to enable the piston to lift the presser foot to the desired extent, the delivery of further air into the chamber or `pocket 72 will be cut-off by virtue of the openings 60h being carried slightly below the groove 66d in the valve. But so long as the approximately 4.5 lbs. pressure is maintained on the treadle the piston will not move down sufficiently to carry the openings 601' below the portion 66e of the valve.

For the delivery of air to the interior of the valve member, the block element 33 is provided with passages 33a and 33h disposed at right angles to each other. Alined with the passage 33a is a fitting 67 adapted to receive and retain the end of a hose line 68. Passage 3311 is aligned withthe longitudinal passage within the valve and its downwardly extending stem 34..As shown in FIG. l the hose line 68 may suitably have connected into it a standard pressure regulating device 69, a standard filter 70, and a lubricant supplying means 71.

Between the top of the valve member 66 and the bottom of the enlarged base of the connecting rod 63 there .is a `small pocket 73 which varies to some extent in its vertical dimension during the operation of the device. In order to have the features function properly it is important that no substantial accumulation of air under pressure should take place Within the pocket 73, since any such accumulation resulting from leakage of high pressure air into the pocket would interfere with the proper functioning of the device. Accordingly this pocket is placed incommunication with the atmosphere by a passage formed by a dead end bore 3811 within the connecting rod and a transverse opening 380 extending from the bore to the outer surface of the connecting rod.

Provision is also made for preventing the delivery of air under pressure from the channels 60g downwardly between the outer surface of the piston and the inner wall of the cylinder, which might then ultimately be discharged to the atmosphere through the passage provided between the lower, reduced diameter portion 60d of the piston and the lower end of the cylinder. To avoid this danger the outer wall of the piston is provided with a groove 60u having the cross-sectional configuration shown in FIG. 3. Any air under pressure which finds its way into the groove 60C will be caused to develop a swirl by virtue of the configuration of the groove, and this swirl will eliminate the further movement of air under pressure` downwardly toward the passage mentioned.

Another feature of the valve member is the provision of the enlarged, radially extending flange 661' having a frusto-conical upper portion in the region of the outlet passages 60j. While the normal position of the flange 661' may be varied slightly by adjustment of the nut 62e, the arrangement is such that the passages 60j are never completely cut-off. They are preferably left open widely enough to permit the free discharge of air from the pocket formed between the inner surface of the piston and the outer surface of the reduced diameter portion of the valve member.

From the foregoing description of the invention it will be appreciatedthat there are four pockets or compartments for the possible accumulation of air in the unit, namely: (l) the high pressure region 72,(2) the low or no super-atmospheric pressure region 73, (3) the further low or no super-atmospheric pressure region between the inner wall 61 of the piston and the outer surface of the reduced diameter portion of the valve above the flange 661' thereof, and (4) a low or no super-atmospheric pressure region below the flange 661V and within the member 62. All ofthe low or no pressure regions mentioned assist in absorbing shocks. and reducing vibrations incident to the power action of the piston.

In FIGS. 7 and 8 there is shown an embodiment of the invention adapted for operation from a knee press member under the control of the operator, instead of from the treadle 29 shown in FIGS. 1 and 2. A part of the structure required for suitable connection with a knee press member may, if desired, be incorporated in all units vso as to adapt them for control either by a foot treadle or a knee press as a particular customer may desire. Therefore a part of the added structure needed forthe knee press control is shown in FIG. 3. This includes a -member 75 at the top of the power unit which is secured to the cylinder and other parts of the structure by means of the bolts 46, as shown in FIG. 3. In the event that the unit is definitely intended to be for control of a foot treadle, this top member 75 may of course be omitted.

Member 75 is provided with an upwardly extending.

flange 7511 around a substantial portion of its planar outline, as shown in FIGS. 7 and 8. At its right end (FIG. 7) the member 75 has an upstanding arm 76 toward the front of themachine and a corresponding upstanding arm 77, largely concealed by other parts in FIG. 8, toward the rear of the machine, These arms are adapted to receive one branch of a U-shaped lever 78,"

the form of which is best shown in FIG. 8. The branch, designated 78a which is thus journaled in the upstanding arms 76 and 77 has secured thereto, between those arms, a sleeve 79, this being secured to the branch 78a by setscrews 80. The other branch 78b of the U-shaped member is connected with a rod 82having a hooked upper end which surrounds the branch 78b adjacent its free end, these parts being held in proper relation to eachk It will be seen from this arrangement that the spring 85 performs the same function as thespring 36 of the embodiment shown in FIG. 2, namely tending to hold the valve member of the unit in its normal inactive position. Extending upwardly from the sleeve 79, at its rearmost end, is an arm 86 by which the sleeve and the U-shaped member 78 may be rocked 'under the control of the operator.

The connections for rocking the arm 86 and the U- shaped lever or member 78 include a link 87 secured to` the arm 86 by a screw 88. At its opposite end the link is connected by a screw 89 with an arm 90. This arm is secured to the upper end of a vertically disposed stud 91 journaled in a sleeve 92 carried yby the member 75. A collar 93 secured to the lower end of stud 91 retains it within the sleeve. A hub portion 94 of arm 90 is secured to the upper end of stud 91 by a screw 95.

For manually operating the stud 91 there is provided a knee press member 96 connected -with a laterally extending portion 97 of an arm 98, the other end of which extends through an opening provided in the upper end of stud-91. A pressure of about 4.5 lbs. on the knee press member 96 will thus rotate stud 91 through a suitable angle within the sleeve 92 and thus `pull the link 87 toward the left (FIGS. 7 and 8). This will cause rocking of the sleeve 79 and the lever 78 in a counterclockwise direction and cause downward movement of block 33, stem 34 and valve member 66 within the piston. As a result, the piston will exert its power assist action to the presser foot, or other device to be operated, in the same manner as the treadle operated mechanism previously described. Accordingly the relatively small amount of force required to be applied to the knee press member will bring about the operation of the piston to supply the additional force required to lift the presser foot or perform some other operation needed in the operation of the sewing machine.

While the invention has been shown and described in relation to a presser foot lifting mechanism, it will be understood that it is applicable to the performance of other manually controlled operations of mechanisms incorporated in a high speed sewing machine. Also it should be understood that various changes may be made in certain parts of the construction herein disclosed, within the scope of the appended claims.

What is claimed is:

l. In a sewing unit including a sewing machine having a device requiring periodic operation under the direct control of an operator, the combination which comprises a cylinder supported in lixed relation to the sewing machine, a piston arranged for reciprocation within said cylinder, connections from said piston to said device for operating the latter, high force spring means for strongly urging said device in one direction, means for delivering air lunder pressure to said cylinder for operating said piston and said device against the action of said spring means, a valve member slidably mounted in said piston for controlling the delivery of air from said air delivering means to said cylinder and for controlling the discharge of air from said cylinder to the atmosphere, and means readily operable by the operator for shifting said valve member.

2. In a sewing unit as set forth in claim 1, low force spring means for normally urging said valve member into a predetermined position, and s-aid means operable by the operator being constructed and arranged to shift said valve member yagainst the action of said last recited spring means to enable delivery of air under pressure to said cylinder.

3. In a sewing unit as set forth in claim 2, means for controlling the rate and extent of delivery of air under pressure to said cylinder in accordance with the extent of movement of said valve member by the force applied thereto by the operator.

4. In a sewing unit las set forth in claim 1, said valve member and said piston being shifted in the same direction within said cylinder, and said means operated by the operator 4being adapted to vary the extent of movement of said Valve member and said piston in relation to said cylinder.

5. In a sewing unit 'as set forth in claim 2, adjustable means for predetermining the upper and lower limits of movement of the valve member in relation to said piston and thereby limiting the movement of said piston in relation to said cylinder in accordance with the extent of movement of said valve member.

6. `In a sewing unit as set forth in claim 5, said adjustable means comprising a screw-threaded member having screw-threaded engagement with the end of said piston and a second screw-threaded member having screw-threaded engagement With a portion of said valve member, said low-force spring means being arranged to normally urge said screw-threaded members into engagement with each other.

7. In a sewing unit as set forth in claim 2, said piston having a wall forming a substantially cylindrical passage through said piston in which said valve member is slidable, said cylinder and said piston and said valve member having surfaces thereon which define a plurality of air chambers, one of said chambers being within said valve member, a second of said chambers being formed between the top of said cylinder and the top of said piston,

said means for delivering air under pressure being connected into said one of said chambers, a passage from said one of said chambers for delivering air under pressure to the inner surface of the wall of said piston, a plurality of passages through the wall of said piston spaced in an axial direction in relation to each other, relative shifting of said valve and piston being adapted to place one of said last mentioned passages in communication with said first mentioned passage, and said piston and cylinder providing passage means for delivering the air under pressure from said one of said passages to said second chamber, whereby said piston is operated by said air under pressure.

8. In a sewing unit as set forth in claim 7, a third chamber being formed between said valve and the inner surface of the wall of said piston, said third chamber being at all times in open communication with the outside atmosphere, a second of said passages through the wall of said piston being so positioned as to place said second and third chambers in communication with each other when said valve member and piston are in a predetermined position in relation to each other.

9. In a sewing unit as set forth in claim 8, said passages extending through the wall of said piston being elongated in a substantially circumferential direction.

i0. In a sewing unit as set forth in claim 9, said last mentioned passages extending at a small angle to a strictly circumferential direction around the axis of the piston.

11. In a sewing unit as set forth in claim 9, said second of said passages having a slightly greater cross-sectional area than said one of said passages.

12. In a sewing unit as set forth in claim 8, further chambers that :are completely enclosed, one of said further chambers being provided at each end of said valve, said chambers being normally at substantially atmospheric pressure.

13. In a sewing unit as set forth in claim 2, said means readily operable by the operator comprising a foot treadle and connections therefrom to said valve member.

14. In a sewing unit as set forth in claim 2, a supporting table having a top member on which said sewing machine is mounted, said table having vertically d-isposed supporting means comprising a plurality of members adjustable in relation to each other to vary the height of said top member, means for selectively securing said cylinder to said vertically disposed supporting means in various positions in relation thereto.

15. In a sewing unit as set forth in claim 14, said means for securing said cylinder being constructed and arranged to vary the Vertical position of said cylinder in relation to said supporting means.

16. In a sewing unit as set forth in claim 14, said means for securing said cylinder being so constructed and arranged as to enable said cylinder to be disposed at different angles to the vertical.

17. In a sewing unit as set forth in claim 2, said means readily operable by the operator comprising a knee press member, and means supported by said cylinder for connecting said knee press member with said valve for shifting the latter.

1S. In a sewing unit as set forth in claim 2, said device requiring periodic operation comprising a presser bar and a presser foot carried by said bar, said presser foot being urged by said high force spring means against work being sewn.

References Cited UNITED STATES PATENTS PATRICK D. LAWSON, Primary Examiner.