US3611963A

US3611963A - Presser bar suspension systems

Info

Publication number: US3611963A
Application number: US30858A
Authority: US
Inventors: John A Herr; Robert B Brauch
Original assignee: Singer Co
Current assignee: SSMC Inc
Priority date: 1970-04-22
Filing date: 1970-04-22
Publication date: 1971-10-12
Anticipated expiration: 1988-10-12

Abstract

In a sewing machine, a presser bar suspension system wherein the presser bar is attached to two leaf springs, which are cantilevered out from a rigid frame slidable vertically in the sewing machine head. The rigid frame which may be raised to elevate the presser foot above the work, is spring biased downwardly against a stop into a position in which only the pressure of the two leaf springs urges the presser foot against the work.

Description

United States Patent [56] References Cited UNITED STATES PATENTS 2,887,969 5/1959 Voigt 1 12/235 3,002,477 10/1961 Silberman 1 12/235 3,495,560 2/1970 Walling 1 12/235 Primary Examiner-Patrick D. Lawson Att0rneys-Marshall .l. Breen, Chester A. Williams, Jr. and

Robert E. Smith ABSTRACT: In a sewing machine, a presser bar suspension system wherein the presser bar is attached to two leaf springs, which are cantilevered out from a rigid frame slidable vertically in the sewing machine head. The rigid frame which may be raised to elevate the presser foot above the work, is spring biased downwardly against a stop into a position in which only the pressure of the two leaf springs urges the presser foot against the work.

PATENTEUUBHZIH?! 3,611,963

" INVENTORS John A. Herr BY Robert B. Brouch WITNESS I W-2,@w

ORNEY PRESSER BAR SUSPENSION SYSTEMS BACKGROUND OF THE INVENTION Movably mounted within the sewing head of a sewing machine are both a needle bar mechanism and a presser bar mechanism, the presser bar mechanism carrying a presser foot. Located below the sewing head is a work-supporting platform within which is carried a work feed mechanism. One well-known work feed mechanism includes a feed dog which operates through a slot in the platform in opposition to the presser foot to carry forward material on the platform so that it may be stitched.

The feed dog may have imparted to it a four-step cyclic repetitive action in that it rises out of the slot to lift the material and the presser foot; it travels forward in the slot; it is lowered into the slot allowing the presser foot to press the material against the work-supporting platform, and finally, the feed dog returns idly beneath the work support to its original position to begin the cycle again.

The presser bar mechanism must be able to cooperate with the feed dog so that the presser bar mechanism may be lifted up by the feed dog along with the material and it must also follow closely the downward movement of the feed dog into the slot. The failure of the presser bar mechanism to follow the downward motion of the feed dog results in a reduction in the effectiveness of the feed of the material to be sewn.

One heretofore well-known type of presser bar mechanism includes a rod fixedly mounted in the upper portion of the sewing machine head. Telescopically and concentrically mounted about this fixed rod is a slidable tubular rod which supports the presser foot. A coiled compression spring is mounted around the upper rod to react against the upward motion of the lower tubular rod. The tubular rod must raise upwardly for two reasons. In one instance, the presser foot must be raised to accommodate the material which is to be sewn and this is done by means of a presser-lifting lever, manually elevated. After the material is in place, the presserlifting lever is released and the compression spring expands driving the tubular rod downwardly. In the other instance mentioned earlier, as the feed dog travels upwardly in the slot, it lifts the presser foot and consequently, the presser bar, and as the feed dog lowers the spring urges the presser foot and presser bar downwardly. Because of the exact timing required for the presser foot to cooperate with the feed dog, retarding forces on the presser bar such as friction and inertia must be minimized.

The frictional force arises from the interface contact between the presser bar and the guides which hold it in lateral restraint and the interface contact between the two telescoping rods. As the presser bar is required to fall more. quickly, the frictional force must be lessened so as to accomplish this end. Therefore, it is desirable to eliminate or at least minimize this interface contact.

The force of inertia is proportional to the mass of the moving parts of the presser bar system. Inertia tends to hang the presser bar in the upward position. Minimizing the force of inertia requires that the mass of the moving parts of the presser bar be decreased so that the presser bar will fall more rapidly.

SUMMARY OF THE INVENTION In accordance with the present invention, a sewing machine is provided with a new presser bar suspension system wherein the presser bar is a rod attached to two parallel leaf springs which extend from a rigid frame slidable vertically in the sewing head. The frame slidable in the sewing head is spring biased downwardly against a stop pin. The frame being slidable in the sewing head allows the presser bar mechanism to be raised by a cammed lever over the material to be inserted onto the sewing platform. When the cammed lever is released the biasing spring urges the rigid frame downwardly until it abuts the stop pin. Now the upward movement of the presser foot and presser bar caused by the feed dog is countered solely by the parallel leaf springs. Therefore, two independent suspensions are realized. One suspension rea'cts when the presser foot is raised by the cammed lever to accommodate material to be sewn; the other suspension reacts with the feed dog. By this construction inertia in the parts which react to the feed dog is minimized, since only a small mass is required in the construction of the presser bar and the cantilever spring suspension, and frictional resistance to presser foot movement with the feed dog is eliminated, since there is no telescoping of rods or other frictionally engaging parts which may bind, as found in the prior art.

It is therefore an object of this invention to prevent undesirable disruption of material feed by providing a new presser bar suspension system, whereby objectionable forces due to friction and inertia are minimized.

Another object of this invention is to design two separate suspension systems in one device therebyallowing the most efficient use of each system for its particular purpose.

Other objects and advantages will be apparent from the following description of one embodiment of the invention, and the novel features will be particularly pointed out hereinafter in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS This invention is illustrated in the accompanying drawings in which:

FIG. 1 is a side elevation view of a sewing head partially cut away to show the needle bar, and the presser bar suspension of the present invention,

FIG. 2 is an exploded perspective of the presser bar suspension system and the manner in which it is to be mounted onto the sewing head,

FIG. 3 is a cross-sectional view taken at lines 33 of FIG. 2 to show the assembly of the presser bar to the leaf springs.

DESCRIPTION OF THE PREFERRED EMBODIMENT With reference to the drawings, the present invention, a presser bar suspension system indicated generally at 11 is shown as embodied in the sewing head 12 of a sewing machine casing. Adjacent the presser bar suspension system is a needle bar 13 with a needle 14 held in place by a clamp 15. The needle bar is endwise reciprocable in bushings l6, and vertical motion is imparted thereto by a crank 17 driven by a drive shaft (not shown). A presser lifting lever 18 is pivoted by a screw I9 in the sewing head and serves to raise and lower the presser bar suspension system as will be described. Below the sewing head, the machine includes a work support bed 20 fitted with a slotted throat plate 21 upwardly through which works a feed dog 22 of the work-feeding mechanism.

The presser bar suspension system shown more particularly in FIGS. 2 and 3, is the subject of this invention. A rigid frame 25 supports two parallel cantilever leaf springs 26 fixed respectively at the upper and lower ends 'of the rigid frame by screws 27.

A presser bar indicated generally at 30 is supported in the extremities of the parallel leaf springs remote from the rigid support. As shown best in FIG. 3, the presser bar is preferably of composite construction with the parts being secured to a common inner rod 31. A lower member 32 has a presser foot 33, attached by a screw 34. The lower member is formed to accommodate the inner rod 31, and a setscrew 35 fixes the lower member to the inner rod. Between the two leaf springs is arranged an upper member 36 which is tubular so as to accept the inner rod 34 and is attached thereto by setscrew 37. The upper portion of the inner rod is drilled and tapped to accept a screw 38 which holds the presser bar onto the upper leaf spring with the aid of a washer 39. The purpose of this construction is to sandwich each leaf spring so as to prevent relative vertical movement between the leaf springs and the presser bar.

The rigid frame 25 is slidably mounted, in the sewing head inner wall by means of a guideway 45 cut into the inner wall as shown in FIG. 2. The presser-lifting lever 18 protrudes through a slot 46 in the inner wall and through a slot 47 in the rigid frame, so that the frame may be raised and lowered. A pin 48 protrudes from the inner wall through a slot 49 in the rigid frame. Attached to the pin and t the upper portion of the frame is a coil tension spring 50 which, upon the release of the presser lifting lever, draws the rigid frame downwardly until the pin 48 contacts the upper extremity of the slot 49. The pin 48 also limits the upward travel of the rigid frame when the lower extremity of the slot 49 contacts the pin.

in operation, the diverse function of the

springs

26 and 50 is apparent. When the presser-lifting lever is raised, it moves the frame, leaf springs, presser bar and presser foot upwardly against the bias of the coiled tension spring 50. When the lever is lowered the frame, leaf springs, presser bar and presser foot move downwardly under the urging of the coil spring. When the presser bar is in operation, only the leaf springs 26 react to the upward urging of the feed dog, and there is no change of stress on the coil spring 50 nor any movement of the rigid frame 25 along the guideway 45. Thus, the frictional forces are eliminated, since there are no movable bearing interfaces with the presser mechanism relatively to the machine frame, and the inertia forces are minimized since the mass of the parts of the presser mechanism which move in response to the feed motions is minimized.

It will be understood that various changes in the details, material, arrangements of parts and operating conditions, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art without departing from the scope and principles of this invention.

Having thus described the nature of the invention, what we claim herein is:

1. in a sewing machine having a casing and a presser bar in said casing to which a work-engaging presser member is secured, a presser bar suspension system comprising two parallel flat leaf springs, means securely fastening said leaf springs to said presser bar, and means for anchoring each leaf spring relatively to said sewing machine casing, said means for fastening each leaf spring to said presser bar being located substantially equidistant from said anchoring means on each of said leaf springs so that the leaf springs constrain said presser bar for movement in a predetermined substantially linear path and support said presser bar completely out of engagement with said sewing machine casing.

2. The presser bar suspension system as recited in claim I, wherein said anchoring means includes a rigid frame guideway formed in said sewing machine casing slidably supporting a rigid frame, and fastening means for securing each of said leaf springs to said rigid frame.

3. The presser bar suspension as recited in claim 2 wherein said guideway in said sewing machine casing is formed substantially parallel to said linear path of presser bar movement, and a second spring means is arranged to act between said sewing machine casing and said rigid frame to bear said rigid frame against a stop means caused on said sewing machine casing.

4. The presser bar suspension system as recited in claim 3 in which a presser-lifting lever is fulcrumed relatively to said sewing machine casing and is engageable with said rigid frame to shift said rigid frame away from said stop means in opposition to said second spring means.

Claims

2. The presser bar suspension system as recited in claim 1, wherein said anchoring means includes a rigid frame guideway formed in said sewing machine casing slidably supporting a rigid frame, and fastening means for securing each of said leaf springs to said rigid frame.