US 3129680 A
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E. H. DOERNER April 21, 1964 BOBBIN THREAD DEPLETION DETECTOR FOR SEWING MACHINES 2 Sheets-Sheet Filed May 23, 1962 R E R M Y O E T. E N m w R w m 1 T H A H Y E m WL E y W n n m W P mm 0 m 0 m Y.-. 2 Y m y E I -UI T F W l. .WWMHIMHUHFIJLHIMWMW m x 5 .Il 4
April 21, 1964 DOERNER 3,129,680
BOBBIN THREAD DEPLETION DETECTOR FOR SEWING MACHINES Filed May 23, 1962 2 Sheets-Sheet 2 Fig. 7 43 INVENTOR. ERNEST H. DOERNER 4. 49 WW E! ATTORNEY United States Patent 3,129,680 BOBBIN THREAD DEPLETION DETECTOR FOR SEWING MACHINES Ernest H. Doerner, Morris Plains, N.J., assignor to The Singer Company, a corporation of New Jersey Filed May 23, 1962, Ser. No. 197,151 4 Claims. (Cl. 112-218) This invention relates to a bobbin depletion detector for sewing machines.
It is desirable in sewing machines, particularly of the lock stitch type, for the operator to know in advance when the bobbin thread is about to run out so she can complete the sewing to the next logical stopping point and rewind the bobbin. In this manner unsuspected run-outs can be avoided and the general quality of the work improved by eliminating the necessity of restitching over paths already perforated by the needle.
It is an object of this invention to provide a sewing machine with means for indicating to the operator that the bobbin thread is nearly depleted. I
It is a more specific object of this invention to provide on the bobbin of a sewing machine magnetic means movable in response to near-depletion of the thread wound thereon to a position in which its field influences a magnetic-reed switch to closure to provide a signal to the operator that bobbin thread exhaustion is imminent.
With the above and other objects in view, as will hereinafter appear, the invention comprises the devices, combinations and arrangements of parts hereinafter set forth and illustrated in the accompanying drawings of a preferred embodiment of the invention, from which the several features of the inveniton and the advantages attained thereby will be readily understood by those skilled in the art.
In the drawings, FIG. 1 is a front elevation view partly in section of a portion of a sewing machine embodying the invention.
FIG. 2 is a top plan view of the devices of FIG. 1.
FIG. 3 is a vertical sectional view taken on line 3-3 of FIG. 2.
FIG. 4 is a vertical sectional View taken substantially on line 44 of FIG. 2, and includes a schematic wiring diagram.
FlG. 5 is a bottom plan detail view partly in section of a bobbin embodying the invention.
FIG. 6 is a sectional view taken on line 6-6 of FIG. 5.
FIG. 7 is a view similar to FIG. 4 showing a modification of the invention.
As illustrated in the drawings, the present invention is shown embodied in a sewing machine of the type shown and described in United States Patent No. 2,862,- 468, dated December 2, 1958, to which reference may be had for a complete understanding of the operation thereof.
Referring now to FIG. 1 there is shown a portion of a sewing machine having a base 10 with vertical end wall 11, and a head 12 carrying a needle bar 13, needle 14, presser bar 15, presser-foot 16 and feed-dog 16a.
A bed shaft 17 drives a hook shaft 18 through bevel gears 19 and 20 to impart rotary movement to a hook 21. A bobbin 22 is shown seated within a bobbin carrier 23 in its relation to the rotary hook 21. A removable slide plate 24 covers the rotary hook mechanism and may be readily pulled back to gain access for bobbin removal and replacement as is well known.
Secured to the end wall 11 by any suitable means, such as screw 25, is a molded plastic block 26 in which is embedded a magnetic reed switch 27 of conventional type and a permanent magnet 28 shown best in proper relative position in FIGS. 2 and 3. The reed switch has ice conducting leads 29 and 30 for external connections to be described later. The permanent magnet 28 is magnetized along its axis with its terminal ends providing poles of opposite polarity as shown by the plus and minus signs. The magnet 28 is positioned and aligned with respect to the reed switch 27 to provide a constant magnetic flux field tending to close but not actually closing the reed contacts of the switch 27. That is to say, the magnet 82 provides a biasing magnetic field for the reed switch which requires a slight but definite additional field of the same polarity as the magnet 28 to cause closure of the reed switch 27. Further, the field created by the magnet 28 is suflicient, by itself, to hold the reed switch closed (when once closed) even when said additional field is removed. This is known as latch action. By the same token, when the reed switch is closed and the additional field is removed, it requires a small but definite subtractive field of opposite polarity to open the reed switch. How these additional and subtractive fields of the respective same and opposite polarity are provided will now be described.
The additional field of the same polarity as the biasing magnet 23 is supplied by the proximity effect of a permanent magnet 31 carried by the bobbin 22 as shown best in FIGS. 5 and 6, the bobbin 22, formed from nonmagnetic material such as aluminum, has its lower flange 33 formed with an internal annular groove 34 within which is seated a circular wire snap-ring 35. One end of the snap-ring 35 embraces a grooved end 36 of the magnet 31 which is slidable within radial slots 37 and 38 in the flanges of the bobbin 22. Normally the flexure of the snap-ring 35 biases the magnet 31 to the radially outward position shown in full lines in FIG. 5 and in dotted lines in FIG. 6. However, when sufficient thread 39 is wound on the bobbin 22, the magnet 31 is forced to a position against the hub portion 40 as shown in full lines in FIG. 6 with the snap-ring 35 flexed as shown in dotted lines in FIG. 5.
From the above it will be perceived that, during the normal course of sewing as thread 39 is pulled from the bobbin 22, it will rotate and with it will carry the magnet 31 in a small circular path close to the hub axis. In this limited path (see FIG. 2) the magnet 31 never gets close enough to the reed switch 27 to add suflicient field flux to that supplied by the biasing magnet 28 to cause closure of the reed switch 27. However, when the bobbin thread supply becomes depleted the flexed spring 35 will overcome the snubbing action of the few remaining turns of thread 39 and the magnet 31 will move to its outer radial position and in its first turn past its nearest position to the reed switch 27 will add suflicient magnetic flux to the field of the biasing magnet 28 to cause closure of the reed switch 27 which, according to the latch action described above, will remain closed even when the bobbin magnet 31 moves away from the proximity position as the bobbin rotates.
As shown in the wiring diagram of FIG. 4, closure of the reed switch 27 applies voltage from source 8-5 to a pilot lamp 41 located in a bracket 42 secured to the head 12 thus lighting the lamp 41 and signalling to the operator that the bobbin thread is about to run out. Lamp 43 connected to the source SS is the lamp conventionally used to illuminate the sewing area and is included here merely to show that the presently existing voltage supply source SS can also be used for the pilot lamp 41.
It is necessary to reset the reed switch 27 to open position and-it is desirable that this be done by a normal operating function connected with bobbin replacement, such, for example, as movement of the slide plate. For this purpose a small permanent magnet 44 is secured to the under side of the slide plate 24 and is so located (FIG. 2) that, as the plate is pulled out and/or pushed in it will traverse a position close to the reed switch 27. It will be understood that the polarity of the reset magnet 44 is related to that of the biasing magnet 28 such that it exerts a sufficiently subtractive elfect on the biasing field flux to open the reed switch. As a result, when a wound bobbin is inserted, the bobbin magnet 31 is out of the field of influence as regards the reed switch 27 so that, when the slide plate 24 is pushed in, the reset magnet takes control and opens the reed switch which is then reset and ready for the next signal actuation.
Due to manufacturing tolerances, particularly related to the relative strength of the various magnets, 28, 31, and 44, some adjustability is desirable so that a final setting can be made to secure the desired latching action. This may be provided by a vertically elongated slot 45 formed in the wall 11 which permits adjustment of the vertical position of the reed switch 27 with respect to magnets 31 and 44.
It may also be desirable to provide independent adjustment of the biasing magnet 28 and the modification of FIG. 7 may be used for this purpose. In'this case the biasing magnet 28 is held in a well 46 formed in the block 26 between a non-magnetic bottoming spring 47 and a nonmagnetic adjusting screw 48 threaded into the well 46. The screw 48 is readily accessible by pushing back the slide plate 24.
In order best to control the flux path influencing the proper poeration of the reed switch 27, the slide plate 24, bobbin 22 and bobbin carrier 23 are all preferably made of non-magnetic material such as aluminum.
Having thus set forth the nature of my invention what I claim herein is:
l. A bobbin thread depletion detector for sewing machines comprising a bobbin, a magnetic reed switch mounted adjacent to said bobbin, a biasing magnet mounted in fixed relation to said switch and providing a flux field for said switch sufiicient to hold it closed, if closed, but insufficient to close it, it open, a magnet rotatable with said bobbin and normally restrained in a first path in which it has no operative effect on said swtich but movable responsively to near-exhaustion of said bobbin thread supply to a second path in which it causes closure of said switch, and a reset magnet movable to a position adjacent said reed switch and of such polarity as to oppose the holding field of the biasing magnet and effect opening of said reed switch.
2. Apparatus according to claim 1 in which the biasing magnet is selectively adjustable in its position relatively to the reed switch.
3. Apparatus according to claim 1 in which the reed switch and biasing magnet are adjustable as a unit in its position relatively to said bobbin magnet.
4. A bobbin thread depletion detector for sewing machines comprising a bobbin, a permanent magnet normally held by the thread wound on the bobbin to a first position closely adjacent to the bobbin axis and movable to a second position radially outwardly from said first position responsively to near-exhaustion of the bobbin thread supply, a magnetic reed switch mounted adjacent to said bobbin, a biasing magnet mounted adjacent to said reed switch, said bobbin magnet and said biasing magnet being so polarized that their combined magnetic effect is additive and elfects closure of said reed switch in the second position of the bobbin magnet, a slide plate covering said bobbin, and a reset magnet mounted on said slide plate and movable therewith to a position adjacent to said reed switch, said biasing magnet and said reset magnet being so polarized that their combined magnetic elfect is subtractive and effects opening of said reed switch when said slide plate is moved to gain access for bobbin replacement.
References Cited in the file of this patent UNITED STATES PATENTS 2,760,024 Tunstall Aug. 21, 1956 2,877,361 Chase Mar. 10, 1959 3,043,931 Gruber July 10, 1962