CA1110118A - Drive mechanism for sewing machines - Google Patents

Abstract

DRIVE MECHANISM FOR SEWING MACHINES

ABSTRACT

A Cardan gear mechanism carrying a pinion gear means in a cantilevered manner such that a work performing means secured thereto can be reciprocated along its major axis. The pinion gear assembly is balanced with respect to load vectors and generally with respect to moment. The main drive shaft is balanced with respect to both load vectors and moment.

Description

This invention relates to apparatus for balancing a Cardan gear type mechanism employed in combination with a sewing machine. ~ore particu-larly, this invention groups particular elements of the Cardan gear mechanism and force balances these elements, and an apparatus is presented showing a particular embodiment thereof.
Many high speed reciprocating machines, such as industrial sewing machines, compressors, engines, power tools, and the like employ some mechanism to translate rotary input motion into reciprocating linear motion.
For example, many industrial sewing machines employ devices based on the slider-crank principle to convert rotary shaft motion into reciprocating linear motion in order to drive a needle bar up and down in synchronism with other mechanisms of the machine. The known slider-crank mechanisms possess large unbalanced inertia forces and moments at high crank speeds. This results in extremely high vlbration levels, noise and wear in the crank mechanisms and associated parts. In addition, due to practical constraints on the physical size of the slider-crank, the linear output of such recipro-cating mechanisms is non-harmonic, which can be a serious disadvantage in timing of the needle bar motion to other thread handling mechanisms, particu-larly in chain stitch machines where harmonic motion is strongly desired.
The high vibrations and impacts of the slider crank mechanism necessitate heavy casting mass and stiEfness to help dampen vibration at high operating speeds.
Alternative means to achieve balanced, harmonic high speed conver-sion from rotary to linear reciprocating motion have involved the use of crank driven oscillating levers and rock shafts. These devices, however, consist of compounded systems

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of linkages, straps and connecting rods ~hich have long been a source of noise, vibration, wear and overthrow in these mechanisms.
In addition, in order -to minimi7e deflection of the lever or the rockshaft, restrictions have been placed on the slze of these par-ts, resulting in a restric~ion to the overall length of the machine. Due to the presence of a main drive crankshaft, rather than a rotary shaf-t, accessory drives required at the front end of the machine must be drlven by very long counter shafts extending the length of the machine.
Eipcyclic internally geared devices, specifically Cardan gears, are well known as a means of converting rotary to linear harmonic motion. There have been several attempts -to integrate the Cardan year mechanism into sewing machines. These attemp-ts include: Reece U.S.P. 2,193,3~; Bell U.S.P. 2,667,135; and Schoij U.S.P. 3,318,27~. The use oE such devices has been restricted by the inability to balance the load vectors and moments created during operation with undesirable effects on bearing life, noise and vibration of the mechanism.
The balancing of load vectors and moments of Cardan gear drives in sewing machines is particularly difficult because space and operational limitations require that the drive extend and be cantilevered ~rom a main journal bearing rather than being supported at both ends. The inability to remove or balance thes~ load vectors results ln rather serious stresses on the ~arious bearings employed in the assembly. This is especially true with respect to the Cardan gear's double speed bearing set which carries -the work performing instrumentality and rotates at twice the speed of the drive shaft bearing set. Thus, in a sewing machine incorporating a Cardan gear mechanism operating at 8000 RPM, the double speed bearing will be ro-tating at l~000 RPM. ~s is appreciated, 8000 RPM is a desirable speed for an industrial sewing machine to operate.

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These problems have been appreciated by prior workers Fiæld ~ v~c;toq~
in the -fir~d such as Schoij wherein two force f~G~ balancing weights are employed. However, simply adding a balancing means to the system is insufficient to produce satisfactory results.
In the past, attempted balancing or cancella-tion of force vectors in the system causes them to be shifted to another site and/or results in the formation of undesirable moments at particular points. As is known in the bearing industry, it is more desirous to attempt to subject a bearing -to -the lowest constant radial load. Another accep-table technique is to subject the bearing to a constant load whereby the shaft or whatever moves in a continuous steady fashion from one element of the bearing to the next exer-ting ~enerally the same -force on each. Tha-t is, in a steacly step~llke motion from one series oE rollers, etc., without jumping randoml~ or exertiny various loads on various elements.
Random jumping is the least desirable situation because the bearing is periodically subjected to force vectors from various angles and of various magni-tudes causing the elemen-ts to bounce with respect to each other. The result is manifested by noise, vibration and shorter life. Such conditions are intolerable in view of sewing machine speeds and the demands pu-t thereupon.
The problem of achieving the proper balancing and constan-t radial load becomes more apparent when the Cardan system and its cantilevered na-ture is considered. Basically a work tool is driven through a reciprocatory cycle at the end of a first cantilevered shaft. The first shaft itself is rotating around its own major axis. Additionally, both tool and the first shaft are carried by and rotated by a second cantilevered shaft around its major axis, the result being that the second shaft introduces rotary motion into -the sys-tem which results in the work tool performing reciprocal mo-tion. Thus, the bearing , set of the first and second shafts are subjected to both rotary and reciprocal forces, and moment in the absence of balancing.
The moment and force vectors from various angles and of various magnitudes would! in the absence of balancing, render the system unsatisfactory. As will be apprecia-ted, these problems are grea-ter due to the cantilevered nature of t:he Cardan gear means.
Balancing of the moment and forces would be simpli~ied if the plnion shaf-t were supported at each end with the work performing means connected therebetween. The same is true with the second shaft. If the first and second shafts were supported at both of their ends, then both moment and force vectors could be balanced out. However, the size, number of parts, etc., involved in such a non-cantilevered device might render it inapplicable for incor poration into a sewing machine. In the can-tilevered system of our invention, it is possible ~.o balance the force vectors to wh1ch the double speed bearing is subjected and to balance both the force vectors and momen-t to which the main bearing is subjected. For various reasons the moment on the double speed bearing is not balanced out. The main counterweight is, however, designed of such a mass and placed at such a location that it cancels out the double speed bearing moment which otherwise would be transferred to the main bearing. The result being that the ma.in bearing means is balanced with regard to bo-th moment and load forces~
Accordingly, the objects of our invention are to provide ;~
a Cardan drive assembly which has one or more of the following advantages: a modularized Cardan gear drive assembly which permits the conversion of rotary motion to reciprocal, helical, elliptical and helical/elliptical motion; a standard modularized Cardan drive unit which may be inserted into a sewing machine frame to perform the alternative functions of driving the needle, looper, .

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etc.; a sewing machine drive unit which is balanced eliminating excessive sound and vibration while permitting higher operational speeds; a balanced Cardan drive module for converting rotary motion to straight line motion; a balanced cantilevered Cardan gear assembly having a double speed bearing which is not exposed to irregular load vectors; a Cardan gear assembly for converting rotary motion into straight Lissajous motion wherein the canti-levered double speed bearing, in operation, is subjected to a constant load vector; a Cardan gear assembly means wherein the elements have been selective~
ly grouped and minimized and then balanced; a Cardan gear mechanism wherein the constant load vector and moment generated by the pinion shaft and related assemblies on the bearing set of the main shaft are negated by balancing means; a Cardan gear assembly wherein a:L:L e:lements carriecl by the double speed bearings are balancecl with regard to the centerline of the pin-ion shaft and then all elements carried by the main shaft are balanced with respect to a line passing through the center of the main shaft; a sewing machine drive system wherein there is a significant reduction in vibration and noise produced by the needle bar such that the weight oE the machine casting may be reduced.
The invention provides a sewing machine including Cardan gear mechanism to deLiver reclprocal motion to a needle bar from a rotating shaft, said mechanism comprising: a housing; a rotary drive shaft journaled in said housing; an internal ring gear fixed within said housing; an end of said drive shaft being extended from a main bearing in said housing in a cantilever fashion and defining a rotational frame means; a pinion gear assembly includ-ing a cantilevered pinion shaft mounted by bearings for rotational. movement within said frame means and having a pinion gear meshing with said internal gear; a work performing device mounted upon said pinion gear shaft at the cantilevered end thereof for reciprocal motion upon rotation of said drive shaft; said pinion gear assembly and said needle bar being statically balanced with respect to the rotational axis of the pinion shaft ~len said bearings are maintained in fixed position; and said rotational frame means, pinion gear assembly and wor~ performing device bei.ng statically and . ~ 6 :

dynamically balanced about a line passing through the centroid of saicl main bearing journaling said drive shaft.
In the embodiment disclosed herein, particular elements of the Cardan gear mechanism and related assemblies are grouped for the purpose oE
balancing. First, the double speed bearing is treated as an independent unit with respect to the overall Cardan gear assembly. That is, the pinion, needle bar, gear assembly, etc., are all balanced such that the double speed bearing is subjected to very minimum load vectors as the pinion shaft is rotated independent of the Cardan gear assembly. In practice, the mass of the work performing means and related elements are balanced by a counter-weight. The counterweight -6a-~:, itself is positioned such that although it has a lower to-tal mass than the items it is balancing, it ;s still su~ficient to balance the pinion shaft and related elements. As is apparent, even though the double speed bearing is subjected to no load vector, once the pinion gear assembly is rotated by -the main drive shaft it will be subjected to a constan-t load vector due to the centri~ugal ef~ect. Because of the particular design of the elements carried by the double speed bearing this load vector lS minimized whereby the bearing life thereof is satisfactory.
Due to the cantilever nature of the system, however, moment on the double speed bearing is not balanced. Ultimately, .if not balanced, lt would create undesirable results at the main bearing.
Applying mathematical analysis it is then possible to determine the cons-tant load vector and moment which the double speed bearing assembly would transmit to the main bearing. Thus, by the proper choice and positioning of a counterbalance means, it is possible to reduce the load vector and the moment to which the main bearing is subjected. ~ach is balanced against the other until an optimum point is achieved.
To summarize, the cantilevered system of a Cardan gear type mechanism must initially be viewed as having two separate systems. The first system includes all elements carried by thé
double speed bearing and is balanced first and the moment and constant load vector determined. The second system includes all elements carried by the main bearing and is balanceable because its characteristics and the moment and constant load vector of the double speed bearing means are determinable.
Other features and .advantayes o~ the invention will appear from the detailed description of a preferred method and embodimen-t o~ the same which will now be given in conjunction with the accompanying drawiDgs in which:

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FIG. 1 is a ver-tical sectional view taken longitu-dinally through the head portion o~ the overhanging arm of a sewing machine;
FIG. 2 is a par-tial view in a vertical section along the line 2-2 of FIG. l;
FIG. 3 is a side view in section of the Cardan gear and related assemblies as shown in E`IG. 1;
FIG. 4 is an exploded isometric view of elements carried by and including the double speed '~earing; and FIG. 5 is a diagrammatic view of FIG. 2 showing the various factors acting upon the system during a work cycle.
Referring now to these drawings and particularly FIG. 1 which shows -the features of the present invention appliecl to an industrial sewiny machine. It comprises a frame having an over-hanging arm 10 termina-ting in a head portion 12. Beneath the overhanging arm is a base portion tnot shown~. Extending longitudinally within the'overhanging arm 10 is a main drive shaft means 14 which is adapted to be driven through a pulley and handwheel mounted thereon adjacent its right end (not shown). The main or drive shaft 14 is journaled by a maln bearing 16 moun-ted near -the left end of the overhanging arm 10.
Secured generally in a cantilevered manner to the left end portion ~ of the shaft means 14 is the Cardan gear assembly or module ~0 which is Eirst described in terms of its components and their cooperat]ve arrangement. Subsequently, the metho~ of balancing will be described. ~o~a~ona I
The,module 2U includes an enlarged extension or'~frame means 18 of shaft 14 suppor-ted in cantilever fashion from bearing 16. As shown, this frame means 18 is shaped to receive a pinion gear assembly 17 as shown in FIG. 3 and 4. The extension 18 is provided w,ith a horizontally ex-tending aperture or cavity 28 7 as well as a cutaway portion 30. As is apparen-t, the cutaw~y portion facilitates the eng~gemen-t of the pinion gear means 22 with -the internal ring gear 2~ mounted within head 12. The aper-ture means 28 carries the double speed bearing means which includes first and second bearing sets 32 and 34 which journal the pinion sha:Et means 36. The set screw 33 is employed to secure the pinion gear 22 -to the pinion shaft 36.
Secured to the left end 40 of the pinion shaft 36 is a lever means 4~ which connects the work performi:ng instrumentality ~2 thereto such that overall a cantilevered system is created. The lever means 44 also connects to the pinion shaft 36 a mass 46 which exerts force on said shaft whereby when balanced by itself there would be a zero load vector exerted on the double speed bearing means. In the preferred embod,iment the mass exer-ting the force is a c,ounterweight means 46 which is secured to lever means ~ with a pin means ~8. The lever means ~4 is provided with a threaded portion 50 designed for engagement with a spanner nut 52. In the preferred embodiment, the lever means is inserted through the aperture means 51 in the shaf-t means 36 and the spanner nut 52 securely locks the elements in a predetermined position. The lever means 44 adjacent its top portion is provided with an aperture 5~. Securely positioned within said aperture by snap ring 26 is a bearing means 56.
The work performing device ~2, in the preferred embodiment, is a reciprocatory needle bar held in position by first and second bearing set means 60 and 62. As is apparent, the needle bar 58 is secured for reciprocating movement by the upper and lower bearingsets 62 and 60 which in turn are secured in the head of the frame. Thus the strap clamp output pin 6~
has a certain degree of freedom to compensate for misalignment and .yet transmit :Eorces between the needle bar 58 and the lever means or connecting rod ~. Referring to FIG. 2, :Lt is well known that when the OlltpUt centerpoint (identified by nurneral 147) of _9_ the Cardan gear is on the pitch diameter of the ring gear 24, the output will be along a straight line path. Thus, no further explanation will be devoted thereto.
The bearing sets hereunder discussion, that is, the maln bearing set 16, the double speed bearing sets 32 and 34, and the bearing means 56 are all provided with a positive oiling system. Oil enters main channel means 68 under pressure and thereafter passes via auxiliary chamleling to each of the respective bearing sets. Bearing set 32 receives oil via channel means 70, bearing set 16 via channel means 72 and 74, bearing set means 34 via 72 and 76 and bearing means 56 via channel means 72 and 78. Any suitable oil pumping system can be employed as is presently employed in conjunction with industrial sewing machines.
The pinion shaft 36 is secured in place by the provision of a thrust washer 80. A combination of the outer race 82 of the bearing set 32 on one side and the frame means 18 on the other secure thrust washer 80. In the preferred embodiment the thrust washer 80 is a material manu~actured by the DuPont Corporation under the trademark "Vespel" The thrust washer 80 provides a substantially friction free abutting surface for the pinion gear 2~ whereby the pinion shaft and related assemblies are fixed with regard to the frame assembly.
The design and mode o balancing this unit whereby the life of the double speed bearings 32 and 34 and the main shaft bearing 16 will now be des-cribed. As shown in ~igure 3J the pinion gear assembly 17 is mounted or telescopically arranged ~ithin the main drive shaft or frame means 18. This results in small diameter double speed bearings minimizhlg liner speed between the circumference of shaft 36 and these bearings. In addition, the strap clamp pin 64 is inserted into bearing 56 in lever means 44 to reduce the dis-tance or moment arm between the needle bar 58 and the lever, thus minimizing moment imposed upon bearings 32, 34 ~!LQ~

, and 16. The strap clamp pin 64 includes a mating portion 65 which is carried w:ithin bearing means 56. This mating portion has a radius of curvature of about one me-ter, which compensates for misalignment. The mating portion means 65 is thus slightly barrelled and free within limits to readjust i-tself within bearing 56.
Next the unit is balanced in a manner so as to require minimum mass of the counterweight 46. Important to this invention is the procedure and .assumptions made to ohtain balancing. For this purpose, the pinion gear assembly 17 and the work performing means 58 are first balanced independently of the remainder of the drive. Contrary to actual use, th,e pinion gear is assumed to be mounted in stationary bearings. Then, under this assumption, the pinion assembly and the work performing means 58 are statically balanced such that load vectors are minimal about the axis 41 of shaft 36 in the X-Y plane passing through the point 147 as indicated in FIG. 2.
This balancing requires the use of counterweight 46. : ' However, the si.ze of the counterweight is dependent upon its distance or radius from axis 41~ By maximizing this distance, the mass required is reduced, minimizing double speed bearing load. Having made the proper assumptions and conditions Eor balanoing of this assembly, the ma-thematical and mechanical techni~ues are within the skill of the art.' Subsequent to this independent balancing of the pinion gear assembly 17, it is incorporated into the drive shaft means 14 in which it rotates about axis 43 of this shaft.
In this environment, the pinion gear shaft, rotating about its own axis 41 and the axis 43 of the drive shaft 14, imposes two forces upon the double speed bearings 32 and 34. These forces are the centrifugal force resulting from rotation o:E the pinion ' ' ~ ' gear assembly and the moment acting upon shat 36 in the Y-Z plane which con-sidering F1gure 3, Z is along the major axis and Xl is perpendicular thereto.
This moment acts in opposite directions on bearings 32 and 34. It has been found that these forces, b~ reason of the present desIgn, present no undue stress upon bearings 32 and 34. Even at hlgh speeds, these forces are gen-erally constant and permit the shaft 36 to roll smoothly from one element of the double speed bearings to the other. That is, there will be a constant load imposed by the pinion shaft 36 on the double speed bearings.
After the pinlon drive assembly 17 has been internally balanced, the entire assembly is balanced in the Xl-Y plane passing through point 15 of the bearing set 16 and in the Xl-~l plane. This balancing requires that load vectors and moments resulting from centrifugal :Eorce be counterbalanced such that their summation about point 15 be ~ero.
In this process, the forces which act through the double speed bearings must be determined. A first radial force F resulting ~rom the work performing instrumentality 58, the left end of pinion shaft 36 and counter-weight 46 can be determined by the following sets of equations.
In the equations which follow: M~ is the mass of the work per-forming means, i.e., the needle bar means; MC is the mass o the balancing means connected to the pinion shaft means; R, is the distance from a line passing through the center of the main bearing means 16 to a line passing through the center o:E the double speed bearing means 32 and 34, i.e., crank radius; W is the angular velocity of the main shaft l~, i.e., the speed at which the main shaf~ is rotating; e is the crank angle, which as shown in Figure 51is the angle between a line connec~ing the centerpoint lines of the pinion shaft means and the main bearing shaft means, and a straight line par-allel to the line swept out ~ ~ \

by the needle ~ar means; and F is -the load exerted by the mass of the elements adjacent to the fron-t encl of the crank. This value does not include the mass contribution of for example the pinion gear, or the journal portion of the bearing sets.
It is because the mass of these elements is distributed sym-metrically about the center of the pinion shaft. ~ and ~ are the radii at which the work instrumentality 58 and the counterweight 46 are attached. lhe force FC of the counterweight moves ellip~ically and thus has X and Y force components. The force FB, due to the mass oE the work ins-trumentality 58 and the cantilevered section of shaft 36, moves in a straight line path along the X axis as shown in FIG. 5. ~, `
Let MC ~ MB and LC ~ LB such that MC(Lc) = MB(LB) Also LC > R
LB ~ R

C < MB
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From this equation, one can now fully appreciate the lessening of the loads imposed on double speed bearings 32 and 34 by reducing the mass of counterweight 46 (Mc) and by increasing the length of the lever arm (Lc).

As MC ~ MB and 2MBRW ~ (MB+MC)RW
the ratio of reduction in load created by work instrumentality 58 and the cantilevered section of shaft 36 on the double speed bearing means to a counterweight in which MC = MB thus becomes (MB~MC)RW

MB-I-MC

B

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The maximum of 1/2 the full load is reached when MC ~ - As is apparent, when MC = MB there is no reduction in full load. In a preferred embodiment the lever arm or radius LC is greater than one-half the pitch diameter of the pinion gear. Because of the fact that MCLc = ~ LB it thus follows that MC will be substantially less than MB.
In addition to determining the force due to the work instrumentality and lever means ~, the force due to the mass of the remainder of shaft 36 is determined. The distribution of these two forces on double speed bearings 32 and 3~ is then determined. Finally, the load vectors resulting from the mass of the frame 18 is determined. With these determinations, one can now sum both load vectors and moments which act through the centroid of the appro-priate elements about the point 15. Counterweights such as 86 and 88 are then added at positlons such that the sum of load vectors and moments about point 15 are zero. Stated another way, the load vectors and moment of the main , --1~--"~
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drive shaft including the pinion gear assembly and drive-n means are balanced with respect to the axis of the main shaft.
It should be noted that this method of balancing is pertinent to a Cardan gear device in which the driven means or work performing instrumen-tality is reciprocated in a straight line. This driven means may be reciprocated in an elliptical, helical or helical/elliptical curve. In these instances the balancing may require variations of this method of balancing.
Those skilled in the art wil] appreciate that other mathematical tec~miques of balancing may be utilized once the proper assumptions are made.
While a preferred embodiment of the invention has been described and shown in some detail it will be understood that various changes may be made in the construction and arrangement of parts without depart:Lng from the invention as defined by the appended claims.

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Claims (9)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A sewing machine including Cardan gear mechanism to deliver reciprocal motion to a needle bar from a rotating shaft, said mechanism comprising:
a housing;
a rotary drive shaft journaled in said housing, an internal ring gear fixed within said housing;
an end of said drive shaft being extended from a main bearing in said housing in a cantilever fashion and defining a rotational frame means;
a pinion gear assembly including a cantilevered pinion shaft mounted by bearings for rotational movement within said frame means and having a pinion gear meshing with said internal gear;
a work performing device mounted upon said pinion gear shaft at the cantilevered end thereof for reciprocal motion upon rotation of said drive shaft, said pinion gear assembly and said needle bar being statically balanced with respect to the rotational axis of the pinion shaft when said bearings are maintained in fixed position;
and said rotational frame means, pinion gear assembly and work per-forming device being statically and dynamically balanced about a line passing through the centroid of said main bearing journaling said drive shaft.

2. An apparatus as recited in claim 1 in which the pinion gear assembly and work performing device are counter-balanced by a mass having a lever arm whose dimension is greater than one half the pitch diameter of the pinion gear.

3. An apparatus as recited in claim 1 in which a counterweight mass means, utilized to counterbalance the -inertia force about the pinion gear assembly, is substantially less than the mass producing said inertia force.

4. An apparatus as recited in claim 1 in which: a lever means extends through one end of said pinion gear shaft; said work performing device is affixed to one end of said lever means; and a counterweight is connected to the other end of said lever means.

5. An apparatus as recited in claim 4 in which the pinion gear assembly and work performing device are counterbalanced by a counterweight mass means having a lever arm whose dimension is greater than one half the pitch diameter of the pinion gear.

6. An apparatus as recited in claim 4 in which the counterweight mass means utilized to counterbalance the inertia force about the pinion gear assembly is substantially less than the mass producing said inertia force.

7. An apparatus as recited in claim 4 in which the distance between the axis of the pinion shaft and the counterweight is substantially greater than the distance between the axis of the pinion shaft and the connection of the work performing means to said lever means.

8. An apparatus as recited in claim 7 in which the mass of the counter-weight is substantially less than the mass of the work performing means.

9. An apparatus as recited in claim 1, 2 or 3 in which said bearings mounting said pinion shaft in said frame means have a diameter substantially less than the diameter of said rotatable frame means to minimize linear speed of said bearings.