Stepper driven work feed patterning for sewing machines

A sewing machine employs stepper motor actuated control for magnitude and direction of work feed including operator influenced feed balancing cam apparatus for shifting the stepper motor actuated control axially relative to or with a stepper motor shaft in order to attain parity between forward and reverse directions of work feed.

BACKGROUND OF THE INVENTION 
This invention relates to sewing machines in which stitch patterning 
capability is provided by means for controlling the magnitude and 
direction of work feed. More particularly, this invention relates to 
sewing machine work feed control by stepper motor actuation as dictated by 
electronic stitch pattern data with novel improved operator influenced 
control of the balance between forward and reverse direction of work 
feeding motion. 
DESCRIPTION OF THE PRIOR ART 
The use of stepper motors as actuators for translating electronically 
stored work feed instructions into sewing machine work feed magnitude and 
direction is well known. In the operation of sewing machine work feeding 
mechanisms there are numerous factors which can vary the effectiveness of 
the work feed in one direction as compared with the opposite direction. 
Such factors may include the nature, thickness, and nap of the fabrics 
being stitched; the surface characteristics of the fabric engaging work 
feed element of the sewing machine; and the nature and surface 
characteristics of the presser device opposing the work feed element. 
The term "balance control" refers to means, usually manually operator 
influenced, for adjusting the sewing machine work feeding mechanism or 
controls so as to attain uniformity in the forward and reverse direction 
of work feed magnitude. 
The U.S. Pat. No. 4,167,912 Sept. 18, 1979 of R.L. Sedlatschek et.al. 
discloses a stepper actuated work feed control for sewing machines in 
which operator influenced adjustment of the balance between opposite 
directions of work feed is provided by a translatory shiftable mounting 
for the entire stepper motor in a direction parallel to the stepper motor 
shaft and manually operable means for shifting the entire stepper and the 
mounting means. The high cost incident to the complicated stepper motor 
mounting required by the construction of U.S. Pat. No. 4,167,912, the 
inordinate space required within the limited confines of a typical sewing 
machine frame, as well as the liklihood of binding forces arising in the 
stepper drive due to variation in the symetry of the translating shiftable 
stepper motor mount all militate against satisfactory utilization of that 
disclosure. 
SUMMARY OF THE INVENTION 
It is the object of the invention to provide a stepper actuated drive 
mechanism for controlling magnitude and direction of sewing machine work 
feeding including a simple and cost effective operator influenced work 
feed balancing arrangement applicable without generating any binding 
forces to the stepper activated drive mechanism. 
The object of the invention is attained in a stepper activated drive 
mechanism including a rotatable drive element capable of shifting a 
follower parallel to the axis of rotation of the drive element by the 
provision of operator influenced cam means actuating in opposition to the 
spring biasing means for bodily shifting the drive element along its axis 
of rotation. A particularly effective embodiment of this invention where 
the drive element is secured on or arranged coaxially of the stepper motor 
shaft involves cam influence in opposition to spring bias of both the 
drive element and stepper motor shaft together.

DETAILED DESCRIPTION 
FIG. 1 illustrates a sewing machine indicated generally at 10 having a 
frame including a bed 11, a standard 12 rising from the bed, and a bracket 
arm 13 overhanging the bed. The driving mechanism of the sewing machine 
includes an armshaft 14 and a bed shaft 15 interconnected by a timing belt 
16 in the standard. A needle 17 carried for endwise reciprocation by a 
needle bar 18 is mounted for movement in bracket arm 13. Any conventional 
connections not shown may be used between the armshaft 14 and the 
needlebar 18 for imparting needle reciprocation. 
The work feeding mechanism includes a feed dog 20 carried by a feed bar 21. 
The feed bar 21 may be supported in the bed 11 by any conventional means 
(not shown) for accomodating work transporting movements of the feed dog 
transversely across the bed 11 as well as vertical movements to shift the 
feed dog alternately into and out of work engagement on work feed and idle 
return strokes of feed dog work transporting movements. 
In FIG. 1 a mechanism is illustrated for imparting work transporting 
movement to the feed dog 20 including a feed drive shaft 22 driven by 
gears 23 from the bed shaft 15, an eccentric cam 24 on the feed drive 
shaft 22, a pitman 25 embracing the eccentric 24 and connected to 
reciprocate a slide block 26 in a slotted feed regulating guideway 27. A 
link 28 pivotally connects the pitman 25 with the feed bar 21 so that 
depending upon the inclination of the guideway, regulation of the 
magnitude and direction of the feed stroke of the feed dog may be 
controlled. 
The guideway 27 is fast on a rock shaft 30 journaled in the bed and a rock 
arm 31 secured on the rock shaft 30 supports a follower pin 32 which 
tracks a spiral cam groove 33 formed radially in a cam member 34 made fast 
on the shaft 35 of a stepper motor 36 secured as by fastenings 37 in the 
sewing machine bed 11. 
The stepper motor 36 is actuated in response to stitch pattern signals 
stored in an electronic stitch pattern memory indicated generally at 40 in 
FIG. 1. The stitch pattern signals may be extracted in sequence from the 
memory at an appropriate time preceeding each stitch in the pattern in 
response to timing pulses from a pulse generator 41, associated with the 
sewing machine arm shaft 14. 
In sewing machine work feed mechanisms of the type described above, the 
fabrics being stitched do not always move an exact amount matching that of 
the work transporting movement of the feed dog. It is frequently the case 
that precisely equal work transporting motions of the feed dog in opposite 
directions of feed will result in noticeably different work feed or stitch 
lengths, and particularly where patterns of stitches are being being 
formed, extremely small stitch length differences of this nature can be 
especially noticeable. 
A preferred embodiment of an operator influenced work feed balancing 
mechanism in accordance with this invention is illustrated in FIGS. 1 and 
2. In this embodiment, the cam member 34 is secured directly on the 
stepper motor shaft 35 and the stepper motor shaft is journaled for 
limited axial movement. 
A bearing ball 50 constrained coaxially of the stepper motor shaft against 
the opposite extermity of the shaft 35 from the cam member 34 is engaged 
and biased toward the cam member 34 by a leaf spring 51 which may be 
retained by the stepper motor fastenings 37. 
At the opposite extremity of the stepper motor shaft 35 adjacent the cam 
member 34 another ball bearing 52 is constrained in a concavity 53 
coaxially in the stepper shaft extremity. The ball bearing 52 is opposed 
by the tapered cam 54 formed on one extremity of a bar 55 endwise 
slidsably constrained in a guide groove 56 formed in the sewing machine 
bed. 
At the opposite extremity of the cam 54 the bar 55 is formed with a rack 57 
guided in mesh with a gear 58 which is fast on a stub shaft 59 to which a 
dial 60 is secured. As shown in FIG. 1, the dial 60 may be arranged so as 
to protrude through an opening 61 in the sewing machine standard 12 for 
ready access by the sewing machine operator. 
By turning the dial 60, the sewing machine operator may influence movement 
of the inclined cam 54 toeffect axial shift of the cam member 34 in 
opposition to the bias of spring 51 to balance the forward and reverse 
directions of work feed movements. 
FIG. 3 illustrates a modification of the operator influenced means for 
effecting work feed balance. 
In the embodiment of FIG. 3 the stepper motor shaft 35 is constrained 
against axial movement by thrust bearing 70 and the cam member 34 is 
formed with a cam shaft 71 separate from but keyed to the stepper motor 
shaft as by the non-circular configuration 73 of the stepper shaft 35 and 
a matching non-circular configuration of a cam shaft bore 74. Between the 
stepper shaft 35 and a shoulder 75 on the cam member 34 a coil spring 76 
is arranged biasing the cam member away from the stepper motor 36. A leaf 
spring 77 secured in the sewing machine frame extends across the free 
extremity of the cam shaft and abuts a ball bearing 78 constrained axially 
in the cam shaft extremity. 
An eccentric 79 journaled in the machine frame at the opposite side of the 
leaf spring 77 from the cam shaft serves to impart controlled force to 
position the cam shaft and with it the cam member 34 in opposition to the 
coil spring 76. A flexible shaft 80 may be used to connect the eccentric 
79 with an operator influenced knob 81 projecting through an access 
opening 82 in the machine frame. 
It will be appreciated that in either embodiments illustrated and described 
herein, the force applied to the cam member and stepper motor shaft to 
influence stitch balance being applied directly along the axis of rotation 
of the stepper motor shaft and/or cam shaft by means of the axially 
constrained ball bearings, will impart virtually no torque opposing 
stepper drive movements. These embodiments thus provide advantageous and 
cost effective operator influenced work feed balancing arrangements for 
stepper driven sewing machine work feed controls.