Sewing machine stitch length override and feed balance for digital feed actuators

A sewing machine is disclosed wherein positioning of the work feeding regulator is controlled by a digital actuator responsive to digital signals applied thereto. The positioning of the work feeding regulator is thereby adjustable in discrete increments. A manual override and feed balance mechanism is provided for effecting continuous positioning of the work feeding regulator.

BACKGROUND OF THE INVENTION 
This invention relates to sewing machines and, more particularly, to sewing 
machine work feeding mechanisms controllable in response to the successive 
application thereto of digital signals. 
In recent years, so called "electronic" sewing machines have gained in 
popularity and have met with commercial success in both industrial and 
domestic applications. These electronic sewing machines typically include 
a memory unit for storing in digital form information to control both the 
needle positioning mechanism and the work feeding mechanism to 
automatically produce a desired pattern. Signals generated from the stored 
information are applied to signal responsive actuators for selectively 
positioning the needle and the work feeding mechanism. These actuators may 
be of either the analog type or the digital type. An analog actuator is 
responsive to an analog signal for positioning its associated mechanism at 
a point along a continuum between two extreme positions. The present 
invention is concerned with digital actuators wherein the actuator 
responds to digital input signals to position its associated mechanism at 
a selected one of a plurality of incrementally displaced discrete points 
between two extreme positions. A problem encountered with actuators of the 
digital type is that it is often desired to position the associated 
mechanism at a point intermediate two of the predetermined discrete 
positions. 
It is therefore an object of this invention to provide a manually operable 
continuously movable override for a digital actuator. 
A further problem inherent in the use of digital actuators becomes apparent 
when such an actuator is used in conjunction with a work feeding mechanism 
for a sewing machine. The feeding characteristics of different fabrics 
differ widely so that feed settings which result in equal stitch lengths 
in forward and reverse directions for one particular fabric, will not 
necessarily result in equal length stitch formation in forward and reverse 
directions when another fabric is sewn upon. The machine therefore has to 
be "balanced" for the particular fabric being stitched. When utilizing an 
actuator of the digital type, the balance point may lie between two of the 
predetermined incrementally displaced discrete positions. 
It is therefore another object of this invention to provide a manually 
operable balance control for a sewing machine utilizing a digital actuator 
for the work feeding mechanism. 
SUMMARY OF THE INVENTION 
The foregoing and additional objects are attained in accordance with the 
principles of this invention in a sewing machine having a work feeding 
mechanism and a feed regulator operatively connected to the work feeding 
mechanism to influence magnitude and direction of feed motion, the feed 
regulator being variable in position over a predetermined range of 
positions between successive stitches, and a driving device operatively 
connected to impart discrete incremental movement to the feed regulator 
over the predetermined range of positions in response to digital feed 
signals applied thereto, by providing manually operable means for 
imparting continuous movement to the work feeding regulator. 
In accordance with an aspect of this invention, the entier driving device 
is shifted in position.

DETAILED DESCRIPTION 
FIG. 1 illustrates a sewing machine with fragments of the work feeding 
mechanism which contributes to changes in the relative coordinates of 
successive needle penetrations. As shown in phantom lines in FIG. 1, the 
sewing machine casing 10 includes 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 arm shaft 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 the bracket 
arm 13. Any conventional connections (not shown) may be used between the 
arm shaft and the needle bar for imparting needle reciprocation. 
The work feeding mechanism includes a feed dog 20 carried by a feed bar 21. 
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, a cam 24 on the feed drive shaft 22, a 
pitman 25 embracing the cam 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 27, regulation of the magnitude and direction of the feed 
stroke of the feed dog 20 may be controlled. 
The inclination of the guideway 27 in the present invention may be 
controlled by an electromechanical digital feed actuator indicated 
generally by the reference numeral 30. The actuator 30 illustratively 
includes as its main driving element a stepping motor 32. Stepping motors 
per se are well known in the art and function to rotate in fixed angular 
increments in accordance with pulses applied thereto from associated 
control circuitry. Neither the stepping motor nor its associated control 
circuitry form a part of the present invention and hence will not be 
described in detail herein. Only as much detail as is necessary for an 
understanding of the present invention will be set forth hereinafter. 
The actuator 30 includes a link 34 pivoted at 36 to a rock arm 38 carried 
on a rock shaft 40 secured to the guideway 27. The position of the link 34 
is controlled by a worm 42 and a worm gear segment 44, pivoted on a shaft 
46. The worm 42 is an extension of the shaft of the stepping motor 32. 
Rotation of the stepping motor 32 causes rotation of the worm 42 and the 
consequent pivoting of the worm gear segment 44, which controls the 
position of the link 34 and the inclination of the guideway 27. 
Illustratively, a reference stop 48 may be provided to cooperate with a 
member 50 mounted on the shaft 46. The reference stop position of the 
shaft 46 may illustratively correspond to the maximum forward stitch 
length and may be utilized by the machine control circuitry (not shown) at 
machine start up. 
A disadvantage of the arrangement shown in FIG. 1, and likewise a 
disadvantage of all digital actuators, is that the inclination of the 
guideway 27, and hence the amplitude of the stitch length, may be 
controlled only by fixed incremental amounts. These fixed incremental 
amounts may not provide for a fine setting of the stitch length and 
further, may not allow an exact feed balance to be obtained. The 
arrangement illustrated in FIG. 1 overcomes this disadvantage and allows 
for the obtaining of both feed balance and fine adjustment of stitch 
length to values intermediate the discrete incremental values obtainable 
through the use of a digital actuator. 
In accordance with the principles of this invention, a first embodiment of 
this invention is constructed wherein the stepping motor 32 is mounted on 
a motor mounting bracket 52 in a conventional manner. The shaft 54 of the 
motor 32 extends out through one side of the bracket 52 and the worm 42 
extends out the other side of the bracket 52 through suitable openings 
therein. A guide bracket 56 is provided, which is fixedly secured to the 
sewing machine casing 10 in a conventional manner, and the motor mounting 
bracket 52 is arranged to be slidably secured to the guide bracket 56. 
Toward that end, the motor mounting bracket 52 includes a first slot 58 
and a second slot (not shown) at its other end. These slots are parallel 
to each other and are also parallel to the axis of the motor shaft 54 and 
the worm 42. Four shoulder screws 60 (only two of which are shown) are 
utilized to secure the motor mounting bracket 52 to the guide bracket 56. 
The shoulder screws 60 fit through the slots 58 and are tightened 
sufficiently to provide frictional engagement so as to hold the motor 
mounting bracket 52 but to allow the motor mounting bracket 52 to slide 
along the guide bracket 56 when the frictional engagement is overcome by 
operator applied forces. 
To accomplish the objects of this invention, two operator controlled knobs 
62 and 64 are provided. The knob 62 is utilized to control the feed 
balance and the knob 64 is utilized to provide a manual stitch length 
setting. The balance knob 62 is mounted on a shaft 66. The shaft 66 
extends through suitable openings in the guide bracket 56 and the motor 
mounting bracket 52. Four retaining rings 68, two on each side of the 
upstanding portions of the motor mounting bracket 52, are provided to 
prevent axial movement of the shaft 66 with respect to the motor mounting 
bracket 52. A nut 70 is fixedly secured to the guide bracket 56. A portion 
of the shaft 66 is provided with threads matching the internal threads of 
the nut 70. This threaded portion of the shaft 66 extends on both sides of 
the guide bracket 56. Operator controlled rotation of the knob 62 thus 
causes the shaft 66 to be axially displaced through the nut 70 relative to 
the guide bracket 56. The amount of displacement is dependent on the 
amount of rotation of the knob 62 and the direction of displacement is 
dependent upon the direction of rotation of the knob 62. The axial 
displacement of the shaft 66 causes the entire motor mounting bracket 52 
to be moved relative to the guide bracket 56. The shaft 66 is arranged 
with its axis parallel to the axis of the motor shaft 54 and the worm 42. 
Therefore, rotation of the knob 62 causes the worm 42 to be axially 
displaced. This axial displacement of the worm 42 results in the pivoting 
of the worm gear segment 44 about the shaft 46, resulting in an angular 
displacement of the guideway 27. In this manner, proper feed balance may 
be obtained without a rotation of the shaft of the stepping motor 32. 
Alternatively, the nut 70 may be secured to the motor mounting bracket 52 
and the retaining rings 68 may be secured to the guide bracket 56 so that 
when the knob 62 is rotated, the shaft 66 is not axially displaced, but 
rather only the motor mounting bracket 52 is moved. 
The knob 64 is utilized to provide manual control of the stitch length over 
a continuum of values so that the operator is not limited by the discrete 
setting applied by a digital control. The knob 64 is mounted on a shaft 72 
which extends through suitable openings in the machine casing 10 and the 
guide bracket 56. At the end of the shaft 72 opposite the knob 64 is a 
friction clutch 74. A spring 76 surrounds the shaft 72 between the machine 
casing 10 and the knob 64 and is adapted to bias the knob 64 away from the 
casing 10. This outward bias is limited by the friction clutch 74 acting 
as a stop against the guide bracket 56. The shaft 72 is axially aligned 
with the motor shaft 54. When the machine operator sets the stitch length, 
the knob 64 is forced toward the casing 10 against the action of the 
spring 76 until the friction clutch 74 engages the end of the motor shaft 
54. At this time, the knob 64 is rotated to turn the motor shaft 54 and 
consequently the worm 42 so that the inclination of the guideway 27 may be 
adjusted to provide any desired stitch length over a continuum within the 
permissible range. 
An alternative construction for obtaining manual stitch length override and 
feed balance in a stepping motor controlled work feeding mechanism is 
illustrated in FIG. 2, wherein elements common to the embodiment shown in 
FIGS. 1 and 2 have the same reference numerals. FIG. 2 is intended to be 
schematic in its representation and hence the mechanisms illustrated 
therein are not shown in great detail. As shown in FIG. 2, the stepping 
motor 32 is mounted in a motor mounting frame 80. The shaft 54 of the 
stepping motor 32 has one end terminating in a threaded portion 82. The 
threaded portion 82 extends through a nut 84 mounted on a nut guide 86 
which in turn is slidably mounted on the motor mounting frame 80 in a 
conventional manner. The nut 84 is connected to the link 34 which is 
pivoted at 36 to the rock arm 38 carried on the rock shaft 40 which in 
turn is secured to the guideway 27 (FIG. 1). Thus, rotation of the shaft 
54 of the stepping motor 32 causes the nut 84 to be axially displaced to 
effect a desired inclination of the guideway 27. Manual control of the 
inclination of the guideway 27 is achieved by providing a balance cam 88, 
pivoted at 90. The balance cam 88 is connected to an operator controlled 
knob (not shown) for rotation about 90. The motor mounting frame 80 is 
connected to a pair of motor mounting levers 92 (only the closer one of 
which is shown) at a motor alignment pivot 94. The levers 92 are connected 
to the sewing machine casing 10 at a pivot 96. A first end of a link 98 is 
connected to the lever 92 at a pivot point 100. The other end of the link 
98 has a cam follower 102 mounted thereon. The cam follower 102 rides 
within a slot 104 of the balance cam 88. The slot 104 provides the camming 
surface and is configured as a portion of a helix so that its end 106 is 
further from the pivot point 90 than is its end 108. Thus, when the 
balance cam 88 is rotated under operation control, this causes an 
approximately linear displacement of the stepping motor 32, in turn 
producing a desired inclination of the guideway 27 without motor shaft 
rotation. 
A third embodiment of apparatus constructed in accordance with the 
principles of this invention is depicted in FIGS. 3A and 3B. As shown 
therein, the stepping motor 32 is held in a motor mount 110 which in turn 
is secured to the sewing machine casing 10 in a conventional manner. The 
shaft 54 of the stepping motor 32 has a threaded end portion 112 which is 
threaded into a nut 114. The nut 114 in turn is secured to a link 34, 
illustratively by a ball joint. To afford manual adjustment, a nut 
rotation plate 116 is provided. The plate 116 is secured to the motor 
mount 110 by shoulder screws 118 which extend through a slot 120 in the 
plate 116. The screws 118 are sufficiently tightened to provide frictional 
forces to only allow the plate 116 to be rotated under operator control. 
Secured to the plate 116 are spring members 122 which prevent the nut 114 
from rotating relative to the plate 116. Also secured to the plate 116 is 
a gear segment 124. Meshed with the gear segment 124 is a gear 126 which 
is mounted on a shaft 128. The shaft 128 is terminated by a knob 130. 
Operator control is effected by the operator turning the knob 130 which in 
turn causes rotation of the plate 116 through the action of the gear 126 
and the gear segment 124. Rotation of the plate 116 causes rotation of the 
nut 114 which moves the link 34 to effect a desired inclination of the 
guideway 27 (FIG. 1). 
A fourth embodiment constructed in accordance with the principles of this 
invention is shown in FIG. 4 wherein the stepping motor 32 is secured to a 
motor mount 140, which in turn is secured to the sewing machine casing 10. 
The shaft 54 of the stepping motor 32 is terminated by a disc and screw 
assembly 142. The screw portion of the assembly 142 is threaded through a 
nut 144 which in turn is connected to the link 34 through a ball joint. 
Rotation of the stepping motor shaft 54 causes an axial displacement of 
the nut 144 which in turn causes the link 34 to move, thereby changing the 
inclination of the guideway 27 (FIG. 1). To afford manual control of the 
inclination of the guideway 27, a disc retainer 146 is threaded on the 
motor mount 140. Rotation of the disc retainer 146 may be effected by an 
arrangement similar to that shown and described with respect to FIGS. 3A 
and 3B. A gear segment 148 secured to the disc retainer 146 is meshed with 
a gear 150 secured to a shaft 152, which is terminated by a knob 154. When 
an operator turns the knob 154, the disc retainer 146 is rotated through 
the coaction of the gear 150 with the gear segment 148. Rotation of the 
disc retainer 146 results in an axial displacement of the disc retainer 
146 and a consequent axial displacement of the disc and screw assembly 
142. This causes a linear motion of the nut 144 and hence an adjustment of 
the inclination of the guideway 27. It is to be noted that this 
arrangement causes an axial displacement of the motor shaft 54 and so may 
only be utilized where the stepping motor 32 is so designed that the motor 
coils are wide enough that the shaft rotor is exposed to a proper amount 
of magnetic flux over a range of linear positions of the shaft 54. 
Accordingly, there has been described an arrangement in a sewing machine 
having a work feeding regulator selectively positionable in response to 
digital signals for providing a manually operable control to achieve 
positioning of the work feeding regulator over a continuum, in addition to 
the discrete positioning provided by the digital actuator. It is 
understood that the above-described arrangements are merely illustrative 
of the application of the principles of this invention. Numerous other 
arrangements may be devised by those skilled in the art without departing 
from the spirit and scope of this invention, as defined by the appended 
claims. While this invention has been illustrated with respect to a 
stepping motor as the digital actuator, it is contemplated that the 
principles of this invention may be applied to arrangements utilizing 
other types of digital actuators. For example, if a whipple tree 
arrangement of linkages is utilized to control the work feeding regulator, 
the entire whipple tree linkage may be mounted in a manner so as to be 
movable as a whole under control of an operator.