Cam adjustment for tension spring of sewing machine head lifter mechanism

An improved sewing machine head lifter mechanism for supporting a sewing machine head in a cabinet includes a support linkage with a spring support mechanism for the linkage. An adjustable cam member is provided for cooperation with the spring mechanism. Thus, the adjustable cam engages one end of a tension spring. The opposite end of the spring engages a head support bracket. The spring is supported intermediate its ends. Pivotal movement of the cam member adjusts tension of the spring to provide the requisite force for supporting the head support bracket and an attached sewing machine head.

BACKGROUND OF THE INVENTION 
In a principal aspect, the present invention relates to an improved sewing 
machine head lifter mechanism including means for adjusting the force 
providing to support the head. 
Typically, a sewing machine head is mounted on a cabinet or table. 
Preferably, the mounting arrangement for the head permits movement of the 
head into a concealed storage position within the cabinet. Movement of the 
head between the storage position and use position is augmented by a 
linkage mechanism attached to the bottom of the sewing machine head. The 
linkage mechanism is generally counterbalanced to assist in movement of 
the sewing machine toward an elevated use position. The linkage mechanism 
also permits movement of the sewing machine head to the interior of the 
cabinet for storage. 
Various types of linkage mechanisms for support and attachment of a sewing 
machine head to a cabinet have been proposed. A typical linkage mechanism 
includes a housing which is attached to the interior of a cabinet. A 
support bracket is attached to the sewing machine head and linkage arms 
connect the bracket with the housing. The linkage arms pivot to permit 
movement of the bracket and attached head between a support or extended 
position and the retracted or storage position. A tension spring provides 
a means to counterbalance or compensate for the weight of the sewing 
machine head thereby making it easier to move the head between the 
projected position and the storage position. A tension spring normally 
must be customed designed and installed in the linkage mechanism for each 
model of a sewing machine head since each model of a head may vary in 
weight. Thus, the support force required for one model head may vary from 
another type. A desirable objective is to have a multi-purpose, universal 
head lifter mechanism which may be adjusted to accommodate the weight of 
the sewing machine head. 
SUMMARY OF THE INVENTION 
Briefly, the present invention comprises the improvement for a sewing 
machine head support or lifter mechanism of an adjustable spring tension 
mechanism. In the preferred embodiment, the adjustable spring tension 
mechanism includes a rotatable cam adjustable to any one of a number of 
positions each of which provides a distinct spring tension and weight 
support characteristic. 
It is thus an object of the present invention to provide a sewing machine 
head lifter mechanism having a variety of settings for support of heads of 
various weight. 
Another object of the present invention is to provide a cam mechanism for a 
sewing machine head lifter mechanism which may be easily adjusted to 
accommodate any one of a number of various weights supported by the 
linkage mechanism. 
Still a further object of the present invention is to provide a lifter 
mechanism for supporting a sewing machine head which mechanism has a 
minimum number of parts, is economical to make and is efficient and easy 
to use. 
These and other objects, advantages and features of the invention will be 
set forth in the detailed description which follows.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The improvement of the present invention relates particularly to a spring 
tension adjustment feature for the sewing machine head support mechanism 
or device illustrated in the drawings. The arrangement of linkage arms for 
the mechanism is not, by itself, new. Such a linkage arm arrangement is, 
upon information and belief, subject matter of a co-pending application 
owned by someone other than the assignee of the present application. The 
present invention constitutes an improvement over the specific linkage. 
Additionally, the present invention constitutes an improvement which may 
be used in combination with other linkages or mechanisms that support a 
sewing machine head or other items. 
Referring, therefore, to FIGS. 1 and 2, a typical sewing machine head 18 is 
illustrated in combination with a support linkage installed in a sewing 
machine cabinet. Thus, cabinet 10 includes a back wall 12, a top deck or 
platform 14 having a hinged portion 16. A sewing machine head 18 is 
attached to an adjustable bracket 20 by appropriate fasteners such as 
bolts and is supported thereby. The adjustable bracket 20 is fixed to a 
head bracket 22. An upper arm 24 and lower arm 26 pivotally link head 
bracket 22 with a housing 28. Housing 28 is fastened to back wall 12 and 
platform 14 and is retained in a substantially fixed position. 
A biasing spring 30 is wrapped around a rod 32 extending between wings or 
plate members 40 and 42 of housing 28. One end 33 of spring 30 is engaged 
with a bracket rod 34. The opposite end 36 of spring 30 engages a cam 38 
attached to the housing 28. A downward force on end 36 acting through rod 
or fulcrum 32 generates an upward force on rod 34 through end 33. In this 
manner, the bracket 20 is supported or biased to maintain the head 18 in 
the projected position of FIGS. 1 and 5. 
FIGS. 3-7 illustrate in greater detail the structure of the linkage and 
support means for the head 18 including the adjustable spring tension 
feature, a feature which finds its origin in the structure and placement 
of cam 38. Thus, referring to FIGS. 3-7, the housing 28 comprises a single 
member having first and second parallel projecting plate members 40 and 
42. Plate members 40 and 42 are joined together by connecting back plate 
member 44. The housing 28 is attached to cabinet 10 by means of fasteners 
(not shown) through openings such as opening 46 in flanges 48 and 49 
comprising extensions from the plate members 40 and 42 respectively. 
Flanges 50 and 51 projecting from back plate member 44 also include 
openings for receipt of fastening means to attach housing 28 to cabinet 
10. 
Upper arms 24A and 24B are pivotally attached at one end to housing 28 by 
means of pivot members 52A and 52B respectively. The opposite ends of 
upper arms 24A and 24B are pivotally connected to head brackets 22A and 
22B respectively. Lower arms 26A and 26B also pivotally connect with 
housing plate members 40 and 42 respectively and with head brackets 22A 
and 22B respectively. Note that uper arms 22A and 24B are attached on the 
outside of plate members 40 and 42 respectively. This construction avoids 
interference between upper arms 24 and lower arms 26. The specific 
relative lengths and position of arms 24 and 26 permit positioning of head 
bracket 22 as shown in FIGS. 1 and 2. 
Spring mounting rod 32 extends between the plate members 40 and 42. The 
spring 30 which includes a center coil 56 fits over rod 32. Rod 32 thus 
serves as a fulcrum for the spring 30. The lower arms 26A and 26B are 
separated by means of a connected spacing rod 58. The lower arms 26A and 
26B are pivotally positioned inside plate members 40 and 42 respectively, 
and cooperate with rod 32 at one end for mounting on bracket 22 and with 
rod 34 at the opposite end for mounting on housing 28. Stop pins 62 limit 
travel of the head brackets 22 by interference with lower arms 26A and 26B 
when pivoted. 
Adjustable brackets 20A and 20B are pivotally attached to head brackets 22A 
and 22B respectively. The adjustable brackets 20A and 20B may be adjusted 
in height and angle of inclination by operation of threaded spacing stud 
64. That is, stud 64 engages flanges 65 and 67 of brackets 20A and 20B, 
thereby controlling the amount of pivotal movement of the brackets 20A, 
20B when head 18 is attached thereto. 
The spring 30 includes one end 33, as previously described, cooperative 
with rod 34. The opposite end 34 cooperates with cam 38. Cam 38 is 
attached to the back plate member 44 and pivots about attachment rivet 66. 
The cam 38 includes a plurality of separate lands 71-76 each of which may 
cooperate with the opposite end 36 of spring 30. Each land 71-76 is a 
discrete, different distance from the center of the pivot axis or rivet 66 
of cam 30. Thus, each land 71-76 provides a distinct and different 
downward force on the end 36 of spring 30. This force is in the 
counterclockwise sense as illustrated in the figures and imparts an upward 
force in the same counterclockwise sense through the end 33 of spring 30 
on the rod 34 connected to head bracket 22. 
Land 76, in the example shown, provides the greatest force in the 
counterclockwise sense since land 76 is most greatly separated from 
mounting rivet 66. Land 71 provides the least amount of force. As a 
result, it is possible to vary the force on the spring 30 and thereby 
compensate for variable weight which will be placed on the adjustable 
bracket 20. Heavier weights will require greater spring tension in order 
to achieve proper counterbalancing. Lighter weights or lighter sewing 
machine heads require less spring tension for counterbalancing. 
FIG. 7 illustrates in phantom the difference between the land 71 associated 
with the least amount of spring 30 force, and the land 76 associated with 
the most amount of spring 30 force for the embodiment disclosed. The 
remaining lands 72-75 provide intermediate forces between the extremes 
represented by land 71 and land 76. 
It is possible to vary the structure of the present invention without 
departing from the scope of the invention. The invention therefore is to 
be limited only by the following claims and their equivalents.