Cloth cutting device in button-hole sewing machine

In a button-hole sewing machine where a piece of cloth is cut from a button hole before or after the sewing operation, a moveable knife cooperating with a stationary knife is driven through a mechanical linkage by an air drive unit and the operating pressure and speed of the moveable knife are changed by adjusting the device associated with the air drive unit.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a cloth cutting device in a button-hole 
sewing machine, and more particularly to a cloth cutting device for 
cutting a piece of cloth to make a button hole or the like before the 
button hole or the like is sewn. 
2. Description of the Prior Art 
A button-hole sewing machine for forming button holes such as eyelet holes 
is well known in the art. A sewing machine of this type is provided with a 
cloth cutting device which cuts a piece of cloth along the contour of a 
desired button hole before or after the button hole is sewn. 
In such a conventional cloth cutting device, a moveable knife is 
mechanically driven by the utilization of the drive force of a main cam, 
so that a piece of cloth is cut by the cooperation of the moveable knife 
with a stationary knife. In a conventional device the moveable knife is 
driven by a mechanical drive source, namely, the main cam as described 
above. Therefore, the stroke of the moveable knife can be adjusted, but 
the operating speed or pressure of the moveable knife cannot be adjusted. 
In other words, the operating speed of the moveable knife is determined 
indiscriminately from the sewing speed of the sewing machine, and the 
operating pressure of the moveable knife is defined by the operating 
speed. Accordingly, the operating speed and the operating pressure cannot 
be adjusted. Therefore, components, including these knives may be broken, 
and sometimes the piece of cloth cannot be cut very well. 
SUMMARY OF THE INVENTION 
In view of the foregoing, an object of the present invention is to provide 
a cloth cutting device for a button-hole sewing machine in which the 
stroke, operating speed and operating pressure of the moveable knife can 
be adjusted. 
The foregoing objects and other objects of the invention have been achieved 
by the provision of a cloth cutting device for a button-hole sewing 
machine in which a piece of cloth is cut along the contour of a button 
hole or the like before or after the latter is sewn. The cutting device is 
comprised of a link mechanism for driving a moveable knife relative to a 
stationary knife and an air drive unit for driving the link mechanism so 
that the piece of cloth is cut by the cooperation of the two knives. 
The nature, principle and utility of the invention will become more 
apparent from the following detailed description when read in conjunction 
with the accompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
One preferred embodiment of this invention will be described with reference 
to the accompanying drawings. 
In FIG. 1 the button-hole sewing machine includes a botton-hole sewing 
machine body 1, the bed 2 of the machine body 1, an arm 3, a needle bar 4, 
a sewing needle 5 which is fixedly secured to the lower end of the needle 
bar, the sewing needle 5 being moved up and down by the needle bar and a 
cloth cutting device 8. 
In the cloth cutting device according to the present invention as shown in 
FIG. 2 a moveable knife 14 is detachably mounted on the end of a hammer 
lever 12. The hammer lever 12 is rotatably mounted on a shaft (not shown) 
which is inserted into a hole 10 and serves as a fulcrum. A stationary 
knife 16 is provided in such a manner that it is in alignment with the 
moveable knife 14. A piece of cloth is cut along the configuration of a 
button hole by the cooperation of the knives 14 and 16. In order to cause 
the moveable knife 14 to cooperate with the stationary knife 16, a 
mechanical linkage 18 is provided. The linkage is composed of lever arm 22 
which is rotatably mounted on a shaft (not shown) which is inserted into 
the hole 20 of the arm 22. One end portion of the lever arm 22 is rockably 
coupled by means of a pushing rod 24 to one end portion of the 
above-described hammer lever 12. 
One of the specific features of the invention resides in the provision of 
an air drive unit for driving the mechanical linkage, that is, the air 
drive unit drives the moveable knife. 
The air drive unit 26 has an air drive cylinder 28. The shaft 30 of the air 
cylinder 28 and the other end portion of the lever arm 22 are rockably 
coupled to each other through a push rod 32. 
An air supply pipe 34 and an air exhaust pipe 36 are connected to the air 
cylinder 28, so that air from a compressor (not shown) is supplied to the 
air cylinder 28 through the air supply pipe 34 and the air in the cylinder 
28 is removed through the air exhaust pipe 36. 
The cloth cutting device of the invention has a solenoid valve 38 in order 
to supply air to the air cylinder 28 and to remove the air from the 
cylinder 28. When the solenoid valve 38 is energized, the air supplied 
through a pipe 40 from the compressor is supplied through the air supply 
pipe 34 to the air cylinder and when the solenoid valve 38 is 
de-energized, the air in the cylinder 28 is removed through the air 
exhaust pipe 36. The solenoid valve 38 is operated according to data which 
have been programmed in a control panel 42, including a microcomputer, 
that is, the solenoid valve 38 is energized and de-energized with desired 
timing. A moveable knife operation selecting switch 44 is provided on the 
control panel 42 so that the operation and non-operation of the hammer 
lever 12 can be freely selected. 
In order to control the operating speed of the moveable knife 14, the air 
supply pipe 34 has a speed controller 46 therein and the air exhaust pipe 
36 also has a speed controller 48 therein. The speed controllers 46 and 48 
are, for instance, needle valves. The air supplying speed and the air 
exhausting speed can be controlled by operating the control knobs 46a and 
48a of the speed controllers 46 and 48 respectively. 
In order to control the operating pressure of the moveable knife 14, the 
pipe 40 has a pressure controller 50 at the middle. The presssure 
controller 50 is, for instance, a needle valve. The pressure of air 
supplied to the air cylinder 28, i.e., the operating pressure of the 
moveable knife 14 can be controlled by operating the control knob 50a of 
the pressure controller 50. 
Further in FIG. 2, reference numerals 52 through 55 designate the various 
ball-type couplings in the mechanical linkage 18. 
The operation of the cloth cutting device according to the present 
invention will be described. When it is desired to cut the cloth at a 
specific time the solenoid valve 38 is energized so that air is supplied 
from the air compressor through the pipes 40 and 34 into the air cylinder 
28. As a result, the shaft 30 of the air cylinder 28 is moved in the 
direction of the arrow A, the lever drive arm 22 is turned clockwise, and 
the hammer lever 12 is turned counterclockwise, in FIG. 2. That is, the 
moveable knife 14 cooperates with the stationary knife 16, to cut the 
piece of cloth under pressure to thereby form a button hole having the 
desired configuration therein. 
After the cutting operation, the solenoid valve 38 is de-energized, and the 
air is discharged from the air cylinder 28 through the pipe 36. 
Accordingly, the air cylinder shaft 30 is moved in the direction of the 
arrow B and the moveable knife 14 is returned to its original position. 
Adjustment of the stroke of the moveable knife 14 can be achieved by 
controlling the period of energization of the solenoid valve 38. 
Therefore, the most suitable stroke can be selected for the thickness of 
the piece of cloth which is to be cut for a button hole. 
The operating speed of the moveable knife 14 can be controlled by operating 
the control knobs 46a and 48a of the speed controllers 46 and 48. 
Therefore, the cloth cutting operation can be carried out at a desired 
speed. 
The operating pressure of the moveable knife 14 can be adjusted by 
operating the control knob 50a of the pressure controller 50. Therefore, 
within the limit of the mechanical strength of components, including the 
knives 14 and 16, the most desirable cloth cutting pressure can be 
provided for the thickness of the piece of cloth to cut for the button 
hole. 
As is clear from the above description, the cloth cutting device of the 
invention utilizes the air drive unit 26 for driving the moveable knife 
14. Therefore, the stroke, operating speed and operating pressure of the 
moveable knife 14 can be determined so as to be in agreement with the 
thickness of the piece of cloth to be cut. No excessively large forces are 
exerted on the components, including the knives 14 and 16. 
In the above-described example, the piece of cloth is cut after being sewn. 
A program for an operation shown in part (a) or part (b) of FIG. 3 is 
written in the ROM (read-only memory) of the microcomputer in the control 
panel 42. When the hammer lever operation selecting switch 44 is turned 
on, the operating sequence, except for the operation of the cloth cutting 
hammer lever (cloth cutting hammer - ON), is effected. When the cloth 
cutting operation is carried out after the sewing operation, an operating 
sequence as shown in part (b) of FIG. 3 will be effected. In this case 
when a presser foot switch (not shown) is turned on, a presser foot (not 
shown) on the sewing machine bed 2 is operated to retain the piece of 
cloth in place. 
Thereafter the start pedal is operated (depressed) so as to turn on the 
operating switch. Idle feeding is carried out by the cloth feeding unit, 
and then sewing is effected according to a button hole sewing pattern. 
When the sewing operation is accomplished, the piece of cloth is returned 
to its original position and the upper and lower threads and the core 
thread are cut. Then the moveable knife 14 of the cloth cutting device 8 
of the invention is operated to cut the piece of cloth. Thereafter, the 
presser foot is turned off to release the piece of cloth. Thus, the hole 
sewing has been accomplished. 
In the case where it is necessary to perform the cloth cutting operation 
with the cloth cutting device 8 prior to the button hole sewing operation, 
the program in the control panel 42 should be changed so as to perform the 
operation sequence in part (a) of FIG. 3. 
As is clear from the above description, in the cloth cutting device of the 
invention a linkage for driving the moveable knife relative to the 
stationary knife and an air drive unit for driving the linkage are 
provided so that the cloth cutting operation is carried out by the 
cooperation of the two knives, with the stroke, operating speed and 
operating pressure of the moveable knife being adjustable.