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18-10-21

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    A sewing machine consists of four basic

mechanisms: a take-up mechanism, a needle-motion mechanism, a material-feeding mechanism,

and a bobbin. Its proper operation requires a delicate balance of these mechanisms. This

paper introduces a computer-simulation model that represents these mechanisms and uses the

model to predict the kinetic behavior of sewing machines. Based on the simulation. a

quantitative understanding of the sewing machine can be achieved that leads to improved

sewing-machine design and better sewing-process control. In particular, the balance of

thread supply and thread requirement is studied. the thread supply is defined as the amount

of thread supplied by the take-up mechanism within one stitch. The thread requirement is

defined as the amount of thread required in one stitch and is controlled primarily by the

bobbin mechanism. Both properties change instantaneously. From a practical point of view,

if the thread requirement were much larger than the thread supply, then there would be skip

stitches (when the loop cannot be formed properly) or even thread breakage. On the other

hand, if the thread requirement were much less than the thread supply, then there might be

poor stitches (with too much thread in the loop) or even needle-jamming. By using the

simulation model, the instantaneous balance of the thread supply and the thread requirement

is quantitatively studied. It is shown that the balance of thread supply and thread

requirement can be changed and optimized by changing the design parameters of the take-up

mechanism. The model is validated experimentally by using a Pfaff lockstitch industrial

sewing machine.
    Industrial sewing machines differ from traditional consumer sewing machines in many

ways. An industrial sewing

machine
is specifically built for long term, professional sewing tasks and is

therefore constructed with superior durability, parts, and motors. Whereas traditional

sewing machines might include nylon or plastic gears, an industrial sewing machine's gears,

connecting rods, housings, and body are typically constructed from high-quality metals,

such as cast iron or aluminum. Beyond that, industrial sewing machines are made to handle

thick materials such as leather, produce faster stitch rates, and incorporate stouter, more

positive feed components than do their consumer equivalents.
    With regard to these types of industrial sewing machines, the primary differentiation

between them is based on the design of the bed. These four different sewing machine bed

styles and their uses are as follows:
    Flatbed: The most common type, these machines resemble traditional sewing machines in

that the arm and needle extend over the flat base of the machine. Workers typically use

this machine for sewing flat pieces of fabric together. Some type of fabric feed mechanism

is usually housed in the bed (see below).
    Cylinder-bed: These machines feature a narrow, cylindrical bed as opposed to a flat

base. This allows the fabric to pass around and under the bed.  Workers employ the

cylinder-bed machine for sewing cylindrical pieces such as cuffs, but it is also useful for

bulky and curved items such as saddles and shoes.
    Post-bed: These machines feature bobbins, feed dogs, and/or loopers in a vertical

column that rises above the flat base of the machine. The height of this column can vary

depending on the machine and its application. Applications that make access to the sewing

area difficult, such as attaching emblems, or boot or glove making, utilize the post-bed

machine.
    Off-the-arm: The least common group, these machines extend a cylindrical bed out from

the back of the machine perpendicular to the direction taken by the bed of the cylinder-bed

machine. This allows for long runs of tubular goods, such as the inseams of trousers, and

is useful for sewing sleeves and shoulder seams.
    Other special-purpose sewing machines exist, as well. Portable and fixed electric units

are often employed for closing large sacks of agricultural products, dog food, etc.

Bookbinders use special machines in their operations. Carpet installers also use special

machines for binding carpet. Embroidering and monogramming machines are used for textile

customization and decorating and are often program-controlled. Special long arm machines

are made for sailmakers and purpose-built machines are available for cobblers.
    Sewing Machine Feeds
    Different industrial sewing machines offer several ways to feed the material.

Typically, industrial mini sewing

machines
that deliver numerous feed capabilities are more expensive. The main types

of feed mechanisms are:
    Drop feed: The feed mechanism lies below the machine's sewing surface. This is probably

the most common feed type. Toothed segments called feed dogs lift and advance the fabric

between each stitch, with the teeth pressing upwards and sandwiching the material against a

presser foot.
    Needle feed: The needle itself acts as the feed mechanism, which minimizes slippage and

allows workers to sew multiple layers of fabric.
    Walking foot: The immobile presser foot is replaced with a foot that moves with the

feed, which allows easier performance on thick, spongy or cushioned materials.
    Puller feed: The machine grips and pulls straight-seamed material as it is sewn and can

perform on large, heavy-duty items such as canvas tents. 
    Manual feed: The feed is controlled entirely by the worker, who can do delicate,

personal work such as shoe repair, embroidering, and quilting. On industrial

overlock sewing machines,

it is sometimes necessary to remove the feed dogs to obtain a manual feed.
    The application of an industrial sewing machine is also an important factor to

consider. For example, some machines come with an automatic pocket setter, while others

include pattern programmability or electronic eyelet buttonholers. Furthermore, the

strength and design of the machine needs to complement the type of material being sewn.

Higher quality machines will likely be necessary for medium to heavy materials, such as

denim, while base level industrial machines may be adequate for lighter materials, such as

cotton.
    Other Considerations
    A particular machine’s available stitch types can vary. There are several dozen

distinct types of stitches, each requiring between one and seven threads. Plain, or

straight stitches are the most commonly used stitches in industrial sewing and include

lock, chain, overlock, and coverstitch. Sailmakers, on the other hand, use zig-zag

stitching to better tolerate seam loading between sail panels.
    Yet another important feature is the size and speed of the industrial

embroidery sewing machine

. More expensive machines will be able to sew more stitches per minute. Larger

machines provide a larger clearance area under the foot and bigger bed size.
    Many industrial machines are sold without motors and can be operated with either clutch

motors or servomotors, depending on the user’s needs. Clutch motors run constantly and

power to the machine is transmitted by depressing a foot treadle to actuate the clutch.

Servomotors run on demand and are speed controllable as well, much as are home sewing

machines with sewing machine motor

. Both motor types are available for 120 or 240 vac power. Raising of the presser

foot is often done with a knee paddle to allow the operator full use of both hands.

Although many home machines are able to do a wide variety of operations, production sewing

often uses machines that are set up for specific tasks such as bar tacking, buttonhole

making, etc. Machines for tailors and seamstresses are likely to be capable of a fuller

range of operations.


   


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