Common Mechanisms in Sewing Machines

Sewing machines are composed of various mechanisms, including plane connecting rod mechanisms, cam mechanisms, gear mechanisms, synchronous toothed belt mechanisms and space connecting rod mechanisms.

 

1. Planar connecting rod mechanisms

Crank rocker mechanism

The following figure is a transmission principle diagram of the pedal mechanism of a sewing machine. In this crank rocker mechanism, the reciprocating swing of the foot pedal 3 is called a rocker, and the crank 1 is driven by the connecting rod 2 to complete a full rotation.

In the crank rocker mechanism, when the crank is very short, an eccentric wheel is often used. The following figure is a tooth lifting mechanism of an industrial flat sewing machine. The tooth lifting eccentric wheel 2 fastened to the main shaft 1 rotates with the shaft, drives the rocker 4 to swing through the large connecting rod 3, and enables the feed dog 8 to move up and down through the tooth lifting shaft 5, rocker 6, and small connecting rod 7.

 

Double rocker mechanism

The following figure is a double-bend needle mechanism of a GN1-1 overlock sewing machine. The large curved needle frame 1 swings back and forth around the axis O1, and the small curved needle frame 3 swings around the axis O2 through the connecting rod 2. The large curved needle frame 1 and the connecting rod 2 can be regarded as rockers, and this type of mechanism is called a double rocker mechanism.

 

Crank slider mechanism

The figure below shows the needle mechanism of a sewing machine. The rotation of the needle bar crank 1 drives the needle bar 3 to reciprocate along the fixed guide through the connecting rod 2. This type of machine is called a crank slider mechanism. The figure below shows the cloth cutting mechanism of a straight knife reciprocating cutting machine, and its mechanism is also a crank slider mechanism.

 

2. Spatial connecting rod mechanism

The figure below shows the double curved needle transmission mechanism of the GN1-1 type overlock sewing machine. The curved needle ball crank 1 at the left end of the main shaft drives the rocker 3 through the connecting rod 2 to complete the reciprocating swing around the large curved needle frame O1-O1. This mechanism is a spatial crank connecting rod mechanism.

 

3.Cam mechanism

In sewing equipment, many components require complex and precise movements, and the cam mechanism uses the specific contour surface of the cam to drive the follower to complete the predetermined movement. Therefore, cam mechanisms are widely used in various types of sewing machines.

The above figure below shows the cam thread take-up mechanism of a sewing machine. When the main shaft rotates, the cam groove will drive the thread take-up lever 4 through the roller, so that the thread take-up lever fulcrum K completes the predetermined motion law, and cooperates with other mechanisms in one sewing to complete the thread feeding, thread collection, tightening the stitches, pulling out new threads in stages, so that sewing can proceed smoothly.

 

4. Gear mechanism

The gear mechanism transmits motion accurately and reliably, and has many applications in sewing machinery.

The figure below is a transmission schematic diagram of the main shaft of an industrial flat-bed sewing machine driving the rotary hook shaft through two pairs of bevel gears. The upper shaft 1 transmits the rotational motion to the vertical shaft 2 through a pair of bevel gears, and the vertical shaft 2 transmits the rotational motion to the lower shaft 3 through a pair of bevel gears, so that the rotary hook moves.

 

In addition, the synchronous toothed belt transmits motion accurately, and due to the flexible body of the synchronous belt, the vibration and noise of the transmitted motion are greatly reduced. In recent years, it has also been widely used in sewing machinery.

 

In recent years, with the maturity and application of electronic control technology, the original sewing machine has gradually transitioned from transmitting motion through mechanical control to using computers to control the mechanism for motion and power transmission with the help of hydraulic or pneumatic components and electromagnets, which has greatly simplified the complex structure of the sewing machine. This has formed a series of new functions for sewing machines, reduced the links of motion transmission, accelerated the response time, and improved the accuracy of the action, such as automatic thread cutting, automatic thread pulling, automatic reinforcement sewing, automatic reverse sewing, variable stitch length sewing, controllable thread tension, automatic presser foot lifting and other functions.

 

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