Conclusion: Mechanical Advantage

Mechanical Advantage

The result of this system is a Mechanical Advantage less than 0.25.

The mechanisms that transfer the force from the upper wheel of the pulley to the sewing mechanism are outside the scope of this analysis. (See Figure 2) The motion is transferred to a horizontal shaft which connects to a cam located directly above the needle. The cam and associated linkage serve to convert the rotary motion of the shaft to a reciprocating, vertical motion. The force from the pulley is also transferred to a vertical rocker that transmits the motion to the bottom of the machine and then over to the bobbin casing. The bobbin casing rotates back and forth with every stroke of the needle.

The point of force application is the needle. The force produced at the needle is less than one-fourth of the force introduced at the treadle. This results in increased speed and control at the point of application. For every cycle of the treadle, the upper wheel turns 4 times, making 4 precise stitches. (See Video on Background Page.)

It is uncommon to find a mechanism with the purpose of reducing force output. However, the intensity of a foot-powered system was too great for the delicate task of a seamstress. The use of a treadle allowed the user to have both hands free to guide the fabric through the needle. The pulley system served to reduce force and increase speed. The resulting elegant little machine was a significant contributor to the industrial revolution and a machine that has stood the test of time.

Note: All calculations per code on MATLAB Position and Velocity Analysis page.