This study considered the motion of the top feed mechanism on lockstitch industrial sewing machines with alternating foot top feed and drop feed. The results obtained are as follows.

(1) The bounce phenomena of presser foot Ⓔ and walking foot Ⓖ is a spring reaction of said parts induced by the restoring force of feed dog Ⓕ or throat plate Ⓗ.

(2) The effects of the constituent factors that cause bouncing are as follows:

a. As the rotating speed increases and bouncing gradually increases, resonance occurs in the proximity of 1800 r/min.

b. There are certain ranges where the bounce of presser foot yp2 and walking foot yw1 decreases intermittently but sharply due to the uniformity in lightness of the mass mi (i = 1 to 7) of all constituent parts.

c. The bounce phenomena of yp2 decreases in direct proportion to the reduction of spring constant k1, of throat plate Ⓗ. On the other hand, that of yw1 shows minimal fluctuation.

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