Motion Behavior of the Needle Thread of A Lockstitch Sewing Machine for Industrial Use

Part 1 : Measurment of Feed Length and Feed Velocity of the Needle Thread during Sewing Operation

Abstract

A lockstitch sewing machine for industrial use has been fitted with a rotary angular meter and a rotary encoder to determine feed length and feed velocity of the needle thread during sewing operation at the range from 250 to 4000 rpm. The needle thread was winded around a V-pulley, having 31 mm in diameter. The V-pulley was mounted between the angular meter axis and the encoder axis on the arm of the machine.
The sewing has been made by employing the spun thred of # 50 and continuous filament thread of # 50 under the constant tension required to pull out the thread through a shuttle spring and constant stroke of the check spring.
Records of feed length curves and feed velocity curves during the stitch cycle have been analysed and the results are summarised as follows :
1) The range of turning angle of the arm shaft required for feed of the needle thread increases with increasing the sewing speed. Thus, when the speeds are lower than ca. 1500 rpm for the use of continuous filament threads and ca. 2000 rpm for the use of spun threads, the needle thread is fed intermittently. When the speed are higher than the above speeds, feed motion of the threads is transformed continuously.
2) θ_v.maxhas been defined as the turning angle of the arm shaft at which the feed velocity of the needle thread had reached its maximum value.In most cases the value of θ_v.max increases with increasing the sewing speed.
3) The maximum feed velocity ΔV_maxof spun threads, at θ_v.max, are greater than those of continuous filament threads; The values of all threads are independent on sewing speeds, except 4000 rpm. Feed velocity at 4000 rpm reache : approximately constant value during the stitch cycle, and its value is larger than feed velocity below 3000 rpm.
4) Value of Δ V_max, at fabric feed scale of 4 is greater than that of scale of 2 in all threads.