Sewing Machine

Overview

The sewing machine is a computerized household machine that forms a lockstitch by interlacing an upper needle thread with a lower bobbin thread. A microcontroller sequences the needle, feed, and hook so the machine can produce straight, zigzag, decorative, and buttonhole stitches selected from a touchscreen. The brushed DC main motor drives the upper shaft through a toothed belt, while two stepper motors set needle position and feed length independently of motor speed.

The machine is organized around a rigid frame and a chain of timed mechanisms. The Housing & Body provides the cast structure and bed; the Main Drive Motor supplies power; and the Upper Arm Shaft distributes that power to the Needle Bar Mechanism, the Hook & Bobbin System, and the Feed Mechanism. Thread handling is managed by the Stitch Formation group, and the whole sequence is governed by the Control Board.

How it works

A stitch forms over one revolution of the upper shaft. The Main Drive Motor motor turns the Upper Arm Shaft, whose crank drives the Needle Bar Mechanism down through the fabric. As the needle rises, it forms a small loop of upper thread; the Hook & Bobbin System rotary hook catches this loop, carries it around the bobbin, and casts it off so the two threads interlock. The take-up lever then pulls the slack upward, drawing the knot into the fabric. Upper-thread tension is set by the discs and spring of the Stitch Formation assembly, which also trims the threads at the end of a seam.

Between stitches, the Feed Mechanism mechanism advances the fabric. An eccentric cam lifts and shifts the feed dog through a rectangular path, and a stepper motor sets how far the work moves, fixing stitch length; dropping the feed dog allows free-motion quilting. The Control Board carries the microcontroller and stepper drivers that coordinate needle position, feed, and hook timing so each stitch lands where the selected pattern requires.