Needle shaped like a helix, positioned horizontally. The needle can be held in place by four rollers around it with axes parallel to the axis of the helix and magnets that prevent the helix from moving forward or back along its axis. Another way is to use two rollers above the helix and a magnet above these. The needle is rotated around the axis of the helix by the rollers, which touch it.
As the helix rotates, the corkscrew motion makes the point of the needle go into and out of cloth like a curved surgical needle. The two-roller setup is convenient if access to the other side of the cloth is restricted, e.g. when sewing the lining of a garment closed.
An advantage over the current sewing machines is the simplicity and the need for only one thread per seam, not two threads, one of which is restricted in length because it is on a bobbin. For long seams, the single-thread design has the advantage of dispensing with the bobbin. Long seams are usually simple (hemming curtains, bedsheets), not zigzag or some fancy design, so the limited seam design options with the helical needle are not a big problem.
The problem is that towards the end of a long seam, a long thread needs to be pulled through the entire seam behind the needle. The friction gets large. The thread is not relatively straight, but in a “spiral binder” seam, which bunches the cloth.