Abstract: The single-sided stitching technology is widely used in composite curved surface preforms and large-scale structural parts because it does not require a stitching table to be installed at the bottom of the fabric, and it also makes an important contribution to the three-dimensional reinforcement of carbon fiber composites. In order to obtain the desired stitches in the carbon fiber preform with the unilateral stitching technology, and avoid the problems of skipped stitches, over-tight or too loose stitches in the stable loop of the stitches, the principle of the unilateral stitching equipment is analyzed and the original in some OSS stitch stitching, the action and time coordination relationship of the lead, hook thread and thread take-up mechanism are redesigned and planned, and the chute type lever thread pulling mechanism is added to the thread loop to be penetrated by the hook thread needle. The added thread take-up mechanism does not cause any thread loss and has a certain thread take-up function. On the basis of effectively avoiding the loop failure problem, the difficulty of designing the thread take-up mechanism is reduced. This paper proposes an idea of suture consumption at each instant of the mechanism, analyzes the matching relationship at each time point, and establishes an improved OSS stitch demand model. The motion cycle diagram is used to visually express the changing laws of each mechanism, and finally verify by stitching samples of different thicknesses. The experimental results show that the various mechanisms are well matched, the sample stitches are formed stably, and the improved mechanism coordination relationship does not have the problem of skipping stitches, which verifies the reliability of the movement trajectory of the unilateral stitching mechanism.

Key words: one-sided stitching, stable stitches, matching relationship, slide lever of hook-shaped mechanism, instantaneous thread demand, motion cycle diagram, composites