The opening size is adjusted according to the requirements of the process parameters. Adjustment of the opening size is realized by adjusting the position of the pin at the upper end of the heald rod. If the pin of the heald rod is moved upwards, the opening size is reduced; if the pin of the heald rod is moved downwards, the opening size is increased. The opening size is adjusted so that the opening is clear and the opening size is consistent every time. The opening size is measured at the position where the first heald is located.