the sheet of metal is moved in a helical trajectory such that the second bend comes into proximity above the first bend.
该金属板沿螺旋形轨迹移动使得该第二弯曲进入该第一弯曲的上方邻近处。
methods: we presented a novel dynamic pitch helical trajectory named exp-helical trajectory, based on the sufficient condition for dynamic pitch helical cone beam ct.