GB846121A - Improvements in or relating to screw and nut devices - Google Patents

Abstract

846,121. Screw and nut gearing. STRANDGREN, C. B. Nov. 1, 1956, No. 33371/56. Class 80 (3). [Also in Group XXIII] In a screw and nut device wherein threaded rollers 8, Fig. 1, are interposed between the screw 6 and nut 1, the thread on each roller is formed as shown in exaggeration in Fig. 5 so that when the full load is applied to the screw and nut the resulting deformation thereof brings all the thread turns of each roller into contact, thereby distributing said load substantially uniformly along the roller. Alternatively or additionally each roller may be divided into end-to-end short sections which are keyed together with a small axial spacing, Figs. 14-17 (not shown). As shown, the screw and nut have multiple threads of opposite hand but equal helix angles. The rollers 8 have single threads and are formed at each end with trunnions 12 rotatable in a ring 13 and with teeth 10 (or an attached pinion) gearing with a toothed ring 3 on the nut. The rings 13 are held, with axial play, by plates 4 secured to the nut. The thread shown in Fig. 5, is obtained by increasingly trimming or rectifying both the upper or screw-engaging face and the lower, or nut-engaging face of successive turns of thread with respect to a standard thread during the grinding of the roller so that the bottoms of the turns lie on arcs of parabolµ ZZ. In the example shown the screw and nut are assumed to have equal cross-sectional areas so that their deformations under load are equal and both thread faces of the roller require the same rectification. Accordingly the roller shown in Fig. 5 has a constant pitch. The threads, shown diagrammatically as straight, are preferably arched. In a grinding machine (see Group XXIII) for simultaneously rectifying both faces of the thread a nut carrier 46, Fig. 9, associated with a screw 44 controlling the pitch of the thread being formed on the roller 8, is mounted on a fixed framework 20 through two pairs of resilient blades, and axial pitchcorrecting movements are imparted to the carrier 46 by a cam-actuated lever 60 linked thereto. The linkage comprises a bar 63 whose ends are connected by resilient blades, which act as pivots, to the lever 60 and to a bar 65 carrying spaced parallel resilient blades 67, 66, these blades being respectively connected to the framework 20 and to the carrier 46 to move the latter. The transmission ratio of the linkage is determined by the spacing between the parallel blades 67, 66. It is stated that the resilient blade connections in the linkage may be replaced by ball or other connections.