Investigation of the operating behaviour of planetary roller screws with different number of threads of spindle and nut

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For the conversion of rotational movements into axial movements and of torques into feed forces, screw drives, such as ball screw drives, sliding thread screws or planetary roller screws (PRGT) are used. PRGT with the same thread number of nut and spindle (Standard-PRGT) are characterized by their high load capacity due to a high number of contact points. The minimum possible overall lead, however, is geometrically and technically limited. Therefore, a high torque to force transmission ratio, as would be advantageous in many applications, is not possible. For PRGT with different thread number of the nut and spindle (Neu-PRGT), the overall lead can be reduced to one-eighth of that of a Standard-PRGT without loss of load capacity. In this way, higher torque to force transmission ratios are possible, which allow for the use of smaller drive motors, or the elimination of transmissions. Also, a self-restraining design, e.g. for use in clamping devices, can be achieved. As a result of these properties, Neu-PRGT offer an alternative to sliding thread screws and hydraulic actuators in many applications. However, the overall lead of Neu-PRGT is dependent on the kinematic conditions in the component and the forces acting in the contact points. The transmission behavior, unlike other screw drives, depends on the conditions in each contact point. The aim of the overall research project is to mathematically describe the transmission behavior of Neu-PRGT and to investigate it experimentally.In the first research period, basic calculation algorithms were developed for the description of the kinematic ratios of PRGT and for the transmission behavior of PRGT, considering the behavior of a single contact point. Standard- and Neu-PRGT were also tested experimentally. The validation of the calculation models showed further research requirements.In the second project phase an overall model of the transmission behavior is to be created. The already developed kinematic relationships and methods for the calculation of the contact point behavior are expanded for this purpose by the internal interrelations of the whole component and the interactions with resulting variables. Further experiments to investigate the behavior of Neu-PRGT are used to validate and optimize the assumptions and correlations.