Development of Friction Drive Screw with Adjustable Lead Angle Mechanism

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Two types of friction drive screw mechanism have been used in practice. One has rolling contacts between a cylindrical shaft and outer surfaces of several radial bearings, and another has rolling contacts between a screw shaft and inner rings of several radial bearings. In this study, a new type of friction drive screw with adjustable lead angle mechanism is developed. This friction drive screw mechanism allows stop, start, reverse and adjustable speed regardless of drive shaft speed. The adjustable lead angle mechanism is driven and controlled by an ultra sonic motor and a reducer. We wish to report on the design and characteristics of a new type of friction drive screw with the adjustable lead angle mechanism which we have developed and of which we have tested the operating performance. Conclusions drawn from the present research are summarized in the following. (1) The unique serial combination of linear and radial bearings makes a screw motion between the friction drive bearing and the drive shaft. (2) Torque required to tilt the lead angle of the friction drive bearing on the drive shaft is numerically analyzed. (3) Operating tests reveal that the adjustable lead angle mechanism allows smooth movement at lead angle ranging from -20 to 20 degree. (4) The rest of friction drive screw, namely a lead angle of 0 degree, is maintained regardless of drive shaft speed. (5) Repeat reciprocating and accelerated motions are also performed by the control of the ultra sonic motor regardless of drive shaft speed.