Development of a pneumatic sensor for measuring the torque of instrument ball bearings

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Virginia Polytechnic Institute


Of the studies that have been conducted on the operational characteristics of instrument ball bearings, a great majority have been in accordance with MIL-STD-206. Since tests in compliance with this specification determine bearing quality or rate bearings comparatively, nothing was known of the operational characteristics of the bearings in their final application. A few investigators have developed sensors to study torque characteristics of instrument ball bearings. However, in no case has a report been made of the effect on torque when both radial and axial loads were varied.

In seeking to obtain improvements in methods of measuring small torques, a pneumatic sensor was developed for testing R-3 instrument ball bearings under varying radial and axial loads. This sensor was based upon the principle of the flapper-nozzle valve. The flapper valve consisted of two orifices in series, one of constant area, the other of variable area, which was determined by flapper position. Since the pressure between the two orifices was dependent upon flapper position, indirect measurements of torque acting on the flapper were obtained by measuring this pressure.

As a result of this study, it was concluded that the pneumatic sensor accurately measured the running torque of R-3 instrument bearings. This statement was based upon good agreement with data from other investigators working under identical conditions.

It was also concluded that for a range of 50 to 200 gm. radial loading, no significant effect on torque was observed. For axial loads in the same range, the torque was found to vary in proportion to the equivalent load acting on the bearing.