221 Apparatus, Specimens, and Procedures 

Test Apparatus for Roller Pairs   Testing was done using the NASA Glen n Research Center Va cuum Roller Rig (Figure 3). The rig allows  for application and measurement of a load pressing the rollers together while having a purposely misaligned and adjustable shaft angle. The rig is depicted in schematic form in Figure 4. A drive motor provides motion to the driving roller. A magnetic-par ticle brake attached to the output shaft imposes  torque on the driven roller. The rig can be operated with the brake not energized. For such a condition the torque transmitted through the roller pair is only the drag torque of the output shaft (drag of the seals and  support bearings). The normal load pressing the ro llers together is provided by an air cylinder. The  cylinder acts through a gimbal point to rotate the pl ate that mounts the driving shaft and drive motor. The  rotation of the drive motor plate displaces the driving roller toward the driven ro ller shaft. The pressure to  the cylinder, and thereby the load between the contacting rollers, is adjusted by a hand-operated valve   (open-loop control). Testing can be done in vacuum or  ambient air. Vacuum is provided by a diffusion  pump with a liquid nitrogen cold trap. The diffusion pump is assisted by a mechanical vacuum pump. Figure 5 provides a simplified schematic labeled wi th some of the nomenclature used herein. 

Figure 3 – Vacuum roller rig. 

A set of sensors on the test apparatus monitors the test conditions. The outputs of the analog sensors  were digitized and stored via a data collection unit at a rate of 0.66 Hz. Each of the sensors and the  methods of calibration will be described in turn.   The misalignment of the driving roller shaft and driv en roller shaft is depicted in an exaggerated manner  in Figure 4(b). The misalignment is measured via a linear variable differential transformer (LVDT). The transducer housing is attached to the bedplate, and the translating, spring-loaded transducer tip contacts against a mechanical stop on the turntable. The mechani cal stop is mounted at a known radial distance  and tangential orientation from the center of the turnt able. Calibrated gage blocks were used to displace  the transducer by known amounts, and using the ri g geometry the equivalent angular rotation of the  turntable was calculated. The preceding steps established the relationship of change in transducer output to the change in relative shaft angle. To establ ish the aligned condition, a special tooling block was  machined to locate the roller-mounting surfaces of the two shafts as parallel. With the shafts aligned by  the tooling block, the transducer ci rcuit balance was adjusted to provide an output of zero. The precision  of this method for aligning the shafts was limited by  the dimensions of the roller mounting surfaces used  as the reference planes. From the test rig drawin g tolerances and geometry, the alignment procedure  using the tooling block to define the zero-degree po sition has an accuracy of no better than 0.11 degree.   The torque on the output shaft is monitored by a st rain-gage type torquemeter of 22 N-m (200 in-lb)  torque capacity. Calibration was done in place using deadweights acting on a torque arm of known length.   NASA/CP-2010-216272