428 When rollers operate in a misaligned condition a force will develop in the direction of the shaft axis [4-7].  In such a condition points on the two rollers in intimate contact and within a “stick” zone of the contact patch are constrained to move in unison. If the points were not in contact the kinematic constraints would provide a slightly different path of motion. The difference in the actual path of motion and that defined by the motion if the points were not in contact gives rise to surface strains and a resultant axial force. A sensor to measure this force is labeled as the “axial force” sensor in Figure 4. The axial force sensor is co-located on the output shaft with the torquemeter sensor. The configuration of the rig did not allow for direct deadweight calibration in place. To calibrate the sensor in place, the following procedure was used. First, a load cell was calibrated via deadweights and then was placed on the free end of the output shaft to act as a reference load cell. A threaded jackscrew acted against the reference load cell and a hard stop in the vacuum chamber. Adjusti ng the ja ckscrew length allowed for changing th e force imparted on both  the reference load cell and the rig’s axial load cell and to the machine frame. In this manner the same force was applied to both load cells, and the reference cell output was used to calibrate the axial load cell sensor in place.   The preceding two paragraphs describe the sensors (and sensor calibrations) to determine two mutually perpendicular forces acting on the driven test roller. A force also acts along a third axis. This is the force directed tangential to the roller diameter and is termed here as the “tangential” force. The tangential force on the input shaft roller acts through a gimbal point (Figure 4(b)). The rotational motion about the gimbal point is restrained by a mechanical link to the turntable structure. A load cell is used to sense the force in said mechanical link to the turntable structure. This sensor was calibrated in place by using a pulley-cable system and dead weights to relate the tangential force applied at the test roller position to the sensor output. During testing, this sensor is also affected by spin moments [4-5] that can develop in roller contacts. The data from the tangential force sensor was recorded for possible future use, but such data were not of immediate interest and are not reported herein.  Shaft speeds and total number of shaft revolutions were measured using encoders on each shaft. The encoder pulses were counted and recorded via a digital pulse counter. The encoder pulses were also monitored by a frequency converter to provide a convenient shaft speed display to the test operator. The encoders provide 6,000 pulses for each shaft revolution.  Test roller conditions were photographed at regular intervals through a viewport. The images were captured digitally using a single-lens reflex camera with a 150 mm micro lens and a 12 million effective pixel image sensor. A debris pan was used to capture debris created from the roller pairs. A video camera recorded the condition of a portion of the debris pan. In spite of several attempts to adjust video camera setting and lighting, the video images failed to capture all that could be observed by eye through the viewport. 

Test Specimens  The test specimens used for this research had a nominal geometry of 35.6 mm outer diameter and a 12.7  mm width. The apparatus requires that at least one roller has a crowned profile to avoid edge loading. The roller on the drive motor (input) shaft was provided a crown radius of 200 mm and was made from steel. The roller on the lower (output) shaft had a flat profile and was made from Ti6Al4V alloy.