223 on the air-piston actuator, load was created on the rigid link and measured on the reference load cell.  This procedure established the relationship of the no rmal load on the test roller acting through the gimbal  point and resulting in a force imparted on the load cell located at the air piston. During testing both the  motor table position and load cell force was recorded. From the table position data and calibration data,  the force attributed to the unbalanced mass on the gimbaled motor plate could be subtracted from the  force value recorded by the load cell. The value remaining from the load cell (after the subtraction operation) is due to the normal force between the te st rollers, and via the calibration curve the load on the  test roller is determined. 

Figure 5 – Simplified schematic view including some of the important sensed data.  (a)  Schematic, front view. (b) Schematic, side view.   When rollers operate in a misaligned condition a forc e will develop in the direction of the shaft axis  [2,3,5,6]. 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 t he points were not in contact give s 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 wi th 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. Adju sting the jackscrew length allowed for changing the  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 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 (F igure 4(b)). The rotational motion about the gimbal  point is restrained by a mechanical link to the turntabl e structure. There is a load cell load in the load path  from said mechanical link to the turntable structure. This sensor was calibrated in place by using a pulleycable 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 a ffected by spin moments (Ref. (2)) 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 intere st 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. normal load braking torquetangential force normal loadnormal load braking torquetangential force normal load normal load axial force normal loadinput shaft output shaft normal load axial force normal loadinput shaftinput shaft output shaft (a) (b)normal load braking torquetangential force normal loadnormal load braking torquetangential force normal load normal load axial force normal loadinput shaft output shaft normal load axial force normal loadinput shaftinput shaft output shaft (a) (b) NASA/CP-2010-216272