SEVENS REASONS WHY OUR THREE AXIS MOMENT WEIGHT SCALE IS UNIQUE

1. Central pivot uses spherical air bearing Conventional moment weight scales use a pair of knife edges which are oriented at right angles. We use a spherical gas bearing which floats the moment arm on a thin film of air. This frictionless pivot has a center of rotation which only varies a few millionths of an inch, even if the scale is severely overloaded while the blade is being inserted in the adapter. There is no wear in this pivot. It retains its full accuracy for 30 years or more, and requires no maintenance.

2. Force restoration technology Conventional moment weight scales use strain gage load cells to measure moment. We use force restoration technology. A laser senses the deflection of the moment arms and electromagnetic actuators apply an equal and opposite force to each moment arm to restore the scale to its original position before the blade was inserted in the adapter. This eliminates mechanical non-linearity and results in a signal to noise ratio which is 1000 times better than a strain gage load cell. The error in comparing blades to a master blade is 0.0003% of full scale.

3. No sliding range weights Unlike conventional moment weight scales, it is not necessary to add weights to a hanger or slide weights along a shaft in order to measure the range of moments from 0 to 30,000 oz-inch. A binary range weight system within the scale automatically lowers the correct weight on the moment beam, resulting in greatly increased dynamic range. It is not necessary to counterbalance the adapter before making a measurement. The scale first measures the moment due to the adapter, and then measures the moment with the blade installed.

4. Automatic blade rotation It is not necessary for the operator to rotate the blade 90 degrees in order to measure the 3^rd axis of the blade. This is accomplished automatically by the scale.

5. Many blades can be measured with the same adapter It is not necessary to use a separate adapter for different blades. As long as the root dimensions are the same, then a single adapter is usually sufficient. An optional pan weight scale can be supplied which measures blade weight with an accuracy of better than 0.0001% of full scale. The on-line computer then converts the measured moment to the value at the correct Z-plane radius. This results in a major saving in system cost and eliminates the need for the operator to repeatedly change adapters.

6. Blades are loaded vertically On conventional moment weight scales, the blade is loaded horizontally in the adapter and hangs down below the machine centerline. When the clamping mechanism is actuated, the blade rocks upward, altering the position of the blade root. On our scale, a hinged adapter allows the blade to be inserted while it is in a vertical position. The blade then hangs straight down, allowing gravity to press the blade root against the adapter. When the blade is clamped, it retains its correct position.

7. Blade is clamped automatically The adapter clamp is actuated by air, rather than using hydraulic cylinders. The air is supplied to the clamp through a flexible coupling inside the machine. There is no need to attach a hydraulic hose to the adapter, and there is no oil within the adapter.  This eliminates the mass shift error which occurs with hydraulic systems when the blade is rotated from a vertical to a horizontal position.

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