Multi-Axis Moment Weight Scales

Product Details

Raptor Scientifics multi-axis moment weight scales are designed for the measurement of large blades, including jet engine fan blades. We manufacture two different scales:

  • The MW904F focuses on measurement speed while maintaining accuracy and repeatability.
  • The MW40KF focuses on very high accuracy and operator ergonomics.

The Model MW40KF Three-Axis Moment Weight Scale is at least 20 times more accurate than conventional multi-axis moment weight scales. It has a sensitivity of 0.02 oz-inch and can measure moment weight up to 30,000 oz-inch. This represents a sensitivity of 1 part in a million! This extraordinary performance is achieved by using the same technology which we use to measure satellite moments. The MW40KF machine automatically measures all three moment weight values (radial, axial, and tangential) without the need for the operator to manually rotate an interface plate or add range weights. A Windows based computer automates the measurement process and displays the measured moment weight.

Why Measure Moment Weight In 3 Axes?

For wide fan blades or large power blades, it is not sufficient to only measure the moment along the radius of the blade; a 3-axis moment weight scale is required. This scale measures radial moment and one component of moment at right angles to the radius; a rotary table is built into the machine to permit the blade to be rotated 90 degrees, so the third component of moment can be measured.

Typical Applications:

These multi-axis moment weight scales are mainly used by both the OEM manufacturers and maintenance, repair and overhaul (MRO) providers for jet engine fan blades and power turbine buckets.

Superior accuracy – 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.

Repeatable, no wear pivots – Conventional moment weight scales use a pair of knife edges which are oriented at right angles. Knife edges wear over time and the scale becomes less repeatable and less accurate. We use a spherical gas bearing which floats the moment arm on a thin film of air as the pivot of our MW40KF and crossed web flexures in our MW904F. Neither technology presents any risk of wear. Our pivots retain their full accuracy for 30 years or more, and require no maintenance.

No hydraulics – No leaks, no high pressure lines and associated risks.

Low Maintenance – There are no consumable components in our scales. Conventional scales use knife edges which wear and hydraulic lines which need to be checked for leaks and refilled. Our scales need very low rate of maintenance and less frequent calibration.

Precision Blade Adapters – Space Electronics manufactures the most repeatable blade adapters that hold the blade exactly in the right position. These adapters enable our customers to make full use of the extreme accuracy of our scales.

Why Our Multi-Axis Moment Weight Scale Is Unique

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.

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.

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.

Automatic blade rotation

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

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.

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.

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.

SpecificationValue
Maximum weight (including tooling)150 lb.
Range of radial blade moment that can be measured w/ specified accuracy *0 to 30,000 oz-inch
Maximum transverse moment that can be measured+/- 1,000 oz-inch
Range of radial moment indication+/- 1,000 oz-inch
Readout sensitivity0.02 oz-inch
Moment linearity0.01 oz-inch
Total radial moment measuring error ***0.01 oz-inch
Total axial/tangential moment measuring error ***0.02 oz-inch
Nominal mounting plate radius**.0.02 oz-inch
Mounting plate dimensionsARP4773

* Combined moment of blade plus adapter
** Nominal distance from fulcrum to vertical adapter mounting surface
*** Tooling error is not included

Accuracy limits assume an environment which is free from drafts, excessive vibration and has a stable temperature.

Optional SE90060 Total Calibration System (for model MW40KF) – With this calibration system, the user can perform both “relative” and “absolute” calibrations for the model MW40KF Moment Weight Scale. This system includes the following items:

– Relative Moment Calibration System – This track and ball calibration system bolts directly to the interface of the MW40KF moment weighing system and provides an 800 oz-in calibration moment which accommodates the “relative” moment measuring range of the MW40KF. Calibration factors for the MW40KF force transducers are determined and recorded automatically by use of incorporated calibration software (included). Accuracy of this calibration system is at least 5 times better than the accuracy specifications for the moment weight system. Mass and distance values are traceable to NIST.

– Absolute Moment Calibration System – This weight hanger provides up to 19,000 oz-in of calibration moment which yields a total “absolute” calibration of the moment weight system.

A storage container is supplied – This container is equipped with recessed clasps and metal reinforced edges and corners. It is suitable for shipping as well as storing the calibration system.

Moment Weight Scales

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