Wheel unbalance measurement system and method

In combination with apparatus for measuring unbalance in a rotatable body wherein at least one force transducer is disposed to provide an electrical signal indicative of periodic unbalance forces coupled thereto through a shaft adapted to support the rotatable body for rotation thereon, and wherein an analog-to-digital converter is coupled to receive the electrical signal and to provide a digital word output corresponding thereto, the improvement comprising means for controlling said analog-to-digital converter to provide said digital words at a predetermined number of angular increments during each revolution of the shaft, a memory containing a plurality of stored digital sine and cosine representative values, ones of said digital sine and cosine representative values corresponding to predetermined ones of said predetermined number of angular increments, means for modifying each of said digital words in accordance with the corresponding stored digital sine and cosine representative values and for limiting each modification to include only one addition function so that digital sine and digital cosine representative quantities are provided during the time the shaft is traversing each of said angular increments, and means for summing the digital sine quantities and the digital cosine quantities for each of said angular increments, whereby digital data is provided for determining unbalance force magnitude and direction in the rotatable body.

A method of calibrating apparatus for measuring unbalance in a body mounted on a spin shaft having an angular reference position relative to a supporting framework therefor and being coupled to a force transducer which provides an unbalance signal having an instantaneous magnitude indicative of a component of the unbalance force which results when the shaft is spun, comprising the steps of applying a known unbalance weight to the spin shaft at a known angular position relative to the angular reference position, spinning the shaft with the known unbalance weight applied thereto, digitizing the unbalance signal indicative of the known unbalance weight, storing a plurality of digital sine and cosine representative quantities corresponding to predetermined angular increments of spin shaft rotation, modifying the digitized unbalance signal in accordance with the corresponding digital sine representative quantity at a plurality of the angular shaft increments while the shaft is being spun, modifying the digitized unbalance signal in accordance with the corresponding digital cosine representative quantity at a plurality of the angular shaft increments while the shaft is being spun, summing the modified signals containing unbalance signal and sine representative factors, summing the modified signals containing unbalance signal and cosine representative factors, whereby uncorrected calibration sums are obtained, spinning the shaft with no load applied, digitizing the unbalance signal indicative of no load shaft unbalance, modifying the digitized no load unbalance signal in accordance with the corresponding digital sine representative quantity at a plurality of the angular shaft increments while the shaft is being spun to obtain combined no load signals containing sine representative factors, modifying the digitized no load unbalance signal in accordance with the corresponding digital cosine representative quantity at a plurality of the angular shaft increments while the shaft is being spun to obtain combined no load signals containing cosine representative factors, summing the combined no load signals containing sine representative factors, summing the combined no load signals containing cosine representative factors, whereby shaft unbalance sums containing sine and cosine representative factors are obtained, applying the shaft unbalance sums containing sine and cosine representative factors to the uncorrected calibration sums containing sine and cosine representative factors respectively, thereby obtaining calibration sums corrected for shaft unbalance and for transducer error in the apparatus.

A method for digitally acquiring calibration constants used in calculation of unbalance data obtained from a wheel balancing apparatus having a spin shaft with a removable known unbalance weight mounted thereon, the spin shaft being mounted on a framework which provides a spin shaft angular reference, and a force transducer mounted in the framework coupled to the spin shaft providing an unbalance signal indicative of a component of the unbalance force relative to the angular reference when the spin shaft is rotated, said method comprising the steps of digitizing the unbalance signal, storing a plurality of digital sine and cosine representative quantities corresponding to predetermined angular increments of spin shaft rotation, processing the digitized unbalance signal in accordance with corresponding ones of the digital sine representative quantities at each angular increment, processing the digitized unbalance signal in accordance with corresponding ones of the digital cosine representative quantities at each angular increment, summing the processed digitized signals containing sine representative factors, summing the processed digitized signals containing cosine representative factors, whereby calibration sums containing force transducer errors are obtained, repeating the foregoing digitizing, processing and summing steps with the known unbalance weight removed from the spin shaft, whereby calibration sums containing shaft unbalance errors are obtained, and digitally correcting the calibration sums containing force transducer errors with the calibration sums containing shaft unbalance errors, whereby digital calibration sums are provided from which apparatus calibration constants are calculated, whereby unbalance data is provided which is substantially free of force transducer and shaft unbalance errors.

Apparatus providing calibrated digital measurement of unbalance in a rotating body, comprising a framework, a spin shaft having an angular reference position relative to said framework, means for mounting said spin shaft for rotation in said framework and for rotating said spin shaft, means mounted in said framework and coupled to said spin shaft for providing an unbalance signal indicative of a component of unbalance force resulting from rotation of said spin shaft, means for detecting angular location of said spin shaft relative to said reference position at a plurality of angular increments during each rotation of said shaft, an analog-to-digital converter for digitizing said unbalance signal, a memory operating to store a plurality of digitial sine representative quantities and a plurality of digital cosine representative quantities corresponding to predetermined ones of said angular increments, a known calibration weight configured for attachment to said spin shaft at a predetermined angular position thereon relative to said reference, means for combining said digitized unbalance signal at each of said angular increments with corresponding ones of said digital sine representative quantities providing digital sine quantities and with corresponding ones of said digital cosine representative quantities providing digital cosine quantities, means for summing said digital sine quantities and for summing said digital cosine quantities so that when said shaft is spun with said calibration weight attached and with said shaft free of any extraneous weight uncorrected calibration sums and unloaded shaft sums are obtained, and means for modifying said uncorrected calibration sums with said unloaded shaft sums to obtain calibration data corrected for shaft unbalance and for calculating and storing digital calibration constants in accordance with said calibration data, whereby error data of both mechanical and electrical origin are detected and stored to provide for removal of such errors from subsequent unbalance data.

A method of calibrating an apparatus for measuring mass unbalance in a rotating body wherein the body is mounted in a known position on a rotating shaft supported in a frame and the shaft is coupled to a sensor which provides an electrical signal indicative of the mass unbalance, comprising the steps of

• spinning the shaft while it is unloaded and monitoring the substantially periodic electrical signal,
• recovering the fundamental sine and cosine coefficients from the unloaded periodic electrical signal,
• storing the fundamental coefficients from the unloaded signal as shaft unbalance values,
• spinning the shaft while it is loaded with a known unbalance mass and monitoring the substantially periodic electrical signal,
• recovering the fundamental sine and cosine coefficients from the known loaded periodic electrical signal, and
• storing the fundamental coefficients from the known loaded signal as calibration values,
• so that when electrical signals are obtained when the body having unknown unbalance is rotated on the shaft and such signals are processed by applying the shaft unbalance and calibration values, corrected mass unbalance location in the body is obtained.

Apparatus for measuring mass unbalance in a rotating body wherein the body is mounted in a known position on a rotating shaft supported in a frame wherein the shaft is coupled to a sensor which provides an electrical signal indicative of the unbalance of the rotating mass, the improvement comprising

• means for receiving the electrical signal when the shaft is rotated unloaded and for providing a fundamental sine and cosine coefficient from the unloaded electrical signal,
• a memory for storing the fundamental coefficients from the unloaded signal,
• said means for receiving being arranged to also receive the electrical signal when the shaft is rotated with a known mass unbalance for providing a fundamental sine and cosine coefficient from the known loaded signal,
• said memory being arranged to also store the fundamental coefficients from the known loaded signal, and
• means for processing the electrical signal provided when a body having an unknown mass unbalance is rotated on the shaft, said last named means being connected with said memory to use the stored fundamental coefficients from the unloaded and known loaded signals whereby data indicative of the unbalance mass location in the body is provided which is corrected for both sensor errors and shaft unbalance errors.

A method of measuring unbalance in a rotating body mounted on a rotating shaft coupled to force transducers which provide unbalance signals indicative of the instantaneous unbalance magnitude component relative to a known angular reference, comprising the steps of

• spinning the shaft with no load mounted thereon, whereby the force transducers provide a no load unbalance signal,
• computing no load unbalance signal numerical quantities representative of the phase and magnitude of the unbalance relative to the known angular reference,
• spinning the shaft with a known calibration weight at a known position mounted thereon, whereby the force transducers provide a calibration unbalance signal,
• computing calibration unbalance signal numerical quantities representative of the phase and magnitude of the unbalance relative to the known angular reference,
• subtracting the no load unbalance signal numerical quantities from the calibration unbalance signal numerical quantities to provide corrected calibration numerical quantities,
• computing calibration constants from the corrected calibration numerical quantities thereby relating force transducer output magnitude and phase to known unbalance forces,
• spinning the shaft with an unknown unbalance weight mounted thereon, whereby the force transducers provide an unbalance signal,
• computing the unbalance signal numerical quantities representative of the phase and magnitude of the unbalance relative to the known angular reference,
• subtracting the no load numerical quantities from the unbalance numerical quantities to provide modified unbalance numerical quantities,
• and applying the calibration constants to the modified unbalance numerical quantities thereby obtaining corrected unbalance data.