Measuring and testing – Rotor unbalance – Dynamic
Reexamination Certificate
2000-11-08
2002-11-26
Kwok, Helen (Department: 2856)
Measuring and testing
Rotor unbalance
Dynamic
C301S005210
Reexamination Certificate
active
06484574
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
None.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable.
BACKGROUND OF THE INVENTION
This invention relates to wheel balancers and in particular to an improved wheel balancer including a wheel rim measurement device configured to map the inner surface of a wheel rim, a wheel rim rotational positioning device, and a correction weight placement indicator, each operating in conjunction to facilitate the proper placement of wheel imbalance correction weights on the wheel rim.
When balancing a vehicle wheel, several potential sources for operator error exist. First, there is a need to identify the proper correction planes on the wheel rim into which correction weights are to be placed. Second, the wheel rim must be correctly rotated to, and held in, a rotational position such that the operator can place an imbalance correction weight in the identified correction plane, and third, the operator must manually apply the imbalance correction weight to the wheel rim in the identified correction plane and at the proper rotational position.
As disclosed in WO Patent No. 97/28431 to Hunter Engineering Company for “Wheel Balancer With Servo Motor”, herein incorporated by reference, the determination of unbalance in vehicle wheels is carried out by an analysis with reference to phase and amplitude of the mechanical vibrations caused by rotating unbalanced masses in the wheel. The mechanical vibrations are measured as motions, forces, or pressures by means of transducers, which convert the mechanical vibrations to electrical signals. Each signal is the combination of fundamental oscillations caused by imbalance and noise.
It is well known in the art that a variety of types of imbalance correction weights are available for placing on the wheel to correct the measured imbalance. For example, adhesive-backed weights, patch balance weights and hammer-on weights are available from a number of different manufacturers. Most balancers assume that the wheel rim/tire assembly will be rotated to a particular rotational position (for example, disposing the desired weight correction position at the top (twelve o'clock) or bottom (six o'clock) rotational positions) for weight placement. This is generally not a problem, unless it would be more convenient to apply the weight with the wheel/tire assembly in a different orientation, for example, the four-five o'clock rotational position when the operator is standing facing the surface of the wheel mounted on the wheel balancer.
As described in the WO 97/28431 patent, drive systems for currently available balancers may be improved to aid in weight placement by automatically rotating and holding the wheel rim to the correct rotational position. Prior art balancers typically require the operator to manually rotate the wheel/tire assembly to the desired position for weight placement. These prior art balancers then use a manual brake or the application of rectified AC current to an AC induction motor to temporarily hold the shaft in the desired position. Manual rotation to the desired position is less than satisfactory since it requires the operator to interpret the balancer display correctly. Moreover, manual rotation itself is not desirable, since it ties up the operator's time and attention. In conventional systems, the balancer motor cannot be used to rotate the wheel/tire assembly to the correct position since available motor controllers used in balancers are incapable of performing this function.
Using the motor itself to provide a braking action is not completely satisfactory either. Such braking is normally accomplished by applying rectified alternating current to an AC motor. This method is inherently subject to error. The actual stopping position may be incorrect if the tire is larger than average or turning too fast for the “brake” to respond. Moreover, although currently available motor braking systems stop the wheel in approximately the correct position, they do not actual hold the tire in position since the motor would heat up if the “brake” was left on. With conventional equipment, a wheel rim/tire assembly with sufficient static imbalance to overcome its own inertia, therefore, can roll away from the braked dynamic weight attachment position as soon as the braking energy is released.
Similarly, currently available balancers require that the wheel rim/tire assembly be manually rotated in practically all circumstances since those balancers have no capability for applying anything other than full power to the balancer motor. That is, the motor in conventional balancers is useful for accelerating the wheel/tire assembly to full speed for determining wheel imbalance, but not for accurately positioning the wheel/tire assembly subsequently for correction of that imbalance.
Accordingly, WO Patent No. 97/28431 discloses a wheel balancer including a shaft adapted for receiving a wheel/tire assembly, having a longitudinal axis and which is rotatable about the axis by a direct current motor so as to rotate a wheel/tire assembly removably mounted thereon. A rotation sensor assembly is provided for measuring rotation of the shaft about its longitudinal axis and a vibration sensor assembly is operatively connected to the shaft for measuring vibrations resulting from imbalance in the wheel rim/tire assembly. A control circuit controls the application of direct current to the direct current motor and determines from vibrations measured by the vibration sensor assembly at least one weight placement position on the wheel/tire assembly to correct the vibrations. The control circuit is responsive to determination of a weight placement position to controllably rotate the wheel rim/tire assembly to bring the weight placement position to a predetermined rotational location and to actively hold the wheel/tire assembly in that location. However, it remains up to the operator to correctly position the correction weight on the wheel rim surface.
To compensate for a combination of static imbalance (where the heaviest part of the assembly will seek a position directly below the mounting shaft) and couple imbalance (where the assembly upon rotation causes torsional vibrations on the mounting shaft), at least two correction weights are required which are separated axially along the wheel surface, coincident with weight location or imbalance correction “planes”. For using clip-on weights the “left plane” comprises the left (innermost) rim lip circumference while the “right plane” comprises the right rim lip. If adhesive weights are used, the planes can reside anywhere between the rim lips, barring physical obstruction such as wheel spokes, welds, and regions of excessive curvature.
With the wheel rim/tire assembly mounted to the balancer, the relative distances from a reference plane (usually the surface of the wheel mounting hub) to the planes are conventionally made known either by manually measuring with pull-out gauges and calipers and then entering the observed values through a keypad, potentiometer, or digital encoder, or by using an automatic electronic measuring apparatus. The radius at which the weights will be placed must also be entered, again either manually or by use of the electronic measuring apparatus. Conventional wheel balancers employ a computer configured to utilize this input weight plane information, together with variable weight amounts and variable radial placements, to identify the proper locations for the imbalance correction weights on the wheel rim. While utilization of such a system facilitates the placement of an imbalance correction weight by placing the vehicle wheel in a preferred, or optimal rotational position for weight placement, it does not reduce other sources of operator error, such as the placement of an imbalance weight in the incorrect balance plane, a poor selection of imbalance planes by the operator, or failure to compensate for the width of the installed imbalance weights.
U.S. Pat. No. 5,915,274 to Douglas for “Method of Correcting Imbalance on a
Colarelli, III Nicholas J.
Douglas Michael
Hünter Engineering Company
Kwok Helen
Polster Lieder Woodruff & Lucchesi L.C.
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