Calibration apparatus and method for improving the accuracy of tire uniformity measurements and tire testing method using same

A method of calibrating a channel of a tire uniformity inspection machine of the type having a force transducer operably coupled thereto, said method comprising the steps of:

• (a) simulating the application to the transducer a force of magnitude greater than any force actually applied to the transducer of the machine during calibration thereof;
• (b) determining at least one value representing the response of at least a portion of the channel to said simulating step;
• and
• (c) determining a calibration factor using said value.

A method of calibrating a channel of a tire uniformity inspection machine of the type having at least one force transducer having a transfer function and being connected to the channel, said channel including a signal processing network and an analog-to-digital converter operably coupled thereto, said analog-to-digital converter having a digital output for a digital signal as well as an analog input, said network having an input operably coupled to said transducer and an output operably coupled to the analog input of said analog-to-digital converter, said method comprising the steps of:

• (a) determining a first value correlated to the magnitude of the digital signal appearing at the digital output of said analog-to-digital converter;
• (b) applying a signal to said network, the magnitude of said signal being correlated to a second value;
• (c) determining a third value whose magnitude is correlated to the product of:
• (i) a fourth value correlated to said transfer function and
• (ii) said second value;
• (d) determining a fifth value correlated to the magnitude of the digital signal appearing at the digital output of said analog-to-digital converter in response to the application of said signal to said network;
• and
• (e) determining a calibration factor correlated to the ratio of said third value to the difference between said fifth value and said first value.

A method of calibrating a channel of a tire uniformity inspection machine of the type having a loadwheel to be pressed against a tire and having at least one force transducer having a transfer function and being connected to the channel, said channel including a signal processing network and an analog-to-digital converter operably coupled thereto, said network having an input operably coupled to said transducer and an output operably coupled to the analog-to-digital converter, said method comprising the steps of:

• (a) determining an initial output generated. by said analog-to-digital converter when the transducer of said machine is substantially unloaded;
• (b) applying a signal of a large magnitude to said network to simulate the application of a force to the transducer;
• (c) determining the magnitude of said simulated force by multiplying said transfer function by said large magnitude;
• (d) determining a second output generated by said analog-to-digital converter, said second output being generated in response to the application of said signal to said network;
• and
• (e) determining a calibration factor as the ratio of the magnitude of said simulated force to the difference between said second output and said initial output.

An apparatus for calibrating a channel of a tire uniformity inspection machine of the type having at least one force transducer connected to the channel by way of a signal processing network, said apparatus comprising:

• (a) an energy source;
• (b) an impedance;
• and
• (c) means for selectively connecting the signal processing network to the energy source through said impedance so as to apply to the channel a signal whose magnitude is greater than any signal generated by the transducer at the time said signal is so applied during a calibration procedure.

A method of testing a tire, said method comprising the steps of:

• (a) mounting the tire on a tire uniformity inspection machine of the type having a rotatable loadwheel mechanically coupled to a force transducer having a transfer function, said transducer being connected to a channel which includes a signal processing network and an analog-to-digital converter having a digital output for a digital signal as well as an analog input, said network having an input operably coupled to said transducer and an output operably coupled to the analog input of said analog-to-digital converter, said channel having been calibrated by carrying out the steps of:
• (i) applying to said network a signal having a magnitude which is greater than the magnitude of any signal generated by the transducer in response to any externally-applied force acting on said force transducer at the time said signal is so applied;
• (ii) determining a calibration factor, based on at least said transfer function, said magnitude of said signal and the magnitude of the digital signal appearing at said digital output in response to said signal;
• (iii) retrievably storing said calibration factor;
• (b) rotating the tire in forced contact with said loadwheel;
• and
• (c) determining the value of at least one nonuniformity-indicating parameter based upon at least one indicated value, I, determined according to an equation of the general form:
• I=(A-T)*C
• where A represents the actual magnitude of said digital signal generated by said analog-to-digital converter in response to said rotation of said tire in said forced contact with said loadwheel, T represents a constant, and C represents said calibration factor.