LabVIEW Performs All Machine Control and Data Processing for a Tire Uniformity Grading Machine

Author(s):
Richard Cichosz - Quantum Controls

Industry:
Automotive

Products:
LabVIEW

The Challenge:
Updating, automating, and adding capability to a 1960's-era test machine for tires.

The Solution:
Creating a superior machine control and data processing system using LabVIEW, SCXI, and DAQ.

Introduction
After searching for a systems integrator that could accomplish all of their required tasks, General Motors Proving Grounds (GM) asked Quantum Controls, a National Instruments Alliance Program member, to automate the operation, data retrieval process, and analysis of data gathered from their Tire Uniformity Grading Machine. We used National Instruments LabVIEW, SCXI, and data acquisition (DAQ) hardware to meet and surpass expectations in performing all three tasks.

The Existing System
The existing Tire Uniformity Grading Machine is located in the GM Tire Lab at the Milford, MI Proving Grounds site. This machine determines the uniformity (roundness) of a tire based on strain gauge measurements taken in the X, Y, and Z axes. An AC motor/variable frequency drive (VFD) combination rotates the tire being tested on a fixed-position shaft. A ballscrew-coupled DC motor drives a load wheel, 33 in. in diameter and 14 in. across the face, that is mounted on a sliding carriage. The sliding carriage moves the load wheel against the tire, making the load wheel simulate the road surface.

The load wheel is attached to the carriage on a fixed axle so the load wheel is free to spin around the axle on its bearings. Because the axle is fixed while the load wheel rotates against the tire, strain gauges are placed on each side of the load wheel in the center of the X and Z axes of the wheel. These strain gauges, manufactured by Lebow, are an integral part of the load wheel assembly and enable accurate measurement of X, Y, and Z forces at the center of the load wheel axle. These measured forces are then translated to the test tire face that is contacting the load wheel (called the tire patch).

The system pushes the load wheel against the tire and holds it with a brake to meet a prescribed force. The system operator controls the level of force (in pounds or newtons) using proportional integral derivative (PID) software in LabVIEW. Once the tire is loaded, it spins at approximately 400 rpm to warm the tire up to operating temperature. The tire then slows to test speed, 60 rpm, and the system gathers test data. The six strain gauge signals (three from each transducer, one transducer on each side of the load wheel) are each routed through their own Ectron signal conditioner/amplifier module and passed to the SCXI rack. The amplified signals are fed into an SCXI-1141 filter module and cascaded into the SCXI-1140 simultaneous-sampling differential amplifier module. LabVIEW then arranges the strain gauge values into a matrix format to prepare them for post-processing calculations.

Critical Timing of Data Samples
One of the major challenges of the project was to sample all six strain gauges a minimum of 1,024 times per revolution at exactly the same positions on the tire and verify that the positions were repeating each revolution. We accomplished this sampling with the pulse train coming from a direct coupled encoder on the tire-mounted spindle. This encoder signal is the sample trigger for the SCXI-1140 module.

The shaft encoder, a BEI HS-35 (1,024 count, optical style), has two channels of pulse trains (A and B) as well as a marker pulse (Z). One of the channels triggers the SCXI-1140 module while the marker pulse and other channels are wired directly into the National Instruments AT-MIO-16XE-10 DAQ board. LabVIEW uses the marker pulse as the trigger to start saving the data samples and also as the counter to determine when enough data has been sampled (eight full revolutions). The load wheel also has a direct-coupled encoder mounted for time interval analysis.

LabVIEW software and the marker pulse also accomplish the encoder signal verification checks on both encoders. The pulses received from the encoder during the test are summed and compared to 1,024 at each marker pulse. This is done simultaneously while acquiring the strain gauge data. If a miscount is detected, the data for that complete revolution is ignored and the test continues until the system gathers eight complete revolutions of verified data. For the user and the engineer, this process ensures that an automatic mode test produces accurate, verifiable, and repeatable results.

The control system performs instantaneous post-processing of the test result data. LabVIEW software collects the thousands of points of strain gauge data in a matrix format, analyzes the data using Fast Fourier Transforms to the 10th harmonic, and presents the compiled results for a given test in a Microsoft Excel spread-sheet format. The compiled data is automatically saved at the end of each test and can be printed on demand.

Multitasking and Systems Integration
We also integrated the LabVIEW software with a proprietary time interval analysis board from Guide Technologies, Inc. (GTI). We used a VI written by GTI to integrate the GTI 650 board into the LabVIEW system. In addition to controlling the machine, spindle drive, carriage drive, warm-up drive, brake, and performing all required test functions, the LabVIEW software also receives work request data through an interface to the Proving Grounds LAN. The operator of the TUG machine selects the work request number on a LabVIEW screen, and LabVIEW then retrieves the information needed to perform the test.

Conclusion
We used National Instruments LabVIEW, SCXI, and DAQ products to integrate a wide variety of hardware and software and to perform sophisticated tasks in our application. These products proved to be superior in the machine control and instrumentation market. All personnel involved were pleasantly surprised by the wide variety of tasks that National Instruments products could accomplish and the speed with which they completed control and data collection, including the post processing of large amounts of data after every test.

For more information, contact:

Richard D. Cichosz

Process Controls Manager

Quantum Controls, Inc.

44747 Helm Court

Plymouth, MI 48170

Tel: (734) 414-1900

E-mail: ichosz@mail.quantumone.com

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