Measuring Sound Quality in an Automotive Production Line Using LabVIEW and NI PXI Hardware

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"With the LabVIEW State Diagram Toolkit, it was possible to share machine operation concepts with Sci-Mech management and the client."

- John Purse, Sci-Mech Technical Services

The Challenge:
Developing a cost-effective solution for production line testing of automotive seating products that can provide objective metrics for suggesting corrective actions to be combined with standardized sound quality metrics so subjective human impressions can be incorporated into the overall acceptability criteria.

The Solution:
Using NI LabVIEW, the Sound and Vibration Measurement Suite, and NI motion control products for control and data acquisition along a 15-station test line where two stations are housed in acoustic test chambers to provide a weighted power tracks test and a lift power test where the acoustic data can be acquired.

Author(s):
John Purse - Sci-Mech Technical Services
Michael Albright - Signal.X Technologies

NI Silver Alliance Partner Sci-Mech Technical Services designs, builds, and integrates instrumentation and automation solutions that satisfy the requirements of fully automated assembly and test cells. Our client supplies engineered seat frames to the North American automotive industry and needed a new test system that could recognize different products and test them against appropriate parameters including sound quality. The parts must meet the highest quality standards and be 100 percent functionally tested before shipping. Our clients have to consider the showroom experience of the customer operating the seat.  

Sound Quality Metrics

The core of a powered seat is the DC motor-driven leadscrew, or a direct worm drive. In a dealer’s showroom, the sound a seat makes sets the customer’s initial perception of vehicle quality.Car manufacturers have to get the sound and vibration behavior exactly right in the new car showroom because power seat noises are primary subjective quality indicators.

We make acoustic measurements on the seat track in the sound-proof stations using the NI PXI-4462 24-bit dynamic signal acquisition (DSA) module with G.R.A.S. Type 46 AE ½ in. prepolarized free-field microphones powered directly from the PXI-4462..   

Noise, vibration, and harshness (NVH) specialist and National Instruments Alliance Partner Signal.X Technologies of Milford, Michigan, worked with Sci-Mech and the customer to measure sound quality metrics using LabVIEW and the Sound and Vibration Measurement Suite. Metrics considered include Peak A-weighted SPL, Zwicker Stationary Loudness (Sones), pseudo time varying loudness, key harmonic detection, periodic and nonperiodic impulse indicators, and rpm variation and drift.  

A key requirement of the production environment is that metrics offer intuitive explanations of possible defects based on industry-standard formulations. It is notable that the metric set is a hybrid of objective and subjective parameters focused on ensuring a repeatable production process. As a set, the metrics can correlate to subjective human impressions of the sound of the seat track as well as direct indication of specific defects that will fail one or more objective metrics. This approach to noise and vibration performance assessment with Signal.X technology ensures only quality seats earn a passing grade.

Functional Testing

The 15-station test line, which includes various platforms and systems, runs on a single Ethernet network. Because of the high digital channel counts required for a project as complex as the current seat cushion assembly and test line, a desktop PC alone could not support the required number of PCI boards. We chose ann NI PXI remote chassis to perform the extensive data acquisition and communicate to the PC-based controller. We also used two NI PXI-6511 low-cost, industrial digital input modules, which provided 128 bank-isolated 24 V inputs.

With bank isolation, it was possible to connect the Turck sensors directly to save assembly time, reduce circuit complexity, and decrease cost. Two NI PXI-6512 low-cost, industrial digital l/O modules for the 128 bank-isolated digital outputs allowed us to connect to the devices directly from the module's breakout box without putting every signal through an optical isolator. With so many channels, this saved setup time as well as panel space.

To control the servo motors of the system, we used an NI 7340 four-axis motion controller and an NI 7774 four-axis motion control interface to a Rockwell Control Logix 5561 controller. Full driver integration with the NI Measurement & Automation (MAX) configuration utility offered an intuitive graphical user interface (GUI) for setup and troubleshooting.

To assist in the software design phase and reduce overall programming time, we used the LabVIEW State Diagram Toolkit to concurrently visualize program architecture and develop code. With the LabVIEW State Diagram Toolkit, it was possible to share machine operation concepts with Sci-Mech management and the client.

We also used the NI Motion Assistant to set up the initial motion profiles. This tool helped save hours of development time and was very useful in the initial setup of our servo motors. It was possible to safely check the acceleration and deceleration ramp profiles and overall velocities of the automotive seat testing system before program implementation.

Benefits of the NI Platform

Sci-Mech with Signal.X Technologies used LabVIEW and NI PXI hardware to deliver an advanced production line test system for seat tracks that incorporates sound quality as a part of the functional tests, ensuring the parts meet the highest quality standards with 100 percent testing.   

Author Information:
John Purse
Sci-Mech Technical Services
312 Alliance Road Unit #1
Milton L9T 2V2
Canada
Tel: 905-693-0866
test@scimech.com

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