Developing a High-Volume Automated Production Test With CompactRIO

Introduction

A Tier 1 valvetrain component supplier needed a reliable system for executing end-of-line functional and performance tests to verify proper complex powertrain component assembly and machining. Reliability and maximum total throughput were key to supporting production volume requirements. Signal.X used CompactRIO to build a system that powers a programmable automation controller (PAC) to execute many functions that, in the past, would have required several different controllers or PLCs.

Two independent CompactRIO units run a test station inside a single test cell. A Windows PC is used to configure and display data from each CompactRIO system, but it is not required for test operation. As data is acquired, it is transferred from the CompactRIO to the PC and from the PC to a server running Signal.X DataManager software for final storage, archival, and database operations. 

Motion Control

We developed a multiaxis, multirate motion control subsystem to manage four control axes with configurable proportional integral derivative (PID) parameters, limits, and interlocks. It uses a real-time update rate of 8 ms with spline interpolation on the CompactRIO field-programmable gate array (FPGA) between 125 µs and 8 ms, depending on the axis.

Data Acquisition and Processing

Although the test cycle is short (~25 seconds), there are approximately 30 to 40 metrics calculated on that data, so data must be available for immediate processing. We implemented processing using concurrent file reading and writing to maximize efficiency while keeping data available as the test is being conducted.

Because the system processes data in parallel to the actual test, the customer can configure it to abort the test early if a metric fails, increasing overall throughput and minimizing wasted time on testing failed parts. We created a custom limit definition editor to set up this processing definition, including filtering, triggering, and revision control for traceability.

Discrete Part Handling

We developed an architecture for traditional discrete control using the CompactRIO controller as a PAC. The heart of this system is a finite state machine that emulates a user-configurable, naturally flexible, and efficient ladder logic style program. This was primarily used in the installation for pneumatic slides, PLC/robot interaction, and fault and error handling. A simple editor was developed so that users can edit slide motions, PLC part transfers, interlocks, and safety sequences.

Features of this program include branching, looping, internal memory storage, jumping, and state forcing. Logic is built for the different modes of operation such as power-up, manual, and automatic, and fault, error logic, and recovery is carried through all modes. This means that traditional and proven control concepts familiar to PLC developers were implemented in the finite state machine. This approach retained all of the power and simplicity of traditional ladder logic and enhanced support for complex floating point computations, alpha numeric manipulation, screen displays, and GUI interaction.

Communications

We used the EtherNet/IP Driver for Industrial Communication that originated in NI Labs to communicate directly with Allen-Bradley ControlLogix PLCs. We used the Simple Messaging Reference Library protocol to communicate between the CompactRIO and the PC for live data streaming and commands. We simplified communication by providing a simple, reliable way to connect to external devices.

Data Management

The volume of data collected on each CompactRIO system presented a development challenge and required planning to ensure reliability and long-term stability. Each test stores approximately 12 channels of data for 25 seconds, resulting in approximately 1.5 MB of Technical Data Management Streaming (TDMS) files. At full production rate, each CompactRIO system produces approximately 2 GB of data per day. Because of this high volume, an external USB hard drive was connected to the CompactRIO to store the data. The data automatically uploads to the PC when connected, but the CompactRIO drive houses a local buffer in case the PC or network is down. Similarly, data automatically transfers from the PC to the DataManager when the server is connected. The PC maintains its own data buffer for quick access and storage if the server is disconnected.

NI Partner Signal.X DataManager

This project used a Signal.X off-the-shelf product for storing, querying, reporting, and archiving test stand data. Based on a standard query language database, the DataManager resides on a server that scans all configured stations on a predetermined schedule, retrieves and archives data files, and inserts test results in the database. Users can query the database to return a production data subset, create reports based on those queries, and automate those reports to be autogenerated and alarmed for trending. Additionally, users can run historical data on the server against new limits for evaluating new metrics and “what-if” scenarios.

The Complete Package

The CompactRIO system forms a complete, reliable, quick, and reconfigurable automated test system controller. Quick cycle time and efficient data use maximizes overall production throughput, which ultimately saves money and improves processes. By adding a complete data management solution, Signal.X has positively impacted upstream processes by isolating warranty returns, understanding assembly defects, and refining test procedures and limits.

NI Solution Benefits

In the past, these processes were separated among individual controllers and PLCs, increasing complexity and cost. The CompactRIO platform combines all of the functions into one hardware component, managed by a single process. Also, LabVIEW programming flexibility means that you can adjust any of those processes from one source code set or configuration screen.

The Bottom Line

Several key technologies used in this project resulted in clear and tangible process improvements and efficiencies, including the following:

• Removing the Windows PC from the critical production path reduced downtime and increased reliability from the real-time OS embedded in the CompactRIO system.
• Because the system processes data in parallel with test, it makes pass/fail decisions quicker and rejects parts upon failure, rather than after completing an entire test.
• By rejecting and retesting parts immediately upon failure, throughput has increased by an average of 5 percent.
• Bringing all of the data into the DataManager with automated reporting, batch processing, and data archiving has eliminated key sources of plant frustration by giving engineers and managers up-to-date production process information and automating tasks that were previously done manually.

In the words of the customer, “The demands of our manufacturing environment and 24/7 production require maximum efficiency and reliability while maintaining the highest quality. This was provided by the architecture that Signal.X Technologies applied to our end-of-line test system. The result is increased throughput, reduced downtime, and an overall improved reliability.”

Author Information:

Robert Hoffman
Signal.X Technologies, LLC
15800 Centennial Dr., Suite A
Northville, MI 48168
United States
Tel: (734) 417-8236
Hoffman@signalxtech.com

^{An NI Partner is a business entity independent from NI and has no agency or joint-venture relationship and does not form part of any business associations with NI.}