Is Linux at the Gates of the Factory?

Open solutions represent an increasingly clear direction for industrial controls. So it's not surprising that something as vital as the "master regulator" of software in a computer—the operating system—attracts enthusiastic supporters for an open-source operating system (OS) like Linux. Originally developed and patented by Linus Torvalds in 1990, Linux has indeed made great waves i...

By Frank J. Bartos May 1, 2004

This article contains online extras.

  • Open-source software

  • Embedded systems/controls

  • Real-time operating systems

  • Linux

  • MS-Windows CE

Linux, other operating systems in action

Open solutions represent an increasingly clear direction for industrial controls. So it’s not surprising that something as vital as the ‘master regulator’ of software in a computer—the operating system—attracts enthusiastic supporters for an open-source operating system (OS) like Linux.

Originally developed and patented by Linus Torvalds in 1990, Linux has indeed made great waves in the world of office automation, telecom, and server applications. Government agencies at various levels have embraced it, particularly in Europe. Backing by major technology companies, such as IBM and Hewlett Packard, hasn’t hurt Linux’s image, either. Reasons for this broad array of support are straightforward: Linux OS has a lot going for it. Open-source code, scalable architecture, a large support community, many contributing developers, and ‘free’ access to source code are among the positives. Yet, there is more to the picture.
Linux is not an inherently real-time system. While definition of ‘real-time’ (RT) is highly application-dependent, an operating system’s RT capability is crucial to industrial users. As a result, real-time versions (extensions) of Linux have evolved, much like that for other OSs. These extensions provide the necessary separation between real- and nonreal-time tasks of an application along with other functions (see ‘Architecture’ graphic, next page). RT operation changes the simple concept of the original Linux OS. For example, a third-party supplier may be needed, along with the cost of service packages, proprietary tools, and maintenance. So using Linux is not necessarily free.

Still, this Unix-like OS is showing up on the factory floor. Current applications center on operator interface (HMI) and data acquisition roles, but wider industrial control applications are coming as more tools for development and networking become available.

Disruptive technology

William Weinberg, director of strategic marketing at MontaVista Software, considers Linux’s openness a ‘disruptive technology’ that threatens legacy, proprietary embedded operating systems. He sees Linux providing numerous benefits on the shop floor, among them:

  • Robust, reliable memory-protected architecture;

  • Excellent throughput, with multiple options for RT response;

  • Fault isolation/management, limiting fatal errors to single (restartable) processes;

  • Availability of communication protocols, tools, and device-driver support;

  • Support for key CPU architectures; and

  • Large, worldwide development community offering quality software.

Besides technical attributes, Weinberg cites commercial benefits to users of Linux, such as ‘royalty-free’ deployment and lower total cost of ownership; various commercial and ‘roll-your-own’ options for OS and tools; open source code; standard application programming interfaces (APIs) to foster software reusability; and more choice of suppliers that minimizes product obsolescence.

On the other hand, Microsoft embedded OSs offer developers a familiar and very rich stack of software functionality, he says. ‘They come with the usual caveats of quality, security, [one supplier] lock-in, and cost.’

Greg Holt, spokesperson for embedded system software provider TimeSys Corp., states, Running Linux on the factory floor offers a number of immediate benefits, including numerous network protocols and services. Holt cites as examples, Ethernet, TCP/IP, HTTP, DHCP (for host configuration), and network file server. ‘[They] bring the factory floor into the connected world, enabling seamless data integration with enterprise-wide systems’ he says.

The company’s TimeSys Linux represents an OS upgraded to real-time capabilities for developers and OEMs working on performance-critical control applications. Holt emphasizes that development benefits of the RTOS include support for high-resolution clocks and timers, periodic thread APIs, and more levels of POSIX compliance.

Modular, scalable, and configurable to various platforms are among the benefits that Marc Serughetti, director of marketing at Wind River Systems, attributes to Linux OS. Another attraction to manufacturing is availability of Linux source code over the long term ,along with support for off-the-shelf devices, he explains. ‘[Potential users] need to look at where Linux is today and with what types of factory devices it’s used.’ Plant equipment ranges widely from custom hardware geared for tightly coupled, RT operation —including safety implications—to less control-oriented operator interfaces, switches, and networking products, and to higher level equipment, such as SCADA system.

‘Linux OS is most appropriate in the shop-floor environment where hardware and software are less tightly coupled,’ says Serughetti. ‘It’s being applied where responsiveness is not critical, for example on COTS [commercial off-the-shelf] boards and HMIs. He also sees many Microsoft Windows applications out there, reflecting the legacy of that operating system.

In real-time Linux architecture, operating system and RT tasks run at highest privilege level O, separated from lower ).

For real-time applications, a higher level, RT version of Linux is needed, an area that Wind River is ‘investigating,’ according to Serughetti. This includes a recent partnership with Red Hat to jointly develop embedded run-time Linux products and tools. Wind River’s core offering is VxWorks, a proprietary RTOS now in version 6.0, intended for high-performance and embedded applications. Enterprise Linux is Red Hat’s core offering.

Cost issues

Not everyone agrees on lower total cost of ownership for Linux. In Serughetti’s opinion, concerns for OS support can override bare cost issues. ‘When users select an operating system, they also look at supplier capabilities; a kernel organization supplies only limited input,’ he says. As for a roll-your-own OS, this can be a very user-dependent benefit in the industrial control arena, where in-house expertise is on the decline. Service support costs can add up rapidly.

Paul Shelton—automation marketing, HMI Products, at Siemens Energy & Automation —provides perspective from his industry sector. Operating system stability, security, reliability, connectivity, etc. are the terms important to customers, rather than which technology lies beneath, he explains. Shelton contrasts Linux as an up-front investment versus ‘pay as you go’ with MS-Windows. He believes total cost is higher for a Linux-based shop-floor HMI solution, unless ‘very high volumes [exist] to amortize the investment.’

In the late ’90s, Siemens transitioned to Windows CE for its HMI panel products. ‘Using a stable, feature rich operating system allowed us to focus on our core competencies that include designing devices and developing application software,’ says Shelton. Today, many HMI features are enabled via Siemens’ ProTool or WinCC Flexible application software. Browser, terminal server client, and third-party application support are among inherent operating system features. ‘The results are stable, flexible, lower cost solutions that are extremely well received by our customers,’ he adds.

Licensing, legalities

Some concerns exist among supporters and detractors of Linux about requirements to disclose developments they make with open-source software. MontaVista’s Weinberg thinks the concerns are exaggerated, and originate from actions of proprietary RTOS suppliers who feel threatened by open-source methods.

Few restrictions apply to modifying and reusing Linux source code, and users have no obligation to expose closely held IP at either the application or driver level, explains Weinberg. Two levels of licensing apply to the Linux kernel. A so-called GNU/General Public License (GPL) and a less restrictive limited (library) license or LGPL. GPL specifies that deployers who copy, modify, or derive GPL code must supply the source code (and binaries) to customers, but not to the larger ‘community.’ Links to GPL libraries carry the same disclosure rule, but virtually all Linux run-time libraries use LGPL—according to MontaVista— which has no disclosure requirement.

‘In practice, the GPL’s small set of requirements is far less onerous than terms and conditions that apply to many proprietary software license agreements (SLAs),’ says Weinberg. ‘SLAs can include full rights to disclose proprietary development project details…restrictions on reuse and deployment of modifications to original source code [and more].’ He cites comparative lengths of licensing documents: GPL-7 pages, Microsoft EULA tools-12 pages, and SLAs for proprietary RTOS-typically 15-25 pages.

However, Weinberg cautions developers building on or deploying GNU-licensed Linux software ‘to understand the implications of mixing and matching GPL and LGPL licensed software with other license types.’

Wind River’s Serughetti agrees that some potential Linux users have concerns about disclosure requirements of Linux. Code modified for a user application has to be disclosed, ‘but this is not where a company’s intellectual property resides,’ he says.

Linux also has run into legal issues, not unusual for a challenger of established technologies. Neither space nor orientation of this article allows for detailed coverage of the SCO Group’s ongoing suit against IBM (and other actions), except to note that it may disturb users and potential users of Linux. SCO claims that Linux is an unauthorized derivative of Unix.

Possibly a more serious issue comes from Europe, where interpretation of an article in the European Patent Convention is being debated. Article 52, Patentable inventions, stipulates that inventions (developments) ‘susceptible to industrial application’ must be patented, a motion contrary to Linux’s concept. Exceptions in the directive may lead to resolving the problem.

Overall, prospects for Linux OS are positive. Several market research firms project lively growth for embedded applications of Linux in the near future. Some of these are destined to enter the factory, where RT versions of Linux will battle their Microsoft and proprietary operating system rivals.

Linux, other operating systems in action

CAMotion Inc. (

An embedded PC running Red Hat Linux controls the robotic machine’s motions. ‘Commanded positions and feedforward effort are provided to four proprietary motion control cards every millisecond,’ says Steve Dickerson, CAMotion chairman. ‘This allows implementing advanced motion profiles and control algorithms, such as vibration suppression, learned feedforward, and state estimation.’ The result is high-speed, accurate motion with a gantry of low weight.

The motive to use Linux on a PC was cost reduction, while having the flexibility to write totally open source software, explains Dickerson. ‘From earlier applications using a commercial, real-time extension to [Microsoft] Windows operating system, CAMotion found that creating applications was more difficult, which along with licensing costs, led to the adoption of Linux,’ he says.’ The system has exceeded our expectations,’ adds Jason Prince, project manager at Excel.

Nimble robot ‘bends backward’

Called the most compact robot in its class, ABB’s IRB 6600 is equipped with a novel ‘backward-bending’ flexible arm, allowing the robot to complete multiple tasks in real-time, including upper arm extension and various wrist movements with precise detail, says the manufacturer. The robot is at home in tough spot welding, material handling, and machine tending applications.

Wind River provided ABB (

More apps online

See two more applications in ‘Online Extra’ sidebars at

Online Extras

Linux OS streamlines dairy-herd management
Bou-Matic, a dairy-equipment manufacturer located in Madison, WI, chose open source code, embedded Linux RTOS from TimeSys Corp. for the company’s ProVantage Network Controller and StepTrakker products because it is said to provide a number of advantages over other embedded operating systems. Besides access to various existing software and firmware,

TimeSys says the benefits included:

ProVantage Network Controller is an existing herd-management/dairy-farm operations product, being upgraded with

Windows CE helps boost injection-molding productivity
Aging, mechanically operated injection-molding machines at National Polymers Inc., located in Lakeville, MN, were holding up efficient production of polypropylene drinking cups (and other products) the company makes by the millions per year. Flexibility and productivity are the keys to success in this highly competitive industry.

In early 2003, the company decided to automate its injection-molding machines. It selected EPCO Machinery LLC, (Fremont, OH) to supply a solution to cut downtime and increase productivity—after a competitive review of automation vendors and system integrators. “[Our] machines were operated by mechanical switches, and they were basically wearing out,” says Wes Anderson, vice president of National Polymers. A huge (3 x 4 foot), antiquated motherboard with a maze of wiring was representative of the electronics.

Integrated automation
A remanufactured 700-ton Van Dorn injection-molding machine controlled by a sophisticated, but easy to operate, integrated automation system from


The compact control system and HMI, which includes Ethernet connectivity, automatically adjusts linear positioning units determining mold and injection part measurements. The HMI allows all kinds of system tracking, including troubleshooting the machine, explains Anderson. Based on results of this upgrade, National Polymers is in the process of installing similar Siemens automation systems on its entire line of injection-molding machines.

Linux community sources
Linux operating system enjoys a large support community of software developers and information sources. Here’s a sampling of Linux sources, including real-time (RT), from which further user information is available:

Wago industrial PC offers real-time Linux or Windows CE

“Customers will find the IPC is a complete solution for machine control, process control, redundant networking, high-speed data collection, and for applications requiring fieldbus master capabilities,” says Mark DeCramer, Advanced Electronics product manager at Wago.

With its 266-MHz Intel Pentium processor, Wago-I/O-IPC boasts 32 MB of memory, 128 KB PLC SRAM battery back up, and RealTime Linux or Microsoft Windows CE embedded operating system. It is programmable using IEC 61131-3 open standard via Wago-I/O-PRO CAA programming tool, which supports all six programming languages of the IEC standard. The programming tool is compliant with the CoDeSys automation alliance, allowing free Web downloads as new technology features are added.