Motion Control Resources
Web Server Delivers Motion on a Platter
by Kristin Lewotsky, Contributing Editor
Motion Control & Motor Association Posted 05/19/2010
Motion systems with web server capabilities give users the advantages of Ethernet without expensive software or specially trained staffers.
In motion control today, Ethernet provides powerful capabilities for networking and operation. Truly leveraging the technology to monitor and update the machinery at a distance requires specialized software, however, limiting utilization. Increasingly, the motion control industry is turning to web server technology fill the gap, providing an easy, quick-start approach to working with Ethernet and motion.
Essentially, web server is a utility designed to interface with the motion controller via any PC, using standards like Ethernet and web browsers. It allows the end-user to monitor and support their own machine without additional engineering software (see figure 1). It typically runs on the hardware as part of the firmware, providing easy connectivity with near plug-and-play operation.
Accessing machines via Ethernet typically takes sophisticated maintenance and diagnostics software, and development software tools, with licenses that can run to thousands of dollars. Maintaining and updating that software, plus training staff to use it, consumes time and money while diverting resources from the company’s core business. “End users probably only interface with a machine beyond normal HMI [human-machine interface] interaction a couple of times a month, if that, so expensive engineering software is not always practical,” says Zuri Evans, Motion Controller Product Manager at Siemens Industry Inc. (Norcross, Georgia). “Web server gives them a simple interface to interact with their machine.”
“You can use web server to do things that you would need a special program to do,” agrees Atef Massoud, Motion Product Engineer at Omron Corp. “That's a big advantage to many OEMs.” Using web server, engineers can perform tasks like setting triggers, viewing and acknowledging alarms, and reading and writing to user variables and system variables alike. If a machine goes down, the OEM or system integrator can log in to the controller directly to troubleshoot or download updates. If the machine isn’t on the Internet, support can still FTP the firmware to the end-user, who can use the web browser interface to download the updates with a few clicks of a mouse. The approach can be used for everything from updating a cam profile to setup and configuration of the machine.
And the technology is getting more powerful all the time. In the past, if a user wanted to access an oscilloscope trace or a tool to monitor or control system parameters, they’d have to create it in the system and download it before the web server could access it. More recent web servers allow users to actually create those tools in the web browser itself, use them, then save them for future access (see figure 2).
Although most offerings with embedded web server capabilities come with templates or basic pages, users or OEMs can customize them using supporting products. They can create separate pages for each machine, then master web pages for the line, for example, with one master page for motion, one master page for safety and logic, etc. "You can build the view that is most specific to your application,” says Joe Lee, Product Manager for Ethernet/IP at Rockwell Automation. “Granted, some configuration will have to be done in the enterprise network to allow secure access to these web servers, but once that's set up, it really doesn't matter where you are, you're able to access this information.”
In addition to minimizing specialized software, a key benefit of web server is accessibility. Forget about using a day-old data snapshot in a production meeting. With web server capabilities, a plant manager can access data like real-time run-rate information right in the conference room, during the meeting (see figure 3). Yes, this information has been available in the past, but the ease of access is new. “Usually you had to have some kind of MES [manufacturing execution systems] architecture to get all of your machine data up into the office environment where you could use it," says Evans. "Now, you have a custom webpage on which you can display all of the run-rate information. You just open up in a web browser, dial into this machine and then display it.”
Packaging lines today can feature over 100 axes and stretch the length of a football field. If the operators are lucky, the machines feature multiple HMIs scattered around. If not, clearing jams can be a major headache, requiring repeated backtracking or semaphore-style communication between operators. Web server allows operators to control the line from a tablet PC or even a smart phone (see figure 4). Instead of having to walk back and forth to the HMI, they can simply take the portable device right to the blockage to jog the jam loose from close quarters. Supervisors, meanwhile, can monitor the status of multiple machines from any point in the plant, or offsite, just by jumping from webpage to webpage.
Meeting the Need
It's important to understand not only the benefits but the limitations of web server. Although pages can offer some HMI functions, they are far from the capabilities of a fully functional HMI (see figure 5). "They’re not meant to replace the HMI now or anytime in the near future," says Evans. "The HMI talks directly to the controller over a dedicated connection, using a dedicated protocol so you can dictate how fast it needs to communicate. When you're talking about a webpage, everything goes over TCP/IP and that was never designed to be deterministic or instantaneous." Then again, the primary rejoinder in the Ethernet debate is not whether the protocol is deterministic, but is it deterministic enough for the application. For the types of functions we discussed, web server and Ethernet performance are quite sufficient.
One sticking point in applying web server is security. The issue is not technology but corporate culture. Even if plant management or engineering wants to add their plant floor network to the corporate network, the IT department may balk. The reluctance may be driven by concerns about making machinery vulnerable to hackers or it may simply be a question of bandwidth. One solution is to use a router to create separate networks so that the machines are on one subnetwork and the corporate systems are on a different one. “VPN allows a secure connection to the corporate network from the Internet,” says Evans. “After the VPN connection is established, you can use a second router as a bridge from the corporate subnet to the machine subnet. You’re basically talking about two separate layers of security between the Internet and the machine.” For additional security, password protection can restrict user privileges, for example setting up a maintenance group, an operators group, a builders group, etc.
Currently, web server doesn’t offer programming capabilities. Users can develop routines in other engineering software then use web server to apply the update to the machine as we discussed, but they can't actually make changes to the user code in the web server. It's a characteristic that cuts both ways. On one hand, end-user staff who only occasionally interface with the machine could find web-server access far more convenient. On the other hand, the easier it is to make significant and comprehensive changes, the greater the likelihood this will take place accidentally or without authorization and impact machine operation. Once web servers offer programming capabilities - and the likelihood is that they will - strict access control and a comprehensive security policy will be essential.
In the end, it comes down to how engineers should best spend their time to bring value to their company. Web server provides them with a tool to leverage the power of remote conductivity without reinventing the wheel themselves. “If the motion control engineer is focused on making trajectory and tuning and so on, he shouldn't waste time writing a web server,” says Massoud. “He should just have a server available so he can enter in a short time position, defaults, and firmware updates.”