Technology Advances Power Integrated Control
Imagine designing a packaging line or material handling system with the control all in one package rather than separate logic control, motion control, vision systems, and bar code over RS-232. Real-world data are sent directly from the control program to a SQL database for analysis, selective sharing with customers or suppliers, and production and quality reporting.
Imagine designing a packaging line or material handling system with the control all in one package rather than separate logic control, motion control, vision systems, and bar code over RS-232. Real-world data are sent directly from the control program to a SQL database for analysis, selective sharing with customers or suppliers, and production and quality reporting. This is not technology from the Starship Enterprise. This integration is not only now possible, but it actually works.
PLCs were designed as fast, robust controllers of discrete logic. It has only been in the last ten years that hardware and software have come together to allow good integration of analog and PID loops. Even recently, data handling was kludgy. Motion integration with a PLC has been difficult requiring an integrator with high levels of knowledge and experience to accomplish a successful installation.
For example, Siemens Energy & Automation (Alpharetta, Ga.) has announced a small PLC with multi-axis motion control module. The module tightly integrates with the PLC yet handles integrated motion of up to four axes. Applications from single positioning to multi-axis interpolation are enabled. A parameterization 'wizard' guides users through setup and start-up.
This has all changed over the last couple of years. Even though PC-based control has not overthrown PLCs as controller of choice, technologies from the PC world are enabling a revolution in how control systems are designed and implemented. Programming editors have become powerful, emulating interfaces like Microsoft's Visual Studio. While more control engineers are able to use C and C++, even the venerable ladder diagram is growing in power. Easy to use function blocks within ladder have added PID, data handling, motion profiles, advanced math, and more.
Discussions with many technology suppliers revealed different emphases and methods of accomplishing integration. One thing is sure, however, control engineers will have tools to accomplish corporate objectives like implementing the packaging line referred to above. Servo motion technology integrated with sequential logic allows quick product changeover. Integration of data collecting equipment like vision, RFID, or bar codes with sophisticated database applications enable e-manufacturing. Advanced alarming and diagnostics improve uptime. All are designed to make a hero of the control engineer.
Motion and loop integration
Paul Hamilton, Schneider Electric Automation (North Andover, Mass.) marketing vp, says, 'Today, Schneider is providing integration within the traditional PLC of discrete, process, and motion control and HMI. Most communications was to independent boxes through serial links. We now have higher level links through intelligent modules. Motion control and loop control are predominant applications plus some serial devices like bar code. An enabler has been IEC function blocks that present functionality to programmers as a canned object.
'Where this goes over time will be tight integration of control functions. One Step Generator allows designers to go from original design environment to defining objects, load to controller, and send to devices in the field. They won't even have to write the program. This integration goes from early design process to code generation.
'Another area in that future direction is that functions in configuration tools allow the tag database to become more and more integrated into a single tool. A weighing module hanging on Ethernet can be tied to a function block in a PLC, so function block and tag names plus PLC logic are tied together. Coming are tools within One Step Generator that tightly integrate this database with visualization, mapping a single tag database to both HMI and control.'
Paul Camuti, Siemens E & A software general manager ties successful integration to the development of open systems. 'Open, standards-based software is the key to integration. We showed an example at the recent packaging show by integrating our control with Cimetrix (Salt Lake City, Ut.) robotics and Cognex (Natick, Mass.) vision system. We provide all logic handling in IEC 61131 and wrap all the special functions into custom blocks. Our focus is to provide one programming editor for motion, logic, configuration, etc. This is engineering integration, which will be valuable to control system engineers.'
One necessary component of overall integration is scalability. John Nesi, Rockwell Automation (Milwaukee, Wis.) Logix NetLinx business strategic marketing manager, explains, 'We have taken a suite of products with a single embedded engine called Logix. It can be like a four-cylinder or a V-8 depending upon the application. It can be in different platforms, yet behave in the same way with a consistent set of instructions and a consistent way of executing those instructions. We can embed motion commands inside the ladder editor then execute a graphic editor to configure moves. Similarly, we have a function block editor that is truly lifted from the DCS world. Blocks can be dragged and dropped into place and connections wired to mimic process loops. Other blocks have been developed for web control using variable frequency drives.'
Adds Tim Reckinger, business unit leader for Rockwell Software (West Allis, Wis.), 'Another great thing is integration of visualization. Tags can be ActiveX components sent to ActiveX containers like RSView. The user can reference a tag in a control database and another tag in a second control database over the network and link the screen to various control databases as simply as browsing the web. It doesn't matter how many databases there are, there is a virtual link to all applications.' Concludes Mr. Nesi, 'In the future, we see bigger and better things for batch control. Look for Logix being driven into smaller, more flexible, and scalable devices.'
The emphasis of the day is e-manufacturing. This concept refers to solving the business problem of tightly coupling manufacturing with customers and suppliers to provide 'mass customized' products to customer requirements while managing material inventories.
'Control systems must offer power and advanced programmability while simultaneously supporting many types of devices (analog, digital, serial) and also be intelligent enough to communicate with the entire enterprise natively,' states Benson Hougland, director of technical marketing at Opto 22 (Temecula, Calif.). 'It must be able to perform advanced functions such as math, control loops, and string handling. Our graphical, flowchart programming tool includes a scripting language built in to give advanced programmers even more means to accomplish their tasks.
'Gaining control over machines is only part of the equation, though. How does one move critical business data from the factory floor to enterprise databases and other applications? Our response is to communicate with all database, MRP, ERP, network management, and other enterprise applications in the ways they understand-XML for data transfer, SNMP for network management and SMTP for e-mail-without the need for special software, proprietary servers, or other middleware components. The protocols necessary for this communication have been embedded in the Ethernet Snap I/O, eliminating development and deployment costs.'
Andy McMillan, Entivity (Ann Arbor, Mich.) co-founder and vp of marketing, says, 'Integrating various web technologies right into the control software enhances rapid communication of critical factory data enabling e-manufacturing success.'
Manufacturing Data Systems Inc. (MDSI, Ann Arbor, Mich.) provides software CNC with internal integration of machine logic, motion control, and information handling. By providing open Application Programming Interfaces (API), integration of third-party technologies is enabled. Vision systems, bar-code readers, and other products are integrated through dynamically linked libraries (dlls) and API programming calls using readily available programming tools like Visual Basic or Visual C/C++.
VMIC (Huntsville, Ala.) supplies PC-based control on a variety of platforms, both hardware and software. The variety of hardware platforms that include VME, ISA/PCI, cPCI, and PC/104+ provides system designers a way to integrate numerous special boards and tools. In addition, its control software can be targeted for Microsoft Windows NT, Windows NT with VenturCom's RTX real-time extension, and Wind River's VxWorks. For example, a VME computer with control running on VxWorks was used at US Steel Fairfield Works to control a new production line and integrate it with existing GE Fanuc PLCs and drives.
Omron Electronics' (Schaumburg, Ill.) strategy for accomplishing integration is DeviceNet. Jon Giardina, PLC product marketing manager, notes that vision, RFID, variable-frequency drives, temperature controllers, plus a host of I/O modules all connect on the network to a PLC integrating the various functions.
Couple vision and motion
Tightly coupling vision and motion in high-speed applications can be a challenge. Jayson Wilkinson, National Instruments (Austin, Tex.) motion control product manager, points out special function blocks within LabView to program the control and C-based Measurement Studio. This combination was used to perform precision alignment in a fiber-optics component manufacturing application. Motion positions the fiber, vision monitors the fusing process, and data acquisition from the same application logs production and quality information.
Scott Kiser, Wonderware (Irvine, Calif.) FactorySuite marketing, notes that InControl integrates within a Windows NT and 2000 environment an ActiveX control editor, DCOM-based distributed communication capabilities, OPC servers and tight integration to Wonderware HMI, multiple interfaces for open and legacy I/O modules, and toolkits providing extensibility. The Factory Object Editor is an ActiveX container, which includes objects such as PID, analog alarm, process for loop feedback, plug-ins to interface to Visual Basic and web applications, plus ability to use third-party ActiveX objects for such things as motion and vision.
There are potential problems facing designers developing an integrated control solution. Mr. Kiser says, 'Based on field data, we believe the most common pitfalls encountered include a mismatch of I/O requirements, inappropriate PC platform, lack of domain or application expertise, and inexperience with configuring I/O systems. Users may attempt to use an I/O system that is undersized or lacks the speed or capabilities required. They may purchase a computer not powerful enough to run all the applications.'
Advantech Automation's (Cincinnati, O.) product manager, Mike Berryman, points to driver development as key for integrating various components within PC-based control. He also mentions stumbling blocks to watch for when developing and implementing a system. 'The system integrator still needs to be knowledgeable about each intelligent device,' he says. 'Engineers must manage data update speeds to assure making decisions on current information. They must also understand the timing of data transfer mechanisms. Data format issues must be addressed as one device may offer string-type values while another is floating point. Finally, a reliable platform must be used.'
There are a number of approaches to integrating various control technologies. These are increasingly factory-proven solutions. In most applications, this is far superior to the old way of trying to tie separate controls together in a limited way with RS-232 or similar proprietary communication. Look also at the blurring lines of distinction among motion control, sequential logic control, process control, data acquisition, and HMI. Choices of architectures, programming tools, and products continue to multiply even in the face of some industry consolidation. Choose your weapon wisely.
PLCopen, IEC 61131-3 address motion integration
Changing consumer needs require changes in manufacturing like smaller batches, packaging differentiation, and product differentiation. On top of this, manufacturers must become ever more efficient.
Motion integration issues, along with maintainability and connectivity to automation, are very important to manufacturing success. Unfortunately, the motion control market is very fragmented, encompassing a wide variety of incompatible systems and solutions. In practice this means that architecture and software tools for development, installation, and maintenance will differ widely. This incompatibility induces considerable costs.
This changing environment, combined with the 'classical' PLC environment integrating more motion control, created a basis for standardization. This vision is shared among many suppliers as part of the PLCopen organization-and resulted in the definition of a PLCopen Motion Control Profile. It is a standard in the programming environment, to harmonize access of motion control functionality across platforms.
This standardization is accomplished through defining libraries of reusable components. The result is less hardware dependent programming, increased reusability of application software, reduced costs for training and support, and applications scalable across different levels of control. The libraries are based on IEC 61131-3 Function Blocks. They standardize interfaces and functionality allowing implementation on multiple platforms. Data hiding and encapsulation further enable use on different architectures, for instance, distributed control. It is open to existing and future technologies. Overall, the standardization is expected to cover around 80% of the motion control market.
The PLCopen task force has defined the following goals for the definition of motion control function blocks:
Simplicity or ease of use for installation & maintenance;
Efficiency in the number of Function Blocks as well as efficiency in design;
Consistency by conforming to IEC 61131-3 standard;
Universality, that is, hardware independent;
Flexibility for future extensions and range of application; and
Function Blocks are the software equivalent of electronic chips. They contain inputs and outputs, with the associated names and data types. Each Function Block contains code to give functionality, and map it to the corresponding environment. The user only sees the interface. The code is hidden-this is called data encapsulation and hiding. A small example of two Function Blocks operating on the same axis is shown in the graphic. Access to the axis is via the Axis_Ref. This is a data-structure describing the drive. All Function Blocks have access to this reference, so the user does not have to know all the internals of the drive or architecture used.
A set of single axis Function Blocks has been defined. The set comprises:
MC_MoveAbsolute; Relative; Additive; Superimposed;
MC_ReadActualPosition; Read Status; ReadAxisError; Reset
MC_ReadParameter; ReadBool Parameter; WriteParameter;
MC_PositionProfile; VelocityProfile; AccelerationProfile
MC_Home; Power; Stop In addition the task force has defined a small set of blocks for synchronized multi-axis support:
MC_Cam Tableselect; Cam In; Cam Out
MC_Gear In; Gear Out
Standardization in the fragmented motion control area is crucial. The PLCopen Motion Control Profile is one such standard.
Information supplied by Jeremy Pollard, North American representative of PLCopen