Industrial Networks Work In Fields, on Buses
As digital industrial networks weave their way through applications it's hard for those applying the technologies to think about working without them. For operators, however, networks are best appreciated when they go unnoticed…in the oil field (Control Engineering, July 1998, p. 114), on the city bus, and in manufacturing and processing.
As digital industrial networks weave their way through applications it's hard for those applying the technologies to think about working without them. For operators, however, networks are best appreciated when they go unnoticed…in the oil field ( Control Engineering , July 1998, p. 114), on the city bus, and in manufacturing and processing.
Digital industrial networks are expanding into other applications. For example, the WorldFIP (Nancy, France) network reached down into device-level networks earlier this year. Initial sales of the Device WorldFIP Development Kit were reported strong by the organization.
Echelon (Santa Clara, Calif.) and Cisco Systems (San Jose, Calif.) agreed in June to jointly develop technology to link Echelon control networks with Internet Protocol (IP)-based data networks to escape "expensive leased line phone networks and increase network management visibility into critical business process control systems." C3 Communications—an Austin, Texas-based subsidiary of Central & Southwest electric utility—is using LonWorks networks and Cisco products in metering automation and telecommunications services.
CANopen fieldbus has jumped on the "bus."
Bus manufacturer Neoplan (Stuttgart, Germany) has developed a hybrid bus for public transportation. CANopen communicates to two servo controllers to drive the wheels, one servo controller for steering, and one frequency controller for the battery.
Additional Profibus, CANopen, ControlNet, Fieldbus Foundation, and Interbus application notes follow. For more about "Networked I/O Stategies…" see the adjacent Year of the Network article.
Only a few of the dozens of networks are mentioned here, but we're interested in hearing about others, especially use of Ethernet for manufacturing and process control. E-mail ideas to email@example.com .
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Profibus makes Opels in Bochum
The Bochum, Germany, production line of Adam Opel AG turns out 1,200 Opel Astra cars daily. Investments of hundreds of millions of German marks have resulted in improvements in environmental production, workplace ergonomics, and productivity.
In 1994 Opel decided to standardize on Profibus open communications at the field level in all European plants for bodyshell production. Now Profibus is being used successfully in most areas, including the press shop through bodyshell production, paint shop, and final assembly. Cost savings and flexiblity using Profibus in Bochum means the digital industrial network will now be installed in other factories of the European Opel/Vauxhall conglomerate.
Press shop, bodyshell
The Bochum site uses over 22,000 tons of steel per month; Opel is Germany's second largest steel consumer. Modern information technology controls supply of steel sheets to Astra production lines. Computers continuously monitor material consumption and coordinate the just-in-time supplies online.
Applying up to 3,200 tons of pressure each, the two modern transfer press lines at Opel's production plant shape as many as 900 fenders, doors, engine hoods, and side panels for Astra models per hour. Sheet steel components for all five European Astra production lines are produced in Bochum; press lines work nearly round-the-clock. Changing dies weighing several tons, which can take several hours in conventional plants, can be done automatically within minutes, using a system of more than 100 electric motors, hydraulic valves, and actuators. Motors and valves from varied manufacturers connect to the central PLC controller through Profibus. Two wires transfer data, parameters, and control commands. Profibus reduces downtime and increases flexibility.
Opel engineers have also installed high-tech systems in the body shop, including approximately 190 computer-controlled robots that do 98% of welding operations. Bochum also claims to be the first automotive plant to use advanced laser technology in volume production scale. A high-energy light beam joins the frame to the outer shell of the Astra engine hood, improving quality. In the fully automated body assembly, robots spot weld 2,000 points.
The robots can rapidly switch among sheet-metal components for the three and five-door Astra hatchback variants, the Caravan, and Cabrio convertible. Hundreds of automated electrical welds take place per minute. Accordingly, the fast control components for short cycle times also must be immune to high electromagnetic interference.
Opel uses multiprocessor PLCs from Bosch and welding robots from GE Fanuc together with a wide spectrum of peripheral components such as Siemens I/O devices, Festo valve blocks, and SWAC operating panels, which all communicate with the PLC through Profibus-DP. Profibus-DP operates here at 12 Mbit/sec, allowing bus cycle times of less than 1 msec.
Profibus-FMS is used for communication between the PLCs at the cell level. And Profibus-DP connects decentral peripherals such as I/O devices, motor drives, valves, and operating panels to the PLC at the field level. Computer integrated manufacturing (CIM) based on open communication systems has proved itself many times in online operation.
Water-based paint shop
After robots and welding machines have assembled the sheet steel components for the Astra bodyshell, vehicles journey 5.5 km through the modern paint shop. Bochum uses water-based paints, rather than conventional organic solvents. Application of the various paint layers takes place largely automatically.
When the door, cockpit, and engine modules are finished, a conveyor system delivers them directly to the final assembly line. The material feed systems are all controlled fully automatic using PLCs from Schneider Automation and Siemens. All peripherals such as I/O devices, motor drives, and operating panels are installed directly adjacent to the assembly line and connected to the PLCs with Profibus-DP. Control cabinets often only contain the PLCs themselves.
The network contains several kilometers of cable; about 300 Profibus-DP devices from a range of manufacturers are used in the final assembly area. To cope with the large distances, fiber-optic cable is also used for Profibus networks at some places. Decentralization has reduced cabling costs considerably. Use of Profibus facilitated recent modernization of the final assembly area in six weeks.
Dipl.-Ing. Michael Volz is operations manager for Profibus International
Paper mill installs Foundation fieldbus
Avenor (Gatineau, Quebec, Canada) recently completed startup of a FOUNDATION fieldbus installation using the new Fisher-Rosemount (Austin, Tex.) Fieldbus PlantWeb Builder suite of products.
Avenor's installation is the first use of device-based PID control in the pulp and paper industry. Four PID control loops, using common function block programming techniques, are distributed amongst transmitters, control valves, and the DeltaV control system. Pulper level control resides in the level transmitter; pulper consistency and storage consistency controls reside in the control system; and storage pressure control resides in the digital control valve actuator/controller.
"Even though we are using a mix of conventional and fieldbus devices, the function block configuration features of DeltaV provide a consistent look-and-feel, regardless of the I/O type or the final destination of the control strategy," explains David St-Onge, Avenor's corporate manager of technology development for process automation.
Avenor's kraft pulper installation combines a mixture of FOUNDATION fieldbus certified and conventional products connected to a Fisher-Rosemount Systems DeltaV controller.
Certified fieldbus I/O devices include three Rosemount transmitters for level, one for pressure, and one for temperature; and five Fisher Controls FieldVue digital valve controllers mounted on a variety of manufacturers' control valves.
Conventional I/O devices include:
Pulp consistency transmitters (2);
Magnetic flowmeter (1);
Discrete inputs(15); and,
Discrete outputs (20).
"We made a strategic decision to implement FOUNDATION fieldbus because we believe the technology is promising and we wanted to learn how to put it to work for us," says mill manager Patrice Cayoutte.
"Level, temperature, and pressure transmitters were commissioned with the device-based control, and were communicating to the control system in a matter of minutes," reports Avenor process automation engineer Trung Phung, resulting in 90% less commissioning time.
Fisher-Rosemount's Performance Solutions group provided project design and engineering. Avenor and local Fisher-Rosemount representative Laurentide Controls shared site services for configuration, installation, and commissioning.
"We did a substantial portion of the work in-house to gain a better understanding of FOUNDATION fieldbus technology and how to use it in future applications," says Mr. St-Onge.
"We see fieldbus technologies potentially eliminating unscheduled downtime by using advanced features such as valve diagnostics," adds Mr. Cayoutte.
David Harrold, senior editorFieldbus Foundation
Interbus connects Ford in U.K.
The Ford plant in Dagenham, U.K., near London, produces four-cylinder diesel engines for mid-sized automobiles. Implementing Interbus to do so, provides benefits of digital communications; decentralized commands and message devices help eliminate switch cabinets.
Using Interbus in the application resulted in 25% space savings, 40% savings in installation costs, and 70% savings in the number of components used, according to Dipl.-Ing. Roland Bent, director, development and product marketing, Electronics, for Phoenix Contact (Blomberg, Germany).
The PC-based system uses Interbus to transmit signals from sensors and actuators through IP67 I/O modules. Ford uses an independent PC plug-in card that safely takes over machine control in case the "soft logic," the Microsoft Windows-based PC software, should crash.
The assembly line was manufacturered by Johann A. Krause Maschinenfabrik GmbH (Bremen, Germany).
CANopen operates robot controllers
Reis Robotics (Obernburg, Germany) a leading robot manufacturer, used the development of a completely new generation of robot controllers as an opportunity to introduce a distributed control structure based on CAN/CANopen. Important developments were simple integration of peripherals such as commercially purchased I/O modules and expandability.
Exxat Automation GmbH/stzp (Weingarten, Germany) installed and integrated the CANopen communications system and communication unit between the controller and the CAN system. The CAN-in-Automation (CiA) organization has specified the application profile CANopen for the serial bus system CAN in industrial automation. CANopen standardizes communications and device functionality. This permits use of devices from various manufacturers mutually compatible and exchangeable in CAN networks.
The control system consists of a robot controller (the RST) which communicates with peripherals through a communication unit over the CAN bus. Communication between the RST and communication unit previously used a VME bus system. But to avoid limiting the RST to any particular bus standard (e.g., VME, ISA, or PCI), the communication unit was implemented on an "M-module," since M-module carriers are available for all common bus systems. The communication unit contains two independent CAN lines.
To provide robot movement up to 12 servo amplifiers per CAN line can be connected, as well as several manual programming devices, and digital numeric controllers. Depending on system requirements, various I/O modules or other peripherals can also be connected. Likewise a CAN line can be used for communication between two RSTs. Maximum participants per CAN line is 63 nodes.
Based on CANopen, user data in the system are transmitted via Process Data Objects (PDOs) without any protocol overhead. All eight data bytes of a CAN object are available for user data. PDOs are categorized according to synchronous or asynchronous transmission. The CANopen master in the system supports both transmission types.
Controlling robot axes should be done synchronously; CANopen defines the mechanism. Servo drives are synchronized using a predefined synchronization object, i.e., data are sent or received quasi simultaneously by all devices after the synchronization object is received. Synchronous PDOs transmit nominal and control parameters to the servo drives. These send back the actual values to the CANopen master using synchronous PDOs as well. The servo amplifier here has its own synchronization object which is sent on a typical cycle time of every 8-12 msec. The RST can set the servo amplifier cycle time.
Connected devices are configured and parameterized by means of Service Data Objects (SDOs). An SDO transfer can also be used to download a program from the manual programming unit through the CAN bus into a flash memory in the servo amplifier.
Implementation of the CANopen master application, CANopen device software in the servo amplifiers, and manual programming units, is based on CANopen standard products from Exxat Automation. CANopen master software had to be expanded to support independent control of two CAN lines and the automatic baud rate search. The software core is the module for the CANopen communication protocol with the function interfaces for the application. Use of the dual ported random access memory and maintenance of the message cycle is part of the application.
Mark Cosmici and Thomas Müller are project managers and development engineers at Exxat Automation GmbH/stzp.
CAN/CANopen Benefits Robotics
Engineers at Exxat Automation, Weingarten, Germany, selected CAN/CANopen for robotics for:
Object-oriented message transmission;
Data transmission speed;
Low cost; and
Multimaster capability, since in larger robotics installations, multiple controllers need to communicate with each other simultaneously and independently.
Cahners Business Information Graphic with information from Exxat Automation.
ControlNet speeds carrot processing
Golden Valley Produce, llc, the nation's third largest carrot shipper, produces 600 tons of baby-cut carrots per day. Baby-cut carrots are the fastest growing of its products, require the highest levels of cleanliness and demand the most processing of any carrot. With these requirements in mind, Golden Valley Produce designed and built a $32 million, 178,000 square foot, state-of-the-art processing facility in Bakersfield, California.
The company needed an automation system that could meet the processing speed and quality requirements of the baby-cut carrot market. Each carrot must be pre-pealed, cut to length, and then packaged in bags weighing between 3 oz to 5 lb (85-2,268 g). The company chose to implement ControlNet, which is a real-time, 5 Mbit/sec industrial communications network.
ControlNet data delivery is based on a cyclic production algorithm. This means that Golden Valley Produce can select and schedule network update rates for each automation device on the network. For instance, the company can specify that data be delivered every 2 msec from one device located in a high-speed area of its process, and every 50 msec for a different device performing less time-critical functions. Further, ControlNet provides a means for prioritizing data delivery.
Time-critical information is sent during the scheduled portion of the Network Update Interval (NUI). Information that can be delivered without time constraints (such as configuration data) is sent during the unscheduled part of the NUI.
ControlNet Helps Process Carrots
Golden Valley engineers selected ControlNet for carrot processing because:
The Producer/Consumer network model allows the user to schedule delivery of each automation device on the network to accurately predict when data will be delivered;
Data delivery prioritization allows accurate prediction of data from each device in the system;
Networked devices can simultaneously access the same data from a single source; and,
Programming and I/O messaging can be done on the same link.
Cahners Business Information Graphic with data from ControlNet International
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