Industrial Wireless Local Area Networks (IWLANs) allow machines to be operated without con- tact. Not only does wire- less technology put an end to elaborate wiring, it improves production processes.
Z vvvtt … zvvvtt … — In the Emden Volks- wagen plant in northeastern Germany, a worker bolts a drive assembly together. He connects the engine block and gearbox, which will eventually be equipped with drive shafts, spring struts and other components to form a functional unit that is then installed in a car body. The man lets go of his power tool, which gently moves back into its original posi- tion. A message in a green font is glowing on the monitor behind him. It says: “Wait for new vehicle.” In the lower portion of the display, in- formation appears, such as the vehicle number and engine type. And a moment later the next engine block is thrust forward.
Until recently, workers at the Emden plant had to use a variety of systems. These ranged
from hand-held screwdrivers to pneumatic types that hung from suspension rails and had to be pulled to the work position each time — a very effort-intensive method of fitting screws and assembling workpieces. In late 2004, how- ever, VW took the production ramp-up of its new Passat series as an occasion to upgrade the plant’s assembly line technology. And since May 2005, the plant has been equipped with IWLAN industrial wireless radio technology, which Siemens optimized for industrial uses. As a result, mobile screw-fitting stations are now controlled through the wireless network, and all the data is transmitted via radio as well.
“We wanted a technology with a future — one that would protect our investment,” says Christian Land from VW’s Plant Engineering
At the Volkswagen plant in Emden, Germany, an IWLAN wireless net- work has significantly improved processes. Machines automatically move to the right positions; dis- plays convey information about work steps (left); and the system ensures that pieces are correctly bolted together (right).
unit. “IWLAN enables us to transmit data reli- ably and securely. It has enabled us to cut costs and increase precision.” Up to now, WLAN has primarily been thought of as a technology for home and office communications. The tech- nology achieves data transfer rates of up to 11 megabits per second at frequencies of 2.4 GHz and up to 54 megabits per second at 5 GHz. In principle, WLAN is suitable for industry — with some modifications.
In a traditional WLAN, for example, data packets are transmitted to a wait queue when there are high volumes of data. On an indus- trial production line, however, this could mean that a roller in a steel mill might fail to receive a control command at the right time and would perhaps rotate at the wrong speed, or that a driverless forklift would continue to move because it didn’t get a stop command at the proper moment.
Siemens therefore developed IWLAN (Pic- tures of the Future, Fall 2004, p. 22). “In an IWLAN environment, data throughput can be reserved and the system is designed with re- dundant antennas,” says Ewald Kuk, head of product marketing for SIMATIC NET at Automa- tion and Drives. “That’s how we achieve the re- quired level of dependability.” The foundation for this is a software technique developed and patented by Siemens. Additional functions like the monitoring of mobile subscribers, an error
the wireless connection. Only if the bolt joints are correct does the mobile station automati- cally move back to its initial position. If they are faulty, the operator sees this on the mon- itor and can immediately correct the mistake or manually note the incorrect bolt joint in the system and fix it later. But improved manu- facturing quality and better ergonomics aren’t the only advantages of this system; workers have shorter distances to cover, because in- structions, manuals and information are all conveyed online.
‘from the office to the shop floor.’ Our product portfolio offers a universal infrastructure for factories and their administration,” says Kuk.
Standardized for Office and Factory. Users want a universal system of communica- tion with only one network and simple diag- nostic options. They expect this network to in- corporate the benefits of robust industrial field bus systems like Profibus as well as Inter- net communication (TCP/IP) with the kinds of features used in offices.
Another interesting IWLAN application is monorail conveyors. These systems, which transport assembly parts, are typically con- trolled via sliding contacts. But because con- tact is mechanical, their level of abrasion is very high — a factor that increases mainte- nance costs. “A simple installation of non-con- tact technology requires fewer cables than a
The solution is the Profinet standard, which is based on Industrial Ethernet. Siemens is al- ready using the latter to manage data commu- nications in automation projects. Profinet en- ables continuity and uniformity at all levels and in all applications. It provides real-time capabil- ity, installation and network technology that is suitable for use in industry, the integration of
message in the event of a lost connection and the creation of redundant paths on the two fre- quencies mentioned above provide extra relia- bility. Applications include wireless links to con- trol systems, mobile diagnostics and service equipment, and driverless transport systems.
VW has based its IWLAN on “RCoax” tech- nology, which works as follows: The screw-fit- ting station is driven by a motor along a rail, and a cable connected to an access node for IWLAN is run along the assembly line. A so- called “leaky waveguide” serves as an an- tenna. A signal of a defined strength escapes through slits at regular points on the wave- guide’s sheathing and forms a limited relay section — thus avoiding reflections and keep- ing electromagnetic radiation as low as possi- ble.
Through a radio module, the screw-fitting station and the workpiece carrier send their positions to the system control unit. The latter compares the reported values, determines the advance increment needed and radios the control commands to the screw-fitting sta-
An IWLAN can link up systems in a wireless network and transfer large amounts of data.
tion, which then adjusts its position accord- ingly.
contact line. That means low installation costs, less wear and tear, and reduced main- tenance. And instead of 500 kilobits per sec- ond in the case of contact lines, we now have a bandwidth of several megabits per second. That makes it possible to quickly transmit not only the usual status information but also complete operations records and production data,” says Kuk.
That makes things easier for workers, who no longer have to pull the heavy suspension gear into position. Nor do they have to enter workpiece data into the system or set the torque. The engine block number and current torque are automatically radioed by the con- trol unit.
Good-bye Mistakes. Thanks to these wire- less data transmissions, work can be con- trolled more efficiently. Work steps, for in- stance, are displayed on monitors. In addition, the torque with which a screw or bolt is tightened is checked. A comparison is made with target values from a database via
“In the IWLAN area, Siemens is at least a year ahead of the competition,” Kuk says. But the company’s specialists are not resting on their laurels. Instead, they are striving to cre- ate a global communication system that ex- tends from the office to the manufacturing line. “Together with Siemens Communica- tions, we’ve developed a concept we call
distributed equipment on the shop floor, high- precision time synchronization for demanding control tasks, simple network administration and protection against unauthorized access and data manipulation.
Profinet has won over Maval, a company headquartered in Valencia, Spain. The com- pany provides automation solutions for a num- ber of large bakeries serving a supermarket chain and wants to offer its customers a new, universal solution at low cost.
Maval favors Profinet because it promises high system availability, a brief start-up period and an uninterrupted production process. It can also be integrated into existing infrastruc- tures without difficulty.
Moreover, the supermarket chain profits from the solution as well as the bakeries. When business ends for the day, employees can reg- ister the remaining stock simply by using a bar code scanner. The information is sent to a server, which calculates how much of a partic- ular product is now required and sends a cor- responding order to the bread factory. A man- ual order, by fax for instance, is no longer needed. The supermarket therefore saves time and avoids errors.
“We offer an integrated system from the shelf to the machines,” says Maval expert Samuel Alonso Pulido. “In the past, different technologies were needed for different areas; now everything uses a single medium with- out any discontinuities.” ■ Evdoxia Tsakiridou
Pictures of the Future | Fall 2005