Pictures of the Future      Fall 2005

Wireless Wizardry

Zvvvtt … zvvvtt …—In the Emden Volkswagen 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 position. 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, information 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, however, 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 unit. "IWLAN enables us to transmit data reliably 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 technology achieves data transfer rates of up to 11 Mbit/s at frequencies of 2.4 GHz and up to 54 Mbit/s 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 industrial 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 (see Pictures of the Future, Fall 2004,  "WLAN and Ethernet"). "In an IWLAN environment, data throughput can be reserved and the system is designed with redundant antennas," says Ewald Kuk, head of product marketing for SIMATIC NET at Automation and Drives. "That’s how we achieve the required 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 message in the event of a lost connection and the creation of redundant paths on the two frequencies mentioned above provide extra reliability. Applications include wireless links to control systems, mobile diagnostics and service equipment, and driverless transport systems. VW has based its IWLAN on "RCoax" technology, which works as follows: The screw-fitting 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 socalled "leaky waveguide" serves as an antenna. A signal of a defined strength escapes through slits at regular points on the waveguide’s sheathing and forms a limited relay section—thus avoiding reflections and keeping electromagnetic radiation as low as possible. 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 station, which then adjusts its position accordingly.

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 control unit.

Good-bye Mistakes. Thanks to these wireless data transmissions, work can be controlled more efficiently. Work steps, for instance, 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 wireless connection. Only if the bolt joints are correct does the mobile station automatically move back to its initial position. If they are faulty, the operator sees this on the monitor and can immediately correct the mistake or manually note the incorrect bolt joint in the system and fix it later. But improved manufacturing quality and better ergonomics aren’t the only advantages of this system; workers have shorter distances to cover, because instructions, manuals and information are all conveyed online.

Another interesting IWLAN application is monorail conveyors. These systems, which transport assembly parts, are typically controlled via sliding contacts. But because contact is mechanical, their level of abrasion is very high—a factor that increases maintenance costs. "A simple installation of non-contact technology requires fewer cables than a contact line. That means low installation costs, less wear and tear, and reduced maintenance. And instead of 500 kbit/s 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.

"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 create a global communication system that extends from the office to the manufacturing line. "Together with Siemens Communications, we’ve developed a concept we call 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 communication with only one network and simple diagnostic options. They expect this network to incorporate the benefits of robust industrial field bus systems like Profibus as well as Internet communication (TCP/IP) with the kinds of features used in offices.

The solution is the Profinet standard, which is based on Industrial Ethernet. Siemens is already using the latter to manage data communications in automation projects. Profinet enables continuity and uniformity at all levels and in all applications. It provides real-time capability, installation and network technology that is suitable for use in industry, the integration of distributed equipment on the shop floor, highprecision 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 company provides automation solutions for a number 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 infrastructures without difficulty.

Moreover, the supermarket chain profits from the solution as well as the bakeries. When business ends for the day, employees can register the remaining stock simply by using a bar code scanner. The information is sent to a server, which calculates how much of a particular product is now required and sends a corresponding order to the bread factory. A manual 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 without any discontinuities."
                                                                                                     Evdoxia Tsakiridou