The demands on modern automobile production are high. The product must be accompanied by detailed data for quality assurance and documentation purposes in almost all production steps. Product processes of supplier parts, modules and subsystems must have maximum reproducibility, and be traceable throughout the process. The clear identification of the supplied modules is extremely important especially in the production of different types of vehicles on one line. Insensitivity to heat and soiling by dust, oil or water is a prerequisite for use of rewritable data memories in the harsh production environment of the automotive industry. Reusable information carrier installed directly on the workpiece or workpiece holder, which can be written and read without contact have proven excellent for these jobs.
Whale of a technology
Siemens provides identification and tracking systems, which are offered under the name of Moby. The robust radio frequency, identification (RFID) systems are available in different versions for a range of tasks - from low-cost data media as a barcode replacement through ID systems for goods logistics to heat-resistant data media for the automotive industry.
Moby, with its writable/readable data memories, has decisive advantages over fixed code systems such as identification by barcode. With fixed code systems an object can merely be identified because all information above and beyond this is stored in a central database. The intelligent Moby identification system on the other hand saves the data on mobile data carriers directly on the object. The object can therefore continue being processed even when the network is overloaded; fails or the central server is unavailable. Another advantage is that subsystems can be started independently of the central data storage. Since setting parameters for processing machines or production controllers can also be saved in the mobile data memories, Moby also helps to minimise the tooling times in the process.
Safe and robust
Every Moby system is basically made up of three components: the mobile data memory (MDS), the write/read device (SLG), and the interface module (ASM). The mobile data memory is mounted directly on the object to be identified. Depending on the type of application, Moby provides different data media-from the simple, low-cost smart labels to the extremely robust memory media for industrial applications. Their strength lies not only in the high data security, but also in the excellent high degree of protection against ambient conditions such as soiling, temperature fluctuations, washing, or exposure to shock.
Up to 32 kb of data can be saved, read, and added to individually as required at the various workstations and production stations. High-temperature data memories are available especially for use in paint shops. The transmission frequency of 1.81 MHz, 13.56 MHz or 2.5 GHz makes Moby largely insensitive to electromagnetic faults. Even extreme ambient influences have no effect on the systems. The information - apart from a few exceptions the energy - is transferred from the writer/ reader, without contact by radio or inductively to the mobile data memory or read out of the memory. The data memory can move past the writer/reader at up to 20 meter per second. The transmission remains uninfluenced by dust and moisture, and non-metallic constructions such as Plexiglas panes or plastic covers. The write/read device can be connected directly to a PC or the interface module by a serial interface.
The interface module is the port to the world of automation and makes sure that the write/read device can communicate with Simatic and Sinumerik controllers and can be integrated in Profibus and some Moby systems in other networks such as Ethernet. The interface module only needs to be supplied with the appropriate parameters once and is then able to handle the data traffic with the mobile data memories independently. Since Moby has no moving parts and operates without contact, the system is free from wear, low maintenance and very robust.
Made for automotive
Of the Moby product family, Moby I is used mainly in the automotive industry. Moby is distinguished by a very high immunity to interference from electromagnetic fields, resistance to soiling and temperature fluctuations. Up to 32 kb are transmitted at a net rate of 0.8 milliseconds per byte. Moby has been equipped with a FRAM memory without batteries for a few years now. And data memories, which can easily be operated in temperatures up to 220 degree C are available for this system especially for the identification of skids (body part carriers).
The new RF identification system Moby P is designed for use in small assembly lines and for production automation. It is suitable both for simple and complex applications and has a convincing price/performance ratio. A fast and reliable data transmission offers short cycle times with high data security. The low cost IQ-Sense interface technique via a two-wire line is available for communication with the Simatic. Apart from the system diagnostics, this allows individual write/read devices to be replaced during operation.
A particularly fascinating solution was chosen in the section of production, in which the powertrain of the new Passat is assembled. Here the engine block and gear have to be fitted with the drive shafts and springs and all peripheral engine components so that a functional drivetrain is finally produced which is ready for installation in the body.
Until now the individual components of the powertrain unit had to be mounted using various nutrunning systems - from handheld EC nutrunners to pneumatic nutrunners - which hung down from overhead rails and had to be pulled to the respective working position by the workers. As assembly technique, it not only demanded constant physical effort but also caused a lot of noise. Besides there was no way of ensuring and documenting the correct execution of the screw tightening process.
Totally new, mobile EC nutrunning stations have now replaced the former nutrunning systems. They not only relieve the worker physically. They also produce a lot less noise and introduce a previously unknown intelligence, which ensures a consistent quality level with a high repetitive accuracy. Every nutrunning station is designed as a suspended unit, which runs in an aluminium section rail and is driven within the assembly station motor. The feed is synchronized exactly with the movement of the push-pallet so that the workstation automatically follows the position of the workpiece carrier on which the drive unit is positioned. At the end of the line of an assembly station the nutrunning station automatically returns to its home position and is positioned exactly parallel to the next workpiece.
The exact position of the nutrunning station is defined by perforated rails running parallel to the carrier section, which supply an absolute path-actual value. The S7- 200 of the individual nutrunning stations communicates with the plant PLC over a radio line consisting of a leak wave conductor and radio modems. The path-actual value of the skid conveyor is synchronised with the nutrunning station among other things and the drive is controlled accordingly. The communication between the Siemens frequency converter Sinamics and the scanning head on the perforated rail of the nutrunning station takes place via RS485 interfaces. A manual forward and reverse of the nutrunner unit, which the worker can control with buttons, is also possible within the respective workstation in addition to the fully automatic operating mode.
The nutrunning station runs on four rollers. It is driven by a Vulkolan wheel, which is pressed against the carrier rail by a spring. If a resistance of more than 150 N occurs - for example due to overloading or collision - the preliminary drive of the assembly is stopped automatically. The frictional connection between the motor and the drive wheel is made by an electromagnetic clutch, which automatically breaks the connection in the event of a power failure or at the press of a button to stop the screwer station from moving.
Visual user guidance
Every nutrunning station incorporates a PC on which the program for guiding the worker and controlling the screw tightening process. A color LCD with touchscreen forms the user interface. At the beginning of the work process the drive unit to be processed appears on the display (different motor-gear combinations are mounted in mixed mode). As soon as a joint has been made correctly, the color of the screw concerned changes to green. If, on the other hand, the system has registered a NOK status, the joint is marked red and an appropriate warning is displayed.