For a manufacturer of plumbing and heating systems, safety is one of the main concerns when purchasing a plant. This is also true in the development of a fully automatic warehouse and crane system and optimal use of the confined space of the warehouse area. Based on a fail-safe communication solution, raw materials are today transported from the warehouse to the corresponding processing machines wirelessly and without human intervention.
The courage to break new ground, a close eye on the market, and the will to constantly improve are decisive factors in the development of new ideas at Viega GmbH & Co. KG. The high innovative strength of the family-owned company, founded in 1899, is reflected in its current range of around 16,000 products for heating and gas installation technology, pipeline systems, and front-wall mounting, flushing, and drainage technology. With more than 3,000 employees and an international clientele, Viega is one of the most successful system providers in building services. In addition, it offers products for industrial plants, the utilities sector, and the shipbuilding industry, which are manufactured at the company headquarters in Attendorn and at three other German locations - in quality "Made in Germany". In 2005, the company established a site in McPherson (Kansas, USA) to be able to supply the American market with special systems.
For the production of pipe connection technology, the company required the construction and commissioning of a new automatic machine rack system at its Thuringia location. The world market leader in molding technology was supported by a regional machine builder/plant constructor from the region, TSK Automation GmbH, in cooperation with the crane builder Kranservice HerZ. TSK implements projects in the field of automation and control technology for industry and public-sector clients. HerZ Kranservice e. K., originally a crane service company, now also builds cranes and offers especially innovative solutions.
To meet the enormous growth in the stainless steel sector, the new plant was to be designed to increase productivity and create valuable production space for further processing stations. The intended benefits of improved warehouse management included rapid availability of pipe bundles within two to three minutes. Viega was looking for a solution to ensure secure data transmission and high system availability while avoiding contact wires, which require maintenance and can be adversely affected by contamination. The minimal space available for the planned warehouse would have to be used optimally. In addition, the strong market demand made an extremely short lead time of seven months necessary.
Problem-free interaction between warehouse and crane
The central element of the solution is a movable rack system with dimensions of 20 x 50 m2 and a height of almost 7 m, consisting of several mobile rack units and four permanently installed storage units. A mobile rack unit consists of two racks, so that hundreds of pipe bundles of different lengths can be stored. Whenever needed, the mobile rack units can open an aisle into which the crane can enter automatically during storage and retrieval.
The benefits of this solution are only fully exploited by using the masterful construction of the Kranservice HerZ scissor lift crane. To gain more storage space at a relatively low ceiling height, the rotary and scissor lift of the crane is placed between two bridge supports that are located farther apart. The rack units of the warehouse could therefore be built about 2 m higher than in conventional design, making eight additional storage locations available per unit. The design of the slew ring enables the load to be transported horizontally along the bridge girder and vertically using the scissor lift; the rotational movement is possible only when the scissor lift is retracted. The entire crane assembly travels on rails down the 100-meter length of the hall. The absolute path coding allows the precise positioning of the crane in all axes. Its rotary motion allows the cantilever racks to be loaded on two sides. Another special feature of the crane is its extendable telescopic forks, which enable it to also reach the rear storage spaces. All of these innovations, compared to previous storage systems at Viega, contribute to the efficient utilization of the limited warehouse area. Mr. Günther is enthusiastic: "By telescoping we were able to install an additional double-sided rack unit in the same floorspace. The travel area of the crane is smaller, this saves even more space."
Wireless communication via IWLAN
Communication between warehouse management, warehouse control, and the controller on the crane was implemented wirelessly via IWLAN (Industrial Wireless LAN). A 95-meter-long RCoax leaky feeder cable runs parallel to the crane's traversing path, forming a defined radio field that is optimized spatially around the leaky feeder cable. A Scalance W788-1PRO access point from the Siemens Simatic Net product range is installed via a power splitter in a central, stationary position. The splitter - used primarily where tracks or monorails diverge - increases the maximum segment length through central supply. The wireless counterpart to the stationary access point is a Scalance W746-1PRO client module on the crane. Significant IWLAN product features such as robustness, IP65 protection, vibration resistance, and a temperature range from -20 °C to +60 °C, ensure a reliable wireless connection and trouble-free operation of industrial applications. Since no contact wires are used, the application is not subject to mechanical wear and tear, and it is maintenance-free. The 5 GHz band according to the standard 802.11a was chosen as radio frequency to minimize radio interference due to metallic objects such as steel beams or machines, as well as interference from sources such as walkie-talkies, mobile phones, wireless remote controls, and electric motors.
The crane controller, which was implemented to the largest possible extent with technology from Siemens, is located in a walk-in cabinet on the crane. On the crane, the Simatic S7-300F series fail-safe CPU controls the connected Simatic ET200M I/O station, whose standard I/O modules also integrate fail-safe modules. The controller can be manually operated using the installed HMI panel, or from the floor via IWLAN. The narrow racks, the thin rack supports, and the weight of the pipe bundles presented especially complex tasks for crane construction and programming. Because the steel beams can flex up to 2 cm and expand due to heat and cold (winter/summer), absolutely correct values can never be expected.
All machinery orders are managed using the warehouse management system (based on the WinCC visualization system, also from Siemens), which has a direct interface to the higher-level SAP-based enterprise resource planning system. As soon as the operator of a machine needs new material for a specific job, he requests this using one of the remote operating terminals in the vicinity of the warehouse. The warehouse is basically represented twice: as a quantity and value image in SAP, and as a detailed batch and bundle image in warehouse management. In SAP it is possible to see how many tons of material are available at what price in the warehouse. At the same time, the warehouse management system provides information about how much of a material can be found at which location and how many bundles can still be retrieved. In this way, the warehouse crane automatically finds the requested material and can bring it directly to the requesting machine. Finally, the operator must transfer the material in "confirmed operation", i.e. for safety reasons he must manually approve the transfer movement.
Secure data traffic with Profinet, Profisafe, and IWLAN
The safety of personnel, materials, and machinery plays a crucial role in the design of a complete system consisting of fully automatic units such as racks, cranes, controls, and load transporters up to production machines; and possibly also a number of automated processing stations on different machines. In the event of danger, the system must be immediately and safely stopped, for example, as soon as a person enters the security perimeter of the warehouse, moving parts get caught on the crane hook, or the emergency-stop switch of a machine is operated.
The combination of Profinet, Profisafe, and IWLAN ensures secure and reliable data traffic, i.e. the safety-related Profinet protocol is transferred wirelessly. Integrated diagnostic options and monitoring systems help identify any errors quickly and reduce downtime. Profisafe is the international communication standard according to IEC 61508 that permits both standard and safety-related communication on one bus. This allows tremendous savings to be achieved in installations and engineering. Additional radio links for transmitting emergency stop signals are not required. The safety-related signals are transmitted in real time and have highest priority over other communication signals. For each transmission path there is a time monitor that triggers in the event of a failure or when a specified delay time is exceeded. Profinet implements this by using deterministic, cyclic data traffic. These deterministic features must, of course, be retained during the radio connection. For example, to achieve an emergency stop function reaction time of approx. 60 ms, it is necessary that the cycle time for data transmission via the radio link does not exceed 16 ms.
In addition to the reliability of the transmission times, data security also plays an important role. This point is more apparent with wireless networks than with wired ones. Data encryption and access control (authentication) are important parts of the security concept. IWLAN relies on the established mechanisms in the IEEE 802.11i standard, which integrates the most up-to-date procedures such as WPA2 (Wi-Fi Protected Access 2) and IEEE 802.1x. This ensures the security of sensitive company data, and thus operational safety.
