Safety rotary encoders from Siko solve civil engineering challenge

Heavy machinery in specialist civil engineering requires precise and reliable components in order to be able to perform the respective functions reliably. When specialist civil engineering company Stump-Franki Spezialtiefbau needed to reliably detect the positions of the elements attached to winches on its pile drivers, it turned to Siko for absolute rotary encoders as part of the safety concept.

Stump-Franki makes subsoil supports for heavy structures such as football stadiums, highway bridges, shopping centres or wind turbines. For this purpose, it manufactures its own pile drivers, which are used to construct foundation piles. The piles are used to divert loads of the structure into deeper layers.

The Franki pile driver has four winches installed at the top – including three Siko rotary encoders for position monitoring. In the front area is the so-called leader, a frame to which the pile or driving pipe made of steel is attached, which is open at the top and bottom. A plug of concrete and gravel is filled into the driving pipe, and with the pile driver, a solid block of steel, the plug, is compacted with very small blows.

The pile driver is a free-fall system. Once the plug is firmly wedged in the pipe by the blows, the drop height is increased and the driving pipe is brought to the final depth in the load-bearing subsoil. Then the plug is impacted with the pile driver. The so-called Franki foot is formed, which acts like a dowel. After the foot has been fabricated, the reinforcement cage is adjusted and plastic concrete is refilled, so that a continuous pile is formed. After the concrete has hardened and the pile head has been capped, the pile is ready to receive the load.

The four winches have different tasks during the driving process: a winch is used to pull the driving pipe, a second is used to drive the pile driver, a bucket for filling with concrete and gravel is attached to the third, and finally there is an auxiliary winch via which a reinforcement cage is lifted in place. Three of the four winches are each monitored with a rotary encoder from Siko, so that it is clear at all times where the pile driver, the auxiliary lift and the bucket are located.

The auxiliary rope is a safety design to ensure that the pile driver shuts off before a hook passes through a rope pulley. This rotary encoder therefore has an end position point beyond which the winch must not continue to rotate. The pipe pulling winch is the most sensitive area of the system; despite the hard blows into the driving pipe, the position must be known at all times.

The rotary encoders are integrated into an automatic control system, which permanently queries the positions and thus also controls the tracking of the cable.

The Siko rotary encoders meet the expectations of safety, precision and robustness that Stump-Franki requires for its applications. The WV58MR encoder used belongs to Siko’s ‘PURE.MOBILE sensor kit’, which was developed exclusively for the high requirements of mobile machines and commercial vehicles.