Crane interface: main trolley continued…
The latest developments on energy and data transmission systems for rope-driven main trolleys are concentrated on the alternative use of conductor bar systems. Besides the compact construction and the low-priced systems engineering, the sturdy conductor bars (well-approved in crane manufacturing) are an advantage. For the equally necessary installation of the electronic data transmission, it is important that it meets the technical demands and standards of the crane operator in terms of transmission speed, performance and transmission security. A final breakthrough of this technique may only be expected after the industrial certification of radio data transmission systems.
In comparison to rope-driven main trolleys, self-driven (machine-house) crane main trolleys have a higher power consumption and a larger amount of data communication at the crane interfaces. The cable package of approx. 50 cables is much larger and hence much heavier (< 50 kg/m). The maximum main trolley speed comes to 250 m/min on the Super-Post-Panamax- STS-CC.
The constructive layout of energy and data transmission systems, in consideration of the much higher static and dynamic loads, require extraordinary diligence in project planning and systems constructed in accordance with the latest findings. For the preferred application of motorised heavy duty cable trolley systems this means that, besides the large-dimensioned chassis, two to five cable trolley drives will be installed at various positions in the system.
To ensure an optimum arrangement of the large number of cables, the state-of-the art solution is now multi-layered, and hence very compact, cable trolleys. This allows for fixing round cables with vast deviations in diameters onto the cable supports, gently and without force. This measure will help to achieve extended durability of the cost-intensive round cables (see Figure 1).
To reduce masses in motion, a consequent light-weight construction using aluminium components is becoming increasingly accepted as a fundamental element of modern cable trolley technique. Gear motors as well as a drive control for cable trolleys integrated into the crane control are decisive factors and provide maximum operational reliability. Stabilisers installed in the cable loops, such as cable clamps or guide rings help to additionally increase the operational reliability of the cable trolley systems. A decisive factor, in comparison to the energy guiding chain systems, is furthermore that noise emission is much lower with the application of standardised rollers with plastic tires as well as large-volume cellular buffers on the trolleys.
In view of the increased risk of failure, energy guiding chains are currently only used in individual cases for the power supply of self-driven crane main trolleys. Due to the extensive large cable package and the high travel speeds, dynamic processes on the long travel distances require increasingly more attention the longer they are in operation. To minimise the width of the energy guiding chain on these cable packages, round cables are often arranged in multiple layers. The resulting additional mechanical loads on the copper wire and optical fiber cables must be compensated by additional constructive measures.
The high weights and dynamic influences again require the installation of reinforced, large-dimensioned energy guiding chains with support rollers. With the additional installation of powermeasurement sensors as well as floating towing arm connections, it is however possible to improve the reliability and availability of the energy guiding chain. Besides the factor of increasing costs, the crane operator also has to face the risk of energy guiding chain failure. Breakage of individual chain links can cause the complete shutdown of the energy and data transmission and result in longer downtime of the complete STS-CC crane.
Even small chains produce quite a lot of noise, but this is even worse on heavy energy guiding chains. It can be twice as much compared to cable trolley systems. Extensive constructive measures are therefore urgently required. Another long term disadvantage is the difficulty to control mechanical wear of the wear-pairing chain latch to guide the channel. With the usual life expectancy in crane engineering at more than 10 years, it is very important to enforce measures to reduce abrasion in the future.
On STS-CC cranes with 2-main trolley technology, the complex power supply to the auxiliary trolley is basically realised by energy guiding chains, due to the short travel distance and the restricted construction site. Again rollersupported energy guiding chains are favoured, analogous to the applications on the RMG-CC, to reduce wear that might be produced due to frequent travel movements.
Interface main trolley: load carrying equipment
The energy and data transmission between the crane main trolley and spreader in case of high hoist speeds of up to 250 m/min and hoist distances of 75 m is preferably realised by spiral or singlelayer cylindrical winding motor cable reels. The alternative use of energy guiding chains is currently restricted to minor hoists which might be given on storage yard cranes.
High load application and large hoist distances of STS-CC require extensive technical measures for stabilisation of the spreader operation. The high mechanical loads that might occur on hoist and depositing movements are absorbed by specially designed round cables, already partly integrated with optical fibers. To assure their permanent function and long lifetime, the reel drive is combined with a frequency inverter control with special software. In spite of this, due to the large, free suspended cable length, the cables are subject to stronger wear on this application. To allow an immediate replacement, the cables on the reel system and on the spreader are equipped with quickconnection elements. Besides these rather passive measures, new cable types and qualities are available, as well as new control possibilities which offer gentler handling of the cables, resulting in a much longer lifetime.
A decisive factor for the long lifetime of the mechanically strong loaded round cables is a properly operating mechanical cable damping. The extreme accelerations and impacts affecting the spreader require a very robust and soft damping of the cable movements (see Figure 2).