Research on the development trend of marine hydraulic crane

Jie-wei DU，Hong-ji ZHOU

School of Energy and Power Engineering，Wuhan University of Technology，Wuhan 430063，China

1.Introduction

In order to improve the barge loading and unloading cargo capacity of the ship in port，average dry cargo ship and bulk cargo ship are equipped with the hydraulic crane．Currently，electric crane and hydraulic crane are the most widely used ones．The explicit parameters comparison between electric crane and hydraulic crane is shown in Table 1．This kind of crane although has shortcomings of high precision machining，inconvenient fabrication and complex installation，it has advantages of light weight，small volume，easy operation，and stable work，by which it can realize step less speed regulation，absorb the impact of load and automatic overload protection，and has good braking ability［1］．In addition，the system is filled with lubrication oil，which will make less component wear，high transmission efficiency，and low environmental temperature and humidity sensitivity．Therefore，the hydraulic crane is widely applied and rapidly developed．This paper introduces the development of the modern ship industry and the current condition of the electric crane and hydraulic crane，and emphasizes on the techniques of hydraulic crane，such as typical system，air-tightness，control technology，fault diagnosis and so on．As the development direction of the ship hydraulic winch is concerned，the improvement of the reliability and technical management level is of an important guiding significance．

2.Application status of marine hydraulic crane

Marine hydraulic crane is a kind of crane that is rapidly developed in 1960s．Hydraulic system of crane，according to the rated working pressure level，can be divided into high，medium and low voltage system．Based on the oil liquid circulation，it can be divided into open，closed and semi-closed system．Open system refers to that the oil pump absorbs oil from the tank，and valve oil to oil motor through the reversing，and the oil discharging of the oil motor returns to the fuel tank through the reversing．Closed system refers to that the oil discharging motor will not return to the fuel tank，but directly backs to pump suction，and the oil forms a closed circulation between the pump and motor oil．In order to compensate the leak in the system，a small fluid infusion pump is set up to fill oil and cooling to form a semiclosed system．In the semi-closed system，usually 30%hydraulic oil exchanges with the fuel tank．The open system crane is relatively simple with low initial cost，and the oil in the fuel tank can be well cooling and precipitation of impurities，and a pump is used to drive several mechanisms to work simultaneously．But the oil contacts with the air in the tank，causing the air mixed easily，and consequently the system works destabilized．In addition，the directional control valve must be used to realize the reversion and control，owing to that the oil pump can only output pressure oil in a single direction．Therefore，the open system is often used on the hydraulic crane with low pressure and small power［2］．The closed system is more complicated with high initial cost and the bidirectional variable oil pump，which achieves the reversion easily，and the volume controls and benefits the improvement of the economical efficiency，drives the oil motor reversal in the shipment，and transfers the oil pump into the oil motor，which in turn drives motor rotation，so that the drop speed is limited，which achieves energy recovery．Thus it is mainly used in crane of the dry cargo ship and bulk carrier which have great pressure and power．

Overall，the most widely used hydraulic crane ship has mainly two typical systems:Libuher B5/14-16 rotary crane and Hagglunds G4024 rotary crane．The hoisting mechanism principle of the hydraulic system Libuher B5/14-16 rotary crane is shown in Figure 1:the lifting hydraulic system adapts the closed system that consists of hydraulic system with hoisting mechanism by two-way proportional variable axial plunger pump A and quantitative oil motor C．The hoisting mechanism principle of the Hagglunds G4024 rotary type crane is shown in Figure 2:

Figure 1．The hoisting mechanism principle of hydraulic system Libuher B5/14-16 rotary crane

Figure 2．The hoisting mechanism principle of the Hagglunds G4024 rotary type crane

It is an early product of Hagglunds in Sweden．Because the ship hydraulic crane system is operated under the conditions of long-term swing，corrosion and strong resistance，which lead to the wear of equipments，the loose of connecting parts，easy corrosion of machines and pipelines，and the failure of automatic control equipment．With fluctuant temperature in the regions while the ship is sailing，it has great influences on the performance of hydraulic oil，and leads to the instability of working performance of hydraulic system．Therefore，to improve the normal operation of the reliability of ship，the requirements on the reliability，sealing，and easy maintenance and the management of hydraulic crane become higher．

3.The development trend of marine hydraulic crane

3.1.Marine hydraulic crane parts and the working medium

Compared with other hydraulic systems，the marine hydraulic crane system has its peculiar characteristics．Firstly，the crane hydraulic system changes frequently with intense work and long time continuous loading and unloading in port．Secondly，the crane hydraulic system has high demands on the management and maintenance，of which the working environment is always high temperature and high humidity，and sometimes special pollution like seawater erosion that will not occur in other hydraulic system．Therefore，the future trend of design of hydraulic components will use the fuzzy reliability design that combine reliability design and optimum design to improve components，and use the nonlinear effect to reduce the volatility of hydraulic components．At present，with the development of casting technology，the performance of hydraulic components is also greatly improved:casting flow can optimize the element internal flow in the body，and it is widely used in the integrated block，improving the flow state，reducing the pressure loss，lowering noise，and realizing the miniaturization of components．In addition，the application of nanometer materials can not only promote the hydraulic components and system lightweight and compact，but also improve the wear resistance and the service life of components．The hydraulic oil is basically taken as the working medium of hydraulic winch，and which is a new direction in its development．Using water based composite liquid as the working medium has the advantages of no pollution，high safety，and sanitation and so on，which meets the requirements of environmental protection．While using water as the medium of hydraulic driving technology has the advantages of simple structure，high efficiency，economy，etc．，which has the prospect of widely application in many fields［3］．At present，the manufacturers of German，Britain，F(xiàn)inland and other countries have used the technology in water hydraulic components．The Danish Danfoss company offers series of NESSIE to complete water hydraulic components，which has been applied in the food industry［4］．In addition，the research and development of the emerging electro-rheological fluids and magneto-rheological fluid will be a major reform and innovation of marine crane technology．Magnetorheological fluid is a kind of smart material，which is influenced by the external magnetic field，and the viscosity of the liquid changes greatly，and is easy to be controlled and continuously controllable［3-5］．The rapid development of electronic technology has been seen in recent 20 years，the reliability of electronic devices is greatly improved，and the integration degree is increased．Now it can be built in electronic devices and circuits of hydraulic components，which means an electronic driving circuit，signal processing and storage and so on are directly installed in the hydraulic parts of the shell．It can not only improve the reliability of hydraulic components，reduce the pipes，decrease the pressure loss and improve efficiency，but also save the installation space and be easier to repair．Therefore，the future hydraulic part is an electro-hydraulic digital integration product which has strong anti pollution ability，work stably，and can be directly interfaced with computer．

3.2.The sealing of marine hydraulic crane parts

Since the birth of hydraulic technology，the leakage has been a big problem．On the ship，on account of its bad working environment，routing all over the world and the great temperature span，an improper operation or mismanagement of the crane can easily cause the leakage of hydraulic oil，leading to the problems such as the working medium waste，the environment pollution，the lower efficiency of system transmission，and so on．On sealing，at present poly tetrafluoroethylene(PTFE)materials are mainly adapted．With the in-depth understanding of the mechanism of materials and sealing，some materials can be added to poly tetrafluoroethylene(PTFE)to meet the requirements of increasing the performance．Many large foreign seal companies，such as BUSAK SHAMBAN，Tetranuor and so on，have the material formula of different applications to enhance a particular aspect of performance．Another innovation in the field of the sealing is focused on the design of seal shape．Nowadays，the availability of finite element analysis and other methods can be adapted to make an analysis of the pressure gradient seal to analyze its sealing performance．In addition，the“O”-shaped sealing ring and spring regarded as elastic body has been widely recognized in the sealing performance to ensure the poly tetrafluoroethylene(PTFE)seals at low pressure．As for the linear sealing and rotating sealing technology，the application of the set of sealing elements to improve sealing performance has become a standard solution．Therefore，in the manufacturing of sealing，the future development of technology lies mainly in these areas．

① The application of new materials，which refers to the research and development of the application and newly filling material development of poly tetrafluoroethylene(PTFE)，is a direction of the sealing technology in the marine hydraulic crane［6］．

②The recognition of sealing mechanism and sealing shape seal，and the development of the seal are all based on a profound understanding of the sealing mechanism．Therefore，the sealing mechanism，as the fundamental research，will still drives the development of sealing technology．

③The method of manufacturing sealing parts．At present，the seal of poly tetrafluoroethylene(PTFE)chiefly uses machining methods，which is flexible on one hand，but on the other hand，how to make an efficient process is still a problem to confront with．

3.3.The control method of marine hydraulic crane

On marine hydraulic crane，the electro-hydraulic servo valve is used primarily to achieve automatic control．However，since the invention of the structure of the electro-hydraulic servo valve，there is little improvement．The development of proportional valve technology is mainly in the increase of the bandwidth and improvement of controlling accuracy，in order to be close to the servo valve performance．Meanwhile，proportional valve technology is developed along the direction of standardization，modularization，and low cost，which promote its application．Adaptive control was firstly put forward by the MIT which is called Parameter optimization model reference adaptive control．Robust control is another solution to anti-jamming and anti-dithering of the system．Moreover，it is also one of the current hot topics in the control group．

In fluid control industry in recent years，a lot of work has been done on the research and application of neural network(NN)，and it remains a hot topic．The basic thought of neural network(NN)is to simulate the nervous system of the human brain from the perspective of bionics，and thus the machine can feel，learn and inference as human beings．It also has a lot of advantages．The most important is that math model is not needed to know to approximate any complex nonlinear relations．Besides，it has great potential in solving highly nonlinear and serious uncertain system control，and these advantages and functions are needed by hydraulic servo system，which can realize the automatic control of Marine hydraulic winch．Using the combination of computer science，electronic technology and hydraulic technology to predict hydraulic system failure and achieve proactive maintenance is the developmental trend for the ship hydraulic winch control technology at present and in the future．Reinforcing the research and development of expert system，building integrated expert knowledge base with learning function，calculating the causes of malfunction through computers and knowledge base，putting forward the repair plan and preventive measures，and developing self compensating system of hydraulic system for self-regulation and self-correcting before the faults occur，above all are beneficial for the working efficiency，safety of the hydraulic crane，high reliability of the hydraulic mechanical transmission，and reducing the work intensity with microelectronics computer control．

With the development of the built-in electronic circuit，the hydraulic liquid cargo mechanical and electrical system can be controlled distributively，and the central industrial serves as central scheduling，allocation，optimal management，monitoring，fault diagnosis and so on．Each subsystem or hydraulic parts can be directly managed by reliable PLC programmable controller，which can complete the function of the acquisition，processing，storing some information on the basis of its own special requirements，and form large complex intelligent control system with highly mechanical and electrical integration of liquid through the“electronic”and“hydraulic”optimization of coordination and division of labor．It can not only save energy，improve the working efficiency and working precision of the hydraulic crane，make the most use of the output function of prime mover，and prevent hydraulic system overload，but also improve the reliability and security of the marine hydraulic crane．

3.4.Fault diagnosis technology of marine hydraulic crane

Fault diagnosis technology for hydraulic system is a new technology which experienced rapid growth in the last 70 to 80 centuries．It is put forward according to the equipment reliability requirements，the needs of modern hydraulic cranes，and the need for timely troubleshoot hydraulic system failures，and is formed by expending basic logic thought in the diagnosis of traditional Chinese medicine to hydraulic engineering technology．The fault diagnosis technology of crane hydraulic is one of the basic measures to guarantee the safe operation of the system，and it can make an early prediction of system fault and put forward some countermeasures and suggestions to avoid or reduce the accident occurrence［8］．But the ship is not equipped with a perfect fault diagnostic system，and it still stays in the theory stage．

Diagnosis method for hydraulic failure，at present，according to the technical different features，can be divided into sensory experience of diagnosis method，system analysis method，the method of fault tree analysis，oil analysis，vibration and acoustic method，ultrasonic method，fuzzy diagnosis method and expert system diagnosis method［9］．Sensory experience，which aims to the technical staff，has been unable to meet the requirements of the rapid development of modern industry．

The diagnosis method for hydraulic system diagram analysis，including sequential inference detection diagnosis and instrument detection method，is to test the performance and parameters by using various instruments measuring equipment value(such as pressure，flow，temperature and so on)，and these data are analyzed to determine fault location．This diagnosis method can be used to detect the hydraulic equipment of a variety of instruments，which has a low investment but can only detect some limited parts，not all parts．The commonly used methods of oil analysis are spectrum analysis，ferrography analysis，magnetic plug detection，particle counting method，etc．Acoustics and vibration method is to detect the vibration and noise of hydraulic components through the use of acoustic instruments．According to the features of vibration law of acoustics，the recognition of wear condition of fault elements and the fault diagnosis of location，degree，nature and development trend are realized．The method of fault diagnosis is suitable for all hydraulic equipments，especially for the fault diagnosis of hydraulic pump and hydraulic motor of higher value，which has great practical significance．

Ultrasonic detection method is the application of ultrasonic detection in vitro and tubing wall hydraulic component shell to measure its internal flow value，of which the commonly used methods are pulse echo and transmission．Fuzzy diagnosis method uses muti-factor diagnosis and simulating human thinking mode to make the fault diagnosis technology develop into the intelligent direction，which has a certain development prospect．The expert system method is considered to be one of the most effective fault diagnosis methods of hydraulic system of crane，and it is a kind of“knowledge based”and artificial intelligent diagnosis system．It infers and judges according to the experts’experience and knowledge in a certain field，and simulates the thinking of experts to solve complex problems［10-11］．The knowledge base of expert system can fast store experience knowledge of experts in many fields，has comprehensive utilization of all kinds of expert knowledge，and opens up a new way in diagnosis technology，which is also an important direction for future development．

4.Conclusion

Nowadays，with the increasing of the average tonnage of bulk cargo ship and dry cargo ship，vessels engaged in different types of transportations are expanding their ability to transport．Large ships containing about 200，000 tons will be the mainstream in the distant future．Therefore，higher requirements are put forward for marine crane，and which has propelled its growth．It is still the mainstream of the times to develop hydraulic control components of high performance to meet the needs of the development of cargo winch of mechanical and electrical integration，to make the green research and development as its aim to environmental protection，and to satisfy the sustainable development of reducing the noise of elements and system，reducing leakage and improving the sealing performance．

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