Output layer is the fourth layer of the network。 Each node of it is corresponding to each fault causes of the hydraulic subsystem。 Output value is the membership size affiliated to the fault causes。 The number of the nodes corresponds to the number of causes of typical faults of the hydraulic system。 Fuzzification  Elimination layer is the  fifth  layer of the network。 It clarifies the fuzzy results of the output layer and outputs the definite diagnosis results。 The clarity calculation is based on minimum threshold value principle (Membership value of fault components should be greater than some thresholds, which is defined in debugging。 The value should be set to an appropriate value。 A large membership value might lead to the ignorance of some faults while a small value may cause false alarms of faults)。

Fig。 2 Characteristic signal of work condition of the hydraulic system of cranes outriggers

1-Temperature sensor; 2-Level sensor; 3-Pressure/flow sensor; 4-Pressure sensor

The characteristic signal of the working condition of the hydraulic system is chosen as follows: the oil temperature of the hydraulic system, oil level in tank, oil pressure and flow of pump exit, operating pressure and oil-relief pressure of the horizontal and vertical hydraulic cylinder of each leg。 The distribution of monitoring signal is shown in figure 2。

Besides the characteristic signal of the working condition,other  signals  are  chosen,  including control signal of stretch/shrinkage of  Horizontal/vertical legs, linkage stretch /shrinkage of Horizontal/vertical  legs and selection signal of half a stretch/all stretch of Horizontal legs, etc。

(1) The oil temperature

When the leg system works properly, the oil temperature is usually 40~60 ℃。But when fault occurs, the hydraulic oil temperature might experience fluctuations。 This might be caused by: leakage of gear pump; leakage or stuck of a leg hydraulic cylinder; leakage or too high adjustment pressure of relief valve, etc。

    (2) Oil level in tank

When the leg system works properly, oil level keeps changing according  to  a  certain  fashion。 When some hydraulic components in the system encounter leakage or other faults,the system's hydraulic oil level will change according to the condition of work。

(3) The oil pressure on gear pump exit

Hydraulic oil pressure on pump exit is determined by external load。 If the system encounters faults, the outlet pressure can experience drastic change。

 (4) Output oil flow of gear pump

If the hydraulic pump encounters faults, the output oil flow will not be able to reach a stable range within a long time。

 (5)Oil pressure of the horizontal rod-less hydraulic cylinder

When the legs stretched out horizontally, oil pressure of rod-less hydraulic cylinder depends on the resistance of the leg。The  resistance  includes  friction resistance and hydraulic resistance of rod-less hydraulic cylinder。 When the legs draw back horizontally, oil pressure of rod-less hydraulic cylinder depends on the oil-relief pressure of back-oil-way。 When the legs stretched out horizontally, if leakage happens to the horizontal hydraulic cylinder or the reversing valves that controls the cylinder, the oil pressure of the rod-less hydraulic cylinder will be below the normal range。 Consequently, the legs cannot move or move sluggishly。 When the legs draw back horizontally, if obstruction happens to the back-pressure value or oil filters, the oil pressure of the rod-less hydraulic cylinder will be above the normal range。 Consequently, the legs cannot return。

(6) Oil pressure of the horizontal rod hydraulic cylinder

  When the legs stretched out horizontally, oil pressure of rod hydraulic cylinder depends on the oil-relief pressure of back-oil-way。 When the legs draw back horizontally, oil pressure of rod hydraulic cylinder depends on the resistance of the leg。The  resistance  includes  friction resistance  and hydraulic resistance of rod hydraulic cylinder。 When the legs stretched out horizontally, if obstruction happens to back-pressure-valve or oil filters, the oil pressure of the rod-less hydraulic cylinder will be above the normal range。 Consequently, the legs cannot move or move sluggishly。 When the legs draw back  horizontally,  if  leakage  happens  to  the  horizontal hydraulic cylinder or the reversing valves that controls the cylinder, the oil pressure of the rod hydraulic cylinder will be below the normal range。 Consequently, the legs cannot return。