| As a typical hydraulic mechatronics machine, digging performance is the coreproperty indicators of excavators. Research on digging performance is not only aprerequisite to match mechanical, hydraulic and control system, but also a basis forobtaining energy saving, high efficient and intelligent excavators. Scholars from homeand abroad have made much progress on research of digging performance. But there aresome drawbacks as following:①the current methods can’t solve the accurate diggingresistance in actual digging process.②The unconformity between the strength analysisand the actual failure mode means that more effective methods for working device staticand dynamic strength analysis are required.③The maximum digging force at the limitconditions can’t be acquired from the existing theoretical digging force model, and themodel is not capable to evaluate digging capabilities of compound digging conditions.④The existing pattern analysis method can’t make accurate assessment of diggingproperties. To solve these problems, this paper presents such theoretical andexperimental researches including digging resistance model in actual digging process,test platform of stress and digging resistance, strength analysis and verification methodsof static and dynamic strength, modeling of theoretical digging force and analysis ofdigging performance. Specific work and results of this study include the followings:1) Based on the principle of planar force system, the mechanical model in whichdigging resistance system was composed by the tangential resistance, normalresistance, and moment of resistance on the cutting edge was proposed, whichmakes it possible to attain exact digging resistance. Combined with kinematic anddynamic models of hydraulic excavators, the computational model was built forsolving digging resistance in actual digging process. It abandons the condition ofusing empirical equation and simulation methods to predict the digging resistance,and makes it possible to analyze digging resistance of working device in realworking process, which provides theoretical basis for relevant researches ondigging performance.2) Synchronous test platforms were built to test the working device attitude, stress andhydraulic cylinder pressure of hydraulic excavator. Then the collection, conversionand fitting of data in several digging process were finished. The correspondingdigging resistance in different conditions was calculated utilizing the test data and the digging resistance model. The equivalent stress of all the test points wascalculated based on the stress-strain relationships. These results provide basis forthe research on digging resistance properties and comparison of stress results.3) The peak values of the dynamic stress in actual digging process and staticsimulation stress under same working device attitude was compared, therelationship between static strength and real dynamic stress was summarized, andthe range of general dynamic load factor was researched. These processes provide afeasible way to solve dynamic load problem in static strength analysis way.4) The dynamic load spectrum of each hinge points of boom and arm in actual diggingprocess was calculated by solving the digging resistance model which based ond’Alembert principle with the data obtained from test. Taking it as the external load,the overall distribution of dynamic stress at arm and boom was simulated withtransient analysis method. Dynamic stress gained from transient analysis anddynamic testing was compared. The comparison of stress from test and simulationnot only verifies the validity of transient analysis process, which is a feasiblemethod for dynamic analysis of structures, but also demonstrate the correctness ofdigging resistance model.5) The rules of overall characteristics, force value and direction features of the diggingresistance were researched by studying the experimental result. In addition, basedon statistics theory, the main range and probability density of resistance coefficient,resistance moment coefficient, resistance angle and difference angle were obtained.Research on digging properties and the changing law of digging resistance in realworking process will benefit a lot in designing and optimizing of working deviceand setting up the theoretical digging force model.6) The concept of limiting digging force and calculation model was proposed based onthe overall characteristics and change law of the digging resistance, which makes itpossible to evaluate the limiting digging ability of the excavator exactly. Based onthe direction features of the digging resistance during the process of compounddigging, the concept of compound digging force, as a new way of assessing diggingperformance in compound digging process, was proposed, and the break throughprovides an evaluation methodology for the digging ability in the process ofcompound digging.7) A new method called atlas analysis based on workspace was put forward as asubstitute for the traditional method in which the digging attitude was the focus. The method can avoid the problem that one digging point may correspond to manydigging gestures in traditional method. Based on the digging resistance from thetest result, the atlas analysis based on workspace and the traditional method wascompared. The results show that the atlas analysis based on workspace is moreaccurate in reflecting the digging ability at certain point, since the digging atlas canobviously disclose the regional distribution law of digging force. Utilizing atlasanalysis method based on workspace, digging performance analysis of fourmedium-sized hydraulic backhoe excavators of similar tonnage suggests that thismethod can not only give a more intuitive vision in theoretical digging force andconstraints factors distribution, but also provide statistical results of digging forceand constraints proportion. This method is valuable as theoretical basis forexcavators’ evaluation and analysis and provides a reliable way for engineeringapplication. |
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