Optimum dimensional synthesis for the working mechanism of a hydraulic excavator to improve the digging performance

Abstract

The direction and magnitude of the digging resistance encountered by an excavator during digging process are usually uncertain. To identify the excavator’s capability to generate digging force to overcome the digging resistance in any direction, a hexahedral actuator force space is mapped to a polygon in bucket force space with the consideration of the whole machine stability constraints of an excavator. Then this polygon is called digging capability polygon. Based on the digging capability polygon, the maximum digging force, isotropy measure of the digging force, and the full exertion proportion measures of the driving capability of the working hydraulic cylinders are defined to quantify the digging performance of any configuration of the working mechanism. Further the average values of each of these indices in the customary digging workspace are used to comprehensively assess the digging performance of an excavator. A multi-objective evaluation function is constructed using the so-called ideal point method to increase all average values of the given indices simultaneously. Optimum dimensional synthesis of the working mechanism is finished by using the genetic algorithm to solve the established optimization problem. The optimization results indicate that the average values of the maximum digging force, isotropy measure of the digging force, and full exertion proportion measures of the bucket cylinder and stick cylinder in the customary digging workspace respectively increase by 1.81%, 1.51%, 9.64%, and 15.15% relative to the initial excavator, and obvious increases in the key workspace parameters of the optimized excavator are obtained. The performance indices proposed in this research can be used to assess the digging performance of an existing excavator and further guide the new excavator design and development. The optimization method provided in this research can be used to design new excavators or improve the existing excavators.