Development of an automated adaptive control system for the working equipment of a single-bucket hydraulic excavator

Abstract

Control of the working equipment of a single-bucket hydraulic excavator remains manual: the speed commands for the boom, arm and bucket cylinders are formed by the operator, who responds to changing soil resistance with a delay of about one second. The automation systems available on the Russian market solve the geodetic task of guiding the cutting edge to the design elevation and do not affect the distribution of working fluid flow when the soil category changes. The aim of the work is to construct and verify by calculation the structure of an automated system that retunes the arm speed command according to the current estimate of specific digging resistance. The calculation was performed on the author's model of a machine of the 4th size group under GOST 30067-93 with an operating mass of 23 t, a bucket capacity of 1.0 m³ and a rated hydraulic system pressure of 34 MPa; the digging resistance estimate was obtained by the recursive least squares method with forgetting at a sampling period of 20 ms; the modes were compared by simulation over 10,000 realisations of the working face. The steady-state relative error of the specific digging resistance estimate was 4,3% for soils of categories I-II and 6,8% for categories III-IV, with a response delay of 0,34 s. The transition from baseline to adaptive control raises technical productivity on category IV soils from 110,0 to 135,3 m³/h and reduces the specific energy intensity of excavation from 0,984 to 0,734 kWh/m³; on category I soils the productivity gain does not exceed 2,6%. The gain averaged over a mixed face reached 10,5% in productivity with a 19,3% reduction in energy intensity. The dependence of the effect on the exponent in the adaptation law is non-monotonic, with an optimum near 0,72. The benefit of the adaptive loop is concentrated in the region of heavy soils and originates from the elimination of relief valve discharges rather than from acceleration of the idle portions of the cycle, which shifts the centre of gravity in control system design from trajectory kinematics to identification of the force interaction between bucket and soil.