Modeling of the limiting digging force of hydraulic excavator based on resistance characteristics

Based on the resistance characteristics, a model of theoretical digging force was proposed in this paper, taking the tangential force, the normal force, and the bending moment into account simultaneously. Utilizing the relation among the normal resistance, the resistance moment, and the tangential resistance in practical digging process, three independent unknown quantities are transformed into only one variable. Afterwards, according to different digging patterns and complete machine limiting conditions, this research derived the constraint inequalities of the limiting digging force (LDF) and established the calculation models for LDF. Then, based on the value distribution laws of the digging resistance coefficient and the resistance moment coefficient, the calculation process and corresponding method of LDF under a given digging posture were obtained. Taking the digging resistance obtained by testing for 35 t hydraulic excavator with backhoe attachment as the reference, this paper compared the calculation results of the theoretical digging force for complete machine with those of the LDF model proposed in this research. The comparative results indicate that the LDF is consistent with the fact that the theoretical digging force is larger than or at least equal to the actual digging resistance. So, the LDF can exactly show the real limiting digging ability of the excavator more accurately. In this way, it can provide basis for mechanism optimization, structural strength design, trajectory planning, and control automation of the excavator.

Active-Side Calculation Method for a Backhoe Hydraulic Excavator with Incomplete Digging Resistance in a Normal State

The digging resistance in a normal state is the key to excavator design and automated excavation. It is difficult to accurately predict, simulate, or directly measure the digging resistance in a normal state due to uncertainties in the soil properties and excavation parameters. In this paper, a research idea is proposed that uses the working device as the entry point to indirectly calculate the digging resistance in a normal state by measuring the motion parameters and the cylinder pressure intensity. Based on the rule of combination for spatial force systems, a method for combining and projecting the system of the digging resistance is proposed in which the system is projected as six parts, and the tangential force, normal force, and bending moment in the plane of symmetry of the working device are the objects of the solution to avoid redundant equations. Based on kinematics and dynamics models of the excavator and the force and moment equilibrium conditions of the working device, equations for the active-side calculation of the incomplete digging resistance are derived. Based on these equations, the motion parameters of the working device and data on the cylinder pressure intensity obtained by measurement are used to calculate the incomplete digging resistance. The validation scheme and process proposed use the incomplete digging resistance as the external load to obtain the simulated stress of the working device through transient analysis. The simulated stress and the measured stress corresponding to the position of the measurement point are extracted and compared. The results show that there is a difference in the size of the numerical value between the simulated and measured stress, but the variation law is highly consistent, which validates the calculation method. In this paper, an active-side calculation method is provided for the incomplete digging resistance in a normal state without considering the soil-tool interaction relationships, which lays a theoretical foundation for the study of the digging resistance characteristics in a normal state, as well as excavator design and automated excavation.

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

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.

Digging performance characterization for hydraulic excavator considering uncertainty during digging operation

A methodology whereby the digging performance of the hydraulic excavator can be determined is presented, with uncertainty during the digging operation being taken into consideration. Natural variability in medium properties and differences in operation styles are the significant sources of uncertainty. The most probable direction interval of the digging resistance obtained from the experimental data is given to quantify the contribution of uncertain medium properties to the variation of the digging resistance direction. A digging capability polygon, which is used to characterize excavator’s capability to apply forces to overcome the digging resistance, is defined by the driving capability constraints of hydraulic cylinders, the stability constraints of the excavator and the most probable direction interval of the digging resistance. A set of significant performance measures, which can be used to quantify the maximum digging capability of the excavator and the exerting extent of the driving capability of hydraulic cylinders, are given based on the digging capability polygon for a given manipulator configuration. The Cartesian workspace of the excavator is discretized into finite digging points to reduce the computational work for global digging performance analysis. Considering differences in operation styles, for each digging point the digging angle is discretized with a certain step and the inverse kinematics approach is taken to derive the manipulator configuration corresponding to each incremental step of the digging angle. Quantitative measures of the global digging performance are proposed according to the performance statistics for all manipulator configurations of all digging points in the entire workspace. These measures can be used to assess the mechanical capability of the working mechanism of a hydraulic excavator and to assess the operation styles used by different operators who have different level of experiences. Finally, the proposed methodology is illustrated using an application example of a 36-ton hydraulic excavator.

Structure Improvement Analysis of Maize Root Stubble Harvester

In order to effectively reduce the crop stubble harvesters digging resistance, enhance stubbles picking rate and intact stubble rate, the Research Group took structure improvement for the Crop stubble harvester and its critical component based on abundant trials. Three physical machines in succession were developed, and a trial contrastive analysis between the optimized harvester and the first harvester was conducted. It turned out that the improved harvester machine was clearly superior to the first machine.

The Calculation for Digging-Resistance of Small-Scale Excavator Based on Torque Method

The torque-based calculation model for digging-resistance of small-scale hydraulic excavator is presented. The simulation model of digging-resistance is built under AMESim environment, and the structural parameters of SWE50 excavator are imported into AMESim and the digging operation is simulated. The parameters gained from the simulation are imported into calculation model, then the correlation between calculation results and simulation results of digging-resistance is obtained, which shows that this calculation model can indicate effectively the dynamic process of resistance during digging operation and is better than the empirical formula. At last the digging-resistance experiment is operated and the actual resistance is calculated by use of experimental data. The calculation model is proved suitable further for analysis and application of the actual digging-resistance.

Design and Analysis of the Digging Spring Tooth of Stubble Harvester

The developed corn stubble harvester can simultaneously finish such as the digging, picking up, cleaning, collection and Stripy laying stubble process and so on, but it cost more man-hour time because of the high digging resistance and high engine power consumption in digging stubble works. The digging spring tooth for corn stubble harvester including self-exited vibration S-shaped spring handle and curved chisel-shaped bionic tooth is designed based on the mechanism of drag reduction of self-excited vibration and bionic drag reduction for reduce digging resistance and power consumption, and the statics analysis of digging spring tooth is done by ANSYS software, the stress and strain distribution diagrams show the design is reasonable.

Resistance Analysis and Experiment of Excavator during Digging Operation

To research the actual resistance for excavator in digging process, the relationship between manipulator motion, cylinder pressure and digging resistance was analyzed. On this basis, the equation for calculating digging resistance of excavator was proposed. By using tension sensor, a digging resistance test was done under the actual digging movement environment. And the obtained inclination angle and hydraulic cylinder signal data were imported into digging resistance calculation equation to get a calculation resistance. After comparing the calculation resistance with the tension sensor readings, the following conclusions can be derived: this calculation equation can reflect effectively the size and dynamic process of actual resistance during digging operation, and it can describe the instantaneous changes and impact status of real resistance much better can the empirical equation in which the resistance is directly proportional to the digging depth.