In the normal working state of hydraulic excavator, the load on each part is constantly changing and complex, so it is impossible to directly measure the relationship between the load on bucket tip and time. When the excavator bucket contacts the soil, the force of the working device is the gravity of the working device and the digging resistance between the bucket teeth given by the soil. According to the analysis of the movement force of the excavator working device, the relationship between the digging resistance between the bucket teeth and the related components of the oil cylinder is established. According to the measurement of the displacement and stress of the boom oil cylinder, the stick oil cylinder and the bucket oil cylinder, the force time mileage of the digging resistance between the bucket teeth is indirectly obtained. Because the cross-section of each cylinder is regular circle, the force of the cylinder is calculated according to the measured strain value and cross-sectional area. It can be further simplified as measuring the stress time history of each cylinder along the axis of the piston rod.
