The existing compound digging force model of hydraulic excavators does not take into account the existence of resistance moments in the actual work of the digging resistance

which results in the calculated compound digging force being smaller and does not reflect the compound digging performance of the excavator in real operation. Therefore

this paper proposes a limit compound digging force model based on the main value interval of the resistance moment and the directional angle of the compound digging force. Selecting any normal compound digging trajectory of a 22 t backhoe hydraulic excavator

its digging resistance and the digging force size are calculated by the proposed model and other theoretical digging force models respectively

and it is verified that the limit compound digging force is the maximum in the digging operation. In addition

based on a 36 t backhoe hydraulic excavator

the trajectory digging force of different theoretical digging force models and the digging force of the main digging area map were solved for the measured digging trajectories under two different working conditions. The results show that the limit compound digging force model can more accurately characterize the digging force performance of the compound digging trajectory

and give the best theoretical digging force characterization of the digging trajectory. The main digging area mapping force shows that the digging force exerted by different digging methods in different working areas is inconsistent.