Abstract: Traditional single degree-of-freedom (DOF) mechanical engineering machinery lacks flexibility because of its structural limitations. Hydraulic engineering machinery can achieve flexible output trajectories, but there still exists some problems such as high costs of manufacturing and maintaining, high accuracy requests, low transmission efficiency and reliability, hydraulic leaks. This is an unsolved thorny issue of long-term. Applying multi-DOF controllable mechanism and metamorphic mechanism to engineering machinery can overcome the deficiency of both traditional products respectively. This new type of construction machinery can obtain flexible output as hydraulic ones when overcome the problems they have, of which the application prospect may be promising. The type synthesis problem is studied. Working principle of traditional hydraulic loaders is analyzed first, based on which the technical action process is obtained using the behavior expression of working principles method. Then the conceptual design on the basis of functional analysis is introduced applying constraint synthesis methods based on screw theory and configuration evolution method combining the innovative design results of controllable mechanisms, metamorphic mechanisms and parallel mechanisms. Series of novel configurations of multi-DOF controllable mechanism type loaders, as well as the ones with metamorphic functions are obtained. Loading experiments are conducted, of which the results verified the feasibility that multi-DOF controllable mechanism can be applied in construction machineries such as loaders, which may also provide some references for the application of the mechanism.

Key words: loader;functional analysis;innovative design;type synthesis;controllable mechanism;metamorphic mechanisms