Dynamics of the cutting apparatus drive of a front-mounted header for grass harvesting

In grass headers of self-propelled and trailed mower-conditioners, the drive of a double-knife cutting apparatus is implemented by two wobble-plate mechanisms mounted on the sidewalls of the header platform and interconnected by long intermediate shafts and couplings. This drive configuration is structurally complex and material-intensive, as it consists of two independent mechanisms. Based on an analysis of existing designs and studies of cutting apparatus drive mechanisms, a new crank-rocker mechanism with flexible elastic links is proposed for driving two knives. A distinctive feature of the proposed mechanism is that the movable flexible elastic links form a closed-loop contour. The use of flexible links makes it possible to reduce the weight and material consumption of the mechanism. Owing to the presence of flexible links, the mechanism does not require high manufacturing and assembly accuracy and is insensitive to frame deformations, which contributes to improved operational reliability. The principal advantage of the proposed crank-rocker mechanism with flexible elastic links is that a single mechanism provides the drive for both knives of the cutting apparatus. Differential equations of knife motion were derived, taking into account the elastic and damping properties of the flexible elastic links of the mechanism. Solving these equations made it possible to determine the kinematic parameters of the cutting apparatus, including knife displacement, speed, and acceleration, while accounting for technological and inertial loads. During the reciprocating motion of the two knives in antiphase, the inertial forces of the knives are not completely balanced. The unbalanced inertial forces caused by the elastic compliance of the flexible links are insignificant. The operating mode of the mechanism lies in the subresonant region of the amplitude-frequency response.