Requirements are formulated on motion trajectory of the front edge of the arm of PNB type loader needed to provide the maximum shoveling of bulk mass under the condition of fitting that trajectory into the dimensions of reception plate. Kinematic schemes are analyzed of mechanisms of shoveling arms. Rational parameters are suggested for that mechanism, which provide a 1.5 times increase of single-time shoveling of bulk load resulting in a 30 % increase of theoretical capacity of the machine. A technique is presented of defining the area embraced by the complex motion trajectory of the front edge of the arm. A mathematical model is designed of motion of the shoveling arm with curvilinear tail part using the techniques of vector algebra, second order central differences and triangulation. Geometric parameters of the mechanism of work tool of the loader are described by a linear equation yielding the functional dependence of coordinates of the position of front edge of the arm on the turning angle of the leading joint and the parameters of kinematic scheme. The effect is studied of the total mass of shoveling arm on the irregularity factor of mechanism motion. It is found that redistribution of mass between the work tool and the tail part of the arm within the given total mass of the tool suppresses the motion irregularity factor.