Trenching etc. excavator with slew and tipping boom

The excavator has tipping and slewing joints, as well as a third joint (1) for rotation-symmetric movement of the forward part (8) of the boom, using the center axis of this arm part as a rotation axis. The third joint is of the ball type and stands between the second joint (11) and shovel. Second and third joints serve to divide the boom arm into three parts (8,9 and 10). The third joint (1) is rotated by a first hydraulic cylinder (6a) as served by holders (32a,24a) on the forward and center (9) arm parts. The center and front parts meet via respective slide plates (2,3). The cylinder is preferably controlled by an ultrasonic or laser device (7) via an output signal. The laser etc. is positioned on the center arm part, and the second joint is stabilized by outer and inner slide plates (15a,b,16a,b); the inner plates are welded to the center arm part, and the outer plates are welded to the rear arm part and portend to the center arm part where they share a contact face with the inner plates.