INTERFERENCE PREVENTION SYSTEM FOR TWO-PIECE BOOM TYPE HYDRAULIC EXCAVATOR

When an arm end exceeds a boundary line K2 and enters a slowdown area R1, a proportional solenoid pressure reducing valve 13 is operated to reduce a pilot pressure for slowing down a first boom cylinder 1A, thereby slowing down an arm end speed. When the arm end exceeds a boundary line K1 and enters a restoration area R2, a restoration gain is calculated in control gain block 200 depending on an intrusion amount by which the arm end enters the restoration area, while a feedback gain is calculated depending on an arm end speed at that time on the basis of functions 204, 205, 206, 207, 208 and 209. In accordance with these gains, a second boom 2 is automatically dumped depending on the intrusion amount of the arm end into the restoration area and the arm end speed at that time so that the arm end is moved for return to the slowdown area. As a result, such work as requiring a work front to be moved toward the operator is continuously smoothly performed and working efficiency is improved.