Path travelled by a working element (e.g. cylinder ) between the turn-off pulse from the directional valve and the end of the movement.
The overrun primarily depends on the masses moved and their velocity, but also on the delays of the signal and control elements in the signalling area (Figure U 6). The switching time of the directional valves is also a factor. Delay influences, which are constant, can be taken into account using derivative action.
The overrun poses great difficulties when approaching a position at any speed. If this happens with switching valves, a crawl speed must first be used. In the case of proportional valves the delay can be brought under control using corresponding specifications for the ramp.
Figure U 6: Comparison of overruns given a fixed stop (a), NC axis with proportional valve (b) and an electro-hydraulic shut-down (c)