1. Hydraulic resistance control for a displacement chamber with a type A hydraulic half bridge (adjustable input and output resistance); use of both control edges of a continuously adjustable 3/2-way directional valve with negative pressure. Together with a differential cylinder with an annular area pressurised at operating pressure (replacement circuit for hydraulic bridge D), the two edge control enables movement control. One example is the copier system in (Figure Z 15). However, the maximum useful cylinder force is only the rod surface area.
In this form, the two-edge control is easier to produce than the valve control with four edges, as only two control edges have to be adapted to one another. However, it does not achieve the force gain and accuracy of a valve control with four edges.
2. Hydraulic resistance control for an actuator with two displacement chambers by two hydraulic half bridges, in which only one resistance can be controlled (combination of type B + C half bridges).
A common application is the control of an actuator with a high response proportional valve (Hydraulic bridge rectifier). As soon as the valve is actuated beyond the range of the overlap/underlap conditions, only the control edges P A (inlet) and B T (outlet) or in the case of opposite directions of movement P B (inlet ) and A T (outlet) are active. This can be interpreted on one type C half bridge in the inlet and a type B half bridge in the outlet. In the area of zero overlap there is generally a valve control with four edges in the case of high response proportional valves (due to the radial clearance on the control spool).
Figure Z 15: Two edge control