Flow rate ratio control device

A control mechanism applied to a fluid circuit mechanism comprising a main channel into which fluid flows, a plurality of branch channels branching from an end part of the main channel, control valves respectively provided in the branch channels, flow rate meters adapted to directly or indirectly measure a flow rate through the main channel and flow rates through the respective branch channels, and a pressure sensor adapted to measure a pressure on an upstream side of one of the control valves in one of the branch channels, the control mechanism comprising:

• a valve control section adapted to control the control valve provided in the one branch channel, to make a pressure on the upstream side of the control valve equal to a given target pressure, and upon the pressure exceeding a pressure lower than the target pressure by a predetermined value, start to control other of the control valves so as to make flow rate ratios of the respective branch channels equal to predetermined ratios;
• and
• a target pressure setting section adapted to set the target pressure lower as the flow rate through the main channel decreases, and output the target pressure to the valve control section.