Delta MMC120 - Manual (Page 21)

MMC120 Linear Motion Control Module Preparing For Installation
Delta Computer Systems, Inc. 360/254-8688 21
Hydraulic System Notes
Hydraulic systems must have enough pressure and fluid volume (accumulator) to move the desired load the
commanded distance at the commanded speed. Inadequate pressure or volume will cause the axis to lag the
target position as the controller attempts to move the axis faster than the system can move.
There should be no flexible hose between the valve and the cylinder being controlled. Hose swells and
contracts as the valve opens and closes, causing oscillation and loss of control.
If proportional valves are used they should have zero overlap and a linear (not curvilinear) response.
Overlapped or nonlinear valves may cause oscillation or hunting.
Valves with slow response cause the Motion Control Module (MCM) to overcompensate for disturbances in
the motion of the system. With a slow value the system will not respond immediately to the control signal, so
the MCM continues to increase the drive signal. By the time the system begins to respond to the error, the
control signal has become too large and the system overshoots. The MCM then attempts to control in the
opposite direction, but again it overshoots. These valves can cause the system to oscillate around the set point
as the MCM overshoots first in one direction, then the other.