Delta MMC120 - Manual (Page 70)

Hydraulic System Problems MMC120 Linear Motion Control Module
70 Delta Computer Systems, Inc. 360/254-8688
Pumps and Accumulators
Insufficient pump and/or accumulator capacity will cause the system response to degrade during a move
because the effective pressure drops.
Pressure transients due to insufficient accumulator volume cause jerky motion, particularly during starts and
stops. Note: Even systems with ‘fast’ pumps usually require at least a small accumulator near the cylinder to
maintain the constant pressure needed to get smooth motion.
Insufficient pump capacity can result in inadequate control when moving many axes simultaneously or when
making long moves. In these cases pressure can drop so much a fully open valve cannot maintain the
requested speed.
Identification and Correction
To identify and correct these problems, make a move with very low (or zero) gains except the FEED
FORWARD terms. Graph the move with DCS120. The graph (ignoring the Position terms) should show:
Drive (green)
Target Speed (purple)
Actual Speed (blue)
If the actual speed and target speed show:
Your valve probably has overlap. Replace the valve with a linear one or try increasing the DEAD BAND
ELIMINATOR value.