Hydraulic System Problems
TMC 188/40 Motion Control Module
Delta Computer Systems, Inc. 360/254-8688
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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 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
forwards. Graph the move with DCSMON. 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
HYSTERESIS.
