Parabolic Curve
A curve that increases flow rate slowly in the middle region of lever travel and quickly at the ends. The operator gains millimeter precision when working near center and gets full speed when pushing the lever all the way; this allows both fine adjustment and fast transport with a single lever.
On a parabolic curve the gain is not constant, it grows with lever angle. Thirty percent away from center you may get perhaps a tenth of full flow rate; in the last thirty percent half of the flow rate comes in. This suits the way people work: fine work at center, coarse work at the ends.
- Control becomes noticeably easier in load placement, attachment alignment, and maneuvering in tight spaces.
- On jobs requiring constant speed it is a disadvantage; holding the lever in the same place gets harder and speed estimation degrades.
- The curve is defined in the controller software; the valve itself does not change, only the signal is remapped.
In AXI's HCT402 kit the joystick characteristic is defined with this logic: millimeter precision in the middle region, high speed at the extremes. On the position control side, a PID based control with typically ±1° accuracy runs. Do not confuse the two layers: one is the operator's feel, the other is the motor's own position accuracy.
Where this term is used: The Importance of Hydraulic Control: Why Should It Be Commanded by an Electronic Signal?