Hydraulics: position control that drifts with oil temperature

Hydraulic positioning is nonlinear and changes with temperature

What happens. A hydraulic axis that is accurate in the morning is sloppier after a few hours of work. The valve, the oil and the load change the response, and the controller settings that suit one condition overshoot or lag in another.

What it costs. Positioning accuracy, and with it part quality, plus slower cycles because operators approach the target gently to be safe. Re-tuning on the machine takes service time.

Why the usual fix fails. A standard controller is set for one operating point. Raising the gain for speed makes the axis oscillate when the oil is thin; lowering it makes the axis slow. Extra sensors do not remove the nonlinearity of valve and cylinder.

How a fixed-price remote diagnosis checks it. From recorded positions, valve commands, pressures and oil temperatures I fit a model of the axis and see how its behaviour moves over the temperature range. The fixed-price remote diagnosis tells you whether a model-based controller would hold the accuracy you need and what it would take to run it on your control hardware.

Background: Control that adapts to drift and wear

Position and force control of hydraulic presses is poor

What happens. The ram overshoots at the change from approach to pressing, the force builds up unevenly, and the same programme gives slightly different parts on a cold and a warm press.

What it costs. Part quality and scrap, particularly for forming and joining jobs where force and stroke are tolerance-critical. Cycles are stretched to let things settle.

Why the usual fix fails. Valve characteristics, compressible oil and a load that changes during the stroke defeat a fixed set of controller values. Operators compensate with slower ramps and dwell times, which cost throughput without removing the cause.

How a fixed-price remote diagnosis checks it. From stroke, force, pressure and valve logs of real cycles I check where the controller loses accuracy and whether a model of the press drive would predict it. The fixed-price remote diagnosis answers whether model-based control of position and force is realistic for your presses and what measurements it needs.

Background: Precision control for robots and machine tools