Electro-mechanical systems typically used in robots have very low delays and are quite simple to build servo controllers for.
Hydraulic systems are much less common in robotics and have delay due to the length of the hydraulic lines. This delay may vary considerably depending on the system conditions.
What methods exist for dealing with this variable delay when designing a position or velocity servo controllers for hydraulic cylinders?
Update: I have spent some time checking academic literature and have found the following books:
- Introduction to Time-Delay Systems - Fridman
- Nonlinear Control Under Nonconstant Delays - Bekiaris-Liberis and Krstic
I have not had a chance to read these enough to have a clear answer to my problem yet. Hopefully this can provide others with a starting point at least. Both authors have many papers on topics regarding control with time delay systems that are nonlinear or varying.