s_masiero said:
ok, but now i feel a littel confused...! let me explein the whole problem:
I have to write a chapter of my thesis and talk about the STABILITY on a hydrulic actuator. i shoud write:
-why stiff hydrulic are better
If you are positioning a mass by push or pulling a spring connected to the mass then would you want to have the spring stiff or weak? You want it stiffer. Systems with a higher natural frequency have 'stiffer springs'.
Do you know what a spring constant is?
Do you know what the natual frequency of a mass and spring is?
Do you know how to calculate the natural frequency?
ftp://ftp.deltacompsys.com/public/PDF/Mathcad - Natural Frequency.pdf
-which are the causes of instability in a hydraulic system
(and in this section i would talk about stiffness of oil, stiffness of pipes, entrained air into oil)
What is your definition of stability? Mine is the tradition control theory version where pole move to the right hand plane or the system as a gain of one with 180 degrees of phase lag.
These are control issues.
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-ways to improve stability in a hydraulic system
(in this section i would talk about:-working at high pressure
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Again I don't thingk stability is the right word. I think you are look for natural frequency or stiffness.
-improve the control system)
Improving the controls will make a big difference but it is hard to compensate for a poorly designed hydraulic system.
-what happens if i work at high pressure
(in this section i wolud talk about:-design of the pipes
ways to increase forces)
Higher pressures do not increase the stiffness or natural frequency. Just the overall gain. Which equation below indicates that?
-what happens if i act on the control system
??? I don't know what you are asking here.
-why it could be the better way to improve stability
The motion controller does contribute to what I call stability by placing the poles of the system as close as possible to the negative real axis. This results in a critically damped or underdamped response.
Buzz words. Not practical yet. At least not for commerial purposes.
-what happens if control is not enough robust
The world begins to shake.
do you think these sections are enough for the chapter? For my work i need some help on develo these arguments. do you think you can help me?
You are trying to take years of info an condense it into a chapter? Will I get the master's degree?
What is the VCCM formula?
What is the formula for natural frequency?
What is the formula for oil flowing through a valve?
What is the formula for the change in pressure as a function of compressing or adding or removing more oil?
What is the operationnal envelope of a hydraulic system?
What is the forumla for a general closed loop transfer function?
When do systems become unstable?
What is a gain margin?
What is a phase margin?
What are poles and zeros?
It seems to me you are not prepared to answer these qestions. You must understand these equations. I have pointed you in the right direction. Now it is time for you to do some research and simulations.
If you insist on saying that raising the pressure will make the system more stable then you will get a poor grade.