# Closed Feedback Loop mechanical system examples

1. Feb 7, 2014

### nakas12

1. The problem statement, all variables and given/known data

Hello everybody I was hoping some of you could give me some some examples of some closed feedback loop mechanical systems.

This is for my controls class where we have to design our own control system. I'm having trouble trying figure out some systems. I know one would be cruise control but that is not an option considering it was shown as an example in our class.

Our goal is to model the system, linearize it and then find the systems transfer function and then find the state space representation.

Any suggestions would be helpful, but please nothing too difficult. Our goal is to use a simple mechanical problem.

2. Feb 8, 2014

### Staff: Mentor

It would be best if you would post your thoughts on such systems first. We don't do your homework for you here (which you know), but we should be able to suggest some systems for you to think about and build upon, as long as you show us your thoughts first. I have a few good suggestions for you, but would like to see how your are thinking about this school project first...

3. Feb 8, 2014

### nakas12

Ok sorry about that. But I'm thinking of having a system with either 1 or 2 degrees of freedom. I was thinking of a simple system where the input would be a force or torque and the output could be some kind of velocity or position.

The transfer function our professor wants though is a 3rd order or more.

4. Feb 8, 2014

### Staff: Mentor

Wouldn't the inputs and output be switched from what you propose? Maybe I'm not understanding the systems you want to model...

5. Feb 8, 2014

### nakas12

Umm I guess. Now I'm a little confused about what you mean. A system that was applied a force such as a car would have a certain velocity that it would to reach like cruise control.

6. Feb 8, 2014

### rude man

How about a home thermostat? The system would include the heater, room heat capacity, etc.

7. Feb 8, 2014

### nakas12

Unforunatley no I can't use that system. It's been used before too many time apparently.

8. Feb 9, 2014

### rude man

Ok, you're manufacturing saline solution for medical use. You start with distilled water continuously flowing into a tank at a constant rate, and a valve that drops salt from a salt container into the tank. A pair of electrodes measures the salt concentration and controls the valve so as to set the concentration to the desired level. Fresh distilled water continuously pours into the tank so the valve will be shutting on and off to keep the saline level constant.

(Salt when dropped in water ionizes almost completely so the water's conductivity is a measure of saline concentration.)

This feedback system has elements of continuous as well as discrete subsystems in it.

If you have trouble with the on-off valve, you could assume a continuously variable valve aperture to control the flow of salt continuously rather than the way a house furnace turns on & off. the analysis would be simpler in that case.

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