transfer function of mechanical devices?

[mImoto]

mechanical transfer function

I am wondering how can I extract the transfer funtion of a real system composed of motor, gears, etc. I mean, is there any empirical method to obtain the transfer function easily? maybe some special instruments?.

For a electronic system I suppose it's easier becuase you have to enter sinusoidal waves and measure the fase and gain change with respect to the input sin (all this supposing the system it's linear). But for mechanical-electrical systems??.

How do you people solve these problems in real life?

thanks a lot,

mimoto

 

[Kral]

1).
If you have the specifications of the components that make up the system, you can write a differential equation for the system and derive the transfer function.
.
2).
Another reasonable solution is to assume the system is second order. Apply a step input (force, displacement, etc), and measure the output response. By measuring the response time, frequency of overshoot, you can estimate the undamped natural frequency (w0) and damping factor (Zeta), by comparing these values with values for similar curves that can be found in any classical control systems text.
3).
Results similar to 2) above can be obtained by measuring the frequency response.

 

[dog1357]

Last time when we did some experiment with a robot, some of the transfer function is known, so the work is easy.
I guess the difficulty is also in how to relate the mechanical item to electrical item.