position control and velocity control in servomotor control

help in servo motors

hi!

Can anyone help me out by clarifying things about position control and velocity control in servomotor controlling, like what it acctually means when using it....?
To what application are they specifically used...? can the both be used together...?
can someone give some literature covering this...

thanks in advance...

Re: help in servo motors

It depends on your application, so for example if you are building cnc drill you will need to position drill head on specific location, in that case you will need position control ... in application like elevator, you will need to adjust velocity of elevation to make it persistent no matter how much load is in box, but also you will need to position it to level with opening, so one can say that it is position/speed control.

About implementation, you need to have encoder unit (linear or circular, depends on application). On encoder you are measuring time between pulses or number of pulses ... As position is dv/dt, it is easy to calculate relative position. You put those values in controller with reference values, and than calculate control values in means of current or voltage on electromotor.