PCI-7344 Encoder Position Feedback to Voltage output

[Tommasos]

Hello,

I am trying to figure out how does the PCI-7344 Motion Controller defines its voltage output to a servo motor's amplifier (torque/current), given the digital position value from a quadrature incremental encoder, in order to control the position of the motor. In detail, the motor's amplifier outputs an emulated encoder signal, which is read by the PCI-7344. The motion controller then compares the reference position value (user input in counts) to the actual position (32-bit digital) from the encoder and outputs a -10/+10V voltage signal as a command signal to the amplifier. However, as the encoder is incremental it can turn infinately, so I cannot establish a relationship of bits/Voltage (am I correct?). So the question is, how does the PCI-7344 decide how high voltage to output based on the position feedback from the encoder. In essence, I am looking for a detailed block diagram or step-by-step walkthrough that desribe the conversion of encoder counts to output voltage. The block diagram provided in the N-Motion User Manual (p 4-26) does not really give this information.

Thank you in advance,

Thomas

[Brian_Beal]

Here is a pretty basic explanation.  There is no direct relationship between encoder counts and voltage output.  The controller keeps track of the position(from the encoder output).  It compares that to the desired position and determines a following error.  The following error is then put through the PID algorithm and the output of that is the voltage to the drive.  Depending on the PID settings, a given error can result in no voltage output or a large voltage output.  I can't speak on specifics of the NI controller, but PID theory can be found all over the web.