Encoder Model

[SK0480]

Ok well Iam building a positioning control systems using a stepper motor...Iam using darlington as a amplifier and encoder to measure the position.

Attached is the schematic...and it would be great if you can provide me some suggestions.

Thanks

[Greg_S-Video]

Hello SK0480

Thank you very much for posting your control model.  You do not need the conversion factor in the feedback loop.  Your system's model is accurate otherwise.  Having the conversion factor in the feedback won't actually act as a conversion factor.  Instead, it will act as a gain which will cause your system to behave differently in simulation than in practice. 

Your signal of interest is motor position.  Since this will be a digital control application, what you will have to do in your code is take in the motor count (pulse) information and use the conversion factor to obtain the motor position and use that as your feedback. 

Since you are dealing with a single input/single output system, you need only concern yourself with motor position for the purpose of compensator design.  For implementation, you will need to account for the conversion from your feedback pulses to a motor position.

Can you please let me know if this is clear?  Thanks again!

[SK0480]

ok so you are saying to not include anything on te feedback loop and just keep the amplifier and motor second order transfer function..

Thanks

[Greg_S-Video]

Hello SK0480

That is correct!  For the purpose of control design, you do not need to put the encoder conversion in your block diagram as it has no relevance to the system dynamics.  You do need to take it into account when you are bringing the feedback in your code though in order to feed back the current position.  Thank you very much for the opportunity to assist you with this.

[shag]

---

@Greg_S-Video wrote:

Hello SK0480

Thank you for this information. To find the number of revolutions for a given number of pulses, simply divide the number of pulses by 16.

For a more detailed explanation:

If you know that the encoder is 16 pulses per revolution then we also know how many revolutions per pulse we have.  To obtain this value, we simply take the inverse value of the pulses per revolution to find the number of revolutions per pulse.

In short, Number of Revolutions = (Number of Pulses) / 16 = (1/16) x Number of Pulses = (0.0625 x Number of Pulses)

So, if you have convert counts to revolutions, multiply the number of pulses by 0.0625 or divide by 16.

I have included a  document that illustrates this step by step but I do not mean to make this situation overly complicated.

This concept will be very important for your success so please let me know if I can provide any further clarification. 

---

Hi Greg,

I need to calculate the velocity of an incremental encoder,

I'm using RE22I (incremental encoder) which can give 8192 counts per revolution,

it has A,B,Z as output signals,

I want to know how can I use this signals to calculate speed at which encoder is rotating.

Please help, thanks in advance.