motion control gain 1/s?

Controllogix5K 1756 L71. RSlogix5K. A proportional gain was set between 25 and 50 for a motion control application. Lowering the P. gain to 25 made the control action slower (because the gain was decreased and consequently the P-band was increased).

But the P-gain's unit was 1/s. what does "1/s" mean? 1 over span? So, 25% over the span?

unsaint32 said:

Controllogix5K 1756 L71. RSlogix5K. A proportional gain was set between 25 and 50 for a motion control application. Lowering the P. gain to 25 made the control action slower (because the gain was decreased and consequently the P-band was increased).

But the P-gain's unit was 1/s. what does "1/s" mean? 1 over span? So, 25% over the span?

Click to expand...

You haven't provided enough information. Is the proportional gain for the velocity loop or the position loop. It makes a difference. s could be seconds but I think it is the Laplace operator so 1/s is an integrator. If velocity error is integrated then you get position error.

The is an overlap in what the PI gains do in Rockwell motion controller the Proportional gain in the velocity loop does the same thing a derivative gain would do in the position loop. The integrator gain in the velocity loop does the same thing as the proportional gain in the position loop. Weird huh, but that is the way the math and control theory work out.

So the integrator in the velocity loop is the same as the proportional gain in the position loop.

The other thing that is a little strange about Rockwell motion control is that the outer loop is usually a position loop. The output or CV of this outer loop is a target or set point velocity for the inner velocity loop. Mathematically the Rockwell method is correct but there is only one encoder position feed back. The actual velocity for the PV for the inner loop must be derived from the encoder. I would prefer to simply use a position PID rather that using an inner PI velocity and outer PI position loop.

We actually provided this option on the HYD02 and M02AS.

The s stands for seconds. This is because the PID equation is generating a velocity command to actuate the drive. 1/s is giving it the right units, your desired control unit per second.

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Al

http://theplchub.com