Two sources of reference value for PID controller

Hello,

I have been solving following problem. I have one speed controller and two sources of the desired speed. One source
is the CAN bus and the second one is an analog input. I need algorithm for bumpless transfer between them. For example at the CAN bus is 1000 rpm and at the analog input is 500 rpm. The speed controller uses CAN bus value and suddenly the communication fails and I should use the value at the analog input. The problem is that there is a different desired speed. If I blindly use this value, I produce sudden disturbance and it is obviously wrong. I have tried to solve this with the FSM in the attachment but I am not sure if it is applicable. Please can anybody give me his meaning about my suggestion? Thanks a lot for any ideas.

This is easy.
speed=f*speed0+(1-f)*speed1
f is a fraction between 0 and 1
If speed0 input fails keep the last speed 0 and ramp f to 0. If speed 1 fails keep the last value for speed 1 and ramp f to 1.

Peter Nachtwey said:

This is easy.
speed=f*speed0+(1-f)*speed1
f is a fraction between 0 and 1
If speed0 input fails keep the last speed 0 and ramp f to 0. If speed 1 fails keep the last value for speed 1 and ramp f to 1.

Click to expand...

May be simple but nicely done. Goes in my bag of tricks

Thank you very much for your elegant solution Mr. Nachtwey. You are a genius.

Mostly I have a bag of tricks that I have accumulated over a lot of time.
I have come across problems like that before.
What I provided assumes that f ramps linearly between 0 and 1. f(t)=t/RampTime but a motor may not like the sudden acceleration. I have formulas for ramping f(t) as 3rd order and 5th order ramps so the velocities and accelerations are smooth.
f(t)=(-2*(t/RampTime)+3)*(t/RampTime)^2
for 3rd order ramps. There have been threads on this before.

Most PID controllers can do it bumpless, it works with a ramp