Ramp up curve in microcontroller??

[bazramit]

hi everyone

I want to ask you if anyone has idea about the ramp up curve ?

Ramp up:when you want to control a motor with the slope of a curve .
so is it pid control ??
or it's a segmentation of the curve and you control each segment to attain the target.

thanx

 

[alec_t]

I think the method you use would depend very much on what sort of motor you have and what the motor is driving.

 

[bazramit]

Hi Mr Alec_t

I have a Dc MOTOR , and i control it by PWM .

but if i want to create a special curve , what is the method used ?

thanx

 

[misterT]

Ramp up:when you want to control a motor with the slope of a curve .
so is it pid control ??

PID system responds based on error and is generally not very good following small changes (trajectories). Simple trajectory follower would use a feed-forward term with a PID controller.

Take a look at this pdf starting from the page 33.

 

[bazramit]

Hi misterT

thanx for your help .
but i want to explain to you what i want in particular:

if I have a motor DC running with 4000 RPM
and I want to change its speed to 8000RPM
So I will use PID loop , and the reponse will be like the exponential response

but what i want to do , is to control the form curve like this:
View attachment 67840

acceleration and deceleration delays are good .
so how I can control this 2 delays ?

eg : I can attain 8000 RPM in 4 sec.
? or I can can do it in 2 sec.
is it the term Kd in the PID loop?
thanx

 

[alec_t]

but if i want to create a special curve , what is the method used ?

If the curve is always the same then I'd use a look-up table for the PWM mark times of the mark/space ratio.

 

[bazramit]

Mr alec_t

No.the curve is not fixed.
I want to create a parameter to change the process of system

thanx

 

[misterT]

If I understand correctly, you want to make the DC Motor speed accurately follow a curve.. any curve.

Are you having trouble generating the curve or making the motor follow the curve?

 

[bazramit]

Hi misterT

when i want to control the motor by pid normally :
the equation is : pwm=pwm+Kp*e+Kd*de/dt+Ki*∫edt

but if i want to put this option(pid) and control the acceleration and deceleration delay ?? what is the equation that add the 2 options?

 

[misterT]

I have hard time understanding what you mean by delays, curves etc. And what you are trying to do.

If all you want is to change the motor speed from one set point to another smoothly during X seconds, all you need to do is to increase/decrease the setpoint linearly for X seconds. Don't change the PID parameters.

Example:
Your motor is spinning 4000 RPM.
You want to smoothly ramp the speed to 8000 RPM in 2 seconds.

Solution.
Increase the set point by 20 every 10 milliseconds until the setpoint equals 8000.

 

[MikeMl]

Read Post # 3 here

 

[bazramit]

hi Freinds

I'm sorry because my language is not very well

thanx