motor control

[james patricio]

Hi guys,

I would like to ask some help from the expert here about my problem. Acually, it's just a follow up question on my previous post. I want to control a motor with an analog voltage output 0 t0 10vdc supplied to the amplifier. I have a digital rotary switch with 0 to 15 positions. My digital to analog scaling is 0-4000 vs 0-10vdc. I already tried it and my problem is the acceleration and deceleration so abrupt whenever I turn my rotary switch abruptly from low to high speed and from high to low speed. Somebody advice me to use timer for acceleration and deceleration. My idea is to use also the timer value to add or subtract from my digital value 0-4000 stored in data register to be converted to analog value. But I could hardly translate my math into ladder logic in this situation. Can anyone give me an additional idea on how to do it? By the way, I'm using mitsi A1SHcpu with A1s62da

Thank you and advance.
james

 

[DickDV]

If the 0-10VDC signal is going into a VFD, simply set the accel/decel ramps in the VFD to limit the rate of change. Even if you rotate the switch quickly from minimum to maximum speed, the drive will only accelerate the motor at the rate set in the VFD.

 

[james patricio]

thanks DickDV for the reply.

Actually the drive unit is not familiar to me. It is an old FANUC analog servo/velocity control. I have no manual for it on how to set the acc/dec. but anyway thanks for the reply.

 

[Electrically_Bound]

I am not familiar with that specific processor, but there are several ways to go about this. If I understand your problem correctly, you are wanting to limit the rate of change of reference. I'm also going to assume that switch position 0 = 0 counts and switch position 15 = 4000 counts (that's 266.6 counts per switch position)

reference = (switch position)(266.6)

filtered reference = filtered reference + filter constant(reference - filtered reference)


where filter constant is a number from 0 to 1. Use a 1 for zero filtering.

Maybe you can translate that into the code you need.

 

[james patricio]

Thanks for the reply Electrically Bound. I am just a bit confused on the second equation, I'm sorry I just want to clarify:
filtered reference = filtered reference + filter constant(reference - filtered reference)
How to get the "filtered reference" coz it appeared three times in the equation? My understanding for this is as follows.. please correct me if I'm wrong. Assuming filtered reference = x; filtered constant = y; reference = z, then the equation above becomes:
x=x+y(z-x), solving for x, x-x=yz-xy, simplify:
0=yz-xy same as xy=yz, solving for x eliminates y.
(xy)1/y=(yz)(1/y)
x=z
If i'm right in simplifying the equation, I would get (filtered reference)x = z (refernce).
thanks again.

 

[Mickey]

Another way to express(document,label) the above formula. ( first order filter)

FV=FV+C(NV-FV)
Where:
FV= Filtered value
C= constant (range 0-1) The smaller the number the more dampening.
NV= New Value