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Anyone good at mechatronics? Transfer functions help.

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andy257

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Hi guys

i am stuck with a couple of problems to do with transfer functions.

For the above system i need to know what the overall transfer function is. I have had a go and got an answer of 0.99mm/V. I am not sure if this is correct or if the units of measurement are correct (mm per volt?)

My next problem i have no idea how to calculte this one

if anyone can help or is experienced in mechatronics i would be ever so greatful

thank you

andy

Both of these are of the basic form

. ----<---[ F(s) ]---<-
. | |
. | |
. Input ---->-----()--->--[ H(s) ]-->------> Output

The transfer function of this type is:

H(s)
1 + H(s)F(s)

Well i'm getting 0.04 mm/V been a while since going control theory

anyone else help me out here? iam really stuck

thanks

andy
bttt

You can work this out using simple algebra. Looking at the block diagram below,

Out/Vin=Kfwd/(1+Kfwd*Kfb)

This looks like homework to me. Work it out and post your answers here, and we'll compare answers. I have an answer for the 1st problem, but haven't looked at the second one.

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Hi, thanks for the reply, i got an answer the first time around. I got 0.99mm/V. Maybe its a calculation error?

(10 * 6) / (1+(10*6)*0.01)

= 0.99mm/V ??????

depending on how i work it out i also can get an answer of 37.5mm/V

am i any closer?

cheers again

andy

andy257 said:
Hi, thanks for the reply, i got an answer the first time around. I got 0.99mm/V. Maybe its a calculation error?

(10 * 6) / (1+(10*6)*0.01)

= 0.99mm/V ??????

depending on how i work it out i also can get an answer of 37.5mm/V

am i any closer?

cheers again

andy
Hold on, dude. There is only one answer to your equation. You don't have options on the order in which you evaluate it. What do you mean, "depending on how i work it out"? Which answer is correct? I'm trying to get you to think for yourself.

well from recalculating it, the answer is 37.5mm/V

(10 * 6) / (1+(10*6)*0.01)

60 / 1 + (60*0.01)

60 / 1 + 0.6

60 / 1.6

= 37.5mm/V , dont know why i got 0.99? i was sure that was correct.

for the 2nd harder system i listed i reckon its this

(6 * 0.1) / 1 + (6*0.1)*(2*1)

0.6 / 1 + (0.6 * 2)
0.6 / 1 + 1.2

0.6 / 2.2

= 0.27 (however the units are beyond me, too many different ones)

RON H

thanks for your time and patience. I was not trying to get others to do the work for me, just give me a helping start. I would be greatful if you could cast your eyes over my solutions to see if they make sense.

oh and if you could tell me what the units might be that would be great

thanks
andy

Andy, I apologize for sounding mean. I guess I'm just a cranky old fart. But I did get you to look at the math again. I got the same answer for the first one. I'm pretty sure it's right, but i was wrong once before. I'll look at the other one when I get a chance.

The trick on the second problem is reading the units (as you discovered, I think). The units of the current to pressure converter are in kPa/mA, and m/s means meters per second (velocity). As a hint, the output units will be in m/s/mA, or meters per second per milliamp, i.e., the output velocity is linearly proportional to the input current. Tell me the answer you get, and I'll tell you if I got the same. No guarantees that I'm right.

Here is a web page that explains kPa, which I don't think is actually important to solving the problem.

thanks ron,

my answer for the second one was 0.27, its posted in my last reply under the working out for my first problem. thanks for your help, your a star.

andy

andy257 said:
thanks ron,

my answer for the second one was 0.27, its posted in my last reply under the working out for my first problem. thanks for your help, your a star.

andy
Yep, that's what I got. Let us know if we were correct.

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