Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

constant tension torque control

Status
Not open for further replies.

EEtryingControl

Newbie level 4
Joined
Feb 24, 2009
Messages
5
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Activity points
1,319
bsm90c-375

I am trying to use an AC servomotor in a winding application that will wind with constant tension.
I read somewhere that the way was constant HP but this makes no sense as current will be very very high at slower speeds.
I have also been trying to use the tension * radius = torque equation but can not get this to work either as test results show varying tension as the role gets bigger and as speed is changed.
I need to know how to calculate my current so that tension remains constant with increase in diameter and speed/rpm.
any insight here would be greatly appreciated
Thanks
 

tension torque radius

interesting problem,

maybe info this will help

h**p://www.avaxhome.ws/ebooks/engeneering_technology/primer_flat_rolling.html

Mr.Cool
 

reel torque control

there is no mention of motor current in this document and that is what I am looking for, current as a function of radius and speed
I=f(r,s)
 

Unfortunately, you didn't yet mention, which measurement quantities are observable in your setup. As another point, the motor type can be important. AC servo isn't a clear specification. General, with an asynchronous motor, torque is nonlinear function of current and slip frequency, assuming CFD operation.

In a recent drive design, a VFD would provide a roughly correct torque estimation respectively direct torque control.
 

The motor is a baldor BSM90C-375
**broken link removed**

Everyone that I have talked to says that the torque and current are linearly proportional.

Im not sure what you mean in your statement about a VFD? Do you mean a variable frequency drive? If so, im not sure how a drive would do anything that I am looking to do, it is necesary in the application to control the motor but is just doing what i tell it to do.
 

O.K., I see that it's basically a brushless DC motor. It has a current proportional torque, that's right. So, if you make the current proportional to reel radius, you get constant tension. Speed doesn't matter in this respect.
 

ok, so the basic theory is that current = desired tension * radius / torque constant of the motor.
This is the equation that I used and when I changed the speed of the incoming paper, the tension changed considerably.
I then tested it at one speed and the tension was not constant as the role built up.
I then tested it at one rpm of the motor and tension was not constant.
I started out believing the above equation but also knowing from testing that speed changed things. while trying to figure out how to account for speed in my calculations i saw that the equation was not experimentally sound.
 

Of course, there are several possible factors, that modify the simple, ideal behaviour. One point is friction, that involves an motor idle current, which is also speed dependant. You may want to measure it by operating your machine with no load. If the machine involves a gear, there may be additional torque and speed dependant losses.

Generally, if the ideal equation doesn't fit, you have to measure the real behaviour and try to define a corrective term. But cause there's no better ideal equation, this is pure empirical, although it may lead to simple linear or quadratic expressions.

As an additional remark, during speed up or slow down of the coil, there's a considerable effect of inertia.
 

Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top