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DC Motor speed control
2

DC Motor speed control

DC Motor speed control

(OP)
Hi

I want to modify a wire drawing machine from torque control to speed control

The machine consist in 5 drawing blocks. Each has it´s own torque control board. The feedback for the control is taken fron the current consumed by each motor´s SCR rectifier.

I want to change the torque control system to a speed control. The feedback signal will be coming from a dancer pulley instaled on each block (potenciometer)

Do you know any company that sell the control board that I nedd to do this?

Thanks

RE: DC Motor speed control

Perhaps a stepper motor drive would be more well suited for your application?  There are many systems available for this.  Or are you referring to motors that are too lagre for stepper drives?

You could also go to a hall effect sensor and count pulses per second.  I would think this would be more accurate.

------------------------------------------------------------------------
If it is broken, fix it.  If it isn't broken, I'll soon fix that.

RE: DC Motor speed control

(OP)
The DC motors are too large. 40kW each


RE: DC Motor speed control

2
Is this, by any chance, an Arboga machine? If that is so, I think a crude speed control (EMF feedback, actually) is already available.

For "real" speed control, you need to add tachometers or encoders to each motor. Or do you have them installed already?

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: DC Motor speed control

(OP)
YES!. its an old Arboga wire drawing machine

The motors already have tachometers. In my 1st post I made a mistake. The feedback will be from the tachometers and the reference speed value from the dancers + individual potentiometers to do a fine adjustment on each black

Where can I get this "crude speed control"?(EMF feedback, actually)

Any guidelines?

Thanks

RE: DC Motor speed control

It depends. How old are the machines. There were Philips dives on the real old ones and Styrkonsult after that. Then, you can have Siemens or just about anything.

Please give me machine type and drive manufacturer/type. I know the guys that used to build and commision those machines and their drives.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: DC Motor speed control

It depends. How old are the machines. There were Philips drives on the real old ones and Styrkonsult after that. Then, you can have Siemens or just about anything.

Please give me machine type and drive manufacturer/type. I know the guys that used to build and commission those machines and their drives.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: DC Motor speed control

(OP)
Thats the one!

We have 2 machine. Both Arboga

One has the Philips drives and is for small diameter wire. This machine is in operation and already has speed control system working

The other for big wire has the torque control with Styrkonsult drives (90% sure) an its out of operation. This is the machine that I want to modify. I do not have the machine type. But I have plenty of pictures to try to identify it

Can I send you the pictures or maybe you help me contact the guys that used to build and commission those machines and their drives

RE: DC Motor speed control

Someone should give you an LPS for that info, Gunnar!!!

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: DC Motor speed control

OK lukin, you can find the address if you learn some Swedish and browse our home-page  smile  (no need to learn Swedish, just look under 'KONTAKT').  

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: DC Motor speed control

(OP)
Ok, thanks. Got it

I will be sending the pictures and any other information that could help to Id the machine

RE: DC Motor speed control

Gunnar

Just out of curiosity, is the crude speed control or EMF feedback accomplished by monitoring the back EMF induced on the armature and converting this EMF into a speed?

How is this monitoring physically accomplished seeing that there are brushes between the armature and any external monitoring devices?

RE: DC Motor speed control

The EMF is calculated from armature voltage and armature current and used as a measure of motor speed. There are several sources of error, one is the non-linear voltage drop in the brushes, another is the temperature dependent winding (and sometimes cable) resistance. Still another source of error is that the excitation also varies with mains voltage and temperature.

The error introduced by the brushes is actually the least problem. The non-linear part of the voltage drop is only half a volt or less. That is not more than a tenth of a percent when you have an armature voltage in the 400 - 600 V range.

Using a constant-current excitation scheme keeps the excitation error small and by calibrating for normal operating conditions, you can keep the armature resistance influence quite low in normal operation.

It is possible to have a speed error less than 1 percent over a 30 - 100 % load change. Good enough for many purposes.

BTW, I have received photographs of the machine and also contacted a friend that immediately identified the machine and also found the original manufacturer. That guy still has spare parts and will be in contact with lukin1977 today or tomorrow. Another great example of how well Eng-Tips works.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: DC Motor speed control

(OP)
Yes Gunnar

I wrote to him a couple of hours ago. Still waiting for his response

Thanks again for your help!

In this case the feedback comes from a tachometer coupled to the each motor shaft (close loop). EMF feedback is called an open loop feedback, right?

RE: DC Motor speed control

No. EMF feedback is also closed loop. As long as you feed something back, it is a closed loop.

Open loop would not produce a very reliable result. It is OK for dimmers and heaters, but not for DC motors.

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

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