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moorthi
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India - Member - moorthi

Join Date: Sep 2007
Posts: 26

Servo Drive

10/20/2009 7:00 AM

we having laser cutting machine. In that machine, they are two servo drives(10A each) used, one for X axis and another one for Y axis movement.

Common power supply board is used for powering the two servo drives.

The power supply board has the following

1. three phase bridge(75A).

2. igbt(50A) connected to 25 ohm high wattage for breaking.

3. circuit board for some control and fault indication.

Dc bus voltage from power supply board is given to servo drives.

problem facing

when the servo drives moving at 50% of speed and below, it works fine and if the speed is above 51% to 100 % speed, we getting break fail indication.

During this time motor is not stopping at exact position.

Can any one, give idea how to correct this problem.

thanks

moorthi

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redfred
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Engineering Fields - Electrical Engineering - Been there, done that. Engineering Fields - Control Engineering - New Member

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Location: Long Island NY
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Good Answers: 981
#1

Re: Servo Drive

10/20/2009 10:54 AM

From the information you've given, I cannot say precisely what could be your problem but I do have an idea. I suspect that the regenerative breaking resistance is too high for the inertia the motors is having to stop at over 50% drive velocities. A common mistake that people make is that the motor resistance is part of this equation and not just the resistor added. So I would start by reducing the value of the braking resistor by the measured resistance. Instead of replacing the 25 ohm high wattage resistor though, you could parallel another resistor with this of a lower wattage. Measure the motor winding resistance and calculate how to reduce the 25 ohm resistor by this value.

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Anonymous Poster
#2
In reply to #1

Re: Servo Drive

10/21/2009 1:25 AM

for servo drives,the external breaking resistor is it necessary?

THANKS

MOORTHI
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redfred
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#3
In reply to #2

Re: Servo Drive

10/21/2009 9:38 AM

Depends on the driver electronics. Without being familiar with the circuit being used or the mechanical load being stopped one cannot say for certain. But since this circuit is using a resistor for dynamic braking, reducing this resistor will increase the braking force available. Hopefully the braking fault at greater than half speed was from insufficient braking.

FYI One design advantage to an added braking resistor is that it and not the electronics will dissipate the energy.

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Anonymous Poster
#4

Re: Servo Drive

10/22/2009 11:50 PM

Is the break working proparly from 0 to 50% of the speed ? What is the value of the DC bus voltage at break alarm?
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moorthi
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India - Member - moorthi

Join Date: Sep 2007
Posts: 26
#5
In reply to #4

Re: Servo Drive

10/23/2009 1:02 AM

during 50% of speed dc bus voltage is 570vdc
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amro moh
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Join Date: Oct 2008
Posts: 2
#6
In reply to #5

Re: Servo Drive

10/23/2009 10:55 AM

Dear moorth Im asking about the dc bus voltage at alarm break condition(50%to 100%) and what is the break type ?
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moorthi
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India - Member - moorthi

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Posts: 26
#7

Re: Servo Drive

10/24/2009 2:14 AM

Dear all friends;

I thanks to all your help. Now i have solved the problem, cutting machine is working fine at all speeds. The natural of problem was that breaking IGBT did not gated whenever the breaking is required,because of the one of the passive component fault.

Thanks

moorthi
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redfred
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#8
In reply to #7

Re: Servo Drive

10/24/2009 9:12 AM

Classic troubleshooting scenario. Initial ideas only get you close to the root of the problem. Glad we could help.

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amro moh (1); Anonymous Poster (2); moorthi (2); redfred (3)

Previous in Forum: current withstand curves for the Generator   Next in Forum: how we calculate capictor panel during the installation time,need formula.
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