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Encoder feedback ICs on ACC-1P card for clipper seems vulnerable


lukewang
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Hi,

 

We are using clipper with ACC-1P option (a piggyback motion card for extra 4 servo channels on the top of clipper) for plasma cutting machines.

 

After over 10 installations on different OEM's plasma cuttin gmachines, we found that encoder feedback ICs on the ACC-1P motion card are very easy to get damaged (almost every ACC-1P card on our machines have been repaired at least once or twice, some of them 4 times!). However, the encoder feedback ICs on base card are hardly damaged.

 

Plasma unit is quite noisy electrically. But I am quite confused with the difference between base card and ACC-1P card. Just wonder if ACC-1P card is really more vulnerable than base card? Anyway we can stop this problem continuing?

 

Thanks.

 

Luke

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The encoder interface circuitry on the ACC-1P is identical to that on the Clipper. Any differences in failure rates are much more likely to be due to different paths in for electrical disturbances.

 

These types of problems are very difficult to diagnose from a distance. But obviously you need to examine very carefully your wiring, shielding, and grounding on the machine.

 

You may want to examine adding protective circuitry, whether diodes or isolation. Our ACC-8D Opt 6 board provides optical isolation for 4 3-channel encoders, and is intended for noisy applications like this.

 

Best regards,

 

Curt

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Hi Curt,

 

We did try some encoder feedback isolation board from the third party. It works fine for the first couple of months. Then something strange happened: axis drifts without any following error but axis position display is unchanged.

 

The same controllers used on laser applications are perfect. That's why it rings my bell on plasma electrical noise.

 

Can you point to me more detailed info of ACC-8D opt 6? I cannnot find it on Delta Tau website. Thanks.

 

Cheers,

 

Luke

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Hi Curt,

 

Thanks for the manual. As we are going to use ACC-8D opt 6 directly with clipper WITHOUT ACC-8D card. So I have a few questions for the manual:

 

We use panasonic servo motor A5 series. if we use ACC-8D opt 6 card for this servo drive, we intend to wire as follows:

(1)Servo drive differential encoder signal outputs A+/A-, B+/B-, C+/C- are led into ACC-8D opt 6 card inputs (TB1).

(2) ACC-8D opt 6 card outputs(TB2) are connected to clipper encoder differential inputs directly.

 

Here are my questions:

(1)on ACC-8D opt 6 card, should I connect 0-GND (TB1, pin 26) to GND on servo drive and leave TB1 pin 25 (+5V) unconnected? remember we are using differential encoder signals.

 

(2)on ACC-8D opt 6 card, should I connect TB2 pin 25(+5V) and TB2 pin 26 (0-GND) to clipper +5V power supply?

 

Thanks for yor help.

 

Cheers,

 

Luke

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On TB1, which accepts the external encoder signals, you are correct that the pin 26 GND signal must be tied to the GND signal of the servo drive(s). But you are not correct that you can leave the pin 25 +5V signal unconnected. This side of the accessory is powered through this pin (which is why the manual says "MUST USE"). So you must have a 5V supply somewhere (it could be in the drives) referenced to this same GND level.

 

On TB2, you can connect both the +5V and GND pins to comparable pins on the Clipper.

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