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11-10-2019 #1
You need to do a bit reading up about servo and stepper motors.
Those servo motors you've removed, are 1.2Nm continuous stall, and will deliver that torque all the way to it's maximum speed of 5000RPM. They also have a higher instantaneous/peak torque, which gives you a boost for fast acceleration.
Stepper motors on the other hand, only produce the rated torque at zero speed. As you increase speed, torque drops of very quickly.
I couldn't find a speed/torque diagram for those HSS steppers, but Leadshine have one published for their similar motor -
Running with a 70VDC supply, torque has dropped to around 1Nm at only 2400rpm, so you have under half the performance of the servo motors you've removed at continuous torque, and probably under 20% once you factor in the instantaneous torque available with the servo, which is where servos excel over steppers.
Those servos you've removed are around the 600-750W power, however you'll struggle to get modern AC servo motors that spin to 5000 (one major benefit of DC motors, is you can spin them very fast with primitive technology!).Last edited by m_c; 11-10-2019 at 10:54 AM.
Avoiding the rubbish customer service from AluminiumWarehouse since July '13.
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11-10-2019 #2
Forgot to mention, I'd guess the vacuum pump will be some kind of simple design with high leakage, so it's unlikely any kind of valve is needed. You just need to plumb the pump to the bed, although depending on the bed design, it may be better to put it through a manifold to control zones (if the bed is machined with zones?), and also some kind of filter to stop anything being sucked through the pump.
Avoiding the rubbish customer service from AluminiumWarehouse since July '13.
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11-10-2019 #3
Thank you M_c.
- Vacuum bed: it has 3-4 connectors on the back, but I'm not sure if are zones. I'll check.
- Motors: Thank you a lot for the info.Last edited by agors; 09-10-2020 at 02:57 PM.
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11-10-2019 #4
I'm thinking at what you said and I did a couple of calculation,
So I'm thinking at alternatives,Last edited by agors; 09-10-2020 at 02:57 PM.
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11-10-2019 #5
If the servos have only be running of 70VDC, then they won't have been running at the full speed anyway (for electric motors, voltage = speed, current = torque).
Those leadshine drives do look like they'd be capable. CNC Drive also do suitable drives (http://cncdrive.com/DG4S_08020.html for 80VDC/20A version).
The key to using those will be making sure the encoders are suitable. You need quadrature encoders, not resolvers which your machine might just be old enough to have.
For modern servo drives, the tacho output from the motor is generally not needed.
Z axis you can do however you want. It's not likely to have a lot of travel, or need to move that fast, so a suitably geared Nema 23/4 motor is likely to be a good option. You will however still need a driver for it.
You'll also need a breakout board of some form, but I would advise against using a parallel port, as it won't be fast enough to get the maximum benefit from the servos.Avoiding the rubbish customer service from AluminiumWarehouse since July '13.
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12-10-2019 #6
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13-10-2019 #7
I would guess that is a quadrature output incremental encoder, however searches have not found any manuals for a 755 encoder.
How many wires does it have?
Ideally you want encoders with differential outputs, which means you're looking at a minimum of 6 wires (+V, Gnd, A-, A+, B-, B+), plus possibly an index pulse (Z-, Z+).
Everything has the potential for failure, but provided you're willing to learn, then most things are possible.Avoiding the rubbish customer service from AluminiumWarehouse since July '13.
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