FOC and ultra small angular move.

Discussions regarding the Field Oriented Control (FOC) implementation on the VESC.
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable
Polux
Posts: 2
Joined: 29 Mar 2016, 11:48
Location: CH
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

FOC and ultra small angular move.

Postby Polux » 29 Mar 2016, 12:15

Hi,
I am new to this forum and new to BLDC motor control. For an industrial application, I want to know what is the smallest possible angular move in position control.
Let me explain. The machine is an XYZ gantry with 1um linear encoders. No problem during normal operation. But the initial setting is made with a camera reading reference targets. The software move the table with very small increments, +/- 2 to 5 microns (yes, microns) to know the orientation of the part to be machined.
For some histocal reason, the head is driven by hi precision balls screw directly by the motor, no gearbox.( Don't know the reason, probably no backlash).
The machine is working very well with DC motors. But motors and home made amplifiers are old, and need to be replaced.

So, knowing the balls screw step is 25mm, a move of 0.002mm will result in a (0.002/25)x360= 0.0288 (0.072 for 5u moves)
Is the controller able to control the motor to make so small moves ?

Thanks

Angelo

rew
Posts: 943
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

Re: FOC and ultra small angular move.

Postby rew » 30 Mar 2016, 12:12

Angelo,

I would expect the ball screw pitch to be something like 2mm per revolution. So that a 2 micrometer movement corresponds to a 1/1000th of a revolution of the motor. The motor movement cannot be expressed in mm, that makes no sense.

As far as I know, as long as the encoders provide sufficient feedback about the position, the motor can be made to do any movement you want. If you do have backlash (and that's quite possible at the micrometer scale), things might be difficult to tune...

pf26
Posts: 310
Joined: 28 Mar 2016, 14:37
Location: FR Valence
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

Re: FOC and ultra small angular move.

Postby pf26 » 30 Mar 2016, 14:13

Hi,
Playing with VESC FOC +encoder (8192 counts per turn), I can achieve movements of a few counts using a 11 poles BLDC. Probably, with more care and good encoder, one can control maybe 10 "electrical" degrees (need to divide this by the pole count to get real degrees out of the motor). That's a lot more coarse than what you need. Maybe using a 300 steps 3 phase stepper motor would do, but I doubt it, because even when the controller produces the right magnetic field, the motor response is not perfectly linear. And if you require the slightest torque, then accuracy drops
I think you better gear (timing belt ?), small bldc can turn very fast...

Polux
Posts: 2
Joined: 29 Mar 2016, 11:48
Location: CH
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

Re: FOC and ultra small angular move.

Postby Polux » 30 Mar 2016, 19:37

Hi,

Yes, the 0.0288 value is in degrees. Ball screws are special, made with small backlash.

Another input I get is: in normal operation, head speed is in the range of 100 to 600mm/s. Thus 240 to 1440RPM. That's why a gear reduction should be low. Assuming gear ratio would be 2 or 3, the minimum angle would raise to 0.0576 to 0.0864, still very low.

I would give it a try.

Angelo


[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable
[phpBB Debug] PHP Warning: in file [ROOT]/vendor/twig/twig/lib/Twig/Extension/Core.php on line 1236: count(): Parameter must be an array or an object that implements Countable

Return to “FOC”

Who is online

Users browsing this forum: No registered users and 1 guest