Lineary actuator - direct drive

| U | V | W | |S-N| |N-S| |S-N| |N-S| |S-N|--------> Force | U | V | W |

(alse U, V and W can be staked on top of each other

Does anyone knows the relationship between coli length and magnetic pitch (I can hardly imagine the coil being 3 times magnet lenght, som it seems so).

Is it possible driving a constant force in any position - imagine:

| U | V | W | N| |N-S| |S-N| |N-S| |S-N|----->(|HEAVYLOAD|) | U | V | W |

Does anyone know the dimensions or how the principles work (is it standard AC motor drive with 120 degrees lack)?!

No one knows how it works, it's all magic!!

And I vote for you leaving this group....

A linear stepping motor is just an unrolled stepping motor - the Douglas W Jones Tutorial is a good place to start.

Coil pitch and magnetic field pitch have to be the same.

Sort of. The force depends on the phase and magnitude of the current through the coils and the exact phase position of the magnets vis-a- vis the coils. You can use a couple of linear Hall sensors (mounted outside the direct magnetic field of coils) to locate the position of the moving magnets (or more precisely, the field they generate) vis-a- vis the fixed coils, though you may well have to correct the Hall outputs for the stray fields from the coils.

The force on the magnets is zero when the magnetic field is in phase with the magnet and rises as the phase difference increases to 90 degrees. Sensible people tend to try to operate at a phase shift of around 45 degrees, which only gives them 70.7% of the maximum force available for a given coil current, but minimises the chance of slipping a step.

You need to be able to program the currents through the two or three sets of coils involved - for which you need a microstepping drive. It is usual to rely on pulse width modulation to control the currents through the coils.

It isn't a good idea to rely the inductance of the coils to filter out the high frequency components in the coil current - the coil leads then radiate a great deal of radio-frequency-interference, which can upset the neighbours and the FCC. Use a pi filter mounted close to the driver to minimise the size f the transmitting antenna.

-- Bill Sloman, Nijmegen

And I vote for you leaving this group....

I'm sorry Asbjorn but if you did some searches on google you can find loads of useful information much more quickly than you will get it here. If then after digesting all the information you have some more specific questions then this is the place to ask and I'm sure many people will be ready to respond.

BTW I did a search and found this interesting document:

It's by no means everything but provides a good start with understanding and was found at the bottom of the first search result from Wikipedia.

Dave.

He who posts from googlegroups should watch his language or risk permanent termination.

...Jim Thompson

I think you have gotten the relative spacing of coils and=20 magnets a little wrong. The cycle of magnetic poles (the=20 length between similar points in the repeating pattern of a=20 pair of magnets and the spaces between them ) must match the=20 cycle of coils (the length between the same point in the=20 repeating pattern of coils). So each 3 coils covers two=20 magnets. By varying the current direction and magnitude of=20 the current in each of the three coils, the set can=20 approximate the effect of a single coil that has an=20 arbitrary position in the coil pattern. That coil will=20 interact with the magnetic cycle of the permanent magnets in=20 a sinusoidal force pattern. There is a relative position=20 that produces maximum force in one direction, another=20 relative position (a half a pattern cycle away) that=20 produces a maximum force in the other direction, and a pair=20 of points half way between those positions that produce no=20 force.

The trick is to know where the magnets are, at all times,=20 with respect to the coil pattern, and continuously adjust=20 the 3 currents (in magnitude and direction) to keep the=20 total effect at one of the force peaks as the magnets move.=20 Which peak you choose depends on which way you want the=20 force to push. This is the linear analog of a permanent=20 magnet, rotary synchronous motor.

--=20 Regards,

John Popelish

| U | V | W | |S-N| |N-S| |S-N| |N-S| |S-N|--------> Force | U | V | W |

(alse U, V and W can be staked on top of each other

Does anyone knows the relationship between coli length and magnetic pitch (I can hardly imagine the coil being 3 times magnet lenght, som it seems so).

Is it possible driving a constant force in any position - imagine:

That would be a voice coil actuator with position sensing. force is related to current. I guess you could use a load cell to sense force against an object.

Bob

| U | V | W | N| |N-S| |S-N| |N-S| |S-N|----->(|HEAVYLOAD|) | U | V | W |

Does anyone know the dimensions or how the principles work (is it standard AC motor drive with 120 degrees lack)?!

Best Regards

Asbjørn

Everybody gets permanently terminated eventually, so Jim's got it more or less right for once.

As an intimidator, he doesn't really hack it, despite his imaginary friends inside the FBI.

-- Bill Sloman, Nijmegen

The same ones you stated are keeping you out of the US?

-- aioe.org is home to cowards and terrorists

Add this line to your news proxy nfilter.dat file

• drop Path:*aioe.org!not-for-mail to drop all aioe.org traffic.

Do pay attention. I was merely suggesting that you tranquillised yourself by taking over one of Jim Thompson's sillier delusions.

-- Bill Sloman, Nijmegen

You pay attention, and put more effort in keeping your lies straight.

Slowman is so-o-o-o-o SLOW that he missed my offer to Bloggs to introduce my "friends" if Bloggs would show his face. So far Bloggs is a no show.

...Jim Thompson

I didn't actually miss it, much as I would have liked to.

It was in the "heat pumps" thread, and I commented on it on January 1,

Jim is reliably out of touch with reality.

-- Bill Sloman, Nijmegen

I find it only slighty interesting that you think that are the only person here who is in touch with reality. How can everyone else in the world be wrong? Humm????????????????????????

Jim Thompson is definitely out of touch with reality. Everybody gets things wrong to some extent, but he gets them wrong remarkably often (whch is why I comment on it).

You don't have the same problem with reality - hardly anybody else does - but you do have a remarkable knack for coming to conclusions that can't be justified by the text that you are quoting, which would suggest that you do need to find yourself a remedial English class.

It is posible that you might be conciously subverting the conventions of logical argument for some hoped-for comic effect, but if you are your dead-pan is pretty much perfect.

-- Bill Sloman, Nijmegen

ly

Thanks for replying - I need to drive a finished motor like the ServoTube XTA3810 with my own circuit, and the force, speed and position controlability have to be individually independent. Thus a magnetic pitch equal the lenght of each coil would creating 'dead zones' where the actuator is unable to push against the object. The actuator must be used as forcer for a grinding machine pressing with a constant pressure and slowly "eating" through the material.

The Faulhaber QUICKSHAFT seems to have a 3,5/3 asymmetric relationship between coil lenght and each magnet, thus making no deadzones where force cannot be supplied to the rod.

I willl look into the material giving as links - once again thanks.

Best Regards

Asbj=F8rn

In a rotary stepper motor, the coil winding pattern repeats with the same pitch as the magnetic field pattern.

The coil winding pattern always includes two or more coils per pitch precisely to avoid this kind of dead zone. With two coils, the arrangement is always designed so that the force generated by each coil follows the sine and cosine of the phase angle as the motor rotates/drives through a single pitch interval.

Dividing a single pitch interval in to 360 degrees, two coils are set up to be 90 degrees apart, three coils 60 degrees and so on - the advantage of increasing the number of phases is that you get a smoother torque/force curve.

It sounds as if you are going to have to do a bit more reading before you fully understand what's going on - don't let it worry you, we've all had to go through it. Eventually, you too will get to say "why didn't I see that earlier" ...

-- Bill Sloman, Nijmegen

Looks like straightforward electromagnetics to me. What is your problem?