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Linear stepper motors

Posted by klcjr89 
Re: Linear stepper motors
March 16, 2018 10:33AM
Quote
o_lampe
You should've kept the forcer until you've made a decent working rail. Now you have to start with narda and it will be hard to find out which part is OK or not.

Or was it so cheap, because it was sold as defect?

Cheap because defective. They aren’t hard to come by, and I’m still devising the best way to cut slots in the linear rail effectively using relatively easy to get tools.
Re: Linear stepper motors
March 16, 2018 12:12PM
Quote
klcjr89
Quote
o_lampe
You should've kept the forcer until you've made a decent working rail. Now you have to start with narda and it will be hard to find out which part is OK or not.

Or was it so cheap, because it was sold as defect?

Cheap because defective. They aren’t hard to come by, and I’m still devising the best way to cut slots in the linear rail effectively using relatively easy to get tools.

Did you see my note about using laminated iron parts, to avoid big eddy current losses at high speeds?


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Re: Linear stepper motors
March 16, 2018 12:16PM
Quote
dc42
Quote
klcjr89
Quote
o_lampe
You should've kept the forcer until you've made a decent working rail. Now you have to start with narda and it will be hard to find out which part is OK or not.

Or was it so cheap, because it was sold as defect?

Cheap because defective. They aren’t hard to come by, and I’m still devising the best way to cut slots in the linear rail effectively using relatively easy to get tools.

Did you see my note about using laminated iron parts, to avoid big eddy current losses at high speeds?

Oh yes, I was aware of how transformers are made using thin laminations (as far as the forcer goes). But I'm sure you see as far as the platen goes, that it will be a modified chinese linear rail to start with. Hopefully the permeability is good enough. The professional made platens are a solid bar and not laminations.

The question is, should the silicon steel be grain-oriented or non grain-oriented for the forcer? I'm thinking grain-oriented based on the following info:

Quote

Grain-oriented electrical steel usually has a silicon level of 3% (Si:11Fe). It is processed in such a way that the optimal properties are developed in the rolling direction, due to a tight control (proposed by Norman P. Goss) of the crystal orientation relative to the sheet. The magnetic flux density is increased by 30% in the coil rolling direction, although its magnetic saturation is decreased by 5%. It is used for the cores of power and distribution transformers, cold-rolled grain-oriented steel is often abbreviated to CRGO.

CRGO is usually supplied by the producing mills in coil form and has to be cut into "laminations", which are then used to form a transformer core, which is an integral part of any transformer. Grain-oriented steel is used in large power and distribution transformers and in certain audio output transformers.[8]

CRNGO is less expensive than CRGO. It is used when cost is more important than efficiency and for applications where the direction of magnetic flux is not constant, as in electric motors and generators with moving parts. It can be used when there is insufficient space to orient components to take advantage of the directional properties of grain-oriented electrical steel.

Edited 5 time(s). Last edit at 03/16/2018 12:21PM by klcjr89.
Re: Linear stepper motors
March 16, 2018 10:11PM
Here's what a toothed MGN15 rail looks like modeled. The forcer would go in between the two carriage blocks.

The flux density will be reduced on the bolt holes, but the only way to see if it will be an issue is to just try it first.

Trying to find a wire EDM facility next for cutting the teeth. Hopefully this will be inexpensive since it's an easy shape to cut repeated several times?



Edited 6 time(s). Last edit at 03/16/2018 10:36PM by klcjr89.
Re: Linear stepper motors
March 17, 2018 01:01PM
I have sourced and bought both 0.25mm grain-oriented silicon steel and 0.35mm non-grain oriented silicon steel.

Do you know which one would be better?

Now to wait for the steel to arrive and find a laser cutting facility. smiling smiley

Edited 2 time(s). Last edit at 03/17/2018 01:02PM by klcjr89.
Re: Linear stepper motors
March 17, 2018 01:35PM
Given that the magnetic circuit will include a significant airgap, I doubt that it will make much difference. But I don't consider myself to be an expert on this matter.


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Disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet.
Re: Linear stepper motors
March 17, 2018 01:39PM
Quote
dc42
Given that the magnetic circuit will include a significant airgap, I doubt that it will make much difference. But I don't consider myself to be an expert on this matter.

David, I found this excerpt in the linear stepper design handbook:

Quote

The forcer armature must be made of
silicon steel laminated sheets, having high saturation level and low
specific losses.

The flux density in the mover’s poles ( B p ) is limited only
by the saturation of the teeth. Excessive saturation absorbs too
much of the excitation MMF or gives rise to extreme heating due to
core losses. As the tooth width is approximately half of the tooth
pitch, the maximum pole flux density can not be much above the
half of the saturation flux density of the steel lamination.

Does that mean I should use the non grain oriented steel? It is confusing since it seems to contradict itself. You want a high saturation level, but not too much, while also keeping losses to a minimum. The grain-oriented steel will have 30% more flux density, but a 5% reduction in saturation compared to non grain oriented steel.

I appreciate your help.

Edited 9 time(s). Last edit at 03/17/2018 01:50PM by klcjr89.
Re: Linear stepper motors
March 17, 2018 02:32PM
I thin the grain-oriented steel will only have more flux density in situations in which there is little or no airgap. In which case, the non-grain-oriented steel would be better in this application if you can drive it close to saturation without the windings overheating.

I think that getting the airgap small will be key to getting enough force, and getting it a consistent size along the length of the motor will be key to getting accurate microstepping.


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Large delta printer, and other 3D printer blog postings: [miscsolutions.wordpress.com]

Disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet.
Re: Linear stepper motors
March 17, 2018 02:35PM
I have found out that the platen bars are made of 1018 steel, and that the Misumi linear guide rails are made from 1045 steel, so there is ~0.27% less iron in the linear guide rail than the 1018 steel.

I hope this won't affect magnetic permeability too much.

Edited 2 time(s). Last edit at 03/17/2018 02:37PM by klcjr89.
Re: Linear stepper motors
March 18, 2018 04:00AM


I see skipped steps, everytime the forcer crosses the mounting holes. If you want to make it more consistent, you'd have to cut the sides of the rails and build the forcer in a C-shape.
VDX
Re: Linear stepper motors
March 18, 2018 05:56AM
... or use not the complete top surface, but only two stripes on the sides for the forcers, so it won't change with the holes ...


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org]
Call for the project "garbage-free seas" - [reprap.org]
Re: Linear stepper motors
March 18, 2018 12:42PM
Quote
691175002
The most difficult part of the project will likely be finding appropriate rail and cutting grooves in it. I think you might end up needing one of the back-mounting variations (ex: [www.automation-overstock.com] ) because hole counterbores in standard rail might cause issues.

The problem with using a bottom mounted linear guide, such as the AG15 series, is that they're hard to come by and also can't be mounted to extrusion as easily therefore making adoption rates low.

Quote
o_lampe

I see skipped steps, everytime the forcer crosses the mounting holes. If you want to make it more consistent, you'd have to cut the sides of the rails and build the forcer in a C-shape.

That is an option, but rules out modifying linear guides directly, which is ok since Misumi offers surface ground bar stock, and in 1018 steel which is better than the linear guide steel for permeability.

The mounting holes will need drilled still. If ball bearings are used (like the forcer I tore apart) to ride along the rail, then precision ball grooves won't need to be ground into the sides of the rail like the Hiwins. Negating the need for carriage blocks altogether, just a way more affordable linear stepper than the commercial offerings.

Edited 3 time(s). Last edit at 03/18/2018 12:48PM by klcjr89.
Re: Linear stepper motors
March 18, 2018 12:48PM
The holes will certainly reduce motor force, but that doesn't guarantee it will lose steps.

The H2W 0602 forcer requires 18mm wide teeth to generate 10N of force. I assume that their rail is appropriately sized, so we can assume that a 15mm wide rail can generate ~8N and the 9mm sections around the holes will do ~5N.

Of course a hole only affects one half of the forcer, and only reaches its full diameter for a few teeth, so its possible you will get more than 5N of force over a hole. The question is then whether torque ripple (or microstep non-linearity from saturation) produces visible print artifacts.

I think its plausible enough to be worth trying, especially if you can find wire EDM cheaply enough. That process tends to vary significantly in cost since typical EDM machines are designed to hold tolerances probably two orders of magnitude more precise than you need.
Re: Linear stepper motors
March 18, 2018 12:52PM
Quote
691175002
The holes will certainly reduce motor force, but that doesn't guarantee it will lose steps.

The H2W 0602 forcer requires 18mm wide teeth to generate 10N of force. I assume that their rail is appropriately sized, so we can assume that a 15mm wide rail can generate ~8N and the 9mm sections around the holes will do ~5N.

Of course a hole only affects one half of the forcer, and only reaches its full diameter for a few teeth, so its possible you will get more than 5N of force over a hole. The question is then whether torque ripple (or microstep non-linearity from saturation) produces visible print artifacts.

I think its plausible enough to be worth trying, especially if you can find wire EDM cheaply enough. That process tends to vary significantly in cost since typical EDM machines are designed to hold tolerances probably two orders of magnitude more precise than you need.

Just to clarify, the 0602 forcer has 15mm wide teeth (60 laminations * 0.25mm thickness for each lamination). The one I tore apart is the same model (they've had different brandings over the years). The 0602 forcer uses the compact motor design, which by my assumption has less force than the standard design.

The compact design is harder to make. I have decided to try the standard design approach first, and it should result in more force over the compact design. It will be slightly more bulky but I think the trade off for more force and ease of manufacture is worth it?

Standard:


Compact (0602 series):


Edited 4 time(s). Last edit at 03/18/2018 01:02PM by klcjr89.
Re: Linear stepper motors
March 18, 2018 01:11PM
Quote
691175002
The holes will certainly reduce motor force, but that doesn't guarantee it will lose steps.

You may not get missed steps, but I think the holes will lead to variations in the sizes of steps.


Delta printer calibration calculator, mini IR Z probe, and colour touch screen control panel: [escher3d.com]

Large delta printer, and other 3D printer blog postings: [miscsolutions.wordpress.com]

Disclosure: I have a financial interest in sales of the Panel Due, Mini IR height sensor, and Duet WiFi/Duet Ethernet.
Re: Linear stepper motors
March 18, 2018 03:04PM
I'm sure robotdigg would be able to send you rails without too many mounting holes, if you ask.
Re: Linear stepper motors
March 18, 2018 03:16PM
Quote
o_lampe
I'm sure robotdigg would be able to send you rails without too many mounting holes, if you ask.

The end goal is to not need the linear carriages, do you think if the linear rail with holes works, it would be possible to design the forcer to be the carriage block as well? Not sure how hard it'd be to design good tolerance 3D printed recirculating balls.
Re: Linear stepper motors
March 18, 2018 06:37PM
This may be a stupid idea, but instead of cutting slots, has anyone considered laminating thin sheets of steel/iron and some other material into a stack, then taking a slice of that?
As long as your sheet material is the right thickness, and to relatively good tolerance it should give you a strip with alternating magnetic and non magnetic surfaces. Again, could be a stupid idea, just throwing it out there. Dunno what tools you guys have, but nothing I have could cut precisely spaced slots in a rail, but laminating it and milling/cutting the excess to get a rail shape seems doable with basic tools.
Re: Linear stepper motors
March 18, 2018 06:48PM
Quote
Trakyan
This may be a stupid idea, but instead of cutting slots, has anyone considered laminating thin sheets of steel/iron and some other material into a stack, then taking a slice of that?
As long as your sheet material is the right thickness, and to relatively good tolerance it should give you a strip with alternating magnetic and non magnetic surfaces. Again, could be a stupid idea, just throwing it out there. Dunno what tools you guys have, but nothing I have could cut precisely spaced slots in a rail, but laminating it and milling/cutting the excess to get a rail shape seems doable with basic tools.

You will need something to hold all of the laminations together, and then would need to surface grind the surfaces. The goal is to mass produce these, so the equipment doesn't put me off for getting the prototypes made.
Re: Linear stepper motors
March 19, 2018 04:57AM
Quote
klcjr89
Quote
Trakyan
This may be a stupid idea, but instead of cutting slots, has anyone considered laminating thin sheets of steel/iron and some other material into a stack, then taking a slice of that?
As long as your sheet material is the right thickness, and to relatively good tolerance it should give you a strip with alternating magnetic and non magnetic surfaces. Again, could be a stupid idea, just throwing it out there. Dunno what tools you guys have, but nothing I have could cut precisely spaced slots in a rail, but laminating it and milling/cutting the excess to get a rail shape seems doable with basic tools.

You will need something to hold all of the laminations together, and then would need to surface grind the surfaces. The goal is to mass produce these, so the equipment doesn't put me off for getting the prototypes made.

I wonder how you could mass produce these and be competitive with the many current mfgs, making these for decades and in various form: flat, two axes (X Y) or even in round form (the guide is round, the coils around it ). And there is a lot more than just cut slots in a bar which in fact is the easiest part if you have the machine tools.


"A comical prototype doesn't mean a dumb idea is possible" (Thunderf00t)
Re: Linear stepper motors
March 19, 2018 12:51PM
Quote
MKSA
I wonder how you could mass produce these and be competitive with the many current mfgs, making these for decades and in various form: flat, two axes (X Y) or even in round form (the guide is round, the coils around it ). And there is a lot more than just cut slots in a bar which in fact is the easiest part if you have the machine tools.

There's really only one manufacturer, and they haven't changed how they make them for the past 30 years (I talked to the owner). There is a market where 1uM precision is not required and many people (and companies) would still buy them. Consider that the platens are in the several $K range. 3DP can benefit from such a reduction in costs.

Edited 1 time(s). Last edit at 03/19/2018 12:51PM by klcjr89.
Re: Linear stepper motors
March 20, 2018 12:19PM
Should this thread be moved here? [forums.reprap.org]
VDX
Re: Linear stepper motors
March 20, 2018 04:08PM
Quote
klcjr89
Should this thread be moved here? [forums.reprap.org]

... sounds sane winking smiley


Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org]
Call for the project "garbage-free seas" - [reprap.org]
gtj
Re: Linear stepper motors
March 24, 2018 11:32AM
Quote
klcjr89
Quote
Trakyan
This may be a stupid idea, but instead of cutting slots, has anyone considered laminating thin sheets of steel/iron and some other material into a stack, then taking a slice of that?
As long as your sheet material is the right thickness, and to relatively good tolerance it should give you a strip with alternating magnetic and non magnetic surfaces. Again, could be a stupid idea, just throwing it out there. Dunno what tools you guys have, but nothing I have could cut precisely spaced slots in a rail, but laminating it and milling/cutting the excess to get a rail shape seems doable with basic tools.

You will need something to hold all of the laminations together, and then would need to surface grind the surfaces. The goal is to mass produce these, so the equipment doesn't put me off for getting the prototypes made.

How about something like the segments of a steel CVT belt? They come in plenty of sizes and shapes. Alternate them with a 3d printed segment of the same size.



At one time I was toying with the idea of putting the coils in the stationary rail and just having the carriage contain a short toothed bar. Kind of like a rail gun. smiling smiley
I think I can design it but there's no way I can build it.
Re: Linear stepper motors
March 29, 2018 03:12PM
The silicon steel has arrived from China. Next up will be to source the permanent magnet and then create a 2D outline to send off to get all the laminations laser cut.

Edited 1 time(s). Last edit at 03/29/2018 03:12PM by klcjr89.
Re: Linear stepper motors
April 10, 2018 12:35AM
I am going to order a 1018 carbon steel linear rail from Misumi and have it wire EDM'd to prove or disprove the ability to modify a linear rail to use as a platen. If it works, the next step will be to print a forcer housing out of igus filament to negate the need for recirculating ball bearings.

Edited 3 time(s). Last edit at 04/10/2018 12:36AM by klcjr89.
Re: Linear stepper motors
April 13, 2018 05:49PM
I actually have my doubts that modifying a linear rail will provide enough magnetic saturation, due to the mounting holes cutting the flux dramatically.
Re: Linear stepper motors
April 14, 2018 03:31AM
I'm tempted to say " told you so", but instead I propose to add some plugs into the mounting holes.
1. put screw in mounting hole
2. press plug ( with tiny hole for allen key ) into the mounting hole
3. cut slots in rail

The smalles screw heads are "button head inbus screws". The head is flat enough to add a substancial plug and the hole for the allen key can be small, too.
You could even cut the mounting holes deeper, if you need a thicker plug.
Press fit plugs might not survive the cutting procedure, so why not cut a thread in the mounting hole and screw the plugs in?
Re: Linear stepper motors
April 14, 2018 12:06PM
Quote
o_lampe
Press fit plugs might not survive the cutting procedure, so why not cut a thread in the mounting hole and screw the plugs in?

Threading would be difficult since the rails come hardened.
Re: Linear stepper motors
April 23, 2018 12:11AM
If I'm going to be creating a new linear rail from scratch, what are some alternative mounting options I could pursue? Assuming:

No holes in the middle of the rail, one hole on each end could be permissible, but that leaves the center floating (not what I want at all).

No holes from the bottom of rail tapped, because this wouldn't really be adoptable on 3D printers if you have to drill a bunch of holes into the length of your extrusions precisely.

Some kind of toe clamp that clamps into a small groove along the length of the rail maybe? I have no idea at this point, honestly.

Edited 2 time(s). Last edit at 04/23/2018 12:24AM by klcjr89.
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