[louieatienza]

Mate, you are dreaming again! :-)
Just how did they get that rook lined up that square in the chuck at the end? Just pop it in and do up the chuck??? Tell me another one!
That tool head - sigh!

I think it would take a little bit of ingenuity to do this in a DIY setting but most can be done. If you watch some of simpsons36's he actually 2-ups this machine, as he has a die-holder for ridgid threading AND a parting tool!

Backlash? How much? Seriously.

Thomson UltraTrue Gearhead on eBay, 100mm frame
Thomson 42 114349 C775 Micron Ultratrue Helical True Planetary UT010 025 0 | eBay
Precision, 4 arc-minutes!
http://www.thomsonlinear.com/website.../ultratrue.php
Also has tapered roller bearings to handle very high axial and radial loads. As in stupid very high... You probably couldn't buy the bearings and raw materials for $200, let alone make it to that precision.

[RCaffin]

Hi Louie

Thomson UltraTrue Gearhead on eBay, 100mm frame

Vade retro me Satana!
Oh dear me, one is tempted! Gear like that should not be wasted!
But right now I can't afford to spend the time on it.

Ian: have a serious look!

Cheers
Roger

[mactec54]

RCaffin

We make our encoders, the minimum we use for any CNC equipment is 14 Bit or 16,384 count per rev, Absolute/Incremental our new one will go up to 20Bit

photo is of our new encoder

[louieatienza]

the important point here is that an encoder with reasonable resolution can be had for a reasonable price. there are ones with higher resolution on the same page, for a little more. time to move on.

id say if you havent come up with a workable mechanical design, its probably not a good idea to try and add a backlash compensating servo system to the list of things to do.

im starting to see why not much progress has been made.....

dmm tech sells a 14 bit encoder for $65

[mactec54]

louieatienza

The Encoder I posted is a Dmm Encoder, the Encoder you are referring to is propriety 14 Bit & is not suitable for a normal application, unless you are a very good programmer, ( C++ ) the new Encoder can be used for any application, it is still propriety, but has standard industrial wiring/configuration, They are the first in the world to manufacture this new type of Encoder

[handlewanker]

OOps double post.
Ian.

[handlewanker]

Hi all, encoders just tell you where you are at, they do not hold back the raging beast when it gets the bit between it's teeth.

Interpreted means, if you are climb milling you don't need the table to take off under it's (the cutter) own steam.

It's about control all the time, from A to B and back to A without the machine reforming the parts due to the tool taking control of the movement.

Hydraulic drive with incompressible oil (practically so) needs to have something to inject the oil at the start to get a movement that is significent as opposed to random.

I toyed with the idea of a drive where a piston injected a fixed amount of oil into a chamber under the action of a cam, with a chamber/piston ratio of 1:60, which means if the piston pumped 60 strokes to the chamber and it moved a table round I turn you have a hydraulic drive with no backlash and a high resolution count.........BUT....

Do that a hundred times and at the hundredth reversal you could have a couple of molecules of oil too much and so you
are out of position and the excess or short fall in the oil supply will not give accurate results....this is similar to a friction drive in all respects.

If the piston pumps as well as sucks the oil on opposite side of the piston, a closed circuit, you could get a 1:60.5 ratio which is as random as you can get.

With an encoder sensing where you are at and a very firm friction drive to give you continuous movement totally under control and without backlash.......hey , all of a sudden you have the ideal drive for all occasions so far noted.

The fly in the honey pot is the ability of the friction drive to resist not being stalled or moved by the cutter forces, one reason the toothed belt, gear, or worm drive is so positive.

The friction drive would consist of two plates off-set to each other, one spring loaded and attached to the input drive with the other attached to the output to the table, with a wheel sandwiched between the plates and transmitting the drive to the second plate......the ratio of the drive derived from the position the sandwiched wheel take on the drive and driven plates.

This method is used in an infinitely variable speed drive attached to an electric motor and has a wheel that moves the two plates relative to one another to give a variable offset, hence a variable speed, dependent on the capacity of the friction to give a torque handling capability to the drive.

It will work for all needs in the ideal 4th axis......size dictates the torque handling ability of the drive by the coefficient of the drive surface friction, but a ratio of 1:60 is not a dream, if you can get an offset to the drive and driven plates of 1:60 with regards to the plate diams and the input/output shaft alignment......encoders are just the jam in the sandwich making sense of the slip in the movement of the two plates......food for thought.

If encoders be the answer to the precise resolution sensing, then friction drive is the answer to the drive itself, having all the necessary functions for forward and revers actions without a dwell point in the action, commonly called backlash.

Now I'm off on another quest for another holy grail, and friction drive might be the answer which has been so close but overlooked by hiding in broad daylight.

From the beginning of time, friction has made possible the invention of wheel in it's many forms.
Ian.

[louieatienza]

Hi all, encoders just tell you where you are at, they do not hold back the raging beast when it gets the bit between it's teeth.

Interpreted means, if you are climb milling you don't need the table to take off under it's (the cutter) own steam.

It's about control all the time, from A to B and back to A without the machine reforming the parts due to the tool taking control of the movement.

Hydraulic drive with incompressible oil (practically so) needs to have something to inject the oil at the start to get a movement that is significent as opposed to random.

I toyed with the idea of a drive where a piston injected a fixed amount of oil into a chamber under the action of a cam, with a chamber/piston ratio of 1:60, which means if the piston pumped 60 strokes to the chamber and it moved a table round I turn you have a hydraulic drive with no backlash and a high resolution count.........BUT....

Do that a hundred times and at the hundredth reversal you could have a couple of molecules of oil too much and so you
are out of position and the excess or short fall in the oil supply will not give accurate results....this is similar to a friction drive in all respects.

If the piston pumps as well as sucks the oil on opposite side of the piston, a closed circuit, you could get a 1:60.5 ratio which is as random as you can get.

With an encoder sensing where you are at and a very firm friction drive to give you continuous movement totally under control and without backlash.......hey , all of a sudden you have the ideal drive for all occasions so far noted.

The fly in the honey pot is the ability of the friction drive to resist not being stalled or moved by the cutter forces, one reason the toothed belt, gear, or worm drive is so positive.

The friction drive would consist of two plates off-set to each other, one spring loaded and attached to the input drive with the other attached to the output to the table, with a wheel sandwiched between the plates and transmitting the drive to the second plate......the ratio of the drive derived from the position the sandwiched wheel take on the drive and driven plates.

This method is used in an infinitely variable speed drive attached to an electric motor and has a wheel that moves the two plates relative to one another to give a variable offset, hence a variable speed, dependent on the capacity of the friction to give a torque handling capability to the drive.

It will work for all needs in the ideal 4th axis......size dictates the torque handling ability of the drive by the coefficient of the drive surface friction, but a ratio of 1:60 is not a dream, if you can get an offset to the drive and driven plates of 1:60 with regards to the plate diams and the input/output shaft alignment......encoders are just the jam in the sandwich making sense of the slip in the movement of the two plates......food for thought.

If encoders be the answer to the precise resolution sensing, then friction drive is the answer to the drive itself, having all the necessary functions for forward and revers actions without a dwell point in the action, commonly called backlash.

Now I'm off on another quest for another holy grail, and friction drive might be the answer which has been so close but overlooked by hiding in broad daylight.

From the beginning of time, friction has made possible the invention of wheel in it's many forms.
Ian.

LOL I hope you're not pulling our legs here... This seems pretty inefficient as the drive motor has to overcome this friction in addition to holding position - which is probaby why you don't see CNC rotary axes built this way. I fail to see how this applies to rotary engraving, or making chess pieces?!

I think a better implementation of this idea would be NuVinci's CVT. Or maybe we can resurrect the Rolamite thread....

[691175002]

Even with a 14 bit encoder, each count is larger than an arc minute. Throw in a few counts of following error and its no longer looking so good.

I don't think encoders are the way to go for DIY rotary tables because they become expensive too fast which defeats the point.

[louieatienza]

Hi all, encoders just tell you where you are at, they do not hold back the raging beast when it gets the bit between it's teeth.

Interpreted means, if you are climb milling you don't need the table to take off under it's (the cutter) own steam.

It's about control all the time, from A to B and back to A without the machine reforming the parts due to the tool taking control of the movement.

Hydraulic drive with incompressible oil (practically so) needs to have something to inject the oil at the start to get a movement that is significent as opposed to random.

I toyed with the idea of a drive where a piston injected a fixed amount of oil into a chamber under the action of a cam, with a chamber/piston ratio of 1:60, which means if the piston pumped 60 strokes to the chamber and it moved a table round I turn you have a hydraulic drive with no backlash and a high resolution count.........BUT....

Do that a hundred times and at the hundredth reversal you could have a couple of molecules of oil too much and so you
are out of position and the excess or short fall in the oil supply will not give accurate results....this is similar to a friction drive in all respects.

If the piston pumps as well as sucks the oil on opposite side of the piston, a closed circuit, you could get a 1:60.5 ratio which is as random as you can get.

With an encoder sensing where you are at and a very firm friction drive to give you continuous movement totally under control and without backlash.......hey , all of a sudden you have the ideal drive for all occasions so far noted.

The fly in the honey pot is the ability of the friction drive to resist not being stalled or moved by the cutter forces, one reason the toothed belt, gear, or worm drive is so positive.

The friction drive would consist of two plates off-set to each other, one spring loaded and attached to the input drive with the other attached to the output to the table, with a wheel sandwiched between the plates and transmitting the drive to the second plate......the ratio of the drive derived from the position the sandwiched wheel take on the drive and driven plates.

This method is used in an infinitely variable speed drive attached to an electric motor and has a wheel that moves the two plates relative to one another to give a variable offset, hence a variable speed, dependent on the capacity of the friction to give a torque handling capability to the drive.

It will work for all needs in the ideal 4th axis......size dictates the torque handling ability of the drive by the coefficient of the drive surface friction, but a ratio of 1:60 is not a dream, if you can get an offset to the drive and driven plates of 1:60 with regards to the plate diams and the input/output shaft alignment......encoders are just the jam in the sandwich making sense of the slip in the movement of the two plates......food for thought.

If encoders be the answer to the precise resolution sensing, then friction drive is the answer to the drive itself, having all the necessary functions for forward and revers actions without a dwell point in the action, commonly called backlash.

Now I'm off on another quest for another holy grail, and friction drive might be the answer which has been so close but overlooked by hiding in broad daylight.

From the beginning of time, friction has made possible the invention of wheel in it's many forms.
Ian.

LOL I hope you're not pulling our legs here... This seems pretty inefficient as the drive motor has to overcome this friction in addition to holding position - which is probaby why you don't see CNC rotary axes built this way. I fail to see how this applies to rotary engraving, or making chess pieces?!

Using NuVinci's design, however, if it's possible, can be integrated with the spindle shaft itself which would make for a very tidy package.

I think a better implementation of this idea would be NuVinci's CVT. Or maybe we can resurrect the Rolamite thread.... Uhing and Zero-Max make linear drives that use threadless rods.

[louieatienza]

Even with a 14 bit encoder, each count is larger than an arc minute. Throw in a few counts of following error and its no longer looking so good.

I don't think encoders are the way to go for DIY rotary tables because they become expensive too fast which defeats the point.

I couldn't agree more. Though I think I've come up with a pretty simple workaround for this (which I don't care to share... yet.) In fact so simple that I've smacked my head repeatedly a few times after I thought of it...

[RCaffin]

Hi Mactec54

We make our encoders, the minimum we use for any CNC equipment is 14 Bit or 16,384 count per rev, Absolute/Incremental our new one will go up to 20Bit

Are these based on the magnetic field sensor chip? It looks like it. I have been watching those with interest.
Are they available - even on a 'field test' basis? I am interested!

Cheers
Roger

[RCaffin]

The Encoder I posted is a Dmm Encoder

Um - that is not quite as simple as it might seem. It is not an incremental rotary encoder as is used for conventional servos (with quadrature A & B lines). Instead it is a sort of non-absolute rotary position sensor, communicating via an SPI bus. Yeah - that would need some serious programming work to make it compatible with any common servo amplifier. Not a simple solution - yet.

On the other hand, the DSN08 goes to 4096 / rev, and is getting close. Give it another couple of years ...

Cheers
Roger

[RCaffin]

Even with a 14 bit encoder, each count is larger than an arc minute.

One arc minute? Absolutely useless of course. Completely out of the question ...
I mean, on a 25 mm diameter, that is all of 3.64 micron step size!
Um ... for a home hobbiest, 3.64 microns might be ... well, almost acceptable. Especially for chess pieces.

I don't think encoders are the way to go for DIY rotary tables because they become expensive too fast which defeats the point.

Cost and functionality are two entirely different matters. I will be contrary here and say that I think incremental (A&B) rotary encoders are in principle THE way to go for DIY. There is no question that they will work: they will. Now, all we have to do is solve the cost problem.
Am I being silly here? I think not. History shows us that what was 'not possible' last year becomes 'possible' this year, and is an 'ebay item' next year.
There is always a way...

Cheers
Roger

[mactec54]

the DSN08 goes to 4096 / rev, and is getting close. Give it another couple of years ...

The New Incremantal Encoder (DSN08 ) has been tested to 20Bit & can be done in any configuration in 10/12/14/17/20 Bit the 4096/ rev will take you to 14 Bit 16384/Rev when used in quadrature

Why 4096/rev/ because this is were the largest market is

There absolute Encoder works very well, & was designed to run with there servo drives, it has many benefits over a normal encoder especially on the communicating side

Most Encoders that are used in the industry have some propriety features & can not be run on any common servo amplifier

[RCaffin]

Hi Mactec54

The New Incremantal Encoder (DSN08 ) has been tested to 20Bit & can be done in any configuration in 10/12/14/17/20 Bit the 4096/ rev will take you to 14 Bit 16384/Rev when used in quadrature

Well, that's very nice and even desirable.

Why 4096/rev/ because this is were the largest market is

360*60/16384 = 1.3 arc minutes. Yes, I can imagine that would be very popular.
Mind you, have a couple of spare bits in the resolution never hurts: it makes servo drives easy to configure. (ie, dealing with backlash and deadbands.)

Their absolute Encoder works very well, & was designed to run with their servo drives, it has many benefits over a normal encoder especially on the communicating side.
Most Encoders that are used in the industry have some propriety features & can not be run on any common servo amplifier

Ah, the old lock-in idea. So they get 100% of their tiny market, instead of a smaller share of the huge open market. A very antique way of thinking which is being steadily demolished by the Internet and Open Systems.

The first company to break ranks with the old ways will get first mover advantage and score big. Might irritate the hell out of their rivals, but that's tough.

Cheers
Roger

[mactec54]

RCffin quote
Ah, the old lock-in idea. So they get 100% of their tiny market, instead of a smaller share of the huge open market. A very antique way of thinking which is being steadily demolished by the Internet and Open Systems.

Your way of thinking is the only thing that is antique , You only have to look at #1 in the world in servo system's Yaskawa, it is no different you can't take there motor & put it on another drive, this is pretty much the the same with all servo systems, that have intelligence servo drive

If you want a dumb servo drive, you can still find them, but there again they don't compare, to a intelligent servo drive

The internet has only made these company's get more exposure, not less, there businesses have huge growth, from the internet, just the opposite of you way of thinking

You have to think that the average hobby builder, use's a 500 count per rev encoder, the average machining center use's 8,000 to 10,000 count per rev encoder

So the Dmm encoder is above the norm at 16384 counts per rev, you have to remember were the encoder is mounted, usually on the back of a motor, in the case of a rotary indexer, you would have some kind of reduction, so the encoder count x the reduction you are going to get a good resolution with a 20Bit encoder (1,048,576,000) counts per rev x the reduction

You also have to remember you were talking stepper motor use for the rotary indexers, the stepper motor does not compare with a servo like this doing the same job

[RCaffin]

Your way of thinking is the only thing that is antique , You only have to look at #1 in the world in servo system's Yaskawa, it is no different you can't take there motor & put it on another drive, this is pretty much the the same with all servo systems, that have intelligence servo drive

Ah well, high end brushless AC motors - a far cry from this market - all our home machines and refitted BPs etc. Yes, point made that I ignored the high end.

But is my thinking antique? Once, only the rich could afford a car, and they had to have a resident chauffer. Then you had to be a serious mechanic yourself to drive one - adjusting the spark and compression etc. Now - teenagers and little old ladies hop in a compact and away they go. Will the servo industry follow in this path? I suspect so, but of course I am guessing.

If you want a dumb servo drive, you can still find them, but there again they don't compare, to a intelligent servo drive

No?
But you can today build a system (or modify an old BP) to get 10 micron or less on an axis, fairly easily. How many people or companies really need better than that? For that matter, how many can hold 0.1 mm consistently on a manual, in production on simple machinery? Sure, an aerospace company might want 0.1 microns ... but there aren't many of those, while there's an awful lot of small engineering shops around. I don't think the low end market is dying.

You have to think that the average hobby builder, use's a 500 count per rev encoder, the average machining center use's 8,000 to 10,000 count per rev encoder

Maybe so, but then, 10 years ago, how many 'average hobby builders' even had a CNC? The 'low-end' market grows, in both volume and performance. History tells us this is always the way.

You also have to remember you were talking stepper motor use for the rotary indexers, the stepper motor does not compare with a servo like this doing the same job

That depends on the specs you want. In many cases a stepper does meet the user's requirements. If you want to go to the shopping mall, you don't need a chauffer-driven 'der grosse' Mercedes.

If someone wants to bequeath me several high-end servo systems (plus a 40krpm spindle drive), who am I to turn them down? But in the meantime...

Cheers

[handlewanker]

Hi, vague as I am about encoders and servos, would I be right in saying that, for example, an encoder is a disc on the end of a final drive shaft that has many lines on it, and the servo motor, driving the shaft, does so until the required number of lines on the encoder disc have passed by the sensing head and then the servo motor stops and holds that position against all forces, and that it will attempt to keep on driving the shaft indefinitely until the line count is reached, whereas a stepper motor will receive pulses from the controller and attempt to move the output shaft for the pulse count and then stop even if the shaft did not move?
Ian.

[mactec54]

RCaffin

It seems that you are completely off track

If someone gave you a high end servo system, you would not know what to do with when you got it, I have lots of them, mostly Yaskawa & Dmm

There is a video a few posts back, with a Hardinge direct drive rotary table this has a accuracy of ( +/- 3 arc-sec ) but is only using a 16384 incremental encoder so are they telling stories about there accuracy??

Or do you know the answer as to how they achieve this, with a 16384 count encoder

You copied what other's had said in post 497 & agreed that this is correct (360*60/16384 = 1.3 arc minutes. Yes, I can imagine that would be very popular.) This is your words & what others said as well

I hope that this can be a learning experience, for those that don't know to much about servo systems & How intelligent servo drives work, so how do they achieve (1 arc-sec with an Encoder with say a 13 Bit=2048 count encoder Its called Electronic gearing, with a simple bit of math you can have a rotary resolution of (1 arc-sec ) Here are some examples of how it is done

So you don't need large Encoder counts, if you have a servo system that can use electronic gearing, large count Encoders are a good thing if you have them as they have many other benefits as to how a drive system will perform, they are not just used for accuracy