Dynatech Servos

[Dave's_Not_Here]

Anyone have first hand experience with Dynatech Servos on a Techno Isel (or any other machine)?

Long story, posted on the Techno Forum, but I had to replace the Z Axis due to a broken glass encoder disk. When asked about replacing the encoder, it was "no, you have to replace the motor et al.

Sounds like a lame way to build a servo... glass parts that render the motor useless!

$875 later, I am supposed to have it tomorrow a.m after 2 1/5 weeks down time.

Lame doesn't begin to describe it.

D

[Al_The_Man]

How is the encoder mounted?
If it is a through hole type, all you generally need is the shaft dia and the resolution, the worst case is if it it is a AC or BLDC and has commutation tracks, but then all you need is the pole count of the motor and a little procedure to align them, and there is many suppliers for this type.
Renco is one that can usually supply a replacement.
Al.

[Dave's_Not_Here]

Originally Posted by Al_The_Man How is the encoder mounted? If it is a through hole type, all you generally need is the shaft dia and the resolution, the worst case is if it it is a AC or BLDC and has commutation tracks, but then all you need is the pole count of the motor and a little procedure to align them, and there is many suppliers for this type. Renco is one that can usually supply a replacement. Al.

Al,

Thanks for the input. I am not sure how it is mounted. All I know is "it's in pieces", so I am having them ship the original one back so I can see for myself what I am up against.

I tried to get them to explain why I needed an entire new servo, brake and encoder, if just the encoder was bad... especially after they had sold a replacement encoder to another Zone member, for $180. All they said was "we installed a test encoder, and it didn't work either, so you need a whole new motor."

This afternoon, I was told "your glass encoder is in pieces." Okay, so if my glass encoder was in pieces, why the hell did they waste their time installing a "test encoder"? If the glass encoder is an integral part of the shaft, and not a separate piece, then how did they install a "test encoder." If the encoder is a separate piece, then why do I need a servo, encoder and brake?

I won't even venture down the path of the "small circuit board" that I was told might be bad... God forbid I might think they could "replace" a circuit board... no, let's just play the "glass encoder" / "test encoder" card... friggin A!

Now, I might not be able to quote the inner workings of a break out board, chapter and verse, but nothing regarding the encoder issue makes a bit of sense.

To be quite frank, I do not understand "glass encoders" on a cnc machine that could execute a hard stop at any point in time... especially with a control interface known for disabling the limit stops... in fact, I can't fathom any part of a cnc machine being made from glass.

UPDATE: Here is a tid-bit of information: "While attempts were made to rectify this in the late 1970s with the introduction of large enclosed glass-scale encoders, many of the problems initially associated with glass encoders, such as ineffective sealing, the fragility of glass and the difficulty associated with fitting the scales, persisted; indeed these problems continue to persist today with this type of technology." So what do you know, 1970's technology being built into a 21st century, cutting edge, cnc machine...

UPDATE II: Just for giggles, I thought I would do a quick Google in an industry I am familiar with... and guess what I found... (see image below) Seems this industry, also created in the 1970's, has been making encoder discs for a long time. It kinda debunks the issue of "etched glass gives a better resolution and offsets the inherent weakness of making a lot of small holes in glass for the light source and receivers." The only reason for using glass, is to replace perfectly good servos every time a cnc machine shatters a friggin glass encoder!

D

[Al_The_Man]

Tempered glass has been used for several decades for encoders, both linear and rotary, one reason is they are very stable at different temperatures.
They may have broken it when trying a new encoder as often with through hole types loctite is used on the set screw which often makes it impossible to remove without damage.
Al.

[Dave's_Not_Here]

Originally Posted by Al_The_Man Tempered glass has been used for several decades for encoders, both linear and rotary, one reason is they are very stable at different temperatures. They may have broken it when trying a new encoder as often with through hole types loctite is used on the set screw which often makes it impossible to remove without damage. Al.

Al,

So, doesn't that imply that the encoder could be replaced without buying an entirely new servo, brake and encoder? Where am I missing the boat? I guess, by assumption, as I am not as educated on servo construction as a lot of people might be, that the glass encoder disc is bonded to the servo shaft and not integral to the encoder housing itself? Either way, what stops them from bonding a new glass encoder disc on a perfectly good $700 servo!?

I still think chemical etched metal encoder discs, (which could easily get into the micron level, though not necessary in this application), attached with whatever means necessary, eliminates the ridiculous fragility of a glass encoder disc... it also defeats the inflated replacement costs associated with the current methodology. God forbid that the end user install a $50 encoder disc or pay the manufacturer $150 to do it for him, when you can sell him an new $875 servo! That's why I asked for my original servo to be returned... why leave $700 on the table so it can be sent off the be recycled back into servo food chain.

D

[Pplug]

I was the one who replaces the encoder on my techno machine. The glass disk for the encoder is mounted on the shaft of the motor by a set screw and is easily removed with the right allen key. If I could get my encoder off and put a new one on myself in a dusty basement anybody can do it!

I don't think the manufacturer or techno will sell parts of an encoder- they will only sell the whole- glass disk, emitter circuit board, and receptor board and housing.

[Al_The_Man]

Are these DC motors or BLDC?
If DC then it is usually very easy to retrofit with another through hole encoder, the BLDC takes a bit of extra work due to alignment of the commutation pulse if these are on the disk.
I have retrofitted many encoders over the years, mainly using Renco (now owned by Heidenhain).
Over the years I have rarely seen broken glass discs, often it is the disc bonding has come free from the hub due to excessive vibration.
Al.

[Dave's_Not_Here]

Originally Posted by Pplug I was the one who replaces the encoder on my techno machine. The glass disk for the encoder is mounted on the shaft of the motor by a set screw and is easily removed with the right allen key. If I could get my encoder off and put a new one on myself in a dusty basement anybody can do it! I don't think the manufacturer or techno will sell parts of an encoder- they will only sell the whole- glass disk, emitter circuit board, and receptor board and housing.

Pplug,

That is what I thought... so why do you think they insisted I had to purchase a complete servo, brake and encoder package? Gee, I wonder...

A company, who could have sold a $180 part two weeks ago, decided to convert it into an $875 sale. Instead of having a customer that would praise their service and recommend them to every interested party, they now have a customer that will make sure everyone knows that they cannot be trusted. I wonder how much that extra $700 will cost them in the long run.

As far as I am concerned, without an acceptable explanation why it "had" to cost $875 or a significant effort on their part to "make it right", there is no reason to change my tune. "Caveat Emptor"

D

[Dave's_Not_Here]

Al,

These are 90v DC, 1,000 RPM motors...

Me thinks I have been taken for a ride....

[Al_The_Man]

Originally Posted by Dave's_Not_Here Al, These are 90v DC, 1,000 RPM motors... .

That would normally be a simple job. The cost for an encoder should be no more than $250.00 max.
Incidentally the two major CNC control manuf. Fanuc and Mitsubishi are still using tempered glass scale in all their encoders.
Al.

[Dave's_Not_Here]

... the same issue that started this whole mess, is still persisting.

I have a very pissed client that will want money back if he misses his Friday delivery date...

I took the old servo apart. It took less than 10 minutes to disassemble and remove the encoder. They never did remove the encoder entirely, as some of the screws were still factory tight. All they did was check for a broken glass encoder disc, then tell me I had to buy a whole new servo package, as the "encoder was not replaceable." (see attachment...) Seems to me that the encoder is replaceable. Now I will have to deal with this issue on top of everything else.

UPDATE: As soon as the tech support hung up, after we resolved the touch pad issue, the spindle refused to turn on. It was working at the beginning of the process... So much for getting caught up on client work.

My guess, they will tell me that the control board or PCI card (or better yet BOTH) are bad and have to be replaced.

D

[Dave's_Not_Here]

Originally Posted by Al_The_Man That would normally be a simple job. The cost for an encoder should be no more than $250.00 max. Incidentally the two major CNC control manuf. Fanuc and Mitsubishi are still using tempered glass scale in all their encoders. Al.

Al,

That's exactly what I thought.

As for the glass encoder discs, I don't think it matters what they are made of, as much as the deception associated with replacement and the control software that disables limit switches.

D