[jaguar36]

That is certainly correct, they work well, are simple, well at least simpler to set up than most, but by my reckoning have a sub par encoder, one and one only digital output and they are expensive for
the power output. Take from that what you will. Its your money and your choice.

They also have tech support that speaks english and you can actually talk to, and they are design and built in the US. That's worth alot to me.

[joeavaerage]

Hi,

They also have tech support that speaks english and you can actually talk to, and they are design and built in the US. That's worth alot to me.

Yes, they do offer excellent support to their customers. As for being designed and built in the US....that's a bit of a double edged sword. Once upon a time the
phrase was 'Made in the USA' now its become 'Mad in the USA'.

Craig

[Teknic_Servo]

Hi joeavaerage,

I say you hound me because every time I post that your servos are too expensive for what they are you come along and try to correct me.

If you look through all the responses Teknic has made to your posts (I agree, there are many), you will not find any examples of where Teknic tried to rebut your opinion about ClearPath (price or otherwise). We do not respond to opinions about Teknic products even if we disagree with them unless they include factual errors, incomplete information, or misleading statements.

The Nyquist Sampling theorem tells us the max theoretical frequency that can be detected is half that of the sampling rate. A Control Engineer will tell you that any reasonable discrimination
cannot be achieved by a sampling rate of less than five times that of the highest frequency of interest, and preferably more like ten times.

Your analogy is interesting. With a perfect ADC, you can accurately digitize and reproduce a signal if your sample frequency is twice the highest frequency component contained in your signal. But from a practical perspective, it is impossible to implement a “brick wall” anti-aliasing filter that allows all frequencies of interest (i.e., up to the Nyquist frequency) but none above that. This is why you oversample. Otherwise, you risk aliasing. (You’re correct that 5-10x oversampling is common, but it’s not for better discrimination, it’s to avoid aliasing.) The point is that the design of the system has to consider all factors—you can’t sample at the theoretical Nyquist frequency unless you can make a brick wall filter. Likewise, a theoretical improvement that you might get from higher encoder resolution doesn’t matter unless other important system requirements are met.

In addition, just because oversampling by 5-10x generally makes sense in a sampling system, it doesn’t mean that 100x or 1,000x oversampling is better. Improvements to individual metrics are always subject to the law of diminishing returns.

You have stated that “a well set up servo with a 10,000 count encoder will be perfect for CNC in every way”. We agree, and would add that increasing ClearPath’s resolution from 12,800 counts per rev to 128,000 counts per rev will not give you more than a marginal improvement in servo performance (which would be mostly due to the more “analog-like” measurement of velocity and its derivatives, as you pointed out). But even that marginal improvement will only be realized if every other metric about the encoder is held constant as you increase the resolution.

Our point is that if you compare a servo using a high-quality 12,800 count per rev optical encoder with a servo using a higher resolution encoder whose resolution is achieved through the extreme interpolation of a magnetic disk, and its data is transmitted serially to the drive (causing phase delay), the higher resolution option will not yield better servo performance. This is because although the resolution is higher, the total system is worse.

Unfortunately, many people are entranced by resolution because it is easy to understand (seemingly), and they are unaware of the other factors that are critical to servo performance. With little effort, Teknic could put a higher resolution encoder in ClearPath, but we will not do so if it causes a downgrade in accuracy, linearity, noise or phase delay, because the slight improvement you would get from increased resolution would be more than offset by the other downgrades.

Thanks,
Bridgette O. – Teknic Servo Systems Engineer

[joeavaerage]

Hi,

If you look through all the responses Teknic has made to your posts (I agree, there are many), you will not find any examples of where Teknic tried to rebut your opinion about ClearPath (price or otherwise). We do not respond to opinions about Teknic products even if we disagree with them unless they include factual errors, incomplete information, or misleading statements.

Nor have I claimed that you or any of the Teknics respondents have been in anyway abusive or argumentative, but you obviously do follow my posts.

I have explained why I think that your encoder is sub-par, not because of it quality or linearity, which I will take at your word is good quality, but rather that the increased resolution allows smoother
motion irrespective of the linearity. You seem unwilling to concede that fact.

oversampling is common, but it’s not for better discrimination, it’s to avoid aliasing.

In this context aliasing and discrimination are the same. Lets imagine there are two signals actually buried in the samples, both at the same frequency but at different phases. If the sampling were
at the Nyquist rate, ie twice the signal frequency, then you could not discriminate between the two signals, at five times oversampling, you maybe able to distinguish that there are in fact two signals,
and at 10 times you maybe able to estimate what those signals are, at 100 times you'll probably have a fair estimate of the phase difference.

5-10x generally makes sense in a sampling system, it doesn’t mean that 100x or 1,000x oversampling is better.

An encoder IS A SAMPLING system, angle is a real continuous variable, and any digital encoder is at best sampling and reporting that sample. An yes 100x is better than 10x and that is
better than 5x. I would agree that in the region of 10x to 100x the cost/benefit ratio becomes questionable but for all that 100x is better than 10x.

Craig

[Teknic_Servo]

Hi Craig,

I’m glad you recognize that we are not hounding you :-)

you obviously do follow my posts

We follow any forum where people ask questions about Teknic products so that we can provide helpful support. Sometimes people inadvertently make incorrect statements about Teknic products—for better or for worse—and our goal is to make sure that people have as good an understanding as possible regarding what Teknic products can and can’t do. And to reiterate, we won’t comment on anyone’s personal opinion if it’s just an opinion and does not include any inaccurate, incomplete, or misleading statements.

Lets imagine there are two signals actually buried in the samples, both at the same frequency but at different phases. If the sampling were at the Nyquist rate, ie twice the signal frequency, then you could not discriminate between the two signals… at 10 times you maybe able to estimate what those signals are, at 100 times you'll probably have a fair estimate of the phase difference.

It’s counterintuitive to most people, but as long as the sampling frequency is greater than the Nyquist frequency (i.e., the signal is strictly bandwidth limited so it only contains harmonics less than half the sampling frequency), and you have a theoretically perfect sampling system, you can reproduce the original signal. For example, if you take two 10 Hz sine waves, phase shift them and add them together, you can reproduce that signal perfectly if you sample it with a perfect sampling system that samples at a frequency only slightly greater than 20 Hz (e.g., 20.1 Hz). The math is complicated and non-intuitive, so if you just plot points on a time-domain curve to visualize this, you will conclude it can’t be done. But it is true. There is no theoretical need to sample at 10-100x.

That said, I think we constantly disagree about encoder resolution because we switch back and forth between the theoretical world and the real world. I will concede that, in theory, if you have two encoders that are identical in all respects except resolution, then up to a point, the encoder with higher resolution will give you better performance. Some applications (unlikely many CNC applications though) will benefit from high-quality resolution up to around 64,000 encoder counts per rev. But if you go much higher than that, you’ll be way past the point of diminishing returns.

On the other hand, if you get your higher resolution (e.g., 64,000 counts per rev) by extreme interpolation of a 2-pole magnetic disk (i.e., one sine wave per rev), using a real-world circuit, that has real-world noise, and real-world drift and run-out, etc., you will get notably worse real-world servo performance than you would with a 12,800 count, high-quality optical encoder.

Thanks,
Bridgette O. – Teknic Servo Systems Engineer

[WesM]

I decided to give the stepperonline servos a try. They are apparently a rebranded Leadshine EL6 servo kit. They seem to have a decent manual and tuning software and are 17 bit encoder servos. Hopefuly I will not regret it, but I always seem to be going off the beaten path on things in life, so why not here too!

The first thing I noticed is they are 220v +/-10%, which means I will have to setup a buck transformer for the 246v AC I have at my home.

I'm curious how you would size the buck transformer to power 3 of these servos. In the manual they have a 5.2a continuous 18.4a peak, 5.5a rms. I found a fairly simple calculator from federal pacific.

https://www.federalpacific.com/tools...ator-selector/

All of the servos should never be hitting peak current at the same time (short of a crash, in which case I want the breakers tripping long before max current is pulled from all 3 servos), so what would be a reasonable expectation for max servo current draw for a knee style machine in this case?

[RCaffin]

Hi WesM

Not so fast.
The spec on the drives is 220 V +/- 10%. That means they can take 220 + 22 = 240 V. That is very close to what you have right now.

The next thing to consider is just what voltage you really do have. Have you measured it at 246 VAC? If so, OK, but should your power company being providing you with such a high voltage? Almost seems to me to be outside the normal Utility Specification.

Have you tried asking them to change the tap on the local transformer to bring your supply down to around 220 V. Such a change might also increase the life of various other bits of equipment around the house - and around your neighbours' houses too. One could almost argue that they should do so to meet their own specs.

Cheers
Roger

[joeavaerage]

Hi,
Chinese voltage specifications are often 220VAC. Here in New Zealand 243VAC is normal, and I hook my Delta (Taiwanese made in China) servos direct to it, no trouble.

I think fair to say that the servos are '200V Class', so anywhere from 200VAC to 250VAC should be OK.

The whole point about having direct off-line servo drives is that you don't have to have power supplies and transformers and things....it would be a backward step to have or require them.

Craig

[WesM]

Hi WesM

Not so fast.
The spec on the drives is 220 V +/- 10%. That means they can take 220 + 22 = 240 V. That is very close to what you have right now.

The next thing to consider is just what voltage you really do have. Have you measured it at 246 VAC? If so, OK, but should your power company being providing you with such a high voltage? Almost seems to me to be outside the normal Utility Specification.

Have you tried asking them to change the tap on the local transformer to bring your supply down to around 220 V. Such a change might also increase the life of various other bits of equipment around the house - and around your neighbours' houses too. One could almost argue that they should do so to meet their own specs.

Cheers
Roger

Yes I did a reading on an existing 30a 240v line to my dryer. It measured 246v. I will try and call the power company and see what they will do about our local transformer. If they can reduce the voltage a bit that would definitely make me feel a lot more comfortable about running these servos on the "240vac".

Hi,
Chinese voltage specifications are often 220VAC. Here in New Zealand 243VAC is normal, and I hook my Delta (Taiwanese made in China) servos direct to it, no trouble.

I think fair to say that the servos are '200V Class', so anywhere from 200VAC to 250VAC should be OK.

The whole point about having direct off-line servo drives is that you don't have to have power supplies and transformers and things....it would be a backward step to have or require them.

Craig

Agreed on the points about having to use extra stuff on a 200v class servo. Reading through the manual the drives do have an over voltage alarm. Would it be reasonable to think that should protect the drive if the voltage is too high for it to handle? I would hate to blow a drive.

[joeavaerage]

Hi,

Would it be reasonable to think that should protect the drive if the voltage is too high for it to handle? I would hate to blow a drive.

The overvoltage alarm is on the DC Link side. 240VAC rectified is 336VDC. I would guess the overvoltage alarm would come on at around 365VDC. This alarm is more about the
DC Link capacitors, and they come under stress when the servo is decelerating rapidly....the servo back-generates into the DC Link, causing a potential over voltage event for the capacitors.
The alarm does not cut the incoming AC supply...so.......no I would not expect an overvoltage alarm to protect the servo drive, at least from an overvoltage input.

Craig

[pippin88]

I have not been able to find clear info on feeding "240v" to "220v" servos.

Australia, like most of the world is nominally going to 230v. In reality my supply can get over 250v. It often runs around 246V.

The standard is 230v + up to 10%. That means 253v. I have solar and I think the inverter is programmed to turn off if the line voltage reaches 256v.

My Delta Servo says 200-230v input. I have not contacted Delta to check whether they will tolerate higher. I suspect they are pretty well protected but I would hate to find out the hard way.

I have chosen to use a bucking autotransformer to lower my voltage by 24v, so end up with near to 220v.

I went with a 625va toroidal for my upcoming build. Cost about $120 AUD. Not much compared to $4000 of servo system.

My VFD says input 180-264v or something, so I'm going to run that straight off the grid.

I looked at https://sound-au.com/articles/buck-xfmr.htm

[pippin88]

Leadshine EL6 data sheet specs
"Single phase or three phase 220V -15%~+10% 50/60HZ"
That is 187-242v

The stepper online E6 specs
"Simple X AC200v-240v, -15% ~ 10%, 50/60hz."
Confusing. Is it 170-264v? 170-264v does seem to be a commonish input tolerance.

The chinese AC servos are getting cheap, and the manuals are a lot better.

[WesM]

Leadshine EL6 data sheet specs
"Single phase or three phase 220V -15%~+10% 50/60HZ"
That is 187-242v

The stepper online E6 specs
"Simple X AC200v-240v, -15% ~ 10%, 50/60hz."
Confusing. Is it 170-264v? 170-264v does seem to be a commonish input tolerance.

The chinese AC servos are getting cheap, and the manuals are a lot better.

I am getting the stepperonline T6 servos, which are 220v +/- 10%. The E6 servos do not come with any tuning software, so you are left working with the panel buttons. The T6 servos use leadshine's tuning software, which has autotune for some of the parameters.

I am going to call my power company and try to get them to reduce the voltage coming from my local transformer (which actually sits on my property 100 feet from my house). If they can get it down to even 230 I would feel a lot better about running these with out a buck transformer.

[WesM]

I talked to my electrical company and they were not willing to do anything. As long as the 240 is +/- 5% its within spec.

I am not willing to risk blowing a drive. so I found an ACME 1 kva buck boost transformer on Ebay for $50. Figured it was worth a shot. I got it today and it seems to be in excellent condition, however for whatever reason all of the leads are clearly labeled except two. X1, X2, X3, X4 and H1, H2 are labeled, so the two unlabeled leads are H4 and H3. Any idea how to identify which is which? What happens if I wire this up to test the output voltage (nothing hooked up to it obviously) and H4 and H3 are swapped vs what is shown in the drawing provided? attached is a pic of the drawing I am supposed to use to buck the 245 to 222.

https://www.cnczone.com/forums/attac...d=493860&stc=1

[joeavaerage]

Hi,

I talked to my electrical company and they were not willing to do anything. As long as the 240 is +/- 5% its within spec.

Surprise, surprise. They'd have to go around the whole country and change ALL the tap changers.....everywhere.......tens of millions or more.
Forget that, you are lucky to have good well regulated power...there are billions of people worldwide whom cannot say the same.

Quite frankly I think you making a mountain out of a mole hill. The servo is '200V Class' is it not? Then so long as you don't put 300V on it it should be fine.

You may be aware that many 230VAC devices have active power factor correction. This is achieved by the rectified input voltage (320VDC nom) being boosted
to 400VDC (nom). This allows the boost circuit to draw quasi-sinusoidal current and thereby drastically improve power factor, so such devices are designed and entirely used
to voltages well in excess of rectified mains voltage.....and they survive. Nearly all 230VAC equipment is designed with this in mind, for example all DC Link capacitors are
400VDC or 450VDC rated, all semiconductors made for 230VAC use are rated to 600VDC and the list goes on.

Craig

[joeavaerage]

Hi,
as far as your autotransformer is concerned, that is called 'phasing'. If you were to wire per the diagram but get H3 and H4 reversed, that would effectively cancel the inductive impedance
of the H1 H2 coil. and with full line voltage the transformer would be hopelessly saturated and pop a fuse....if you are lucky, or blow the transformer up if you are not lucky.

You need to phase the coils, and do yourself a favour use a current limited 12VAC source to do it. Once the coils are phased, then you can hook them in series and know that the
inductive impedance of each coil is additive.....not destructive.

Craig

[WesM]

Hi,



Surprise, surprise. They'd have to go around the whole country and change ALL the tap changers.....everywhere.......tens of millions or more.
Forget that, you are lucky to have good well regulated power...there are billions of people worldwide whom cannot say the same.

Quite frankly I think you making a mountain out of a mole hill. The servo is '200V Class' is it not? Then so long as you don't put 300V on it it should be fine.

You may be aware that many 230VAC devices have active power factor correction. This is achieved by the rectified input voltage (320VDC nom) being boosted
to 400VDC (nom). This allows the boost circuit to draw quasi-sinusoidal current and thereby drastically improve power factor, so such devices are designed and entirely used
to voltages well in excess of rectified mains voltage.....and they survive. Nearly all 230VAC equipment is designed with this in mind, for example all DC Link capacitors are
400VDC or 450VDC rated, all semiconductors made for 230VAC use are rated to 600VDC and the list goes on.

Craig

Oh no I definitely did not expect them to make a significant effort, but figured I would ask to see if they could adjust it down to 240 at least.

I noticed on page 18 of the T6 servo manual (and the Leadshine EL6 manual as well) they actually say the main power port can be supplied with 220v +/- 15%. If that is the case then that would be 253VAC. Like you said, its probably fine.

https://www.cnczone.com/forums/attac...d=493862&stc=1

Hi,
as far as your autotransformer is concerned, that is called 'phasing'. If you were to wire per the diagram but get H3 and H4 reversed, that would effectively cancel the inductive impedance
of the H1 H2 coil. and with full line voltage the transformer would be hopelessly saturated and pop a fuse....if you are lucky, or blow the transformer up if you are not lucky.

Craig

Well dang, thats a little more excitement than I'm looking for, thanks for the heads up.

[pippin88]

I'm trying to get a definite answer out of Delta.

But even if it is 230+10%, that's only 253v
My line voltage was 250v today.
I think on a sunny summer day (plenty of solar on rooftops around here) it will be higher

A bucking transformer to bring down by 24v has added 3% to servo cost for me.

I would like it if it is unnecessary, but have erred on side of caution.

[WesM]

Stepperonline got back to me, they said the T6 drives should be powered by 220 +/- 15%. But they did not recommend running the drives at or over 250v long-term as it would likely shorten the life of the drives. So like Craig said, they are probably fine on the 242-246VAC I am seeing at my house.

[joeavaerage]

Hi,
a majority of industrial electrical use is for induction motors.

An induction motor will with a given load draw more current with less voltage. This may seem counterintuitive, but as the voltage drops the slip increases and therefore the motor draws more current.
Its often called 'brown out'. This is a big reason why power companies maintain high line voltages....so their customers don't end up with a whole bunch of burnt out induction motors due to brown out
for which they would blame the power company.

With a servo drive the incoming AC voltage is rectified to DC. When a servo is decelerating it will generate back into the drive pushing the DC Link voltage higherthan the rectified mains,
many tens of volts higher. Servo drives have to contend with this, it is the reason for 'braking resistors'.

If you have a high line voltage, lets sat 250VAC when its rectified it will be 353VDC. If the servo has a peak allowable DC Link voltage of 400VDC then there is reduced headroom for the DC link capacitors to absorb any
back-EMF from the servo. At 405VDC the braking resistor will turn on to limit or reduce the DC Link voltage. All this is absolutely normal with an AC servo. Any well designed and manufactured servo
drive will survive 250VAC no sweat. The key consideration is 'well designed and manufactured'.

Craig