Hi All,

I'm building a CNC plasma, I plan on using the MB3 and ESS combo with Clearpath SDSK Servos run by Mach 4.

Before a cut is made the torch height needs to zero on the surface of the material to be cut first then raise to say 3mm above the surface and begin cutting.

So as the title suggests I'm wondering if the Clearpath HLFB on the Z axis of the plasma cutter can be used to trigger a condition in Mach 4 (Zero the torch height) when the plasma torch touches the plate before cutting.

From what I've seen most people use a micro switch or continuity test to set zero pos for the torch but this adds complication and potential failure points to the construction.

I'm hoping with a bit of code and the right settings in the Clearpath UI this could be achieved by having Mach 4 monitor the amp draw from the servo HLFB. During the steps outlined above when the torch touches the material, the amp draw goes above a set point, Mach 4 will then zero the Z height and proceed with the next step.

Has anyone done anything like this using the HLFB?

Cheers,
J

Hi,
by the time the current has increased by as little as 0.1A because the tip has bottomed out on the plate the gearing is such that the tip will be damaged.
There is no way to have the servo react to a 'feather weight touch' otherwise the servo itself has to be 'feather weight' and can no longer accelerate the axis.

Aside from that: what the hell are you going to use as a fault code from the servo?. The problem with Clearpath servos is that they only have one digital output.
You need a least one output to signal a servo fault, be it overheat, over current, overvoltage or plain Following Error. Without that the servo might fault out due to one
of those conditions and stop all motion, but uless it can signal that fact to Mach then Mach is going to carry on with the rest of the servos and the machine will crash.

That's what steppers did, one would stall but Mach would carry on without knowing that one of the axes has stalled and CRASH!!!

Do you actually have the servos yet? If not I would stop and reconsider whether they are the best design for your purpose. Don't get me wrong, its not because they're poor
quality, they are good quality, but Teknics have taken so many shortcuts to make them appealing for first time servo buyers that they have compromised many of the good things
about modern AC servos, and most particularly the dearth of digital outputs. My Delta B2 series servos have six independent digital outputs, two analog outputs, and auxiliary
encoder outputs vs Clearpaths one digital output. Oh, and by the way the Delta servo is cheaper and twice the power!.

Craig

Yes I have ordered the clearpath servos. They are on their way. I have more plans for CNC builds in the future so I'm might look into Delta servos for the next one.
Thanks for the insight on what the output is used for. I'll see what else I can come up with for torch zeroing.
Cheers,
J

Hi,
torch zeroing is done by g31 probing. Issue a g31 move which takes the torch in the negative direction until it touches the plate. The contact event is sensed by electrical
continuity to the plate. The position at which the 'probe event' occurred is latched into registers within Mach ready for use.

Craig

Hi gyrojeremy,

ClearPath has two features which may be used (depending on your mechanics and other details of your situation) to allow you to set the zero position without a sensor: Hardstop Homing and Zone Torque Limiting.

joeaverage has stated that this cannot be done because the response from the host will be too slow or the increased torque through the gearing will be too low for the servo to detect before it’s too late. This is true with many servos, but ClearPath can drive to the zero position with a low (user-defined) torque limit (with either of the features mentioned above), so it can carefully monitor and limit the applied force.

Moreover, inside a ClearPath servo, the Position/Velocity compensator is completely synchronized with the vector torque control. ClearPath’s TSPD (Total Servo Phase Delay—the elapsed time from when the encoder feedback and currents are read until the PWM outputs to the motor are modulated) is less than 50 microseconds. With ClearPath making the decision on when the torque is high enough to signal probe contact (as opposed to the host CNC controller), the motion can be stopped very quickly.

The implementation of these features will depend on the specific machine design and application, so I can’t say for certain whether you will be able to use the features mentioned on your particular machine. But if you give us a call, we’d be happy to discuss your personal requirements and see if using one of these features is a possibility. Please feel free to contact Teknic directly at https://teknic.com/contact or give us a call at 585-784-7454.

Hi joeaverage,

It is true that there is only one physical status output on ClearPath-SD series motors. That said, ClearPath-SD's HLFB output can, depending on how you configure your motor, simultaneously provide the following data to your controller: real-time torque usage, MoveDone, In-position, and fault status. (Note that in addition to what I wrote above, the ClearPath-SC series motors have a software communication interface, so host applications can query the motor for additional information.)

Even if you were to only monitor the shutdown state of ClearPath (and not the other data mentioned above), the Mach controller can still easily stop the other axes from moving and crashing when any motor shuts down. I’m not sure why you think this is not possible; almost all machine designers do this with ClearPath. ClearPath’s HLFB (High Level Feedback Output) can provide this fault feedback as well as provide the signal to allow the use of the Hardstop Homing or Zone Torque Limiting features. If you’re interested how this works, please download a ClearPath user manual.

What you said about the ClearPath being designed specifically to appeal to “first time servo buyers” is incorrect. You’ve mentioned this on other forums before, but I wanted to address this here because others reading your post may not realize it, so I will quote/paraphrase what a colleague of mine recently wrote to you:

Design decisions made for the ClearPath motors were done with our typical OEM user base in mind (generally experienced controls engineers in a wide variety of machine automation industries). In addition to high-performance and value, these companies tend to value overall system reliability very highly. By incorporating many features into the motor’s firmware, we were able to remove the need for many additional inputs and outputs, thus increasing the overall system reliability.

Our experience over more than thirty years of technical support has proven that the biggest cause of malfunction in machines using servos is electrical corruption of the input and output signals, or intermittent or bad connection of one or more signal wires. We, and our customers, have found that overall system reliability is greatly enhanced by reduced wiring.

Despite the fact that Teknic products are designed for the OEM market (see the About Us page on our website), a side effect of the reduced wiring problems and the ease with which a ClearPath servo system can be implemented, is that many corporate end-users and hobbyists have been attracted to ClearPath. And even though we didn’t set out originally to sell to end-users and hobbyists, we are happy that ClearPath has been well-received, and we enjoy supporting such a wide range of people and applications. Supporting first-time users has been an interesting experience for us over the years since ClearPath was introduced, and it has led us to create even better website features, documentation, and support videos among other things. And that is a win for everyone.

Jon K. – Teknic Servo Systems Engineer

Hi,
using a torque limit to detect the presence of the plate is to drive the tip of the plasma into the plate...if you think that is good for your $500USD watercooled Hypertherm plasma tip ....
go for your life. I'm saying that NO servo should be used in this manner. Lets ay you set a torque limit of 1Nm being a suitable value to get worthwhile acceleration
of the axis. Then that same 1Nm would be applied via the ballscrew to the plasma torch before any over-torque detection could occur. It does not matter how
fast the servo can react it will and must apply its torque BEFORE it can detect that the torch has impacted the plate. The force will likely destroy the tip.

That is what a G31 probing move is for. There will be a certain amount of after-run AFTER the plasma tip has contacted the plate, depending on the speed of the probing move
and the deceleration of the axis. At 50mm/min probing speed and 0.15g acceleration the after-run of my mill is 1.15um. The force between the tip and the plate at 1.15um
interference is minimal. This is the strategy used by nearly all manufacturers to set torch height and is supported by all controllers.

Fact: Clearpath has one, and only one digital output, and by PWM of that output one, and only one, analog variable.
Clearpath servos use an encoder of 12800 count per rev
Clerapath want $517 for a 400W servo

Compare to these facts: Delta (B2 series) has six digital programmable digital outputs, two analog outputs, a full suite (A,B,Z) auxillary output encoder
and an analog input for velocity and torque modes.
Delta (B2) has a 160,000 count per rev encoder, vastly better.
Delta (B2) 750W kit (servo, drive and cables) costs $438.

With Delta I get twice the power of a Clearpath servo for less money.

My opinion is that Clearpath have poor IO capability, modest (at best) encoder resolution, and are expensive for what you get. This is assessment of FACT. It is not misinformation
or disinformation, but a personal assessment of FACT. I can well understand that you don't like it....but tough, I have an opinion and am entitled to it.

I understand also, and certainly approve that you should wish to correct any factual misinformation about your products but I do not have to agree with your conclusions or opinions,
facts yes, opinions no.

Now lets talk about OP's actual situation.

He needs a signal to indicate when the plasma tip touches the plate. Lets say you devise a strategy to use the HLFB to indicate that condition, then how would you indicate
a Following Error or overload condition? You only have one output, and by definition if you use it to signal one condition you cannot use it to signal a fault as well, its one or the other.

the Mach controller can still easily stop the other axes from moving and crashing when any motor shuts down. I’m not sure why you think this is not possible;

Of course its possible, that is after all the primary purpose of the HLFB.....but you can only use it once.

What you said about the ClearPath being designed specifically to appeal to “first time servo buyers” is incorrect. You’ve mentioned this on other forums before, but I wanted to address this here because others reading your post may not realize it, so I will quote/paraphrase what a colleague of mine recently wrote to you:

Design decisions made for the ClearPath motors were done with our typical OEM user base in mind (generally experienced controls engineers in a wide variety of machine automation industries). In addition to high-performance and value, these companies tend to value overall system reliability very highly. By incorporating many features into the motor’s firmware, we were able to remove the need for many additional inputs and outputs, thus increasing the overall system reliability.

Our experience over more than thirty years of technical support has proven that the biggest cause of malfunction in machines using servos is electrical corruption of the input and output signals, or intermittent or bad connection of one or more signal wires. We, and our customers, have found that overall system reliability is greatly enhanced by reduced wiring.

Despite the fact that Teknic products are designed for the OEM market (see the About Us page on our website), a side effect of the reduced wiring problems and the ease with which a ClearPath servo system can be implemented, is that many corporate end-users and hobbyists have been attracted to ClearPath. And even though we didn’t set out originally to sell to end-users and hobbyists, we are happy that ClearPath has been well-received, and we enjoy supporting such a wide range of people and applications. Supporting first-time users has been an interesting experience for us over the years since ClearPath was introduced, and it has led us to create even better website features, documentation, and support videos among other things. And that is a win for everyone.

All opinion only, and not all of which I agree with.

For instance your name for your servos 'Stepper Killers', is that or is that not designed to entice first time buyers?

I would agree that Tecknics do a a masterly job at supporting customers, and I have never claimed otherwise. I would also commend that Tecknics follow on-line forums for any issues related
to your products, to whit, you and your colleagues have taken me to task about my opinions on forums other than this one. As I have stated I base my opinions on the facts of Clearpath servos
and and willing to change my opinion in light of new facts, but refuse to be badgered out of my opinion without new facts. That you don't like it is immaterial to me.

Hi joeaverage,

I'm saying that NO servo should be used in this manner. Lets ay you set a torque limit of 1Nm being a suitable value to get worthwhile acceleration
of the axis. Then that same 1Nm would be applied via the ballscrew to the plasma torch before any over-torque detection could occur. It does not matter how
fast the servo can react it will and must apply its torque BEFORE it can detect that the torch has impacted the plate. The force will likely destroy the tip.

With a little ingenuity, we have developed ways to detect the plate without applying the full torque that’s used to accelerate the axis (please see the ClearPath user manual). There are thousands of axes out there that use ClearPath’s hardstop homing and/or zone torque limiting to home axes, detect objects in the servo’s path, or clamp material in place, many of which involve sensitive equipment. There are some applications for which we don’t recommend this approach because of application-specific factors. This is why we suggested that the OP reach out to Teknic to see if these features could be used in his system. The facts and circumstances of the situation matter a great deal in determining whether or not a certain feature should be used, but to categorically say that it can’t be used under any circumstances is a generalization that isn’t accurate.

Fact: Clearpath has one, and only one digital output, and by PWM of that output one, and only one, analog variable.

Yes, ClearPath has one output, but by implementing PWM modulation of that output, we are not attempting to create a single analog output. Instead, depending on the controller, Teknic generally recommends that customers use the HLFB output mode called “ASG with measured torque”. This mode can simultaneously convey: 1) fault status, 2) the fact that the motor is moving, 3) how much torque it’s using while moving, and 4) when it’s finished moving and settled. (Please see the user manual.)

Clearpath servos use an encoder of 12800 count per rev

This is mostly correct: ClearPath fractional hp NEMA 23/34 motors have a 12,800 count optical encoder; integral hp NEMA 56/143/D100 ClearPath motors have a 64,000 count per rev optical encoder. (There are technical reasons for this difference that are not germane here.)

Delta (B2) has a 160,000 count per rev encoder, vastly better.

It would be fair (although incomplete) to say that the Delta encoder has more resolution based on its specs, but it isn’t accurate to say that the encoder is vastly better. Resolution is not the only figure of merit for an encoder, and the number of counts per revolution does not convey any information about the accuracy of those counts. There’s also the question of the practical usability of such extreme resolution, whether for positioning repeatability or control fidelity—there are other much more limiting factors once the resolution gets above 8,000 counts per rev (although higher resolutions between 8,000 and 64,000 may make sense under certain circumstances and deliver meaningful improvements in performance).

In order to get extremely high resolution out of a magnetic encoder (or even a high-quality optical encoder, for that matter) you have to do an extreme amount of interpolation. An encoder on a motor at the price point you mention will typically have noise, drift and other variability that makes the accuracy about 15 times (!) worse than the resolution. And if that isn’t enough, the filtering required to pull that fine a signal from the noise means that the servo gets its information delayed (and if it’s a serial encoder, the communication delays make it even worse). This all has a significant negative impact on servo performance.

Finally, even with a hypothetical “perfect” encoder, the mechanical imperfections in the motor and bearings will turn that extreme resolution into random noise, so even if you don’t care about poor accuracy, the noise means your servo loop gets no smoothness or dynamic performance benefit either.

We know all this because our engineers evaluated these encoders for ClearPath (and again recently for some yet unreleased products). So the above are all empirically proven facts. My opinion is that certain servo manufacturers emphasize resolution because many people will assume that “more must be better” and will not understand (or be aware of) the other important technical points. 

My opinion is that Clearpath have poor IO capability, modest (at best) encoder resolution, and are expensive for what you get. This is assessment of FACT. It is not misinformation
or disinformation, but a personal assessment of FACT. I can well understand that you don't like it....but tough, I have an opinion and am entitled to it.

You seem angry, and I’m not sure why you think Teknic is trying to change or invalidate your opinion. We are just trying to clarify some complex technical points. We have no objection to you having your own opinion. No product is a perfect fit for everyone. Your priorities for a servo system are clear, and you should make the choice you deem most appropriate. I’m sorry if I came across in any way that suggested that you should change your opinion or that you do not have a right to one.

Now lets talk about OP's actual situation.

He needs a signal to indicate when the plasma tip touches the plate. Lets say you devise a strategy to use the HLFB to indicate that condition, then how would you indicate
a Following Error or overload condition? You only have one output, and by definition if you use it to signal one condition you cannot use it to signal a fault as well, its one or the other.

Again, with a little ingenuity, it’s not hard to convey multiple things to the controller with only one output. I’m not sure why you keep saying this is not possible when a quick review of the ClearPath user manual (it’s a free download) explains how this works (specifically the section that covers ASG w/ measured torque).

Quote

Despite the fact that Teknic products are designed for the OEM market (see the About Us page on our website), a side effect of the reduced wiring problems and the ease with which a ClearPath servo system can be implemented, is that many corporate end-users and hobbyists have been attracted to ClearPath. And even though we didn’t set out originally to sell to end-users and hobbyists, we are happy that ClearPath has been well-received, and we enjoy supporting such a wide range of people and applications.

All opinion only, and not all of which I agree with.

When I explain how and why we designed ClearPath for our experienced OEM customers, I don’t understand how you can say that’s an opinion. Every one of the engineers at Teknic who participated in the ClearPath design project can attest to the fact that we designed ClearPath for our core customer base, not first-time servo users. That said, I have to admit we were pleasantly surprised by how big the market of first-time users is, and how much they like ClearPath.

For instance your name for your servos 'Stepper Killers', is that or is that not designed to entice first time buyers?

The name, which started as an internal joke during product development and eventually stuck, has nothing to do with enticing first-time [servo] buyers. Many OEMs still use stepper motors in their products. “Stepper killer” is our attempt to humorously state that we believe we have a product that can beneficially replace stepper motors in many of their applications. (I say many, not all, applications because stepper motors are still a good choice in many applications, especially when the power requirement is low and the motor frame size needs to be smaller than NEMA 23. That’s why Teknic offers standalone drives (only to OEMs) that can control stepper motors in a closed-loop servo manner.)

I would agree that Tecknics do a a masterly job at supporting customers, and I have never claimed otherwise. I would also commend that Tecknics follow on-line forums for any issues related
to your products, to whit, you and your colleagues have taken me to task about my opinions on forums other than this one. As I have stated I base my opinions on the facts of Clearpath servos
and and willing to change my opinion in light of new facts, but refuse to be badgered out of my opinion without new facts. That you don't like it is immaterial to me.

Again, please don’t feel like we are trying to badger you. We sincerely are not. Teknic’s two reasons for responding to forum posts are to answer questions and correct factual errors. If you state your opinions, regardless of how negative about a Teknic product, without any misstatements of fact, or materially incomplete (i.e., misleading) commentary, we will rarely post a response. And if you post a misstatement of fact that puts a Teknic product in a better light than it deserves to be based on the facts, we will correct that too. (Look around this forum and YouTube, and you will see we have done this many times). Our goal is to help others understand motion control technology and apply it in a way that makes them successful. If this forum’s members (and the general market) are well-educated, they will choose the best products for their needs. We think that’s a great outcome for everyone.

Jon K. – Teknic Servo Systems Engineer