Homing with ClearPath Servo's hard stop

[chjade84]

I wanted to give the ClearPath hard stop homing method a try since it's supposed to be quite accurate and my homing switches aren't. I was wondering if you knew how I may accomplish this since the motors don't give any real "feedback" as far as I can tell once they've homed - or a real way to tell them to home. From what I understand, my best option would be to have them home automatically on the first enable after the software starts. That's easy to set up. The harder part is to have the software set the axis home locations since it won't use its homing routine and won't get feedback from a sensor saying it's been reached. Any idea? Page 103 in the manual here: https://www.teknic.com/files/downloads/ ... manual.pdf

Thanks!

[spumco]

I read the manual after you posted this and couldn't figure an easy way for the HLFB signal to communicate to your controller. Was hoping somone else had an idea so I didn't bother posting "I don't know either."

I think it's time for you to call Clearpath as they may have an idea - at least getting you in the ballpark so you can integrate what they tell you with UCCNC. The only thing - admittedly vague - I could come up with is this:

- HOME ALL button tied to user-written macro which enables each drive sequentially.
- servo 1 enabled, which starts the auto homing sequence, reaches home, sends HLFB ASG-Position signal.
- macro registers ASG-position signal and writes "homed" to axis in UCCNC, then
- enables servo 2 and lather, rinse, repeat.

The HLFB ASG-Position pins are not set in UCCNC as 'limit' or 'homing' pins, just general inputs. I don't think you can use the pin later for other functions (like Servo On) as that would require direct programming via PC to switch the HLFB mode.

So the queston to ask Clearpath (Teknics) is - what, if any, HLFB signal is used by the motor when auto homing is complete?

Let us know what you find out...

-Ralph

[spumco]

It should be easy enough to set UCCNC Machine coords from code once you have reached Axis home with the drive.

Same if you used ABS encoders. The encoder talks with UCCNC and tells it where it is at and UCCNC resets teh machine coords to the abs values.

Just a thought, (;-) TP

(;-) TP

Terry,

The Clearpath servos don't have encoder outputs. That's one of the features they left out to cut down cost. All it has is a "High Level Feedback" (HLFB) switch you can program to respond to various conditions. That was kind of the general/vague idea I suggested - use the HLFB switch to trigger an I/O pin, and have a macro in UCCNC recognize the pin as a 'homed' signal.

And this is one of the reasons I quit thinking about Clearpath servos for my mill. Other stuff, maybe. But not for my mill.

-Ralph

[Regulator]

Eagerly watching where this thread goes....lol, as I'm a clearpath user but didn't think there was a possible way to make hard stops work.

[ThreeDJ16]

I know this thread is a month old, but isn't the ClearPaths signal out a fault signal, therefore needing a power down after it occurs? A couple of friends are using the bump stop method, then just manually zero their program and reset power on the Clearpaths. Personally think that is a crappy way to have to run them. You would think that the makers of Clearpath would incorporate an easier homing method by adding one more signal out besides a fault.

It's also one of the reasons I've been looking at DMM servos for my axis setup, as they have a zero pulse output along with a fault output. So you zero to a normal switch, then back off to the zero pulse. So it takes 1 homing input for all 3 axis, then 1 additional homing input for each axis to do this and also requires a special homing macro. I did this on my Emco lathe with closed loop steppers and a hall effect sensor on each ball screw pulley. Works out very accurate.

-=J

[1JUMPER10]

I wanted to give the ClearPath hard stop homing method a try since it's supposed to be quite accurate and my homing switches aren't. I was wondering if you knew how I may accomplish this since the motors don't give any real "feedback" as far as I can tell once they've homed - or a real way to tell them to home. From what I understand, my best option would be to have them home automatically on the first enable after the software starts. That's easy to set up. The harder part is to have the software set the axis home locations since it won't use its homing routine and won't get feedback from a sensor saying it's been reached. Any idea? Page 103 in the manual here: https://www.teknic.com/files/downloads/ ... manual.pdf

Thanks!

Set up your hard stops so that they stop the gantry (or axis) at a square position. I set my CP's to hardstop home on power up but as you state, they can also be set to home on first enable. The servos will home to the hard stop then back off the distance you specify in their firmware. For example, your hard stops are at the Y0 end of your axis travel. For most machines (well, mine anyway) this is the front. The servos travel until they contact the hard stop then back off 1" (or what ever number of counts specified in firmware). Your gantry is now square and stopped in its home position. To set this position as the home position just click the "Y" axis home button in UCCNC (assuming you don't have any home switches enabled!). That's it. Your axis is squared and homed.

[spumco]

Possible update to the homing situation for anyone considering Clearpath servos.

I'm final stages of an industrial automation build and we're using Clearpath MCPV servos and Pulse Burst positioning mode, commanded by a PLC. I was struggling with some homing and positioning sequencing & E-stop situations when I stumbled across the "Manual Hard Stop Homing" feature in the user manual. While this feature will seriously solve some of my issues, it occurred to me that we discussed Clearpath homing and UCCNC last year.

I think that this homing mode may make it easier to integrate Clearpaths with UCCNC (or other systems). I'm sure the user manual and Teknic folks can explain it better, but I think this mode works as follows:

Manual hard stop homing set in servo
1. Servo is powered, ENA not asserted. No movement.
2. ENA asserted, servo place in 'homing ready' state. Still no movement, unlike Automatic Homing.
3. Move toward hard stop home position is commanded. Move must be long enough to reach hard stop.
4. Servo moves at internally programmed speed to hard stop.
5. Hard stop hit, torque folds back, and the servo stops, registers the encoder position as home, then asserts the HLFB output.
6. Servo will move off the stop (or not) depending on Home Offset programmed in servo.

Assuming one could live without the HLFB output being used for a servo fault condition, the HLFB could be programmed to assert an ASG (move complete, on position) output. This could be read by UCCNC as a 'homed' state during a homing macro sequence for use by other features (tool change position, soft limit calcs, etc.).

It also means a dual-servo gantry could be homed properly. One servo is enabled, the other is not so it freewheels. First servo is commanded to home and the homing offset is set to a very small amount - it drags the other side of the gantry (or whatever) along. Once that is complete the HLFB-ASG output signals UCCNC macro to home the other servo. That one hits its hard stop and backs off the same amount.

Result - both sides homed, squared, and UCCNC is aware via the HLFB signal that everything is sorted out without the servos fighting each other a bit during the homing routine.

Limitations appear to be that it's only available on MCPV and SD models, in pulse burst and S&D modes. Also you lose the fault output if you want any move complete info for UCCNC to read. And I wouldn't want to drag a big, floppy gantry all the way down the table with one servo very often... But if it's parked near the stops as part of the shutdown routine I think most machines would be fine.

This application for Clearpaths and UCCNC doesn't have anything to do with my current project but i figured I'd throw this out there for consideration. Have a read of the manual and maybe some Clearpath owners will be able to make use of it.

-Ralph

[ThreeDJ16]

This is the very reason I'm only considering DMM servos. At least with them you can use the fault output for its intended purpose (shut down all axis if one faults). With DMM you have a second option which is the zero reference output, so you can home to any standard switch and it backs off until it hits the z ref from the encoder position. So you get very accurate homing and fault output. I'm doing the same thing now without servos. Emco had a brilliant idea of adding hall effect sensors on the ball screw pulley. So it hits a standard home switch, then backs off until the hall effect kicks in, which is very repeatable. I would think the Z ref on an encoder would be even more accurate with repeatability.

Come on Clearpath, just one more freakn output or at least a passthrough for the encoder z ref.

-=J

[spumco]

Yes, another output would be nice... I belive the SC series permits accessing the encoder and other useful functions - at an increased price. Not so much on the SD and MC series.

And this is why I'm using DMM's with UCCNC for my personal mill and another plasma build in the near future.

It's just that the Clearpaths are rather easy to set up on what is essentially a very dumb pick-and-place machine we're building.

[mschoonmaker]

Anybody had any success using the Clearpath SDSK motors with UCCNC controllers, utilizing the "hard stop homing"?