Controlling Acorn's axis enable signals with homing macro?

[erer44]

In order to use clearpaths in 'home on enable' mode, I would like to be able to control the output of the drive enable pins with a homing macro. Couldnt find anything mentioning this in the manual, the PLC, or searching these forums. My other option is running the enables through relays but I'd rather not if Acorn can just do it in software. Is this possible? Thank you

[Richards]

One of the first things that interested me about ClearPath servos was the auto homing routine. That was over a year ago. I've considered using it several times since then but each time, after running the numbers, I keep going back to proximity sensors. Why? In a completely controlled system where the stop point of each axis was only an inch or two away from 'home', auto homing would be practical. But, my experience comes from using a router. My router was relatively large, five feet by ten feet. The jog speed of that router was set to twenty inches per second. Even at that speed, it took over six seconds for the long axis to travel the complete distance. At one-half inch per second, I would have been waiting four minutes for the axis to travel it's complete distance. At my age, there is no guarantee that I'll still be upright in four minutes. In a perfect world homing the machine would happen just once per power-up cycle, but things happen. If a motor faults, power has to be cycled and homing would be part of that power cycling. For me, it makes more sense to use a N/C sinking proximity sensor on each axis. They cost less than $6 each and they've been very reliable. I can jog an axis to get close to a sensor and then run a homing routine.

In my case, that is a more practical solution.

[Gary Campbell]

You will be better off connecting the ENA circuit to one of the relays, or directly to VCC and COM

Have you used the "home on enable" feature yet?

[martyscncgarage]

CNC4PC has been working on a board that plugs into the Acorn Step/Dir headers and Clearpath cables plug into it. I provided some input, but I don't have any CP motors so I have not been able to test them.
Buy the clearpath cables and DON'T Whack the ends off! (though CNC4PC thoughtfully added terminal blocks if you did)

Arturo is very open to feedback, so perhaps one of you power users very familiar with Clearpath motors could give the board a try and do a review here and provide CNC4PC feedback as well.

https://www.cnc4pc.com/c86accp-clearpat ... oller.html

[Gary Campbell]

A couple thoughts on this... ClearPath power and control cables come in 2 lengths. 10 ft. or 55 ft. Other than small mills or routers, 10 ft is too short. 55 ft is obviously too long, and in most cases a single 55 ft cable can be cut in 2 sections. Since these 55' cables cost $85 or $112 most users will cut them in half. And then the obvious... who wants 20' plus coils wire laying around a control?

I like the plug and play aspect of this product for those that are challenged by reading a schematic, but wonder if there is a practical use for it in the real world?

[cnckeith]

experiment for you guys...

an idea for clearpath hard stop homing would be... edit the acorn home program to not use the M91/2

instead use G91

so assuming that the machine is parked at 1" away from hard stop and clearpaths in hard stop homing mode.

the home program would look like this

G91 x-4 F20 ; move incrementally negative 4 inches at 20 inches per minute

now the clearpath would be enabled by this line and start moving while looking for the hard stop.. once it hits the hard stop the clearpath stops listening to the Acorn step output and 'takes over' ignoring the rest of the G91 move while it backs off the hard stop and stops. Acorn will just keep on putting out the steps until all of them are sent.. then goes to next line..

M26/X ; set home at current position

as long as the clearpath hard stop back off procedure finishes before the G91 x-4 F20 line is done sending steps this might work, (if you need more time increase the G91 line length or slow down the F command)

i heard there are several hard stop homing options with clearpath, i ran this idea by the teknic guys , they said it would probably work with the regular hard stop homing.. i haven't had the time to test it, i don't know whether the clearpath will start listening to the steps in the G91 line again after it finishes the hard stop back off? or does it need a estop cycle? to start paying attention to the step signal... or? something to look into..

alternative maybe better way...is time based..

G91 X-.01 F20 ; just to enable the axis
G4 P4 ; Wait for 4 seconds
M26/X

[Dave_C]

I've played with this a bit myself since I have Clear Path Servos on my mill:

Here is what I looked into, Clear Path servos have the option to "home on enable" but that is not the best part. If while doing the servo setup and using the Clear Path software, after you select "home on enable" you can also select to use a soft stop and enable to a pulse!

This was included so that if you hard stop moves a bit, and some will, then the motor hits the stop and stalls, backs off to a predetermined pulse on the encoder and then it is homed. VERY Accurate but slow in some cases as you have to lower the torque so the motor doesn't hit the stop hard and then lower the approach speed as well. If you are a long distance away it can take minutes to home.

The enable to a pulse part is not well defined but it is called "precision Homing" and the instructions start on page 182 of the manual I have.

If you park your machine close to the home position then this is a good option! Now in order to get it to home on an Acorn machine you have to select the option to "jog to home" rather than home to switches. So once you start to jog each axis it becomes enabled and will home.

So basically you can build a machine without using ANY limit or homing switches as the Clear Path software will let you set the length of travel but then so will CNC 12 so no big deal there.

Dave C.

[martyscncgarage]

I've played with this a bit myself since I have Clear Path Servos on my mill:

Here is what I looked into, Clear Path servos have the option to "home on enable" but that is not the best part. If while doing the servo setup and using the Clear Path software, after you select "home on enable" you can also select to use a soft stop and enable to a pulse!

This was included so that if you hard stop moves a bit, and some will, then the motor hits the stop and stalls, backs off to a predetermined pulse on the encoder and then it is homed. VERY Accurate but slow in some cases as you have to lower the torque so the motor doesn't hit the stop hard and then lower the approach speed as well. If you are a long distance away it can take minutes to home.

The enable to a pulse part is not well defined but it is called "precision Homing" and the instructions start on page 182 of the manual I have.

If you park your machine close to the home position then this is a good option! Now in order to get it to home on an Acorn machine you have to select the option to "jog to home" rather than home to switches. So once you start to jog each axis it becomes enabled and will home.

Dave C.

Precision homing is the way to do it!
Yes Park the machine OR jog it close BEFORE homing.

[cnckeith]

alternative maybe better way...is time based..

G91 X-.01 F20 ; just to enable the axis and clear path to take over the axis...
G4 P4 ; Wait for 4 seconds for clear path to finish
M26/X ; set home at current location

[Richards]

Precision homing looks interesting; but, page 187 of the rev 3.05 manual seems to say that a hard stop must always be present. The procedure given is that the first time precision homing is used, the hard stop is used to set the exact position desired. Subsequently, as long as the hard stop is within +/- one-half turn (of the shaft), the motor will use the encoder count set when the original physical home was established.

Item (c) states: " Max. Error Between Original (Calibrated) Physical Home and Current Physical Home. Precision Homing will successfully complete as long as the Current Physical Home position does not exceed +/- 1/2 rev from Original Physical Home.

So, if I understand things properly, if I had a 1605 ballscrew attached to the axis (16mm diameter x 5mm pitch) to an RLN style motor with 800 encoder counts per revolution, as long as the hard stop was detected +/- 2.5mm from the original position, the motor would self-home to 0.01mm (5mm / 800 counts per revolution). That's 0.00025" if I've placed the decimal correctly.

That option is certainly worth looking at. Currently, I don't have a motor attached to a ball-screw driven linear stage. All of the parts to make a test setup are in a box, but I doubt that using a hacksaw, hammer and file to fabricate a base would give any repeatable accuracy and the Harbor Freight dial indicators that I have only guess to the nearest 0.001".

If anyone can run a test on a reliable and repeatable axis, I would certainly like to read their results.