Joe's 1000x600x200 steel and aluminium router started

[devmonkey]

Call me stupid, but what exactly do you adjust to make the gantry square once the whole sequence has finished? What is the purpose of step 4? Do you have separate cotrol of the two X distances in 6?

Hi Kit,

Quick answer, once the sequence is finished the gantry is square.

So the normal single motor home search (used by everything from gbrl on your 3d printer, mach3 and the DDCS) is:
1. Drive axis until home switch activates (at which point you have likely gone past it)
2. Retract axis very slowly until home switch releases (you are now at 'home').

In a setup with two motors one driving each side of the gantry adjust the switches/inductive targets so that when each respective release point is reached the axis is square.

Challenge now is to 'trick' the controller that is executing the single motor home search algo above into locating the point where both switches exactly release.

This is what the logic I described does. Step 4 is required during retraction as when a motor's home switch releases that motor is at 'home', whilst the remaining motor isn't yet there so requires more steps. My board never generates steps, it only suppresses steps if required. So in this case DDCS still believes it needs further retraction so continues to generate retraction steps, however my board only passes these onto the motor that has not yet reached 'home'. When this motor does finally activate it's switch both motors are at 'home' and my board signals this to the DDCS.

If your question was due to believing that because at step 2 both motors have activated their home switch and the DDCS has been signalled meant that the motors were at 'home' then this is not true. It wouldn't work as you may have overshot due to the momentum of the gantry and the angular momentum in the screw and it is highly unlikely the hysteresis of two switches is identical. This is why everyone does the very slow retraction until release which avoids both these problems.

This whole process will re-square a machine that has gone out of square. The machine only goes out of square if a driver misses some steps due to noise, a motor stalls or if someone turned a ballscrew by hand when the machine was off.

[Scustom]

Nice work devmonkey!!
Really interesting build!

[JAZZCNC]

Call me stupid, but what exactly do you adjust to make the gantry square once the whole sequence has finished? What is the purpose of step 4? Do you have separate cotrol of the two X distances in 6?

Ok your Stupid. . . .But so am I because I'm not seeing it either.?

To me it's just homing each axis separately, waiting until both inputs go high and backing off until both go low then moving both to a set distance.! It's not doing any individual axis correction and as the switches don't move it's not corrected anything.? Yes, you can square the gantry by offsetting switches using this method, which is how mach3 etc do it but so can any homing system really.!

If you want a true squaring system then it needs to drive each motor separately and adjust to a set distance. For instance, the CSlabs squaring system gives you options to measure the offset between the switch triggers and gives you the option to apply a correction to a set distance or let the system do it automatically. In which case it drives both motors until the first switch goes high then backs both off until it goes low, then it drives the opposite motor until switch goes high measures the difference and moves that axis only the measured difference. It's strange to watch as it does a little dance and the gantry is then aligned to the first switch.
If you want to apply an extra offset to twist either side then you can set a +/- distance for either side which it will apply after homing. It then backs both off a set distance if required.

[JAZZCNC]

Challenge now is to 'trick' the controller that is executing the single motor home search algo above into locating the point where both switches exactly release.

This is what the logic I described does. Step 4 is required during retraction as when a motor's home switch releases that motor is at 'home', whilst the remaining motor isn't yet there so requires more steps. My board never generates steps, it only suppresses steps if required.

I do a similar thing with the Cslabs IP-M controller that doesn't home each axis individual. I just do it using a modified macro which basicly homes twice and controls the drive enable using an output connected to a relay...! . . Simplizzzs

[devmonkey]

Ok your Stupid. . . .But so am I because I'm not seeing it either.?

To me it's just homing each axis separately, waiting until both inputs go high and backing off until both go low then moving both to a set distance.! It's not doing any individual axis correction and as the switches don't move it's not corrected anything.? Yes, you can square the gantry by offsetting switches using this method, which is how mach3 etc do it but so can any homing system really.!

If you want a true squaring system then it needs to drive each motor separately and adjust to a set distance. For instance, the CSlabs squaring system gives you options to measure the offset between the switch triggers and gives you the option to apply a correction to a set distance or let the system do it automatically. In which case it drives both motors until the first switch goes high then backs both off until it goes low, then it drives the opposite motor until switch goes high measures the difference and moves that axis only the measured difference. It's strange to watch as it does a little dance and the gantry is then aligned to the first switch.
If you want to apply an extra offset to twist either side then you can set a +/- distance for either side which it will apply after homing. It then backs both off a set distance if required.

Hi Jazz,

When you say any homing system can do this, the DDCS cannot as you proved yourself, infact no system can unless it is aware there are two motors on a single axis, i.e it has axis slaving, my board allows me to use the DDCS with two motors to square the gantry.

I also have the correction offset logic so you don't have to manually move the switches but currently no way to update these offsets without reloading the arduino as I haven't coded it yet. So in this test they were hard coded to zero, I thought this was the simplest way to explain how it works...LOL

Cheers, Joe

[JAZZCNC]

Hi Jazz,

When you say any homing system can do this, the DDCS cannot as you proved yourself, infact no system can unless it is aware there are two motors on a single axis, i.e it has axis slaving, my board allows me to use the DDCS with two motors to square the gantry.

Well I'm not sure how I have proved this my self.? but yes I agree if the system isn't designed to slave motors independently then it can't, but most systems like Mach3 or Linux CNC that use slaved motors independently can which is more what I was meaning. Your system appeared to just be doing what they do, but they don't Auto square the gantry to a set amount, they just move to switches that you set to square the gantry. (actually, I think Linux CNC can now.!).

Anyway good job all the same, I wasn't knocking your efforts just didn't see any auto squaring(offsetting) going on only hitting switches.!

[devmonkey]

Well I'm not sure how I have proved this my self.? but yes I agree if the system isn't designed to slave motors independently then it can't, but most systems like Mach3 or Linux CNC that use slaved motors independently can which is more what I was meaning. Your system appeared to just be doing what they do, but they don't Auto square the gantry to a set amount, they just move to switches that you set to square the gantry. (actually, I think Linux CNC can now.!).

Anyway good job all the same, I wasn't knocking your efforts just didn't see any auto squaring(offsetting) going on only hitting switches.!

I'm attempting to use the standalone DDCS controller for this machine Jazz rather than a PC. Before making this custom board I read Boyan's thread on these controllers here:
http://www.mycncuk.com/threads/10187...ion-controller

I was just quoting your posts in that thread where you tested one of these controllers and proved that it was not possible to slave motors and this obviously being a problem for machines with >1 motors per axis. Here you go:
http://www.mycncuk.com/threads/10187...5579#post85579

Maybe your miss understanding what was meant.? It was me who said doesn't work and I'm talking about Slaved axis. As in two motor/drives on separate outputs working as one axis.
That controller is exactly the same one I have and it DOESNT allow slaved motors. This video is just showing it working as 3 + 1 which the controller will do no problem. The fact they have twin screws means they are using dodgy practise of using one output to control two drives or even worse one drive to control two motors.?

IT DOESNT SLAVE TRUST ME.!!!!

I'm using the 4-axis version with much newer firmware but it still doesn't support slaving, hence the creation of this board to add the capability without the operator or the controller needing to know it is there, it just works passively in the background when required. The 4th axis is obviously then still available to use as a 4th axis as well.

For me the most important function is (re)squaring the gantry before every job, I think you are more concerned with setting up the initial squareness without moving targets. To be clear none of the methods implemented in any of the controllers perform auto squaring they all require some square reference setup on the machine to search for, whether that reference is the actual switch actuation point or some other position offset from it. Just like none of them support auto tramming or auto planaring (new word).

[JAZZCNC]

I'm using the 4-axis version with much newer firmware but it still doesn't support slaving, hence the creation of this board to add the capability without the operator or the controller needing to know it is there, it just works passively in the background when required. The 4th axis is obviously then still available to use as a 4th axis as well.

So if you still have 4th axis spare then you must be controlling 2 drives with 1 output.?

[devmonkey]

So if you still have 4th axis spare then you must be controlling 2 drives with 1 output.?

Yes, that is the whole point of this board I made, it enables the use of a single axis controller output and single home input to safely drive and also correctly home/resquare a dual motor axis with dual home switches. The controller executes its normal procedures without any knowledge that there are two motors and two switches.

[Kitwn]

Ok your Stupid. . . .But so am I because I'm not seeing it either.?

Actually that should be "Ok you're Stupid' but the grammar police will let you off just this once

What confused me was the homing being set by the release of the switch. I only speak LinuxCNC which sets the homing on the (second) activation of the switch after the gantry has backed off and run in again slowly. An upgrade to version 2.8 includes the ability to have two separately controlled motors with their own switches to square the gantry. Then it runs off the switches by a set distance which can be slightly different for the two sides to fine-tune the squaring.

Yes, that is the whole point of this board I made, it enables the use of a single axis controller output and single home input to safely drive and also correctly home/resquare a dual motor axis with dual home switches. The controller executes its normal procedures without any knowledge that there are two motors and two switches.

That's basically what my board was designed to do but I opted to create all-new step pulses while the controller believed the machine was stationary. It also acted as the splitter for sending the pulses from one output axis of LinuxCNC to two motor drivers during normal operation. 'Great minds', eh?