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CandCnc 5 axis (really a 4 axis) system problem
« on: October 28, 2013, 01:21:40 PM »
Hello,

I bought a 5-axis Bladerunner/MP3000 servo system recently to control a gantry system with a rotary feature on the head. Unfortunately their 5-axis system is not really a 5-axis system, it's a 4 axis system with a 5th motor driver that is connected to the same pulse output as the y-axis, so only 4 axis can be independently controlled by Mach3, the problem is that the Y and A(the slaved gantry axis) axis cannot be controlled independently so squaring up the gantry is my problem, they can't be homed(referenced) independently so any squaring has to be done manually, like by manually trying to loosen the pulley or power down the motors and move into place, then power it back up and hope it stays, each time the machine is turned on.

The people and CandCnc said that if I "used my head" I wouldn't have to square the gantry, or do it twice anyway, so the manual process shouldn't be a big deal, and none of their other customers have needed to square their systems, so that's their answer. Their manual points out the reasons why it's a good idea to have independent home switches on the gantry axis(to square the system), but when you buy their 5-axis system apparently the reasoning for having independent homing goes away and smart people don't need it, but I need it.

Does anyone have a workaround for this? Tom at CandCnc said that if I wanted a system that was a true 5 axis system I needed to buy a system from someone else, I will certainly accept his advice for the next machine but I'm hoping to use their system for this machine,  I'm hoping someone smarter than me or Tom has figured out an easy way to address this less than 5 axis homing problem.

Thanks!

Offline BR549

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Re: CandCnc 5 axis (really a 4 axis) system problem
« Reply #1 on: October 28, 2013, 01:47:14 PM »
OK What makes you think you need to square the gantry more than once at startup?  Servos do not loose steps.

Was your gantry built/installed square?

I have cut endless miles of material with a plasma table without constantly resquaring the gantry.

At most at the end of your table install a set of stops that allow the gantry to be square when bumped up against the stops. Jog over next to the stops turn off the drives and push the gantry up against the stops , turn the drives back on, done deal.

Just a thought, (;-) TP



Re: CandCnc 5 axis (really a 4 axis) system problem
« Reply #2 on: October 28, 2013, 02:39:03 PM »
Hi BR549,

I should clarify, the guys at CandCnc said if I "used my head" I would only have to square the system once and not have to re-square it even after turning the machine off for the night. We know the gantry needs to be squared though because we have another 4 axis system at the same customer that was having a problem with the gantry being square, originally we tried to do it without separate home switches, but it didn't work. It's a production machine operated and cleaned and maintained by regular hourly workers so sometimes it would get out of square when they were cleaning or whatever when the power is off and getting it back was not something a $8/hr operator can be expected to do by manual manipulation, it was hard and took a while for their trained guys to do it, especially compared to pushing a "Y-ref" button. I think the CandCnc manual explains the reasons why having independent home switches is a good idea for a gantry, particularly for a paying customer. I have a stepper driven plasma cutter that doesn't have it, but I wouldn't sell that to a customer.
The machine is a foam router and the gantry is 8 feet long so if it's off a little it makes a big difference over 8 feet. Since it's a servo system, and the operators are the above mentioned, having a physical stop doesn't seem like a good idea, they regularly drive the thing into the over-travel switches, maybe if the stop(s) was removeable that would be ok.
I'm hoping we can come up with a quick fix(I was really hoping it was a 5 axis system) like maybe an additional LPT card or a 2-port LPT card? Has anyone tried that with a CandCnc system? Does that work with their special drivers?

Thanks

Offline BR549

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Re: CandCnc 5 axis (really a 4 axis) system problem
« Reply #3 on: October 28, 2013, 03:16:51 PM »
Yes you can use a 2nd LPT card and get all 6 axis if needed. Their electronic slaved axis was just a way to get all the axis needed with 1 LPT card to run a gantry style machine with a 4th axis.

(;-) TP

Offline Jeff_Birt

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Re: CandCnc 5 axis (really a 4 axis) system problem
« Reply #4 on: October 28, 2013, 04:41:39 PM »
Back in the day when all servo drives were analog if you had a large gantry machine with a servo motor on each side you would have one side slaved to the other. The slaved side would follow the master by means of a signal between the two servo drives that kept them in sync. With more modern controls, stepper motors, or digital servo drives you can sync the master and slave in different ways. With a large gantry the ability to auto-square is handy as things do happen that can knock the gantry out of square.

Twenty years ago when all most PCs had was a parallel port and serial port a lot of schemes were used to provide more I/O for hombres projects. One of these schemes was multiplexing the parallel port pins (using them for more than one thing) and a few places still do this as they are clinging tooth and nail to the crusty old parallel port. If you have five separate stepper drives than there is no reason at all you can't use all five of them fully unless a manufacturer is hobbling them with 20 year old technology.

It may take some rewiring but you could use a SmoothStepper (or similar external motion controller) to get the I/O you need to run everything properly.
Happy machining , Jeff Birt
 
Re: CandCnc 5 axis (really a 4 axis) system problem
« Reply #5 on: October 29, 2013, 04:17:02 PM »
Thanks BR549, I'll try a second LPT port and see what happens, after going through the process I realize I should have used 2 LPT ports in the first place instead of trying to get some extra inputs using a pre-made multiplexed system.
Thanks Jeff for the tips on using a Smoothstepper or some kind of controller, that looks like it might work better than what I'm doing.