Thanks for the great report, Rob. Good luck with that first paying project. Your idea of suppressing motion on the first motor to reach it's switch sounds like it should work. If I remember right, long years ago there was a fellow in Finland that proposed a yearly contest for the most innovative "work around."
Rayh
--- [EMAIL PROTECTED] wrote:
From: Rob Jansen <[EMAIL PROTECTED]>
To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net>
Subject: Re: [Emc-users] Homing using 2 motors per axis
Date: Sun, 16 Mar 2008 09:00:14 +0100
Clint,
home with the motors on. My machine's motors are not strong enough to
hurt the machine when they run into the stops so I usually just crash
the axis then home... Oh ya, stepper motors...
This method is brutal but effective.
Brute and destructive on my machine ...
It happened once, while overshooting the home switch and if I now place a hair ruler on the bearing block (made out of 6082-T651 alu) I can see it's bent ...
I used the manual procedure you described a few times but the problem, as Rayh acknowledges, is that the motors move to a full step position when the controllers are switched on and at that time there already is a misallignment of max. 0.02 mm.
But I'll leave this as it is for now - A full step is 0.025 mm and the two axes are 1220 mm apart so that gives a max. 0.001 degree error. If a customer wants more accuracy, they'll have to pay enough for me to upgrade my machine ;-)
Rayh,
As long as you don't have to worry about loosing steps, both motors could be driven from the same set of step and direction pulses -- except when trying to find home. I'm thinking of a real kludge here but since you can home anytime, you could build a little switch that disconnects one drive from the step and direction signals at a time while the other one homes. Once both are homed, send the motion pulses to both and you should have a well behaved system.No lost steps seen here the last few weeks and I have made some funny mistakes - like running an 18mm end mill through a 15mm workpiece at 400 mm/min ... Ruined my workpiece but both the milling bit and the machine's zero position were not affected at all.
I found a simple and effective solution for the kludge that you described above: a few logic gates to disable the stepper pulse to the axis when the corresponding home switch triggers during a travel towards the switches. The homing signal to EMC is only activated when both axes are homed.
I'll add this solution some day, but I first need to finish the machanical/electrical construction: mounting of the energy chains, mounting all electronics in the control cabinet, add an extra plate to the table and ... and ... and ...
Just got a phonecall: my first customer is finished and wants to deliver materials and milling data coming Friday - originally this was planned two weeks later.
So I've still got 5 days to get the machine in a proper shape, including today.
Luckily I don't have to start milling right away but it should at least look as if I'm ready O:-)
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