Re: [Emc-users] Homing using 2 motors per axis
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.netSubject: Re: [Emc-users] Homing using 2 motors per axisDate: 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:-) Rob - This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse012070mrt/direct/01/___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users - This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse012070mrt/direct/01/___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Homing using 2 motors per axis
Rayh, the whole gauntry acts as a swivel :-} It's all made of aluminium sheet 15 mm thick, 30 cm wide and 70 cm height with two 80x80 beams of 122 cm long. If I remove one of the ball screws I can move that side a few centimeters without applying too much force. I thought of adding a timing belt like Dennis mentioned but was afraid there is too much elasticity in such a long belt (when using two motors). When switching on the power supply to the motors both stepper motors will switch to a full step so one motor may move clockwise while the other goes ccw, one full step means 5 mm (pitch of ball screw) / 200 (steps/rev) = 0.025 mm difference. This does not seem too much so maybe I should not worry too much about this and just measure the difference between both sides from time to time. There never is a problem during operation of the machine - at least not after setting up the stepper timing correctly. Meanwhile I decided to leave it as it is, there are enough tother things I have to do before the machine is 'finished' - unless of course someone has a complete canned solution that I could use. My next machine will most likely use just one motor with a belt drive to two ball screws but I have to look at the specs for the timing belts first to see if this will give me the accuracy wanted. Regards, Rob [EMAIL PROTECTED] wrote: Hi Rob I've been curious about these dual drive axes for quite a while now. There are several possible mechanical lashups with something like this. It seems to me that in order to allow separate homing of each drive, there would have to be a swivel on one side or the other of the mechanical slide. Is that the case with your machine? Rayh - - This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse012070mrt/direct/01/___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Homing using 2 motors per axis
Hi RobThat sounds like it should work since the two motors will not bind against a rigid frame. You're right about those motors jumping whichever direction they please when you apply power. 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.Rayh--- [EMAIL PROTECTED] wrote:From: Rob Jansen [EMAIL PROTECTED]To: "Enhanced Machine Controller (EMC)" emc-users@lists.sourceforge.netSubject: Re: [Emc-users] Homing using 2 motors per axisDate: Thu, 13 Mar 2008 07:51:11 +0100 Rayh, the whole gauntry acts as a swivel :-} It's all made of aluminium sheet 15 mm thick, 30 cm wide and 70 cm height with two 80x80 beams of 122 cm long. If I remove one of the ball screws I can move that side a few centimeters without applying too much force. I thought of adding a timing belt like Dennis mentioned but was afraid there is too much elasticity in such a long belt (when using two motors). When switching on the power supply to the motors both stepper motors will switch to a full step so one motor may move clockwise while the other goes ccw, one full step means 5 mm (pitch of ball screw) / 200 (steps/rev) = 0.025 mm difference. This does not seem too much so maybe I should not worry too much about this and just measure the difference between both sides from time to time. There never is a problem during operation of the machine - at least not after setting up the stepper timing correctly. Meanwhile I decided to leave it as it is, there are enough tother things I have to do before the machine is 'finished' - unless of course someone has a complete canned solution that I could use. My next machine will most likely use just one motor with a belt drive to two ball screws but I have to look at the specs for the timing belts first to see if this will give me the accuracy wanted. Regards, Rob [EMAIL PROTECTED] wrote: Hi Rob I've been curious about these dual drive axes for quite a while now. There are several possible mechanical lashups with something like this. It seems to me that in order to allow separate homing of each drive, there would have to be a swivel on one side or the other of the mechanical slide. Is that the case with your machine? Rayh - - This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse012070mrt/direct/01/___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users - This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse012070mrt/direct/01/___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Homing using 2 motors per axis
Rob, I have a machine with 2 motors on the y axis. This is how I home both motors together... I have a positive adjustable stop on both ends. This is a bolt with lock nuts. When both ends of the axis are on these stops the machine is aligned and in what I refer to as the Hard y zero. To get the motors coordinated I either crash the motors into the stops at slow jogging speed until both motors stall then do a normal home (I have a home switch on one end). Or, I manually turn the screws until they are on the stops with the power to the motors off then back off and and 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. Clint B Quote from Emc-users Digest,Vol23,Issue 38: Message: 3 Date: Thu, 13 Mar 2008 07:51:11 +0100 From: Rob Jansen [EMAIL PROTECTED] Subject: Re: [Emc-users] Homing using 2 motors per axis To: Enhanced Machine Controller (EMC) emc-users@lists.sourceforge.net Message-ID: [EMAIL PROTECTED] Content-Type: text/plain; charset=utf-8 Rayh, the whole gauntry acts as a swivel :-} It's all made of aluminium sheet 15 mm thick, 30 cm wide and 70 cm height with two 80x80 beams of 122 cm long. If I remove one of the ball screws I can move that side a few centimeters without applying too much force. I thought of adding a timing belt like Dennis mentioned but was afraid there is too much elasticity in such a long belt (when using two motors). When switching on the power supply to the motors both stepper motors will switch to a full step so one motor may move clockwise while the other goes ccw, one full step means 5 mm (pitch of ball screw) / 200 (steps/rev) = 0.025 mm difference. This does not seem too much so maybe I should not worry too much about this and just measure the difference between both sides from time to time. There never is a problem during operation of the machine - at least not after setting up the stepper timing correctly. Meanwhile I decided to leave it as it is, there are enough tother things I have to do before the machine is 'finished' - unless of course someone has a complete canned solution that I could use. My next machine will most likely use just one motor with a belt drive to two ball screws but I have to look at the specs for the timing belts first to see if this will give me the accuracy wanted. Regards, Rob [EMAIL PROTECTED] wrote: Hi Rob I've been curious about these dual drive axes for quite a while now. There are several possible mechanical lashups with something like this. It seems to me that in order to allow separate homing of each drive, there would have to be a swivel on one side or the other of the mechanical slide. Is that the case with your machine? Rayh - - This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse012070mrt/direct/01/ ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Homing using 2 motors per axis
Hi RobI've been curious about these dual drive axes for quite a while now. There are several possible mechanical lashups with something like this. It seems to me that in order to allow separate homing of each drive, there would have to be a swivel on one side or the other of the mechanical slide. Is that the case with your machine?Rayh--- [EMAIL PROTECTED] wrote:From: Rob Jansen [EMAIL PROTECTED]To: EMC Mailinglist emc-users@lists.sourceforge.netSubject: [Emc-users] Homing using 2 motors per axisDate: Mon, 10 Mar 2008 08:24:23 +0100 Gentlemen, My milling machine uses 2 ball screw spindles with separate motors (and separate microstep drivers) to move the Y-axis portal which is 1.2 meter wide. To do accurate homing, each axis should have its own homing switch and the motors should be controlled using different I/O signals. This, most likely, has been done before. Does anyone have some information, or maybe even a pointer to a complete implementation for this? Before I start reading through the integrator and HAL manuals I though I try it "the easy way" first ... Regards, Rob - I keep always telling collegues there is no easy way ... - This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse012070mrt/direct/01/___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users - This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse012070mrt/direct/01/___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Homing using 2 motors per axis
I had a similar problem. I solved it by using a toothed timing belt between each screw, such that both sides were forced to stay in alignment. That way, I didn't need to worry about misalignment during either homing or actual milling. I only used one homing switch for the axis this way. It seems to work fine. If anyone sees a problem with this solution, I'd like to know about it so I can take preventive measures. I recently finished my machine, so I don't have a lot of experience with it yet. But, so far, it's working fine! Dennis - This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse012070mrt/direct/01/ ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
