Re: [Emc-users] Stepper response
On Mon, 26 Nov 2012, Jon Elson wrote: craig wrote: What useful information can be extracted from sensing stepper voltage and current responses? Mariss Freimanis of Gecko did quite a bit of work on this a while ago, called the unstallable stepper, I think. There should still be some info on the Geckodrives web site about it. The problem, of course, is if one motor slows down to prevent a stall, all the other motors need to also slow down by the same amount, or you still make a mess of the part. I think this is where Mariss fell down, as he didn't have a sensible way for the drive to report what it was doing back to a CNC control with software-generated steps out the parallel port. Are there useful differences in the waveforms for missing steps? nearly missing steps? Once you've missed a step, all is lost as the stall is in progress. What Mariss was doing was measuring the phase angle between current and voltage, and he could keep the stator pole just less than 90 degrees ahead of the rotor pole, to develop maximum torque. When the phase angle exceeded this, you had to back off or move into the stall territory. with an encoder on the motor shaft and a linear encoder on the axis gantry could linuxcnc be configured to detect a stall maybe as simple as a loose motor connector -- LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial Remotely access PCs and mobile devices and provide instant support Improve your efficiency, and focus on delivering more value-add services Discover what IT Professionals Know. Rescue delivers http://p.sf.net/sfu/logmein_12329d2d ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Stepper response
kqt4a...@gmail.com wrote: with an encoder on the motor shaft and a linear encoder on the axis gantry could linuxcnc be configured to detect a stall maybe as simple as a loose motor connector Yes, of course it can. You need a way to read the encoders into the PC. Mesa and Pico Systems (my company) make boards that can do this, as well as output step pulses at fast rates smoothly. You can, in theory, read the encoders via the parallel port, but there are a bunch of limitations on that. You would only need one encoder (either linear or rotary) per axis, not two. Jon -- LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial Remotely access PCs and mobile devices and provide instant support Improve your efficiency, and focus on delivering more value-add services Discover what IT Professionals Know. Rescue delivers http://p.sf.net/sfu/logmein_12329d2d ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Stepper response
with an encoder on the motor shaft and a linear encoder on the axis gantry could linuxcnc be configured to detect a stall maybe as simple as a loose motor connector Putting encoders on a stepper is an obvious idea that occurs to everyone faced with positioning errors, but it turns out that nagging details make it not so good in practice. The basic problem is that there's not much one can do after a following error: the steppers tend to be run with maximum rated current already, so it's not like we can drive them harder to catch up. Also, the problems with steppers tend to occur because we drove them into difficulty such as mechanical resonance or binding---the solution tends to be to slow down, not drive harder. Additionally, by nature steppers can only screw up by one step, so a real-time course correction is not really possible, it's only good for 'oops, we're screwed'. In conclusion, stepper drivers/motors are cheap and simple, and work reliably within their design envelope. Encoders make them complicated and expensive for little gain, so they tend not to be used. -- LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial Remotely access PCs and mobile devices and provide instant support Improve your efficiency, and focus on delivering more value-add services Discover what IT Professionals Know. Rescue delivers http://p.sf.net/sfu/logmein_12329d2d ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Stepper response
There are stepper drivers that can extract feedback for detecting missing steps, but they require parameters be set to match the particular motor. One such device is the TMC246 from www.trinamic.com See: http://www.trinamic.com/index.php?option=com_contentview=articleid=171Ite mid=302 I looked at basing a product around this concept but decided that it was not practical to offer a general purpose driver with this function because it would be too hard to support unless you sold matching motors. Steve Stallings -Original Message- From: craig [mailto:cr...@facework.com] Sent: Sunday, November 25, 2012 10:58 PM To: emc-users@lists.sourceforge.net Subject: [Emc-users] Stepper response The post: /Re: [Emc-users] Spindle position, direction and Index with only one channel.// // //On 11/24/2012 5:01 PM, James Boulton wrote:// / /Has anyone on list used a stepper as an encoder like this: http://home.clear.net.nz/pages/joecolquitt/stepper_as_encoder.html James// / got me reconsidering something I thought about some time ago and laid aside because I have the neither the expertise nor the time to investigate it. What useful information can be extracted from sensing stepper voltage and current responses? Are there useful differences in the waveforms for missing steps? nearly missing steps? If there are, the detection of such events could be quite useful. For many application 1 or 2 missing steps before stopping might be quite acceptable. If one could detect such things, one might be able to work much faster in materials with highly variable hardness/ resistance (e.g. knots in wood). or be able to stop replace a dull tool and finish the job still within acceptable tolerances. Inexpensive sensors and microprocessors might be able to implement the needed feature extraction and pattern recognition at relatively low cost. Has anybody seriously looked at this? Does anyone know of good models of stepper physics that could be used to guess what to look for? Craig -- Monitor your physical, virtual and cloud infrastructure from a single web console. Get in-depth insight into apps, servers, databases, vmware, SAP, cloud infrastructure, etc. Download 30-day Free Trial. Pricing starts from $795 for 25 servers or applications! http://p.sf.net/sfu/zoho_dev2dev_nov ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users -- Monitor your physical, virtual and cloud infrastructure from a single web console. Get in-depth insight into apps, servers, databases, vmware, SAP, cloud infrastructure, etc. Download 30-day Free Trial. Pricing starts from $795 for 25 servers or applications! http://p.sf.net/sfu/zoho_dev2dev_nov ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
[Emc-users] Stepper response
The post: /Re: [Emc-users] Spindle position, direction and Index with only one channel.// // //On 11/24/2012 5:01 PM, James Boulton wrote:// / /Has anyone on list used a stepper as an encoder like this: http://home.clear.net.nz/pages/joecolquitt/stepper_as_encoder.html James// / got me reconsidering something I thought about some time ago and laid aside because I have the neither the expertise nor the time to investigate it. What useful information can be extracted from sensing stepper voltage and current responses? Are there useful differences in the waveforms for missing steps? nearly missing steps? If there are, the detection of such events could be quite useful. For many application 1 or 2 missing steps before stopping might be quite acceptable. If one could detect such things, one might be able to work much faster in materials with highly variable hardness/ resistance (e.g. knots in wood). or be able to stop replace a dull tool and finish the job still within acceptable tolerances. Inexpensive sensors and microprocessors might be able to implement the needed feature extraction and pattern recognition at relatively low cost. Has anybody seriously looked at this? Does anyone know of good models of stepper physics that could be used to guess what to look for? Craig -- Monitor your physical, virtual and cloud infrastructure from a single web console. Get in-depth insight into apps, servers, databases, vmware, SAP, cloud infrastructure, etc. Download 30-day Free Trial. Pricing starts from $795 for 25 servers or applications! http://p.sf.net/sfu/zoho_dev2dev_nov ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Stepper response
craig wrote: What useful information can be extracted from sensing stepper voltage and current responses? Mariss Freimanis of Gecko did quite a bit of work on this a while ago, called the unstallable stepper, I think. There should still be some info on the Geckodrives web site about it. The problem, of course, is if one motor slows down to prevent a stall, all the other motors need to also slow down by the same amount, or you still make a mess of the part. I think this is where Mariss fell down, as he didn't have a sensible way for the drive to report what it was doing back to a CNC control with software-generated steps out the parallel port. Are there useful differences in the waveforms for missing steps? nearly missing steps? Once you've missed a step, all is lost as the stall is in progress. What Mariss was doing was measuring the phase angle between current and voltage, and he could keep the stator pole just less than 90 degrees ahead of the rotor pole, to develop maximum torque. When the phase angle exceeded this, you had to back off or move into the stall territory. Jon -- Monitor your physical, virtual and cloud infrastructure from a single web console. Get in-depth insight into apps, servers, databases, vmware, SAP, cloud infrastructure, etc. Download 30-day Free Trial. Pricing starts from $795 for 25 servers or applications! http://p.sf.net/sfu/zoho_dev2dev_nov ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
