Jim Fleig - CNC Services wrote: > A system has to be chosen for to retrofit a mill that will be cutting 3D > surfaces. Curve intersecting curve intersecting flat on an angle, etc. I > have retrofit similar mills with Centroid systems and the users regularly > program at 100 ipm and observe that the mills average about 60 ipm (as low as > 10 - 15 ipm in very curvy detail or tight corners and up to 95 ipm on almost > flat curves and wide open corners). Does anyone have experience with EMC or > Mach3 achieving the same level of performance as the Centroid system? If > yes, what configuration was used? > Some time ago I did some testing and got a block processing speed of about 680 blocks/second on a 600 MHz Pentium. This was doing a 10,000 G1 segment move that worked its way completely around a 2" circle. I'm sure a faster CPU could have done it faster. I was exploring the difference between G61, G61.1 and G64 modes. > > EMC's PID loop has a cycle rate of 1000 times per second. Is this a fact? > If yes, are there any options to get the PID loop to run faster? There is > motion control hardware available for Mach3 that is capable of a PID loop > with a cycle rate of 5000 times per second. > 1000 Hz is the default, there is no specific limit. The CPU and communication to the servo interface has to be fast enough to leave some CPU time available for the GUI, OS, etc. I have gone to 5 KHz with my interfaces and faster CPUs, and a 2 GHz CPU should be able to do 10 KHz. > Although EMC receives feedback in realtime it does not adjust commands to the > axes if the axes are getting closer to exceeding the following error limits. > I do not know this to be true. This is a statement from the supplier of > motion control hardware for EMC and Mach3. > Currently, EMC2 doesn't have "feedrate compensation", ie. bringing down the feedrate override when following error rises. It could easily be implemented OUTSIDE of most of EMC, with a small HAL component that would watch following error and use the halui interface to change the feedrate override. The algorithm of how much to change the feedrate override, and how to decide when it was safe to go back up is not so clear. My Allen-Bradley 7320 had this, when it passed 50% or something of the following error limit, it abruptly cut feedrate to 50%, when the error dropped, it would abruptly go back to 100%. Not a very good scheme, and it could set my Bridgeport rocking nicely!
EMC most certainly DOES "adjust commands to the axes" in real time, based on the PID settings, to attempt to minimize following error every servo period, at least in all versions using servo feedback. This is the basis of a servo system, looking at feedback and applying a command to the "plant". Jon ------------------------------------------------------------------------------ Create and Deploy Rich Internet Apps outside the browser with Adobe(R)AIR(TM) software. With Adobe AIR, Ajax developers can use existing skills and code to build responsive, highly engaging applications that combine the power of local resources and data with the reach of the web. Download the Adobe AIR SDK and Ajax docs to start building applications today-http://p.sf.net/sfu/adobe-com _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
