On Sat, 19 Mar 2016 09:52:55 -0700 Chris Albertson <albertson.ch...@gmail.com> wrote:
> On Fri, Mar 18, 2016 at 11:46 AM, Nicklas Karlsson < > nicklas.karlsso...@gmail.com> wrote: > > > I am planning to use a micro controller for stepper step pulse generation. > > I have considered to use an inverter card but special purpose stepper > > circuits are cheap so I use one of these instead. It should be possible to > > feed timer values then toggle should happen via DMA timer output compare > > values. > > > > Can anyone suggest how an ideal step generation curve should look? > > Constant acceleration up to top speed? Constant deceleration from top speed > > to zero? Or just stop generating pulses? > > > > So you are NOT using LinuxCNC. You are planning to roll your own? No i use Linuxcnc and it currently communicate via Ethernet with a micro controller so i stick with this solution for now. I discovered motion planner in Linuxcnc have maximum speed and maximum acceleration so I have to stick with these to avoid following error at high speed. I have chosen a micro stepping driver so I guess linuxcnc servo loop is to slow for the toggling. To output a square pulse on micro controller is very little software, I think DMA transfer of table value to timer comparator registers will work really well, othewise I could use several timer or software. As is now I use the micro controller for DC motors with encoder. For angle measurement I already have encoder and plan to add resolver. For motor types I have DC and plan to add BLDC, PMSM and Asyncronous. Maybe I also add sensorless. There are some software libraries available at least binaries maybe I use these or write my own. > > I've done this a few times. My purpose for using CNC is robotics and these > robots use motors of various type and move not unlike CNC machines. All of > these motors I always control using some microprocessor. (ARM or AVR) > > Generally the pulse rate generator is at the lowest "layer" of abstraction > in your software and gets requests from some high layers to do things like > move at some rate to some location. Your software has to try to do what it > is requested but subject to physical properties of the motor and mechanical > system. You have to program this in. Likely maximum acceleration is a > function of current speed. Likely the range of position is limited and so > on. Some requests might have speed or acceleration limits embedded in them > > After this there is one more important thing that really is done my some > layer above the pulse generator and that is planning. Say you are going to > make a U-turn (reverse a motor direction) you might need to slow down > before. This is called "planning" and it's always hard and with robots who > work in a changing environment maybe not possible. But if you are > interpreting G-Code you can always just read ahead. > > Ok there is one case where the pulse generator CAN and should do some > planning. If it gets a request to "move to location X" it should > accelerate to maximum speed, move for some time then DECELERATE and stop at > "X" using other max > > There are some cases where the pulse generator MUST work with more then one > motor at the same time. What if the request is to "move in a circle" or > if doing threading on a lathe to move the spindle and leadscrew in > "lock-step". In my case I want to move a caterpillar-tread robot along an > arc of given radios so that it passes through the center of a doorway. > The limiting factor is the performance of the "outside" tread motor. In > general what running multiple motors one of then will hit a performance > limit first and the others need to have their accelerations limited. > > The easiest thing for you to do is use software that others have written > and get it to work some how on the platform your choose (An ARM based SBC > like the beagle bored or "Pi") For CNC work LinucCNC already does what > you need and for robotics look up "ROS". Both of these can run on a > computer the size of a credit card. > > > > Now getting to your specific question of wetter to use constant > acceleration (linearly increasing speed) or some kind of curve. The above > should have answered this. The pulse generator will try for maximum > performance which is constant acceleration but may run into physical > limitation of the motor and mechanics where available torque is a function > of speed and this will cause acceleration if tapper off. On the other > hand if the request has an embedded limit you may not het mechanical > limitations and you can actually do constant acceleration up to the > commanded speed. > > > > > > > > > > > -- > > Chris Albertson > Redondo Beach, California > ------------------------------------------------------------------------------ > Transform Data into Opportunity. > Accelerate data analysis in your applications with > Intel Data Analytics Acceleration Library. > Click to learn more. > http://pubads.g.doubleclick.net/gampad/clk?id=278785231&iu=/4140 > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users -- Nicklas Karlsson <nicklas.karlsso...@gmail.com> ------------------------------------------------------------------------------ Transform Data into Opportunity. Accelerate data analysis in your applications with Intel Data Analytics Acceleration Library. 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