The preferred way to set up a standard stepper machine is with the Step Configuration Wizard. See the Getting Started Guide for more information on the Step Configuration Wizard.
This chapter describes some of the more common settings for manually setting up a stepper based system. Because of the various possibilities of configuring EMC2, it is very hard to document them all, and keep this document relatively short.
The most common EMC2 usage is for stepper based systems. These systems are using stepper motors with drives that accept step & direction signals.
It is one of the simpler setups, because the motors run open-loop (no feedback comes back from the motors), yet the system needs to be configured properly so the motors don't stall or lose steps.
Most of this chapter is based on the sample config released along with EMC2. The config is called stepper, and usually it is found in /etc/emc2/sample-configs/stepper.
With software step generation, the maximum step rate is one step per two BASE_PERIODs for step-and-direction output. The maximum requested step rate is the product of an axis's MAX_VELOCITY and its INPUT_SCALE. If the requested step rate is not attainable, following errors will occur, particularly during fast jogs and G0 moves.
If your stepper driver can accept quadrature input, use this mode. With a quadrature signal, one step is possible for each BASE_PERIOD, doubling the maximum step rate.
The other remedies are to decrease one or more of: the BASE_PERIOD (setting this too low will cause the machine to become unresponsive or even lock up), the INPUT_SCALE (if you can select different step sizes on your stepper driver, change pulley ratios, or leadscrew pitch), or the MAX_VELOCITY and STEPGEN_MAXVEL.
If no valid combination of BASE_PERIOD, INPUT_SCALE, and MAX_VELOCITY is acceptable, then hardware step generation (such as with the EMC2-supported Universal Stepper Controller)
One of the major flaws in EMC was that you couldn't specify the pinout without recompiling the source code. EMC2 is far more flexible, and now (thanks to the Hardware Abstraction Layer) you can easily specify which signal goes where.
As it is described in the HAL Introduction and tutorial, we have signals, pins and parameters inside the HAL.
The ones relevant for our pinout are:
signals: Xstep, Xdir & Xen
pins: parport.0.pin-XX-out & parport.0.pin-XX-in
Depending on what you have chosen in your ini file you are using either standard_pinout.hal or xylotex_pinout.hal. These are two files that instruct the HAL how to link the various signals & pins. Further on we'll investigate the standard_pinout.hal.
This file contains several HAL commands, and usually looks like this:
# standard pinout config file for 3-axis steppers # using a parport for I/O # # first load the parport driver loadrt hal_parport cfg="0x0378" # # next connect the parport functions to threads # read inputs first addf parport.0.read base-thread 1 # write outputs last addf parport.0.write base-thread -1 # # finally connect physical pins to the signals net Xstep => parport.0.pin-03-out net Xdir => parport.0.pin-02-out net Ystep => parport.0.pin-05-out net Ydir => parport.0.pin-04-out net Zstep => parport.0.pin-07-out net Zdir => parport.0.pin-06-out # create a signal for the estop loopback net estop-loop iocontrol.0.user-enable-out iocontrol.0.emc-enable-in # create signals for tool loading loopback net tool-prep-loop iocontrol.0.tool-prepare iocontrol.0.tool-prepared net tool-change-loop iocontrol.0.tool-change iocontrol.0.tool-changed # connect "spindle on" motion controller pin to a physical pin net spindle-on motion.spindle-on => parport.0.pin-09-out ### ### You might use something like this to enable chopper drives when machine ON ### the Xen signal is defined in core_stepper.hal ### # net Xen => parport.0.pin-01-out ### ### If you want active low for this pin, invert it like this: ### # setp parport.0.pin-01-out-invert 1 ### ### A sample home switch on the X axis (axis 0). make a signal, ### link the incoming parport pin to the signal, then link the signal ### to EMC's axis 0 home switch input pin ### # net Xhome parport.0.pin-10-in => axis.0.home-sw-in ### ### Shared home switches all on one parallel port pin? ### that's ok, hook the same signal to all the axes, but be sure to ### set HOME_IS_SHARED and HOME_SEQUENCE in the ini file. See the ### user manual! ### # net homeswitches <= parport.0.pin-10-in # net homeswitches => axis.0.home-sw-in # net homeswitches => axis.1.home-sw-in # net homeswitches => axis.2.home-sw-in ### ### Sample separate limit switches on the X axis (axis 0) ### # net X-neg-limit parport.0.pin-11-in => axis.0.neg-lim-sw-in # net X-pos-limit parport.0.pin-12-in => axis.0.pos-lim-sw-in ### ### Just like the shared home switches example, you can wire together ### limit switches. Beware if you hit one, EMC will stop but can't tell ### you which switch/axis has faulted. Use caution when recovering from this. ### # net Xlimits parport.0.pin-13-in => axis.0.neg-lim-sw-in axis.0.pos-lim-sw-in
The files starting with '#' are comments, and their only purpose is to guide the reader through the file.
There are a couple of operations that get executed when the standard_pinout.hal gets executed / interpreted:
If you want to change the standard_pinout.hal file, all you need is a text editor. Open the file and locate the parts you want to change.
If you want for example to change the pin for the X-axis Step & Directions signals, all you need to do is to change the number in the 'parport.0.pin-XX-out' name:
linksp Xstep parport.0.pin-03-out
linksp Xdir parport.0.pin-02-out
can be changed to:
linksp Xstep parport.0.pin-02-out
linksp Xdir parport.0.pin-03-out
or basically any other numbers you like.
Hint: make sure you don't have more than one signal connected to the same pin.
If external hardware expects an “active low” signal, set the corresponding -invert parameter. For instance, to invert the spindle control signal:
setp parport.0.pin-09-invert TRUE
If your spindle can be controlled by a PWM signal, use the pwmgen component to create the signal:
loadrt pwmgen output_type=0
addf pwmgen.update servo-thread
addf pwmgen.make-pulses base-thread
net spindle-speed-cmd motion.spindle-speed-out => pwmgen.0.value
net spindle-on motion.spindle-on => pwmgen.0.enable
net spindle-pwm pwmgen.0.pwm => parport.0.pin-09-out
setp pwmgen.0.scale 1800 # Change to your spindle's top speed in RPM
This assumes that the spindle controller's response to PWM is simple: 0% PWM gives 0RPM, 10% PWM gives 180 RPM, etc. If there is a minimum PWM required to get the spindle to turn, follow the example in the nist-lathe sample configuration to use a scale component.
Some amplifiers (drives) require an enable signal before they accept and command movement of the motors. For this reason there are already defined signals called 'Xen', 'Yen', 'Zen'.
To connect them use the following example:
linksp Xen parport.0.pin-08-out
You can either have one single pin that enables all drives, or several, depending on the setup you have. Note however that usually when one axis faults, all the other ones will be disabled as well, so having only one signal / pin is perfectly safe.
As you can see in [.] by default the stepper configuration assumes no external E-STOP button. 2
To add a simple external button you need to replace the line:
linkpp iocontrol.0.user-enable-out iocontrol.0.emc-enable-in
with
linkpp parport.0.pin-01-in iocontrol.0.emc-enable-in
This assumes an E-STOP switch connected to pin 01 on the parport. As long as the switch will stay pushed3, EMC2 will be in the E-STOP state. When the external button gets released EMC2 will immediately switch to the E-STOP-RESET state, and all you need to do is switch to Machine On and you'll be able to continue your work with EMC2.
1 the fastest thread in the EMC2 setup, usually the code gets executed every few microseconds back
2 An extensive explanation of hooking up E-STOP circuitry is explained in the wiki.linuxcnc.org and in the Integrator Manual back