Stepper Configuration
Introduction
The preferred way to set up a standard stepper machine is with the Step Configuration Wizard. See the Getting Started Guide.
This chapter describes some of the more common settings for manually setting up a stepper based system. Because of the various possibilities of configuring Machinekit, it is very hard to document them all, and keep this document relatively short.
The most common Machinekit 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 Machinekit. The config is called stepper, and usually it is found in '/etc/emc2/sample-configs/stepper'.
Maximum step rate
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' 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 consider using hardware step generation (such as with the Machinekit-supported Universal Stepper Controller, Mesa cards, and others.)
Pinout
One of the major flaws in LinuxCNC was that you couldn’t specify the pinout without recompiling the source code. Machinekit is far more flexible, and now (thanks to the Hardware Abstraction Layer) you can easily specify which signal goes where. See the HAL manual for more detailed information on HAL.
As it is described in the HAL Introduction and tutorial, we have signals, pins and parameters inside the HAL.
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Note
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We are presenting one axis to keep it short, all others are similar. |
The ones relevant for our pinout are:
signals: Xstep, Xdir & Xen
pins: parport.0.pin-XX-out & parport.0.pin-XX-inDepending 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.
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 Machinekit'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, Machinekit 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-inThe lines starting with '#' are comments, and their only purpose is to guide the reader through the file.
Overview
There are a couple of operations that get executed when the standard_pinout.hal gets executed/interpreted:
-
The Parport driver gets loaded (see the Parport section of the HAL Manual for details)
-
The read & write functions of the parport driver get assigned to the base thread [1]
-
The step & direction signals for axes X,Y,Z get linked to pins on the parport
-
Further I/O signals get connected (estop loopback, toolchanger loopback)
-
A spindle-on signal gets defined and linked to a parport pin
Changing the standard_pinout.hal
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:
net Xstep parport.0.pin-03-out
net Xdir parport.0.pin-02-outcan be changed to:
net Xstep parport.0.pin-02-out
net Xdir parport.0.pin-03-outor basically any other 'out' pin you like.
Hint: make sure you don’t have more than one signal connected to the same pin.
Changing polarity of a signal
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 TRUEAdding PWM Spindle Speed Control
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 RPMThis assumes that the spindle controller’s response to PWM is simple: 0% PWM gives 0 RPM, 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.
Adding an enable signal
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:
net Xen parport.0.pin-08-outYou 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 drives will be disabled as well, so having only one enable signal / pin for all drives is a common practice.
External ESTOP button
As you can see in the standard_pinout.hal file by default the stepper configuration assumes no external ESTOP button. [2]
To add a simple external button you need to replace the line:
net estop-loop iocontrol.0.user-enable-out iocontrol.0.emc-enable-inwith
net estop-loop parport.0.pin-01-in iocontrol.0.emc-enable-inThis assumes an ESTOP switch connected to pin 01 on the parport. As long as the switch will stay pushed[3], Machinekit will be in the ESTOP state. When the external button gets released Machinekit will immediately switch to the ESTOP-RESET state, and all you need to do is switch to Machine On and you’ll be able to continue your work with Machinekit.