cnc-club.ru

2.7 Commands
This section simply lists all of the commands that can be sent to the motion module, along with detailed explanations of what
they do. The command names are defined in a large typedef enum in emc2/src/emc/motion/motion.h, called cmd_code_t. (Note
that in the code, each command name starts with EMCMOT_, which is omitted here.)
The commands are implemented by a large switch statement in the function emcmotCommandHandler(), which is called at the
servo rate. More on that function later.
There are approximately 44 commands - this list is still under construction.
2.7.1 ABORT
The ABORT command simply stops all motion. It can be issued at any time, and will always be accepted. It does not disable the
motion controller or change any state information, it simply cancels any motion that is currently in progress.1
2.7.1.1 Requirements
None. The command is always accepted and acted on immediately.
2.7.1.2 Results
In free mode, the free mode trajectory planners are disabled. That results in each joint stopping as fast as its accel (decel) limit
allows. The stop is not coordinated. In teleop mode, the commanded Cartesian velocity is set to zero. I don’t know exactly what
kind of stop results (coordinated, uncoordinated, etc), but will figure it out eventually. In coord mode, the coord mode trajectory
planner is told to abort the current move. Again, I don’t know the exact result of this, but will document it when I figure it out.
2.7.2 FREE
The FREE command puts the motion controller in free mode. Free mode means that each joint is independent of all the other
joints. Cartesian coordinates, poses, and kinematics are ignored when in free mode. In essence, each joint has its own simple
trajectory planner, and each joint completely ignores the other joints. Some commands (like JOG) only work in free mode. Other
commands, including anything that deals with Cartesian coordinates, do not work at all in free mode.
1 It seems that the higher level code (TASK and above) also use ABORT to clear faults. Whenever there is a persistent fault (such as being outside the
hardware limit switches), the higher level code sends a constant stream of ABORTs to the motion controller trying to make the fault go away. Thousands of
’em. . . . That means that the motion controller should avoid persistent faults. This needs to be looked into.
Developer Manual V2.6.9-14-ga2399e1, 2015-08-31 9 / 78
2.7.2.1 Requirements
The command handler applies no requirements to the FREE command, it will always be accepted. However, if any joint is in
motion (GET_MOTION_INPOS_FLAG() == FALSE), then the command will be ignored. This behavior is controlled by code
that is now located in the function set_operating_mode() in control.c, that code needs to be cleaned up. I believe the command
should not be silently ignored, instead the command handler should determine whether it can be executed and return an error if
it cannot.
2.7.2.2 Results
If the machine is already in free mode, nothing. Otherwise, the machine is placed in free mode. Each joint’s free mode trajectory
planner is initialized to the current location of the joint, but the planners are not enabled and the joints are stationary.
2.7.3 TELEOP
The TELEOP command places the machine in teleoperating mode. In teleop mode, movement of the machine is based on
Cartesian coordinates using kinematics, rather than on individual joints as in free mode. However the trajectory planner per se
is not used, instead movement is controlled by a velocity vector. Movement in teleop mode is much like jogging, except that it
is done in Cartesian space instead of joint space. On a machine with trivial kinematics, there is little difference between teleop
mode and free mode, and GUIs for those machines might never even issue this command. However for non-trivial machines like
robots and hexapods, teleop mode is used for most user commanded jog type movements.
2.7.3.1 Requirements
The command handler will reject the TELEOP command with an error message if the kinematics cannot be activated because the
one or more axes have not been homed. In addition, if any joint is in motion (GET_MOTION_INPOS_FLAG() == FALSE), then
the command will be ignored (with no error message). This behavior is controlled by code that is now located in the function
set_operating_mode() in control.c. I believe the command should not be silently ignored, instead the command handler should
determine whether it can be executed and return an error if it cannot.
2.7.3.2 Results
If the machine is already in teleop mode, nothing. Otherwise the machine is placed in teleop mode. The kinematics code is
activated, interpolators are drained and flushed, and the Cartesian velocity commands are set to zero.
2.7.4 COORD
The COORD command places the machine in coordinated mode. In coord mode, movement of the machine is based on Cartesian
coordinates using kinematics, rather than on individual joints as in free mode. In addition, the main trajectory planner is used
to generate motion, based on queued LINE, CIRCLE, and/or PROBE commands. Coord mode is the mode that is used when
executing a G-code program.
2.7.4.1 Requirements
The command handler will reject the COORD command with an error message if the kinematics cannot be activated because the
one or more axes have not been homed. In addition, if any joint is in motion (GET_MOTION_INPOS_FLAG() == FALSE), then
the command will be ignored (with no error message). This behavior is controlled by code that is now located in the function
set_operating_mode() in control.c. I believe the command should not be silently ignored, instead the command handler should
determine whether it can be executed and return an error if it cannot.
Developer Manual V2.6.9-14-ga2399e1, 2015-08-31 10 / 78
2.7.4.2 Results
If the machine is already in coord mode, nothing. Otherwise, the machine is placed in coord mode. The kinematics code is
activated, interpolators are drained and flushed, and the trajectory planner queues are empty. The trajectory planner is active and
awaiting a LINE, CIRCLE, or PROBE command.
2.7.5 ENABLE
The ENABLE command enables the motion controller.
2.7.5.1 Requirements
None. The command can be issued at any time, and will always be accepted.
2.7.5.2 Results
If the controller is already enabled, nothing. If not, the controller is enabled. Queues and interpolators are flushed. Any movement
or homing operations are terminated. The amp-enable outputs associated with active joints are turned on. If forward kinematics
are not available, the machine is switched to free mode.
2.7.6 DISABLE
The DISABLE command disables the motion controller.
2.7.6.1 Requirements
None. The command can be issued at any time, and will always be accepted.
2.7.6.2 Results
If the controller is already disabled, nothing. If not, the controller is disabled. Queues and interpolators are flushed. Any
movement or homing operations are terminated. The amp-enable outputs associated with active joints are turned off. If forward
kinematics are not available, the machine is switched to free mode.