The LCS Command [MLEPC]

The LCS (local coordinate system) transformation command is used to set up an alternate coordinate system on the machine. This command is valid for all machine types, but some functions may not be available on specific machines. The following LCS command functions are available:

The LCS feature is most useful when the tool axis is not parallel to the machine’s Z axis. The LCS definition tells the controller how the tool is oriented with respect to the machine’s axes. With this information, most LCS capable controllers can perform length compensation, diameter compensation, canned cycles and circular interpolation, all in the local coordinate frame. Without LCS, the NC programmer must often specify the exact tool diameter and length, requiring the post-processor to perform these functions substituting linear and rapid interpolation codes.

\textbf{LCS / } \big[\,\textbf{TRFORM},\big] \; \ldots

The TRFORM keyword can optionally be added at the start of any LCS command. It has no effect on the LCS command, but is included for consistency with other transformation commands such as LIMIT and PLOT.

Fixed LCS Formats

\textbf{LCS / } \mathtt{<\!matrix\!>} \begin{bmatrix} ,\! \begin{array}{l} \textbf{NOW} \\ \textbf{NEXT} \end{array}\,\end{bmatrix}

The <matrix> defines the location and orientation of the new local coordinate system in part coordinates. The matrix can be specified using the standard post-processor transformation syntax (see “The ORIGIN Command”). The optional NOW and NEXT keywords following the matrix definition specify whether the new coordinate frame should be established immediately (NOW) or deferred to the next motion (NEXT). The default if neither is specified is determined by the post-processor author.

\textbf{LCS /} \begin{pmatrix}\begin{array}{l} \textbf{NOW} \\ \textbf{NEXT} \end{array}\end{pmatrix}

The NOW and NEXT formats, without a matrix definition, establish the LCS based on the current or next tool axis orientation. A tool axis by itself provides only enough information to define the Z component of the new LCS. GENER uses built-in rules to define the orientation of the LCS X and Y axes. By default, the X axis component of the LCS will lie in the machine ZX plane and point in the positive machine X axis direction. When the LCS Z axis is already parallel to the machine X axis, GENER instead aligns the LCS Y axis in the machine YZ plane with a positive Y component. This default can be changed with the $LCAUTO macro variable (see “Motion-Related Variables”).

Automatic LCS Formats

\textbf{LCS / AUTO}\; \big[,\mathit{type}\,\big] \ldots

GENER has the ability to automatically establish or cancel LCS. The behavior is defined by the optional type value, as follows:

\textbf{LCS / AUTO } \big[,\textbf{0}\,\big]\; \big[,\textbf{ON},a \,\big]\; \big[,\textbf{OFF},b \,\big]

Type 0 is the default form of LCS for V23 and later generated posts. The optional ON,a and OFF,b couplets define how LCS is to be automatically activated and deactivated during the sequence of positioning motions that link the cutting motions of the NC program.

The ON,a couplet defines how LCS is to activated (if at all) during the positioning motion(s) that precede cutting motions. The following activation options are available:

ON,a

0

do not activate LCS

1

at the end of the positioning sequence

2

after the last positioning motion that includes a rotary axis (default)

3

same as 2, or before the last positioning motion, whichever occurs last

The OFF,b couplet defines how LCS is to deactivated (if at all) during the positioning motion(s) that follow cutting motions. The following deactivation options are available:

OFF,b

0

do not deactivate LCS

1

at the start of the positioning sequence

2

before the first positioning motion that includes a rotary axis (default)

3

same as 2, or after the first positioning motion, whichever occurs first

\textbf{LCS / AUTO},\mathbf{1-4}

Types 1 through 4 provide the following automatic LCS functionality:

1

Create a new LCS on each positioning motion with a changed tool axis.

This is the default when running with a V14 generated post.

2

Create a new LCS just before the feed motion that follows a positioning

motion with a changed tool axis.

Cancel LCS on a positioning motion following the last feed move.

This is default mode for V15 through V22 generated posts.

3

Create a new LCS each time an MSYS command is encountered,

using the matrix defined on the MSYS command.

4

Create a new LCS each time an MSYS command is encountered,

using the inverse of the matrix defined on the MSYS command.

The default behavior of the LCS/AUTO command can be changed with the $LCAMOD, $LCAON and $LCAOFF macro variables. With types 0 through 2 of the AUTO format, the $LCAUTO macro variable can be used to control the alignment of the X or Y local coordinate system axes (see here).

\textbf{LCS / AUTO}, \textbf{FEED}, \begin{pmatrix}\begin{array}{l} \textbf{ON} \\ \textbf{OFF} \end{array}\end{pmatrix}

By default, automatic LCS changes with types 0 through 2 only occur on RAPID motions. Specify the modal FEED,ON couplet to also enable automatic LCS changes to occur with feed motions at or above the high feed threshold defined by the FEDRAT/RAPID command. Specify FEED,OFF to return GENER to the default RAPID-only behavior.

LCS Activation/Deactivation

\textbf{LCS /} \begin{pmatrix}\begin{array}{l} \textbf{ON} \\ \textbf{OFF} \end{array}\end{pmatrix}

The ON and OFF keywords enable or disable the LCS feature. OFF returns to the standard machine coordinate frame and cancels the modal AUTO format if enabled. ON re-establishes the LCS feature, either by reactivation the AUTO mode or by outputting the last local coordinate frame that was in effect.