The HOMEPT Command [MLEPC]

The HOMEPT command allows the part programmer to change and restore the home position. This command is valid for all machine types, but some functions may not be available on specific machines.

The following HOMEPT command functions are available:

The home position is defined by QUEST, but it can be modified at any time with the HOMEPT command. GENER recognizes three different types of machines when it comes to home point processing:

  • A “fixed home” machine is one that has a fixed “lights-on” position that is always used for the home position. The HOMEPT command has no effect on fixed home machines.

  • A “reference home” machine is one that has a machine tool builder defined coordinate system that is different from that of the workpiece coordinate system. This includes both the G28 style fixed reference position and the G53 style reference coordinate system types.

  • A “no home” machine is one that has a single workpiece coordinate system.

GENER uses the home position to estimate motion position timing and to obtain a sense of direction following any motion to home. The GOHOME command positions the tool at rapid to the home position.

Reference Home Position Definition

The reference home position defines the initial position of the machine at the start of post-processing and whenever the machine is moved to a home position. The home position definition in QUEST can be changed by coding the following:

\textbf{HOMEPT / } {\small \sim}\!\begin{pmatrix}, \begin{pmatrix}\begin{array}{l} \textbf{XAXIS} \\ \textbf{YAXIS} \\ \textbf{ZAXIS} \\ \textbf{UAXIS} \\ \textbf{VAXIS} \\ \textbf{WAXIS} \\ \textbf{QUILL} \\ \textbf{AAXIS} \\ \textbf{BAXIS} \\ \textbf{CAXIS} \\ \textbf{AAXIS},\textbf{TABLE} \\ \textbf{BAXIS},\textbf{TABLE} \\ \textbf{CAXIS},\textbf{TABLE} \\ \textbf{RAM} \big[,n \,\big] \\ \\ \textbf{NEXT} \end{array}\end{pmatrix} \begin{bmatrix} ,\! \begin{array}{l} \mathit{value} \\ \textbf{MINPOS} \\ \textbf{MAXPOS} \\ \textbf{UNKPOS} \end{array}\,\end{bmatrix} \end{pmatrix}

Home point positions can be defined either in absolute machine coordinates, or as symbolic coordinates that define the relative position of the reference home position with respect to the machine envelope. Symbolic coordinates are only valid for reference home machines.

  • Select MINPOS if the reference position for the specified axis moves the machine to the extremity of the axis travel in the negative direction.

  • Select MAXPOS for the reverse.

  • Select UNKPOS if the reference position is at neither extremity.

  • Enter a coordinate value if the home position is known.

GENER uses the reference home point settings to establish a sense of direction for safe positioning motion analysis on a return-from-reference motion. The string “?.???” will be shown in the verification listing file axis column display for any axis that is at a symbolic position. The same string “?.???” will also be shown in the travel summaries for any axis that has remained at a symbolic position for the entire program. Symbolic positions are not included in travel calculations.

Only those axes referenced in the HOMEPT command will be taken to the home position. See here for a table correlating axes name keywords with machine axes. The NEXT keyword can be specified break the motion to the home point into a series of steps. For example, the following command will first retract the Z axis to the home point and then move X and Y axes:

HOMEPT/ZAXIS,MAXPOS,NEXT,XAXIS,UNKPOS,YAXIS,UNKPOS
GOHOME

G91 G28 Z0
G28 X0 Y0

Machine Home Position Definition

Reference home machines using a G53 style reference coordinate system must output a coordinate value for each axis taken to the home position. These reference coordinate values are defined in QUEST and can be changed by coding the following:

\textbf{HOMEPT / ABSOL}, {\small \sim}\!\begin{pmatrix}, \begin{pmatrix}\begin{array}{l} \textbf{XAXIS} \\ \textbf{YAXIS} \\ \textbf{ZAXIS} \\ \textbf{UAXIS} \\ \textbf{VAXIS} \\ \textbf{WAXIS} \\ \textbf{QUILL} \\ \textbf{AAXIS} \\ \textbf{BAXIS} \\ \textbf{CAXIS} \\ \textbf{AAXIS},\textbf{TABLE} \\ \textbf{BAXIS},\textbf{TABLE} \\ \textbf{CAXIS},\textbf{TABLE} \\ \textbf{RAM} \big[,n \,\big] \\ \\ \textbf{NEXT} \end{array}\end{pmatrix} ,\mathit{value} \end{pmatrix}

The machine reference coordinate axes values do not have any effect on travel checking and motion analysis. Only those axes that are moved to the home position will be output. To continue the example above:

HOMEPT/ABSOL,ZAXIS,400,NEXT,XAXIS,0,YAXIS,0
GOHOME

G90 G53 Z400
G53 X0 Y0

Reset Home Position

The following command removes any program defined home position information and reverts home positioning to QUEST defaults.

\textbf{HOMEPT / NOMORE}