The SAFPOS Command [MLEPC]

The SAFPOS command allows the part programmer to change and restore the tool and head change position. The tool and head change positions are defined by QUEST, but they can be modified at any time with the SAFPOS command. The following SAFPOS command functions are available:

GENER recognizes three different types of machines when it comes to tool change and home point processing:

  • A “fixed home” machine is one that has a fixed “lights-on” position that is always used for the tool and head change positions. The SAFPOS 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 tool and head change positions to estimate motion position timing and to obtain a sense of direction following any tool or head change.

Reference Tool/Head Change Position

The reference tool and head change positions define the position of the machine during a tool or head change operation. The tool and head change position definitions in QUEST can be changed by coding the following:

\textbf{SAFPOS / } \big[\,\textbf{HEAD},\big] \; {\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{pmatrix} \!,\! \begin{array}{l} \mathit{value} \\ \textbf{MINPOS} \\ \textbf{MAXPOS} \\ \textbf{UNKPOS} \end{array} \end{pmatrix} \,\end{pmatrix}

Specify the HEAD keyword when defining a head change position. Omit the HEAD keyword when defining a tool change position. Tool change and head change positions can be defined either in absolute machine coordinates, or as symbolic coordinates that define the relative position of the reference change position with respect to the machine envelope. Symbolic coordinates are only valid for reference home machines.

  • Select MINPOS if the reference change 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 change position is at neither extremity.

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

GENER uses the reference change point settings to establish a sense of direction for safe positioning motion analysis when returning from a tool or head change operation. 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 SAFPOS command will be moved during a tool or head change operation. See here for a table correlating axes name keywords with machine axes. The NEXT keyword can be specified break the motion to the change point into a series of steps. For example, the following command will first retract the Z axis to the home point and then move the X axes:

SAFPOS/ZAXIS,MAXPOS,NEXT,XAXIS,MINPOS
LOAD/TOOL,1

G91 G28 Z0
G28 X0 T1 M06

Machine Tool/Head Change Position

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

\textbf{SAFPOS / ABSOL}, \big[\,\textbf{HEAD},\big] \; {\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] \end{array}\end{pmatrix} , \mathit{value} \end{pmatrix}

The machine reference tool change and head change (specify the HEAD keyword) coordinate axes values do not have any effect on travel checking and motion analysis. Only those axes that are moved to the tool or head change position will be output. See here for a table correlating axes name keywords with machine axes.

Reset Tool/Head Change Position

The following command removes any program defined tool or head change position information and reverts tool or head change positioning to QUEST defaults.

\textbf{SAFPOS / } \big[\,\textbf{HEAD},\big] \,\textbf{NOMORE}