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1 Introduction
14
Fig. 1.2-6
Fig. 1.2-7
Absolute Coordinate Specification
When absolute coordinates are specified,
the tool travels a distance measured from
the origin of the coordinate system, i.e., to
a point whose position has been specified
by the coordinates.
The code of absolute data specification is
G90.
The block
G90 X50 Y80 Z40
will move the tool to a point of the above
position, irrespective of its position before
the command has been issued.
Incremental Coordinate Specification
In the case of an incremental data specification,
the control system will interpret the coordinate
data in such a way that the tool will travel a
distance measured from its instantaneous
position.
The code of incremental data specification is
G91. Code G91 refers to all coordinate values.
The block
G91 X70 Y-40 Z-20
will move the tool over the above distance from
its previous position.
An incremental data may be defined to be
referred to a single coordinate as well. Standing
behind the address of the coordinate, character
I refers to the incremental specification of the
given coordinate value.
In block
G90 XI-70 Y80 Z40
the data of X is interpreted as an incremental value, whereas data Y and Z are - for code G90 -
interpreted as absolute coordinates.
Modal Functions
Some codes are effective until another code or value is specified. These are modal codes. E.g., in
program detail
N15 G90 G1 X20 Y30 F180
N16 X30
N17 Y100