
B–62073E–1/04 2. INTERFACE BETWEEN CNC AND PMC–NA OR NB
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6 After the control system is switched to positioning control, the control unit starts applying linear interpolation
to the Z–axis and the spindle. Prior to linear interpolation, the control unit specifies an identical time
constant in the acceleration/deceleration circuits of the Z–axis and the spindle. It also sets an identical
servo loop gain in the positioning control circuits of the Z–axis and the spindle. If it does not specify them,
correct linear interpolation cannot be applied. Time constants of acceleration/deceleration circuits and ser-
vo loop gains of the positioning control circuits of the Z–axis and the spindle to be used in rigid tapping must
be specified as parameters beforehand.
7 Linear interpolation is applied to the Z–axis and the spindle. The distance moved and the feedrate of the
Z–axis and the spindle are calculated as follows.
Move distance Feedrate
Z–axis
Z = Distance between R and Z point
( mm, inch )
Fz = F command value
( mm/min, inch/min )
Spindle
S = Z × ( S command value/F command value )
× 360
( deg )
Fs = S comand value
8 The dwell command can be executed at the bottom of the hole. After the dwell command is executed, linear
interpolation is applied to the Z–axis and the spindle so that the tap is returned from point Z to point R on
the Z–axis while the spindle is rotated in the reverse direction. Both the tap movement along the Z–axis
and the spindle rotation are in opposite directions to those described in 7 above.
9 If the return to the initial position command (G98) is executed, the tap is returned to the initial position on
the Z–axis.
This is the entire sequence of rigid tapping. If another G84.2 is specified after that, the same procedure
is repeated. In the second or later sequence of G84.2, however, steps 5 and 6 are not executed because
the control system of the spindle has already been switched to positioning control.
If either i) or ii) below occurs in the rigid tapping (G84.2), the control system of the spindle is switched from
positioning control to spindle control and the time constant of the acceleration/deceleration circuit and the
servo loop gain of the positioning control circuit of the Z–axis are returned to normal values. Then the RTAP
signal is set low. After this, the next operation is started. When the RTAP signal goes low, the torque limit
signal, TLML, must be set low in the PMC.
(i) A canned cycle of drilling other than G84.3 is specified. For example, G81 is specified.
(ii) A canned cycle of drilling is canceled. That is, G80 or a G code of the 01 group such as G00, G01,
G02, or G03 is specified.