Fagor 8055 EN, Programming Manual

Page: 116 / 482

·116·
Programming manual
CNC 8055
CNC 8055i
7.
ADDITION
AL PREP
ARATORY FUNCTIONS
·M· & ·EN· M
ODELS
S
OFT
: V02.2
X
Lo
ok-ahe
ad (G5
1
)
7.4 Look-ahead (G51)
Programs consisting of very small movement blocks (CAM, digitizing, etc.) tend to run very slowly.
Those programs may be executed at high machining speed using the "Look-Ahead" function.
The look-ahead function analyzes in advance the path to be machined (up to 75 blocks) in order
to calculate the maximum feedrate for each section of the path. This function provides smoother
and faster machining in programs with very small movements, even in the order of microns.
When operating with "Look-Ahead", it is a good idea to adjust the axes so their following error (lag)
is as small as possible because the contouring error will be at least equal to the minimum following
error.
Programming format:
The programming format is:
G51 [A] E B
Parameter "A" permits using a standard working acceleration and another one to be used when
executing with Look-Ahead.
If parameter "B" is not programmed, the square corner management at the corners is canceled.
The square-corner management at the corners is valid for the look-ahead algorithm with jerk
management and for the look-ahead algorithm without jerk management.
Considerations for execution:
When calculating the feedrate, the CNC takes the following into account:
• The programmed feedrate.
• The curvature and the corners.
• The maximum feedrate of the axes.
• The maximum accelerations.
• The jerk.
If any of the circumstances listed below occurs while executing with Look-Ahead, the CNC slows
down to "0" at the previous block and it recovers the machining conditions for Look-Ahead in the
next motion block.
• Motionless block.
• Execution of auxiliary functions (M, S, T).
• Single block execution mode.
• MDI mode.
• Tool inspection mode.
If a Cycle Stop, Feed-Hold, etc. occurs while executing in Look-Ahead mode, the machine may not
stop at the current block, several additional blocks will be necessary to stop with the permitted
deceleration.
A (0-255) It is optional and it defines the percentage of acceleration to be applied.
When not programmed or programmed with a "0" value, the CNC assumes the
acceleration value set by machine parameter for each axis.
E (5.5) Maximum contouring error.
The lower this parameter value is, the lower the machining feedrate will be.
B (0-180) It makes it possible to machine square corners using the Look-ahead function.
It indicates the angular value (in degrees) of the programmed corners, below which,
the machining operation will be carried out in square corner mode.
B
Block I+1
Block I