Rockwell Automation 8520-MUM 9/Series CNC Mill Operation and Programming Manual Documentation Set - Manual (Page 461)

Programming Feedrates
Chapter 18
18-13
The system installer may install an optional external deceleration switch if
desired. Typically, this is a mechanical switch mounted on the machine
axes inside the hardware overtravel switches (refer to documentation
prepared by the system installer for details on the application and location
of this switch).
When this feature is active any axis moves that are to take place at a
cutting feedrate (e.g., G01, G02, G03) use a special feedrate assigned in
AMP. When this feature is active any axis moves that are to take place at a
rapid feedrate (e.g., G00) also uses a special feedrate assigned in AMP.
These feedrates are independent of each other and typically have different
values. These feedrate changes take place immediately when the feature
becomes active, even if this is in the middle of block execution.
Important: The feedrate set for the external deceleration feature for
cutting moves can not exceed the maximum cutting feedrate.
If this feature is used simultaneously with the Dry Run feature the
feedrates that are assigned to External decel feature are used. The
feedrates for this feature are not related to the Dry Run feedrates although
the operation of this feature is similar to Dry Run.
This feedrate is unaffected by the feedrate override switch, and the rapid
override switch settings and operates as if the switches are set at 100
percent. Blocks that are programmed to move at the rapid feedrate are still
executed in the rapid mode.
Typically this feature is used to protect the machine from harsh or sudden
stops. If a very high feedrate is active at the time that a hardware
overtravel occurs damage to the machine may result if a sudden stop is
performed at the overtravel or the machine may coast past a safe range for
axis motion. If the switch is installed before the overtravel area the
feedrate of the move is reduced and the amount of coast into the overtravel
area will be much less.
If the current feedrate is less then the feedrate set for the external
deceleration feature, it will be accelerated to the external deceleration
feedrate. This may cause problems with part finish or may damage the
tool if this feedrate is higher than that which the part should be cut.
WARNING: It is possible for the system installer to write PAL
to allow the operator to select the external deceleration feedrate
at any time. This means that during normal automatic operation
the operator can select external decel and replace all feedrates in
the program with the external decel feedrates. This may result
in damage to the machine, part, or injury to the operator.
18.3.2
External Feedrate Switch