Siemens SINUMERIK 840C Installation Instructions Manual page 727

11.92
2nd case: Axis is at the reference point cam
Rather than accelerate to the reference speed, the axis accelerates immediately to the
reference point cutoff speed (MD 284*).
Speed
MD 284*
Reference point cam
Axis is at reference point cam
3rd case: Axis is behind the reference point cam
Since the signal state of the "Deceleration" signal is the same after the reference point as it
was before, the control assumes that the axis is still ahead of the reference point cam and
therefore accelerates to the reference approach speed (MD 296*), i.e. the axis travels at high
speed toward the limit switch (EMERGENCY STOP), as the software limit switches are not in
force prior to or during reference point approach.
Speed
MD 296*
Reference point cam
Axis is behind reference point cam
If referencing is repeated several times, the software limit switches are exceeded by the
following error if the cam is not reached. The automatic direction recognition function is used
to remedy this.
In order to circumvent the problems posed by case 3, it was necessary to integrate a complex
system of travel interlocks in the PLC. It was therefore decided that the SINUMERIK System
800 should provide an option which would solve the problem without additional PLC support
during reference point approach. This option is referred to as automatic reference point
approach, i.e. reference point approach with automatic direction recognition.
© Siemens AG 1992 All Rights Reserved
SINUMERIK 840C (IA)
1
2
Reference point pulse
0
Reference point pulse
6FC5197- AA50
10 Axis and Spindle Installation
10.4.4 Reference point approach
2000 units
Path
3 4
Reference point
Limit switch
Path
Reference point
10–37