Hardware Limit Switches; Software Limit Switches - Siemens SINUMERIK 808D Function Manual

4.3.2

Hardware limit switches

Function
Every axis has a hardware (HW) limit switch for each traversing direction, which prevents the slide from moving out of the
slide bed.
If the hardware limit switch is crossed, the PLC signals this to the NC via IS "Hardware limit switch plus/minus"
(DB380x.DBX1000.1 or .0) and the movement of all axes is stopped. The braking method can be specified via MD36600
BRAKE_MODE_CHOICE (braking behavior at hardware limit switch).
Effectiveness
HW limit switch monitoring is active after the control has started up in all modes.
Effect
● When a hardware limit switch is passed in either direction, alarm 21614 "Hardware limit switch + or -" is triggered.
● The axis is stopped according to the setting in MD36600 BRAKE_MODE_CHOICE (braking behavior at hardware limit
switch).
● If the axis is assigned to an interpolatory grouping with other axes, then these are also stopped according to the method
selected in MD36600 BRAKE_MODE_CHOICE (braking behavior at hardware limit switch).
● The direction keys in the approach direction are disabled.
Remedy
● Reset
● Move in the opposite direction (in "JOG" mode)
● Correct the program
4.3.3

Software limit switches

Function
They are used to limit the maximum traversing range on each individual axis.
There are two pairs of software limit switches for each machine axis. They are defined in the machine axis system using the
following machine data:
MD36100 POS_LIMIT_MINUS (1st software limit switch minus)
MD36110 POS_LIMIT_PLUS (1st software limit switch plus)
MD36120 POS_LIMIT_MINUS2 (2nd software limit switch minus)
MD36130 POS_LIMIT_PLUS2 (2nd software limit switch plus)
Effectiveness
● Software (SW) limit switch monitoring is activated after reference point approach in all modes.
● The position of the software limit switch can be approached.
● The 2nd software limit switch can be activated via the "2nd software limit switch plus/minus" interface signal
(DB380x.DBX1000.3 or .2) from the PLC. The change becomes active immediately. The 1st software limit switch
plus/minus is then de-activated.
● The SW limit switch monitoring does not function for endlessly turning rotary axes, i.e. if MD30310 ROT_IS_MODULO =
1. (Modulo conversion for rotary axis and spindle)
Effect/reactions
Based on the mode, different responses to an attempted software limit switch violation are possible:
AUTO, MDA:
● The block that would violate the software limits switches is not started. The previous block is terminated properly.
Function Manual
01/2017
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