The machine can not return to zero

The reason:

（1）The origin switch contact is stuck and cannot operate;

（2）The origin block cannot press the origin switch to the switch action position;

（3）Water into the origin switch causes the switch contacts to rust and make poor      contact;

（4）The origin switch line is disconnected or the input signal source is faulty；

（5）PLC input point is burned out.

Countermeasure:

（1）Clean up the stuck part, make its active part move smoothly, or replace the  shape switch;

（2）Adjust the installation position of the travel switch so that the zero switch contact can be successfully pressed to the switch action position by the stop block;

（3）Replace the travel switch and take waterproof measures;

（4）Check whether the switch circuit is open and short circuit, and whether there is a signal source;

（5）Replace the input point on the 1/0 board, set the parameters, and modify the PLC program.