Limit switches, most commonly seen in linear mechanisms to restrict motion to a safe range, are used to identify that the motor has reached its end of travel. If either the positive (L+) or negative (L-) signal becomes active, the Commander core is instructed to immediately stop all advancement in that direction but will allow movement in the opposite direction.  As such it is important to ensure the placement of the positive limit at the end of positive travel and negative limit at the end of negative travel. The polarity of limit inputs is set with the POL[axis](Bit3).

When designing your limit circuit, here are a few points to keep in mind: 

  1. It is especially important that the motor must stop when the signal is active.
  2. To prevent nuisance limit faults that can stop your system, ensure that electrical noise does not trigger your limits as active.
  3. To operate in a fail-safe manner, the signal line must be designed to trigger as active when the cable connecting the limit switch to the Commander core becomes disconnected.

With the above points in mind think about your limit circuit and the active logic level in your system.

Limit error

By default IERR=0, which will trigger a limit error MST[axis](bit8~9) when a limit switch is set to active.  Once the limit error is set, use the CLR[axis] command to clear the error in ASCII mode or the ECLEAR[axis] command in standalone mode.

When using the end limit during the homing modes, the ERC (deflection counter clear) signal can be setup to clear the limit errors that accrue due to homing automatically.

The limit error states can be ignored by setting IERR=1. In this case, the motor will still stop when the appropriate switch is triggered; however, it will not enter an error state.

ASCII

CLR

IERR

ERC[axis]

MST[axis]

Standalone

ECLEAR[axis]

⎯

⎯

MST[axis]

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