Use of hardware limit switch as reference switch (P-AXIS-00329)

If a hardware limit switch of an axis shall be used as reference switch this parameter has to be set to 1.

The state of the limit switch can be transmitted to the CNC either via the PLC interface (see [HLI]) or by reading the drive digital inputs directly if the used drive type supports this (see also P-AXIS-00321).

Variable name

Type

Permissible range

Axis type

Dimension

ref_cam_is_limit_switch

BOOLEAN

0 / 1

T, R

----

CAUTION

Using a hardware limit switch as reference switch is only possible if the drive amplifier does not go into an error state if the hardware limit switch is actuated.

If the hardware limit switch is actuated the drive stops independently and accepts only setpoint values that move the drive away from the hardware limit switch. The deceleration the drive uses to stop must be set up in the drive amplifier. Because the drive follows the CNC only conditionally if the limit switch is actuated, position lag monitoring and window monitoring are disabled during homing.

The procedure during homing is as follows:

  1. Drive on limit switch
  2. Reverse movement
  3. Referencing the axis either on the falling edge of the limit switch or the falling edge of the limit switch followed by the zero pulse of the encoder (see also P-AXIS-00084).

Homing on hardware limit switch for gantry axes:

CAUTION

Homing on hardware limit switches for gantry axes is only possible if the switching position of all switches is at the mechanically same position.In other words: If the gantry system would travel on the limit switches these would have to be actuated simultanuosly.

In contrast to the NC controlled homing on reference cams a relative movement between the axes occurs already during the homing sequence. The reason is that the axes stop independently and do no longer follow the setpoint values of the CNC. The relative movement between the axis is proportional to the position difference of the switching positions of the limit switches.

For each axis of a gantry system the homing procedure described above is executed. Additionally at the end of homing the gantry system is moved away from the limit switches until all switches are not actuated.