BECKHOFF AX2000 PROFIBUS DP communication profile - Manual (Page 45)

6.1.6 Start homing run
After switching on the 24V auxiliary voltage the system must first of all carry out a homing
run.
Take care that the position of the machine zero point (reference point) permits the following
positioning operations. The parameterized software limit-switches in the AX2000/2500 may
not be effective. The axis could then drive up to the hardware limit-switch or the mechanical
stop. There is a danger of damage being caused.
If the reference point (machine zero point) is approached too fast, with high moments of
inertia in the system, then it might be overrun, and the axis could then drive up to the
hardware limit-switch or the mechanical stop. There is a danger of damage being caused.
The homing run is started by the control word (STW) Bit 11 = 1. The start of the homing run is
detected by a positive transition edge for Bit 11.
If Bit 11 is set to 0 again, before the reference point has been reached, then the homing run is can-
celed. Status word (ZSW) Bit 17 remains at 0 (reference point not set).
A set reference point is a precondition for all the positioning functions of the linear axis.
The reference point switch is wired up to a digital input on the AX2000/2500.
Depending on the type of homing run, you can freely shift the zero crossing point of the motor shaft
within one turn, by using the parameter “Zero-point offset” (NI-offset). Furthermore, you can fix the
position value to be the reference point by using the reference offset.
After the homing run, the amplifier signals “InPosition”, thereby enabling the position controller.
The velocity for the homing run is transmitted with the setpoint HSW (PZD 2), as a 16-bit value.
Multiplying this by the value of PNU 1894 determines the 32-bit speed. The sign is not evaluated.
Conditions :
State of the state machine = “Operation enabled”
No warning message (ZSW Bit 7 = 0)
The following diagram uses the homing run Type 1 (negative direction of motion, positive rotation,
starting point in negative direction relative to the reference switch) as an example to illustrate the
signal sequence of the relevant bits in the manufacturer-specific state.
PROFIBUS for AX2000/2500 45
BECKHOFF
12/05
Appendix