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TB127 Rev2 Homing to Reference Marks with Software Travel Limits
If you are looking for directions on how to set up software travel limits and are not using reference homing
marks please see Technical Bulletin #289
Software Version 7 14 and Later
Although Centroid strongly recommends the use of limit switches Reference Mark Homing has its advantages with
"No limit switch" operation of the machine This feature provides the same convenience that physical home switches
provide No need to reset WCS zero position each time the power is removed from the control
The main advantage of "Home to Reference Marks" is no need for physical limit/home switches This yields quicker and
less expensive control installation it also eliminates the possibility of any errors due to faulty switches or wiring It is
however important that the home to reference marks feature is set up correctly because machine damage can result
from improperly set travel limits The reference marks for homing are typically set near the center of the table travel and
the software limits are set for both positive and negative travel from that mark The Z axis alignment mark should be at
the maximum Z height allowed by the hardware The alignment marks can be scribed permanently into the machine
casting or made from tags applied to the casting Below is a typical setup of alignment mark application for a knee mill
To set the control for Reference Mark Homing
Press F1 Setup
Press F3 Config
Enter the password 137 press Enter
Press F1 Control
Cursor down to "Machine Home At Pwrup" and select "Ref Mark HS"
Press F10 Save
The use of alignment marks for homing is basically the same as the use of limit switches however instead of the
machine moving the axes until it detects a limit switch the machine operator must first move the table to pre determined
marks and then home the machine See illustration below The control will look for the first marker pulse coming from
the encoder and set home there Just as the axis travels in one specified direction to find a limit switch it will travel from
the alignment mark to the marker pulse in the specified direction every time
Note After the machine completes it homing function the lines may appear to be misaligned slightly This is
dependant on where the index pulse on the encoder is in reference to the alignment marks on the machine This
is normal
To setup the control for positive and negative travel limits
Press F1 Setup
Press F3 Config
Enter the password 137 press Enter
Press F2 Machine
Press F1 Jog
This will highlight the first axis to be changed Use the arrow keys to cursor over to the Travel field Enter the amount
of travel the table can move from the home position to the end of the ball screw without the ball screw bottoming out
against the end stop This amount can be found by going into the Machine Coordinate screen by depressing the ALT + D
keys jogging the axis in the minus direction close to the end of travel then depress the E STOP to release the power to
the motors and moving the table by hand until the end is reached Record the number on the DRO Subtract about 25
inches 6 35 mm from this number and enter it into the Travel field as a negative number Repeat this procedure for
the plus travel only enter a positive number in the field Repeat this for all other axes If the Z axis homes at the top limit
of its travel only the Travel field
The F10 Park function Dos and F1 Park Linux allows for quick and easy homing of the machine before machine
shutdown
When the operator wants to shut the machine down depressing the F10 or F1 Linux Park key will send the axes
back to within 1/4 revolution of the homing marks The alignment marks are now aligned for the next day When the
machine is turned on visually inspect the alignment marks to make sure the axes haven't been moved and then press
CYCLE START to home the machine Homing will be very quick since the motors are only 1/4 turn off of the marker
pulse
Document History
Rev1 Created on 2002 04 24 by #000
Rev2 Created on 2014 09 25 by #369