404LXR Series Product Manual
Chapter 3 - How to Use the 404LXR
28
Setting Home Sensor
The 404LXR is equipped with a “home” position reference sensor. This is located on the same
bracket as the limit sensors and the target is located between the limit targets. This sensor is
typically used in conjunction with the encoder “Z” marker (refer to “Z” channel reference below). If
the unit is equipped with this option it will be set at the “Z” channel location. If another home
location is desired the home target can be adjusted by loosening the screws on the target and
sliding it along the track. Note
: If the home sensor is used without “Z” channel, repeatability is
reduced to +/-5 microns.
Z Channel Position Reference
The Z channel is an output on the encoder. Many servo controllers support this input. The Z
channel on the 404LXR is located in one of three positions, (positive end, mid travel, or negative
end). The location depends on how the unit was ordered (See Chapter 2,
Order Number
Nomenclature
). The Z channel is a unidirectional device. This means that the final homing direction
must occur in one direction. The 404LXR is set that the final home direction is to be toward the
positive side of the table (See Chapter 2,
Dimensional Drawing
, for positive direction definition).
The repeatability of the Z channel is equal to +/- 2 resolution counts of the encoder (except for 0.1
micron scales which have a repeatability of +/-1 microns). Thus the repeatability
of the “Z” channel
equals:
Encoder Resolution Z Channel Repeatability
5 micron
+/- 10 micron
1 micron
+/- 2 micron
0.5 micron
+/- 1 micron
0.1 micron
+/- 1 micron
NOTE: Home repeatability is also very dependent on controller input speed and homing algorithms.
The above repeatability does not include possible controller tolerance. Additionally, to achieve the
highest repeatability the final homing speed must be slow. Slower final speed usually results in
higher repeatability.
NOTE
: The “Z” channel output is only one resolution count wide. Thus the on-time may be very
brief. Due to this some controllers may have difficulty reading the signal. If you are experiencing
the positioner not finding the “Z” channel during homing, try reducing final homing speed; also refer
to your controller manual for frequency rates of the “Z” channel input.
Grounding / Shielding
All cables are shielded. These shields are to be grounded to a good earth ground. Failure to
ground shields properly may cause electrical noise problems. These noise problems may result in
positioning errors and possible run away conditions.
