Rockwell Automation LZ Series Linear Motors - Manual (Page 26)

Publication LZ-UM001A-EN-P - January 2008
26 Troubleshooting
Mechanical displacement of one electrical cycle = motor magnetic pitch (180
o
)
in inches multiplied by two. Note that the published specification may already
be in “cycles.” In this case do not multiply by two.
Use the following equation to calculate back EMF constant:
V
ptz
= V
(pK-pK)
x 0.5 (V)
Note:
Where:
ptz = peak to zero or peak of sinewave
ptp = phase to phase
When comparing to the published motor back EMF constant, make sure you
convert the units as necessary.
If values do not match verify that you have installed the correct magnetic
channel and coil assemblies and they have the correct air gap.
Checking the Magnet
Channel Butting Polarity The magnetic channels must be butted such that the magnet polarity sequence
is alternating (north-south) throughout the whole travel. It is difficult to use
the back EMF method to check this on motor coils with multiple sets.
Analyzing the trapezoidal Hall effect signal over the whole travel is the best
method of evaluating proper magnet channel polarity.
1. Refer to the Motor Phasing Diagram for the expected Hall waveshape.
2. With the drive power OFF, verify that the Hall circuit is connected to
the drive per the interface wiring specifications.
3. Disconnect the motor leads from the drive.
4. Turn the Hall power supply ON (driver power ON).
mechanical displacement of one cycle (in)
cycle time (s)
------------------------------------------------------------------------------------------------------ velocity
in
s
----- =
Vptz
Velocity
in
s
-----
---------------------------------- Back EMF constant
Voltsptz ptp [ ]
in
s
-----
-------------------------------------- =
Voltsptz ptp
[ ]
in
s
-----
-------------------------------------- 0.707 × Back EMF constant
VoltsRMS ptp [ ]
in
s
-----
------------------------------------------ =