WAM Arm – User’s Manual
www.barrett.com
© 2008 Barrett Technology®, Inc.
Document: D1001, Version: AH.00
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Optical Encoders – When the WAM is first powered on, the motor controllers use
Hall-effect sensors and six-step commutation for control until an initial hall
transition occurs. Then they switch to using the incremental encoders for smoother
commutation until the encoder index pulse is observed (once per motor revolution).
Then they begin a factory-calibrated commutation loop for precise torque control.
•
Magnetic Encoders – When the WAM is first powered on, the motor controllers use
the absolute magnetic encoder to begin a factory-calibrated commutation loop for
precise torque control.
MECH
:
•
Optical Encoders – MECH tells you how many encoder counts there are between the
present location and the index pulse. Unless you want to write your own cogging or
torque ripple cancellation code, these properties are not important. It is only
important to know the orientation of the rotor magnets inside the stator for low-level
commutation and any types of perturbation cancellation you may wish to implement
•
Magnetic Encoders – MECH is the raw magnetic encoder feedback, absolute within
one rotation of the motor.
MOFST
:
•
Optical Encoders – MOFST is the distance in encoder counts between the index
pulse of the encoder and the start of an electrical cycle for that motor (a point where
the magnets are aligned with a single phase coil).
•
Magnetic Encoders – MOFST is the encoder reading at the start of an electrical
cycle.
Q5:
How do I calculate the desired Maximum Torque (MT) values for each joint?
A5:
Table 9 – Maximum Torque (MT) mA to Nm conversion table
(Note: Cable limits chosen to be approx 20% of the rated breaking strength)
Motor:
1 2 3 4 5 6 7
Stall
(Nm):
1.49 1.49 1.49 1.49 0.356 0.356 0.091
Peak
(Nm):
6.31 6.31 6.31 6.31 1.826 1.826 0.613
Cable
limit
(Nm):
1.8 1.8 1.8 1.6 0.6 0.6 N/A
Nm/A–published: 0.457 0.457 0.457 0.457 0.236 0.236 0.067
Nm/A–actual: 0.379 0.379 0.379 0.379 0.157 0.157
0.058
Example:
What should the motor 3 Max Torque (MT) be set to in order to not exceed the designed
cable limit?
(1.8 Nm) / (0.379 Nm/A) * (1024 Units/A) = 4863
setProperty(bus, 1, MT, FALSE, 4860); // Cable limit = 4860
setProperty(bus, 2, MT, FALSE, 4860); // Cable limit = 4860
setProperty(bus, 3, MT, FALSE, 4860); // Cable limit = 4860
setProperty(bus, 4, MT, FALSE, 4320); // Cable limit = 4320
setProperty(bus, 5, MT, FALSE, 3900); // Cable limit = 3900
setProperty(bus, 6, MT, FALSE, 3900); // Cable limit = 3900
setProperty(bus, 7, MT, FALSE, 3200); // J7 Gears (max stall = 1600)
