|Форум АСУ в Україні
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|Автор:||san [ 20 вересня 2014, 20:06 ]|
|Тема повідомлення:||Torque Production|
Case notes: Robots that use motors in the joints present a motion-control challenge. Should the application produce torque using a six-step technique or sinusoidal commutation for brushless dc (BLDC) motors?
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Arecent consulting project involved selection of electric motors and motor drives for a true articulated joint robot. One major design constraint is that the motors must be physically placed right at the articulated joints, which severely limits the physical size and weight of the motors. A “strong” robot requires maximizing the amount of torque from the embedded small, lightweight electric motors.
As for motor type, a three-phase brushless dc (BLDC) permanent magnet motor with rare earth magnets would appear to be the best choice. Power density is high, and no maintenance should be required unless motor bearings fail. As for the motor drive, since the motors must be operated from a relatively low voltage dc power supply, a traditional three-phase, six transistor MOSFET (metal-oxide semiconductor fieldeffect transistor) bridge would seem to be the appropriate selection for the power drive circuit. The next design question is to determine the type of motor commutation scheme. Traditional choices would be either six-step (trapezoidal) or sinusoidal (vector control) commutation. The motor is equipped with directly mounted Hall sensors for monitoring rotor position. Hall sensors provide input for a six-step commutation state machine and, since the motor output effectively goes through a substantial speed reduction before engaging the load, the Hall sensor edges, along with a linear interpolation routine, can be used to provide rotor angle feedback with sufficient resolution to drive a sinusoidal algorithm.
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