Encoder-free Servo Motors
2014 R&D 100 Winner
Industrial conveying and handling machines typically use expensive permanent magnet synchronous drives (“servo”) or cheaper induction motors equipped with brakes and clutches. Induction motors, because of their design, suffer from efficiency losses. Servo drives, meanwhile, are seen as less durable because they are equipped with sensitive encoders and extra wiring.
Engineers at Mitsubishi Electric Corp. have eliminated the worst features of both designs with the Sensor-less Servo Drive Unit FR-E700EX Series and Sensor-less Motor MM-GKR, which controls speed or position without the need for an encoder. Unlike conventional servo motors, the FR-E700EX Series uses a sensor-free vector control method, called a “virtual motor model”, for its control algorithm. The model, or “observer”, is programmed into the drive unit and estimates motor flux with the algorithm. Referring to the flux, the observer arranges vector control. With input of voltage and current information on the motor, the observer calculates inner parameters of the motor like flux, and estimates the speed and position of the rotor. This approach doesn’t require detection capabilities of typically encoder-equipped servos, allowing Mitsubishi to reduce motor complexity.
Mitsubishi Electric Corp.
|Mitsubishi Electric Corp's Sensor-less Servo Drive Unit FR-E700EX Series and Sensor-less Motor MM-GKR development team (l-r): Satoru Terashime, Masato Ito, Daisuke Nishijima, Akira Satake, Yosuke Hachiya and Eigo Totoki.|
The Sensor-less Servo Drive Unit FR-E700EX Series and Sensor-less Motor MM-GKR Development Team from Mitsubishi Electric Corp.
Yosuke Hachiya, Principal Developer, Mitsubishi Electric Corp.
Masati Ito, Principal Developer, Mitsubishi Electric Corp.
Daisuke Nishijima, Principal Developer, Mitsubishi Electric Corp.
Akira Satake, Principal Developer, Mitsubishi Electric Corp.
Satoru Terashima, Principal Developer, Mitsubishi Electric Corp.
Eigo Totoki, Principal Developer, Mitsubishi Electric Corp.