8
Rear
7
10
4
9
3
Front
2
5
1
6
9
Hall sensor circuit The open collector output of Hall sensors does not normally have its own pull-up resistance, as this is integral in maxon controllers. Any excep- tions are specifically mentioned in the relevant motor data sheets.
Winding arrangement The maxon rhombic winding is divided into three partial windings, each shifted by 120°. The partial windings can be connected in two different manners - “Y” or “Δ”. This changes the speed and torque inversely proportional by the factor 3 . However, the winding arrangement does not play a decisive role in the selection of the motor. It is important that the motor-specific parameters (speed and torque constants) are in line with requirements.
Sinusoidal commutation The high resolution signals from the encoder or resolver are used for generating sine-shape motor currents in the electronics. The currents through the three motor windings are related to the rotor position and are shifted at each phase by 120° (sinusoidal commutation). This results in the very smooth, precise running of the motor and, in a very precise, high quality control. Properties of sinusoidal commutation − More expensive electronics − Field-oriented control (FOC) − No torque ripple − Very smooth running, even at very low speeds − Approx. 5% more continuous torque compared to block commutation − Highly dynamic servo drives − Positioning tasks
Wiring diagram for Hall sensors Hall sensor supply voltage
R Pull-up
Control circuit
« ∆ »-circuit
«Y»-circuit
Hall sensor output
W 1
W 1
U 1-2
U 3-1
U 1-2
U 3-1
GND
W 2
W 2
W 3
W 3
The power consumption of a Hall sensor is typically 4 mA (for output of Hall sensor = “HI”).
U 2-3
U 2-3
Bearings and service life The long service life of the brushless design can only be properly exploited by using pre- loaded ball bearings. − Bearings designed for tens of thousands of hours − Service life is affected by maximum speed, residual unbalance and bearing load
Currents in sine and block commutation
Sinusoidal phase currents
Block-shaped phase currents
Legend 1 Star point 2 Time delay 30°e 3 Zero crossing of EMF
300° 0°
60° 120° 180° 240° 300°
Technology – short and to the point 67 For further explanations, please see page 190 or “The selection of high-precision microdrives” by Dr. Urs Kafader.
Turning angle
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