Position feedback
Since the birth of brushless motors, Hall effect sensors have been the main force for commutation feedback. Since three-phase control requires only three sensors and the unit cost is low, they are often the most economical choice for commutation from the perspective of BOM cost. A Hall effect sensor that detects the position of the rotor is embedded in the stator of the motor so that the transistors in the three-phase bridge can be switched to drive the motor. The three Hall effect sensor outputs are generally labeled as U, V, and W channels. Although Hall effect sensors can effectively solve the problem of BLDC motor commutation, they only meet half of the requirements of BLDC systems.
Although the Hall effect sensor enables the controller to drive a BLDC motor, unfortunately its control is limited to speed and direction. In three-phase motors, Hall effect sensors can only provide angular position within each electrical cycle. As the number of pole pairs increases, the number of electrical cycles per mechanical turn increases, and as the use of BLDC becomes more prevalent, the need for precise position sensing increases. To ensure a robust and complete solution, the BLDC system should provide real-time location information so that the controller can track not only speed and direction, but also travel distance and angular position.
To meet the demand for more stringent location information, a common solution is to add incremental rotary encoders to BLDC motors. In general, in addition to Hall effect sensors, incremental encoders are added to the same control feedback loop system. The Hall effect sensor is used for motor commutation, while the encoder is used to track position, rotation, speed and direction more accurately. Since the Hall effect sensor provides new position information only when each Hall state changes, its accuracy is only six states per power cycle; for a bipolar motor, it is only six states per mechanical cycle. . The need for both is negligible compared to an incremental encoder that can provide resolutions in thousands of PPRs (number of pulses per revolution) that can be decoded to four times the number of state changes.
to sum up
High-precision, tight control loops give BLDC motors an edge in many areas. Increased accuracy means less power loss, higher accuracy, and better control for BLDC operation for end users. Currently, BLDC motors have been used in a wide variety of fields, including surgical manipulators, driverless cars, assembly line automation, etc., and will soon gain a place in many other areas not yet envisioned. The BLDC motor market is growing, and the requirements for BLDC motors have remained the same: the market needs high-efficiency and durable motors with low-cost, high-precision position sensing feedback. When used with BLDC motors, the AMT31 Series encoders save valuable time during installation while simplifying development and manufacturing processes. With its versatility, the ability to complete programming and zeroing settings in seconds, and compatibility with AMTViewpointGUI, the AMT31 encoder is well suited to the needs of the fast-growing BLDC market.
