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REEL ON A REEL AVAILABLE Proner Series FASTON Crimp Terminals Product Information • Available in 6.3, 4.8 and 2.8mm size • Low insertion force • Mate with 0.8 and 0.5mm Tabs • Available in productionready full reel packaging Speed of application, uniform reliability and low per-line cost have made TE’s FASTON products the industry leader in the appliance and automotive industries. The Proner Series FASTON Crimp Terminals available from RS provides the most effective way of assuring stable electrical & mechanical performance. Applied with matching tooling, the ‘F’ crimp offers precise tensile strength and conductivity that will last the life of the circuit. This method of termination also assures maximum resistance to vibration and corrosion. www.rs-components.com/TEReceptacleTerminals Optical encoder integration for BLDC-motor feedback By Dr. David Lin The majority of wasted electrical energy in the industry comes from oversized motors and fixed speed drive systems. Thus energy efficient motion control system should adapt in the future to the actual load demand from the application. BLDCMotors meet this requirement through electronic commutation and variable speed control. Commutating the motor pole winding at the optimal rotor position is essential for reducing electrical losses when managing variable speed and load situations. The following article discusses different Hall sensor arrangement and technology trends in integration. Reliable feedback of the rotor position is important for the performance of the total motion control system. It allows a precise commutation of the stator windings and minimizes electrical losses in the motor. Typically the 120˚ in phase shifted UVW signals are used to activate commutation in the BLDC-motor driver. Different options are available today to generate the UVW signals. This could be using Hall sensors or switches which are built into the windings or mounted on a small PCB; calculation by software with data based on the back-EMF from the stator winding; attaching an optical or magnetic encoder to the motor axis; or the integration of advanced single-chip optical or magnetic encoder ICs into the motor housing. Hall sensors or switches are widely used in BLDC-motors due to their low component cost. The sensorless approach requires effective algorithm to calculate UVW from the measured back-EMF. Also a fast microprocessor or DSP is needed to reduce execution time and minimize the additional latency time introduced. The limitation with sensorless UVW generation can be seen on fast load changes, at low speed and out of sync operation. Sensing the absolute rotor position in hardware is regarded as the most reliable option. Attaching an optical or magnetic encoder unit to the BLDC motor is advantageous when very high precision dynamic positioning is required and if the application is not cost sensitive. Hall sensor for commutation Using three discrete Hall sensors/switches in a BLDC motor generates UVW signals based on the sensor mounting position, either in the stator windings, or assembled on a small PCB at 0˚, 120˚ and 240˚locations opposite the rotors permanent magnets. In some cases a magnetic pole ring attached to the axis can be used. Figure 1 shows on the left side the mechanical position of the three Hall sensors/switches and the resulting UVW signals generated. The position accuracy of the UVW signals in relation to the actual rotor position depends on the mounting tolerances and matching of the Hall sensors/switches sensitivity and stability. Since the magnetic field will vary quite a lot over temperature, rotor speed and operating life time (permanent magnet ageing) a position error can add-up easily to +/-3˚ or more. Another approach uses four integrated Hall sensors and signal conditioning to generate a sine/cosine signal, where the Fig. 1: Options of BLDC motor position sensing for commutation. Dr. David Lin responsible for magnetic sensor products and applications at iC-Haus - www.ichaus.de - He can be reached at david.lin@ichaus.de www.electronics-eetimes.com Electronic Engineering Times Europe November 2013 31


EETE NOV 2013
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