Nov/Dec 2013 - Vector - Page 35 D R I V E S & SWITCHGEAR Concrete production technology is a complicated process and electric power is used in almost every stage of concrete preparation. One of the most energy consuming stages is when the concrete is mixed in concrete mixers. There are many techniques proposed in literature on how to make concrete mixers more efficient through control applications [1, 2, 3, 4]. Most of these papers are, however, not concerned with electric motors which drive the mixers. Mechanical power of the mixer blades is developed by the electrical drive connected through a gear or directly to the shaft where the blades are attached. The electric drive efficiency is therefore important for the energy consumption of the concrete plant. A permanent magnet motor with two degrees of mechanical freedom The effectiveness and advantages of an energy-efficient concrete mixer drive using a synchronous permanent magnet motor to develop helical rotor movement. by Dr. Oleksandr Dobzhanskyi and Dr. Rupert Gouws, North-West University The issue of permanent magnet machines versus induction motors for concrete mixers is well-debated. Some concrete mixer producers [5] suggest applying permanent magnet machines which usually have higher power density and efficiency, but also higher cost. Induction machines still dominate in the concrete production process. This article introduces a novel design for a permanent magnet drive for concrete mixers. The proposed motor’s high efficiency and simple structure promise energy savings and lower cost advantages. The motor is not a conventional synchronous permanent magnet motor and the machine is designed so that two degrees of mechanical freedom (TDMF) of the rotor is achieved by the magnets skewed on its surface. In other words, the rotor of the machine moves helically (rotary and liner movements are combined). There are various designs of electric machines with TDMF already proposed in literature, but most of them are induction or reluctance types of motors [6 – 9]. L Chen et al [10] have designed a permanent magnet motor with TDMF. However, there are two windings (rotary Fig. 1: The motor with TDMF. Fig. 2: Stator and rotor dimensions of the machine.