New-Tech Magazine Europe | Dec 2015 Digital edition

may provide enough encouragement for designers of battery-operated appliances to take advantage of capacitive encoders to boost the efficiency of next-generation drive systems. On the other hand, the emergence of new regulations governing efficiency of electric motors show that regulators are taking a progressively tougher attitude toward the efficiency of electric- motor systems. These include the EU’s latest IEC 60034-30-1 standard, which has introduced a new Super Premium Efficiency level for three- phase induction motors. In the US, the Department of Energy (DoE) will bring new legislation into force in mid 2016 that both increases minimum efficiency standards and includes types of motors not previously covered. The DoE’s analysis estimates that more than 70% of the total potential energy savings achievable through the new legislation can be realized through system-level savings such as improving component efficiency and using smaller motors where possible. Capacitive encoders can help towards using smaller motors, and allow designers to reduce the power draw of their entire systematic government agencies continue to focus more sharply on this area. Conclusion Affordable automation in the form of small mobile robots and civil drones could revolutionize activities such as manufacturing, distribution and asset management. Low-power, precision capacitive encoders can deliver valuable savings in overall energy consumption for these motor-rich mobile applications, while also streamlining development and manufacturing as well as reducing maintenance overheads so helping to reduce ownership costs. As emerging government regulations indicate an increasingly strict attitude to the energy efficiency of motor systems, designers could find even more incentives to adopt this technology.

Power in 4-motor system

Operating voltage Current at highest reso- lution

Type

Encoder model

0.12W

6mA

5V 5V 5V

Capacitive

AMT10

1.7W 3.2W

85mA

Optical

Competitor 1 Competitor 2

160mA

Magnetic

Table 1. Encoder power consumption comparison

disk, which is often needed when using optical encoders. At the same time, the capacitive encoder provides equivalent or superior accuracy compared to other encoder technologies, with a typical accuracy value of 0.2 degrees. Another advantage of the capacitive encoder is that resolution can be adjusted dynamically, whereas optical encoders are fixed such that changing the resolution requires fitting a different encoder. Adjustable resolution delivers advantages in development, by allowing engineers to make any changes to prototypes quickly and easily, and also aids production supply-chain management by allowing a single stock- keeping unit (SKU) to be used in multiple motor controls of different resolutions. The encoder housing is designed for easy assembly and supports multiple mounting options. In addition, multiple sleeve sizes are provided to suit commonly used motor shaft diameters. Energy Savings and Efficiency Gains The AMT encoders have very low current requirements, with some series drawing less than 10mA of current at the highest resolution. This corresponds to 0.2W in a four-motor system operating at 5V. Recall that optical and magnetic encoders can draw considerably higher current, thereby significantly increasing overall power consumption in a multi- motor system. Table 1 shows the power consumed purely by the encoders of a four-motor system such as a drone or mobile robot, comparing the performance of CUI AMT capacitive encoders with optical and magnetic alternatives. Capacitive encoders are shown to offer a superior energy-efficient solution, and can give designers more freedom to manage the limited power budget in mobile and battery-

operated applications. Moreover, the capacitive encoder’s operating current is independent of the resolution setting, which allows the encoder settings to be optimized without compromising application power consumption. When paired to a brushless dc motor, capacitive encoders also allow faster and easier digital “zeroing” to align the encoder U, V and W signals with the rotor windings. To align an optical encoder, the rotor is usually locked in a known position and the code wheel is physically aligned. The motor is then back-driven while using an oscilloscope to verify correct alignment of the back-EMF and encoder zero-crossing points. This is an iterative process that can take 15 to 20 minutes, although small errors may remain. These errors prevent the motor running at maximum efficiency, thereby wasting precious battery energy. It is even possible that the inability to optimize alignment may force the engineer to over-specify the motor to ensure the desired torque. In contrast, digital zeroing by programming the encoder using a software application ensures perfect alignment every time. The process takes seconds to complete and eliminates unit-to-unit variability. The motor is energized to lock the rotor in the desired position, and the encoder is set to zero at this position using a single command. No additional instruments are required. By allowing accurate, repeatable alignment, this technique ensures that the motor is able to run smoothly at optimum efficiency thereby delivering best performance and maximizing battery life in mobile applications. Benefits Beyond Battery- Operated Applications Market demands for better performance

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