Motor and drive systems: Advanced motors, encoders, applications
An axial variable flux permanent magnet motor, pancake motors, advanced encoders, and applications were among discussions at the 12th annual Motor & Drive Systems 2015 conference and exhibition. The event covered technical advancements on the design and integration of motor, drive systems, and motion control for manufacturing, industrial, packaging, and traction applications. The 12th annual conference was held Jan. 21-22 in Orlando, Fla. Some presentations from Jan. 21 are summarized below.
Axial variable flux PM motor
I-Motor R&D Co. in Kyoto, Japan, developed an axial variable flux permanent magnet (PM) motor with an electronic drive to precisely reposition the rotatable rear winding. This technique will provide a motor with better high-power efficiency over a wide speed range than current field weakening techniques, according to Dan Jones, president, Incremotion Associates Inc.
He described the motor design, motor performance, and motor testing that resulted in 17 pages of data. Results were positive, though higher speeds and larger offset testing are needed, Jones said.
Dual axial gap wheel motor
A brushless dc motor can be integrated into a working rotor as a road wheel, a fan, a pump, or anything that produces rotation from electricity. Electric propulsion can be used for personal transportation. Placing the electric prime mover in the hub of industrial machines improves reliability and reduces wear with fewer moving parts. Wheelmotors reduce the footprint of the drive system, freeing up valuable space for other uses, according to Victor Wowk, president, Machine Dynamics Inc.
Wheelmotor origins began early with the internal combustion engine driven wheel, hydraulic motors on farm machinery, and with the Lohner-Porsche electric wheel in 1903. More recent applications include gear motors on mine trucks and in diesel locomotives, and submarine motors, each conserving space compared to conventional motors, he explained. A pancake motor is narrow and larger in diameter. Wheelmotors eliminate drive components, decrease space and provide more torque at slow speed without belts, chains, couplings or gears.
Dual-axial gap motor uses both sides of magnets, no rotor iron, two stator windings, two motors, and two controllers for redundancy. The design removes heat more efficiently than a traditional motor design, with a shorter path to the outside. While the redundant design decreases efficiency, it increases reliability, Wowk said.
Fewer wheelmotor parts mean less cost and higher reliability, Wowk said. Plus, the design offers maximum torque at zero speed, while operating without oxygen, underwater, and in a vacuum. The Mars landers use wheelmotors, Wowk said; almost no energy is consumed at stop, torque production is close to the point of use, and they free space in a vehicle for other purposes.
The Electric Auto Association believes electric cars will always outperform gasoline, Wowk said, because electrons flow faster than atomized fuel. Wheelmotors are naturally regenerative, but even so, no electric vehicles (EVs) use wheelmotors yet.
Traction motors, electric 2-wheelers
The world’s largest market for traction motors is electric-powered two-wheelers, according to Ed Benjamin, senior managing director, eCycleElectric Consultants. Benjamin said the world fleet of electric-powered two-wheelers is approximately 225 million vehicles in service. Annual sales are more than 31 million units per year and are expected to grow to approximately 130 million per year.
Benjamin said manufacturers range widely and include manufacturers of bicycle, scooters, motorcycles, automobiles, and component makers for electric powered two-wheelers.
Prices and designs vary widely, including a design where pedaling activates the motor, and another where an Apple iPhone application serves as the controller.
China is the largest manufacturer and user of ebikes, with 200 million in use. Southeast Asia and the European Union have 10 million each, Japan has 1.5-2 million, and the U.S. market has about 500,000, but that number is growing quickly, Benjamin said, with the 200,000 sold in 2014 representing twice as many sold in the prior year.
Market opportunities include ebikes themselves and their components: batteries, packaging, chargers, motors, controllers, connectors, user interfaces, and communications. Those entering in the market must plan for appropriate pricing in a competitive market, the need to support the factory during and after production, and perhaps a six-week head start before any design is copied in the market. At present, brushless dc permanent magnet motors comprise most of the market, and opportunities abound, Benjamin said, equating today’s ebike market maturity to the automobile market’s in 1906.
Rotary encoders provide critical information about motor shaft position and rotational direction, velocity, and acceleration. The need for encoders has increased dramatically with the rise of applications requiring precise motion control; current encoders offer little intelligence to the motion control designer. New technology offers diagnostic and programming capabilities that can speed time to market and reduce field failures and downtime, according to Jeff Smoot, vice president of motion control, CUI.
Programmability allows customization for need, resolution, poles, manufacturing data, and date codes. Versatility includes the ability to do proportional-integral-derivative (PID) control, zero position set (brushless dc motor), and index pulse, and alleviate the need to purchase a new encoder if the motor or motion system design changes, Smoot explained.
Diagnostics available include encoder status (good, bad, or mounting issues) for faster troubleshooting, fewer field failures, and data that allows scheduling of preventive maintenance, Smoot said. (Polling the encoder at start-up avoids damaging equipment with incorrect settings.)
Inductive multiturn rotary encoders
In a motion control system, closed-loop performance can be improved with inductive multiturn rotary encoders. While single-turn encoders with optical scanning have seen much success in servo motors (particularly in low-speed applications), the need has increased for application-specific, custom or functionally safe products. Applications requiring good control characteristics, high accuracy, dynamic performance, efficiency, and durability can benefit from the next generation of inductive encoder technology, according to Jonathan Dougherty, product specialist automation, with Heidenhain.
Optical encoders are fragile, and there’s a risk of contamination in rugged applications. Resolvers are more robust, but with the lower cost comes resolution and accuracy issues, Dougherty said. Inductive encoders provide a range of capabilities, which include operation without bearings, a functional safety option, high resistance to contaminants, high vibration and shock resistance, and fewer components that decrease failure probability, Dougherty said.
Mounting replacements for optical encoders are available for easier retrofits.
Applications include wind turbines, packaging, automation, handling machines, robotics, paper machines, timber industry, steel industry, textile industry, and injection molding machines.
Magnetic encoders, integrated
In recent years, there’s been some migration from optical to magnetic motor feedback from advancements in modern integrated magnetic sensors, including lower costs, rapid customization of geometry, attachment methods, and performance features. Custom kit and component solutions can be integrated into existing customer systems in a variety of applications, said John Santos, chief engineer-sensors, Timken.
Timken, established in 1899, has been in the sensor business for 15 years, Santos said, and now offers third- and fourth-generation Hall effect sensor encoder products in kits, modular encoders, and complete assemblies. On-axis and off-axis magnet encoders are available; Timken offers the off-axis type of encoders.
Data rates exceed optical sensors, field programmability is available, and extended temperature ranges of -40 to 125 C are available.
Applications include mining trucks, where an electric motor is mounted on the axle powered by a diesel in front; and in agriculture in tractor global positioning system (GPS) steering feedback, Santos said; tractor axle torque monitoring prevents drive line damage. Other applications include medical and lab equipment to provide consistent positioning in moist or harsh environments, in test tube handling machines, magnet resonance imaging (MRI) machines, print head position feedback on 3D printers, and for linear actuators used in other automation applications. Market trends include increased sophistication, higher resolution, higher accuracy, faster update and data speed, and field programmability.
Voltage and current measurement techniques for motor drive and power converter design are important for motor drive performance, according to Dr. Dal Y. Ohm, president, Drivetech Inc. Different sensor types and sensing circuits are used in motor drives, requiring knowledge of sampling, types, and applications, including trapezoidal versus sine, sensorless versus sensorless, temperature variation, and motor types including permanent magnet, dc, induction, and switched reluctance motors. Phase current sensing is critical for high-performance control, Ohm said.
– Mark T. Hoske, content manager, Control Engineering, firstname.lastname@example.org.
- Motor and drive systems can be made more efficient and capable with upgrades to new technology.
- Wheel motors or pancake motors seem to have wide variety of applications, including electric vehicles (EVs), though they’re not applied there yet.
- Intelligent, inductive, and magnetic encoders offer advantages that include better closed-loop operations.
Can newer motor and drive systems and sensing technologies improve the efficiency of your motion control applications?
See related articles on CNC machines and encoders and linear encoders (linked below), and visit the discrete sensors page on the Control Engineering website.