Non-contact power supply
Technical equipment and systems need power, but electricity can only be stored in small quantities. If wired power is the preferred option, the cables often get in the way. One remedy is provided by systems based on induction or radio waves. But the cost of such systems is mostly greater than their benefit. A new method of "free" power transmission is setting new standards in terms of efficiency and space-saving. It enables actuators and sensors in industrial applications and technical systems to be powered conveniently and at low cost, continuously or discontinuously depending on requirements.
Wired supply is essential in many applications subject to high power demand. But thanks to MOSFET technology and energy-saving components, modern-day sensors and miniature drives and circuits are highly efficient. They are easily able to work with „maximum“ power outputs in the triple-digit milliwatt range. Though batteries are capable of supplying this power, their size is then usually many times greater than the useful energy they provide. Also, galvanic primary and secondary elements are not reliable in continuous duty over longer periods of time; they are simply used up too quickly, or age too rapidly. Power transmitted by radio waves leaves most of the input energy unused, often then causing interference in the surrounding area, and it is also unable to transmit power into a Faraday‘s cage – that is to say, any technical equipment inside a metal housing. Inductive systems, for their part, work only with very tight coil spacing, and so are limited in range. A new process devised by Triple Sensor Technologies GmbH (TST) based in Jena, Eastern Germany, bypasses the limitations of the familiar chemical and physical energy storage and transmission methods.
The new patented process is based on the magnetic transfer of a rotary motion from a source to a receiver. In the receiver – the generator module – this rotary motion is then converted into electricity. Inventor Dr. Lausch from Triple Sensor Technologies GmbH (TST) highlights the particular advantages of the new solution: "The transmitter module is very compact, and can easily be worn on a belt for medical implants for example. Its effective range is nevertheless about 50 cm. There are no emission losses as with radio waves, even under no load, as the transmitter only has to deliver more power when some has been tapped by the receiver. Moreover, the generator module is easy to locate for mobile probes." The currently available mobile receiver modules, measuring 10 x 12 mm (diameter by length) allow up to 100 mW of power to be transmitted. To ensure the transmitter module design is as compact as possible, the manufacturer is working with miniature drive specialist FAULHABER. Adapted standard products provide the scaled power output in line with requirements and – also very important – the necessary compact, easy to program controller.
On the belt: efficiency off the rack
The engineers in Jena took their pick from the wide range of miniature drives offered by FAULHABER. Since the universal application model demanded both continuous duty and short-time power supply, they chose wear-free EC motors in 20 mm outer diameter and with a length of 60 mm. In this design, the only wearing mechanical parts are the rotor bearings. Selected ball bearing materials and special lubricants allow for high speeds and service lives of several tens of thousands of hours. Despite their compact size, the miniature drives deliver big performance. They can be loaded well beyond their continuous torque limit for short periods on startup, which is a key advantage. This means the transfer module is able to supply power both continuously over long periods of time and on tap in short spells as required. As a result, swallowed capsules can be powered, as can dosage systems implanted in the body, or hermetically sealed sensors in technical systems which only need to be powered on demand, such as for parameter polling. To control the heart of the transfer module – the EC motor – the developers chose compact motion controller measuring just 34 x 25 x 14 mm (W x H x D). Together with the Motion Manager operator control software, the parameters can be set quickly and cost-effectively for any specific application case.
Of course, the applications of the ultra-miniature drives are not merely limited to the outer transfer module. Miniature drives are also outstandingly well suited to use on the generator side too. Depending on the task at hand, the power module can also be adapted to the power demand of various miniature motors for mobile operation. In this, too, the extensive product range offers the developers a broad basis for achieving precisely tailored solutions. It includes EC and DC motors, and offers diameters from 12 and 10 mm, through 6 mm variants, down to just 1.9 mm. And of course, flat penny motors or non-mechanical loads such as sensors can also be supplied with mobile power. So the right non-contact powered drive is available for virtually any mechanical task, and minor adaptations can be easily made. The new concept for the first time permits relatively far-reaching, efficient non-contact power transmission. Compact in design, based on standard components such as miniature motors and motion controllers. Both the transmitter and receiver modules are scalable to adapt to specific power requirements. In this, too, the manufacturer is able to profit from the wide range of miniature drives available.
An EC motor powers a magnet in a special fixture inside the transfer module. Under no load, the drive merely has to compensate for the friction losses of the bearings; it consumes no additional energy. When a power module is then introduced into the virtually spherical transfer space, a small magnet there couples to the alternating field density of the source magnet. This starts the small magnet itself rotating, generating a current in appropriately wound coils. This current is then available as useful load as long as the outer rotating field is exciting the generator. This secondary-side power draw naturally slows the outer magnetic field of the transfer module; the consumed energy has to be resupplied by the drive motor of the outer module in order to maintain the magnet‘s rotation speed. The use of a magnetic coupling enables the power to be transmitted through all non-magnetic materials. Even biological tissue, plastic, nonferrous heavy metal, titanium or amagnetic stainless steel shells are no obstacle. Consequently, the process is suitable for many different medical and technical applications.