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New applications for energy at the press of a button

Frank Schmidt -October 13, 2012

Mechanical energy can be found everywhere – in the movement of doors, windows or machine components, the vibration of motors, the pressing of door handles or switches. These energy sources, which typically remain unused, can be tapped by means of energy harvesting to power electronic devices.

An example is self-powered wireless technology, which draws its energy from indoor light, temperature differences and motion. One of the core elements of this technology is a mechanical energy converter that generates enough energy from a key-press to send radio signals. This enables battery-less wireless automation solutions that operate maintenance-free for different fields of application including industry or transportation. Offering an efficient concept, manufacturers (OEMs) should consider specific design-in requirements when integrating the mechanical energy converter to ensure optimal performance.

Next generation of energy harvesting

 

With the ECO 200 the third generation of electromechanical converters has recently been introduced to market. See Figure 1. Combined with a wireless transmitter module, the converter incorporates all of the components and functions of battery-less wireless technology – and forms the basis for realizing customized, energy harvesting switching solutions easily.

The combination enables more than a million switching cycles to be completed in optimized applications. This makes the technology suitable for industrial applications such as battery-less hand-held transmitters or wireless position switches. For a fast implementation of customized solutions based on energy harvesting wireless technology, developers can use a starter kit – with no need for a deep knowledge of energy harvesting.

 

Figure 1: The ECO200, a battery-less wireless energy harvester

 

Energy converter

As the name suggests, an energy converter converts mechanical energy into electrical energy, which it makes immediately available. To be versatile, the energy converter needs to have certain properties. First, it should have a good level of efficiency so that as little energy as possible is wasted. A good level of efficiency also enables small forces and movements to be used effectively. Other key factors are a long lifespan, compact design and low cost.

An energy converter in the latest generation combines these sometimes conflicting requirements in an efficient concept. A magnetic flux is passed through two magnetically conductive laminations by a small but very strong magnet, and is enclosed in a U-shaped core. An induction coil is wrapped round this core. The magnetic parts are held in position by a plastic frame and a spring-loaded clamp.

The U-shaped core leading through the coil is movable – it can take up two positions, each of which touches the opposite magnetic poles – and in each end position the magnetic flux is reversed in the U-core. This design ensures maximum magnetic flux alteration through the coil with minimal movement of the core – and therefore high efficiency.

Moreover, the energy output does not depend on the speed of actuation. A mechanical energy store in the form of a leaf spring takes care of this. It forms the interface to the actuation of the energy converter. As the leaf spring is bent more, it stores mechanical energy until the magnetic forces can no longer hold the U-core in its position.

If the spring forces exceed the holding power of approximately 3.5 newtons (N), the core flips quickly into its second position, accelerated by the spring. This generates a voltage pulse in the induction coil. The speed with which the core flips largely determines the amount of energy that can be taken from the coil – and is always constant, as the spring always accelerates the U-core in a similar way, irrespective of how quickly it was tensioned. See Figure 2.

 

 

Figure 2: Components of the ECO 200 are 1 clamp, 2 leaf spring, 3 lamination, 4 coil, 5 magnet, 6 U-core, 7 coil former

 

So each actuation produces a small electrical pulse that can be used immediately for the brief operation of electronic circuits. One particularly useful application is to combine it with a wireless transmitter as this makes it possible to have a switch that has no wires or batteries – and is therefore maintenance-free.

 


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