Energy harvesting at the press of a button

Energy harvesting at the press of a button

Technology News |
By eeNews Europe

One example is self-powered wireless technology, which draws its energy from indoor light, from temperature differences and motion.

One of the core elements of this technology is a mechanical energy converter that generates enough energy from a keypress to send radio signals. This enables batteryless 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, EnOcean’s third generation of electromechanical converters has recently been introduced to market. Combined with a wireless transmitter module, the converter incorporates all of the components and functions of batteryless 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 batteryless 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.

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

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.

EnOcean’s ECO 200 energy converter for motion energy harvesting.

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.

Key characteristics

This next-generation energy converter offers a higher number of cycles, greater efficiency of energy conversion and an improved size when compared with the previous generation. Weighing less than 3 ounces and measuring just under 0.28 inches in height, the converter can be integrated into lightweight, slim-line devices. The typical actuating force of 3.5 N is easily produced by manual operation, for example, and can be reduced even further in the overall design if necessary.

The number of switching cycles offered by the converter depends on the precision of the stimulus. With the maximum allowed contact travel of 0.04 inches, more than 300,000 switching cycles are typically completed. With shorter contact travel, the converter switches at the latest after 0.03 inches of spring deviation, significantly more than a million switching cycles are possible. This means a switch can be operated 100 times a day for more than 25 years.

With 120-microwatts of energy, a stabilized voltage of 2V and an according wireless batteryless module, it is possible to transmit three radiotelegrams per operation over a distance of up to 900 feet in open spaces or 90 feet inside buildings. This energy conversion works in both actuating directions. The return movement delivers another energy pulse and so allows start/stop signals to be transmitted, which can be used for functions such as door and blind control or light dimming.

Key characteristics of the ECO 200 energy converter.

Design-in rules

The self-powered wireless module can be connected to the energy converter without soldering thanks to spring contacts and is simply snapped into a suitable plastic housing. This ensures a reliable connection that can be assembled at low cost. The energy converter connects to the board via gold-plated spring contacts that compensate for any assembly tolerances.

ECO 200 snap connects to wireless module.

To ensure that the energy converter can consistently meet the specified characteristics, such as a long lifecycle and high energy output, manufacturers should take a number of design rules into account when installing the device in the respective application. The ECO 200 should be firmly connected via the interfaces indicated (free of play) and the minimum actuation stroke of 0.7 inches on the leaf spring should be strictly observed – these are decisive factors for reliable operation. The maximum actuation stroke of 0.13 inches is also important for ensuring that no premature damage occurs to the converter.

The following table gives an overview of the most important design-in rules manufacturers should consider when integrating the energy converter into a case:

Design considerations for the ECO 200. Click on images to enlarge.

Faster development with a starter kit

EnOcean offers the next generation mechanical energy converter also in a starter kit. Including a variety of energy converters and modules, the kit enables a faster creation of several energy-autonomous wireless sensors. The kit consists of a switch module for building services, a mechanical energy converter with the matching switch module including a sample case, a temperature sensor module, an USB gateway and PC software for visualization.

With the switch module it is possible to implement energy-autonomous wall mounted switches or handheld transmitters. The combination of mechanical energy converter and the according switch module is the basis for a variety of maintenance-free wireless switches in an industrial environment. The solar-powered sensor module can measure temperature in a room or on machinery, for example. The USB bidirectional gateway transfers both measured data and switch commands to a PC. Data is received via the PC software, which visualizes all information on the computer, giving the user a real-time view of all that is happening.

ESK 300C starter kit.

This complete starter kit enables virtually all basic application variations of energy harvesting wireless technology. Using the starter kit’s components, users can implement switches and interior temperature sensors plus a variety of industrial switches, such as wireless position switches, solutions to control gates or for condition monitoring. Additionally, the USB gateway enables visualized monitoring of all activities in the network.

Application: stop button for buses

Applications are appearing in the public transport sector, such as BMAC’s wireless stop button for buses. While other pushbuttons need to be connected to the battery of the bus via yards of cable, this stop button functions with a small battery-free wireless module. When a passenger presses the stop button, the mechanical energy converter converts this small movement into electrical power and a radio signal is sent to the receiver module. This activates the stop display and the audible stop signal. The transmitted radio signal is unique to each stop button, so there is no interference with other buttons in this bus or other buses nearby. The receiver module is connected to the vehicle electronics. After installation, each stop button in the bus is programmed for its own logic circuit – for example front, middle, rear or wheelchair users. The self-powered solution saves over 100 yards of cabling in the bus, and there is no longer any need to replace defective cables, which can be time-consuming.

Bus-stop button.

Application: cable harness checking

As application example from the automotive sector: the company SEMD, a German-based provider of products and services for electro-technical and medical industries, has developed a tester to verify proper assembly of complex wire harnesses. An automotive cable harness consists of numerous interconnected cables and requires up to one hundred unique connectors. Employing energy harvesting wireless technology, SEMD confirms proper placement and connection when the harness is snapped into the harness panel. This mechanical motion generates electricity to send radio signals to the quality assurance system confirming each connection point was properly connected.

The individual test components can be exchanged speedily and simply without altering the entire support device. The system is integrated in a PC-based network, enabling operation by conventional server technology. Using this wireless testing a cable harness manufacturer can cut production time plus substantially reduce production costs by 35 to 48 percent.

Automotive cable harness testing makes use of mechanical energy
to generate control signals

Application: machine monitoring

Self-powered wireless technology can also be used to monitor and control large-scale industrial facilities. When monitoring the status of machines, for example, sensors can collect data on wear and tear, consumption levels or the necessary maintenance intervals, and report deviations or irregularities. The batteryless solutions can be mounted wherever they are needed, for example on moving machine parts, and moved again later as required. This gives plant operators extremely reliable data that can prevent unscheduled production downtime. Moreover, the technology can be used to control barriers, unlock gates and monitor cold chains or the status of container doors during transport.

The technology of energy harvesting switches and sensors enables numerous other fields of application in buildings, transport and industry. With this ready-to-go system, device manufacturers can implement individual wireless switching solutions based on energy harvesting wireless technology quickly and easily. Using the open wireless standard ISO/IEC 14543-3-10 as a guiding principle, batteryless products can be combined seamlessly with industrial controls and receivers from a wide range of vendors providing flexibility in system planning and implementation.

About the author: Frank Schmidt, CTO and co-founder, EnOcean GmbH

Frank Schmidt is a pioneer of energy harvesting and a member of the management team at EnOcean. As chief technology officer, he is responsible for the overall technical orientation, patent-related activities as well as the relationship management with educational, research and scientific organizations. Before joining EnOcean, he was at the central research department of Siemens AG where he created self-powered wireless sensor technology as early as 1995. He has been granted more than 40 patents for his energy harvesting inventions and is the author of numerous technical publications in this field. Frank studied physics at the Technical University of Chemnitz, Germany.

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