DC-Micromotors

Keeping an eye on the temperature with the right drives

Keeping an eye on the temperature with the right drives

Keeping an eye on the temperature with the right drives

Keeping an eye on the temperature with the right drives

Thermal imaging cameras can make an important contribution to breaking chains of infection. With their help, for example, sick people can be quickly and easily detected upon arrival at the airport. Thermographic methods are also suitable for detecting heat leaks in buildings or for industrial quality control, as product properties often depend on precisely set temperatures. Hot rolling, laminating or glass tempering are typical examples. DC micromotors and small stepper motors are indispensable in all these cases, for example to precisely adjust the focus and zoom of optical thermography systems.

Fever is usually an indication of an infectious disease. Even if the increased temperature is not necessarily caused by the Corona virus, it offers a clue for closer examination. Once this symptom has been recognised in a traveller, targeted tests can then be carried out and further immediate measures taken. A major advantage of temperature measurement by thermal imaging camera is its suitability for mass use. The procedure is contactless, takes only a few seconds and can be automated. It can therefore be used at the airport, at border controls or in other lock situations without significantly restricting people's freedom of movement.

Non-contact temperature measurement: from bolometers to quantum wells

For fast and relatively reliable temperature measurement on the human face, the best place is the inner corner of the eyelid on the eye. Unlike the forehead, which can cool down considerably due to sweating, the temperature at this point is very constant. It can be determined from the infrared radiation that emanates from the surface of the body. Most thermal imaging cameras capture this radiation in a similar way to normal digital cameras with an image sensor that has up to one million pixels. Each pixel of this image sensor is a tiny so-called bolometer, a thermal receiver a few square micrometres in size. It is only 150 nanometres thin and is heated by thermal radiation within 10 milliseconds by about one fifth of the difference between the temperature of the object and its own temperature. The temperature curve on the detected surface is calculated from the sum of these values. In the optical representation, this results in the thermal image with the familiar colour shading: the brighter, the warmer.

Apart from the bolometer, there are other methods to measure the temperature contactlessly and "optically". For example, certain types of sensors detect the wavelength of the radiation and derive the temperature from it. However, wavelength detection and bolometers are not only used to measure fever in humans. Another typical application is the search for temperature leaks in the insulation of buildings. Less well known, but also widespread, is the use of thermography for quality control. Whether metal, plastic or glass, in thermal processing steps the quality of the product often depends decisively on a precisely set temperature. That is why processes such as hot rolling, laminating or glass tempering are often monitored with thermal imaging cameras. In the case of solar cells, thermography detects damage in the structure by means of power-hungry "hotspots". Thermography also plays an important role in security technology. For example, a heat scan can reveal overheated electrical components in a control cabinet or hot-running bearings in machines long before they reach a critical state.

Another method of determining temperature is used in atmospheric and space research: the quantum well infrared photodetector (QWIP). It consists of alternating, very thin semiconductor layers and uses a quantum effect. The layers restrict the quantum mechanical states that a particle can assume there. Incoming infrared waves influence the state. Meaningful images can be obtained from this. Thermal imaging cameras that use this method are characterised by particularly high-resolution "colours" in the range of up to 10 mK. There are also thermographic methods that do not rely on the existing thermal radiation, but turn the tables, so to speak, with active illumination: An infrared light source illuminates the observed scene like an ordinary photo spotlight, the camera becomes a night vision device. This method is used, for example, in anti-terrorist operations in dark rooms. The infrared light remains invisible to the target.

The right drive solution for every task

Whichever method is used, electromagnetic waves must always be collected, bundled and directed to the respective receivers for measurement and imaging. In principle, this works in a similar way to visible light in "normal" photography and the same optical elements are used: To focus and zoom, lenses are moved, apertures are adjusted, filters are brought into position and shutters are operated. With the bolometric method, the heat pixels must also be recalibrated at short intervals so that points with the same temperature appear equally bright in the image. To do this, most devices automatically move a black shutter in front of the sensor to adjust all pixels to the same value. The faster this shutter moves, the shorter the dead time, i.e. the time it takes for the shutter to move.

For all these applications, drives are needed that work as efficiently as possible, are compact and can be controlled precisely. In addition, they should be easy to integrate into the application. It is therefore no wonder that DC microdrives and small stepper motors from the product range of drive specialist Faulhaber are widely used in thermographic devices. For example, DC-Micromotors of the 1524...SR series are often used for focus and zoom in optical devices. The precious metal commutated DC motors with a diameter of only 15 mm and a length of 24 mm operate without cogging, deliver a torque of 2.8 mNm with a very low power consumption and, on top of that, are extremely light thanks to their high power density with a weight of only 18 g. Even when drives are used in extremely small dimensions, they can be used in a wide range of applications. Even if drives are to find space in extremely small micro lenses, there are suitable motors. Here, DC micromotors with diameters of only 8 or 10 mm can be integrated, which also impress with their power density.

For the movement of filters and shutters, stepper motors are often the best choice, e.g. the type DM0620 in combination with an integrated spindle. The two-phase disc magnet stepper motor is only 9.5 mm long with a diameter of 6 mm and delivers 20 steps per revolution. In addition, the extensive product range includes many other motors that are suitable for use in optical devices, including matching gearheads, encoders and other accessories. A suitable solution can therefore be found for practically any application. The drive components have already proven themselves in conventional optical systems for many years. This also applies to the automatic, motorised alignment of cameras on pan-tilt racks. Here, among other things, the compact and low-vibration stepper motors from Faulhaber find a typical area of application.

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