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Head mounted medical vision system sets new standards

Head mounted medical vision system sets new standards
Keyhole surgery has driven a new paradigm in high precision procedures, but it takes considerable effort to identify small structures with the naked eye, and magnifying glasses and stationary stereoscopic microscopes are impractical. But a new kind of optical system is revolutionising work on micro structures.

Working with magnifying glasses and microscopes greatly limits freedom of movement in surgical operations. With magnifying glasses, the distance from the object is fixed, and microscopes are usually cumbersome and impractical. In addition, there is a very limited field of vision with both solutions. Life Optics, an Austrian high-tech company within this field, has found much sought-after remedy: a state-of-the-art microscope head set. This cutting-edge solution offers unlimited freedom of movement. The system has autofocus functionality, so the user does not have to stay at a specific distance - a key benefit compared with magnifying glasses. Furthermore, the two independent lens systems guarantee a three-dimensional field of vision.

Infinitely variable zoom function, autofocus and parallax control demand complex mechanics when it comes to adjusting the head-mounted operation microscope. In order to provide a compact, reliable and light-weight solution, Life Optics teamed up with Faulhaber Group Company PRECIstep, a specialist in micro-stepper motors. The result was high-precision technology in the smallest possible space. In the basic version, available as Varioscope AF3, users can move freely in a working distance of 300 to 600 mm. The foot-operated zoom function allows infinitely variable magnification from 3.6 to 7.2. The field of vision is 30 to 144 mm, and the pupillary distance can be individually adjusted to each user. 

The Varioscope M5 provides an extendible modular optical system. Changeable oculars extend the magnification range, and integrated lighting addresses the problem of shadows. An extended possibility of adjustment for individual eye data is a particularly user-friendly solution. With an optional video camera, procedures carried out by the user can be precisely recorded. Thus, Life Optics has come up with a scalable solution tailored to a range of different requirements. And, thanks to its ingenious design, the device can be effortlessly transported from one workplace to another.

Micro-stepper motors
This highly complex yet portable system relies to a large extent on state-of-the-art micro-stepper motors. Unlike DC motors, stepper motors move on per pulse at a step angle dependent on their specific design. Thus, the number of digital pulses output always corresponds to a defined rotation. As a result, additional linear or angular position sensors are not required. The construction of the drive is smaller and lighter, and it is simpler to control. The Varioscope requires two motors for each eye. The AM 1020 at a diameter of 10 mm for the focus setting and the AM 0820 at a diameter of 8 mm for the zoom. The focus drive operates more or less continuously, as it has to compensate for every movement of the head.

Vision systems of this size are precision instruments and make particularly high demands on the accuracy of positioning. The problem of inaccuracies due to 'play' in the mechanics was solved by PRECIstep by using a spindle with micro-toothing. With a pitch of 0.2mm and in conjunction with the built-in motors, it allows a resolution of 10µm. Both focus and zoom are set absolutely backlash-free and without jolts at high resolution. For this reason, the spindle shafts are also given an additional fine polish, a process which is normally only used in precision watches. In conjunction with a special lubricant, the level of friction is reduced considerably and thus also the initial breakaway torque.

Stepper motors are suitable for many positioning tasks. These miniature units can accelerate up to 1200 rpm in one step and without overshooting. The use of high-quality NdFeB magnets with superior temperature resistance is the key to their performance. Indeed, the motors are able to provide continuous problem-free operation at 70°C housing temperature for a period of several days - without interruption. In this case, the coil may actually reach a temperature of 120°C and the magnet up to 100°C - without any limitation on service life or effectiveness. A special lubricant that is particularly stable against temperature and aging supports these properties. The Faulhaber product range is exclusively distributed in the UK and Ireland by EMS.
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