Vision Systems for Micro Surgery

The continuing movement for more precise procedures in medicine is combining with increased availability of miniature devices to bring new possibilities to keyhole surgery, dental technology, and for industrial uses as well.

In the past, surgeons worked with magnifying glasses and microscopes in performing precision procedures.

Today a new optical system using miniature stepper motors for each eye, mounted on and worn as a headset is permitting crystal-clear views of even the smallest vessels.

Due to their physical nature, use of microscopes and magnifying glasses limits freedom of movement in surgical procedures. Because the human body is like other natural phenomena, nothing has a standard positioning and dimension, so the limited field of vision encountered with microscopes and magnifying glasses poses additional problems.

An answer to these issues has been developed by Lifeoptics of Vienna, Austria. It has developed a state-of-the-art headset that offers auto focus and uses two independent lens systems that result in a 3-dimension view.

The basic version of the headset is Varioscope AF3 and incorporates an infinitely variable zoom function, auto focus, and parallax control. In order to achieve these ends, the unit uses microstepper motors from the Faulhaber Group company, ARSAPE. In use, the headset allows users to see clearly in an area distant from the object from 300 to 600 mm. Magnification is varied from 3.6 to 7.2 through a foot-operated zoom. With two different lenses, the distance of the user's pupil from the object is individually adjusted. The field of vision is from 30 to 144 mm.

Another model, the M5, offers an extendable modular optical system with changeable oculars to extend the range of magnification. The model has integrated lighting to eliminate shadows. Optionally there is a video camera to permit recording of procedures. Due to the overall lightweight of Varioscopes, they move easily from one venue to another.

Micro-stepper motors enable portability and precise focus. These motors move per pulse at the step angle defined in their specific design. As a result, the number of digital pulses output always correspond to a defined rotation, eliminating the need for linear or angular position sensors. Drives are smaller, lighter and simple to control.

Varioscopes utilize two motors for each eye with the ARSAPE AM 1020, with a diameter of 10 mm, used for focus, and the ARSAPE AM 0820, with an 8 mm diameter, for the zoom. Drives are continually operating, compensating for every head movement.

With the challenge of maintaining accuracy of positioning that might be caused by mechanical play in a vision system that requires such a high degree of accuracy, ARSAPE uses a spindle with micro-toothing, resulting in both focus and zoom that are free of backlash and have no jolts at high resolution. The spindle shafts are given an additional fine polish and work in conjunction with a special lubricant that reduces friction and initial breakaway torque. There is additional pre-tensioning on the precision ball bearings by disk springs to achieve zero-backlash movement at torques to 1 N.

Miniature stepper motors are suitable for many positioning tasks. They can accelerate to 1,200 rpm in one step without over-shooting. Use of high-quality NdFeB magnets with superior temperature resistance is key to their performance. Motors can provide continuous problemfree operation at 70º C housing temperature for several days, without interruption.

Too, these stepper motors use 3 V operating voltage where DC motors require at least 5 V control voltage for sensor technology. Miniature stepper motors may be supplied for operating voltages to 12 V.

To learn more about the Varioscope systems, visit www.lifeoptics.com. For more details on miniature stepper motors, visit www.faulhabergroup. com/arsape. TMD