Austrian manufacturers have created a microscope headset that lets doctors examine patients with 3D vision during surgery. The system, from Lifeoptics, Vienna, Austria, (lifeoptics.com), combines the best features of magnifying glasses and microscopes to a portable device.

To create the compact and lightweight design, Lifeoptics used microstepper motors from Faulhaber Group company Arsape, Switzerland, (www.faulhaber-group.com/arsape). Unlike DC motors, stepper motors move one step angle per pulse, an amount dependent on the motor's design. Thus, the number of digital output pulses 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 microscope requires two 3V motors per eye. Traditional dc motors need 5V control voltage. The AM 1020 has a 10-mm diameter for focusing and the AM 0820 has a 8 mm diameter for the zoom. The focus drive operates more or less continuously, as it has to compensate for the surgeon's head movement.

Vision systems of this size are precision instruments that make high demands on positioning accuracy. The problem of inaccuracies due to play in the mechanics is solved using a spindle with micro-toothing. Motors with a 0.2-mm pitch allow a resolution of 10-µm. Focus and zoom are backlash-free and suffer no jolts at high resolution. For this reason, the spindle shafts are also given an additional fine polish, a process normally used only in precision watches. A special lubricant also reduces friction along with breakaway torque.

These units can accelerate to 1,200 rpm in one step and without overshooting. NdFeB magnets with high temperature resistance are key to their performance. The motors operate continuously at 70°C for several days.