Electro Mechanical Systems has supplied Precistep micro-stepper motors to Life Optics to allow it to develop a compact, reliable and light-weight head-mounted microscope. The result was high-precision technology in the smallest possible space. Each system has two motors, one 8mm diameter and one 10mm, which provide dynamic zoom and focus controls, delivering the high precision and accuracy required for this demanding application.
In the basic microscope version, available as Varioscope AF3, users can move freely in a working distance of 300 to 600mm. The foot-operated zoom function allows infinitely variable magnification from 3.6 to 7.2. The field of vision is 30 to 144mm 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 shadows. With an optional video camera, procedures carried out by the user can be precisely recorded.
Unlike DC motors, stepper motors move on per pulse at a step angle dependent on their specific design so 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 Varioscope requires two motors for each eye: the AM 1020 at a diameter of 10mm for the focus setting and the AM 0820 at a diameter of 8mm for the zoom.
The focus drive operates continuously as it has to compensate for every movement of the head. Inaccuracies due to 'play' in the mechanics were corrected using a spindle with microtoothing. With a pitch of 0.2mm and in conjunction with the built-in motors, it allows a resolution of 10um. Focus and zoom are set absolutely backlash-free and without jolts at high resolution, and the spindle shafts are given an additional fine polish.
In conjunction with a lubricant, the level of friction is reduced, as well as the initial breakaway torque. An additional pre-tensioning on the precision ball bearings by disk springs facilitates zero-backlash movement at torques of up to 1N. The miniature units can accelerate up to 1200rpm in one step and without overshooting. The use of high-quality NdFeB magnets with superior temperature resistance is the key to their performance.
The motors are able to provide continuous problem-free operation at 70C housing temperature for a period of several days without interruption. In this case, the coil may actually reach a temperature of 120C and the magnet up to 100C without any limitation on service life or effectiveness. A special lubricant that is particularly stable against temperature and aging supports these properties. The micromotor has a 3V operating voltage and the miniatures can be supplied for operating voltages up to 12V.
Schott Systeme will be using the Metav exhibition in Dusseldorf to showcase the latest version of its Pictures by PC software for design and machining. This latest release is to include numerous additions to the company's existing full machine-simulation module. By displaying machining directly from generated NC code, this visualisation of milling as it occurs on the shop floor helps to eliminate errors in damaged parts, fixtures and machine crashes.
