On the scent of biological data processing

"To sound someone out", this phrase is familiar to all of us. In the context of nerve cells, however, some medical scientists have taken this statement literally. The complex interplay of individual nerve cells or entire groups of nerves has developed into an increasingly practice­related field of fundamental research. The data acquired here can improve the use of control interfaces for artificial limbs or help alleviate the impact of nervous disorders like Parkinson’s disease with new therapies. Here, too, state-of-the-art miniature motors are the key to success. They represent reproducible, accurate motion with minimal space requirement, an important prerequisite in the µm-world of nerve cells.

Modern science gets to the bottom of things. Working hypotheses are made, then test series are arranged to show if the thesis was right or if totally different preconditions are true. Particularly in the complex field of biological data processing the practical in vivo measurement of nerves sets high standards for the ­measuring equipment. An important instrument for neural research is produced by the Thomas Recording GmbH, Giessen, ­Germany. Their multichannel micro­electrode manipulator systems allow simultaneous measurements in different areas of the plexus. Here a compact ­construction is decisive for easy-to-operate devices. For this reason the measuring expert relies on the miniature drive ­specialist FAULHABER. Small drives ­adapted to the particular application ensure ­complex, precisely controlled motion in small spaces.

A mere "question of nerves"

Many diseases, disabilities or consequen­ces of accidents result from injuries or ­disorders of the nerve cells. Nowadays, loss of sight, phantom pain following amputation, ­control of artificial limbs or Parkinson have thus become fields of intense medical research. First successes like electronic visual aids for the blind or aural implants for deaf persons have become apparent. However, researchers depend on mecha­nical tools for on site measurements to reach competent results. Since nerve cells, and even nerve fibers or united cell structures are naturally very small, all suitable tools have to be filigree: capillary quartz glass-insulated platinum/tungsten re­cor­d­ing electrodes with a diameter of only 80 µm have to be positioned accurately to one cell and reproducibly in the tissue.

Special devices were available before for individual recording electrodes. However, the specialists from Gießen developed new, small and compact multi­channel manipulators for simultaneous measurements. The electrodes of the three- or five-channel units can be ­positioned independent of each other. The units weigh only 250g or 300g and allow positioning distances of 1 µm to 15.000µm. The relocation speed lies between 1...200µm/s. The XYZ manipulator can cover and reproduce distances of Z=0...30mm, X=±10mm and Y=±10mm.

The necessary motion of the electrode fiber is realized by a patented silicon-hose electrode drive. This is the only way to ensure pinpoint, repeatable and therefore verifiable measurement results. The defined preload of the vibration-damping silicone rubber drive hose has to be maintained continually. In case of the three- and five-channel units this function is ­carried out by EC miniature motors with a diameter of 6 mm with suitable transmission attachment. A larger model with up to 32 measuring fibers uses small drives with diameters of 10 mm. Each fiber is ­controlled individually and therefore one small drive is required per channel. ­Absolute "power dwarves" are required for this purpose due to the number of channels.

Small, reliable, accurate

The demand for minimum unit dimensions results from the restricted conditions in the small casing. In addition, special demands are placed on reliability; after all, the test series are expensive and frequently cannot be simply repeated. Therefore the drive must not fail during operation. The third demand is on precision and dynamics. The load of the silicon hoses must be maintained at a nearly constant level and adjusted quickly if necessary. FAULHABER provides specially matched drive components for this purpose.

Electronically commutated DC motors (EC motors) are the drives to choose for fast dynamic and precisely controllable movements. A ball bearing mounted permanent magnet equipped rotor rotates in a stator formed by three coils. These motors are predestined for thousands of failure-free operating hours since only the ball bearings are subject to wear. ­Electronic commutation and low inertia of the small rotor ensure fast implementation of ­control commands.

Naturally, small motors can only gen­erate low torque values, and therefore the necessary power has to be derived from the rotational speed. However, high rotational speeds are unfit for many applications, and therefore the manufacturer offers suitable transmission attachments for individual series motors. These transmissions are made to suit the motor ­diameter and can simply be plugged onto the motor drive shaft. A multitude of stepped gear reduction ratios allows the selection of the optimum rotational speed range or torque increase. In the case of the manipulator systems a gear reduction of 1:625 was chosen. Another advantage for some applications is the positioning accuracy of the miniature motors which was further improved by the gear ­reduction ratio. The per se rather high resolution of the EC motors is increased drastically even further by the gearing depending on the gear reduction ratio and version (standard or free of play).

State-of-the-art miniature drives are a robust and precise power source for ­virtually any purpose and application. ­Perfectly tailored and cost effective drive solutions are the rule if the miniature drive ­specialist is contacted early during the development of an application. In this manner the economic optimum can be achieved – without curtailing the ­functionality. Nowadays, miniature drives are used in outer space, astronomy or the deep sea, in automation as much as in medicine and research, in the shape of standard motors, modified or special drives tailored to suit the appli­cation in ­question.