Multichannel microelectrode manipulator is an important instrument for neural research.

State-of-the-art miniature motors are playing a pivotal role in the micro-world of nerve cells when it comes to research to develop new therapies for Parkinson’s disease and other nervous disorders.  Data are also being used to improve the use of control interfaces for artificial limbs, writes Jim Lostetter in the August issue of Medical Design.

Lostetter is Manager–Faulhaber DC Motors, MicroMo Electronics (micromo.com), Clearwater, FL.

An important instrument for neural research is produced by the Thomas Recording GmbH, (thomasrecording.com) Giessen, Germany The multichannel micro­electrode manipulator system lets simultaneous measurements be taken in different areas of the plexus. Its miniature drive by Faulhaber GmbH, (faulhaber.com) Schönaich,Germany, enables complex, precisely controlled motion in small spaces.

Many diseases, disabilities or consequen­ces of accidents result from injuries or ­disorders of the nerve cells. Loss of sight, phantom pain following amputation, ­control of artificial limbs, and Parkinson’s disease represent fields of intense medical research. Successes like electronic visual aids for the blind or aural implants for deaf persons are apparent. However, researchers depend on mecha­nical tools for onsite measurements to reach competent results. Since nerve cells and even nerve fibers or united cell structures are naturally very small, capillary quartz glass-insulated platinum-tungsten re­cor­d­ing electrodes diameters of 80 µm are used.

The electrodes of the three- or five-channel units can be ­positioned independent of each other. The units weigh only 250 g or 300 g and allow positioning distances of 1 µm to 15.000 µm. The relocation speed lies between 1...200 µm/s. The XYZ manipulator can cover and reproduce distances of Z = 0...30 mm, X = ± 10 mm and Y= ± 10  mm.

The necessary motion of the electrode fiber is realized by a silicone rubber electrode drive hose. This pinpoints repeatable and verifiable measurement results. The defined preload of the vibration-damping silicone rubber drive hose is maintained continually. With 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. One small drive is required per channel. ­And each is powered by an EC miniature motor.

The demand for minimum unit dimensions results from the restricted conditions in the small casing. Special demands are placed on reliability because the tests are expensive and complex. The load of the silicone rubber hoses must be precisely 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 allow for the selection of 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 high resolution of the EC motors is increased further by the gearing, depending on the gear reduction ratio and version (standard or free of play).

Looking ahead, state-of-the-art miniature drives will continue to serve as precise power sources for medical research as miniature drive ­specialists are contacted early during the development of applications.