Medical tech­nology is a broad field and many of its appli­ca­tions need drive systems, including dental chairs (Fig. 1) with their adjustable head­rests, diag­nostic equip­ment and CT scan­ners (Fig. 2), X-ray and phys­ical therapy equip­ment, lighting systems for oper­ating rooms, and auto­mated posi­tioning units in oper­ating tables, stair lifts and the like. Such appli­ca­tions often call for compact drives with rela­tively low power that have to work very reli­ably and with high posi­tioning accu­racy.

Dura­bility, quiet oper­a­tion, a wide range of speeds and precise speed control are addi­tional require­ments to be met. For such cases, users are well advised to use the config­urable ECI-42 drives from drive specialist ebm-papst. The modular system for drives enables customers to put together customized vari­ants by combining various tested and vali­dated modules such as brakes, encoders, etc. (Fig. 3).

42 mm motor, trans­mis­sion, brake and encoder

Figure 1: Medical equip­ment often needs compact and rela­tively low-powered drives, for example for various adjust­ments on dental chairs.

A great deal of appli­ca­tion exper­tise is involved in the devel­op­ment of compact, elec­tron­i­cally commu­tated, brush­less internal rotor motors. This makes them perfect for use in medical equip­ment, and their users benefit from complete drive solu­tions from a single source. High power density makes the drives very compact, which is helpful when designing equip­ment as it often enables more compact dimen­sions.

At the heart of all the config­u­ra­tions is a brush­less, elec­tron­i­cally commu­tated internal rotor motor with a diam­eter of 42 mm and stator lengths of 20 or 40 mm. It achieves output levels of around 45 or 90 watts at a nominal torque of 110 or 220 mNm and a nominal speed of 4,000 rpm. Its effi­ciency rating is up to 80%. The motors come in stan­dard designs of 24 and 48 VDC safety extra-low voltage. Hall sensors for rotor posi­tion detec­tion are inte­grated, and the motor is actu­ated by an external, closed-loop controller. Inte­grated elec­tronics modules with func­tion­ality such as speed or posi­tion control with optional bus inter­face are already in devel­op­ment.

Trans­mis­sion and brake modules for various require­ments

Figure 2: CT scan­ners need reli­able and quiet drives to mini­mize noise emis­sions.

Various trans­mis­sion modules are avail­able to reduce the high speed of the internal rotor drives and bring the drive torque to an appro­priate level for the appli­ca­tion. Along with plan­e­tary and spur gears with various reduc­tion ratios, space-saving EtaCrown crown gear­heads based on inno­v­a­tive crown-gear tech­nology can also be supplied, for example. The Noise­less­Plus 42 plan­e­tary gear­head guar­an­tees ultra-quiet oper­a­tion and with the Optimax 42 trans­mis­sion (Fig. 4), there is now an extremely rugged, over­load-proof one- or two-stage plan­e­tary gear­head with IP50 or even IP54 degree of protec­tion that also works with the small 42 mm drives.

If the appli­ca­tion in ques­tion demands holding or safety brakes for quick emer­gency stop or, for example, to safely main­tain the posi­tion of lifting equip­ment in the event of a power supply failure, modules with perma­nent-magnet or spring-oper­ated brakes can be added to the drive unit, ruling out risks for the patient. In this way, posi­tions can also be held precisely and securely over longer periods for X-rays.

Measuring posi­tions with high-reso­lu­tion encoders

An encoder module can be inte­grated in the drive unit for precise posi­tion measure­ment. Its magnetic incre­mental encoder works with a reso­lu­tion of 12 bits, which increases depending on the selected trans­mis­sion solu­tion so that a preci­sion of up to 0.08 degrees can be achieved at the output shaft. Optional lower reso­lu­tions are also possible.

Figure 3: The ECI-42 modular system for drives enables customers to put together customized vari­ants by combining various tested and vali­dated modules.

In the next stage of devel­op­ment, there will be an absolute multi-turn module (up to 17-bit reso­lu­tion in the single-turn and up to 32-bit in the multi-turn range). The rota­tion counter works without batteries, instead using an energy-harvesting system based on the Wiegand effect so that the energy needed to store the rota­tion infor­ma­tion is gener­ated from a rotating magnetic field. That makes backup batteries, trans­mis­sions and related main­te­nance work unnec­es­sary.

Prac­tical connec­tors

Figure 4: With the Optimax 42, there is now an extremely rugged, over­load-proof one- or two-stage plan­e­tary gear­head with IP50 or even IP54 degree of protec­tion that also works with the small 42 mm drives.

Customized 42 mm drives put together using ebm-papst’s modular system for drives meet the require­ments for IP50 or IP54 degree of protec­tion and provide a variety of options for elec­trical hookup. These include industry-stan­dard connec­tors, in which the radial angled plug with bayonet connector can rotate and engages auto­mat­i­cally. An axial plug is avail­able for space-crit­ical appli­ca­tions; an alter­na­tive, preassem­bled cable connec­tion is also possible.

The indus­trial-grade drives are ideal for prac­ti­cally all medical equip­ment appli­ca­tions that require energy-effi­cient small drives. Thanks to defined preferred types, selected drive config­u­ra­tions can be deliv­ered within 48 hours, which means that sampling, for example, can be done very quickly. The drives can be config­ured and ordered via the online portal idt-config.ebmpapst.com.