Creating the bebionic3 prosthetic

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Faulhaber Motor 1024…SR

Prosthetic and Motor Innovation Go Hand in Hand

Steeper is the leading provider of innovative prosthetic, orthotic and assistive technology products and services.

As an international manufacturer of upper extremity prosthetic products Steeper is further building on the success of the bebionic3, the most advanced commercially available bionic hand in the world today.

Already using powerful 15mm Ø FAULHABER motors in the bebionic3 hand Steeper once again turned to the expertise of Electro Mechanical Systems, the UK’s leading provider of small drive solutions and the long term distribution partner for the Faulhaber Group.

The bebionic3 is already ground breaking and offers full compliancy in its motion with each digit individually powered. However the challenge for the next development was to replicate this functionality, but design a much smaller hand that delivered the same degree of compliance without compromising performance and in so doing opening up the opportunity to a much wider group and transforming the lives of amputees worldwide.

To achieve the goals set out by Steeper Technical Director Ted Varley, it was clear that a high power Ø 10mm motor gearbox and encoder was required. As Ted explained “our design philosophy is to keep the motors in the palm of the hand as this has the advantage of allowing a more efficient gearbox design, as well as bringing the weight closer to the wrist for lower perceived mass thereby allowing full flexing of the fingers and more realistic movement.”

In consultation with EMS and Steeper, FAULHABER developed a brand new 10mm Ø motor complementing the already successful ‘SR’ series.

The new motor 1024M006SR was a completely new construction compared to its predecessor. A new end cap was designed providing easier assembly with the Faulhaber range of optical and magnetic encoders. A new cover and material was used with more accurate brush positioning for increased performance even at higher temperature range and new commutator & brushes were integrated with more accurate segment geometry for a cleaner commutation signal. A totally new coil construction was developed with 60% more copper than its predecessor and in combination with a new rare earth magnet exceptionally high performance was guaranteed. Improved tolerance on the shaft for better alignment & higher efficiency, improved alignment of the bearings and their positioning reduces contamination from the brushes resulting in even higher system efficiency and longer lifetime.

The advances in this motor design resulted in a huge step change and best in class performance when tested in the application especially with consistently high torque even in repeat grip patterns driving up to stall condition. Highly dynamic and with a flat speed/torque curve representing a strong consistent torque across the speed range made this motor ideal for the application. The addition of a robust planetary gearhead and 3-channel magnetic encoder with flying leads including the motor power supply made this combination much easier to package compared to other products and therefore ideal according to Mr Varley.

This was only half the story though as the requirements for a thumb actuator was altogether more challenging!

Based on the same motor technology Steeper were looking for a complete in-line linear actuator in the smallest dimension but capable of delivering high force at the tip of the thumb proximal.

Once again Faulhaber were able to develop a complete actuator solution calling on the competences and synergies of other Faulhaber Group companies. Project managed by an experienced team in Switzerland, FAULHABER were able to integrate a high precision 4-point contact bearing from their Group Company Micro Precision Systems (MPS), enabling them to develop the most powerful and importantly smallest linear actuator capable of sustaining axial forces up to 300N.

The unique characteristic of the high precision 4-point contact bearing and high axial force capability meant that a considerably shorter overall length could be achieved when compared to conventional bearings.

MPS are precision engineers working with sub-micron tolerances and are specialists in miniature balls. Having evolved supplying the watch industry with precision balls down to Ø 0.15mm they are now specialists in developing complex microsystems in the fields of medical devices, biocompatible devices, aerospace, defense and the watch industry. The synergies with the FAULHABER Group and motor technologies including DC, BLDC and stepper motors give design engineers boundless opportunities.

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