3D Printing Is Revolutionizing The Manufacture Of Prostheses

In the past, the production of prostheses and orthoses using the conventional methods was long, complex and therefore expensive. Additive manufacturing promises to remedy this. However, in the practical environment of orthopedic technology, it quickly became clear that the established additive printing processes with just one print head were not economical enough because the manufacturing process was time-consuming and did not meet the expectations of the medical profession.

The Pro-O-light network faced the challenge of improving this situation together with the Mittweida University of Applied Sciences and partners from the mechanical engineering and electrical industries. As part of a project funded by the BMWI, a new printer was to be developed that uses a rotating work table and up to four printheads working simultaneously . Thanks to this new approach, high working speeds can be achieved.

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In less than 60 minutes to the prosthesis

Since the print heads only work unidirectionally, it is possible to design a special print head nozzle geometry. With an average use of four printheads, a prosthesis can be printed in under 60 minutes . In addition, the new process creates a lighter orthosis with an open, comfortable structure. The drive technology, for which the JAT (Jena drive technology) is responsible, plays a decisive role.

How the 3D printer works

In order to achieve the high production speed, it was necessary to use several print heads at the same time and with medium travel distances. However, since these would interfere with their mechanical guides during the printing process, a new technology had to be developed. This consisted of not placing the workpiece on a fixed table or a table that can be moved in the XYZ direction as usual, but rather setting it in rotation during the printing process . Since the geometries already have a tangential alignment of the print head nozzle with the workpiece, much higher printing speeds can be achieved.

Powertrain requirements

A special printhead drive concept is required to achieve the required process speed when printing the prostheses. The new type of printing will make it possible to increase the process speed by a factor of ten. This requires the simultaneous use of several heads and an additional increase in printing speed through the development of a printing head with a new nozzle geometry.

One of the biggest challenges was the interaction of the print heads and their drive:

• Contrary to the current state of the art, the printheads do not have to move to their working position one after the other and carry out the printing process there, but at the same time position themselves individually to the printing geometry - a collision of the printheads is impossible.
• So they are placed at the right tangent at the right time and the right amount of print material is extruded during this dynamic process.
• The constantly changing scope, different speeds for the respective printhead, the associated calculation of different amounts of material and the dependency of these components are a completely new but necessary manufacturing approach.

Drive system for price sensitive applications

The Ecostep drive system was chosen to achieve the cost target. It is particularly well suited for price-sensitive applications because it works with a multi-pole servo motor with feedback in the form of an encoder. Compared to the drive technologies without a closed position controller, significantly higher dynamics and operational safety are achieved since there is no risk that the motor will lose its position. The drive controller also offers high connectivity to higher-level systems such as a PLC.

Seminar tip

Participants in the basic seminar on servo drives learn the basic knowledge of how to optimally parameterize servo drives and how to control and control functions in motion controllers.

The realization of the drives

• The mechanical construction of the 3D high-speed rotary printer requires a total of twelve Ecostep drives.
• Spindle drives are used for the horizontal and vertical Y and Z linear axes, which are responsible for flexible positioning of the extruder.
• The motor is the Ecostep motor from the 23S21 series with an absolute encoder feedback.
• The same type of drive also positions the rotary table.
• Four Ecostep 17H13 motors with incremental encoders are used to convey the material in the print heads specially developed for this application.
• These three axes are interpolated linearly. The algorithm is integrated in the Ecovario D114 servo amplifier. Since this servo amplifier is a compact double output stage, six amplifiers control the twelve motors in total.

User meeting mechatronic drive technology

The focus of the user meeting mechatronic drive technology is on the mechanical components of gears, clutches and brakes as well as their design, dimensioning and interaction in the overall mechatronic system.

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Drives for highly dynamic applications

In order to achieve the best possible printing result in terms of precision and speed, a high level of accuracy of the drives is essential . Especially in such highly dynamic applications, the Ecostep drives show their strengths, because even with fluctuations in load, thanks to the position feedback, exact tracking of the specified path is guaranteed. Because with the Ecostep drives, analogously to classic but also more expensive servo drives, both speed and position are regulated.

On the finishing line

Already now, about half a year before the end of the project, it is assumed that the set target criteria in terms of precision and dynamics will be achieved . The fact that the innovative printing process contributes to better medical care makes their commitment even more valuable. As is so often the case with projects of this type, in which several actors are involved, the devil is ultimately in the details and in the coordination among the actors. Prototypes are already being tested for their practical suitability.