Recent developments of compliant mechanisms built by additive manufacturing confirm their potential for highprecision applications in harsh environments. Several projects are presented, from simple flexure pivots to complex 3D compliant mechanisms designs, to show the advantages and challenges of the design, manufacturing and testing of such systems. Focus is put on the specific design methodology, the integration of electrical functions, the guiding and lifetime performance results to highlight the potential for future high-precision applications such as high-precision, cryogenic or space.
First, the redesign of simple flexure blades and crossed-blade pivots has been performed. The guiding performances have been compared to simulations. Then, more complex architectures of compliant mechanisms have been designed, manufactured and tested. For example, the European Space Agency (ESA) project Compliant Mechanisms based on Additive Manufacturing (COMAM) and the European H2020 project Prototype for Ultra Large Structure Assembly Robot (PULSAR). This project validates the positioning of tiles integrated on 3D printed flexible pivots and gimbals with a repeatability better than 1 μm. ESA selected CSEM for a new project, the development of a new compliant mechanism with a rotary to linear motion transformation. It is presented here with a novel 3D printed monolithic architecture made of stainless steel.
The CLUPI (CLose-UP Imager) instrument is a high-resolution camera mounted onto the Drill of the ExoMars 2020 rover mission carried out by the European Space Agency (ESA) and Roscosmos. The CLUPI development is under the responsibility of Thales Alenia Space Switzerland whereas the Principal Investigator is Dr. Jean-Luc Josset from the Space Exploration Institute. In the frame of the development CLUPI instrument, the CSEM developed and delivered three models of a flexure-based Focus Mechanism. The CLUPI Focus Mechanism (CFM) design utilizes flexure guides to allow very accurate frictionless adjustment of the focal distance of the imager. Such design must also comply with very stringent requirement from the ExoMars mission, especially regarding the low Martian temperatures and the launch/landing load environment. This article presents the three main challenges encountered during the development of the mechanism and how these were addressed: resilience, performance and reliability. This article then draws the lessons learnt from this development including potential design improvements for a similar design and general rules to applicable to any development involving compliant mechanism.
Based on a new concept to build flexible structures by metallic 3D printing that has been developed at CSEM, several compliant mechanisms have been redesigned for Additive Manufacturing (AM). In addition to the new geometric possibilities offered by AM, the needs for machining and assembly after printing are drastically reduced. Support structures under flexure blades are thus minimized and the overall process becomes more streamlined. Moreover, this idea allows us to advantageously design and produce monolithic cross blade flexure pivots with interlocked flexures. Thanks to this concept, CSEM is now developing and testing new architectures of Compliant Mechanisms based on Additive Manufacturing (COMAM) for the European Space Agency (ESA) in the frame of a GSTP research project.
The use of Additive Manufacturing (AM) processes for space and terrestrial applications is a constantly growing topic of interest from the main actors in the industry. In the perspective of its future developments in the space field and for terrestrial applications, CSEM tackled the challenge of producing compliant structures based on SLM (Selective Laser Melting). In this framework, high performance stainless steel flexures with thickness below 380 micron offering bending fatigue resistance above 15 million cycles under realistic load cases were produced. On the other hand topology optimization software and specific design rules are applied to produce optimized structural parts and monolithic compliant structures. The second part of this paper describes the successful redesign of electrical SlipRings Assemblies (SRA) rotors intended for space applications. This project was run jointly with RUAG Space Switzerland, based on their expertise in the field of space grade SRAs and thanks to the know-how developed by CSEM in the field of AM-based mechanical (re)design. The novel architecture based on the combination of additive manufacturing, casting and remachining enables a significant reduction of the manufacturing and assembly costs and risks.
For the development of the Focus Mechanism of the CLUPI instrument of the ExoMars 2020 mission, the CSEM implemented a design based on flexible structure technology and the use of Commercial Off-The-Shelf (COTS) components. This choice was essentially motivated by the availability of the miniature sensor and actuator components. Such approach presents many challenges such as:
the qualification of the OTS voice-coil motor and Linear Variable Differential Transformer (LVDT),
the implementation of a reliable launch locking system,
the design of a flexible structure mechanism compatible with harsh mechanical environment.
The present article describes each of the above problematics and the investigation carried by CSEM to find solutions meeting the mission needs and constrains.
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