Text: Andreas Schmitz
ICRA 2024: MIRMI scientists receive Best Paper Award
NEWS, Research, Robotics |



What did you find out?
Mehmet Can Yildirim: Currently, the definition of dynamic manipulation for robots is limited to manipulators that can perform pick-and-place tasks rapidly. On the other hand, humans can perform various dynamic manipulation tasks easily; throwing objects or catching them while moving is common in our lives. However, when we transfer such capability to robots, we question how to allow robots to perform such impactful and dynamic motions.
The state-of-the-art answer to this question is to use robots with joint elasticities. One of the most fundamental and excessively used joint architecture is the Series Elastic Actuator (SEA), which is very simple: between the speed reducer and link, a spring is added. By temporarily storing and releasing energy in the springs, elastic robots can outperform rigidly actuated systems with similar motor characteristics. Highly dynamic maneuvres such as jumping, kicking and throwing are now within reach. Nevertheless, the timing of the energy storage and release mechanism is not independent. Therefore, optimal motions for SEA-type systems can be characterised as resonant excitation signals, i.e. oscillatory swing-up motions that exploit the system’s natural frequencies. This approach can be inefficient and potentially dangerous. Our research team has addressed this challenge by introducing a novel Bi-Stiffness Actuation (BSA) design.
The key innovation in BSA lies in its ability to independently control the storage and release of energy within the actuator's spring. Unlike SEA, BSA is not restricted by the system's resonance. This allows for more precise control over link motion and achieving higher velocities in a shorter timeframe.
What have been the main challenges during your research?
Mehmet Can Yildirim: To show that the BSA concept can be applied, we went through different mechanism concepts that can limit the motion of the spring while decoupling the link from the system. One initial hurdle involved replicating the mechanism's ability to seamlessly switch between a "hold" state and a "decoupled" state. Simply engaging and disengaging the spring while loaded would create an uncontrolled release of energy, similar to abruptly turning on a faucet with high pressure. Our team explored various design options to overcome this challenge, prioritising solutions that minimised additional weight and complexity.
One significant obstacle involved translating the theoretical switch-and-hold mechanism of BSA into a functional physical prototype. While the concept held promise in simulations, the physical implementation presented unique challenges. Unlike existing actuator designs with established limitations, BSA ventured into new territory. There were no existing boundaries or established "dos and don'ts" from previous studies to learn.
State-of-the-art robot joints are reached to the point that the necessary states that someone reads or controls are known. However, with such a new concept, we didn’t know which data we would need for sure or wouldn’t. Given this, several redundancies were added to the system. These redundancies were added not only to control our concept but to study it as well.
Where do you see practical scenarios for your research?
Mehmet Can Yildirim: As mentioned previously, we humans, our motions aren’t bound only to simple quasi-static and pick-and-place-like motions; even for a simple task, we can throw catch objects daily if we want. One exciting potential application of BSA technology is enabling robots to perform dynamic throwing motions. Currently, robots in warehouses and other industrial settings primarily perform pick-and-place tasks. BSA's ability to achieve high, controlled velocities opens the door for robots to perform throwing actions, significantly expanding their range of capabilities. Imagine a warehouse robot effortlessly tossing boxes onto pallets or sorting objects by throwing them into designated bins. Combining BSA's dynamic actuation with a robot's superior precision, we can envision a future where robots seamlessly integrate throwing motions into their tasks, leading to a more versatile and efficient robotic workforce.

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