Towards a Passive Adaptive Planar Foot with Ground Orientation and Contact Force Sensing for Legged Robots

Adapting to the ground enables stable footholds in legged locomotion by exploiting the structure of the terrain. On that account, we present a passive adaptive planar foot with three rotational degrees of freedom that is lightweight and thus suited for highly dynamic legged robots. Its low laying pivot joint provides high stability towards kinking. Information about the relative foot sole pose, and accordingly, the ground orientation is gathered by inertial measurement units (IMUs) placed on the foot sole and the shank. A complementary filter is presented that fuses these orientation estimates with an angular encoder to obtain a drift-free relative foot sole pose. The passive adaptive planar foot has been tested and compared to the classical point foot design on a variety of terrains and shows superior traction performance, especially on compressible soils. Being mounted on the quadrupedal robot ANYmal, the foot provides a reliable contact detection based on the fusion of the built-in 6-axis force/torque transducer and the IMUs. This allows to walk and trot on uneven terrain, loose soils, as well as climbing up a ramp and stairs while keeping the entire foot sole in ground contact all the time.

Friction and damping of a compliant foot based on granular jamming for legged robots

Peter Eckert, Simon Lukas Hauser, Auke Ijspeert, Alexandre Tuleu

Moving away from simple foot designs of current quadruped robots towards a more bio-inspired approach, a novel foot design was implemented on the quadruped robot Oncilla. These feet mimic soft paw-pads of dogs and cats with high traction and soft underlying tissue. Consisting of a granular medium enclosed in a flexible membrane, they can be set to different pressure/vacuum conditions. Tests of general properties such as friction force, damping and deformation were completed by proof of concept tests on the robot. These included flat ground locomotion as well as ascending a slope with different inclination. Comparison tests with the previous feet were performed as well, showing that the new feet have a high friction and strong damping properties. Additionally, the speed of flat ground locomotion is comparable to the maximum speed of the robot with the previous feet while retaining the desired trotting gait. These are promising aspects for legged locomotion. The jamming of granular media previously has been used to create a universal gripper which in the future also opens up opportunities to use the feet both in locomotion and simple object manipulation (although the manipulation is not tested here).

Ieee2016

Compliant universal grippers as adaptive feet in legged robots

Simon Lukas Hauser, Auke Ijspeert, Mehmet Hasan Mutlu

This work investigates the usage of compliant universal grippers as a novel foot design for legged locomotion. The method of jamming of granular media in the universal grippers is characterized by having two distinct states: a soft, fluid-like state which in locomotion can be used to damp impact forces and enable passive shape adaptation especially on rough terrain, and a hard, solid-like state that is more suited to transmit propulsion forces. We propose a system that actively uses and switches between both states of a foot design based on granular jamming and detail the implementation on a quadruped robotic platform. The mechanism is inspired by the stiffness varying function of the tarsal bones in a human foot, and our aim is to understand how the change of foot stiffness can be used to improve the locomotion performance of legged robots. Using the same open loop trot gait in all experiments, it is shown that a fast state transition enables the robot to profit from both states, leading to more uniform foot placement patterns also on rough terrain compared to other tested feet. This results in overall faster gaits and even enables the robot to climb steeper inclined surfaces.

2018

Compliance, locomotion and local computation in (self-) reconfigurable modular robots

Simon Lukas Hauser

Animals display an enormous versatility and a remarkable ability to adapt to changes in environment and terrain. Research in bio-inspired robotics strives to transfer these skills to robots, including legged systems. Even though animals seemingly effortlessly perform most of their activities on rough terrain, this feature seems to be particularly difficult to achieve in their robotic counterparts. We hypothesize that perturbations caused by e.g. rough terrain are not handled by the central nervous system, but rather by local modifications of the locomotion system such as legs and feet. Modifications can include changing mechanical properties such as spring and damping characteristics, as well as adjustments in the movement pattern of the locomotion. In this thesis, we isolate instances where a specific component, in our view, needs such modifications to fulfill different functionalities in a locomotion cycle. Further, we introduce the concept of mode-switches: a local computation is performed to induce these changes in functionalities by changing the dynamical response of the component. We then present one mode-switch method in hardware, jamming of granular media, that can switch the functionality of a foot between impact damping'' and propulsion force transmission'', and we show how this regularizes step sizes on rough terrain. We then present one mode-switch method in control, a force feedback strategy named tegotae''. This switches the functionality of leg movement between displacing the leg'' and

displacing the body'', and we show how this informs the controller about which legs are bearing less weight and thus are more suited to be moved. We suggest that these methods can be applied to any legged structure and use modular robots to demonstrate these concepts. In parallel, we also improved our previously developed self-reconfigurable modular robot platform

Roombots'' such that they perform a variety of tasks centered around adaptive and assistive furniture with up to 12 modules. This includes demonstrations of self-reconfiguration, mobile furniture, object manipulation, interaction capabilities and the development of a user interface. With these improvements, this platform can in the future also be used for further locomotion research where the shape-shifting ability could be of major importance.

EPFL2019

Compliance, locomotion and local computation in (self-) reconfigurable modular robots

Simon Lukas Hauser

displacing the body'', and we show how this informs the controller about which legs are bearing less weight and thus are more suited to be moved. We suggest that these methods can be applied to any legged structure and use modular robots to demonstrate these concepts. In parallel, we also improved our previously developed self-reconfigurable modular robot platform

EPFL2019