Andre Rosendo

Soft Manipulators and Grippers: A Review

Soft robotics is a growing area of research which utilises the compliance and adaptability of soft structures to develop highly adaptive robotics for soft interactions. One area in which soft robotics has the ability to make significant impact is in the development of soft grippers and manipulators. With an increased requirement for automation, robotics systems are required to perform task in unstructured and not well defined environments; conditions which conventional rigid robotics are not best suited. This requires a paradigm shift in the methods and materials used to develop robots such that they can adapt to and work safely in human environments. One solution to this is soft robotics, which enables soft interactions with the surroundings whilst maintaining the ability to apply significant force. This review paper assess the current materials and methods, actuation methods and sensors which are used in the development of soft manipulators. The achievements and shortcomings of recent technology in these key areas are evaluated, and this paper concludes with a discussion on the potential impacts of soft manipulators on industry and society.

Pneupard: A biomimetic musculoskeletal approach for a feline-inspired quadruped robot

Feline locomotion combines great acrobatic proficiency, unparalleled balance and higher accelerations than other animals. Capable of accelerating from 0 to 100 km h-1 in three seconds, the cheetah (Acinonyx jubatus) is still a mystery which intrigues scientists. Aiming for a better understanding of the source of such higher speeds, we develop a biomimetic platform, where musculoskeletal parameters (range of motion and moment arms) from the biological system can be evaluated with air muscles within a lightweight robotic structure. We performed experiments validating the muscular structure during a treadmill walk, successfully reproducing animal locomotion while adopting an EMG based control method.

Stretch reflex improves rolling stability during hopping of a decerebrate biped system.

When humans hop, attitude recovery can be observed in both the sagittal and frontal planes. While it is agreed that the brain plays an important role in leg placement, the role of low-level feedback (the stretch reflex) on frontal plane stabilization remains unclear. Seeking to better understand the contribution of the soleus stretch reflex to rolling stability, we performed experiments on a biomimetic humanoid hopping robot. Various reflex responses to touching the floor, ranging from no response to long muscle activations, were examined, and the effect of a delay upon touching the floor was also examined. We found that the stretch reflex brought the system closer to stable, straight hopping. The presence of a delay did not affect the results; both the cases with and without a delay outperformed the case without a reflex response. The results of this study highlight the importance of low-level control in locomotion for which body stabilization does not require higher-level signals.

Development of a minimalistic pneumatic quadruped robot for fast locomotion

In this paper, we describe the development of the quadruped robot “Ken” with the minimalistic and lightweight body design for achieving fast locomotion. We use McKibben pneumatic artificial muscles as actuators, providing high frequency and wide stride motion of limbs, also avoiding problems with overheating. We conducted a preliminary experiment, finding out that the robot can swing its limb over 7.5 Hz without amplitude reduction, nor heat problems. Moreover, the robot realized a several steps of bouncing gait by using simple CPG-based open loop controller, indicating that the robot can generate enough torque to kick the ground and limb contraction to avoid stumbling.

Muscle roles on directional change during hopping of a biomimetic feline hindlimb

Cats, from tiny domestic cats (Felix Catus) to big tigers (Panthera Tigris), are well known for their great acrobatic skills and hunting ability. Aiming to better understand how the feline family interacts with the environment, we adopt a biomimetic approach on a hopping feline hindlimb. Using air muscles to simulate the compliance of biological muscles, this robotic hindlimb has seven muscles and changes hopping direction. We individually evaluate and estimate muscles contribution to the jumping direction. Finally, we successfully control the hopping direction using a non-linear curve fitting from experimental results, hopefully contributing to the understanding of our biological counterpart.

Improving hopping stability of a biped by muscular stretch reflex

Animals have several peripheral feedback control networks such as stretch reflexes that are supposed to be contributing to stability of their behavior. In this paper, we focus on rolling stability of hopping of a biped robot, and investigate several schemes on an experimental robot for implementing the stretch reflex: no reflex, undelayed and delayed reflex, how they contribute to the stability. For eliminating effect of changing environment and initial postures, we conduct large number of hopping experiments on a real robot. From the experimental results, we can conclude (1) two reflex schemes, with delay and without delay, can both increase the frontal stability in hopping, and (2) the delay time has little influence on the stability. By these result, we can derive a stable hopping controller for a biped robot, and may be able to understand the mechanism of human adaptive hopping as well.

A Yank-Based Variable Coefficient Method for a Low-Powered Semi-Active Power Assist System

In this paper, we developed a power assist system to help users on carrying heavy loads. This system uses the user input force and position to generate an aiding force, reducing the burden on carrying heavy loads. We adopted a semi-active methodology, combining an active with a passive element, aiming to match the best traits from both, and also considering a lighter motor, which makes the system reach its limit force. To control this lightly actuated semi-active system we proposed a proportional controller which has its gain tuned accordingly to the yank value; this is calculated by the derivative of the force. The controller method herein amplifies the system response whenever the user intends to change his movement, producing a better handling of the system and saving actuator power for either periodical or non-periodical movements. Future applications may involve creating a light assist system for portable applications or assist in heavy industrial environments.

Producing alternating gait on uncoupled feline hindlimbs: muscular unloading rule on a biomimetic robot

Studies on decerebrate walking cats have shown that phase transition is strongly related to muscular sensory signals at limbs. To further investigate the role of such signals terminating the stance phase, we developed a biomimetic feline platform. Adopting link lengths and moment arms from an Acinonyx jubatus, we built a pair of hindlimbs connected to a hindquarter and attached it to a sliding strut, simulating solid forelimbs. Artificial pneumatic muscles simulate biological muscles through a control method based on EMG signals from walking cats (Felis catus). Using the bio-inspired muscular unloading rule, where a decreasing ground reaction force triggers phase transition, stable walking on a treadmill was achieved. Finally, an alternating gait is possible using the unloading rule, withstanding disturbances and systematic muscular changes, not only contributing to our understanding on how cats may walk, but also helping develop better legged robots.

Design Principles for Soft-Rigid Hybrid Manipulators

In nature, manipulators have evolved into different morphologies with varying rigidity to accomplish different tasks. Soft and continuum tentacles of the octopus, rigid and strong pincers of the crab and ligamentous jointed fingers of the human demonstrate the relationship between the complexity of a host’s task space and the design of its manipulator. Thus, the purpose of use a robotic manipulator should be considered as an important design parameter which governs the choice of appropriate materials and design rules. For tasks which require delicacy and strength at the same time, such as human-machine interaction, agriculture or robotic surgery hybrid soft-rigid manipulator designs should be investigated. Here, we present four design principles for building hybrid robot manipulators which incorporate soft and rigid materials and demonstrate each principle with working examples.

Improving Efficiency for an Open-Loop-Controlled Locomotion With a Pulsed Actuation

Open-loop control strategies for legged robot locomotion have been investigated by many researchers because of the advantages in terms of simplicity and robustness, although the influence of control inputs to locomotion performance is not fully clarified. This paper investigates two of the most basic forms of control input, sinusoidal and pulsed signals, to be used in a class of hopping robot based on parallel elastic actuation. Our results show that a pulsed torque outperforms its sinusoidal counterpart with a lower energy expenditure. Moreover, the pulsed driving torque is capable of keeping the same energy efficiency, while changing the forward hopping velocity, which is not possible with the sinusoidal driving torque. Such findings will help shape the future of robotics by achieving higher energy efficiencies within legged robots, while maintaining behavioral diversity.