Robotics

17 pages, 9604 KiB

Open AccessArticle

An Arch-Shaped Electrostatic Actuator for Multi-Legged Locomotion

by Yusuke Seki and Akio Yamamoto

Robotics 2024, 13(9), 131; https://doi.org/10.3390/robotics13090131 - 30 Aug 2024

A simple actuator to create non-reciprocal leg motion is imperative in realizing a multi-legged micro-locomotion mechanism. This work focuses on an arch-shaped electrostatic actuator as a candidate actuator, and it proposes the operation protocol to realize a non-reciprocal trajectory. The actuator consists of [...] Read more.

A simple actuator to create non-reciprocal leg motion is imperative in realizing a multi-legged micro-locomotion mechanism. This work focuses on an arch-shaped electrostatic actuator as a candidate actuator, and it proposes the operation protocol to realize a non-reciprocal trajectory. The actuator consists of two hard and flexible sheets and a leg attached to the flexible sheet. The flexible sheet is deformed through an electrostatic zipping motion that changes the height and/or angle of the attached leg. The fabricated prototype weighed 0.1 g and swung about 15 degrees with the applied voltage of 1000 V. The swinging force exceeded 5 mN, five times the gravitational force on the actuator’s weight. Large performance deviations among prototypes were found, which were due to the manual fabrication process and the varying conditions of the silicone oil injected into the gap. The trajectory measurement showed that the leg tip moved along a non-reciprocal trajectory with a vertical shift of about 0.3 mm between the forward and backward swings. The prototype locomotion mechanism using four actuators successfully demonstrated forward and backward motions with the non-reciprocal swing motion of the four legs. The observed locomotion speed was about 0.3 mm/s. Although the speed was limited, the results showed the potential of the actuator for use in multi-legged micro-locomotion systems. Full article

(This article belongs to the Special Issue Recent Trends and Advances on Robotics and Mechatronics within the IFToMM Technical Committee on Robotics and Mechatronics)

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16 pages, 23045 KiB

Open AccessArticle

Tetherbot: Experimental Demonstration and Path Planning of Cable-Driven Climbing in Microgravity

by Simon Harms, Carlos Giese Bizcocho, Hiroto Wakizono, Kyosuke Murasaki, Hibiki Kawagoe and Kenji Nagaoka

Robotics 2024, 13(9), 130; https://doi.org/10.3390/robotics13090130 - 30 Aug 2024

Abstract

In this paper, we introduce Tetherbot, a cable-driven climbing robot designed for microgravity environments with sparse holding points, such as space stations or asteroids. Tetherbot consists of a platform with a robotic arm that is suspended via cables from multiple grippers. It achieves [...] Read more.

In this paper, we introduce Tetherbot, a cable-driven climbing robot designed for microgravity environments with sparse holding points, such as space stations or asteroids. Tetherbot consists of a platform with a robotic arm that is suspended via cables from multiple grippers. It achieves climbing locomotion by alternately positioning the platform with the cables and relocating the grippers with the robotic arm from one holding point to the next. The main contribution of this work is the first experimental demonstration of autonomous cable-driven climbing in an environment with sparse holding points. To this end, we outline the design, kinematics, and statics of the Tetherbot and present a path planning algorithm to relocate the grippers. We demonstrate autonomous cable-driven climbing through an experiment conducted in a simulated microgravity environment using the path planning algorithm and a prototype of the robot. The results showcase Tetherbot’s ability to achieve autonomous cable-driven climbing locomotion, thereby demonstrating that cable-driven climbing is a viable concept and laying the foundation for future robots of this type. Full article

(This article belongs to the Section Aerospace Robotics and Autonomous Systems)

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21 pages, 5591 KiB

Open AccessArticle

Design of a Three-Degree of Freedom Planar Parallel Mechanism for the Active Dynamic Balancing of Delta Robots

by Christian Mirz, Mathias Hüsing, Yukio Takeda and Burkhard Corves

Robotics 2024, 13(9), 129; https://doi.org/10.3390/robotics13090129 - 27 Aug 2024

Viewed by 302

Abstract

Delta robots are the most common parallel robots for manipulation tasks. In many industrial applications, they must be operated at reduced speed, or dwell times have to be included in the motion planning, to prevent frame vibrations. As a result, their full potential [...] Read more.

Delta robots are the most common parallel robots for manipulation tasks. In many industrial applications, they must be operated at reduced speed, or dwell times have to be included in the motion planning, to prevent frame vibrations. As a result, their full potential cannot be realized. Against this background, this publication is concerned with the mechanical design of an active dynamic balancing unit for the reduction of frame vibrations. In the first part of this publication, the main design requirements for an active dynamic balancing mechanism are discussed, followed by a presentation of possible mechanism designs. Subsequently, one the most promising mechanisms is described in detail and its kinematics and dynamics equations are derived. Finally, the dimensions of a prototype mechanism designed to experimentally validate the concept of active dynamic balancing are defined using the example of Suisui Bot, a low-cost Delta robot. Full article

(This article belongs to the Special Issue Recent Trends and Advances on Robotics and Mechatronics within the IFToMM Technical Committee on Robotics and Mechatronics)

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22 pages, 10563 KiB

Open AccessArticle

Low-Cost Cable-Driven Robot Arm with Low-Inertia Movement and Long-Term Cable Durability

by Van Pho Nguyen, Wai Tuck Chow, Sunil Bohra Dhyan, Bohan Zhang, Boon Siew Han and Hong Yee Alvin Wong

Robotics 2024, 13(9), 128; https://doi.org/10.3390/robotics13090128 - 27 Aug 2024

Viewed by 404

Abstract

Our study presents a novel design for a cable-driven robotic arm, emphasizing low cost, low inertia movement, and long-term cable durability. The robotic arm shares similar specifications with the UR5 robotic arm, featuring a total of six degrees of freedom (DOF) distributed in [...] Read more.

Our study presents a novel design for a cable-driven robotic arm, emphasizing low cost, low inertia movement, and long-term cable durability. The robotic arm shares similar specifications with the UR5 robotic arm, featuring a total of six degrees of freedom (DOF) distributed in a 1:1:1:3 ratio at the arm base, shoulder, elbow, and wrist, respectively. The three DOF at the wrist joints are driven by a cable system, with heavy motors relocated from the end-effector to the shoulder base. This repositioning results in a lighter cable-actuated wrist (weighing 0.8 kg), which enhances safety during human interaction and reduces the torque requirements for the elbow and shoulder motors. Consequently, the overall cost and weight of the robotic arm are reduced, achieving a payload-to-body weight ratio of 5:8.4 kg. To ensure good positional repeatability, the shoulder and elbow joints, which influence longer moment arms, are designed with a direct-drive structure. To evaluate the design’s performance, tests were conducted on loading capability, cable durability, position repeatability, and manipulation. The tests demonstrated that the arm could manipulate a 5 kg payload with a positional repeatability error of less than 0.1 mm. Additionally, a novel cable tightener design was introduced, which served dual functions: conveniently tightening the cable and reducing the high-stress concentration near the cable locking end to minimize cable loosening. When subjected to an initial cable tension of 100 kg, this design retained approximately 80% of the load after 10 years at a room temperature of 24 °C. Full article

(This article belongs to the Section Industrial Robots and Automation)

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18 pages, 2405 KiB

Open AccessArticle

Experimental Comparison of Two 6D Pose Estimation Algorithms in Robotic Fruit-Picking Tasks

by Alessio Benito Alterani, Marco Costanzo, Marco De Simone, Sara Federico and Ciro Natale

Robotics 2024, 13(9), 127; https://doi.org/10.3390/robotics13090127 - 26 Aug 2024

Viewed by 449

Abstract

This paper presents an experimental comparison between two existing methods representative of two categories of 6D pose estimation algorithms nowadays commonly used in the robotics community. The first category includes purely deep learning methods, while the second one includes hybrid approaches combining learning [...] Read more.

This paper presents an experimental comparison between two existing methods representative of two categories of 6D pose estimation algorithms nowadays commonly used in the robotics community. The first category includes purely deep learning methods, while the second one includes hybrid approaches combining learning pipelines and geometric reasoning. The hybrid method considered in this paper is a pipeline of an instance-level deep neural network based on RGB data only and a geometric pose refinement algorithm based on the availability of the depth map and the CAD model of the target object. Such a method can handle objects whose dimensions differ from those of the CAD. The pure learning method considered in this comparison is DenseFusion, a consolidated state-of-the-art pose estimation algorithm selected because it uses the same input data, namely, RGB image and depth map. The comparison is carried out by testing the success rate of fresh food pick-and-place operations. The fruit-picking scenario has been selected for the comparison because it is challenging due to the high variability of object instances in appearance and dimensions. The experiments carried out with apples and limes show that the hybrid method outperforms the pure learning one in terms of accuracy, thus allowing the pick-and-place operation of fruits with a higher success rate. An extensive discussion is also presented to help the robotics community select the category of 6D pose estimation algorithms most suitable to the specific application. Full article

(This article belongs to the Section Sensors and Control in Robotics)

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25 pages, 14907 KiB

Open AccessArticle

Closed-Form Continuous-Time Neural Networks for Sliding Mode Control with Neural Gravity Compensation

by Claudio Urrea, Yainet Garcia-Garcia and John Kern

Robotics 2024, 13(9), 126; https://doi.org/10.3390/robotics13090126 - 23 Aug 2024

Viewed by 358

Abstract

This study proposes the design of a robust controller based on a Sliding Mode Control (SMC) structure. The proposed controller, called Sliding Mode Control based on Closed-Form Continuous-Time Neural Networks with Gravity Compensation (SMC-CfC-G), includes the development of an inverse model of the [...] Read more.

This study proposes the design of a robust controller based on a Sliding Mode Control (SMC) structure. The proposed controller, called Sliding Mode Control based on Closed-Form Continuous-Time Neural Networks with Gravity Compensation (SMC-CfC-G), includes the development of an inverse model of the UR5 industrial robot, which is widely used in various fields. It also includes the development of a gravity vector using neural networks, which outperforms the gravity vector obtained through traditional robot modeling. To develop a gravity compensator, a feedforward Multi-Layer Perceptron (MLP) neural network was implemented. The use of Closed-Form Continuous-Time (CfC) neural networks for the development of a robot’s inverse model was introduced, allowing efficient modeling of the robot. The behavior of the proposed controller was verified under load and torque disturbances at the end effector, demonstrating its robustness against disturbances and variations in operating conditions. The adaptability and ability of the proposed controller to maintain superior performance in dynamic industrial environments are highlighted, outperforming the classic SMC, Proportional-Integral-Derivative (PID), and Neural controllers. Consequently, a high-precision controller with a maximum error rate of approximately 1.57 mm was obtained, making it useful for applications requiring high accuracy. Full article

(This article belongs to the Section Intelligent Robots and Mechatronics)

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14 pages, 4926 KiB

Open AccessArticle

Eight-Bar Elbow Joint Exoskeleton Mechanism

by Giorgio Figliolini, Chiara Lanni, Luciano Tomassi and Jesús Ortiz

Robotics 2024, 13(9), 125; https://doi.org/10.3390/robotics13090125 - 23 Aug 2024

Viewed by 270

Abstract

This paper deals with the design and kinematic analysis of a novel mechanism for the elbow joint of an upper-limb exoskeleton, with the aim of helping operators, in terms of effort and physical resistance, in carrying out heavy operations. In particular, the proposed [...] Read more.

This paper deals with the design and kinematic analysis of a novel mechanism for the elbow joint of an upper-limb exoskeleton, with the aim of helping operators, in terms of effort and physical resistance, in carrying out heavy operations. In particular, the proposed eight-bar elbow joint exoskeleton mechanism consists of a motorized Watt I six-bar linkage and a suitable RP dyad, which connects mechanically the external parts of the human arm with the corresponding forearm by hook and loop velcro, thus helping their closing relative motion for lifting objects during repetitive and heavy operations. This relative motion is not a pure rotation, and thus the upper part of the exoskeleton is fastened to the arm, while the lower part is not rigidly connected to the forearm but through a prismatic pair that allows both rotation and sliding along the forearm axis. Instead, the human arm is sketched by means of a crossed four-bar linkage, which coupler link is considered as attached to the glyph of the prismatic pair, which is fastened to the forearm. Therefore, the kinematic analysis of the whole ten-bar mechanism, which is obtained by joining the Watt I six-bar linkage and the RP dyad to the crossed four-bar linkage, is formulated to investigate the main kinematic performance and for design purposes. The proposed algorithm has given several numerical and graphical results. Finally, a double-parallelogram linkage, as in the particular case of the Watt I six-bar linkage, was considered in combination with the RP dyad and the crossed four-bar linkage by giving a first mechanical design and a 3D-printed prototype. Full article

(This article belongs to the Section Neurorobotics)

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Robotics, Volume 13, Issue 9 (September 2024) – 7 articles

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