Actuator Concept Research Articles

Human-robot cooperative control system based on serial elastic actuator bowden cable drive in ExoArm 7-DOF upper extremity exoskeleton

The exoskeleton of the upper limb is an external parallel kinematic chain to the human arm. The device is designed to apply a specific torque of interaction to the human body resulting from bilateral teleoperation or rehabilitation. Its task is to work comfortably with the human arm. This paper presents the structure of the developed device and the control system of its joints. The construction of the joints’ drive system was performed based on the Bowden cable transmission. Based on the Bowden cable flexibility, it is possible to control the generated drive torque following the serial elastic actuator concept. The article presents joint control methods minimizing the influence of friction in the closed-loop Bowden cable conduit system. We also present the methods of estimating the torque of interaction with the operator based on the ExoArm 7-DOF exoskeleton dynamics model.

Fault-Tolerant Tracking Control of Discrete-Time T-S Fuzzy Systems With Input Constraint

Active fault-tolerant control strategy aimed at tracking is studied for a class of discrete-time Takagi-Sugeno (T-S) fuzzy systems in the presence of input constraint and additive fault. In the fault-free case, the state space of the system is partitioned based on the presence or absence of inputs. Using the parallel distributed compensation technique, input-to-state stability is proved for the error dynamics. For input constraint satisfaction, a model predictive control based reference-management unit is proposed in the form of an online optimization module that solves a quadratic programming problem. In the faulty case, the fault-free system is used as a reference model that satisfies the input constraint. Then, the concept of virtual actuator is used to make the behavior of the faulty system similar to the behavior of the fault-free system by controlling the performance degradation. In this article, a full-order observer can be used for fault estimation. In order to keep the control input of the faulty system within the admissible range defined for the fault-free system, a constraint-change scenario is considered. After detecting the fault, the constraint on the input of the fault-free system is changed in a way to keep the control input of the faulty system in the specified range. All design criteria are formulated as a linear matrix inequality problem. In order to evaluate the proposed control approach, simulations are performed on two systems: a 3-DoF helicopter and a 2-D overhead crane.

An MR-Safe Endovascular Robotic Platform: Design, Control, and Ex-Vivo Evaluation.

Cardiovascular diseases are the most common cause of global death. Endovascular interventions, in combination with advanced imaging technologies, are promising approaches for minimally invasive diagnosis and therapy. More recently, teleoperated robotic platforms target improved manipulation accuracy, stabilisation of instruments in the vasculature, and reduction of patient recovery times. However, benefits of recent platforms are undermined by a lack of haptics and residual patient exposure to ionising radiation. The purpose of this research was to design, implement, and evaluate a novel endovascular robotic platform, which accommodates emerging non-ionising magnetic resonance imaging (MRI). We proposed a pneumatically actuated MR-safe teleoperation platform to manipulate endovascular instrumentation remotely and to provide operators with haptic feedback for endovascular tasks. The platform task performance was evaluated in an ex vivo cannulation study with clinical experts ( N = 7) under fluoroscopic guidance and haptic assistance on abdominal and thoracic phantoms. The study demonstrated that the robotic dexterity involving pneumatic actuation concepts enabled successful remote cannulation of different vascular anatomies with success rates of 90%-100%. Compared to manual cannulation, slightly lower interaction forces between instrumentation and phantoms were measured for specific tasks. The maximum robotic interaction forces did not exceed 3N. This research demonstrates a promising versatile robotic technology for remote manipulation of endovascular instrumentation in MR environments. The results pave the way for clinical translation with device deployment to endovascular interventions using non-ionising real-time 3D MR guidance.

Regional Development Problems at the 11th Session of Unesco General Conference (1960) and the Belorussian SSR

This article based on declassified materials of the Belorussian SSR Ministry of Foreign Affairs analyses the problems of regional development, discussed by UNESCO during the “Year of Africa” and the participation of the Republic representatives in this discussion. The approaches to solving regional problems generated by the Organization in the 1950s are stated. The paper considers the international situation and the preparations for the 11th session of the General Conference. Positions of session participants and its results are characterized in the article. The author holds to the concept of significant actuation of the Belorussian SSR in international organizations of the UN system during the years of the Khrushchev’s Thaw and the conversion of UNESCO by mid-60s into the priority in this area of foreign-policy activities of the Republic. After the signing of the UN Charter in 1945 the Republic became the subject of international relations and international law, but continued to remain the subject of the Soviet federation, which limited its sovereignty and affected its international activities.

Review of Adaptive Shock Control Systems

Drag reduction plays a major role in future aircraft design in order to lower emissions in aviation. In transonic flight, the transonic shock induces wave drag and thus increases the overall aircraft drag and hence emissions. In the past decades, shock control has been investigated intensively from an aerodynamic point of view and has proven its efficacy in terms of reducing wave drag. Furthermore, a number of concepts for shock control bumps (SCBs) that can adapt their position and height have been introduced. The implementation of adaptive SCBs requires a trade-off between aerodynamic benefits, system complexity and overall robustness. The challenge is to find a system with low complexity which still generates sufficient aerodynamic improvement to attain an overall system benefit. The objectives of this paper are to summarize adaptive concepts for shock control, and to evaluate and compare them in terms of their advantages and challenges of their system integrity so as to offer a basis for robust comparisons. The investigated concepts include different actuation systems as conventional spoiler actuators, shape memory alloys (SMAs) or pressurized elements. Near-term applications are seen for spoiler actuator concepts while highest controllability is identified for concepts several with smaller actuators such as SMAs.

Self-sensing active control of emulated tangential tool vibration hardware-in-the-loop

This study tests the dual functionality of a piezoelectric transducer for active control of emulated tool vibration. The concept of a self-sensing actuator is here applied jointly with adaptive feedback active vibration control as hardware-in-the-loop. It controls pre-recorded tangential tool vibrations at the tool holder’s first bending mode. This work shows that the selected building blocks of the complete control loop are key to the design. It opens perspectives for a single transducer design and a simultaneous tool condition monitoring function. 10 dB attenuation of tool vibrations, bending-mode-focussed control command and feedback signal-to-noise-ratio of 20 demonstrate the system’s functionality.

Method for simulative reproduction, verification and technical adaptation as part of biological kinematics studies

Bionic development approaches are a widespread method of adapting inspirations from nature to technical applications. In case of models which are hard to analyze, a superficial examination is often not sufficient and a microscopic analysis is not feasible due to the delicate biological structure. By reproducing the biological model, a simulation, thus a verification and finally an abstraction with a possible simplification of the desired design aspects can be achieved. To streamline this process, a method for conducting biological kinematics studies is proposed. A kinematic analysis of the cervical spine of American barn owls serves as an example to demonstrate the method. Especially in this case, an analysis of the cervical spine was difficult to perform because, for example, X-rays of the living animal provide only poor image resolution. In addition, it cannot be guaranteed that all possible head movements are executed to the limits during the observation. For the analysis, cervical vertebrae recorded by micro computed tomography are virtually aligned according to the biological model. Based on this virtual model, an abstract kinematic model is established and adapted into simplified technical joints via computer-aided design software. With the help of this model, all possible poses of the cervical spine and thus the end effector position can be determined in a simulation environment by means of inverse kinematics algorithms. The resulting reachability map has revealed that by reducing the individual angles of the vertebrae, or even by removing a whole degree of freedom, it is possible to keep the mobility of the entire system nearly constant. In addition, this reachability map provides important information for biologists, which allows the verification of previously made assumptions about owl’s cervical spine mobility. The bionic design process of kinematics can be streamlined by the method described for reproducing, verifying and transferring biological hypotheses. In some cases this is what makes technical adaptation possible at all. Taking into account the simplifications of the individual movements carried out in this way, optimized actuator concepts can be used in the future and thus more efficient robot joints can be developed.

Digital Hydraulic Technology for Linear Actuation: A State of the Art Review

This paper analyses the current state of the art in linear actuation with digital hydraulics. Based on the differences in their aims the paper partitions the area into four actuation concepts – parallel valve solutions, single switching valve solutions, multi-chamber cylinders, and multi-pressure cylinders. The concepts are evaluated based on accuracy and smoothness of motion, switching load, reliability, efficiency and the number of components required.

3D Biofabrication Using Living Cells for Applications in Biohybrid Sensors and Actuators.

In this paper, we highlight the concept of biohybrid sensors and actuators built by incorporating living cells into artificial systems. Instead of using the materials extracted from cells, these approaches utilize cells to dynamically generate functional materials and to provide the native intracellular environment for the proper functioning of the materials. By incorporating the functional cells into artificial devices/chips, the cell-based biohybrid approaches can be applied to create portable odorant sensors with high sensitivity and to create biohybrid muscle actuators for applications in both drug screening and soft robotics.

Innovative Actuation Concepts for Variable-length Connecting Rods

Innovative Actuation Concepts for Variable-length Connecting Rods

A Novel Simple, Adaptive, and Versatile Soft-Robotic Compliant Two-Finger Gripper With an Inherently Gentle Touch

AbstractIn soft robotics, there is still a great need for a universal but simple gripper that realizes a high level of adaptability as well as a gentle touch to a wide variety of unknown objects of different size, shape, stiffness, and weight without the use of sensors or vision. Various, mostly complex grippers already exist based on certain actuation concepts. However, each solution has specific limitations, especially regarding gripping different soft and delicate objects. Therefore, this paper introduces a new approach to design a simple, adaptive, and versatile soft robotic two-finger gripper that is based on compliant mechanisms. More specifically, an inherently gentle touch is realized by utilizing an optimally synthesized mechanism with distributed compliance in combination with a conventional linear actuator. It is shown by finite elements method (FEM) simulations that the gripper realizes a high force and motion transmission at the same time. Furthermore, it is demonstrated by tests with a gripper prototype that reliable, safe, and fast grasping as well as manipulation are possible for a wide variety of objects. It is shown that beside regular and stiff objects also very challenging objects can be easily gripped, e.g., small, irregular, soft, and squeezable objects like fruits, berries, and vegetables. Moreover, it is confirmed that the developed compliant two-finger gripper can be used beneficially without sensors and control for differently sized and shaped objects with a comparable weight.

A Novel Inflatable Actuator Based on Simultaneous Eversion Retraction.

Inflatable robotics is a promising area for the deployment of low-cost structures that are easy to transport and deploy while allowing safe interactions with humans and the environment. One of the key elements in the development of inflatable robots is their actuation system. In this work, we introduce the original concept of a Simultaneous Eversion-Retraction Inflatable Actuator, used in the actuation of an inflatable joint of a long-range manipulator. Through an analytical study, simple relations about the total stroke and the effective area are obtained. These relations are compared to finite elements simulations and contrasted with experimental data obtained from tensile tests of an actuator prototype. The results show that the proposed design outperforms existing concepts in terms of total stroke and force distribution through the entire stroke, which makes it suitable for the actuation of long reach inflatable arms.

Concept and Prototype of Soft Actuator for Liquid Nitrogen Temperature Environments

A prototype of a soft actuator for extreme environments was fabricated, and driven in a cryogenic temperature environment. Previous soft actuators cannot be used for robots in extreme environments because resin, the main fabrication material, exhibits weak environmental characteristics. Therefore, this study proposes the application of polyimide (PI) films to soft actuators. PI is characterized by excellent environmental resistance. However, the welding of PI is difficult because of its high resistance. In this study, a welding method was developed for PI films. This method does not require pretreatment, or the use of adhesives or additives to reduce resistance. Hence, an actuator that utilizes all the characteristics of PI was realized. The actuator was characterized in a cryogenic environment, which is one of the extreme environments, and was successfully driven at a liquid nitrogen temperature of 78 K. This proposed technology is not limited to cryogenic environments and is expected to provide extreme environmental resistance to existing soft robots.

Expanding Pouch Motor Patterns for Programmable Soft Bending Actuation: Enabling Soft Robotic System Adaptations

The use of soft robots to interact with soft, fragile, and even living things has spurred interest in the development of soft robotic systems that can deform and adapt themselves to their environment through their inherent compliance. Current soft pneumatic actuator concepts require significant redesign to be repurposed from one function to another, and a complete soft robotic system may be composed of multiple types of actuators with varying materials, designs, and manufacturing methods. This complicates the process of designing and manufacturing soft robots that can tackle new tasks and environments. This work introduces a repeatable pattern of pouch motors with geometric constraints allowing the actuator to produce a programmable bending deformation. By varying the dimensions of the pattern, it is possible to produce different motions that can be used to build diverse robotic components, such as a soft robotic arm or a large soft robotic gripper.

Soft Endoluminal Robots Propelled by Rotating Magnetic Dipole Fields

Medical procedures often involve a device moving through a natural lumen of the human body (e.g., intestines, blood vessels). However, with existing technology, it is difficult, impossible, or traumatic to reach certain locations. In this article, we present a magnetically actuated soft-robotic concept for use in endoluminal applications (e.g., capsule endoscopes and catheters). The soft endoluminal robot is a simple device comprising two or more permanent magnets, axially magnetized and embedded co-axially with alternating polarity in a compliant body, with an optional internal lumen, actuated by an external rotating magnetic dipole field. We use simulations to elucidate the actuation concept’s underlying physics and, combined with experiments, demonstrate how the proposed concept outperforms other potential variations. We experimentally demonstrate the robustness to misalignment between the soft robot and the applied field, enabling operation in different applications without precise knowledge of the robot’s orientation or precise control of the actuator dipole field. Experiments are then performed inside a synthetic bowel to compare capsule-endoscope-size robots and multi-component robots formed by connecting multiple capsule-endoscope-size robots axially. Finally, experiments in a synthetic stomach show how the concept lends itself to directed self-assembly in the stomach, thus creating robots that are larger than could be swallowed.

A Novel Self-Moving Framed Piezoelectric Actuator

Utilizing the inherent advantages of the piezoelectric driving technology, such as good adaptability to vacuum environment and no electromagnetic interference, a novel self-moving framed piezoelectric actuator is proposed, simulated, and tested in this study, holding a potential application for magnetic confinement fusion. Four piezoelectric composite beams form a framed piezoelectric actuator. Two orthogonal vibration modes are excited and coupled in the framed piezoelectric actuator, producing a microscopic elliptical motion at its driving feet. Due to the friction, the framed piezoelectric actuator can move on a rail, thereby constructing the railed carrying system. Numerical simulation is carried out to confirm the operation principle and to conduct the dimensional optimization of the proposed framed piezoelectric actuator. A prototype of the proposed framed piezoelectric actuator with a weight of 83.8 g is manufactured, assembled, and tested, to verify the piezoelectric actuation concept. The optimal driving frequency of 20.75 kHz is obtained for the proposed actuator prototype, and at the excitation voltage of 400 Vpp its maximum mean velocity of 384.9 mm/s is measured. Additionally, the maximum load weight to self-weight of the proposed actuator prototype reached up to 10.74 at the excitation voltage of 300 Vpp. These experimental results validate the feasibility of the piezoelectric actuation concept on the railed carrying system.

An Open-Source Social Robot Based on Compliant Soft Robotics for Therapy with Children with ASD

Therapy with robotic tools is a promising way to help improve verbal and nonverbal communication in children. The robotic tools are able to increase aspects such as eye contact and the ability to follow instructions and to empathize with others. This work presents the design methodology, development, and experimental validation of a novel social robot based on CompliAnt SofT Robotics called the CASTOR robot, which intends to be used as an open-source platform for the long-term therapy of children with autism spectrum disorder (CwASD). CASTOR integrates the concepts of soft actuators and compliant mechanisms to create a replicable robotic platform aimed at real therapy scenarios involving physical interaction between the children and the robot. The validation shows promising results in terms of robustness and the safety of the user and robot. Likewise, mechanical tests assess the robot’s response to blocking conditions for two critical modules (i.e., neck and arm) in interaction scenarios. Future works should focus on the validation of the robot’s effectiveness in the therapy of CwASD.

Testing of High-Lift Common Research Model with Integrated Active Flow Control

A 10%-scale high-lift version of the Common Research Model and an active flow control (AFC) version of the model equipped with a simple-hinged flap were successfully tested. The main objective of the test was to develop an AFC system that can provide the necessary lift recovery on a simple-hinged flap high-lift system while minimizing its pneumatic power requirement. The tests were performed in the 14- by 22-Foot Subsonic Tunnel at the NASA Langley Research Center. Three types of AFC devices were examined: the double-row sweeping jets (DRSWJ), the alternating pulsed jets (APJ), and the high-efficiency low-power (HELP) actuators. The DRSWJ and the APJ actuators used two rows of unsteady jets, whereas the HELP actuators used a combination of unsteady and steady jets, to overcome strong adverse pressure gradients while minimizing the mass flow usage. Nozzle pressure ratio, mass flow consumption, and the power coefficient were used for judging the performance efficiency of the AFC devices. The current data are presented with the Transonic Wall Interference Correction System method applied. The HELP actuation concept was effective in controlling flow separation in the linear region of the curves comparing lift coefficient to mass flow rate. The HELP actuation achieved a targeted lift coefficient increment of 0.5, thus meeting the lift performance goal of the NASA Advanced Air Transport Technology project.

A Fuzzy Virtual Actuator for Automated Guided Vehicles.

In the last decades, virtual sensors have found increasing attention in the research community. Virtual sensors employ mathematical models and different sources of information such as actuator states or sensors, which are already existing in a system, in order to generate virtual measurements. Additionally, in recent years, the concept of virtual actuators has been proposed by leading researchers. Virtual actuators are parts of a fault-tolerant control strategy and aim to accommodate faults and to achieve a safe operation of a faulty plant. This paper describes a novel concept for a fuzzy virtual actuator applied to an automated guided vehicle (AGV). The application of fuzzy logic rules allows integrating expert knowledge or experimental data into the decision making of the virtual actuator. The AGV under consideration disposes of an innovative steering concept, which leads to considerable advantages in terms of maneuverability, but requires an elaborate control system. The application of the virtual actuator allows the accommodation of several possible faults, such as a slippery surface under one of the drive modules of the AGV.

Adaptive Concrete Beams Equipped With Integrated Fluidic Actuators

The rapidly growing world population is a great challenge for the building industry. With the scarcity of resources, it is not possible to provide the upcoming humanity with sufficient living- and work places and infrastructure with current construction methods. For wide-spanning beams and slabs the decisive design criteria is mainly determined by deformations rather than stresses, since deflections must be limited. This leads to structural elements, which are not fully exploited. However, if the deformations can be reduced significant material savings can be achieved. This article presents a solution, which allows beams to react actively to loads by use of integrated actuators. Sensors, actuators and a control unit enable components subjected to bending to adapt to these loads. The newly developed integrated hydraulic actuators allow the structure to react specifically to any possible load, by adjusting the internal hydraulic pressure. This is an enormous advantage in load bearing systems because there is often no dominant load case. This internal actuation concept is a new approach, as previous adaptive structures either have externally added actuators or compose of truss structures in which single bars are actuated. In this paper the concept is explained analytically, simulated with the finite element method and validated experimentally.