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The constantly increasing amount of machines operating in the vicinity of humans makes it necessary to rethink the design approach for such machines to ensure that they are safe when interacting with humans. Traditional mechanisms are rigid and heavy and as such considered unsuitable, even dangerous when a controlled physical contact with humans is...
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... this paper, we are proposing an improved soft actuator using silicon rubber reinforced with polyester fibers specifically tailored to achieve rotary motion. The actuator is designed to be used in a robotic arm combined with soft stiffness-controllable robot links [16] as presented in Figure 1. As the actuator is designed to drive a robotic arm any nonlinear behavior is highly undesired since that would require more complicate control. ...
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... can be noticed, none of the tested actuators characteristics is linear and all of them reflect a presumed elastomer strain- stress curve (Figure 7). In Figure 10, all the curves are presented in the same plot for comparison purposes. On the left hand side all the curves are plotted with respect to the real pressure data. ...
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... a unification makes it clearly visible that the circular actuator reinforced with the least spacing presents the most linear characteristics. It is interesting to note that the square actuator behaves in a way very similar to the circular one (Figure 10b, red and dark blue lines consequently). The only difference lies in the initial part of the actuation curve. ...
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... actuator characteristics compared to the model is pre- sented in Figure 11. Statistical evaluation of the tested actua- tor versions is presented in Table I. ...
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... deviation from linear characteristic (see Fig. 10b The results of the torque measurement at rest actuators angle (0 o ) are presented in Figure 13 and a statistical data evaluation is presented in Table II. As expected the highly reinforced actuator with the circular cross-section presents the most linear behavior. All the other actuators are less linear. This effect is related to the ...
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... deviation from linear characteristic (see Fig. 10b The results of the torque measurement at rest actuators angle (0 o ) are presented in Figure 13 and a statistical data evaluation is presented in Table II. As expected the highly reinforced actuator with the circular cross-section presents the most linear behavior. ...
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... cross-section distortion causes its geometry to change, and that makes the torque increase in a nonlinear fashion. All the torque curves are presented in the same plot for comparison, Figure 12b. To make them more Pressure [bar] Torque [Ncm] torque vs pressure error bars Pressure [bar] Torque [Ncm] torque vs pressure error bars Average deviation from linear characteristic (see Fig. 12c Figure 12b. ...
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... its geometry to change, and that makes the torque increase in a nonlinear fashion. All the torque curves are presented in the same plot for comparison, Figure 12b. To make them more Pressure [bar] Torque [Ncm] torque vs pressure error bars Pressure [bar] Torque [Ncm] torque vs pressure error bars Average deviation from linear characteristic (see Fig. 12c Figure 12b. As discussed in IV- A, a square-shaped actuator quickly becomes round under the pressure, and this is a suspected reason for the higher torque it provides when compered to similarly reinforced circular one. For the tested dimensions (length of the square cross- section equal to diameter of the circular one) the active ...
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... the torque curves are presented in the same plot for comparison, Figure 12b. To make them more Pressure [bar] Torque [Ncm] torque vs pressure error bars Pressure [bar] Torque [Ncm] torque vs pressure error bars Average deviation from linear characteristic (see Fig. 12c Figure 12b. As discussed in IV- A, a square-shaped actuator quickly becomes round under the pressure, and this is a suspected reason for the higher torque it provides when compered to similarly reinforced circular one. ...
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Citations
... The diameters of these FEAs range from 1 mm to 12 mm [9], making them suitable for a broad spectrum of applications, including walking robots and soft grippers. FMAs brought about the design paradigm of reinforcing entire robot bodies, thereby inspiring inventions such as soft swimming fishes [10], marine soft gripper [11], rotary actuators [12], soft medical instruments [13], and bending actuators [14]. Notably, the research in [5] studied the relationship between the fibre angle and the resulting deformation of the pressurised fibre-reinforced actuators. ...
Fibre-reinforced soft robots are often considered in the design of fluid elastomer actuators, to counter ballooning and potential bursting when exposed to high levels of pressure. They also enhance deformation and navigation through confined spaces. These attributes are critical in applications such as minimally invasive surgical (MIS) procedures that use sub-12 mm diameter trocar ports. While soft robots with fully reinforced actuation chambers have not yet attained this level of miniaturisation, this paper outlines the fabrication and characterisation of miniaturised soft manipulators with reinforced actuation chambers on the sub-centimetre scale (i.e., less than 10 mm). Two robots are presented with diameters of 9.5 mm and 7.8 mm. They have four pneumatic actuation chambers per robotic segment, with a free central working lumen. Additionally, two robotic segments are serially connected to enhance dexterity and flexibility. This research advances the miniaturisation of soft manipulators with reinforced chambers and an inner free lumen, enhancing their use in applications within confined and unstructured environments.
... 2 These grippers typically consist of specially designed asymmetric air chambers or channels that cause bending in one direction when fluid flows in or out of the chambers. [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] Some grippers utilize overlay units like airbags, resulting in elongation or shrinkage of the structure. 9,10,39,40 Most of these grippers rely on positive pressure for actuation, but they suffer from limited bending angles within a single unit due to highly inflated chambers. ...
... 9,10,39,40 Most of these grippers rely on positive pressure for actuation, but they suffer from limited bending angles within a single unit due to highly inflated chambers. [21][22][23][24]28,29,[31][32][33][34][36][37][38][39][40] Consequently, multiple chambers are often required (over 3 units) to achieve effective grasping. For example, Kim et al. present an origami gripper that utilizes a modified Miura-ori pattern, whose design methodology can produce unfolding/bending angles of *100°at 200 kPa using three chambers (units). ...
Soft robotic grippers and hands offer adaptability, lightweight construction, and enhanced safety in human-robot interactions. In this study, we introduce vacuum-actuated soft robotic finger joints to overcome their limitations in stiffness, response, and load-carrying capability. Our design-optimized through parametric design and three-dimensional (3D) printing-achieves high stiffness using vacuum pressure and a buckling mechanism for large bending angles (>90°) and rapid response times (0.24 s). We develop a theoretical model and nonlinear finite-element simulations to validate the experimental results and provide valuable insights into the underlying mechanics and visualization of the deformation and stress field. We showcase versatile applications of the buckling joints: a three-finger gripper with a large lifting ratio (∼96), a five-finger robotic hand capable of replicating human gestures and adeptly grasping objects of various characteristics in static and dynamic scenarios, and a planar-crawling robot carrying loads 30 times its weight at 0.89 body length per second (BL/s). In addition, a jellyfish-inspired robot crawls in circular pipes at 0.47 BL/s. By enhancing soft robotic grippers' functionality and performance, our study expands their applications and paves the way for innovation through 3D-printed multifunctional buckling joints.
... They exhibit passive kinematics. To overcome the issues of silicone robots, [6] has suggest to add threads or fabrics to constrain the deformation of the silicone material and the desired robot shape [6]. [7] proposed a Spring-Reinforced Actuator (SRA) that explores the intermediate state between muscle hydrostats and endo-skeletal mechanisms. ...
... They exhibit passive kinematics. To overcome the issues of silicone robots, [6] has suggest to add threads or fabrics to constrain the deformation of the silicone material and the desired robot shape [6]. [7] proposed a Spring-Reinforced Actuator (SRA) that explores the intermediate state between muscle hydrostats and endo-skeletal mechanisms. ...
... FEAs fabrication: 5. 3D printed mold, 6. Casted FEAs(6) have been removed from the mold and heated to remove the wax material from the inside. ...
... In general, the cross section geometry would, however, still not be constant as the chamber behaviour during actuation will aim to maximize its cross section area, and will finally reach a circular cross section shape. This effect has been discussed in more detail in [7]. Therefore in the proposed solution, the semicylindrical chambers have been substituted with cylindrical ones [8]. ...
... This allows for easier data fusion and modeling, and influences positively other areas of the STIFF-FLOP projects. Such a solution is not application-specific and similar actuators have been embedded in other soft robotics systems for manipulation, grasping, prosthetics and locomotion [7,10,11]. ...
... To achieve differential stretching, the bellows are partitioned into several compartments before different pressure supplies are provided to each chamber, thereby achieving different bending angles [15]. Rotary flexible actuators, which are typically used in two robotic links, can rotate a particular geometry to provide movement [16]. Existing soft actuators designed for finger exoskeletons adopt a single-structure actuator [17][18][19]. ...
A robotic digit with shape modulation, allowing personalized and adaptable finger motions, can be used to restore finger functions after finger trauma or neurological impairment. A soft pneumatic robotic digit consisting of pneumatic bellows actuators as biomimetic artificial joints is proposed in this study to achieve specific finger motions. A parametric kinematic model is employed to describe the tip motion trajectory of the soft pneumatic robotic digit and guide the actuator parameter design (i.e., the pressure supply, actuator material properties, and structure requirements of the adopted pneumatic bellows actuators). The direct 3D printing technique is adopted in the fabrication process of the soft pneumatic robotic digit using the smart material of thermoplastic polyurethane. Each digit joint achieves different ranges of motion (ROM; bending angles of distal, proximal, and metacarpal joint are 107°, 101°, and 97°, respectively) under a low pressure of 30 kPa, which are consistent with the functional ROM of a human finger for performing daily activities. Theoretical model analysis and experiment tests are performed to validate the effectiveness of the digit parametric kinematic model, thereby providing evidence-based technical parameters for the precise control of dynamic pressure dosages to achieve the required motions.
... Ballooning may also introduce actuation inconsistency, interfere with embedded sensors and can put the robot at risk of bursting. To prevent the elastomer from ballooning, fibre-reinforced design of each actuation chamber was first proposed in [11], and has since been established in different applications, such as marine grasping manipulators [12], minimally invasive surgery (MIS) [13], [14] and interventional tools [15], assistive technologies [16]- [18] and rotatory actuators [19]. The concept is to wrap in-extensible fibre around the FEAs to restrain the radial expansion while allowing longitudinal elongation. ...
Fluid elastomer actuators are a prevalent design paradigm in the field of soft robotics. To prevent the elastomer from ballooning and increase the actuation consistency, a fibre-reinforced design is commonly utilised, with the effect of the fibre angle on the robot's performance well established. However, the impact of the geometry of the fibre-reinforced chambers has not been tested. This paper explores two chamber geometries, circular and semi-circular, using measurements in alignment with minimally invasive surgery (MIS) to determine if there is a difference in performance. The fabrication process of robots with different chamber geometries is first streamlined, then the characterisation of each robot is experimentally identified. The results show the chamber geometry plays an important role in affecting the performance of the robots, e.g., with a stiffness variation greater than 20% between the two designs.
... For example, Fras et al. developed a pneumatic rotary actuator made of silicone rubber and reinforced with polyester fiber. e maximum actuator rotation angle was 90°; however, it could only rotate in one direction [9]. Furthermore, a team from the Covenant University of Nigeria developed a pneumatic soft rotary actuator to be used for gesture control. ...
An antagonistic pneumatic bidirectional rotary flexible joint was developed to improve both safety and environmental adaptability of service robots and associated human interactions. The joint comprises two semicircular rotary actuators with positive and negative symmetrical distributions and a pneumatic brake. As such, it achieves forward and reverse rotations, and its damping and braking are adjustable in real time, enabling it to maintain its position. According to the force/torque balance at the free end of the rotary actuator, the rotation angle static model was established. The relationship between the actuator rotation angle, driving torque, impedance torque, and air pressure was obtained experimentally. The brake airbag was manufactured using additive manufacturing and silicone gel casting technologies. The mathematical model of the braking torque was established next, and the model was verified through experiments. Furthermore, an experimental system was constructed to carry out the air pressure-angle, air pressure-torque, and speed response experiments without the load on the joint. The results have shown that the joint can achieve any position within ± 68.5° when the driving air pressure varies from 0 to 0.30 MPa; the time required to reach the maximum angle was 0.85 s. The joint has shown good adjustable damping characteristics. Lastly, the braking torque reached 4.21 Nm at 0.32 MPa, effectively maintaining the position.
... By altering the geometry of the chamber and the robot's body, and by using materials of varying degrees of stiffness and flexibility, one can produce an almost infinite array of poses. Research in this field shows that from just a handful of primary motions (including contraction, elongation, bending and twistingsee Figure 4) an almost infinite range of complex motions can be achieved [30][31][32]. In the STIFF-FLOP project, the aim was to create a soft robot manipulator capable of complex motions including bending and elongation ( Figure 3B). ...
... By altering the geometry of the chamber and the robot's body, and by using materials of varying degrees of stiffness and flexibility, one can produce an almost infinite array of poses. Research in this field shows that from just a handful of primary motions (including contraction, elongation, bending and twisting-see Figure 4) an almost infinite range of complex motions can be achieved [30][31][32]. ...
... By altering the geometry of the chamber and the robot's body, and by using materials of varying degrees of stiffness and flexibility, one can produce an almost infinite array of poses. Research in this field shows that from just a handful of primary motions (including contraction, elongation, bending and twistingsee Figure 4) an almost infinite range of complex motions can be achieved [30][31][32]. [33]; (B) Soft robot segment bending due to strain-limiting material being used on one side of the actuator [30]; (C) Soft robot segment rotating due to its toroidal geometry [31]. ...
In recent years we have seen tremendous progress in the development of robotic solutions for minimally invasive surgery (MIS). Indeed, a number of robot-assisted MIS systems have been developed to product level and are now well-established clinical tools; Intuitive Surgical’s very successful da Vinci Surgical System a prime example. The majority of these surgical systems are based on the traditional rigid-component robot design that was instrumental in the third industrial revolution—especially within the manufacturing sector. However, the use of this approach for surgical procedures on or around soft tissue has come under increasing criticism. The dangers of operating with a robot made from rigid components both near and within a patient are considerable. The EU project STIFF-FLOP, arguably the first large-scale research programme on soft robots for MIS, signalled the start of a concerted effort among researchers to investigate this area more comprehensively. While soft robots have many advantages over their rigid-component counterparts, among them high compliance and increased dexterity, they also bring their own specific challenges when interacting with the environment, such as the need to integrate sensors (which also need to be soft) that can determine the robot’s position and orientation (pose). In this study, the challenges of sensor integration are explored, while keeping the surgeon’s perspective at the forefront of ourdiscussion. The paper critically explores a range of methods, predominantly those developed during the EU project STIFF-FLOP, that facilitate the embedding of soft sensors into articulate soft robot structures using flexible, optics-based lightguides. We examine different optics-based approaches to pose perception in a minimally invasive surgery settings, and methods of integration are also discussed.
... Torsional actuations driven by pneumatic deformation of spiral or helix-shaped tubes were proposed, 22,23 but their rotary angles are small compared with the lengths of the actuators. Although actuators with pleated chambers could produce significant torque under large positive pneumatic pressures, [24][25][26][27] they are prone to bursting due to over pressurization and lead to failure. To circumvent this disadvantage, vacuum-driven actuators are attracting spotlights in recent years. ...
Robotic joints are fundamental components in artificial graspers and manipulators, and they are designed to achieve high dexterity to carry out various tasks. Traditional robotic hands are often driven by rigid joints, such as tendons and electric motors, resulting in bulky and complex designs. Soft robotics, composed of flexible and compliant materials, offers promising solutions to mimic the human hands and handle delicate objects safely. In this article, we propose a simple yet effective V-shape pneumatic torsional actuator (V-PTA) as the building blocks of soft grasper and manipulators. The proposed actuator is capable of producing large angular changes and twisting torque, responding fast to pneumatic changes, and scaling to appropriate dimensions easily. Because the design is generic and modular in nature, these lightweight actuators could also be assembled to form a variety of patterns of structures to suit the needs of individual tasks. We further fabricated robotic graspers and manipulators based on multiple V-PTA and demonstrated that our design could offer solutions to execute daily laboratory operations that interact with small and irregular components. Experimental data confirmed that the V-PTA building block structure could potentially pave the path forward for miniature robotic automation in laboratory or industrial settings.
... In particular, fluidic-driven robots are rather cost-efficient and have been extensively explored for applications in the industrial sector where robots work closely together with humans [8], [9], in minimally invasive interventions [10]- [13], and rehabilitation [14]. However, as a result of their inherently soft property, the ability to exert forces on the environment, when required, and effectively change the stiffness on demand is challenging and yet to be further explored [15]- [17]. ...
... where C t is the 6×6 total stiffness matrix integrated from the tip to base. Equation (17) indicates that, when the wrench is an infinitesimal value, the deformed tip position can be calculated byT 0t e∆ $ t Me .T 0t is the free-space transformation matrix. If a wrench force is exerted to the tip, (11) and (17) can be combined and the general deflection model for the k th segment can be written as ...
Soft robotic manipulators have been created and investigated for a number of applications due to their advantages over rigid robots. In minimally invasive surgery, for instance, soft robots have successfully demonstrated a number of benefits due to the compliant and flexible nature of the material they are made of. However, these type of robots struggle with performing tasks that require on-demand stiffness i.e. exerting higher forces to the surrounding environment. A number of semi-active and active mechanisms have been investigated to change and control the stiffness of soft robotic manipulators. Embedding these mechanisms in soft manipulators for spacerestricted applications can be challenging though. To better understand the inherent passive stiffness properties of soft manipulators, we propose a screw theory-based stiffness analysis for fluidic-driven continuum soft robotic manipulators. First, we derive the forward kinematics based on a parameterbased piece-wise constant curvature model. It is worth noting, our stiffness analysis can be conducted based on any freespace forward kinematic model. Then our stiffness analysis and mapping methodology is conducted based on screw theory. Initial results of our approach demonstrate the feasibility comparing computational and experimental data.
