34 research outputs found
Improving Soft Pneumatic Actuator Fingers through Integration of Soft Sensors, Position and Force Control, and Rigid Fingernails
We seek to overcome two key limitations which limit the abilities of Soft Pneumatic Actuators (SPAs) to grasp and manipulate objects: 1) Current SPAs lack position or force sensor feedback, which prevents controlling them precisely, and 2) the tip of the SPA is compliant and has high friction against common surfaces, causing the SPA to stick against surfaces when grasping objects from above. Our experiments suggest that we can achieve low steady-state error and overshoot in position and force using feed-forward models that relate pressure, force, and curvature along with a PID controller. We also compare several fingernail designs and show that the best-performing design significantly outperforms having no fingernails when grasping a set of common objects from a table
Data-driven bending angle prediction of soft pneumatic actuators with embedded flex sensors
In this paper, resistive flex sensors have been embedded at the strain limiting layer of soft
pneumatic actuators, in order to provide sensory feedback that can be utilised in predicting their bending
angle during actuation. An experimental setup was prepared to test the soft actuators under controllable
operating conditions, record the resulting sensory feedback, and synchronise this with the actual bending
angles measured using a developed image processing program. Regression analysis and neural networks
are two data-driven modelling techniques that were implemented and compared in this study, to evaluate
their ability in predicting the bending angle response of the tested soft actuators at different input
pressures and testing orientations. This serves as a step towards controlling this class of soft bending
actuators, using data-driven empirical models that lifts the need for complex analytical modelling and
material characterisation. The aim is to ultimately create a more controllable version of this class of soft
pneumatic actuators with embedded sensing capabilities, to act as compliant soft gripper fingers that can
be used in applications requiring both a ‘soft touch’ as well as more controllable object manipulation
Safe Grasping with a Force Controlled Soft Robotic Hand
Safe yet stable grasping requires a robotic hand to apply sufficient force on
the object to immobilize it while keeping it from getting damaged. Soft robotic
hands have been proposed for safe grasping due to their passive compliance, but
even such a hand can crush objects if the applied force is too high. Thus for
safe grasping, regulating the grasping force is of uttermost importance even
with soft hands. In this work, we present a force controlled soft hand and use
it to achieve safe grasping. To this end, resistive force and bend sensors are
integrated in a soft hand, and a data-driven calibration method is proposed to
estimate contact interaction forces. Given the force readings, the pneumatic
pressures are regulated using a proportional-integral controller to achieve
desired force. The controller is experimentally evaluated and benchmarked by
grasping easily deformable objects such as plastic and paper cups without
neither dropping nor deforming them. Together, the results demonstrate that our
force controlled soft hand can grasp deformable objects in a safe yet stable
manner.Comment: Accepted to 2020 IEEE International Conference on Systems, Man, and
Cybernetics (IEEE SMC 2020
Strain Sensor-Embedded Soft Pneumatic Actuators for Extension and Bending Feedback
For soft robots to leave the lab and enter unstructured environments, proprioception is required to understand how interactions in the field affect the soft structure. In this work, we present sensor-embedded soft pneumatic actuators (sSPA) that can observe both extension and bending. The sensors are strain sensitive capacitors, which are bonded to the interior of fiber-reinforced extension actuators on opposing faces. This construction allows extension and bending to be measured by calculating the mean and difference in sensor responses, respectively. The sSPAs are bonded together to form a flat fascicle to increase the force output and prevent buckling under load, and are robust to component failure by incorporating redundancy. In this paper, we discuss the fabrication of the sensors and their subsequent integration into the actuators. We also report the work capacity and sensor. response of the sSPA fascicles under extension, bending, and the combination of both modes of deformation. The sensor- embedded soft pneumatic actuators presented here will advance the field of soft robotics by enabling closed-loop control of soft robots
Bending angle prediction and control of soft pneumatic actuators with embedded flex sensors - a data-driven approach
In this paper, a purely data-driven modelling approach is presented for predicting and controlling the free bending angle response of a typical soft pneumatic actuator (SPA), embedded with a resistive flex sensor. An experimental setup was constructed to test the SPA at different input pressure values and orientations, while recording the resulting feedback from the embedded flex sensor and on-board pressure sensor. A calibrated high speed camera captures image frames during the actuation, which are then analysed using an image processing program to calculate the actual bending angle and synchronise it with the recorded sensory feedback. Empirical models were derived based on the generated experimental data using two common data-driven modelling techniques; regression analysis and artificial neural networks. Both techniques were validated using a new dataset at untrained operating conditions to evaluate their prediction accuracy. Furthermore, the derived empirical model was used as part of a closed-loop PID controller to estimate and control the bending angle of the tested SPA based on the real-time sensory feedback generated. The tuned PID controller allowed the bending SPA to accurately follow stepped and sinusoidal reference signals, even in the presence of pressure leaks in the pneumatic supply. This work demonstrates how purely data-driven models can be effectively used in controlling the bending of SPAs under different operating conditions, avoiding the need for complex analytical modelling and material characterisation. Ultimately, the aim is to create more controllable soft grippers based on such SPAs with embedded sensing capabilities, to be used in applications requiring both a ‘soft touch’ as well as a more controllable object manipulation
Directly Printable Flexible Strain Sensors for Bending and Contact Feedback of Soft Actuators
This paper presents a fully printable sensorized bending actuator that can be calibrated to provide reliable bending feedback and simple contact detection. A soft bending actuator following a pleated morphology, as well as a flexible resistive strain sensor, were directly 3D printed using easily accessible FDM printer hardware with a dual-extrusion tool head. The flexible sensor was directly welded to the bending actuator’s body and systematically tested to characterize and evaluate its response under variable input pressure. A signal conditioning circuit was developed to enhance the quality of the sensory feedback, and flexible conductive threads were used for wiring. The sensorized actuator’s response was then calibrated using a vision system to convert the sensory readings to real bending angle values. The empirical relationship was derived using linear regression and validated at untrained input conditions to evaluate its accuracy. Furthermore, the sensorized actuator was tested in a constrained setup that prevents bending, to evaluate the potential of using the same sensor for simple contact detection by comparing the constrained and free-bending responses at the same input pressures. The results of this work demonstrated how a dual-extrusion FDM printing process can be tuned to directly print highly customizable flexible strain sensors that were able to provide reliable bending feedback and basic contact detection. The addition of such sensing capability to bending actuators enhances their functionality and reliability for applications such as controlled soft grasping, flexible wearables, and haptic devices
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Soft pneumatic actuators with integrated resistive sensors enabled by multi-material 3D printing
The concept of soft robots has garnered significant attention in recent studies due to their unique capability to interact effectively with the surrounding environment. However, as the number of innovative soft pneumatic actuators (SPAs) continues to rise, integrating traditional sensors becomes challenging due to the complex and unrestricted movements exhibited by SPA during their operation. This article explores the importance of utilising one-shot multi-material 3D printing to integrate soft force and bending sensors into SPAs. It highlights the necessity of a well-tuned and robust low-cost fabrication process to ensure the functionality of these sensors over an extended period. Fused deposition modelling (FDM) offers a cost-effective solution for embedding sensors in soft robots, directly addressing such necessity. Also, a finite element method (FEM) based on the nonlinear hyper-elastic constitutive model equipped with experimental input is developed to precisely predict the deformation and tip force of the actuators measured in experiments. The dynamic mechanical test is conducted to observe and analyse the behaviour and resistance changes of conductive thermoplastic polyurethane (CTPU) and varioShore TPU (VTPU) during a cyclic test. The flexible sensor can detect deformations in SPAs through the application of air pressure. Similarly, the force sensor exhibits the ability to detect grasping objects by detecting changes in resistance. These findings suggest that the resistance change corresponds directly to the magnitude of the mechanical stimuli applied. Thus, the device shows potential for functioning as a resistive sensor for soft actuation. Furthermore, these findings highlight the significant potential of 3D and 4D printing technology in one-shot fabrication of soft sensor-actuator robotic systems, suggesting promising applications in various fields like grippers with sensors and rehabilitation devices
Directly Printable Flexible Strain Sensors for Bending and Contact Feedback of Soft Actuators
This paper presents a fully printable sensorized bending actuator that can be calibrated to provide reliable bending feedback and simple contact detection. A soft bending actuator following a pleated morphology, as well as a flexible resistive strain sensor, were directly 3D printed using easily accessible FDM printer hardware with a dual-extrusion tool head. The flexible sensor was directly welded to the bending actuator’s body and systematically tested to characterize and evaluate its response under variable input pressure. A signal conditioning circuit was developed to enhance the quality of the sensory feedback, and flexible conductive threads were used for wiring. The sensorized actuator’s response was then calibrated using a vision system to convert the sensory readings to real bending angle values. The empirical relationship was derived using linear regression and validated at untrained input conditions to evaluate its accuracy. Furthermore, the sensorized actuator was tested in a constrained setup that prevents bending, to evaluate the potential of using the same sensor for simple contact detection by comparing the constrained and free-bending responses at the same input pressures. The results of this work demonstrated how a dual-extrusion FDM printing process can be tuned to directly print highly customizable flexible strain sensors that were able to provide reliable bending feedback and basic contact detection. The addition of such sensing capability to bending actuators enhances their functionality and reliability for applications such as controlled soft grasping, flexible wearables, and haptic devices
Design and Fabrication of Soft 3D Printed Actuators: Expanding Soft Robotics Applications
Soft pneumatic actuators are ideal for soft robotic applications due to their innate compliance and high power-weight ratios. Presently, the majority of soft pneumatic actuators are used to create bending motions, with very few able to produce significant linear movements. Fewer can actively produce strains in multiple directions. The further development of these actuators is limited by their fabrication methods, specifically the lack of suitable stretchable materials for 3D printing.
In this thesis, a new highly elastic resin for digital light projection 3D printers, designated ElastAMBER, is developed and evaluated, which shows improvements over previously synthesised elastic resins. It is prepared from a di-functional polyether urethane acrylate oligomer and a blend of two different diluent monomers. ElastAMBER exhibits a viscosity of 1000 mPa.s at 40 °C, allowing easy printing at near room temperatures. The 3D-printed components present an elastomeric behaviour with a maximum extension ratio of 4.02 ± 0.06, an ultimate tensile strength of (1.23 ± 0.09) MPa, low hysteresis, and negligible viscoelastic relaxation