Soft haptics using soft actuator and soft sensor

Abstract

In this paper, we presented fabric-based soft tactile actuator and soft sensor. The force characterization result indicates that the actuator is able to produce force up to about 2.20(┬▒0.017)N, when it is supplied with 80kPa of pressurized air. Hence it is capable of producing sufficient amount of force, which surpasses the human’s haptic perception threshold. The thin, sheet nature of the material creates lightweight actuator, which improves the payload-to-weight ratio. The pneumatic-based operation principle creates a safer human-machine interface. Thus, it eliminates possible occurrence of safety issues such as the danger of applying high voltages to user’s skin in case of malfunction. Direct force coupling of the soft actuator with the sensor is established to enable transmission of force information from the sensor to the actuator. The test profile indicates that the actuator is able to produce similar force profile as that of the sensor. This opens up possibility of developing soft tactile sensors and actuators based gloves, which can be paired and applied in virtual-reality based training and rehabilitation programs. Superimposition of multiple soft actuators would create an array that provides shape and size specific haptic feedback.

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FPGA implementation of a FA-1 mechanoreceptor model for efficient representation of tactile features

Abstract

Spatiotemporal spike patterns from a population of mechanoreceptors provide a concise representation of tactile stimuli that facilitates rapid sensory processing in the brain. Efficient models of mechanoreceptors are needed for the adoption of spike-based processing for robotic tactile sensing applications. This paper presents a biomimetic model of the fast-adapting type 1 (FA-1) mechanoreceptor, implemented on a field-programmable-gate-array (FPGA). The simplicity of this model enables its realization on large arrays of sensing elements while operating with sub-millisecond temporal precision required to capture deformation patterns. We illustrate this capability by interfacing with a 4096 element tactile sensor array with a 5.2 kHz sampling rate. Through physical experiments, we demonstrate the discrimination of force magnitude and local curvature during transient mechanical contact, using spike patterns obtained from the model. The approach has the potential to deliver responsive full-body tactile sensing in robotic and prosthetic applications.

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Design, kinematics, simulation of omni-directional bending reachability for a parallel structure forceps manipulator

Abstract

This paper presents a 5-DOF manipulator which consists of three parts, 1-DOF translational joint, a bendable skeleton (2-DOF for Omni-directional bending motion), and a rotatable forceps gripper (1-DOF for rotation, 1-DOF for opening/closing). The bendable segment in the manipulator achieves two orthogonal bending DOFs by pulling or pushing three parallel universal-joint-based shaft chains. Forward and inverse kinematics of the bendable skeleton is analyzed. The workspace calculation illustrates that the structure of the three parallel shaft chains can reach a bending angle of 90 degree in arbitrarily direction. The reachability of the manipulator is simulated in Adams®. According to the surgical requirements, the manipulator is actuated to draw circle during the tests while the end effector is kept bending at 60 degree. The results show that the end effector can precisely track the planning trajectory (precision within 1 mm).

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Delicate manipulations with compliant mechanism and electrostatic adhesion

Traditional rigid robotic hand manipulator has been used in many field nowadays due to its advantages of large gripping force and stable performance. However, this kind of rigid manipulator is not suitable for gripping fragile objects since it is motorized and force control can be a problem. It is also not suitable to grip object with different shapes since the manipulator is rigid and not compliant. In this study, a novel manipulator with gripping capability is designed and fabricated. The manipulator combines electrostatic adhesion actuation with soft manipulators. The manipulator has high flexibility and can be compliant to different shapes due to the property of the materials. It is very promising to do delicate manipulations in industry field and biomedical field.

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A compliant modular robotic hand with fabric force sensor for multiple versatile grasping modes

Abstract

This paper presents the development of a compliant, modular, reconfigurable, and sensorized robotic hand with multiple grasping capabilities. Each finger consists of a soft pneumatic actuator with embedded fabric force sensor and a detachable casing. The casing has a through hole for housing the actuator and special connectors for attachment to other casings. One casing each from the thumb and finger parts has a protrusion for connecting both parts together via a screw tightening system. The through-hole design allows different grasping length to be achieved and the inflated pneumatic channel of the actuator locks it in place. The modular robotic hand is capable of various versatile grasping tasks by simply changing the bending direction of the actuator, the distance between the thumb and finger parts, the grasping length of the actuator, or attaching/detaching additional fingers to the hand. (1) Hook grasping with single finger, (2) pinching with pad opposition, (3) reverse grasping for holding a pipe-like object, (4) wrap grasping with palm opposition, as well as (5) picking up an object through its handle with one thumb and two or more fingers were illustrated. These studies show the capability of the compliant modular robotic hand in performing various types of grasping by simply using different configurations of the casings. The excellent payload-to-weight ratio of the robotic hand was demonstrated. Also, the fabric force sensor that was embedded in the soft actuator indicated the difference in grasping forces that were applied to different objects during hook grasping. The modular robotic hand has the potential to broaden or substitute the usage of existing robotic hands, especially in applications where soft versatile configurable grasping is desired.

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Human-Compliant Body-Attached Soft Robots Towards Automatic Cooperative Ultrasound Imaging

Abstract

Ultrasound imaging procedures are deemed as one of the most convenient and least invasive medical diagnostic imaging modalities and have been widely utilized in health care providers, which are expecting semiautomatic or fully-automatic imaging systems to reduce the current clinical workloads. This paper presents a portable and wearable soft robotic system which has been designed with the purpose of replacing the manual operation to cooperatively steer the ultrasound probe. This human-compliant soft robotic system, which is equipped with four separated parallel soft pneumatic actuators and is able to achieve movements in three directions. Vacuum suction force is introduced to attach the robot onto the intended body location. The design and fabrication of this soft robotic system are illustrated. To our knowledge, this is the first body-attached soft robot for compliant ultrasound imaging. The feasibility of the system is demonstrated through proof-of-concept experiments.

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Simultaneous Temperature Compensation and Synchronous Error Elimination for Axial Displacement Sensors Using an Auxiliary Probe

Abstract

The output stability of the displacement sensors is an important issue for safe operations in magnetic bearing supported high-speed rotor system. This paper proposes an effective postprocessing solution to the problems of temperature drift and synchronous measuring error for the axial displacement sensor in a 10-kW magnetically suspended motor. The proposed configuration of the axial displacement sensor consists of three probes: one pair is used to eliminate the synchronous measuring error, and the third probe is employed for the consideration of temperature drift. First, the generating mechanism of the synchronous measuring error caused by the improper assemble is presented, and an operational amplifier is proposed to obtain an accurate position of the axial center by adjusting the weights of sensing signals from one pair of probes. Then the scheme of temperature compensation using an auxiliary probe is presented. In order to obtain accurately the characteristics of temperature drift at the operating point, the detailed procedure is given to determine the temperature-drift ratio. Finally, the terms related to temperature drift and synchronous error in the final output of the displacement sensor are both eliminated. Experimental results on a magnetically suspended motor test rig show the effectiveness of the proposed solution.

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Development of a compact continuum tubular robotic system for nasopharyngeal biopsy

Abstract

Traditional posterior nasopharyngeal biopsy using a flexible nasal endoscope has the risks of abrasion and injury to the nasal mucosa and thus causing trauma to the patient. Recently, a new class of robots known as continuum tubular robots (CTRs) provide a novel solution to the challenge with miniaturized size, curvilinear maneuverability, and capability of avoiding collision within the nasal environment. This paper presents a compact CTR which is 35 cm in total length, 10 cm in diameter, 2.15 kg in weight, and easy to be integrated with a robotic arm to perform more complicated operations. Structural design, end-effector design, and workspace analysis are described in detail. In addition, teleoperation of the CTR using a haptic input device is developed for position control in 3D space. Moreover, by integrating the robot with three electromagnetic tracking sensors, a navigation system together with a shape reconstruction algorithm is developed. Comprehensive experiments are conducted to test the functionality of the proposed prototype; experiment results show that under teleoperation, the system has an accuracy of 2.20 mm in following a linear path, an accuracy of 2.01 mm in following a circular path, and a latency time of 0.1 s. It is also found that the proposed shape reconstruction algorithm has a mean error of around 1 mm along the length of the tubes. Besides, the feasibility and effectiveness of the proposed robotic system being applied to posterior nasopharyngeal biopsy are demonstrated by a cadaver experiment. The proposed robotic system holds promise to enhance clinical operation in transnasal procedures.

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Active Balancing Control of AMB-Rotor Systems Using a Phase-Shift Notch Filter Connected in Parallel Mode

Abstract

The vibration controllability is an important feature in the applications of active magnetic bearings (AMBs). This paper addresses the two key challenges on the active balancing control of AMB-rotor systems: presenting a parallel-mode scheme to enhance the notch performance at high speeds, and proposing a phase-shift notch filter to ensure stable operations over the entire speed ranges. First, both the frequency characteristics of the simplified notch filter in series and in parallel mode are discussed. The analysis shows that the closed-loop system with a parallel-mode notch filter has a deeper notch depth and faster convergence. The capacities of the synchronous current elimination are also improved at high speeds. Then, an improved phase-shift notch filter connected in parallel with the controller is modeled and analyzed. In order to understand the sensibility of the proposed solution to phase-shift variations, the stability analysis of the closed-loop system in the entire operational speed range is performed using the frequency response method. Experimental results on a high-speed centrifugal air blower test rig show the effectiveness of the proposed solution.

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