Three-dimensional Force Sensor Research Articles

Human-redundant robot interaction and redundancy utilization based on three-dimensional force sensor

To make full use of redundant characteristics, the inverse kinematics algorithm based on augmented Jacobian matrix with the goal of avoiding joint limit and obstacle is adopted. Then, admittance control system is established for human-robot interaction, and force control is converted into motion control of robot. Through the expansion of Jacobian matrix, the model of joint limit avoidance is established. Regarding obstacle avoidance in human-robot interaction process, the potential function gradient is calculated and augmented Jacobian matrix is formed. Thus, comprehensive control model of human-robot interaction and obstacle avoidance is established. When the external force is applied, the robot can move smoothly along the human hand. The robot's motion process is smooth and compliant. At the same time, when performing task of avoiding joint limit, the values of the joint angle are within the set range. The average angle margin of the four joints is over 60 %. So the goal of avoiding the joint limit is achieved. When adding obstacle avoidance in the interaction control, the difference value between the minimum distance and safe distance is always positive. The safety margin of the distance is over 20 %. So the robot does not contact with the obstacle. So human-robot interaction and redundancy utilization can be realized simultaneously.

A Highly Sensitive MEMS Three-Dimensional Force Sensor based on Piezoresistive Cantilever with Stress Concentration

A Highly Sensitive MEMS Three-Dimensional Force Sensor based on Piezoresistive Cantilever with Stress Concentration

A three-dimensional fiber Bragg grating wrist force sensor with separation elastic structure

PurposeThe use of a force sensor to estimate the external force of manipulator not only needs to deal with the signal noise of the sensor itself but also needs to solve the coupling interference of the sensor itself, especially the axial force. The purpose of this paper is to develop a three-dimensional fiber Bragg grating (FBG) wrist force sensor, which has a simple structure and reduces the coupling influence between several axes.Design/methodology/approachA particular separation elastic structure with four FBGs is devised for the three-axial force sensor. One FBG is suspended on the profile of central cylinder and the other three FBGs are pasted on the elastic beam surface of the over and under measuring bodies, respectively. Finite element analysis (FEA) simulation has been implemented to the strain distribution characteristics, the output characteristics of each direction and the coupling effects of the structure. Furthermore, theoretical derivation and experimental results are used to compare, which have a good consistency.FindingsThe experiment results show that the maximum repeatability error of the sensor is 6.75%, the maximum nonlinear error is 5.36%, the maximum coupling interference is 4.73% and the minimum sensitivity is 1.58 pm/N.Originality/valueA three-dimensional force sensor based on FBG adopts a particular separation elastic structure. The sensor can reduce the coupling influence between several axes, especially the coupling interference in the z-direction is 0.

Flexible Three-Dimensional Force Tactile Sensor Based on Velostat Piezoresistive Films.

The development of a high-performance, low-cost, and simply fabricated flexible three-dimensional (3D) force sensor is essential for the future development of electronic skins suitable for the detection of normal and shear forces for several human motions. In this study, a sandwich-structured flexible 3D force tactile sensor based on a polyethylene-carbon composite material (velostat) is presented. The sensor has a large measuring range, namely, 0-12 N in the direction of the normal force and 0-2.6 N in the direction of the shear force. For normal forces, the sensitivity is 0.775 N-1 at 0-1 N, 0.107 N-1 between 1 and 3 N, and 0.003 N-1 at 3 N and above. For shear forces, the measured sensitivity is 0.122 and 0.12 N-1 in x- and y-directions, respectively. Additionally, the sensor exhibits good repeatability and stability after 2500 cycles of loading and releasing. The response and recovery times of the sensor are as fast as 40 and 80 ms, respectively. Furthermore, we prepared a glove-like sensor array. When grasping the object using the tactile glove, the information about the force applied to the sensing unit can be transmitted through a wireless system in real-time and displayed on a personal computer (PC). The prepared flexible 3D force sensor shows broad application prospects in the field of smart wearable devices.

Highly robust mechanical sensing platform inspired by a scorpion structure for 3D-mechanical signal perception

Three-dimensional force sensors play a crucial role in the aerospace industry and precision mechanical manufacturing. However, the current sensors still lack sufficient stability in the sensing of spatial mechanical forces and struggle to distinguish dynamic and static pressure signals. Coincidentally, scorpions in nature show a remarkable capacity to perceive three-dimensional stress with exceptional stability and sensitivity. This is primarily attributed to the highly sensitive sensing structure and stable multilayer structure in the slit sensilla of a scorpion. Inspired by this design, we develop a biomimetic sensing platform capable of accurately detecting the magnitude, position, and loading rate of a spatial force. This bionic system consists of an alternating combination of carbon fiber board (CFB) and hydroxylated multiwalled carbon nanotubes-styrene–isoprene (HMCNSI). Specifically, the flexible HMCNSI polymer enhances fatigue resistance, while the rigid CFB offers support and protection, resulting in exceptional robustness and stability of the sensing platform. The platform exhibits a rapid response time (14 ms), a fast recovery time (28 ms), and excellent sensitivity (GF = 46 for strain 0–3 %; GF = 118.3 for strain 3–6 %). Furthermore, the mechanical sensing platform can distinguish dynamic and static loads, identify exertion force rates in the range of 0.1–1 m/s and force magnitudes within 30 N, and provide a high positioning accuracy of 1 mm. The proposed biomimetic sensing platform exhibits promising applications in the field of precision detection of spatial forces such as human-machine interactions and intelligent robotics.

Flexible 3D Force Sensor Based on Polymer Nanocomposite for Soft Robotics and Medical Applications.

The three-dimensional (3D) force sensor has become essential in industrial and medical applications. The existing conventional 3D force sensors quantify the three-direction force components at a point of interest or extended contact area. However, they are typically made of rigid, complex structures and expensive materials, making them hard to implement in different soft or fixable industrial and medical applications. In this work, a new flexible 3D force sensor based on polymer nanocomposite (PNC) sensing elements was proposed and tested for its sensitivity to forces in the 3D space. Multi-walled carbon nanotube/polyvinylidene fluoride (MWCNT/PVDF) sensing element films were fabricated using the spray coating technique. The MWCNTs play an essential role in strain sensitivity in the sensing elements. They have been utilized for internal strain measurements of the fixable 3D force sensor's structure in response to 3D forces. The MWCNT/PVDF was selected for its high sensitivity and capability to measure high and low-frequency forces. Four sensing elements were distributed into a cross-beam structure configuration, the most typically used solid 3D force sensor. Then, the sensing elements were inserted between two silicone rubber layers to enhance the sensor's flexibility. The developed sensor was tested under different static and dynamic loading scenarios and exhibited excellent sensitivity and ability to distinguish between tension and compression force directions. The proposed sensor can be implemented in vast applications, including soft robotics and prostheses' internal forces of patients with limb amputations.

Research on mode adjustment control strategy of upper limb rehabilitation robot based on fuzzy recognition of interaction force

In the process of robot-assisted training for upper limb rehabilitation, a passive training strategy is usually used for stroke patients with flaccid paralysis. In order to stimulate the patient's active rehabilitation willingness, the rehabilitation therapist will use the robot-assisted training strategy for patients who gradually have the ability to generate active force. This study proposed a motor function assessment technology for human upper-limb based on fuzzy recognition on interaction force and human-robot interaction control strategy based on assistance-as-needed. A passive training mode based on the calculated torque controller and an assisted training mode combined with the potential energy field were designed, and then the interactive force information collected by the three-dimensional force sensor during the training process was imported into the fuzzy inference system, the degree of active participation σ was proposed, and the corresponding assisted strategy algorithms were designed to realize the adaptive adjustment of the two modes. The significant correlation between the degree of active participation σ and the surface electromyography signals (sEMG) was found through the experiments, and the method had a shorter response time compared to a control strategy that only adjusted the mode through the magnitude of interaction force, making the robot safer during the training process.

Bionic octopus-like flexible three-dimensional force sensor for meticulous handwriting recognition in human-computer interactions

With the advantages of high flexibility, multifunctional integration, and wearing comfort, flexible tactile sensors hold great potential for application in the field of intelligent sensing system and human-computer interaction. However, the high sensitivity acquisition and the issue of decoupling of complex tactile signals, and improving compatibility of flexible tactile sensors in human-computer interfaces are still serious challenges in current research. In this study, drawing inspiration from the body structure of an octopus, we developed a flexible three-dimensional (3D) force sensor in which a CNT/Ecoflex conductive elastomer as the body of the bionic octopus-like sensor could capture the normal component of 3D spatial force, meanwhile a laser-induced graphene sensing film transferred to Ecoflex (LIG/Ecoflex) as the tactile wrists of the bionic octopus sensor could discern the magnitude and direction of the tangential component of the 3D spatial force. The bionic sensor offered excellent sensing and wearable characteristics, including fast and efficient response, cyclic stability, and flexible skin-fit performance. The unique structural design of the sensor enabled spatial force sensing capability and precise decoupling and output of 3D forces through the use of a multilayer perceptron (MLP) for mapping and calibration. The octopus-inspired flexible 3D force sensors were further attached to the fingertips of human fingers for successful extraction of handwriting minutia of wearer, showcasing their promising potential in areas such as smart wearables, handwriting recognition, and interactive human-computer interfaces.

A Novel Fiber Bragg Grating Three-Dimensional Force Sensor for Medical Robotics

A Novel Fiber Bragg Grating Three-Dimensional Force Sensor for Medical Robotics

Iontronic Capacitance-Enhanced Flexible Three-Dimensional Force Sensor With Ultrahigh Sensitivity for Machine-Sensing Interface

Iontronic Capacitance-Enhanced Flexible Three-Dimensional Force Sensor With Ultrahigh Sensitivity for Machine-Sensing Interface

Design and Experimental Results of a Three-Dimensional Force Sensor for Shearer Cutting Pick Force Monitoring

The main focus of this work is the design and development of a three-dimensional force sensor for the cutting pick of a coal mining shearer’s simulated drum. This sensor is capable of simultaneously measuring the magnitude of force along three directions of the cutting pick during the cutting sample process. The three-dimensional force sensor is built based on the strain theory of material mechanics, and reasonable structural design is implemented to improve its sensitivity and reduce inter-axis coupling errors. The strain distribution of the sensor is analyzed using finite element analysis software, and the distribution of the strain gauges is determined based on the analysis results. In addition, a calibration test system is designed for the sensor, and the sensitivity, linearity, and inter-axis coupling errors of the sensor are calibrated and tested using loading experiments in three mutually perpendicular directions. Modal simulation analysis and actual cutting pick testing of the coal mining machine’s simulated drum are conducted to study the dynamic characteristics and functionality of the sensor in practical applications. The experimental results depict sensitivities of 0.748 mV/V, 2.367 mV/V, and 2.83 mV/V for the newly developed sensor, respectively. Furthermore, the cross-sensitivity error was lower than 5.02%. These findings validate that the sensor’s structure satisfies the measurement requirements for pick-cutting forces.

Three-dimensional force detection and decoupling of a fiber grating sensor for a humanoid prosthetic hand.

A fiber Bragg grating (FBG) based three-dimensional (3D) force sensor for a humanoid prosthetic hand is designed, which can precisely detect 3D force and compensate for ambient temperature. FBG was encapsulated in polydimethylsiloxane (PDMS) for force sensitization and immobilization, and the structural parameters of the sensor were optimized by using finite element simulation, so that its sensitivity to 3D force is enhanced. In the meantime, the calibration experiments for normal force fZ, shear force fX/fY, and temperature were conducted, and the 3D force data were decoupled using the least square (LS) and backpropagation (BP) neural networks decoupling methods, so that an overall decoupling error is 0.038. The results show that the sensor has a simple structure, high sensitivity, high linearity, good creep resistance, and rapid decoupling, providing a successful design for the 3D force detection of a humanoid prosthetic hand.

Research of a Cross-Interference Suppression Method for Piezoresistive Three-Dimensional Force Sensor.

Cross-interference is not only an important factor that affects the measuring accuracy of three-dimensional force sensors, but also a technical difficulty in three-dimensional force sensor design. In this paper, a cross-interference suppression method is proposed, based on the octagonal ring's structural symmetry as well as Wheatstone bridge's balance principle. Then, three-dimensional force sensors are developed and tested to verify the feasibility of the proposed method. Experimental results show that the proposed method is effective in cross-interference suppression, and the optimal cross-interference error of the developed sensors is 1.03%. By optimizing the positioning error, angle deviation, and bonding process of strain gauges, the cross-interference error of the sensor can be further reduced to -0.36%.

Handrim Wheelchair Propulsion Technique in Individuals With Spinal Cord Injury With and Without Shoulder Pain: A Cross-sectional Comparison.

The aim of this study was to compare handrim wheelchair propulsion technique between individuals with spinal cord injury with and without shoulder pain. A cross-sectional study including 38 experienced handrim wheelchair users with spinal cord injury was conducted. Participants were divided into the "shoulder pain" ( n = 15) and "no-shoulder pain" ( n = 23) groups using the Local Musculoskeletal Discomfort scale. Kinetic and spatiotemporal aspects of handrim wheelchair propulsion during submaximal exercise on a motor-driven treadmill were analyzed. Data were collected using a measurement wheel instrumented with three-dimensional force sensors. After correction for confounders (time since injury and body height), linear regression analyses showed that the pain group had a 0.30-sec (95% confidence interval, -0.5 to -0.1) shorter cycle time, 0.22-sec (95% confidence interval, -0.4 to -0.1) shorter recovery time, 15.6 degrees (95% confidence interval, -27.4 to -3.8) smaller contact angle, and 8% (95% confidence interval, -15 to 0) lower variability in work per push compared with the no-pain group. Other parameters did not differ between groups. This study indicates that individuals with spinal cord injury who experience shoulder pain propel their handrim wheelchair kinematically differently from individuals with spinal cord injury without shoulder pain. This difference in propulsion technique might be a pain-avoiding mechanism aimed at decreasing shoulder range of motion.

Calibration of piezoelectric three-dimensional force sensor considering angle deviation

Calibration of piezoelectric three-dimensional force sensor considering angle deviation

Three-Dimensional Force Sensor Based on Fiber Bragg Grating for Medical Puncture Robot

In medical puncture robots, visible light, infrared and ultrasound images are currently used to guide punctures. The lack of information about the interaction forces between the puncture needle and soft tissue in different directions during the puncture process can easily lead to soft tissue being damaged. The current three-dimensional force sensors are large and can only be mounted on the base of the puncture needle, which does not allow for easy integration. Moreover, the force transfer to the base introduces various disturbing forces and the measurement accuracy is low. To reduce the risk of soft tissue being damaged and to enhance the intelligent control strategy of the puncture robot, this paper designs a three-dimensional force sensor based on fiber Bragg gratings. The sensor is very small and can be integrated into the back end of the puncture needle to accurately measure the interaction forces between the puncture needle and the soft tissue in different directions. The puncture needle wall is designed with notched bending of a multilayer continuous beam, which can increase the sensitivity of axial stiffness, while maintaining the sensitivity of the sensor to lateral bending and torsion, and also reduce the crosstalk between the axial and lateral forces. The finite element method is used to optimize its structural parameters, and a BP neural network based on the global optimal fitness function is proposed to solve the decoupling problem between the three-dimensional forces, which effectively improves the detection accuracy of the force sensor. The experimental results show that the measurement error of the sensor is less than 1.5%, which can accurately measure the interaction force between the puncture needle and the soft tissue and improve the safety of the puncture process.

A Force Decoupling Method for Simultaneously Measuring Vertical and Shear Force

Wearable device-based shear force sensing has been a challenging problem, whereas shear-force sensing plays a crucial role in motion measurement and robot manipulation. This paper presents a three-dimensional (3-D) flexible force sensor for measuring uniaxial vertical (i.e., normal) and 2-D shear forces. The proposed sensor is fabricated with silica gel and force-sensitive resistors (FSRs). A novel force decoupling method based on the hemispherical structure has been developed, which only requires calibration from the vertical direction, i.e., Z-axis. Experiments were carried out with a triaxial linear motion stage and a 3-D force sensor. Results show that the sensing module could measure Z-axis force ranging from 0 to 10 N with RE (relative error) of 3.2%, and shear forces (X- and Y-axes) ranging from 0 to 1.6 N with an RE of 5.5% and 5.9%, respectively. The proposed sensing module can be employed in application scenarios that require measuring interfacial stress.

Flexible capacitive three-dimensional force sensor for hand motion capture and handwriting recognition

Handwriting recognition has been widely studied as an important signal transmission method in the field of human–computer interaction. Flexible capacitive three-dimensional (3D) force sensor is widely used in this field because of its high sensitivity, large dynamic response range and good mechanical stability. However, traditional flexible capacitive 3D force sensors based on the array structure usually only sense 3D force with equivalent forward pressure rather than the decoupling of real 3D force in space. Herein, we design a flexible capacitive 3D force sensor with petal-like electrode to capture various hand movements in 3D space and further decouple 3D force to 1D force along [Formula: see text], [Formula: see text] and [Formula: see text] directions. The sensor presents a high sensitivity (1.1 kPa[Formula: see text]at the pressures below 1 kPa), a fast response (63 ms) and excellent repeatability under continuous pressure. In addition, the electrode with eight-petal structure helps simplify the decoupling process of 3D force. Through handwriting test, the sensor presents good sensing performance for hand motion capture and handwriting recognition, which is expected to be applied in the field of human–computer interaction.

An active compliant docking method for large gear components based on distributed force sensor

PurposeLarge gear components widely exist in the transmission system of helicopters, ships, etc. Due to the small assembly clearance of large gear components, using an automatic docking system based on position control will lead to forced assembly. The purpose of this paper is to reduce the assembly stress of large gear components by an active compliant docking technology based on distributed force sensors.Design/methodology/approachFirstly, aiming at the noise interference in three-dimensional force sensor (TDFS), Kalman filter and Savitzky–Golay filter are used to process the sensor’s output signal. Secondly, the active compliant docking control model is constructed according to the principle of impedance control. Thirdly, the contact force is calculated based on the Euler equation, and the impedance control parameters are tuned by the particle swarm optimization algorithm. Finally, an active compliant docking system of a large gear structure based on distributed force sensor is built in the laboratory to verify the proposed method.FindingsThe experimental results show that the contact force and contact torque gradually decrease in all directions and are always in the safe range during the docking process. The feasibility of this method in practical application is preliminarily demonstrated.Originality/valueThe distributed TDFSs are used to replace the traditional six-dimensional force sensor in the active compliant docking system of gear components, which solves the problem of the small bearing capacity of the conventional active compliant docking system. This method can also be used for the docking of other large components.

Gait-stride-and-frequency-based human intention recognition approach and experimental verification on lower limb exoskeleton

In the research of lower extremity exoskeleton, how to achieve synchronization between human and machine is quite significant. The intention recognition, which can be divided into three categories including EMG-based, EEG-based and biomechanics-based, is one of the effective implementation methods. In this paper, a new biomechanics-based method to realize the intention recognition is proposed. Compared with the mainstream, this method identifies the characteristic value of stride and frequency during walking, which describes human intention mathematically and concretizes the intention of human movement, improving the accuracy of recognition result and streamlining the algorithm. In addition, the impedance model is designed to further correct the recognition error. The main contents of this paper can be roughly summarized as follows. Gait feature event points are detected according to the angular signals of exoskeleton joints and the pressure signals of foot sole during the wearer’s walking process. Then the whole gait cycle is segmented by the identified gait feature event points, which is used to identify the wearer’s gait step and frequency in the gait cycle and output the trajectory transformed from standard gait trajectory by the recognized stride and frequency. Moreover, the interactive force signal collected by the three-dimensional force sensors mounted on the four-legged bar is provided as input to the designed impedance controller to adjust the transformed trajectory again. Also, the final trajectory is input to the Proportion Integral and Differential (PID) controller to realize the motion function of the lower extremity exoskeleton based on the wearer’s intention recognition result. Moreover, a simple hardware platform of lower limb exoskeleton is designed and built for practical experimental verification, which involves three kinds of gait respectively having constant stride, constant frequency and time-varying stride and frequency. The feasibility and reliability of the proposed algorithm can be concluded by analyzing the satisfactory experiment result.