Due to the complex working environments, robots need to sense and react to their various interactive surroundings with the help of tactile perception. Material recognition, one of the basic applications of tactile perception, can be achieved by further interpreting and representing the tactile data collected by tactile sensors. Suitable control strategies can be implemented to ensure stable and efficient operation of robots if the contacting materials are accurately recognized. Therefore, in this paper, a soft, deformable, and self-powered tactile sensor based on magnetoelectric materials is developed. Structural design, working principles, and shape optimization of this magnetoelectric tactile sensor are first described. Fabrication and assembly of the magnetoelectric tactile sensor are then introduced. The material recognition experiments including the voltage ratio ranges study, test 1 (velocity change), and test 2 (size and shape change) are performed to validate the effectiveness of the proposed magnetoelectric tactile sensor. The experimental results show that the recognition accuracy is high (around 90% for soft materials and 100% for hard materials) regardless of sizes and shapes of the contacting materials. © 2023 Elsevier B.V.

Haptic information of biological tissues is important in applications and research in medical fields, including force and tactile feedback. Due to resource limitation, various biological tissues may not be easily accessible, so as to hinder their haptic research and development. Therefore, in this paper, force and tactile feedback of five pig tissue samples are respectively reproduced by using a combination of haptic device and interface. Specifically, the haptic device is used to reproduce the force-displacement relationship, while the haptic interface is used to provide various and controllable touch sensations to human fingers. First, the force-displacement relationships of five pig tissue samples are derived via compression tests. Second, the haptic device with two springs and a customized raceway is designed, modeled, and fabricated. Third, compression tests are performed on the haptic device to verify its reproduction accuracy. Later, the pneumatic haptic interface is designed and fabricated. Last, the haptic device and interface are combined and tested. The proposed haptic device and interface can provide accurate force feedback as well as various and controllable tactile feedback to human fingers. © 2024 Elsevier B.V.

Robot-assisted minimally invasive surgery enables surgeons to tele-perform elaborate surgical operations to patients with less damage and pain. Besides force feedback provided by the surgical robot to the surgeon, touching sensations are also important for the surgeon to acquire the complete conditions of the patient. Thus, tactile display devices are crucial elements in surgical robots. Meanwhile, various sensations of magnetorheological (MR) fluid can be provided to human fingers because its stiffness, elasticity, and viscosity can be controlled by applied magnetic field. Therefore, in this paper, a new tactile display device based on MR fluid is proposed. This device has high magnetic conduction efficiency, less magnetic leakage, no MR fluid leakage, and overcomes the major drawbacks of the existing tactile display devices based on MR fluid in literatures. Firstly, the design of the tactile display device is described in detail, followed by its fabrication and assembling methods. Secondly, the working current range of the tactile display device is determined by using electromagnetic finite element method (FEM) simulation. Thirdly, the mathematical model to characterize the compression and shear behaviors of the tactile display device is developed. Then, the tactile display device is tested in terms of normal and shear contact forces, followed by its elastic and shear moduli analysis. Finally, the unknown parameters in the mathematical model are figured out, and the model is validated by using structural FEM simulation. The experimental results show that the elastic and shear modulus range of the proposed tactile display device are respectively 3-7.5 kPa and 1.4-5.0 kPa, which can cover the mechanical properties of various human viscera. © 2023 The Author(s). Published by IOP Publishing Ltd.

In this paper, we proposed an IMU-based locomotion mode identification (LMI) system for ankle-foot prostheses. Specifically, an IMU sensor was mounted on the heel to collect the foot's dynamic information during walking. Then processing the dynamic data can estimate the foot trajectory for calculating the inclination grade of the terrain. It is noteworthy that our environment is constructed according to the inclination grade for ergonomics. For example, when the inclination angle ranges from 3 degrees to 11 degrees, the environment should be a ramp. On the other hand, when walking on different terrains, people prefer to move their feet around the ground's exterior. It is helpful for people to get the required foot clearance and, at the same time, minimize the energy needed for transporting the lower limbs. Therefore, with the estimated inclination grade, the presented method can precisely predict/identify the locomotion mode. Experimental results show that the average accuracy can reach 98.4% in five daily locomotion modes, including level-ground walking, stair ascending/descending, and upslope/downslope walking. © 2023 SPIE.

Taking advantage of the magnetically controllable rheological properties of magnetorheological (MR) fluid, MR dampers are widely used in many engineering fields. Much effort has been made to improve the performance of MR dampers. Structural optimization is one of the popular methods to effectively improve the performance parameters of MR dampers. Most MR damper optimizations are focused on parts with regular shape, but shapes governed by equations can bring out more possibilities and further optimal results. Therefore, in this paper, a new MR damper is designed and optimized based on B-spline curves in order to maximize the controllable output damping force while saving the input power for the prosthetic knee. First, design principle of dividing the parts of the MR damper into two categories is introduced. Then, B-spline curves are used to form the piston shape, which is one of the crucial parts inside the magnetic circuit. Later, the optimal B-spline curve and other geometric parameters inside the magnetic circuit are obtained through simulation and optimization. Furthermore, the optimized MR damper is fabricated, assembled and tested. Finally, the proposed MR damper is compared with the ones in our previous work. Experimental results match well with the simulation ones. When working at the frequency of 1.0 Hz and the amplitude of 10 mm, the proposed MR damper has large maximum damping force and dynamic ratio, with acceptable equivalent damping. The proposed MR damper also performs better than the prototypes in our previous work in terms of maximum damping force, field dependent force, equivalent damping, dynamic range, and force-to-power ratio.

Magnetorheological (MR) fluid, whose rheological properties can be changed reversibly by applied magnetic field, offers superior capabilities and opportunities since its invention. The most crucial feature of MR fluid is its controllable and continuous yield stress. Taking this advantage, MR fluid is gaining popularity in various medical applications to meet their force/torque requirements. In this review article, progress of medical applications of MR fluid in the last two decades are systematically reviewed, mainly focused on six categories: lower limb prosthesis, exoskeleton, orthosis, rehabilitation device, haptic master, and tactile display. With MR fluid, natural and stable limb motions in lower limb prostheses, exoskeletons, and orthoses, flexible muscle trainings in rehabilitation devices, and high transparency and resolution haptic feedback can be realized. Relevant discussions and future perspectives are also provided.

The concept of synergy has drawn attention and been applied to lower limb assistive devices such as exoskeletons and prostheses for improving human-machine interaction. A better understanding of the influence of gait kinematics on synergies and a better synergy-modeling method are important for device design and improvement. To this end, gait data from healthy, amputee, and stroke subjects were collected. First, continuous relative phase (CRP) was used to quantify their synergies and explore the influence of kinematics. Second, long short-term memory (LSTM) and principal component analysis (PCA) were adopted to model interlimb synergy and intralimb synergy, respectively. The results indicate that the limited hip and knee range of motions (RoMs) in stroke patients and amputees significantly influence their synergies in different ways. In interlimb synergy modeling, LSTM (RMSE: 0.798° (hip) and 1.963° (knee)) has lower errors than PCA (RMSE: 5.050° (hip) and 10.353° (knee)), which is frequently used in the literature. Further, in intralimb synergy modeling, LSTM (RMSE: 3.894°) enables better synergy modeling than PCA (RMSE: 10.312°). In conclusion, stroke patients and amputees perform different compensatory mechanisms to adapt to new interlimb and intralimb synergies different from healthy people. LSTM has better synergy modeling and shows a promise for generating trajectories in line with the wearer's motion for lower limb assistive devices.

Making full use of the magnetically controllable rheological properties of magnetorheological (MR) fluid, MR actuators have been applied in many engineering fields. To adapt to different application scenarios, parameters of MR actuators often need to be optimized. Previous MR actuator optimization was focused on finding optimal combinations of geometric dimensions and physical parameters that meet certain requirements. The parts with optimized dimensions were still in regular shape, which might not bring optimal damping performance. Therefore, in this paper, shape optimization of MR damper piston based on parametric curve is performed for the first time. First, the regional magnetic saturation problem in the previous prototype is stated. Then, the MR damper with normal piston is simulated as a reference. Later, Bezier curve, one of the typical parametric curves, is used to form the piston with optimized parameters, and the MR damper with optimized piston is also simulated. Finally, prototypes of the MR dampers with normal and optimized pistons are fabricated and tested. Compared with the MR damper with normal piston, the one with optimized piston has larger field dependent force and total damping force under relatively large current, with about 52% and 24% maximum increasing percentage, respectively. The controllable force range of the MR damper with optimized piston is also larger than that with normal piston.

Background: Lower limb assistive devices have been developed to help amputees or stroke patients. To precisely mimic the required function, researchers focused on how to estimate/predict the required knee angle for knee devices. Research question: The objective is to estimate the motion of the human knee joint during walking using the kinematics of wearer's thigh measured by a single Inertial Measurement Unit (IMU). The hypotheses are that the proposed method can precisely estimate knee angle and have good universality on different subjects, speeds and strides. Method: 8 healthy subjects walked on the level ground at three different speeds. An IMU mounted on the thigh was employed to collect the kinematic information of the thigh including angular velocities and accelerations. A long short-term memory (LSTM) neural network model was adopted to model intra-limb synergy between the motion of thigh and the knee joint. Such that with the trained LSTM model, the knee angle can be precisely predicted. Results: Compared with the existing studies, the proposed approach based on an LSTM model has better estimation performance. The average RMSE for eight subjects can be limited to 3.89 degrees. The proposed method has speed and stride adaptability. Significance: The proposed method is promising to generate a desired and harmonious knee trajectory in line with thigh motion for assistive robotic devices.

Harvesting energy from human motions is a promising solution to the power issue for wearable electronics. Recently, various energy harvesters were developed to capture the motion of the lower limbs such as the rotary motion of the knee and ankle joints to generate electricity. However, these devices would increase the users' burden for walking and at the same time alter the users' walking gait. It may also induce potential harm to the users' bodies. In this paper, we develop a lightweight human knee energy harvester to capture energy from the knee motion. To reduce the effect of the harvester on the users' gaits, a variable radius drum-cable mechanism with variable transmission ratio is employed to allow the generated torque to match the torque of the human knee joint. Experimental results indicate that when walking with the harvester, the changes to the users' walking gait are small, compared with normal gait. The Pearson's coefficient and root mean square error between the angle curves of the knee joint when walking with and without the device are over 0.96 and less than 5.96 degrees, respectively. Metabolic cost testing shows no statistically significant difference between harvesting and normal walking.