An Inductance-Based Sensing System for Bellows-Driven Continuum Joints in Soft Robots.

6 - Inductive and magnetic sensors

The resistivity of a sample can be deduced from the change in mutual inductance between two coils when the sample is inserted. It is shown that with simple equipment for measuring mutual inductance over a range of frequencies, the method can be used to measure resistivities from 2 × 10-9 ohm cm upwards, and the necessary functions are tabulated.

Soft robots use active deformable structures to provide highly capable yet simple and robust robotic systems. Motion sensors for soft robots must, therefore, be able to provide joint position sensing on deformable, multiple degrees of freedom (DOFs) joints often found in soft robot architectures and whose kinematics are not accurately described by closed-form mathematical models. This article proposes a method for designing dielectric elastomer sensor systems for such soft robots. The method is presented as a case study of a soft sensor system for an existing robotic manipulator designed for magnetic resonance image-guided surgery to the prostate. A calibration method based on support vector regression (SVR) is proposed to calibrate the coupled, multi-DOFs sensor system without a model. A prototype sensor system is built and is shown to reach a precision of 0.3 mm root mean square/1.2 mm maximum when calibrated with SVR. These results show sufficient precision for many applications and suggest th...

The author describes how the skin depth in the classical skin effect region can be found by measurement of the change in mutual inductance between two coaxial coils, caused by a metal sample being brought into the inner one coil of the coils.

Induction coilgun works on the principle of electromagnetic induction between an array of coils, which are wound on a long insulating barrel of appropriate length, and an electrically conducting projectile placed inside the barrel. Previously charged high voltage capacitor banks are sequentially discharged into the coils through high voltage solid-state switches leading to the generation and flow of high magnitude impulse currents through the coils. Time-varying magnetic flux thus produced by the pulsed currents through the coils interact with the projectile inside and induce a resultant current on it. The electromagnetic force exerted on the projectile is a product of the excitation current through the coil (i <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> ), induced current on the projectile (i <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf> ), and the mutual inductance gradient (dM <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cp</inf> /dx, i.e., the change in mutual inductance between the coil and the projectile as the projectile travels through the coil). The induced current on the projectile depends on the level of magnetic coupling between the coil and the projectile, which is governed by their geometric property, viz., diameter, number of winding layers in the coils, and number of winding turns per layer of the coils; diameter, length, shape, and material of the projectile as well as the projectile’s position w.r.t. the coils as it moves along the barrel. In this paper, the following parameters, viz., number of winding layers of the coil, number of winding turns per layer of the coil, and the projectile length are varied, keeping the pulsed power source (PPS) parameters as well as the projectile’s outer diameter and mass fixed. The analysis is performed using a commercially available Finite Element Method (FEM)-based software, Ansoft Maxwell. Results obtained from the analysis are used to design and develop a two-stage induction coilgun in the author’s laboratory.

This paper presents the modelling, simulation, and speed control aspects of a 3-phase 6/4 linear switched reluctance motor (LSRM) drives. The Linear switched reluctance motor (LSRM) has never been a popular choice for direct-drive linear motion control system; because it is difficult to control and its output has high torque ripples. It is also due to the fact that the actuator's characteristic is highly dependent on its complex magnetic circuit, which is difficult to model, simulate, and control.Fourier series expression of phase self- inductance under the assumption of negligible mutual effect and various losses is introduced to describe the nonlinear dynamic model of SRM.Simulation results have shown the rationality of model and validity of control strategy. By virtue of MATLAB/SIMULINK, the models of various subsystems are achieved and the modelling procedure is described in detail. Linear segmented switched reluctance motor (LSSRM) using full pitched winding can give 40 - 80% higher torque than conventional SRM for the same frame size. This increase in torque is due to the increase in aligned inductance. However, full pitch winding results in high copper loss, and high active weight. Hence, in this paper, single tooth or concentric winding to replace the full pitch winding of LSSRM is proposed. In order to obtain the same flux paths as with full pitch winding, all the three phases must be excited simultaneously. The torque is produced due to changes in mutual inductance. This method of winding results in reduction of copper, and therefore, weight. With such an arrangement, one phase only requires DC supply.

The inductive power transfer (IPT) technology is drawing increasing attention. Variations in the height of the secondary coil are inevitable due to the fluctuations in the height of the electrical equipment or the pressure of the tires, which leads to variations in the coils' parameters (self-inductances and mutual inductance). The coils' parameters and load variations can dramatically affect the performance of the IPT system. In this article, a unified mathematical model, which can describe multiple compensation topologies, is established. A design method is proposed to obtain suitable topology and component parameters based on the unified mathematical model and the nondominated sorting genetic algorithm II (NSGA-II). In addition, not only the stable output voltage/current is achieved, but the efficiency and cost are also improved. Finally, two experimental prototypes were built to verify the effectiveness, which has the output characteristics of constant current (CC) (3.5 A/600 W) and constant voltage (CV) (72 V/100 W). The results show that the output fluctuations are less than 5.63%, and the maximum efficiency is above 94.69% when the coils' parameters (the primary self-inductance changes from 85.76 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$102.2 \mu \text{H}$ </tex-math></inline-formula> , the secondary self-inductance changes from 86.26 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$102.35 \mu \text{H}$ </tex-math></inline-formula> , and the mutual inductance changes from 38.2 to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$72.1 \mu \text{H}$ </tex-math></inline-formula> ) and load (double change) vary.

For the B-dot used for high-power transmission lines, due to its special structure, the current method to obtain its mutual inductance is calibration experiments and there lacks an effective method to estimate its mutual inductance at the design stage. In this paper, the mutual inductance of this kind of B-dot is studied by simulation and theoretical analysis. Through simulation, the frequency response of the mutual inductance is obtained and it is found that the mutual inductance at high frequency which is the main working frequency range of the B-dot is lowest and stable. Through theoretical analysis, the approximate calculation formula of mutual inductance at any frequency is derived. Using the experimental results in previous reference, the theoretical results and the simulation results are verified. The influencing factors of the B-dot’s mutual inductance at high frequency are analyzed. The results show that the number of wire loops, the inner radius of wire loops and the radius of hole are positively related to the mutual inductance, and the height of the center of the wire loops is negatively related to the mutual inductance. Among these four factors, increasing the inner radius of wire loops can improve the mutual inductance more significantly. The work in this paper reveals the physical meaning of the mutual inductance change and provides guidance for the design of the B-dot.

Mutual inductance between primary wire and circular Rogowski coil varies with the position of primary conductor, the deviation of mutual inductance referred to center of circle causes the measurement error. Usually, the mutual inductance of Rogowski coil can be calculated by the summation of each turn of coil, however the spatial distribution characteristics of mutual inductance deviation has not been revealed. A concise analytical formula of mutual inductance is derived based on the summation form and verified by experiment in this paper, which leads to three characteristics of mutual inductance deviation. The first is the mapping relation of mutual inductance deviation between inside and outside Rogowski coil which established connection between positional accuracy and anti-interference ability. The second is the zero deviation line of mutual inductance deviation given by simple equation, which describes the position of primary wire where the measurement error vanishes. The third is approximate function on turns number, inner and outer radius of Rogowski coil and measurement error, which is easy to calculate and simplifies the design progress of Rogowski coil. Furthermore the formula and characteristics of mutual inductance can be generalized from uniform Rogowski coil and perpendicular primary wire to discontinuous PCB RC, primary conductor with cross section, and inclined primary wire. The mapping relation, zero deviation line and improved formula of mutual inductance deviation are discussed.

This article introduces a dome-type soft tactile sensor that can autonomously adjust its stiffness to evaluate surface contact characteristics, including the elastic modulus, contact force, and the presence of abnormal hardness within soft materials, using a strain gauge as a single sensing element. The strain sensor element is placed at the tip of the dome to measure the deformations during contact that reflect the properties of the contacted object. Using machine learning techniques, the sensor system can accurately predict these characteristics in various materials with an error rate of less than approximately 8%. A hybrid approach that combines experimental and simulation data enables the sensor to be trained effectively, generating sufficient data for accurate predictions without extensive experiments. The high accuracy results of the machine learning models demonstrate that the sensor system can precisely calculate the elastic modulus and depth of the defect. The adaptability and precision of the proposed sensor make it ideal for applications in medical diagnostics and other fields requiring careful interaction with soft materials. Furthermore, its innovative approach can be referenced for exploiting the properties of soft materials to achieve task-specific morphology without redesigning soft sensors or soft robots.

Flexible/stretchable sensors comprising soft structures that do not interfere with the softness of the bodies of soft robots are essential for achieving soft robots with superior operational performance. These sensors are expected to be applicable as sensing skin for humanoid robots and as interfaces for human-robot interactions. Herein, we refer to flexible/stretchable sensors investigated for soft robotics applications as “soft sensors” and review recent research trends. Specifically, we discuss optical, resistive, capacitive, and inductive soft sensors with emphasis on their materials and structures.

With the development of various electronics, the way of transmitting energy by wire has brought increasingly negative effects on the operability and convenience of products. As wireless power transfer (WPT) technology requires no transmission lines, it has received increasingly wide attention. Most of the previous research on the technology of magnetic resonant coupling WPT mainly focused on the transmission of energy in the air. This paper establishes the wireless power transfer system model under non-ferromagnetic metallic environment and studies the effect of non-ferromagnetic metallic environment on coil self-inductance L, mutual inductance M and coil resistance R of WPT system. On this basis, the study on the relationship between coil diameter and mutual inductance is carried out for aluminium pipe, and the relationship between coil diameter and diameter of metal pipe at the maximum mutual inductance is fitted. Besides, experimental verification is conducted for the change of mutual inductance between the coils of WPT system in the aluminium pipe, presenting that the actual measurement results of mutual inductance in the aluminium pipe are consistent with the theory.

This work presents a novel methodology to adjust the inductance of real coils (electronically) and to cancel out serial losses (up to tens or even hundreds of Ohms in practice) electronically. This is important in various fields of electromagnetic sensors (inductive sensors), energy harvesting, measurement and especially in the instrumentation of various devices. State-of-the-art methods do not solve the problem of cancellation of real serial resistance, which is the most important parasitic feature in low- and middle-frequency bands. In this case, the employment of serial negative resistance is not possible due to stability issues. To solve this issue, two solutions allowing the cancellation of serial resistance by the value of the passive element and an electronically adjustable parameter are introduced. The operational ranges are between 0.1 and 1 mH and 0.1 and 10 mH, valid in bandwidths from hundreds of Hz up to hundreds of kHz. The proposed concepts are experimentally tested in two applications: an electronically tunable oscillator of LC type and an electronically tunable band-pass RLC filter. The presented methodology offers significant improvements in the process of circuit design employing inductors and can be beneficially used for on-chip design, where serial resistance issues can be very significant.

This article is based on the usage requirements of lower limb rehabilitation medical exoskeleton robots, and designs a joint motor mainly used for the hip and knee joints of lower limb rehabilitation exoskeleton robots as the main driving component; Analyzed the mechanical characteristics and torque output characteristics of the joint motor, and established a simulation model based on Maxwell software for calculation. The entire joint motor adopts a FOC control scheme. By verifying the application of physical prototypes, it is demonstrated that the joint motor has excellent performance in robot joint design; The rehabilitation range of motion for hip and knee joints has been determined, providing technical support for the design and development of rehabilitation medical exoskeleton robots.

Anti-bacterial and multi-functional smart wearable sensor based on organo-hydrogel for diagnosis of the anterior cruciate ligament injuries, and sensing glove for rehabilitation of joints motion