In the study we propose and examine a novel concept, eMR-TMD as we call it, replacing a standard tuned mass damper (TMD) by an electrical harmonic oscillator (RLC circuit). The concept employs an electromagnetic energy harvester (EEH) to extract energy from vibrations, an RLC circuit in which serial resonance phenomenon occurs and a magnetorheological (MR) damper. The approach does not require modifications to the structural part of the system, i.e. no additional mass and spring are needed. The essence of the concept relies on the introduction of a tuned RLC circuit between the EEH coil and the control coil of the MR damper. The RLC circuit parameters we select in such a way so that the electrical resonance frequency is close to or equal mechanical resonance frequency in which the eMR-TMD concept is applicable. Moreover, it is required that the RLC circuit's quality factor is greater than 1 and then the voltage activated the MR damper is higher than the EEH induced voltage at the resonance frequency. Fulfilling the criteria allows tuning the current in the MR damper's control coil so that it is maximized at resonance frequency and minimized at high excitation frequencies. To prove the concept's potential we test the engineered eMR-TMD system experimentally under sinusoidal excitations. We compare the obtained test results with those acquired with the MR damper powered directly from the EEH (dMR-EEH concept) and when the MR damper's control coil is not powered (without TMD concept).

This paper presents the design and implementation of a Tactile/Force sensor which has been used on a 3-DOF decoupled parallel mechanism for Human-Robot Interaction purposes.The sensor, called HexaTactile, is a soft tactile sensor array based on six MEMS barometers, where each of them is covered by a silicone layer in the form of an incomplete pyramid. HexaTactile consists of six soft and highly sensitive tactile modules which are placed on six sides of a cube to allow simultaneous measurement of the force in the positive and negative directions along the x, y and z axes. Some of the advantages of this sensor can be regarded as its high precision, excellent linearity (coefficient of determination r2=0.99), low cost and low noise. The accuracy of the sensor is 0.01 N, within a range of 4 N and therefore HexaTactile can be suitably attached to a robot end-effector for human-robot interaction applications. Then, using the proposed force sensor some control scenarios, including fixed admittance control and active admittance control are applied for human-robot interaction purposes. From the experimental tests, it has been revealed that the active admittance control solved the drawbacks of fixed admittance control, for the considered case studies.

In the field of wearable robots, actuator efficiency and user safety are frequently addressed by intentionally adding compliance to the actuation unit. However, the implications compliance has on the actuator’s overall performance in different conditions and activities are not fully understood, largely due to single task-focused experimental evaluations of these devices. To overcome this, our paper analyzes the effects that changing mechanical compliance has on the actuator’s overall performance in different ideal conditions in an experimental test setup. The torque performance and electrical energy consumption of an orthotic, adjustable-compliance knee joint actuator are evaluated during emulated walking and sit-to-stand-to-sit movements. Furthermore, the feasibility of combined operation of a dual mechanical compliance configuration during walking is investigated, and its outcomes reported in this work. The results demonstrate that varying mechanical compliance can lead up to 50% energy savings compared to a no-compliance configuration and show that, in general, changing compliance level leads to either energy-optimal or power-optimal actuator performance, but not both.

This study presents the design and system integration of the 13-degree-of-freedom legged platform, GAZELLE. The goal of this research is to develop a fast and reliable biped platform for walking experiments. Rapid leg movement can increase robustness in walking stability. During external push or walking on uneven ground, fast leg movement can realize an abrupt change on the landing position. GAZELLE is characterized by a lightweight design, a link-driven structure for low leg inertia, a wide range of motion, and a direct-stacked fin air-cooling module. The actuator is designed using a special type of harmonic drive (lightweight CSF type) and a 200 W brushless DC motor with high power density. The knee and ankle joints are link-driven; hence, the actuators can be placed on the upper position, and the leg inertia is reduced. A novel air cooler design for the cylinder-type motor, which is extremely light and highly efficient, is introduced herein and realized by stacking cooling fins to the motor housing. This study also includes a brief introduction of a stabilizing controller and the walking experiment results of GAZELLE.

Hydraulically actuated manipulators are commonly used for material handling or at construction sites due to the high power density of hydraulic systems. Dig assistance systems or payload monitoring systems for excavators become more common to increase the efficiency and productivity. In this paper, a novel approach for estimating the dynamic parameters of a payload (including the mass) attached to the last link of a hydraulically actuated rigid body manipulator is proposed. Motion equations for the open chain rigid body system including the payload are derived. The motion equations are formulated as a linear regression model exploiting the linearity in the base dynamic parameters. Furthermore, a dynamic model for the neglected closed kinematic chains and the friction is proposed. A least squares optimization problem for minimizing the error between the model based torque and measured torque with respect to the payload parameters is defined. The optimization problem is simplified with assumptions on the center of gravity and the inertia of the payload, which leads to a more robust estimation of the payload mass with a recursive least squares algorithm. Post processing of the estimated payload is suggested and heuristics for the calculation of characteristic values like the accumulated handled mass are shown for the special case of a material handling and an earthmoving excavator. Finally, the novel approach for the payload estimation is validated on both experimental excavators for typical working cycles. The overall performance meets the requirements of ± 3%.

We address in this paper the problem of planning motion of free floating robot with state constraints. Due to the conservation of angular and linear momentum during the in-air motion, the problem is two-fold: one needs to design, in addition to the in-air motion, the initial impulse that imparts the robot with the appropriate momentum to perform a desired motion. The existence of state constraints such as joint limit makes the planning problem even more challenging. We propose in this paper a new method to address this problem. The method is a homotopy method which deforms an arbitrary path connecting the desired initial and final states to a feasible trajectory between these states, that is a trajectory that meets the system’s dynamics and constraints. From this trajectory, the method extracts both the controls and initial momentum needed to perform the motion. The deformation of path is leaded by geometric heat flow which is defined by a Riemannian metric that encodes the system dynamics and state constraints. We illustrate the method by designing somersault motions for a diver robot.

The nano scale motions of piezoelectric actuated nano-positioning systems are very sensitive to operating tasks, external disturbances, as well as variations of system dynamics. In this paper, a data-driven Iterative Feedback Tuning (IFT) based Active Disturbance Rejection Control (ADRC) approach is developed to optimize the control performance by conducting controller parameter tuning iteratively from experimental test data. In particular, a parameterized input-output form of the linear ADRC controller is derived for the nano-positioner, where the IFT algorithm is applied to solve the established optimization problem to get the optimal control parameters. The proposed method is verified in simulations where the selection of control criterion and the impact of update step-size are also discussed. Single-axis and dual-axes real-time experiments are finally conducted on an X-Y piezoelectric actuated nano-positioner, which demonstrate significant performance improvement on nano-positioning and tracking over the conventional ADRC method.

A technique to identify feedthrough coupling in an unstable one degree-of-freedom electrostatic bearing is described. The feedthrough is caused by the simultaneous use of electrodes for differential capacitive sensing and electrostatic actuation. Cancellation of the feedthrough over a broad frequency band is necessary for the system to be practically stabilizable. A feedforward filter based on open-loop estimates of the feedthrough is adequate for designing a stabilizing controller, however, the resulting stability margins are poor because the closed-loop feedthrough differs from the open-loop estimates which determine the filter. The main contribution of the paper shows how the initial feedforward filter can be updated using feedthrough estimates obtained by testing the closed-loop system at its nominal operating point. It is demonstrated that the improved feedthrough cancellation facilitates the implementation of an updated controller which reduces sensitivity function peaking and increases the closed-loop bandwidth.

Transverse ricochetal brachiation is a sophisticated locomotion style that mimics athletes swinging their bodies with their hands on a ledge in order to propel themselves for a leap to a target ledge. This paper describes the development of a transverse ricochetal brachiation robot (TRBR) and outlines motion control strategies for active flight body posture compensation. The crucial design parameters were obtained by formulating an optimization problem with the goal of maximizing flight distance. Shoulder joints with switchable stiffness were used to enable resonance excitation via the swinging of a robot tail during the swing phase, while enabling tight arm-and-body engagement during the flight phase. Novel electric grippers were designed to provide the required holding forces as well as quick-release functionality to ensure that the kinetic energy accumulated during the swing phase could be transferred smoothly to the flight phase. The reference trajectory of the robot tail was obtained using an optimization procedure based on a dynamic model of the swing phase. We also adopted a dynamic model for the flight phase to elucidate the effects of midair body rotation with the aim of developing body posture compensation methods. Simulation and experimental results demonstrate the efficacy of the proposed body posture compensation method based on a successive loop closure design in improving flight body posture during transverse ricochetal brachiation. The integration of arm swing motion with tail compensation also proved highly effective in enhancing hang time and travel distance.

Energy harvesting by using functional materials in suspension systems bear potential to win-back certain (even if low) amounts of vibrational energy, otherwise dissipated via the conventional (passive) dampers. Piezoelectric (PE) ceramics are functional materials that can be used for transforming mechanical energy into electrical and vice versa. In this paper, we study the capabilities and efficiency of energy harvesting (EH) with PE transducers under two different kinds of external excitation: i) Periodic and ii) stochastic. An appropriate nonlinear lumped parameter electromechanical model (LPEM) is brought into the two-port network notation. Laboratory experiments were conducted under periodic external force-controlled excitation performed on a universal test machine (UTM). The two-port model parameters were identified and the model was validated by comparing results of numerical simulations and experiments. Extended simulations have been conducted to investigate the EH capabilities of PE transducers in automotive applications, i.e. EH in suspension systems under the standardized road conditions. The analysis results of the power conversion and EH efficiency are presented and discussed.

Soft robots and manipulators with inflatable links possess inherent safety characteristics that make them a very interesting choice for tasks requiring human-robot interaction. However, they may face important challenges in their performance due to low structural stiffness. Accurate positioning of the end effector may prove a difficult task due to limitations in gravity compensation, or due to the occurrence of oscillations during motion, especially in the absence of precise information about the payload that is being manipulated. In this paper a novel approach to the design and control of a robot with an inflatable link is proposed, where the link assumes the triple role of compliant structural element, touch sensor, and active mechanism to adjust the performance of vibration control algorithms. For this, a vision sensor is placed inside the link to provide information about the structural deformation. The sensor is used to measure the tip displacement, and also to detect contact of the link surface with the surrounding environment. The concept was implemented on a two-joint rigid manipulator with a single inflatable link. Experiments on vibration control and contact detection of the inflatable link are reported where the control system was able to significantly reduce tip oscillations, including when a payload was added to the tip. The robot was also able to make binary detection of contact between the inflatable link and the user, and change its operation mode accordingly.

This paper presents an approach to mobile robot 6D localization based on a 3D laser scanner in GPS-denied scenarios. Commonly, 6D localization using laser scanners is performed with the use of extraction and association of the features or by comparison of the whole scans (very often off-line) using the ICP algorithm or its modifications. However, in some unstructured non-urbanized rough terrain environments, feature extraction does not seem to be reliable enough. For such kind of environment, we present a new method to mobile robot localization in GPS-denied applications, called PSD (Point-to-Surfel Distance). Unlike state of the art localization methods using laser scanners, we consider every single laser scanner measurement as an observation and use Point-to-Surfel Distance for correction of position and orientation of the robot. Mobile robot localization is based on a specific representation of the terrain in the 2.5D surfel map (terrain height and inclination). The simulation tests compared our method using extended Kalman filter (EKF) and single laser scanner measurements with an up-to-date method using particle filter (PF) and comparing the scan lines with the reference map and with another method using Gaussian mixture maps. The tests confirmed that the proposed method provides satisfying results for GPS-denied scenarios in rough terrain without extractable landmarks and our method is thirty times faster than the PF method (serial implementation). KITTI benchmark tests and real terrain experiments confirmed its usefulness and advantages as well.

Based on the multiple wedge effects, magnetically manipulated petal-shaped capsule robots (PCRs) using circle-based profiles have achieved an advantageous comprehensive driving performance, which lies in acquiring the high fluid dynamic pressure to ensure the good self-centering ability inside the pipe, the fast steady swimming speed and the low fluid resistance torsion moment. Nevertheless, the limited parametric choice of the circle-based profile hinders the further improvement in the comprehensive driving performance. This paper presents a general profile optimization method using polynomial curve for PCRs to further enhance the comprehensive driving performance. Applying the fluid lubrication theory, the fluid dynamic pressure, the steady swimming speed and the fluid resistance torsion moment are derived under the polynomial profile constraints. Selecting the steady swimming speed and the fluid resistance torsion moment as the optimization objectives, the PCR is optimized using the polynomial profile by the proposed method. Afterwards, a comparative investigation into the optimized and the circle-based PCRs and the non-PCR (the ordinary spiral-type capsule robot) has been conducted both theoretically and experimentally, showing that the optimized PCR using the polynomial profile improves the comprehensive driving performance significantly compared with its counterparts.

Active magnetic bearing (AMB) supported rotor systems require advanced control strategies to meet the increased performance requirements of more and more demanding applications. To meet the particular requirements for the performance under changing dynamics, an adaptive control structure is a task worth pursuing. This paper studies adaptive multi-input multi-output (MIMO) pole placement applied to the control commissioning of an AMB-supported rotor system. The control tuning approach is based on a rigid body model, and the parameter estimation is carried out with a recursive extended least squares (RELS) based algorithm for the MIMO system. The proposed approach is studied by simulations and validated with both a 2-degree-of-freedom (2-DOF) and a 4-DOF AMB system.

This paper presents the design, analysis, and control of a novel compact, large range 1-DOF micro manipulation mechanism. Leaf flexures were incorporated into a modular multilayer design configuration to achieve large range motion with a high natural frequency. The modular design of the proposed mechanism makes it usable as a building block to construct higher DOF-mechanisms. Computational analysis was conducted to verify the static and dynamic responses of the proposed mechanism and to ensure low flexures stress, high natural frequency, and large workspace. The mathematical model was developed to establish the derivation of a robust observer-based Sliding Mode (SM) controller. To improve the precision of tracking performance, the SM controller was augmented with adaptive Fuzzy Disturbance Observer (SM-FDO). Another robust control technique (H∞) was implemented in this work to characterize and compare the performance of SM-FDO. The mechanism was fabricated using 3D printing technology and a Voice Coil Motor (VCM) was used to deliver the actuation for its capability to provide large displacements. Experiments were performed to verify the computational modeling of the proposed mechanism and to evaluate the performance of the developed controllers. Several experimental results showed that the adaptive nature of SM-FDO allowed this controller to have superior robustness and tracking performance over the other implemented robust controller.

In bone surgery, drilling of bone without causing severe damage to tissue is a critical procedure. Particularly for skull, spine, and special kinds of orthopedic surgeries, the process of bone drilling requires high accuracy and precision since excessive drill protrusion can cause damage to nerves, blood vessels, and nearby organs. To enhance safety of drilling, a new breakthrough detection technique that does not require the installation of a sensor for force or torque measurement is proposed. This technique relies only on the measurement of current flowing through the motor of an electric drill to monitor drilling progress. By measuring the amount of current while executing stepwise drilling and applying a hysteresis thresholding algorithm, the breakthrough event can be effectively identified in real-time. Experimental tests of a drill prototype utilizing this scheme showed that breakthrough could be consistently detected. This prevents over drilling, enabling reliable drilling operation which can minimize tissue damage.

This paper presents comprehensive investigations on a new multi-pole multi-layer magnetorheological (MR) brake. This unique design features MR working gaps set between two-layer individual coils. Independent current supply was proposed to generate more flexible braking torque and lower power consumption. In this article, an exploded-view drawing of the proposed MR brake was presented, and theoretical analyses of the braking torque and temperature characteristic were conducted. Then, finite element analysis was performed to verify the effect of the magnetic field superposition. A prototype MR brake was fabricated and tested to evaluate the magnetic field superposition, preliminary dynamic behavior, temperature and the performance of individual input current. The results show that the magnetic field superposition has much influence on the braking torque, and individual current supply results in different power consumption and torque ranges. Moreover, the dynamic response performance of this brake is less affected by the slip speed. Furthermore, the maximum steady-state slip power of the proposed brake is about 160 W, and the greater the slip power is, the faster the temperature increases. The results also have verified the correctness of the structure and magnetic circuit design.

Hydro viscous clutch (HVC) is a power transmission unit which relies on shear stress of fluid to transmit driving torque. The conventional pressure control system suffers from high minimum operating pressure problem. This makes the HVC has a large drag torque and greatly limits the usage flexibility. In this article, a valve-and-pump compounded pressure control (VCPC) system is proposed for the hydro viscous clutch (HVC) to enlarge the working pressure range in the low pressure direction. The pressure of the control cylinder is adjusted by the rotary speed of pump or the electro-proportional relief valve (ERV) when the VCPC system works on different pressure stage. The adaptive robust control (ARC) algorithm and the feedforward PID algorithm are introduced into the VCPC system for the purpose of obtaining better pressure tracking performance. The effectiveness of the proposed VCPC system is validated through the compared experiments. Electromagnetic interference is considered and experiment results are carefully analyzed. It can be concluded that the pressure control range is increased by 38% with the proposed VCPC system. And compared with conventional control algorithms, the ARC algorithm has a better pressure tracking performance and relatively smooth input signal on low pressure stage.

In order to improve the performance of a magnetically levitated (maglev) axial flow blood pump, three-dimensional (3-D) finite element analysis (FEA) was used to optimize the design of a hybrid magnetic bearing (HMB). Radial, axial, and current stiffness of multiple design variations of the HMB were calculated using a 3-D FEA package and verified by experimental results. As compared with the original design, the optimized HMB had twice the axial stiffness with the resulting increase of negative radial stiffness partially compensated for by increased current stiffness. Accordingly, the performance of the maglev axial flow blood pump with the optimized HMBs was improved: the maximum pump speed was increased from 6000 rpm to 9000 rpm (50%). The radial, axial and current stiffness of the HMB was found to be linear at nominal operational position from both 3-D FEA and empirical measurements. Stiffness values determined by FEA and empirical measurements agreed well with one another. The magnetic flux density distribution and flux loop of the HMB were also visualized via 3-D FEA which confirms the designers' initial assumption about the function of this HMB.

In most Atomic Force Microscopes (AFM), a piezoelectric tube scanner is used to position the sample underneath the measurement probe. Oscillations stemming from the weakly damped resonances of the tube scanner are a major source of image distortion, putting a limitation on the achievable imaging speed. This paper demonstrates active damping of these oscillations in multiple scanning axes without the need for additional position sensors. By connecting the tube scanner in a capacitive bridge circuit the scanner oscillations can be measured in both scanning axes, using the same piezo material as an actuator and sensor simultaneously. In order to compensate for circuit imbalance caused by hysteresis in the piezo element, an adaptive balancing circuit is used. The obtained measurement signal is used for feedback control, reducing the resonance peaks in both scanning axes by 18 dB and the cross-coupling at those frequencies by 30 dB. Experimental results demonstrate a significant reduction in scanner oscillations when applying the typical triangular scanning signals, as well as a strong reduction in coupling induced oscillations. Recorded AFM images show a considerable reduction in image distortion due to the proposed control method, enabling artifact free AFM imaging at a speed of 122 lines per second with a standard piezoelectric tube scanner.