Force Feedback Signals Research Articles

Using force or EMG envelope as feedback signal for motor control system

PurposeThis work studied muscle neuro-mechanics during symmetrical up-going ramp (UGR) and down-going ramp (DGR). Aim: to evaluate during the modulation of muscular action the outcome of force feedback (FF) or neural feedback (NF) on the behavior of the trailing signals - i.e. the EMG envelope (eEMG) for FF or force signal for NF. MethodSubjects: 20. Investigated muscles: dorsal interosseous (FDI) and tibialis anterior (TA). Detected signals: force and EMG. Visual feedback: force (FF), eEMG (NF). Effort triangles: ramps duration 7.5 s, vertex at 50 and 100 % of the maximal voluntary action. Eventually, each subject performed FF50%, FF100%, NF50% and NF100% per each muscle. In each condition the areas beneath the force and eEMG signals were computed to calculate the ratios between the DGR and UGR values during the different tasks (force area DGR / force area UGR; eEMG area DGR / eEMG area UGR). Electro-mechanical coupling efficiency (EMCE) was estimated through the eEMG area / force area ratio for both UGR and DGR in each condition. Resultsa) FF. FDI: eEMG area ratio was 0.84 ± 0.15 and 0.73 ± 0.17 for FF50% and FF100%, respectively. TA: eEMG area ratio was 0.88 ± 0.11 and 0.91 ± 0.17 for FF50% and FF100%, respectively. b) NF: FDI: force area ratio was 1.18 ± 0.13 and 1.17 ± 0.13 for NF50% and NF100%, respectively. TA: force area ratio was 1.17 ± 0.21 and 1.07 ± 0.19 for NF50% and NF100%, respectively. c) DGR EMCE was greater than UGR EMCE in all four tasks. ConclusionThe influence of UGR on deployed EMCE in the following force decrement phase underpins the changes of trailing signals area during DGR. This underlines the necessity of a careful evaluation of the features of FF or NF for experimental studies or rehabilitation purposes involving the motor control system.

Shaking‐table substructure test using a MDOF boundary‐coordinating device

AbstractBoundary coordination is necessary for a shaking‐table substructure test (STST), which includes transferring forces and displacements between the tested and numerical substructures. Unlike other real‐time hybrid tests (RTHTs), the physical substructure is mounted on a shaking table and excited by the inertial force, which naturally requires a force control for boundary coordination. However, the natural velocity feedback in hydraulic actuators and high‐frequency noise in the force feedback signals makes it difficult to achieve force control. To solve these difficulties, in this study, a multi‐degree‐of‐freedom (MDOF) boundary‐coordinating device (BCD) is developed to simultaneously implement the boundary shear force and bending moment by the inertial force generated from shaking masses that are uniaxially driven by electromagnetic actuators. An STST framework was developed based on the BCD. The bottom two stories of a four‐story steel moment frame were selected as the physical substructure. A hydraulic shaking table was employed for ground excitation, and the BCD was used as the boundary coordinator for the numerical substructure, that is, the top two stories of the frame. To trace high‐frequency force signals, an enhanced three‐variable control (ETVC) method is proposed. Furthermore, an error‐response negative‐feedback compensation (ENC) method was developed to reduce the adverse effects of loading errors. Several rounds of STST tests demonstrated that the boundary commands were effectively traced by the BCD, so that the STST framework could consistently reproduce the seismic behavior of engineering structures.

Large-Area and Low-Cost Force/Tactile Capacitive Sensor for Soft Robotic Applications.

This paper presents a novel design and development of a low-cost and multi-touch sensor based on capacitive variations. This new sensor is very flexible and easy to fabricate, making it an appropriate choice for soft robot applications. Materials (conductive ink, silicone, and control boards) used in this sensor are inexpensive and easily found in the market. The proposed sensor is made of a wafer of different layers, silicone layers with electrically conductive ink, and a pressure-sensitive conductive paper sheet. Previous approaches like e-skin can measure the contact point or pressure of conductive objects like the human body or finger, while the proposed design enables the sensor to detect the object’s contact point and the applied force without considering the material conductivity of the object. The sensor can detect five multi-touch points at the same time. A neural network architecture is used to calibrate the applied force with acceptable accuracy in the presence of noise, variation in gains, and non-linearity. The force measured in real time by a commercial precise force sensor (ATI) is mapped with the produced voltage obtained by changing the layers’ capacitance between two electrode layers. Finally, the soft robot gripper embedding the suggested tactile sensor is utilized to grasp an object with position and force feedback signals.

Development and application of multi-axis hybrid simulation for seismic stability of steel braced frames

This paper presents the development and application of multi-axis pseudo-dynamic hybrid simulation for evaluating the seismic stability of steel braced frame structures. The advanced hybrid testing system used to perform hybrid simulation is first described, followed by the development of hybrid simulation and main challenges, namely the friction forces generated in the testing system and high-frequency noise in force feedback signals. The strategies proposed to overcome these challenges are then described. Two pseudo-dynamic hybrid simulations consisting of a two-tiered concentrically braced frame where a full-scale wide-flange column part of the frame is physically tested while the rest of the frame is numerically analysed are finally presented. The test results serve to verify the hybrid simulation technique, evaluate experimentally the seismic stability response of columns of steel multi-tiered concentrically braced frames and validate the findings of past fibre-based numerical models used to assess the seismic response of multi-tiered braced frames.

Boundary control of a vertical nonlinear flexible manipulator considering disturbance observer and deflection constraint with torque and boundary force feedback signals

In this paper, boundary control (BC) laws are designed to find a BC solution for a single-link nonlinear vertical manipulator to suppress the link’s transverse vibrations and control the rigid body nonlinear large rotating motion. The governing equations of motions and boundary conditions, which all consist of a set of PDEs and ODEs have been derived based on the Hamilton principle. It is desired to regulate large angular orientation, suppress the flexible link’s transverse vibrations and compensate the boundary disturbance simultaneously. The amount of elastic boundary vibration has remained within the constraint range. By considering novel Barrier-Integral Lyapunov functional in order to prevent the amount of boundary deflection from violating the constraints and avoiding any simplifications, in the presence of external boundary disturbance, proper control feedbacks and boundary disturbance observer are adopted in order to reach control objectives and to compensate external boundary disturbance effects simultaneously. By choosing proper boundary feedback, system states are proven to be uniform ultimate bounded and converge exponentially toward a small neighbourhood of zero. In order to illustrate the performance of the proposed control approach, numerical simulation results are provided.

Tactile needle probe for minimally invasive tissue identification during epidural space insertion

This paper presents a novel optical fiber-based needle probe designed to measure the tactile force at needle tip during needle insertions. By fusing the measurements along inserting paths, the probe can provide visualized tissue layer breaking information such as cutting force and layer thickness within the internal organ structure. The sensing system then can confirm types of tissue and localize needle tip by analyzing force feedback signal. The performance of the developed probe was validated via insertions on various bio tissues. Experimental results show that the sensing needle can provide reliable force information and estimation of the tissue types.

Robust Cascade Vision/Force Control of Industrial Robots Utilizing Continuous Integral Sliding-Mode Control Method

This article presents a robust cascade vision/force approach to control industrial robots interacting with unknown workpieces considering model uncertainties. This cascade structure, consisting of an inner vision loop and an outer force loop, avoids the conflict between the force and vision control in the traditional hybrid methods without decoupling force and vision systems. To apply an advanced image-based visual servoing (IBVS) compensator, some newly modified image features are used that render an invertible image interaction matrix. A practical task-based method is proposed to extract the features corresponding to the desired path in a three-dimensional space. An adaptive robust Kalman filter is adopted for filtering the noise in the force feedback signal. A robust continuous integral sliding-mode control (CISMC) method is developed for both IBVS and force compensators. CISMC exploits the advantages of the modified supertwisting algorithm to reduce the chattering. The stability of the proposed cascade controller is proved. Additionally, a contact detector algorithm is developed to manage the robot's free motion and its interaction with the workpiece. To evaluate the performance of the proposed method, several experimental tests are performed and compared with other well-known methods. The results show the superiority of the proposed approach.

HapFIC: An Adaptive Force/Position Controller for Safe Environment Interaction in Articulated Systems.

Haptic interaction is essential for the dynamic dexterity of animals, which seamlessly switch from an impedance to an admittance behaviour using the force feedback from their proprioception. However, this ability is extremely challenging to reproduce in robots, especially when dealing with complex interaction dynamics, distributed contacts, and contact switching. Current model-based controllers require accurate interaction modelling to account for contacts and stabilise the interaction. In this manuscript, we propose an adaptive force/position controller that exploits the fractal impedance controller's passivity and non-linearity to execute a finite search algorithm using the force feedback signal from the sensor at the end-effector. The method is computationally inexpensive, opening the possibility to deal with distributed contacts in the future. We evaluated the architecture in physics simulation and showed that the controller can robustly control the interaction with objects of different dynamics without violating the maximum allowable target forces or causing numerical instability even for very rigid objects. The proposed controller can also autonomously deal with contact switching and may find application in multiple fields such as legged locomotion, rehabilitation and assistive robotics.

Peg-in-a-hole by haptic teleoperation

This paper presents the experimental study on the application of the peg-in-a-hole task in the proposed haptic teleoperation system. Motion references from the user towards the remote manipulator and force feedback signals from the remote environment towards the user are transmitted through a virtual reality layer where the remote operation is simulated in real-tme. Various physical interactions occuring in the bilatral loop are modelled and controlled through the introduction of virtual spring-damper elements. Modeling and controller design of the teleoperation system is made modular and straightforward with the use of identical virtual dynamics. The design approach combines the introduction of the middle layer of virtual reality and modeling of all interactons by identical virtual spring-dampers. The haptic teleoperation system is experimentally evaluated with experienced and unexperienced users in the bilateral loop. Experimental results show that stable peg-in-a-hole operation is achieved in presence of bounded time-delays in all communication channels between the user, virtual reality layer and remote environment. Improvements of the teleoperation performances in terms of position tracking and total operation time are also observed in experiments.

Design and compliant estimate of robot gripper with light-emitting diode and photodiode positioning

Generally, robot gripper is the tool to enhancing the efficiency and ability of grasping task of robot manipulator. The interaction between the object and the grasping finger is the main target of robotic gripper design stage. For this research, robot gripper is then proposed as the new method of robot gripper force control using real-time estimate force feedback signal in order to achieve higher performance of grasping objects. Robot gripper kinematics is also analyzed and adjusted to more practical development. The object manipulation is also identifiable using recursive least square estimation technique of both hard and soft objects during grasping. Force controller of robot gripper is obtained using real-time estimate force feedback signal by the recursive least square method. Comparison of proportional–integral–derivative controller gains is tuned with different force feedback signals, normal force feedback, and estimate force feedback during grasping hard and soft objects validated by experiment. The results of design and development are illustrated by simulation and experimental methods. In addition, due to the limitation of electromagnetic interference, signals will not affect other instrumentations with restricted working condition. The range of gripper motion is detected by applied visible light signal of light-emitting diode and photodiode as limit sensors.

A Mixed-Initiative Haptic Teleoperation Strategy for Mobile Robotic Systems Based on Bidirectional Computational Trust Analysis

The goal of this paper is to improve the performance of joint human–robot systems while balancing human experience through computational trust analysis in telerobotics applications. A mixed-initiative approach is enabled by scaling the manual and autonomous controls using a function of computational human-to-robot trust. A dynamic haptic force feedback scaling strategy is performed via a function of computational robot-to-human trust to adjust the assistive force and, hence, physical workload of the operator. Passivity-based methods are used to guarantee the stability of the overall framework. Moreover, guidelines are provided to adjust the transparency of force feedback and velocity signals while guaranteeing passivity. An experimental study with 30 human subjects demonstrates a 12.8% increase in task performance and a 10.7% decrease in operator workload when the proposed strategy is used as compared to a manual autonomy allocation approach. The results also indicate that the proposed method yields higher operator satisfaction compared to manual and optimal autonomy allocation methods and is 10.1% more trusted by the operators than the optimal allocation method.

Experimental investigation of a compound force tracking control strategy for electro-hydraulic hybrid testing system with suppression of vibration disturbances

Electro-hydraulic hybrid testing, which imposes the desired acceleration and force on the specimen in parallel, is a novel structural testing method for structures or facilities and is extensively applied in civil and seismic engineering. To efficiently suppress the surplus force resulted from the acceleration motion of the specimen during the force control process, a compound force tracking control strategy comprised of a force and voltage feedforward controller (FVFC) and feedforward inverse with disturbance observer (FIDOB) controller is presented in this research. The FVFC controller as an inner loop feedforward component is first constituted by the generated force feedback signal and the real-time control voltage signal of the acceleration actuator so as to compensate for the acceleration motion of the specimen for a better disturbance rejection performance, and the FVFC controller requires little information of the system dynamic structure or parameters. The FIDOB controller composed by a feedforward inverse controller and an inverse model-based disturbance observer is then combined with the FVFC controller as an outer loop to further deal with the remaining disturbances for the FVFC-controlled electro-hydraulic hybrid testing system. The inverse model applied in the FIDOB controller is obtained with the frequency domain complex curve fitting and zero magnitude error tracking technology with respect to the proportional–integral controlled static loading system. Hence, the proposed controller integrates the advantages of the FVFC controller and FIDOB controller in terms of easy implementation and high tracking performance. Finally, comparative experiments are carried out on an uniaxial electro-hydraulic hybrid testing test rig with the xPC rapid prototyping technology and experimental results demonstrate the effectiveness of the proposed control strategy.

Force Discrimination Ability of the Human Hand near Absolute Threshold for the Design of Force Feedback Systems in Teleoperations

Force discrimination ability is an important surgical skill for micro or minimally invasive surgeries. This article analyzes the force perception of the human hand for lowintensity stimuli. Psychophysical experiments were conducted to measure just noticeable differences (JNDs) at four reference forces below 1 N. Reference forces are chosen to be in the range of forces in minimally invasive surgery that do not follow Weber's law. The force discrimination ability of two groups of subjects, surgeons and non-surgeons, is compared. Results demonstrate a superior ability of surgeons in discriminating small forces. The relationship between the JND and stimulus near absolute threshold is modeled. The application of the model in the design of force feedback systems for surgical teleoperation is discussed. In a force augmenting teleoperation system, the force feedback signal is amplified based on the characteristics of the human perception system. Therefore, the degraded human sense of touch at low-intensity forces would be compensated.

Development of a monolithic compliant SPCA-driven micro-gripper

This paper develops a monolithic compliant SPCA-driven micro-gripper for micro-assembly and describes the mechanism design, kinematic model, static model, control strategy and experimental verification of micro-gripper. The paper includes the following points: (1) the MCM integrates the lever mechanism and parallelogram mechanism so as to magnify the SPCA input and transform the linear input of SPCA into the clamping movement of gripping jaw. In addition, the kinematic model of the MCM is established to describe the relationship between the SPCA input and the output displacement of gripping jaw. (2) The static model of movement jaw is established to analyze the inherent relationship between the gripping force and the strain angle of flexible hinge. (3) The control strategy based on the incremental PID algorithm is applied to control the gripping manipulation of micro-gripper. The control strategy selects the visual or force feedback signal according to the contacting condition between the gripping jaw and clamped micro-object. Finally, a series of experiments were performed to validate the kinematic model, static model and control strategy of micro-gripper. In addition, a glassy micro-tube with 150μm diameter was clamped non-destructively by the developed micro-gripper.

Human-inspired feedback synergies for environmental interaction with a dexterous robotic hand

Effortless control of the human hand is mediated by the physical and neural couplings inherent in the structure of the hand. This concept was explored for environmental interaction tasks with the human hand, and a novel human-inspired feedback synergy (HFS) controller was developed for a robotic hand which synchronized position and force feedback signals to mimic observed human hand motions. This was achieved by first recording the finger joint motion profiles of human test subjects, where it was observed that the subjects would extend their fingers to maintain a natural hand posture when interacting with different surfaces. The resulting human joint angle data were used as inspiration to develop the HFS controller for the anthropomorphic robotic hand, which incorporated finger abduction and force feedback in the control laws for finger extension. Experimental results showed that by projecting a broader view of the tasks at hand to each specific joint, the HFS controller produced hand motion profiles that closely mimic the observed human responses and allowed the robotic manipulator to interact with the surfaces while maintaining a natural hand posture. Additionally, the HFS controller enabled the robotic hand to autonomously traverse vertical step discontinuities without prior knowledge of the environment, visual feedback, or traditional trajectory planning techniques.

Point Cloud-Based Model-Mediated Teleoperation With Dynamic and Perception-Based Model Updating

In this paper, we extend the concept of model-mediated teleoperation for complex environments and six degrees of freedom interaction using point cloud surface models. In our system, a time-of-flight camera is used to capture a high-resolution point cloud model of the object surface. The point cloud model and the physical properties of the object (stiffness and surface friction coefficient) are estimated at the slave side in real-time and transmitted to the master side using the modeling and updating algorithm proposed in this paper. The proposed algorithm adaptively controls the updating of the point cloud model and the object properties according to the slave movements and by exploiting known limitations of human haptic perception. As a result, perceptually irrelevant transmissions are avoided, and thus the packet rate in the communication channel is substantially reduced. In addition, a simple point cloud-based haptic rendering algorithm is adopted to generate the force feedback signals directly from the point cloud model without first converting it into a 3-D mesh. In the experimental evaluation, the system stability and transparency are verified in the presence of a round-trip communication delay of up to 1000 ms. Furthermore, by exploiting the limits of human haptic perception, the presented system allows for a significant haptic data reduction of about 90% for teleoperation systems with time delay.

Compensation Technique for Capacitive Crosstalk in Continuous-Time Electro-Mechanical Sigma-Delta Modulators

This paper presents a readout interface for gyroscopes, where the Coriolis rate signal is converted into a bitstream using a 4th-order continuous-time electro-mechanical sigma-delta modulator. The used gyroscope has separate sense and feedback electrodes allowing full continuous-time readout. A severe drawback arises when a gyroscope with this non-collocated design is employed, since the readout is active during force-feedback. Charge feed-through, caused by parasitic capacitances of the sensor in combination with force-feedback signals, drive the charge integrator front-end into saturation. This paper presents a technique for the compensation of this capacitive crosstalk, enabling stable closed-loop readout interfaces.

Downcoiler surface fault prediction for a hot strip steel mill

This paper studies the means of detecting steel strip surface defects produced by a hot strip mill downcoiler. The analysis is based on the force feedback signals taken from the side-guide and the pinch-roll of the steel mill. The study compares the results from two approaches. One approach is to apply principal component analysis (PCA) on the autoregressive (AR) model spectrum, and the other is to apply PCA on the signal periodogram. The spectrum estimation processes help eliminate the noise effects, and the PCA then distinguishes the signals into different clusters. Some of these clusters will then represent the problematic strips. The analysis results on the data from China Steel Corporation (CSC) show that PCA in conjunction with the AR model is able to separate a major portion of the defective processes, and that PCA with the periodogram is not as effective. However, the two processes sometimes compensate for each other, and the combination of the methods may provide improved results.

Using piezoelectric technology to improve servo gripper performance in mini‐ and microassembly

PurposeAims to research the possibilities of using piezoelectric technology to improve accuracy and other characteristics of parallel servo grippers.Design/methodology/approachThe paper presents in detail two different kinds of developed two‐fingered servo grippers based on piezoelectric technology with parallel moving mechanics. The first gripper is based on standing wave ultrasonic motors. The other gripper is a traditional gripper, the characteristics of which have been improved with integrated piezoelectric stack actuators. Both servo grippers have been tested and the test results and experiences are introduced in the paper.FindingsIt is possible to improve the accuracy and characteristics of a parallel servo gripper with piezoelectric technology.Research limitations/implicationsIn the future it is necessary to concentrate on the mechanical design of gripper bodies and the fingers. Grasping force feedback signal should be even more linear and noiseless.Practical implicationsPiezoelectric stack actuator's limited displacement is a problem in many practical applications when elastic or rough surface parts are handled. When integrated piezoelectric stacks are used with servo grippers, it is very important to focus on gripper's mechanical design and especially on the mechanical rigidity for getting the best possible results.Originality/valueFurther developed versions of these servo grippers can be used in high accuracy industry applications instead of traditional servo gripper technologies.

Vibration and noise control of structural systems using squeeze mode ER mounts

This paper presents vibration and noise control of flexible structures using squeeze mode electro-rheological mounts. After verifying that the damping force of the ER mount can be controlled by the intensity of the electric fild, two different types of ER squeeze mounts have been devised. Firstly, a small size ER mount to support 3 kg is manufactured and applied to the frame structure to control the vibration. An optimal controller which consists of the velocity and the transmitted force feedback signals is designed and implemented to attenuate both the vibration and the transmitted forces. Secondly, a large size of ER mount to support 200 kg is devised and applied to the shell structure to reduce the radiated noise. Dynamic modeling and controller design are undertaken in order to evaluate noise control performance as well as isolation performance of the transmitted force. The radiated noise from the cylindrical shell is calculated by SYSNOISE using forces which are transmitted to the cylindrical shell through two-stage mounting system.