Effect Of Static Friction Research Articles

Development of Backdrivable Servovalve With Feedback Spring for Enhanced Electro-Hydraulic Torque Actuator

This letter proposes a novel backdrivable servovalve to implement a torque-controlled electro-hydraulic actuator. The proposed backdrivable servovalve simultaneously contains the characteristics of a flow-control servo valve (=feedback spring) and a pressure-control servovalve (=pressure feedback port). Consequently, the torque control performance of electro-hydraulic torque actuators (EHTAs), which consist of the backdrivable servovalve and rotary vane-type hydraulic actuators, can be enhanced. First, the effective torque bandwidth, which represents the region where the torque output remains constant within a 90 $^{\circ }$ phase lag, is improved. Second, torque-based control algorithms developed for electric motors are realized in a wide frequency region. Finally, although the effect of viscous friction increases, the effect of static friction is reduced. With these advantages, we achieved an enhanced EHTA with calculated torque output of −372 $\sim$ 355 Nm; this could facilitate in the development of a high-performance interactive robot system. The proposed backdrivable servovalve and enhanced EHTA were evaluated through experiments.

Friction and noise suppression for force control system based on integration of observer and force sensor information

Measuring and controlling external force from the environment and human beings are essential to realize the future application of the robot systems for medical, nursing, and personal support systems. This paper proposes a friction and noise suppression for force control system based on the integration of the reaction torque observer and force (torque) sensor information. The proposed method performs external force estimation by integrating the low-frequency component information of the force sensor and the high-frequency component of the force information estimated by reaction torque observer (RTOB). By using the low-frequency component of the force sensor, the effect of static friction can be suppressed, and the high-frequency part of RTOB can be used to attenuate the noise component. As a result, the performance of the force control system can be enhanced. The proposed method is evaluated through the experiments of the force control and bilateral control as a position/force hybrid control.

Fine Sensorless Force Control Realization Based on Dither Periodic Component Elimination Kalman Filter and Wide Band Disturbance Observer

This paper proposes a new force estimation approach based on the dither periodic component elimination (DPCE) Kalman filter and the disturbance observer (DOB) for realization of a fine sensorless force control system under the existence of static friction. A dither signal is inserted to the desired reference signal to eliminate the effect of static friction of a ball-screw system. The DOB estimates the periodical torque caused by dither signal. The DPCE Kalman filter uses the periodical torque for the estimation of the high-order torque responses to achieve the torque estimation with the elimination of periodic component. The problem of noise in the force sensation and the effect of static friction are reduced effectively by using the DPCE Kalman filter. Therefore, the bandwidth of the force sensing is increased and the wide band DOB is achieved. As a result, this paper has accomplished the fine sensorless force control realization. The force control experiments of a ball-screw system are carried out to verify the validity and effectiveness of the proposed method.

Parametric Synthesis of the Control System of the Balancing Robot by the Numerical Optimization Method

This article is devoted to parametric synthesis of a control system of a two-wheeled balancing robot. From the mathematical point of view, the robot is an inverted pendulum type object with a pivot point placed on the wheel axis. This device is unstable while deenergized. Devices of this type are excellent labor atory stands for testing and debugging control algorithms of unstable nonlinear systems. The inverted pendulum math model is well studied theoretically but, when designing a particular device many additional tasks arise such as taking into account the error in measuring the tilt angle and the influence of actuator nonlinearities. In this paper, one of these tasks is solved, namely, the problem of reducing the amplitude of the robot’s oscillation around the equilibrium position. In practice, this oscillation almost always occurs in such systems and leads to various negative effects, such as increased energy consumption, increased wear of an actuator and heating of its windings, etc. Therefore, reducing the amplitude of the oscillation is an important task. To solve this task, the authors of the article propose to use the method of numerical optimization of the regulator, which is well recommended for solving many problems. The article analyzes the behavior of the device near the equilibrium position and identifies the causes of the self-oscillation. Further the method of its simulation is proposed. On the basis of numerical experiments, the main reason for the increase in the amplitude of the oscillation is revealed. The reason is an overlay of the reverse peak of the device transient process on the peak caused by a torque throw. The throw is generated by a combination of actuator backlash and static friction effects which cause the robot self-oscillation. The authors propose a technique of adjusting the regulator, aimed at reducing the magnitude of the reverse peak of the transition process and, as a consequence, reducing the amplitude of the oscillation. The effectiveness of the technique is confirmed experimentally by the results of numerical simulation of the robot’s behavior and the results of testing the coefficients obtained in a real device. The use of the technique allowed reducing the oscillation amplitude in a real device by almost three times.

Mathematical modeling of pneumatic semi-rotary actuator with friction

In this paper, the problem of modeling a pneumatic semi-rotary actuator for precise control in the presence of friction for future robotic manipulator applications is addressed. Precise commercial pneumatic components have become increasingly available and are widely applied in the processes and manufacturing industry. The robustness of pneumatic actuator solutions is limited by the precision of the system controller positioning, which depends on sophisticated algorithms that must deal with the highly nonlinear nature of the pneumatic system operation by means of the use of controllers that require suitable system knowledge. In this study, aiming at obtaining such a suitable model for a class of pneumatic semi-rotary actuator, the pressure dynamics in its chambers is modeled. The overall modeling task involves a detailed experimental identification of the curves of the mass flow rate related to the control voltage of the servovalve and its relationship with the pressures in the piston chambers. Moreover, friction was formulated with the LuGre model on account of its ability to represent different effects that comprise friction phenomena, including Coulomb, viscous and static friction effects, resulting in a comprehensive mathematical model for supporting future development of a nonlinear controller. Finally, validation in open loop was performed with comparisons between experimental and simulation results.

A Composite Bolted Joints Non-Linear Stiffness Model and its Application

The paper presents a nonlinear stiffness model on the bearing damage and bolt-load distribution rule of composite bolted joints. Based on the experimental stress-strain curves of composite single-bolted joints, the bearing damage process of structures can be divided into:linear non-damage stage; nonlinear damage propagation stage and linear degeneration stage. In this paper, the composite bolted joints are represented by a system of springs in which the static friction effects between laminates are considered in the linear stage, the non-linear interlaminate shear behavior and the nonlinear damage function for composite are defined and failure behavior based on the energy abortion principle is simulated in the linear degeneration stage. At last, the multi-fasters spring model is analyzed by importing the single-faster spring model.Comparing with the experimental data of multi-fasters shows the numerical result is in good agreement with experimental curves and has little error on the bolt-load distribution, which satisfies to the requirements in the engineering.

Study on Single-yarn Pullout Test of Ballistic Resistant Fabric under Different Preloads

During bullet penetrating fabric, the pull-out force of yarn in fabric is related to the impact resistance of fabric when the yarn is pulled out from the fabric. The complex uncrimping and friction slip behavior occur during the yarn pullout process, which is critical to learn the impact resistance of fabric. Based on digital image correlation technique, the deformation behavior of Kevlar 49 fabric subjected to preload during the single-yarn pullout process was studied in this paper. The pullout force and displacement curve shows a straight rise and an oscillated decrease. In the linear rise stage, the yarn uncrimping causes a static friction effect. The maximum of the pullout force is not linearly increased with the preload. In the oscillating descending stage, the local descent of the pullout force indicates that the yarn end is gradually withdrawn from the fabric, and the local rise indicates that the yarn end moves to the next weft/warp interaction until the yarn is completely pulled out. The shear deformation of fabric corresponds to the single-yarn pullout process.

Friction models for evaluating dynamic stresses in non-bonded flexible risers

This paper addresses friction models used for evaluating dynamic stresses in non-bonded flexible risers. A review of the most commonly used methods to model friction between layers in such structures was performed. Four models for calculating friction under dynamic contact pressure and constant shear interaction stick stiffness conditions were then formulated to enable stress calculation of cross-sections exposed to variable tension and bending loads. The friction models were implemented into a computer code used for numerical studies. A sensitivity study was carried out to determine the optimum shear interaction stick stiffness parameter, K0, with respect to representing the plane surfaces remain plane assumption. This was followed by an investigation of the performance of the developed models with respect to the tendon axial force next to the outermost fibre position. The proposed friction models were also verified against full scale tests in terms of bending moment-curvature data. As the test data indicated less bending stiffness in the stick domain than that can be obtained by the plane surfaces remain plane assumption, a method to estimate the parameter K0 was proposed, which accounted for the shear deformation of the plastic layers. The initial strain concept was further applied to deal with the significant hysteresis observed in the test data for low internal pressures pointing the way forward with respect to dealing with this effect in stress analysis. Furthermore, a friction model comparison study was carried out for investigating the static friction effect on the axial force at the outermost fibre position and the bending moment-curvature relationship.

Current-independent torque control of permanent-magnet synchronous motors

A current-independent torque equation for the permanent-magnet synchronous motor (PMSM) aiming at direct-drive servo applications is derived from a first principles model. Instead of measuring currents, all required control parameters are derived from optical incremental encoder measurements. The results are verified on a real system in test series showing the effect of static friction and proving the obtained torque model.

Design and Implementation of Model-Predictive Control With Friction Compensation on an Omnidirectional Mobile Robot

This paper presents and discusses the implementation results of a model-predictive control (MPC) scheme with friction compensation applied to trajectory following of an omnidirectional three-wheeled robot. A cascade structure is used with an inverse kinematics block to generate the velocity references given to the predictive controller. Part of the control effort is used to compensate for the effects of static friction, allowing the use of efficient algorithms for linear MPC with constraints. Experimental results show that the proposed strategy is efficient in compensating for frictional effects as well as for tracking predefined trajectories.

The Mechanism Analysis of Horizontal Vibrated Conveyor with Inclination

Considering the transition effect of static friction to dynamic friction, a two degree-of- freedoms vibration model of a new type of horizontal vibrated conveyor with inclination which can be used for continuous charging of electric arc furnace is formulated using d'Alembert principle. Based on the proposed vibration model, a program is wrote and the transmit mechanism is investigated. Computational results reveal numerous interesting conveying characteristics which can be used to forecast and control the vibration of the scrap and the conveyor.

Sliding mode control of a permanent magnet direct drive under non‐linear friction

PurposeThe purpose of this paper is to find a simple structure of motion controller for permanent magnet direct drive. Application of sliding mode controller theory and equivalent disturbance estimator creates proper non‐linear characteristics, which ensures controller robustness against friction.Design/methodology/approachThe position and speed controller is based on robust design methodology introduced by a sliding mode technique. The paper proposes a combination of sliding mode controller and proportional integral (PI) equivalent disturbance estimator. The friction model is Coulomb friction with a large static friction effect. The double boundary layer is used to compensate the effect of stiction. The synthesis is performed using simulation techniques and subsequently the behaviour of a laboratory speed control system is validated in the experimental setup. The control algorithms of the system are performed by a microprocessor floating point DSP control system.FindingsThe proposed sliding mode controller structure with equivalent disturbance estimator guarantees expected robustness against friction. Experimental results show that the control approach can decrease the tracking error, enhance the system's robustness and attenuate high‐frequency chattering in the control signal.Research limitations/implicationsThe proposed controller was tested on a single machine under well‐defined conditions. Further investigations are required before any industrial applications.Practical implicationsThe proposed controller synthesis and its results may be very helpful in robotic systems where non‐linear friction is a characteristic for many industrial robots and manipulators.Originality/valueThe method of sliding mode controller synthesis was proposed and validated by simulation and experimental investigations.

An analytical model for the prediction of load distribution in highly torqued multi-bolt composite joints

This paper presents the development of an enhanced analytical approach for modelling the load distribution in multi-bolt composite joints. The model is a closed-form extension of a spring-based method, where bolts and laminates are represented by a series of springs and masses. The enhancement accounts for static friction effects between the laminates, a primary mechanism of load transfer in highly torqued bolted joints. The method is validated against detailed three-dimensional finite element models and where possible, experimental results. The effect of varying bolt-torque and bolt-hole clearance on the load distribution in a three-bolt, single-lap joint is investigated and the method proves to be robust, accurate and highly efficient. Finally, the method is employed in a parameter study, where increasing bolt torque levels can be used for achieving a more even load distribution in multi-bolt joints.

Surge and Drag Analysis for Extended Reach Casing and Casing Flotation Operations With Centralizers: A Design Challenge?

Summary Refining advanced technologies for the successful completion of wells is paramount in high-risk, high-cost environments. Challenges are associated with complex well architectures and with the successful completion of wells deploying conventional or floated casing or liner strings. A key part of the design process is to be able to predict both maximum downhole surge pressures and dynamic and static friction effects. The analysis also needs to take into account the impact of using centralizing devices. Understanding these effects during both casing running and reciprocation is important so that appropriate operational decisions can be made. Specific challenges are associated with running liners through casing strings or hole sections with limited annular clearance. Centralizers are primarily installed on a casing string to provide adequate stand-off for primary cementing operations; however they are also sometimes used to aid in the deployment of casing strings. To achieve adequate stand-off, calculations are performed to determine the number of centralizers, their placement, and spacing frequency. Drag modeling is performed to ensure that the casing string will reach its target depth. This requires predictions of both static and dynamic drag effects that take into account the impact of centralizers and surge pressures on drag. In cases where non-rigid centralizers are used, conventional torque and drag models underestimate frictional drag effects. Similarly it is considered that steady state surge models under-predict maximum surge pressures. To address these concerns, both improved models and comprehensive analysis are required. This paper describes the analytical models that are used to incorporate additional forces associated with centralizers. Both conventional and floated casing running scenarios, especially in close tolerance extended reach wells, are considered.

Sliding-Mode Control With Double Boundary Layer for Robust Compensation of Payload Mass and Friction in Linear Motors

Direct drives with linear motors have been recently attracting the attention of both industry and academia. The main peculiarity of these systems is the lack of mechanical reduction and transmission devices, which makes the influence of some uncertain electromechanical phenomena (e.g., friction, cogging forces, etc.) and load disturbances much more significant than in the case of conventional rotary actuators. This paper describes a control system for a tubular synchronous linear motor based on a sliding-mode control (SMC) and a proportional-integral (PI)-based equivalent disturbance observer. The distinctive peculiarities of the proposed scheme are the use of a control law that guarantees the stability of the system regardless of the payload mass, the adoption of a double boundary layer addressing effectively the harmful effects of static friction, and the introduction of a simple PI-based equivalent disturbance observer that avoids steady-state errors regardless of model uncertainties and external disturbances. The reduced computational cost of the control law, alongside with the introduction of the effective design criteria for the SMC and the disturbance observer, makes the implementation of the proposed approach as simple as standard cascaded linear control schemes using industrial microcontrollers. The aforementioned considerations are validated by extensive experiments.

Adaptive satellite attitude control in the presence of inertia and CMG gimbal friction uncertainties

A nonlinear adaptive attitude controller is designed in this paper that compensates for dynamic uncertainties in the spacecraft inertia matrix and unknown dynamic and static friction effects in the control moment gyroscope (CMG) gimbals. Attitude control torques are generated by means of a four single gimbal CMG pyramid cluster. The challenges to develop the adaptive controller are that the control input is multiplied by uncertainties due to dynamic friction effects and is embedded in a discontinuous nonlinearity due to static friction effects. A uniformly ultimately bounded result is proven via Lyapunov analysis for the case in which both static and dynamic gimbal friction is included in the dynamic model, and an extension is provided that illustrates how asymptotic tracking is achieved when only dynamic friction is present in the CMG model.

The effects of static friction and backlash on extended physiological proprioception control of a powered prosthesis

In general, externally powered prostheses do not provide proprioceptive feedback and thus require the user to rely on cognitively expensive visual feedback to effectively control the prosthesis. Applying the concept of extended physiological proprioception (EPP) to externally powered prostheses provides direct feedback to the user's proprioceptive system regarding the position, velocity, and forces applied to the prosthesis. However, electric elbows with EPP controllers developed at the Northwestern University Prosthetics Research Laboratory have exhibited unexplained "jerky" behavior in both clinical fittings and bench-top operation. In addition, the development of limit cycles, a specific type of constant-amplitude oscillation, had been observed in bench-top use of these elbows. Backlash and static friction within the EPP system were found to be primarily responsible for the development of limit cycles. Reducing static friction and backlash improved the system's performance. These results suggest that to most effectively implement EPP, prosthesis manufacturers should design prosthetic components that minimize static friction and backlash.

Suppression of Parametric Resonance in Cantilever Beam With a Pendulum (Effect of Static Friction at the Supporting Point of the Pendulum)

The dynamic response of a parametrically excited cantilever beam with a pendulum is theoretically and experimentally presented. The equation of motion and the associated boundary conditions are derived considering the static friction of the rotating motion at the supporting point (pivot) of the pendulum. It is theoretically shown that the static friction at the pivot of the pendulum plays a dominant role in the suppression of parametric resonance. The boundary conditions are different between two states in which the motion of the pendulum is either trapped by the static friction or it is not. Because of this variation of the boundary conditions depending on the pendulum motion, the natural frequencies of the system are automatically and passively changed and the bifurcation set for the parametric resonance is also shifted, so that parametric resonance does not occur. Experimental results also verify the effect of the pendulum on the suppression of parametric resonance in the cantilever beam.

A neural network approach for force and contour error control in multi-dimensional end milling operations

The problem of controlling the average resultant cutting force together with the contour error in multi-dimensional end milling operations is considered in this study. Two sets of neural networks are used in the control system. The first set is used to specify the feed rate to maintain a desired cutting force. This feed rate is resolved along the feed axes using a parametric interpolation algorithm so that the desired part shape is obtained. The second set is used to make corrections to the feed rate components specified by the parametric interpolation algorithm to minimize the contour error caused by the dynamic lag of the closed-loop servo systems controlling the feed drives. In addition, the control system includes a feedforward input to compensate for static friction effects. Experimental results are presented for machining two-dimensional circular slots and a three-dimensional spherical surface to show the validity of the proposed approach.

Static Friction Effects During Hard-on-Hard Contact Tasks and Their Implications for Manipulator Design

In this article, we present the results and implications of our experimental study into the effects of static, nonlinear, fric tion during hard-on-hard contact tasks where making a stable contact is problematic. Experiments have been conducted with a PUMA 560 manipulator to address the hard-on-hard con tact stability problem and to stress the importance of damping (active-velocity feedback, and passive-nonlinear friction) for hard-on-hard applications typified by robotic drilling. Experi mental results reveal that during hard-art-hard contact, active damping is inoperative because of quantization, leaving only passive damping to stabilize the system. However, passive damping characteristics vary between joints. Most importantly, the last three joints of the manipulator, which are more af fected by contact force disturbances than others. lack sufficient passive damping, which we argue should match their respec tive joint stiffnesses to achieve contact stability. Therefore, we conclude that manipulator joints with low passive damping should have high-resolution encoders for velocity feedback. These are required to stabilize a force control system making a hard-on-hard constrained contact. The lower the joint friction, the higher the resolution required. This constitutes the main contribution of this article to manipulator design.