Load Sensor Research Articles

Singular Configuration Analysis and Singularity Avoidance with Application in an Intelligent Robotic Manipulator

Recently, robotic sensor systems have gained more attention annually in complex system sense strategies. The robotic sensors sense the information from itself and the environment, and fuse information for the use of perception, decision, planning, and control. As an important supplement to traditional industrial robots, co-bots (short for co-working robots) play an increasingly vital role in helping small and medium-sized enterprises realize intelligent manufacturing. They have high flexibility and safety so that they can assist humans to complete highly repetitive and high-precision work. In order to maintain robot safe operation in the increasing complex working environment and human–computer intelligent interactive control, this paper is concerned with the problem of applicant accuracy analysis and singularity avoidance for co-bots. Based on the dynamic model with load and torque sensors, which is used to detect the external force at the end of the robot, this paper systematically analyzes the causes of singularity phenomenon in the robot motion control. The inverse solution is obtained by analytical method and numerical method, respectively. In order to ensure the smooth and safe operation in the whole workspace, it is necessary for a robot to avoid singularity. Singularity avoidance schemes are utilized for different control tasks, including point-to-point control and continuous path control. Corresponding simulation experiments are designed to verify the effectiveness of different evasion schemes, in which the advantages and disadvantages are compared and analyzed.

The TecALSens project: new solutions for load sensors in aeronautics

In this paper the TecALSens project, developed within the Systems ITD of the Clean Sky 2 programme, is presented. The objective of the project is to design and validate a novel load sensor for aeronautic application based on thin-film sensing technology. So far, thin-film as sensing element has not been used in commercial aeronautic products: The outcome of this project tries to close this gap by providing a new class of load sensors complying with demanding aeronautic requirements. More and all electric aircraft configuration can benefit from the implementation of force measurement. This is an example of revolutionary approach to A/C design and a key enabler for achieving the environmental goals set by the European agenda up to 2050. Current project activities show very promising results: TecALSens provides a new approach to the design and manufacturing of load sensors for aeronautic applications. Especially, this new class of load sensors overcomes some of the drawbacks of strain gauge-based solutions. The final outcome of the project complies with the expected technology readiness level (TRL) 5. TecALSens outcome widens the possibilities offered by force sensing in aeronautics and strongly supports the evolution of aircraft design toward a more environmental friendly approach.

High-sensitivity fiber-optic Fabry-Perot transverse load sensor based on bubble microcavity

A miniature fiber optic transverse load sensor based on bubble microcavity is fabricated and demonstrated for transverse load sensing. The bubble is fabricated by using of the arc discharge to fuse a section of hollow capillary, which is spliced to a single mode fiber (SMF) end. In the entire fabrication process, only a fusion splicer is needed. When the transverse load is applied to the microcavity, the cavity length of the sensor is changed, then the load can be detected by investigating the cavity length. The white light interference (WLI) demodulation method based on digital cross-correlation technology is used to demodulate the cavity length, and the transverse load sensitivity and temperature sensitivity of the sensor are tested. For the 145-μm-long bubble microcavity, the sensor has a good linear response in the load range of 0 N to 0.88 N. A high cavity length-transverse load sensitivity of 311.3 nm/N and a high resolution of 0.19 mN are obtained. Moreover, the temperature sensitivity of the sensor is very low, and it does not need temperature compensation in practical use. Due to the miniature size, low cost, easy fabrication, high sensitivity, and low temperature sensitivity, the sensor has a high potential for transverse load sensing.

Modeling and Simulation of the Impact of Temperature on Single Point Load Cell using Trnsys 16.0: Measured, Uncompensated and Error Data for Zaria Kaduna State

A load cell is a piece of machined metal called a transducer or load sensor. As a measuring device, the entire framework is prone to the impact of environmental forces which can produce errors in the load cell output. The most significant force or input modifier is high ambient temperature. Typical meteorological year document demonstrates that in March, April, and May the temperature in Zaria can surpass 40ºC degrees on some days, including in most parts of northern Nigeria. It then implies that most weighing scales in the open environment will normally have a diminished sensitivity and along these lines yield wrong outcomes which can affect critical decisions with respect to weight control and well-being. Thus, this research aims to model and simulate the impact of high ambient temperature on a load cell using TRNSYS simulation studio. And its specific objectives are; to develop the model mathematically using the method of high gain feedback in a closed-loop to measure and compensate for errors due to ambient temperature above 40°C, to program the model using FORTRAN programming language at the back end, to simulate the model using a typical year meteorological weather data file for Zaria (11.0855°N, 7.7199°E). The procedures to model and simulate the effect of high ambient temperatures on load cell sensitivity include; the development of the model mathematically using the equation for high gain feedback in a closed-loop, programing the model using FORTRAN programming language (g 95 in Code block IDE), simulation of the model using a typical year meteorological weather data file for Zaria, (obtainable from meteorological Agencies). In the simulation, 75 kg was used as the sample weight. And the data obtained shows that in March at 1416.0 h, when no load is applied, there is a drift in the output range of the system even though the ambient temperature 20.152°C is within the scope of load cell compensation. Noticeably, the feedback system re-calibrated the scale thus eliminating the error and returning the gauge to 0.0 kg. The highest ambient temperature in March was recorded at 1981.0 h as 47.246°C with a corresponding error of 0.142. The feedback system evaluates the uncompensated value, eliminates the error and returns a correct value of 75 kg corresponding to the measured value. In April a drift in the system output range was also noticed at 2160.0 h, with a corresponding error of 0.150 before the feedback system re-calibrated the scale to 0.0 kg. The highest ambient temperature for April is 46.48°C at 2292.0 h and the corresponding error is 0.139. The feedback system again evaluates the uncompensated value, resolves the error and returns 75 kg corresponding to the measured value or known weight. While in May a drift in the system output range was also noticed at 2880.0 and the feedback system quickly returns the value to 0.0 kg. The highest ambient temperature of 46.86 is seen at 3037.0 h with a corresponding error of 0.141. The feedback system again evaluates the uncompensated value, resolves the error and returns 75 kg corresponding to the measured value.

Gas leakage detection and level monitoring system based on IoT

Liquefied Petroleum Gas (LPG) is widely used for heating, cooking, automotive fuel, and a variety of other applications around the world. Liquefied Petroleum Gas is highly flammable. There had been many serious accidents, such as explosions and fires involving leakage of liquefied gas. If a leak is not noticed early enough, such accidents can have dangerous consequences. The problems of gas leakage and cylinder availability are faced daily. LPG is a flammable gas that is used to power heating appliances. The risk of structural fire, asphyxiation, or explosion is increased if this gas escapes. This problem can be solved by developing an effective means of detecting gas leaks. The user will be alerted via ThingSpeak as soon as a gas leak is detected. This project also deals with the percentage of gas remaining in the cylinder, which is determined by a sensor known as a load cell, and the percentage of gas remaining in the cylinder is constantly updated in ThingSpeak. When a gas leak is detected, the buzzer makes sound. In addition to this, gas levels are often detected and the user is alerted via ThingSpeak. The main goal of this project is to create a gas leak detection and monitoring system based on the Internet of Things (IoT). With the use of a gas sensor and a load sensor, this system will be able to monitor gas leakage and gas level. This data is transmitted to the user via the Internet of Things and displayed using ThingSpeak.

Distributed Sliding Mode Fault‐Tolerant LFC for Multiarea Interconnected Power Systems under Sensor Fault

This paper focuses on the problem of load frequency control and sensor fault‐tolerant control in the multiarea power grid. To solve these problems, a sliding mode control strategy based on an interval observer is designed. First, an interval observer is designed to obtain the boundary estimation information of the system state online, which is used to reconstruct the load disturbance online. Based on the reconstructed values, an integral sliding mode controller is designed to keep the system frequency stable when the load is disturbed. Then, sensor fault is diagnosed by interval residual. An augmented observer is designed to estimate sensor fault online by equivalent transformation, and the sensor fault is compensated by the fault estimation to reduce the influence of fault on system performance and ensure the reliable and stable operation of the power system. The simulation results show the superiority of the proposed control strategy.

The Validity and Reliability of Two Commercially Available Load Sensors for Clinical Strength Assessment.

Objective: Handheld dynamometers are common tools for assessing/monitoring muscular strength and endurance. Health/fitness Bluetooth load sensors may provide a cost-effective alternative; however, research is needed to evaluate the validity and reliability of such devices. This study assessed the validity and reliability of two commercially available Bluetooth load sensors (Activ5 by Activbody and Progressor by Tindeq). Methods: Four tests were conducted on each device: stepped loading, stress relaxation, simulated exercise, and hysteresis. Each test type was repeated three times using the Instron ElectroPuls mechanical testing device (a gold-standard system). Test–retest reliability was assessed through intraclass correlations. Agreement with the gold standard was assessed with Pearson’s correlation, interclass correlation, and Lin’s concordance correlation. Results: The Activ5 and Progressor had excellent test–retest reliability across all four tests (ICC(3,1) ≥ 0.999, all p ≤ 0.001). Agreement with the gold standard was excellent for both the Activ5 (ρ ≥ 0.998, ICC(3,1) ≥ 0.971, ρc ≥ 0.971, all p’s ≤ 0.001) and Progressor (ρ ≥ 0.999, ICC(3,1) ≥ 0.999, ρc ≥ 0.999, all p’s ≤ 0.001). Measurement error increased for both devices as applied load increased. Conclusion: Excellent test–retest reliability was found, suggesting that both devices can be used in a clinical setting to measure patient progress over time; however, the Activ5 consistently had poorer agreement with the gold standard (particularly at higher loads).

Energy Saving on a Full-Size Wheel Loader Through Variable Load Sense Margin Control

Abstract This paper presents the formulation of a variable load sense control strategy suitable to achieve power savings in hydraulic systems using postcompensated load sensing (LS) hydraulic control architectures. Such architecture is typical in off-road construction machinery. The paper also describes the application of the proposed control strategy referred to as variable load sensing margin (VLM) on a full-size wheel loader. The paper first presents the rationale for the proposed strategy, showing how the state-of-the-art LS architecture present in commercial machines has a margin for lowering the throttling losses present at the control valves. A feedforward controller, derived from an empirical study on a reference vehicle, is used to control the flow to the front-end loader functions. Test results show improvements of the hydraulic power consumption up to 45%, based on the commanded speed of each front-end loader actuator. The paper also describes a gain scheduling pressure feedback control strategy, which is used to allow controlling also functions that include priority. For the case of off-road vehicles, this is typically the steering function. The experimental results show good performances with an error in controlled velocity below 5%, which is achieved when the front-end loader functions are used concurrently with the steering.

Fiber Optic Load Cells with Enhanced Sensitivity by Optical Vernier Effect.

Developing technologies capable of constantly assessing and optimizing day-to-day activities has been a research priority for several years. A key factor in such technologies is the use of highly sensitive sensors to monitor in real-time numerous parameters, such as temperature and load. Due to their unique features, optical fiber sensors became one of the most interesting and viable solutions for applications dependent on those parameters. In this work, we present an optical fiber load sensor, called load cell, based on Fabry–Pérot hollow cavities embedded in a polymeric material. By using the load cells in a parallel configuration with a non-embedded hollow cavity, the optical Vernier effect was generated, allowing maximum sensitivity values of 0.433 nm N−1 and 0.66 nm °C−1 to be attained for vertical load and temperature, respectively. The proposed sensor’s performance, allied with the proposed configuration, makes it a viable and suitable device for a wide range of applications, namely those requiring high thermal and load sensitivities.

A blockchain‐enabled secured fault allocation in smart grids based on μ PMUs and UT

Improvements in the high accuracy of micro-phasor measurement unit (μPMU) and synchrophasor unit provide the distribution network a special perspective to access full observability in the presence of renewable distribution generations (DGs). In this regard, modelling the uncertainty effects for accurate fault detection in smart grids has become a novel turning point. This research work attempts to develop a novel stochastic architecture based on unscented transform (UT), which requires a very few number of μPMUs, to communicate in a secured blockchain-enabled structure to allocate and detect the smart grid irregularities and faults. Such a blockchain-based technique can be beneficial for encrypting the data transmitted among the μPMUs in the smart grid consisting of a variety of distributed energy sources (DERs) and high impedance fault events, while incorporating the uncertainties associated with the load and individual installation sensors. The proposed stochastic structure benefits from voltage measurement and uses its angle in event placement that performs more efficiently than the conventional sensors based on high-voltage and current metering. The simulation results show the great precision and effectiveness of the proposed model during various fault scenarios in smart grid.

THE HEAT TREATMENT EFFECT ON THE MAGNETOELASTIC SENSITIVITY OF HIGH-CHROMIUM STEEL TO LOW-CYCLE ELASTIC DEFORMATIONS IN THE MAGNETOELASTIC MEMORY MODE

The magnetoelastic tests’ results for the 30Kh13 steel samples hardened and tempered at different temperatures are presented. The samples premagnetized to saturation are treated to a fivescore-cycle stretching effect. It is followed by repetition with the load increase by 50 MPa. The magnetic field intensity of the residual magnetization is recorded synchronously with the active load. The high structural sensitivity of magnetoelastic irreversible demagnetization  = ∆H/∆σ in the low loads’ part is shown and explained. It allows using this parameter for non-destructive quality control of steels with properties close to 30Kh13 and the same composition products. Samples with a high tempering temperature of 600...700 С make it possible to create peak (limit) load sensors and fatigue damage sensors on their basis. It is proposed to use them in the form of glued foil or wire elements that can work off-line.

Tibiofemoral dynamic stressed gap laxities correlate with compartment load measurements in robotic arm-assisted total knee arthroplasty.

AimsIt is unknown whether gap laxities measured in robotic arm-assisted total knee arthroplasty (TKA) correlate to load sensor measurements. The aim of this study was to determine whether symmetry of the maximum medial and lateral gaps in extension and flexion was predictive of knee balance in extension and flexion respectively using different maximum thresholds of intercompartmental load difference (ICLD) to define balance.MethodsA prospective cohort study of 165 patients undergoing functionally-aligned TKA was performed (176 TKAs). With trial components in situ, medial and lateral extension and flexion gaps were measured using robotic navigation while applying valgus and varus forces. The ICLD between medial and lateral compartments was measured in extension and flexion with the load sensor. The null hypothesis was that stressed gap symmetry would not correlate directly with sensor-defined soft tissue balance.ResultsIn TKAs with a stressed medial-lateral gap difference of ≤1 mm, 147 (89%) had an ICLD of ≤15 lb in extension, and 112 (84%) had an ICLD of ≤ 15 lb in flexion; 157 (95%) had an ICLD ≤ 30 lb in extension, and 126 (94%) had an ICLD ≤ 30 lb in flexion; and 165 (100%) had an ICLD ≤ 60 lb in extension, and 133 (99%) had an ICLD ≤ 60 lb in flexion. With a 0 mm difference between the medial and lateral stressed gaps, 103 (91%) of TKA had an ICLD ≤ 15 lb in extension, decreasing to 155 (88%) when the difference between the medial and lateral stressed extension gaps increased to ± 3 mm. In flexion, 47 (77%) had an ICLD ≤ 15 lb with a medial-lateral gap difference of 0 mm, increasing to 147 (84%) at ± 3 mm.ConclusionThis study found a strong relationship between intercompartmental loads and gap symmetry in extension and flexion measured with prostheses in situ. The results suggest that ICLD and medial-lateral gap difference provide similar assessment of soft-tissue balance in robotic arm-assisted TKA.Cite this article: Bone Jt Open 2021;2(11):974–980.

BLDC 모터 및 유압식 브레이커 기반의 하이브리드 동력의지 개발

The purpose of this study was to develop a hybrid-powered prosthetic knee and ankle (power leg) using the brushless DC (BLDC) modules and hydraulic breakers of stance and swing phase control. The system comprised BLDC motors for the swing phase control unit and hydraulic cylinders for the stance phase control unit. An individual could walk using a low-power battery for a longer time than with a fully active or powered prosthetic leg. Moreover, the individual could walk by applying less kicking force. More stable lateral symmetry was exhibited than a prosthesis of stance phase control type. The gait algorithm is classified into five gait events using the inertial and load sensors: heel contact, heel rise, toe-off, swing flexion, and swing extension. We controlled the hydraulic breaker’s resistance force at each gait event and generated gait motion using the BLDC motors. The reliability of the system was evaluated by a transfemoral amputee subject. By comparing the gait character between the power leg and the stance phase control type prosthesis, we confirmed that the power leg improved the center of pressure (COP) of the lateral symmetry by about 71% from the center.

Numerical and experimental studies on needle impact characteristics in ultrasonic shot peening

Ultrasonic shot peening(USP) is an advanced surface treatment technology for obtaining excellent surface properties or manufacturing a three-dimensional curved surface of the metal sheets. The impact of the medium driven by ultrasonic vibration is significant to parameter optimization and excellent performance of the USP technology. However, the impact characteristics of the medium lack careful study, which is a complex dynamic analysis involving many factors, such as collision, plastic deformation, air pressure, etc. In this paper, a detection system is successfully developed to investigate the needle impact force and frequency against the material surface, consisting of a piezoelectric load sensor, oscilloscope, and a single needle USP device. Moreover, the FE model of the needle impact is developed simultaneously to study the characteristics of residual stress implantation induced by needle impact. Based on the experiment and FE simulation results, it is discovered that the impacts with high speed primarily determine the thickness of the modified layer implanted with residual stress during multiple impacts at different rates. According to residual stress implantation characteristics, the low-speed impact whose speed does not reach 50% of the maximum impact speed was defined as the ineffective impact. Besides, increasing the amplitude of ultrasonic vibration results in a significant increase in the maximum impact force and the effective impact frequency. The travel distance of needle impact has a considerable effect on the effective impact frequency, but it has little effect on the maximum impact force. Finally, it was concluded that the low air pressure plays a positive role in the needle impact. Furthermore, excessive air pressure hinders the needle impact and results in a decline in the effective impact frequency and the maximum impact force.

IoT Based LPG Gas Level Detection & Gas Leakage Accident Prevention with Alert System

Liquefied Petroleum Gas (LPG) is widely used for cooking fuel in developing countries for economic reasons, for energy-rich fuel source that contains the higher calorific value, for clean fuel with low carbon emission and for a portable that is available in even the faraway of areas. Therefore the proposed gas leakage detection and monitoring system for the gasoline content present in household LPG cylinder is developed. Usually, the capacity of LPG in cylinder is not determined in an exact manner and a cylinder when the gas is about to empty will be a difficult situation for the one who uses LPG gas for cooking continuously. By using IoT, the information of the near to the empty level of LPG gas in the cylinder will send to the user and the gas refill method by using telephonic ordering can be conducted. The purpose of this research is the detection of gas leakage and monitoring the LPG gas cylinder weight regularly to know the remaining value of gas in the cylinder. When the gas leakage is sensed, the warning signal and alarm sound will be active and also switch on exhaust fan automatically to decrease the gas concentration. The weight of LPG is measured using the load sensor (SEN-10245) and the output of the sensor is connected with Arduino MKR Wifi 1010 microcontroller. The user can know the validity of LPG usage daily because the amount of LPG gas will publish as events and watch them come through in real-time using the Wia IoT cloud platform. Consequently, the user is alerted by giving SMS notification to their mobile phone when the LPG level is critically low (below 20%) by use of the integration function of the Wia IoT platform call Twilio, using its web service APIs. Then by detecting the gas leakage with MQ6 gas sensor, this research work indicates for gas leakage condition and also helps to prevent the LPG gas burst accidents in the home.

Designing the Calibration Process of Weigh-In-Motion Systems

Weigh-In-Motion (WIM) systems provide information on the state of road traffic and are used in activities undertaken as part of traffic supervision and management, enforcement of applicable regulations, and in the design of road infrastructure. The further development of such systems is aimed at increasing their measurement accuracy, operational reliability, and their resistance to disturbing environmental factors. Increasing the accuracy of measurement can be achieved both through actions taken in the hardware layer (technology of load sensors, the number of sensors and their arrangement, technology used in the construction of the pavement, selection of the system location), as well as by implementing better system calibration algorithms and algorithms for pre-processing measurement data. In this paper, we focus on the issue of WIM system calibration. We believe that through the correct selection of the calibration algorithm, it is possible to significantly increase the accuracy of vehicle weighing in WIM systems, from a practical point of view. The simulation and experimental studies we conducted confirmed this hypothesis.

In-Tire Distributed Optical Fiber (DOF) Sensor for the Load Assessment of Light Vehicles in Static Conditions.

Modern vehicles are using control and safety driving algorithms fed by various evaluations such as wheel speeds or road environmental conditions. Wheel load evaluation could be useful for such algorithms, particularly for extreme vehicle loading or uneven loads. For now, smart tires are only equipped by tire pressure monitoring systems (TPMS) and temperature sensors. Manufacturers are still working on in-tire sensors, such as load sensors, to create the next generation of smart tires. The present work aims at demonstrating that a static tire instrumented with an internal optical fiber allows the wheel load estimation for every wheel angular position. Experiments have been carried out with a static tire loaded with a hydraulic press and instrumented with both an internal optical fiber and an embedded laser. Load estimation is performed both from tire deflection and contact patch length evaluations. For several applied loads from 2800 to 4800 N, optical fiber load estimation is realized with a relative error of 1% to 3%, almost as precisely as that with the embedded laser, but with the advantage of the load estimation regardless of the wheel angular position. In perspective, the developed methodology based on an in-tire optical fiber could be used for continuous wheel load estimation for moving vehicles, benefiting control and on-board safety systems.

Пластинчатые амортизаторы-демпферы в натяжных устройствах ленточнопильных станков

The article analyses strengths and weaknesses of bandsaw machines. While analysing we have found the relationship between the weaknesses and the tension of a band saw. Its use as a cutting tool leads to a decrease in the lateral rigidity and stability of the cutting section on the pulling chain. This leads to fluctuations in the cutting width, a decrease in the geometric accuracy of sawn timber and an increase in the roughness of the side surfaces of a kirf. The main types of tensioning unit mechanisms, which strengthen the tension and maintain its stability during operation, are defined, and common design flaws are described. Oil-filled metal plate dampers promote space-saving and low-inertia dampers for bandsaw machines with any basic saw blade tensioning mechanisms. The influence of the device on the level of dynamic fluctuations of the tensile force caused by the artificial eccentricity of the tension pulley was studied. The efficiency was evaluated by computer oscillography of the tensile load sensor signal and subsequent computer processing of the obtained oscillograms. The effectiveness of using damper devices is confirmed by the quality of sawing, which is characterized by a lower level of roughness of the lateral surfaces of the cut while reducing the variation in thickness of a workpiece. Methods of eliminating flaws with different types of tensioning units are reviewed, and the effectiveness of using oil-filled plate dampers is evaluated. The article presents the research technique and parameters of the experimental unit as well as the conclusions on the effectiveness of damping devices. For citation: Alekseev A.E., Dumanskij I.O., Prokhorov A.V. Plate Dampers in the Tensioning Units of Bandsaw Machines. Lesnoy Zhurnal [Russian Forestry Journal], 2021, no. 5, pp. 142–149. DOI: 10.37482/0536-1036-2021-5-142-149

DESIGN AND ANALYSIS OF ADVANCED WALKER CUM ROLLATOR

Over the year’s walker or rollator have helped many elderly people to overcome the barrier of dependency. As the age grows, the muscles and bones suffer weakening due to lack of calcium because of which person has to depend on others for their movement. This unwanted condition creates a bad physiological and psychological impact on the victim and slowly pulls them out of all possible types of interactions with society. Thus, to make the walker more users friendly, safe, and reliable, a new design or solution is proposed. This not only addresses the problem which is prevalent in the elderly section of society but also will be helpful to people with other disabilities. The proposed design of the walker is to increase the safety and movability of the user. The design of this walker is advanced as it consists of various sensors like an Obstacle sensor, GPS, and Load Sensor. In this paper, the design and analysis of an advanced walker cum rollator is elaborated, which significantly reduces the challenges faced by the elderly and specially challenged in day-to-day life.

Simultaneous transverse load, refractive index, and high-temperature sensor based on michelson interferometer

An all-fiber sensor based on single-mode fiber (SMF) and simple fusion technology for simultaneous transverse load, refractive index, and high-temperature measurement is proposed and experimentally demonstrated. The device consists of a fiber taper by manual control of splicer and a cap-like structure formed at the end face of SMF by discharging. Demodulated by wavelength, experimental results show that the transverse load, refractive index (RI), and high-temperature wavelength sensitivities of the cap-like MI sensor are −1.412 nm/N, 200.07 nm/RIU, and 8.4 pm/°C, respectively. Demodulated by intensity, the sensor has the RI sensitivity as high as −145.54 dB/RIU, and the cross-sensitivities of transverse load and temperature are 0.0032RIU/N and 0.00002RIU/°C. The cap-like MI optical fiber sensor has the advantages of small volume, easy manufacture, low cost, high reliability, and good mechanical strength which are very important in the application in oil exploitation and monitoring structural health.