Flexible strain sensors have aroused widespread concern due to their potential applications in detecting human motion and health. Carbon-based materials are surpassing candidate materials for flexible strain sensors with superior performances, because of their outstanding electrical conductivity, lightweight and flexibility, and excellent stability. In order to satisfy the detecting requirements for different strain forms in practical applications, various types of strain sensors based on carbon materials have been designed and prepared, including tensile, pressure, bending, torsion, and multiplex strain sensors. Herein, the latest advances in the preparation of flexible carbon-based strain sensors are reviewed according to the strain types. Furthermore, the potential applications and existing challenges of sensors in the field of human motion and physiological information detection are summarized. This review aims to provide some references for further exploitation of high-performance flexible carbon-based strain sensors.

Wearable Carbon-Based Resistive Sensors for Strain Detection: A Review

Strain gauge made of thick-film resistors (TFRs) has great potential for civil engineering applications due to its relatively high strain sensitivity, good stability, low manufacturing cost, mass productability, and long life. Nevertheless, a persistent shortcoming of strain sensors is their thermal sensitivity. Temperature-insensitive strain measurement is important for applications. To address this issue, a thick-film resistor strain sensor with low temperature-sensitivity should be proposed and fabricated. In this paper, the effect of resistor paste components and firing temperatures on the temperature coefficient of resistance (TCR) of TFRs were studied systematically. TFRs made of various RuO2 concentrations (10 wt% to 30 wt%) fired on Al2O3 substrate at different firing temperatures (Tf) was investigated. The relationships between sheet resistivity, TCR and gauge factor (GF) were studied. The results show that hot TCR increases with increasing RuO2 concentration and firing temperature. In the vicinity of the minimum of the resistance–temperature curve (Tmin), the temperature has the least influence on the resistance value, and it can be considered that the TFR is temperature insensitive in a certain range. The effect of temperature on output strain can be evaluated by the ratio of TCR to GF. The results show that TCR, the ratio of TCR to GF and Tmin are all depended on sheet resistivity of thick-film resistors. By changing the concentration of the conductive phase and firing temperature, the sheet resistivity of TFRs can be controlled, and then strain sensors with low temperature-sensitivity for different ambient temperatures can be achieved.

Temperature characteristics of thick-film resistors and its application as a strain sensor with low temperature-sensitivity

The invention discloses a lifting platform for electric power overhauling. The lifting platform for electric power overhauling comprises a base and universal wheels which are arranged under the base. A horizontal movement platform is arranged above the base. Sliding grooves are formed in the side walls of the two sides of the base correspondingly. Lead screws are arranged in the sliding grooves. Lead screw bases are arranged on the two sides of each sliding groove correspondingly. Motors used for driving the lead screws are arranged on the inner sides of the lead screw bases. Sliding blocks are arranged on the two sides of the horizontal movement platform correspondingly. The sliding blocks are arranged on the lead screws in a sleeving mode and can move in the axis direction of the lead screws. A vertical movement platform is arranged above the horizontal movement platform. Four lifting devices are arranged between the vertical movement platform and the horizontal movement platform. According to the lifting platform for electric power overhauling, three-direction movement of the lifting platform in the horizontal direction and the vertical direction can be achieved.

Lifting platform for electric power overhauling

The invention discloses a real-time high-precision detection method and system for a bolt pre-tightening force based on a piezoelectric ultrasonic wafer The piezoelectric ultrasonic chip is used as an ultrasonic excitation source to be attached to a bolt head, and a high-precision fitting relationship between an ultrasonic flight time difference and the bolt pre-tightening force is established byusing the change law of an ultrasonic single-wave time difference with the stress value; and real-time detection of the bolt pre-tightening force is achieved by using the mathematical relationship Compared with the prior method using the ultrasonic probe, the method provided by the invention eliminates the error caused by the uncertainty of the thickness of the coupling agent, and further improves the measurement accuracy by using the single-wave time difference Low-error-rate measurement of the bolt pre-tightening force is achieved at low cost and without influencing the structural performance

Real-time high-precision detection method and system for bolt pre-tightening force based on piezoelectric ultrasonic wafer

Aiming at studying the variation of the machine tools' dynamic characteristics in generalized manufacturing space,a concept of generalized modal and dynamic stiffness is put forward. Finite element method is employed to set up dynamic models for a three-axis gantry-type machine tool and a four-axis vertical machine tool. Modal and dynamic response analysis are carried out through out the whole manufacturing space with dynamic model modified method,in order to establish generalized modal function and stiffness map function respectively. By means of generalized modal analysis for three-axis gantry machine tool,the first five order natural frequencies of the machine tool through out the manufacturing space are obtained. The results show that the maximum change of natural frequencies can reach up to 25% during machining process,so complete modal information is obtained to provide data for performance optimization of machine tool. With the analysis of generalized dynamic stiffness for four-axis vertical machine tool,it can be concluded that the best working state in some frequency is not the best one for another,and then the theoretical support is present for the process optimization and accuracy promotion of machine tools.

Dynamic Characteristic Analysis for Machine Tools Based on Concept of Generalized Manufacturing Space

A piezoelectric dynamometer can produce thermal forces because of temperature fluctuations, thus affecting measurement precision. To investigate the influence of the thermal force on the dynamomete...

A novel piezoelectric dynamometer based on double-sensor for thermal compensation

The invention provides a six-degree-of-freedom lifting platform car, belonging to the field of engineering machinery, and particularly being applied to mobile transportation and position fine-tuning of aerospace test pieces on a test bench. The six-degree-of-freedom lifting platform car comprises a lifting platform base, a transverse mobile platform, a lifting mechanism and a test piece supporting frame. The six-degree-of-freedom lifting platform car has the advantages of realizing movement and fine tuning on any direction on the horizontal position, fine tuning on the vertical height and fine tuning around the rotation angle of a vertical center shaft for the carried test pieces. The six-degree-of-freedom lifting platform car has heavy carrying weight and high mounting precision, can realize self locking of the test pieces, and ensures the accuracy of test experiments.

Six-degree-of-freedom lifting platform car

Purpose




This paper aims to improve calibration and force measurement accuracy of multi-sensors’ piezoelectric dynamometer used in thrust measurement of rocket/air vehicle engine.




Design/methodology/approach




This paper presents a mapping solution method of sensors’ outputs based on the Kirchhoff thin plate theory, builds force-deformation differential equations with specific boundary conditions, uses finite difference (FD) method to solve the equations and analyzes outputs in offset loading forces in four-sensor square layout in main direction. The resultant force deviations calculated by the Kirchhoff theory are optimized with sequence quadratic program (SQP) method, and a calibration method of multiple loading points (MLP) based on the Kirchhoff theory is presented. Experiments of static calibration and verification are complemented to contrast the novel and single loading point (SLP) calibration method.




Findings




Experiments of static calibration and its verification show that at a loading force of 5,000N, the average resultant force deviations with MLP is 17.87N (0.35% FS) compared with single loading point method 26.45N (0.53% FS), improving calibration and measurement precision.




Originality value




A novel calibration method with MLP is presented. Force distributions of multiple sensors of main direction in piezoelectric dynamometer with offset loading force are solved with the Kirchhoff theory. The resultant force deviations calculated by Kirchhoff theory are optimized with the SQP method.

A novel calibration method based on Kirchhoff theory for piezoelectric dynamometer

Abstract It is important to improve the natural frequency of test device to improve measurement accuracy. First-order frequency is basic frequency of dynamic model, which generally is the highest vibration energy of natural frequency. Taking vector force test device (VFTD) as example, a novel dynamic design method for improving first-order natural frequency by increasing structure stiffness is proposed. In terms of six degree-of-freedom (DOF) of VFTD, dynamic model of VFTD is built through the Lagrange dynamic equation to obtain theoretical natural frequency and mode shapes. Experimental natural frequency obtained by the hammering method is compared with theoretical results to prove rationality of the Lagrange method. In order to improve the stiffness of VFTD, increase natural frequency and meet the requirement of high frequency test, by using the trial and error method combined with curve fitting (TECF), stiffness interval of meeting natural frequency requirement is obtained. Stiffness of VFTD is improved by adopting multiple supports based on the stiffness interval. Improved experimental natural frequency is obtained with the hammering method to show rationality of the dynamic design method. This method can be used in improvement of first-order natural frequency in test structure.

A Novel Dynamic Method to Improve First-order Natural Frequency for Test Device

The invention discloses a piezoelectric small-range large-range ratio force-measuring device, which comprises piezoelectric crystal groups, fastening bolts, a pressure plate, sealing rings and a lead joint. The piezoelectric crystal groups serve as force-sensing elements and have the characteristics of high sensitivity, high stiffness and high natural frequency, and requirements of a high-precision test can be met. One X0 piezoelectric crystal group is arranged in the main direction, the other four Y0 crystal groups are arranged in two lateral directions, and thus vector forces in the main direction and the lateral directions are tested respectively. The fastening bolts are used for preloading piezoelectric crystal plates in the main direction and the lateral directions, the preloading force and a lateral force range can be adjusted, and the difficulty of testing a large range ratio of the main direction force and the lateral direction force can be solved. Due to the design of a two-way push-pull structure, influences on the test precision by outside temperature changes can be avoided. The test device has the advantages that the structure is simple, packaging is convenient, adjustment is convenient, and high-precision three-dimensional dynamic force test can be realized.

Piezoelectric small-range large-range ratio force-measuring device

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