High-precision Measurement Instrument Research Articles

Accuracy improvement of laser tracker registration based on enhanced reference system points weighting self-calibration and thermal compensation.

Improving the accuracy of large measurement systems consisting of multiple laser trackers and Enhanced Reference System (ERS) points is technically challenging. In practice, standard devices with precise distance limits are often used to improve the registration accuracy of laser trackers. However, these standard devices are expensive and need to be calibrated by the Coordinate Measuring Machine (CMM). In addition, the stability of ERS points can significantly affect registration errors. Therefore, this paper proposes a laser tracker registration method based on ERS point-weighted self-calibration and thermal deformation compensation. First, a self-calibration method for simple standard devices based on multilateration measurements is presented, which only utilizes large measurement systems without additional high-precision measurement instruments. Based on this, a weighted registration optimization algorithm for the registration process of a relocation laser tracker is proposed. Then, the position errors of ERS points caused by temperature changes are calculated and compensated based on the thermal deformation coefficient of large structural components. The compensated ERS points are used for the registration of the laser trackers. Finally, the effectiveness of the proposed method is demonstrated by a field measurement experiment on a large spherical shell. Compared with the most widely used benchmark method, the proposed method reduces the average registration error of all ERS points from 0.103 to 0.02mm.

Comparison of 3-D Self-Calibration Methods for High-Precision Measurement Instruments

Three-dimensional self-calibration for high-precision 3-D measurement instruments can separate the system errors using an auxiliary artifact, with accuracy comparable to that of the instrument to be calibrated, having significant advantages in terms of production costs and realization conditions. The auxiliary artifact is rotated and/or translated to different positions. From measurements of the artifact in various positions, the system errors of the measurement instrument are separated after the elimination of the artifact’s errors through the self-calibration model. In this study, an iterative optimization method in 2-D self-calibration was extended to 3-D and compared with an established 3-D self-calibration method, namely the equation method based on least squares. The optimization method involves an optimization of 3-D instrument to eliminate its system errors by a correction function during an iterative loop. The equation method is used to establish a 3-D self-calibration model and solve the overdetermined equation model by least squares. The uncertainties of these two methods were analyzed using different approaches. The two methods were compared by simulation with the separated system errors and the effect of calibration when the artifact position scheme changed. Experiments on a computed tomography (CT) instrument were conducted to confirm the effectiveness of the two methods of 3-D self-calibration, through the mutual verification of results.

Design, calibration, and application of the position sensitive detector-based photoelectric reference ruler

A photoelectric reference ruler is designed based on position sensitive detector (PSD) for providing the reference length. A calibration method of the photoelectric reference ruler is proposed, which introduces the common points for transition between the PSD coordinate systems. The common points are confirmed based on the special workpiece with positioning holes. Through placing the 1.5-in. ball target on the positioning holes, the coordinate systems and the common points for transformations are structured by high-precision measurement instruments. After the calibration, the double-theodolites system is oriented by the photoelectric reference ruler and operated to measure the spatial points and distances in the experiment. The mean error is <0.18 mm in points measurement and <0.14 mm in distance measurement, and the feasibility of the proposed calibration method is validated. Compared with the traditional reference ruler, the photoelectric reference ruler is proved to be applicable for measurement system orientation and spatial large-scale measurement.

3-D Self-Calibration for High-Precision Measurement Instruments With Hybrid Positions

Calibrating high-precision 3-D measuring instruments by using traditional calibration methods is challenging because these instruments require the use of higher-precision calibration artifacts. Self-calibration models can separate system errors from overall measurement errors by using auxiliary artifacts with accuracy within that of the object to be calibrated; therefore, such models have substantial advantages in terms of production costs and realization conditions. This article proposes a least-squares-based 3-D self-calibration model involving a hybrid position of the artifact. In this model, the calibration artifact is rotated or translated from its initial position to other positions and then used to execute measurements. Compared with existing 3-D self-calibration models, which require four positions, the proposed model involves three positions, including a hybrid position obtained through both rotation and translation. Thus, the proposed model requires fewer steps and a shorter processing time. Simulations were conducted to evaluate the 3-D self-calibration model, and the simulation results validated its ability to separate system errors from overall measurement errors generated by noise. An error propagation ratio of < 1 was also obtained for the model, indicating that the model can suppress noise. Experiments conducted using a computed tomography instrument confirmed the effectiveness and repeatability of this model; specifically, the standard deviation among the artifacts back to the initial position after the 3-D self-calibration process was less than that observed before the calibration process.

State Primary Standard of Unit of Specific Heat Capacity of Solids (Get 60-2019)

The results of studies designed to improve the State Primary Standard of the unit of specific heat capacity (GET 60-74) carried out from 2017 to 2019 are described. A complex of high-precision measurement instruments that form the new State Primary Standard of the heat capacity of solids (GET 60-2019) at the head of which is the KA-S4 high-precision calorimeter was created. A set of standard measures of specific heat capacity was created to reproduce and transmit the unit from GET 60-2019 to lower-echelon measurement instruments. The measurement chain for transmission of the unit of specific heat capacity from GET 60-2019 to lower-echelon measurement instruments was developed. The expanded uncertainty of measurements performed on the basic KA-S4 adiabatic calorimeter of the standard complex in the working temperature range of GET 60-2019 does not exceed 0.27–0.36% with conformance factor k = 2.

The Research and Development of High-precision Measuring Instrument Based on ARM Embedded System

This paper focuses on the research and development of high-precision measurement instruments based on ARM, which is a kind of AC(Alternating Current) and DC(Direct Current) resistance measuring instruments for cables and wires. The instrument has a good human machine interface, can automatically collect data of temperature, voltage and other parameters through sensors. After the collected data is transmitted to the CPU for processing and calculation, the resistance, inductance, phase angle are obtained and displayed on the screen.The instrument has the ability to automatically switch ranges, perform complex calculations and automatically compensate for errors, and can flexibly change functions and expansion modules for use in electronics and industrial applications.

A Multipurpose Small-Scale Smart Factory For Educational And Research Activities

As manufacturing industry is moving its steps towards a more digital, smart and flexible scenario, the changes required to achieve the expectations of the Industry 4.0 (I4.0) framework are numerous and extensive. Though, a general lack of understanding of how new technologies could be integrated and shall be implemented is present, limiting the rate of adoption of such changes and the related beneficial impacts. This paper describes the implementation of a smart-factory at the University of Applied Sciences and Arts of Southern Switzerland (SUPSI) aiming at filling the gap in I4.0 related skills development thorough a learning by doing approach, and providing a research platform that could foster collaboration of practitioners and academia on the development and testing of new technologies. The developed factory integrates different production technologies such as additive manufacturing, laser processing and milling, in order to produce a highly customizable item consisting in a TANGRAM game-set, packaged into personalized boxes. The entire factory is coupled with its digital twin, which is fed by an exhaustive monitoring infrastructure composed by vision systems and high precision measurement instruments, allowing to track in real time plant processes. The design has been carried out in order to make the smart factory serving as a mean to face both educational and research challenges at many different levels. As an educational mean, students and professionals have the chance to dive into manufacturing history experiencing both classical automation topics (PLC, MES and SCADA programming, precision axes control and pneumatics), as well as more advanced technologies, typical of the most advanced smart-factories (IoT, vision systems, simulation and digital twin, advanced measuring methods and smart production management systems).From a research point of view, the factory functions as a pilot plant for internal research and applied industrial projects, on the top of which applications, manufacturing methods and technologies are developed, tested and integrated.

Error model of geomagnetic-field measurement and extended Kalman-filter based compensation method.

The real-time accurate measurement of the geomagnetic-field is the foundation to achieving high-precision geomagnetic navigation. The existing geomagnetic-field measurement models are essentially simplified models that cannot accurately describe the sources of measurement error. This paper, on the basis of systematically analyzing the source of geomagnetic-field measurement error, built a complete measurement model, into which the previously unconsidered geomagnetic daily variation field was introduced. This paper proposed an extended Kalman-filter based compensation method, which allows a large amount of measurement data to be used in estimating parameters to obtain the optimal solution in the sense of statistics. The experiment results showed that the compensated strength of the geomagnetic field remained close to the real value and the measurement error was basically controlled within 5nT. In addition, this compensation method has strong applicability due to its easy data collection and ability to remove the dependence on a high-precision measurement instrument.

Online coplanarity measurement of IC leads based on single camera vision system

To improve the measurement accuracy and speed of online coplanarity measurement of integrated circuit (IC) leads, a new single camera vision system for small outline packaging IC leads was developed. Firstly, a novel imaging optical structure with multiple reflection mirrors and a total reflection rectangular prism was devised. With this structure, the two side views of IC leads are captured at the same time in a small field of view. To guarantee a good assembly quality, the relationship between the assembling deviation of optical components and measurement error is investigated. Secondly, a fast algorithm for the coplanarity measurement of the IC leads is proposed. This algorithm mainly consists of three parts: the IC lead tips searching, the local sub-pixel positioning and the local image correction. Finally, a high precision measurement instrument is used to verify the accuracy of the proposed approach. The experimental results show that the proposed approach is effective in measuring the coplanarity of IC leads in real-time and the measuring error of the standoff is less than 4 μm. Furthermore, the proposed method can gain higher measuring speed and accuracy than existing methods.

Preliminary exploration of the measurement of walking speed for the apoplectic people based on UHF RFID.

The number of the apoplectic people is increasing while population aging is quickening its own pace. The precise measurement of walking speed is very important to the rehabilitation guidance of the apoplectic people. The precision of traditional measuring methods on speed such as stopwatch is relatively low, and high precision measurement instruments because of the high cost cannot be used widely. What's more, these methods have difficulty in measuring the walking speed of the apoplectic people accurately. UHF RFID tag has the advantages of small volume, low price, long reading distance etc, and as a wearable sensor, it is suitable to measure walking speed accurately for the apoplectic people. In order to measure the human walking speed, this paper uses four reader antennas with a certain distance to reads the signal strength of RFID tag. Because RFID tag has different RSSI (Received Signal Strength Indicator) in different distances away from the reader, researches on the changes of RSSI with time have been done by this paper to calculate walking speed. The verification results show that the precise measurement of walking speed can be realized by signal processing method with Gaussian Fitting-Kalman Filter. Depending on the variance of walking speed, doctors can predict the rehabilitation training result of the apoplectic people and give the appropriate rehabilitation guidance.

Low frequency noise elimination technique for 24-bit Σ-Δ data acquisition systems.

Low frequency 1/f noise is one of the key limiting factors of high precision measurement instruments. In this paper, digital correlated double sampling is implemented to reduce the offset and low frequency 1/f noise of a data acquisition system with 24-bit sigma delta (Σ-Δ) analog to digital converter (ADC). The input voltage is modulated by cross-coupled switches, which are synchronized to the sampling clock, and converted into digital signal by ADC. By using a proper switch frequency, the unwanted parasitic signal frequencies generated by the switches are avoided. The noise elimination processing is made through the principle of digital correlated double sampling, which is equivalent to a time shifted subtraction for the sampled voltage. The low frequency 1/f noise spectrum density of the data acquisition system is reduced to be flat down to the measurement frequency lower limit, which is about 0.0001 Hz in this paper. The noise spectrum density is eliminated by more than 60 dB at 0.0001 Hz, with a residual noise floor of (9 ± 2) nV/Hz(1/2) which is limited by the intrinsic white noise floor of the ADC above its corner frequency.

Radar-Based High-Accuracy Angle Measurement Sensor Operating in the K-Band

The growing need for high-precision measurement instruments in modern industrial facilities leads to new measurement principles to reduce sensor costs while maintaining accuracy. A novel measurement principle suited for these applications is based on radar, which originally is associated with measurements in free space. For high precision, guided waves can be used to prevent disturbing reflections from the environment. Another advantage of a waveguide-based measurement is that the electromagnetic wave can be guided in a circle to measure rotational motions, which are in particular relevant in machine tools. This paper describes an FMCW radar sensor in the K-band for angle measurements. The sensor principle is described in detail, including its high-frequency components and the mechanical constraints to achieve a full angle range of 360°. The propagation characteristics of the radar signal in a curved waveguide with an adapted feeding structure using a Riblet coupler are presented. In addition to simulations, measurements with a prototype setup are presented to verify the radar-based angle measurement principle. The achieved accuracy is ±0.05° which corresponds to an accuracy in distance of ±125 μm.

Simulation of Thermal Behavior in High-Precision Measurement Instruments

In this paper, a way to modularize complex finite-element models is described. The modularization is done with temperature fields that appear in high-precision measurement instruments. There, the temperature negatively impacts the achievable uncertainty of measurement. To correct for this uncertainty, the temperature must be known at every point. This cannot be achieved just by measuring temperatures at specific locations. Therefore, a numerical treatment is necessary. As the system of interest is very complex, modularization is unavoidable to obtain good numerical results.

Inverse Problem of Phase Distribution Identification using Intensity Images

The optical phase distribution measurement is an important technology for many industrial applications. However, it requires a high precision measurement instrument which usually is expensive, delicate and requires laborious maintenance care. In this study, a new method which reconstructs optical phase distribution from intensity images has been developed. This method enables simple phase distribution measurement without expensive optical equipments and installation space. Firstly, the light is differently modulated by some optical systems, and intensity images of modulated light are measured by CCD camera. An inverse problem which reconstructs the phase distribution from the proposed measurement system is set up. This inverse problem is reduced to an unconstrained optimization problem which can be solved with non-linear optimization method such as BFGS method. The ill-posedness of the problem was overcome with regularization using a priori information whose unknown phase distribution is smooth. The effectiveness of the proposed method was demonstrated through some numerical simulation.