Figure 3 - available via license: CC BY
Content may be subject to copyright.
The characteristics of light sources. It includes a light intensity distribution curve, image of the light sources, and image of light transmission areas. (a) The light source of 1/2 0 θ = by simulation; (b) the light source of 1/2 1.8 θ = by measurement; (c) the light source of 1/2 5.5 θ = by measurement.
Source publication
- [...]
A new displacement sensor with light-field modulation, named as time grating, was proposed in this study. The purpose of this study was to reduce the reliance on high-precision measurements on high-precision manufacturing. The proposed sensor uses a light source to produce an alternative light-field simultaneously for four groups of sinusoidal ligh...
Contexts in source publication
Context 1
... 3 compared several light sources with different divergence angles and light intensity distributions. Theoretically, when the divergence angle is 0°, and intensity distribution is very uniformity, there is no measurement error caused by light-field distribution, as shown in Figure 3(a). However, an ideal parallel light source does not exist, and the actual light-field distributions are shown in Figure 3(b) and Figure 3 Firstly, it can be seen from the light intensity distribution curve provided by the light source manufacture that the light intensity distribution in the central region is very uniform and in the surrounding area presents a concentric distribution, and as the scattering angle increases, the uniformity of the light intensity distribution deteriorates. ...
Context 2
... when the divergence angle is 0°, and intensity distribution is very uniformity, there is no measurement error caused by light-field distribution, as shown in Figure 3(a). However, an ideal parallel light source does not exist, and the actual light-field distributions are shown in Figure 3(b) and Figure 3 Firstly, it can be seen from the light intensity distribution curve provided by the light source manufacture that the light intensity distribution in the central region is very uniform and in the surrounding area presents a concentric distribution, and as the scattering angle increases, the uniformity of the light intensity distribution deteriorates. If the transmission surfaces are arranged in the central area of the light spot, the characteristic of uniformity of the light intensity can be made fully utilize, and the influence of uniformity of light intensity distribution may be effectively solved. ...
Context 3
... when the divergence angle is 0°, and intensity distribution is very uniformity, there is no measurement error caused by light-field distribution, as shown in Figure 3(a). However, an ideal parallel light source does not exist, and the actual light-field distributions are shown in Figure 3(b) and Figure 3 Firstly, it can be seen from the light intensity distribution curve provided by the light source manufacture that the light intensity distribution in the central region is very uniform and in the surrounding area presents a concentric distribution, and as the scattering angle increases, the uniformity of the light intensity distribution deteriorates. If the transmission surfaces are arranged in the central area of the light spot, the characteristic of uniformity of the light intensity can be made fully utilize, and the influence of uniformity of light intensity distribution may be effectively solved. ...
Context 4
... the transmission surfaces are arranged in the central area of the light spot, the characteristic of uniformity of the light intensity can be made fully utilize, and the influence of uniformity of light intensity distribution may be effectively solved. Secondly, the divergence angle will change the shape of the light transmission areas, which becomes more blurred as the light divergence angle increases, as shown in Figure 3(b) and 3(c). When the light source's half-angle equal to 5.5 °, the shape of the light transmission areas become very blurred and difficult to distinguish. ...
Context 5
... order to examine the influence of scattering on measurement errors, two light sources with half divergence angles of 1.8° and 5.5° were used for comparative experiments, as shown in Figure 3. The other parameters in the two experiments remained the same, including the same sensor prototype, mounting structure, photodetector, and signal processing system. ...
Context 6
... deeply analyze the influence of scattering, a simulation model for the proposed sensor was constructed using TrancePro, and the model was shown in Figure 8(a). Using the 5.5° light intensity distribution curve in Figure 3, the parameters of the light source are set in the software, so that the light intensity distribution and the scattering angle of the light source for the simulation are similar to the real situation. The simulation effect of the light source is shown in Figure 8 Using the sinusoidal transmission surfaces of Figure 1 as a research object, the simulation of the light intensity distribution of the sinusoidal light transmission areas is shown in Figure 9(a). ...
Citations
... According to the idea of "space-time coordinate conversion," a coordinate system of uniform motion is the key to measure space with time [19]. e traveling wave can be divided into the space traveling waves and the time traveling waves by the time grating sensors. ...
Because the output signal of the time grid sensor is so weak and is easily affected by the disturbing noise, it is difficult to extract the induction signal containing the position information, when the time grid sensor is used to detect the rotor position of the permanent magnet synchronous motor (PMSM). In this paper, an adaptive monostable stochastic resonance method is proposed to realize the weak signal detection of the time grid sensor. The tunnel magnetoresistance effect sensor (TMR) is adopted to detect the change of the rotor magnetic field of the motor in this method, and the detection model of the time grid sensor about PMSM is constructed. The monostable stochastic resonance theory is applied to extract the induction signal of the time grid sensor. As to the problem of the tuning the parameters of the monostable stochastic resonance system, the genetic algorithm is adopted to optimize the parameters of the monostable stochastic resonance system. The experimental results show that the monostable stochastic resonance method based on the genetic algorithm can effectively detect the weak induction signal of the time grid sensor about PMSM. This method solves the problem of the weak signal extraction of the time grid sensor for PMSM, and the detection accuracy is also improved.
... The difference with the above sensors is that reduce the processing requirement of grating lines. At the moment, the time-grating inductive sensor, the time-grating capacitive sensor, and the time-grating moving light field sensor [20][21][22][23][24][25][26] have been suitable for industrial production and applications (e.g. rotary table for small and medium-sized machine tool, the high-speed servo motor). ...
The paper proposes a novel inductive angular displacement sensor based on time-grating to measure large-diameter hollow rotating mechanical components in large science facilities. The sensor design includes a stator, a rotor with two layers of windings. The stator is fabricated according to the dimension of the rotor, which is the large-diameter hollow rotary mechanical components. Based on the electromagnetic induction, the theoretical model of angular displacement measurement is derived by mathematical equations in detail. The sensor design ensures integration of the large-diameter hollow rotating mechanical components with the stator, and solves the problem that the sensors cannot be coaxially installed in the closed-loop control process of large mechanical rotating parts. The performance of the sensor is evaluated by tests of the prototype sensor fabricated by printed circuit board technology, which manifests the effectiveness of the proposed sensor. The results demonstrate the peak-to-peak value of original dynamic error is 124 ″ over 0 ° - 360 ° range, and the measurement error mainly includes first-order and second-order harmonic components. Therefore, the original errors are reduced by optimizing the angular displacement algorithm of the sensor, optimized results demonstrate the final accuracy of the sensor is ±3.5 ″ over the 0 °- 360 ° measurement range.
... In addition, the front-end circuit noise and environmental noise also need to be filtered, and the core algorithm of the high-order filter is convolution, so FPGA's parallel raw data filtering capabilities are more convenient. In terms of latency, although FPGA clock frequency is not as high as that of commercial CPUs, their clock is at the level of several hundred MHz (ns-level clock), which has already met the low latency requirements of this platform [29][30][31]. In addition, the FPGAs' internal circuit structure and pins can be reprogrammed, with flexible and rich resource extensions, and it is easy to implement subsequent structural and algorithm optimization. ...
Among various nanometer-level displacement measurement methods, grating interferometry-based linear encoders are widely used due to their high robustness, relatively low cost, and compactness. One trend of grating encoders is multi-axis measurement capability for simultaneous precision positioning and small order error motion measurement. However, due to both lack of suitable hardware data processing platform and of a real-time displacement calculation system, meeting the requirements of real-time data processing while maintaining the nanometer order resolutions on all these axes is a challenge. To solve above-mentioned problem, in this paper we introduce a design and experimental validation of a field programmable gate array (FPGA)-cored real-time data processing platform for grating encoders. This platform includes the following functions. First, a front-end photodetector and I/V conversion analog circuit are used to realize basic analog signal filtering, while an eight-channel parallel, 16-bit precision, 200 kSPS maximum acquisition rate Analog-to-digital (ADC) is used to obtain digital signals that are easy to process. Then, an FPGA-based digital signal processing platform is implemented, which can calculate the displacement values corresponding to the phase subdivision signals in parallel and in real time at high speed. Finally, the displacement result is transferred by USB2.0 to the PC in real time through an Universal Asynchronous Receiver/Transmitter (UART) serial port to form a complete real-time displacement calculation system. The experimental results show that the system achieves real-time data processing and displacement result display while meeting the high accuracy of traditional offline data solution methods, which demonstrates the industrial potential and practicality of our absolute two-dimensional grating scale displacement measurement system.
In terms of reducing the coding complexity and manufacturing difficulty caused by the increase in coding density of the fractional encoding parts in absolute displacement measurement, a simple graphic shift coding method that increases the grid spacing of the incremental code and cancels the small coding value was proposed in this article. First, the displacement measurement is converted into the time difference measurement using the orthogonal modulation of light intensity. Increase the size of the gate distance to reduce the amount of encoded data without reducing the sensor resolution. Then, the decimal place of the absolute code channel is replaced by the pixel array of the image sensor, and the fractional part of the absolute code channel is canceled. Furthermore, with shift coding of pattern variations, the proposed method realizes a cursor shift coding which can be cycled for a plurality of times, solving the problem of increasing encoding density caused by the increase in cursor encoding range effectively. Based on the above principle, a prototype has been developed that achieves
$\mu \text{m}$
-level measurement accuracy with mm-level encoding pitch, further reducing the absolute encoding density for long-distance measurements, and has an effective range of 530 mm. Finally, the practical numerical results demonstrate that the measurement error of the sensor is
$\pm 0.1~\mu \text{m}$
within a short period of 0.6 mm, the absolute measurement repetition accuracy can be up to
$\pm 0.2~\mu \text{m}$
, and the measurement precision is
$\pm 2~\mu \text{m}$
in the whole range.
To enlarge the measurement range of traditional eddy current displacement sensors, a novel eddy current linear sensor for displacement measurement with high accuracy and long range is proposed in this article. The sensor consists of a stationary component with metal reflection conductors and a movable component with spiral coils. The metal reflection conductors below the movable component will generate an eddy current and radiate an eddy current magnetic field after the high-frequency alternating excitation signal is applied to field spiral coils. The inductive electromotive forces (EMFs) will be generated in inductive spiral coils. The measurement of displacement relies on the inductive EMFs variation of inductive spiral coils caused by the change of coupling areas between the spiral coils and the metal reflection conductors. The absolute positioning is realized by the combination of a coarse measurement channel and a fine measurement channel. The structure and measurement principle are described in detail. A sensor prototype is fabricated by printed circuit board (PCB) technology, and the experiments are carried out. Based on the experimental results, some error sources are analyzed and the sensor is optimized. The experimental results show that the sensor can achieve absolute positioning, and the worst-case error is 6.75
$\mu \text{m}$
within the measurement range of 500 mm.
The scanning laser Doppler vibrometer (SLDV) is an extremely valuable method for studying the dynamic properties of vibrating objects, such as those in industrial production, entomology research, and biomedical testing. The traditional SLDV method scans samples using an inclined laser, which ignores the three-dimensional (3D) information of the sample, resulting in a relatively complicated calculation process. In industrial processes and scientific research, the measured target may have a known 3D regular surface. When a structure with height information moves laterally, it causes a change in longitudinal information, which is of great benefit in the analysis of the 3D vibration and displacement information of the target. In this paper, continuous and interval scanning laser Doppler methods are proposed to expand the measuring capability of SLDV methods, based on the scanning on spherical structures. First, a spherical structure is introduced to simplify the solution to spiral vibrations. The high-precision displacement can also be calculated by fitting the circular scanning curve. Finally, the scanning method for 3D displacement measurement is experimentally validated, and the theoretical errors are demonstrated. This work provides a new methodology to realize both periodic and nonperiodic displacements in all degrees of freedom with high accuracy using a single-point SLDV, which is expected to have a long-term impact on industry vibration analysis and biological motion research. Most importantly, setting a reflector with a spherical surface on the end effector of the micro-nano robot can realize the 3D cross-scale repeated localization.
There is urgent demand for new absolute Linear Displacement Measurement (LDM) technology with high resolution and high precision, during the development of high-end numerical control technology. In previous research, we found that displacement measurement based on the image processing method performs well, however, the volume increases when using an imaging lens, and the system is susceptible to factors such as virtual focus. In this paper, the lensless LDM image optical path is established based on grating projection imaging, then the absolute grating coding method is operated based on M−sequence pseudo-random coding. A linear displacement subdivision algorithm is then deployed based on the digital image recognition algorithm. An LDM device with a measuring range of 250 mm was designed to test the performance of the proposed method. The device shows a measurement resolution of 1 nm and measurement accuracy of 1.76 μm in the range of 250 mm. This work lays a foundation for further research on high performance LDM technology.
