Keqing Lu

A planar capacitive sensor for 2D long-range displacement measurement

A planar capacitive sensor (PCS) capable of 2D large-scale measurement is presented in this paper. Displacement interpretation depends on independently measuring the periodic variation in capacitance caused by the change in the overlapping area of sensing electrodes on a moving plate and a fixed plate. By accumulating the number of quarters in each direction and the specific position in the final quarter, the large-scale measurement is fulfilled. Displacements in X- and Y-direction can be measured independently and simultaneously. Simulation shows that a shorter gap distance and a longer electrode guarantee better sensitivity. Experiments based on a PCS test bench demonstrate that the PCS has a sensitivity of 0.198 mV/μm and a resolution of 0.308 μm. An electric fringe effect and other possible measurement errors on displacement interpretation accuracy are discussed. The study confirms the high potential of PCSs as innovative 2D long-range displacement sensors.

A Novel Method for the Micro-Clearance Measurement of a Precision Spherical Joint Based on a Spherical Differential Capacitive Sensor

A spherical joint is a commonly used mechanical hinge with the advantages of compact structure and good flexibility, and it becomes a key component in many types of equipment, such as parallel mechanisms, industrial robots, and automobiles. Real-time detection of a precision spherical joint clearance is of great significance in analyzing the motion errors of mechanical systems and improving the transmission accuracy. This paper presents a novel method for the micro-clearance measurement with a spherical differential capacitive sensor (SDCS). First, the structure and layout of the spherical capacitive plates were designed according to the measuring principle of capacitive sensors with spacing variation. Then, the mathematical model for the spatial eccentric displacements of the ball and the differential capacitance was established. In addition, equipotential guard rings were used to attenuate the fringe effect on the measurement accuracy. Finally, a simulation with Ansoft Maxwell software was carried out to calculate the capacitance values of the spherical capacitors at different eccentric displacements. Simulation results indicated that the proposed method based on SDCS was feasible and effective for the micro-clearance measurement of the precision spherical joints with small eccentricity.

A novel double-ball-bar with two spatial linkages and one spherical joint

As a typical comprehensive error measurement method, the double-ball-bar (DBB) has been invented and used widely for evaluating and diagnosing the accuracy of NC machine tools. However, due to the expansion length of DBB’s bar is very limited, the working efficiency of the DBB is greatly reduced and different length bars are mostly used to realize different measurement ranges. In this paper, a novel DBB with two spatial linkages and one spherical joint was presented to implement a wide detection range and simplify the operation. The structure of the proposed device was firstly introduced. The working principle of the device was then described, and the mathematical model for detecting machine’s accuracy was also built. According to the angle of spatial linkages and lengths of two bars, circular motions trajectory which is caused by interpolation movement of two shafts can be calculated and compared with theoretical value to evaluate machine tool’s accuracy. Finally, the simulation was done to validate the feasibility of the proposed device. The results show that the proposed DBB has reasonable structures. Moreover, the measuring range can cover a large region of space and it is continuous.

Nonlinear analysis of cylindrical capacitive sensor used for measuring high precision spindle rotation errors

A novel cylindrical capacitive sensor (CCS) with differential, symmetrical and integrated structure was proposed to measure multi-degree-of-freedom rotation errors of high precision spindle simultaneously and to reduce impacts of multiple sensors installation errors on the measurement accuracy. The nonlinear relationship between the output capacitance of CCS and the radial gap was derived using the capacitance formula and was quantitatively analyzed. It was found through analysis that the thickness of curved electrode plates led to the existence of fringe effect. The influence of the fringe effect on the output capacitance was investigated through FEM simulation. It was found through analysis and simulation that the CCS could be optimized to improve the measurement accuracy.

Noise reduction of laser scanning data based on self-estimated angular threshold

Laser scanning is widely applied to reverse engineering. Nonetheless, the involvement of scanning equipment and laser probe, as well as the measurement environment itself renders the process more vulnerable to noise which will cause failures in boundary detection, data segmentation and reconstruction of smooth curves and surfaces, thus putting forward the demand for noise reduction. Among the methods used in noise reduction of laser scanning data, the angular method is particularly suitable for scan line data. However, this method as well entails threshold that largely relies on the experience of engineers, which may introduce unwanted uncertainty. In this paper, an algorithm based on self-estimated angular threshold for reducing noise of laser scanning data is proposed. Firstly, the factors affecting angular threshold are analyzed and a mathematical model for SAT is established. Then the concrete algorithm that consists of judgment of impulse noise, modification of the coordinates and average filtering is described. Finally, a simulation test and an experimental case are employed to evaluate the performance of the algorithm on noise reduction of laser scanning data.