Xiaomei Chen

Bio: Xiaomei Chen is an academic researcher from University of Huddersfield. The author has contributed to research in topics: Grating & Image processing. The author has an hindex of 5, co-authored 13 publications receiving 67 citations. Previous affiliations of Xiaomei Chen include Cranfield University & German National Metrology Institute.

A novel pitch evaluation of one-dimensional gratings based on a cross-correlation filter

Abstract: If one-dimensional (1D), p–period and arbitrarily structured grating position-related topographical signals coexist with noise, it is difficult to evaluate the pitch practically using the centre-of-gravity (CG) method. The Fourier-transform-based (FT) method is the most precise to evaluate pitches; nevertheless it cannot give the uniformity of pitches. If a cross correlation filter a half period of sinusoidal waveform sequence (pT period), cross-correlates with the signals, the noise can be eliminated if pT is equal to p. After cross-correlation filtering, the distance between any two adjacent waveform peaks along the direction perpendicular to 1D grating lines is one pitch value. The pitch evaluation based on the cross-correlation filtering together with the detection of peaks position is described as the peak detection (PD) method in this paper. The pitch average and uniformity can be calculated by using the PD method. The computer simulation has indicated that the average of pitch deviations from the true pitch and the pitch variations are less than 0.2% and 0.2% for the sinusoidal and rectangular waveform signals with up to 50% uniform white noise, less than 0.1% and 1% for the sinusoidal and rectangular waveform signals and 0.6% and 2.5% for the triangular waveform signal if three waveform signals are mixed with Gaussian white, binomial and Bernoulli noise up to 50 % in standard deviation, one probability and trial probability respectively. As the examples, a highly oriented pyrolytic graphite (HOPG) with 0.246 nm distance between atoms and a 1D grating with 3000 nm nominal pitch are measured by a ultra-high vacuum scanning tunneling microscope (UHV STM) and a metrological atomic force microscope (AFM) respectively. After the position-related topographical signals are cross-correlation filtered, the 0.240 nm and 3004.11 nm pitches calculated by using the PD method are very close to the 0.240 nm and 3003.34 nm results evaluated by the FT method.

Atomic force microscope cantilevers as encoders for real-time forward and backward displacement measurements

Abstract: Atomic force microscope cantilevers have been investigated for their use as the encoder for real-time high-resolution displacement measurements, when paired with a 1D sinusoidal grating of well-known pitch. For a known one-directional (forward or backward) displacement measurement, the decoding algorithm is based on directly counting the integer periods of the grating and calculating the fractional parts at the beginning of the displacement and at the actual position by using one cantilever. Using two cantilevers arranged in the quadrature phase shift positions on the grating makes the measurement of two-directional (forward and backward) displacements possible. The decoding algorithm directly unwraps the phase between two encoded signals. Cross-correlation filtering and the differentiation process of two encoded signals are found to be very successful to guarantee the implementation of real-time displacement measurements by suppressing noise and reducing the offset and tilt of the encoded signals.

Ribbed force sensor

Abstract: In one embodiment, a force sensor apparatus is provided including a tube portion having a plurality of radial ribs and a strain gauge positioned over each of the plurality of radial ribs, a proximal end of the tube portion that operably couples to a shaft of a surgical instrument that operably couples to a manipulator arm of a robotic surgical system, and a distal end of the tube portion that proximally couples to a wrist joint coupled to an end effector.

A review on tribology of polymer composite coatings

Abstract: Self-lubricating polymer composite coatings, with tailorable tribological and mechanical properties, have been widely employed on mechanical parts to reduce friction and wear, which saves energy and improves the overall performance for applications such as aerospace satellite parts, shafts, gears, and bushings. The addition of functional fillers can overcome the limitations of single-polymer coatings and extend the service life of the coatings by providing a combination of low friction, high wear resistance, high load bearing, high temperature resistance, and high adhesion. This paper compares the heat resistance, and the tribological and mechanical properties of common polymer matrices, as well as the categories of functional fillers that improve the coating performance. Applicable scopes, process parameters, advantages, and limitations of the preparation methods of polymer coatings are discussed in detail. The tribological properties of the composite coatings with different matrices and fillers are compared, and the lubrication mechanisms are analyzed. Fillers reduce friction by promoting the formation of transfer films or liquid shear films. Improvement of the mechanical properties of the composite coatings with fillers of different morphologies is described in terms of strengthening and toughening mechanisms, including a stress transfer mechanism, shear yielding, crack bridging, and interfacial debonding. The test and enhancement methods for the adhesion properties between the coating and substrate are discussed. The coating adhesion can be enhanced through mechanical treatment, chemical treatment, and energy treatment of the substrate. Finally, we propose the design strategies for high-performance polymer composite coating systems adapted to specific operating conditions, and the limitations of current polymer composite coating research are identified.

Brittle film-induced cracking of ductile substrates

Abstract: In the traditional view, hard protective coatings allow improving mechanical performance of ductile materials by increasing surface hardness and wear resistance. However, due to the film extremely low fracture toughness, cracks could easily initiate in the brittle film subjected to tensile stresses, and some of them could propagate towards the substrate. Counter-intuitively, instead of protecting the ductile substrate, a brittle film can cause its premature fracture, as demonstrated here experimentally. If a micro-crack can be initiated in the ductile substrate due to the film cracking, then the whole system would be much easier to fail because of the stress concentration in front of the crack tip under tensile stress. In the present study, cracking of brass ductile substrate induced by brittle TiN film fracture was observed. Analytical calculation based on energy conservation during crack propagation is presented to explain this phenomenon of film-induced cracking. It is shown that crack depth penetrated into the substrate is a function of both crack velocity and the number of dislocations emitted from the crack tip. Relatively thick brittle films and fast propagating cracks favor fracture of the ductile substrates. The critical crack velocity, which can induce brass substrate cracks is 61 m/s. The presence of a film could not only prevent dislocations escaping from the surface of the crystal and inhibit dislocations emitting from surface dislocation sources, but also initiate a channel crack with high velocity due to brittle film fracture. Both contribute to crack propagation in soft substrates. This study provides an alternative view to the notion that a brittle film can protect the ductile substrate from damage. This is an interesting natural phenomenon. Caution must be taken when designing brittle coating protection systems.

Force sensor temperature compensation

Abstract: In one embodiment, a force sensor apparatus is provided including a tube portion having a plurality of radial ribs and at least one fiber optic strain gauge positioned over each rib of the plurality of radial ribs. The strain gauges are comprised of a negative thermo-optic coefficient optical fiber material in one embodiment. A proximal end of the tube portion is operably couplable to a shaft of a surgical instrument that is operably couplable to a manipulator arm of a robotic surgical system, and a distal end of the tube portion is proximally couplable to a wrist joint coupled to an end effector. In another embodiment, adjacent fiber optic strain gauges with differing thermal responses are used to solve simultaneous equations in strain and temperature to derive strain while rejecting thermal effects. In yet another embodiment, a thermal shunt shell is over an outer surface of the tube portion. An advantageous surgical instrument having improved temperature compensation is also provided.