Matteo Lancini

A Novel Algorithm for EMG Signal Processing and Muscle Timing Measurement

This paper presents a new method for the automated processing of surface electromyography (SEMG) signals, particularly suited for the detection of muscle activation timing. The method has an intermediate level of complexity between simpler (but less performing) and more complex (but in general slower) methods, and is successfully used in the development of biomedical devices for rehabilitation carried out by our group. The method proposed here is based on a statistical approach for threshold computation that is implemented without the need of maximum voluntary contraction or relaxed state, usually required to overcome the difficulty in obtaining the threshold value. The method is compared with 10 popular automated standard methods using different types of simulated signals that approximate the behavior of real SEMG signals. Both the number of activations detected and the onset time measured are analyzed. The algorithm is then applied to real SEMG signals acquired from healthy subjects. The results are finally compared with the literature values. The results show that the proposed algorithm is the best performing method when both the number of activations and the activation timing are considered. In real applications, the algorithm gives the results compatible with the well-agreed literature data.

Rolling Contact Fatigue and Wear Behavior of High-Performance Railway Wheel Steels Under Various Rolling-Sliding Contact Conditions

An experimental investigation was carried out to study and compare the response to cyclic loading of the high-performance railway wheel steels ER8 EN13262 and SUPERLOS®. Rolling contact tests were performed with the same contact pressure, rolling speed and sliding/rolling ratio, varying the lubrication regime to simulate different climatic conditions. The samples, machined out of wheel rims at two depths within the reprofiling layer, were coupled with UIC 900A rail steel samples. The wear rates, friction coefficients and hardness were correlated with the deformation beneath the contact surface. The crack morphology was studied, and the damage mechanisms were identified. The distribution of crack length and depth at the end of the dry tests was analyzed to quantify the damage. The main difference between the steels lies in the response of the external samples to dry contact: SUPERLOS® is subjected to a higher wear and lower friction coefficient than ER8, and this reduces the density of surface cracks that can propagate under wet contact conditions. The analysis of feedback data from in-service wheels confirmed the experimental results.

Healthcare Sensor System Exploiting Instrumented Crutches for Force Measurement During Assisted Gait of Exoskeleton Users

Powered exoskeletons can be used by the persons with complete spinal cord injury to achieve bipedal locomotion again. The training required before being able to efficiently operate these orthotics, however, is currently based on the subjective assessments of the patient performance by his therapist, without any quantitative information about the internal loads or assistance level. To solve this issue, a sensor system was developed, combining the traditional gait analysis systems, such as ground reaction force platforms and motion capture systems, with Lofstrand crutches instrumented by the authors. To each crutch three strain-gauge bridges were applied, to measure both axial and shear forces, as well as conditioning circuits with transmission modules and a triaxial accelerometer. An inverse dynamics analysis, on a simplified biomechanical model of the patient wearing the exoskeleton, is proposed by the authors as a tool to assess both the internal forces acting on shoulders, elbow, and neck of the patient, as well as the loads acting on joints. The same analysis was also used to quantify the assistance provided to the patient during walking, in terms of vertical forces applied by the therapist to the exoskeleton. The tests showed a therapist assistance contribution reported as a fraction of the subject body weight up to 40% with an average close to 0% and a standard deviation value of 14%. This paper presents the description of the measurement system, of the post-processing analysis, as well as the results of the proposed approach applied to a single Rewalk user during training.

Feasibility study of a vision system for on-line monitoring of rolling contact fatigue tests

Wear and Rolling Contact Fatigue (RCF) tests on wheel/rail specimens are important to develop wheels of new materials for improved lifetime and performance, able to operate in harsh environments and at high rolling speeds. We have studied the feasibility of a novel non-invasive all-optical system, based on a high-speed video camera and two laser illumination sources, which is able to continuously monitor the dynamics of the specimens used to test wheel and rail materials, in a laboratory test bench. Surface micro- and macro-topography are monitored using blob analysis and 3D laser triangulation respectively. Blob analysis yields to good discrimination among the specimens, in terms of wear induced surface damage; the 3D measurement, which is characterized by a resolution of 0.033 mm, is able to monitor RCF effects. The system is described with the aid of end-cycle specimens, as well as of intermediate specimens, prior to its installation in the test bench for rolling contact tests.

A novel optical apparatus for the study of rolling contact wear/fatigue based on a high-speed camera and multiple-source laser illumination

Rolling contact wear/fatigue tests on wheel/rail specimens are important to produce wheels and rails of new materials for improved lifetime and performance, which are able to operate in harsh environments and at high rolling speeds. This paper presents a novel non-invasive, all-optical system, based on a high-speed video camera and multiple laser illumination sources, which is able to continuously monitor the dynamics of the specimens used to test wheel and rail materials, in a laboratory test bench. 3D macro-topography and angular position of the specimen are simultaneously performed, together with the acquisition of surface micro-topography, at speeds up to 500 rpm, making use of a fast camera and image processing algorithms. Synthetic indexes for surface micro-topography classification are defined, the 3D macro-topography is measured with a standard uncertainty down to 0.019 mm, and the angular position is measured on a purposely developed analog encoder with a standard uncertainty of 2.9°. The very small camera exposure time enables to obtain blur-free images with excellent definition. The system will be described with the aid of end-cycle specimens, as well as of in-test specimens.

A fast autofocus setup using a liquid lens objective for in-focus imaging in the macro range

A fast and reliable optical setup is here presented for in-focus imaging of objects in the macro range. The setup uses a camera equipped with an objective embedding a liquid lens, whose focal length is voltage-controlled. The defocus condition of the image is controlled by means of two indexes, both suitable for coarse and for fine adjustments. A purposely designed algorithm makes use of the two indexes, switching from one to the other to position the image in focus by adequately controlling the liquid lens focal length. The setup has been calibrated by means of target planes of known contrasts, and applied to process biomedical images such as fingerprints.

Residual vibration reduction with commanded motion optimization

Residual vibrations affect machines at the end of commanded motion and represent an amplification factor for the work cycle. Furthermore, in repetitive cyclic movements, residual vibrations can lead to an important degeneration of the executed motion, due to a summation effect of undesired dynamic phenomena. For these reasons, the problem of residual vibrations is widely studied in literature and it is faced with different techniques. A first type of approach consists in the production of a structural device realized with proper mechanical solutions devoted to avoid the sources of vibrations. The second approach consists in introducing passive/active physical elements able to attenuate vibrations, by passively consuming their mechanical power or by actively counteracting them with external mechanical power. A third approach is the smart definition of the motion profile of each machine movable part to minimize the vibrational effects. The proposed work is addressed in this direction, with an optimization approach based on the Fourier transformation of the motion profile. More precisely, the natural frequencies of the system are evaluated through experimental tests, the designed motion profile is transformed with a Fourier analysis, a band around the natural frequencies of the system is suppressed from the motion profile spectrum, an antitransformation is implemented to obtain a temporal function, and, finally, a proper optimization is implemented to respect desired kinematical constraints. Experimental results confirmed a significant improvement, in terms of residual vibrations, with respect to the state of the art of motion profiles specifically designed for residual vibrations reduction.Copyright

Monitoring Upper Limbs During Exoskeleton-Assisted Gait Outdoors

Powered exoskeleton can restore locomotion to spinal cord injury subjects but measuring their impact on the upper limbs is critical, since repeated excessive loads are strongly correlated to chronic pain at shoulder level.

Effect of Wear on Surface Crack Propagation in Rail–Wheel Wet Contact

The interaction between wear and rolling contact fatigue in wet contact was investigated by means of experiments on a two-disk test bench. Specimens of various railway wheel steels were coupled with specimens of the same rail steel, subjected to rolling and sliding wet contact with varying sliding/rolling ratio. Some tests with a dry rolling–sliding contact phase preceding wet contact were carried out as well (dry–wet tests). The pressurization of the fluid entrapped in the surface cracks was the cause of a rapid and severe damage in the dry–wet tests, due to the nucleation of surface cracks by ratcheting in the dry phase, which subsequently propagate in the wet phase. In the wet tests, the fluid pressurization effect was much mitigated due to the absence of initial surface cracks; the specimens subjected to higher sliding/rolling ratio showed the best performance against rolling contact fatigue, due to the effect of wear in reducing the length of surface cracks. A model for assessing the interaction between wear and rolling contact fatigue was proposed, based on the correction of the classical Paris law for crack propagation by taking into account the effect of wear on crack length reduction. The application of the model to the experimental tests allowed finding a correlation between the model predictions and the occurrence of fatigue failure.

Experimental characterization of an autofocus algorithm based on liquid lens objective for in-focus imaging in the macro range

The experimental characterization of an autofocus algorithm using a liquid lens objective is presented. The objective embeds an electro-wetting based lens whose focal length is voltage controlled. Two sharpness indexes are used to measure the image focus condition in the algorithm allowing a very robust and accurate setting of the focus. The algorithm has been characterized using target images differing both in the contrast and in the spatial frequency along measurement depth range from 70 to 2 mm. both static and dynamic tests were performed revealing the ability of the algorithm to follow rapid variations of the target position.