Ben J. Halkon

Vibration measurements using continuous scanning laser vibrometry: velocity sensitivity model experimental validation

This paper builds on a previous study in which the theoretical description of the velocity sensed by a single laser beam incident in an arbitrary direction on a rotating target undergoing arbitrary vibration was extended to continuous scanning laser vibrometer measurements on targets with flexible cross sections. The velocity sensitivity model was written in terms of either laser beam orientation angles or deflection mirror scan angles, with the latter found to be the most useful for continuous scanning applications. The model enables the prediction of the laser vibrometer output for any measurement configuration on any target. The experimental validation presented in this paper confirms that additional components appear in rotating target measurements that are associated with both the scanning system configuration and any misalignment between the scanning system and target rotation axes. This paper will show how use of the velocity sensitivity model enables the vibration engineer to make laser Doppler vibrometry measurements with confidence.

Rotor vibration measurements using laser doppler vibrometry : Essential post-processing for resolution of radial and pitch/yaw vibrations

Background: Laser Doppler vibrometry is now a well established technique enabling noncontact vibration measurements in the most challenging of environments. Rotor vibration measurements are often highlighted as a major application of Laser Vibrometers due to their non-contact operation and inherent immunity to shaft run-out. Method of Approach: In such measurements, resolution of the individual axial and torsional vibration components is possible via particular arrangement of the laser beam(s). Resolution of the radial or pitch / yaw vibration components, however, can only be achieved by essential post-processing of the data from simultaneous orthogonal measurements. Results: This paper describes the principle and rigorous examination of a novel, dedicated resolution algorithm enabling, for the first time, real-time post-processing of the outputs from standard commercial instruments. Conclusions: The system performed well, even in the presence of noise and other typical measurement errors, and was implemented successfully in an engine vibration study.

Development of a synthetic human thigh impact surrogate for sports personal protective equipment testing

Synthetic impact surrogates are widely used in the sporting goods industry in the evaluation of personal protective equipment. Existing surrogates, exemplified by those used in safety standards, have many shortcomings, primarily relating to their mass, stiffness, geometries and levels of constraint which limit their biofidelity and subsequent usefulness in personal protective equipment evaluations. In sports, absence from competition is a primary severity measure for injuries; consequently, blunt trauma injuries, such as contusions and lacerations, become pertinent and serious concerns. It is important, therefore, that synthetic surrogates provide an adequate description of these soft tissues to effectively evaluate injury risk. A novel, multi-material human thigh surrogate has been presented with consideration to the tissue structures, geometries and simulant materials used. This study presents the detailed development stages undertaken to fabricate a multi-material synthetic soft tissue surrogate with skin, subcutaneous adipose and muscle tissue components. The resultant surrogate demonstrates the successful use of sequential moulding techniques to construct a full-scale anatomical human impact surrogate which can be used in personal protective equipment testing.

A novel phase-aligned analysis on motion patterns of table tennis strokes

A wide range of human motion represent repetitive patterns particularly in racket sports. Quantitative analysis of the continuous variables during the different phases of the motion cycle helps to investigate more deeply the specific movement of the racket or player. Table tennis biomechanics research to date lacks the necessary detail of phase decomposition and phase-based quantitative analysis. Therefore, this study proposes a novel velocity-based piecewise alignment method to identify the different phases of a table tennis forehand stroke. A controlled experiment was conducted on a number of players of two differing ability levels (experts vs. novices) to implement this novel methodology. Detailed results are shown for the quantitative analysis on multiple strokes of the two groups of participants. Significant differences were found in both the displacement and velocity of the racket movement in the backswing, forward swing and follow-through phases. For example, it is clear that experts’ strokes show higher racket resultant velocity than novices during both the forward swing and follow-through phases by up to a factor of two. Furthermore, the phase-based approach to analysing racket motions leads to interrogation over a greater duration than the traditional time-based method which is generally only concerned with impact ±0.25s.

A systematic approach to the characterisation of human impact injury scenarios in sport

Background In contact sports (eg, American football or rugby), injuries resulting from impacts are widespread. There have been several attempts to identify and collate, within a conceptual framework, factors influencing the likelihood of an injury. To effectively define an injury event it is necessary to systematically consider all potential causal factors but none of the previous approaches are complete in this respect. Aims First, to develop a superior deterministic contextual sequential (DCS) model to promote a complete and logical description of interrelated injury event factors. Second, to demonstrate systematic use of the model to construct enhanced perspectives for impact-injury research. Method Previous models were examined and elements of best practice synthesised into a new DCS framework description categorising the types of causal factors influencing injury. The approachs internal robustness is demonstrated by consideration of its completeness, lack of redundancy and logical consistency. Results The models external validity and worth are demonstrated through its use to generate superior descriptive injury models, experimental protocols and intervention opportunities. Comprehensive research perspectives have been developed using a common rugby impact-injury scenario as an example; this includes: a detailed description of the injury event, an experimental protocol for a human-on-surrogate reconstruction, and a series of practical interventions in the sport of rugby aimed at mitigating the risk of injury. Conclusions Our improved characterisation tool presents a structured approach to identify pertinent factors relating to an injury.

The use of rapid prototyping in the design of a customised ankle brace structure for ACL injury risk reduction

Rapid prototyping, or additive manufacturing, is becoming more useful in creating functional prototypes, especially when customisation is required. This paper explores the use of three-dimensional (3D) printing in designing a customised ankle brace structure for anterior cruciate ligament (ACL) injury risk reduction. A new process is proposed to obtain ankle flexion angles and the corresponding foot surface strain associated with high ACL injury risks through motion analysis. This data is used in the design of the customised ankle brace structure and printed using rapid prototyping. One customised ankle brace structure was printed and tested to demonstrate this proposed framework. The ankle flexion range of motion (ROM) was significantly reduced in the high-risk ankle positions with the ankle brace structure. Rapid prototyping could thus be used to design customised ankle brace structures and this is useful in reducing fabrication time and complexity of customisation.

Continuous scanning laser vibrometry for measurements on rotating structures

It is readily accepted that a Laser Vibrometer measures target velocity in the direction of the incident laser beam but it is essential that, for correct measurement interpretation, the target velocity be considered in terms of the various target motion components. This paper begins with a review of the theoretical description of the velocity sensed by a dual mirror scanning Laser Vibrometer incident in an arbitrary direction on a rotating target of flexible cross-section undergoing arbitrary vibration. This comprehensive velocity sensitivity model can be applied to any Laser Vibrometer measurement configuration on any target and is sufficiently versatile to incorporate time dependent beam orientation. This is described in this paper with particular reference to continuous circular scanning Laser Doppler Vibrometry. The velocity sensitivity model allows a detailed analysis of the form of the measurement that is obtained in actual scan configurations. For example, additional components occur in a circular scanning Laser Vibrometer measurement on a rotating target that can be shown to be due to a combination of instrument configuration and target misalignment. In this paper, the measured data obtained from a circular scanning measurement on a rotating target undergoing axial vibration is investigated as a means of demonstrating the usefulness of the comprehensive velocity sensitivity model.

Table tennis and computer vision: a monocular event classifier

Detecting events in table tennis using monocular video sequences for match-play officiating is challenging. Here a low-cost monocular video installation generates image sequences and, using the Horn-Schunck Optical Flow algorithm, ball detection and location processing captures sudden changes in the ball’s motion. It is demonstrated that each abrupt change corresponds to a distinct event pattern described by its combined velocity, acceleration and bearing. Component motion threshold values are determined from the analysis of a range of table tennis event video sequences. The novel event classifier reviews change in motion data against these thresholds, for use in a rules based officiating decision support system. Experimental results using this method demonstrate an event classification success rate of 95.9%.