The development of a new artificial model of a finger for assessing transmitted vibrations.

Prolonged exposure of the hand to tool-induced vibrations is associated with the occurrence of conditions such as vibration white finger. This study involves the development of a new artificial model that approximates both loading and vibration behaviour of the human finger. The layered system uses polypropylene "bones", encased in a cylinder of low modulus, room-temperature curing silicone gel (to replicate subcutaneous tissues), with an outer layer of latex (to replicate the dermis and epidermis). A protocol for manufacture was developed and dynamic mechanical analysis was carried out on a range of gels in order to choose a range close to the mechanical properties of the human finger. The load-deflection behaviour under quasi-static loading was obtained using an indenter. The indentation measurements were then compared with a set of validation data obtained from human participant testing under the same conditions. A 2-D FE model of the finger was also used to assess vibration responses using existing parameters for a human finger and those obtained from the tested materials. Vibration analysis was conducted under swept sinusoidal excitations ranging from 10 to 400Hz whilst the FE finger model was pressed 6mm toward the handle. Results were found to compare well. This synthetic test-bed and protocol can now be used in future experiments for assessing finger-transmitted vibrations. For instance, it can aid in assessing anti-vibration glove materials without the need for human subjects and provide consistent control of test parameters such as grip force

The apparent mass and mechanical impedance of the hand and the transmission of vibration to the fingers, hand, and arm

Although hand-transmitted vibration causes injury and disease, most often evident in the fingers, the biodynamic responses of the fingers, hand, and arm are not yet well understood. A method of investigating the motion of the entire finger–hand–arm system, based on the simultaneous measurement of the biodynamic response at the driving point and the transmissibility to many points on the finger–hand–arm system, is illustrated. Fourteen male subjects participated in an experiment in which they pushed down on a vertically vibrating metal plate with their right forearm pronated and their elbow bent at 90°. The apparent mass and mechanical impedance of the finger–hand–arm system were measured for each of seven different contact conditions between the plate and the fingers and hand. Simultaneously, the vibration of the fingers, hand, and arm was measured at 41 locations using a scanning laser Doppler vibrometer. Transmissibilities showed how the vibration was transmitted along the arm and allowed the construction of spectral operating deflection shapes showing the vibration pattern of the fingers, hand, and arm for each of the seven contact conditions. The vibration patterns at critical frequencies for each contact condition have been used to explain features in the driving point biodynamic responses and the vibration behaviour of the hand–arm system. Spectral operating deflection shapes for the upper limb assist the interpretation of driving point biodynamic responses and help to advance understanding required to predict, explain, and control the various effects of hand-transmitted vibratio

Obstacle Avoidance in Underwater Bottom Navigation

An Obstacle Avoidance System (OAS) based on sonar for an Autonomous Underwater Vehicle (AUV) is described. Specific procedures are developed to perform temporal filtering on the sequence of input sonar scans. Tunable thresholds take into account different levels of environmental noise so to focus the avoiding effort on real obstacles

Design and vibrational characterisation of a novel instrumented handle for grip force measurement.

The dynamic modelling of the hand-transmitted vibration is usually performed using special handles. These are designed for measuring grip force and typically follows the example reported in ISO 10819. Limitations in the use of such handle are: high complexity of the structure, thermal drift of strain gage, dependence of the grip force to the position of hand and the total weight. The aim of this paper is to report on the design and dynamic characterisation of an instrumented handle for the measurement of the grip force. The handle is designed in order have a low weight and to be compliant with ISO-10819 and ISO-15230. The handle also allow the measurement of transmissibility with a laser Doppler vibrometer directly on the hand surface (see N Paone and L Scalise, IMAC 2006). The transducers used are 2 miniature ring load cell contained inside the handle with almost no thermal drift. The paper is also focusing on the handle characterisation by performing experimental and numerical analysis via mobility measurements. The test demonstrated that the handle has a working frequency band of :0 - 2000 Hz. Calibration test performed have reported for the grip force a measurement range of 400 N and uncertainty of 0.12 % f.s