GB2495559A

GB2495559A - Handheld device for monitoring a user's exposure to vibrations from vibrating equipment

Info

Publication number: GB2495559A
Application number: GB201117839A
Authority: GB
Inventors: Martin Thompson; Mark Harper
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-10-14
Filing date: 2011-10-14
Publication date: 2013-04-17
Anticipated expiration: 2031-10-14
Also published as: GB201117839D0; GB2495559B

Abstract

A portable device is held between the fingers of one hand and measures the exposure of an operator to vibration from a tool handle 1D. The device comprises a stem or neck 3B which joins two relatively wide portions. The stem fits between the operators fingers. One of the two wide portions 1A,3A (the module) sits on top of the hand, across the back of the fingers, and contains a battery and a processor for conditioning and recording signals from vibration sensors. The other wide portion 1C,3C (the foot) sits under the fingers, on the palm side of the hand, and is held in contact with the tool handle 1D in use. The device contains acceleration sensors for measuring vibrations along orthogonal Cartesian axes. At least the component of acceleration that occurs parallel to the direction of the top of the fingers is measured using a sensor 3H in the foot. Measuring this component of acceleration in the foot rather than in the module means that any rotation of the device about the line of contact 1F with the handle 1D does not result in spurious vibration readings.

Description

Enhancement to hand arm vibration sensors This invention relates to a portable wire-less system for monitoring exposure of a person to hand-arm vibration when using vibrating equipment.

Excessive exposure to hand-arm vibration is known to cause a heaith problem known as "white finger" that causes numbness and pain and, for this reason there is an international standard ISO-8041 that specifies the maximum exposure levels that are considered safe and a European Directive xxx that requires employers to ensure the safety of their employees.

A battery powered instrument described in patent specification G8241 3189 (the contents of which is incorporated herein by reference) is held between the fingers of one hand and measures the cumulative exposure of the user to vibration from equipment that the user is holding. Instruments for measuring cumulative vibration exposure will be referred to in this

specification as dosimeters'.

The dosimeter described in GB24 13189 is convenient to use, accurate and reliable. However, there is one perceived problem. It is found that, if used without a glove, it is possible for fore-aft motion to be amplified as the body of the device containing the acceleration sensors rotates about the point of contact. Even though when gloves are worn this problem goes away and users are expected to wear gloves, it remains a matter for improvement.

This invention resides partly in the recognition of the above problems and partly in the provision of a solution.

Currently there are no cheap and easy-to-use personalised devices available to measure hand-ant vibration on a regular basis. Yet the EU legislation previously referred to requires the monitoring of such vibration. The new Directive acknowledges the possible damaging consequences of vibration for human health and lays down maximum dosages of vibration exposure to avoid "white finger". White finger is a medical condition of numbness or pain that arises from continuous use of vibrating tools. In extreme cases white finger can lead to loss of one or more digits. The new Directive lays down a careful specification of what cumulative vibration dosage the user is allowed to be exposed to. Above this specified dosage, work must stop for that day. The Directive does not suggest how this exposure is to be measured. Technically, vibration measurements can be made with high quality expensive hardware that exists on the market today. This hardware will have been used in research work involved in the definition of the standards. The device disclosed in EPI 586875 (the teaching of which are incorporated herein by reference) resulted from endeavours to provide a vibration dosimeter that is light, unobtrusive, comfortable and easy to use even when wearing work gloves, sufficiently inexpensive to be given to every worker, calculates the vibration dosage accurately and provides a clear indication of when the dosage limit has been reached.

The device is formed in a cufflink shape having a stem section which fits between any pair of fingers and having a base which sits on the underside of the hand and makes contact with a handle of a machine which is being gripped by the user.

Fig I Hand gripping dosimeter and handle' illustrates a cross section of the device of EP1586875 whilst in use on a user's hand which is gripping onto a handle. Each unit is formed from a hollow plastics moulding with a main body 1 A containing the processor, the acceleration sensors, the battery and the warning LED, stem I B which in use sits between two digits of the user's hand and foot IC which when in use is in contact with the machine handle IF at the line of contact IF causing vibrations in the hand. Vibrations are transmitted from the handle I E through line of contact 1 F into the foot IC along a stem 1 B, which passes between the user's fingers, to the hollow main compartment 1A.

As seen from Figure 2 Cut-away view of dosimeter', the main compartment 2A contains a circuit board 2E carrying contacts 2F. After assembly of the circuit board 2E, insertion of the board into the compartment 2A, and fitting of a lid (not shown) through which the contacts 2F project, the compartment is filled with a settable resin so that just the tips of these contacts are exposed, thus forming means for external charging and communication. In addition to the contacts 2F, the circuit board 2E caries a triaxial accelerometer 2H, a processor 21, a warning lamp 2G, a memory module 2J, a battery 2L and a timer 2K. There is the possibility that accelerometer 2H measures only in two orthogonal directions in the plane of the top of the hand in which case accelerometer 2M would be needed to measure in the direction of the stem 2W Details and arrangement of the electronic/electrical features are explained in detail in the aforementioned referenced documents which are incorporated into this document by reference.

In this form there is some possibility of the main body IA in Figure 1 rotating about the line of contact IF and giving accelerations along the direction of the top of the fingers that are an amplified version of the acceleration in that direction at the line of contact IF entirely due to the length of the stem 18 that keeps the triaxial accelerometer away from the vibrating handle I F. These would be spurious accelerations. It is our experience that, as long as a working glove is worn, no such amplification occurs as the glove prevents the spurious rotation.

However this invention describes a means to avoid this rotation and therefore produces a dosimeter that works even without a working glove.

This benefit is obtained by moving the measurement of one or more components of the triaxial acceleration into the foot 1C itself. As long as the motion in the direction along the top of the fingers (i.e. the direction substantially parallel to the proximal phalanges of the digits of the user's hand between which the dosimeter is held; the proximal phalanges being those between the metacarpals and intermediate phalanges) is measured in the foot I C instead of in the main body 1A, there can be no rotation acceleration caused by the length of the stem.

As shown in Figure 3 Cut-away of enhanced dosimeter' and Figure 4 Side view schematic of cut-away dosimeter' the original horizontal acceleration measurement 211 in figure 2 has been moved from the main body IA, 4A to the foot 3C, 4C shown as lET, 414. Also shown is the battery 3L, 4L and connecting pins 3F, 4F.

The foot 3C, 4C is now a hollow (optionally plastic) moulding with the sensor 3H, 411 encapsulated within it. In the case when sensor 3H, 4H only measures in bi-axial directions it is possible to retain sensor 3M, 4M with connecting wires 4Q in the main body 3A, 4A to measure acceleration along the direction of the stem 3B, 4B. This direction is not affected by the rotation about the point of contact. The measurement in the foot 3C, 4C entails some connecting wires 4P running up the now hollow stem 3C, 4C from the sensor 3H, 4H in the foot IC, 4C to pads IN, 4N on the circuit board 3E, 4E in the main body IA, 4A. These wires 4P can be encapsulated within the stem IC, 4C.