GB2438731A

GB2438731A - Apparatus for measuring the dynamic coefficient of friction of a surface

Info

Publication number: GB2438731A
Application number: GB0710316A
Authority: GB
Inventors: Mark Collins; David Robert Bunting
Original assignee: Surface Control Ltd
Current assignee: Surface Control Ltd
Priority date: 2006-05-30
Filing date: 2007-05-30
Publication date: 2007-12-05
Anticipated expiration: 2027-05-30
Also published as: GB2438731B; GB0710316D0

Abstract

Disclosed and claimed is a device for measuring the dynamic coefficient of friction of a surface, the device comprising a track 1 shaped to mimic an arc of travel of a pendulum, a shoe mounted so as to be movable along the track, means (spring G) for providing an initial propulsion force to propel the shoe along the track, means for measuring the velocity of the shoe at a plurality of points (V1, V2, V3) during its travel along the track; and computing means for calculating the coefficient of friction from changes in velocity of the shoe as it moves along the track. The invention also provides (claimed in claims 8,10) an apparatus for determining the slip resistance of a floor surface at a plurality of locations on the floor surface, the apparatus comprising: a location device for identifying and recording the location of the apparatus; means for measuring one or more physical properties of the floor surface relevant to slip resistance at each location; a data processor programmed to compare measured values for each of the said physical properties of the floor surface at each location with comparison data; and an output device operatively linked to the data processor for informing a user of the apparatus whether the slip resistance of the floor at a given location is within acceptable limits.

Description

S

MONITORING APPARATUS

This invention relates to a device for determining the slip resistance of a surface, more particularly, the invention relates to a device for determining the slip resistance of a floor surface.

Background of the Invention

According to the UK Health & Safety Executive's own statistics, slips, trips and falls on level ground consistently count for around 1 in 3 major injuries, and for over 1 in 5 injuries in workplace areas throughout Great Britain that result in a 3 day absence from work. The HSE statistics indicate that there are at least 35,000 injuries per annum due to slips, trips and falls and suggest that the majority of these accidents are slips.

Various factors contribute to slipping accidents, and the HSE have identified six factors considered to be of particular importance: * The nature of the floor * Contamination of the floor * Footwear considerations * Pedestrian factors * Cleaning * Environment The Workplace, (Health, Safety and Welfare) Regulations, 1992, require that floors must not be slippery, so as to expose any person to a risk to their safety. Methods have been developed for testing the inherent slipperiness of a floor surface, and two methods of measuring the slipperiness of a floor are referred to in HSE publications. These are the pendulum Coefficient of Friction (CoF) test; and a surface micro-roughness meter test.

The pendulum coefficient of friction test is now the subject of a British Standard, BS 7976. The pendulum test instrument (TRL Pendulum Tester) uses an arm with a rubber shoe mounted on the end that swings from a fixed height. The contact arc COLI (0B3)

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chord length and depth are carefully controlled. The shoe is raised vertically against a spring that controls the pressure on the floor. Frictional engagement with the floor results in a loss of momentum and consequently so the swinging arm rises to a lower height at the end of the swing. A scale converts the reduced height into a coefficient of friction measurement.

Although the pendulum instrument is considered to provide an accurate assessment of the slipperiness of a floor in both dry and contaminated (e.g. wet conditions), it suffers from the drawback that it requires a skilled operative both to use it and to interpret the results. Moreover, according to the HSE, the pendulum meter is currently the only portable instrument that accurately simulates the action of a foot slipping on a wet floor.

The slipperiness of a floor may also be gauged by measuring the surface roughness of a flooring material. A number of types of roughness tests exist (see the HSE publication: The assessment of pedestrian slip risk' published by the Health and Safety Executive 10/04) and such methods, in theory, give a good indicator of floor slip resistance.

The surface micro-roughness meters measure a parameter known as the Rz' parameter which is calculated as the mean value of several peak- to valley measurements on the floor surface. According to the 1-ISE, in most circumstances, both pendulum CoF and surface micro-roughness readings are required to give an accurate indicator of the slipperiness of a floor surface. The HSE classification of slip risk, based on pendulum measurements, classifies pendulum values of 0-24 as high risk, values of 25-35 as moderate risk, values of 36-64 as low risk and values of 65+ as extremely low risk.

The classification for Rz surface roughness (microns) states that a surface roughness of below 10 microns is classified as providing a high potential for slip, a surface roughness between 10 and 20 microns is classified as providing a moderate potential for slip, whereas a surface roughness of 20 or above is stated to provide a low potential for slip.

COIl (GB3) a A major problem with the methods and instruments currently available for measuring the slipperiness of a floor is that, in practice, they require near laboratory conditions, and require setting up and data interpretation by skilled personnel. They are therefore not suitable for routine use and regular floor monitoring in an average work environment such as a supermarket where the condition of the floor, and hence its slipperiness, will typically fluctuate considerably, i.e. change of contamination problem, alteration of floor substrate, change of cleaning personnel, change of staff using test equipment, poor statistical record monitoring. Therefore, at present, there remains a need for an apparatus that is simple to set up and use and which can be used by unskilled staff, i.e. staff that have no interpretation knowledge of slip causes or staff with only a minimum of training, to determine whether or not a floor is safe for the public to walk over.

Summary of the Invention

The present invention sets out to provide an apparatus for monitoring the condition of a floor that is quick and simple to set up and use and can be used by staff with a minimum of training.

Accordingly, in a first aspect, the invention provides an apparatus for determining the slip resistance of a floor surface at a plurality of locations on the floor surface, the apparatus comprising: a location device for identifying and recording a location of the apparatus; means for measuring one or more physical properties of the floor surface relevant to slip resistance at each location; a data processor programmed to compare measured values for each of the said physical properties of the floor surface at each location with comparison data; and an output device operatively linked to the data processor for informing a user of the apparatus whether the slip resistance of the floor at a given location is within

acceptable limits.

Preferably, the apparatus comprises means for measuring two or more physical properties of the floor surface relevant to slip resistance at each location.

COLt (GB3) I, The physical properties of the floor surface that are relevant to slip resistance are typically selected from: a) the dynamic coefficient of friction of the floor surface; b) the micro- profile of the floor surface, and c) the reflectance of the surface.

In one embodiment, the means for measuring one or more physical properties of the floor surface comprises means for measuring the dynamic coefficient of friction of the floor surface.

In another embodiment, the means for measuring one or more physical properties of the floor surface comprises: (i) means for measuring the dynamic coefficient of friction of the floor surface; (ii) means for measuring the micro-profile of the floor surface; and (iii) optionally means for measuring the reflectance of the surface.

In a further embodiment, the means for measuring one or more physical properties of the floor surface comprises: -(i) means for measuring the dynamic coefficient of friction of the floor surface; (ii) means for measuring the reflectance of the surface; (iii) optionally means for measuring the micro-profile of the floor surface.

In a preferred embodiment, the means for measuring one or more physical properties of the floor surface comprises: -(i) means for measuring the dynamic coefficient of friction of the floor surface; (ii) means for measuring the reflectance of the surface; (iii) means for measuring the micro-profile of the floor surface.

In one embodiment, the measurement of the dynamic coefficient of friction of the floor surface is carried out using a friction-measuring device containing a ferris wheel mechanism.

The ferris wheel mechanism can operate in a manner similar to the known pendulum device but, instead of having only a single pendulum arm that swings under the force of gravity, the ferris wheel mechanism comprises a plurality of arms (e.g. four arms) mounted on a central rotating spindle, the arms having feet, at least the radially outer surface of which feet are formed from a high friction material COLI (GB3) $ such as rubber. The spindle is mounted on an axle that is capable of moving only in a forwards direction and is coupled through a sprung mechanism to an electric motor. In use, the motor is powered for a predetermined time sufficient to rotate the spindle by I/n turn (when there are n feet -for example a 1/4 turn when there are 4 feet) allowing one of the feet to come into contact with the floor to be tested.

At the instant the foot touches the floor, the power is turned off and the foot is allowed to continue moving, gradually coming to a halt as friction with the floor surface takes effect. A measurement is taken of the distance between the first point of contact and the stopping position and this information is recorded in the data processor. The process is then repeated until a desired number (e.g. 4 to 6) separate movements of the foot have been measured and, from the measurements, the dynamic coefficient of friction is calculated.

As an alternative to a ferris wheel mechanism, the wheel can be replaced by a drum having a plurality of rubber feet mounted around its periphery. A motor turns an axle gearing which enables the Ferris style drum to turn, similar to that of a spring loaded device, the pads attached to the ferris wheel make contact with the surface under test and is maintained for a pre-set distance whilst the energy absorbed is monitored by the digital torque measurement device. The torque information is sent to PC software. A series of measurements are taken. The software converts torque calculations into dynamic co-efficient of friction specifics.

The micro-profile of the floor surface can be measured by means of a digital micron profile meter. Diamond stylus digital micron profile meters are commercially available and comprise a diamond tipper stylus (e.g. a 2 jim diamond stylus) that is in physical contact with the surface and tracks along the along the surface recording micro-undulations of the surface.

As an alternative to the diamond stylus digital profile meter, an optical (and hence non-contact) method can be employed in which the peaks and troughs of the surface are detected by scanning a light along the surface for a predetermined distance.

The reflectance of the surface may be measured using a digital gloss meter. Digital gloss meters are available commercially and operate by directing light of a COLI (0B3) if $ predetermined strength onto the surface, and measuring the amount of light reflected back from the surface.

The data processor is programmed to compare measured values for each of the physical properties of the floor surface at each location with comparison data which can, for example comprise historical data consisting of previously measured values for each location or/and as a reference standard when setting up the first inspection.

The location device is preferably one which is capable of determining the position of the apparatus to an accuracy of within about 5 metres, more preferably within about 4 metres, for example within about 3 metres, and most preferably within about 2 metres. The location device may be provided with a transceiver, and the location of the device may be determined by communication with one or more external transceivers positioned at fixed, known locations relative to the apparatus.

For example, where the apparatus is intended for use in a supermarket or department store or other shop, a plurality of transceivers may be positioned at fixed location around the supermarket, store or shop, communication between the external transceivers and the transceiver in the location device serving to establish the location of the apparatus.

Whereas the various component parts of the apparatus can be spatially separated (e.g. the data processor and/or the output device could be remote devices communicating by, for example, radio waves, to the location device and measuring means), it is preferred that the means for measuring one or more physical properties of the floor surface, data processor, output device, and location device (other than any external transceivers) when present, are all mounted in or on a common housing.

The apparatus may have only one output device, or may have a plurality of output devices.

Each output device is operatively linked to the data processor and informs a user of the apparatus whether the slip resistance of the floor at a given location is within acceptable limits. Information regarding the slip resistance can be imparted to the CCLI (0B3) user in a variety of ways. For example, the output device can comprise one or more visual or audio elements for indicating whether the slip resistance of the floor at a given location is within acceptable limits.

In one embodiment, an output device is provided which comprises one or more lights that light up to indicate whether the slip resistance of the floor at a given location is within acceptable limits.

Slip Risk Classification 0-24 High 25-35 Moderate 36-64 Low 65+ Extremely low The lights may comprise green and red indicator lights, the green light indicating that the slip resistance of the floor at a given location is within acceptable limits and the red light indicating that the slip resistance of the floor at a given location is not within acceptable limits.

Alternatively or additionally, an output device may be present which provides an alphanumeric visual display. The alphanumeric visual display can be provided by, for example, a screen or a printer or both.

In one preferred embodiment, an output device is present which provides a print out informing the user of the slip resistance of the floor.

The output devices typically provide information which informs the user whether or not the floor meets a predetermined slip resistance requirement without the requirement for the user to carry out complex calculations and without the need for any particular skill or experience on the part of the user. For example, the output device may provide an index number or letter indicative of the state of the floor so that the user can see, either straightaway or by reference to a simple key or chart, whether the floor requires attention. In one embodiment, the output device may also provide information as to what type of remedial action is required. it will be COLt (G83) appreciated therefore that the apparatus may be used by an unskilled or semi-skilled operative.

In another aspect, the invention provides an apparatus for determining the slip resistance of a floor surface at a plurality of locations on the floor surface, the apparatus comprising: means for measuring two or more physical properties of the floor surface relevant to slip resistance at each location; a data processor programmed to compare measured values for each of the said physical properties of the floor surface at each location with comparison data; and an output device operatively linked to the data processor for informing a user of the apparatus whether the slip resistance of the floor at a given location is within

acceptable limits.

The apparatus preferably comprises a location device as hereinbefore defined for identif'ing and recording the location of the apparatus In a still further aspect, the invention provides a method of monitoring the slip resistance of a floor surface at one or more locations on the floor surface, which method comprises using an apparatus as hereinbefore defined to: (a) measure one or more physical properties of the floor surface relevant to slip resistance at each location; (b) compare measured values for each of the said physical properties of the floor surface at each location with comparison data; and (c) inform a user of the apparatus whether the slip resistance of the floor at a given location is within acceptable limits.

Accordingly, in a further aspect, the invention provides a device for measuring a dynamic coefficient of friction of a surface, the device comprising of a motor that turns the axle gearing which enables the Ferris style drum to turn, similar to that of a spring loaded device, the pads attached to the ferris wheel make contact with the surface under test and is maintained for a pre-set distance whilst the energy absorbed is monitored by the digital torque measurement device. The torque COLI (GB3)

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information is sent to PC software. A series of measurements are taken. The software converts torque calculations into dynamic co- efficient of friction specifics.

In a further aspect, the invention provides a device for measuring the dynamic coefficient of friction of a surface, the device comprising; a track having an arcuate portion which is shaped to mimic an arc of travel of a pendulum; a shoe mounted so as to be movable along the track, and means for biasing part of the shoe into contact with the surface as it moves along the arcuate portion of the track; means for providing an initial propulsion force to propel the shoe along the track; means for measuring the velocity of the shoe at a plurality of points during its travel along the track; and computing means for calculating the coefficient of friction from changes in velocity of the shoe as it moves along the track.

The deice may form part of an apparatus for determining the slip resistance of a floor surface as defined herein.

The arcuate track is shaped to mimic an arc of travel of a pendulum, i.e. the track is bowed in a downwards direction. The arcuate track can be formed by a rail or pair of substantially parallel rails upon which is mounted a carriage that carries the shoe.

The carriage may be provided with one or more rollers or pairs of rollers that engage the track and allow the carriage to move along the track. The arcuate track may have a substantially horizontal portion of track adjoining one or both ends thereof.

The device comprises means for providing an initial propulsion force to propel the shoe along the track. The means for providing the initial propulsion force is typically configured so that it imparts an accelerating force to the shoe (or carriage carrying the shoe) up to but not beyond the start of the arcuate portion of the track.

Once the accelerating force is removed, the shoe (or carriage) will gradually lose velocity as it moves along the arcuate portion of the track as a consequence of COIl (GB3) frictional engagement with the underlying surface. The velocity of the shoe (or carriage) is measured by a plurality (e.g. three or more, for example three) of measuring devices and the reduction in velocity is determined, Since the rate of deceleration of the shoe is dependent on the friction between the shoe and the underlying surface, the rate of deceleration can be used to calculate the dynamic coefficient of friction of the surface.

The means for providing an initial propulsion force can take a number of different forms. For example, it could be a solenoid-driven or hydraulic ram or plunger.

Preferably, however, it comprises a spring which is compressed and then released.

In one preferred embodiment, the means for providing an initial propulsion force comprises a compressible spring, a mechanism for compressing the spring, a latch for holding the spring in a compressed state, and release means for releasing the latch to allow the spring to decompress.

In order to ensure that part of the shoe remains in contact with the surface as it travels along the arcuate portion of the track, a biasing means is provided for biasing the shoe against the surface. The biasing means typically takes the form of a biasing spring.

The part of the shoe that is biased into contact with the surface is typically formed of rubber, and most preferably a 4S grade of rubber as defined herein.

The device may be calibrated using a pendulum tester, e.g. a TRL pendulum tester, in which case the arcuate portion of the track has a radius of curvature corresponding to the radius of the path followed by the pendulum in the pendulum tester. Calibration may be achieved using the methods described below.

In another aspect, the invention provides a method of measuring the dynamic coefficient of friction of a surface using a device as described in herein; wherein the method comprises; positioning the device on the surface; imparting an initial propulsion force to the shoe to propel the shoe along the track; COIl (GB3) measuring the velocity of the shoe at a plurality of points during its travel along the track; and calculating the coefficient of friction from changes in velocity of the shoe as it moves along the track.

Further aspects and embodiments of the invention are as set out below and as defined in the claims.

Brief Description of the Drawinas

Figure 1 is a schematic view of a device according to one embodiment of the invention.

Figure 2 is a schematic view of a device forming part of the apparatus of Figure I for measuring the dynamic coefficient of friction.

Figure 3 is a side view of a conventional pendulum apparatus for measuring the coefficient of friction of a floor surface. The pendulum apparatus does not form part of the invention.

Figure 4 is a schematic diagram illustrating the mode of action of the pendulum apparatus of Figure 3.

Figure 5 is a partial view from below of an apparatus for measuring the coefficient of friction of an underlying surface according to a second embodiment of the invention.

Figure 6 is a schematic side view of the apparatus of Figure 5.

Figure 7 is an isometric view of the apparatus of Figure 5 Figure 8 is a side sectional elevation of the apparatus shown in Figure 5 with the carriage in the latched primed position.

Figure 9 is a side sectional elevation of the apparatus shown in Figure 5 showing the position of the carriage shortly after release of the latch.

COLI (G83) a Figure 10 is a side sectional elevation of the apparatus shown in Figure 5 showing the carriage at the end of its travel following release of the latch.

Figure 11 a is a side sectional elevation of the apparatus shown in Figure 5 with the lever arm in a raised position.

Figure 1 lb is a side sectional elevation of the apparatus shown in Figure 5 with the lever arm in a partially lowered position and the compression spring lightly compressed.

Figure lIc is a side sectional elevation of the apparatus shown in Figure 5 with the lever arm in a fully lowered position and the compression spring fully compressed.

Detailed Description of the Invention

The invention will now be illustrated, but not limited, by reference to the specific embodiment shown in the accompanying drawings.

An apparatus according to one embodiment of the invention is shown in Figure 1 and comprises an outer casing 2 which may be formed from sheet metal panels, and an internal frame (not shown) on which are mounted various other components of the apparatus.

The casing is preferably water resistant and, purely by way of example, the dimensions of the casing can be height: 200 mm; width: 250 mm; and length: 400 mm. It is emphasised though that these dimensions are merely exemplary and the casing may of course have different dimensions. The casing and its contents may be selected so that the device is of manageable weight.

Within the casing 2 and mounted on the frame (not shown) is a processor 4 linked to or containing a memory or data storage device such as a CD ROM or DVD drive.

The processor 4 is linked to a power supply and onloff switch 6, a first output device 8, a second output device 10, a location device 12, a device 14 for measuring the dynamic coefficient of friction of the underlying floor surface, a digital micron profile meter 16 and a digital gloss meter 18. The processor is also connected to a COLI (053) USB port 20 or other data port so that data can be taken from or introduced into the data processor.

The device for measuring the dynamic coefficient of friction is shown in more detail in Figure 2 and comprises a drum 22 having 7 rubber pads 24 around its periphery. By way of example, the rubber pads can have dimensions of 75 mm X mm X 6mm and be made from 4S rubber ("standard simulated shoe sole"), a grade of rubber developed by the UK Health and Safety Laboratory (HSL) and the UK Slip Resistance Group (UKSRG).

The drum 22 is mounted on a spindle 26 which is driven by a drive means 28 which in turn is driven by a train of sprockets and cogs, of which only the sprocket 30 is shown. The sprocket is rotated by a wonn gear 32 which is connected to electric motor 34. A digital dynamic torque measurement device 36 is mounted about drive means 28 and is connected by RS232 cable 38 to the data processor 4.

The device measures the dynamic coefficient of resistance of the underlying floor surface as follows: The motor turns the axle gearing which enables the Ferris style drum to turn, similar to that of a spring loaded device, the pads attached to the ferris wheel make contact with the surface under test and is maintained for a pre-set distance whilst the energy absorbed is monitored by the digital torque measurement device. The torque information is sent to the PC software. A series of measurements are taken. The software converts torque calculations into dynamic co-efficient of friction specifics.

The digital micron profile meter 16 ("surface microroughness meter") measures the "peak-to-valley" distances of uridulations in the floor surface at a number of points within a defined distance and then calculates the mean "peak-to-valley" distance.

The measurement can be made using a 2 p.m diamond-tipped stylus that follows the profile of the floor surface over a length of, for example, 12 mm, or the measurement can be made by an optical scanning method that involves measuring the peaks and valleys along a 12 mm linear path. An advantage of using the optical scanning method over the diamond tipped stylus method is that it does not involve contact with the floor and hence avoids the potential problem of the stylus COLI (0B3) becoming clogged or snagged on the surface. Whichever method is used, the digital micron profile meter conveys to the data processor information about the roughness of the surface.

The digital gloss meter 18 operates by directing a beam of light of a known strength onto the floor surface and then measuring the light reflected back from the floor.

The results of the measurements are then relayed to the data processor and compared to historical data.

Thus, the data processor receives measurements from each of the device 14 for measuring the dynamic coefficient of friction, the digital micron profile meter 16 and the digital gloss meter 18. The results from each instrument are then compared with historical data for that particular location. Depending on whether or not there has been a deterioration in one or more of the parameters of the floor compared to historical data, a simple pass-fail signal is then Sent to the first output device 8 which comprises red and green lights, red to indicate that the floor has failed the slip test, and green to indicate that the floor has passed the slip test. A signal can also be sent to output 10 which comprises a printer that can provide a print out of the measured parameters of the floor surface so that the reasons why the floor may have failed the slip test may be determined.

A full set of data corresponding to the measurements made can be taken from the apparatus via the USB port 20.

The advantage of the apparatus of the invention is that it allows the slipperiness of a floor su.rface to be measured quickly and simply by staff who have received only a minimum of training. For example, after aspillage in a supermarket, the floor may be mopped clean but there may still be traces of residue that could increase the slipperiness of a floor. Using the apparatus of the invention, the floor can be tested to see whether it is safe to allow members of the public to walk over it. In another example, the apparatus can be used routinely at daily, weekly or even at several times daily intervals to monitor the condition of the floor on an ongoing basis so that problems of floor deterioration and wear can be addressed before they reach a point at which the floor is hazardous.

Coil (0B3) An apparatus according to a second embodiment of the invention is shown in Figures 5 to I ic. The apparatus provides a more compact and portable alternative to the standard TRL pendulum tester, an example of which is shown in Figure 3, and which forms no part of the invention.

The TRL Pendulum Tester method represents the currently approved method of measuring the Coefficient of Friction of floor surfaces. The pendulum tester uses a swinging pendulum arm A with a rubber shoe S mounted on its end. The rubber shoe is formed from the same grade of 4S rubber described above in relation to the embodiment of Figures 1 and 2. The contact arc chord length and depth are carefully controlled using the adjustment screws C on the base of the pendulum tester. As shown in Figure 3, a typical chord length used in the test is a length of mm. The rubber shoe S is raised vertically against a spring B that controls the pressure on the floor. The pendulum is released from a defined starting height so that it swings down bringing the shoe S into contact with the floor surface. Friction between the shoe S and the floor results in a loss of momentum and so the swinging arm rises to a lower height at the end of the swing. A scale converts this reduced height into a coefficient of friction measurement.

The apparatus of Figures 5 to lie replicates the behaviour of the pendulum by using a compressed spring G to provide the equivalent potential energy of the pendulum when raised to its starting position.

When the force of the compressed spring 0 is released, it urges a carriage bearing a rubber shoe H along a track I with the same shape as the swing of the pendulum over the distance where the shoe is in contact with the floor. Frictional forces on the shoe slow it down as it passes over the floor surface. The apparatus measures the speed of the shoe at multiple points (V1, V2 & V3) during its travel and from these measurements computes the equivalent pendulum measurement and hence the coefficient of friction of the surface under test.

The following is a simplified description of the measurement equations that neglects a number of effects for simplicity. The potential energy (PE) of the pendulum device is given by COLI (GB3) PE= m.g.h1 where m is the mass in kilograms g is the acceleration due to gravity, approximately 9.81 m.s2 h1 is the initial height in metres The potential energy is converted to kinetic energy (KE) that is maximum at the lowest point of travel.

KE1 &/2.m.v 2 The effect of friction reduces the Kinetic Energy so that the pendulum rises to a lower height at the end of its swing. The potential energy at this point is PE2m.g.h2 The height h2 is effectively measured by the pointer on the pendulum that records the maximum height reached.

If the pendulum were released from the height h2, this would result in a Kinetic Energy KE2&/2.m.v22 The difference between the initial height and the final height is primarily due to the loss of energy to friction. We can set the equations equal PE1=KE1 and PE2=KE2 But we can calculate the loss of Potential Energy as PE1-PE2 and therefore PE-PE2 = KE1-KE2 The coefficient of friction indicated by the pendulum device can be simply measured as a function (F) of the height difference h1-h2, this being indicated on the scale of the machine. The function F is a easily calculated from the geometry of the pendulum machine based on the angle of deflection of the machine's pointer.

So the Coefficient of Friction, COF = F(h1-h2) COLI (6B3) By transposing the equations above and removing common terms we get 2g (hl-h2) Vj2-V22 and therefore COF F((v12-v2)/2g) It can therefore be seen that by measuring the changes in velocity and relating that difference to the calibration data measured from the pendulum the coefficient of friction can be determined to give the same result as would have been given by the pendulum for the same surface.

An apparatus embodying the principles set out above is illustrated in Figures 7 to 1 Ic. As shown in Figure 7, the apparatus comprises a housing 102 with removable side panels 104 that conceal the moving parts of the apparatus.

Mounted on one end of the support frame is a box 106 that contains the electronic controls (not shown) for the apparatus. Set into the upper surface of the box are control buttons 108 and a small display screen 110. A handle 112 extends from the upper surface of the box.

The interior workings of the apparatus are shown in Figure 8 which is a side sectional elevation.

Within the housing 102 is a longitudinally extending frame member 114 having an inverted channel section, within which is disposed a bar 116 of circular cross section. A buffering spring 118 is mounted about the bar at one end thereof, and a propulsion spring 120 is mounted about the bar at the other end thereof. The frame member 114 is provided at its lower end with a laterally extending flange 122, which is substantially horizontal at either end but has a central portion 124, which is arcuate in shape. The flange 122 serves as a track upon which is mounted a carriage 126. Two pairs of rollers 128 and 130 serve to hold the carriage in place on the flange. -Attached by means of pivot mounting 132 to the lower part of the carriage is an arm 134, upon which is mounted a rubber shoe 136. The arm 134 and hence the rubber COLI (GB3) shoe 136 are biased in a downwards direction by means of biasing spring 138. An adjustment screw 140 allows for fine adjustment of the position of the arm 134 and shoe 136.

The housing 102 is provided with adjustable feet, 144, which allow the housing, and hence the rubber shoe 136, to be raised and lowered.

After manufacture and typically before despatching to a customer or end user, the apparatus is set up by calibrating with a pendulum tester, e.g. a standard pendulum tester of the type shown in Figure 3. Thus, the adjustment screws 140 and 144 are adjusted so that the set-up corresponds to the set-up of the pendulum tester. After calibration, the adjustment screws 140 and 144 are typically locked against further adjustment before the device is sent out to the customer or end user.

Mounted just above the bar 116 are three infrared sensors 142, each consisting of a pair of elements, one of which is an infrared emitting LED and the other of which is an infrared optical transistor. In practice, an infrared beam is established between the LED and transistor, the beam being broken as the carriage is moved along the track. The time taken for the carriage to break each successive beam provides a means of measuring the velocity of the carriage as it moves along the track, and data from the three infrared sensors are conveyed to the controller in the box 106.

Located at one end of the housing is a digital gloss meter, 146, the output from which is conveyed to the controller within box 106.

Figure 8 illustrates the apparatus in a loaded' configuration, with the spring 120 in a compressed state. The spring is retained in the compressed state by virtue of the carriage, which is held in place by latch 148. Latch 148 has a hooked latch portion which engages a boss (not shown) on the carriage. A push rod 152 provides a means of releasing the latch.

Figures 1 la, I Ib, and lie illustrate the manner in which the propulsion spring 120 is compressed.

COLI (GB3)

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Firstly, lever arm 154 is lifted and this has the effect of moving the pivoting strut 156 and an associated slider 158 rearwardly, so that the slider engages the carriage 126. The lever arm is then pivoted towards the closed position as shown in Figure 11(b), moving the slider 158 and carriage 126 into contact with the spring 120, thereby compressing the spring. When the lever arm 154 is fully depressed and is in the fully closed state, the spring is fully compressed and the carriage is held in place by means of the latch 148.

In order to use the apparatus, the push rod 152 is depressed thereby lifting the latch member 148 to release the carriage, which is then propelled along the track 132. As the carriage moves along the arcuate portion 124 of the track, the shoe 136 comes into contact with the surface, so that friction between the surface and the shoe has the effect of slowing down the movement of the carriage. The rate of deceleration of the carriage is measured by means of the infrared sensors 142. At the end of the track 122, the carriage is brought to a halt by means of the buffering spring 118.

The rate of deceleration of the carriage is a function of the dynamic coefficient of friction of the surface. Computer software within the box is capable of converting the measured rates of deceleration of the carriage into coefficient of friction figures.

The figures are then either transmitted to a remote device for reading out or are displayed on the display screen 110 on top of the box 106.

The coefficient of friction figures may be combined with readings from the digital gloss meter 146, to give an easily understood indication of the slip resistance of the floor in the manner described above in respect of the embodiments shown in Figures 1 and 2.

An advantage of the apparatus shown in Figures 5 -11 c is its compact nature. The device is of lightweight construction and is portable in contrast to the more cumbersome pendulum tester devices. The apparatus can be easily carried under one arm and provide a simplified digital read-out indicative of the state of the surface.

Equivalents COL I (GB3) It will readily be apparent that numerous modifications and alterations may be made to the specific embodiments of the invention described above without departing from the principles underlying the invention. All such modifications and alterations are intended to be embraced by this application.

Whatever arrangement is utilised for determining the COF of a floor surface, it will be appreciated that the results obtained will be such that a direct comparison may be deduced in relation to measurements made using the pendulum test instrument in accordance with BS 7976.

COLI (GR3)

Claims

CLAIMS

1. A device for measuring the dynamic coefficient of friction of a surface, the device comprising; a track having an arcuate portion which is shaped to mimic an arc of travel of a pendulum; a shoe mounted so as to be movable along the track, and means for biasing part of the shoe into contact with the surface as it moves along the arcuate portion of the track; means for providing an initial propulsion force to propel the shoe along the track; means for measuring the velocity of the shoe at a plurality of points during its travel along the track; and computing means for calculating the coefficient of friction from changes in velocity of the shoe as it moves along the track.

2. A device according to claim 1 wherein the means for providing an initial propulsion force comprises a compressed spring.

3. A device according to claim I or claim 2 wherein the part of the shoe is biased into contact with the surface during its travel along the arcuate portion of the track by means of a biasing spring.

4. A device according to any one of the preceding claims wherein the part of the shoe that is biased into contact with the surface is formed of rubber.

5. A device according to any one of the preceding claims wherein means are provided for measuring the velocity of the shoe at three or more positions along thc track.

6. A device according to claim 5 wherein means are provided for measuring the velocity of the shoe at three positions along the track.

7. A device for measuring the dynamic coefficient of friction of a surface, the device being substantially as described herein with reference to the drawings Figures 5 to tic.

CCLI (083) 8. Apparatus for determining the slip resistance of a floor surface at a plurality of locations on the floor surface, the apparatus comprising: a location device for identifying and recording the location of the apparatus; means for measuring one or more physical properties of the floor surface relevant to slip resistance at each location; a data processor programmed to compare measured values for each of the said physical properties of the floor surface at each location with comparison data; and an output device operatively linked to the data processor for informing a user of the apparatus whether the slip resistance of the floor at a given location is within acceptable limits.

9. Apparatus according to claim 8 which comprises means for measuring two or more physical properties of the floor surface relevant to slip resistance at each location.

10. Apparatus for determining the slip resistance of a floor surface at a plurality of locations on the floor surface, the apparatus comprising: means for measuring two or more physical properties of the floor surface relevant to slip resistance at each location; a data processor programmed to compare measured values for each of the said physical properties of the floor surface at each location with comparison data; and an output device operatively linked to the data processor for informing a user of the apparatus whether the slip resistance of the floor at a given location is within acceptable limits.

11. Apparatus according to claim 10 comprising a location device for identifying and recording the location of the apparatus.

12. Apparatus according to any one of claims 8 to 11 wherein the physical properties of the floor surface relevant to slip resistance are selected from (a) CCLI (GB3) the dynamic coefficient of friction of the floor surface, (b) the micro-profile of the floor surface, and (c) the reflectance of the surface.

13. Apparatus according to claim 12 wherein the means for measuring one or more physical properties of the floor surface comprises means for measuring the dynamic coefficient of friction of the floor surface.

14. Apparatus according to claim 13 wherein the means for measuring the dynamic coefficient of friction of the floor surface comprises a ferris wheel pendulum mechanism.

15. Apparatus according to claim 13 wherein the means for measuring the dynamic coefficient of friction of the floor surface is a device as defined in any one of claims Ito 7.

16. Apparatus according to claim 12 wherein the micro-profile of the floor surface is measured by means of a digital micron profile meter.

17. Apparatus according to claim 12 wherein the reflectance of the surface is measured using a digital gloss meter.

18. Apparatus according to any one of the preceding claims wherein the comparison data comprise historical data consisting of previously measured values for each location.

19. Apparatus according to any one of claims 8 to 18 wherein the means for measuring one or more physical properties of the floor surface, data processor, output device, and location device when present, are mounted in or on a common housing.

20. Apparatus according to any one of claims 8 to 19 comprising a plurality of output devices operatively linked to the data processor for informing a user of the apparatus whether the slip resistance of the floor at a given location is within acceptable limits.

COLI (G83) 21. Apparatus according to any one of claims 8 to 20 wherein an output device comprises one or more visual or audio elements for indicating whether the slip resistance of the floor at a given location is within acceptable limits.

22. Apparatus according to claim 21 wherein the output device is provided with one or more lights that light up to indicate whether the slip resistance of the floor at a given location is within acceptable limits.

23. Apparatus according to claim 22 wherein the lights comprise green and red indicator lights, the green light indicating that the slip resistance of the floor at a given location is within acceptable limits and the red light indicating that the slip resistance of the floor at a given location is not within acceptable limits.

24. Apparatus substantially as described herein with reference to the accompanying drawings Figures 1 and
2.

25. A method of monitoring the slip resistance of a floor surface at one or more locations on the floor surface, which method comprises using an apparatus according to any one of claims 8 to 24 to: (a) measure one or more physical properties of the floor surface relevant to slip resistance at each location; (b) compare measured values for each of the said physical properties of the floor surface at each location with comparison data; and (c) inform a user of the apparatus whether the slip resistance of the floor at a given location is within acceptable limits.

26. A method of measuring the dynamic coefficient of friction of a surface using a device as described in anyone of claims I to 7; wherein the method comprises; positioning the device on the surface; imparting an initial propulsion force to the shoe to propel the shoe along the track; measuring the velocity of the shoe at a plurality of points during its travel along the track; and COIJ (GB3) calculating the coefficient of friction from changes in velocity of the shoe as it moves along the track.

COLI (063)