WO2003102552A1

WO2003102552A1 - Friction sensor

Info

Publication number: WO2003102552A1
Application number: PCT/CA2002/000811
Authority: WO
Inventors: Casey K. Dundass; Timothy S. Leggett
Original assignee: Insurance Corporation Of British Columbia; Intranstech Corp.
Priority date: 2002-05-31
Filing date: 2002-05-31
Publication date: 2003-12-11
Also published as: AU2002302280A1; AU2002302280A8

Abstract

A friction sensor for determining the coefficient of friction of a subject surface. The friction sensor has a housing having an upper panel and test surface mounted on a platform movable in a vertical direction from an upper position co-planar with the upper panel and a lower position within the housing. A sensor assembly having a rotating member senses the amount of rotation of the rotating member over the test surface in order to determine the test surface's friction. The friction sensor may be embedded in the subject surface and controlled from a remote location.

Description

TITLE OF THE INVENTION

FRICTION SENSOR

FIELD OF THE INVENTION

The invention relates to devices for measuring the friction of a surface.

BACKGROUND OF THE INVENTION

There are sometimes compelling reasons to determine the friction of a given surface. One such example is in relation to the surface of roadways. There are an ever-increasing number of motor vehicles on the roads and highways. Along with the immediate health concerns associated with traffic accidents are concerns including delays to other motorists and costs in time and wasted fuel as a result of accidents. Often, these accidents could be prevented had the motorists been timely advised of the appropriate speed for the current road conditions.

U.S. Patent No. 2,849,701, teaches a highway condition indicating system. The '701 patent teaches the use of a plurality of signs along the highway to visually, or possibly audibly, indicate to motor vehicle drivers the safe speed and the reason for it. Sensing devices, which act to detect the existence of variable weather conditions such as fog, ice, rain or snow, control the signs. These sensing devices include moisture detectors, light sensitive devices, and thermometers. While this provides information beneficial to the motorist, the system does not provide an accurate assessment of the actual road condition.

Methods of measuring a slippage resistance coefficient of a surface have been developed. Examples include U.S. Patent Nos. 4,187,714 and 4,909,073.

The '714 patent teaches a surface friction tester in the form of a friction sled that is pulled by an individual over a surface in order to determine the coefficient of friction of the surface. A material having the characteristics of a vehicle tire tread is attached to a base plate. A spring scale is used to measure the force required to pull the sled over the surface. Because the friction sled must be pulled by the individual across the road surface, its use disrupts traffic. The device is best suited for accident investigation and is not practical for use in association with a system for determining the appropriate speed for the road conditions.

U.S. patent No. 4,909,073 to Takahashi et al. teaches a towable apparatus for measuring the resistance against slippage on a road surface. The apparatus has two measuring wheels connected to one another by a torsion bar. The rotational speed of one of the measuring wheels is forcibly altered. A slippage resistance on the road surface is measured by detecting a torque generated on the torsion bar due to the difference in rotational speed. While the towable apparatus provides a method for measuring the slippage resistance, it must be towed behind a vehicle, thereby resulting in a disruption of traffic. It is also costly to operate as a result of fuel expenses. It also requires at least one individual be involved with the testing (driving the tow vehicle)

Accordingly, it is an object of an embodiment of the present invention to provide an improved friction sensor that may be permanently installed in a road or surface to be tested.

It is a further object of an embodiment of the invention to provide a friction sensor that does not substantially interfere with the continuity of the surface to be tested.

It is a further object of an embodiment of the present invention to provide a friction sensor that may be operated automatically or from a remote location.

It is a further object of an embodiment of the present invention to provide a friction sensor that may be used in a system for informing motorists of the road conditions.

Further objects will become apparent with reference to the following summary of the invention and to the description of the preferred embodiment that follows. SUMMARY OF THE INVENTION

According to the present invention there is provided a friction sensor for determining the coefficient of friction of a subject surface. The friction sensor has a housing defining an enclosure and having an upper panel. A platform is located in the enclosure and is movable in a vertical direction between a lower position within the enclosure and an upper position. A test surface is fixedly attached to the platform. The friction sensor also comprises a sensor assembly for determining the friction of the test surface.

The present invention is also directed to the friction sensor defined above, wherein the test surface is co-planar with the upper panel when the platform is in the upper position. The sensor determines the friction of the test surface when the platform is in the lower position. Preferably, the housing is cylindrical and has a top end defined by the upper panel and an opening.

In another aspect of the invention, the testing surface has a friction characteristic similar to a friction characteristic of the subject surface.

In another aspect of the invention, the platform has a size and shape corresponding to the size and shape of the opening.

In another aspect of the invention, the sensor assembly comprises a rotating member and a drive for causing the rotating member to travel over and in contact with the test surface.

In another aspect of the invention, the friction sensor further comprises a bias restraint acting on the rotating member. Preferably the bias restraint is a torsion spring and is connected to the rotary member.

In another aspect of the invention, the friction sensor further comprises a sensor for detecting the amount of rotation the rotating member undergoes without slippage.

In another aspect of the invention friction sensor further comprises a rotatable arm coupled to the rotating member. In another aspect of the invention, when the platform is in the lower position, the rotating member may travel from an internal surface to the test surface by the action of the rotatable arm.

In yet another aspect of the invention, the friction sensor further comprises a controller for determining a coefficient of friction based on the amount of rotation of the rotating member.

Preferably, the sensor is a potentiometer and the controller comprises a processor.

The present invention is also directed to the use of a friction sensor defined above:

a) to determine an appropriate speed for a road;

b) as part of a system for automatically alerting motorists of road conditions; and/or

c) as part of a system for automatically alerting motorists of road conditions wherein a motorist is advised of the appropriate speed for the road condition.

The present invention is also directed to a method of determining friction conditions of a subject surface comprising providing a test surface co-planar with the subject surface, withdrawing the test surface from its co-planar relationship with the subject surface to a test position, testing the test surface to determine its friction characteristics, and returning the test surface to a position co-planar with the subject surface.

The present invention is also directed to the method described above, wherein the testing comprises rotating a rotary member in contact with the test surface and determining the tendency of the rotary member to slip on the test surface. The present invention is also directed to the method defined above, wherein the step of determining comprises providing a resistance to rotation of the rotary member and sensing the maximum amount of rotation of the rotary member.

Other aspects of the invention will be appreciated by reference to the detailed description of the preferred embodiment and to the claims that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiment of the invention will be described by reference to the drawings thereof in which:

Fig. 1A is a front perspective view of a friction sensor according to the preferred embodiment of the invention showing a platform of the sensor in an upper position;

Fig. IB is a front perspective view of the friction sensor of Fig. 1 with the platform lowered into the housing;

Fig. 2 is a rear perspective view of the friction sensor of Fig. 1 with the outer cover removed;

Fig. 3 is a side perspective view of the friction sensor of Fig. 2 from the opposite side;

Fig. 4 is a perspective view of the friction sensor of Fig. 2 from an alternative angle;

Fig. 5 is an enlarged perspective view of the sensor assembly of the fiiction sensor of Fig. 2.

Fig. 6 is a partially exploded perspective view of the friction sensor of Fig. 3 showing the internal assembly separated from the bottom plate. Fig. 7 is a perspective view of the friction sensor of Fig. 1 showing it in connection with a controller and a variable display sign.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The friction sensor according to the invention is embedded in a subject surface, such as a roadway, for which a determination of the friction of the surface is desired. The friction sensor has a platform with a test surface forming part of the subject surface. The test surface has similar characteristics to the subject surface. The platform may be lowered into the interior of the friction sensor in order to accurately determine the fiiction of the platform test surface. When used in association with roads, an appropriate speed for the condition of the road surface may be determined based on the friction of the platform surface, which speed is then transmitted to motorists.

The preferred embodiment of a friction sensor 60 is illustrated in Fig. 1A. A housing 1 defines an enclosure for the internal assembly 65 (shown in Figs. 2-4) of the friction sensor 60. Preferably, housing 1 is welded to a bottom plate 23, however other methods of fixedly or removably attaching the two are possible. An upper panel, for example, top cover plate 6, is attached to housing 1, preferably by way of hex bolts 44. Hex keys (not shown) are used to remove the hex bolts 44. Preferably a unique hex pattern will be used to provide tamper proofing.

A test surface 39 is attached to a platform 7, best illustrated in Fig. 2. The platform 7 sits atop support shaft 16 and vertical slider rods 18. The slider rods 18 are mounted to wall 4 by means of bushings 17 and act to guide platform 7 when it is in motion. Wall 4 is attached to a base 21. Support shaft 16 has a nut 20 recessed into its base and is mounted about lead screw 8. Nut 20 is connected to, preferably by welding, and is threaded about lead screw 8. A thrust bearing (not shown) for supporting a compression load is seated in the thrust bearing mount 30 and supports the lead screw 8. Thrust bearing mount 30 is attached to base 21. A thrust bearing seal (not shown) seated in a machined pocket in the thrust bearing mount 30 protects the thrust bearing from debris. Radial bearing 9 is connected, preferably by way of removable bolts, to wall 4. Shim 22 is used to position the lead screw 8 in the correct location and ensure proper fit. Radial mount 9 is a radially sealed bearing that limits the linear motion (side to side) of the lead screw 8.

A screw motor 3 (seen in Fig. 3) has a sprocket (not shown) that actuates a drive belt 19. Drive belt 19 passes through wall 4 and is connected to lead screw sprocket 32 that in turn is connected to lead screw 8. Screw motor 3 may be mounted atop motor mount 10 (shown in Fig. 3), which in turn is mounted on base 21.

The platform 7 and test surface 39 may be displaced vertically (by a vertical drive such as screw motor 3) to be co-planar with cover plate 6 (as shown in Fig. 1A), or withdrawn within housing 1 (as shown in Fig. IB) so as to be approximately co-planar with an internal surface hereinafter referred to as a divider plate 5 (as shown in Figs. 2 and 3).

When the platform is withdrawn within housing 1, an opening 55 is formed adjacent top panel 6. The platform 7 has a size and shape corresponding to the size and shape of the opening 55. Screw motor 3, through drive belt 19 and sprocket 32 may cause lead screw 8 to rotate in a first direction so as to force the nut 20 and support 16 upward or in the reverse direction to lower platform 7.

Positioning of the platform 7 is controlled by two limit switches 38, 58, shown in Fig. 3. Limit switch mounts 37 are bolted to wall 4. Each limit switch 38, 58 has a metal tab (not shown) that passes through wall 4. The limit switch trip washers 34, 54 shown in Fig. 2, actuate the limit switches 38, 58, respectively by way of contact with the metal tab. For example, when the platform 7 reaches its upper position, the limit switch trip washer 54 makes contact with the metal tab of its respective limit switch 58 and informs a controller (not shown) that the platform 7 is in the correct position, thereby stopping screw motor 3. When limit switch trip washer 34 makes contact with limit switch 38, the controller is informed that platform 7 is in the lowered position. One of the limit switch trip washers 34, 54 is mounted on each of the slider rods 18. The limit switch trip washers can be set and adjusted to enable changes to the location of the raised and lowered test platform position.

Preferably the test surface 39 is affixed to platform 7 by way of bolts connecting from the underside of the platform 7. By using bolts from the underside of the platform 7, different test surfaces may be attached to the platform depending on the type of subject surface in which the friction sensor 60 is installed, for example, but not limited to concrete, asphalt, metal or wood. Preferably the test surface 39 is made from carbon steel with a granular powder coating to provide a rough texture to simulate a road surface, however other materials of suitable strength, durability and having the appropriate characteristics of the intended subject surface may be used.

A sensor assembly generally referred to as reference numeral 50 has a rotating member such as test wheel 14 coupled to a sensor (not shown). In the preferred embodiment the sensor is secured within a sensor housing 28. Sensor mount 29 and sensor cover 31 aid to position the sensor within the sensor housing 28. Preferably, the sensor is a potentiometer having a sensor shaft (not shown). Test wheel 14 is attached to a rod 26, which in turn is connected, preferably by way of a screw, to the sensor shaft. Four bolts 67 (shown in Fig. 2) are used to connect the sensor cover 31, sensor mount 29, and sensor housing 28 to an arm 11. Arm 11 locates the test wheel 14 at the appropriate sweep radius and provides a protective covering for the sensor wires (not shown). Arm 11 also provides added weight to the sensor assembly 50, thereby increasing the downward force on the test wheel 14.

Arm 11 is mounted on block 25 by means of a hinge 12. Hinge 12 allows vertical displacement of the test wheel 14 while traveling over material that has accumulated on test surface 39, such as snow, ice, liquid, sand, gravel, etc. Block 25 is connected to a drive such as friction motor 2 by a shaft (not shown) extending through divider plate 5.

The sensor assembly 50 is driven by friction motor 2 such that it sweeps across the test surface 39. The sensor records the rotary position of the test wheel 14 as it rotates across the test surface 39. A bias restraint such as a torsion spring 15 about rod 26 provides resistance to the rotation of the test wheel 14 and when the wheel begins to slip, the friction of the test surface can be calculated as described in more detail below.

Testing of the test surface 39 will now be described in more detail. As the sensor assembly 50 is rotated across the test surface 39, friction between the wheel 14 and test surface 39 causes test wheel 14 to rotate. Torsion spring 15 is coupled to the wheel 14 and as the wheel continues to rotate, the resistive force in the spring 15 increases in an amount proportional to the amount of wheel rotation. Eventually, the force in the spring 15 resisting wheel motion is equal to the friction force (force causing wheel to rotate) acting on the wheel. When these two forces are equal, wheel 14 stops rotating and begins to slide for the remainder of the sweep of the sensor assembly 50. As sensor assembly 50 sweeps across the test surface, the rotary motion of the wheel 14, and therefore the corresponding displacement of the spring 15, is transmitted to the sensor by way of rod 26 and attached to the sensor shaft. A voltage corresponding to the amount of rotation of wheel 14 is transmitted by the sensor to the controller. A direct proportional relationship exists between the amount of spring rotation and the friction force. Once the friction force is calculated the coefficient of friction can be obtained. The coefficient of friction is determined by a mathematical relationship between the normal force (equivalent to weight of sensor assembly 50 on test surface 39) and the friction force (drag force resisting motion of wheel 14). The coefficient of friction is determined by dividing the friction force by the normal force. The coefficient of friction provides a measurement of how slippery the test surface, and therefore the surrounding surface, is. Based on the coefficient of friction (how much traction is available), a recommended safe travelling speed for the subject surface in which the fiiction sensor is installed can be calculated. When used in a road, this speed may be displayed on a variable message sign 68 (shown in Fig. 7), preferably digital, mounted on the side of the highway for passing motorists. A slippery outline or the like could also light up to attract the attention of motorists. The information could also be directed to maintenance crews so as to advise them when their services are needed; for example, if de-icing is required on a roadway.

While not shown in the drawings, wires from the various electrical components, such as friction motor 2, screw motor 3, limit switches 38, 58 and the sensor are all connected to female connector mount 35 mounted on base 21. Female connector mount 35 in turn connects to male connector mount 33, as shown in Fig. 3. Male connector mount 33 is mounted on bottom plate 23. Wires (not shown) attached to male connector mount 33 exit the fiiction sensor 60 through the underside of bottom plate 23 and travel to the controller. Preferably a protective covering such as a steel tube connected to the underside of bottom plate 23 in order to protect the wires exiting from the bottom of the sensor from shearing during the installation of the friction sensor 60 in the desired surface. The power and activation signal for the motors 2, 3 and potentiometer comes from the controller. Preferably the controller 43 is located some distance away from the friction sensor 60 as shown in Fig. 7. Preferably, the controller is a control and data acquisition board that is fed from a power supply unit that converts 1 ION AC to 24 N DC at 6 amps. The male and female connector mounts 33, 35 secure and position the snap in electrical connectors (not shown) that provide power to the motors 2, 3 and to the sensor. Output measurements from the fiiction sensor 60, for example from the sensor, or the limit switches travel to the controller. The controller then sends the appropriate signal to the friction sensor. It is anticipated that initially this system will use PC based control and analysis. However it is contemplated that other control systems may be used; for example, a dedicated custom designed processor that will run and execute the control software program could be used. Other sensors such as thermocouples and humidity sensors could also be added in order to acquire surrounding environmental conditions and better assess the conditions for driving. When combined with the controller, these additional sensors could provide an indication of when testing by the friction sensor should be conducted. It is also contemplated that the friction sensor could be activated manually.

Preferably, the friction sensor 60 has a height of 14.75 inches and a diameter of 10.75 inches. Preferably, the radial edge of test surface 39 and platform 7 defines an arc having a radius of 4.875 inches and test surface 39 and platform 7 are .25 inches thick, 3.275 inches in width and 9.21 inches in length. The distance between the upper and lower positions of the platform is approximately 4 inches. It is anticipated that other dimensions may be used.

Preferably, the fiiction sensor 60 is embedded in a road surface such that the top plate 6, and test surface 39 when platform 7 is in the upper position, is flush with the road surface. Upon receiving a signal from the controller, platform 7 is lowered into housing 1 forming an opening 55 (shown in Fig. IB). When the test surface is in position the coefficient of friction is determined as discussed above. Once the coefficient of friction is determined, platform 7 (and test surface 39) is re-elevated to the road level for continued use by the motoring public. The length of time to conduct the test is approximately 15 to 20 seconds from the time the platform 7 first starts lowering to the time it is returned to its starting position. It is anticipated that tests will be programmed to occur automatically on a prescribed frequency such as every 10-15 minutes. However, as discussed above, this could be varied so as not to cause excess use of the fiiction sensor when it is not needed. For example, during times of dry weather, the friction sensor could be placed in a standby mode, ready to be activated if conditions requiring testing should develop. Activation could take place by manually (an individual sending the appropriate signal from the controller), or automatically should a sensor detect moisture or the like.

Preferably, the fiiction sensor 60 will be placed in the travelled tire path of vehicles and oriented such that the opening 55 will have the 3.275 inches width facing the same direction as traffic flow. This orientation will minimize the effect of the opening 55 on smaller vehicle tires, such as bicycles, that should happen to pass over top. Preferably the friction sensor will safely support a distributed load of 10,000 lbs.

In order to obviate concerns about pedestrians getting their hands or feet caught in the opening 55, it is contemplated that the fiiction sensor could incorporate an additional sensor to detect an intruding object and stop the platform 7 from moving before a foot or hand is caught.

Locating pins 36 and male connector mount 33, shown in Figs 3, 4 and 6 are welded or otherwise connected to bottom plate 23. Base 21 of the interior assembly 65 has two locating holes 45 that correspond to the size, shape and positioning of the locating pins 36.

Female connector mount 35 has connector hole 46 shaped and sized to accept male connector mount 33 when base 21 properly positioned on base plate 23. The locating pins

36 provide a precise orientation for the interior assembly 65. Preferably the housing 1, bottom plate 23, male connector mount 33 and locating pins 36 are permanently installed in the surface in a desired location. When the top cover plate 6 is removed, the interior assembly 65 can be removed as one unit (all components are attached together and can slide in/out of the housing 1). The locating pins 36 ensure the interior assembly 65 is positioned properly when it is being installed into the housing 1. This design also allows for an easy and quick change of the inner components should a malfunction occur.

Locating pins 36 also act to ensure that the electrical connector mounts 33 and 35 are aligned and will engage and secure the electrical connections. The friction sensor is weather resistant and is capable of operating over a wide range of temperatures. Almost all components are made of steel, although other materials of sufficient strength and durability may be used. The friction sensor 60 is designed to accommodate debris such as gravel, stones and small objects within an acceptable limit. Should debris physically prevent the unit from operating properly, the sensor will report a failure to the controller and cease testing. The effects of water and sand on the test surface 39, and therefore the road surface, are actual elements that the friction sensor will measure. Therefore, it is expected that these elements will enter the system. The friction sensor is equipped with a hole 46 in housing 1. Hole 46 provides an exit for debris such as water, sand, rocks, leaves, etc. that enters the interior of the housing 1 through opening 55. An optional drainage pipe (not shown) can be attached to the hole 46 in order to carry the debris underground and out to the shoulder of the road. It is also contemplated that the friction sensor could be equipped with a flushing system having nozzles that would spray the interior of the housing 1 so as to drive accumulated debris towards, and out, the hole 46.

It will be appreciated by those skilled in the art that the preferred and alternative embodiments have been described in some detail but that certain modifications may be practiced without departing from the principles of the invention.

Claims

1. A friction sensor for determining the coefficient of friction of a subject surface comprising:

a housing defining an enclosure and having an upper panel;

a platform located in said enclosure and being movable in a vertical direction between a lower position within said enclosure and an upper position;

a test surface fixedly attached to said platform;

a sensor assembly for determining the fiiction of said test surface.

2. The friction sensor of claim 1, wherein when said platform is in said upper position, said test surface is co-planar with said upper panel.

3. The fiiction sensor of claim 2, wherein said sensor determines the friction of said test surface when said platform is in said lower position.

4. The friction sensor of claim 1 wherein said housing is cylindrical and has a top end defined by said upper panel and an opening.

5. The fiiction sensor of claim 4 wherein said platform has a size and shape corresponding to the size and shape of said opening.

6. The fiiction sensor of claim 1 wherein said sensor assembly comprises:

a rotating member; and,

a drive for causing said rotating member to travel over and in contact with said test surface.

7. The friction sensor of claim 6 further comprising a bias restraint acting on said rotating member.

8. The friction sensor of claim 7 wherein said bias restraint is a torsion spring and said torsion spring is connected to said rotary member.

9. The friction sensor of claim 8 further comprising a sensor for detecting the amount of said rotation said rotating member undergoes without slippage.

10. The friction sensor of claim 9 further comprising a controller for determining a coefficient of friction based on said amount of rotation.

11. The friction sensor of claim 9 wherein said sensor is a potentiometer.

12. The friction sensor of claim 10 wherein said controller comprises a processor.

13. The use of a friction sensor according to claim 1 to determine an appropriate speed for a road.

14. The use of a friction sensor according to claim 1 wherein said friction sensor is used as part of a system for automatically alerting motorists of road conditions.

15. The use of a friction sensor as in claim 14 wherein a motorist is advised of the appropriate speed for the road condition.

16. The friction sensor of claim 1 wherein said testing surface has a friction characteristic similar to a friction characteristic of said subject surface.

17. The friction sensor of claim 6 further comprising a rotatable arm coupled to said rotating member.

18. The friction sensor of claim 17 wherein when said platform is in said lower position, said rotating member may travel from an internal surface to said test surface by the action of said rotatable arm.

19. A method of determining friction conditions of a subject surface comprising:

providing a test surface co-planar with the subject surface;

withdrawing said test surface from its co-planar relationship with said subject surface to a test position; testing said test surface to determine its friction characteristics; and, returning said test surface to a position co-planar with the subject surface.

20. The method of claim 19 wherein said testing comprises: rotating a rotary member in contact with said test surface; and, determining the tendency of said rotary member to slip on said test surface.

21. The method of claim 20 wherein said step of determining comprises: providing a resistance to rotation of said rotary member; and sensing the maximum amount of rotation of said rotary member.