Transducer for a rotating body

A load cell assembly for sensing force and/or moment components on a rotating body supported by a frame includes an axle having opposite ends joined to the frame. A hub is supported by the axle and rotatable about a longitudinal axis thereof. A load cell body joined to the hub and the rotating body is used to sense force and/or moment components between the hub and the rotating body.

BACKGROUND

Wheel force transducer or load cells for measuring forces along or moments about three orthogonal axes are known. The wheel force transducer typically is mounted between and to a vehicle spindle and a portion of a vehicle rim. The transducer measures forces and moments reacted through a wheel assembly at the spindle as the vehicle is operated.

One form of a wheel force transducer that has enjoyed substantial success and critical acclaim has been the SWIFT transducer sold by MTS Systems Corporation of Eden Prairie, Minn. and is described in detail in U.S. Pat. Nos. 5,969,268 and 6,038,933. Generally, this transducer includes a load cell body having a rigid central member, a rigid annular ring and a plurality of tubular members extending radially and joining the central member to the annular ring. A plurality of sensing circuits are mounted to the plurality of tubular members. The rigid central member is mounted to the vehicle spindle, while the annular ring is attached to the vehicle rim. An encoder measures the angular position of the load cell body allowing the forces transmitted through the radial tubular members to be resolved with respect to an orthogonal stationary coordinate system. An external slip ring assembly provides power to and receives signals from the sensors on the load cell body.

SUMMARY

Aspects of the present invention relate to measuring and/or sensing forces and/or moments applied to a rotating body for example a wheel of a vehicle such as but not limited to a motorcycle.

A first aspect comprises a load cell assembly for sensing force and/or moment components on a rotating body supported by a frame. The assembly includes an axle having opposite ends joined to the frame. A hub is supported by the axle and rotatable about a longitudinal axis thereof. A load cell body joined to the hub and the rotating body is used to sense force and/or moment components between the hub and the rotating body.

A second aspect comprises a combination of a frame portion of a motorcycle or similar wheel assembly and a load cell assembly for sensing force and/or moment components on the motorcycle or similar wheel assembly. The load cell assembly includes an axle mounted at each end to the frame portion and a hub supported by the axle. A rim is provided and a tire is supported on the rim. A load cell body is operatively joined to the hub and the rim.

A third aspect comprises a load cell assembly for sensing force and/or moment components on a rotating body supported by a frame. The assembly includes an axle joined to the frame on at least one end of the axle. A hub is supported by the axle and rotatable about a longitudinal axis thereof. A load cell body is joined to the hub and the rotating body to sense force and/or moment components between the hub and the rotating body. A slip ring assembly is disposed in the hub having a first member movable relative to a second member, the first member being rotatable with the hub.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

The Figures herein provided illustrate load cell systems well-suited for measuring force and moment components of a rotating body, and in one embodiment, a rotating body rotating on and about an axle supported at each end. An example of such a rotating body is a rolling wheel on, for instance, a trailer, cart or a vehicle such as but not limited to motorcycles. In the illustrative embodiments herein described, a motorcycle application will be used in view of its particular usefulness.

FIGS. 1A and 1Billustrate a load cell system10as applied to a rear wheel assembly13of a motorcycle, wherein the motorcycle is not shown in its entirety, but can be considered as represented by sprocket11and swing arm17. Likewise,FIGS. 2A and 2Billustrate a load cell system10′ as applied to a front wheel assembly19of a motorcycle, wherein the motorcycle is not shown in its entirety, but can be considered as represented by frame portion (front forks)15. The load cell system10′ is substantially similar to the load cell system10. Accordingly, where the same reference numbers have been used those parts have the same function.

With specific reference toFIGS. 1A and 1B, load cell system10generally includes a hub and axle assembly12, a transducer14and a tire and rim assembly16. In this embodiment, the hub assembly12and elements connected thereto rotate about a longitudinal axis of an axle18that extends between and is joined to portions of the frame as is used to support the rear wheel of the motorcycle.

Operatively connected to the hub assembly12is a drive assembly, herein the drive sprocket11although other forms of drive devices such as a shaft and gear assembly, belt, etc. can be used. A brake disc30is also illustrated as mounted to the other end of the hub assembly12. Typically, the size and location of the sprocket11and brake disc30will correspond to that made by the manufacturer, where the load cell system10can accommodate these elements. In this manner, the load cell system10can thereby accurately record real-life forces and moments present on a motorcycle wheel assembly.

The hub assembly12is split, herein generally along the centerline of wheel assembly and comprises portions40and42. Hub portions40,42are joined together with the transducer14located therebetween with fasteners43. In one embodiment, coupling teeth46can be provided to effectively transmit loads therebetween by increasing friction by the increased surface area provided by the mating teeth. Generally, the transducer has a central hub64and annular ring66. The hub portions40and42are joined to the central hub64, while a rim adapter assembly67is joined with fasteners65to the annular ring66(which can include mating teeth) and to a wheel rim69with fasteners75.

In one embodiment, the transducer14is a separate component from rim adapter assembly67and one or both hub portions40,42, which conveniently allows the transducer14to be used many times with different types of wheel assemblies since then only the hub portions40,42and/or rim adapter assembly67need be specifically designed to particular wheel assembly.

The transducer14for measuring force and moment components is secured to the hub assembly12and to rim adapter assembly67and used to support a tire on rim69. The transducer14thus replaces a portion of the rim and carries force and moment loads between the hub12and the tire. It should be understood various forms of transducers can be used and incorporated in a manner as taught herein; however one particularly convenient transducer is as described in U.S. Pat. No. 5,969,268, the content of which is herein incorporated by reference in its entirety, wherein actual dimensions may be changed in order to accommodate the expected loads, size constraints and sensitivity.

In the exemplary embodiment illustrated inFIG. 3, transducer14includes an integral load cell body62fabricated from a single block of material. The body62includes the rigid central hub64and the rigid annular ring66that is concentric with the central hub64. A plurality of radial tubes70joins the central hub64to the annular ring66. In the embodiment illustrated, the plurality of radial tubes70comprises four tubes71,72,73and74. Each of the tubes71-74extend radially from the central hub64toward the annular ring66along corresponding longitudinal axes. Although illustrated wherein the plurality of radial tubes70equals four, it should be understood that any number of tubes three or more can be used to join the central hub64to the annular ring66. Preferably, the plurality of radial tubes70are spaced at equal angular intervals about a central axis indicated at76.

In the embodiment illustrated, flexure members81,82,83and84join an end of each radial tube71-74, respectively, to the annular ring66. The flexure members81-84are compliant for displacements of each corresponding radial tube71-74along the corresponding longitudinal axes.

A plurality of sensors, for example strain sensors, can be mounted on the plurality of tubes70to sense strain therein. Although the plurality of sensors can be located on the plurality of radial tubes70to provide an indication of bending stresses therein, in one embodiment, the strain sensors are mounted conventionally to provide an output signal indicative of shear stresses in the walls of the plurality of radial tubes70. In the embodiment illustrated, four sets of strain sensors are provided on each tube71-74, preferably, approximately at the center of the longitudinal length of each tube. As described in U.S. Pat. No. 5,969,268, a first pair of strain sensors is provided on an upwardly facing portion of each radial tube71-74. A second pair of strain sensors is mounted on a downwardly facing surface approximately 180 degrees from the first pair of strain sensors. The first and second pairs of strain sensors on each tube71-74are connected in a conventional Wheatstone bridge to form a first sensing circuit on each radial tube71-74. A third pair of strain sensors is mounted approximately 90 degrees from the first pair of strain sensors while a fourth pair of strain sensors is mounted approximately 180 degrees from the third pair of strain sensors. The third and fourth pairs of strain sensors on each tube71-74are also connected in a conventional Wheatstone bridge to form a second sensing circuit on each radial tube71-74. Commonly, the plurality of sensors comprises resistive strain gages. The plurality of sensors can function as shear sensors to provide an indication of shear stresses created in the radial tubes70. If desired, the plurality of sensors can be mounted to the radial tubes70to function as bending sensors to provide an indication of bending stresses in the radial tubes70. In this embodiment, the bending sensors can be located at a root of the tube or start of the fillet joining each tube71-74to the central hub64. In addition, other forms of sensing devices such as but not limited to optically based sensors or capacitively based sensors can also be used. In addition or in the alternative, the flexures81-84can be used as sensing structures with suitable sensing devices detecting strain or displacement thereof.

In the embodiment illustrated having four radial tubes71-74, eight individual shear-sensing Wheatstone bridges can be used. The number of sensing circuits can be increased or decreased, depending on the number of radial tubes used.

Output signals from the sensors or sensing circuits are indicative of force and moment components transmitted between the central hub64and the annular ring66in up to six degrees of freedom. It should be understood that the number of strain sensors and the number of sensing circuits can be reduced if measured forces and moments of less than six degrees of freedom is desired. Further details regarding resolving the signals from the sensors of the transducer14as force and moment measurements are described in U.S. Pat. No. 5,969,268; however, again it should be understood that other forms of transducers may be used.

In one embodiment, power is supplied to and output signals are obtained from the plurality of sensors by a controller and/or recorder112through a slip ring assembly114as the tire rim69, transducer14and hub12with elements connected thereto rotate on bearings120.

Referring toFIG. 5, a first embodiment of a slip ring assembly114includes an outer member130secured to the central hub64so as to rotate therewith such as with a pin through aperture132. An inner member134is secured to the axle18and remains stationary therewith. For instance, a key136can be provided to mate with a corresponding longitudinal groove138provided in the axle18, which can be solid. A brush and slip ring assembly139are operably coupled to members130and132in the annular space therebetween. If desired, an encoder assembly140can also be provided in the annular space. Cabling144from the brush assembly139with respect to the inner member134can extend along the length of the groove138, while cabling146from the brush assembly139with respect to the outer member130can be routed to circuitry of the transducer14.

The slip ring assembly114and bearings120are held in place longitudinally along axle18through a concentric loading assembly151around the axle18. The concentric loading assembly151includes spacers150,152and154(each having a bore through which the axle18extends) in compression along with the inner races of the bearings120and inner member134when the axle18is placed in tension by axle nut156. It should be noted that the location of the slip ring assembly114on the axle18allows seals162used to protect the bearings120and also the slip ring assembly114, while the overall design allows access to the brush assembly139when repair is necessary.

If desired an external encoder170to monitor the angular position of the wheel assembly can be used. For instance, a sprocket or similar rotating member176can be used to drive a drive wheel of the encoder mounted somewhere else on the motorcycle.

FIGS. 6A,6B and6C illustrate a load cell system10″ as applied to another rear wheel assembly13′ of a motorcycle, wherein the motorcycle is not shown in its entirety, but can be considered as represented by sprocket11and swing arm17. Likewise,FIGS. 7A,73and7B illustrate a load cell system10′″ as applied to another front wheel assembly19′ of a motorcycle, wherein the motorcycle is not shown in its entirety, but can be considered as represented by frame portion (front forks)15. The load cell systems10″ and10′″ are substantially similar to each other, but have also have similar components to those discussed above with respect to the load cell systems10and10′. Accordingly, where the same reference numbers have been used those parts have the same function as described above.

With specific reference toFIGS. 6A,6B and6C, load cell system10″ generally includes the split hub (portions40,42) and axle assembly12, the transducer14and the tire and rim assembly16, which rotate about and on the axle shaft18that extends between and is joined portions of the frame as is used to support the rear wheel of the motorcycle. In this embodiment, the hub portions40,42are joined to the sprocket11and brake disc30, respectively, as well as to the central hub64of transducer14. The annular ring66of transducer14is joined to the rim69using a spoke assembly200comprising a spoke hub support202and a plurality of spokes204. In the illustrative embodiment, the spoke hub support202includes portions206and208suitably fastened such as with bolts to annular ring66on opposite sides thereof. This construction conveniently allows the transducer14to be used many times with different types of wheel assemblies where the hub portions40,42and/or spoke assembly200need be specifically designed to a particular wheel assembly.

As in the previous embodiments, power is supplied to and output signals are obtained from the transducer14through a slip ring assembly214mounted within the hub assembly12as the tire rim69, transducer14and hub assembly12rotate.

Referring also toFIG. 8, the slip ring assembly214includes an outer member216secured to the central hub64so as to rotate therewith such as with a pin through aperture218. An inner member220is secured to the axle18and remains stationary therewith. For instance, a keyway221in the inner member220can be provided to mate key elements on a spacer described below.

A brush and slip ring assembly (not illustrated but similar to that of slip ring114) are operably coupled to members216and220(schematically separated inFIGS. 63 and 6C). Connectors230and232connect to transducer14, while wires234extend outwardly toward an end of the axle18. If desired, an encoder assembly can be provided in the slip ring assembly214, or an external encoder can be used. A suitable slip ring assembly is available from Michigan Scientific Corporation of Charlevoix, Mich., USA.

The slip ring assembly214is held in place longitudinally along axle18through a concentric loading assembly250around the axle18. In the embodiment illustrated, concentric loading assembly250includes an axle spacers259,260and load spacer262with ends thereof cooperating with each other so as to mount and support bearing assembly264. It should be noted axle spacer260includes a longitudinal groove280parallel to axle18through which wires234extend and then out through aperture282and guided through a channel284in a wire guide286proximate swing arm17.

Likewise, on the opposite side of axle18an axle spacer266and load spacer268have ends that cooperate so as to mount and support bearing assembly270. A sleeve271can be disposed along the axle radially inward from inner member220. The thickness of the sleeve271allows the various components supported by the axle to adapt to the diameters of different axles. The axle spacers260,266, load spacers262,268, inner races of bearings264,270and inner member220(each having a bore through which the axle18extends) are loaded in compression with tightening of axle nut275and tension on the axle18. Each end further includes seals272and274to prevent water and other contaminates from reaching the slip ring assembly214.

It should be noted the slip ring assembly114,214are located on the axle18between the bearings and in the hub12preferably inline with the central hub64, or stated another way so as to intersect with a central plane of the load cell body62.

Furthermore, the load cell body62is not sensitive to loads (such as chain or braking loads on a motorcycle) that are not reacted to the annular ring66(i.e. tire contact patch) of the load cell body62, which are rather shunted into the bearings.

A similar construction is used in the front wheel assembly ofFIGS. 7A-7C, where the same reference numbers have been used to identify similar functioning elements as those described above.

Although illustrated above where the axle18is supported at both ends of the frame, aspects herein described can be used on a frame where the frame supports the rotating body such as a wheel from one side. For instance, aspects of the invention can be used on a single sided swing arm as found on some motorcycles. Also, tire testing machines and truck axles commonly have a quill shaft to drive the rotating body. In all of these other embodiments, the slip ring assembly can be mounted so that a first member rotates with the hub (which need not always be split) and a second member is held stationary where the wires exit toward the frame along a groove in the axle and/or through a channel formed in an axle spacer as described above. Likewise, for all embodiments that have a hollow or partial hollow axle (e.g.FIG. 6C), an aperture291can be provided at any point along the length where the wires234from the slip ring assembly can then extend into and thus along the axle within its bore. Rings or brushes of the slip ring assembly can also be directly attached to or formed on the axle if desired.