A positioning arrangement for positioning a rotor relative to a shaft includes a collar provided with a formation cooperable with a corresponding formation provided upon the shaft to resist relative angular movement between the collar and the shaft, the collar being provided with an external, generally axially extending rib cooperable with a part of the rotor to deform the said part of the rotor to resist relative rotation between the collar and the rotor.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority from UK Patent Application No. 1210894.0 filed in the name of Goodrich Control Systems on Jun. 20, 2012.

BACKGROUND

This invention relates to an angular positioning arrangement, and in particular to an angular positioning arrangement suitable for use in securing a rotor of a resolver or position sensor associated with a rotary shaft of an actuator against angular movement relative to that shaft. However, it may be used in other applications.

Where a resolver or rotary position sensor is associated with a rotatable shaft, for example associated with an actuator, to provide position information, it is important that the rotor of the resolver or position sensor is firmly and reliably secured to the shaft in a known angular position relative to the shaft. Any movement of the rotor relative to the shaft, or incorrect angular installation of the rotor relative to the shaft, may result in incorrect position information being supplied to an associated controller which could result in inappropriate control over the actuator or other device of which the shaft forms part or with which it is associated. Furthermore, it is desirable for the axial position of the rotor to be accurately aligned with an associated stator.

One technique used in positioning and securing a rotor of a position sensor or resolver to a shaft is to, prior to installation, move the rotor of the sensor relative to a stator thereof until the output of the position sensor reaches a null-point value. Once this position has been reached, the rotor and stator are both marked to indicate the relative positions occupied by the rotor and stator when in the null-point position. The stator is then mounted in position upon the actuator or other device with which it is to be used such that the stator position is fixed. The rotor is then positioned upon the actuator shaft, with the actuator occupying a known position which will, in use, correspond to the null-point position of the sensor. Keeping the shaft stationary, the rotor position is adjusted to bring the markings into alignment with one another.

In order to secure the rotor in this position relative to the shaft, the rotor is formed with a pair of slots. Once correctly positioned upon the shaft, the shaft is deformed, for example by swaging, to force part of the shaft material into the slots of the rotor, and thereby prevent relative movement between the shaft and the rotor.

US2011/0241498 describes another technique for securing a resolver rotor to a shaft. It includes a bearing by which the resolver is mounted upon the shaft, and a lock arrangement for locking the resolver in a chosen angular orientation relative to the shaft.

US2008/0279652 describes a coupling in which one component is provided with a series of serrations received within recesses formed in another component.

There is a desire to provide an alternative positioning arrangement whereby a rotor can be secured to a shaft in a desired angular position. Furthermore, there is a desire to provide an arrangement which allows removal of the rotor from the shaft, for example to allow replacement of the rotor in the event that replacement thereof is required.

SUMMARY

According to the present invention there is provided a positioning arrangement for positioning a rotor relative to a shaft, the positioning arrangement comprising a collar provided with a formation cooperable with a corresponding formation provided upon the shaft to resist relative angular movement between the collar and the shaft, the collar being provided with an external, generally axially extending rib cooperable with a part of the rotor to deform the said part of the rotor to resist relative rotation between the collar and the rotor.

Preferably, the formation provided on the collar comprises a spline formation cooperable with a corresponding spline formation provided upon the shaft.

Conveniently, the said generally axially extending rib is one of a plurality of ribs or serrations provided upon the collar. The said part of the rotor is conveniently provided with one or more grooves to aid deformation by the rib. The grooves are conveniently substantially annular grooves. Alternatively, they could comprise parts of, for example, a screw threaded region of the rotor.

Preferably, the rib extends over only part of the axial length of the collar, allowing the collar formation to mate with the corresponding formation of the shaft prior to engagement occurring between the rib and the said part of the rotor. Consequently, after initial insertion of the collar, angular movement of the rotor to the desired position is permitted. Further axial movement of the collar results in deformation and engagement occurring between the collar and the rotor to position and retain the rotor against angular movement relative to the shaft.

Preferably, a clamp arrangement is provided to secure the collar to the shaft. The clamp arrangement conveniently comprises a clamp member keyed to the collar against angular movement relative thereto, and a lock nut threadingly engaged with the shaft and serving to clamp the clamp member to the collar to prevent or resist axial movement thereof. The lock nut is preferably provided with at least one slot into which part of the clamp member can be deformed, after tightening of the lock nut, to resist rotation of the clamp member relative to the lock nut. As a consequence, angular movement of the lock nut relative to the collar is resisted. Further, since rotation of the collar relative to the shaft is not permitted, it will be appreciated that this arrangement prevents rotation of the lock nut and so ensures that the lock nut cannot work loose, in use.

DETAILED DESCRIPTION

Referring to the accompanying drawings, a positioning arrangement10is shown for use in securing a rotor12of a resolver or position sensor (the remainder of which is not shown) to a shaft14, for example associated with an actuator (not shown) or the like. The positioning arrangement10is operable to secure the rotor12and shaft14to one another such that both axial and rotary movement therebetween is resisted.

The positioning arrangement10comprises a collar16of annular form which is positioned over and encircles a part of the shaft14. The collar16is provided, on its inner surface, with a series of spline formations18which, in use, cooperate with corresponding formations20provided upon the adjacent part of the shaft14so as to key the collar16to the shaft14, resisting relative angular movement therebetween. Whilst resisting angular movement, the cooperation between the spline formations18,20permits axial movement of the collar16to occur relative to the shaft14.

On its external surface the collar16is provided with a series of ribs22, each rib extending generally axially of the collar16. As best shown inFIG. 2, each rib22includes a reduced height part22aextending from one end of the collar16to an intermediate part thereof, and a full height part22bextending from the intermediate part to the other end of the collar16.

The collar16is received within a bore or opening24formed within the rotor12. The bore or opening24is of stepped diameter, defining a part24aof internal diameter approximately equal to or slightly larger than the diameter of the reduced height parts22aof the ribs22and smaller than the diameter of the full height parts22bof the ribs22. The part24aof the bore or opening24is formed with a series of annular grooves26. The positioning of the grooves26is such that, when the collar16occupies the assembled position shown inFIG. 1, the grooves26lie adjacent the full height parts22bof the ribs22.

By way of example, it is envisaged that the diameter of the full height parts22bof the ribs22will be in the region of 0.03 mm to 0.07 mm greater than the internal diameter of the part24bof the bore or opening24.

The positioning arrangement10further comprises a clamp arrangement30operable to secure the collar16against axial movement, in use. The clamp arrangement30comprises a clamp member32which encircles part of the shaft14and bears against an end of the collar16. As shown inFIG. 2, the collar16is shaped to define a pocket34into which a projection36provided on the clamp member32extends such that the collar16and clamp member32are keyed to one another against relative angular movement.

The clamp arrangement30further comprises a lock nut38which is in screw threaded engagement with thread formations provided upon the shaft14and which serves to clamp the clamp member32against the collar16which, in turn, clamps the collar16against a step24bof the bore or opening24.

As shown inFIG. 4, the lock nut38is shaped to define a series of recesses40. The clamp member32is shaped to include a relatively thin walled part42which extends adjacent and encircles the lock nut38. The recesses40may serve to allow engagement of the lock nut by an appropriate tool to allow tightening thereof onto the shaft14. In addition, as described below, once assembled the thin walled part42may be deformed into the recesses40to lock the nut38against rotation.

In use, during assembly, the rotor12and associated stator are marked so as to provide an indication of their relative orientations when occupying a null-point position as described hereinbefore. The stator is then mounted in the desired position, and the rotor12is introduced onto the shaft14. Once the rotor12has been located upon the shaft14, the collar16is located upon the shaft14with the spline formations18of the collar16engaging with the corresponding formations20provided upon the adjacent part of the shaft14such that angular movement of the collar16relative to the shaft14is not permitted. At this stage in the assembly process, however, the collar16is only partially introduced into the part24aof the bore or opening24of the rotor12, as shown inFIG. 5. In this position, the cooperation between the collar16and the rotor12is such that relative angular movement therebetween is permitted, as the full height parts22bof the ribs22have not yet been introduced into the part24aof the bore or opening24of the rotor12. Whilst in this position, the rotor12is rotated to the correct angular position relative to the stator, whilst the shaft14is held in the desired angular orientation.

Once the desired orientation of the rotor12has been attained, the rotor12is locked to the shaft14by fully inserting the collar16. This may be achieved by positioning the clamp member32against the collar16with the projection36thereof located within the recess34, and by tightening of the locking nut38. Alternatively, it may be achieved by application of a suitable load to the collar16to fully introduce it, subsequently using the clamp member32and locking nut38to secure the collar16in position.

Regardless of the technique used to fully insert the collar16, the action of fully inserting the collar16results in the full height parts22bof the ribs22bearing against the part24aof the bore or opening24formed with the grooves26. As shown inFIG. 3, the relative diameters of these parts results in the full height parts22bof the ribs22cutting into and deforming the part24aof the bore or opening24of the rotor12formed with the groove26such that relative angular movement between the collar16and the rotor12is not permitted. As the collar16is secured to the shaft14against relative rotation by virtue of the cooperation of the spline formations18,20, it will be appreciated that the positioning arrangement serves to correctly position, and resist relative angular movement between, the rotor12and shaft14.

The formation of the grooves26in the rotor12serves to ensure that the deformation thereof which occurs upon the insertion of the collar16does not result in the formation or application of unacceptably high hoop stresses. However, it is recognised that with some designs of rotor12(for example rotors with a relatively large cross-sectional area) there may not be a need for the grooves26in the rotor12to reduce the developed hoop stresses.

Once the lock nut38has been tightened to securely clamp the clamp member32and collar16in position, the thin walled part42of the clamp member32is deformed into at least some of the recesses40. As a consequence, rotation of the nut38relative to the clamp member32is not permitted. As the clamp member32is keyed to the collar16by virtue of the location of the projection36within the recess34, and the collar16is splined to the shaft14, it will be appreciated that the lock nut38is thus secured against rotation relative to the shaft14and so is prevented from working loose.

The arrangement described hereinbefore is thus advantageous not only in that it provides a relatively simple installation process and allows accurate positioning of the rotor12upon the shaft14, but also axial alignment of the rotor12with the stator can be achieved to a good degree of accuracy, as the rotor12can be clamped against a shoulder (not shown) provided on the shaft14by the action of the clamping arrangement30.

Once installed, the rotor12is securely fixed to the shaft14against movement relative thereto. Furthermore, it is accurately positioned relative thereto. As a result, the output of the sensor may be of good accuracy.

Furthermore, if there is a need to remove the rotor12, this can be achieved by appropriate deformation of the thin walled part42of the clamp member32to allow rotation and removal of the lock nut38. Once the lock nut38has been removed, the clamp member32and collar16can be extracted and the rotor12removed. Subsequent reassembly will, most likely, require replacement of the clamp member32, but the other parts may be reused.

Whilst the description hereinbefore and the accompanying drawings relate to a specific embodiment of the invention, it will be appreciated that a wide range of modifications and alterations may be made thereto without departing from the scope of the invention as defined by the appended claims.