Knob retention

A user control knob retention system includes a nut (20) which has a base (25). The base includes two opposing nut end faces (23a, 23b), and a threaded bore (21) aligned with a base central axis (29). A wall (27) extends transversely from a first one of the nut end faces. The wall defines an inner surface (42) which comprises a circular arc coaxial with the central axis. The wall extends at least partially around a circumference of the base to define a capture space (26). An insert (30) rotatably retained within the capture space includes a body having a cylindrical shape. A retention barb (34) disposed on an outer cylindrical surface of the insert is configured for engaging an interlocking element (54) formed on an interior bore (58) of a user control knob (50).

BACKGROUND OF THE INVENTION

1. Statement of the Technical Field

The inventive arrangements relate to user control knobs which are mounted on rotatable control shafts, and more particularly to methods and systems for retaining user control knobs in position on rotatable control shafts.

2. Description of the Related Art

Many devices, including electronic devices, utilize manually operated rotatable control elements. These control elements include a shaft which rotates for purposes of actuating an electronic or manual control. Conventional shafts have a D-shaped cross-sectional profile. The D-shaped cross-sectional profile includes a planar face on a portion of the shaft which facilitates indexing of the knob in the proper orientation on the shaft. The D-shaped profile is also useful because it prevents rotation of knob relative to the shaft. A retention system is often provided to secure the knob on the shaft. A common retention system comprises a set screw threaded into the knob. The set screw engages the shaft to prevent the knob from sliding off the shaft.

Knob retention systems that use set screws can, under certain circumstances, permit control knobs to slide off the shaft and become lost. Most often, such loss occurs when the set screws become loose and/or the electronic device is accidentally dropped. These kinds of failures are undesirable, especially for equipment used by first responders or military operators. In order to overcome these limitations, designers have developed alternative knob retention solutions. For example, one such solution uses specialized knob inserts and customized control shafts in which special grooves have been provided. The insert is designed to snap into the groove. The control is then secured into the housing of the electronic device. Finally, a knob is snapped onto the insert.

Existing solutions which overcome the set-screw problem are not entirely satisfactory. The required customization of control shafts generally tends to increase component costs since these custom features are not normally included in commercial control shafts. Another problem with existing solutions is that the normal axial play which is present in rotatable controls tends to inhibit proper assembly of knobs onto the inserts. In other words, the shafts tend to rotate as the insert is being snapped into the specialized grooves formed on the shafts. When the knob must be removed from the electronic device, the shafts are sometimes damaged or can be pulled out of the control, due to the axial forces which must be applied during knob removal. Also, knob inserts sometimes become lodged within the knobs, and damage can occur to such inserts during knob removal.

SUMMARY OF THE INVENTION

Embodiments of the invention concern a knob retention system. The system comprises a nut which includes a base. The base has a generally cylindrical shape including two opposing nut end faces and a threaded bore aligned with a base central axis. A wall extends from a first one of the nut end faces in a direction parallel to the central axis. The wall defines an inner surface which forms a circular arc coaxial with the central axis. The wall extends less than an entire circumference around the base to define a capture space. An insert is rotatably retained within the capture space by the wall. The insert includes a body having a cylindrical shape, a retention barb disposed on an outer cylindrical surface of the insert configured for engaging an interlocking element formed on an interior bore of a user control knob, and a D-shaped bore extending along an insert central axis. A user control knob has an interior bore aligned with the base central axis and the insert central axis. The interior bore has an inner profile adapted for receiving the nut and the insert therein, and includes an interior wall which defines an interlocking element for engaging the retention barb. The threaded bore of the nut is configured to engage a plurality of threads provided on a collar of a control element, and the D-shaped bore is configured to receive a rotatable shaft of the control element.

The invention also concerns a method for retaining a knob on a rotatable shaft of a control element. The method includes positioning a cylindrically shaped insert within a capture space provided on a first end face of a nut. This step involves aligning a central D-shaped bore of the insert with a central axis defined by a threaded bore of the nut. The method continues by facilitating rotational displacement of the insert within the capture space using an inner bearing surface formed of a wall. The wall projects transversely from the first end face and extends at least partially around a circumference of the nut to define a circular arc coaxial with the central axis. The method continues with inserting a rotatable shaft of a control element through threaded bore and the D-shaped bore. The nut is threaded onto a collar of the control element coaxial with the rotatable shaft. The insert is then urged into a bore of a control knob which has an inner profile adapted for receiving the insert therein. A barb formed on the insert is engaged by an interlocking element formed on an interior wall of the bore to secure the control knob on the rotatable shaft.

DETAILED DESCRIPTION

The invention concerns a user control knob retention system. A perspective view of the retention system is shown inFIG. 1, installed on a control element10. The control element10is a conventional design comprising a control housing18which encloses a circuit device (not show). The circuit device can be any of a variety of well known circuit devices that are designed to be axially rotated for purposes of controlling a piece of equipment, such as a portable electronic device. As such, the circuit device can be a rotary switch, encoder, potentiometer, or rheostat without limitation. A plurality of pins11conventionally extend through the housing18for purposes of forming electrical contacts with the circuit device. The pins are most commonly attached to a printed wiring board or the rigid or flexible variety. A rotatable shaft14is commonly used to actuate the circuit device. The shaft extends into the housing and is coaxial with a collar12. The collar12is generally threaded to accommodate a retention nut.

The control element10is conventionally secured to a portable electronic device by inserting the shaft and collar through an opening17formed in a wall15of a case. As shown inFIG. 2, the housing18is normally retained inside the case of the portable electronic device while the collar and shaft extend outside. A retention nut is commonly threaded onto the collar12and secures the control element in the opening of the case wall. In conventional arrangements, a knob is provided on the shaft14to facilitated actuation of the control element. Commercial off-the-shelf control elements commonly have a shaft14which include a substantially planar shaft face16. The remainder of the shaft can have a cylindrical or rounded profile such that the shaft overall has D-shaped cross-sectional profile. The control knob will often have an internal passage with a complimentary D-shaped profile for receiving the shaft14. The D-shaped profile facilitates alignment of the control knob on the shaft and prevents the knob from slipping on the shaft as the knob is rotated.

The retention system of the present invention includes a nut20(sometimes referred to herein as a retention nut) which is configured to secure the control element10within an opening17formed in a case wall15of an electronic device. The nut preferably has a generally cylindrical outer shape as shown. As used herein, the phrase “cylindrical shape” is intended to include nuts that have a round outer profile as shown. However, this phrase can also potentially include nuts that have other outer profile shapes without limitation. For example, the outer surface of the nut can have several facets, provided that such shapes do not interfere with rotation of the nut within an interior of a control knob as hereinafter described.

The nut20includes a threaded bore21which extends through a base25in alignment with a base central axis29. The base25also has two opposing nut end faces23a,23b. A nut wall27extends transversely from a first one of the nut end faces23ato an upper portion22, in a direction which is generally aligned with the base central axis29. One or more notches28are advantageously provided along the upper portion22so that an upper portion of the nut has a castellated feature. The notches associated with the castellated feature are advantageously configured to receive a bit of a tool. As such, the notches can be advantageously configured to facilitate threading of the nut onto the collar12.

The nut wall27defines an inner surface42which comprises a substantially circular arc coaxial with the base central axis29. It can be observed inFIG. 2that the wall extends partially around a periphery or circumference of the base25to define a capture space26. In a preferred embodiment, the nut wall can have a U-shaped configuration which includes a gap formed in the wall to facilitate insertion of an insert30within the capture space26. The nut can be formed of any suitable material. For example, the nut can be formed of a metal or polymer material having sufficient rigidity to secure the control element on within the opening17. The nut can be formed by casting, machining or other suitable means.

Referring now toFIGS. 1-4, an insert30is rotatably retained within the capture space26by an inner surface42and a lip24. The insert includes a body31having a generally cylindrical shape. The insert includes a D-shaped bore which extends through the body31along a central axis35. The D-shaped bore is sized and shaped for snug engagement with the D-shaped shaft14of the control element10. The insert also includes a flange32. The flange serves as a bushing configured to facilitate rotational engagement of the insert within the capture space26of the nut. More particularly, the flange has a circular profile defined by an outer cylindrical face33. The outer cylindrical face33is snugly fitted within the inner surface42of wall27to facilitate rotation of the insert30relative to the nut20when the insert is present in the capture space and the central axis35of the insert is aligned with a central axis29of the nut. Similarly, a surface of insert end face37is configured to rotatably engage the nut end face23awhen the insert is retained within the capture space.

The insert can be formed of the same or a different material as compared to the retention nut20. For example, the insert can be formed of a metal or polymer material having sufficient rigidity to facilitate securing of a user control knob to the retention system. The insert can be formed by casting, machining or other suitable means.

In some applications, it can be desirable to increase or decrease an amount of resistance associated with the rotation a control element shaft14. Accordingly, a friction control disk40is optionally included in the retention system for selectively increasing or reducing an amount of friction associated with the rotation of the insert30within the capture space26. The friction control disk is advantageously disposed between the flange32and the lip24. This arrangement is best understood with reference toFIGS. 1 and 3. In a preferred embodiment, the friction control disk is fitted snugly between the flange and the lip so that the disk provides a predetermined amount of resistance to rotation of the insert relative to the nut. In order to achieve a desired amount of friction, the friction control disk40can be formed of a metal, rubber, polymer or silicone material as appropriate to provide a desired resistance associated with rotation of the shaft14. In an alternative embodiment, the friction control disk can be disposed between the flange32and the nut end face23a.

The insert includes a retention barb34disposed on an outer cylindrical surface of the insert. The retention barb is configured for engaging an interlocking element54which is formed on an interior bore58of a user control knob. For example, the interlocking element can be an indent formed on the interior bore58. In such embodiment, the retention barb can be formed as a raised element extending partially or completely around a periphery of the cylindrical body33. The raised element can have a profile which in cross-section forms a ridge, nub, bump or other feature configured for engaging an interior of a bore58formed in a user control knob50. In an alternative embodiment shown inFIG. 5, the retention barb can be formed as an indented portion extending partially or completely around a periphery of the insert, and configured to engage an interlocking element54which is formed as a nub, bump or ridge disposed on the interior bore of a user control knob.

The knob retention system further includes a user control knob50having an interior bore58. The insert30and nut20are positioned within the user control knob as shown in FIGS.1and3-4. More particularly, the user control knob50is disposed so that a central axis51of the user control knob is generally aligned with the base central axis29and the insert central axis35. The interior bore58is defined by an interior wall59which has an inner profile adapted for receiving the nut20and the insert30therein. As such the inner bore can include a nut cavity52and an insert cavity57. The nut cavity52has a shape which is sized and shaped for receiving the body of the nut20therein. More particularly, the nut cavity is sized and shaped to allow the body of the nut to be received within the cavity and to allow the user control knob to rotate around the body of the nut20when the nut is secured to the collar12.

The insert cavity57is configured to snugly receive the insert therein and to removably secure the user control knob to the insert. As such, the insert cavity57includes an interlocking element54that is shaped to engage the retention barb of the insert therein. The interlocking element54is configured to engage retention barb34in a snap-lock engagement so that the user control knob is securely attached to the insert, but can be removed when sufficient axial force is exerted upon the user control knob. Of course, for those embodiments where the retention barb34is comprised of an indent in the cylindrical body of the insert (instead of a projection, bump or nub) then an interlocking element54would not be an indented surface, but would instead be replaced by an appropriate nub or projection formed on the interior bore of the user control knob. Such an arrangement is illustrated inFIG. 5.

The insert30can optionally include one or more orientation flukes36that are generally aligned with the insert central axis51as shown. For example, these orientation flukes can be disposed on an outer surface of the insert30as show. The orientation flukes36are advantageously arranged so that they can be aligned with one or more slots56disposed on the interior bore of the user control knob50, when the user control knob is properly oriented relative to the insert. The orientation flukes are preferably arranged in an asymmetrical pattern on the periphery of the insert so that they will align with the slots56only when the control knob50is in a predetermined orientation relative to the insert. Moreover, the orientation flukes advantageously have a predetermined orientation relative to the D-shaped bore38so that the user control knob will have a predetermined orientation relative to the shaft of control element10.

Those skilled in the art will appreciate that the above-described retention system has numerous advantages over conventional retention systems that are currently used for attaching user control knobs to rotatable shafts. The system described inFIGS. 1-4avoids the need to include set-screws for retaining a user control knob in place on a control shaft. In contrast to the prior art, this result is achieved without the need for customized control shaft designs. Accordingly, commercial, off-the shelf control element components with conventional D-shaped control shafts can be used with the retention system. The result is a significant reduction in costs associated with control element components.

A further advantage of the inventive arrangements is the enhanced mechanical support that the retention system provides for control shaft14. Note that the insert30is firmly secured within the nut20, which is mechanically supported by the case wall15. Moreover, the insert30is disposed coaxial about the control shaft. With the foregoing configuration, the retention system provides enhanced structural support to the shaft14. This additional structural support provides the shaft with a greater ability to withstand forces applied to the shaft in a direction transverse to the central axis51. Accordingly, the shaft14is provided with improved resistance to damage caused by impacts and other applied forces.

The invention also concerns a method for retaining a knob on a rotatable shaft of a control element, using the retention system inFIGS. 1-4. Prior to beginning the process a collar and shaft of a control element can be pre-positioned in an opening17of a case wall15for an electronic device (not shown). Thereafter, the method can begin by positioning a cylindrically shaped insert30within a capture space26provided on a first end face23aof a nut20. This step can include guiding the insert through a gap in the wall27wall and sliding the insert in a direction transverse to the base central axis29. The insert is inserted within the capture space to align the central D-shaped bore38of the insert with a central axis29defined by a threaded bore of the nut. As will be appreciated from the foregoing description of the retention system, a rotational displacement of the insert within the capture space will be thereafter facilitated by the inner surface42(an inner bearing surface) formed of wall27. The method further includes limiting an axial movement of the insert within the capture space. This limitation upon axial movement is facilitated by the lip24and the end face23aof the nut. In some embodiments, this limitation of axial movement can also involve disposing the friction control disk40between the flange33and the lip24

After the insert has been positioned within the capture space, a rotatable shaft of a control element is inserted through the threaded bore of the nut and the D-shaped bore of the insert. The nut is then threaded onto the collar12of the control element10. More particularly, the nut is threaded down onto the collar12until an end face23bof the nut is securely engaged with a surface of a case wall15. This step can be facilitated by engaging with a tool at least one of the notches28formed on the upper portion of the nut.

Once the nut20is securely threaded onto the collar12, the method continues by urging the insert30(which is retained within the capture space26) into the interior bore58of the user control knob50. In some embodiments of the invention, this step can also include receiving at least one of the orientation flukes36within one of the slots56that are formed on the interior wall comprising the interior bore58. More particularly, the orientation flukes can be used to align the control knob on the rotatable shaft14.

The inner profile of the user control knob receives the insert in an insert cavity57and receives the nut within the nut cavity52. The insert is urged into the inner bore of the user control knob until the retention barb34provided on the insert is engaged with the interlocking element54. At this point, the user control knob50is removably secured to the insert and can function to rotatably actuate the rotatable shaft14. More particularly, the user control knob can rotate about the nut20which is fixed to the collar12, thereby actuating rotational movement of the shaft14. If the friction control disk is used, the method can further comprise controlling a rotation resistance of the shaft by means of the friction control disk disposed between the insert and a portion of the nut.

In the event that the knob must be removed from the shaft14for any reason, a sufficient amount of axial force applied to the user control knob will disengage the interlocking element54from the retention barb34, thereby releasing the user control knob from the shaft.