Patent Publication Number: US-2011061489-A1

Title: Rotary control knob apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to rotary control knobs for automotive and consumer electronics applications, and more particularly to an improved rotary control knob apparatus that minimizes axial tilting of the knob. 
     BACKGROUND OF THE INVENTION 
     Rotary knobs are commonly used in connection with automotive or consumer electronic products such as radios for user-adjustment of control parameters such as volume and tuning. A typical knob assembly comprises several mechanically coupled parts, and tolerance variations in the manufacture of the constituent parts can result in tolerance stack-up that allows the knob to axially tilt, or wobble, with respect to its mounting surface. Since this tilting or wobbling is aesthetically unpleasing, and can reflect unfavorably on the quality of the product, what is needed is a rotary control knob assembly in which the axial orientation of the knob is tightly controlled even though the parts of the assembly are subject to the usual manufacturing tolerance variations. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved rotary control knob apparatus including a stationary knob retainer having a cylindrical post and an annular knob that slides over the retainer post, where the exterior periphery of the retainer post has a distributed array of compliant protrusions that contact the inner periphery of the knob to provide a resilient sliding interference fit between the knob and the retainer post. In a preferred arrangement, the retainer is secured against the rear surface of a control panel trimplate, and the knob is axially captured between the trimplate and a retainer flange extending radially outward from the base of the cylindrical post. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an exploded isometric view of a rotary control knob apparatus according to this invention. 
         FIG. 2  is an assembled isometric view of the rotary control knob apparatus of  FIG. 1 . 
         FIG. 3  is an enlarged isometric view of a knob retainer element illustrated in  FIG. 1 . 
         FIG. 4  is an isometric cross-sectional view of the rotary control knob apparatus of  FIG. 2 , minus the circuit board and push-button actuator of  FIG. 2 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the drawings, and particularly to  FIGS. 1-2 , the reference numeral  10  generally designates a rotary control knob assembly mounted with respect to a trimplate  12  of an electronic product such as an automotive radio. The assembly  10  includes an annular control knob  14 , a knob retainer  16 , a push-button actuator  18 , and a circuit board  20 . The knob retainer  16  is preferably an injection-molded plastic part; it includes a hollow cylindrical post  22  and a cup-shaped flange  24  that extends radially outward from the base of the post  22 . The push-button actuator  18  slides into the hollow retainer post  22 , whereas the knob  14  slides over the retainer post  22  and is compliantly supported within the cup-shaped retainer flange  24 . The trimplate  12  is provided with an opening  26  through which the grip portion  28  of knob  14  extends, and an inwardly depending cylindrical flange  30  that engages a set of radial ridges  32  formed on a toothed flange  34  of knob  14  to capture knob  14  between trimplate  12  and the cup-shaped retainer flange  24 . A set of ribs  35  extending radially outward from the cylindrical flange  30  nest in complementary slots  36  formed in the rim  24   a  of retainer flange  24  to rotationally lock retainer  16  to trimplate  12 . A spring-loaded plunger  37  disposed in a circular well  38  formed in the base of the cup-shaped retainer flange  24  slidingly engages a convoluted surface of knob  14  inboard of the toothed flange  34  to impart a detent effect as the knob  14  is rotated with respect to the knob retainer  16 . 
     The circuit board  20  is fastened to the trimplate  12  so as to engage and axially capture the knob retainer  16  with respect to the trimplate  12 . The circuit board  20  may additionally include lighting components (not shown) for backlighting graphics formed on the face  40  of push-button actuator  18 , contacts (not shown) for interfacing with the push-button actuator  18 , and a U-shaped optical sensor  42  with legs that straddle the toothed knob flange  34  to detect rotation of the knob  14 . The circuit board  20  also includes an opening  44  for accommodating the circular well  38  of knob retainer  16 . 
     As mentioned above, the principle objective of the present invention is to provide a rotary control knob assembly  10  in which the axial orientation of the knob  14  is tightly controlled even though the parts of the assembly  10  are subject to the usual manufacturing tolerance variations. This objective is achieved, according to this invention, by providing a resilient sliding interference fit between the knob  14  and the hollow cylindrical retainer post  22  on which the knob  14  is supported. In the illustrated embodiment, the interior periphery of the annular rotary knob  14  is smooth, and compliant features that provide the resilient sliding interference fit are formed on the exterior periphery of the hollow retainer post  22 . 
     As best seen in  FIG. 3 , the compliant features on the exterior periphery of the retainer post  22  comprise a distributed array of protrusions  46  that extend radially outward to contact the smooth inner periphery of the annular knob  14 . As seen in  FIG. 3 , the protrusions  46  are distributed around the circumference of the post  22 , at both upper and lower ends of the post  22 . In the illustrated arrangement, three protrusions  46  are distributed around the upper end of the post  22 , and four protrusions  46  are distributed around the lower end of the post  22 . The upper surfaces of the protrusions  46  are tapered as shown to facilitate assembly of the knob  14  onto the retainer post  22 , and slots  48  formed in the cylindrical wall of the retainer post  22  on both sides of each protrusion  46  allow the protrusions  46  to bend radially inward as the knob  14  is slid over the post  22 . In this way, each of the protrusions  46  resiliently presses against the inner periphery of the knob  14  to support the knob  14  for tilt-free rotation with respect to the retainer post  22 . 
     The exterior periphery of the retainer post  22  also includes a distributed array of non-compliant axial ribs  50  that extend radially outward from the wall of the post  22 , but do not ordinarily engage the inner periphery of the knob  14 . In the illustrated embodiment, some of the ribs  50  provide a complementary axial recess  52  on the inner periphery of the hollow retainer post  22 ; the recesses  52  accept complementary axial ribs  53  formed on the exterior periphery of push-button actuator  18  to properly orient and rotationally lock the push-button actuator  18  with respect to the retainer  16 . For purposes of this invention, however, the axial ribs  50  on the exterior periphery of the retainer post  22  provide a hard stop to limit radially inward bending of the protrusions  46  in the event that lateral force applied to the grip portion  28  of knob  14 . 
     Referring to  FIGS. 3-4 , the cup-shaped retainer flange  24  is also provided with a distributed array of compliant tabs  54  that extend radially inward from the rim  24   a  of flange  24  to axially support the knob  14  when it is slid over the retainer post  22 . A circular or domed boss  56  is formed on the upper surface of each tab  54  to minimize the area of contact with the knob  14 , as the knob  14  rotates with respect to the tabs  54 . And as seen in  FIG. 4 , the inwardly depending cylindrical flange  30  of trimplate  12  engages the ridges  32  on toothed flange  34  of knob  14  to capture knob  14  between trimplate  12  and the tabs  54  of retainer flange  24 . Thus, knob  14  contacts the retainer  16  at the protrusions  46 , the bosses  56  on tabs  54 , and the ridges  32  on retainer flange  34 ; and a suitable lubricant is applied to these contacting surfaces to ensure smooth rotation of the knob  14 . 
     In summary, the rotary control knob apparatus  10  of the present invention provides a simple and cost-effective way of mounting and rotatably supporting an annular rotary control knob  14  such that the axial orientation of the knob  14  is tightly controlled even though the retainer  16  on which the knob  14  is mounted is subject to customary manufacturing tolerance variations. The distributed array of compliant protrusions  46  on the exterior periphery of the hollow retainer post  22  provide a resilient sliding interference fit between the retainer post  22  and the inner periphery of knob  14  to achieve a highly reliable and substantially tilt-free rotational mounting of the knob  14 . Additional mounting rigidity is achieved by locking and securing the retainer  16  to the trimplate  12 . 
     While the present invention has been described with respect to the illustrated embodiment, it is recognized that numerous modifications and variations in addition to those mentioned herein will occur to those skilled in the art. For example, the push-button actuator  18  may be omitted, rotation of the knob  14  may be sensed in a different manner than shown, the retainer  16  may be directly fastened to the trimplate  12 , and so on. Also, it may be possible to form the compliant features  46  on the inner periphery of the knob  14  instead of on the exterior periphery of retainer post  22 . Accordingly, it is intended that the invention not be limited to the disclosed embodiment, but that it have the full scope permitted by the language of the following claims.