Abstract:
A knob assembly for the switch of a radio is provided which prevents the switch from being rotated to certain positions except when the knob is moved in an axial direction after contact with a stop. The knob may be returned to a location where other switch positions may be selected without requiring further axial motion of the knob on the part of the radio operator.

Description:
FIELD OF THE INVENTION 
   This invention relates to radios, and, more particularly, to an improved knob assembly for operating the switch of the radio to prevent inadvertent movement of the switch to the “off” and “Z-all” positions. 
   BACKGROUND OF THE INVENTION 
   Satellite radios include a switch which is movable to a number of positions, typically, “off,” “channels 1–5” (or more), “scan,” “front panel,” which allows the channels and modes of operation to be selected using the key pad on the front panel of the radio, and, “Z-all.” The Z-all position refers to zero-all which clears the encryption cipher keys in the radio. When switching channels, current switch designs allow the radio to be inadvertently turned off. The radio must then reboot, essentially cutting off communication for the duration of the reboot. 
   The switches presently employed with satellite radios also permit inadvertent movement to the Z-all position. Although the radio is protected while in the Z-all position by requiring actuation of the volume up button, it is desirable to prevent inadvertent movement to the Z-all position directly. There is a need for an improved device for controlling the operation of the switch of satellite radios to protect against inadvertent switch movement. 
   SUMMARY OF THE INVENTION 
   This invention is directed to a knob assembly for the switch of a radio, and particularly a satellite radio, which prevents the switch from being rotated to the off and Z-all positions except when the knob is moved in an axial direction after contact with a stop. The knob may then be returned to a location where other switch positions may be selected, without requiring further axial motion of the knob on the part of the radio operator. 
   The knob assembly comprises an outer knob, coupled to the stem of the radio switch, and a position control element held in a fixed position relative to the switch. The position control element is formed with a circumferentially extending track within which a pin formed on the outer knob is movable to position the switch so that a particular channel or mode of operation may be selected. If an attempt is made to rotate the knob to the off or Z-all positions, the pin in the outer knob engages one of two stops located within the channel of the position control element. The outer knob must then be pulled in an axial direction to clear the stop before it can be rotated to the off or Z-all positions. Preferably, each stop has a beveled surface which faces the pin of the outer knob when it is in position to select the off or Z-all positions. The pin rides up along a beveled surface when the outer knob is rotated from such positions, thus allowing the pin to clear the stops without requiring the operator to pull the outer knob in an axial direction. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The structure, operation and advantages of the presently preferred embodiment of this invention will become further apparent upon consideration of the following description, taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a perspective view of the knob assembly of this invention coupled to the switch of a satellite radio, the housing of which is partially shown; 
       FIG. 2  is an exploded view of the knob assembly, including the switch and a portion of the housing of the radio depicted in  FIG. 1 ; 
       FIG. 3  is a plan view of the outer knob of the knob assembly, showing the switch positions; 
       FIG. 4  is a plan view of the position control element of the knob assembly; 
       FIG. 5  is a cross sectional view of the outer knob, taken generally along line  5 — 5  of  FIG. 3 ; 
       FIG. 6  is a cross sectional view of the position control element, taken generally along line  6 — 6  of  FIG. 4 ; 
       FIG. 7  is an assembled, cross sectional view of the outer knob and position control element; 
       FIG. 8  is a side view of the position control element; 
       FIG. 9  is a side view of the position control element with the pin of the outer knob illustrated in contact with one of the stops located in the track of the position control element; 
       FIG. 10  is a plan view, in partial cross section, depicting the position of the outer knob with its pin as shown in  FIG. 9 ; 
       FIG. 11  is a side view of the position control element with the pin of the outer knob illustrated in contact with the other of the stops located in the track of the position control element; 
       FIG. 12  is a plan view, in partial cross section, depicting the position of the outer knob with its pin as shown in  FIG. 11 ; and 
       FIGS. 13–15  are side views of the position control element depicting how the pin of the outer knob moves axially to clear the stops in the track of the position control element. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring initially to  FIGS. 1 and 2 , the knob assembly  10  of this invention is intended to control the rotation of the stem  12  of a switch  14  used in a satellite or other type of radio  16 , and prevent inadvertent movement of the switch  14  to the off or Z-all positions. Only a portion of the chassis  17  of the radio  16  is shown in the Figs. for ease of illustration. The knob assembly  10  comprises and inner knob  18 , a position control element  20 , an outer knob  22 , a compression spring  24 , a retention clip  26  and a switch position label  28 . The inner knob  18  is coupled to the switch  14  and may be rotated to selected positions to place the radio in different modes of operation, e.g. plain text, cipher text or load mode, for example, when used with a satellite radio. Inner knob  18  is formed with a projection  30  which acts as a position indicator to denote which mode of operation of the radio  16  is active. A flange  31  extends from the position control element  20  and into contact with a projection  29  from the chassis  17  of the radio  16 . The position control element  20  is seated on the inner knob  18  and held in a fixed position relative to switch  14  by engagement of its flange  31  with the projection  29 . 
   The position control element  20  and outer knob  22  are the key elements of the knob assembly  10  which control rotation of the stem  12  of switch  14 . As best seen in  FIGS. 3–7 , the position control element  20  has a longitudinal axis  32  and is formed with a circumferentially extending track  34  defining a top wall  36 , a bottom wall  38  and a side wall  40  extending between the top and bottom walls  36 ,  38 . For purposes of the present discussion, the terms “top,” “bottom,” “up,” “upwardly,” “down” and “downwardly” refer to vertical locations or directions with the components of the knob assembly  10  oriented as shown in the Figs. The track  34  has a height dimension which is measured in a direction parallel to the longitudinal axis  32  and extending between its top and bottom wall  36 ,  38 . A section  33  of the track  34  has a height dimension “A,” noted in  FIG. 6 , which extends from a location near the Z-all position  42  in a clockwise direction to the a location near the off position  44 , as viewed in  FIG. 3 . The remainder of the track  34 , which encompasses only the Z-all position  42  and off position  44  and is identified as section  35  in  FIG. 3 , has a height dimension “B.” The height dimension B is greater than that of A, for purposes described below. 
   As shown in  FIGS. 8–15  and described in more detail below, a first stop  46  and a second stop  48  are located within the track  34  of the position control element  20  and are circumferentially spaced from one another. The stop  46  is located near the Z-all position  42 , and the stop  48  is located near the off position  44 . Each stop  46 ,  48  has a vertical surface  50  and a beveled surface  52 . The beveled surface  52  of stop  46  faces the beveled surface  52  of stop  48 . 
   The stem  12  of switch  14  extends through a bore  54  in the position control element  20  and into engagement with a slot  56  at the base of the outer knob  22 . A bore  58  in the outer knob  22  receives the spring  24 , which encircles the switch stem  12 . The clip  26  retains the spring  24  in position within the outer knob  22  so that it bears against and urges the outer knob  22  toward the position control element  20 . The outer knob  22  is formed with a pin  60 , which, when the outer knob  22  and position control element  20  are coupled to one another, extends within the track  34  of the position control element  20 . 
   Referring now to  FIGS. 3–15 , the operation of the knob assembly  10  is discussed. As best seen in  FIG. 7 , the pin  60  of the outer knob  22  is urged by the spring  24  into a first axial position, i.e., into engagement with the bottom wall  38  of the track  34  in the position control assembly  20 . The pin  60  slides along the bottom wall  38  as the outer knob  22  is rotated within section  33  of the track  34 , which, in turn, moves the switch  14  to selected positions. With the pin  60  located within section  33  of the track  34 , the switch  14  can select each of the channels and all other modes of operation of the radio  10  with the exception of the Z-all position  42  and the off position  44 . When the operator rotates the outer knob  22  toward the Z-all position  42 , its pin  60  contacts the vertical surface  50  of the first stop  46  and prevents further movement of the switch  14  before the Z-all position  42  is reached. See  FIGS. 9 and 10 . Similarly, rotation of the outer knob  22  in the opposite direction toward the off position  44  eventually results in contact between the pin  60  and the vertical surface  50  of the second stop  48 . See  FIGS. 11 and 12 . Consequently, engagement of the pin  60  with stops  46  and  48  prevents inadvertent advancement of the switch  14  into the section  35  of the track  34  where the Z-all and off positions  42 ,  44  are located. 
   In order to place the switch  14  in either the Z-all position  42  or the off position  44 , the radio operator must grasp the outer knob  22  and pull it in an axial direction, e.g., to a second axial position away from the position control element  20 , thus overcoming the spring force exerted by spring  24  acting in the opposite direction. The pin  60  of the outer knob  22 , in turn, is lifted from the bottom wall  38  of the track  34  in a direction toward its top wall  36 . The height “B” of the track  34  in the area of section  35  is sufficient to allow the pin  60  to clear either one of the stops  46  or  48 . See  FIGS. 6 and 13 . Rotation of the outer knob  22  when in this second, axial position allows the pin  60  to pass over the stops  46  or  48  and enter the section  35  of track  34  where the switch  14  may be moved to either the Z-all or off positions  42 ,  44 , as desired. See  FIG. 14 . The outer knob  22  may be returned to section  33  of the track  34  by merely rotating it in the desired direction. The pin  60  engages the beveled surface  52  of one of the stops  46  or  48 , and rides up along such surface  52  until it clears the stop  46  or  48  and enters section  33  of track  34 . See  FIG. 15 . There is no need to pull axially on the outer knob  22  to exit section  35  of the track  34 . 
   While the invention has been described with reference to a preferred embodiment, it should be understood by those skilled in the art that various changes may be made and equivalents substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.