Abstract:
A device is disclosed for use with adjustable rotary controls such as potentiometers to provide a means for locking the control knob and to provide varying amounts of drag force to aid in fine adjustments. A locking shoe assembly having integral locking shoes with cam surfaces is attached to the control panel with the rotary control shaft extending through its center. A locking knob with internal cams fits over the locking shoe assembly. A control knob with an integral land surface is attached to the rotary shaft, holds the locking knob in place and extends into the locking shoe assembly. Rotation of the locking knob engages the various cam surfaces thus binding the land surface and the control knob.

Description:
BACKGROUND OF THE INVENTION 
     It has been found desirable to have locking knobs on electrical instruments so as to prevent inadvertent adjusting once set and to avoid displacement caused by vibrations and the like. The prior art teaches several different devices that accomplish this purpose. Most of these devices are somewhat complicated in construction since they require many components to constitute the locking device. Because of the unnecessary complicated design of the prior locking devices, the assembly of such devices is more costly and time consuming than would be if the device had a minimal amount of components. 
     OBJECTS OF THE INVENTION 
     An object of the present invention is to provide a locking knob device for use with instruments that has but a few components. 
     Another object of the present invention is to provide a locking knob that will prevent inadvertent adjustments or motion of a control shaft of a rotary controlled device. 
     Still another object of the present invention is to provide complete locking or unlocking of the movement of a control knob without affecting the set position of the knob. 
     The above objects are given by way of example, thus other desirable objectives and advantgages achieved by the present invention may occur to those skilled in the art. The scope of the invention is to be limited only by the appended claims. 
     BRIEF SUMMARY OF THE INVENTION 
     The above objects and other advantages are achieved by the present invention. A locking control knob is provided for use with rotary control devices. The rotary control devide is mounted through a panel and is retained with a suitable nut. A locking shoe assembly having a corresponding cavity therein is press-fitted over the nut. This prevents the locking shoe assembly from rotating. The locking shoe assembly has a plurality of integral locking shoes extending therefrom. A locking knob is then slid over the locking shoe assembly. A control knob is then slipped onto the shaft of the rotary control device so that the control knob land extends through the locking knob and is inside the plurality of locking shoes. Set screws on the locking knob are then tightened to secure the knob to the control shaft. The locking knob is retained by a raised external knurl on the control knob. Locking is accomplished by rotating the locking knob, internal cams therein being forced against the integral locking shoes of the locking shoe assembly, thus bringing the locking shoes to bear upon the control knob land, thereby preventing the control knob from turning. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of the present invention; and 
     FIG. 2 is an exploded partial section view of the present invention; 
     FIG. 3 is a top planar view of the locking shoe asembly of the present invention; 
     FIG. 4 is a bottom planar view of the locking knob of the present invention; 
     FIG. 5 is an exploded partial section of the panel and the locking shoe assembly according to another embodiment of the present invention; 
     FIG. 6 is an exploded perspective view of yet another embodiment of the present invention; and 
     FIG. 7 is an exploded partial section view of the embodiment of the present invention shown in FIG. 6. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A description of the invention follows referring to the drawings in which like reference numerals denote like elements of structure in each of the several Figures. 
     The locking device 10 of the present invention is shown in FIGS. 1 and 2 having a molded locking shoe assembly 12, a locking knob 14 and a control knob 16. A rotary control device 18 having a rotary control shaft 19, such as a potentiometer, is mounted through a panel 20 and is fixedly attached thereto by a nut 22 tightened over the rotary control threads 24. The molded locking shoe assembly 12 has an internal cavity 26 being of proximate dimension to fit tightly over nut 22. Although the molded locking shoe assembly 12 may be press-fitted over nut 22, other methods of fixedly attaching the molded locking shoe assembly 12 to the rotary control device 18 may be used such as bonding the molded locking shoe shoe assembly 12 to the control panel 20 with a suitable adhesive material such as epoxy or the like. FIG. 5 shows another embodiment of the present invention in which the rotary control device 18 is fixedly attached to panel 20 by locking shoe assembly 12 which has a threaded cavity 27 to screw onto rotary control threads 24. 
     The molded locking shoe assembly is preferably molded from plastic and as can be seen in FIG. 3 has preferably two locking shoes 28a and 28b cylindrically extending therefrom and integrally attached at one end with externally inclined surfaces 29a and 29b and inner surfaces 29c and 29d. The molded locking shoe assembly 12 has a circumferential receiving slot 30 with a shoulder 32. The purpose of circumferential receiving slot 30 is to receive the control knob 16. Through bore 33 is dimensioned slightly larger than the diameter of shaft 19 so as to permit free rotation thereof. Control locking knob 14, as can be seen in FIG. 4, preferably has two internal integral cams 34a and 34b in the same direction as surfaces 29a and 29b. The locking knob 14 is placed axially over molded locking shoe assembly 12. The internal integral locking cams 34a and 34b of locking knob 14 are dimensioned so as to be in close promixity with the integral locking shoes 28a and 28b of molded locking shoe assembly 12 in the unlocked position. Control locking knob 16 has a land portion 36 of such dimension as to fit within central recess area 30 and to be in proximity with the integral locking shoes 28a and 28b. 
     The preferred embodiment of the present invention contemplates attaching control knob 16 to rotary shaft 19 by means of set screw 40. Other means of attachment are also contemplated, such as epoxying, etc. Control knob 16 has a retention surface 42 dimensioned such that it engages surface 44 of locking knob 14 such that locking knob 14 is held in longitudinal position but is free to rotate about the axis of the rotary control shaft 19. Both locking knob 14 and control knob 16 have outer knurled grasping surfaces 46 and 48, respectively, which facilitate movement of the knobs by an operator. 
     Locking shoes 28a and 28b have stop surfaces 50a and 50b at the distal other end, respectively, and locking cams 34a and 34b have stop surfaces 52a and 52b, respectively. These surfaces of the locking shoes and the locking cams come together at the fully unlocked position, i.e. little or no force is being exerted by the locking cams against the locking shoes. 
     Turning to the operation of the present invention, in the unlocked position there is no physical contact between cams 34a and 34b, locking shoes 28a and 28b or land 36 so that control knob 16 is free to rotate in either direction, thereby rotating shaft 19 of rotary control device 18. To achieve the locking, locking knob 14 is rotated in the direction opposite that of the internal incline of the integral cams 34a and 34b such that the internal cams 34a and 34b engage the integral locking shoes 28a and 28b of molded locking shoe assembly 12. Maximum lock of control knob 16 occurs in less than a 180° turn of locking knob 14 from the fully unlocked position. The distal other end of molded locking shoes 28a and 28b are thus forced radially inward, forcing the inner surfaces 29c and 29d to come in contact with land portion 36 of control locking knob 16, thus locking the control knob 16 in position. To unlock the device the locking knob 14 is rotated in the same direction as that of the internal incline surface of locking cams 34a and 34b so as to disengage the locking cams 34a and 34b from the molded locking shoes 28a and 28b permitting them to return back to their original position thus freeing control knob 16. 
     It is also possible to have a finite amount of drag force while adjusting rotary control 18. This can be accomplished by rotating locking knob 14 only sufficiently enough to cause cams 34 to force shoes 28 into slight engagement with land 36 until the amount of drag force required is achieved. A finite amount of rotational drag force on the rotary control will aid an operator in making fine adjustments. Another embodiment of the present invention, shown in FIGS. 6 and 7, contemplates a rotary control device that not only has a rotational control function but a push and/or pull function. In order to facilitate the in and out motion of the control knob, a different means for retaining the locking knob must be provided to hold the locking knob in a longitudinal, stationary position with respect to the mounting panel 20 other than surface 42 as discussed above. Turning now to the embodiment shown in FIGS. 6 and 7, the locking device 10&#39; has an annular retention ring 54, a molded locking shoe assembly 12, a locking knob 14&#39; and a control knob 16&#39;. The inner surface 56 of annular retention ring 54 is dimensioned so as to fit over surface 58 of molded locking shoe assembly 12 but not over cam surfaces 29a and 29b and to be able to rotate freely about molded locking shoe assembly 12. The outer surface surface 60 of annular retention ring 54 is perferably the same dimension as the outer knurled surface 48&#39; of locking ring 14&#39;. Outer surface 61 of annular retention ring 54 is preferably dimensioned so as to fit snugly within the inner surface 62 of locking knob 14&#39;. The function of locking knob 14&#39; is the same as that of locking knob 14 described above. Annular retention ring 54 and locking ring 14&#39; are fixedly attached together at surface 63 of locking knob 14&#39;. In one embodiment, the annular retention ring 54 and locking knob 14&#39; are ultrasonically welded together. An energy director surface 64 is provided, as is known in the art, for the ultrasonic welding purpose. When annular retention ring 50 is fixedly attached to locking ring 14&#39; and when locking shoe assembly 12 is fixedly attached to the panel 20 and rotary control device 18, the locking ring 14&#39; will be held relatively fixed in a longitudinal axis with respect to panel 20. The annular locking ring 54 takes the functional place of the surface 42 in the embodiment of the present invention shown in FIGS. 1 and 2 in holding the locking knob 14/14&#39; in a relatively fixed longitudinal position. Since the control knob 16&#39; is no longer required for retaining locking knob 14&#39; , is can be fixedly attached to rotary control shaft 19 to not only provide rotational motion thereof, but to provide a push and/or pull motion along the longitudinal axes of the rotary control device when the locking knob 14&#39; is in the unlocked position. The surface 42&#39; and the knurled surface 48&#39; of control knob 16&#39; are dimensioned such as to fit within the inner diameter 66 of locking knob 14&#39;. The control knob 16&#39; is mounted on shaft 19 such that control knob 16&#39; can move in and/or out and still remain with the circumferential receiving slot 30 of molding locking shoe assembly 12.