Slider mechanism
BACKGROUND OF THE INVENTION 
     This invention pertains to a slider mechanism and, more particularly to such a mechanism which is self-locking and which can be used to hold telescopically adjustable members of a leg or stand in adjusted height position. The self-locking slider mechanism has a friction member movably mounted on one tubular member and frictionally engaging a second tubular member. The friction member has means associated with it to require a greater force manually applied lengthwise of the stand or leg to decrease the length thereof than to increase the length thereof, whereby height adjustment may be achieved while supporting a load. One use is for a music stand wherein a desk will support musical scores while still enabling manual height adjustment. The slider mechanism is also usable in other types of stands and adjustable leg structures. 
     DESCRIPTION OF THE PRIOR ART 
     Many different types of mechanism are known for holding a stand in adjusted height position. These mechanisms can either be of the type which are mechanically moved into and out of a positive locked condition or of a type which frictionally holds components of the stand in an adjusted height position. For many uses, a stand of the latter type is preferred when relatively light loads are supported by the stand and ease of stand height adjustment is an important consideration. 
     In stands of the latter type, there are several different known structures for holding the stand in adjusted height position. With the stand having inner and outer tubular members, one structure has had a series of spring fingers mounted on one of the tubular members and frictionally engaging the other tubular member. Another structure has had a split plastic collar associated with one tubular member and spring-urged into engagement with the other tubular member. In these friction structures, there must be sufficient frictional resistance to enable the stand to support the necessary load and, in adjusting the height of the stand, this frictional resistance must be overcome. This is no problem when the height of the stand is to be decreased, since the base of the stand will merely be pressed against the floor. However, in increasing the height of the stand, it is necessary to hold one tubular member of the stand while the other tubular member is being pulled to cause relative movement therebetween. Therefore, minimizing the amount of force required to increase the height of the stand is desirable. 
     The invention disclosed hereinafter provides for a slider mechanism usable in many different types of stands and adjustable leg structures which require a greater force manually applied lengthwise of the device to decrease the height of the stand or the leg structure than to increase the length thereof whereby the device may perform its intended function of supporting a required load while requiring minimal force to increase the height thereof. The invention also provides for controlled lowering movement. 
     SUMMARY OF THE INVENTION 
     The primary feature of the invention disclosed herein is to have a slider mechanism which may be usable in many types of stands and adjustable leg structures that are capable of supporting any device or apparatus requiring length or height adjustment. 
     In accomplishing the foregoing, the components of the invention can be selected and sized to fit the tubular members of the stand or leg structure, to provide sufficient pressure and, therefore, frictional resistance to support a varied number of loads. 
     Additional features of the invention reside in the fact that the components of such an invention are comparatively low cost and the invention eliminates the need for expensive locking collars, manual locking collars, and counterbalances; yet the invention holds the designed weight. 
     The features of the invention which allows it easy up, frictional resistance down, when in vertical position makes the invention adaptable to ease downward loads when the stand or leg structure is released by some other mechanical holding or locking structure. This can provide a safety feature to gradually ease the load downward. 
     The above described features make this device applicable to many products and/or equipment; the major group being performance equipment. Applications are in music stands, conductors&#39; stands, microphone stands, lighting stands for both ambient lighting for homes and offices, and professional lighting stands used in lighting the areas of theatrical performances and photographic studios. Other related performance equipment being speaker stands, instrument stands, stools, chairs, instrument holders and musical accessory holders. Also, this invention can be incorporated in computer equipment stands, camera tripods, display devices such as advertising easels or signage posts, survey equipment (tripods) and artist easels for both working and display. 
     A further object of the invention is to provide, in combination, a stand and a self-locking slider mechanism comprising, an outer tubular member, a floor support secured to the lower end of the outer tubular member, an inner tubular member telescopically adjustable within the outer tubular member, a desk attached to the upper end of the inner tubular member, the improvement comprising, a friction means on the inner tubular member engaging the outer tubular member for releasably holding the inner and outer tubular members in adjusted position, said friction means enabling telescopic adjustment of said tubular members by a manual force applied lengthwise of said tubular members, and means mounting the friction means to require a greater manual force when lowering the stand than when raising the stand. 
     With the invention disclosed herein, the stand is self-locking and can be adjusted with a minimum of pushing or pulling force lengthwise of the stand while providing a high load-carrying capacity in performance position. The self-locking slider mechanism is a self-contained subassembly and has components which can be simply changed to vary the amount of load-carrying capacity of the stand as well as the required force for achieving height adjustment. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective elevational view of a music stand, illustrating one use of the slider mechanism; 
     FIG. 2 is a fragmentary vertical section, on an enlarged scale of the music stand shown in FIG. 1; 
     FIG. 3 is a fragmentary vertical section on a further enlarged scale, taken generally along the line 3--3 in FIG. 2; 
     FIG. 4 is a transverse section on an enlarged scale taken generally along the line 4--4 in FIG. 2; 
     FIG. 5 is a transverse section on an enlarged scale taken generally along the line 5--5 in FIG. 2; and 
     FIG. 6 is a transverse section on an enlarged scale taken generally along the line 6--6 in FIG. 2. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A stand using the slider mechanism embodying the invention is shown in FIG. 1 and indicated generally at 10. The stand is illustrated as a music stand having a music desk 11 at the upper end thereof. However, the principles of the invention can be embodied in stands of other types, such as microphone and light stands as well as adjustable leg structures. Reference to a stand is for illustrative purposes only. 
     The stand has a pair of relatively adjustable members 15 and 16 which are adjustable lengthwise of each other to establish the height of the stand. As shown, these members are an inner tubular member 15 and an outer tubular member 16 which are telescopically adjustable with respect to each other. The inner tubular member 15 mounts the music desk 11 by means well known in the art, such as a releasably-locked, pivot mounting. The outer tubular member 16 is fixed to a base at its lower end, with the base having the legs 17, 18 and 19. 
     The connection of the base to the outer tubular member 16 is shown particularly in FIG. 2 and is a structure known in the art wherein a collar 20 secured to the legs surrounds the lower end of the outer tubular member 16 and has an end plate 21 mounting a member having a series of downwardly-inclined spring fingers 22 and which is held thereto by a rivet 23 to permit insertion into the open lower end of the outer tubular member and with the spring fingers retaining the structure in assembled relation. 
     The inner tubular member 15 is guided in its movement relative to the outer tubular member 16 by a tubular guide 25 mounted within the upper end of the outer tubular member 16 and having a central opening through which the inner tubular member extends. The tubular guide 25 is a structure known in the art wherein a pair of semi-circular members, formed of a suitable plastic, are assembled together to form an annular member positioned within the upper end of the outer tubular member and which are held in assembled relation by a surrounding retainer clip 26 having angled spring grippers that engage into the outer tubular member 16. The tubular guide 25 has an opening of a size to receive wedge-defining surfaces on the inner tubular member 15 to spread apart the pair of semicircular members of the tubular guide to cause the angled spring grippers to press into the outer tubular member and prevent pull-out of the tubular guide. The tubular guide can be pried out, if necessary, by use of a suitable tool when the enlargement is not positioned therein. 
     The self-locking slider mechanism is carried at the lower end of the inner tubular member 15 and is shown particularly in FIGS. 2-6. This slider mechanism has a body member 30 which is in the form of an elongate member preferably formed of a rigid relatively slippery plastic. As seen in FIG. 4, the body member 30 has a curved exterior side 33 and a pair of opposite slightly diverging flat sides 31 and 32 with a recess 50 between top and bottom walls 34 and 34a. 
     The body member 30 is fixed to the inner tubular member 15 by staking an end of the inner tubular member onto an attaching element 35 integral with an end of the body member. As seen in FIG. 2, the attaching element 35 has a round end flange 35a and a connecting section formed of four ribs 35b-e at adjacent right angles (FIGS. 2 and 6). The staking of these two parts together by an oppositely applied compressive force below the end flange 35a locks the body member to the inner tubular member with the inner tubular member being widened in one direction and narrowed in the other, as seen in FIGS. 3 and 6. The widened part has curved sides 36 and 36a forming a tapered enlargement greater than the diameter of the inner tubular member to effectively form the wedge, previously referred to, when the inner tubular member 15 has moved to an upper limit position. 
     The body member 30 has the elongate internal recess 50 extending lengthwise thereof and which opens to one side thereof as seen in FIGS. 4 and 5. An inclined wall 51 defines the bottom of the internal recess 50 and, as seen in FIG. 2, this wall inclines upwardly and outwardly relative to the internal recess. A ramp plate 55 of rigid material, such as metal, is positioned within the elongate internal recess 50 and extends for substantially the entire length thereof and is in spaced parallel relation with the inclined wall 51. An elongate upwardly tapering ramp member 56, having a width closely approximating the width of the internal recess 50 and a length approximately half the length of the internal recess, is mounted within the internal recess for guided movement along the length thereof, as well as along the ramp plate 55 which engages the inner side thereof. The ramp member 56 has an insert 60 of friction material extending from an outer face for engagement with the inner surface of the wall of the outer tubular member 16 and also has a sloped inner face 61 engaging the ramp plate. 
     The ramp member 56 has a pair of central recesses 56a and 56b defining a pair of flexible legs 62 and 62a with protrusions 63 and 63a, respectively, to snap into grooves 64 and 64a in the walls 31 and 32 of the body member to movably retain the ramp member in association with the body member after assembly together to facilitate assembly with the inner and outer tubular members. 
     A pair of relatively stiff compression springs 65 and 66 are positioned between the inclined wall 51 of the body member and the ramp plate 55, with these springs being held in position by annular raised ribs 67 and 68 formed integrally with the inclined wall 51. A third less stiff compression spring 70 extends between the bottom wall 34a of the body member 30 and the ramp member 56, with a portion of the length of the spring being captured within an interior opening of the ramp member 56 as seen in FIG. 2. 
     The components of the slider mechanism are assembled with relatively tight tolerances whereby the slider mechanism, when assembled with the stand components, has the ramp member 56 positioned generally as shown in FIGS. 2 and 3 wherein the ramp member is at a short distance from an upper end of the internal recess 50. In this position, the pair of compression springs 65 and 66 are slightly compressed, as is the third compression spring 70. This provides sufficient pressure of the friction material 60 against the inner surface of the wall of the outer tubular member 16 to retain the music stand in an adjusted height position. The components are also selected and sized to provide sufficient pressure and, therefore, frictional resistance, whereby the desk 11 of the stand can support a load such as, for example only, the musical scores of a performer. 
     If the height of the stand is to be adjusted upwardly, a relatively small amount of force is required after application of sufficient thrust to achieve initial breakaway of the holding action by the slider mechanism, since the pressure applied by the friction insert 60 will be reduced because of the ramp member 56 moving inwardly of the internal recess 50 as permitted by the downward inclination of the ramp plate 55, the sloped surface 61, and the relatively weak spring 70. More particularly, manual force applied lengthwise of the stand by engaging of the inner tubular member 15 and holding of the outer tubular member 16 will cause outward movement of the inner tubular member and, as this movement occurs, the ramp member 56 and friction insert 60 are substantially free to move downwardly and inwardly relative to the inner tubular member to a position where less pressure is applied against the inner surface of the outer tubular member wall. Although minimal force is desirable for increasing the height of the stand, the components are selected and designed to assure that the stand tubular members will not separate if the stand is picked up by the desk 11 or by the inner tubular member 15. 
     When the desired height is achieved, the ramp member will again be positioned, as shown in FIG. 2, to retain the stand in adjusted position. The resistance to downward height adjustment of the stand is because of such movement tending to move the ramp member 56 further upwardly in the elongate internal recess 50 which is in a direction upwardly of the inclined ramp plate 55. The ramp plate can move inwardly to permit this upward movement, but such movement is resisted by the relatively stiff compression springs 65 and 66. The force of these springs is selected so that a predetermined amount of downward force exerted lengthwise of the stand and on the inner tubular member 15 will overcome the force of the springs adequately to permit relative movement between the friction insert 60 and the outer tubular member 16. 
     It will be evident there could be changes in the structure to vary the amount of force required to decrease the height of the stand. There could be a change in either the thickness of the ramp plate 55, the characteristics of the friction insert 60 or the strength of the springs. The force to increase the length or height of the stand will go up proportionally to the force required to decrease the height of the stand. 
     The slider mechanism requires a greater force manually applied lengthwise of the stand to decrease the length of the stand than to increase the length of the stand and the breakaway force required preparatory to increasing the height of the stand is adequate to assure that the tubular members will not separate when the stand is picked up by the inner tubular member 15. 
     As pointed out in the SUMMARY OF THE INVENTION, the slider mechanism is usable with many different types of stands and adjustable leg structures and is not limited to use only with a music stand which is shown in FIG. 1 and described for illustrative purposes only.