Abstract:
The present invention provides a control drum, such as a tilt drum for a Venetian blind, with adjustable friction elements (such as spring legs), so that the friction between the control drum and the control shaft (e.g., tilt rod), can be greatly reduced during installation and then can be greatly increased once the drum has been installed on the control shaft. The present invention accordingly permits easy installation without sacrificing the benefits of an interference fit between the control drum and control shaft.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Applicants claim priority to U.S. Provisional Application No. 60/115,027, filed Jan. 7, 1999, which is herein incorporated by reference. This application is also related to U.S. patent application Ser. No. 09/481307, which is also incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to adjustable coverings for architectural openings, and, in particular, to a control drum for the tilt cords of adjustable window coverings in which the friction between the drum and the control shaft can be selectively manipulated. 
     BACKGROUND OF THE INVENTION 
     It is known to use adjustable coverings over architectural openings. Such adjustable coverings include cellular panels, Venetian blinds, and many other systems for controlling the passage of light, vision, or air through the architectural openings. For example, cellular panels and Venetian blinds can be adjusted by retracting or extending them, and Venetian blinds may be further adjusted by tilting the slats comprising part of the blind. 
     Tilter mechanisms for Venetian blinds have been created in a variety of configurations. One such tilter mechanism is described in U.S. Pat. No. 5,341,865 “Fraser et al.”, which is hereby incorporated by reference. As shown therein, a tilter mechanism typically includes a tilt drum (also called a “tilt roll”) that is co-axially mounted on an elongated tilt rod and is adapted to receive the forward and rear ladder laces of the Venetian blind. When the tilt rod is rotated, it rotates the drum in unison therewith, which wraps one of the ladder laces and unwraps the other, thereby causing the slats of the Venetian blind to tilt open and closed about longitudinal/horizontal axes. The tilt rod (and drum) can be rotated by a variety of tilters, including by gear mechanisms driven by a remotely controlled motor or by the manual force of the Venetian-blind user. Tilter mechanisms are also employed to effect adjustment of other adjustable coverings for architectural openings. 
     In a Venetian blind, the tilter, tilt drum, and tilt rod are all generally located within the headrail housing of the blind (along with other mechanisms such as pulleys and locks to facilitate lifting of the blind). Tilt drum supports are also fixedly attached to the headrail housing to support the tilt drums and/or tilt rod along the length of the headrail. The tilt drum supports prevent the tilt rod from sagging due to the weight of the blind and generally prevent axial movement of the tilt drums relative to the headrail housing. 
     It is desirable that the tilt rod not be permitted to move axially within the headrail housing. If the tilt rod becomes dislodged from the tilter, for example, the blind cannot be tilted. Moreover, if the tilt rod slides axially within the headrail, it can interfere with other mechanisms, such as the lock for the blind&#39;s lifting mechanism. To avoid these problems, the tilt rod can be held in place by a tight connection to the tilter; however, providing a tight fit in the tilter has been found to be cumbersome and difficult during assembly of the blind. Accordingly, the tilt rod is often manufactured in polygonal cross-section that can be slid into a mating, but not tight-fitting, connection in the tilter. 
     The tilt rod is then held laterally in place by tight fitting connection to the tilt drum. A tight fit between the tilt drum and tilt rod prevents the drum from accidentally sliding relative to the tilt rod. Moreover, because the tilt drums are prohibited from moving laterally by fixed tilt drum supports, the tilt rod can be kept in place without requiring a tight connection to the tilter. 
     Generally, at least one-half pound of force of interference fit is required between the drum and the tilt rod. Due to manufacturing tolerances, however, the interference-fit force of prior art tilt drums on the tilt rod may be as much as four pounds or more. A high interference-fit force can make it frustrating and difficult to assemble the tilt drum onto the tilt rod. 
     SUMMARY OF THE INVENTION 
     The present invention provides a control drum, such as a tilt drum for a Venetian blind, with adjustable friction elements (such as spring legs) so that the friction between the control drum and the control shaft (e.g., tilt rod), can be greatly reduced during installation and then can be greatly increased once the drum has been installed on the control shaft. The present invention accordingly permits easy installation without sacrificing the benefits of an interference fit between the control drum and control shaft. 
     In particular, the apparatus of the present invention includes: a drum body, defining an axial passage adapted to receive the control shaft of an adjustable covering for an architectural opening; at least a first adjustable friction element (such as a spring leg) mounted on the drum body, the first adjustable friction element being moveable from a resting position to a release position; wherein the first adjustable friction element into the axial passage when in the resting position and does not encroach into the axial passage when in the release position. 
     The control system of the present invention includes a control shaft having an axis of rotation and having an axial length substantially in excess of its diameter; a drum body, slidably mounted on the control shaft and rotatable about the axis of rotation of the control shaft, the drum body including first and second ends and an axial hole being adapted to a receive the control shaft; at least a first adjustable friction element (such as a spring leg) mounted on the drum body, the first adjustable friction element being moveable from an engaged position to a release position; wherein the first adjustable friction element, when in the engaged position, impedes the drum body from sliding relative to the control shaft, and, when in the release position, permits the drum body to slide relative to the control shaft. 
     The apparatus and system of the present invention can be advantageously used to secure a control shaft in an adjustable covering for an architectural opening. The method of the present invention includes the following steps: inserting a control shaft into one end of an axial hole defined by a drum body; releasing an adjustable friction element (such as a spring leg) mounted on the drum body to permit the control shaft to slide completely through the drum body via the axial hole; sliding the drum body to a desired position on the control shaft; engaging the adjustable friction element to impede further sliding of the drum body relative to the control shaft; fixedly attaching a drum support to a headrail housing; and substantially impeding movement of the drum body relative to the headrail housing except for rotation of the drum body about the axis of rotation of the control shaft. 
     The present invention is described in greater detail with respect to the following drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a fragmented, isometric view of the top, left, and front of a Venetian blind utilizing the apparatus and system of the present invention. 
     FIG. 2 is a fragmented, broken-away, isometric view of the rear, top, and right of a tilt drum, drum support and other elements of a Venetian blind according to the present invention; 
     FIG. 3 is an isometric view of the front, top, and left of a tilt drum made in accordance with the present invention; 
     FIG. 4 is an isometric view of the front, bottom, and left of the drum of FIG. 3; 
     FIG. 5 is a left end view of the drum of FIG. 3; 
     FIG. 6 is a cross-sectional view taken along line  6 — 6  of FIG. 5; 
     FIG. 7 is a top view of the drum of FIG. 3; 
     FIG. 8 is a front view of the drum of FIG. 3; 
     FIG. 9 is a bottom view of the drum of FIG. 3; 
     FIG. 10 is the same view as FIG. 6 but showing the tilt rod inserted through the drum; 
     FIG. 11 is the same view as FIG. 10, but showing the spring legs of the drum pressed to a release position; 
     FIG. 12 is an isometric view of the top, front, and left of the drum of FIG. 3 with one of the ladder laces installed on the drum; and 
     FIG. 13 is a top view of the drum and ladder lace of FIG.  12 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention provides a control drum and system for an adjustable covering of an architectural opening. The drum of the present invention can be adjusted to permit easy assembly onto a control shaft but, after assembly, a sufficiently tight fit on the control shaft to inhibit the control shaft from moving relative to the drum and axially within the headrail housing. Although the present invention is described with relation to a tilting mechanism for a Venetian blind, it is not limited to use with a Venetian blind. Rather, it will be recognized by those of skill in the art that the present invention could be used to control a function in any adjustable covering for an architectural opening that can be controlled by wrapping and/or unwrapping a cord via rotation of a control drum. As such, the terms “tilt drum,” “tilt rod,” and “Venetian blind,” are merely exemplary of the control drum, control shaft, and adjustable covering of the present invention. 
     FIG. 1 shows a Venetian blind  16  constructed according to the present invention. For convenience, several component parts of the present invention are described in directional terms such as “left,” “right,” “top,” and “bottom.” It should be understood that these directional terms describe the relative positions of the parts as they are oriented in the Figures and are not limiting of the present invention. 
     Slats  18  of the Venetian blind  16  are supported by and manipulated by cord ladders  20 . Cross-cords  22  in the cord ladders connect front and rear ladder laces  24 ,  26 . In the exemplary embodiment shown in FIG. 1, there are two cord ladders  20 , but, depending on the transverse length of the headrail housing  14 , more ladders  20  could be employed. The bottom of each ladder  20  is connected to a bottom rail  28 . The top of each ladder  20  and particularly each set of front and rear ladder laces  24 ,  26  is connected to a tilt drum  10  such that when the tilt drum  10  rotates, one of the ladder laces  24 ,  26  is wrapped onto the tilt drum  10  while the other is unwrapped therefrom. In this way, one end of each cross-cord moves up while the other moves down, thus causing a corresponding tilt about horizontal axes of the slats  18  being supported by the cross-cords  22 . 
     The tilt drum  10  is rotated by its connection to a tilt rod  12 , which, in turn, is rotatably connected to a tilter  30 . The tilt rod  12  extends the majority of the length of the headrail housing  14  and passes through an axial passage  32  defined, in part, by axial holes  34  in the tilt drums  10  (FIGS.  6 - 8 ). A variety of tilters  30  can be used to accomplish rotation of the tilt rod  12  (and tilt drums  10 ), including a worm shaft/pinion combination as described in U.S. Pat. No. 5,341,865, previously incorporated herein by reference. Alternatively, an automated tilter  30  can be employed, such as a remotely controlled motor located within the headrail housing  14  capable of driving the tilt rod  12  to rotate in either direction. A preferred motorized tilting apparatus is described in U.S. patent application Ser. No. 09/481307, previously incorporated by reference. 
     As seen most easily in FIG. 2, each tilt drum  10  is supported by a tilt drum support  36 . The supports  36  are fixedly attached to the headrail housing  14 . Preferably, the attachment of the supports  36  to the headrail housing  14  is accomplished by tabs  38 ,  40  extending from a base  42  and end walls  44  of the support  36  that engage matching openings and grooves in the headrail housing  14 . However, any suitable form of attachment can be used, including screws, adhesives, etc. 
     Each tilt drum support  36  includes end walls  44  having support surfaces  46  that engage bearings  48  on the tilt drum  10 . The support surfaces  46  are arcuately shaped to accept the bearings  48  of the tilt drum  10  such that the tilt drum  10  can rotate freely within the support  36 . Preferably the support surfaces  46  do not extend axially past the bearings  48  of the tilt drum  10  so as not to interfere with the operation of spring legs  50  provided thereon. The operation of the spring legs  50  is explained below. Preferably, the end walls  44  of the support  36  are spaced to accept a tilt drum body  52  between them in a close-fitting, but not interference-fitting, relationship. In other words, enough space is provided between the end walls  44  of the support  36  and end walls  54  of the tilt drum body  52  to permit the tilt drum body  52  to rotate within the support  36  without being significantly impeded by frictional contact with the end walls  44 ; however, the end walls  44  of the support  36  are spaced close enough together to prevent any significant lateral movement of the tilt drum body  52  within the support  36 . 
     The end walls  44  of the support  36  are preferably not connected to the base  42  of the support  36  except near the front wall  56  of the headrail housing  14 . This disconnection between the end walls  44  and the majority of the base  42  allows the base  42  to flex relative to the end walls  44 . This permits the base tabs  38  to be inserted under the bottom wall  58  of the headrail housing  14  first. The base  42  of the support  44  then flexes easily to allow the end-wall tabs  40  to be snapped under a ledge  60  formed by the front wall  56  of the headrail housing  14 . 
     Each tilt drum support  36  further includes an ear  62 , which extends from an end wall  44  above one of the support surfaces  46  and above the tilt rod  12 . The ear  62  is preferably created at such an angle and height so as not to interfere with the rotation of the tilt drum  10  or of the tilt rod  12 . However, the ear  62  is preferably situated to impede the tilt drum  10  from becoming dislodged from the tilt drum support  36 . In other words, the distance from the top of the tilt rod  12  to the bottom of the ear  62  should be less than the distance from the bottom of the support surface  46  to the top edge of the support surface  46 . 
     Each tilt drum support  36  also includes an opening  64  on the base  42  thereof that matches an opening (not shown) on the bottom wall  58  of the headrail housing  14  and is adapted to receive the ladder laces  24 ,  26  for connection to the tilt drum  10 . Preferably, the opening  64  is provided across nearly the full length of the base  42  to permit the ladder laces  24 ,  26  to be spaced as far apart as practically possible when entering the support  36 . As explained in U.S. Pat. No. 5,341,865, previously incorporated herein by reference, this spacing helps avoid the problem of the uppermost slat  18  of the blind  16  being “stuck” in its tilted position. The entire support  36  is preferably molded as a single piece from a resin having a high plastic memory. 
     A preferred embodiment of the tilt drum  10  of the present invention is shown in various views in FIGS. 3-13. The tilt drum body  52  defines, in part, an axial passage  32  adapted to receive the tilt rod  12 . As used herein, tilt drum body  52  (FIG. 9) is defined to include the bearings  48  and the portion of the tilt drum  10  between (and including) the end walls  54 , but does not include the spring legs  50  (unless the spring legs  50  are mounted within the drum body  52 ). Further, the axial passage  32  (FIG. 6) is defined as the elongated axial hole  34  between the bearings  48 , along with axial extensions thereof in either axial direction (including beyond the ends of the bearings  48 ). As shown in FIGS. 3-13, the cross-sectional shape of the axial passage  32  and axial hole  34  can be defined by axially spaced parts of the drum body  52 . In the exemplary embodiment shown in FIGS. 3-13, the bottom and sides of the axial passage  32  are defined by the U-shaped bearings  48 , and the top of the axial passage  32  is defined by the underside of a top drum wall  66 . The cross-sectional shape of the axial passage  32  can most easily be seen in FIG. 5, which is a left-side view of the tilt drum  10  with the spring legs  50  in an “engaged position” (the engaged position is explained below). Again, however, as shown by the dotted lines in FIGS. 6-9, the axial passage  32  extends beyond the bearings  48  of the tilt drum  10  in either axial direction. In an alternative embodiment, the axial passage  32  can be defined by a completely enclosed axial hole extending from one bearing  48  to the other (and axial extensions thereof in either direction). 
     The tilt rod  12  can be of any polygonal cross-sectional shape. The axial hole  34  (i.e., that part of the axial passage  32  located between (and including) the bearings  48  of the tilt drum  10 ) corresponds closely to the non-circular cross-section of the tilt rod  12 . As such, the cross-sectional shape of the axial hole  34  shown in FIGS. 2-13 is merely exemplary. The axial hole  34  need only correspond closely enough to the shape of the tilt rod  12  such that when the tilt rod  12  rotates, the tilt drum  10  rotates with it. As discussed, it is not preferred, according to the present invention, that the axial hole  34  be so small as to create a high interference-force fit with the tilt rod  12 . Rather, the cross-section of the axial hole  34  is preferably slightly larger than the cross-section of the tilt rod  12  so that the tilt rod  12  slides easily through the axial hole  34  during mounting of the tilt drum  10  onto the tilt rod  12 . The frictional force to keep the tilt drum  10  from unwanted sliding relative to the tilt rod  12  is supplied by the spring legs  50 , which will be described further below. 
     The ladder laces  24 ,  26  can be connected to the tilt drum  10  by any number of means, including those discussed in U.S. Pat. No. 5,341,865, previously incorporated herein by reference. In the exemplary embodiment shown in FIGS. 2-13, the ladder laces  24 ,  26  are attached to the tilt drum  10  by left and right hooks  68 ,  70  and corresponding left and right pinch points  72 ,  74 . As shown most clearly in FIGS. 12 and 13, each ladder lace  24 ,  26  is threaded between a middle wall  76  on the drum body  52  and one of the hooks  68 ,  70 . The free end of the ladder lace  24 ,  26  is then forced down into one of the pinch points  72 ,  74 . In this manner, some of the tension in the ladder laces  24 ,  26  created by the weight of the slats  18  and bottom rail  28  is borne by the hooks  68 ,  70 , decreasing the chance that the ladder laces  24 ,  26  will be pulled free of the pinch points  72 ,  74 . 
     Excess length of the ladder laces  24 ,  26  is tucked into holes  78  provided in the drum body  52  (FIGS. 2,  12 ,  13 ). Notably, the holes  78  are placed so that when the ladder laces  24 ,  26  are tucked therein, the ladder laces  24 ,  26  not to interfere with the axial passage  32  (or axial hole  34 ) through the drum body  52 . For simplicity, in FIGS. 12 and 13 only the rear ladder lace  26  is shown as connected to the drum body  52  via the left hook  68  and left pinch point  72 . As partially shown in FIG. 2, it will be appreciated that the front ladder lace  24  is connected to the drum body  52  in mirror image via the right hook  70  and right pinch point  74 . 
     Mounted on each of the bearings  48  are spring legs  50  and spring leg stops  80 . Each spring leg  50  has a generally U-shape and is mounted to the tilt drum body  52  at hinge points  82  on bearings  48 . The hinge points  82  and spring legs  50  are made of a material that has a “memory”, i.e. is resilient, in that it tends to return to its original shape. In this preferred embodiment, the entire tilt drum  10 , including the drum body  52 , the hinge points  82 , and the spring legs  50 , are molded as a single piece out of a plastic material, preferably a resin with a high plastic memory and relatively high coefficient of friction, such as polycarbonate. 
     As shown most clearly in FIGS. 6 and 8, when the tilt drum  10  is not mounted on the tilt rod  12 , the spring legs  50  are in a resting position and biased into that position due to the resiliency of the material at the hinge points. In this resting position, the lower portion  84  of each spring leg  50  encroaches slightly on the axial passage at points  86 ,  87 . Because the spring legs  50  are flexible at their hinge points  82 , however, the lower portion  84  of each spring leg  50  can be pressed down and in towards its respective spring leg stop  80 , thereby permitting the tilt rod  12  to occupy the axial passage  32 . For example, if the tilt rod  12  is inserted into the left end of the tilt drum  10  (as the drum  10  is oriented in FIG.  8 ), the frictional force of the tilt rod  12  as it is inserted will naturally cause the left spring leg  50  to be pushed towards its spring leg stop  80 , thereby opening up the axial passage  32  on the left side of the tilt drum  10 . When the tilt rod  12  is threaded through the axial hole  34  and reaches the right spring leg  50 , the right spring leg  50  (which encroaches on the axial passage  32  in its resting position at point  86 ) will create resistance against the further insertion of the tilt rod  12 . By pushing the lower portion  84  of the right spring leg  50  towards its spring leg stop  80 , the right spring leg  50  clears the axial passage  32  and allows the tilt rod  12  to be pushed fully through the tilt drum  10 . 
     Once the tilt drum  10  is mounted on the tilt rod  12 , as shown most clearly in FIG. 10, the interior surface  88  of each spring leg  50  contacts the bottom surface  90  of the tilt rod  12 . This will be referred to herein as the “engaged” position of the spring legs  50 . When in the engaged position, the spring legs  50  are slightly displaced from their resting position. Because the spring legs  50  and hinge points  82  are made from a material having memory, the spring legs  50  naturally try to return to their resting positions, thereby exerting an upward force on the tilt rod  12 . This creates a substantial friction force between the tilt rod  12  and the tilt drum  10  that prevents the tilt drum  10  from accidentally sliding axially along the tilt rod  12 . The amount of friction force between the tilt rod  12  and tilt drum  10  can be adjusted by varying the amount the spring legs  50  encroach into the axial passage  32  when in their resting position and by constructing the spring legs  50  and hinge points  82  from materials having higher or lower resiliency, as desired. 
     Once the tilt drum  10  is mounted onto the tilt rod  12 , it can be slid to its desired position on the tilt rod  12  by pressing down on one or both of the spring legs  50 . In particular, the spring legs  50  can be moved from the engaged position to a “release position” to allow the tilt drum  10  to be slid readily along the tilt rod  12 . As shown in FIG. 11, the spring legs  50  can be pressed down and in towards their respective spring leg stops  80  such that the interior surface  88  of each spring leg  50  loses contact with the tilt rod  12 . In that position, there is no interference between the spring legs  50  and the tilt rod  12 , and the tilt drum  10  can be readily slid along the tilt rod  12  to the desired position. In practice, it is not always necessary to press the spring legs  50  down far enough to separate the spring leg  50  from contact with the tilt rod  12  entirely. Rather, the “release position” may comprise simply pressing hard enough on the spring legs  50  to equalize substantially the upward force exerted by the spring legs  50  in their attempt to return to their resting position. In that instance, the spring legs  50  may still be lightly touching the tilt rod  12  in their release position, but they will not create enough friction to impede significantly the sliding of the tilt drum  10  along the tilt rod  12 . 
     In addition, only one spring leg  50  need be pressed to its release position at a time. It is generally only necessary to release the spring leg  50  opposite the direction in which one desires to slide the tilt drum  10 . For example, referring to FIG. 10, if one desired to slide the tilt drum  10  to the left along the tilt rod  12 , one need only release the right spring leg  50 . The left spring leg  50  automatically tends to release when moved in that direction. 
     The spring leg stops  80  are preferably molded into the body  52  of the tilt drum  10  on the bearings  48  and prevent the spring legs  50  from being pressed down too far. In addition, in the preferred embodiment shown in the drawings, the lower portion  84  of each of the spring legs  50  is at an angle to the upper portion  92 , so that when the spring legs  50  are in a resting position, the lower portion  84  lies substantially perpendicular to the tilt drum&#39;s  10  axis of rotation. This makes it easier for someone to push down the spring legs  50  to install the tilt drum  10  on the tilt rod  12 . 
     The front view of the tilt drum  10  shown in FIG. 8 demonstrates that a substantially right triangularly shaped space  94  is formed between the upper portion  92  of each of the spring legs  50  and the end of its respective bearing  48 . The uppermost angle a of that triangularly shaped space  94  is at the hinge point  82  and preferably is in the range of  15  to  45  degrees when the spring legs  50  are in their resting position. A right angle is formed between the bearing  48  and the top of the spring leg stop  80 . The height of this triangularly shaped space  94  (i.e., the distance from the top of the spring leg stop  80  to the hinge point  82 ) is approximately the vertical height of the tilt rod  12 . The length of the hypotenuse of the triangularly shaped space  94  (the length of the upper portion  92  of the spring leg  50  from the hinge point  82  to the interior surface  88 ) is substantially greater than the vertical height of the tilt rod  12 . The thickness of the material at the hinge point  82  is thin enough to permit flexing and thick enough to prevent breakage during normal use. That thickness will vary depending upon the materials used. 
     The present invention permits the tilt drum  10  to be manufactured to looser tolerances while still ensuring that the friction between the tilt drum  10  and the tilt rod  12  is low enough to permit easy installation and high enough to prevent the tilt drum  10  from accidentally sliding relative to the tilt rod  12 . In addition, because the tilt drums  10  are prohibited by the drum supports  36  from moving laterally within the headrail housing  14 , the tilt rod  12  is also impeded from lateral movement without necessitating a tight connection to the titer  30 . 
     It will be apparent to those skilled in the art that modifications may be made to the embodiment described above without departing from the scope of the present invention. For example, the particular position and shape of the spring legs  50  can easily be varied. The spring legs  50  could be reoriented to connect to the bottom of the drum bearing  48  and contact the top of the tilt rod  12  when in the engaged position. Moreover, the spring legs  50  could be attached to the interior of the tilt drum body  52  such that they encroach on the axial hole  34  defined by the tilt drum body  52  rather than just the axial passage  32  beyond the ends of the tilt drum body  52 . 
     Further, it is recognized that the drum support  36  could engage and support the tilt rod  12  directly rather than supporting the tilt drum  10 . As discussed, in the preferred embodiment, the drum support  36  provides support surfaces  46  that engage bearings  48  on the tilt drum  10 . This arrangement is preferred when used with the tilt drum  10  construction described above. Assume, for example, the drum support  36  engaged the tilt rod  12  directly outside of the preferred tilt drum  10 . If the tilt rod  12  (and drum  10 ) slid to the left within the headrail housing  14 , the left spring leg  50  would bump into the end wall  44  of the drum support  36 , potentially releasing the left spring leg  50  and allowing the tilt rod  12  to slide relative to the tilt drum  10 . However, if the spring legs  50  are moved within the tilt drum body  52  or are configured so as to otherwise alleviate this problem, the drum support  36  can support the tilt rod  12  directly (thereby indirectly supporting the tilt drum  10  by virtue of the drum&#39;s mounting on the tilt rod  12 ). As such, “drum support,” as used herein, refers to a support that engages either the tilt drum  10  or the tilt rod  12 . 
     Moreover, it should be understood that separate spring legs  50  are not critical to the present invention and are merely examples of a adjustable friction elements according to the present invention. Rather, the tilt drum body  52  could, itself, be shaped to create adjustable friction when mounted on the tilt rod  12 . For example, the axial hole  34  formed by the tilt drum body  52  could be made slightly arcuate (rather than linear as depicted in FIGS. 3-13) by curving the top drum wall  66  such that it is higher at its connection to the middle wall  76  than at its connection to the bearings  48 . This would cause the top drum wall  66  to encroach on the axial passage  32  when the tilt drum body  52  was in a resting position (i.e., not mounted on the tilt rod  12 ). The tilt drum body  52  would then be deformed slightly (by flattening the top drum wall  66 ) to mount the tilt drum body onto the tilt rod  12 . Once mounted on the tilt rod  12  (the “engaged position” in this embodiment), the top drum wall  66  would exert a downward pressure on the tilt rod  12  to create a substantial frictional force between the tilt drum  10  and the tilt rod  12 . The tilt drum body  52  could then be “released” from the engaged position by pushing down on middle wall  76 , thereby flattening the top drum wall  66  allowing the tilt drum body to slide easily along tilt rod  12 . In this embodiment, top drum wall  66  is manufactured of a material having a high plastic memory and is of a thickness to allow it to be flexed but not broken during normal use. 
     The present invention should thus not be limited except by the following claims.