Patent Application
20100061798
This invention relates to bearings for articulated arm joints, and particularly to a bearing with adjustable resistance on an articulated support arm for a dental light.
Dental examination lights are mounted on articulated arms that provide multiple rotation axes for flexible positioning of the light via bearings between arm segments. Each bearing requires a balance between ease of movement and maintenance of position. A resistance adjustment may be provided for each bearing in order to achieve and maintain an ideal resistance for each axis of rotation during years of use.
A bearing may include an axle in a bushing in a housing. Resistance adjustment may be provided by setscrew mounted in a radially-oriented threaded hole in the housing. Tightening the setscrew moves it inward against the bushing, distorting and/or offsetting the bushing against the shaft, thus increasing the turning resistance of the shaft. A disadvantage of this type of adjustment is that the housing must be much thicker to accommodate the radially-oriented setscrew hole than would otherwise be necessary for strength of the housing.
The inventors realized that the bearing housing thickness could be reduced if the setscrew hole could be oriented tangentially to the bushing, rather than radially. They devised a tangential setscrew that pushes against a cutout in the bushing. A ramp in the housing converts tangential movement of the bushing into radial inward movement of a portion of the bushing, thus providing resistance adjustment.
The invention is explained in the following description in view of the drawings that show:
When the setscrew is turned in a tightening direction, it pushes tangentially against the abutment 47. This pushes the ramp contact surface 44 against the ramp 30, which pushes the first end 42 of the bushing radially inward against the axle 24, thus increasing the rotation resistance of the axle within the bushing. Since the setscrew is oriented tangentially, the threaded hole 34 requires much less radial thickness in the housing 22 than a radially-oriented setscrew. This reduces material cost, weight, and overall thickness of an articulated arm, such as those used for dental examination lights.
The bushing may be made of sintered bronze impregnated with oil, including a material known as Oilite®, or it may be made of another material. The threaded hole 34 has a side opening into the bushing channel 28. The side opening has a maximum opening width of less than half the diameter of the threaded hole 34, for example up to 30-40% of the threaded hole diameter, so that the setscrew is retained in the threaded hole. A thread gripping means such as a thread compound or plastic O-ring may be used on the setscrew to avoid accidental loosening of the setscrew during operation of the articulated arm. However, the setscrew will normally be in frictional contact with the abutment 47, which will also prevent loosening.
The ramp 30 may be curved as shown, or it may be straight. A curved ramp reduces the likelihood of binding of the contact surface 44 of the bushing between the ramp and the axle. It also reduces the likelihood of over-tightening the bushing because the mechanical advantage of the ramp decreases as the setscrew is tightened. A curved ramp may be formed for example by milling the channel 28 with a rotary milling tool, such that the ramp curvature is formed by the cutting diameter of the milling tool. Or it may be formed by other known means. The second end 32 of the bushing channel is also shown as curved. This exemplifies a milling method of forming the channel, but is not otherwise significant. The ramp contact surface 44 of the bushing may be beveled as shown or rounded.
The setscrew 36 may have a rounded end 37 as shown. This allows the setscrew to turn relatively smoothly against the abutment 47 at the end of the cutout 46 without grabbing the abutment with threads. Also, the contact angle of a curved end 37 with the abutment 47 provides a radially outward force component on the end of the setscrew that helps to retain the setscrew in the threaded hole 34.
The figures show the abutment 47 and setscrew 36 near the first edge 42 of the bushing. However, this position is not an essential aspect of the invention. The abutment and setscrew may be some distance from the first edge 42 of the bushing, but is preferably within about 90° of the first edge. The cutout 46 is also not an essential aspect. An abutment 47 can be provided as a radially outward boss (not shown) on the bushing. However, such a boss is less compact and harder to fabricate than a preferred cutout as shown.
While one or more embodiments of the present invention have been shown and described herein, such embodiments are provided by way of example only. Variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.
