Extensible and Retractable Rod

This invention relates generally to multisection telescoping rods and, more particularly, to telescoping measuring rods (e.g., leveling rods).

When the telescoping sections of a measuring rod are extended, it is important that they be rigidly held in coaxial alignment, with each section being firmly supported within the next larger section. Heretofore such stability has been achieved by sizing each section so that, when fully extended, a substantial portion of the section remains in the next larger section of the rod and has a close clearance fit therewith. While this construction has provided the necessary rod rigidity, the substantial amounts of friction generated in the close clearance fit areas as the sections are telescoped in and out has resulted in excessive wear of the rod sections and has made the sections rather difficult to extend and retract with respect to one another. The large area of close clearance fit has also increased the expense of the rods.

Reference may be made to U.S. Pat. Nos. 2,980,456 and 3,103,375 describing telescoping poles generally in the field of this invention.

Among the several objects of this invention may be noted the provision of an improved telescoping rod which is rigid and stable when fully extended; the provision of such a rod which is easy to extend and collapse; the provision of such a rod which is dielectric, enabling it to be safely used around electric power lines and the like; the provision of such a rod which is pleasing in appearance and relatively inexpensive to manufacture; and the provision of such a rod which is durable in use.

Generally, an extensible and retractable rod of this invention comprises an outer tubular section and an inner section of substantially constant outside diameter telescopically received in the outer section for extension and retraction relative thereto. The outer section has a first internal shoulder spaced from but relatively close to one end of the section, and a second internal shoulder spaced substantially farther away from said one end, said outer section being dimensioned to have a first inside diameter between said one end of the section and the first shoulder, a second inside diameter greater than the first between said first and second shoulders, and a third inside diameter greater than the second between the second shoulder and the other end of the section. The first inside diameter of the outer section is dimensioned for a relatively close clearance fit between the sections, and the second inside diameter of the outer section is dimensioned for a relatively loose clearance fit between the sections. The inner section has stop means at one end thereof engageable with the second shoulder of the outer section for limiting extension of the two sections relative to one another. Means is provided for releasably locking the inner section in an extended position relative to the outer section, with the relatively close clearance fit between the sections rigidly holding the sections in generally coaxial alignment.

FIG. 1 is an elevation of a two-section extensible and retractable rod of the present invention, the upper section being shown extended with respect to the lower section;

FIG. 2 is an enlarged sectional view of a portion of FIG. 1 showing a spring detent for locking the upper section in extended position;

FIG. 3 is a horizontal section taken on line 3--3 of FIG. 2;

FIG. 4 is an enlarged sectional view of a portion of FIG. 1 showing a spring detent for securing a plug in the end of the lower section; and

FIG. 5 is an enlarged sectional view of a portion of FIG. 1, showing the upper section retracted inside the lower section.

Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

Referring now to the drawings, a measuring rod of the present invention, designated in its entirety by the reference numeral 1, is shown as comprising a plurality of cylindrical, substantially concentric tubular sections of the same length but progressively smaller in size, telescopically assembled for extension and retraction relative to one another. By way of example, two tubes 3,5 have been shown in the drawings. However it will be understood that more tubular sections may be used. The outside diameter of each section is substantially constant.

In accordance with this invention, the construction of the rod is such that when fully extended the two sections 3,5 are stably held in coaxial alignment. More specifically, the outer (or base) section 3 has two internal shoulders adjacent its upper end, which is open to receive the inner section 5 therein (see FIGS. 2 and 5). The first shoulder, designated 7, is spaced from but relatively close to the upper end of section 3, while the second shoulder, designated 9, is spaced farther away below the first shoulder. Section 3 has a substantially constant first inside diameter D-1 between the upper end of the section and the upper shoulder 7, a second substantially constant inside diameter D-2 greater than the first D-1 between the upper shoulder 7 and the lower shoulder 9, and a third substantially constant inside diameter D-3 between the lower shoulder and the lower end of the rod. Diameter D-1 is sized for a close clearance fit between the sections and D-2 for a relatively loose clearance fit between the sections, an annular gap 11 thus being formed between the sections in the area between the upper and lower internal shoulders 7, 9 of the base section 3.

The lower ends of the tubular sections 3,5 are closed by plugs, the plug in the largest diameter section 3 being designated 13 and the plug in the upper section 5 being designated 15. The latter plug is formed with an integral peripheral flange 17 at its bottom extending radially outwardly beyond the outer surface of the section. The outside diameter of flange 17 is less than diameter D-3 of the base section but greater than diameter D-2 for engagement of the flange with the lower internal shoulder 9 of the base section, flange 17 thus constituting stop means for limiting extension of the two sections relative to one another. It is preferable that the diameter of flange 17 be only slightly less than diameter D-3 for ensuring a close fit of the flange at its periphery inside the larger section. Flange 17 also has a plurality (e.g., two) of notches 19 therein, the purpose of which will appear hereinafter. Three pins, each designated 21, also serve to secure the plug 15 in position inside the lower end of section 5.

Indicated generally at 23 in FIG. 2 is means for releasably locking the upper section 5 in an extended position relative to the base section 3. This means comprises an opening 25 in the base section between the first and second internal shoulders 7,9, and a detent pin 27 (constituting detent means) mounted in a diametrical bore 29 in plug 15 in the upper section 5 for radial movement between a retracted position (FIG. 5) in which the sections are extensible and retractable relative to one another, and an extended position (FIG. 2) in which it projects through an opening 31 in the upper section and thence through the opening 25 in the base section for locking the upper section in extended position with respect to the base section. Means 23 also includes a coil compression spring 33 inside the plug bore 29 for biasing the detent pin 27 toward its extended position. The pin is formed for engagement with an internal shoulder 35 in the plug bore for restricting the outward (rightward as viewed in FIG. 2) movement of the pin.

To lock the upper section 5 in extended position with respect to the outer base section 3, section 5 is pulled upwardly until flange 17 engages the lower internal shoulder 9 of section 3, and then twisted until openings 25 and 31 are in registry, whereupon detent pin 27 springs through the opening 25 in the outer section for locking the sections together. When in this position, the upper section is held in rigid coaxial alignment with respect to the base section by means of its close clearance fit with the base section in the area between the upper end of the base section and the upper internal shoulder 7 of that section. The fact that the flange 17 of plug 15 in the upper section has a close fit inside the base section also assists in ensuring rod rigidity. On the other hand, the fact that there is a loose clearance fit between the sections in the area between internal shoulders 7 and 9 results in a reduction in the amount of friction generated as the sections 3,5 are extended and retracted relative to one another, thereby making the sections easier to telescope in and out and reducing the wear on the sections. This loose clearance fit in this area also avoids binding of the sections as they are extended with respect to one other. The reduced wall thickness of each section in the area between the internal shoulders 7 and 9 as compared to the area between the upper end of the section and the first shoulder also decreases the amount of material (e.g., fiberglass) required to make the section, with a consequent decrease in the cost of making the rod.

As shown best in FIG. 4, the plug 13 in the lower end of the largest diameter (base) section 3 is secured in place by means comprising an opening 37 in the section adjacent its lower end and a button 39 mounted in a bore 41 extending diametrically through plug 13 for movement in the radial direction with respect to the base section between a retracted position (not shown) in which the plug is removable from the section and an extended position (FIG. 4) in which the button extends through the opening 37 in the base section for securing the plug in position. The button is urged toward its extended position by a coil compression spring 43 in bore 41 reacting at one end against the wall of the base section and at its other end against the button, the latter of which is formed for engagement with an internal shoulder 45 in bore 41 for restricting the outward (rightward as viewed in FIG. 4) movement of the button in bore 41. A relatively long locking screw (or screw member) 47 may be threaded axially through button 39 and bore 41 for engagement with the wall of the base section to lock the button in its extended position. A second smaller screw 49 is also provided to assist in securing the base plug 13 in place.

When the rod of the present invention is collapsed from its fully extended position, the closed lower end of the upper section 5 moves from a position adjacent the upper end of the base section 3 (FIG. 2) to a position in which it is closely adjacent the closed lower end of the base section (FIG. 5). As the upper section is retracted into the lower section, air trapped between the closed ends of the sections is vented through the notches 19 in flange 17 into the annular space 11 between the sections and thence to atmosphere. The rush of air through this space 11 serves to blow any dirt and grit out from between the rod sections. This reduces abrasion of the rod sections as they are extended and retracted.

In view of the above, it will be seen that the several objects of the invention are achieved and other advantageous results attained.

As various changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.