Worm Gear Mechanism

This invention relates to mechanical gearing arrangements and particularly to worm and worm gear drives.

Worm and worm gear arrangements have long been universally known as advantageous drive mechanisms for unilaterally transferring power and motion from one rotating gear element to another. Very simply, the mechanism comprises a worm and a worm gear, the worm having a helical thread which meshes with the teeth of the worm gear, the axes of the two elements lying at substantially right angles. Conventionally, rotation of the worm causes a corresponding rotation of the gear, neither of the elements being movable along its axis. Uses of the worm and worm gear mechanism have been as old and as broad as the mechanical arts themselves and are too numerous to list. One field in which the mechanism has proved exceptionally useful and with which the worm and worm gear arrangement of the invention is particularly concerned is that of measurement, adjustment, positioning, and the like. Because of the high degree of precision required, very fine-pitch worms and gears are there employed for the transmission of uniform angular rotation rather than power. In each of such prior art arrangements, the rotating worm transmits only a corresponding rotation to the worm gear, the latter being conventionally fixed against lateral movement along its axis as mentioned. An objective of the present invention is a new and novel worm and worm gear mechanism of general utility in which the rotation of the worm imparts to the worm gear not only a corresponding rotation but also a precise displacement of the worm gear along its axis.

The foregoing and other objectives are realized in one illustrative worm and worm gear mechanism according to the invention comprising a worm having a helical thread formed thereon mounted for rotation about its longitudinal axis and a worm gear having teeth meshing with the helical thread of the worm. The axes of the gear and worm lie at substantially right angles, the worm being mounted so as to prevent lateral movement along its axis. According to one feature of the mechanism, the worm gear is formed substantially cylindrically shaped and is mounted for rotation in a cylindrical hole having helical threads formed on its inner surface. The latter threads mesh with corresponding helical threads cut across the worm gear teeth. When the worm is rotated, it conventionally causes a corresponding rotation of the cylindrical worm gear. As a departure from conventional worm and gear mechanisms, however, the rotation of the cylindrical worm gear also causes its movement along its axis much as a rotated screw in a threaded hole.

The organization and operation of a worm and worm gear mechanism according to the invention together with its features will be better understood from a consideration of the detailed description of one illustrative embodiment thereof which follows when taken into conjunction with the accompanying drawing in which:

FIG. 1 is a perspective, partial sectional view of a worm and worm gear mechanism according to the invention;

FIG. 2 is a cross-sectional view of the mechanism of FIG. 1 taken along the line 2--2; and

FIG. 3 is a cross-sectional view of the mechanism of FIG. 1 taken along the line 3--3.

An illustrative mechanism according to the invention is shown in FIGS. 1 and 2 as comprising a worm 10 having a helical thread 11 formed thereon and a cylindrical worm gear 12, the longitudinal axes of elements 10 and 12 lying at substantially right angles. Worm 10 is freely fitted for rotation in a cylindrical hole 13 formed in a mounting member 14. Worm 10 is prevented from lateral movement along its axis by an annular collar 15 rotatably fitted in a circular recess 16 formed on a face of member 14 and a retaining plate 17. Plate 17, which may be affixed to member 14 in any convenient manner, has a hole at 18 to rotatably admit a shaft extension 19 of worm 10. Although extension 19 is shown unterminated, it will be appreciated that in practice extension 19 may be fitted with a manually operated finger wheel or may be connected to a machine drive, for example, as dictated only by the context in which the mechanism is put to use.

Cylindrical worm gear 12 has a plurality of spur teeth 20 formed on its surface parallel to its longitudinal axis, which teeth are dimensioned and spaced to mesh with helical thread 11 of worm 10. Gear 12 is rotatably fitted in a cylindrical hole 21 formed in member 14 transverse to hole 13 and has cut across its teeth 20 a helical thread 22 (FIG. 3). The latter thread is dimensioned and spaced to mesh with a corresponding thread 23 circularly formed on the inner surface of hole 21. Except for the engagement of threads 22 and 23, gear 12 is unrestrained in movement along its longitudinal axis as may be required for a particular use.

In the operation of the mechanism of the invention, the rotation of worm 10 conventionally causes a corresponding rotation of cylindrical worm gear 12 as the result of the engagement of helical thread 11 and spur teeth 20. A rotation of worm 10 in the direction, for example, as indicated by arrow 24 in FIG. 1 causes gear 12 to rotate in the direction indicated by arrow 25. As a departure from the operation of known worm and worm gear mechanisms, the rotation as described of cylindrical worm gear 12 also causes its movement along its longitudinal axis in the direction as indicated by arrow 26 as the result of the engagement of helical threads 22 and 23. Although not shown in the drawing, cylindrical worm gear 12 may advantageously be adapted to control devices and other mechanisms requiring extremely fine adjustments and high precision. In practice, for example, a mechanism having a cylindrical worm gear of 0.3125 inch outside diameter having 32 teeth each having side walls at 60 degrees, a face of 0.0039 inch and a depth of 0.0192 inch and further having 40 helical threads per inch, was driven along its axis precisely 0.0008 inch by one rotation of a worm of 0.190 inch outside diameter having 32 helical threads per inch.

What has been described is considered to be only one illustrative worm and worm gear mechanism according to the principles of the invention and it is to be understood that various and numerous other arrangements may be devised by one skilled in the art without departing from the spirit and scope of the invention as defined only by the accompanying claims.