Harmonic drive gear assembly with asymmetrical wave generator and associated flexspline

• US 20070101820A1
• Filed: 11/04/2005
• Published: 05/10/2007
• Est. Priority Date: 11/04/2005
• Status: Active Grant

• Current Assignee: Northrop Grumman Systems Corporation (Northrop Grumman Corporation)
• Original Assignee: Northrop Grumman Corporation
• Inventors: Bulatowicz, Michael
• Granted Patent: US 7,552,664 B2
• Time in Patent Office: Days
• US Class Current: 74/640
• CPC Class Codes: F16H 2049/003 Features of the flexsplines therefor
• CPC Class Codes: F16H 49/001 Wave gearings, e.g. harmonic drive transmissions harmonic drives specially adapted for positioning programme-controlled manipulators B25J9/1025
• CPC Class Codes: Y10T 74/19 Gearing

Abstract

A wave generator has a circular spline, a flexspline inside the circular spline and a plug inside the flex spline. The plug is asymmetrical and is preferably formed to comprise a semi-elliptical first portion and a semi-cylindrical second portion. The diameter of the semi-cylindrical portion coincides with the major axis of the semi-elliptical portion. Gear teeth on the circular spline and on the flex spline are meshed in only a first zone and unmeshed in a second zone. The flexspline in the harmonic drive gear assembly according to the present invention preferably has only one tooth fewer than the circular spline so that the circular spline rotates through and arc defined by one gear tooth for each complete revolution of the flexspline.

Claims

1. A harmonic drive gear assembly comprising:

a circular spline formed as a hollow cylinder having a first plurality of inner gear teeth formed to extend around an inner circumferential portion of the hollow cylinder;

a flexspline formed as a thin-walled hollow cylinder having an outer circumference smaller than that of the inner circumferential portion of the circular spline, the flexspline having a plurality of outer gear teeth extending around an outer circumferential portion of the thin walled hollow cylinder, the flexspline being formed to be placed inside the circular spline such that a portion of the inner gear teeth and portion of the outer gear teeth are meshed; and

a wave generator formed for placement within the flexspline, the wave generator including a plug having a first side region having a first selected curvature and a second side region having a second selected curvature, and a bearing assembly placed around a peripheral portion of the plug such that the bearing assembly extends around both the first and second side regions and conforms to the first and second curvatures, the wave generator being arranged to fit closely within the flexspline such that flexspline has first and second side regions that have the first and second selected curvatures of the first and second side regions of the plug, respectively, the gear teeth of the flexspline and the circular spline being meshed in a first angular zone of the circular spline and being completely disengaged in a second angular zone of the circular spline.

2. The harmonic drive gear assembly of claim 1 wherein the first side region is formed to have a semi-ellipsoidal configuration having a semi-elliptical end having a major axis of a selected length and the second side region is formed to have a semi-cylindrical configuration having a semicircular end having a diameter that coincides with the major axis of the semi-elliptical end of the first side region.

3. The harmonic drive gear assembly of claim 2 wherein the circular spline has a plurality of N inner gear teeth and the flexspline has N-1 external gear teeth such that the circular spline rotates through an angle defined by one of the inner gear teeth for each complete rotation of the flexspline,

4. The harmonic drive gear assembly of claim 1 wherein the first and second side regions of the plug are asymmetrical with respect to one another.

5. The harmonic drive gear assembly of claim 1 wherein the plug has a lengthwise cavity formed therein such that the center of gravity of the plug is on its axis of rotation.