A gear device includes an internal gear, an external gear, and a wave generator. The external gear includes a cylinder section, a diaphragm, and a boss section. The diaphragm includes a first coupling section, a second coupling section, and a diaphragm main body. A ratio of the length from one opening end of the cylinder section to the surface of the diaphragm on the opposite side of the opening end in a rotation axis direction to the length from the inner circumferential surface of the boss section coupled to the second coupling section to the outer circumferential surface of the cylinder section in the radial direction is 1.0 or more and 5.0 or less, and t(C)≥t(A), where t(A) represents the thickness of the inner circumferential end of the diaphragm and t(C) represents the thickness of the outer circumferential end.

A robot includes a base, a first arm that is provided to be rotatable with respect to the base, and a gear device that transmits a driving force from the base to the first arm. The gear device has a flexible gear. The flexible gear has a cylindrical body portion and a bottom portion that is connected to one end portion of the body portion. The bottom portion has a metal flow radially extending from a center side to an outer peripheral side of the bottom portion.

A gear device includes an internal gear, an external gear having flexibility, a wave generator, a cross roller bearing, and a first seal and a second seal. The external gear includes a cylindrical body section including a first end portion, with which the wave generator is in contact, and a second end portion on the opposite side of the first end portion, external teeth provided on the outer circumferential surface of the first end portion, an annular diaphragm section provided on the outer side of the second end portion, and a boss section provided on the outer side of the diaphragm section. The first seal is sandwiched between the boss section and an outer ring of the cross roller bearing. The second seal includes a proximal end fixed to the outer ring and a distal end in contact with the outer circumferential surface of an inner ring.

The addendum tooth profile of the inner teeth and outer teeth of a strain wave gearing is stipulated by a first and second similar curve obtained from the curve segment from an inflection point to a low point in a movement trajectory when the meshing of both teeth is approximated by rack meshing. The addendum tooth profile of the inner teeth is stipulated by a curve generated at the inner teeth in the process of the addendum profile of the outer teeth moving from the inflection point to the apex of the movement trajectory. The addendum tooth profile of the outer teeth is stipulated by a curve generated at the outer teeth when the addendum profile of the inner teeth moves from the inflection point to the apex. The addendum profile of the outer teeth makes double contact with the addendum profile and dedendum profile of the inner teeth.

An elastic transmission element is used in a strain wave gear. Such strain wave gears are also referred to as Harmonic Drives. The elastic transmission element is also referred to as a flexspline. Outer toothing is formed on the elastic transmission element. Furthermore, at least one strain gauge for measuring a mechanical strain of the elastic transmission element is arranged on the elastic transmission element. The at least one strain gauge is formed as a coating directly on a metallic surface of the elastic transmission element.

In the cup-shaped externally toothed gear, the outside end face profile of the diaphragm is defined by a first concave circular arc having a first radius, a second concave circular arc that has a second radius and is smoothly connected to the first concave circular arc, an inclined straight line that is smoothly connected to the second concave circular arc and is inclined toward an inside straight line with respect to the center axis line, the inside straight line defining the outside profile of the diaphragm. The second radius is larger than the first radius, and the thickness of the diaphragm is gradually decreased from the side of the boss to the side of the cylindrical body. The stress concentration in the boss-side joint portion of the diaphragm can be relieved, whereby enhancing fatigue strength of the flexible externally toothed gear.

A relieving portion is formed between a first external tooth portion and a second external tooth portion in the external teeth of a flexible externally toothed gear of a flat strain wave gearing. The length L1 of the relieving portion in the tooth trace direction is within the range of 0.1 to 0.5 of the tooth width L of the external teeth. The maximum relieving amount t from the tooth top land of an external tooth in the relieving portion is 3.3×10.sup.−4<t/PCD<6.3×10.sup.−4 where the PCT is defined as the pitch circle diameter of the external teeth. The tooth face load distribution of the external tooth in the tooth trace direction can be equalized, and a flat strain wave gearing having a high transmitted-load capacity can be achieved.

A fusion gear reducer includes a first-stage gear reduction unit and a second-stage gear reduction unit both in a housing. The first-stage gear reduction unit includes a sun gear, a planet gears support, planet gears spaced around the sun gear and meshed therewith, and a ring gear around the planet gears and meshed therewith. The second-stage gear reduction unit includes spaced rollers arranged as a circle, roller grooves, wells formed on an inner surface of the housing, and a cam surface formed on an outer surface of the ring gear so that the ring gear is output of the first-stage gear reduction unit and input of the second-stage gear reduction unit. The roller grooves are disposed on outer surfaces of the planet gears so that the planet gears are output of the second-stage gear reduction unit. The simplified fusion gear reducer solves the problem of bulkiness of gear reducer.

A flex spline torque transfer device using force applied at multiple positions for each area of contact between the flex spline and outer ring. The positions of at which force is applied may be outside the areas of contact. This design may also be used in conjunction with a magnetic method of applying force to the flex spline, mechanical force acting as a constraint to prevent the flex spline from fully disengaging from the outer ring.

A wave generator of a strain wave gearing has a rigid plug provided with an elliptical outer peripheral surface, and a roller bearing. The outer peripheral surface of the plug is provided with a major-axis-side outer-peripheral surface portion formed at a major axis position L1, and a minor-axis-side outer-peripheral surface portion formed at a minor axis position L2. The major-axis-side outer-peripheral surface portion is a tapered surface that is tapered along a center axis line, and the minor-axis-side outer-peripheral surface portion is an inverted tapered surface that is tapered in the opposite direction. An externally toothed gear can be supported and flexed into an elliptical shape without partial contact by using the wave generator in which the roller bearing is used.