Harmonic Drive Systems Inc.

Harminic Drive Systems Inc.

Xin Yue Zhang

Yoshihide Kiyosawa

Noboru Takizawa

Jun Handa

Keiji Ueura

Toshimi Yamagishi

An externally toothed gear of a dual-type strain wave gearing is provided with first and second external teeth having different teeth numbers, and a gap formed between these teeth as a cutter clearance area for tooth cutters. The maximum width Lof the gap is 0.1 to 0.3 times the width L of the externally toothed gear. The depth from the tooth top land of the first external teeth to the deepest part of the gap is 0.9 to 1.3 times the depth of the first external teeth, and the depth from the tooth top land of the second external teeth to the deepest part of the gap is 0.9 to 1.3 times the depth of the second external teeth. The tooth bottom fatigue strength of the externally toothed gear provided with differing numbers of first and second external teeth is increased.

Dual-type strain wave gearing

In a silk hat-shaped external gear for a strain wave gearing, t(A)&#x3e;t(C)&#x3e;t(D)&#x3e;t(B) is satisfied, where the thicknesses of the inner circumferential end (A), the middle part (B) and the outer circumferential end (C) of the diaphragm body portion of a diaphragm are t(A), t(B) and t(C), and where the thickness of the barrel-side end part (D) of the curved portion of the diaphragm is t(D). With reference to the thickness of the middle part (B), the thickness of the inner circumferential end (A) of the diaphragm is set so as to be thicker than conventional silk hat-shaped external gears. It is possible to realize an externally toothed gear capable of preventing diaphragm rupture due to thrust force at high load torque and having high fatigue strength.

Externally toothed gear for strain wave gearing

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 Lof 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&#xd7;10&#x3c;t/PCD&#x3c;6.3&#xd7;10where 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.

Flat strain wave gearing

An externally toothed gear of a dual-type strain wave gearing is provided with first and second external teeth having different teeth numbers, and is flexed into an ellipsoidal shape by a wave generator. When t() represents the tooth bottom rim wall thickness of the first external teeth, and t() represents the tooth bottom rim wall thickness of the second external teeth, the ratio of t()/t() is set to a value satisfying 0.5&#x3e;t()/t()&#x3c;1.5. Accordingly, a dual-type strain wave gearing can be achieved with which the first and second external teeth having different teeth numbers can be suitably flexed to form excellent meshing states with respective internally toothed gears.

An externally toothed gear of a dual-type strain wave gearing is provided with first and second external teeth having different teeth numbers. The first and second external teeth are flexed by a wave generator by the same flexing amount, into an ellipsoidal shape. The average pressure angle of main-tooth-surface sections of tooth profiles of the first external teeth having a low teeth number is less acute than the average pressure angle of main-tooth-surface sections of tooth profiles of the second external teeth having a high teeth number. Accordingly, a dual-type strain wave gearing can be achieved with which the first and second external teeth having different teeth numbers can be suitably flexed to form excellent meshing states with respective internally toothed gears.

A wave generator () for a flat-type strain wave gearing () has a first elliptical outer circumferential surface (S) of a first wave generator portion (S) defined by a first elliptical curve (C), and a second elliptical outer circumferential surface (D) of a second wave generator section (D) defined by a second elliptical curve (C). Compared to using a wave generator for which the contour is defined by a single elliptical curve, differences between the ball load distribution of the first wave generator portion (S) and the ball load distribution of the second wave generator portion (D) can be suppressed, both ball load distributions can be equalized, and the equivalent ball load can be reduced; therefore, an increase in the lifespan of the wave generator bearing can be achieved.

Wave generator and strain wave gearing

The flexible bearing of the wave generator for a wave gear device is a deep-groove ball bearing in which an outer race and an inner race form an annular flexible bearing ring capable of bending in a radial direction. A ball diameter Da is set to be 5 to 15% greater than that of each model of the currently available product. Dimensions of orbital plane radii ro, ri of the inner and outer races are set so that the ratio ro/Da of the orbital plane radius ro of the inner race and the ball diameter Da, as well as the ratio ri/Da of the orbital plane radius ri of the outer race and the ball diameter Da, are both in the range of 0.51 to 0.52. With this configuration, the service life of the flexible bearing can be extended.

Wave generator for wave gear device

In a cup-type or 'silk hat'-type wave gear device (), the rim thickness t of the flexible externally toothed gear () thereof satisfies the relations (0.5237Ln(R)&#x2212;1.32)d&#x2266;t&#x2266;(0.8728Ln(R)&#x2212;2.2)d if the reduction ratio R of the wave gear device is less than 80, and (1.5499Ln(R)&#x2212;5.8099)d&#x2266;t&#x2266;(2.5832Ln(R)&#x2212;9.6832)d if the reduction ratio R is equal to or greater than 80, where d is the radial deflection, measured at the position of the major axis of the neutral circle of the rim, in a state in which the flexible externally toothed gear is bent into an elliptical shape. The effective face width L of the external teeth () is a value within the range of 21 to 30% of the pitch circle diameter. Such settings make it possible to increase the bottom fatigue strength of the flexible externally toothed gear and improve the load capacity of the wave gear device ().

Wave gear device

A flat type wave gear device is realized having a much improved load capacity. When d is an amount of radial flexing at a major axis location of a rim neutral circle of the flexible external gear of a flat type wave gear device flexed into an elliptical shape and t is the rim thickness of the flexible external gear, then(0.5237 Ln()&#x2212;1.32)&#x2266;(0.8728 Ln()&#x2212;2.2)when the reduction ratio R of the wave gear device is less than 80, and(1.5499 Ln()&#x2212;5.8099)&#x2266;(2.5832 Ln()&#x2212;9.6832)when the reduction ratio R of the wave gear device is 80 or more. Using this setting makes it possible to increase the tooth root fatigue limit strength of the flexible external gear, thereby making it possible to improve the load capacity of the flexible external gear.

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Azumino, Japan

Xin Yue Zhang