Material or article handling – Vertically swinging load support – Grab
Patent
1984-06-19
1986-12-02
Spar, Robert J.
Material or article handling
Vertically swinging load support
Grab
901 15, 901 23, 901 29, 901 26, B66C 100
Patent
active
046261656
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a wrist mechanism of an industrial robot and, more particularly, to a wrist mechanism with plural degrees of freedom having built-in differential units and facilitating compensation of the dragging drift of the wrist mechanism.
BACKGROUND ART
An industrial robot is designed to hold a robot hand on the free end of the wrist thereof and is constituted for various robot actions, such as gripping a workpiece with the robot hand, transporting a workpiece between a plurality of positions, and assembling motions. In order to carry out these robot actions, the arm joined to the robot body, the wrist joined to the free end of the arm, and the hand held by the wrist, each have a certain degree of freedom, to enable movement and positional changes of the robot hand within a space for the desired robot actions. Accordingly, the wrist joined to the free end of the robot arm has a mechanism generally of two or three degrees of freedom. When the wrist mechanism has plural degrees of freedom, particularly when the wrist comprises internal differential units, the turning motion of the external mechanism is liable to cause fundamentally unnecessary movements, generally known as "dragging drift", of the wrist. In general, the dragging drift of the wrist is compensated by the correcting action of the driving source of the wrist mechanism, until the robot hand holding part of the wrist is located at a desired position in a desired attitude.
DISCLOSURE OF THE INVENTION
Accordingly, it is an object of the present invention to provide a wrist mechanism of an industrial robot having built-in differential units and plural degrees of freedom, and facilitating compensation of the dragging drift of the wrist.
The present invention provides a wrist mechanism of an industrial robot comprising an outer wrist provided on the free end of the robot arm; an inner wrist pivotally supported on bearings within the outer wrist and adapted to be driven by a driving force transmitted through the robot arm for pivotal movement; a robot hand holding part journaled onto the inner wrist and adapted to be turned by a rotative force applied thereto by an external unit; one set of driving and driven gears provided within the inner wrist to transmit the rotative force to the robot hand holding part; and a reduction gear provided within the inner wrist to transmit the rotative force at a reduced revolving rate to the driving gear of the set of driving and driven gears; in which, as mentioned above, providing the reduction gear within the inner wrist restricts the dragging drift within a small degree proportional to the reduction ratio, whereby the compensating action by the wrist driving source is facilitated. Particularly, employment of a known Harmonic Drive mechanism (registered trade mark), and a reduction gear of a compact construction and high reduction ratio, as the reduction gear will avoid any increase in the size of the wrist even if the reduction means is formed within the wrist mechanism.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an exemplary articulated industrial robot equipped with a wrist mechanism according to the present invention, showing the external construction thereof; and
FIG. 2 is a longitudinal sectional view taken on the line A--A in FIG. 1, showing the constitution of the essential sections of a wrist mechanism according to the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring to FIG. 1, there is shown an industrial robot having a robot body 10 mounted on a swivel pedestal 12 for swivel motion in the directions indicated by the double-headed arrow "I". The robot body 10 is fixed to the swivel pedestal 12 with bolts or the like. A robot upper arm 16 is joined pivotally at the tail end thereof to the upper end of the robot body 10, for swing motion about an axis C.sub.1 in the directions indicated by double-headed arrow "II". A robot forearm 20 is joined pivotally to the upper end 18 of the robot upper arm 16, for up-down swin
REFERENCES:
patent: 3826383 (1974-07-01), Richter
patent: 4431366 (1984-02-01), Inaba et al.
patent: 4548097 (1985-10-01), Zimmer
Inagaki Shigemi
Ito Susumu
Nakashima Seiichiro
Dayoan D. Glenn
Fanuc Ltd
Spar Robert J.
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