Material or article handling – Vertically swinging load support – Grab
Patent
1985-08-19
1988-06-14
Spar, Robert J.
Material or article handling
Vertically swinging load support
Grab
901 21, 901 26, 901 29, B66C 100
Patent
active
047508582
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
The present invention relates to a wrist assembly for an industrial robot, and more particularly, to a two-axes wrist assembly of the chain-drive system.
2. Background Art
Generally, a two-axes wrist assembly provided at the free end of the robot arm of an industrial robot comprises a base wrist unit joined to the free end of the robot arm so as to be rotatable relative to the free end of the robot arm about a first axis intersecting the longitudinal axis of the robot arm at right angles, and a fore wrist unit joined to the base wrist unit so as to be rotatable relative to the base wrist unit about a second axis intersecting the first axis at right angles. The shaft-drive system and the chain-drive system have been well-known driving systems for driving the base wrist unit and the fore wrist unit of a wrist assembly of the above-mentioned type. Ordinarily, the shaft-drive system requires many power transmitting parts to transmit the rotation of two power transmitting shafts extended along the longitudinal direction of the robot arm through bevel gears to the base wrist unit and the fore wrist unit, which disadvantageously increases the total weight of the robot arm and the wrist assembly.
On the other hand, the chain-drive system is able to couple sprockets engaging chains directly with the base wrist unit, and hence only a reduced number of power transmitting parts are necessary and the robot arm and the wrist assembly can be formed in lightweight constructions.
Accordingly, chain-drive wrist assemblies have widely been employed recently in industrial robots.
A conventional ordinary chain-driven two-axes wrist assembly is shown in FIGS. 1 and 2. Referring to FIGS. 1 and 2, the wrist assembly of this type has a base wrist unit 2 which is provided, at the opposite sides thereof, with shafts 2a and 2b. The base wrist unit 2 is supported by the shafts 2a and 2b so as to be rotatable relative to the robot arm 1 about a first axis .beta. intersecting the longitudinal axis of the robot arm 1 at right angles. A fore wrist unit 3 is supported on the base wrist unit 2 so as to be rotatable about an axis .alpha. intersecting the first axis .beta. at right angles. A first sprocket 4 disposed on one side of the base wrist unit 2. A first chain 5 extended along one side of the robot arm 1 is wrapped round the sprocket 4. The other shaft 2b of the base wrist unit 2 is a hollow shaft. A shaft 6 supported coaxially with and within the hollow shaft 2b extends through the shaft 2b and is connected through a pair of bevel gears 7 and 8 to the fore wrist unit 3. A second sprocket 9 disposed on the other side of the base wrist unit 2 is attached to the shaft 6. A second chain 10 extended along the other side of the robot arm 1 is wrapped round the sprocket 9.
The wrist assembly of this constitution requires the chains 5 and 10 to be extended along the opposite sides of the robot arm 1 so as to correspond to the sprockets 4 and 9 disposed on the opposite sides of the base wrist unit 2, respectively. Therefore, the thickness of the robot arm needs to be increased in order to accommodate the chains 5 and 10 therein, and hence the sizes of the components for supporting the robot arm 1 need to be enlarged. To make the robot arm 1 capable of motion about the longitudinal axis thereof, in particular, it is a general practice to provide the robot arm 1 with a gear in the form of a flange and to transmit the driving force of a motor to the gear. In such a case, the enlargement of the thickness of the robot arm 1 entails the enlargement of the diameter of the gear.
Furthermore, since the base wrist unit 2 of the wrist assembly of the above-mentioned constitution is supported on the opposite sides thereof on the free end of the robot arm 1, the range of motion of the base wrist unit 2 is liable to be restricted by the robot arm 1, which results in the degradation of the kinematic functions of the wrist assembly.
DISCLOSURE OF THE INVENTION
It is an object of the present invention to provide a compact an
REFERENCES:
patent: 3922930 (1975-12-01), Fletcher et al.
patent: 4030617 (1977-06-01), Richter
patent: 4417845 (1983-11-01), Burton
patent: 4496278 (1985-01-01), Kaise
patent: 4557662 (1985-12-01), Terauchi et al.
Nakashima Seiichiro
Terada Akihiro
Toyoda Kenichi
Doyle Jennifer
Fanuc Ltd.
Spar Robert J.
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