Elbow joint of an industrial robot

An elbow joint of an industrial robot comprises a first arm part which is yoke-formed at the joint and an end of a second arm part located between the yokes. On the sides of the end of the second arm part which face the respective yokes, bearing seats are provided in which shaft journals are journalled. The shaft journals are connected together by a pull rod, which extends through the end and the shaft journals, and are received in, and extend through, through-holes in the respective yokes. The shaft journals are fixed to the yokes by means of nuts threaded onto the accessible part of the shaft journals on the opposite side of the respective yokes.

BACKGROUND OF THE INVENTION 
An industrial robot normally comprises an arm having several degrees of 
freedom of movement, the free end of the arm supporting a hand in the form 
of a gripper or the like. The arm often comprises a first arm part and a 
second arm part interconnected by an elbow joint. This invention relates 
to an elbow joint of an industrial robot. 
In industrial robots it is a requirement that the robot arm can repeat, 
with great accuracy, programmed patterns of movement. If changes-even 
small changes-in the programmed final position of the hand occur as a 
result of replacement or repair of parts in, for example, the arm, this 
may require reprogramming of the robot, which is very time-consuming in 
the case of complicated patterns of movement of the robot arm. 
SUMMARY OF THE INVENTION 
The present invention relates to a device by means of which an arm part in 
the robot arm, after replacement, can be adjusted with satisfactory 
tolerance to the same position as earlier, thus avoiding reprogramming. 
According to the invention, the robot arm comprises a first arm part, which 
is yoke-shaped at the elbow joint, and an end of a second arm part, which 
end is fitted between the yokes. The invention is characterized in that 
the end of the second arm part, on the sides thereof facing the respective 
yokes, is provided with bearing seats in which sleeve-shaped shaft 
journals are journalled. The shaft journals are rotatably fixed to the end 
by means of a pull rod extending through the end. The shaft journals are 
fitted into through-holes in the respective yoke and fixed there by nuts 
screw-threadedly connected onto the accessible part of the shaft journals 
on the opposite side of the respective yoke. 
By loosening one nut and tighening the other, the connected shaft journals 
in the yoke holes are displaced in one or the other direction and the 
first arm part is laterally moved with respect to the second arm part. In 
this way, a lateral adjusting of up to about two millimeters can be 
achieved, which is sufficient to avoid reprogramming after relacement of, 
for example, an arm part.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIGS. 1 and 2 show a known industrial robot which can utilize the elbow 
joint according to the invention to connect a first arm part 1, which 
provides yokes 3 at one end thereof (see FIG. 3), with the end 4 of a 
second arm part 2, which end 4 can fit between the yokes 3. As can be seen 
in FIG. 3, which shows a preferred embodiment of elbow joint according to 
the present invention, the end 4 is provided with bearing seats 5 in which 
shaft journals 6 are journalled by means of conical bearings 7. A pull rod 
8 having threaded ends 8a, 8b passes through the end 4 and the shaft 
journals 6. Nuts 9, provided with suitable locking washers, are threadedly 
connected to the opposite ends of the pull rod 8 and, by adjusting these 
nuts 9, the shaft journals 6 can be pressed against the bearing seats 5 
and the backlash between the journals 6 and the seats 5 can be adjusted. 
The yokes 3 are provided with through-holes for receiving the shaft 
journals 6 which project outwardly of the yokes 3. These outwardly 
projecting parts of the shaft journals 6 are threaded (see 6a) and 
provided with nuts 10 and are protected by covers 11. By tightening the 
nut 10 on one side of the elbow joint and loosening the corresponding nut 
10 on the other side of the elbow joint, the arm part 2 can be laterally 
moved in relation to the arm part 1, whereby the maximally required 
lateral movement can be estimated at approximately two millimeters. 
The device is very practical since it permits simple assembly and 
dismantling of the elbow joint. To replace an arm part, for example, the 
covers 11 are first removed followed by the nuts 9 and 10. The pull rod 8 
is also removed. The shaft journals 6, which do not rotate but are fitted 
in their respective holes in the yoke 3 by wringing fit, are removed by 
means of a withdrawing tool (not shown) which is threadedly connected to 
an internal thread in the through-holes of the shaft journals 6 through 
which the pull rod 8 projects in the assembled joint. Thereafter, the arm 
parts 1 and 2 are separated. 
Assembly is performed in the opposite sequence. The arm part 2 is fitted in 
between the yokes 3. The shaft journals 6 are inserted through the holes 
in the yokes 3 and are connected together by the pull rod 8, the nuts 9 
being tightened to ensure that a suitable backlash is obtained in the 
elbow joint. Thereafter, the nuts 10 are screwed on and the arm part 2 is 
adjusted in relation to the arm part 1. Finally, the covers 11 are fitted 
on. 
Various modifications can be made to the illustrated arrangement and all 
such modifications falling within the scope of the following claims 
represent aspects of this invention.