Electric heating – Metal heating – Work holders
Reexamination Certificate
1999-06-29
2001-05-29
Shaw, Clifford C. (Department: 1725)
Electric heating
Metal heating
Work holders
C219S125110
Reexamination Certificate
active
06239408
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a positioner used for rotating or changing the orientation of a work-piece to be processed such as being welded or cut.
BACKGROUND OF THE INVENTION
In recent years, techniques of industrial robots have progressed rapidly, and consequently, a positioner, one example of robot supporting peripherals, has drawn attention from the market.
A conventional positioner is described with reference to FIG.
4
.
FIG. 4
illustrates a construction of the conventional positioner exclusively used for welding. In
FIG. 4
, rotary table
21
made from conductive material receives jig
32
thereon and rotates jig
32
. A work-piece to be processed is positioned with jig
32
. Conductive pipe
22
is press-fitted as a rotary shaft into the center of rotary table
21
. Conductive collector ring
23
is fixed to a section near to the other end of pipe
22
, and a lower face of a collector ring is finished flat and contacts carbon brush
24
. Carbon brush
24
is shaped as a ring, and is urged by spring
25
upwardly so that carbon brush
24
keeps contacting with collector ring
23
with a given contact-pressure, and welding current thus runs across carbon brush
24
and collector ring
23
. Carbon brush
24
is placed concentrically with rotary shaft
22
in such a manner that it does not directly contact shaft
22
. Pins
26
fix carbon brush
24
at its lower face in order to avoid being rotated by frictional force created at the contact face with collector ring
23
. Carbon brush
24
is coupled to a welding-power-supply disposed outside with cable
34
. Motor
27
drives rotary table
21
and has first pulley
28
on its spin shaft. Rotary shaft
22
has second pulley
29
. First and second pulleys
28
and
29
are coupled with timing belt
30
so that the spin of motor
27
is transferred to second pulley
29
via first pulley
28
and timing belt
30
, and shaft
22
is thus rotated. Jig
32
mounted on rotary table
21
is usually coupled with hoses, e.g. through which compressed air travels for clamping the work-piece, as well as coupled with cables from a sensor detecting the work-piece. These hoses and cables
33
run through hollow-shaft
22
before being coupled to the work-piece. Outer housing
31
has windows through which a user can monitor an inside operation.
The positioner constructed as discussed above, has the following advantages over a positioner having a carbon brush disposed on an outer rim of a collector that is in contact with the collector ring: the body is smaller in a radial direction, a flat contact face between the collector ring and carbon brush can be easily processed, and its flatness can be easily maintained. The positioner having this structure has been thus widely used.
However, this conventional positioner still has problems, i.e. carbon brush
24
wears out because of abrasion at the contact face with collector ring
23
due to the rotation of rotary table
21
. The remaining abrasive powder on the contact face sometimes makes the contact between collector ring
3
and carbon brush
24
unstable. This unstable contact increases a voltage drop on the contact face, which makes welding current unstable. As a result, defective welding occurs. In an extreme case, the contact face would spark, which can damage significantly both the contact faces of the collector ring
23
and carbon brush
24
. Therefore, the abrasive powder on carbon brush
24
must be removed, and the damaged contact faces must be repaired, so that additional maintenance cost is required.
Further, the maintenance work, such as replacing the worn-out carbon brush
24
, and repairing the contact faces of collector ring
23
and carbon brush
24
, requires cumbersome work such as dismounting the rotary shaft
22
in order to remove these elements.
SUMMARY OF THE INVENTION
The present invention addresses the problems discussed above, and aims to provide a positioner which realizes stable welding current by preventing the influence of abrasive powder as well as simplifies the maintenance work of replacing the carbon brush.
In one preferred mode of the present invention, a positioner comprises the following elements:
(a) a conductive rotary table on which a work-piece is placed;
(b) a conductive rotary shaft holding the rotary table;
(c) a conductive collector ring fixed concentrically to the rotary shaft;
(d) a carbon brush contacting a face of the collector ring;
(e) a motor for driving the rotary shaft;
(f) a first pulley disposed on an output shaft of the motor;
(g) a second pulley disposed on the rotary shaft which is coupled to the first pulley with a timing belt so that the rotary shaft can synchronously rotate with the first pulley; and
(h) an outer housing for accommodating the rotary shaft driving section including the collector ring and carbon brush.
Radial grooves are formed on the contact face of the carbon brush with the collector ring, and the carbon brush can be split into plural sections.
The positioner of the present invention allows abrasive powders on the contact faces to be discharged through the radial grooves formed on the contact face of the carbon brush. The contact between the collector ring and carbon brush thus becomes stable, and neither an abnormal-voltage-drop nor spark occur therebetween. The collector ring and carbon brush thus become much more durable. Further, because the carbon brush can be split into plural sections, it can be replaced without dismounting the rotary shaft of the positioner.
REFERENCES:
patent: 4577089 (1986-03-01), Olson et al.
patent: 4831234 (1989-05-01), Myers
patent: 5813875 (1998-09-01), Ishikawa et al.
Matsushita Electric - Industrial Co., Ltd.
Shaw Clifford C.
Wenderoth , Lind & Ponack, L.L.P.
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