Positioner

Abstract: A positioner includes a conductive rotary table (1) on which a work-piece is placed, a conductive rotary shaft (2) holding the rotary table (1), a conductive collector ring (3) fixed concentrically with the rotary shaft (2), and a carbon brush (4) contacting one face of the collector ring (3). The carbon brush (4) has radial grooves (4a) formed on its contact face with the collector ring (3), and can be split into plural sections. Abrasive powder produced by friction between the brush (4) and collector ring (3) can be discharged through the grooves (4a) to outside of the brash, which eliminates sparks between these two elements, of which durability is thus substantially improved. Further, since the carbon brush (4) is split into plural sections, it can be replaced with ease without dismounting the rotary shaft (2), which reduces maintenance problems.

Description: 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 of peripherals supporting robots, 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 collector ring is finished flat and contacts carbon brush 24. Carbon brush 24 shapes 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, 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 in which a carbon brush is disposed on outer rim of a collector ring with keeping contact with the collector ring: a smaller body in a radial direction, a flat contact face between the collector ring and carbon brush can be processed with ease and its flatness can be easily maintained. The positioner having this structure has been thus widely used. However, this conventional positioner has still 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 23 and carbon brush 24 unstable. This unstable contact increases a voltage drop on the contact face, which makes welding current unstable. As a result, a defective welding occurs. In an extreme case, the contact face would spark, which can damage significantly both the contact faces of 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 a cumbersome work such as dismounting the rotary shaft 22 in order to remove these elements. US-A-4 831 234 discloses an automatic welding turntable for welding together the cut-apart halves of a reconditioned torque converter. A motor rotates the torque converter while wire is fed to the stinger of a wire-fed arc welder. The turntable is disposed on a conductive shaft, and a brush is maintained in electrical contact with the shaft to ground the torque converter through the shaft. US-A-4 420 199 discloses a rotary joint cable connector comprising at least two electrically conductive slip ring members with freely rotatable contact surfaces which are mutually frictionally engaged with one another. The slip ring members are made of a suitable electrically conductive material such as copper, and include a plurality of radially extending grooves. US-A-4 805 829 discloses a positioning device having a rotatable and tiltable work table for placing components to be worked on. The device has a frame and a support mounted on the frame having bearings for rotatably supporting a housing. The work table is also rotatably mounted relative to the housing, and may be rotated using a hydraulic motor. 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. The present invention provides a postioner as set out in claim 1. In one preferred mode of the present invention, a postioner 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. Brief Description of the Drawings Fig. 1 shows a construction of a positioner in accordance with an exemplary embodiment of the present invention. Fig. 2A is a plan view illustrating a carbon brush of the present invention. Fig. 2B is a side view illustrating the carbon brush of the present invention. Fig. 3 illustrates a construction of a welding system that employs a robot and a positioner. Fig. 4 shows a construction of a conventional positioner. Description of the Preferred Embodiment An exemplary embodiment of the present invention is described hereinafter with reference to the accompanying drawings. Fig. 1 illustrates an exemplary embodiment of the present invention. Fig. 2A and Fig. 2B show a carbon brush employed in a positioner of the present invention. In Fig. 1, rotary table 1 made from conductive material, on which a work-piece is placed with jig 13. At the center of rotary table 1, conductive rotary shaft 2 is mounted by press-fitted or other methods. Conductive collector ring 3 is fixed to the other end of shaft 2, and a lower face of collector ring is finished flat and contacts carbon brush 4. Carbon brush 4 shapes as a ring, and is urged by spring 5 upwardly so that carbon brush 4 keeps contacting with collector ring 3 with a given contact-pressure, welding current thus runs across carbon brush 4 and collector ring 3. Carbon brush 4 is placed concentrically with rotary shaft 2 in such a manner that it does not directly contact shaft 2. Pins 6 fix carbon brush at its lower face in order to avoid being rotated by frictional force created at the contact face with collector ring 3. Pins 6 are inserted into holes punched on insulator plate 8 disposed at lower section of outer housing 7. Because pins 6 are inserted slidably into the holes, carbon brush 4 can keep the given contact pressure against collector ring 3 by spring 5, and also carbon brush 4 is prevented from being rotated by the rotation of collector ring 3. Motor 9 drives rotary table 1 and has first pulley 10 on its spin shaft. Rotary shaft 2 has second pulley 11. First and second pulleys 10 and 11 are coupled with timing belt 12 so that the spin of motor 9 is transferred to second pulley 11 via first pulley 10 and timing belt 12, and shaft 2 is thus rotated. The embodiment in Fig. 1 employs pulleys and a timing belt as a mechanism of transferring the driving power of motor 9; however, other another mechanism comprises e.g. a plurality of gears, can effect the same result. Jig 13 mounted on rotary table 1 is usually coupled with hoses, e.g. through which compressed air travels for clamping the work-piece, as well as cables from a sensor detecting the work-piece. These hoses and cables 14 run through hollow shaft 2 before being coupled to jig 13. Cable 15 coupled to carbon brush 4 forms a path for welding current. Carbon brush 4 in accordance with this exemplary embodiment is detailed hereinafter. Fig. 2A and Fig. 2B illustrate an example of a carbon brush. Fig. 2A is a plan view of carbon brush 4 split into two sections. Radial grooves 4a are formed on an upper face of carbon brush 4. Fig. 2B is a side view of carbon brush 4. Since an end face of groove 4a opens to outer rim, Fig. 2B shows the end face of grooves 4a. Abrasive powder produced by the abrasion between carbon brush 4 and collector ring 3 is thus collected in the grooves 4a formed on the upper face of carbon brush 4, and travels grooves 4a to outside. The powder is thus discharged. This construction leaves no chances for the abrasive powder to remain between collector ring 3 and carbon brush 4. The contact between the collector ring 3 and carbon brush 4 thus becomes stable, and neither an abnormal-voltage-drop nor spark occurs therebetween. Collector ring 3 and carbon-brush 4 thus become much more durable. Because carbon brush 4 is split into two sections, it can be removed just by pulling out pins 6, which eliminates a cumbersome work, i.e. dismounting the positioner per se including pulling out the rotary shaft 2. Carbon brush 4 can be thus restored through a reverse procedure with ease. In this embodiment, radial grooves are formed on the upper face of carbon brush 4; however, in addition to the radial grooves, arc-shaped grooves 4b as shown in broken lines are formed concentrically with shaft 2 on the upper face, thereby increasing the effect. The concentric grooves 4b can be formed in a multi-layered structure, e.g. double or three-layer. The cross section of the groove 4a shows a rectangular; however, it can be U-shaped or V-shaped. Fig. 3 illustrates a welding system employing a robot and the positioner of the present invention. In Fig. 3, work-piece 17 (in this case, the work-piece is to be welded) is placed on rotary table 1 of positioner 16. Welding torch 19 is mounted on a tip of robot 18, and coupled to an output terminal of welding power supply 20. A polarity of welding power supply 20 depends on a welding method to be practiced. Cable 15 pulled out from positioner 16 is coupled to an output terminal of another polarity of the welding power supply. Cable 15 is electrically coupled to rotary table 1 via carbon brush 4, collector ring 3 and rotary shaft 2. Electric arc is generated between the work-piece 17 held on table 1 and welding torch 19, thereby welding the work-piece. As the exemplary embodiment of the positioner of the present invention discussed above proves that the abrasive powder produced by the friction between the carbon brush and collector ring is collected in the grooves formed on the upper face of carbon brush, and is discharged through the grooves to outside. The positioner of the present invention thus leaves no chances for the abrasive powder to remain between the collector ring and carbon brush. The contact resistance between the collector ring and carbon brush, therefore, becomes stable, so that stable welding can be practiced continuously. Since no spark is generated between the collector ring and carbon brush, both the elements become more durable. Since the carbon brush is split into two sections, it can be removed and restored with ease, and this structure leaves no needs to disassemble the positioner including dismounting the rotary shaft 2. The construction of the positioner thus reduces maintenance problems. The present invention provides an excellent and durable positioner that practices stable welding and reduces maintenance problems.

Claims: A positioner comprising: (a) a conductive rotary table (1) on which a work-piece is disposed; (b) a conductive rotary shaft (2) holding said rotary table; (c) a collector ring (3) fixed to said rotary shaft: and (d) a brush (4) contacting said collector ring, wherein said brush is a disc-like brush comprising carbon, and said collector ring (3) is a disc-like collector ring, and a flat face of said brush (4) contacts with a flat face of said collector ring (3), characterised in that radial grooves (4a) which open to outside of said brush (4) and a groove (4b) which is concentric with said rotary shaft (2) are formed on the flat face of said brush (4) contacting with the flat face of said collector ring (3). A positioner as claimed in claim 1, further comprising: (e) driving means (9, 10, 11, 12) for driving said rotary shaft (2); and (f) an outer housing (7) for accommodating said collector ring(3) and said brush (4). A positioner as claimed in Claim 1 or 2, wherein said brush (4) is split into at least two sections.

Inventors: TAKAHASHI WATARU, TAKAHASHI, WATARU
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1999
Main classification: B23K37
IPC codes: B23K9, B23K37, H02K7, B23Q3