GB2134074A

GB2134074A - Articulated robot

Info

Publication number: GB2134074A
Application number: GB08401820A
Authority: GB
Inventors: Hirotoshi Yasuoka
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1983-01-24
Filing date: 1984-01-24
Publication date: 1984-08-08
Also published as: FR2539662A1; JPS59134690A; FR2539662B1; GB2134074B; GB8401820D0

Abstract

An articulated robot includes a generally cylindrical stationary unit 12 having an outer peripheral surface formed with a circumferential gear 30, and having a cable joint 22 provided adjacent to its bottom to which control cables 24 extending from a control circuit are connected. A generally cylindrical rotary unit 20 is supported rotatably about the stationary unit 12. A rotary unit driving motor 16 is mounted on the rotary unit 20 and the motor is connected to a motor gear 32 meshing with the circumferential gear 30 on the stationary unit 12. When the motor gear 32 is driven by the motor 16 it rotates the rotary unit 20 about the stationary unit 12. An articulated robot arm composed of a plurality of arm elements is connected to the rotary unit 20, and carries at its free end a working member which is movable to a selected working position. The working member may, for example, be a welding torch. A plurality of articulating motors are provided for driving the arm elements, respectively. A plurality of cables extend from the cable joint 22 to the rotary unit 20 along the axis of rotation of the rotary unit to supply electric current to the motors. <IMAGE>

Description

SPECIFICATION Articulated robot Background of the Invention 1. Field of the Invention This invention relates to an articulated robot which is particularly useful for arc welding.

2. Description of the PriorArt Arc welding is widely used for various production purposes, since it provides a joint having excellent mechanical properties between the base metal and the metal to be welded thereto. Recently, robots have become more often used for welding in order to obtain uniform mechanical properties in all welded joints and to minimize the labor required for the welding work.

Articulated arc welding robots have been developed and include welding torches which are movable in substantially all directions from and to points which require welding.

One example of an articulated arc welding robot is essentially shown in Figure 1. It includes a stationary unit 12 secured to a foundation 10 by bolts 14, and having an upwardly extending cylindrical wall. A motor 1 6 is mounted in the center of the stationary unit 12. The accommodation of the motor 16 in the hollow interior of the stationary unit 12 renders the entire robot compact in construction. The motor 1 6 has an output shaft connected to a speed reducer 1 8 which reduces the rotation of the motor 1 6 to a desired speed.The speed reducer 1 8 has an output shaft connected to a rotary unit 20 in order to rotate the rotary unit 20 about the stationary unit 12 in a desired direction, which is the same direction of rotation as that of the motor 1 6. An articulated robot arm (not shown) is connected to the rotary unit 20, and carries a welding torch (not shown) at its free end. The arm is also provided with a plurality of articulated arm elements (not shown), respectively.

A cable joint 22 is provided at the bottom of the stationary unit 12, and a plurality of cables 24 extend from the cable joint 22 to the motor 16, for rotating the rotary unit 20, and to the articulating motors for supplying electric current thereto. The stationary unit 12 has an annular base portion 27 projecting radially from the lower end of its upstanding cylindrical wall. The cables 24 are held by the base portion 27, extend along the cylindrical wall of the stationary unit 12, and are held by the top wall 26 of the rotary unit 20. The top wall 26 has a plurality of holes 26a, equally spaced apart (for example, four holes as shown in Figure 2), through which the cables 24 extend.If control cables extending from a control circuit are connected to the cable joint 22, electric current is supplied to the motors through the cables 24 so that the rotary unit 20 and the robot arm may be rotated or moved as required to move the welding torch from and to points which require welding.

The fact that the cables 24 are held by both the stationary and rotary units 1 2 and 20, however, presents a serious disadvantage. If the rotary unit 20 is rotated by a particular angle which is, for example, shown at 0 in Figure 2, the cables 24 which are held at point A by the top wall 26 of the rotary unit 20 are rotated to point B, while the lower portions of the cables are immovably held by the stationary unit 12. The cables 24 are, therefore, twisted, stretched and experience high tension, resulting in the fatigue and early breakage of the cable cores. The frequent breakage of the cable cores impairs the reliability of the robot. In order to avoid this problem, it is necessary to limit the angle of rotation of the rotary unit 20, resulting in a limited range of robot operation.

Summary of the Invention It is, therefore, an object of this invention to provide an articulated robot in which a rotary unit is rotatable without subjecting cables to any tension resulting in their breakage.

It is another object of this invention to provide an articulated robot having an improved reliability.

It is still another object of this invention to provide a robot which is operable over a wide range.

These objects are attained by an articulated robot comprising a rotary unit supported rotatably on a stationary unit, an articulated robot arm supported on the rotary unit and carrying at its free end a working member which is movable from one working position to another, a motor for rotating the rotary unit, a plurality of articulating motors for moving a plurality of elements of the arm, and a plurality of cables for supplying electric current to the motor for rotating the rotary unit and to the articulating motors through a cable joint provided on the stationary unit, characterized in that the stationary unit is provided with a circumferential gear around its outer periphery, the motor for rotating the rotary unit being mounted on the rotary unit and being operationally connected to the gear on the stationary unit to rotate itself and the rotary unit about the stationary unit, the cables extending from the cable joint to the motors along the axis of rotation of the rotary unit.

According to this invention, the motor for rotating the rotary unit is rotatable about the stationary unit, and the cables lie in the axis of rotation of the rotary unit. These features prevent any undue tension from occurring in the cables when the rotary unit is rotated, thereby preventing the early breakage of the cable cores and ensuring the reliability of the robot over a long period of time. The rotary unit is rotatable through a greater angle, and the robot has, therefore, a wider range of effective operation.

Brief Description of the Drawings Figure 1 is a fragmentary side elevational view, partly in section, of a conventional articulated arc welding robot; Figure 2 is a sectional view taken along the line Il-Il of Figure 1 and showing cables twisted when the rotary unit has been rotated; Figure 3 is a side elevational view, partly in section, of an articulated arc welding robot embodying this invention; Figure 4 is a sectional view taken along the line IV-lV of Figure 3; and Figure 5 is a view similar to Figure 4, but showing the rotary unit which has been rotated by a particular angle from its position shown in Figure 4.

Detailed Description of the Invention An articulated arc welding robot embodying this invention is generally shown in Figure 3. It includes a number of structural elements or features which are substantially equivalent to their counterparts in the conventional robot shown in Figure 1. The equivalent parts, are therefore, designated by the same reference numerals used in Figure 1, and will not be described in detail.

In the robot of this invention, a generally cylindrical stationary unit 1 2 has a radially outwardly projecting flange 28 which is formed with a circumferential gear 30 along its outer periphery. A motor 1 6 for rotating a rotary unit 20 and a speed reducer 18, connected to an output shaft of the motor 1 6, are mounted on the outer periphery of the rotary unit 20. The speed reducer 1 8 has an output shaft provided with a motor gear 32 which meshes with the gear 30 on the stationary unit 12. The rotary unit 20 is rotatably supported on the stationary unit 12 by bearings 34. If the motor 1 6 is rotated, the gear 32 is rotated about its own axis and also along the gear 30 encircling the stationary unit 12. It, therefore, follows that the motor 1 6 itself and the rotary unit 20 rotate about the stationary unit 12.

According to another salient feature of this invention, all the cables 24 extending from a cable joint 22 are collected so as to extend along the axis of rotation of the rotary unit 20. If the rotary unit 20 is, for example, rotated by a particular angle 0 from its position shown in Figure 4 to the position shown in Figure 5, resulting in the displacement of a particular cable from point A to point B, no undue tension occurs in the cable 24 since the motor 1 6 to which the cable 24 is connected rotates with the rotary unit 20 about the stationary unit 12. Therefore, the rotation of the rotary unit 20 does not cause any breakage of the cores of the cables 24.

Claims

1. An articulated robot comprising: a generally cylindrical stationary unit having an outer peripheral surface formed with a circumferential gear, and a cable joint to which control cables extending from a control circuit are connected; a generally cylindrical rotary unit supported rotatably about said stationary unit; a rotary unit driving motor mounted on said rotary unit having an output shaft to which is operably connected a motor gear, wherein said motor gear meshes with said circumferential gear, said motor gear being driven by said motor to rotate said rotary unit about said stationary unit; an articulated robot arm connected at one end to said rotary unit and carrying at its free end a working member which is movable to a selected working position, said arm being composed of a plurality of arm elements;; a plurality of articulating motors each adapted to drive one of said arm elements; and a plurality of cables extending from said cable joint to said rotary unit driving motor and said articulating motors through said stationary unit along the axis of rotation of said rotary unit to supply electric current to said motors.

2. An articulated robot as set forth in Claim 1, wherein said rotary unit driving motor is rotatable about said stationary unit with said rotary unit.

3. An articulated robot as set forth in Claim 2, wherein a speed reducer is provided between said output shaft of said rotary unit driving motor and said motor gear.

4. An articulated robot as set forth in Claim 3, further comprising bearing means on said stationary unit for supplying said rotary unit.

5. An articulated robot as set forth in Claim 4, wherein said cables are held by said rotary unit at a point above said stationary unit.

6. An articulated robot as set forth in Claim 1, wherein said working member is a welding torch.

7. An articulated robot as set forth in Claim 1, wherein said working member is a clamping member.

8. An articulated robot substantially as hereinbefore described with reference to Figures 3, 4 and 5 of the accompanying drawings.