GB2135230A - Apparatus for rotationally driving an arc welding robot - Google Patents

Abstract

The robot includes a rotary body 20 rotatably supported on a stationary body 12, a robot arm connected at one end to the rotary body and provided at its free end with a welding torch which is movable to a desired position, and a rotary drive motor 16 which is easy to service and which drives the rotary body. The stationary body is provided on an outer periphery thereof with a row of teeth 24, while the motor, which is secured to the outer roll of the rotary body, has a drive gear 26 which is engaged with the teeth. Backlash is prevented by a drive gear train 28 and a backlash control gear train 30 through which the motor gear and the teeth are engaged. <IMAGE>

Description

SPECIFICATION Apparatus for rotationally driving an arc welding robot Background of the invention The present invention relates to an articulated arc welding robot.

Arc welding is widely used in various fields of manufacture since it provides a joint having excellent mechanical properties between the base metal and the material welded thereto. A robot is often used for welding in order to provide the welded joint with uniform mechanical properties and to save labor required for the welding work. More specifically, an articulated arc welding robot is used, which is a robot having a welding torch which is movable in all directions from one welding point to another.

A conventional articulated arc welding robot is constructed as shown in Figure 1. The robot includes a stationary body 12 secured to a foundation 10 by bolts 14 and an upwardly projecting cylindrical wall.

A rotary drive motor 16 is mounted at the center of the stationary body 12. The mounting of the motor 16 within the stationary body 12 makes the apparatus compact.

The motor 16 has a drive shaft connected to a speed reducer 18 which reduces the rate of rotation of the motor 16 to a desired speed. The reducer 18 has an output shaft connected to a rotary body 20.

The rotary body 20 is rotatably supported on the stationary body 12 by a bearing member 21 so that it may rotate about the stationary body 12 in the direction in which the motor 16 rotates.

An articulated robot arm (not shown) is connected to the rotary body 20. This arm carries a welding torch at its free end. The robot arm is also provided with a number of articulating motors each adapted to drive a corresponding articulating shaft. Drive cables (not shown) extending from a cable joint 22 at the bottom of the stationary body 12 are connected to the 16 and the articulating motors.

A control cable extending from a control circuit is connected to the cable joint 22, and electric current is supplied to the motors through the drive cables to thus move the rotary body 20 and the robot arm so that the welding torch is moved to a desired welding position.

The location of the motor 16 within the stationary body 16, however, makes it troublesome to repair the motor 16 since it is necessary to remove the motor from the stationary body 12 to effect any repairs. Thus, repair of the motor 16 requires a long time, and hence compels the welding line to stay out of operation for a long time.

In view of the drawbacks of the prior art as hereinabove described, it is an object of this invention to provide an apparatus for rotationally driving an arc welding robot, which includes a rotary drive motor which is easy to repair and which can drive the robot with a high degree of accuracy.

Summary of the invention The above and other objects are attained by an apparatus for driving an arc welding robot including a rotary body supported rotatably on a stationary body, a robot arm connected to the rotary body and provided at its free end with a welding torch which is movable to a desired position, and a motor for rotatably driving the rotary body, the motor being rotatable to rotate the rotary body and thereby the robot arm in a desired direction, characterized in that the stationary body has an outer periphery provided with a row of peripherally extending fixed teeth, the rotary body has an outer wall to which the motor is secured, an idler gear is provided between a motor gear connected to the motor and the fixed row of teeth, the motor gear, idler gear and fixed row of teeth define a drive gear train for driving the rotary body, a backlash control gear is provided between the motor gear and the fixed row of teeth, and the motor gear, backlash control gear and row of fixed teeth define a backlash control gear train which is separate from the drive gear train.

Brief description of the drawing Figure 1 is a fragmentary longitudinal sectional view of a conventional apparatus for rotationally driving an arc welding robot; Figure 2 is a longitudinal sectional view of an arc welding robot driving apparatus embodying the invention; Figure 3 is a fragmentary sectional view taken along a line A-A in Figure 2 showing a drive gear train and a backlash control gear train; Figure 4 is a sectional view taken along a line B-B in Figure 3; Figure 5 is a view illustrating the positions of a pin-receiving hole in a torsion shaft and a pinreceiving hole in a control gear shaft; Figure 6 is a view illustrating the torsion shaft elastically twisted from its position shown in Figure 5 to enable the alignment of the two holes to receive a pin therein to secure the torsion shaft in its twisted position to the control gear shaft; and Figure 7 is a schematic view of a speed reducer employed in the apparatus of Figure 2.

Description of the preferred embodiments A preferred embodiment of the invention will now be described with reference to the drawings.

An apparatus for the rotational driving of an arc welding robot embodying the present invention is shown in longitudinal section in Figure 2. The inventive apparatus includes a number of elements which substantially duplicate their counterparts in the conventional apparatus hereinbefore described, and hence those elements are designated by the same reference numerals as those used in Figure 1, and specific descriptions of those elements are omitted.

The apparatus of the invention is characterized by the location of a rotary drive motor on the outer side of a rotary body, which facilitates the repair of the motor, and the provision of a drive gear train and a backlash control gear train which ensure a high degree of accuracy in the rotational driving of the rotary body by the motor.

According to this embodiment, a stationary body 12 has a base portion 13 on an outer peripheral surface of which is provided a row of peripherally extending fixed teeth 24. A cylindrical portion 11 extends upwardly from the base portion 10.

The rotary body 20 has a cylindrical outer wall surrounding the cylindrical portion 11 of the stationary body 12. The motor 16 is secured to a supporting portion 25 of the rotary body 20 at the lower end of the latter. The motor 16 has an output shaft connected to a speed reducer 18 which is, according to this embodiment, of the harmonic drive component type including, as shown in Figure 7, a wave generator 51, a circularspline 52 and a flexible spline 53. The reducer 18 has an output shaft provided with a motor gear 26. A drive gear train and a backlash control gear train are provided between the teeth 24 on the stationary body 12 and the motor gear 26.

When the motor 16 rotates, the motor gear 26 rotates about its own axis and along the teeth 24.

Thus, the motor 16 rotates the rotary body 20 while moving around the stationary body 12.

If the motor gear 26 were directly engaged with the teeth 24, the rotation of the motor gear 26 might not be transmitted accurately to the rotary body 20 due to backlash which might develop between the teeth 24 and the gear 26 as a result of manufacturing error, wear or the like. This would make it difficult to drive the rotary body 20 with a high degree of accuracy.

In order to avoid any such problem, the drive gear train for driving the rotary body includes an idler gear 28 disposed between the motor gear 26 and the teeth 24, and a backlash control gear train which includes a backlash control gear 30 disposed between the motor gear 26 and the teeth 24. The backlash control gear train defines a gear train which is separate from the drive gear train.

The idler gear 28 includes an assembly of a first idler gear 28a and a second idler gear 28b as shown in Figure 4, although it is also possible to employ a single gear. If the first and second idler gears are positioned slightly spaced apart from each other, it is possible to avoid the backlash which might otherwise develop between the teeth 24 and the motor gear 26 due to manufacturing error. It is thus possible to avoid any reduction in the accuracy of rotation of the rotary body, even if manufacturing error may exist in those gears.

The backlash control gear 30 likewise includes a combination of a first control gear 30a and a second control gear 30b. One of the backlash control gears, namely, the second control gear 30b in the present embodiment, has a torsion shaft 32, eleatically twisted to a certain extent, secured to a shaft 34 of the other control gear when the motor gear 26 is operationally engaged with the teeth 24. The torsion shaft 32 may be made of chromium-molybdenum steel.

The torsion shaft 32 has a pin-receiving hole 36 at its upper end, while the shaft 34 of the first control gear 30a has a pin-receiving hole 38 extending at an angle to the hole 36, as shown in Figures 5 and 6. By elastically twisting the torsion shaft 32 to a certain extent, the hole 36 is aligned with the hole 38. A pin 40 is fitted in the aligned holes 36 and 38 to secure the torsion shaft 32 in its elastically twisted position to the control gear shaft 34. The elastically twisted torsion shaft 32 thus produces a force urging it to return to its untwisted position. This force creates a displacement between the first and second control gears 30a and 30b, and this displacement fully absorbs any backlash between the motor gear 26 and the teeth 24.

The force urging the torsion shaft 32 to return to its untwisted position should be made larger than the load on the motor gear 26. This presents the load on the motor from giving rise to the problem of backlash between the motor gear and the teeth 24.

According to the invention, the motor for driving the rotary body is mounted on the outer wall of the rotary body. The motor is, therefore, very easy to repair, as hereinabove described.

Furthermore, according to the invention, it is possible to avoid completely any error in the rotation of the rotary body due to backlash between the motor gear and the fixed teeth on the stationary body, thereby providing a high degree of accuracy in the rotation of the rotary body due to the provision of the fixed teeth on the outer periphery of the stationary body, the provision of the idler gear between the motor gear and the fixed teeth to define the drive gear train for driving the rotary body, and the provision of the backlash control gear between the motor gear and the fixed teeth to define the backlash control gear train, which is separate from the drive gear train.

Although the embodiment hereinabove described employs a combination of two idler gears in the drive gear train for driving the rotary body and a combination of two backlash control gears in the backlash control gear train, it is also possible to provide a geartrain composed of additional combinations of idler gears and a backlash control gear train composed of a corresponding number of combinations of backlash control gears.

Claims (7)

1. In an apparatus for rotationally driving an arc welding robot of a type having a rotary body supported rotatably on a stationary body, a robot arm connected at one end to said rotary body and provided at a free end with a welding torch which is movable to a desired position, and a motor for rotationally driving said rotary body, said motor being rotatable to rotate said rotary body and thereby said robot arm in a desired direction,the improvement wherein said stationary body has an outer periphery provided with a row of peripherally extending fixed teeth, said rotary body has an outer wall to which said motor is secured, and said motor is connected to a motor gear which is engaged with said teeth.

2. The apparatus as set forth in claim 1, further comprising a drive gear train and a backlash control gear train through which said motor gear and said teeth are engaged with each other.

3. The apparatus as set forth in claim 1, wherein said stationary body comprises a base portion on which said teeth are provided and a cylindrical portion extending upwardly from said base portion.

4. The apparatus as set forth in claim 3, wherein said rotary body comprises a cylindrical portion surrounding said cylindrical portion of said stationary body and supported rotatably about said stationary body by a bearing assembly, and a motor supporting portion extending radially outwardly from said cylindrical portion to support said motor.

5. The apparatus as set forth in claim 2, wherein said backlash control gear train comprises a combination of a first control gear and a second control gear, each having a shaft and facing one another, one of said control gears having a torsion shaft elastically twisted and secured to a shaft of the other control gear.

6. The apparatus as set forth in claim 5, wherein the shaft of said first control gear has a pin-receiving hole at one end thereof, the shaft of said second control gear surrounding said shaft of said first control gear and defining said torsion shaft, said torsion shaft having at an end thereof a pin-receiving hole extending at an angle to said pin-receiving hole of said shaft of said first control gear, said pinreceiving hole of said torsion shaft being, when said torsion shaft is twisted, alignable with said pinreceiving hole of said shaft of said first control gear to enable said two pin-receiving holes to receive a pin therein.

7. An apparatus for rotationally driving an arc welding robot substantially as hereinbefore described with reference to Figures 2 to 7 of the accompanying drawings.