Conveying apparatus for coating line

In a coating line conveyor for an automobile body, in which the body is movable along a path and rotated on an axis parallel to the path, the article is stopped in its erect attitude without impact force. The article is supported so that the combined center of gravity of the article and its supports is located directly below the axis of rotation of the article when the article is erect. Rotation is stopped by removing rotating power from the article supports in response to a signal generated by a sensor when the article is in its erect condition. The article then rocks back and forth under its own inertia and rapidly approaches a stable erect condition by a naturally damped oscillating motion.

BRIEF SUMMARY OF THE INVENTION 
This invention relates to conveyors, and more particularly to improvements 
in a conveyor for carrying an article such as an automobile body along a 
coating line and rotating the article while the coating is baked and 
dried. 
In painting an article such as an automobile body on a coating line, it has 
been found desirable to apply a thick coat of paint in order to reduce the 
number of coats to be applied and to improve the smoothness of the coated 
surface. To prevent sagging of the thick coat of paint, drying and baking 
are effected as the painted article is rotated on a horizontal axis. This 
procedure produces a high quality coated surface. 
When the rotation of the painted article is interrupted or stopped, it is 
desirable to have the article situated in an erect attitude. In the case 
of an automobile body, the body should be stopped with the roof section up 
and with the bottom section down. 
A prior technique for effecting stopping of rotation of a painted article 
is disclosed in Laid-Open Japanese Patent Application No. 51168/1989. As 
shown in FIGS. 20 to 24 of that application, when an automotive body is in 
an erect attitude, a roller 67, at the upper end of a control rod 
assembly, enters a recess 61a of a cam 61 which is fixed on a shaft for 
rotating the automotive body. When a switch 69 (shown in FIG. 9), at a 
monitor position on the coating line, is manually actuated, control rod 62 
rises, a clutch 51 is disengaged, and roller 67 enters recess 61a, thereby 
stopping the automotive body when it reaches an erect condition as it 
rotates under its own inertia. In the Laid-Open Japanese Patent 
Application, a shock-absorbing spring 63 is built into the control rod 
assembly between roller 67 and the control rod 62 for the purpose of 
alleviating shock which occurs as the automotive body stops rotating. 
In the above-described prior art technique, as the automotive body, in 
rotation by virtue of its own inertia, is stopped by compression of the 
spring acting against the inertial force, it is difficult to eliminate 
impact force altogether. 
The principal object of this invention is t provide an article conveying 
and rotating mechanism with a simple and effective means for stopping 
rotation of the article without shock. Another object is to achieve rapid 
stoppage of rotation of the article. Still another object is to provide 
for stopping of rotation of the article without interrupting its forward 
motion. 
In accordance with the present invention, impact force is eliminated. The 
article is supported so that the combined center of gravity of the article 
and its supports is located directly below the axis of rotation of the 
article when the article is in its erect attitude. Rotation is stopped by 
removing rotating power from the article supports in response to a signal 
generated by a sensor when the article is in its erect condition. The 
article then rocks back and forth under its own inertia and rapidly 
approaches a stable erect condition by a naturally damped oscillating 
motion. 
More specifically, the conveying apparatus in accordance with the invention 
comprises: rail means; a carriage movable along and guided by said rail 
means, said carriage comprising front and rear upright columns and front 
and rear rotating shafts mounted respectively in said columns for rotation 
on a common axis substantially parallel to said rail means; support arm 
means on said shafts for supporting an article to be painted with the 
combined center of gravity of said article and said support arm means 
being directly below said axis when the article is in an erect attitude; 
conveyor chain means for moving said carriage along said rail means; means 
providing an endless chain for effecting rotating of said article; said 
conveyor chain means and said endless chain means being juxtaposed in 
parallel relationship to each other along said rail means and movable 
relative to each other at different speeds; sprocket means on said 
carriage engageable with said endless chain; means connecting one of said 
rotating shafts in driving relationship to said sprocket means; means for 
sensing when said article is in an erect attitude, said sensing means 
being mounted at a predetermined position along said rail means; and 
means, responsive to said sensing means, for effecting disengagement of 
said endless chain from said carriage sprocket when the article is in an 
erect attitude at a predetermined position in the path of said carriage; 
whereby the rotating force transmitted from said endless chain means to 
said article is removed when the article is substantially in its erect 
attitude and said article rapidly approaches a stable erect condition by 
rocking motions of diminishing magnitude without the application of impact 
forces. 
Further objects, details and advantages of the invention will be apparent 
from the following description, when read in conjunction with the drawings 
.

DETAILED DESCRIPTION 
As shown in FIG. 1, an automobile body B is conveyed, in the direction of 
arrow a, along a coating line, by a carriage 1 having a plurality of 
wheels W for running on rails R laid along the coating line. The carriage 
is also provided with a plurality of casters W' to allow the carriage to 
be moved about on a floor. Box-type upright columns 1A and 1B are provided 
at the front and rear ends of the carriage. In the top end section of 
these columns rotating shafts 2A and 2B are rotatably mounted on bearings 
on a common axis parallel to the direction of movement of the carriage 
along the rails W'. L-shaped rotating support arms 3A and 3B are mounted 
on the opposed end sections of the rotating shafts. Jigs 4A and 4B, for 
mounting and supporting the front and rear ends of automotive body B, are 
provided on the ends of the rotating support arms 3A and 3B respectively. 
A swinging pendulum-type weight lever 5 is suspended from the rear 
rotating support arm 3B. The support arms are arranged so that, when the 
automotive body B is in its erect attitude, i.e. with the roof up, the 
combined center of gravity of the automotive body B and the rotating 
support arms 3A and 3B is located directly below the axis of rotation. 
In a frame at the lower end of the rear upright column 1B, a cross shaft 6 
is rotatably mounted in bearings at a right angle to the direction of 
travel of the carriage on rails W'. A sprocket 7 is fixed to one end of 
this cross shaft. Sprocket 7 is engaged with an endless chain 8, which 
moves in the direction of the arrow b along the baking and drying section 
of the coating line. 
Carriage 1 is conveyed in the direction of the arrow c by pusher dogs P, 
mounted on a conveyor chain 9, and tiltable to engage lock plates 10 on 
the carriage. Conveyor chain 9 and endless chain 8 travel in opposite 
directions so that, when sprocket 7 is engaged with chain 8, the sprocket 
rotates. In an alternative embodiment, chains 8 and 9 can travel in the 
same direction, but at different speeds. In either case, the chains travel 
relative to each other. Accordingly, even if one of chains 8 and 9 fails 
to operate, the sprocket 7 is rotated as long as the other chain is 
operating. 
A bevel gear (not shown) on sprocket shaft 6 meshes with a mating bevel 
gear (not shown) mounted on the lower end of a vertical transmission shaft 
11 in the interior of the rear upright column 1B, and a third bevel gear 
(not shown) on the upper end of transmission shaft 11 meshes with a fourth 
bevel gear (not shown) on rotating shaft 2B. Shaft 2B therefore rotates to 
turn rotating support arm 3B. Automobile body B is rotated by arm 3B, and 
shaft 2A on front upright column 1A is rotated through body B, so that the 
body B and support arms 3A and 3B are rotated as a unit about the common 
axis of shafts 2A and 2B. 
As shown in FIG. 1, endless chain 8 extends over a sprocket 12 at the end 
of the baking and drying section of the coating line. From sprocket 12, 
the chain extends back over an intermediate sprocket 12A to a horizontally 
movable tension sprocket 12B. From sprocket 12B, chain 8 extends to a 
driving sprocket (not shown), which causes the chain to move in the 
direction of arrow b. 
Sprocket 12 can be raised and lowered. When sprocket 12 is lowered to the 
position indicated by broken line in FIG. 1, chain 8 inclines downward and 
disengages sprocket 7. When chain 8 disengages the sprocket, rotating 
power is removed from automotive body B, and body B gradually comes to 
rest in an erect attitude after rocking back and forth in a swinging 
motion about the common axis of shafts 2A and 2B. 
To minimize the time required for the body to come to a standstill, a 
sensor is used to issue a signal when the body is in, or close to, its 
erect position. In response to this signal, sprocket 12 is lowered to 
disengage chain 8 from the sprocket 7. Operation of the sensor will be 
explained by referring to FIGS. 1 to 3. At the end of the baking and 
drying section of the coating line, there are provided upper and lower 
sensors, each comprising a light beam generator and a photosensitive 
detector. The upper sensor S1 is a body sensor, which operates when its 
light beam is interrupted by the body B rotating on the carriage. While 
the body B is in its erect attitude, the beam of sensor S1 is interrupted. 
A lower sensor S2 is a bottom level sensor for sensing the level condition 
of the bottom surface of the body. When body B is erect, the light beam of 
sensor S2 passes immediately under the bottom of the body. Sensors S1 and 
S2 are enabled when a limit switch LS1 is activated by the carriage, and 
are disabled when a limit switch LS2 is activated. 
With the limit switch LS1 activated, the automotive body B advances, while 
rotating, into the effective zone of sensors S1 and S2, where, when two 
conditions are satisfied at the same time, that is, when the beam of the 
sensor S1 is interrupted by the body while the beam of the sensor S2 is 
not interrupted, a piston rod 13' of actuator cylinder 13 is extended. The 
forward end of piston rod 13' is connected to the upper end of a lever 
(not shown), which is connected at its lower end to a horizontal shaft 
rotatably mounted on a frame F. A toggle link 14 is connected between this 
horizontal shaft and the free end of a tilt lever 16 one end of which is 
pivotally connected by a pin 15 to frame F. The tilt lever 16 carries 
sprocket 12 around which endless chain 8 extends. When piston rod 13' 
extends, toggle link 14 folds, and tilt lever 16 tilts downward about pin 
15. Thus, sprocket 12 moves downward to move chain 8 away from the 
engagement with sprocket 7, interrupting the transmission of rotating 
power to the automobile body B. 
When the light beam of the body sensor S1 is interrupted while the light 
beam of sensor S2 is not interrupted, body B is in its erect position. 
When the body is erect, rotating power is removed, but the body continues 
to move past its erect position because of its inertia. Because the 
combined center of gravity of body B and support arms 3A and 3B is located 
below the axis of rotation of shafts 2A and 2B, the body will reverse 
direction and rock back and forth until it reaches a stable erect 
condition. Because rotating power is removed from the automobile body when 
it is substantially erect. the magnitude of the rocking motion of the body 
is small, and the time interval from the interruption of power until the 
body stops rocking is minimized. 
After the transmission of rotating power to body B is interrupted, body B 
is carried forward on carriage 1 while the rocking motion takes place. 
After sprocket 7 passes over sprocket 12, limit switch LS3 is actuated, 
and causes piston rod 13' to contract, moving the tilt lever 16 upward to 
return chain 8 to its upper position. When in its upper position, chain 8 
can continue to rotate the sprocket on the following carriage until the 
automobile body on that carriage reaches a location on the coating line at 
which its rotation is to be stopped and rotates to its erect attitude. 
Actuation of limit switch LS1 places sensors S1 and S2 in an operative 
state, while the limit switch LS2 holds sensors S1 and S2 in the 
inoperative state. Limit switch LS1 is not actuated until the carriage 
reaches the end of the baking and drying stage, which is the position in 
which rotation of the automobile body is to be stopped. The 
sensor-enabling operation of limit switch LS1, therefore, prevents tilt 
lever 16 from being accidentally lowered, for example, if a worker passes 
sensors S1 and S2. 
With the conveying apparatus in accordance with the invention, when the 
article to be painted, which is rotating on an advancing carriage, reaches 
the end of the baking and drying stage, and the sensors, operating 
together, determine that the body has rotated to its erect attitude, chain 
8 is tilted downward to disengage from sprocket 7 on carriage 1. Since the 
combined center of gravity of the article to be painted and the support 
arms is located directly below the axis of rotation, the article rapidly 
comes to rest in its erect attitude, with a diminishing rocking motion, 
within a minimum time of rocking. Since stopping of rotation of the 
article takes place without impact, shock is eliminated. Moreover, forward 
motion of the carriage can continue as the rotation of the article is 
stopped. It is therefore possible to stop the article in its erect 
position quickly, without impact, and without interrupting the forward 
motion of the article. 
Various modifications can be made to the apparatus described. For example, 
the sprocket which engages the chain which delivers rotating power to the 
article can be located at the forward end of the carriage, provided that 
the chain is appropriately positioned. Other types and arrangements of 
body attitude sensors can be used. Still other modifications can be made 
without departing from the scope of the invention as defined in the 
following claims.