Method and apparatus for six-sided vacuum painting of parts

A method for six-sided painting of parts, such as boards, the parts having a top, bottom, sides, and ends, in a vacuum painting system having a feed conveyor, a vacuum painting chamber, and a take-out conveyor wherein the a first part is placed end-to-end with a second part on the feed conveyor, each part having a leading end and a trailing end, and the first part and second part enter the vacuum painting chamber end-to-end, the parts exiting the vacuum painting chamber onto the take-out conveyor end-to-end with the leading end of each part exiting the vacuum painting chamber first, consisting of the steps of: PA1 (a) sensing the presence of the leading end of the first part along the take-out conveyor while the trailing end of the first part is within the vacuum painting chamber; PA1 (b) moving a movable carriage along the take-out conveyor toward the vacuum painting chamber to a position intermediate the leading end and trailing end of the first part; PA1 (c) moving the movable carriage a short distance along the take-out conveyor away from the vacuum painting chamber in order to approximate the speed of the movable carriage to the speed of the take-out conveyor; PA1 (d) gripping the first part with gripping means attached to the movable carriage; PA1 (e) moving the movable carriage a short distance along the take-out conveyor away PA1 from the vacuum painting chamber in order to separate the trailing end of the first part from the leading end of the second part; and PA1 (f) releasing the first part so that the trailing end of the first part and the leading end of the second part become painted. An apparatus for carrying out the above method is also disclosed, consisting of a sensor adjacent the take-out conveyor for sensing the leading end of the first part; a relay responsive to the sensor; a movable carriage adjacent the take-out conveyor and adapted to move in either direction along the take-out conveyor and positionable along the first part on the take-out conveyor, the motion of the movable carriage being responsive to the relay; and gripping pins mounted on the movable carriage for gripping the first part, the gripping pins being responsive to the relay.

BACKGROUND OF THE INVENTION 
This invention relates to an apparatus and method for six-sided board 
painting. 
In manufacturing operations that produce millwork such as moldings, sills, 
frames, etc., it has been the practice to vacuum paint the workpiece on an 
assembly line. The stock is put in a bin and each piece is fed onto a 
conveyor line, with the pieces abutting each other end to end along the 
conveyor. Each piece enters a vacuum painting apparatus, where paint is 
sprayed onto the piece under a vacuum. The piece then exits the apparatus 
onto another conveyor to be dried and heat-treated. 
In order to paint each piece on six sides, that is, the top, bottom, sides, 
and ends, it is necessary to keep each piece slightly separated from the 
following piece. If this were not done, the paint would not be able to 
reach the trailing end of the lead piece or the leading end of the 
following piece. Industry practice has been to insert a staple in the 
trailing end of the lead piece to separate this piece slightly from the 
following piece. When the boards have been painted, the staples must be 
removed. 
Inserting and removing staples is a time-consuming, labor-intensive, 
potentially health-damaging operation. The constant twisting, gripping 
movement of removing the staples can cause such ailments as carpal tunnel 
syndrome. 
In addition, the staples caused a partial loss of vacuum within the vacuum 
painting chamber because the boards were spaced apart as they entered the 
chamber. The gap between the boards caused a partial loss of vacuum 
because the seals of the vacuum painting chamber could not close tightly 
around the boards. This partial loss resulted in reduced painting 
efficiency and waste of paint. There are also environmental concerns if 
paint escapes from the vacuum chamber into the surrounding air. 
Another earlier solution to the problem of painting the ends of the boards 
is the optional vacuum take-away system offered by Advanced Manufacturing 
and Development (AM&D) of Willitz, Calif. This system causes parts to 
separate in the application chamber, allowing the ends to be coated. 
However, the inventor has found that this vacuum take-away system leaves 
undesirable streaks on the boards. Indeed the operator'manual for this 
system states that the belts of the conveyor will cause transfer marks to 
the bottom side of the part when the bottom is being painted. The inventor 
has also found that this vacuum take-away system cannot operate well near 
the maximum speed of the conveyor. 
There is a need for an apparatus for six-sided painting of parts such as 
boards, moldings, sills, and frames that allows the ends of the parts to 
be painted in a vacuum painting system and is adjustable for part size 
(length and width) and the speed of the conveyor. 
SUMMARY OF THE INVENTION 
A method for six-sided painting of parts, such as boards, the parts having 
a top, bottom, sides, and ends, in a vacuum painting system having a feed 
conveyor, a vacuum painting chamber, and a take-out conveyor wherein the a 
first part is placed end-to-end with a second part on the feed conveyor, 
each part having a leading end and a trailing end, and the first part and 
second part enter the vacuum painting chamber end-to-end, the parts 
exiting the vacuum painting chamber onto the take-out conveyor end-to-end 
with the leading end of each part exiting the vacuum painting chamber 
first, consisting of the steps of: 
(a) sensing the presence of the leading end of the first part along the 
take-out conveyor while the trailing end of the first part is within the 
vacuum painting chamber; 
(b) moving a movable carriage along the take-out conveyor toward the vacuum 
painting chamber to a position intermediate the leading end and trailing 
end of the first part; 
(c) moving the movable carriage a short distance along the take-out 
conveyor away from the vacuum painting chamber in order to approximate the 
speed of the movable carriage to the speed of the take-out conveyor; 
(d) gripping the first part with gripping means attached to the movable 
carriage; 
(e) moving the movable carriage a short distance along the take-out 
conveyor away from the vacuum painting chamber in order to separate the 
trailing end of the first part from the leading end of the second part; 
and 
(f) releasing the first part so that the trailing end of the first part and 
the leading end of the second part become painted. 
An apparatus for carrying out the above method is also disclosed, 
consisting of a sensor adjacent the take-out conveyor for sensing the 
leading end of the first part; a relay responsive to the sensor; a movable 
carriage adjacent the take-out conveyor and adapted to move in either 
direction along the take-out conveyor and positionable along the first 
part on the take-out conveyor, the motion of the movable carriage being 
responsive to the relay; and gripping pins mounted on the movable carriage 
for gripping the first part, the gripping pins being responsive to the 
relay.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows a vacuum painting system in which the present invention is 
used. The vacuum painting system consists of a feed conveyor 10, a vacuum 
painting chamber 12, and a take-out conveyor 14. Parts P are placed 
end-to-end on the feed conveyor 10. Each part P has a leading end E1 and a 
trailing end E2. For convenience of description, the processing of two 
parts, P1 and P2, referred to respectively as the "first part" and "second 
part", will be described. 
To prepare the system for operation, paint or other coating is loaded into 
a reservoir 16 and a vacuum blower (not shown) is activated, causing the 
coating to be pumped into the base of the vacuum painting chamber 12. Due 
to the vacuum in the vacuum painting chamber 12, the coating is suctioned 
up, then vaporized. 
The first part P1 enters the vacuum painting chamber 12 with its leading 
end E1 entering the chamber 12 first. As the part moves through the vacuum 
painting chamber 12, it is passed through the coating vapor and is coated. 
The negative pressure created inside the vacuum painting chamber 12 by the 
vacuum blower pulls surrounding air into the chamber 12. When the part 
exits the vacuum painting chamber 12, the air passes through the small 
openings around the part at a controlled velocity and draws the excess 
coating back into the vacuum painting chamber 12. There is thus no loss to 
over spray or evaporation. 
However, in order to paint the ends (E1, E2) of the parts, the parts may 
not remain end-to-end within the vacuum painting chamber. Industry custom 
has therefore been to separate the ends (E1, E2) of the parts before the 
parts enter the vacuum painting chamber 12, as by inserting a staple S 
into the trailing end E2 of the first part or leading end E1 of the second 
part. See FIG. 2. This staple must be manually removed after the part is 
painted. 
The insertion and removal of the staples S is a time-consuming, 
labor-intensive operation. Furthermore, repeated twisting motions required 
to remove the staples may cause ailments such as carpal tunnel syndrome. 
Furthermore, the small space between the parts as the parts pass through 
the input seal 18 of the vacuum painting chamber may cause a partial loss 
of vacuum. This may cause reduced coating efficiency and coating may 
escape into the environment. 
In the method of the present invention, illustrated beginning with FIG. 3a, 
a sensor 30 senses the presence of the leading end E1 of the first part P1 
along the take-out conveyor 14 while the trailing end E2 of the first part 
P1 is within the vacuum painting chamber 12. In FIG. 3a, it should be 
noted that the trailing end E2 of part P1 abuts the leading end E1 of part 
P2. 
In the next step (FIG. 3b), a movable carriage 32 is moved along the 
take-out conveyor 14 toward the vacuum painting chamber 12 to a position 
intermediate the leading end E1 and trailing end E2 of part P1. The 
movable carriage 32 has a gripping means 34, such as pins 36, for gripping 
the part P1. 
Next (FIG. 3c), the movable carriage 32 is moved a short distance along the 
take-out conveyor 14 away from the vacuum painting chamber 12 in order to 
approximate the speed of the movable carriage 32 to the speed of the 
take-out conveyor 14. The purpose of this is to avoid leaving streaks on 
the part after it is gripped. 
Next (FIG. 3d), the gripping means 34 grips the first part P1. Note that 
the trailing end E2 of the first part and leading end E1 of the second 
part still abut. 
In FIG. 3e, it is seen that the carriage 32 moves a short distance along 
the take-out conveyor 14 away from the vacuum painting chamber 12 in order 
to separate the trailing end E2 of the first part P1 from the leading end 
E1 of the second part P2. The coating in the vacuum chamber now coats 
trailing end E2 and leading end E1. 
Finally (FIG. 3f), the gripping means 34 releases the first part P1. Motion 
of the feed conveyor 10 then causes part P2 to again abut part P1, and the 
two parts then exit the chamber 12 end-to-end. 
Optionally, the movable carriage 32 and gripping means 34 may be placed on 
a movable frame and the frame may be moved from one take-out conveyor to 
another take-out conveyor. Thus, the same mechanism may be used in 
different production lines. Alternatively, multiple frames may be used, 
with one frame in production and the others being readied for use, such as 
by cleaning or adjustment. 
The movable carriage may be adjusted vertically and horizontally in 
relation to the take-out conveyor and vacuum painting chamber to 
accommodate differences across production lines and different lengths and 
widths of parts. 
An apparatus 40 for carrying out the method of the present invention is 
shown in FIG. 4. The apparatus comprises a sensing means 30 adjacent the 
take-out conveyor 14, for sensing the leading end E1 of the part P1. The 
sensing means 30 preferably comprises an optical sensor 30a, such as a 
laser transmitter and receptor. Alternatively, a mechanical sensor such as 
an interrupter in the path of the part could be used, or any equivalent 
sensing means. 
The apparatus 40 (FIG. 5) further comprises a relay means 42 responsive to 
the sensing means 30. Preferably, the relay means 42 is electronic and 
receives a signal from the optical sensor 30a when the leading edge E1 of 
the first part P2 interrupts the optical sensor 30a. Most preferably, the 
relay means 42 is a programmable relay 42a which may control multiple 
relays 44, 46 at different time intervals as will be further discussed 
below. 
The apparatus 40 also comprises a movable carriage 32 adjacent the take-out 
conveyor 14 adapted to move in either direction along the take-out 
conveyor 14 and positionable along the first part P1 on the take-out 
conveyor 14. The motion of the carriage 32 is responsive to the relay 
means 42. 
The apparatus 40 also comprises a gripping means 34 mounted on the movable 
carriage 32 for gripping the first part P1. The gripping means 34 is also 
responsive to the relay means 42. Preferably, the gripping means 34 
comprises a pair of pins 36, one on either side of the part P1, the pins 
36 being driven to engage and release the part P1. The gripping means 34 
also comprises pistons 38 driving the pins 36, the pistons 38 being driven 
by a first air solenoid 50. Other equivalent gripping means such as 
frictional pads or suction cups could also be used. 
The apparatus 40 may also preferably comprise a first flow control valve 52 
between the first air solenoid 50 and the pistons 38, the flow control 
valve 52 being adapted to regulate the speed at which the pistons 38 drive 
the pins 36 toward and away from the part P1. 
The apparatus 40 also preferably comprises a second air solenoid 54 driving 
the movable carriage 32 and a second flow control valve 56 between the 
second air solenoid 54 and the carriage 32, the flow control valve 56 
being adapted to regulate the speed at which the movable carriage 32 moves 
along the part P1. 
Operation of the apparatus 40 is as follows. When the optical sensor 30a 
detects the leading E1 of the first part P1, a signal is sent to the 
programmable relay 42a. The distance at which the optical sensor 30a is 
positioned from the vacuum painting chamber 12 is set so that the trailing 
end E2 of part P1 will be within the vacuum painting chamber 12 when the 
leading end E1 trips the sensor 30a. Thus, parts of different length will 
require the sensor 30a to be adjustably positionable along the take-out 
conveyor 14. Most preferably, the trailing end E2 of part P1 will be about 
one-half inch within the vacuum painting chamber 12 from the entrance seal 
18 when the sensor is tripped. 
The programmable relay 42a then closes relay 44, in turn causing second air 
solenoid 54 to activate and move the carriage 32 toward the vacuum 
painting chamber 12. 
After a time interval, set in programmable relay 42, the direction of 
travel of carriage 32 is reversed, and the carriage 32 moves away from the 
vacuum painting chamber 12 at a speed approaching that of the conveyor 14. 
Speed matching will minimize the chance of causing the paint along the 
sides of the part to streak due to contact with the gripping pins 36. 
After another time interval, programmable relay 42 causes relay 46 to 
close, activating first air solenoid 50 which in turn causes the gripper 
pins 36 to close and engage the part P1. Programmable relay 42 then causes 
the carriage 32 to move away from the vacuum painting chamber 12 a slight 
distance, to separate the trailing end of part P1 from the leading end of 
part P2. Coating in the chamber 12 then coats trailing end E2 and leading 
end E1. 
Programmable relay 42 then causes gripping pins 36 to release the part P1. 
Part P2, driven by feed conveyor 10, then pushes against part P1, pushing 
part P1 out of the vacuum painting chamber 12. 
The time intervals for the various events discussed above may be adjustable 
to accommodate different part lengths and different conveyor speeds. 
In addition, flow control valves 52, 56 may be adjusted to control the 
speeds at which the carriage 32 moves and at which the pins 36 close. 
Preferably, the apparatus 40 is mounted on a frame 60 with 
ground-contacting wheels 62 so that the apparatus may be moved from one 
take-out conveyor to another. In a minimal configuration, the sensing 
means 30, carriage 32, and gripping means 34 are mounted on the frame. 
More optimally, the relay means 42, solenoids 50,54, and flow control 
valves 52, 56 are also mounted on the frame 60. 
Preferably, the apparatus 40 also includes first adjustment means 70 for 
adjusting the carriage 32 and the gripping means 34 vertically in relation 
to the take-out conveyor 14, to accommodate various heights of the 
conveyor 14 off the ground. The apparatus 40 may also include second 
adjustment means 80 for adjusting the carriage 32 and gripping means 34 
horizontally in relation to the vacuum painting chamber. The apparatus 40 
may also include third adjustment means 90 for adjusting the gripping 
means 34 horizontally in relation to the part, to accommodate various part 
widths. The apparatus 40 may also include fourth adjustment means 100 for 
adjusting the sensing means 30 horizontally in relation to the vacuum 
painting chamber, to accommodate various part lengths. 
In the preferred embodiment, first adjustment means 70 may comprise a first 
gear rack 72 and first adjusting wheel 74, the movable carriage 32 being 
moved vertically along the first gear rack 72 by turning first adjusting 
wheel 74. 
Second adjustment means 80 preferably comprises a second gear rack 82 and 
second adjusting wheel 84, the movable carriage being moved horizontally 
along the second gear rack 82 by turning second adjusting wheel 84. 
Third adjustment means 90 preferably comprises a first slot 92 and a first 
adjustment pin 94 slidingly engaged with the first slot 92, the gripping 
means 34 being attached to the first adjustment pin 94. 
Fourth adjustment means 100 preferably comprises second slot 102 and second 
adjustment pin 104 slidingly engaged with the second slot 102, the sensing 
means 30 being attached to the second adjustment pin. 
Optionally, rollers 110 may be used to move the part from the vacuum 
painting chamber onto the take-out conveyor 14. 
The present invention may be embodied in other specific forms without 
departing from the spirit or essential attributes thereof, and it is 
therefore desired that the present embodiment be considered in all 
respects as illustrative and not restrictive, reference being made to the 
appended claims rather than to the foregoing description to indicate the 
scope of the invention.