Conveyors: power-driven – Conveyor section – Endless conveyor
Reexamination Certificate
2001-10-22
2004-05-25
Ridley, Richard (Department: 3651)
Conveyors: power-driven
Conveyor section
Endless conveyor
C198S459500, C198S782000
Reexamination Certificate
active
06739449
ABSTRACT:
The present invention refers to a stopping device suitable to be fitted to automation modules for printed circuit boards and in particular to machines for electrical testing of printed circuit boards. The present invention further refers to a method for stopping printed circuit boards.
Specific reference will be made herein to machines for electrical testing of printed circuit boards, it being understood that the stopping and starting device according to the invention can be applied at any point of an automation line for printed circuits at which it is necessary to stop the printed circuit for a particular process and then start it again with a high acceleration. Thus the stopping and starting device according to the invention can be applied, for example, to modules with a telecamera to film the printed circuit and to modules for marking the circuit board.
A printed circuit board (PCB) is a base or substrate of insulating material on which electrical connections of various components which are to be installed generally by welding are traced, normally by a subtractive chemical or etching process.
These printed circuit boards, before application of the components, are tested, that is they are checked and analysed to verify that all the nets present on them are insulated from each other and that there is electrical continuity between all the points in each net.
The electrical test stage of a printed circuit board therefore comes at the end of the manufacturing cycle of the board. The machines used to perform this type of test are normally equipped with a universal contact grid, that is with a constant pitch (generally 100 mils: 2.54 mm) also known by the name of “needle bed” or “needle board”.
Since the printed circuit board to be tested has points of connection between the different components disposed in a variable manner—and therefore not referable to a constant pitch grid—an interfacing device (adapter or fixture) that allows an electrical connection to be made between the test points of the printed circuit and the measurement points of the machine is interposed.
Conveyor belts are generally used for automation of the PCBs on test machines. In particular two belts are used which convey the PCBs on both sides.
According to the weight of the PCB and the friction coefficient between the PCB and the belts a limit is defined for the acceleration to be given to the PCB. In fact if an acceleration greater than this limit is imparted, the hold between the surface of the PCB and the belts is lost and the PCB jumps out of the conveyor belts.
Consequently, because of said limit of acceleration, the maximum speed of the PCB is reduced. The maximum speed of the PCB proves to be a very important factor, since the production (number of PCB tested per time unit) of the test machine is given by the speed of travel of the PCBs.
In prior art test machines various devices have been used to optimise acceleration of the PCBs. For example, the use of devices such as pushers and pressure wheels is known to the art.
The pusher is positioned behind the PCB when the PCB is in the stop position. In this manner the pusher pushes on the rear edge of the PCB, in the direction of travel, giving it a high acceleration.
However the pusher is not suitable to be employed in test machines since it interferes with the fixtures and there are difficulties in synchronization between test unit and pusher. Furthermore the pusher has to be adjusted according to the length of the PCBs processed: this leads to a waste of time at each production change.
The pressure wheel applies pressure on the upper surface of the PCB, imparting an additional force on the belts from the top downward, which is added to the force of the weight of the PCB. Thanks to this force applied by the pressure wheel a greater friction is obtained between the PCB and the belts, thus allowing the PCB to be given a greater acceleration so as to reach a high speed in the shortest time possible.
In prior art test machines, stopping devices are used to stop the PCB, for example when it reaches the vicinity of the test area. The stopping devices of the prior art have moveable stoppers. The stopper is moved toward the belts so that the PCB hits against it. In this case the PCB travelling at high speed bounces backward off the stopper and then stops in abutment against the stopper. To avoid this rebound another solution provides for the belts to decelerate when the PCB is in the vicinity of the stopper.
Both systems have the drawback of wasting too much time and thus increasing the production cycle time.
In fact the rebound of the PCB against the stopper causes a waste of time due to its backward and subsequent forward movement, and the deceleration of the belts must be gradual, according to the friction coefficient between belt and PCB, otherwise if the acceleration is too sharp the PCB could jump out of the belts.
To resume forward movement of the PCB, the stopper is moved away and thus the belts carry the PCB forward. In this case too there is a waste of time, since the acceleration to be imparted to the PCB on restarting is again limited by the friction coefficient between the PCB and the belts.
In prior art test machines it is evident that much of the cycle time of the machine is wasted in idle time before and after stopping of the PCB.
The object of the present invention is to eliminate the drawbacks of the prior art, providing a stopping device for automation modules of printed circuit boards that is able to minimize idle times before and after stopping and is efficient, versatile, practical and simple to make.
This object is achieved according to the invention with the characteristics listed in appended independent claim
1
.
Another object of the invention is to provide a method for stopping the printed circuit boards that allows the cycle time of the machine to be reduced and the production per unit of time to be increased.
This object is achieved in accordance with the invention with the characteristics listed in appended independent claim
1
.
Advantageous embodiments of the invention are apparent from the dependent claims.
The stopping device for printed circuit board automation modules according to the invention provides at least one stopper to stop the PCB and at least one pressure means which acts on the PCB when it abuts against the stopper to prevent it from rebounding.
When the PCB has to move on from its stopping position, the pressure means, which is advantageously a wheel, comes into action again applying pressure on the PCB so as to accelerate it.
Said solution allows the rebound of the PCB against the stopper to be eliminated, a high deceleration of the PCB to be obtained when it arrives in the stopping position and a high acceleration of the PCB to be obtained on restarting. All this enables the machine cycle to be speeded up, thus increasing production.
Furthermore, with said solution the use of pushers with all the related drawbacks is eliminated.
REFERENCES:
patent: 3104054 (1963-09-01), Rabinow
patent: 3951402 (1976-04-01), Skinner
patent: 4163550 (1979-08-01), Armstrong
patent: 4189271 (1980-02-01), Hasegawa
patent: 4203588 (1980-05-01), Joosten
patent: 5094443 (1992-03-01), Young, Jr.
patent: 6471050 (2002-10-01), Ikeda et al.
patent: 6505831 (2003-01-01), Henn et al.
Mang Paul
Wetzel Gert
Mania Technologie Italia SpA
Nixon & Vanderhye P.C.
Presta Frank P.
Ridley Richard
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