WO2003063569A1

WO2003063569A1 - Automated optical inspection system with staging conveyor

Info

Publication number: WO2003063569A1
Application number: PCT/US2003/001180
Authority: WO
Inventors: Timothy W. Mccarthy; Eric L. Aldrich; Iii John J. Snyder
Original assignee: Teradyne, Inc.
Priority date: 2002-01-22
Filing date: 2003-01-15
Publication date: 2003-07-31
Also published as: TW200302686A

Abstract

An automated optical inspection (AOI) system for printed circuit boards that simply provides increased throughput. Boards are moved through the system on a continuous conveyor. When one board reaches the inspection area, it is disengaged from the conveyor, but the conveyor can continue to move. While the first board is being inspected, the conveyor moves a second board into a staging area just outside the inspection area. When inspection of the first board is completed, it is re-engaged to the conveyor and the first board moves out of the inspection area while the second board moves into it. In this way, the transport time is reduced using very simple machinery.

Description

AUTOMATED OPTICAL INSPECTION SYSTEM WITH STAGING CONVEYOR

This invention relates generally to factory automation and more specifically to conveyor systems. In the manufacture of printed circuit boards and other similar electronic assemblies, the printed circuit board is processed by several pieces of equipment in steps. The boards are moved between and through the equipment on conveyors.

FIG. 1 shows in schematic form a portion of a manufacturing line for printed circuit boards. Boards, such as boards 140 are processed by oven 110, which reflows solder to secure components (not shown) to the board 140. Boards move through oven 110 on a conveyor. The conveyor has an input section 112 and an output section 114. In FIG. 1, board 140 is shown on the output section 114 after having been processed by oven 110.

After the boards are processed by oven 110, they are passed to an inspection stage, here automated optical inspection (AOI) equipment 120. AOI equipment 120 inspects the boards for defects. The boards likewise move through the AOI equipment 120 on a conveyor, which also has an input section 122 and an output section 124.

In many pieces of AOI equipment, the board cannot be inspected while it is moving. Rather, the board is brought into the equipment and held in a fixed location. One or more cameras scans the board and generates an image that is then processed to detect defects.

FIGs. 2A and 2B illustrate the manner in which the board is held stationary. FIG. 2 A shows one side of board 140 riding along a flexible member 210, which is part of the conveyor. Member 210 is moved in the direction of motion of the conveyor. For example, member 210 is driven by a gear, wheel or other convenient mechanism. Board 140 is guided along a rail 230. Similar structure guides and propels the opposite side of board 140.

A sensor (not shown) detects when board 140 is positioned below the cameras inside AOI equipment 120. When board 140 reaches the appropriate location, the motion of member 210 is stopped. Further, the clamp 220 is engaged to drive board 140 against a lip on rail 230.

FIG. 2B shows clamp 220 engaged. Clamp 220 is engaged by a solenoid or other similar electrical or mechanical device operating under control of a computerized controller in the AOI equipment 120.

As shown in FIG. 2B, when engaged, clamp 220 pushes board 140 against the upper lip of rail 230. This upper lip serves as a stop to position board 140 in an up- down direction. Additionally, clamp 220 prevents member 210 from moving. In this way, board 140 is positioned accurately relative to the cameras inside AOI equipment

120.

Once the inspection is completed, clamp 220 is again lowered to the position of FIG. 2 A and member 210 is again driven. In this way, board 140, after having been inspected is driven out of AOI equipment 120 on section 124 (FIG. 1) of the conveyor on to the next stage of the manufacturing line.

Following the AOI equipment, the boards might then be passed to some post

AOI equipment 130. The boards are likewise passed through the post AOI equipment on conveyors. The precise nature of the post AOI equipment will depend on the specific manufacturing operation. In fact, the order of the steps is shown here simply for illustration and the number and order of steps is likely to be different in various manufacturing operations. .

However, it is commonplace for the boards to move through equipment on conveyors. If one piece of equipment has a smaller throughout than the others, i.e. processes fewer boards per minute, the boards might be removed from the conveyor and buffered before the slower pieces of equipment. The slower equipment might then be operated for a longer period of time to process the required number of boards.

Or, multiple pieces of slow equipment might be used so that the slow operations do not become the bottleneck. However, it is undesirable to have to handle and buffer the boards. It would be preferable if the boards moved through as many manufacturing stages as possible without having to be removed from the line. Often, each piece of equipment in the manufacturing processes the same number of printed circuit boards in a minute. In this way, the boards may pass continuously from one piece of equipment to another on the conveyors.

Ideally, each piece of manufacturing equipment would process boards as fast as possible - but still at the same rate as all of the other pieces of equipment. In reality, it is often the case that the faster equipment is slowed to operate at the rate of the slowest equipment in the line. Because the manufacturing line represents a large capital investment, it is desirable for the line to produce as many boards as possible. It is therefore undesirable to have to slow the faster equipment. It would be desirable to speed up the slower equipment. '

The AOI equipment, such as AOI equipment 120, is often one of the slower, if not the slowest, piece of processing equipment in a manufacturing line for electronic assemblies, such as printed circuit boards. One reason for this is because the time, sometimes called transport time, that the boards must spend on the conveyor moving to the inspection area. Because the conveyors of the AOI machine and the conveyor of the upstream equipment are not synchronized, a board can not be moved by both conveyors simultaneously. Rather, the board is passed off from one conveyor to the next. Thus, the input section of the conveyor 122 must be large enough to hold an entire board to be processed.

Typically, an AOI system will be designed to inspect boards that are as large as are likely to be encountered in a manufacturing operation. For example, an AOI machine might be designed to accept a 40 inch board. Thus, the input area 122 of the conveyor must be 40 inches long to receive that board. But, most boards actually manufactured are shorter - for example 10 inches.

This means that when the AOI system is ready to inspect the next board, the shorter board must move down the entire 40 inch input area 122, despite the fact that the board is only 10 inches long. In other words, the board moves an additional 30 inches before it even begins to enter the inspection area. If the conveyor moves at a rate of 10 inches a second, it takes a typical 10 inch board an extra 3 seconds of transport time on the input section 122 before it begins to enter the inspection area. This transport time must be added to the inspection time in determining the throughput of the AOI system.

Some prior art AOI systems use separate input and output conveyors. An X-Y stage talces the boards off the input conveyor and moves it to the inspection area.

Once inspected, the X-Y stage moves the board to the output conveyor. While one board is being inspected, another board can be moving on the input conveyor to the X- Y stage. Thus, this transport time on the input conveyor does not need to be added to the inspection time to determine the throughput of the AOI equipment. An alternative approach is known as a "dual lane" system. In a dual lane system, two conveyors run in parallel. The camera head moves back and forth over the two conveyors to inspect boards on each conveyor. As the camera is inspecting the boards on one conveyor, a board is moving into the inspection area on the other conveyor. Likewise, the transport time on the conveyors is not added to the inspection time to compute throughput of the machine.

The drawback of these dual conveyor systems is the added cost and complexity of having two conveyors. Not only is there additional equipment required for two conveyors, but there must be additional machinery to direct the boards to the appropriate conveyor at the appropriate time. SUMMARY OF THE INVENTION With the foregoing background in mind, it is an object of the invention to provide a simple and low cost way to increase the throughput of a manufacturing line on which boards move on conveyors.

The foregoing and other objects are achieved in a manufacturing operation in which electronic assemblies such as printed circuit boards are passed along conveyors through and between pieces of equipment. In at least one piece of equipment, the boards are stopped at a work station, such as the inspection station of a piece of AOI equipment, so that the other boards continue to move along the conveyor.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be better understood by reference to the following more detailed description and accompanying drawings in which

FIG. 1 is a schematic illustration of a prior art manufacturing line for electronic assemblies;

FIG. 2A is a schematic illustration of a prior art prior art board clamp in an unengaged position; FIG. 2B is a schematic illustration of a prior art prior art board clamp in an engaged position; FIG. 3 A is a schematic illustration of board clamp according to the invention in an un-engaged position; FIG. 3B is a schematic illustration of board clamp according to the invention in an engaged position; and FIG. 4 is a schematic illustration of a piece of AOI equipment according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT We have developed a simple and low cost way to increase the throughput of manufacturing equipment, such as an AOI system, in which an electronic assembly must be stopped for an operation to be performed on it. Rather than employ a conveyor and clamp system as shown in FIG. 2A and FIG. 2B, we have developed a conveyor and clamp system as shown in FIG. 3 A and 3B. As in the prior art, the board 140 is moved by a flexible member, such as belt 210. The edge of board 140 is guided by a guide member, such as rail 230. Also as in the prior art, rail 230 includes a lip above board 140. And, also as in the prior art, a clamp presses the board against the lip of rail 230 at the point in the operation where board 140 is to stop. In this way, board 140 is properly positioned relative to the cameras (not shown) in the AOI equipment both in the direction of its motion an in the up and down direction.

However, unlike the clamp of the prior art, clamp 310 does not prevent belt 210 from moving when engaged. Rather, clamp 310 includes a projection 312 that when engaged (FIG. 3B) lifts board 140 off of belt 210. In this way, belt 210 can continue to move while board 140 is stopped.

Once board 140 is inspected, clamp 310 is disengaged by returning it to the position of FIG. 3 A and board 140 again moves along belt 210.

The advantage of such an arrangement might be more fully appreciated in connection with the example of FIG. 4. FIG. 4 shows a piece of manufacturing equipment in which the board stops during operation. In this example, that equipment is AOI system 420. AOI system 420 includes a work area, such as inspection region 450, in which the board being inspected is held stationary.

As in the example above, the input section 122 is 40 inches long. Boards 140A and 140B are only 10 inches long. The inspection time for a circuit board is 25 seconds and it takes 2 seconds to move the board from the end of input section 122 into inspection area 450, clamp the board and otherwise prepare to run the test.

In a prior art, single conveyor system, it would have taken 3 second to move a 10 inch board from the end of the conveyor to the end of the end of input section 122. An additional 2 seconds to move the board into inspection area 450 and 25 seconds for camera 424 to complete the inspection. Thus, a total of 30 seconds was required for a board. Consequently the maximum throughput of the machine was 2 boards per minute.

With the invention, the conveyor continues to move while a board is in the inspection area, thus saving the 3 seconds of transport time in input section 122. In this way, the time to process one board drops to 27 seconds - representing a 10% increase in throughput.

In greater detail, AOI system 420 includes a controller 422. Controller 422 receives inputs from two sensors 460A and 460B. Sensor 460A senses when a board reaches the end of the input stage 122. Sensor 460B senses when a board is positioned in inspection area 450. Controller 422 sends commands to motor 470 to control motion of the conveyor.

Initially, a board passes along the conveyor until sensor 460B detects that the board is properly positioned in inspection area 450. At this time, controller 422 activates clamp 310. At this time, board 140B stops in the inspection area and board 140B is inspected.

While board 140B is being inspected, a second board 140 A can be loaded onto input section 122. Because belt 210 can continue to move, board 140 A can be moved all the way to the end of the input section 122. When sensor 460 A detects board 140A at the end of the input section 122, controller 422 stops the conveyor.

When the inspection of board 140B is completed, clamp 310 is disengaged. Belt 210 again moves, moving both boards 140 A and 140B through the system. When 140A reaches the inspection area, it can be stopped at the desired location, but board 140B can continue to move off the conveyor to a downstream piece of equipment. And, when a new board is ready from the upstream equipment, the conveyor can again be moved to bring another board into the staging area at the end of the input section 122.

Of significance, a single, continuous conveyor can be used to move the boards into and out of the inspection area 450. Thus, very simple mechanical hardware is needed. And, the conveyor operates largely independently of the rate at which the conveyors of the upstream and downstream machines run.

Having described one embodiment, numerous alternative embodiments or variations might be made. For example, the staging conveyor is not limited to use in AOI equipment. Nor is the invention limited to belt type conveyors. The invention might be employed with conveyors with articulated segments or with conveyors created from moving members, such as wheels. By changing the shape of the clamp, the invention could be made to work with conveyors constructed in other ways.

Furthermore, the invention is not limited to clamps that lift the board off the conveyor or that position a board by pressing it against the positioning rails. The board might be pushed against any form of stop. Additionally, one of skill in the art could conceive of numerous other ways in which to clamp a board, such as by pinching it between two finger type elements.

Nor is it strictly necessary that the board be "clamped" in the sense that it is completely immovable. In some embodiments, it could be sufficient to simply remove the board from the drive mechanism.

As a further example, it should be appreciated that the invention might operate in reverse. A board might be rigidly attached to the conveyor when it is desired to move the board and that attachment might be released when it is desired to stop the board.

Furthermore, it should be appreciated that the preferred embodiment was described in connection with a continuous conveyor that stretched from the input segment, through the work area to the output section. It should be appreciated that such a result could be achieved with a single belt. Or, substantially the same simplicity might be achieved by multiple belts that are controlled to move together as a continuous conveyor.

Therefore, the invention should be limited only by the spirit and scope of the appended claims.

Claims

What is claimed is

1. Processing equipment for electronic assemblies of the type having a work area in which the electronic assemblies are stationary and a conveyor moving the electronic assemblies from an input section, through the work area to an output section, comprising: a) • a stop above the conveyor; b) clamp having a projection adapted to push the electronic assembly off the conveyor into the stop while allowing the conveyor to move.

2. The processing equipment of claim 1 wherein the conveyor is a continuous conveyor.

3. The processing equipment of claim 2 wherein the conveyor is a belt type conveyor.

4. The processing equipment of claim 1 wherein the stop comprises a portion of a guide member for guiding an electronic assembly.

5. The processing equipment of claim 1 wherein the stop is positioned in the work area.

6. The processing equipment of claim 1 additionally comprising a first sensor disposed in the work area for sensing when an electronic assembly is in the work area and a second sensor in the input section for sensing when an electronic assembly is located at the end of the input section.

7. The processing equipment of claim 6 additionally comprising a motor for driving the conveyor.

8. The processing equipment of claim 7 additionally comprising a controller having inputs coupled to the first sensor and the second sensor and a first output coupled to the clamp and second output coupled to the motor.

9. The processing equipment of claim 8 wherein the controller actuates the clamp when first sensor senses an electronic assembly and de-activates the motor when the second sensor senses an electronic assembly.

10. The processing equipment of claim 1 used in a manufacturing line with upstream and processing equipment moving electronic assemblies on conveyors, with the conveyor of the upstream processing equipment operating asynchronously with respect to the conveyor.

11. A method of operating automatic inspection equipment of the type having a conveyor moving electronic assemblies from an input section, through a work area, comprising: a) moving a first electronic assembly on the conveyor to the work area; b) disengaging the first electronic assembly from the conveyor while it is being inspected in the work area; c) moving a second electronic assembly through the input section while the first electronic assembly is disengaged from the conveyor.

12. The method of claim 11 additionally comprising re-engaging the first electronic assembly to the conveyor and moving the first electronic assembly away from the work area while moving the second electronic assembly toward the work area.

13. The method of claim 11 wherein the conveyor is a continuous conveyor.

14. The method of claim 11 additionally comprising stopping the conveyor when the second electronic assembly reaches the end of the input area.

15. Processing equipment for electronic assemblies of the type having a work area in which the electronic assemblies are stationary and a conveyor moving the electronic assemblies from an input section, through the work area to an output section, comprising: a) a first sensor in the work area; b) a second sensor at the end of the input section; c) a motor for driving the conveyor; d) a clamp in the work area adapted to disengage an electronic assembly form the conveyor while allowing the conveyor to move; and e) a controller, having inputs coupled to the first sensor and the second sensor and the clamp and a first output, coupled to the clamp, for actuating the clamp in response to an output of the first sensor and a second output, coupled to the motor, for actuating the motor in response to the output of the second sensor.

17. The processing equipment of claim 16 wherein the work area includes a camera for automated optical inspection of the electronic assembly.

18. The processing equipment of claim 16 wherein the conveyor is a continuous conveyor running from the input section, through the work area to the output section.

19. The processing equipment of claim 18 wherein the clamp comprises a projecting member and an opposing stop with a gap therebetween adapted to receive an electronic assembly.

20. The processing equipment of claim 19 wherein the stop comprises a portion of a guide member