WO1993014909A1

WO1993014909A1 - Apparatus for loading, unloading and precisely positioning articles with respect to a table

Info

Publication number: WO1993014909A1
Application number: PCT/US1993/000770
Authority: WO
Inventors: Dan Shteinitz; Michael Kozak; Omri Brandstatter; Michael Elent
Original assignee: Orbotech Ltd.; Orbotech Inc.
Priority date: 1992-01-31
Filing date: 1993-01-28
Publication date: 1993-08-05
Also published as: IL100825A0; IL100825A

Abstract

Apparatus for precisely positioning an article on a supporting surface formed (14) with two registration shoulders (14a, 14b) at an angle to each other corresponding to that of, and engageable with, a registration corner on the article. The apparatus includes a gripper assembly (20) having a coupling pivotal about an axis perpendicular to the supporting surface such that when the gripper assembly (20) is moved to bring the registration corner of the article into engagement with one of the registration shoulders (14a, 14b) further movement of the gripper assembly (20) and article in the same direction pivots the gripper assembly (20) and article until the registration corner of the article is also brought into engagement with the other registration shoulder.

Description

APPARATUS FOR LOADING, UNLOADING AND PRECISELY POSITIONING ARTICLES WITH RESPECT TO A TABLE

FIELD AND BACKGROUND OF THE INVENTION The present invention relates to apparatus for loading, unloading and precisely positioning articles on tables or other supporting surfaces. The invention is particularly useful in apparatus for loading, unloading and precisely positioning PCBs (printed circuit boards) on an inspection table, e.g., for optically inspecting them, and is therefore described below with respect to this application.

PCBs are inspected for defects by automatic optical inspection apparatus in which the accurate positioning of the PCB on the inspection table is of critical importance. The PCBs commonly used today have thickness ranges from 0.1 to 3.5 mm and sizes of up to 25" x 25". Many are of low rigidity and tend to buckle under the slightest force applied to their contours. For these reasons, the PCBs are usually placed on the. table manually and are precisely positioned by positioning pins mounted on the table received within registration holes in the PCB. However, as in all mass-production fields, it is desirable to automate the handling of PCBs, and particularly to place them accurately on the inspection table.

In the automatic machines presently known for handling PCBs, the above operations are generally separated in space and performed by different types of devices. Thus, in some known machines, the PCBs are picked up from a supply stack with a gripper carried by a manipulator, are conveyed to an intermediate alignment table for preliminary accurate centering of the PCB by means of rollers and side pushers controlled by optical positioning sensors, and are then loaded onto the inspection table by means of another manipulator carrying a gripper which finally releases the PCB above locating pins on the inspection table to which the PCB is clamped by vacuum. After inspection has been completed, the PCBs are unloaded from the inspection table by still another gripper device carried by another manipulator. Machines are also known wherein the loading and unloading operations may be performed simultaneously by two grippers moving linearly together.

However, the need for accurate centering operations devices requires very high precision in the manipulators carrying the grippers in order to maintain the accuracies achieved during the alignment of the PCB on the intermediate table when conveying them to the inspection table. Because of the large dimensions of some PCBs, the manipulators require long arms and/or sliding rails. This not only increases the cost of such equipment, but also • increases their sensitivity to misalignment. A further serious drawback in the previously- proposed systems is the requirement for considerable floor space for the equipment, and as a consequence, for more travel distances and for more time for the loading, positioning, and unloading operations. Besides the loading, positioning and unloading operations required in handling PCBs, it is often necessary to inspect the PCBs from both sides. Known inverting devices usually include grippers for taking a workpiece from one location, turning it over, and releasing it at another location. Such inverting devices also require considerable floor space, generally corresponding to at least double the size of the PCBs.

Another known kind of inverting mechanism inverts the whole stack of PCBs after they have been scanned on one side and unloaded onto the return stack in the normal position. The inverting mechanism then inverts the whole stack and returns the inverted stack to the loading location, whereupon the inverted PCBs are again loaded onto the inspection table for examination of the inverted side of each PCB. However, such arrangements make the whole machine more complicated and therefore more expensive. OBJECTS AND BRIEF SUMMARY OF THE INVENTION An object of the present invention is to provide improved apparatus for precisely positioning an article on a supporting surface, and particularly a PCB on a table. A further object of the invention is to provide an improved inverter for inverting flat articles, particularly PCBs, which inverter takes up very little floor space and is particularly useful in the foregoing loading and unloading apparatus. According to one aspect of the present invention, there is provided apparatus for precisely positioning on a supporting surface an article having a registration corner, comprising: a registration device carried by the supporting surface and formed with two registration shoulders at an angle to each other corresponding to that of, and engageable with, the registration corner of the article for precisely positioning the article on the supporting surface; a gripper assembly for gripping the article; and a drive including a conveyor arm for moving the gripper assembly and the article gripped thereby towards the two registration shoulders; the gripper assembly including a pivotal coupling pivotal about an axis perpendicular to the supporting surface, such that when the drive moves the gripper assembly to bring the registration corner of the article into engagement with one of the registration shoulders, further movement of the gripper assembly and article in the same direction will pivot the gripper assembly and article about the pivotal axis until the registration corner of the article is also brought into engagement with the other of the registration shoulders, thereby precisly positioning the article on the supporting surface.

According to another aspect of the present invention, there is provided an inverter apparatus for inverting flat articles, comprising: a panel normally in a horizontal position for receiving the article to be inverted; suction means for retaining the article on the panel; a stop at one edge of the panel; and pivotal means for first pivoting the panel to an acute angle while the suction means is non-operative, to cause the article to slide by gravity to the stop at the one edge, and for subsequently pivoting the panel 180° from its normal horizontal position about an intermediate axis of the panel parallel to the one edge, while the suction means is operative, to thereby cause the article to be inverted and to be permitted to drop by gravity in the inverted position when the suction means is made non-operative after the inversion. As will be more apparent from the description below, apparatus constructed in accordance with the foregoing features provides some or all of the following advantages: the capability of fully automatic handling of PCBs, including loading, unloading and/or inverting, by apparatus requiring a relatively small floor space; accurate positioning of the articles (e.g., PCBs) without the need for an intermediate table or conveyor; short positioning time and distance; less sensitivity to misalignments in the manipulator or in the stack of PCBs; less sensitivity to the flexibility of the PCBs; high reliablity; and low cost.

Further features and advantages of the invention will be apparent from the description below.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is herein described, by way of example only, with reference to the accompanying drawings wherein:

Fig. 1 is a three-dimensional view illustrating one form of apparatus for handling printed circuit boards in an automatic manner to and from an optical inspection station;

Fig. 2 illustrates the drives for the loading and unloading gripper assemblies in the apparatus of Fig. 1 ;

Fig. 3 illustrates more particularly the portion of the apparatus of Fig. 1 for precisely positioning the PCBs on the inspection table, but including a modification in the construction of Fig. 1. Fig. 4 illustrates the inverter unit for optionally inverting the printed circuit boards after they have been unloaded from the inspection table and before returned to the return stack; and Fig. 5 is an exploded view of the inverter unit of

Fig. 4.

DESCRIPTION OF A PREFERRED EMBODIMENT The Overall Apparatus

The apparatus illustrated in the drawings is for automatically loading PCBs from a supply stack in a precise position on an inspection table for optically inspecting the PCBs, and then for automatically unloading the PCBs, after inspection, to a return stack. The illustrated apparatus also includes an inverter unit which may be optionally actuated in order to invert each PCB after inspection and before it is returned to the return stack, whenever it is desired to optically inspect both sides of the PCBs; in such case, the so-formed inverted return stack becomes a supply stack for automatically loading the PCBs inspected from one side onto the inspection table but this time in inverted position.

The PCBs are generally supplied in a stack of 20-150 units per stack. Each stack may contain PCBs of different patterns and/or different sizes. Some or all of the PCBs may be separated from the others by separator paper sheets. In such a case the apparatus will also transfer the separator sheets from the supply stack to the return stack for separating the PCBs there from each other.

The overall apparatus illustrated in Fig. 1 comprises a trolley 2 for receiving from a production line a supply stack of PCBs to be inspected arranged in a special cassette 2' , and another trolley 4 for receiving the return stack of PCBs after inspection.

The stack of PCBs from trolley 2 is received in a self-levelling stack holder 6, which includes an automatic - lifting mechanism for continuously lifting the stack from . the bottom to maintain the topmost PCB at a predetermined vertical position. A similar stack holder 8 is provided for receiving the empty cassette for the return stack of PCBs after inspection, in which case the stack is continuously lowered in order to maintain the topmost PCB at a predetermined vertical position. Such self-levelling stack holders are well known and facilitate the handling of the PCBs when loaded onto the apparatus for inspection, and when unloaded therefrom after inspection.

The PCB inspection apparatus itself is generally designated 10. It includes a horizontal table 12 on which each PCB is to be precisely positioned to enable the PCB to be optically inspected for defects, etc. Since the inspection apparatus 10 does not form a part of the present invention, details of its construction and operation are not set forth herein.

Table 12 for receiving each PCB to be inspected is provided with a registration device, generally designated 14 (Fig. 3), of L-shaped configuration to define two registration shoulders 14a, 14b at a right-angle to each other projecting from the table surface. The registration shoulders 14a, 14b are engageable with a predetermined registration (right-angle) corner (PCBa, Fig. 3) of the PCB in order to precisely position it on the table.

The illustrated apparatus includes a vertical base column or post 16 to one side of table 12 receiving the PCBs. The PCBs are conveyed individually from the supply stack holder 6 to the table 12 by table-loading means including a conveyor arm 18 mounted at one end to the vertical column 16, and carrying at its opposite end a PCB gripper assembly 20. After inspection, the PCB is conveyed from table 12 to the return stack holder 8 by table- unloading means including a second conveyor arm 22, also mounted at one end to the vertical post 16, and carrying at its opposite end a second gripper assembly 24. The illustrated apparatus further includes an inverter unit, generally designated 26, overlying the return stack holder 8 for inverting each PCB, if desired, before it is received on the return stack. Thus, if the apparatus is to inspect both sides of the PCBs, each PCB may be inverted by the inverter unit 26, after inspection and before it is returned to the return stack; and after the PCBs have been examined on one side and loaded into the return stack holder 8 in the inverted position, the return stack becomes a new supply stack on holder 6 for inspecting the second (inverted) side of each PCB. The PCB Loading and Unloading Units

Fig. 2 more clearly illustrates the drives for the two conveyor arms 18 and 22.

Conveyor arm 18, which loads the PCBs on the inspection table 12, is carried by a carriage 30 which is movable vertically along the vertical column 16 by an electric motor M. fixed to the vertical column. Motor M- rotates a feed screw 32 mounted to the vertical column 16 via a bearing assembly 33 and is receivable within a nut 34 carried by the carriage 30. Conveyor arm 18 is mounted to the carriage 30 via a second bearing assembly 35 enabling the arm to be rotated by motor M_ about a vertical axis parallel to that of the vertical column 16. Motor M₂ is carried by carriage 30 and is coupled to conveyor arm 18 via belt drive 36 and pulleys 36a.

The gripper assembly 20 is coupled to its conveyor arm 18 by a transmission which includes a belt drive 38 and timing pulleys 38a, 38b. Such transmission rotates the gripper assembly 20 the same angle, but in the opposite direction, as it is rotated by its motor M₂, such that the gripper assembly remains at the same orientation in the horizontal plane when the conveyor arm 18 is rotated about the axis parallel to the parallel column 16.

The unloading conveyor arm 22 is similarily mounted on a carriage 40 movable along vertical column 16 below carriage 30 of the loading conveyor arm 18. The unloading conveyor arm 22 is driven vertically by motor M^ which is fixed to the vertical column 16 and rotates a feed screw 42 mounted to the vertical column via a bearing assembly 43 and is receivable within a nut 44 carried by carriage 40. Conveyor arm 22 is mounted to the carriage 40 via a second bearing assembly 45 enabling the arm to be rotated by motor M. about a vertical axis parallel to that of the vertical column 16. Motor M. is carried by carriage 40 and is coupled to the unloading conveyor arm 22 by a belt drive 46 and pulleys 46a.

Gripper assembly 24 is also coupled to conveyor arm 22 by a transmission, including belt 48 and timing pulleys 48a, 48b, which rotates the gripper assembly the same angle, but in the opposite direction, as it is rotated by its motor drive M.. The arrangement is such that gripper assembly 24, as gripper assembly 20, also remains at the same orientation in the horizontal plane when its conveyor arm is rotated by motor M. about the vertical axis.

It will thus be seen that in the arrangement illustrated in Fig. 2, the two arms 18, 22, can move independently along the same vertical column to any selected height, and can independently rotate to any working angle about the same verical axis, i.e., parallel to the axis of the vertical column 16. It will also be seen that the transmissions 38, 38a, 38b and 48, 48a, 48b will rotate the respective gripper assembly 20, 24 the same angle, but in the opposite direction, as their respective motors M_, M., such that the two gripper assemblies remain at the same orientation in the horizontal plane when their respective conveyor arm is rotated about the vertical axis.

Gripper assembly 20, carried by the loading conveyor arm 18, includes a large-surface suction head 50, and a small-surface suction head 52. The large-surface suction head 50 has a sufficiently large surface so as to be able to hold a PCB firmly against it; whereas the small- surface suction head 52 is capable of gripping only a relatively small surface of the PCB, permitting the remainder of the PCB, particularly when a large PCB is being handled, to droop back into contact with the table 12. Thus, the large-surface suction head 50 extends over a surface area of about the same order of magnitude as that of the largest PCB to be handled by it, whereas the surface area of the small suction head 52 is a small fraction (e.g., smaller by at least one order of magnitude) of that surface.

As will be described more particularly below, the large-surface suction head 50, together with the small suction hed 52, grips the PCB and conveys it to the vicinity of the registration device 14, but in the final movements of the PCB to its precise position with respect to the registration shoulders 14a, 14b, the suction of the large- surface head 50 is interrupted, while the suction in the small-surface head 52 is maintained so that the latter head moves the PCB into its final precise position with respect to the registration shoulders.

Fig. 1 illustrates the large-surface suction head 50 as including a large rectangular frame 50a having a plurality of suction cups 50b depending from its lower surface and extending over a surface area of about the same order of magnitude as that of the largest PCB to be handled by the gripper assembly 20. The small-surface suction head 52 is one suction cup at a corner of the frame 50.

In the modification illustrated in Fig. 3, the large-surface suction head 50' is in the form of a large, hollow rectangular housing defining an inner suction chamber, with the lower wall 51 of the housing formed with a plurality of uniformly-distributed suction openings 51a to firmly hold the PCB. Suction is supplied to head 50' via a suction line 51b. The small-surface suction head 52 is as in Fig. 1, in the form of a simple suction cup supplied with suction via line 52a. Also, as in Fig. 1, suction cup 52 in Fig. 3 is mounted forwardly of the corner of the large- surface suction head 50' facing the registration shoulder 14 of the inspection table 12, since it cooperates with that shoulder.

In both Figs. 1 and 3, the small-surface suction head 52 is mounted to the large-surface suction head 50' (or 50 in Fig. 1 ) by a mounting assembly which permits a plurality of degrees of movement of head 52 with respect to head 50'. Thus, the small-surface suction head 52 is carried by a stem 54 rotatably received within a hollow vertical shaft 56 coupled by coupling device 58 to a horizontal piston 60 telescopingly received within a horizontal air cylinder 62. Horizontal cylinder 62 is in turn carried by a vertical cylinder 64 mounted by pivot pin 66 to the large- surface suction head 50' for free pivotal movement about a vertical axis. The large-surface head 50' is in turn mounted to the end of the loading conveyor arm 18 by a stem 68 depending from arm 18.

As the large-surface suction head (50 in Fig. 1, or 50" in Fig. 3) is moved vertically by motor - or horizontally by motor M~, it carries with it the small- surface suction head 52. However, head 52 may be moved independently of the large-surface head in the vertical direction by cylinder 64 fed with fluid via fluid line 64a. Head 52 may also be rotated in a horizontal plane with respect to the large-surface head by pivot pin 66 between cylinder 64 and the suction head. Head 52 may further be moved horizontally towards and away from the large-surface head by controlling the fluid applied via lines 62a, 62b to the cylinder 62 to control the extension or retraction of its piston 60.

The control of cylinder 62 via line 62a, 62b, as well as of cylinder 64 via its fluid line 64a, is effected by a control unit indicated at 70 in Fig. 3, which is a part of an overall control system supervising all the operations of the apparatus. Control unit 70 also controls the vacuum applied to the large-surface head (50 in Fig. 1, or 50' in Fig. 3) via its suction line 51b, and also the vacuum applied to suction cup 52 via its suction line 52a. The normal position of suction cup 52, as determined by the angular location of cylinder 64 on its vertical pin 66, is substantially along the bisector line of the registration shoulders 14a, 14b on the inspection table 12. As will be described more particularly below, these registration shoulders are engaged by the registration corner PCBa (Fig. 3) of the PCB during its final movement by the vacuum cup 52 to precisely position the PCB. The - respective corner of the large-surface suction head (50 or 50") carries a plate 72 having a cutout 73, which serves as a guide for guiding the suction cup 52 back to its home position after it has brought the PCB registration corner PCBa into engagement with both of the registration shoulders 14a, 14b. For this purpose, cutout 73 is formed with an apex 73a which, in the final positioning operation, is located on the bisector line of the registration shoulders 14a, 14b so as to guide the vacuum cup 52 back to its home position. The Inverter Unit 26

As indicated earlier, the inverter unit 26 overlies the return stack holder 8 and, whenever desired, inverts each PCB before it is received on the return stack in holder 8. The purpose of inverting the PCB is to facilitate the optical inspection of both its sides when this is desired. The inverter unit 26, as more particularly illustrated in Figs. 4 and 5, includes a vertically- extending frame 80 pivotally supporting a panel 81 which is normally disposed horizontally. Panel 81 is pivotal about a first axis 82 occupied by a shaft along one edge 81a of the panel, and also about an axis 83 extending along an intermediate portion of the panel (e.g., along its central axis) parallel to axis 82. Panel 81 is pivotal about axis 82 by a pair of arms 84, 85 at its opposite sides, with axis 82 passing through one end of the arms and axis 83 passing through their opposite ends. To arm 85 is fixed an actuator member 86 whose opposite end includes a hinged connection 86a to a piston stem 87 movable through one end of a cylinder 88. The opposite end of cylinder 88 is coupled by a hinged connection 88a to one of the vertical frame members 80.

A stop 89 extends along the edge 81a of panel 81. Stop 89 projects above the surface of panel 81 so as to be engaged by the edge of the PCB when the panel is pivoted about axis 82. Stop 89 is also slidable towards the transverse edge 81b of the panel (extending perpendicularly to its edge 81a) to frictionally move with it the PCB whose edge engages stop 89 during the pivotal movement of the panel about axis 82. The slidable stop 89 is driven by an air cylinder 90 towards the panel edge 81b, and the latter edge includes a second stop 91 engageable with the PCB when driven towards that edge. It will thus be seen that the two stops 89 and 91 precisely locate the PCB on the panel 81 irrespective of the size of the PCB and its initial location on the panel.

Panel 81 is pivoted about its intermediate axis 83 by a rotary actuator 92, which may also be pneumatically actuated. The panel is of hollow construction, and its upper face is formed with a plurality of suction openings

81c for suctionally holding the PCB thereon. The suction is applied, to the interior of panel 81 via a hollow housing 93 secured to the bottom face of the panel and coupled to the rotary actuator 92.

OPERATION

Loading and Unloading of the PCB

The stack of PCBs to be inspected is brought in cassette 2' by trolley 2 to the loading stack holder 6 which, as mentioned earlier, preferably includes an automatic lifting mechanism for maintaining the topmost PCB in the stack at a predetermined vertical position. If a PCB is already on the inspection table 12, the unloading conveyor arm 22 is first pivoted and lowered (by motors M. and M-., Fig. 2) to bring its gripper assembly 24 over the PCB on the table, whereupon the vacuum in the gripper assembly 24 is actuated to grip the PCB and to convey it to the return stack holder 8.

A new PCB may then be applied to the inspection table 12 by pivoting and lowering the loading conveyor arm 18 (via motors M₂ and M_. , Fig. 2) to bring its gripper assembly 20 to overlie the topmost PCB in the supply stack 6, to grip it, and then to convey it to the inspection table 12. It will thus be seen that the two conveyor arms 18 and 22 can be operated simultaneously and independently of each other so that unloading conveyor arm 22 removes the PCB from the inspection table 12 as conveyor arm 18 brings a new PCB- to the inspection table for inspection. In order to peal and easily separate the uppermost PCB from the underlying one in the stack, the vacuum supply means may first apply suction to the small-surface suction cup 52, then apply air pressure to the cylinder 64 to lift the suction cup 52 in order to peal the corner of the PCB from the next one and to allow air to enter in between the two. Suction may then be applied to the large-surface suction head (frame 50a and suction cups 50b in Fig. 1, or frame 50' and suction openings 51a in Fig. 3), while suction cup 52 is returned to its initial position at the same level as the large-surface suction head, so that the PCB is firmly gripped by both the large-surface and small-surface suction heads, which heads then lift the gripped PCB. Precise Positioning of the PCB on Table 12 The loading of conveyor arm 18, driven by its vertical motor M- and horizontal motor M~ (Fig. 2), initially conveys the PCB to the vicinity of the registration device 14 on the inspection table 12. Thus, both the large suction head 50, and the small suction cup 52 firmly hold the PCB to the underface of the gripper assembly 20 during this initial movement of the PCB. When the PCB is in the vicinity of the registration device 14, the suction in the large suction head 50 is interrupted, while the suction is maintained in the small suction cup 52 engaging the PCB adjacent to its registration corner PCBa.

Linear motor 62 is then operated to move the small suction cup 52 towards the registration device 14 of the inspection table 12. The PCB registration corner PCBa will most likely engage first one shoulder (e.g., 14a) of the registration device 14, but the pivotal mounting of the suction cup 52 in the coupling 58, and the pivotal mounting of the cylinder 64 via vertical pin 66, will permit the suction cup, and the PCB grippby it, to pivot about the vertical axis of coupling 58 while turning around the vertical arms of cylinder 64, until the registration corner PCBa firmly contacts both registration shoulders of the registration device 14. When the suction to the large suction head 50 is interrupted, the portion of the PCB opposite to that gripped by the small suction head 52 will tend to droop into contact with the inspection table 12, so that during the final positioning movement of the PCB towards the registration shoulders by actuating linear motor 62, this portion of the PCB will be dragged along the table. However, since the two pivotal couplings permit the free movement of the suction head 52 about its own vertical axis and the axis of rotation of cylinder 64 on pin 66, and also since only a small corner of the PCB is being gripped at that time, the described arrangement allows considerable force to be applied to the PCB to firmly press it into the right-angle corner of the registration device 1 without risk of buckling the PCB. As soon as the PCB has thus been precisely positioned with respect to the registration device 14, the suction to suction cup 52 is interrupted; linear motor 62 is actuated to return the suction cup 52 to its normal position approximately in line with the bisector angle of the registration device 14, as guided by cutout 73 of the guide plate 72; and the gripper assembly 20 is then returned to its normal position ready for conveying another PCB to the inspection table after the inspection of the one on the table has been completed. The Inverter Unit 26

If the PCBs are to be inspected on only one side, the inverter unit 26 is not used. However, if the PCBs are to be inspected on both sides, the inverter unit 26 is used in order to invert each PCB after its removal from the inspection table 12 by the unloading conveyor arm 22 and its gripper assembly 24, and before it is applied to the return stack holder 8.

When the inverter unit 26 is used, its panel 81 is normally located in a horizontal position as shown in Fig. 4, overlying the return stack holder 8, so as to receive the PCB being returned by the unloading conveyor arm 22 and its gripper assembly 24. After the PCB has been deposited on the upper face of panel 81 , cylinder 88 is actuatfed to tilt panel 81 at an acute angle (preferably 60°) about horizontal axis 82 extending adjacent edge 81a of the panel. This tilting of the panel causes the PCB thereon to slide about the upper face of the panel until the edge of the PCB engages stop 89 adjacent edge 81a of the panel. Immediately thereafter, cylinder 90 is actuated to move stop 89 towards edge 81b of the panel. This also moves the PCB (by its frictional engagement with the stop) towards edge 81b of the panel until the PCB engages stop 91 at that edge. The PCB is thus now precisely registered with respect to panel 81.

Suction is then applied to the interior of panel 81 so that the PCB is firmly gripped by the suction holes 81c in the upper face of the panel. The panel 81 is first pivoted 180° about its central axis 83, by rotary actuator 92, and is then pivoted 60° about its axis 82 by cylinder 88, so that the gripped PCB now assumes an inverted horizontal position on the lower face of the panel. At this time, the suction is interrupted, whereby the PCB drops by gravity on top of the topmost PCB in the return stack holder 8.

Inverter 26 is then returned to its normal position, as illustrated in Fig. 4, preparatory for receiving and inverting the next PCB to be removed from the inspection table and to be inverted before applied to the return stack holder 8. Possible Variations

While the invention has been described with respect to one preferred embodiment, it will be appreciated that many variations may be made.

For example, the suction cup 52 may be mounted with its linear motor 62 and vertical cylinder 64 on the table 2 via pin 66, instead of on the large-surface suction head 50, so that the suction cup 52 can swing out and into the loading area of the PCBs. In such case, the PCB will have to be dropped onto the table entirely before the suction cup 52 swings in and picks up the PCB's corner for final positioning. In such an arrangement, the suction cup 52 would "pull" the PCB into its final corner position, as distinguished from the illustrated preferred embodiment wherein the suction cup 52 "pushes" the PCB into its final corner position.

A further variation would be to utilize only the large-surface suction head 50 which would be mounted to the loading conveyor arm 20 via a pivotal coupling corresponding to coupling 66, and a linear motor corresponding to linear motor 62. In such an arrangement, the masses involved in the positioning process would be much larger, and therefore such an arrangement would not be suitable for thin PCBs which might be damaged or buckled during the process. However, an advantage of such an arrangement is that the PCB would be held up entirely while positioning proceeds, and would not be dragged partially on the table as in the described arrangement. Such a modification might be preferred for more rigid PCBs.

Many other variations, modifications and applications of the invention will be apparent.

Claims

sufficient only to grip a small area of the article adjacent to the its registration corner; said first suction head being coupled to said first drive means; said second suction head being coupled to said first suction head by said linear motor and said pivotal coupling to bring said registration corner of the article into engagement with both of said registration shoulders on the table.

4. The apparatus according to Claim 3, further including a control means for interrupting the suction to said first suction head to release the article therefrom while the suction in the second suction head is maintained and said linear motor is actuated to effect said further movement of the second suction head and article bringing said registration corner of the article into engagement with both of said registration shoulders.

5. The apparatus according to Claim 4, wherein said first suction head includes a plurality of suction cups.

6. The apparatus according to Claim 4, wherein said first suction head includes a suction chamber and a wall formed with a plurality of suction openings.

7. The apparatus according to any one of Claims 2-6, wherein said pivotal coupling between said conveyor arm and said gripper assembly is located on said first suction head to be substantially along the bisector line of said registration shoulders.

8. The apparatus according to any one of Claims 2-7, wherein said first suction head carries a guide formed with a cutout for guiding the second suction head back to a home position after it has brought the registration corner of the article into engagement with both of said registration shoulders on the table.

9. The apparatus according to any one of Claims 2-8, wherein said piston is coupled to said gripper assembly, and said cylinder is coupled to said conveyor arm via said pivotal coupling.

10. Apparatus according to any one of Claims 2-9, wherein said registration corner of the article, and said registration shoulders on said supporting surface, both form right-angles.

11. The apparatus according to any one of Claims 1-10, wherein said supporting surface is a horizontal inspection table for receiving articles for examination, said apparatus further including: a vertical column laterally of said table; table-loading means for conveying the articles individually from a supply stack to the table for examination and including said gripper assembly, drive and conveyor arm mounted at one end to said vertical column and rotatable about an axis parallel to said vertical column; and table-unloading means for conveying the articles individually from the table, after examination, to a return stack, including a second conveyor arm mounted at one end to said vertical column and rotatable about an axis parallel to said vertical column, a second gripper assembly carried at its opposite end for gripping the article on the table after examination and for conveying it to the return stack, and second drive means for driving said second arm; said second conveyor arm, second gripper assembly, and second drive means being constructed as said first- mentioned conveyor arm, gripper assembly, and drive means.

12. The apparatus according to Claim 11 , wherein each of said drive means includes a linear drive for driving its respective arm vertically along said vertical column, and a rotary drive for rotating its respective arm horizontally about said axis parallel to said vertical column.

13. The apparatus according to Claim 12, wherein each of said gripper assemblies is coupled to its respective conveyor arm by a transmission which rotates the gripper assembly the same angle, but in the opposite direction, as it is rotated by its respective rotary drive, such that the gripper assembly remains at the same orientation in the horizontal plane when the conveyor arm is rotated about said axis parallel to said vertical column.

14. The apparatus according to any one of Claims 11-13, wherein said second arm is mounted to said vertical column below said first arm.

15. The apparatus according to any one of Claims 11-14, wherein: each of said articles has a said registration corner; and said table includes two of said registration shoulders at an angle to each other corresponding to that of, and engageable with, the registration corner of the article.

16. The apparatus according to any one of Claims 11-15, wherein said table-unloading means includes an inverter mechanism overlying said return stack for inverting each article before it is received on the return stack.

17. The apparatus according to Claim 16, wherein said inverter mechanism comprises: a panel normally in a horizontal position for receiving the article from the gripper device of the table-unloading means; suction means for retaining the article on the panel; a stop at one edge of said panel; and pivotal means for first pivoting the panel to an acute angle while said suction means is non-operative, to cause the article to slide by gravity to said stop at said one edge and, for subsequently pivoting said panel 180° from its normal horizontal position about an intermediate axis of the panel parallel to said one edge, while said suction means is operative, so as to invert the article and to permit the article to drop by gravity in said inverted position on the return stack when the suction means is again made non-operative.

18. The apparatus according to Claim 17, wherein said inverter mechanism further includes: a frame member on which said panel is pivotally mounted; a second stop facing a second edge of the panel at a right angle to said first stop; said first-mentioned stop being slidable along said one edge of the panel; said apparatus further including a drive for sliding said stop along said one edge towards said second edge, to bring said article into engagement with said second stop before the panel is pivoted 180°.

19. The apparatus according to Claim 18, wherein said pivotal means comprises a first pivotal device for first pivoting the panel to an acute angle about said one edge to bring the article into engagement with said slidable stop, and a second pivotal device for subsequently pivoting the panel 180° from its normal horizontal position about said intermediate axis of the panel.

20. Apparatus for inverting flat articles, comprising: a panel normally in a horizontal position for receiving the article to be inverted; suction means for retaining the article on the panel; a stop at one edge of the panel; and pivotal means for first pivoting the panel to an acute angle while said suction means is non-operative, to cause the article to slide by gravity to said stop at said one edge, and for subsequently pivoting said panel 180° from its normal horizontal position about an intermediate axis of the panel parallel to said one edge, while said suction means is operative, to thereby cause the article to be inverted and to be permitted to drop by gravity in said inverted position when the suction means is made non-operative after the inversion.

21. The inverter apparatus according to Claim 20, further including: a frame member on which said panel is pivotally mounted; a second stop facing a second edge of the panel at a right angle to said edge; said first-mentioned stop edge being slidable along said one edge of the panel; said apparatus further including a drive for sliding said stop along said one edge towards said second edge, to bring said article into engagement with said second stop before the panel is pivoted 180°.

22. The inverter apparatus according to Claim 20, wherein said pivotal means comprises a first pivotal device for first pivoting the panel to an acute angle about said one edge to bring the article into engagement with said slidable stop, and a second pivotal device for subsequently pivoting the panel 180° from its normal horizontal position about said intermediate axis of the panel.

23. The inverter apparatus according to any one of Claims 21-22, wherein said table is dimensioned to receive printed circuit boards to be inspected.