US 3625377 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
United States Patent  Inventors Robert C. Bohannon;
William H. McDaniel, both of Greensboro,
21 Appl. No. 52,446
 Filed July 6, 1970  Patented Dec. 7, H71
 Assignee Western Electric Company Incorporated New York, N.Y.
 STACKED SHEET FEEDER 13 Claims, 5 Drawing Figs.
 References Cited UNITED STATES PATENTS 935,538 9/l909 North 3,146,902 9/!964 Voelker ABSTRACT: A retractable conveyor individually feeds printed circuit boards from a stack into a processing machine. As the conveyor retracts toward the machine from an extended position over the stack, it cams a releasable pickup device downwardly into gripping engagement with the top board on the stack at a position forward of the stack center. As the conveyor starts to extend again, it cams the pickup device upwardly to lift the engaged board into an inclined position over the stack and in the path of extension ofthe conveyor, whereupon further extension causes the conveyor to engage the inclined board and separate it from the stack. The pickup device is thereupon released so that the board drops on the conveyor to be carried into the processing machine during the next retraction.
PATENTED DEC 7l97| 3625377 sum 2 BF 3 PATENTEDDEB H97! 7 3525377 sum 3 or a STACKED SI-IEET FEEDER BACKGROUND OF THE INVENTION When processing printed circuit boards, it is common to individually feed the boards serially into a processing station from a stack. Typically, the top board on the stack is gripped by a suitable pickup device and fed by a traversing conveyor to the processing machine. Presently contemplated schemes for this apparatus have several severe limitations; e.g., the pickup device must have sufficient power to lift the entire weight of the board, and the traversing conveyor is relatively long and bulky.
SUMMARY OF THE INVENTION The present invention provides a compact, versatile machine for separating and advancing stacked sheets (e.g., printed circuit boards) serially into a processing station wherein the holding power of the pickup device can be much less than the normal force necessary to lift and carry the individual boards.
In an illustrative embodiment, a retractable conveyor is supported for reciprocal movement along an axis between an extended position over a stack of printed circuit boards and a retracted position adjacent a component insertion machine or other processing apparatus located forward of the stack. A releasable pickup device mounted for movement toward and away from the stack at a location forward of the stack center is connected to a pivotal arm having a cam surface in contact with the conveyor.
Initially, as the conveyor is retracted toward the processing machine, the conveyor cams the pivotal arm downwardly to move the pickup device into gripping engagement with the front portion of the top board on the stack. After reaching its fully retracted position, the conveyor starts to extend again toward the stack to cam the pickup device upwardly. This action lifts the gripped board into inclined relation across the axis and over the stack. Further extension of the conveyor causes the latter to contact the inclined top board and strip it from the stack.
When the conveyor is fully extended, its movement is again reversed to start a second retraction. At this point, the pickup device is released to permit the inclined separated top board to drop on the conveyor. The board is carried by the conveyor during the associated retraction to be received in the processing machine.
Each time a board is stripped during an extension of the conveyor, the stack may be incrementally moved upwardly by a distance equal to a board thickness so that the next board is in position to be gripped by the pickup device during the succeeding retraction of the conveyor.
BRIEF DESCRIPTION OF THE DRAWING The nature of the invention and its advantages will appear more fully from the following detailed description taken in conjunction with the appended drawing, in which:
FIG. 1 is an elevation view of a separating and advancing apparatus constructed in accordance with the invention as such apparatus starts a typical cycle of operation; and
FIGS. 2-5 are elevational views similar to FIG. 1 but illustrating the apparatus at successively latter points during the operation cycle.
DETAILED DESCRIPTION Referring now to the drawing, FIG. 1 illustrates a mechanism 9 for (a) stripping individual sheets 11-11, illustratively printed circuit boards, from a stack 12; and (b) serially advancing the stripped sheets from the stack to the right in a horizontal plane 13 to a terminal area 14. The area 14 represents the interface of the output of the mechanism 9 and the input of a suitable processing apparatus represented generally at 16. illustratively, the apparatus 16 may be a component insertion machine of the type described in US. Pat.
No. 3,291,351, issued to H. S. Butterworth et al. on Dec. I3, 1966. For purposes of illustration only, the machine 16 is shown as having an input conveyor belt 17 for receiving boards advanced to the terminal area 14 by the mechanism 9.
The mechanism 9 includes a retractable conveyor 18 which is supported on a fixed frame 19 for reciprocation in the horizontal plane 13 between the illustrated fully extended position over the stack 12 and a fully retracted position adjacent the terminal area 14. (For purposes of this description, a retractive movement of the conveyor to the right will cause an advance of an article that it conveys.)
The conveyor 18 includes (a) a first rear axle 20 movably supported in an elongated horizontal slot 21 in the frame 19, the axle extending perpendicular to the plane of the paper; (b) a second intermediate axle 22 parallel to the axle 20 and supported on the frame 19 adjacent the terminal area 14 for rotation about its axis; and (c) a third forward axle 23 parallel to the first and second axles and supported for movement perpendicular to the horizontal plane 13, e.g., within an elongated vertical slot 24 on the frame 19 below the axle 22. The axles 20, 22, and 23 respectively carry support pulleys 26, 27, and 28. A conveyor belt 29 extends in a path from a fixed point 31 on the frame 19 and successively around the pulleys 26, 27, and 28 to terminate back at the fixed point 31.
A first microswitch 32 mounted on the frame 19 is supported near the right end of the horizontal slot 21 in the path of the first axle 20 so that the switch 32 is engaged and closed by the axle 20 whenever the conveyor reaches its rightmost or fully retracted position in the plane 13. Similarly, a second microswitch 33 mounted on the frame 19 is supported near the top end of the vertical slot 24 in the path of the third axle 23, so that the switch 33 is engaged and closed by the axle 23 whenever the latter is in its uppermost position, e.g., whenever the conveyor reaches its most extended position in the plane 13 as illustrated in FIG. 1.
The reciprocatory movement of the retractable conveyor 18 is accomplished in a conventional manner via a reversible drive motor 34, whose speed is preferably made adjustable to allow synchronimtion of the retractable conveyor with the belt 17 of the processing machine 16. The motor is coupled through a belt 35 to a drive pulley 36 on the axle 22. The motor is suitably connected to be successively reversed in response to successive alternate closures of the switches 32 and 33. Details of the required connecting circuitry will be apparent to those skilled in the art and will not be described here.
Tension may be maintained on the conveyor belt 29 at all times during its reciprocatory movement by means of an arrangement that illustratively includes (a) a fourth pulley 37 supported for rotation on the frame 19 rearward of the horizontal slot 21; (b) a fifth pulley 38 supported for rotation on the frame 19 above the axle 22; and (c) a sixth pulley 39 supported for rotation on the frame 19 below the vertical slots 24. (If desired, of course, the pulley 38 can be mounted for rotation on the axle 22 instead of on a separate support.) A tensioned cable 40 is affixed to the first axle 20 and extends successively around the pulleys 37, 38, and 39 to a fixed point on the third axle 23 to provide the required force on the belt 29.
A releasable, vacuum-operated pickup device 41 is mounted for movement toward and away from the top of the stack 12 at a position forward of the stack axis (designated 42 in the figure) for engagement with the front end of the top board on the stack. (As shown, the front ends of the boards are maintained in a desired vertical plane by stacking the boards uniformly against a front stop 42A.) While the internal portions of the device 41 are not illustrated in detail in the drawing, the device may illustratively be solenoid-actuated and spring-biased wherein the application of an exciting voltage to a solenoid (represented only by a pair of externally accessible terminals 4343) causes an internal movable plunger (not shown) to move upwardly within a cylinder against the spring bias from a pivotally mounted gripping surface 44,
which communicates internally with the cylinder. The vacuum thereby created during the time that the surface 44 is in engagement with an article (e.g., the top board 11 of the stack) will cause the surface 44 to firmly grip the article.
With this arrangement, the subsequent removal of the exciting voltage from the solenoid terminals 43 permits the spring bias to move the plunger downwardly toward the gripping surface 44, thereby breaking the vacuum and causing the surface 44 to release its grip on the engaged article.
The solenoid terminals 43 are suitably connected for l excitation upon the closure of the microswitch 32 and (2) deexcitation upon each closure of the other microswitch 33.
The pickup device 41 is carried by an arm 51 that is pivotally mounted on the frame 19 by a pin 52 for movement in a vertical plane, so that the device 41 can move back and forth across the horizontal plane 13 as the arm 51 is pivoted. The device 41 is so located on the arm 51 that the gripping surface 44 of the pickup device is mounted out of contact with the top board on the stack 12 except when the arm approaches its lowermost position.
The arm 51 also carries a cam 53 having a lower bearing surface that includes (a) a relatively long left segment 56 that is essentially parallel to the plane 13 in the position shown in FIG. 1 and (b) a relatively short right segment 57 that forms a sharp angle with the plane 13. The segments 56 and 57 intersect in a region 58 that defines the lowest portion of the cam 53. As shown, the region 58 may be positioned horizontally adjacent the pickup device 41 as projected in the plane of the drawing.
The pivot pin 52 is so positioned vertically on the frame 19 with respect to the conveyor 18 that the lower bearing surface of the cam 53 is urged at all times into positive contact with a roller 59 mounted on the rear axle of the conveyor. In the extended position of the conveyor shown in FIG. 1, the roller 59 is in engagement with the left segment 56 of the cam surface.
The stack 12 is supported on a table 61 which is vertically movable with respect to the frame 19. The table 61 may be advanced upward by one or more increments related to the thickness of one of the boards 11 on the stack 12 in timed relation to the movement of the conveyor 18, so that successive boards may be brought up to a desired height that permits engagement with the gripping device. In particular, the table 61 may be moved by a lead screw 62 which is coupled via a set of gears 63 to a conventional stepping motor 64. The motor 64 is suitably connected to be stepped upon successive closures of the microswitch 33. If the board thickness varies, the stepping motor may be further regulated by a suitable control system including a pair of photosensors (not shown) located at the desired height of the stack, so that the resulting movement of the table 61 automatically brings the successive boards up to the desired height.
OPERATION A cycle of operation of the mechanism 9 will now be described. It is assumed that (a) the conveyor 18 is initially in the fully extended position shown in FIG. 1; (b) no boards on the stack 12 have yet been engaged by the pickup device 41; and (c) the reversible drive motor 34 has just been energized in a direction to start the retraction of the conveyor 18 from its leftmost extended position shown.
As the conveyor retracts, the rear axle 20 moves to the right along the horizontal track 21 and the roller 59 correspondingly moves along the cam surface. During this movement, the pickup device 41 is maintained in its raised position until the roller reaches the region 58. As the axle 20 retracts past the plane of the region 58, the movement of the roller-59 to the right along the right segment 57 of the cam surface causes the pickup device to move down across the plane 13 and into engagement with the right edge of the top board on the stack 12 (see FIG. 2). At this point, the conveyor has retracted to a position essentially clear of the stack.
When the axle 20 engages and closes the microswitch 32 at the conclusion of the conveyor retraction, the drive motor 34 reverses and the solenoid of the pickup device 41 is energized to apply vacuum to the gripping surface 44, which thereby grips the engaged top board. The conveyor now starts to extend to the left from its fully retracted position, and the resulting leftward movement of the roller 59 against the steeply inclined right segment 57 of the cam surface lifts the pickup device 41 back across the plane 13 (FIG. 3). Since the pickup device is in firm gripping engagement at this time with the front edge of the top board, such board is pivoted into inclined position about its rear edge across the plane 13. As shown, the conveyor has just approached the stack at this point.
Continued extension of the conveyor 18 to the left causes an additional roller 71 (FIG. 4), supported for rotation on the axle 20 and having a diameter larger than the pulley 26, to engage the inclined top board and to separate the board from the stack; illustratively, the rollers 59 and 71 may have the same diameter. Simultaneously, the support pulley 28 in the vertical slot 24 approaches its uppermost position.
When the conveyor has reached its fully extended position over the stack, the support roller 28 engages and closes the microswitch 33 to deenergize the solenoid of the pickup device 41. The resulting loss of vacuum on the gripping surface 44 releases the grip of the pickup device on the front end of the separated inclined board 11 to permit such board to fall gently on the conveyor belt 29.
The engaging of the microswitch 33 by the support pulley 28 also (a) actuates the stepping motor 64 (FIG. 1) to index the stack 12 upwardly to place the next board in position to be gripped; and (b) reverses the drive motor 34 again to start a second retraction-extension cycle of the conveyor 18. This time, as the conveyor retracts to the right (as shown in FIG. 5), the separated top board 11 carried thereby is advanced to the terminal area 14 and into the adjacent processing machine 16.
As the separated board is so advanced, the forward motion of the roller 59 along the cam surface again moves the pickup device 41 downwardly into engagement with the new top board on the stack 12 to be gripped thereby when the microswitch 32 is contacted as described above. Hence, at the beginning of the next succeeding extension of the conveyor 18 to the left, the corresponding movement of the roller 59 along the cam segment 57 will again cause the pickup device 41 to lift the gripped board into the required inclined position across the plane 13 to be first separated from the stack and then conveyed into the processing machine. This sequence of steps continues for each board in the stack.
It will be apparent from the foregoing description that the gripping force that is necessary in the pickup device 41 can be much less than that required in the more conventional techniques for lifting and supporting the full weight of a board. Moreover, the relatively short horizontal travel of the retractable conveyor 18 results in a considerable saving in size and bulk.
It is to be understood that the above-described embodiments is merely illustrative of the principles of the invention. Many variations and modifications will now be apparent to those skilled in the art. For example, since only the front edges of the successive boards positioned against the front stop 42A are engaged by the pickup device, a wide variety of board lengths extending rearwardly from the front stop may be accommodated by the apparatus. Accordingly, it is intended that the scope of the appended claims not be limited to the specific disclosure herein contained.
What is claimed is:
1. In an apparatus for successively stripping sheets from a stack and for advancing the stripped sheets serially in a forward direction along a prescribed horizontal axis from the stack to a terminal point forward of the stack:
a retractable conveyor supported for reciprocation along the axis between an extended position over the stack and a retracted position adjacent the terminal point for carrying successive sheets from the stack to the terminal point;
a pickup device supported for movement toward and away from the stack for releasably gripping the top sheet of the stack at a location forward of the stack center;
camming means linking the pickup device and the conveyor for moving the pickup device into gripping engagement with the top sheet of the stack when the conveyor retracts in the forward direction to the tenninal point and for moving the pickup device away from the stack to position the gripped top sheet in inclined relation across the axis when the conveyor starts to extend in the reverse direction away from the terminal point, whereby a further extension of the conveyor causes the latter to engage the inclined sheet to strip the sheet from the stack; and
means rendered effective when the conveyor reaches the extended position for releasing the grip of the pickup device on the stripped sheet to permit the sheet to be carried by the conveyor to the terminal point during a succeeding retraction of the conveyor.
2. Apparatus as defined in claim 1, further comprising, in combination, means supporting the stack for vertical movement, and normally unoperated means for incrementally moving the supporting means upwardly by a distance equal to the thickness of one of the sheets.
3. Apparatus as defined in claim 2, further comprising means rendered effective when the conveyor reaches its fully extended position for operating the incremental moving means.
4. Apparatus as defined in claim 1, in which the pickup device comprises, in combination, control means operative when energized for gripping a surface engaged thereby and thereafter operative when deenergized for releasing the grip on the surface.
5. Apparatus as defined in claim 4, further comprising, in combination, first sensing means operated when the conveyor reaches its fully retracted position for generating a first output indication, and means responsive to the occurrence of the first output indication for energizing the control means of the pickup device.
6. Apparatus as defined in claim 5, in which the grip-releasing means comprises, in combination, second sensing means operated when the conveyor reaches its fully extended position for generating a second output indication, and means responsive to the occurrence of the second output indication for deenergizing the control means of the pickup device.
7. Apparatus as defined in claim 6, in which the conveyor comprises, in combination, a rear axle, an intermediate axle, and a forward axle disposed in parallel relation:
means supporting the intermediate axle for rotation adjacent the terminal point; 1
means supporting the rear axle for reciprocation forwardly toward and rearwardly away from the terminal point along the axis; and
a conveyor belt disposed around the rear, intermediate, and
8. Apparatus as defined in claim 7, further comprising means for tensioning the conveyor belt.
9. Apparatus as defined in claim 7, further comprising means for supporting the first sensing means in the path of the rear axle adjacent the intermediate axle for operation of the first sensing means upon engagement thereof by the rear axle.
10. Apparatus as defined in claim 7, in which the conveyor further comprises means supporting the forward axle for movement in a vertical plane disposed through the intermediate axle.
11. Apparatus as defined in claim 10, further comprising means for supporting the second sensing means in the path of the forward axle adjacent the intermediate axle for operation of the second sensing means upon engagement thereof by the forward axle.
12. Apparatus as defined in claim 10, further comprising means for reversibly rotating the intermediate axle to reciprocate the conveyor.
13. Apparatus as defined in claim 12, further comprising means res ons ive to the occurrences of successive first and second ou put indications for successively reversing the rotating means.