US 3589938 A
Description (OCR text may contain errors)
June 29, 1971 BLEWETT ETAL 3,589,938 METHODS FOR APPLYING LIQUID T0 ARTICLES WITHOUT TOUCHING THE ARTICLES 12 Sheets-Sheet 1 Filed July 11, 1968 I NVE/V TORS J. H. BLEWETT H. K. mum/w AM. ATTORNEY June 29, 1971 J. H. BLEWETT ETAL 3,589,938
METHODS FOR APPLYING LIQUID TO ARTICLES WITHOUT TOUCHING THE ARTICLES Filed July 11, 1968 12 Sheets-Sheet 2 June 29, 1971 J. H. BLEWETT ETAL 3,589,938
METHODS FOR APPLYING LIQUID TO ARTICLES WITHOUT TOUCHING THE ARTICLES Filed July 11, 1968 12 Sheets-Sheet s F/Gr 7 June 29, 1971 J. H. BLEWETT ET'AL METHODS FOR APPLYING LIQUID TO ARTICLES WITHOUT TOUCHING THE ARTICLES 12 Sheets-Sheet 4 Filed July 11, 1968 June 29, 1971 J, w -r EI'AL 3,589,938 METHODS FOR APPLYING LIQUID T0 ARTICLES WITHOUT TOUCHING THE ARTICLES Filed Juiy 11, 1968 12 Sheets-Sheet 5 mm 5 mm June 29, 1971 BLEwETT ErAL 3,589,938
. METHODS FOR APPLYING LIQUID T0 ARTICLES WITHOUT TOUCHING THE ARTICLES Filed July 11, I968 12 Sheets-Sheet 6 FIG? /5 June 29, 1971 J. H. BLEWETT ETAL METHODS FOR APPLYING LIQUID T0 ARTICLES WITHOUT TOUCHING- THE ARTICLES 12 Sheets-Sheet 7 Filed July 11, 1968 J. H. BLEWETT E L June 29, 1971 3,589,938 mmaons FOR APPLYING LIQUID TO ARTICLES WITHOUT TOUCHING THE ARTICLES Filed July 11, 1968 12 Sheets-Sheet 8 June 29, 1971 BLEwETT ETAL METHODS FOR APPLYING LIQUID '20 ARTICLES WITHOUT TOUCHING THE ARTICLES 12 Sheets-Sheet'Q Filed July 11, 1968 June 29, 1971 BLEWETT EI'AL 3,589,938 METHODS FOR APPLYING LIQUID TO ARTICLES WITHOUT 'IOUCHING THE ARTICLES 12 Sheets-Sheet 10;
Filed Julyll, 1968 METHODS FOR APPLYING LIQUID TO ARTICLES WITHOUT" Filed July 11, 1968 J. H. BLEWETT ETA]- MAN. 7" W 151 nes- AUTO F/G-ZO SPEED /8 CONTROL 0%: H uo7 FIG-Z/ CARRIAGE PM 3% MAGNET UP LIFT DWELL CAM H8 COMB DWELL COMB VARNISH COMB MOVES OVER TO wELL To VARNISH VARISTORS TRANSFERq DWELL COMB I DWELL OVES M MOVES MOVES DOXWN Q F ES DWELL: K :DWELL 0| P CAM COMB COMB MOVES OVER COMB CAM |I6 LJMITSWITCH RACK |5| CLOSED SWITCH oPEN ADVANCE CAM I49 June 29, 1971 BL w T-r EI'AL 3,589,938
METHCDS FOR APPLYING LIQUID 'ro ARTICLES WITHOUT 'roucnme THE ARTICLES 12 Sheets-Sheet 18 Filed July 11, 1968 United States Patent US. Cl. 117-212 Claims ABSTRACT OF THE DISCLOSURE Coating fluid is applied to an article, without contacting a body of the article with means other than the fluid to be applied. An applicating member, having at least one tooth with a concavity therein, is dipped into a bath of coating fluid, retracted and fluid retained in and about the concavity by capillarity. The member is then brought into noncontacting relation with the article so that a portion of the article lies within the fluid-filled concavity. A quantity of fluid within the concavity contacts and flows about the article, coating it. Simultaneous coating of a plurality of paramagnetic-leaded electrical devices utilizes magnetic holding of the devices, during the coating process, and an applicator with a plurality of spaced teeth arranged in a comblike array.
BACKGROUND OF THE INVENTION This invention relates geenrally to methods for applying liquid coatings to articles. In a specific example, the invention relates to applying a protective varnish coating to each of a multiplicity of varistors, simultaneously and automatically, without contacting the varistors other than with the coating material. Accordingly, the general objects of the invention are to provide new and improved methods for such purposes.
In the past, a protective junction-coating resin, hereinafter called varnish, was applied to electrical devices, such as varistors, by means of a hypodermic needle and syringe. With the syringe filled, an opertaor forced a small amount of the varnish out of the hand-held syringe and directed it at the varistors, one at a time. One disadvantage of this technique is that the amount of varnish exuded from the syringe depends on the operators sense of feel and may vary from varistor to varistor as well as from operator to operator.
Another disadvantage is that the operators would frequently touch the varistors with the end of the hypodermic needle and cause contamination of or possible damage to the varistor.
Still another disadvantage is the slow speed of manually applying the varnish to the varistors one by one. Accordingly, specific objects of this invention are to overcome the aforementioned problems and disadvantages by providing new and improved methods for applying controlled amounts of varnish to a plurality of varistors without contacting them.
Other objects are to provide new and improved methods:
(l) for applying a liquid coating, such as varnish, in such a way that the liquid is caused to flow around the article being coated;
(2) for applying such a coating to a multiplicity of articles automatically; and
(3) for applying the coating to the articles without touching them.
SUMMARY The foregoing and other objects are accomplished, in accordance with certain features of the invention, by pro- Patented June 29, 1971 viding an applicator member having a concave recess, in one surface, of a size somewhat larger than a portion of an article to be coated. First, the applicator is engaged with a coating liquid such that a quantity of the liquid is retained in the recess by capillary action. Then, the applicator member and article are brought into close, noncontacting proximity, so that the recess surrounds a portion of the article to be coated and the liquid contacts the article. The liquid then flows from the applicator member onto the article, to coat the article without touching it with the applicator member.
In specific embodiments of the invention, the applicator member is dipped into a bath of coating liquid, to coat both the recess and surrounding portions of the member, and is brought into proximity to an article to be coated so that liquid flows onto the article both from the recess and the surrounding portions of the member. Preferably, the article is held down during application of the liquid. For simultaneous coating of many articles, and/or spaced portions of one article, a plurality of the applicator members are arranged in a comblike array of teeth on an elongated support member. Preferably, the teeth are spaced by slots, which are longer than the depth of immersion of the teeth in the coating liquid, to prevent liquid from flowing from one tooth to the next. In accordance with a specific embodiment, for automatically applying varnish to a plurality of varistors, apparatus is provided for automatically extracting racks of varistors from a canister, guiding the racks to a varnish-applying station, applying varnish simultaneously to all varistors in the rack, and inserting the rack of coated varistors into another canister. The varistors rest in evenly spaced notches, formed along the length of the racks, and are held down magnetically during the coating operation.
Other objects, advantages and features of the inven tion will be apparent from the following detailed description of specific examples and embodiments thereof.
BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:
FIG. 1 is an isometric view of a coated varistor;
FIGS. 2 and 3 are front and end elevations, respectively, of the coated varistor;
FIG. 4 is an isometric view of a rack loaded with unvarnished varistors;
FIG. 5 is an isometric view, with portions broken away, showing the overall arrangement of the major machine components;
FIG. 6 is an end elevation, with two racks shown in phantom, of a canister from which the racks of uncoated varistors are withdrawn, viewed along line 6-6 of FIG. 5;
FIG. 7 is a front elevation of the same apparatus, viewed along line 77 of FIG. 6;
FIG. 8 is a front cross-section along line 8-8 of FIG. 5, with the canister removed, illustrating a station for unloading the racks from a canister;
FIG. 9 is a partial end elevation of the same apparatus, viewed along line 9-9 of FIG. 8;
FIG. 10 is a plan view of the transfer table, viewed along line 10-10 of FIG. 5;
FIG. 11 is a front elevation of the same mechanism, viewed along line 11-11 of FIG. 10;
FIG. 12 is a cross-section taken along line 12-12 of FIG. 11;
FIG. 13 is a rear elevation of the varnish-applying station, viewed along line 13-13 of FIG. 5;
FIG. 14 is a cross-section viewed along line 14-14 of FIG. 13;
FIG. 15 is a cross-section of the varnish-applying station motor drive, viewed along line 15-15 of FIG. 13;
FIG. 16 is an isometric view of a portion of the varnishapplying comb, showing the relation of the comb to a varistor at the time of varnish application;
FIGS. 17 and 18 are front and end views, respectively, of one pair of applicator teeth, with portions of FIG. 18 broken away for clarity;
FIG. 19 is an isometric view of the load station, partly in cross-section, for returning the racks to a canister;
FIG. 20 is a schematic drawing of an electrical control circuit;
FIG. 21 is a cam timing chart; and
FIG. 22 is a schematic drawing of a pneumatic circuit.
DETAILED DESCRIPTION In the following detailed description of a specific embodiment of the invention, the process to be performed will be described generally with reference to FIGS. 1-4, following which the relation among the major component mechanisms of an automatic machine for performing the process will be described with reference to FIG. 5. After that, the specific method steps and the mechanical movements of each mechanism will be described separately, in the sequence in which they perform the process, with reference to FIGS. 6 through 19. Finally, the operation of the complete machine will be described with reference to the control circuits and mechanisms illustrated schematically in FIGS. 20-22.
Process performed Referring to FIGS. 1-3, a coated varistor 31 in accordance with the invention consists of two parallel overlapping wire leads 32-32 (of solder-coated, copperplated steel), between which two back-to-back semiconductor diode chips 33-33 have been soldered. As best seen in FIGS. 2 and 3, the chips 33-33 plus the entire area Where the leads overlap is coated with a varnish 34, such as Dow Corning Semiconductor Junction Coating 'Resin type XR-6l-043A. This resin is a fairly viscous fluid having a consistency similar to ordinary varnish, of the order of 100 to 150 centipoises at 25 C. The varnish must flow around and coat the entire exposed surfaces of both diode chips, as well as flow into a generally rectangular space 35 between the chips.
Referring to FIG. 4, a plurality of uncoated varistors 36-36 (fifty in the specific example) are placed in a rack 37 which holds them in an accurately spaced relationship for the coating process. The rack 37 consists of two notched sides 38-38, having aligned notches 39-39 for supporting the varistor leads 32-32, and front and rear tie rods 41-42 for holding the sides together. The varnish coating 34 is applied to all the uncoated varistors 36-36 in the rack simultaneously, without touching the uncoated varistors with the varnish-applying mechanism and, as a consequence, without contaminating or damaging the varistors.
Relation among major machine components A complete varnish-coating apparatus 43, as shown in overall outline in FIG. 5, is comprised of an unloading station 44 connected to a loading station 46 by a rack transfer table 47. A varnish-applying station 48 is placed at an appropriate position on the transfer table 47, between the unload and load stations, and a panel 49 with the electrical controls is positioned to the rear of the racktransfer table 47. Pneumatic and electrical circuits to air cylinders and an electric motor complete the apparatus.
A canister 51, containing a supply of vertically stacked racks 37-37 of uncoated varistors is placed in position on the unloading station 44. The lowermost rack 37 is released by escapements 52-52 and is lowered into alignment with guide tracks 53-53 on the transfer table 47, so that it is in a position to be engaged by a reciprocable transfer bar 56. When the transfer bar 56 is shifted to the left, it engages one of the racks 37 and, when next shifted to the right, draws it from the canister onto the 4 guide tracks 53-53. Successive operations of the transfer bar 56 withdraw additional racks from the canister 51 and, at the same time, push the preceding racks along the guide tracks 53-53 beneath the varnish-applying station 48 and finally into a canister 51' on the load station 46.
The transfer bar 56 moves from left to right and back again, as viewed in FIG. 5. During the return stroke and the following pause, the varnish coating 34 is applied at the varnish-applying station 48. The varnish-applying station 48 is operated in synchronism with the cycle of the, transfer bar such that one rack of uncoated varistors is coated for each cycle of the transfer bar 56. Specifically, completion of the cycle of the transfer bar 56 initiates the varnish application, and completion of the varnish application initiates the next transfer bar cycle.
The varnish coating 34 is applied to the uncoated varistors 36-36 by causing an applicator member, in the specific example comprising the comb 57 having a pair of applicator teeth 58-58 for each uncoated varistor in the rack 37, to be dipped into and withdrawn from a trough 59 containing the varnish 34. The comb 57 is then shifted rearward, as viewed in FIG. 5, with the varnish 34 clinging to the teeth 58-58, so that it is positioned over the varistors 36-36 resting in the rack 37. The comb 57 is then lowered toward the varistors so that the varnish 34 touches the uncoated varistors 36-36, but the teeth 58-58 do not, and a predetermined amount of the varnish flows onto each varistor as will be described in further detail hereafter. A magnet (not shown in FIG. 5) holds the varistors down in the rack 37 so that, when the comb 57 is lifted and returned to the varnish trough, the varistors will not stick to it and be lifted from the rack.
When the varnishing cycle is completed, transfer of the racks 37-37 is once again initiated. The rack 37 of varistors just coated is pushed from beneath the varnish-applying stations 48 into the bottom of the loading canister 51'. When the rack 37 of coated varistors 31-31 is in position within the canister 51', it is raised until it is held by latch mechanisms 61-61 above the next rack to be pushed into the canister 51. This completes one cycle of operation. When the canister 51 is empty, it is replaced by a full one and when the canister 51' is full, it is replaced by an empty one.
METHODS AND MECHANICAL MOVEMENTS Unload station Referring to FIGS. 6 and 7, the canister 51, from which the racks 37-37 are unloaded, is shown; it being understood that the loading canister 51, has the same construction. The canister 51 has end openings 62-62 to clear portions of the escapements 52-52. The end openings 62-62 in the canister 51' clear portions of the latch mechanisms 61-61. The canisters 51 and 51' also have lower and wider end openings 63-63 to permit the racks 37-37 to be withdrawn or inserted into the canisters. Four spaced pins 64-64 support the lowermost rack 37, and thus the column of racks above, when canisters 51 and 51 are not on the varnish-coating apparatus 43. A set of four locating holes 66-66 in the bottom sections of each canister 51 serve to locate the canister precisely on the unload station 44. Specifically, as the canister 51 is placed on the unload station 44, the locating holes 66-66 fit over a set of four correspondingly spaced mounting pins 67-67 projecting upward from a table top 68, as shown fragmentarily in phantom in FIGS. 6-7. This serves to position the canister 51 precisely with respect to the unloading apparatus next to be described.
Referring now to FIGS. 8-9, as a canister (not shown) is first lowered into position on the locating pins 67-67, the tie rods 41 and 42 of the lowermost rack 37 temporarily come to rest on a pair of escapement fingers 71-71 which are a part of the escapements 52-52 previously mentioned. The canister 51 continues to descend, leaving the racks 37-37 suspended on the escapement fingers 71-71, until it rests on the table top 68. In this position, the supporting pins 64-64 are situated at a level below the bottom of a rack 37 when it is cradled in the rack support guides 76-76 in their lowermost position.
When an air cylinder 72 (FIG. 8) is actuated, its piston raises rack support rods 73-73, which pass through bearings 74-74 in the table top 68 and terminate in rack support guides 76-76, until the column of racks 37-37, for which the two lowermost racks are shown in phantom, is lifted slightly clear of the escapement fingers 71-71. After this, the escapement fingers 71-71 are withdrawn by air cylinders 77-77 from beneath the rack tie rods 41 and 42 and the piston of the air cylinder 72 is lowered. As it descends, and after the tie rods 41 and 42 of the lowermost rack 37 reach a position just below the withdrawn escapement fingers 71-71, the escapement fingers are returned by springs in the cylinders 77-77 to their initial positions in time to catch and support the next rack 37 by its front and rear tie rods 41 and 42. The piston of the air cylinder 72 continues its downward movement, with a rack 37-37 cradled in its rack support guides 76-76, until the piston reaches its lowermost position. At this point, the rack 37' is aligned with the transfer table 47 and is ready to be pulled onto it.
Valves 78 and 79, which are shown in FIG. 8 and operate from cam surfaces 81 and 82 respectively, control the operation of the escapement fingers 71-71 and the return of the piston of air cylinder 72 to its bottom position.
Transfer table Referring now to FIGS. -12, the transfer table 47 consists of a flat plate 83 on which the rack guides 53-53 and guard rails 84-84 are mounted. Midway between the rack guides 53-53, the transfer bar 56 is mounted in slide bearings 87-87 (FIG. 12) which are fastened in supports 88-88. Additional supports 89-89 are provided for the rack guides 53-53 and the guard rails 84-84. A plurality of leaf springs 90-90 (one shown in FIG. 10) are mounted at intervals along the rear guide 53, to urge the racks 37-37 lightly against the front guide 53 so that the racks will always be exactly positioned at the varnish-applying station 48. The guard rails 84-84 limit axial movement of the uncoated varistors 36-36 so that they too will be accurately located at the varnish-application station 48.
The transfer bar 56 is moved from left to right and returned by the piston of an air cylinder 91, which is connected to the transfer bar 56 by a connecting link 92. A stop 93 determines the end of the stroke of the piston of the air cylinder 91 and permits adjusting the end-of-thestroke position of the transfer bar 56 within the limits of a stop screw 94.
The transfer bar 56 is slotted in appropriate places to receive a set of five pawls 54a-54e. The pawls 54a-54e may rotate freely about pivot pins 9696 (one shown at the left of FIG. 11), each pawl being so constructed that its center of gravity is below the point of rotation. This causes the pawls 54a-54e to stand with their points oriented in an upward direction. A plurality of stop pins 97-97 limit the rotation of pawls 54a-54e to a clockwise direction as viewed in FIG. 11. Consequently, when the transfer bar 56 moves to the right, the pawls 54ai-54e engage the rack tie rods 41 or 42. Since they cannot rotate counterclockwise because of the stop pins 97-97, the pawls 54a-54e pull the racks 37-37 along the guides 53-53 by means of the pawls engaging the tie rods 41 and 42. However, when the transfer bar 56 returns to the left, the tips of the pawls 54a-54e strike the tie rods 41 and 42, rotate clockwise (because there is nothing to prevent this), and then slide beneath the tie rods 41 and 42. Consequently, movement of the transfer bar indexes the racks 37-37 from left to right only.
Referring now to FIG. 11, and starting with one rack 37 (shown fragmentarily in phantom) in position to be withdrawn from the canister 51, the transfer bar 56 is actuated and moves its first full stroke from left to right. In so doing, the pawl 54a engages the front tie rod 41 of the first rack 37 and pulls it into position to be engaged by the pawl 54b. The transfer bar 56 is returned to its starting position so that (a) the pawl 54a engages the front tie rod 41 of a second rack 37 to be withdrawn from the canister 51 and (b) the pawl 54b engages the front tie rod 41 of the first rack already withdrawn. The second full stroke of the transfer bar 56 to the right positions the second rack 37 in the place formerly occupied by the first one and moves the first one into position so that its rear tie rod 42 can be engaged by the pawl 540. The transfer bar 56 is then returned leftward to its starting position. The third full movement of the transfer bar 56 to the right will withdraw a third rack 37 from the canister 51 and move the second rack 37 into position so that its rear tie rod 42 can be engaged by the pawl 54c and move the first rack into position so that its rear tie rod 42 can be engaged by a pawl 54d. This sequence of operations continues until the pawl 54c has pushed the rear tie rod 42 of the first rack 37, and consequently the rack itself, as far as it can to the right. At this point, one rack 37 is in position in the varnish-applying station 48. After coating, the racks are pushed out of the varnish-applying station 48 and into the load station 46 by the following racks 37-37 of varistors to be coated. 1
At the start of the stroke of the piston of the air cylinder 91, a speed control cam 98 (FIGS. 10 and 12) holds a pilot valve 99 closed and continues to hold it closed until the speed control cam 98 (which is mounted on the transfer bar connecting link 92) is moved to the right beyond a cam follower 101. During the time the pilot valve 99 is closed, air flow is restricted and the piston of air cylinder 91 moves slowly. When the pilot valve 99 opens, the air flow restriction is removed and the piston moves rapidly.
At the end of the stroke, when the transfer bar connecting link- 92 strikes the stop screw 94, the cam 98 strikes a cam follower 102 (FIG. 10) and actuates another pilot valve 103. This admits air to the right end of the air cylinder 91 and fully returns its piston to the left end of the air cylinder for the next cycle. An interlock limit switch 104 assures that the piston has returned to its starting position. The limit switch must be held closed by an interlock cam 106 in order to start the next cycle. When a limit switch 107 is actuated by the cam 106, as the return stroke of the piston of the air cylinder 91 is completed, it starts the varnish-application cycle which will be described next.
Varnish-applying station Referring now to FIGS. 13-15, the varnish-applying station 48 is driven by an electric motor 108 through drive gears 109 and 111. The gear 111 is fastened to a driving member 112, which is connected to a camshaft 113 through a single-revolution, solenoid-operated clutch 114. A comb-shifting cam 116, a varnish-dipping cam 117 and a magnet-lift earn 118 are fastened to the camshaft 113.
The comb 57 is shifted by the cam 116 acting through a bell crank 121 which pivots about a fixed pin 122. One end of the bell crank 121 has a cam roller 123 which bears on the comb-shifting cam 116 and, on the other end, a cam roller 124 is mounted, which cooperates with a slot 126 in a member attached to a pair of parallel comb support rods 127-127. A spring 128 holds the cam roller 123 against the cam 116 so that the ends of the bell crank 121 will follow the motion of the cam and cause the comb 57, suspended in a comb support 127', to dwell over the varnish trough 59 for dipping into the varnish 34 or over the varistors for applying the varnish 34 in accordance with the comb transfer cam diagram (see FIG. 21). A
timing mechanism (not shown) can be incorporated into the system for stopping the cam shaft 113, and hence the cam 116, so that the duration of dwell can be specifically controlled.
The comb 57 is moved up and down, in order to dip it into the varnish 34 in the varnish trough 59, by means of the varnish-dipping cam 117, a cam follower 129 and a comb support carriage 131. The level of the varnish 34 in the trough 59 is maintained by a varnish supply 59. Springs 132-132 hold the comb-support carriage 131 and the cam follower 129 against the varnish-dipping cam 117, so that the comb-support carriage 131 follows the motion of the cam 117. Accordingly, the comb 57 moves down into the varnish; dwells slightly to pick up the varnish; moves up out of the varnish and dwells while it is shifted to a position over the varistors by the combtransfer cam 116; moves down to the varistors and dwells slightly to give the varnish time to transfer to the varistors; and finally moves up to clear the varistors, all as shown by the varnish-dipping cam diagram in FIG. 21.
The coated varistors 31-31 tend to stick to the varnish comb 57 and to be lifted from the rack 37 when the comb is retracted after coating. In order to prevent this, the varistors 31-31 (shown in FIG. 14) are held down in the rack 37 by a channel-shaped bar magnet 148 which is as long as the comb 57. The magnet 148 is raised into position beneath the varistors 31-31 by means of the magnet-lift cam 118, acting through a bell crank 133, a connecting rod 134 with ball joints 136-136, a lever 137 and a magnet-lift carriage 138. A spring 139 applies downward force on the lever 137 and, through the connecting rod 134 and the bell crank 133, holds a cam roller 141 against the cam 118 so that the magnet-lift carriage 138 will follow the motion of the cam 118. The magnetlift carriage moves up to a position in close proximity to the varistors (see FIG. 18'); dwells during the application of the varnish; moves back down to clear the varistors and dwells during the rack advance according to the magnet-lift cam diagram of FIG. 21. The bell crank 133 pivots about a fixed pin 142, while the lever 137 pivots about a fixed pin 143 and is forked to engage a pin 144 fixed 1n the magnet-lift carriage 138. The downward movement of the connecting-rod end of the lever 137, due to rotation of the cam 118, results in upward movement of the forked end of the lever 137 and the magnet-lift carriage, and vice versa. The length of the connecting rod 134, in cooperation with the ball joints 136-136, is adjusted so that, in the extreme upward position of the magnet-lift carriage 138, the magnet 148 is held just beneath (e.g., /s to inch away from) the varistors 31-31. In thls pOSltion, the magnetic force is great enough to overcome the opposing attractive force of the varnish which tends to lift the varistors.
The drive motor 108 continuously rotates the driving member 112. A cam 149 is a circular one attached to the cam shaft 113, as shown in FIG. 15, and cooperates with a limit switch 151. The limit switch 151 is held open by the cam 149, except when a cam follower 152 drops into a notch 153 in the cam 149 for a moment. This actuates the piston of the rack-transfer air cylinder 91, which at the end of its stroke, energizes a clutch solenoid 154 through the limit switch 107. Energizing the clutch solenoid 154 actuates the single-revolution clutch 114 which connects the driving member 112 to the camshaft 113 and, therefore, they rotate together for one revolution.
The cams 116, 117, and 118 are fixed to the camshaft 113. Their relationship and shape is such that, starting with the comb 57 in the varnish 34, the cam 117 withdraws the comb 57 from the varnish 34, the cam 116 shifts the comb 57 to a position over the varistors 31-31 where it dwells, and the cam 118 moves the magnet-lift carriage 138 upward beneath the varistors and dwells. During the dwell of the shift and lift cams 116 and 118, respectively, the comb-dipping cam 117 lowers the comb 57 to its final position over the uncoated varistors 36-36, with the teeth 58-58 partially surrounding but not touching the varistors to coat the varistors. Further rotation of the camshaft 113 causes: 1) the dip cam 117 to raise the comb 57, (2) the magnet-lift cam 118 to lower the magnet-lift carriage 138, and (3) the comb-shifting cam 116 to move the comb 57 toward the right. Completion of rotation of the camshaft 113 returns the comb 57 to its starting position in the varnish trough 59,and the magnet-lift carriage 138 to its lowermost position.
The events which occur during varnishing of the varistors can best be understood by referring to FIGS. 16-18, showing the details of construction of the applicator member and its relationship to the articles being coated. In the specific embodiment, the applicator member resembles a comb comprising an elongated horizontal body member 57-A from which the individual applicator teeth 58-58 project downward in two spaced, parallel rows, R1 and -R2 extending in the X direction indicated in FIG. 16. In the Y direction, the teeth are arranged in spaced columns (C1, C2, etc.) of two teeth per column, running perpendicularly to the rows. The lower faces of the teeth are flat, generally rectangular, and lie in a common horizontal plane, as illustrated in FIG. 16.
Each individual tooth 58 is formed with a concave recess 58-A in its lower face, comprising a generally semicircular groove in the specific embodiment, running in the Y direction such that the recesses of each pair of teeth in each column are aligned in theY direction as shown. The recesses divide the lower face of each tooth into two parts, forming fiat, rectangular land areas 58-B, 58-B, one on each side of each recess along the X direction. The comb body is formed with a plurality of elon gated vertical slots 57-B, 57-B, which define the teeth in each row and isolate the teeth from each other. Also, the comb body is of inverted U-shaped cross section, as shown in FIG. 18, which defines, in effect, further elongated vertical slots 57C, 57-C. These slots define and isolate the individual teeth in each column C1, C2, etc.
As best seen in FIG. 17, each recess 58-A is large enough to encompass the portion of the article to be coated (in the specific example, one of the diode chips 33-33 and the portions of the leads 32-32 soldered thereto), and is of such generally fitting curvature that the recess may be placed over the portion of the article to be coated and surround the upper portion of the same fairly closely, without touching the article. The size and shape of a recess 58-A are two of the factors which affect the amount of varnish that the associated tooth can carry and transfer to the article being coated.
.As best illustrated in FIG. 18, the width W of each tooth (also a fatcor which affects the quantity of varnish being transferred), and thus each recess, is approximately the same as that of the chip 33 to be coated so that each tooth, when lowered, covers one of the chips. For other sizes and shapes of articles to be coated, the recess is similarly made a little larger than the article and shaped to fit fairly closely over the portion of the article to be coated. As is apparent from FIGS. 17 and 18, the teeth are separated (1) in the X direction by the slots 57-B, 57-B in accordance with the spacing of the uncoated varistors 36-36 in the rack 37 (FIG. 4) such that each column of two teeth covers portions of a corresponding varistor, and (2) in the Y direction by the slots 57-C, 57-C in accordance with the spacing of the chips 33-33 such that the two teeth in each column encompass the two chips of a corresponding varistor. In general, the number and spacing of the teeth are selected by the number and spacing of the articles to be coated where more than one article is coated at a time, and/or by the number of separate portions of each article to be coated, where spaced portions of each article are to be coated. In the specific example, each of fifty varistors are simultaneouly coated, with one hundred teeth being provided, arranged in fifty rows of two columns each.
In coating the varistors, the comb 57 is first dipped into the trough 59 of varnish 34 and then raised by the lifting mechanism previously described. The depth of immersion (distance D in FIG. 16), and the rate of withdrawal are among the factors which determine the amount of varnish adhering to the teeth 58-58. As depicted in the drawing, fairly large drops or menisci of varnish are retained in the recesses by capillary action, and a substantial additional quantity of varnish is retained on the surrounding portions of each tooth. The slots 57-B and 57-C are made longer than the maximum expected depth of immersion of the teeth (thus substantially longer than the depths of the recesses 58-A, 58-A) so that the upper ends of the slots are never filled with varnish. With this arrangement, the varnish 34 is prevented from flowing from one tooth to another, ensuring that each tooth carries essentially the same amount of varnish (for a given depth of immersion and withdrawal rate), regardless of any slight deviations from horizontal in the attitude of the comb 58.
As the teeth 58-58 move into proximity with the portions of the uncoated varistors 36-36, the varnish flows from the cavities 58-A, 58A and adjacent portions of the teeth to coat the entire surface of the surrounded portions of the varistor with the desired quantity of the varnish. The varnish also flows inwardly between the two teeth of each column along the varistor, as viewed in FIG. 18, to entirely fill the small space 35 between the diode chips 33-33 to capillary action.
As the teeth are withdrawn fromthe proximity of the varistors, the varnish no longer receives support by adherence to the teeth 58-58 and, therefore, drops are released to flow completely around the varistors 31-31. The final result is a shell of varnish 34, as shown in FIGS. l-3, surrounding the varistors.
Loading station Referring now to FIG. 19, a canister 51, which is identical to the canister 51 except that it is empty, is placed on a load station table 158. Alignment of the canister 51 with the cooperating apparatus is obtained in the same manner previously described for the unload station 44. The racks 37-37 of coated varistors are pushed along the guide tracks 53-53 onto rack support guides 76'76'. A piston of an air cylinder 159 is connected to the rack support guides 76'-76' by means of support rods 73'-73' which pass through the load station table 158.
Latch mechanisms 61-61 are mounted on the load station table 158 at both ends of the canister 51'. The latch mechanism 61-61 consist of latch supports 162-162 and latches 163163 which can rotate upward from their horizontal position but not downward. The latches 163-163 are long enough to extend into the canister 51' beyond front and rear tie rods 41 and 42 of a rack 37 (FIG. 4).
When the piston of the air cylinder 159 moves upward, it lifts the rack 37 by means of the support rods 73-73 and the rack support guides 76'76'. The upward movement of a rack 37 causes its front and rear tie rods 41 and 42 to engage the latches 163-163 and rotate the inner ends upward. When the rack 37 has been raised far enough, its tie rods 41 and 42 clear the ends of the latches 163-163 permitting the latches 163-163 to fall back (rotate) of their own weight to the horizontal position. When the piston of the air cylinder 159 is retracted, the rack 37 descends until its front and rear tie rods 41 and 42 rest on the tops of the latches 163-163. The racks 37-37 previously lifted remain supported at a level higher than the top of the next rack 37 which will enter the canister 51'. The piston of the air cylinder 159 continues to descend until the rack support guides 7676 are in aligned position with guide tracks 53-53 to receive another rack 37.
1 0 AUTOMATIC OPERATION Electrical circuit The automatic operation of the varnish apparatus can be understood best in conjunction with the electrical schematic FIG. 20, the cam chart FIG. 21, and the air schematic FIG. 22.
In operation, when a master selector switch 164, FIG. 20, is turned to the on position, power is applied to the drive motor 108 of the varnish-applying station 48. The drive motor 108 then rotates the driving member 112 continuously (see FIG. 15) as long as the master selector switch 164 is in the on position. The cam 149 holds the limit switch 151 open during each revolution of the camshaft 113 except for a short dwell at the start of the cycle as shown by the rack advance cam diagram in FIG. 21.
The apparatus, in the preferred embodiment, is set in automatic operation by tlirning a selector switch 166 (FIG. 20) to the automatic position, which disconnects a manual push-button switch 167 from the circuit and connects the interlock limit switch 104 (FIGS. 10-12) into the circuit. Since the piston of the rack transfer air cylinder 91 is in its retracted position, the interlock limit switch 104 is held closed by the interlock cam 106 (see FIG. 10). The limit switch follower 152 rests in the notch 153 (FIG. 15) and, therefore, the limit switch 151 is closed. This establishes a current path through the switches 104, 166, and 151 and a solenoid 168, as shown in FIG. 20. Energizing the solenoid 168 actuates air valves which admit air to the rack-transfer cylinder 91 and cause the racks 37-37 to be transferred one position to the right. When the piston of air cylinder 91 reaches its fully extended position to the right, it actuates an air valve which: (1)
causes the piston to return to its starting position and (2) causes the pistons of unload and load air cylinders 72 and 159 (FIG. 22) to ascend and descend.
Near the end of the return stroke, to the left, of the piston of air cylinder 91, the interlock cam 106, on the piston rod, closes a limit switch 107 (FIG. 10) momentarily and energizes the solenoid 154 of the single-revolution clutch 114 (see FIG. 15) causing it to drive the camshaft 113 and the cams 116, 117, 118 and 149 through one revolution. This, in turn, causes the varnish station 48 to go through one varnish-applying cycle, i.e., apply varnish 34 to one rack 37 of the varistors 36-36 with the events taking place in the timed relationship shown in FIG. 21. At the end of the varnish-applying cycle, the limit switch follower 152 drops into the notch 153 of the rack advance cam 149, closes the limit switch 151 and establishes a current path through the limit switch 104, the selector switch 166, the limit switch 151 and the solenoid 168. [Energizing the solenoid 168 actuates air valves which admit air to the rack transfer cylinder 91, thus repeating the cycle. Cooperation and control of the other apparatus components are achieved through a pneumatic control circuit which is described next.
Pneumatic circuit When the solenoid 168 is energized, refer to FIG. 22, it shifts a valve 171 and admits pilot line air (previously filtered and regulated), flowing from a source P through a load-cylinder valve 172, through the valve 171, to a rack-transfer cylinder control valve 173. This shifts the rack-transfer cylinder valve 173 so that it admits air from the source P to the rack-transfer cylinder 91 through a flow control valve 174 in the uncontrolled direction. The flow control valve 174, and the other flow control valves, are unidirectional. They permit the unrestricted flow of air in one direction but regulate the flow in the other direction. The admission of air to the rack-transfer cylinder 91 advances its piston to the right, Withdrawing one rack 37 from the canister 51 and pushing any other racks one position along the transfer table. During the initial portion of the advance, the pilot valve 99 is held closed by the speed control cam 98, which is fixed to the piston rod of the air cylinder 91, so that the air being exhausted from the racktransfer cylinder 91 must pass through a slow-advance flow control valve 176 in the controlled direction. Further advance of the piston of the rack-transfer air cylinder 91 permits the pilot valve 99 to open. When the pilot valve 99 opens, a second exhaust path through a flow control valve 177 is provided in parallel with the flow control valve 176. This increases the rate of exhaust and regulates the rapid advance of the piston of the transfer air cylinder 91.
When the piston of the rack-transfer air cylinder 91 reaches its extended position to the extreme right, the racks 3737 have been transferred one position to the right and the speed control cam 98 shifts the pilot valve 103. This admits pilot line air simultaneously to the racktransfer air cylinder valve 173, an unload station air cylinder valve 178 and to a timer valve 179 through a pilot valve 187.
First with respect to the rack-transfer air cylinder valve 173, pilot line air admitted from the pilot valve 103 to the rack-transfer air cylinder valve 173 shifts the valve 173 back to its initial position which admits air to the right side of the transfer air cylinder 91. This causes the piston to retract to the left and return to its starting position. The air cylinder 91 exhausts through the flow control valve 174 in the regulated direction so that the speed of the return can be controlled by this valve.
Second, with respect to the unload-station cylinder valve 178, pilot line air from the pilot valve 103 shifts the unload-station cylinder valve 178 and admits air from the source P to the unload-station cylinder 72 through a flow control valve 181 in the unrestricted direction. This causes the piston of the cylinder 72 to rise to the top of its stroke and lift racks 3737 off the escapement fingers 5252. As the piston rises, the exhaust air flows through flow control valve 183 in the controlled direction thus permitting the regulation of the speed or ascent of the piston. As the piston nears the top of its stroke, the cam 82, which is fixed to the piston rod, shifts the valve 79. This admits air from the source P to the escapement valve 78 and pilot line air to the valve 178 and a valve 182. The pilot line air shifts the valve 182 and connects the escapement air cylinders 7777 to the escapement valve 78.
Completion of the stroke of the piston of the unload air cylinder 72 causes the cam 81 to shift the escapement valve 78 which applies air from the source P to the escapement cylinders 7777 through the valve 182. The air forces the pistons of the escapement air cylinders 7777 to extend outwardly thus withdrawing the escapement fingers 7171 so they clear the rack tie rods 41 and 42. The application, by the valve 79, of the pilot line air to the unload-station cylinder valve 178, returns the valve 178 to the position shown in FIG. 22. This applies air from the source P to the upper end of the unload-station air cylinder 72 through a flow control valve 183 in the uncontrolled direction. Application of air to the upper end of the unload air cylinder 72 causes its piston to descend and its exhaust to flow through the flow control valve 181 in the regulated direction, thus providing a means of controlling the speed of descent. As the piston descends, the cam 81 allows the valve 78 to close. This traps air in the escapement cylinders 7777 and holds the escapement fingers 7171 open until the piston of the air cylinder 72 descends far enough for the cam 82 to allow the spring returned valve 79 to return to the exhaust position. This, in turn, allows the spring returned valve 182 to return and exhaust the escapement air cylinders 7777. Springs in the air cylinders 7777 return the pistons and, therefore, the escapement fingers 71--71. The cams 81 and 82 are fixed in relationship to each other so that the escapement fingers 52- 52 are held apart just long enough for one rack 37 to pass the escapement fingers 7171, as the piston of the unload-station cylinder 72 descends, before the fingers are returned to support the rest of the column of racks 37-37.
Third, with respect to the timer valve 179, application of pilot line air by the pilot valve 103 to the pilot valve 187, shifts the valve 187 and applies air to the timer valve 179. The timer valve 179 shifts and also starts the timing. The shifting of the timer valve 179 applies pilot line air to the load-cylinder valve 172, which shifts this valve, and applies air from the source P to the lower end of the load air cylinder 159 through a flow control valve 184 in the unrestricted direction. This causes the piston of the load air cylinder 159 to ascend. The upper end of the air cylinder exhausts through a flow control valve 186 in the regulated direction, thus permitting control of the speed of ascent. After an interval, as determined by the setting of the timer valve 179, the valve 179 returns to the exhaust position and exhausts the pilot operated valve 172 which, in turn, exhausts the load air cylinder 159 through the fio-w control valve 184 in the regulated direction. Adjustment of the flow control valve 184 controls the speed of descent of the piston of the load air cylinder 159.
Since the valve 103, at the end of the stroke of transfer air cylinder 91 directs pilot line air simultaneously to the unload air cylinder valve 178, the transfer air cylinder valve 173 and, through the valves 187 and 179, the load air cylinder valve 172, the pistons of both the unload and load air cylinders, 72 and 159 respectively, ascend while the piston of the transfer cylinder 91 returns to its starting position. At the top of its stroke, the piston of the unload air cylinder 72 shifts the valve 79 which causes the piston to return to the bottom of its stroke. The piston of the load air cylinder 159 is returned to its bottom position by the timer valve 179 when it shifts at the end of its time cycle.
From the foregoing, it can be seen that, when the racktransfer solenoid 168 and its air valve 171 have been actuated, all air cylinders act cooperatively through one cycle. Further, the air cylinder actuation takes place only when the motor driven cam 149 cooperating with the limit switch 151 initiates the cycle. The speed with which the cycles are repeated is controlled by regulating the speed of the drive motor 108 by means of the speed control 188.
From the foregoing description, it may be seen that the preferred embodiment of the invention provides a new automatic method of applying varnish simultaneously to large numbers of articles, which is improved over,
the older methods because it is much faster and does not contaminate or damage the articles. It is to be understood that various changes may be made from the specific details illustrated without departing from the spirit or scope of the invention.
What is claimed is:
1. The method of applying a coating of liquid to a portion of an article without contacting the article, which comprises:
engaging an applicator member with the coating liquid so as to cause a quantity of the liquid to be retained by capillary action in a concave recess formed in one surface of the member, the recess being of a size somewhat larger than the portion of the article to be coated; and
bringing the member into close, noncontacting proximity with the article so that the recess surrounds the portion of the article to be coated and the liquid flows from the applicator member onto the article to apply the coating.
2. The method as recited in claim 1, wherein:
(a) a lower portion of the applicator member, including the recess, is dipped into and withdrawn from a bath of the coating liquid, the depth of immersion and the withdrawal rate being selected to coat the recess and surrounding portions of the application member with a predetermined quantity of the liquid, greater than the quantity required for coating; and
(b) the member is lowered into proximity with the article for a time such that a desired amount of the liquid flows onto the article from the recess and surrounding portions of the member, after Which the member is withdrawn from proximity with the article.
3. The method as recited in claim 2, for use with a viscous coating liquid, further comprising the step of holding the article down during the application of the liquid, to facilitate withdrawal of the applicator member from the article.
4. The method of applying a protective liquid coating simultaneously to the bodies of a plurality of axially leaded electrical devices comprising:
supporting said plurality of devices, by their axial leads,
in an ordered array;
dipping an applicator in a solution of protective liquid and removing said applicator from said solution, the applicator having a plurality of recesses therewithin for retaining the liquid to be applied by capillary action, said recesses being oriented to cooperate with said ordered array; and
engaging said applicator with said devices, without physical contact therebetween other than the liquid to be applied, so that the bodies of said devices contact the liquid held by capillary action within the recesses, whereby the liquid flows about the bodies to provide protective coatings thereon.
5. The method of applying varnish to the two semiconductor bodies, each, of a plurality of leaded varistors, without physically contacting the semiconductor bodies with means other than the varnish to be applied, comprising:
engaging an applicating member with varnish to be applied, the member having two parallel rows of aligned recesses with an isolation between each of said recesses, each of the recesses having a dimension greater than one dimension of one of said bodies, so that varnish is retained in said recesses by capillary action, the isolation between each recess ensuring that equal quantities of varnish can be retained within said recesses without maintaining the aligned recesses precisely level; and bringing the applicating member into proximal relation with a plurality of oriented leaded varistors so that the dual bodies of the varistors lie within corresponding recesses of the two rows of the applicating means, without physical contact therebetween, so that a portion of said bodies engage the menisci of varnish retained by capillary action within the recesses, thereby permitting varnish to flow about the peripheries 4 of said bodies.
References Cited UNITED STATES PATENTS 3,108,537 10/1963 Way et a1. 118-243X 3,121,020 2/1964 Low 118-243X WILLIAM L. JARVIS, Primary Examiner US. Cl. X.R.