Built-in type speed control for conveyorized continuous etcher

BACKGROUND OF THE INVENTION (A) Field of the invention 30

This invention lies in the field of automatic speed control apparatus for etching machines and, more particulartv, automatic control apparatus of the analog type.

(B) Description of the prior art 35

Metallic or metalized control elements have been used in several forms as the means of introducing etchable material into an analog type speed control. The material of the control element is etched to destruction and moni- 40 tored as a measure of the degree of actual material removal from articles being simultaneously etched in an etcher. In one successful operation the material has been fed into the control in the form of a continuous length of straight metal wire, and it has in other instances taken 45 the form of an interrupted or a continuous length of structurally weak foil or film laminated to or coated upon a substrate which provides the necessary structural strength as the carrier.

Analog type control apparatus for use with etching ma- 50 chines is disclosed in the prior art. See U.S. Letters Pat. No. 3,388,023. However, such prior art apparatus contains the analog control element in a separate unit, where it is monitored under conditions similar to those existing in the main spray chamber of the spray etching ma- 55 chine. However, the required similarity of conditions is difficult to obtain. The control element must be etched under conditions which, in terms of the total number of etching conditions affecting etch rate of the material from the articles in the main spray chamber, must at least in go part be similar to or duplicates of the total number affecting such article etch rate.

The problem is not to interfere with the main etching process, and at the same time to achieve a relatively unencumbered and straightforward manner of subjecting 65 the control element to a like process wherein at least some of the same factors are taken into account, such as temperature, mode of application, composition, state of ionization, and flow rate of the etchant; dissolution and handling and physical characteristics of the control 70 element material such as its thickness, opacity, conductivity, and manner of transport and relative movement between it and the etchant when contacted by the latter; etc.

SUMMARY OF THE INVENTION

This invention provides a continuous spray etching machine having a spray chamber through which articles to be etched are continuously advanced, and which spray chamber is provided with a built-in automatic control having a simplified mode of loading, feeding, and disposition, of its supply of control element strip, and having a convenient disposition exposing the strip to actually existing conditions within the article spray chamber, all without interference with or effect upon the path of the passing articles. The articles are advanced by means of a steadily running drive motor for article conveying means with, which the machine is equipped. The speed control is an automatic control, which control senses the degree of material removal from a control element strip that is likewise being steadily advanced while being etched, and which control automatically controls the conveying means in response to the degree of material removal sensed, by regulating the speed of the drive motor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view from inside a continuous spray etching machine embodying the present invention.

FIG. 2 is a view like FIG. 1, but with only two of the main parts shown and occupying their preassembly position.

FIG. 3 is a schematic diagram of the speed control circuit of the etching machine.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 of the drawings, a continuous spray etching machine 10 is shown having a fluid tight spray chamber 12 provided with the usual six walls, of which the front wall 14 and left side wall 16 are illustrated. The chamber contains vertically directed spray nozzles including rows of upper nozzles 18 which direct pressure induced sprays of liquid etchant downwardly.

Continuously running conveying or feed means is provided for feeding each article 19 to be etched longitudinally through the etcher 10 and, in the various types of etchers contemplated for using our invention, the articles can either be separate in a series, or together in a common web from which they are ultimately separated into individual articles after etching. The articles for the broad purposes of this disclosure are either carried in a vertical disposition when conveyed longitudinally through the etcher as aforesaid, or carried horizontally in which case the etcher employed is one of the types called a horizontal etcher. Examples of the articles are printed etched circuits, perforated metal sheets, gridworks, and flat springs, all of which are selectively coated in the desired areas with an etch resist so that only the exposed portions remaining are etched away.

The etcher as actually illustrated is of the horizontal type having a horizontally disposed roller conveyor 20. In operation, the articles being introduced onto the conveyor move thereon from a loading or inlet station, indicated by an arrow 22, thence in the longitudinal direction of the arrow through a suitably covered opening, not shown, in the chamber front wall 14, and through the chamber 12 and out the chamber rear wall, not shown, so as to continue on the conveyor through the rest of the etching machine for further treatment including rinsing. The etched articles are received by suitable apparatus such as a stacker provided at the outlet station of the etcher.

All rollers in the conveyor 20 turn at the same speed and in the same direction, being fixed in groups on a series of parallel, power driven roller shafts 24 which are

3,663,724 journalled crosswise in the etcher in a common plane. A hollow, longitudinally extending conveyor side rail 26 is fixed in the chamber adjacent the chamber left side wall 16, and houses in its box shaped interior a walking beam 28 which constantly swings in an endless closed path in a vertical plane inside, the side rail. Each roller shaft 24 has, at least at the end thereof adjacent the walking beam 28, a journalled portion supported at that end in a bearing hole 30 in the side rail, and further has an integral crank portion, not shown, supporting at that end the walking beam so that the latter in swinging will coordinate the speed and direction of the shafts.

A conveyor drive motor 32, coupled thereto by a reduction drive including gearing 34, directly drives some selected one of the roller shafts such as the shaft 24α, identified by its distinguishing subscript, which in turn drives the walking beam indicated at 28 on one side of the machine and also drives a companion walking beam which it will be understood is provided on the opposite side of the machine.

The conveyor 20 has a speed control which provides automatic control thereover by regulating the speed of the conveyor motor 32, and novelty is felt to reside in the coacting components of such control which, as disclosed herein, include a supply roll 36 of control element strip 38 in a particular substrate-mounted laminated form, a pull-feed 40 for the strip, a stationary guide 42 in part inside and in part outside of the chamber, a fibre optic monitoring device 44 for the strip, and a feed-back servo control circuit having, among others, photocell components 46 connected in an electric line 48 of the control circuit.

Specifically, a post 50 which supports the supply roll 36 is supported by the guide 42 at the inlet station of the etcher in an out of the way position upstanding from the top of the side rail 26. The laminated strip 38 unwinds from the roll 36 and consists of a lamina of backing such as flexible transparent Mylar plastic tape, and an outside lamina thereon of an opaque material to be etched, such as a thin foil coextensive in length and width with the Mylar tape. The material of the lamina being etched is selected so that, ideally, it has similar etching characteristics to the articles; in practice, if the articles have surfaces of a metal in elemental or alloy form, then the etched lamina will usually be made of about the same metal material.

The pull-feed 40 comprises a vertically aligned pair of confronting flat rolls receiving a portion of the strip therebetween so as to draw it in a direction parallel but opposite to the article movement. The upper roll is an idler 52 and the lower roll is a capstan 54.

One of the roller shafts such as shaft 24b, identified by its distinguishing subscript, is connected by a gear train 56 to drive the capstan 54 slower, and in the opposite direction of turning to, the conveyor rollers but always at the same relative or proportional speed thereto. Hence, the laminated control element strip 38 moves at a fixed speed ratio to movement of the articles through the chamber 12.

A relieved outlet portion 58 of the strip guide 42 provides an upward offset in the outer end 60 of the guide so that it forms an open horizontal alley at the bottom through which the waste strip passes from the rolls 52 and 54. The strip is led forwardly to a point where it can feed downwardly and collect in a suitable receptacle, not shown.

The cover for the strip opening in the chamber front wall 14 prevents the spray from splashing outside of the chamber, and includes a stationary tunnel or inverted channel 62 and a complementarily telescopically interfitting movable channel 64. The channel 64 has positions dictated by an affixed guide block 66 which increase or decrease the effective length of the strip portion exposed to the impinging etchant spray. The adjusted position is selected externally by means of a tool operated lead-screw threaded through the block 66, and the adjustment compensates for such variables encountered in the field as the material thickness on the strip compared to the material thickness of the articles being etched, strip speed compared to article speed, the comparative etch rate of the respective materials of the strip and articles, and the comparative exposed lengths in the chamber 12 as between the strip and the articles in terms of their travel.

The strip guide 42 is removably carried on the side rail 26 so as to enable the guide to be preloaded or prethreaded with strip before being introduced into the etcher. For that reason, the clearance—particularly the lateral working clearance—is made appreciable between the guide 42 and each of the channels 62 and 64 covering the strip opening in the chamber front wall 14.

The outer end 60 of the strip guide is centered by an anchor, not shown, atop the conveyor side rail 42 to insure transverse and longitudinal registry at all times between the rolls 52 and 54 and a strip guiding groove, not shown, which is formed in the guide 42 in an underside position aligned with the upwardly offset outlet portion 58 thereof.

At its inner end (FIG. 2), the guide 42 is formed with a generally U shaped lateral offset therein defined by a diagonally related pair of opposed cam legs 67. The legs 67 are adapted to cam against the confronting corners 69 of an upstanding sensing head 71 which fits within and is interengaged by the just noted U shaped offset. The sensing head 71 is carried by the conveyor side rail 26 and is included as part of the fibre optic monitoring device 44. A cut out 73 at the bottom of the adjacent side of the head 71 offsets the head at that side to define with the rail 26 a strip alley for purposes which will now become evident.

The guide 42 is slotted longiudinally along the top and bottom to define a central strip groove 75. A semicircular loop forming portion 77 presented by the inner end of the guide receives the intervening loop of strip joining an upper strip flight 79 and a lower strip flight 81. The two flights of strip move in opposite directions, each bridging across the U shaped lateral offset in the guide 42 without touching it.

When the guide and sensing head 71 interengage, the head 71 is between and interfits with the camming legs 67 and the strip flights 79 and 81. The interengagement provides an aligning action insuring longitudinal and transverse alignment between the guide and side rail 26 at the inner end of the former. The side rail extends through and past the etching chamber and, within the chamber itself, the portion of the guide 42 is only a fraction, such as onethird or a little more, of the length of the side rail portion in the chamber.

The supply rolls 36 are large enough that replacement for a near empty roll is required only infrequently. When required, the guide 42 is withdrawn from the etcher, and a replacement roll 36 is substituted upon the post 50. The new strip 38 is drawn off and trained over the guide so as to loop back about the semicircular portion 77 of the inner end. The operator then grasps the outer end 60 of the guide with one hand so as to clamp the upper and lower strip flights 79 and 81 thereto, and then with his other hand the operator introduces and indexes the guide into its final position on the side rail in the etching chamber. Finally, the lower flight 81 is inserted between the rolls 52 and 54, and the waste end or free end is led at a lower level beneath the supply to the waste receptacle.

The article 19 in the usual case is treated in the machine for a particular percentage of overetch. In that case, the effective length of exposed strip 38 is adjusted so that a point of discontinuity 38α which will be occurring is in the right place, at the same time at which the article 19 when it leaves the chamber will have been exposed to the etchant spray just long enough to acquire the particular percentage of overetch desired.

The backing remains intact during etching, and gives transparency to the strip as soon as freed of the etchable material carried thereby. Blow off air is introduced by a

3, pipe 70 to keep the newly exposed backing from having the etchant collect on the discontinuity 38α and interfere with the transparency.

Ideally, the discontinuity 38α stabilizes at a point falling between longitudinally aligned first and second moni- 5 toring openings 72 and 74 formed in the sensing head 71 and defining a pair of spaced apart vertical axes. The fibre optic device 44 further includes two bundles of light conducting fibres, one of which being on opposite sides of the upper flight 79 of the strip at the location of the 10 first monitoring opening 72 and the other being on the opposite sides at the location of the second monitoring opening 74. A common lamp 76 and a lens 78 register at one end of the bundles whereas the individual photocell components 46 respectively register at the other end of 15 the bundles of fibres. The point of material discontinuity on the backing, known as breakthrough, can be optically monitored with photosensing means located in the main externally of the spray chamber, and the article speed is automatically accurately controlled by the automatic con- 20 trol circuit for the conveyor in the way now to be set forth.

In the control schematic of FIG. 3, power from a set of input lead wires 80 is transformed to low voltage alternating current and applied to the lamp 76, the power is also applied by an SCR (silicon controlled rectifier)' 25 power supply circuit 82 to the conveyor drive motor 32, and the power is applied by a differential amplifier circuit 84 to an SCR-operated reversible servomotor 86.

By a mechanical connection suitably provided, the drive motor 32 carries an electric tachometer 88 on the 30 shaft therewith, the output of the tachometer 88 being adjustable and applied by a feedback loop circuit 90 to control the SCR power supply 82 for the drive motor 32. The rotational position of the servomotor 86 is transmitted through an interconnection 92 to mechanically 35 position the slider 94 of a potentiometer which adjusts the output just referred to from the electric tachometer 88.

In operation of the present photosensing speed control, light from the lamp 76 falling upon the photocell com- 40 ponents 46 controls the latter, and the photocells in the line 48 in turn control the differential amplifier 84 which by SCR-delivered, direct current pulses sets the position of the servomotor 86. The mechanical connections to the tachometer and to its output potentiometer slider from _4gthe respective motor 32 and servomotor 86 enable the tachometer, by its automatically varied output, to regulate the conveyor by sensing the speed of the drive motor 32 and changing it to the proper value for the etching conditions. 5θ

The above operating sequence is entirely automatic once the servocircuit is properly adjusted for the control factors.

The adjustment is readily made by allowing light from the lamp 76 to fall upon the more remote or second one 55 of the photocells 46 and by blocking off the other photocell to keep it darkened. The slider 96 of a potentiometer connected to line 48 is adjusted to introduce a base electrode biasing current into one branch of the differential amplifier circuit 84 exactly equal to current through a θθ grounded line 98 introducing the base biasing current into a companion branch of the differential amplifier circuit 84. A no output, null condition results, and the servomotor 86 coupled to the output of the circuit 84 holds its position. This simulated condition is replaced during regu- ₆₅lar operation by the actual null condition caused by the midposition location of breakthrough on the strip 38. It is apparent that if either the light level decreases on the more remote, illuminated photocell or the covered and darkened photocell 46 receives light, the null condition ₇₀will cease in actual operation, causing the servomotor 86 to step slowly by increments unidirectionally one way or the other.

Conveying speed will accordingly increase or decrease with changes in light, such changes being directly con- 75 ,724 trolled by the point at which breakthrough is being reached in the steadily advancing control element strip. Downward spray from the nozzles 18 and the other nozzles, not shown, falls in common upon the strip and upon the articles.

More specifically, the additional blocking of light by the control element strip is indicative of a slowed down etching rate and the need for systematically slowing down the conveying means. Hence, the conveyor motor progressively slows and perforce slows both the article movement and the strip movement until the breakthrough point moves retrogressively to strip movement to the desired null creating or midposition relative to the monitoring opening means 72 and 74. Conversely, increased uncovering of the photocell light source by the strip indicative of premature breakthrough causes speedup of the conveyor motor until the breakthrough or discontinuity point 38α can be delayed until it advances in the direction of strip travel to the null position about midway between the first and second monitoring openings 72 and 74.

Various information on specific details of the connections of the circuit and on the operation of the individual components thereof are described in the same assignee’s U.S. Letters Patent No. 3,388,023, the disclosure of which is incorporated in entirety herein by reference.

It can be appreciated that the path of the articles feeding through the spray chamber and the path of the strip do not encroach and, while coordinating movement of the same on identical headings, the feed means for the articles and the separate feed means for pulling the control element strip do not interfere with one another. Although such pull-feeding of the control element strip by the rolls is satisfactory, especially with the convenience of the pre-threading technique described, it is understood that other advantageous ways of introducing a control element into the spray chamber can be utilized.