US 3356605 A
Description (OCR text may contain errors)
1967 F. J. SCHMIDT ELECTRODEPOSITION MONITOR 3 Sheets-Sheet 1 Filed March 1967 Fly.
FRANCIS J. SCHMIDT BY/7IWZ11 W/fwflm AGENT Dec. 5, 1967 Filed March 2,
ELECTRODEPOSITION MONITOR 3 Sheets-Sheet 2 '5. O I; E5
| I z I q- I I I A" II H "I 8 o n BF a P- 0F a a a I!) ID ID 0 m 0 O INVENTOR.
FRANCIS J. SCHMIDT WM 0 WW AGENT Dec. 5, 1967 F. J. SCHMIDT ELECTRODEPOSITION MONITOR 3 Sheets-Sheet 5 Filed March 2, 1967 INVENTOR. FRA/vc/s J. SCH/WOT, 5v fi MV V WWW AGENT United States Patent ABSTRACT OF THE DISCLOSURE Stress in electrodeposit formed at given current density is determined by feeding strip electrode from supply roll into electrodeposition bath, and depositing upon immersed portion of strip at current density of interest. Stress is determined by measuring by instrumental means the resulting displacement of strip, which bows inward or outward as result of stress in deposit. Current density applied to work pieces in same bath may be adjusted in accordance with instrumental measurement of stress to produce desired value of stress in deposits on work pieces. Fresh portion of strip is provided by advancing strip from supply roll, taking up used portion on takeup roll.
Reference to copending application This application is a continuation-in-part of my copending application Ser. No. 326,706, filed Nov. 29, 1963, entitled Electrodeposition Monitor, now abandoned.
Specification This invention pertains to the art of electrodeposition, and more particularly to the monitoring and control of the current employed in electrodeposition to produce a coating having predetermined internal stress (or lack of stress).
In the art of electrodeposition, and particularly the art of electroplating, it is Well known that the particular current density employed is one of the parameters which determine whether the deposit produced is in a state of internal tension, compression, or whether it is substantially stress-free. Ordinarily a stress-free deposit is desired, although there are certain conceivable situations in which an internal stress of given sign and magnitude may be desirable. The presently conventional means of adjusting the current to produce the desired state in the deposit is largely empirical. In my copending application for US. Patent, Ser. No. 437,623, Feb. 18, 1965, parent Ser. No. 246,743, Dec. 24, 1962, now abandoned, entitled Device for Measuring Electrofinishing Stresses, and assigned to the assignee of the present application, there is disclosed a device and the mode of its application to determine which particular value of current density produces a given internal stress in the coating. This, briefly, is accomplished by depositing coatings upon a conductive substrate of known thickness and elastic characteristics, and observing the bending of the substrate when the desired thickness of deposit has been applied. The current in the main or production electrodeposition apparatus may then be adjusted to produce the current density which has been found to produce the desired result. However, in large production deposition baths the composition and deposition characteristics may change with use, both by depletion and by accretion of impurities. Since these changes occur gradually, during use of the bath, it is highly desirable that some means to be provided to monitor and adjust the current automatically to maintain the desired deposit characteristics, since unwanted stresses in deposits may produce defects such as peeling and susceptibility to corrosion which, unfortunately, are not immediately obvious, but appear only during the life of the coated part. When it is considered that parts used in large quantities, such as auto- "ice mobile bumpers, are electroplated in continuous plating baths of the kind described, it is evident that the elimination of defective production is of economic importance even beyond the value of the plated part, since defects in such plated parts may impair the reputation of a much more expensive product of which the plated item is only a minor but conspicuous or essential part.
This specification describes a device for automatically controlling the current in a continuous plating operation to minimize (or otherwise adjust) stress in the deposited coating. It may also be used to determine the effect upon the appearance or other characteristics of the coating of variations in current density.
In one embodiment of my invention, a cell is provided which is electrically similar to the type of cell whose basic properties are employed in an embodiment of my referenced invention for measuring stress in electrodeposited coatings. However, the test electrode, which in most processes is the cathode, instead of consisting of a flat metal sheet which is divided by slits into a number of separate tongues, as disclosed in my copending application, is composed instead of a plurality of strips of metal which are fed continuously from top to bottom over guides and thereby constitute the test electrode.
A number of these strips, located vertically side by side present a surface which is electrically similar to the continuous surface of a single electrode or, even more nearly, to the individual tongues of the electrode disclosed in my copending application. While the individual strips are maintained approximately vertical in their progress downward through the bath, they are given freedom to move slightly in response to curvature resulting from tension or compression stresses in the deposited coating. This is accomplished by stretching the strip between two sheaves or rollers which are located one vertically over the other, the strip thus being free for small lateral displacements. In accordance with the known art and also the teachings of my invention earlier referred to, if the electrodeposited coating is in tension, the strip will tend to be bowed in the direction of the coating, i.e., it will be concave on that side. If the coating is in compression, the strip will be bowed around a center away from the coating, that is to say, so that it will become convex on the side carrying the coating. The current distribution in such a plurality of anode strips will be substantially the same as that in the conventional Hull cell; that is to say, the current density to electrode strips nearer to the counterelectrode is greater than that to electrode strips farther away, the counter electrode being inclined at an angle to the faces of the strips. The deflection of such a strip will not be so great as to produce any marked changes in the current density to the strip. To measure such a small displacement advantage may be taken of the conductivity of the strip by placing a solenoidal winding behind the strip, preferably with its axis normal to the strips surface, and measuring the inductance of the coil. If the strip is displaced toward the winding, it will, in general, tend to reduce the inductance. This assumes that the strip is electrically conductive and that any ferromagnetism of the coating is negligible either because of the frequency employed or because of the thinness of the coating. If the permeability of the strip or of the coating is sufiiciently high, the inductance may be increased. In any event, it will be changed. A convenient and standard way of measuring changes in the inductance of such a coil is to determine changes in the frequency of an oscillator in which the coil forms part of the oscillating circuit. It is evident that a variety of methods may be used to determine the amount by which the strip has been displaced.
After downward passage through the field associated with the cell test electrode region, the strip may be drawn upward through the bath for further examination and be either stripped of its coating and reused or, as is likely to prove more practical, be simply discarded. It is true that there will be some current flow to the strip in its upward passage. It is assumed that this will be negligible because of the greater distance of the strip at that time from the Hull cell anode. If, in a given design, this should prove not to be true, an insulating sleeve may be inserted in the bath to lengthen the path of flow between the counterelectrode and the strip. This can be made adequate to reduce unwanted currents.
The strip which has been removed from the bath may be inspected physically for appearance, or may be tested for the determination of various factors which can be determined by instruments, such as smoothness or thickness of coating.
The indications of the deflection of the strip during its passage through the cell may be employed in several ways. They may simply be transmitted to a human operator who will use the information to decide what current density is required to give the deposit that he desires. Alternatively, the outputs of the devices for measuring the displacement of the strip may be fed into some data processing device whose result is used to adjust the bath current directly. This may conveniently be means for selecting the particular strip (or deflection sensor) associated with the desired value of deflection, and control means responsive to the output of the selected deflection sensor to adjust the current.
The preceding description is of the most general version of my invention, in which a plurality of strips is employed to determine stresses resulting at a plurality of different current densities. It is applicable to electrodeposition operations generally in which coating stress may, with variation in current density, increase for a while and then decrease, then increase again, possibly crossing the stress axis several times. For those particular baths in which, over the working range of cur-rent densities, the stress varies monotonically, it is possible to use a single strip which is plated at the current density actually in use on the work pieces. The deflection of such a strip will indicate the direction in which the current density should be adjusted to produce the desired result, and, by sufficiently frequent or continuous observation of the deflection of the strip and current density adjustments, the current density may be caused to oscillate with adequately small amplitude around the desired value, with correspondingly small deviations of deposit stress from the desired value. This simplified scheme, while less elegant and somewhat less accurate than the more elaborate multi-strip approach, is simpler and cheaper.
Thus I achieve a number of novel and useful objects. I make possible the continuous monitoring, and the automatic control, of the current density employed in electrodeposition to maintain desired deposit characteristics despite variations in the characteristics of the medium, or bath, employed. Achievement of this object produces economy and improvement in product characteristics. I also reduce the use of skilled labor in supervising the operation. I further produce a continuous sample, easily retained for reference, of the quality of deposit produced during the operation of the bath over prolonged periods of time. My invention produces various other benefits and useful advantages which will become apparent to those skilled in the art, in the course of the further specification and description.
For the better understanding of my invention, I have provided figures of drawings in which:
FIG. 1 represents a plan view of the mechanical part of an embodiment of my invention;
FIG. 2 represents in elevation the embodiment represented in plan in FIG. 1, and schematically the electrical portion of such an embodiment;
FIG. 3 represents a convenient mode of application of an embodiment such as that represented by FIGS. 1 and 2;
FIG. 4 represents an alternate mode of applicationof such an embodiment; and
FIG. 5 represents an embodiment of a simplified version of my invention, more restricted in its application than that represented by FIGS. 1 and 2, but also less expensive.
FIG. 1 represents the plan view of an embodiment of my invention which is shown partly in elevation and partly schematically in FIG. 2. A tank or bath 10 similar to that in the conventional Hull cell and here represented as being of transparent plastic material contains a counter-electrode 12 suitable for the deposition of a material whose deposition is to be controlled. It is connected through rheostat 14 to a current source 16, here represented as a battery, which is connected by way of amrneter 18 to the test electrode. The test electrode (or, more simply, electrode) is not a single piece of metal but consists of a plurality of strips 20, 22, 24, 26 and 28 which are carried upon a supply reel 30 which is supported by a shaft 32 which rotates in bearings 34 and 36. Counterelectrode 12 is is oriented at an angle to the faces of electrode strips 20 through 28, inclusive, in order that the path lengths from each such strip to counterelectrode 12 may be different, producing different current densities at each such strip when the potential difference between each such strip and the counterelectrode 12 is the same. Ammeter 18 is represented as connected to bearing 36. What is actually required in this instance is that the electrical connection be made to all of the strips 20 through 28 inclusive, and this is conveniently symbolized by connection to bearing 36, it being assumed that shaft 32 and drum 30 are of metal and are in electrical connection through bearing 36 with arnmeter 18. In practice a more formal slip ring and brush arrangement would probably be desirable, but since such a device is completely conventional, it is not represented here, purely to avoid complicating the drawing unprofitably. The various electrode strips pass from drum 3%) over sheave or roller 38 into bath 39, pass around rollers 40 and 42 upward out of the bath over rollers 44 and 46, and are taken up by takeup roller 48, which is carried by shaft 50 which rests in bearings or pillow blocks 52 and 54. No framework or mechanical structure is shown to support the various bearings or, in the case of the rollers or sheaves, even supporting shafting. Such structure has been completely conventional for a number of centuries and to represent it would complicate the drawing and render more difficult the explanation of the operation of my invention.
It is evident that in their passage through the bath 39, the various cathode strips 20 through 28 will be plated by passage of current from anode 12 through bath 39 to the electrode strips. It is also evident that while arnmeter 18 will give a correct reading of the total current flowing through anode 12, the current density to the various cathode strips will vary, strip 20 being plated at the high est current density and strip 28 at the lowest. This effect is quite similar to the effect observed in the Hull cell which,.however, conventionally employs a fixed single cathode and is used to determine only the appearance produced by electrodeposition at various current densities.
In general, the stresses in electrodeposits are a function of the current density. This function is, in general, not monotonic. However, for convenience in representing a variety of possible effects, I have chosen to represent the situation which would occur if the linear stress in the electrodeposit were in fact a monotone function of current density, with high current density producing a deposit which is in tension and low current density producing a deposit which is in compression. Thus, in FIG. 2, electrode strip 28 is represented as bowed out to the left in the direction of anode 12 by the compressive stress in a coating upon it. Electrode strip 24 is represented as being per fectly straight, an indication of the fact that the particular current density at which it is plated produces a substantially stress-free deposit. Electrode strip 20 is represented as bowed inward, or to the right, away from counterelectrode 12. Such bowing would be indicative of a deposit in tensile stress. It is a purpose of my invention to determine which of the electrode strips is operating, or being deposited at a current density which will produce a minimum of stress. For this purpose, I have provided a plurality of position sensors, represented by rectangles 56 and supported by a bafiie 57. This insulating baffle 57 serves an additional convenient purpose in that it will tend to minimize any diversion of plating current to the portions of the electrode strips 20 through 28 which have moved beyond roller 40 and are moving up from roller 42 to roller 44. While a number of devices for measuring the displacement of a metal strip, such as one of the elec trode strips, are known, a particularly convenient form for my purpose is an inductor which is located and so oriented that a displacement of the cathode strip adjacent to it will cause its inductance and thus its reactance to vary. By including such an inductance as one of the frequency-determining elements in a conventional oscillator circuit, the output frequencyof such an oscillator may be made to depend upon the displacement of the metal strip from the inductor. In FIG. 2, I have represented a plurality of such oscillators 58 which are connected by a multiconductor cable 59 individually to the appropriate sensors or inductors 56. Each such oscillator 58 is represented as connected to a tuned detector circuit 69. This detector circuit may be a resonant circuit which is tuned to give peak response at the oscillator frequency which is produced when the corresponding electrode strip is at its de sired displacement from the corresponding inductor 56. In the present case, this desired displacement would correspond to the displacement of strip 24. Since displacement on either side of the desired frequency will cause the output of a tuned circuit to decrease, it is evident that the oscillator 58.3 associated with strip 24 will be the strip uniquely tuned to match the tuning of its associated detector circuit 60.3 and therefore that one tuned detector circuit will produce a higher output voltage than any of the other circuits. The outputs of the various tuned detector circuits will feed through their buffer diodes 62 individually to the windings of relays 64- whose o posite winding terminals are brought together and connected through a resistor 66 to ground, which is also the common point for the various tuned detector circuits 60. The functioning of this circuitry is as follows: Assuming that the tuned detector 60.3, Which is associated with electrode strip 24, is producing an output voltage higher than that of any of the other tuned detector circuits, current will flow from it through its associated butter diode 62.3 and the winding of its associated relay 64.3 through resistor 66 to ground. If the resistance of resistor 66 is large compared with the resistance of the winding of a relay 64, the potential across resistor 66 will be very nearly equal to the peak output potential of the tuned detector circuit which is feeding it. Assuming an appreciable difierence between the output of the tuned detector circuit 60.3 associated with electrode strip 24 and those of the other, somewhat detuned, detector circuits, the potential produced across resistor 66 will be greater than the output potentials of the other detector circuits, and the diodes 62 associated with them will therefore be biased off. In other words, the only tuned detector circuit which will actually be feeding current to resistor 66 and therefore the only tuned detector circuit which will actually be feeding current through a relay coil of relays 64 will be the tuned detector circuit 60.3 which has the highest output. Thus, only one of the relays 64 will actually be excited at any given time. It will be observed that the contacts of the relays 64 are so arranged that, if none of the relays is excited, the connection to terminal 68 of controlled power supply 70 is simply carried through the normally closed contacts of the relays back to the uppermost of the array 72 of terminals on the power supply. If one of the relays is excited, it will break the connection to the uppermost of the array of terminals 72 and transfer the connection with common terminal 68 to an intermediate one of the array of termi nals 72. Controlled power supply 70 is required to be a source of deposition current, connected by conductors 74 to the actual tank plating circuit and capable of being adjusted by connection of common terminals 68 to a specific one of terminals 72, to furnish a specific current to the electrodeposition circuit. In other words, connection of terminals 68 to a selected one of terminals 72 determines the particular current which the power supply will provide. This corresponds, of course, to setting a tap switch to a particular point; but the convenience of using relays in this particular embodiment of my invention requires that terminals rather than switch points he provided for connection to the relay contacts.
It is evident that the results provided by the embodi ment of my invention which have been described thus far will not bear any particular relation to the desired stress-free product unless the solution or bath 39 em ployed in container 10 is representative of the deposition medium whose product is to be controlled, and the current density provided by power supply 70 corresponds to the current density which produces the desired test result in the plating of one of the electrode strips 20 through 28. The current density is, of course, a function of the total current provided through conductors 74 and the of the area of work pieces in the main deposition tank at one time. These are design and operating parameters which obviously must be arranged for in the design of power supply '78 and the relationship provided between the selection of a terminal of array 72 and the corresponding current provided through conductors 74. The problem of making bath 39 representative of the medium actually used in the plating bath to be controlled may be solved in one of two simple ways. The container 16 may be perforated so that it may be mounted to support the electrodes and other structure in the main plating tank. to be served, in which case, the bath 39 will, of course, be part of the main plating bath. Such use of a Hull cell is completely conventional, and may also be the most convenient way of applying my invention. However, it is quite common in plating baths to provide circulating means so that the bath may be circulated continuously. If some circulating means for the entire bath is conveniently available, it may be more convenient to set up the embodiment represented in FIG. 1 and part of FIG. 2 independently of the main bath itself and simply provide for a portion of the circulated main bath to be fed to container 10 and allowed to overflow back into the main electrolyte circuit from some convenient drain point. What is essential is that the bath 39 in container 10 shall be an accurate sample of the deposition medium actually being employed in the main plating tank. The adequacy of the sample will, of course, take account not only of chemical composition but also of temperature.
Thus far, nothing has been said about the means for driving the cathode strips 20 through 28 and the speed with which they should be fed. Since the object of coating the strips is to achieve a simulation of the coating of the work pieces in the main plating tanks, the passage of the strip from its entry into bath 39 to its reaching roller 40 should require a length of time equal to the time that the actual work pieces are in the main plating tanks. Deposition at a given current density for a given length of time will produce a fixed thickness of deposit. This means that the deflection of the cathode strips will occur over a length of strip extending between roller 38 and roller 40* and, in consequence, will extend over a strip initially unplated and finally completely plated. Thus, the total deflection of the cathode strip under the operating conditions of the present invention will not be identical with that which would result if the same length of cathode strip were uniformly plated; but the deflection actually observed can be related exactly with the plating stress. The factors discussed thus will in practice not impair the utility of the device. A further advantage of depositing, upon the electrode strip, substantially the same thickness of deposit that will be applied to work pieces, is that, after its withdrawal from the bath 39 and passage over roller 44, the deposit may be examined visually or its thickness may be checked automatically by various known methods or other characteristics may be measured. Means for measuring these parameters are not shown in detail because they are well known in the art and the single convenient variable parameter, current, is used in the present invention to control the stress in the deposited coating. If examination of the deposit upon the strip after it has been withdrawn from the bath on its way to takeup reel 48, should indicate that something in the nature of the coating is unsatisfactory, appropriate changes in bath composition or speed of traverse of the work through the main plating techniques may be made by human intervention in accordance with the known art. It is a possible alternative to provide for intermittent advance of the electrode strips by controlling the operation of motors 76 and 78 through a conventional time or clock switch which operates them for a period suflicient to provide a completely fresh electrode surface exposed between rollers 38 and 40, then stops the motors for a length of time equal to the length of time that the work pieces are submitted to treatment, and then repeats its cycle once more. When this alternative mode of operation is employed, the properly significant value of deflection of the strips such as 20, 24, and 28 will exist only at the end of the period during which the motors 76 and 78 are stopped. It is thus necessary, in this alternative mode, that the sensing system comprising 56, 58, 60, 62, and 64 be rendered inactive (conveniently, by additional contacts on the time switch) at all time except at the end of that stop period, when the sensing system is briefly activated. In order that the value of plating current provided through conductors 74 by controlled power supply 70 shall not be altered except during activation of the sensing system, relays 64 may be of the conventional latching type which employs two coils, one to latch the relay into a first position, and a second coil to unlatch the relay and lock it into its second position. In such case, each such latching relay must be equipped with an additional pair of contacts so that, when it is excited through its buffer diode 62 and latched into its first position, the closing of the additional pair of contacts will excite the second coil of all the other relays to unlatch them. This method is conventional, and other similar conventional devices are known and may be used. It will be recognized that, in this alternative method, the speed of motors 76 and 78 may be as high as convenient so that the time required to advance a fresh sample of electrode strip into position will be minimized.
The rotation of reels 3i and 48 to advance the electrodes is accomplished by advancing means represented as motors 76 and 78 which are represented as belted to the respective shafts 32 and 50. Since it is desired that the strips 20 through 28 be reasonably free to deflect under their internal stresses while in transit from roller 38 to roller 40, the tension upon these strips should not be excessive. Therefore, it appears desirable that the motor 76 be used as the speed determining motor and that the motor 7 8 be used to apply only suflicient torque to insure that the strips pass over the various rollers and are wound up on takeup reel 48 at moderate but not excessive tension. Since the tension in the strips will be of very slight effect in reducing small deflections, it results that the tension in the strip is not extremely critical; but excessive tension would reduce the sensitivity of the device to the appearance of stresses in the deposited. coating. This, obviously, is to be avoided.
FIG. 3 represent the structure of FIGS. 1 and 2 installed in a main plating tank 80. In this mode of installation the tank 10 is provided with apertures 82 in its walls so that the electrolyte 84 in the main tank may circulate freely into and outof tank 10, rendering its content representative of the content of the main plating tank 80. Details of the auxiliary equipment, shown in FIGS. 1 and 2, are omitted here because the reduced scale would render them undecipherable.
FIG. 4 represents an alternative mode of application of the structure of FIGS. 1 and 2 to a main electrodeposition tank 86, which is provided with a pump to recirculate the electrolyte 92. The discharged electrolyte from pump 90 is passed through a T94, whose outlets are throttled by valves 96 and 98. By partially closing valve 96, a pressure drop is created which will cause some of the circulating medium 92 to pass through valve 98 (which may be adjusted to control the flow more exactly) and thence into tank 10. Tank 10 for the present mode of installation is located at a higher level than the level of medium 92 in the main tank 86, and is provided with a floor drain 100 which discharges the medium 92 back into the main tank 86. In operation, valve 98 may be adjusted to maintain a continuous flow of medium 92 through the tank 10 to preserve a suitable level in tank 10. Thus there is maintained a continuously representative sample in tank 10 of the medium 92 which is being used in the main tank 86.
The work pieces and electrodes in the main tanks 80 and 86 have not been represented, since they are part of well known art, and may have a wide variety of embodiments.
It is evident that the basic principles of my invention are subject to modification in accordance with the known art to meet particular requirements. For example, it is possible to insulate the various test electrode strips from each other and provide separate electrical connections to each such strip. Then current may be fed separately via each separate electrical connection from independently adjustable separate sources. In such an embodiment the various current densities to the various electrode strips may be adjusted at will, without the necessity of orienting the different strips so they will lie at different distances from the counterelectrode. Such a procedure is necessarily more complicated than the embodiment I have represented, and I have therefore not represented it as preferred; but it is feasible, should particular circumstances render it desirable. Similarly, I have represented the electrode strips as descending vertically through the region in which deposition upon them takes place; but it is obvious that, if it were desired, they might be caused to move horizontally through the bath, or at an angle. This ordinarily would have no advantages, but is perfectly feasible. The embodiment which I have represented is my preference over these alternatives because of its simplicity, which not only achieves economy, in general, but renders it more easily understood by potential users.
While the foregoing embodiments of my invention have the advantage that they are applicable in all electrodeposition baths in which deposit stress is a function of current density, itis possible to employ a still simpler embodiment for those baths in which, over the usual working range, stress is a monotone (whether increasing or decreasing) function of current density. Such an embodiment is represented in FIG. 5. Since a number of the elements represented in FIG. 5 are similar to, but not necessarily identical with, elements represented in FIG. 2,
such similar elements in FIG. 5 are given reference num-,
bers 100 higher than their cognates in FIG. 2. Thus electrode 112 is the cognate of electrode 12.
In this simplified embodiment a single strip 128 is employed for test purposes. It is plated at the average current density being employed to plate the work; and, after a suflicient time has elapsed to produce a deposit thick enough to deflect the strip 128 in a direction and amount indicative of the magnitude and sign of the stress in the deposit, such deflection is sensed by position sensor 156,
and the current to the plating circuit is adjusted in the direction (increase or decrease) which will alter the stress toward the value of stress desired (which may be zero). Clearly, it is necessary, to permit this procedure, that a given value of observed stress shall indicate uniquely whether the plating current should be increased or decreased; that is, the known relation between stress and plating current density must be monotone increasing or decreasing, since this means that the sign of the derivative never changes.
Such a relation is reported, for example, for the following copper electroforming bath:
Copper sulfate oZ./gal 32 Sulphuric acid oz./gal 810 Temperature degrees C 35 Current density amps. sq. ft -40 Stress range lbs./sq. in 500 to +450() Referring in detail to FIG. 5, a counterelectrode 112 is immersed in bath 139. A supply reel 130, running on bearings 136, carries a store of a single electrode strip 128 which runs over rollers 138, 140, 142, 144, and 146 back to a takeup reel 148. Motor 178 draws the strip 128 when it is to be moved, and motor 176 maintains moderate tension on it. The deflection of strip 128 is sensed by sensor 156, which is single, and is connected by cable 159 to oscillator 158 in some fashion (many are known) which causes the frequency of the output of oscillator 158 to be altered by variations in the deflection of strip 128. Oscillator 158 has its output connected to a discriminator 160. While this discriminator is the cognate of the tuned detectors 60 of FIG. 2, it differs from them in that it produces a D-C output which varies not only in magnitude but also in sign with the magnitude and sign of the deflection of strip 128 from sensor 156. Barrier 157 serves the same function as does barrier 57 of FIG. 2. It'may be observed that, for a bath of good throwing power, it may be desirable to provide the back of strip 128 with an insulating coating of cheap lacquer or similar material to insure that only one side of the strip is plated. This will insure maximum sensitivity of the stress observation. This is, of course, well within the scope of the known art.
The embodiment of FIG. 5 has been chosen to illustrate specifically the mode of operation in which the strip 128 is moved rapidly into position, plated, and its deflection is then measured and the plating current is adjusted accordingly. For this purpose, motors 176 and 17 8" are represented with their ungrounded driving power terminals connected by a common conductor 202 to a contact segment 204 of a rotating timing switch 206. Timing switch 206 comprises a clock motor 208 which drives a rotating contact 210 clockwise over a circular path which comprises insulating segments 212 and 214 and contact segments 204 and 216. Rotating contact 210 is connected to a power source, not shown. The proportionin-g of the various segments (and the speed of rotation of clock motor 208i are such that the period of traverse of rotating contact 210 over insulating segment 212 is the length of timedesired for the plating operation on strip 128. The subsequent period of contact of rotating contact 210 with contact segment 216 is sufficient for adjustment of the plating current from plating power supply 170, by means to be described hereinafter. Following its contact with contact segment 216, the rotating contact 210 remains on insulating segment 214 for a brief period, which is determined primarily by the necessity of-preventing simultaneous contact between contact segments 216 and 204 through the finite breadth of rotating contact 210. Then rotating contact 210 comes in'contact with contact segment 204, exciting motors 176 and 178 for a period long enough to advance strip 128 by a sufficient amount to present a fresh, unplated portion for plating. The duration of this period will be determined primarily by the speed of motors 176 and 178, which may be as rapid as mechanical considerations permit. Then, when rotating contact 208 moves to insulating segment 212, the motors stop and the fresh portion of strip 128 is plated.
The events which occur when rotating contact 210 is in contact with contact segment 216 will now be considered in detail. Oscillator 158 operates at a frequency which, as has been previously mentioned, is a function of the displacement of strip 128 from sensor 156, and its output is fed to discriminator 160, whose output is a D-C voltage which is a function, in magnitude and sign, of the frequency of oscillator 158 and thus of the displacement of strip 128' from sensor 156. One output terminal of discriminator 160 is grounded, and the other output terminal is connected to an input terminal of amplifier 218, whose other input terminal is connected to the movable contact of potentiometer 220, which is fed a D-C potential bipolar with respect to ground from D-C source 222. Amplifier 218 is a bipolar D-C amplifier whose Ol1tput capabilities are suitable for driving the armature of motor 224, which is represented as having a permanent field supplied by magnet 226, in order that the direction of rotation of motor 224 may be dependent upon the polarity of the potential applied to its armature. The shaft of motor 224 is connected to drive directly the movable contact of variable-ratio autotransformer 228, and, through electromagnetic clutch 227, the movable contact of potentiometer 220. Amplifier 218 has the additional characteristic that it produces an output only when it is furnished power from contact segment 214 through conductor 230, which also engages clutch 227. The mode of operation of the assemblage comprising amplifier 218, motor 224, potentiometer 220 and autotransforrner 228 is as follows: when amplifier 213 receives power over conductor 230 it produces an output whose polarity and magnitude depend upon the difference between the output signal of discriminator 160, and the potential of the movable contact of potentiometer 220. The output signal of discriminator 160 is a measure of the desired corrective displacement of the movable contact of autotransformer 228. Spring 229, during the period prior to engagement of clutch 227 by excitation of conductor 23%, sets potentiometer 220 so its output is at ground potential. When clutch 227 is engaged, subsequent rotation of 220 produces an output voltage proportional to the displacement of the contact of autotransformer 228. The output of amplifier 218 will therefore be proportional, in magnitude and sign, to the diiference between these two values. The polarity of the connection of the output of amplifier 218 to the armature of motor is such as to cause motor 224 to rotate in such a direction as to reduce this diiference to zero-in other words, to displace the movable contact of autotransformer 228 by the desired amount. When rotating contact 210 leaves contact segment 216, clutch 227 disengages itself and spring 229 will center potentiometer 222, amplifier 218 will remain quiescent, and the position of the movable contact of autotransformer 228 will remain undisturbed until the amplifier 218 is again rendered operative when rotating contact 210, having completed a revolution again reaches contact segment 216. Thus, each time the plating operation on a portion of strip 128 has been completed, autotransformer 228 will be reset, if necessary, to the proper position to cause it to apply to plating power supply the proper input potential to correct for any undesired deflection sensed by sensor 156.
The direction of the changes produced by the described operation will be determined by the polarity of connections among the various elements. The general requirement which must be fulfilled is that the plating current be changed in that direction which, from the known relation between stress and plating current (which must be initially determined for the particular bath and plating conditions employed, in accordance with the known art), will tend to correct a sensed undesired deflection of strip 128. Preferably, the magnitude of the change produced should besuch as to reduce the undesired deflection to zero. In practice, this is unlikely to be achieved exactly, but (since the period of rotation of clock motor 208 may be made small compared with the time required for the occurrence of substantial changes in the composition or other plating conditions) frequent corrections will permit the values of plating current to oscillate with small amplitude around the ideal value, and any resulting stresses in the deposit produced will be satisfactorily small.
It should be observed that the particular system comprising amplifier 218, motor 224, potentiometer 220, and its D-C source 222 is simply a particular embodiment of a servo system which may be replaced in practice by any servo system which can adjust the setting of autotransformer 22% in accordance with the output of discriminator 160. Also, the signals resulting from the instrumental deflection sensing may be electrical phaseor pulse-position-rather than frequencyor (at the output of the discriminator) amplitude-modulated. The most valid general statement one can make is that the signals will be functions of the magnitude and sign of the deflections sensed. Similarly, the use of autotransformer 228 is merely exemplary, and it is perfectly feasible to replace it and plating power supply 170 by any other device which can be caused to adjust the plating current furnished through conductors 174 in accordance with the intermittent application of output signals received from discriminator 160. It should, however, be noted that the output of discriminator 160 is properly significant of the plating conditions, and the required current change, only at the completion of the plating of a sample of strip 128; provision must therefore always be made, as in the present embodiment, to insure that the output of discriminator 160 is effective only at the proper time in the cycle of operation.
It is, of course, feasible to operate a single-strip device of the general kind represented by FIG. in the manner described in detail for the embodiment of FIG. 2, in which the strip 123 slowly moves continuously, so that the deflection sensed by sensor 156 is an average indication of the history of the plating operation for the time required for unrolling a length of strip 128 over a distance equal to the Spacing between rollers 138 and 140, and the plating current is adjusted continuously (or continually) in accordance with the sensed deflections. This latter method may be somewhat simpler but also may be somewhat less sensitive.
Alternatively, it would be possible to provide successively exposed portions of strip electrode 128 with different current densities for deposition, instrumentally measure the deflection resulting from each current density, store this information, and, upon completing a cycle of measurements, determine the value of current density which most nearly produces the desired deposit stress, and adjust the current used in plating the workpieces to that value (or even interpolate between the two adjacent sampling current densities which produce the two values of deposit stress nearest to that desired). Those skilled in the art will recognize this as being primarily an application of modern information processing and control tech niques to achieve, by a single electrode strip along the general lines disclosed by FIG. 5, the results taught by a plurality of electrode strips according to the disclosure of FIGS. 1 and 2. Except under most unusual circumstances, it would appear to have little to recommend it. The period for complete sampling over the entire current range will necessarily be extended over that required with a plurality of strips; the data processing and control equipment required may be expected, at the present time, to exceed in cost the cost of providing for a plurality of strips. Furthermore, while the edge effect which causes current to be somewhat concentrated at the edges of a strip electrode may be rendered negligible by making a single strip electrode somewhat wider than would be needed for a plurality of strips, the mutual edge shielding 12 effect of the plurality of strips is a benefit at least worth considering.
The appended claims are in subparagraph form in accordance with a request of the Commissioner of Patents, to facilitate reading. The division into subparagraphs is not necessarily indicative of relative importance of the elements recited, nor of any necessary relation among such elements.
What is claimed is:
1. Monitoring means for an electrodeposition system composing:
(a) a bath representative of the deposition medium of the system to be monitored;
(b) a counterelectrode immersed in said bath;
(c) a plurality of electrode strips;
(d) storage means for storing said electrode strips;
(e) support means for supporting said electrode strips for advance from said storage means through said bath;
(f) advancing means for advancing said electrode strips on said support means;
(g) current means for driving current between the said counterelectrode and the said electrode strips at different current densities on different electrode strips to produce electrodeposits upon said electrode strips;
(h) instrumental deflection sensing means to sense the deflection of each said electrode strip with respect to the said support means.
2. A device claimed in claim 1 further comprising:
(i) selection means connected to said instrumental deflection sensing means to select the electrode strip whose deflection most nearly approximates a desired deflection, and to actuate control means responsively thereto;
(j) control means connected to said selection means and to controlled power supply means to control the current supplied by said supply means responsively to actuation by the said selection means.
3. Monitoring means for an electrodeposition system comprising:
(a) a plurality of extensive electrodes;
(b) counterelectrode means;
(c) means for supporting and advancing said plurality of extensive electrodes through a bath representative of the deposition medium of the system to be monitored, a portion of each said electrode in the said bath being supported only at the extremes of the said portion;
(d) current means for providing current flowbetween the said bath and the said electrodes at diflierent current densities for different electrodes to produce an electrodeposit upon the said electrodes;
(e) instrumental deflection sensing means for sensing the deflection of each said portion from a straight line between the ends of the said portion.
4. Monitoring means as claimed in claim 3 further comprising:
(f) means for controlling an electrodeposition current responsively to the deflections sensed by the said instrumental sensing means.
5. Monitoring means as claimed in claim 4 in which the said means for controlling an electrodeposition current comprises:
(1) means for selecting the said strip whose deflection as sensed by the said instrumental deflection sensing means is most nearly zero;
(2) means for controlling the said electrodeposition current to be proportional to the current density existing at the said selected strip.
6. In combination:
(a) a bath of electrodeposition material;
(b) a counterelectrode immersed in said bath;
(c) a plurality of electrode strips;
((1) a supply reel for storing a supply of said plurality of electrode strips;
(e) a plurality of support rollers for carrying said electrode strips from said supply reel into and out of said bath;
(f) a takeup reel for taking up the said electrode strips after passage over the said support rollers;
(g) advance means to advance the said electrode strips from the said supply reel over the said support rollers to the said takeup reel;
(h) current supply means connected to provide current between the said counterelectrode and the said plurality of electrode strips at diflFerent current densities to different electrode strips of the said plurality, to cause electrodeposition upon said electrode strips;
(i) a plurality of instrumental deflection sensing devices, equal in number to the number of said electrode strips, located in the said bath each adjacent to the portion of an electrode strip extending between two of said support rollers, to sense the deflection of the said portion of a said electrode strip from a straight line tangent to the said two support rollers.
7. The combination claimed in claim 6, further combined with:
(j) selecting means for selecting from the said plurality of deflection sensing devices the deflection sensing device which is sensing a substantially zero deflection, and
(k) means for adjusting the current output of a con trolled power supply to a value proportional to the current density provided to the said electrode strip selected by the said selecting means.
8. The combination claimed in claim 6, in which a said instrumental deflection sensing device comprises:
(1) an electrical reactance element whose reactance is a function of the deflection to be sensed;
(2) an oscillator whose frequency is determined in part by the reactance of the said electrical reactance element;
(3) a frequency-selective circuit connected to receive the output frequency of the said oscillator.
9. The combination claimed in claim 7, in which the said selecting means comprises:
(1) a plurality of diodes connected to the outputs of the said instrumental deflection sensing means, and
(2) a common resistance connected to receive the output of any of the said diodes of the said plurality.
10. The combination claimed in claim 9, in which each diode of the therein said plurality is connected to the therein said common resistance through the winding of a relay whose contacts are connected to control the current output of a controlled power supply.
11. Monitoring means for an electrodeposition system comprising:
(a) a bath representative of the deposition medium of the system to be monitored;
(b) a counterelectrode immersed in said bath;
(c) an electrode strip;
(d) storage means for storing said electrode strip;
(e) support means for supporting said electrode strip for advance from said storage means through said bath;
(f) advancing means for advancing said electrode strip on said support means;
(g) current means for driving current between the said counterelectrode and the said electrode strip to produce an electrodeposit upon said electrode strip;
(h) instrumental deflection sensing means to sense the deflection of said electrode strip with respect to the said support means.
12. A device claimed in claim 11 further comprising:
(i) control means connected to said instrumental deflection sensing means and to power supply means to control the current supplied by said supply means responsively to signals which are functions of the magnitude and sign of the deflection sensed by said instrumental deflection sensing means.
13. A device claimed in claim 12 further comprising:
(j) timing means connected to cause said advancing means to operate intermittently during first periods of time, and to cause said control means to respond to said signals intermittently during second periods of time.
References Cited UNITED STATES PATENTS 2,762,763 9/1956 Kenmore et al 204206 2,868,702 1/1959 Brennan 204206 JOHN H. MACK, Primary Examiner.
T. TUNG, Assistant Examiner.
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,356,605 December 5, 1967 Francis J. Schmidt It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.
Column 12, line 11, for "composing" read comprising Signed and sealed this 7th day of January 1969.
Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissioner of Patents