US2783199A - Electrolytic grinding apparatus - Google Patents

Description

Feb. 26, 1957 G. E. COMSTOCK 3D ELECTROLYTIC GRINDING APPARATUS 3 Sheets-Sheet 1 Filed April 15, 1953 HHU INVENTOR, [Em/v55 E. 50M57Z70K 3rd BY M4 41am ATTORNEY Feb. 26, 1957 ca. E. coMsTocK 30 2,783,199

ELECTROLYTIC GRINDING APPARATUS Filed April 13, 1953 3 Sheets-Sheet 2 //V5ULATION I INVENTOR. EEOR'GE E. 6'0M5T0LK 3rd.

ATTORNEY Feb. 26, 1957 G. E. COMSTOCK 3D ELECTROLYTIC GRINDING APPARATUS 3 She ets-Sheet 3 Filed April 13, 1953 QWLUR hum 520355 6.. DansracK 5117(- A TTOENEY United States Patent ELECTROLYTIC GRINDING APPARATUS George E. Comstock 3d, Holden, Mass., assignor to Norton Company, Worcester, Mass, a corporation of Massachusetts Application April 13, 1953, Serial No. 348,285

15 Claims. (Cl. 204-218) This invention relates to electrolytic grinding and more particularly to a system and apparatus for effecting stock removal electrically from a conductive work-piece face.

One of the objectsof this invention is to provide a system and apparatus of the above-mentioned nature that is well adapted for ease and convenience of installation in factories or plants already provided with alternating current circuits or sources and that is of dependable control or regulation to effect eflicient stock removal electrically under widely varying conditions of practical requirements and use and is of desirable simplicity in manual setting. Another object is to provide, in a system and apparatus of the above-mentioned nature, controls of the flow or conversion of electrical energy for stock removal so as to provide, at the locus of electrical stock removal, voltage and current characteristics best suited for dependable, safe and eificient stock removal with reliable and efficient variation in current regulation for widely varying conditions at the above-mentioned locus.

Another object is to provide a system and apparatus for effecting stock removal from a conductive work-piece by electrolytic decomposition at the work-piece face and to provide for dependable and flexible control of the conversion of alternating current energy to unidirectional or direct current energy at the locus of electrolytic decomposition in order to provide thereat voltage and current characteristics of the direct current energy best suited for eflicient and safe stock removal. Another object is to provide a system and apparatus of the justmentioned character in which the widely varying conditions at the locus ofstock removal, caused by the exigencies or requirements met with in practice, efiect control of the voltage and current characteristics, and particularly current control in relation to voltage control, in a thoroughly dependable and quick-acting manner, of the direct current energy at the work-piece face so as to provide good safety and efiiciency of operation. Another object is in general to provide an improved grinding apparatus and control system for electric stock removal at the workpiece face, in which current-limit level may be dependably changed automatically as required by changing conditions at the work-piece face, such as changes in area, real or apparent, changes in resistance thereat, etc.

Another object is to carry out the above-mentioned objects, severally or jointly, in which the apparatus and system effect reliable controls of the electrical energy at the work-piece face and also under open-circuit condi tions as when that work-piece and companion electrode element or elements are separated and particularly when they are brought together. Another object is to carry out the above-mentioned objects, severally or jointly, in which the apparatus and system, supplied initially from an alternating current source, effect, in a simple and dependable manner, controls at the direct-current locus of work-piece decomposition or erosion that guard against initial current surges or flashes that would otherwise take 2,783,199 Patented Feb. 26, 1957 ice 2 7 place when the work-piece is brought in co-acting relation at the above-mentioned locus.

Other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the features of construction, combinations of elements, arrangements of parts and in the several steps and relation and order of each of the same to one or more of the others thereof, all as will be illustratively described herein, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings, in which are shown illustratively the mechanical and electrical features of my invention and in which similar reference characters refer to several parts throughout the several views of the drawings.

Figure 1 is a front elevation, with certain parts shown or indicated diagrammatically, of the grinding machine;

Figure 2 is a fragmentary side elevation thereof;

Figure 3 is a fragmentary horizontal sectional view on an enlarged scale, showing certain mechanical and electrical features of one form of grinding wheel in relation to a work-holder and certain electrical features related thereto;

Figure 4 is a fragmentary or detached front elevation of a wheel guard cover and associated electrolyte-distributing parts as related to the grinding wheel of Figure 3 and as seen from the front'in Figure 1 and from the left in Figure 3; and

Figure 5 is a diagrammatic representation of the apparatus, including the conductive wheel element of Figures 14, and the electrical energy supply system associated therewith and of the co-acting controls therefor.

As conducive to a clearer understanding of certain features of my invention it may here be noted that there are many advantages to be gained in stock removal by electrolytic grinding in which, by the co-action of an electrolyte and direct or unidirectional current, stock is removed from the work-piece by electrolytic decomposition of the work face, especially for machining hard cemented carbides (such as cobalt-bonded tungsten and/or titanium carbide) whereby, when the rotating conductive element or face of the grinding wheel contains abrasive grain, the cutting action of the abrasive grain may be very materially supplemented. Most industrial plants or factories are equipped with or wired for alternating current energy, usually and illustratively three-phase and of 60 cycles. One of the objects of my invention is to provide efficient and dependable electrolytic grinding apparatus and compact, simple, and co-acting controllable energy supply system that needs only to be electrically connected to the existing alternating current supply lines and controllably furnish, at the locus of stock removal, the required unidirectional current or electrolytic action. As heretofore attempted to be practiced, so-called electrolytic grinding has encountered various difiiculties or the systems or apparatus have inherent limitations or there arise phenomena detrimental to or destructive of the grinding wheel, and these handicaps become all the more serious where, as is frequently the case, it is desirable to use diamond grinding wheels, which are costly. Another aim of this invention is to avoid or alleviate such handi caps, shortcomings or risks and to provide more flexible and more efiicient controls, in response to changes in harmful direction of the electrical conditions at the locus of electrolytic decomposition of the work-piece, at greater stock removal capacity, of the conversion of the alternating current energy, whether or not electrolytic decornposition is accompanied by abrasive action.

In stock removal by electrolytic decomposition at the work face, the conductive work-piece is made the anode, and at the work-wheel interface, where there may or may not be physical contact and where there may or may not be accompanying abrasive action, there is adequately supplied a suitable electrolyte, which also serves as a coolant, and it is desirable to use high current density since the rate of electrolytic decomposition at the work-piece face is proportional to current flow. Various conditions can occur or be brought into being at the work-wheel interface that will cause detrimental actions, such as arcing, current surges, high-intensity flashes, etc., which can also cause damage or cause excessive rates of wheel wear which, particularly where diamond abrasives are embodied in the wheel, can prove prohibitively costly. It can be shown that a desirable characteristic of supply of direct current for the electrolytic circuit is one where the voltage across the work-wheel interface is maintained sub stantially constant up to the point where the electrolytic current flow approaches a critical value above which deleterious arcing occurs, followed by current-limiting action at a selectable current value less than the critical current, to reduce the voltage across the work-wheel interface to prevent the current from reaching or exceeding the critical value. A further object of this invention is to effect conversion of alternating current electrical energy into direct current energy at the work-wheel interface with the energy conversion controlled, in response to conditions at the work-wheel interface so that the just-described characteristic of energy supply at the work-wheel interface is provided in a simple, compact, efiicient and reliable manner and moreover in a manner to vary the level of current control automatically to meet a variety of varying or variable conditions, both at starting and runnmg.

In describing my invention I prefer to do so in connection with an electrolytic grinding apparatus in which the grinding wheel, while conductive, also contains abrasive grains and also because certain protective actrons which the system of my invention achieves serve also to excellent advantage where both electrolytic and abrasive action take place conjointly, as is frequently desirable in practice. Any suitable mechanism or arrangement may be employed for mounting and driving the conductive grinding wheel and for mounting or supporting, or even for resting thereon for manual movement (as in so-called off-hand grinding), a work-piece, such as a cemented carbide tool or other piece of work or object to be ground or machined, whereby to obtain relative movements between the grinding wheel and the supported work. Many and various forms of mechanism are well known for cooperatively relating a grinding wheel and a work-piece for relative movement therebetween and providing for various relative adjustments and/ or movements between the grinding wheel spindle and the work together with various manual or automatic controls for such adustments and movements. For example, I may utilize a machine such as is shown in U. S. Patent 2,101,781, in which a work-table, underlying an adjustably mounted and rotatively driven grinding wheel spindle, is movable and reciprocable relative to the grinding wheel and is mounted on a cross slide for shifting it transversely, that Is, forwardly or rearwardly of the machine, relative to the grinding wheel; in the machine of that patent the work-table can be reciprocated upon the transverse or cross slide by manual means or by fluid pressure mechanism as there described, while the cross slide may be man ually or mechanically moved to advance the work-table and the work-piece supported by it in steps or at a rate according to the setting of the infeed mechanism or according to the manual actuation thereof, as by a hand wheel. Or, I may utilize a grinding machine, by way of further illustration, of the type or kind disclosed in Patent 2,381,034, the machine of that patent being particularly adapted to shaping tool bits, particularly bits or tools of the above-mentioned hard cemented carbides, and in that machine the operator manually shifts the holder or carrier that supports the work-piece or tool, relative to an adjustable table or support and relative to the flat side face of the grinding wheel, according to various curvatures of surfaces or fiat surfaces, sometimes with the aid of templates or with the aid of various adjust ments of various angularities, according to the specific character of surface shaping that the particular tool or tool bit requires. These two patented disclosures are illustrative of two of the many types of grinding machines to which our system and controls are applicable for effecting stock removal by electrolytic decomposition at the face of the work-piece.

Accordingly, in the drawings, I have shown in Figures 1 and 2, a driving mounting forthe, rotating conductive element together with an illustrative work-piece and workholder or support, with a work-table for the latter depicted largely diagrammatically, particularly insofar as its adjustability and movement relative to the rotating grinding wheel are concerned, inasmuch as much adjustability and movement, and the mechanism for effecting them, may take any suitable or known form, and many thereof are well known in the art.

Thus, the apparatus may have a base or main frame 10 which, at its rear, supports a column or vertical standard 11 which, as indicated by the arrows thereon, is rotatively adjustable about a vertical axis and is also adjustable in up-and-down direction; the column 19 supports a wheel head 12, in which is journaled a grinding Wheel spindle 13 which projects both forwardly and rearwardly of the wheel head, and at its rear end carries a pulley 14 which is driven by a belt 15 from a pulley 16 on the shaft of a motor 17, which is suitably carried by the top of the standard 11.

The front end of the spindle 13 is appropriately con structed to have or is provided with means for mounting a grinding wheel thereon, as by providing it with tapered portion 21 (Figures 3-6) that is received into the tapered bore of a flanged sleeve 22, a nut 23 which is threaded onto the spindle 13 holding the flanged sleeve 22 securely in place. The flanged sleeve 22 is suitably constructed to carry and has secured thereto a grinding wheel which is electrically conductive and which is illustratively and preferably constructed, as is shown in Figures 3 and 4 and as is later to be described.

When the grinding wheel is so mounted at the front end of the spindle 3.3 it substantially overlies or overhangs a work-table 24, which is reversibly movable and reciprocable, as indicated by the double-headed arrow in Figure 1, being supported in suitable lengthwise extending ways provided in the cross slide diagrammatically indicated at 25, the latter being adjustable or movable, reversibly, as indicated by the double-headed arrow in Figure 2, being suitably carried or supported, for that purpose, on suitable ways provided in the base 10.

The work-piece W, which for purposes of better illustrating certain features of my invention, may be considered to be a block of cemented carbide and suitable means are provided for releasably holding or clamping it to facilitate control of its movement relative to the operative face of the grinding wheel, and such means may comprise a heavy-worit-holding bar 27, which is provided with a suitable hole or recess 23 in which the work W is received and in which it is clamped securely, as by a clamping screw 29. in the electrolytic grinding circuit the work W is to serve as the anode in the electrolytic cell and accordingly suitable provision is made for connecting the work W appropriately into the electrical circuit, and such means may comprise a suitably heavy connector screw 30 by which a conductor may be clamped, carried by and threaded into the work'holding bar 27, as is better indicated in Figures 3 and 5. The work-holding bar 27 may in turn be carried "by a visc, generally indicated at 31; the vise may be of any suitable construction and may, for example, comprise a fixed vise jaw 32 and a movable clamped and held, as by the screw 34, manually operable,

as by the handle 35. The vise 31 can rest on the worktable 24, with which, when suitably secured thereto, it is movable according as the work-table 24 is moved or actuated as in the above-mentioned Patent 2,101,787, or relative to which the vise may be manually moved, as in the above-mentioned Patent 2,381,034, in either case to effect the desired or controlled traversing movement or movements of the work W relative to the grinding'wheel and to effect the desired feeding and the retracting movements thereof relative to the wheel. As indicated in the drawings, we may provide suitable means such as bolts 36 for clamping the vise 31 at any desired angularity to the work-table 21, where it is desired that the vise move with the table, the bolts being simply omitted when it is desired to manually shift or control the movements of the vise and Work-piece W relative to the table. In Figures 1 and 2 the grinding wheel is generically indicated by the reference character CR, and by way of illustration but not by way of limitation it is constructed to present a conductive ring surface 'at its flat annular sideface which, according to the rotational setting about its vertical axis, of the column 11 which supports the wheel head 12, may be given any desired angularity relative to the longitudinal path of movement of the movable work-table 24, according to the needs of any particular grinding job, but for greater simplicity of description the wheel head may be considered as set so that the plane of the operative annular side face of the wheel extends parallel to the line .along which the work-table 24 is movable or rcciprocable.

A suitable wheel guard 38 is provided, being secured to :the wheel head by suitable brackets 39 and being provided 'with a hinged front cover 40 so that access to the wheel spindle 13 may be gained for mounting or demounting the grinding wheel; the wheel guard with its cover 40 may be shaped substantially as shown in Figures l-4, being cut away as shown to expose a suitable portion of the front face of the wheel where the conductive ring surface is operative and so that the work W may be presented thereto, and to expose a complementary back portion of the wheel for purposes about to be described.

Suitable means are provided to supply a suitable electrolyte to the region of contact or of juxtaposition between the grinding wheel CR and the work W; such means may comprise a broad-mouthed nozzle N, which is preferably adjustably positionable, as by a suitable length of deformable metal tubing 41, which is connected to and supported by a rigid pipe 42 secured to the wheel guard as indicated (see also Figure 4). Accordingly, deformable tube 41 may be manually bent and set to give the nozzle N the desired location, the mouth of the nozzle being appropriately dimensioned to discharge the liquid electrolyte at and throughout the entire width of the conductive ring surface of the Wheel CR, where the Work-piece W is presented to the latter.

In Figure l I have shown a tank 44 containing liquid electrolyte 45; the latter can be a solution of sodium chloride in water, preferably reasonably concentrated; for example, when the tank is full of pure water, a surplus of common salt may be added thereto so as to leave a quantity of undissolved salt which simply rests on the bottom of the tank. Other salts can be used, but for keeping corrosion at a minimum the very corrosive salts, such as calcium chloride, magnesium chloride and sodium chloride are preferably avoided. Salt, such as sal ammoniac ammonium chloride) can be used. The carbonates, such as sodium carbonate-and potassium carbonate, can be used and in some cases may be preferred, as they are somewhat less corrosive than sodium chloride.

Mounted on the cover plate 46 of the -tank 44 is an electric motor 47 which drives a pump 48, the input end of which is connected by a pipe 49 to the inside of the tank 44, with the open end of thepipe being preferably near the bottom of the tank. The output end of the pump 48 is connected by suitable piping 50, and a suitable length ofrflexi'ble hose 51 to a valve 52 on the end of the pipe 42 which is secured to the hinged wheel guard cover 40. An arrangement such as just described may be used to supply the work-wheel interface adequately with electrolyte; from that location the electrolyte copiously runs out of the bottom of the wheel guard and it and any drippings thereof are eventually collected by a large pan 53 which is built around the top edge of the Work-table 24, and as shown in Figure 2, a spout 54 carried by the work-table and movable therewith discharges the pan-collected liquid into a stationary pan 55 that is suitably supported by the base 10 of the machine and which extends throughout the full length of maximum travel of the spout 54 as the latter moves with the work-table. A return pipe 56 extends from the pan 55 to the tank 44.

The wheel CR may be of any suitable construction and has a suitable conductive element or face, which I arrange to co-act in effecting, in the electrical energy conversion and supply system, control or modification of the alternating current energy to provide direct current energy of the earlier above described characteristic of substantially constant voltage across the work-wheel interface followed by current limiting action with diminished voltage so that critical current values are not reached or exceeded. Illustratively the wheel of my system and apparatus may have-a single conductive face and illustratively, for that purpose, maybe constructed as shown in Figures 3 and 4 about to be described in detail.

Referring now to Figures 3 and 4, the single-conductive-faced wheel is there generally indicated by the reference character 60, and in order also to gain certain advantages in achieving electrical insulation or isolation, the wheel 60 comprises a strong rigid backing B of any suitable cured plastic or the like, such as Bakelite resin; at its center it has molded into it a hole (Figure 3) so that it can be received onto the flanged sleeve 22. As better appears from Figure 3, the backing B has an outer rim-like or annular portion which is of greater thickness than the central portion which is received onto the flanged sleeve 22 and which is clamped between the flange and the spanner nut 61; this outer portion of greater thickness presents an annular side face, being the left side face as viewed in Figure 3 and being the front face as viewed in Figure 4, and at that face and preferably coaxially therewith the wheel 60 carries a conductive abrasive ring CR1 which presents, in the illustrative construction, an annular conductive face with which the workpiece W and the electrolyte can co-act. This ring CR may be secured to the backing B in any suitable manner, but preferably the ring is constructed so that it is embedded in the non-conductive material of the backing B and preferably it is assembled to the backing itself when the latter is initially molded out of the uncured resinous material which is, during the molding process, made to flow about the faces of the ring except its operative face and to become interlocked therewith upon curing of the resinous or other plastic, as under heat and pressure; for better interlocking the ring CR may be of a conformation that provides a continuous annular dovetail D (Figure 3), which can be integrally formed at the back of the ring.

As above indicated, it is sometimes desirable that the rotating conductive element in electrolytic grinding contain abrasive grains and the wheel 60 may be constructed also in a manner to facilitate embodiment of abrasive grains when and where desired. For the grinding of hard cemented carbides, such as those illustratively mentioned above, suitably bonded diamond grains, as a bort, are usually employed because silicon carbide abrasive grains are hardly as effective on cemented carbides, while alumina grains grind them hardly at all. While, in the illustrative embodiments of my invention I prefer to use diamond abrasive grains, grains of other materials,

including silicon carbide and aluminum oxide, may be employed, and. as is later made clear, in electrolytic grinding, stock removal may be effected solely by electrolytic decomposition ofthe metal at the work-face Without any material abrasive action by any of the grains in the rotating conductive ring or face. Where grains are employed, in order that the ring CR be conductive, the abrasive grains are metal-bonded, and particularly where diamond'grains are employed it is preferred that they be embodied in only a relatively small depth in relation to the overall thickness of the ring itself and accordingly, as is clear from Figure 3, the ring CR comprises an outer abrasive or grain-containing portion 6201? small thickness or depth, and an inner and usually thicker and heavier portion 63 that need not contain any grains and is of metal throughout, serving as a strong rigid support or backing for the thinner diamond-bearing portion 62. Where a dovetail element D is employed, it forms part of the metal backing portion 63, as shown in Figure 3, and may be integrally formed or molded therewith or turned or machined to the desired shape.

In making the conductive abrasive ring CR any suitable or known methods or techniques may be employed and need not be described in detail here. For that matter, the patented art describes how, with the use of powdered metal, to make up a unitary integral abrasive ring or annulus having an outer diamond-bearing abrasive portion and an inner support portion wholly of metal. I might note, however, that a usual method of manufacture comprises placing in a suitably shaped mold, to the desired depth, powdered metal that is to correspond to the non-abrasive backing portion and, after leveling or smoothing off, placing thereover a suitable depth of a mixture of diamond particles and powdered metal, to correspond with the abrasive portion and, after leveling or smoothing off, subjecting the contents of the mold to substantial pressure and then sintering the pressed piece, usually in a protective atmosphere such as hydrogen. By appropriately shaping the mold parts the backing portion 63 may be conformed to have a projecting dovetail part or ring, such as the dovetails D of Figure 3, or, as above noted, and since the backing portion 63 contains no abrasive grains, the dovetails D need not be formed by molding but can be turned or machined to the desired shape after pressing and sintering are completed.

Any suitable metal bond appropriate for bonding the abrasive grains and for giving the rings suitable electrical conductivity may be used. In the abrasive-containing portion of each ring. such as the portions 62 of Figure 3, the concentration of abrasive grains should, of course, not be so great as to detrimentully affect electrical conductivity. For finely divided diamond as the abrasive grain, a concentration thereof in the abrasive portion on the order of 25% or less by volume is suitable. Of the many and various metals that are usable for metalbonding the diamond grains, i prefer to employ a mixture of copper and tin powders in the proportion of about 82% copper and 18% tin, making for both excellent electrical conductivity and good bonding of the grains, and this same mixture of copper and tin is employed in making up the non-abrasive backings, such as the portions 63 of Figure 3, and I set out the just mentioned mixture of copper and tin as an illustration.

The wheel 60 is driven in clockwise direction as viewed in Figures 1 and 3, at a suitable speed to give its conductive ringface suitable surface speed for appropriate abrasive action, and suitable means are provided to electrically connect its conductive ring CR into the electrical circuit so that the conductive ring is the cathode, for electrolytic decomposition at the face of the work-piece W; such means conveniently comprises a slip ring constructed and coaxially mounted for rotation with the grinding wheel spindle 13, and a suitable coacting mounting for supporting a brush that bears against the slip ring.

In Figure 3 I have shown such a slip ring as S and it is preferably carried by the non-conductive backing the conductive ring CR is operative.

back B has been molded and curved with the ring CR v interlocked, at the front face, with the cured molded in sulating material, and then secured in position by a suitable number of vequi-angularly spaced tension tie-members 65, which extend through suitable holes in the back B and are anchored, as by threading, at their inner ends to the conductive ring CR in which tapped holes are.

provided in the backing portion 63 thereof; the outer ends of these tie-members, which preferably take the form of long screws preferably made of copper or of a coppertin alloy, extend into suitable countersunk holes in the:

slip ring S thus to clamp the latter securely and concentrically in position at the back face of the wheel back B and at the same time forming multiple electrical connections of high-current-carrying capacity between the slip ring and. the conductive ring CR The screws may be headed, in which case the heads are countersunk into the slip rings, or the screws may be headless, in which case those portions that extend into the countersunk holes in the slip rings may be radially expanded by pressure or by peening to fill up the tapered holes in the slip ring, the taper being appropriately proportioned to the cold-flow characteristics of the metal of the screw shank to facilitate cold-flow expansion thereof as just mentioned. The faces of the slip rings may then be machined, as by turning in a lathe, or by grinding, to

be sure that they fall in a plane at right angles to the axis of the grinding wheel and to be sure that the ends of the screws 65 are flush with the faces of their respective slip rings, thus to insure smooth coaction with the brushes of the circuits in which the parts are to coact.

As is better shown in Figure 3, the wheel head 12 has secured to it, as by cap-screws as shown, a bracket 66 which extends in a radial direction relative to the grinding wheel 60 and which is constructed in any suitable way to insulatingly support a brush 67 which is spring-pressed to the left to bear against the face of the rotating slip ring S Suitable means are provided, such as a connector screw 68, for electrically connecting the springpressed brush 67 into the energy-supply and control circuit arrangement of our system, which is diagrammatically shown in Figure 5.

In Figure 5 the conductive abrasive ring CR with the work W presented to it, are diagrammatically shown, as are also the slip ring S and brush 67 as well as the connector screw 30, for electrically connecting the work W to one side of the direct-current energy-supply circuit and connector screw 63 for connecting the brush 61 to the other side thereof. In Figure 5 I also indicate an alternating current power circuit, which may be any of the types usually found in factories or industrial plants, and it may be singleor multiple-phase; for illustrative purposes, it may be a three-phase power supply line, usually 60cycle, and of any suitable voltage; illustratively 440 volts, and in Figure 5 this power line is represented by the reference characters 2 p 2 From such a power line or source of alternating current supply, I make provision for converting alternating current energy to direct current energy supply for coaction with the anodic Work W and the rotating wheel ring CR with the electrolyte between the latter, for electrolytic decomposition at the face of the work W, all in a manner and under coacting controls to achieve a number of advantages and safeguardagsome oi -which have been indicated earlier above.

In Figure the broken-line rectangle MA, with the parts diagrammatically shown within it, represents a magnetic amplifier of the self-saturating type constructed and arranged for A. C. input and for D. C. output, with appropriate rectifiers and control windings. While the magnetic amplifier MA as well as other such devices later described, are shown as arranged for three-phase alternating current energy input, that is not to be interpreted by way of limitation but rather as illustrative, inasmuch as these self-saturating magnetic amplifiers serve our purposes also when arranged and constructed for A. C. input of other than three-phase, such as single-phase, two-phase, etc.', and their functioning, coactions and controls are essentially the same as, and are well-illustrated in, the three-phase structures herein disclosed.

In Figure 5 the magnetic amplifier MA comprises a suitable number of reactor units, six in number, for threephase A. C. input, diagrammatically shown at I, II, III, IV, V, and VI, each reactor unit comprising a gapless laminated core of steel of very high permeability, diagrammatically indicated in Figure 5, each core being linked by power of output windings and by appropriate control and/ or biasing windings. In the illustration each reactor unit has a power winding PW, and these are interconnected with rectifiers RF in the manner shown, with the three-phase power line p p p connected by conductors 71, 72, '73 respectively to the input terminals of the magnetic amplifier MA those input terminals being respectively, as shown, between adjacent paired rectifiers RF--RF; direct current energy output is delivered at the output terminals 74, 75, leading from the interconnected power windings PW, as shown in Figure 5.

The above described parts of the magnetic amplifier MA are, in each of the reactor units, so proportioned to each other that when interconnected as shown and as above described they will be capable of delivering a direct current output which, illustratively, can be on the order of 24 volts at an amperage on the order of 150 amperes, when energized on the input side by three-phase alternating current of 60 cycles at suitable voltage; since the construction, action and operation of such a self-saturating magnetic amplifier are known, these aspects thereof need not be in detail herein described. It might, however, be noted that the just described magnetic amplifier MA is commercially available. may be on the order of 32 volts, in which case a stepdown transformer T is interposed as is diagrammatically indicated in the drawings.

However, the peculiarities and variables that are vir tually inherent in the actions or coactions that take place across the interface where stock removal from the workpiece, W is electrically effected impose a number of difficulties and handicaps which work against simply connecting the D. C. output of the magnetic amplifier across the work-wheel interface, particularly if the desired precision of grinding and safety or protection for the wheel conductive element and the work-piece are also sought, and accordingly I have made readily adaptable provisions and relatively simple coacting circuit arrangements for dependably controlling the conversion of alternating current energy to electrical energy of voltage and current characteristics that are determined and controlled by the variables that occur at the work-wheel interface. These provisions and circuit arrangements will now be described.

In the illustrative embodiment I provide each of the six reactor units I, II, III, IV, V, VI with three control windings BW, RW, CW, which are energized in a manner later described to affect the saturable cores of the reactors. The windings BW of the several reactor units are connected for conjoint or simultaneous energization, as by connecting them in series as shown, their common cir- Its A. C. input voltage cuit terminating at terminals 79, 76. In similar manner the several windings RW are interconnected, the resultant circuit terminating at terminals 77, 78. Windings CW are also in similar manner interconnected, with connecting terminals at 81, 82. Windings BW are bias windings which, when energized, bias the several reactor units in known manner, being energized by unidirectional current.

For this latter purpose and for other purposes latter explained, I make suitable provision for deriving unidirectional current energy from the power line 12 11 p For example, from one of the phases of the three-phase power circuit I connect, as by conductors 82, 83, a voltage regulator or stabilizer VS, which may be of any suitable or known construction to provide at its output 60-cycle alternating current energy at a fixed or constant voltage, such as 115 volts, in order that thereby variations or fluctuations in the voltage of the three-phase supply be not reflected in the control circuits of the system; accordingly, conductors 84, lead from the output side of the voltage stabilizer and provide a constant voltage circuit, from which relatively steady potentials may be provided and utilized.

Across the steady voltage circuit 84, 85 is connected the primary of a transformer T whose secondary is connected as shown to the input terminals of a rectifier bridge RB, across the substantially constant voltage output terminals of which are connected conductors 86, 87, across which are bridged a number of resistors provided with taps so that the fixed voltage drop or constant unidirectional potential may be fractionalized or subdivided as required or needed. One of these resistors R serves to energize the bias windings B-W of magnetic amplifier MA at the selected or desired potential derived from the fixed voltage across the output circuit 86, 87 of the. rectifier bridge, in that a conductor 88, connected to one side of the resistor R at conductor 87, leads to bias winding terminal 79, and another conductor 89 leads from the other connecting terminal 76 through a protective resistance R to the adjustable tap on resistor R Accordi-ngly, energization of the bias winding BW of the power magnetic amplifier MA may be manually set by appropriately shifting the tap on resistor R The-control windings CW of the power magnetic amplifier MA having their connecting terminals at 81, 82, are preferably controllably energized under the control of a magnetic preamplifier MA which has a unidirectional current output at terminals 91, 92, which are connected by conductors 93, 94, through a suitable resistor R to the terminals 81, 82 of the control windings CW of the power amplifier MA like the latter, the preamplifier MA may comprise six reactor units diagrammatically indicated by the reference characters VII, VIII, IX, X, XI, XII, each unit comprising a gapless laminated core composed of steel of high permeability, with their respective output or power windings PW interconnected with rectifiers RF as shown, the three-phase power line being connected by conductors 95, 96, 97 between the respective paired rectifiers as shown, the unidirectional or direct current energy output being furnished by connections as shown to the amplifier output terminals 91, 92.

The preamplifier MA is provided with bias windings BW one for each reactor unit, and they are connected for conjoint or simultaneous energization as by connecting them in series as shown, with the common circuit terminating at terminals 98, 99. Unidirectional energizing current for the bias windings, of selectable or adjust-- able value, is derived from the constant voltage rectifieroutput circuit 86-87, across which is connected a resistor- R provided with a s'hiftable tap; a conductor 100 con nects amplifier terminal 98, through circuit conductor Means are provided for effecting coaction between thepreamplifier MA and the power amplifier MA all underthe control and direction of the peculiarly variable conditions at thework-wheel interface, for causing the electrical stock removal action at the latter to take place at maximum safe intensity; these include means for translating these electrical variables and include certain windings which I place on the reactors of the two amplifiers to respond thereto. To the D. C. output terminals 74, 75 of the power amplifier MA I connect, by conductors 104-, 105, the conductive wheel member CR and the workpiece W, the latter being made anodic by connc2ting conductor 105 to the connector screw 30, and the con nection of the negative output terminal 74 of the power amplifier to the conductive wheel member CR being made by connecting conductor 104 to the connector screw 68 of the slipring brush 67,

Across the D. C. power output circuit 104. HES l connect a resistor R illustratively of about 3 ohms; resistor R provides a small load on the D. C. output side of the power amplifier MA so that the operation of the latter and of associated circuits need not be undesirably atfected by an open-circuit value of voltage were the direct current circuit actually interrupted at the work-wheel inter face, as by removal of the work W from coacting relation with the electrolyte and the conductive ring CR and accordingly there is always effective, across the workwheel interface, a definite D. C. voltage even with no current flow through the electrolytic interface cell. An illustrative interface voltage for this purpose may he, say, volts.

Various factors and variable at the interface can cause departures from the desired or most suitable values of D. C. voltage across the work-wheel interfact and of the current flowing thereacross for stock removal from the workpiece W. Changes in applied voltage can be conveniently measured by the voltage across the small-load resistance R in which they are reflected; certain voltage changes I make operative to affect preferably the pro amplifier MA in a manner later described. As .for changes in current across the interface, I make provision for causing certain response thereto to take place preferably in both the power amplifier MA and in the preamplifier MA}; in this latter connection I employ one or more interface-current-responsive devices which. so .far as certain features of my invention are concerned, may take any suitable form. lllustratively I may employ a device which preferably is in the form of a core CO that extends about or envelops one of the conductors, such as conductor 104, that lead to the conductive wheel element CR and work-piece W, the core CO having thereon a winding 106. The core CO may be of any suitable construction or arrangement, preferably and illustratively it is torus-shaped. and it is made of transformer iron or steel of suitable permeability. The magnetic field produced by the current flowing in conductor 104 extends circularly about the conductor, being coaxial therewith, and with the torusshaped iron core CO positioned coaxially with the conductor 104, the core forms a high-permeability path for the flux and the flux density in the core varies with the magnitude of the current flowing through the conductor. The parts are so proportioned in relation to the current magnitudes that, as the interface ca is for increasing current, the core moves closer and closer to saturation on its permeability curve. The action of the winding 1525 can in this manner be affected or varied according as-interfacc current flow changes in magnitude.

Winding 106 is energized in an alternating current circuit and hence the just-described action of the core affects and changes the impedance of the winding 106.

I provide a transformer T of which the primary is energized from the steady or constant voltage circuit 84, 85 above described, and of which the secondary is connected in series with the winding 106 across the input terminals, as shown of a rectifier bridge RB across the output terminals of which are connected conductors 107, 108, across which, in turn, are bridged resistors R R the latter are thus energized by unidirectional current resulting from the full-wave rectification of the rectifier bridge and at a voltage which changes as the voltage across the input terminals of the bridge is changed by changes in impedance of the winding 106.

Resistor R is provided with a shiftable tap so that any desired fraction of the variable voltage thereacross may be made available, and such a selected unidirectional potential I utilize to energize the control windings RW of the power magnetic amplifier MA More particularly, a conductor 109 connects the amplifier ter minal 77 to one end of resistor R by way of conductor 108, and a conductor 110 connects the other terminal 78 of the windings RW to the shiftable tap of the resistor R3, through a protective resistance R18, a shown in Figure 5.

The windings RW of the power amplifier MA are thus steadily energized by unidirectional current, but the effect of the windings RW on the respective reactor units of the power amplifier MA and upon the output of the latter is under the control of the current flowing across the work-wheel interface, and in accordance with certain other features of my invention, later described, other controls are made to coact therewith for purposes later described. Varying conditions at the work-wheel interface can and do call for substantial changes in current flow thereacross. For example, at one point in a stock-removal operation, as, for example, when the actual or apparent contact between the work and the wheel is of relatively high resistance, current flow across the interface may be small, but as that resistance is decreased, as by bringing about more intimate contact or increased pressure of contact, current flow substantially correspond ingly increases. With resultant increase in current out put of the power amplifier MA the output voltage of the latter across the output terminals 74, falls off or declines, causing a drop in the energy dissipated at the work-piece face and loss in rate of stock removal. At low values of interface current, unidirectional flux in the core CO is correspondingly low and the impedance of winding 106 is high so that there is a relatively high reactance drop in the secondary output circuit of trans former T and the alternating potential applied to the input of the rectifier bridge RE is correspondingly low; accordingly, the unidirectional voltage across the rectifier output circuit 107, 108 is low and the energization of windings RW of the power amplifier, derived from the resistor R is also low. When, however, the workwheel interface calls for increased current flow thereacross the current of the increasing current flow increases the unidirectional flux in the core CO, driving the latter more and more toward saturation and thereby correspondingly lessening the impedance of winding 106 and the impedance drop thereacr-oss so that more and more of the alternating voltage of the secondary of transformer T is efiective at the input terminals of the rectifier bridge RB correspondingly the unidirectional output voltage of the rectifier bridge and the voltage across resistor R are increased, as is also the unidirectional energization of the windings RW of the power amplifier. The increasing energization of windings RW affect the cores of the reactor units of the power amplifier in directions to cause the unidirectional voltage at it output terminals 74, 75 to increase as against the inherent drop in output voltage that would otherwise take place. With th resultant compensation for decline in output voltage of the power amplifier, the call for increase in interface current as required by the changed or changing conditions at the interface can be and is satisfied and loss in rate of stock removal avoided.

The arrangements just described has many advantages from the viewpoint of structural elements involved in that the latter, such as the variable impedance device.

comprising the winding 106 and core CO, the transformerT the full-wave rectifier bridge RBliand tapped.

resistor R are relatively simple in construction, and the accompanying circuit arrangements are also relatively simple, all as will now be seen; moreover, these parts when interrelated as above described, with each other and with the work-wheel interface achieve numerous practical advantages of coaction and operation; for example, varying or changing conditions at the work-wheel interface effect dependable and substantially propionate responses to current changes across the interface and do so without material loss or wastage of energy flowing across the interface, and it is possible to avoid substantial heat losses in that oneneed not employ a series resistor in the work-wheel interface circuit; thereby however, I do notv mean to exclude a resistor from the scope of my invention except where and as stated in the claims. Also, these responses are efficiently translated into proportionate values of voltage or current or both, such as the unidirectional potential across the rectifier output circuit 107, 108, which are of a magnitude appropriate or suitale for directly energizing control windings of the magnetic amplifier or amplifiers employed. In the above described embodiment the windings RW of the amplifier MA will be seen to be directly energized from this circuit 107, 108, and this takes place at variable voltage and current of magnitudes suited to the construction of the power amplifier. For setting or changing the standard of operation for compensation of voltage drop in the output of the power amplifier, the variable tap at the resistor R may be appropriately set. Also, the secondary winding of transformer T may be provided with a tap as shown, for similar purposes. Either or both may be set, according to the range of change in standard of operation to be effected.

Coacting with the above, as above indicated, are other features, also under the dictation or control of the peculiarly varying conditions at the locus of electrical stock removal from the work-piece face. Among other control windings, preferably applied to the magnetic preamplifier MA are windings VW, one for each of the reactor units VII, VIII, IX, X, XI, XII and suitably connected, illustratively in series as shown, for conjoint or simultaneou energization, from the amplifier terminals 113, 114, whereby the windings VW, in coaction with the bias windings BW may be connected, as is about to be described, to achieve certain controls over the voltage which the power amplifier MA applies to the workwheel interface. Across the substantially steady or constant voltage circuit $6, 87 earlier above described I provide a resistor R that has a tap as shown, by which any portion of the voltage across the resistor R may be selected as a fixed or steady reference voltage against which to measure the voltage across the work-wheel interface, a voltage which can change substantially according to various factors including changing conditions at the work-wheel interface.

These two voltages, that is, the selected reference voltage tapped from resistor R and the voltage across the work-wheel interface W-CR I bring into coaction to control the energization of the preamplifier winding VW, in a circuit which extends from preamplifier terminal 113, then conductor 115, a protective resistor 116, a unilateral valve or rectifier UV, resistor tap, then the selected portion of resistor R conductor 87, conductor 117, and by brush 67 and slipring S to the conductive Wheel element CR which is one side of the work-wheel interface, and from the work-piece W, which is the other side of the workwheel interface, by way of conductor 118, to the other preamplifier terminal 114. In this circuit arrangement, as will be seen by the just described circuit connections, the reference voltage set or selected by the tap on resistor R and the voltage across the work-wheel interface, both unidirectional, are in opposition to each other. So long as the voltage across the interface is less than the selected reference voltage at resistor R so that the fixed reference voltage determines the direction in which current flow would take place in the described series circuit, which in cludes the preamplifier windings VW, current flow to and through the windings VW need not take place, for there need not be any interference with the self-control which the work-wheel interface conditions can variably effect through the windings RW of the power amplifier MA as earlier above described, and accordingly the unilateral valve or rectifier UV is included in the circuit to block current flow to the preamplifier windings VW.

The bias windings BW of the preamplifier are energized, by setting the tap on resistor R so that with no current flowing in the control windings VW the preamplifier MA is biased, and stands biased, at or just below cut-01f, so that the preamplifier has a zero output and hence control windings CW of power amplifier MA are, and stand, de-energized. The bias windings BW of the power amplifier, by adjustment of the tap at resistor R are energized at a value to bias the amplifier above cut-off to provide unidirectional output, to the work-wheel interface, at the desired voltage which, should it inherently fall off because of increase in interface current, the latter effects compensation for the voltage decline by increasing the energization of windings RW in a direction to increase the bias and thus correspondingly raise and substantially restore the voltage across the work-wheel interface.

However, should the voltage across the work-wheel interface exceed that of the selected reference voltage at resistor R so that the resultant difference in voltage determines flow of current in reverse direction, the rectifier UV permits such flow to take place and the preamplifier control windings VW are energized. The resultant energization of windings VW, in relation to the cut-off bias eifect of bias windings BW biases the reactor units above cut-off and causes a current fiow at the D. C. output of the preamplifier at its terminals 91, 92 which are connected to the control windings CW of the power amplifier MA As a result windings CW are energized in direction and amount to bias power amplifier toward cut-01f so that the output voltage at terminals 74, 75 of the power amplifier MA is reduced and prevented from materially exceeding the selected reference voltage at resistor R.

I am thus enabled to select, for any particular kind or type of grinding job, a suitable or thereto appropriate voltage to apply across the locus of electric stock removal from the work-piece, a voltage which, for electrolytic decomposition at the w0rk-face, may be on the order of 10 volts or 15 volts, or more, up to about 30 volts; a single manual control, set by the operator, suflices. Voltage may be maintained or regulated for substantial constancy, under certain varying conditions at the work-wheel interface and, as later described, other controls step in automatically under other conditions. Effective conduction may be broken, as by moving the work-piece completely out of relation to the conductive element of the apparatus, as in offhand grinding, or conduction may be interrupted while a work-piece is being removed for replacement; under such circumstances, the windings RW of the power amplifier stand substantially de-energized and the voltage across the amplifier output terminal 74, 75, to which the small-load resistance R is permanently connected, stands at the selected value as determined by the setting, at resistor R of the energizing current for the bias windings BW. As described later, I also make provision for guarding against current surges or flashes when the work-piece is brought into conductive relation. Thereafter, so far as voltage constancy is concerned, certain changes in interface conditions determine the coaction of the above described parts, such as the energization of power amplifier win-dings RW to compensate for voltage decline and to maintain good rate of stock removal so long as the selected interface voltage is not exceeded and to bring into action the preamplifier windings VW to effect energization of the power amplifier windings CW to guard against the interface calling for and receiving thereacross voltage in excess of the selected and appropriate value.

However, and particularly in effecting stock removal by electrolytic decomposition, it is advantageous to avoid surges and flashes on making or breaking work-wheel contact and it is desirable to make provision against permitting interface conditions to call for and receive magnitudes or densities of current as are damaging to the apparatus; for example, in electrolytic grinding, arc-over, which can be caused in the manner earlier above indicated, can be destructive to the element or elements of the grinding wheel, and such destructive action can be especially cost-1y where the conductive element is expensive to manufacture or where it contains costly diamond abrasive grains. An illustrative and preferred form of controls, coacting with the above voltage control, may include the preamplifier MA which I provide with control winding IW, one for each of the reactor units VII, VIII, IX, X, XI, XII, which, as shown in Figure 7, are interconnected, illustratively in series, for conjoint or simultaneous energization, their circuit terminating at connecting terminals 121, 122. These I arrange so that they will respond to a number of characteristics of interface conditions such as those which are conducive to current surges or flashes and such as call for current increases in excess of a selected safe maxi-- mum current value which can be just below the current value at which harmful or damaging arcing would occur. For example, makes or breaks at the work-wheel interface under conditions permitting otherwise safe high current values or densities can cause detrimental surges, flashes, arc-overs and the like; also for one type of grinding .job the critical arcing current value may be 40 amperes, and in such case it may be desired to limit current rise across the work-wheel interface to a value of, say, 30 amperes, thus also providing an ample margin of safety.

{\cross the fured or steady unidirectional voltage circurt 86, 87, I bridge a resistor R' and provide it with a tap as shown so that any fraction of the voltage drop across the resistance may be selected as a standard against which to measure changes in interface current; bythe structural elements and circuit arrangements above described," including the saturable impedance devices 106-CO, the transformer T and the rectifier bridge RB current changes across the interface W-CR are translated into a substantially proportionately varying unidirectional voltage across the circuit 167, 108, and across the latter I bridge a resistor R which I also provide with a tap as shown, so that any selected fractional part of the voltage drop thereacross may be utilized.

These resistors R R with their respective taps, I arrange in circuit with the preamplifier windings 1W in such manner that the resistor potential drops arein opposltion to each other. Coacting and also in circuit with resistors R and R is a resistor R as is later explained, it modifies the effect which resistor R is to have as against the reference standard set by resistor R and does so, through means later described, so that when work-wheel interface resistance is low (as because of large contact area) there can be high current flow across the interface, and vice versa, and so that other advantages are achieved. This circuit extends from preamplifier terminal 121, then by conductor 123, through a protective resistor R through a unidirectional valve or rectifier UV through resistor R through the resistor tap and the selected portion of the resistor R conductor 87, conductor 124, selected portion of resistor R and its tap, and then by conductor 125, to the other preamplifier terminal 122.

Disregarding resistor R for the moment, the settings or adjustments, as by setting the tap on resistor R and the tap on resistor R may be-so made that the selected fixed or steady voltage across the selected portion of resistor R is equal to the voltage across the selected portion of resistor R when the current across the interface equals the selected safe valuewhich is not to be materir DArsonval torque coil.

ally exceeded, illustratively 30 amperes where the critical or destructive arcing current is 40 amperes, as assumed in the above given illustration. Accordingly, so long as the interface current is at or below the safe maximum value, the voltage drop at resistor R which is proportional to the interface current, is equal to or less than the reference voltage drop provided by resistor R"; these voltages are in opposite directions in the series circuit of the preamplifier windings IW, and no current fiows through the latter so long as the reference voltage at resister R preponderates over the current-responsive voltage drop at resistor R because the unidirectional valve UV stops or blocks current flow in that direction. So long as these conditions exist, varying or changing interface conditions can call upon and effect, by the arrangements earlier above described, actuation of the power amplifier windings RW to compensate for declining voltage or to call upon and energize the voltageresponsive windings BW of the preamplifier in turn to energize the control windings CW of the power amplifier to maintain the work-wheel voltage substantially constant or to prevent excessive rise in that voltage.

Still disregarding resistor R as soon, however, as an interface condition arises calling for more than the selected safe maximum current value such as the abovementioned 30 amperes, and sucha condition can illustratively arise as by a substantial increase in interface area or substantial and sometimes sudden increase in pressure between the work and wheel, the current-responsive voltage drop across theselected portion of resistor R exceeds the reference voltage drop at resistor R and with the former preponderant, current can now flow through the preamplifier current-responsive windings IW, for the direction of flow is the same as that permitted by the valve or rectifier UV in the above described series cir cuit, which includes the windings IW. Accordingly, the biasof the'reactor'units of the preamplifier MA is changed to permit or cause current flow at its output terminals 91, 92 to the control windings CW of the power amplifier MA in a direction and amount to bias the power amplifier downwardly toward cut-off and thus hold the current output of the latter and the current across the interface against materially exceeding the selected safe value.

Considering now resistor R in Figure 5, I provide means for making it effective to supply a unidirectional voltage in a direction subtractive with respect to the reference voltage drop across resistor R under work-wheel interface conditions earlier above suggested. In the form shown, I provide two circuits arranged to affect the action of resistor R one of these circuits measures work-wheel resistance and the other measures the degree to which detrimental arcing or sparking threatens.

As shown diagrammatically in Figure 5 I provide what is in effect a computing device to continuously determine the ratio of voltage across the work-wheel interface to the current thereacross, thus always to measure interface resistance throughout varying interface conditions; in the illustrative form shown at 130, this device utilizes an electrodynamometer multiplying element coacting with a It has a shaft 131 suitably pivoted as at 132 and 133 and to which are secured coils 134, 135, and 136. Coil 134 operates in or coacts with the magnetic field of a stationary coil 137; coils 135 and 136 operate in orcoact withthe respective magnetic fields produced by permanent magnets 138 and 139. The resultant torque effect upon shaft 131 is translated by suitable means to control the magnitude of the voltage across resistor R preferably by utilizing a light beam and a photocell and amplifier arrangement to respond to changes in the rotary position of shaft 131. Thus, shaft 17 I r 137 carries a mirror 141 which receives light from a suitable source or lamp 142, via a suitable lens or lens systems 143, so that, according to the rotary shift of shaft 131, as determined by the coils and their coacting magnetic fields, the beam of light reflected by the mirror correspondingly affects the conductivity of the photocell such as a twin photocell 145 and the resultant current changes amplified as by a D. C. amplifier 146 whose D. C. output varies according to the rotational shift of shaft 131.

Stationary coil 137 and moving coil 134 together form an electrodynamometer combination; its moving coil 134 is connected to respond proportionately to the current called for by the work-wheel interface and for this purpose it is convenient to connect it, by conductors 147 and 148 respectively to the tap and to one end of a resistor R bridged across the circuit 107-108 which is energized as earlier described, by unidirectional potential that is always substantially proportional to interface current. Moving coil 135 of the DArsonval'combination 135138 is connected to respond proportionately to the voltage across the work-wheel interface, as by connecting it across the latter by conductors 151, 152. The stationary coil 137 of the electrodynamometer combination 134-137 is energized by the output of the D. C. amplifier 146, and has the resistor R in series with it, the circuit being as follows:

:From one output terminal of amplifier 146, conductor 153, stationary coil 137, conductor 154, resistor R and by conductor 155 back to the other output terminal of the amplifier.

The electrodynamometer 134-137 produces a torque proportional to the product of the photocell-amplifier output current and the interface current across the wheel CR and work W and the DArsonval combination 135-138 produces a torque proportional to the voltage across the interface CR W; the circuit connections are such, in relation to the polarities involved, that these two torques, in their effects upon the shaft 131 and mirror 141, are opposed, and accordingly the shaft and mirror respond to any difierence between the two, in either direction, and thereby cause corresponding increase or decrease in the photocell-amplifier output to restore equality and thus maintain balancing of the opposing torques. The resulted change in unidirectional current flow in the above-described amplifier circuit effects corresponding change in the potential drop across the resistor R with results and actions later described. The twin-photocell and D. C. amplifier arrangement 145146 may be of any suitable or known form or embodiment so that, for whatever position the mirror 141 is given upon balancing the two opposed coil torques, the D. C. amplifier output stands at a corresponding value as does also the potential drop across resistor R preferably the amplification factor therefor is chosen or made sufficiently high so that slight or small net coil (and mirror) movements are reflected in substantial amplified output current changes, resulting in rapid responses to changes in the above electrical quantities that affect the torques exerted by the moving coils.

If I is the photocell amplifier output current, then the equation of torque balance takes the form KE =l I where:

=work-wheel voltage,

l =work-wheel interface current, and K=a proportionality constant.

output current, as above described, is fed through the resistor R in such direction that the potential drop terface current may increase.

thereacross is in a direction opposite to that across the selected portion (selected reference voltage value) of resistor R in the circuit cf current-responsive control windings 1W of the current-supply system, being, in the illustrative embodiment here shown, the control windings 1W of the pro-amplifier MA whose action was above briefly described without reference to resistor R For clarity, that circuit of resistors R and R is as follows, bearing in mind that control windings 1W are connected across pie-amplifier terminals 121122: from erminal 121, conductor 123, protective resistor R unidirectional valve UV resistor R resistor tap and selected portion of resistor R", conductor 37, conductor 124, selected portion of resistor R and its tap, and by conductor 125 to the other terminal 122. In this series circuit, the reference voltage drop at resistor R is in one direction; it fixes the standard or value of work-Wheel interface current level beyond which control windings 1W are to act to prevent material increase. In that same series circuit, the voltage drop across resistor R operates in a direction opposite to the voltage drop across resistor R" so as to subtract from the latter and thereby change or vary the just-mentioned standard or value of workwheel interface current level against which the workwheel current responsive voltage drop across selected portion of resistor R is to act.

When the work-wheel interface resistance is low, as when there is large area of work-wheel juxtaposition or even smaller such area plus substantial pressure of contact, it is desirable to maintain high current flow and density at the work-wheel interface for efiecting high rate of stock removal from the work W; with low interface resistance, the photocell-amplifier output current is low as is also the voltage drop across resistor R and the latter has low subtractive effect upon the drop across resistor R The net effect of these two resistor drops is therefore to maintain high the standard or limiting value up to which the interface current may thus increase or continue at a high level for high rate of stock removal. Should interface current commence to increase above this standard, the current-responsive voltage drop across the selected part of resistor R exceeds the reference voltage which is the voltage drop at resistor R minus the low or minimum drop across resistor R and with drop at resistor R now preponderant, current can flow through control windings IW in the direction permitted by the valve UV in the above circuit, so that the output of preamplifier MA biases the power amplifier MA downwardly and thus hold the output of the latter and the interface current from materially exceeding the safe selected valueas modified by the resistance across the interface, a resistance which, in the above is illustratively low, or at a minimum for a given type of grinding job. Thus a safe current limit, illustratively of 30 amperes may be imposed and automatically maintained.

Now, as conditions at the interface change, as by lessening the area of contact or of juxtaposition between work W and wheel CR as when the work is traversed to diminish overlap, thus increasing the interface resistance, the electrodynamometer-DArsonval combination faithfully follows the resistance change With prompt re sponse to its increments of change and causes correspond ing increase in the voltage drop across resistor R thus increasing the magnitude of the subtractive voltage factor in relation to the fixed reference voltage drop across resistor R and correspondingly shifting in downward direction the standard or limiting value up to which in- That means that as inter face resistance increases as a result of changing interface conditions in a direction to increase risk were a high level of current value or density to be maintained, the level at which current is limited is also diminished. Ac-

cordingly, the voltage drop at resistor R becomes constandard in that the drop across resistor R is at a higher value (the interface resistance being higher) and the difference between the fixed reference voltage drop across resistor R and the now greater voltage drop across resistor R is lower. As a result current can flow through the control windings IW in the direction permitted by the valve UV so that the output of pro-amplifier MA biases the power amplifier MA further downwardly and hold its output and the interface current from exceeding the now lower selected value as affected by the increased or higher interface resistance. In this manner, the current limit level may be automatically lowered, from the above illustrative ampere level, as interface resistance increases, down to zero value for open-circuit condition at the interface, and, of course, reverse operation takes place to raise the standard at which interface is limited as interface resistance decreases, up to the selected maximum level of, say, the above illustrative 3D ampcres.

These actions are of value and advantage and meet many varying conditions of practice. For example, there may be relative traverse between grinding wheel and work-carrying table 24 (Figures 1, 2 and 3), as by longi 'tudinal movement or reciprocation of the table, and in the course thereof apparent or actual area of contact between work W and conductive element CR (as well as pressure of contact) may vary; also the work W may be run off or run onto the face of ring CR and these factors respectively decreased and increased. There may be relative infeed movement, as by inward movement or feed of the cross slide 25, and in that manner also variables introduced. Or, where the work W is manually manipulated, as in offhand grinding or as in the abovementioned Patent 2,381,034, such variables are also introduced; in these cases, as when grinding the nose of a tool, work-wheel interface is small and resistance high and frequent makes and breaks, electrically speaking, can take place between work-piece and conductive element. The electro-dynamometcr DArsonval elements effect rapid response to the variables that can come into being under such widely varying conditions of practical use and with corresponding faithfulness and rapidity set or vary the effective reference voltage (the difference between fixed reference voltage drop at resistor R and the variable voltage drop at resistor R so that a safe current-limit level for whatever condition arises is automatically set throughout and for the many changes in interface conditions that can occur while maintaining high rate of stock removal for that particular condition. On Open circuit, the lowest value or standard of currentlimit level is set, for with the work out of effective conductive relation to the wheel, the resistance is highest and the voltage drop at resistor R is the highest; relative parts and their constants may be selected or adjusted so that any desired minimum value of currentlimit level may hethus achieved. Here a practical advantage is that when Work and wheel are brought into or out of conductive relation, the current-supply system is automatically at or promptly brought to its lowest current-limit value and contact may be effected or interrupted without detrimental reactions such as current surges, flashes, or the like; this is particularly advantageous where the work-piece is manually manipulated as in off-hand grinding in the course of which many makes and breaks may occur.

According to other features of my invention, I am enabled also to maintain highest or maximum rate of stock removal for or at any of the various different work-wheel interface conditions. I noted above, as an illustration, how certain of the controls may be set and operated by providing a margin of safety, as it were, between the critical arc-over current value at higher levels of operation; say 40 amperes, and a selected safe maximum current value for that level, say 30 amperes, beyond which material current increases are not to take place;.it will be appreciated that the larger this margin, the less eflicient is the stock removal operation. By arrangements of parts and coactions about to be described, this margin may be greatly reduced and highest efficiency with maximum safe current density achieved for whatever interface condition exists, with dependable protection against arcing and like detrimental effects. As above described, the dynamometcr-DArsonval apparatus is provided also with a torque producing coil i36 operating in the magnetic field of the permanent magnet 139, as a convenient or suitable way to modify the torque balancing action above described with respect to the torque coilsand 134, thus to affect the shift of the mirror and the output of the amplifier 146 that energizes the resistor R Coil 136 I arrange to be energized in response to detection of any work-wheel interface condition that is on the verge of effecting arcing or sparking; threatened or incipient arcing or sparking is made at once to affect the power supply controls so the detrimental arcing or sparking cannot occur and it does so while maintaining highest current flow across the interface consistent with no detrimental arcing or sparking, thus establishing, for whatever condition, the narrowest possible margin between whatever is the critical arcing current for that condition and the actual safe current flow. Wide margins on the order of the abovementioned illustrative difference between 40 amperes and 30 amperes need not be resorted to; instead, for a 40 ampere critical arcing current which is to be avoided, the apparatus can maintain a current flow and thus also higher current density at values closely approximating and just short of the critical value and just short of actual arc'over. Arcing or sparking is accompanied by large increase in fluctuation of both interface current and interface voltage. During normal or not: arcing and non-sparking stock-removal operation, even though interface voltage and current stand or are at substantially constant effective values for any given inter face condition, the electrical action in stock removal is reflected in fluctuations in instantaneous values of vol tagc and current and these occur at relatively low frequencies. but when arcing or sparking occurs, these fluctuations in instantaneous values take place at much highc frequencies, frequencies on the order of several hundred er second and higher, and the transition from non-arcing or sparking is accompanied by intermediate rise or increase in frequency of these fluctuations. A condition of threatened or incipient arcing or sparking may thus be detected by frequencies within the transition range of change of frequency. Tell-talc frequency, corresponding to threatened or incipient arcing or sparking, is within the range of about 350 to 500 cycles.

Accordingly, I provide a high-pass filter 161' and connect it across the work-wheel interface by conductors 161, 162, with a series capacitor 163 in the connecting circuit to block flow of unidirectional current from the D. C. interface circuit while permitting the filter 169 to respond to the components of the interface electrical fluctuations. This filter can have a cut-off or blocking action to all frequencies below frequencies of from about 350 cycles per second to about 500 cycles so that it passes on to an A. C. amplifier 164 which may be of any suitable or known form and need not be shown or described in detail, all higher frequencies. its transition or cutoff characteristic may be relatively steep for a selected frequency in the above range or for a selected narrow band of frequencies within that range or it may have substantial slope, covering a substantial spread or band of frequencies in that range, preferably the former in order to give, at its output and at the output of the amplifier 164, a rapid and relatively powerful response to frequency increase corresponding to incipient arcing or sparking. Suitable plate and other voltages for the internal circuit of amplifier 164 may be derived from the steady voltage circuit 8485 and the same is true as to the D. C. amplifier 146 and its photocell circuit; both amplifiers are shown as, connected to steady voltage circuit 8485 for these purposes.

The amplified output of amplifier 164 is passed to the input of a full-wave rectifier RB whose rectified output is connected by conductors 166, 167 to the DArsonval torque coil 136 on the torque-balancing metering unit 130 above described, with such regard for polarities that the torque effect produced by coil 136, in response as above described to interface conditions threatening or about to invite detrimental arcing or. sparking, is in a direction the same as that of interface voltage torque coil 135' and opposite to that of coil 134 of the electrodynamometer 134137. Torque coil 136, when so energized, causes pivotal shift of the shaft 131 and mirror 141 of the position at which torque-balance has to occur by increased output, initiated by the changed light effect of mirror 141 on the twin photocell 145, of the photocell-amplifier 145-446 to the dynamometer movable coil 134, thus causing increased current flow to the resistor R and increase in the voltage drop thereacross. That, as will now be clear, decreases the difference between the selected fixed reference voltage drop at resistor R' and the just mentioned increased voltage drop across resistor R immediately preventing rise of and slightly lowering the current-limit level of the power supply to the work-wheel interface, as by the action of current-control windings 1W upon the pre-amplifier AM and resultant control of the current output of the power amplifier AM It will be noted that by the resultant action and effect, a lowering of the current-limit level down to some arbitrary or selected level need not be had to provide a wide margin of safety between critical arcing current and actual interface current; instead the action and result can be to maintain the highest interface current just bordering on incipienceof. detrimental arcing or sparking even as incipient conditions vary or change from moment to moment, and thus maximum efficiency and capacity of stockremoval may be maintained with dependable protection against damaging arcing or sparking. For example, as the work-piece, in its traverse, is gradually run off of the conductive wheel element CR thus progressively diminishing overlap or area of contact between the two until there is complete interruption of conduction therebetween, each increment j of such relative movement betweenwork and wheel, while achieving progressive lowering of the current-limit level by the coactions of the balancing torque'coils 135 and 134 asearlier above described in response to changes in interface resistance, tends to encourage possibility of arcing or sparking inasmuch as, with diminishing juxtaposed areas of apparent or real contact, current densities tend to increase and that is conducive to localized current concentrations in turn conducive to arcing or sparking; nevertheless, by the action of torque coil 136 and its response to interface frequencies of incipient arcing, arc-over is prevented while maintaining always highest possible current flow and density for any momentary interface condition as traverse continues, and this proceeds throughout the wide range of change in interface conditions as traverse continues, always adjusting current-limit level to the changes. Con verse actions and controls for safety and for maximum efficiency take place on reverse stroke of the workpiece, as when it is first brought at one end into contact with the conductive wheel element and their overlap progressively increased; here initial conduction takes place safely at lowest current-limit level as above earlier described, and that level is progressively raised with increase in overlap as dictated by changes at the interface and may be held at just below arcing or sparking incipience according to whatever is the changing or instantaneous condition at the work-wheel interface. Thus it is possible to maintain the current limit level at a point or value where threatened or incipient arcing a y 22 or sparking cannot reach a magnitude damaging or de-' structive of apparatus, and thus efliciency and capacity of stock removal materially enhanced. I

The system and apparatus provided in this invention will thus be seen to achieve the various objects above noted or indicated, together with many thoroughly practical advantages. The widely varying work-Wheel interface conditions eifect dependable control of the electrical energy supplied thereto and thus the apparatus and system can readily meet the many and varied requirements met with in many and various types of grinding operatious; this is furthermore achieved in a manner not only to provide dependable protective action but also to effect and maintain high efliciency of action. Moreover, where the plant or factory is already equipped withalternating current energy supply, these and many other advantages are attained bydependable and flexible controls by the interface conditions of the conversion of the alternating current energy to direct current energy.

Current and voltage values at the work-wheel interface or interface set out above will be understood to be illustrative, for by the various circuit arrangements and adjusting devices, such as adjustable taps on resistors and transformer windings, a wide range of standards of operation at other current or voltage values is achievable according to the particular grinding operation or requirements to be met. However, the apparatus and system, when once adjusted or set, functions automatically and in a self-accommodating manner, so far as the operation is concerned, in shifting the system and apparatus to meet the requirements, for example, another type of grinding job, for all the operator need do in such a case is to set the voltage-standard resistor R at its tap, and he need not make any other readjustments.

Also, in other respects the system and apparatus pro- Vides flexibility; for example, the above-described setting of resistor R may be made so that the bias windings BW bias the power amplifier PW for full-conduction rather than to provide, as in the above illustration, the selected voltage, at its output terminals 74, 75, whereupon regulation of the output voltage proceeds under the action and control of the voltage-compensating control windings RW and of the control windings CW as the latter are in turn controlled by the voltage-responsive windings VW of the pre-amplifier MA Such setting is preferred where the voltage-compensating windings RW are, as is usually the case, relatively not too powerful, acting principally to add only a relatively small positive bias in order appropriately to compensate for voltage drop in response to current increase, and vice versa, and where the voltagecontrolled response of the windings CW do not contribute positivebias because of the blocking action of the rectifier UV. i

In any case, so far as the operator is concerned, the apparatus may be by him operated and controlled with few and simple panel controls which, in view of all of the foregoing, will be seen to be the single tap control for resistor R with, of course, a main on-olf switch.

The system and apparatus will thus be seen to be thoroughly practical, dependable and well adapted to achieve dependable self-protection and safety of use or operation throughout widely varying conditions met with in practice.

As many possible embodiments may be made of the mechanical features of the aboveinvention, and as the art herein described might be varied in various parts, all without departing from the scope of the invention, it is to be understood that all matter hereinabove set forth, or shown in the accompanying drawings, is to be interpreted as illustrative and not in a limiting sense.

- I claim:

1. In electrolytic grinding apparatus, in combination a work-support and rotatable .wheel means having a conductive part whereby a conductive work-piece and the face of the wheel conductive part are interrelated for agen as relative movement therebetween, with means for supplying liquid electrolyte to the interface between the workpiece and said conductive part for electrolytic decomposition at the work-piece face, a saturable-core magnetic amplifier having power Winding means energized by alternating current and having rectifier means in circuit therewith to provide unidirectional current at its output terminals and having control winding means for affecting the core saturation thereof, a satnrable-core control magnetic amplifier having power winding means energized by alternating current and having rectifier means in circuit therewith for energizing said control winding means of said first magnetic amplifier and having control winding means for affecting its own core saturation, means connecting the positive side of said output terminals to the work-piece and the negative side thereof to said wheel conductive part for effecting electrolytic decomposition at the work-piece face, means responsive to interface current, means responsive to the potential across said interface, means correlating said two last-mentioned means to convert their respective responses into a measore of interface resistance, means for energizing said second control winding means in accordance substantially with changes in said measure of interface resistance to effect responsive amplification by said control amplifier of the energy the latter supplies to said first control winding means and thereby to vary the current at said output terminals of said first amplifier substantially inversely to interface resistance changes, frequency-responsive means electro-responsively inter-related with said interface and responsive to electrical fluctuations at the interface of frequency values caused by incipience of arcing or sparking across the interface, and means controlled by said frequency responsive means for limiting current output at said terminals to a value just short of arc-over or sparking at said interface.

2. In apparatus as claimed in claim 1 in which said last-mentioned means comprises means operating upon said correlating means to raise its standard of conversion into resistance measurement.

3. In electrolytic grinding apparatus, in combination, a work support and a conductive rotatable member whereby a conductive work-piece and said member are interrelated for relative movement therebetween, with means for supplying electrolyte to the, interface between the workpiece and said member for electrolytic decomposition at the work-piece face, a saturable-core magnetic amplifier having power winding means energized by alternating current and having rectifier means in circuit therewith to provide unidirectional current at its output terminals and having control winding means for affecting the core saturation thereof, a saturable-core control magnetic amplifier having power winding means energized by alternating current and having rectifier means in circuit therewith for energizing said control winding means of said first magnetic amplifier and having control winding means for affecting its own core saturation, means connecting the positive side of said output terminals to the work-piece and the negative side to said conductive member to provide for electrolytic decomposition at the work-piece face, means responsive to interface current changes for affecting said first control winding means in a direction to substantially maintain the voltage across said interface against changes caused by changes in current demanded thereby, means respon sive to changes in voltage across the interface above a selected value for energizing said control winding means of said control amplifier to affect its energy supply to said power amplifier control winding means and thereby prevent substantial upward departures in voltage across said interface whereby current demanded thereby may vary with interface conditions, interface current-responsive means and means responsive to the potential across the interface with means integrating their respective responses into substantially a measure of interface re- 24 sistance throughout changes in interface conditions, means for energizing said control winding means of said control amplifier in response to interface currents above a selected value to effect current-limiting at said output terminals, and means for modifying the action of said last-mentioned means to shift the level of current-limiting in response to said measure of interface resistance.

4. An apparatus as claimed in claim 3 in which said last-mentioned means for energizing said control winding means comprises a circuit providing a reference voltage in series with a unidirectional valve and a resistor providing a voltage drop substantially proportional to interface current and in which said modifying means comprises means responsive to changes in said measure of interface resistance for affecting the coaction between said reference voltage and said resistor in said last mentioned circuit.

5. An apparatus as claimed in claim 4 in which said last-mentioned means comprises a resistor energized in inverse response to changes in said measure of interface resistance and thereby providing a voltage drop varying inversely as said interface resistance, said last-mentioned resistor being connected in the circuit of said reference voltage and said resistor with its voltage drop acting in a direction opposite to that of said reference voltage.

6. In apparatus for electrical stock removal from a conductive work-piece, in combination, means for effect ing stock removal from a conductive work-piece by electric current flow from the work-piece face comprising conductive means and means including a work support for interrelating the conductive means and the workpiece for relative movement therebetween during stock removal and thereby providing an interface between the work-piece and said conductive means of variable electrical resistance as interface conditions change during stock removal, means for supplying electrical energy to the interface between the work-piece and said conductive means comprising electromagnetic power Winding means energized by alternating current and having its output connected by conductors to said work-piece and said conductive means with means for varying the output energy comprising saturable core means having control winding means adapted upon change in energization to change the magnetic saturation of said core means and thereby increase or decrease the current of said output energy according to the direction of change of energization of said control winding means, and means for varying the output current of said energy-supplying means substantially inversely to said interface resistance variation comprising a metering device for measuring interface resistance and having means connected to respond to changes in interface current and means connected to respond to changes in interface voltage with means integrating the two to evaluate resistance, means for energizing said control winding means with means responsive to changes in said evaluated resistance to vary the energization of said control winding means in direction to decrease said current output upon increase in said resistance and to increase said current output upon decrease of said resistance.

7. In an apparatus for electrical stock removal from a conductive work-piece, in combination, a work-support for the work-piece, a conductive part for coaction in electric stock removal from the workpiece face and providing with the latter an interface at which conditions are variable as relative movement takes place between the workpiece and said conductive part, means for supplying electrical energy having its output connected to said conductive part and to the work-piece and having control means adapted to affect the voltage and current of the energy delivered to said interface, means adapted to affect said control means in directions to maintain substantially constant the voltage across said interface whereby interface current may vary as interface conditions change, means responsive to changes in interface current above a selected 25 I value for affecting said control means in direction to effect current-limiting action upon said source and thereby limit interface current, said last-mentioned means comprising means providing a selectable reference potential for selecting the value at which interface current is limited as a maximum, interface current-responsive means and means responsiveto the potential across the interface with means integrating their respective responses into substantially a measure of interface resistance throughout changes in interface conditions, and means for modifying the action of said reference-voltage means to shift the level of current-limiting in response to said measure of interface resistance.

8. In an apparatus for electrical stock removal from a conductive Work-piece, in combination, a work-support for the work-piece, a conductive part for coaction in electric stock removal from the workpiece face and providing with the latter an interface at which conditions are variable as relative movement takes place between the workpiece and said conductive part, means for supplying electrical energy having its output connected to said conductive part and to the work-piece and having control means adapted to affect the voltage and current of the energy delivered to said interface, means adapted to affect said control means in direction to maintain substantially constant the voltage across said interface whereby interface current may vary as interface conditions change, means responsive to changes in interface current above a selected value for affecting said control means in direction to effect current-limiting action upon said source and thereby limit interface current, and means responsive to changes in interface resistance for affecting said control means in direction to depress the level of said current-limiting action as interface resistance increases and operating reversely upon subsequent decreases in interface resistance, said interface-resistance-responsive means comprising opposing torque coils with means for energizing one of them proportionately to interface current and with means for energizing the other proportionately to interface voltage and means providing said torque coils with respective magnetic fields of which one comprises an electromagnetic winding adapted to be variably energized to achieve balance, means variable according to and responsive to the conjoint effects of said opposing torque coils to achieve balance of torque for energizing said winding, said means for affecting said control means comprising means responsive substantially. proportionately to the variable energization of said windmg.

9. In apparatus for electrical stock removal from a conductive work-piece, in combination, means for effecting stock removal from a conductive work-piece by electric current flow from the work-piece face comprising conductive means and means including a work-support for interrelating the conductive means and the workpiece for relative movement therebetween during stock removal, and means for supplying unidirectional electrical energy to the interface between the work-piece and said conductive means and having control means for affecting the supply of electrical energy to said interface, said control means comprising opposing torque coils with means for energizing one of them proportionately to interface current and with means for energizing the other proportionately to interface voltage and means providing said torque coils with respective magnetic fields of which one comprises an electro-magnetic winding adapted to be variably energized to achieve balance, means variable according to and responsive to the conjoint effects of said opposing torque coils to achieve balance of torque for energizing said winding, and means for controlling said control means comprising means responsive substantially proportionately to the variable energization of said winding.

10. An apparatus as claimed in claim 15 in which there is provided a third torque coil with means providing V 26 a it with a magnetic field to exert torque in a direction op posite to that exerted by the torque coil that is energized proportionately to interface current, frequency-responsive means having means relating it to the interface for response to changes in frequency, caused by changes in electrical conditions at said interface, of fluctuations in instantaneous electrical values caused by incipience of arc-over at the interface, and means controlled by said frequency-responsive means for energizing said third torque coil and thereby changing the standard of coacting operation of said first-mentioned opposing torque coils.

11. An apparatus as claimed in claim 10 in which said frequency-responsive means comprises amplifying means having an output connected to control the energization of said third torque coil and having an input with means interposed between said interface and said input for detecting changes in frequencies caused by fluctuations in instantaneous electrical values corresponding to incipience of detrimental arcing or undesired sparking at said interface.

12. In an apparatus for electrical stock removal from a conductive work-piece, in combination, a work-support for the work-piece, a conductive part for coaction in electric stock removal from the work-piece face and providing with the latter an interface at which conditions are variable as relative movement takes place between the work-piece and said conductive part, means for supplying electrical energy having its output connected to said conductive part and to the Work-piece, regulating means operating upon said supply means for controlling the value of a function of the electrical energy delivered at said output and variably dissipated at said interface during said stock removal and during said relative movement, and means comprising a computing device having means responsive to changes in potential across said interface and having means responsive to changes in interface current and having means integrating the resultant potential and current changes substantially into the quotient of interface potential and interface current, and means responding substantially proportionally to changes in said quotient for affecting said controlling means and cause it to regulate said function of said electrical energy at a dififerent value.

13. In an apparatus for electrical stock removal from a conductive work-piece, in combination, a work-support for the work-piece, a conductive part for coaction in electric stock removal from the work-piece face and providing with the latter an interface at which conditions are variable as relative movement takes place between the work-piece and said conductive part, means for supplying electrical energy having its output connected to said conductive part and to the work-piece, control means adapted to affect the value of a function of the electrical energy delivered to said interface, said control means comprising a circuit providing a reference voltage in series with a unidirectional valve and a resistor, means responsive to changing electrical conditions at said interface for substantially measuring accompanying changes in interface resistance, means for supplying electrical energy to said resistor to provide an IR drop in said series circuit, and means responsive to said resistance-measuring means for substantially proportionally changing the energy supplied to said resistor and thereby affecting the coaction between said reference voltage and said resistor and said control means to change the current delivered to said interface substantially inversely as interface resistance changes.

14. In an apparatus for electrical stock removal from a conductive work-piece, in combination, a work-support for the work-piece, a conductive part for coaction in electric stock removal from the work-piece face and providing with the latter an interface at which conditions are variable as relative movement takes place between the work-piece'and said conductive part, means for supplying electrical energy having its output connected to said conductive part and to the work-piece, control means adapted to affect the value of a function of the electrical energy delivered to said interface, means responsive to changing electrical conditions at said interface for substantially measuring accompanying changes in interface resistance, and means responsive to said resistancemeasuring means and operating upon said control means to change the current delivered to said interface substantially inversely as interface resistance changes, said resistance-measuring means comprising opposing torque coils With means for energizing one of them proportionately to interface current and with means for energizing the other proportionately to interface voltage and means providing said torque coils with respective magnetic fields of which one comprises an electromagnetic winding adapted to be variably energized to achieve balance, means variable according to and responsive to the conjoint eifects of said opposing torque coils to achieve balance of torque for energizing said Winding, said means for effecting said control means comprising means responsive substantially proportionately to the variable energization of said winding.

15. in, an apparatus for electrical stock removal from a conductive work-piece, in combination, a work-support for the work-piece, a conductive part for coaction in electric stock removal from the Work-piece face and providing with the latter an interface at which conditions are variable as relative movement takes place between the Workpiece and said conductive part, means for supplying electrical energy having its output connected to said conductive part and to the work-piece, control means adapted to affect the value of a function of the electrical energy delivered to said interface, means responsive to changing electrical conditions at said interface for substantially measuring accompanying changes in interface resistance, said last-mentioned means comprising means responsive to changes in the potential across said interface and means responsive to changes in current flow across said interface with means correlating said two last-mentioned means to convert their respective responses into a measure of interface resistance, means responsive to said resistance- Ineasuring means and operating upon said control means to change the current delivered to said interface substantially inversely as interface resistance changes, means lectrically associated With said interface and responsive to frequency changes effected by changes in electrical interface conditions, and means controlled by said frequency-responsive means for affecting said control means in direction to limit current flow across said interface.

References Cited in the file of this patent UNITED STATES PATENTS 2,092,859 Seaverson Sept. 14, i937 2,084,870 Schmidt June 10, 1941 2,245,192 Gugel June 10, 1941 2,287,755 Barth June 23, 1942 2,488,856 Few Nov. 22, 1949 2,545,413 Ferret-Bit Mar. 13, 1951 2,547,615 Bedford Apr. 3, 1951 OTHER REFERENCES Keeleric: Steel, Mar. 17, 1952, vol. 130, No. 3, pp. 84 to 86, article entitled Electrolytic Grinding.

New Processes For Machining and Grinding, Report No. MAB-18-M of National Research Council, Jan. 18, 1952, appendix VI, pages 1 to 9 and Figs. 1 to 4.

Claims (1)

1. IN ELECTROLYTIC GRINDING APPARATUS, IN COMBINATION A WORK-SUPPORT AND ROTATABLE WHEEL MEANS HAVING A CONDUCTIVE PART WHEREBY A CONDUCTIVE WORK-PIECE AND THE FACE OF THE WHEEL CONDUCTIVE PART ARE INTERRELATED FOR RELATIVE MOVEMENT THEREBETWEEN, WITH MEANS FOR SUPPLYING LIQUID ELECTROLYTE TO THE INTERFACE BETWEEN THE WORKPIECE AND SAID CONDUCTIVE PART FOR ELECTROLYTIC DECOMPOSITION AT THE WORK-PIECE FACE, A SATURABLE-CORE MAGNETIC AMPILIFER HAVING POWER WINDING MEANS ENERGIZED BY ALTERNATING CURRENT AND HAVING RECTIFER MEANS IN CIRCUIT THEREWITH TO PROVIDE UNIDIRECTIONAL CURRENT AT ITS OUTPUT TERMINALS AND HAVING CONTROL WINDING MEANS FOR AFFECTING THE CORE SATURATION THEREOF, A SATURABLE-CORE CONTROL MAGNETIC AMPLIFER HAVING POWER WINDING MEANS ENERGIZED BY ALTERNATING CURRENT AND HAVING RECTIFER MEANS IN CIRCUIT THEREWITH FOR ENERGIZING SAID CONTROL WINDING MEANS OF SAID FIRST MAGNETIC AMPLIFER AND HAVING CONTROL WINDING MEANS FOR AFFECTING ITS OWN CORE SATURATION, MEANS CONNECTING THE POSITIVE SIDE OF SAID OUTPUT TERMINALS TO THE WORK-PIECE AND THE NEGATIVE SIDE THEREOF TO SAID WHEEL CONDUCTIVE PART FOR EFFECTING ELECTROLYTIC DECOMPOSITION AT THE WORK-PIECE FACE, MEANS RESPONSIVE TO INTERFACE CURRENT, MEANS RESPONSIVE TO THE POTENTIAL ACROSS SAID INTERFACE, MEANS CORRELATING SAID TWO LAST-MENTIONED MEANS TO CONVERT THEIR RESPECTIVE RESPONSES INTO A MEASURE OF INTERFACE RESISANT, MEANS FOR ENERGIZING SAID SECOND CONTROL WINDING MEANS IN ACCORDANCE SUBSTANTIALLY WITH CHANGES IN SAID MEASURE OF INTERFACE RESISTANCE TO EFFECT RESPONSIVE AMPLIFICATION BY SAID CONTROL AMPLIFER OF THE ENERGY THE LATTER SUPPLIES TO SAID FIRST CONTROL WINDING MEANS AND THEREBY TO VARY THE CURRENT AT SAID OUTPUT TERMINALS OF SAID FIRST AMPLIFER SUBSTANTIALLY INVERSELY TO INTERFACE RESISTANCE CHANGES, FREQUENCY-RESPONSIVE MEANS ELECTRO-RESPONSIVELY INTER-RELATED WITH SAID INTERFACE OF RESPONSIVE TO ELECTRICAL FLUCTUATIONS AT THE INTERFACE OF FREQUENCY VALUES CAUSED BY INCIPIENCE OF ARCING OR SPARKING ACROSS THE INTERFACE, AND MEANS CONTROLLED BY SAID FREQUENCY RESPONSIVE MEANS FOR LIMITING CURRENT OUTPUT AT SAID TERMINALS TO A VALUE JUST SHORT OF ARC-OVER OR SPARKING AT SAID INTERFACE.

Images