US1918483A - Truing apparatus - Google Patents

Description

July 18, 1933. H D, MUNDAY 1,918,483

TRUING APPARATUS Filed July 26, 1929 4 Sheets-Sheet 1 J4 INVENTOR 110mm flMlmday k1. ATTORNEY July 18, 1933. 4-1.0. MUNDAY TRUING APPARATUS Filed July 26, 1929 4-. Sheets-Sheet 2 INVENTOR flomcefl/Vanday m ATTORNEY.

. lull-ll i July 18, 1933. H. o. MUNDAY TRUI'NG Ar rgng 'qs Filed July 36', 1929 v 4 Sheets-Sheet" s mww y 1933. H. D. MUNDAY 1,918,483 "TRUING APPARATUS Filed July 2 1929 I f f4 Sheets-:Sheet 4 mmm,a-wi

INVENTOR V Harare BMW 274. BY

M ATTORNEY such commutators.

Patented July 18, 1933 UNITED s' ATasf HORACE n. Minibar, or scnannc'rmr, zmwqroni:

"meme APPARATUS I Application filed m 26,

This inventionrelates to methods of and apparatus for grinding and particularly to methods and devices for grinding or truing commutators or collector rings of electric machines. I

It is the resent practice to grind commutators or collector rings by means of a motordriven abrasive wheel mounted on across feed slide carriedby a carriage which in turn is mounted on a pair ofways parallel to the commutator, means being provided to give the abrasive wheel an axial movement'relative'to the 'cemmutator. One disadvantage of the present practice, as carried out by the device justdescribed as well as similar devices now in use, is that the attentionof the operator is required throughout the, grinding operation. Another disadvantage of this practice is that, generally, itis necessary to 2 remove some of the'brush holdersor other parts of the machine in order to permit the entrance of the grinding wheel into contact with the commutator. Furthermore, during the grinding operation it is the general practice to take 011' all orsome of the use'fuli l'oad of the electric machine. Also, the grinding operation as now performedconsumesa considerable time and as a result it is not usually performed as often as itshould be.

By the use of the'preferred forms of the present invention Ilavoid thedisadvantages incident to present practice as above noted. My improved grinding device {is automatic and requires little or no] attention during actual operation. In using many forms of my invention it is unnecessary to remove any i of the brush holder or other parts of the machine, and it is also unnecessary tojtakeofi' any of the useful load from the machine.

vices constructed in accordance with the present invention is their adaptability to the truing of commutators having ridges or ruts as well as greater effectiveness in truing ground by an abrasive block which is fed forward toward the commutator in a general radial direction, there is very little more grinding of the ridges of the commutator than the ruts or other low parts of the coin- When a commutator is 1929. Serial mi. 35L170. mutator. When the abrasivefirst'brought into contact with thecomniutator it contacts with the'ridges only andfor-a short time the ridges are ground downto theex clusion of the remaining parts of the commutator.

advantagesjust noted and provide a grinding devicewhich will serve to grind down the ridges continually untiltheycare eliminated.

Numerous obj ects" and advantages of my invention other than those above-mentioned will be apparent from the .following descrip-. tion taken in connection with the accompanying drawings wherein, Figure liS a fragmentary side elevation of a commutator and brush holder and one form of myimprove'd commutator truing meansae" 1 v Figure 2 is vayperspective view of one-of the parts shown in Figure 1'. w. y Figure3 is a view similar to Figure l but 'Ishowing azmodified form of truing device Figure 4 is a sectionalview of a brush holder and associated therewith-a modified form of truing. means. V F

, Figures 5 and 6 are front and side views respectively of a brushholder and associated therewith a stillfurther modifiedform of .truingmeans. 4 v u Figure? is a viewsimilarto Figurefi n I but showingafurther modification. A further important advantage of the dey Figure 8 isja view similartovFigure 6 but showing a yet. further modification. Figure .9 is a view similarto Figure 4, but showing a further modification], Figure 10 is a sectional view showing, another modification. o Figurell shows inside elevation a cornmutator surrounded by a brush holder ring and associated with such commutatora 'further modified commutator truing device.

Figure 12 is a view of the structure, shown By the ,pr'ese "t invention I: avoid the dis- 65' .nient to te pressure member.

Figure is a fragmentary plan view of the structure shown in Figure 14.

Figure 16 is a detailed view of one of the parts shown in Figures 14 and 15.

Figure 17 is a side view partly in section on theline17*-17 of Figure 18, and shows a modification .wherein a camis employed to give a positive advancement to the pressure member and Figure 18 is a fragmentary plan view of the structure shown in Figure 1 In theforms of invention herewith. lllllS- trated, I employ preferably as a truing or abrading means,an abrasive'ribbon' or strip such as a strip of sand paper and associated with such strip is a suitablysupported pressure member adapted to. engage the strip and press the same against the high-spots of the commutator. v invention herein illustrated,I preferably provide some means for feeding the abrasive strip between thepressure member and the commutator 'or other part, which it' is desired to true, so that fresh or unworn abrasive surfaces may bebrought into contact with the commutator as desired.

A number of different means may emplbyed"ifor feeding the abrasive ribbon.

When theribbon is drawn against the rota-- tion of the commutator, I may if desired,

employ for this purpose a small motor with speed reducing'gear connected to a reel on.

which the'abrasive'ribbon is wound. If the abrasive ribbon moves with the rotation of the commutator, such a motor may if desired be omitted andreliance'had .on the friction of the commutator to draw the abrasive ribbon" along. In the" latter case Ioftenfihd it advisable to provide some means for hindering the movement of the abrasive strip,

7 such for example as a clockescapement mechanism for hindering the rotation of thewheel, which, carries the ribbon. If the commutator is on an electric machinewhich runs in both directions, a small motor should be used to wind up one end of the ribbon while other delaying v means.

the unwinding of the ribbon on the other roll is hindered by the clock escapement or Torque-limiting means, such a resistance in the armature circuit of motor 214, may be used'to. limit'the pull of the motor to an amount that will not pull in two the abrasive strip. Invthis way the motor serves the purpose of a spring Also-in the forms of with constant tension and infinite length, or of a Wei ht with a long drop.

Since t e abrasive ribbon is flexible, means ma be provided by which the ribbon may ma e contact with the commutator over a considerable peripheral span, thus for this purpose the pressure member may have its active end formed as an arc conforming to that of the commutator.

The pressure member may ress steadily or differentially or with de ayed action.

' Where there are no flat spots in the commutator, it, being desired to grind only ridges, a steady pressure may be used. If it is desired togrind out. flat spots, a differential pressure or delayed action pressure may be employed, or a positive or non-reversible feed may be ,used, or such a feed maybe used in conjunction with means for delaying the advance or forward movement of the abrasive or its tangential. movement Itowardithe' commutator.. v v s,

The principles underlying the operation of the various forms of my invention herein disclosed will be particular] pointed out, in connection with thespeci c descriptions of these forms. While my improved truing means is particularly adapted for truing commutators and slip rings','it will be understood that such means maybe applied to the truing of shafts, rollsand similar bodies which it is desired to cut to true, round or V cylindricalshape. v. Figures 1 and 2 show one form of my invention. The abrasive member or sand paper 109 ribbon 21 is unwound from a reel22 and passes thence under some or allfof' a set of brushi holders 23, from which the brushes have been removed and wooden or, other blocks of the same dimensions substituted. In this form of my invention each block is divided intotwo-parts of wedge'shape designated respectively by the reference characters 24'and 25. By employing blocks of this form,

a differential pressure of the abrasive rib- 'bon against thecoinmutator 26 is given by the block when advanced by the pressure finger 27 of. the brush'holder, that is, less pressure will be required to stop the advance of thei block into the low spot of the, commutator than will be required by thehigh spot of the commutator to shove the wooden block backwardg a This is due to the friction between the wedges 24 and 25andthe sides of the brush- 1 holder box. 'Such friction resists all motion of the wedges,'either toward or away from the commutator. When a low spot of the commutator passes under the'brushholder,

the spring moves the wedges through the box toward the commutator until the strip 21 is pressed against the commutator surface. 'As

it is. apparent that the friction above mentionedis "opposing the. action of thespring 27, the pressure of the strip on the com- 6 erably 10 tator to cause this backward mutator at the low spot will be the difference between the force of the spring and oppos-, ing friction. In other words of the strip on the low spot will be considless than the force of the spring 27. On t e other hand when a high spot comes under the brush holder and as a result the strip and the wedges are pushed back, the force which must be exerted by the commumovement, must be one which will overcome the friction of the wedges against the brush'holder box and in addition it must overcome the pressure of the spring 27 In other words, the pressure between the abrasive strip and the commutator as a high spot of the commutator is coming under the brush-holder, is considerably greater than the pressure of the spring. The result therefore of the use of the wedges 24 and 25- is to cause greater abrasion of the high spots than the low spots and because of this difierential pressure effect, the high spots located circumferentially of the commutator in line with the low spots will be eliminated.

It is to be noted that the use of wedges create a resistance to the motion of the pressure finger, which resistance may. be described as of a passive character, that is, while resisting motion in one directionit does not correspondingly assist motion-inthe opposite direction. By employing a resistance of this character I am able to produce the difierential abrading effect which trues the commutator.

To consolidate or unify the pressure of the individual blocks located in successive brush holders in line with one another,'I may provide a trough or U shapedmember 29 made of horn fiber or leatheroid paper about or inch thick. This'trough slipped under the brush holder boxes 31 and loosely laced thereto by cords 32 passing through holes 33 in the sides of the trough .and over the tops of the brush holder boxes. 1

The friction of the commutator 26 rotating as indicated by the arrow 28, draws the abrasive ribbon from thereel 22 under the trough 29. The wooden blocks bear against the hollow part of the trough and force the trough against the abrasive ribbon and the ribbon against the commutator with the differential pressure that will grind out the flat spots. To permit a slow motion only, of the reel 22, the gear 41 on the shaft of the reel may be belted by a chain belt 42 to the gear 43 driving the clock escapement mechanism 44, the speed being changed by adjustment of the weights 45 on the escapement arm 46. i

Instead of the wooden block being cut into parts, a solid block may beemployed and smeared with asphalt to give a delayed action. Orif desired a divided block such as is shown in Figure 1, may be used together with asphalt. Or if desired, the brushes may be left in the brush holders and used without the pressure which may advantageously any friction or asphalt added as hindering means, bearing on the trough 29.or directly on the abrasive ribbon without the use of the trough. Such a constructionfcould advantageously be used to eliminate ridges in the commutator; also flat spots if there is considerablebrush friction or other meansof resisting brush movement. I

When'there is a tendencyto chatter, I may if desired, secure the trough 29 or anequivalentspacer' such as a flat"non-'stre tchable sheet form of material, against side or tangential movement, as for example by tying the trough to some'stationarv part of the machine other than the brush-holder by a cord be passed through the side holes 33 of the trough.

Figure -3 shows how a ridge 51tand a commutator 52 may be ground down' 'by means of a sand paper ribbon 53. Swivelledat 54 is a timber 55 having-ablock or step 56 hollowed out at the top over which top is stretched the canvas or leather strip 57 5e cured at its ends by the screws 58, such canvas strip pressing the sand paper ribbon over a considerable peripheral span against the commutator 52. The weight 61 on the lever 62 on the fulcrum 63 raises one end of the timber 55 and presses the sand paper ribbon against the commutator 5 2. 7 The speed of passage of the sand paper ribbon may be controlled by the clock escapement mechanism 64 gearedto thereel: 65. The commutator rotates in the direction of the arrow 66.. If it is desired to grind out a flat spot in the commutator, the canvas strip 57 may be omitted, the wooden block or step pressing the sand pa er ribbon against the commutator. In this case the timber 55, may be raised with a difierential pressure or tion, or it may be raised positively, that is non-reversibly or it'may beraised positivelyand with delayed action.

, Pressure members operating on other principles may be employed for truing the commutator or other cylindrical member. may if desired clamp-the pressure member to the brush holder box or provide some means whereby its retrograde movement is limited and in this case depend upon structural rigidity of the brush holder to exert more pressure on the high spots than on the low spots of the, commutator. \Vhile parts of the brush holder, such as the brush holder box are usually regarded as fixed supports .or strength members theseparts are adapted to yield slightly when subjected to the upward thrust caused by a high art of the commutator coming under the a rasive and as a result the brush holder causes the abrasive to exert-a very strong pressure on the high part,"

thus abrading the high part rapidly.

- I may also ifdesired, provide means by which theadvancement of the pressure member toward the commutator may be definitewith delayed ac- 1y limited so that the abrasive strip will not touch or will just skim the flat spots, and when such a limiting means is employed, I may maintain the pressure member in its most advanced position by the usual brush holder finger employed for advancing the brush through the brush holder. Withfsuch a construction it is clear that the brush holder finger may be made to exert its full pressure on the high spots and none or little on the low spots of the commutator. Or it desired, the pressure member may be merely a brush mounted in a brush holder, so constructed or arranged as to provide for considerable friction of the brush inthe brush holder box or where there/is a weight added to thelbrush' holder finger to exert a strong pressure against backward movement of the brush. Delayed action hindering means may be used to delay the advance of the pressure member into the flat 's ots of the commutator, thus confining the abrading eflect to the high spots of the commutator. An example of such delay action'hindering means is the asphalt above mentioned. It is obvious that structures other than brush holders may be used as supports for the pressure members 'to'press i the sand paper ribbon against the high parts mentioned.

of the commutator. One advantage of the use of brush holders as supports for the pressure members when the truing operation is performed while the electric machine is in operation, is that the brush holders are generally located at neutral points of the commutator and any tendency to short circuit the commutator bars by reason of the abrasive picking up'copper is minimized.

Figures 4 to 18,inclusive, illustrate other embodiments of my invention employingone or another of principles of operation above In the construction shown in Figure 4, I

i provide a means for limiting thebackward movement of the abrasive away from the commutator, any. backward movement in excess of the adjusted limit requiring distor tion or structural yielding of the brush holder and connected parts. In this figure I make use'of'an iron strap 80 formed with a foot 82 and hinged at 83 to a block 84 in which is mounted the temper screw 85 and a thumb screw 86 which serves to secure to the block 84 ametalstrap87; Strap 87 is provided at its lower end Withi'a foot 88, the foot 88 and the foot 82 being positioned beneath the walls of the brush holder'box The strap. 87 is slotted to the point 89 to permit adjustment of the strap 87 to fit a brush-holder an inclined inner end.

In assembling the device shown in Figure 4, the two sheet metal straps are inserted through the brush-holder box, the block 84 being then thrown back on its hinge and the pressure member 91 inserted. The strap 87 is then secured to the block 84 and the tembox with per screw 85 adjusted to give the desired amount of pressure on the sand paper from the yielding brush holder structure. a

I find that in certain cases it may be desirable to limit'the forward motion of the pressure member, so as to prevent the abrasive from being pressed against the flat spot of the commutator. In the device shown in Figures 5 and 6, I provide a means for limiting the advance of the pressure members instead of limiting the backward movement as is'the case in Figure 4. In Figures 5jand 6 I provide a pressure member 101 which may be formed as a solid block of wood or fiber, or may, be divided into'wedge shaped parts as indicated by the dotted line 102 in Figure 6. At the top and on either side of the pressure member this member is formed with shoulders 103 which serve to support the temper screws 104 positioned near diagonally opposite corners of the pressure member 101.

The ends of the temper screws 104 abut on the front and rear walls respectively of the brush holder box 106. The heads 107 of the temper screws are graduated circumferentially and these graduations are adapted to cooperate with pointers 108 extending upwardly from the shoulders 103, to indicate the adjusted position of the temper screw. The threads of the temper screws are of such pitch that variations in position of the ends of the screws may be indicated readily to Within 1/1000 of an inch. The use of abutting inclined endsurfacesin the wedge members in Figures 5and 6 serves to give a lateral thrust to the two parts in opposite directions so that they frictiona-lly engagetwo opposite walls of the brush-holder box. The friction is subtracted from the pressure of the pressure finger in causing the advance and is added to the pressure of the pressure finger tov resist backward motion of the pressure member due to a high part of'the commutator and in this manner the abrasive efiect is increased over that due to the pressure finger acting alone. The wedgeprinciplehas been briefly mentioned in connection with Figure 8 and explained in more detail in connection with Figure 1.

' In setting up the device shown in Figures 5 and 6 the lowest flat spot of the commutator is brought under the pressure member and.

'cut can be taken on the flat spot as for example when it is desired to thoroughly clean up the flat spot. A variation of this procedure. is to adjust thescrews 104 so that only the highest part of the high part will make contact'with the sand. paper ribbon and then adjust the screws occasionally to allow a slight advance ofthe pressure member, as the highest part is wornoif,

Figure 7 shows one form of my invention applied to a brush holder having apigtail retaining screw in the front wall ,of the brush-holder box. In this form of my invention, I'substitute for the ,pigtail retaining screw it thumb-screw115 and I provide a pressure member 116 having aninclined outer end against which the thumb-screw 115 is adapted to abut. It is clear that when turning the thumb-screw'to the right, the lim t of retrograde movement of themember- 116 is moved nearer to the commutator and by turning the thumb-screw to the left, the limit is moved to the opposite direction. By

adjusting the thumb-screw in-this wa ,just.

the pressure desired can be exerted ycthe pressure member on" the high spot of the commutator and can be made sufiicient to insure truing action and at the sametime not great enough to tear the sandpaper. The pressure member 116 may beformed ofrlgid material such as wood or fiber or if desired its lower part may be formed of rubber or other yieldable material.

The pressure member 125 shown in Figure 8 has secured in it a stud 126 passing freely through a hole in a horizontal side portion of a strap 127, a vertical side portion of which is secured to the brush-holder box by the thrumb-screw 128 which has been substituted for the usual pigtail retaining screw. Thumb nuts129 above and below the horizontal top portion of the L or T-shaped strap 127 serve to'limit both the forWardand backward movement of the pressuremember125.

I preferably form the strap 127 Y of two parts 130 and 131 which are connected together by means of the screw 132 threaded into the part 130 and having jam-nuts 133 between which and the part '131 is positioned a stiff spring washer 135. The nuts 133 are adjusted so as to subject the washer 135 to considerable pressure. The washer 135 forms a relief means in case thepressure member 125 is subjectedto an undesirably high pressure tending to force it upward through the brush-holder box and so preventsinjury to t the parts such as tearing the sandpaper, when for example the commutator has a very deep low spot or when the lower of the nuts 129 is adjusted too high on thestud 126. 7

The pressure member 125 may if-desired' be divided into two wedges asindicated by a dotted line in Figure 8'and the stud 126 threaded into one of the wedges,.-preferably the lower wedge. I mayif desired,use the brush holder pressure finger to advance the ressure member 125 and the pressure finger in conjunction with thelwedges may be employed for frictional hindering of the movement of the abrasive. It is obvious that such frictionally hindered movement maybe employed with or without the means for limiting the forward or backward movement, this limitingl efl'ect dependin upon the position of the t limb-nuts 129; he constructionalranged as described may be used with or without the relief means depending upon ing of such form that they are spaced from one another at their upper ends as indicated at 146. Extending through the upper end of each part is .a thumb screw 148 which when tightened will serveto forcethe lower ends of the parts outwardly against the sides of the brush-holder box and thus clamp the pressure member tightly in the box. When the screw 148 is tightened so that the pressure member is held rigidly in the box, I depend upon the structuralyielding of the brush holder to resistretrograde movement of the abrasive. I may however, use the device shown in Figure 9 with'thescrew 148tightened sufliciently to cause a frictional len agement between the pressuremember an the sides of the brush-holder box, but notsufiicient to prevent forward movement of the pressure member underaction 'ofthe brushholder pressure finger 150 or other means for pressing the pressure member forward in the brush-holder. With-the thumb-screw 148 adjusted in this manner, the operation of the device for truing a commutator is similar to the operation of the device described in con nection with Figures 1 and 2.

a pair of wedges constituting the pressure member. Adapted to bear near one end on the carbon brush and near its other end on the pressure member is an equalizer bar 173. The brushholder pressure finger 174 engages and presses against the bar 173. The sandpaper ribbon .is drawn under the pressure member whileat the same timethe brush 169 which is located at one side of the sandpaper strip is free to make contact with the comfan guard at the outer end of the commutator;

Y of abrasive paperso as ports Surrounding the part ofthe tube 204 near the brush-holder boxes is secured so as to prefrear wheels of an automobile.

mutator. isa stud 185 passin 186 in the upper we hole in the equalizer of this stud is to keep that. they can be drawn out of the brushholder box as aunit.

Another purpose is to limit the advance of the ressure member and for this purpose I provi e two nuts 190 which can be adjusted to rest on the top of the brushholder box and limit the advance of the pressure member to contact with a part of the commutator of any elevation desired. The equalizer bar 173 can be kept substantially horizontal by adjustment of thumb-screw 191 threaded in one end.

Large electric machines are often surrounded by a brush holder ring or have a In truing commutators of this construction difiiculty is experienced in positioning a strip to obtain a long tangential approach of the paper to the commutator, and where a fan guard is employed there is difiiculty in introducing the ribbon into position where'it may be properly fed beneath "the pressure member.

Figures 11,12 and 13 show a means for introducing a roll or drum 198 of sandpaper 199 under a brush holder ring 200. The sandpaper roll or shaft 202 which is supported and driven somewhat similarly to the shaft which drives the The pin 203 in the hole in the end of the shaft 202 engages the wooden drum 198 through a notch in the end of the drum. The steel the drum and encloses tube 204 supthe shaft 202.

commutator is a fiber tube 205 which serves to 3 insulate the tube.204 from contact with the live parts of the electric machine. tube is held by a clamp 206,.the other end of The steel which is secured to some fixed support such as the bearing ,cap of the electric i'nachine, as shown for example in Figure 11. The thin insulating fiber tube 205 surrounds the inner steeltube 204 near the commutator and extends under and, somewhat beyond the clamp 226 by which it is held tightly to the steel tube 204. In this way no grounds can be made on the steel tube 204 except beyond I the end of the fiber tube 205.

The general. positioning of the drum 198 relative 'tothe commutatoris obtained by properly locating the clamp 206 on the tube 204 and the connection of the clamp with the bearing cap of the machine. Smaller axial Y adjustments of the drum may be obtained by means of a j which threadedly engages the stud 209anchored in the clamp 206. The hub 208 turns freely in the upper end of the clamp 211, the

lower end of which is clamped tightly to the 7 tube 204. The rims 212 of the drum are fiber drum 19.8 is connected to a' hand wheel 207, the hub 208 of holders.

so that contact of the drum with the live parts of the electric machine will do no harm. A sprocket gear 213 serves to connect the shaft 202 with the drivmgmotor 214 through reducing gears. The winding-off drum 198a is connected to a clock escapement similar to that shown in Figures 1 and 3. A handwheel on the motor shaft permits manual. adjustment or operation.

As a means for guiding the abrasive ribbon so that it will approachthe brush holder in a" general tangential direction I provide a guide 220 which is supported from the tube 204 by a structure designated generally by reference character 225 and which comprises a clamp 226 which serves to clamp to the tube 204 the slotted arm 228 on which is mounted the clamp 229 adjustable along the 220 to'difi'erent angular positions with respect to the tube 204, as well as radial adjustment (along the slots) on arm 228. Slots in the plate 230 permitvertical adjustment on the fibre rod 227. The supporting structure 225 therefore provids for a very wide range of adjustments of the guide 220 so as to adapt the guide for use with machines having a variety of brush-holder and commutator assemblages. A sheet of fibre 232 positioned under the pressure members in the erably prevent its tangential movement 1n one or both directions, and serves to unify the pressures of the pressure members, as well as to kee; the ribbon from catchin on sharp parts 0 thebrushholders. The bre sheet 232 may conveniently be made slightly wider than the length of the drums so that cords or wires such as 232' can be run from the inner and the outer edges of the fibre sheet past the ends of the drums to some substantial point of attachment, such as the brush-holder yoke 200, or to an anchorage outside the electrical machine. Another functionof the fibre sheet in addition to those mentioned is to form afunnel approach so that the abrasive strip can be inserted 'under the brush-holders while the machine 1s running, by merely sticking the end of the strip under the sheet 232 and letting the revolving commutator draw it under the brush- This fibre sheet 232 serves as a substitute for the fibre trough 29 described elsewhere in connection with Figure 1.

The tube 204 may be kept from turning by means of cap-screw 233 threaded in the screw 262 projects into a slot in the rod 254 and prevents it from turning.

clamp 206, the inner end of thescrew engag ing a slot 234 in the tube 204'. The sprocket gear is splined on the shaft to permit some axial movement without the necessity of 241 by the cap-screw 244 is the block 245 vertically adjustable on the said strap. This block supports a pair of sprin s 249 which force the wedge 251 to the rig t by acting on one of several pins 252 projecting from the sides of the wedge. The wedge 18' held in position by the walls of the slot in strap 241 and the shoe 253 integral with the lower end of rod 254 slidable in a hole'in block 245. Between the shoe andtheblock is a stiff spring 255, the tension on which can be adjusted bymeans of the nuts 259. This spring serves as a relief means. Set-screw 261 in the lower end of strap 241 abuts on the front wall of the brush-holderbox and serves to .bracethe strap against movement. 'Set- In the form of invention shown in Figures 17 and 18, the pressure member is advanced towards the commutator by the cam 272, which swivels on the pin 273 mounted on a air of notched discs 274 integrally united y the cross-bar 275, said discs and cross-bar" being adjustably secured by-the cap-screw 276 to the strap 281, which is similar to the strap shown in igure 16 and is similarly secured to the brush holder. The cam 272 is turned toward the left into contact with themember 271 by means of springs 283. j j

In the above described forms of my invention where dependency is had upon structural yielding or structural rigidity to obtain the desired resistance to small retrograde movement radially of the commutator, I have obtained such structural yielding by the con struction of a pressure memberor the structure of some part connecting the pressure member with a stationary support. It will however, be understood that such yielding may be caused to occur in the abrasive strip itself by providing an abrasive strip which is compressible in a direction of its thickness.

Thus if desired I may employ afabric strip secured to the back of the sandpaper strip so that the fabric of the fabric strip will serve as a spacer between the sandpaper strip and the pressure member.. Such'fabric strip need not in all cases be. united to the sandpaper.

strip beneath'the pressure member. Where the fabric strip is united the sandpaper strip, the fabric strip will prevent'tearmg of the flexible abrasive strip under excessive tension. I i I In the operation of the truing device shown inziFigures 1113, the device is mounted on the-frame of the machine to be trued substantially as described, and shown in-Figures 11 f and12.

The dynamo electric machine may be assumed to run in both directions, such-as a motor driving steel mill rolls. In starting the operation the main ortion of the sandpaper strip will have been rolled on. the windin -oif drum, 198a, eitherby disengagement 0 the retarding clock 'escapement, or,

preferably before mounting on the motorv frame. The free .end of the sand a er stri is then run-underone or more 0 t ebrus holders mounted on one or more of the brush holder studs, and'securedby any convenient means, as by a tack or'two, to the winding-up drum, 198.. a

Pressure members, such'as shown in Fig. 8, are substituted for the brushes in the brush holders under whichthe sandpaper strip is rum-and the coo eratingstationary.parts 130' clamped to the rush holders; A. thin fibre sheet, 232, may. then be inserted between the brush holders and the sandpaper strip and theends of the fibre sheet secured to some stationary part, such as the brush holder ring 200. The connections between the sheetand the ring should preferably be inelastic so that any to-and-from movement of the sheet is avoidedto a considerable extent. The mill motor is then started andalso. the small feedingmotor 214. l a

This type of pressure ,device' Fig. 8) may be used in-several ways, as previously described. Assume that it is used-as aspacing member, thus hurdling the flat parts. The

pressuremember in: the brush holder box-is then advanced by backingofl' the upper thumb-nut 129 till a small to-and-fro 'movement of this member is felt. The lower thumb-nut 129 is then. screwed .tightlv against the horizontal part 131. Nuts 133 may be setup till spring 135 is'well cornpressed- The proper amount of pressure can be judged by such indications as the quiver of the brush holder or pressure member, the jerking of the abrasive strip or its tension,

and by the amount of copper dust coming off. Then at each reversal of the mill motor the effect of the grinding can beobserved and connecting parts fromthe brush holder. Or the adjustments can be made while the for aninstant. As'long. as the bottom of I a flexible abrasive member and means for I from the winding,

friction means for block.

machine is at rest. On large machines it is advisable to keep a jet of air playing on the commutator to or take other means to keep it out. Now and then the pressure member is advanced by adjustment of the thumb-nuts 129 as the various-signs indicate that the high parts have been reduced to some extent. The operation is continued till the commutator becomes true.

This application, is a continuation in part of my copending application Serial Number 278,748 filed May 18, 1928. v

- Having now described my invention what I claim and desire to secure by Letters Patent is:

1. A commutator truing device comprising a flexible abrasive member, a brush holder havin' a brush guide, a pressure block positione in said guide and adapted to advance toward the commutator, means for drawing the abrasive member past the rotatin commutator and under the pressure bloc and -hindering motion of said '2. In a dynamo electric machine having a rotatin commutator with high and low parts circum erentially in said commutator, comprising a pressure member, a guiding and supporting member for said pressure member, actuating means for advancing said pressure member towards said commutator, means for yieldingly resisting movement of said pressure member in at least one direction without corresponding assistance tomovement in the opposite direction, in anyone of a plurality of positions automatically attained, to the end that said pressure member either hurdles said low parts or at least bears substantially less heavily on said low parts than on said high parts,

passing said flexible abrasive member between said pressure member and said commutator.

3. In a device for truing a rotating commutator having high and low spots, an abrasive strip, means for positioning said strip so that a portion commutator, means for feeding said strip so as to bring new portions of said stri into contact with said commutator, means or advancing said portions radially towards said commutator and asphalt means for delaying said advance.

4. In a dynamo electric machine having a rotating commutator with high and low parts circumferentially in line, means for truing said commutator, comprlsmg a pressure member, a guiding and supporting member for said pressure member, a flexible abrasive member positioned against said commutator and under said pressure member, means for advancing said pressure member into contact with said abrasive member, means for 'trograde movement drive the copper dust away line, means for truing and at a distance thereof contacts with said blocking said pressure member against rerelative to said guiding and supporting mem r) due to the reaction thrust of said high part, means for passing said flexible abrasive member between said pressure member and said commutator, the

vguiding and supporting memberbeing adapted for slight structural yielding to permit the high partof said commutator to pass under the. ressure member. a

5. Ina ynamo electric machine having a rotating commutator with'high and low parts circumferentially in line, means for truing. said commutator, comprising a pressure member compris ng a flexible strip forming an engaging part of said pressure member and adapted to conform under pressure to the curved surface of the commuta- V tor and span a circumferential portion thereof, a flexible abrasive member positioned between said pressure-member andsaid commutator, means for advancing said pressure member and so pressing said abrasive member againstsaid commutator, means located laterally of said pressure member for passing said flexible abrasive member between said pressure member and said commutator.

6. In a dynamo rotating commutator with high and low parts, means for grinding said commutator, comprising a flexible abrasive member positioned to engage said commutator,fa pressure member adapted to press said flexible abrasive member into frictional engagement with said rotating commutator, the said friction causing said flexible abrasive member to be drawn along ast said rotating commutator, and means or limiting the move ment of said flexible abrasive member to a speed substantially less than the surface speed of said rotating commutator;-

7. In a dynamo electric machinehaving a rotating commutator with high and low parts, a truing device comprising a flexible abrasive member, a spacing or .pressure member positioned adjacent to the commutator from the high part thereof somewhat less than the thickness of, said flexible abrasive member, said flexible abrasive member being positioned under said pressure member and pressed thereby into frictional engagement with the high part of said rotating commutator, said frictional engagement with said rotating commutator causing said flexible abrasive member to be drawn along past said rotating commutator, and

means for limiting the rate of movement of said block towards said commutator, an

electric machine having a towards said commutator to a distance from the high part thereof somewhat less than the thickness of said flexible abrasive member,

said flexible abrasive member being positioned under said pressure member and pressed thereby into frictional engagement with the hi h part of said rotating commutator, said rictional engagement with said rotating commutator causing said flexible abrasive-member to be drawn along past said rotating commutator, at a rate of movement substantially less than the rate of movement of said commutator.

9. In a dynamo electric machine having a rotating irregular commutator with high and low parts circumferentially in line, means for truing said commutator comprising a ressure member, a flexible abrasive memr, positioned and adapted to be moved tangentially, under said ressure member, actuating means for a vancing said pressure member toward said commutator, and means for resisting movement of the pressure member in at least one direction without correspondingly assisting the movement in the opposite direction, whereby said pressure member presses substantially harder on the abrasive member when in registration with parts of the commutator of relatively slight altitude than when in registration with the lower parts of the commutator.

10. In a dynamo electric machine having a rotating irregular commutator with high and low parts circumferentially in line, means for truing said commutator comprising a pressure member, a flexible abrasive member, positioned and adapted to be moved tangentially, under said pressure member,

' rotating irre actuating means for advancing said pressure member toward said commutator, and means for frictionall pressure mem r in at least one direction without correspondingly assisting the movement in the o posite direction, whereby said pressure mem er presses substantially harder on the abrasive member when in registration with parts of the commutator of relatively slight altitude than when in registration with the lower parts of the commutator.

11. In a dynamo electric machine having a for truing said commutator comprisin a pressure member, a flexible abrasive mem er, positioned and adapted to be moved tangentially, under said pressure member, actuating means for advancing said pressure member toward said commutator, and delayed action means for slowing down movement of said pressure member whereby the pressure of said pressure member on said abrasive member is substantially greater when the abrasive member registers withthe high part than when it registers with the low part. I

12. In a device for truing a rotating com" mutator, an abrasive strip, means for positioning said strip so that a portion thereof contacts with the commutator, means for resisting retrograde movements of the strip with relatively great increase in resisting force with slight increase in retrograde displacement until a predetermined resisting force is exceeded and thereafter permitting substantial retrograde movement without substantial increase in resisting force.

HORACED. IMUNDAY.

resisting movement of the lar commutator with high and a low parts c rcumferentially' in line, means as v lzs Y

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