US2924913A - Grinding machine - Google Patents

Description

Feb. 16, 1960 Filed May 2?, 1958 J. KLAR ET AL GRINDING MACHINE u .1" Hi1- 3 Sheets-Sheet 1 5 maryn .t. Kunr'holm H 'rney Feb. 16, 1960 J. KLAR ErAL GRINDING MACHINE Filed May 27, 1958' 3 Sheets-Sheet 2 INVENTORS John ft'lar By martm Lkumholm H Tney Feb. 16, 1960 J. KLAR HAL 3 GRINDING. MACHINE Filed May 2'7, 1958 i 3 Sheets-Sheet 3 I Lfi QQQ '1' ,0; ma az 34 W- OID. FEED MOTOR MOTOR INVENTORS John ffla r BYWZarlIn .L ffuniholm o neg United States Patent GRINDING MACHINE John Klar, West Boylston, and Martin L. Kuniholm,

Worcester, Mass., assignors to Heald Machine Company, Worcester, Mass., a corporation of Delaware Application May 27, 1958, Serial No. 738,137 11 Claims. (Cl. 51-88) This invention relates to a grinding machine, and more particularly to automatic grinding machines having means for controlling the feed rate thereof.

fInternal grinding machines employ various methods for holding the workpieces. The workpiece may be chucked or, in the simplest type of grinder, it may be supported between rollers or on shoe-type supports. The object is to support the work while it rotates about a fixed center 7 shoes or rolls. If, then,external and internal grinding be carried on simultaneously, the internal operation need notcomplicate the external operation, but it is obvious that the external operation does affect the internal operation; this is because of the fact that, if the workpiece is supported on rolls or shoes, this causes a change in the position of the work center-line and, therefore, complicates the problem of holding size on the internal surface.

The problem is resolved if means be provided for guaranteeing that the work center line arrive at a constant position in relation to the work supports at the same time or before the internal abrading means arrives at its sizeholding position. The problem is complicated, however, when the grinding stock allowance fluctuates, as it normally does, resulting in' a variation in the rate of stock removal due to the resultant variations in spindle work and machine deflections which, in turn, are caused by the abrading means becoming dull or glazed to difiering ,degrees.

One type of grinding feed mechanism that is well known operates to bring the wheel and work into engagement and then to maintain a definite pre-set force between the wheel and the work. The cycle time is a variable which is dependent on the magnitude of this force, the amount of grinding stock, the speed of and condition of the abrading member, work speed, etc. An alternate feed method, also wellknown,-consis ts in causing the wheel relatively to approach the work at a present rate. This method results in a cycle time which remains constant but must be longer than the average time of the first method. Thisis because of the fact that the retracted position of the feed member must besufliciently far from the finish position to accommodate a workpiece with the maximum grinding stock and thefactthat the feed rate cannot be set faster than the rate at which the abrading means and machine are able toremove stock. Hence, time is inevitablywasted on all workpieces'withless than the maximum stock allowance. Now, in a'combination automatic grinder where outer and inner surfaces are ground simul- 2,924,913 Patented Feb. 16, 1960 taneously, it has been pointed out that a necessary condition to successful operation is that the internal and external feed be so synchronized that, irrespective of initial stock conditions, the arrival of the outer surface at a given sizeeither earlierthan or co-incidental with the arrival of the internal abrading means at its reference point is necessary in order to hold a uniform internal size. This requirement makes it necessary to use feeds having constant rate so that both rates, internal and external, can be preset to arrive at the size holding reference point simultaneously or in any desired relationship, continuously and repetitively. The disadvantage of this method has been shown to be a wastage oftime on workpieces with less than the maximum possible stock-but the present invention combines the advantages of the latter method with those ofthe former method by eliminating the time wasting feature of the latter methods.v The system of. control embodied in this invention is particularly well adapted to cope with the above problem and offers an easy solutionswhether the machine feed actuatorbe hydraulic, electrical or mechanical. The difiiculties presented by the prior arthave been obviated in a manner by the present invention.

It is, therefore, an outstanding object ofthe invention to provide an improved means for controlling feed rates in a grinding machine as a function of the power absorbed by the grinding wheel or wheels.

Another object of this invention is the provision of a means in a grinding machine whereby the machine is able to sense the amount. of grinding stock to be removed from each workpiece. a

It is a further object of this invention to provide a grinding machine havingmeans for governing the feed in accordance withworkpiece stock allowance thus shortening the time cycle on every workpiece having less than however unequally the grinding stock may be distributed between outer and inner surfaces and however many] times the feeds are halted and started as a consequence of maintaining the preset horsepower level, the arrivals of both inner and 'outer abrading surfaces at their terminal points relative to the workpiece center line will be 00- incidental. i

Another object of this invention is to provide a grinding machine having an electrical horsepower level control system of simple design with inherent dependability and v long life expectancy.

Although the novel features which are believed to be j characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself as to its ob ects and advantages, the mode of its operation and the manner of its organizatiom'may be better. understood by referring to the following description,

taken in connection with the accompanying drawings forming a part thereof, and in which: t

Figure 1 is a front eleyational view of a grinding principles of the present. inventionz 3 chine embodying the Figure 2 is a plan view of the machine;-' anddrive apparatusdncorporated in Figure 3 is a schematic viewfof certain aeanca iina} the machine.

Referring first to Fig'urejs land 2, .jwherein' arebe st; I I d d the'grinding machine, indicated generallyby the referencewnume ral 10, 1s shown as being of the typeshowiiand describef shown the general featureso'f the invention,

novel the feeds are so controlled that,

in the co-pending patent application of William D. Schmidt and Almon Townsend, Serial Number 445,152. A base 11 has mounted at one end a workhead 12 driven by a motor 13. Mounted on the base l l for movement parallehto the axis" of the wheelhead' isa table 14 onwhichis mounted a wheelhead l'driven by a motor 16. Adrive piston 17 is associated with the wheelheadlZ and' a work support -18 of the" shoetype extends upwardly from the base '11, to supportaworkpiece 19 which; for the purposes of -descriptiomis shown as being an inner race of a bearing. An internal abrasive wheel- 21- is associated 'whh the-wheelhead 15.- Also mounted on the-base 11 is a secondary-table 22 mounted forpivotal adjustment and carrying an exte'rnah'wheielhead 23 driven by-a motor 24'andadapted to'carry an external abrasive wheel-25.' A suitable wheehdres'sing apparatus 26 is mounted- 'on' the'hase 'and is provided'with a 'di'amond 27 "adapted to dress the' external wheel'25 and ai -diamond 28{adaptedito dress the internal 'wheel 21'.

A feed mechanism 29 feeds the=internal grinding Wheel 21 relatively to the work andis driven through a mag-.

netic clutch 31 (see F-igtir'eii') by afrnotor-=32'. A feedmechar'iism 33 feeds the external grinding wheel 25-rela-' tive to: the work and: is :driven' through a magnetic'clutch 34. by amotor 35. The machine is otherwise -as-described in' the above-mentioned. patentapplication of Schmidt and Townsendx I Referringynow'toFigure 3, power lines 36, 37, and

38areiconnec'ted-to a source of 3-phase electrical power;

not. shown, and are :connected throughfuses 39, '41, and

42 to leads 43, 44,;and 45.2:These leads. are connected through, starter contactors46, 47, .andt48' toleads 49, 5-1, and, 52' connected. to the internalfdiameter. wheel motor24. The leads 43,44, and'45 are also'connected respectively through starter contactors53, 54, and 55' to leads 56, 57', and 58 connected togthe outside diameter wheel motor 24. r

Connected in the' lead 52 is the primary 59 of a current transformer 61, having a secondary coil 62; The ends of the secondary coil 62. are connected to opposite sides of a rectifier 63, one of the leads having inserted: therein an A.C. ammeter 64; The outputside of the rectifier 63 is connected to'leads 65, and 6 6 across-which is connected the resistance element 67 -.of a rheostat 68. The contact arm 69 of-the rheostart is connected back to the line 65. The line 65 is also-connected to-one. end of the' resistance element 71 of a variable resistor-72, the contact arm 73 thereof being connected to one side :of the coil 74 of a normally-open sensitive relay-75; One side of the switch element 76 of the relay75 is connected'toa 0 line 77 by means of a lead 78.

Inserted in the lead 58 associated with the motor 24 is the primary coil 79ofa current transformer 81. The

secondarycoil 82 is connected by leads to the input sides nected to the lead 85. The switch elements 96- are-con nect'ed] across the switch element 76 associated with the relay. 75, so that one of. the: leads from the switch element 96, isconnected by the lead 78 to the line 77. The other sides of the switch elements 76'and 96, are connected through a lead 97 to one side of the coil 98 forming' part of a normally-closed relay 99.- The other side oi the coil 98 is'connected by a, lead v101 to.a line 102. Theline's 77 andf102 are connected to opposite-polarities of, a source of direct current electricity, not-shown; the

polarity. is, of course, immaterial to the"operation. of the apparatus. 'Ac'rossvthe coil 98 is connected a resistor; 103 in iseries with; a capacitor 104. One side of the cu d.

contactor 105 associated with the relay 99 is connected to" the'line77 byalead'107. Theot'her sideof't'h'e contactor 105 is connected to the coil 108 of the magnetic clutch 31. The actuating coil 109 associated with the magnetic clutch 34 is also connected to the same side of the contactor 105 as is the coil 108. The other sides of the coils 108 and 109 are connected to the line 102. a The line 77 is connected by a lead 111 to one side of the rotor of the outside diameter feed motor 35. The line 77 is also connected by-a lead'112 -to one side of the internal diameter feed motor 32. The other sides of each of these motors are connected together and through a lead 113 to the line 102. The field coil 114 associated with the motor 32 is connected on one end to the line 77 and on theother end to a variable resistor 115, the contact arm of which is connected through the lead 113 to the line 102. In the same manner, one end of the-field coil 115 associated wi h, the outside. diameter feed motor 35 "is connected tome, lead V 111' Le 'nnect'ing it"to' the line 77'. The otherfsidefof the fi fcldcoil 1 16'- is connected toone side of a' Lvar'iable resistorlll f, the contact arm of which is connected throughtlielead' 113, m H6102; l v.

"The operation of the apparatus will now be readily understood in vi'ew'of, the'above description." The pawer drawn by the internal diameterfwheelfm'otor. 1'6'is cated to thecurrent' transformer byfthepassage of one phase'of the current throughthe primary coil 59 thereof.

The voltage appears acrossthe output coil '62 which is 'pro v portional tothe currentinftheleafd 152 and therefore ap'-.

proximately. indicative" of nertia d awn, by the motor; The output signal of thecur'rent transformer 61 is alter nating "but, after treatment by the rectifier 63, emerges as a series of'direct currentjp'ulsesjofa iriagnitu'deindicative of the power drawn by the rnotori' Therelay is so constructed that; whenthe'size'of the p lScs rea'ching it is great enough, theswi'tch "element76jwill close.

Inthe same way, the current drawn by the motor 24iis,

felt by the primary coil' 79' of thecurrent' transformer 81. An alternating voltage appears on thc output leads of the coil 82 indicative of the power drawn by t he" motor 24. This alternating signal is rectified 'by the rectifier 83 and is impressedon the coil 94 of the relay" 95. When agiven pulseis large enough, the switch 96 closes; The closure ofeithen'or both of the switch elements 76 and .96causes a flow of current through the coil 98 of the relay-91am current'pa'sses from the line 77 through the lead 78; through one ofythe two switches 76-and96, andthroughthelead97, the coil 98 and'the lead 101 to the line 102. A similar; current' passes through the resistor 103 and the capacitor 104. A sumcientflow of current through the coil 98*causes an ope' n ingof the contactor 105' thus cutting off the flow of" current to the coils 108' and 109 associated with the clutches 31 and 34 respectively. As is evident from "a study of Figure' -3, themotors 32 and 35* operate continuously but the deactivation of the clutches-"108 and 109 causes "the cutting-off-pf power transmittal fromf these motors to the feed me'chanisms 29 and'33. It will f be understood that the relays 75-and are very-sensitive.

The variable resistance 68 acts as a means of adjustingthe 1 sensitivity of thereby 75 anda variable '-res'istancc SSperformsa similar function in 'conne'ction with ftli'c 4 relay 95. An additionalfadjustrrient ofsensitivity'isprovided' by the variable resistance's '72 and 92;-'= Suppose that the control he setat= 3 hp; 'As the wheel feedsinto' the work the'powerloading increases fromit's freerunning. value towards the 3 hp. valuje. Th'e'contact carryingarmature of thesensitiverelayaor solenoid-actaf ated switch 75 is subjectto. two opposingiforces; there'lay" spring tries. to maintaimtherelay: contact open while the pulsing at twice the supply current frequency, and only the difference betweenthe magnetic force and the spring force is available to effect closure. If this switch element be used to control the feed through an on-oif device such as a magnetic clutch, a rapid functioning'results. This becomes especially true if two clutches (as for an internal feed and external feed, such as we have in the present case) be operated from one ordinary sensitive relay. At the threshold of operation the switch element 76 (and the switch element 96, for that matter) behaves like a faulty rheostat with a large voltage drop across the contact. This, in turn, results in feeding of the clutch which operates at the slightly lower energy level, while the other clutch fails to drive. This situation could not be tolerated on a machine for simultaneously grinding outer and inner surfaces for the previously-described reason that a necessary condition of the operation of such a machine is accurate synchronization of the internal and external feeds. To avoid this difliculty the operation of the sensitive relay is converted from an erratic to a positive action by providing the relay 99 which is shunted by an integrating capacitor 104 and resistor 103. The function of the integrating capacitor is to accumulate the pulse energy delivered by the switch elements 76 and 96 and, when the energy level reaches that required by the resistor 103 and the relay 99, it causes a sustained (unpulsed) actuation of the relay 99. The positive action on the relay 99 efficiently and cleanly interrupts both feeds, whereupon the power loading of the spindle motors diminishes until the switch elements 76 and 96 are both open. The energy accumulated in the capacitor 104 dissipates meanwhile through the resistor 103 and the coil 98 of the relay 99 until it reaches the level where release of the contactor 105 occurs. The contactor then closes with a positive action and the energization of the coils 108 and 109 and the operation of the feed mechanisms 29 and 33, respectively, are again actuated.

The power differential between pull-in and dropout of the relay 99 is related to the values of the capacitor 104 and the resistor 103 which are in parallel with the relay, and related as well as to the internal resistance of the relay itself. These elements can be so chosen that the feed advances by small or large increments, each type of performance having its own advantages in specific cases. In the preferred embodiment a relay 99 is used having a high internal resistance and a resistance is placed in series with the capacitor to reduce the .current flowing through the sensitive relays 75 and 95. The switch element 76 and 96, because of the low pressure vibratory.

type of operation (with consequent arching) would not otherwise have a long nor dependable life expectancy. In a specific example the relays 75 and 95 have an internal resistance of one ohm, the resistor 103, a resistance of 10,000 ohms, the capactor 104, a capacity of 4 microfarads, and the relay 99 an internal resistance of 10,000 ohms. Suppose that it is desired to set up the grinding machine to simultaneously grind the outer and inner surfaces of a ring where the maximum stock found on the outer surface is .030" on the diameter and .025" on the inner diameter. Suppose further that it is possible to remove .028 from the outer surface in 28 seconds and .026" on the inner surface in 26 seconds, these rates being close to, but safely under'the critical point where the abrading surface might be severely crushed or damaged. This would allow .002 for further finishing of each surface. Instead of setting the rates on internal and external feeds to a 28th second cycle (the slower of the two) the present invention makes it possible to set the feed rates of each at a much faster rate, say, 4 times faster or 7 seconds. At the same time the danger of exceeding the critical wheel pressure is overcome by setting the external and internal power load adjustments to values which are consistent with that face value producedby the 28 second cycle on the outer surface and 26 second cycle onthe internal surface. A

comparison can now be made between the time taken by two machines, one equipped with this invention and one without. The average grinding stock will be assumed to be .014" on the outer surface and .013" on the inner surface. Without this power control the cycle time would be an unvarying 28 seconds. With this control the 7 seconds pre-set rate would accomplish the first .014" of feed (where no stock is encountered) in one half the 7 seconds or 3 /2 seconds. The second half of the feed would require 14 seconds. The total average time with the use of this invention would be 14 plus 3% or 17% seconds, compared to the 28 seconds for the machine without it. This is a large saving in time and the machine is rendered 60% more productive in rough grinding.

While certain novel features of the invention have been shown and described and are pointed out in the annexed claims, it will be understood that various omissions, substitutions,and changes in the forms and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention.

The invention having been thus described what is claimed as new and desired to secure by Letters Patent is:

1. A grinding machine, comprising an internal grinding wheel, an internal wheel motor, an external grinding wheel, an external wheel motor, an internal feed mechanism, an external feed mechanism, a first means for driving the internal feed mechanism, a second means for driving the external feed mechanism, and means operative when the power consumed by either motor exceeds a predetermined value to render both the first and the second means inoperative.

2. A grinding machine, comprising an internal grinding wheel, an internal wheel motor, an external grinding wheel, an external wheel motor, an internal feed mechanism, an external feed mechanism, a first means for driving the internal feed mechanism, a second means for driving the external feed mechanism, a third means giving a signal proportional to the power consumed by the internal wheel motor, a fourth meansgiving a signal proportional 1 to the power consumed by the external wheel motor, and means operative when the signals from either the third or the fourth means exceeds a predetermined value to render both the first and the second means inoperative.

3. A grinding machine for use in simultaneously abrading external and internal surfaces of a workpiece, comprising an internal grinding wheel, internal wheel motor, and external grinding wheel, an external wheel motor, an internal feed mechanism, an external feed mechanism, a first motor for driving the internal feed mechanism, a second motor for driving the external feed mechanism, a first means giving a signal proportional to the power consumed by the external wheel motor, and a relay operative when the signal from either first or the second means exceeds a predetermined value to render both the first and second motors inoperative.

4. A grinding machine, comprising an internal grinding wheel, an internal wheel motor, an external grinding wheel, an external wheel motor, an internal feed mechanism, an external feed mechanism, a first means including a motor and clutch for driving the internal feed mechanism, a second means including a motor and clutch for driving the external feed mechanism, a third means giving the signal proportional to the power consumed by the internal wheel motor, a fourth means giving a signal proportional to the power consumed by the external wheel motor, and means operative when the signals from either the third or the fourth means exceed a predetermined value to render both clutches associated ,with the first and second means inoperative.

5. A grinding machine for use in simultaneously abrading external and internal surfaces of a workpiece, comprisinganinternal grinding wheel, an internal wheel motor, an external grinding wheel, an external wheel motor, an internal feed' "rne chanism, an external feed mechanism, a first means for driving the internal feed mechanism, a second means for driving the external feed mechanism, a third means giving a signal proportional to the power consumed by the internal wheel motor, a first relay operated when the signal from the third means exceeds a predetermined value, a fourth means giving a signal proportional to the power consumed by the external wheel motor, a second relay operated'when the signal from the fourth means exceeds a predetermined value, and a third relay actuated by the operation by. either the first or the second relay to render both the first and second means inoperative to drive their? respec: tive feed mechanisms.

6. A grinding machine for use, in simultaneously abrading external and internal surfaces of a workpiececomprising an internal grinding wheel, an internal: wheel motor, an external grinding wheel, an external wheel motor, an internal feed mechanism, aneexternal feed mechanism, a first means including a motor; and. clutch for driving the internal feed mechanism, a second means including a motor and clutch for driving the external feed mechanism, the third means giving a signal proportional to the power consumed by the internal; wheel motor, a first relay operated when the signal from the third means exceeds a predetermined value, av fourth means giving a signal proportional to the powercon sumed by the external wheel motorya second relay operated when the signal from the fourth means, exceeds av predetermined value, and a third relay actuated by the operation by'either the first or the secondrelay to render both the clutches of the first and second means inoperative to connect their respective motors totheir respective feed mechanisms.

7. A grinding machine for use in simultaneously abrading external and internal surfaces of a workpiece,'com-. prising an internal grinding wheel, an internal wheel motor, an external grinding wheel, an external wheel motor, an internal feed mechanism, an external feed mechanism, a first means including amotor and clutch for driving the internal feed mechanism, a second means.

including the motor and clutch for drivin glthe external feed mechanism, a first current transformer connected in a lead to the internal wheel motor giving asignal protion of either the first or second relay to render both clutches of the first and second means inoperative to connect their respective motors to their respective feed mechanisms.

8. A grinding machine for use. in simultaneously abrading' external and internalsurfaces of a workpiece, an internal grinding wheel, an internal wheel motor. of the alternating current type, an external grinding wheel, an external wheel motor of the alternating:

current type, an internal feed mechanism, an external feed mechanism, a first means including a=motor and clutchfor driving theinternal feed mechanism, a second means including a motor and clutch for driving thefexternal feed mechanism, a third. means giving a signal proportional to the power consumed-by the. internal wheel motor, a first .'sensitive relay, operated whenfthesigrial from the third means exceeds. a. predetermined value, a fourth meansjgivinga signal'prop'or tionalto the power consumed'by the external wheel motor, a second sensitive relay operated when the signal from the fourth means'jexceedsa predetermined-value,"

a third relay actuatedby' th'e 'operation of eithith first. or the second relay to render both clutches of the are; and second means: inoperative to connect their respective motors to their! respective feed mechanisms, and a capacitor connected across the third relay to render'it insensitive to. high frequency opening and closing of the first and second relays.

9. A grinding machine for use in simultaneously abrading internal and external surfaces of a workpiece, comprising an internal grinding wheel, an internal wheel motor of the alternating current type, an external grinding wheel, an external; wheel motor of the alternating current type, an internal feed mechanism, an external feed mechanism, a first means including a motor and clutch for driving the internal feed mechanism, a second means including a motor and clutch for driving the external feed mechanism, a first current transformer connected in a lead. totheinternal wheel motor giving a signal proportional to the powerconsumed thereby, a first sensitive relay operated when the signal from the first'current transformer exceeds a predetermined value, a. second currenttransformer connectedin a lead to the external wheel motor giving a signal proportional to the power consumed thereby, asecond sensitive relay operated when the signal from the second current transformer exceeds. a predetermined value, a third relay actuated by the operation of either the first or second relay to render both clutches of the first and second means inoperative to connect their respective motors to their respective feed mechanisms, anda capacitor connected across the coil of the third relay to render it insensitive to high frequency opening-and closing of the first and second relays. I

10. A grinding machine, comprising a grinding wheel, a wheel motor of the alternatingcurrent type, a feed mechanism, a first means for driving the feed mechanism, a second means giving a signal proportional to the power consumed by'the wheel motor, a sensitive relayoperated when the signal from the second means exceeds a predetermined value, a second relay actuated by the operation of the sensitive relay to render the first means inoperative to drive the feed mechanism, and a capacitor connected across the coil of the second relay to render it insensitive to high frequency opening and closing of the first and second relays.

11. A grinding machine for use in simultaneously finishing external and internal surfaces of revolution of a workpiece, comprising aninternal grinding wheel, an internal wheel motor for carrying on the finishing operation on the internal surface, an external grinding wheel, an external wheel motor for carrying on the finishing operation on the external surface, an internal feed mechanism, an external feed mechanism, the feed mechanisms being arranged to bring the internal and external finishing operations to a conclusion at approximately the same time, a first means for driving the internal feed mechanism, a second means for driving the external feed mechanism, a third means giving a signal proportional to the power consumed by the internal wheel motor in carrying on thefinishing operation of the internal surface, a fourth means giving a signal proportional to the power consumed by the external wheel motor in carrying on the finishing operation on'the external surface, the feed ratesbeing substantially greater than the rate which will maintain the power consumed by the wheel motors below the said predetermined values during the finishing cycle, the predetermined values being those above which operation is destructive of the wheel, and means operative when the signals from either the third or the fourth means. exceedfa predetermined. value to render both the f l $995 5 t tt e i i i l a a Refg -ence Cited in the file of this patent UNITEDfSTATES PATENTS 2,694,883 ,Balsiger Nov. 23, 1954 2,807,916 Squire Oct. 1 1957

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