US3902278A

US3902278A - Grinding machine for generating an epitrochoidal surface

Info

Publication number: US3902278A
Application number: US524445A
Authority: US
Inventors: Herbert Rudolph Uhtenwoldt; Richard Earl Crossman
Original assignee: Cincinnati Milacron Heald Corp
Current assignee: Cincinnati Milacron Heald Corp
Priority date: 1973-04-11
Filing date: 1974-11-18
Publication date: 1975-09-02
Anticipated expiration: 1992-09-02

Abstract

A grinding machine for generating an epitrochoidal surface or the like, including means for generating a true epitrochoid and for providing for the use of a cam while using the generating means for maintaining normalcy and preload of the cam against a cylindrical follower.

Description

United States Patent 1191 1111 3,902,278 Uhtenwoldt et a1. Sept. 2, 1975 [54] GRINDING MACHINE FOR GENERATING 3,757,474 9/1973 Pedersen 51/105 R AN EPHTROCHOIDAL SURFACE 3,800,621 4/1974 Hoglund 5l/D1G. 32 3,816,996 6/1974 Uhtenwoldt 51/DIG. 32 Inventors: Herbert Rudolph Uhtenwoldt, 3,828,481 8/1974 Uhtenwoldt 51/1310. 32

Worcester; Richard Earl Crossman, Leominster both of Mass FOREIGN PATENTS OR APPLICATIONS 1,239,213 4/1967 Germany 51/97 R [73] Ass'gneei Cmcmna" Mllacmn'fleald 1,117,569 6/1968 United Kingdom 51/95 R Corporation, Worcester, Mass.

OTHER PUB ICATI N [22] Filed: Nov. 18,1974 L O S Abrasive Engineering, Newest Trochoid Grinder, [2]] Appl. No.: 524,445 M 22,

Related US. Application Data [63] Continuation Of 561. No. 349,924, April 11, 1973, W 'F dbandcmed- Assistant Examzner-N1cho1as P. Gd1c1 Attorney, Agent, or Firm-Norman S. Blodgett; Gerry 52 us. (:1. 51/50 PC; 51/95 WH; 51/101 R; Blodgett SI/DIG. 32; 82/13; 90/20 [51] Int. Cl B24b /16; B24b 19/08 57 BS C [58] Field of Search 51/50 R, 50 PC, 95 WH,

5l/97 NC 105 R 105 EC 101 R 16593 A grlndmg machme for generatmg an ep1trocho1dal DIG 82/1 surface or the like, includlng means for generating a true epitrochoid and for providing for the use of a cam References Cited While using the generating means for maintaining normalcy and preload of the cam against a cylindrical fol- UNITED STATES PATENTS lowen 2,428,971 /1947 Hauser 51/50 R 3,730,052 5 1973 Harlin 90 7 Clams, 21 Drawlng Flgures 1| 1 I I 11 1 J 1 1 V 1 I 1 1,1 1 I 1 20 I111 L l 12,111 I //----"J I o 29" j 7 F111 5 f 1 l3 PATENTEDSEP 2197s 3 902,278

SHEET 3 GE NERATE TRUE EP/TROCHOID COMPENSATE F OR NON-NORMAL! TY VARY SHAPE DE SIRE D SHAPE POINT P MINOR CIRCLE EPITROCHOID FIG 4 BASE CIRCLE FIG. 3

&

SHEET PATENTEU SE? 975 SHEET SHEET PATENTED SEP 2 I975 FIG. I0

FIG. II

PATENTEDSEP 2197s SHEET LAL GRINDING MACHINE FOR GENERATING AN EPITROCI-IOIDAL SURFACE BACKGROUND OF THE INVENTION This is a continuation of application Ser. No. 349,924 filed Apr. 1 l, 1973. now abandoned.

The manufacture of grinding machines for the production of non-circular surfaces is a highly developed art and considerable interest has been applied to the generation of the internal epitrochoidal surface which is used in the housing of a Wankel engine. There are two basic principles employed for machining an epitrochoidal surface, (a) cam following, and (b) generation, as shown in the Bayer U.S. Pat. No. 2,870,578. Most machines used in the prior art make use of a master cam whose surface is reproduced on the workpiece. For instance, the patents of Davies U.S. Pat. No. 2,42l,548, of Appleton U.S. Pat. No. 3,259,021, and that of Hoglund U.S. Pat. No. 3,663,! 88 show such machines in which the shape of the finished workpiece is dictated by the shape of a master cam. The driving action for moving the workpiece rotatably relative to the grinding wheel, has been introduced through the cam follower to the cam surface. The difficulty with such constructions is that, first of all, the amount of friction that is available between a cam follower and a master cam is limited, which means that large amounts of metal removal are not possible. Furthermore, tremendous wear takes place between the cam follower and the cam surface, largely due to the amount of power transmitted through these surfaces. In other words, the larger amount of power that is transmitted (enabling the removal of large amounts of stock), the greater the wear between the surfaces, thus introducing error beyond allowable tolerance. Another limitation that has been introduced into the prior art machines. is the problem of maintaining normalcy between the grinding wheel and the surface to be finished. Lack of normalcy introduces variations in grinding force, the vector of grinding force, variations in relative speed between the grinding wheel and the workpiece. and the like, all introducing errors of various magnitudes into the finished surface. The only way to avoid such errors (or at least maintain them below a predetermined tolerance), is to grind very slowly with small forces. Since such a grinding machine is a rather large capital investment, the long grinding cycle makes the workpiece expensive and tends to eliminate it economically from being competitive in the market place. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore, an outstanding object of the invention to provide a grinding machine for generating an epitrochoidal surface which permits the introduction of large amounts of power without at the same time introducing error into the shape of the finished surface.

Another object of this invention is the provision of a grinding machine for generating an internal epitrochoidal surface which permits the removal oflarge amounts of stock in a unit time and,thercfore, permits short grinding-cycle times.

A further object of the present invention is the provision of a grinding machine for producing an epitrochoid in which a high capital expenditure for the machine is justified by the fact that the amount of such expense which needs to be applied to each workpiece for the process of generating the surface is small.

It is another object of the instant invention to provide a grinding machine for the generation of an epitrochoidal surface which is made up of relatively simple rugged parts, permitting operations for long periods of time without shutdown for maintenance or repair; the parameters of the epitrochoid (R R and E) are adjustable and do not require different rolling contact elements for each engine size and shape variation.

A still further object of the invention is the provision of a grinding machine for generating an epitrochoid, which machine is simple to operate with the use of relatively unskilled labor.

Another object of the invention is the provision of a grinding machine for non-circular internal surfaces, wherein a shape and normalcy generating elements are confined in one area; more specifically, these elements are confined to the workhead and no motions are transmitted to the wheelhead.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

SUMMARY OF THE INVENTION In general, the invention consists of a grinding machine for generating an epitrochoidal surface having a base, having a column extending upwardly for the base, and having a wheelhead mounted on the column, the wheelhead including a vertical spindle on the lower end of which is mounted an abrasive wheel. Means is provided for moving the wheelhead relative to the column selectively in a vertical and a horizontal direction and a workhead is mounted on the lbase capable of holding a workpiece on which the said surface is to be generated by the abrasive wheel or other cutting tool. The workhead moves the workpiece horizontally relative to the spindle to produce an epitrochoidal pattern.

The workhead includes a table mounted on the base for sliding motion in a first horizontal feed direction normal to the trochoid surface, a workpiece platen mounted on the-upper part of the table for rotation relative thereto about a vertical major axis, l, and a shaft mounted on the lower part of the table for rotation about a minor axis, II. The lower end of the shaft is formed'with a cylindrical stub which is rotatably carried in a hydrostatic bushing mounted on the base, the axis of the said cylindrical stub being displaced from the said minor axis.

More specifically, the shaft is formed as an upper part which is rotatably carried in the table and a lower part which has the cylindrical stub. The upper and lower parts are slidably joined for lateral movement to adjust the amount, E, by which the stub axis is displaced from the minor axis.

BRIEF DESCRIPTION OF THE DRAWINGS The character of the invention, however, may be best FIG. 4 is a diagrammatic representation of the method by which anepitrochoid-is generated.

FIG. 5 is a vertical sectional view of the machine taken on the line V-V ofFIG. 2.,

FIG. 6 is a vertical sectional view taken on the line VI-VI of FIG. 5,

FIG. 7 is a plan view of a portion of the machine as viewed along the line VII--V-II of FIG. 5. i

FIG. 8 is a vertical sectional view. taken on the line VIIIVIII of FIG. 7,

FIG. 9 is an end elevational view machine shown in FIG. 7,

FIG. 10 is a plan view ofa portion of the machine as viewed along the line X-X of FIG. 5,

FIG. 11 is an end elevational view of the portion of the machine shown in FIG. 10, p

FIG. 12 is a plan view of a portion of the machine as viewed along the line XIIXII of FIG. .6,

FIG. 13 is an end view of the portion of the apparatus shown in FIG. 12, I

FIG. 14 is a horizontal sectional view of the machine taken on the line XIV-XIV of FIG. 5, I

FIG. 15 is a plan view of a portion of the machine,

FIG. 16 is a vertical endelevational view ofthe portion of the machine shown in FIG. 15,

FIG. 17 is a vertical sectional view taken on the line XVIIX\ /II of FIG. 15,

FIG. 18 is a vertical sectional view taken on the line XVIII-X\ III of FIG. 15,

FIG. 19 is a vertical sectional view taken on the line XIXXIX of FIG. 15, I I I I FIG. 20 is a vertical sectional view taken on the line XX-XX of FIG. 15, and v FIG. 21 is an elevational view of a portion of the apparatus shown in FIG. 15. l

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIGS. 1 and 2, which best show the general features of theinvention, the grinding machine, indicated generally by the reference 'numeral 10, is shown as having a base 11 from one side of which extends a vertical hollow column 12. A wheelhead 13 is mounted on a feed slide 1614 and a vertical slide 16. It includes a vertical spindle 14 on the lower end of which is mounted an abrasive wheel 15. A cylinder 16b is provided for moving the wheelhead l3 vertically relative of the portion of the FIG. 5 shows a sectional view through the table 23' with the workhead l8 suitably mounted for rotation in roller bearings 36 and having a worm gear 37 mounted on its lower end for'producing the rotation. Mounted at the top of the workhead is a cam 38 which engages a cam follower 39 mounted on an arm 41 which is fastened to the base 11 throughan abutment 42 (see FIG.

2). The cam 38 is used when appropriate to give the ultimate shape of the finished surface. The cam can be shaped by grinding it in the present machine just as though it were a workpiece. The cam may have changes or corrections to the true epitrochoidal shape to compensate for thermal distortion of the housing during the operation of the engine or to compensate for grinding wheel force variations due to the presence of an exhaust port acting as an interruption of the surface.

These variations are provided by employing a control system incorporating a stepping motor, not shown.

The table 23 is formed of four major parts. a bottom part 43 that is fastened to the base 11, a second part 44, a third part 45, and a top part 46 in which the workhead 18 is mounted. The second part 44 and the third part 45 are slidable relative to one another for adjustment, while the third part 45'and the top part 46 are similarly adjustable, these being in a transverse plane;

i.e., transversely of the grinding machine 10 and in the plane of the drawing of FIG. 2. The third part 45 is I formed in two parts which are rotated relative to one another by means of a large diameter roller bearing 47. Extending between the second part 44 and the bottom part 43 is a shaft 48. This shaft consists of an upper part 49 and a lower part 51 which are slidable relative to one another in the plane of FIG. 5 by means of

interengaging ways

52 and 53 and locked in that position of adjustment by a bolt 54. The lower part 51 of the shaft 48 is provided with a cylindrical portion 55. which resides in a bore in aring 56 which is attached to an abutment extending upwardly from the bottom part 43 by to the column 12, while a steeping motor 17 is provided in a generally epitrochoid pattern in a manner which will be described more fully hereinafter in connection with the description of the table 23 which is mounted on the base 11 and which carries the workhead 18.

The front surface of the column 12 is provided with ways 24 on which a plate 25 is vertically slidable. The wheelhead l3 and its associated equipment are mounted on this plate. The plate is suspended from cables 26 which pass over

pulleys

27 and 28 mounted at the top of the column 12, the other end of the cable being attached to a weight 29 located in the interior of the column.

means of

reed plates

57 and 58. The

reed plates

57 and 58 permit the ring 56 a degree of resilient normal motion .in a horizontal plane when the cam 38 is used to control the grinding. When generating, however, suitable stops are provided to lock the ring. The shaft 48 also has its upper part 49 carried in

bearings

59 and 61 and it is provided with a worm gear 62 by which it-is rotatably driven about the axis defined by these two bearmgs.

Spaced from the shaft 48 is a secondary shaft 63, rotatably carried in the second part 44 of the table by means of roller bearings 64 and 65. It also is provided with a worm gear 66 by which it is rotated in these bearings. The lower end of the shaft 63 is provided with a downwardly-extending cam follower 67 which is suitably carried in a passage between two guides 68 as will be described more fully hereinafter.

Mounted in the second part 44 is a motor 69 whose output shaft carries a gear 7'1. This gear engages a gear 72 which, in turn, engages a gear 73. The gear 73 drives a shaft and worm which. in turn. drives the worm gear 37, while the gear 72 drives another worm which en gages the worm gears 62 and 66, aswillbe described more fully hereinafter. 51 r FIG. 6 shows particularly well the way in which the various partsof the table 23 are slidably mounted on one another. As isevident in the'drawing, the bottom portion 43 issecurely bolted to the base 11 by means of bolts 74. It shows particularly well the construction of the

ways

52 and 53 that permit adjustment between the upper part 49 and the lower part 51 of the shaft 48. The third part 45 of the table is slidably mounted on'the second part 44 by means of the ways 75 and 76. It might besaid that the second part 44 is suspended from the third part 45 and hangs downwardly from it.In the same manner the third part 45 is suspended from its outer portion 77 by means of the bearings 47. The other portion 77 rests on upwardly-extending abutments of the bottom part 43. For instance, in the righthand side in the drawing (at the front in the grinding machine) the bottom part 43 is provided with an upwardly-directed abutment 78 having a flat upper sur face 79 on which the outer portion 77 slidably rests. At the other side the bottom part 43 is provided with an upwardly-directed abutment 81 having an upwardlydirected V-way 82 in which rests a similarly configured way 83 extending downwardly from the outer portion 77 of the third part 45.

In FIGS. 7, 8, and 9 are shown the details of the cam follower 39 on its arm 41. The arm 41 is of dove-tail construction and is slidably engaged in

dovetail ways

84 and 85 on top of the abutment 42. Its position is adjustable by means of a screw 86 threaded into the body of the abutment and having a head engaging a plate 87 extending downwardly from the outboard end of the arm 41.

FIGS. and 11 show the details of the top part 46 of the table 23 and showing the workhead 18 in place. First of all. the top part 46 is divided into relatively

adjustable parts

88 and 89 of which only part 89 is shown in FIG. 11. The manner in which 88 and 89 are adjustable relative to one another is best shown in FIG. 6. The lower part 89 is disc-shaped and carries the bearings 36, the gear 37. and of course, the workhead 18. The upper part 88 is provided with slots 91 and fastening bolts 92. In addition, a peg 93 extends downwardly from the upper part 88 into a groove 94 formed on the upper surface of the lower part 89 at one side of the parts. At the other side a similar peg 95 slides in a groove 96.

Parts

88 and 89 fit together to form the upper part 46 of the table. which is rotatably carried in the bearings 47 which. in turn. are carried by the third part of the table. This third part is shown in FIG. 11 and shows at one side its V-way 83 and on the other side the flat way 97, which is slidablc on the surface 79,

of the abutments 78 of the bottom part 43 of the table.

Suitable oil passages

98 and 99 are associated with the

ways

83 and 97. respectively, to provide them with bydrostatic oil. FIG. 10 also shows the manner in which the gear 73 operates a worm 101 to drive the gear 37 at the bottom of the workhead 18.

FIGS. 12 and 13 show the detailsof the second part 44 of the table which, it will be recalled. is suspended from the top part 46 by means of the ways 75 and 76. For that purpose, the secondpart 44 is provided with dovetails 102 and 103 along with a= gibl'04. Extending through the part 44 is a shaft 105, 'on oneend of which is mounted the gear 72 operating worms 106 and I07 which engage-and drive the worm gears 62 and 66, re spectively. The latter gears are, of :course, associated with the shaft 48 andthe shaft 63, respectively. The shaft is suitably mounted in bearings and the end plate 108 is shown in FIG; 13 as holding the entire assembly together. i 1

FIG. 14 shows the details of the bottom part 43 of the table 23. It shows the manner in which the block 56 retains the cylindrical portion 55 of the lower part 51 of the shaft 48. As is clearly-indi.cated, the block 56 is supported by leaf or

reed plates

57 and 58 whose other ends are connected to abutments 109 fastened to the bottom surface of the part 43. Suitable stops are provided selectively to limit (or to prevent altogether) the swinging motion of the block 56 on the resilient support provided by the-reed plates. Also clearly shown are the parallel spaced guides 68 which retain and guide the cam follower 67 associated with the shaft'63. At one side of the part 43 is the abutment 78 at the upper part of which are'provided the flat'surfaces 79 for supporting the pads or ways 97 associated with the outer portion 77 of the part 45. At the other side is the abutment 81 which carries the V-way which supports and guides the way 83 also associated with the part 45.

' FIGS. 15-21 show the details of the part 45 and the manner in which precautions have been taken to protect the interior of the table 23 from dust, dirt, and other by-products of the grinding operation. It is centrally provided with a large bore 111 with recesses above and below it for carrying the bearings 47. The details of this construction are shown in FIG. 17 where the recesses for the bearings 47 are indicated by the

reference numerals

112 and 113. FIG. 18 shows the V.-way 83, while FIG. 19 shows the pad 97.

i The operation of the grinding machine 10 will now be readily understood in view of the above description. First of all, the grinding machine 10,-shown in FIGS. 1 and 2, is operated in a more or less conventional manner. The abrasive wheel 15 on its spindle 14 is rotated in the wheelhead13 by means of the motor 20 which is of the twin-screw hydraulic type. It is moved axially along with-the plate 25 underthe impetus of the cylinder 16. The weight of the plate, wheelhead, etc, is taken up by the cables 23 operating over the pulleys 27 and28 and by use of the weight 29. Oscillatory motion of the abrasive wheel while operating against theworkpiece surface takes place .by means of the eccentric 34 operatedby the motor 35. In-feed motion of the abrasive wheel 15 takes place by means of the stepping motor 17, operating on the cross slide l6a forming part of the plate 25. Dressing takesplace by means of the dressing apparatus 31 which is selectively moved in and out of operative position by means of the gear 33 reacting with the rack 32. The normal feeding movement of the abrasive wheel 15 transversely of its axis is brought about by the stepping motor 17. All of these motions that have been described above are those that would be used in grinding an internal cylinder. Further motions are introduced by means of the table 23 to produce a non-circular shape in the workpiece to produce the epitrochoidal surface 22.

. With particular reference to FIGS. 5 and 6, there are two types of motions that take place in the table 23. First of all, there are the sliding and rotating motions which take place in every cycle in order to cause the abrasive wheel to form the proper surface in the workpiece. Secondly, there are the adjustments that can be made in the parts to produce the proper geometric relationship between the parts during an initial adjustment. FIG. 3 shows the manner in which various compensatory movements are added to the generation of the true theoretical epitrochoid in order to produce the desired shape and these are produced by continuous sliding variations introduced in various ways. The third part 45 of the table slides on the bottom part 43 in the plane of FIG. 5, while the rest of the table including the top part 46 and the second part 44, as well as the workhead l8, rotate inside of the third part 45 due to the presence of the large roller bearing 47. In other words, the workpiece which has been fastened to the workhead I8 is subjected to sliding motion due to the sliding between the part 45 and part 43 and to rotating motion or swinging motion due to its presence in the bearing 47.

The other type of motion, which is for adjustment, takes care of the problem of generating an epitrochoid 'as shown in FIG. 4. These are taken care of by the sliding motion between the upper part 49 and the lower part 51 of the shaft 48 whereby the eccentricity E is adjusted. The radius of the major or base circle R is adjusted by the adjustable sliding motion between the two

parts

88 and 89 of the part 46 of the table. The radius R of the minor circle is determined by the adjusted relationship between the second part 44 and the part 45 from which it is dependent; this adjustment takes place by virtue of the ways 75 and 76 engaging the dovetails 102 and 103, respectively.

Referring again to FIG. 5, the operation of the motor 69, operates through the

gears

71, 72, and 73 to operate the

worms

101, 106, 107 which, in turn, serve to operate the worm gears 37, 62, and 66. Understanding the operation of the table motion is easier if one understands that the shaft 63 and its rotation combine with the engagement of the cam follower 67 with the guide 68 only to reinforce the swinging motion of the part 46 about the main bearings 47 in addition to the swinging motion introduced by the main shaft 48. The rotation of the shaft 48 (which acts as a crank when E is other than zero) causes the entire upper part 46 of the table to slide along the

ways

79 and 82. The sliding motion is purely longitudinal and moves the workpiece toward and away from the grinding wheel axis in a straight line. Of course, at the same time that this motion is taking place, the workhead 18 is being rotated. The upper part 46 is being swung about the major axis presented by the bearings 47, so that the swinging action takes place in a harmonic manner. This is reinforced by the engagement of the cam follower with the guide 68 as the shaft 63 is being rotated. This causes the grinding wheel to maintain normalcy with the surface which it is grinding. The introduction of the cam 38 into the situation means that an over-ride movement is provided in the longitudinal direction, that is to say, movement of the entire upper part 46 along the

ways

79 and 82. This cam serves only the purpose of varying the shape of the epitrochoid slightly away from the theoretical shape to conform to manufacturers specifications. This may be necessary from practical considerations to provide better operation of the Wankel engine rotor within the housing chamber. An examination of FIG. 3 shows that the true epitrochoid is generated because of the fact that the workpiece is being rotated about the axis of the workhead 18 (as defined by the bearings 36), while at the same time, it is being moved longitudinally by the crank provided by the shaft 48. Next, the compensation for non-normality takes place by the swinging action of the upper part 46 about the major axis of the bearings 47 due to the operation ofthe shaft 48 and the shaft 63. The shape can be varied, in accordance with manufacturers specifications, due to the shape of the cam 38 and its engagement with the cam follower 39. The cam 38 is allowed to over-ride the motion due to the shaft 48 because of the fact that the block 56, which carries the cylindrical portion 55 of the lower portion of the shaft 48, is mounted in the resilient reed plates 57 and 58 (and these plates are released from their stops), so that the cam action tends to move the whole upper part 46 of the table backwardly in accordance with the shape of the cam. Finally, after all of these motions have been taken into consideration, the desired shape of the workpiece surface 22 is obtained.

Referring to FIG. 4, it can be seen that the true epitrochoid is obtained by the trace or locus of a point P as the minor circle rotates around the base circle. In the present machine the radius R, of the base circle is determined by adjustment of the two

parts

88 and 89 of the upper part 46 of the table. This has the effect of changing the distance between the center line of the bearing 47 and the center line of the workhead bearing 36. The size of the radius R of the minor circle can be adjusted by means of the adjustment between the

portions

44 and 45 of the table indicated in FIG. 5. It will be recalled that the portion 44 is suspended from the inner part of the portion 45 by means of the ways and 76 on the one hand and the

ways

102 and 103 on the other hand (as is seen in FIG. 6). Finally, of course, the eccentricity E can be changed by the ad justment possible between the upper and lower parts of the shaft 48. Adjustment of the portion 44 relative to the body 45, of course, changes the distance between the axis of the large bearing 47 and the axis of the hearing 59 in which the upper part of the shaft 48 is carried, while the adjustments between the upper and lower parts of the shaft 48 change the distance between the axis of the bearing 59 and the axis of the bearing provided by the ring 56 in which the lower portion 55 of the shaft 48 is carried. This, of course, has the effect of changing the amount of reciprocation of all of the

upper parts

44, 45, and 46 of the table relative to the bottom part 43. Because of the ratio of the gearing, the epitrochoid is formed with two lobes. Naturally, if the ratio of the gearing were changed to three-to-one, a three-lobe element would be obtained. When the present apparatus is used, if the eccentricity E is reduced to zero, it can be understood that the grinding wheel will generate a cylinder having a radius R plus R If, on the other hand, the eccentricity is changed so that E equals R then a cycloidal figure will be obtained which is tangential to the major circle at one point and is spaced from the major circle by the distance 2 R at a point from the tangent point. The intermediate position, where E is less than R gives the epicycloid form that is desirable in use with the Wankel housing.

One of the outstanding features of the present invention is that it is possible to adjust R and R to provide a desired workpiece surface. This means that the large cost of the machine is justified by the fact that the purchaser is not limited to a given set of epicycloidal dimensions. Furthermore, when the ring 56 is allowed to float on the floor of the bottom portion 43 of the table (by removing the stops which otherwise engage the ring and the reed plates 57 and 58), it is possible to bring the cam 38 into operation to determine the shape of the finished circle. Under these conditions in which manufacturers specifications or variations from the perfect epicycloidal form are introduced, it can be seen that the major portion of power for stock removal is still introduced through the main drive portions of the grinding machine. This is not affected by the fact that a smaller amount of additional movement is introduced by the cam 38. Since all of the driving power is introduced into the workpiece through the gearing and the shape of the surface is determined by the bearings and other elements which carry n'oneof the power introduction. the wearing of such power transmission gears does not affect the shape of the finished surface. It is possible, therefore, to use very high rates of stock removal. The problem of power introduction into the grinding cycle is an important one because most Wankel engines are plated with a very hard material before the finished surface is ground into it. This means that the grinding operation which is performed on the present invention is performed under the most adverse conditions. That is to say. not only is it desirable to remove as much stock as possible in a given time, but the stock that must be removed is of a very difficult nature to grind.

There are two basic principles being employed for machining the epitrochoidal surface in a Wankel engine. (a) cam following, and (b) generation. The subject invention deals with a machine that is uniquely arranged so that it can do both. Both principles have advantages and drawbacks. Cam copying has the advantage of accurate part-to-part duplication if the cam surface and follower interface stiffness can be made high enough (straight interface providing normalcy and contact over long contact line). However, the cam has to be made on another machine and corrections added by trial and error to compensate for errors due to machine dynamics. With a generator, especially of the type of the present invention, with prototype parts the engine parameters R". R and E can be adjusted and varied to machine housing with die-cast models or cams without requiring costly cams for other machines. When using the subject machine for cam following, the generator is used to maintain normalcy of wheel feed location and cam follower to trochoidal surface and, by means of a resilient member, to preload the cam and follower. One precision generator may be used to make the cam for many production machines and'the machines using cams would have a less accurate and less expensive generator to maintain normalcy and preload (the radial precision comes from the cam).

Because of the nature of the present construction. it is possible to build the grinding machine very ruggedly, so that the use of high stock-removal rates do not result in deflection of the grinding machine of such a nature as to decrease its accuracy in forming the desired surface, nor are there elements which wear sufficiently to introduce inaccuracy into the grinding operation. In the past, because of the limited power that it was possible to introduce into the workpiece. it was necessary to grind the surface with several passes of light stock removal. Because of the many grinding parameters entering the situation. it required highly skilled labor in order to perform this operation, particularly since the plating with the hard material results in a rough surface. Since the use of the present machine allows the grinding to reach finish size with a maximum of feed rate and extremely large grinding forces, the desired surface "can be reached within tolerance by a person having only moderate skill in the operation of a grind- 5 ing machine.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come with the scope claimed.

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

l. A machine tool for generating an epitrochoidal surface, comprising a. a base,

b. a column extending upwardly from the base,

c. a toolhead mounted on the column and including a vertical spindle on the lower end of which is mounted a tool,

d. means for moving the toolhead relative to the column in a vertical and a horizontal direction,

e. a workhead mounted on the base and capable of holding a workpiece on which the said surface is to be generated by the tool, the workhead moving the workpiece horizontally relative to the spindle in an epitrochoidal pattern, the workhead including:

1. a table mounted on the base for sliding motion in a first horizontal direction,

2. a workpiece platen mounted on the upper part of the table for rotation relative thereto about a vertical major axis,

3. a shaft mounted on the lower part of the table for rotation about a minor axis, the lower end of the shaft being formed with a cylindrical stub which is rotatably carried in a bushing mounted on the base, the axis of the said cylindrical stub being displaced from the said minor axis, and

f. a cam means mounted on the workpiece platen for overriding, on occasion, the sliding motion of the table produced by the said shaft.

2. A machine tool as recited in claim 1, wherein the shaft is formed as an upper part which is rotatably carried in the table and a lower part which has the cylindrical stub, the upper and lower parts being slidably joined for lateral movement to adjust the amount by which the stub axis is displaced from the minor axis.

3. A machine tool as recited] in claim 1, wherein the table is formed as an upper part which carries the platen and a lower part which carries the shaft, the upper and lower parts being slidably engaged for adjustment of the distance between the major axis and the minor axis.

4. A machine tool as recited. in claim 3, wherein the table is provided with an intermediate part having an upper portion slidably engaging the upper part of the table for relative adjustment therebetween and having a lower portion slidably engaging the lower part of the table for relative adjustment therebetween.

5. A machine tool as recited in claim 4, wherein the intermediate part of the table is rotatably mounted in a bearing ring which, in turn, is slidably mounted on the base for movement in the said first direction.

6. A machine tool as recited in claim 5, wherein a motor is mounted on the table for causing the rotation of the shaft end of the platen.

7. A machine tool for generating a surface similar to an epitroehoid on a workpiece by means ofa tool, comprising: I Z,

a. a bottom part, b. an intermediate part slidably mounted on the bottom part for movement in a straight line, c. a top part mounted on the intermediate part for rotation relative thereto about a first axis, d. a workhead for carrying the workpiece mounted I on the top part for rotation relative thereto about.

a second axis parallel to and spaced from the said first axis,

e. a shaft having an upper part journaled in the top part and a lower part journaled in the bottom part, the axes of the upper and lower parts being spaced

Claims

1. A machine tool for generating an epitrochoidal surface, comprising a. a base, b. a column extending upwardly from the base, c. a toolhead mounted on the column and including a vertical spindle on the lower end of which is mounted a tool, d. means for moving the toolhead relative to the column in a vertical and a horizontal direction, e. a workhead mounted on the base and capable of holding a workpiece on which the said surface is to be generated by the tool, the workhead moving the workpiece horizontally relative to the spindle in an epitrochoidal pattern, the workhead including: 1. a table mounted on the base for sliding motion in a first horizontal direction, 2. a workpiece platen mounted on the upper part of the table for rotation relative thereto about a vertical major axis, 3. a shaft mounted on the lower part of the table for rotation about a minor axis, the lower end of the shaft being formed with a cylindrical stub which is rotatably carried in a bushing mounted on the base, the axis of the said cylindrical stub being displaced from the said minor axis, and f. a cam means mounted on the workpiece platen for overriding, on occasion, the sliding motion of the table produced by the said shaft.

3. a shaft mounted on the lower part of the table for rotation about a minor axis, the lower end of the shaft being formed with a cylindrical stub which is rotatably carried in a bushing mounted on the base, the axis of the said cylindrical stub being displaced from the said minor axis, and f. a cam means mounted on the workpiece platen for overriding, on occasion, the sliding motion of the table produced by the said shaft.

3. A machine tool as recited in claim 1, wherein the table is formed as an upper part which carries the platen and a lower part which carries the shaft, the upper and lower parts being slidably engaged for adjustment of the distance between the major axis and the minor axis.

4. A machine tool as recited in claim 3, wherein the table is provided with an intermediate part having an upper portion slidably engaging the upper part of the table for relative adjustment therebetween and having a lower portion slidably engaging the lower part of the table for relative adjustment therebetween.

7. A machine tool for generating a surface similar to an epitrochoid on a workpiece by means of a tool, comprising: a. a bottom part, b. an intermediate part slidably mounted on the bottom part for movement in a straight line, c. a top part mounted on the intermediate part for rotation relative thereto about a first axis, d. a workhead for carrying the workpiece mounted on the top part for rotation relative thereto about a second axis parallel to and spaced from the said first axis, e. a shaft having an upper part journaled in the top part and a lower part journaled in the bottom part, the axes of the upper and lower parts being spaced from each other and parallel to the first and second axes, f. a motor producing rotation of the shaft and of the workhead, and g. a drive producing eccentric movement of the top part about the said first axis to maintain normalcy between the tool and the workpiece surface, the top part being formed in two slidably-connected parts for adjustment of the distance from the first axis to the axis of the upper part of the shaft, the upper and lower parts of the shaft being slidably connected for adjustment of the distance between their axes.