US2844137A - Mechanism for generating the helical thread on grinding worms for gear grinding machines - Google Patents

Description

y 22, 1958 I A. RICKENMANN 2,844,137

MECHANISM' FOR GENERATING THE HELICAL THREAD ON GRINDING WORMS FOR GEAR GRINDING MACHINES Filed Sept. 17, 1956 5 Sheets-Sheet 1 ly 1958, A. RICKENMANN 2,

a MECHANISM FOR GENERATING-THE HELICAL THREAD on v GRINDING WORMS FOR GEAR GRINDING MACHINES 1 Filed Sept. 17, 1956 3 Sheets-Sheet 2 fi 1? R9 /JW wk I N 5 E NE July 22, 1958 I4QICKENMAN N 2,844,137 ING THE HELICAL THREAD ON GEAR GRINDING MACH s MECHANISM F0 Sheets-Sheet 3 A R GENERAT GRINDING WORMS FOR Fig. 5

Filed Sept. 17, 1

MECHANISM FOR GENERATING THE HELICAL "THREAD ON GRINDING WORMS FOR GEAR GRINDING MACHINES Alfred Rickenmann, Kusnacht, nearZurich, Switzerland, assignor to Reishauer-Werkzeuge A. G., Zurich, Switzerland Application September 17, 1956, Serial No. 610,132 Claims priority, application Switzerland June 11, 1956 2 Claims. (Cl. 12511) The present invention relates to gear grinding machines operating according to the generating principle, and has the general object of producing accurate grinding worms for such grinding machines.

The grinding worm used as the grinding tool in gear grinding machines of the kind referred to is mounted on the grinding spindle of the gear grinding machine and has a tooth rack profile in the section perpendicular to the helix angle. The dimensions thereof as regardsthe pressure angle and pitch correspond normally to the basic rack profile of the toothing to be ground. In order to be able to grind gears on gear grinding machines of the kind referred to which gears are to have high accuracy of profile it is an indispensable necessity that the portions of the grinding worm which are active in the grinding process are dressed with outstanding accuracy for the working operation. a The present invention has the'special object of producing a pitch of the helical thread of the highest possible accuracy and freedom from wobble. Accordingly it is not directed to the'devices required for the finishing of the flanks. of the grinding worm as required for the dressing of for example straight profile flanks, but exclusively to the mechanism which guides such devices over the helical thread of the grinding tool. Ever since gear grinder machines operating according to the generating principle have been" made, a lead screw withlead screw nut have been used' for the production of the helical thread of the grinding worm. The drive of the lead screw is effected from the spindle on which the grinding worm to be dressed is mounted, through various transmission elements including a change gear train. The latter is selected in accordance with the pitch to'be produced. The lead screw nut is in a direct con-' nection to a carriage which carries the dressing .device proper. This carriageis displaced during the dressing operation parallel tothe axis of the spindle at a speed which is accurately determined by the rotational speed and by the pitch of the grinding worm to be generated.

"Ihe accuracy attainable in these conditions of the pitch of the grinding worm depends on the accuracy of the machine components forming part of the transmission mechanism described hereinabove. If very accurate grinding worms are to be produced-as required for the grinding of first class gearsattention is called in the first place to the use of accurate lead screws, lead screw nuts and gears which must comply with high requirements in true-running and pitch.

-It is well known in the art that in spite 'of fulfilling all these detail requirements the accuracy desired is.in many cases not attained, which means that the present standing of.the art does not permit to keep below certain tolerances. It is to be remarked that the errors still existing ice on the grinding worm are caused by a sum of separate errors. The following sources of errors are to be mentioned in the first place:

(1) Run-out errors of the change gears.

(2) Accumulative and adjacent pitch errors of the change gears.

(3) Pitch errors of the lead screw.

(4) Wobbling errors of the lead screw.

(5) Faults in the axial bearings of the lead screw.

The Wobbling errors of the lead screw is the deviation. of the actually existing helix from the theoretical helix.

(the development of which is a straight line), Within one helical turn. It happens frequently that the lead screw checked in one plane of measuring has an excellent pitch accuracy but is on the other hand fraught with Wobbling errors, the magnitude of which exceeds the pitch error ascertained in the aforesaid plane of' measuring.

Of necessity the sources of errors mentioned hereinabove make themselves felt somehow. It is quite possible that various faults may add up during one working phase, and on the other hand may partly compensate one another. The result on the finished profiled grinding worm consists in that errors of different magnitude are to be found. When then the problem is set to reduce the errors still present this can be attained with the means hitherto known only in that elements of machinery are used which are practically free from any faults. quently gears and lead screws of extraordinarily high accuracy have to be fitted. The production thereof would involve such extraorbitant costs that they would hardly be bearable economically.

grinding worms in question can be made at narrower tolerances than hitherto without requiring the machinery elements of the dressing mechanism to have abnormally high accuracy. The idea of the invention consists in that the displacement imparted by the lead screw to the lead screw nut per revolution of the grinding worm amounts to a multiple of the pitch of the grinding worm to be generated, and that the longitudinal movement of the lead screw nut is transmitted by means of a lever transmission to the carriage designed for accommodating the dressing device and is at the same time reduced at the ratio of the aforesaid multiple. the invention the errors transmitted from the lead screw to the dressing tool are of necessity reduced by the aforesaid multiple.

The invention will be explained hereinafter with reference of an embodiment illustrated by way of example. The dressing mechanism in question can either be built Fig. 1 is a plan view of a dressing mechanism in sec-.

tion'on the line II of Fig. 2, with diagrammatic partillustration of the hydraulic control;

Fig. 2 is a cross-section of the dressing mechanism on the line IIII of Fig. 1;

Fig. 3 is a detail of the dressing mechanism in section on the line III-III of Fig. 1;

Fig. 4 is a part-view from the left in the direction of the arrow IV of Fig. 1;

Fig. 5 is a cross-section of the dressing mechanism on the line VV of Fig. 1;

Conse- 7 By this measure according to- 3 Fig. 6 is a cross-section of the dressing carriage on the line VIVI of Fig. 1;

Fig. 7 is a side-elevation within the part portion marked VIIVII of Fig. 1;

Fig. 8 is a detail of the control-mechanism in section on the line VIIIVIII of Fig. 6.

Construction of the mechanism for the production of grinding worms The casing 1 which is closed laterally by a lid 3 carries a motor 9 attached to it by means of a flange. The motor shaft 20 thereof is coupled by means of a sleeve 10 to a shaft 4 which is in turn rotatably journalled in ball bearings in the casing 1 and lid 3. The shaft 4 carries two gears 11, 12 which are keyed to it. The gear 11 is in mesh with an idler gear 15 which meshes also with a gear 13. The idler gear 15 is rotatably journalled in the lid 3 and in a bearing arm 1005 of the casing 1. The gear 12 is in mesh with a gear 14. The two gears 13, 14 are each rotatably journalled in two ball bearings 19, 24, respectively, on a shaft 5. Their longitudinal position on the shaft is determined by the two end faces 1301, 1401, the aforesaid ball bearings 19, 24, the intermediate rings 27, 28 and circular spring clips 25, 30. The shaft 5 is likewise journalled rotatably on ball bearings in the casing 1 and in the lid 3. It carries in addition to the aforesaid gears 13, 14 the lamellae-clutches 16, 17 respectively associated with them, the clutch sleeve 18 slidably mounted there between, and the two gears 40, 50. The clutch sleeve 18 is provided with a groove 181 into which two slider blocks 29 (Fig. 2) are fitted. The latter are pivotally mounted on two pins 26 fixed in the double lever 32. The double lever 32 is pivotally mounted on an axle 22 vertically fitted into the casing 1. The forked arm of this lever is connected to a piston 37 (Fig. 1) by a pin 33 which is retained in the piston rod 36. This piston is slidably fitted into the casing 1. The gear 40 is in mesh with a gear 41 keyed to a spindle 6. The latter is likewise rotatably journalled in the lid 3 and casing 1, the longitudinal positioning being effected by the two end faces 411, 601. On the conical end 602 of the said spindle a flange disc 46 is mounted which is arrested by a screw 44. The flanged disc 46 carried arworm of abrasive materialhereinafter referred to as the grinding worm 45-which is clamped on irnmovably by the aid of a counter flange 47 and of screw 48. The grinding worm is of a single start right hand thread and has in the section perpendicular to the helix angle a toothed rack profile corresponding to that of the basic rack. A helical thread of the pitch s is to be generated on the grinding worm 45.

The gear 50 keyed on the left hand side end of the shaft 5 forms with the gears 62, 63, 64 four-partite change gear set which is to be selected and inserted in accordance with the pitch to 'be generated on the grinding worm 45 (see Fig. 4). The slotted bracket 53 of this change gear set is pivotally mounted on a bushing 49 fixed to the lid 3, and can be fixed in the position desired by means of a screw 54. The two gears 62, 63 are keyed to a bush 60 which is in turn rotatably journalled on a distance sleeve 59 mounted on the pin 57.

The last one, 64, of the said four change gears is keyed to the left hand side end of the lead screw 7, which is rotatably mounted, parallel to the shaft 6, in the casing 1 and lid 3. It is positioned in the longitudinal direction by the end face 701 and the nut 69. The lead screw nut 70 mounted on the threaded portion 702 has a rib 705 (Fig. 2) which is fitted accurately into the longitudinal groove 1001 running parallel to the axis of the lead screw in the casing 1. By this measure the said guide spindle nut 70 is restrained from rotating. On top of the said nut there is a transverse groove 706 into which a slider block 81 is fitted slidably. The latter is on the other hand pivotally centered on the cylindrical end 771 of a pin 77 which is screwed into the lever 75. This lever 75 is keyed to an axle 74, which is rotatably mounted in the casing 1 .4. about a vertical axis, and is provided with a second pin 76. The protruding end 761 of the latter pivotally carries a slider block 82 which is fitted slidably into a transverse groove 711 of a cross piece 71. The latter is attached to a shaft 8 by means of a conical pin 72.

A rib 712 arranged on the cross piece 71 engages into a groove 1002, which runs accurately parallel to the axis of the shaft 8. The shaft 8 is guided longitudinally slidably in the lid 3 and in the casing 1. The right hand side end (Figs. 1 and 5) of the shaft 8 which protrudes beyond the casing 1 is screwed to a spindle 84. Thelatter is rotatably journalled in a carriage 85, and a gear 86 is keyed to it, which in turn meshes with a gear 87. The latter, as well as a hand wheel 39 are keyed on a shaft 88 which is likewise journalled in the carriage 85. By turning the hand wheel 39 the position of the carriage can be adjusted which serves in the first place for adjusting the dressing tool to an existing thread of the worm. The carriage 85 is slidably fitted on the two guide ways 1003, 1004 (Fig. 6). It carries an upper carriage 90, the guide ways 901, 902 (Fig. 5) of which are arranged at right angles to those of the carriage 85. On the top face 903 of said carriage 90 the dressing tool 98 is attached. In the present case it has the shape of a turning tool the profile of which corresponds to that of the gap of a toothed rack. The dressing tool 98 is held fast by means of a clamp 94, and .is clamped against the top face 903 by the aid of a screw and nut 96.

Obviously quite diiferent means could be used for dressing the grinding worm 45, for example a crusher, or a device provided with two dressing tools, each of which operates on one of the two flanks of the grinding worm.

In the upper carriage 90 there is a bore 904 which runs parallel to the guide ways 901, 902 and houses a piston 99. The latter is restrained from rotating by a screw 102 engaging a groove 993, and is screwed to a threaded spindle 106, which is guided and rotatably journalled in the carriage 85. A band wheel 107 connected to said spindle serves for adjusting the dressing tool 98 in the radial direction.

In order to demonstrate the manner of operation of this dressing mechanism, a hydraulic control system is shown in the present embodiment. The same comprises a gear pump 122 (Fig. 1) which feeds pressure oil from a sump 123 into a pipe 124. The oil pressure is controlled by a relief valve 125, while the overflowing oil can be drained to the said sump through a pipe 126. The pressure pipe 124 is connected to a valve (Fig. 7) which is in turn in communication with the main control piston 37 and with the piston 99 through various pipes.

Working process As the starting point for the following explanations the conditions of operation may be chosen as illustrated in the Figs. 1 to 8.

The motor 9 drives, through the clutch sleeve 10, the shaft 4 with the two gears 11,.12.

Since the chamber 371 is connected by the pipe 128 and the chamber 1192 (Fig. 8) to the pressure oil pipe 124, while the chamber 372, which is closed by the lid 38, is connected by the pipe 127 and the chamber 1191 to the drain pipe 129, the piston 37 is movedto the left (Fig. 1). This has the consequence that to the double lever 32 a force or anti-clockwise torque is applied, and accordingly the clutch sleeve 18 is forced to the right (Fig. 1). In these conditions the clutch 17 is engaged, and accordingly the shaft 5 is driven from the gear 12 by the gear 14 in mesh therewith. The gear 13 connected to the clutch 16 which is set in rotation by the gear 11 through the idler gear 15, runs idly. From the shaft 5 the rotary motion is transmitted on the one hand by the pair of gears 40, 41 to the spindle 6 and to the grinding worm 45 fixed thereto, and on the other hand through the four change gears 50, 62, 63, 64 to the left hand thread lead screw'7. The rotation of the lead screw 7 causes a displacement of the nut 70'towards the left (Fig. 1). Of necessity this displacement effects through the slider block 81 (Fig. 2) a rotary motion in the anti-clockwise direction of the lever 75' (Fig. 1). During this rotational movement the slider block 82 centered by the pin 76 carries the cross piece 71 and the shaft 8 connected without play therewith likewise along to' the left. Through the threaded spindle 84 (Fig. 5) screwed to the shaft 8 this displacement is imparted to-the carriage 85 and ac cordingly also to the carriage 90 and lthe dressing tool 98 fixed thereon, which partake therein. The upper carriage 90 is in the working position. The chamber 991 (Fig. 6) which is in communication through the pipe 103 to the pipe 128 which at this moment carries pressure oil, and accordingly this chamber is under pressure. The carriage 90 is forced so far in the direction towards the grinding worm 45 until the lid 105 screwed to it abuts on the piston 99. The chamber 992 is in communication with the drain pipe 129 through the pipes 104, 127 and the chamber 1191 (Fig. 8). In these conditions the carriage 85 and the upper carriage 90 move to the left together with the dressing tool 98 (Fig. l). The latter produces the desired helical thread on the rotating grinding worm 45.

In the embodiment illustrated by way of example the single start grinding worm 45 has a pitch s. Consequently the dressing tool 98 and the components 90, 85, 84, 8, 71 connected thereto have to displace themselves towards the left (Fig. 5), exactly the amount of the pitch s per one revolution of the grinding worm 45. In order to attain this displacement of the magnitude s on the shaft 8, the lead screw nut 70 has to perform a movement S (Fig. l). The magnitude thereof is accurately determined by the proportion s:r=S:R or the equation If it is further assumed that R=x.r, the above equation can be rewritten S=x.s

Owing to this lever transmission the faults existing and effective on the lead screw (errors in pitch, wobbling errors etc.) are not transmitted in their full magnitude to the shaft 8, the dressing tool, 98 and to the grinding worm 45, respectively, but to an extent reduced by the ratio x. Consequently it is possible in this manner to generate on the grinding worm 45 a helical thread which is very accurate as regards pitch and freedom from wobble, with out the necessity of using an excessively accurate lead screw 7, the production of which would hardly be economically bearable.

The stroke described of the dressing tool 98 to the left (Fig. 1) comes to an end when the stop 112 attached to the carriage 85 abuts on the reversing lever 115 (Figs. 6 and 7) and turns the same as well as the shaft 116, journalled in the casing 1, and the lever 117, in the anti-clockwise sense. Consequently the pre-con-trol piston 119 (Fig. 8) is moved towards the right, until it abuts on the lid 121. As soon as this, has happened, pressure oil can pass from the pipe 124 through the chamber 1192 into the pipe 127. Consequently the chamber 992 (Fig. 6) which is closed by the lid 105 and is in communication with the pipe 127 through the pipe 104 is filled with pressure oil. At the same time the chamber 991 is discharged, which is connected to the drain pipe 130 through the pipes 103, 128 and the chamber 1193 (Fig. 8). The carriage 90 and the dressing tool 98 fixed thereon are pushed back a distance H (see Fig. 6) away from the grinding worm 45. Moreover. pressure oil flows also into the chamber 372 (Fig. 1), while oil contained in the chamber 371 can flow off through the pipe 128 and the chamber 1193 (Fig. 8) into the drain pipe 130. The piston 37 (-Fig. 1) consequently moves towards the right and turns the lever 32 in the clockwise direction. Thereby the working stroke clutch 17 is disengaged, the

the latter .as well as the lead screw 7 change their senseof rotation. This change of sense of rotation has the effect that the lead screw nut is carried at once to the right (Fig. 1) while the lever begins to turn in the clockwise direction. To this rotational movement forcibly a displacement towards the right of the cross piece 71 and of the shaft 8 is co-ordinated, in which also the spindle 84, the carriage and the upper carriage with the dressing tool 98 have to partake. At the end of the return stroke the abutment 111 fixed to the carriage 85 (Fig. 7) bears on the reversing lever 115 and turns the same, the shaft 116 and the lever 117 in the clockwise direction. The valve 119 connected to the latter is accordingly moved towards the left into the position illustrated in Fig. 8. As soon as this displacement has been carried out, there 1s communication through the chamber 1192 between the pressure pipe 124 and the pipe 128. Pressure oil flows from the latter through the pipe 103 straight into the chamber 991 (Fig. 6) and moves the upper carriage 90 with the dressing tool 9 8 into the working positron. The oil contained in the chamber 992 is returned to the sump 123 (Fig. 1) through the pipes 104, 127 and the chamber 1191 (Fig. 8). The chamber 372 is likewise discharged over the same system of pipes. On the other hand pressure fluid penetrates now through pipe 128 into the chamber 371 and moves the piston 37 towards the left, which entails at the same time a rotary movement of the lever 32 in the counter-clockwise direction, and a displacement of the clutch sleeve 18 towards the right. Thereby the connection with the return stroke clutch is broken, and the working stroke clutch 17 is engaged. As soon as the reversal control movements described hereinabove are terminated, exactly the same conditions prevail in the whole mechanism and in the hydraulic control sys tem as those which had been chosen the starting point of the descrpition of the working process. The grinding worm 45 turns in the direction indicated in Fig. 1, and the carriage 85 with the upper carriage 90 and the dressing tool 98 move at working speed from right to left.

What I claim as myinvention and desire to secure by Letters Patent, is:

l. A mechanism for generating the helical thread on grinding worms for gear grinding machines operating according to the generating principle, comprising in combination: a base, a spindle journalled in the said base, and in operation carrying the grinding worm to be dressed, a driving mechanism comprising reversing clutch means mounted in said base and in operation coupled to the said spindle, a lead screw mechanism mounted in the said base parallel to the said spindle and comprising a threaded lead screw and a lea-d screw nut in screw engagement with one another, transmission means journalled on the said base and rotationally coupling the said lead screw mechanism to the said spindle, a dressing carriage mounted on the said base slidably in a direction parallel to the said spindle, a dressing means proper mounted on the said dressing carriage, lever means pivoted on the said base and engaging the said lead screw mechanism with a larger lever arm .and the said dressing carriage with a smaller lever arm transmitting axial movement from the said lead screw mechanism to the said dressing carriage at a reduced ratio, adjustment means adapted to adjust in operation the said dressing means proper in a direction perpendicular to the said spindle, and an automatic control system responsive to the position of the said dressing carriage and operatively connected to the said reversing clutch means and to the said adjustment means, sequentially operating the same,

the chambers of the said cylinders on opposite sides of the said pistons being. alternately connected by the said valve to the said pump and to "thetsaid sump.

References Cited in the file thisp'atent UNITED STATES PATENTS 2,286,045- Wickr'nan June 9, 1942 FOREIGN PATENTS 722,871 Great Britain Feb. 2, 1955 879,639 Germany Sept. 27, 1954

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