US3102528A

US3102528A - Grinding wheel truing mechanism for precision grinding machines

Info

Publication number: US3102528A
Application number: US57706A
Authority: US
Inventors: Bertram H Steinhard
Original assignee: Cincinnati Milling Machine Co
Current assignee: Milacron Inc
Priority date: 1960-09-22
Filing date: 1960-09-22
Publication date: 1963-09-03
Anticipated expiration: 1980-09-03
Also published as: GB904085A

Description

Sept. 3, 1963 B. H. sTElNHARD 3,102,523

GRINDING WHEEL TRUING MECHANISM FOR PRECISION GRINDING MACHINES Filed Sept. 22, 1960 3 Sheets-Sheet 1 t \RW S TIN mw n N/ m N i H m uw@ WN am VT ew m A m W www @S @ww e D W f 1, Il. im ,1:2 Gf .e n. enf/? -L Le- N \\w l m3 NQ m NQ obl w NU En@ N v we om Sept. 3, 1963 B. H. STEINHARD 3,102,528

GRINDING WHEEL TRUING MECHANISM FOR PRECISION GRINDING MACHINES Filed Sept. 22, 1960 3 Sheets-Sheet 2 w .H J mw m NE D x, m m /G m wf Il "B f,

. v JXQ w@ u mw WM@ /\,hm\ n IV QS 2. M MANIF@ Sept 3, 1963 B. H. STEINHARD 3,102,528

GRINDING WHEEL TRUING MECHANISM FOR PRECISION GRINDING MACHINES Filed Sept. 22, 1960 3 SheeS-Sheel'. 3

INVENTo-R. BER T/P/JMH. STE/NH/RD y MTTURNEYS United States Patent O 3,102,528 GRENDING EL TRUING MECHANESM FOR PRECISXN GRHNDENG MACHINES Bertram H. Steinhard, Cincinnati, (Ehio, assigner to The Cincinnati Milling Machine Company, Cincinnati,

Ohio, a corporation of Ohio Filed Sept. 22, 1960, Ser. No. 57,706 7 Claims. (Cl. 12S- 11) This invention relates to a grinding wheel truing mechanism for a precision grinding machine.

In a grinding machine to be Iused in grindingan arcuatev shape such as a 4ball track in the :inner race of an annular bearing, the grinding machine must be equipped with a truing mechanism that will ,give the proper grinding wheel contour for the job. It is sometimes necessary to true a 180 degree arc of a circle, particularly in grinding machines designed `to finish parts to be nsed in extremely small bearings commonly classed in the miniature category. It is common practice to swing the truing tool in an arc such that in the parked or terminal position, the truing tool is clear of the grinding Wheel. When truing a 180 radius, however, or an arc each end of which is tangent to a surface of the wheel, the truing tool is left in contact with the grinding wheel at the end of the truing pass. With such continued contact during the grinding operation, the grinding wheel would become glazed and dull along the line of contact with the truing tool. The truing tool would be subjected to lexcessive heating by prolonged contact with the grinding wheel which might cause fracturing. It fracture should not occur, the tuning tool would nevertheless -be subjected to unnecessary abrasion tending to dull it and to reduce its efficiency as a truing tool. The same problem is encountered in truing devices wherein it is desired to true a complex contour including an arc of less than 180` degrees but which is is tangent to one side of the grinding Wheel, that side being the one on which the truing tool is normally parked at the end of a truing cycle.

In the preferred form of this invention, the truing mechanism has three motor means. One provides the swinging movement of the truing tool necessary to true an arcuate shape" on the periphery of a grinding Wheel. Another provides a fixed stroke to advance and retract the truing tool relative to the periphery of the grinding wheel to eliminate contact between the truing tool and the grinding wheel during the grinding operation. The third motor means provides movement of the truing mechanism, including the swinging and ixed stroke motors, toward the grinding wheel during machine use to account for the reduced diameter of the grinding wheel as it is trued and worn away.

It is therefore an object of this invention to furnish a truing mechanism that may be used to true a 180y degree radius, or other radius tangent to a Isurface of a lgrinding wheel, on the periphery of a grinding wheel, the mechanism including means to remove the truing tool from grinding Wheel contact at an end of the inal radial swing of the tool.

yIt is a further object to provide a mechanism which gives a fixed retraction stroke in a truing mechanism A,that is independent of the arcuate motion of the truing tool and of the compensation movement accounting yfor grinding wheel attrition.

Still another object is to provide a retraction mechanism in a truing attachment that gives rigid truing tool support in the advanced position to give accurate grinding wheel contouring.

Other objects and advantages of the present invention should be readily apparent by reference to `the following specification, considered in conjunction with the accompanying drawings form-ing a part thereof, and it is to be 2 understood that .any modifications may be made in the exact structural details there shown and described, within the scope of the appended claims, without departing -from or exceeding the spirit of the invention.

A clear understanding of the construction and operation of the mechanism can be obtained from the following detailed description and the attached drawings wherein:

FIG. 1 is a sectional View of a grinding machine wheelhead.

FIG. 2 is a section of the wheelhead of FIG. 1 on line 2*2. y

FIG. 3 is a-section of FIG. 1 on line 3 3.

FlG. 4 is a section of FIG. l online 4 4.

FIG. 5 is a sectional view of a compensation motor.

FIG. 6 is a schematic hydraulic circuit.

The :section views in FIGS. l and 2` show a grinding machine wheelhead 10. Fixed to the wheelhead by bolts 12 is a V-slide 14 received in the V-way 16 in the machine base 18. The wheelhead is movable toward and away from a workpiece (not shown) by a feed `mechanism (not shown) to effect abrasive contact between the rotatable grinding wheel 20 mounted in the wheelhead 1t)l and the workpiece.

Located in the wheelhead 10 behind the grinding Wheel 2d is a radius tru-ing mechanism. A diamond nib 22 is carried by a yoke 24 which is pivotally receive-d in a bracket 26. The yoke is pivotal on balls 28, 3d which are received between pins y32, 34, fixed in the yoke 24, and ball seats 36, 38, respectively, fixed in the bracket 26. The pins 32, 34 are received, respectively, in annular bearings 40, 42 Ifor rotation relative to the bracket 26 when a pinion lgear 44, iixed on the pin 34, is rotated by operation of a pair of plungers46, 48.

In FIG. 3, the plungers `46, 48 are shown as having rack portions engaged with the pinion 44 on the top of the pin 34 (FIG. l). The lengthof the stroke ofthe

plungers

46, 48 determines the length of arc through which the yoke 24 and diamond nib 22 (FIG. l) are swung. The stroke is variable by adjustment of screws 50J 52 which are rotatably adjustable relative to the bracket 26. Rotation of the screws 50, 52 causes nuts 54, 56 to move along the axis of the screws (the nuts are prevented Jr'rom rotating by means not shown). These nuts 54, 56 are stops, the position of which determines the length of the stroke of the

pliungers

46, 48 and consequently the amount of angular movement of the pinion 44 which is iixed to rotate the yoke 24 in the bracket 26. .Each of the screws 50, 52 has a retainer 7G, `'72 xed thereto in which a damping spring '74 is received and held therein by caps 58, 60'.

The stop `screws 50,52 are received through the caps 58,

6d for limited longitudinal movement. The amount of this movement is ydetermined by the amount that the retainers 70, 72 are allowed to move between the caps 58,

6i) and shoulders 62, 64 in the

bores

66, 68. The springs 58, 6d decelerate the movement of the plungers `46, 48 as they reach the end of a stroke and move the screws 50, 52 through theirV limited longitudinal movement, to prevent sudden stopping of the movement `of the plungers which would cause vibrations in the truing yoke 24 and bracket 2,6, the vibration-s causing adverse truin-g conditions.

FIGS. l and 2 show that Ithe bracket 26 is xed to a slide member 76 by bolts 78. The slide member 76,v the bracket 2n, and the yoke 24- together comprise a truing tool carriage. The slide member '76 is longitudinally movable toward and away from the grinding `wheel 20 on balls received in ball tracks between the slide member 76 and rails d2, $4 which are xed by bolts 86 to a channel member S8. rilhe channel member dity is iixed tothe wheelhead iii by bolts 9d. A cover plate 92 covers the slide member 76 on one side and exible accordionpleat covers 94, 913 enclose the slide member 'i6 between the bracket 26 and the channel member 88 and between v tively.

pinions 182, |104 (FIG. 4) are received in the cage mem-l bers 98, and engaged with racks 106, 108, respectively, fixed to the rails `82, 84 and racks 1111, 112 fixed to the slide member 76. As the slide member 76 moves,

the pinion 104 is rolled and carries the cage member 100 along one half of the distance that the slide member 76 moves. This prevents the improper positioning of the balls `80 and cage member 1110 during machine operation due to slippage of the balls rather than rolling motion only. The other cage member 98 and the pinion 182 operate in the same Way. t

FIG. 1 shows the mechanism by whichpthe carriage supporting the truing tool 22 is moved toward and away from the grinding wheel i -to eliminate and provide, respectively, clearance therebetween. At the rear end of the slide member 76 is a multi-diameter cylinder bore 114. Received in the. bone is apiston 116 which is threadedlyengaged 'with a screw 118. The screw 118 is rotatable relative to the wheelhead 18' on a bearing 120, but is not movable along its longitudinal axis relative to the wheelhead 10. The piston 1116 then is fixed relative to the `wheelhead 10 and the slide member 76 moves relative to the piston. A flange plate 122 is iixed to the end of the slide member 76 by bolts 124 The piston -116 extends through Ithe iiange plate 122. An aligning plate 126 is fixed to the piston 116 at its rear end. Extending from the aligning plate 126 is a pin '128 which is received for longitudinal movement through the iiange plate 122. Since the slide member 76 is longitudinally movable relative yto the piston 1116, the flange plate 122 moves relative to the aligning plate 126. The flange plate 122 cannot rotate however, being iixed to the slide member 76 which is received only for'longitu-dinal movement toward and away from the grinding wheel 28. The pin 1.28 then prevents the ali-gning plate 126 and piston 116 from rotating.

The rearward movement of the flange plate 1-22 is stopped by a spacer `138 received on the piston 116 between the flange plate 122 and the aligning plate 126. The fonward movement of the flange plate 122 is stopped by a shoulder 132 on the piston 116. This amount of movement is a fixed amount. v(The movement can be altered by changing the thickness of the spacer 138.) Nor- K mally, the flange plate 122 is held against the spacer 138 by a spring 134 which is received between the flange plate 1-22 and a shoulder 136 on the piston 116. When iiuid runder pressure is introduced into the forward portion of the cylinder bore '114 from a fluid passage 138, the reaction forces between the forwardvend or" the cylinder bore 114 and the piston 1116 causes the slide member 76 to move lforward toward the grinding wheel 2t)` until the flange plate 122 engages the shoulder 132. The spring `134 is compressed. When thefluid pressure is relieved,

der bore 114, a snap ring 144 prevents the plunger 148 from leaving the piston bore 138.

To provide `for reduction in size of the grinding 1 heel as it is trued away, the piston i116 must be advanced. Advancing the piston 116 advances the retracted position of the slide member 716 toward the grinding wheel since rearward movement of the slide member 76 is stopped by ,the aligning plate 126 fixed to the vpiston 116. Ad-

vancement of the piston is achieved by rotating the screwV 11-8 which is Ithreadediy engaged with the piston 116. By the construction described, the piston 116 does not rotate and the screw =118 does not move axially. Thus the piston 116 operates as a nut when the screw 118 is rotated and the position of the lpistonrelative to the fwheelhead 10 may be changed by rotation of the screw 118.

ln FIG. 5, a piston and cylinder motor is shown, the operation of which provides incremental rotation of the screw 118. A cylinder 145 slidably receives a piston 148.

- The top of the cylinder is closed by a cap .150. An adthe spring `forces the slide member 76 rearward, away from the `grinding wheel 28, until the flange plate 122 engages the spacer 130 which is forced against the align ing plate 126.

The piston 116 has a bore `138 into which the screw '118 extends. Received in the bore and 'adapted to engage the end of the screw 118 is a plunger 141i. The end of the bore 138 is open to the cylinder bore 114. As pres surized fluid is put into the bore 114, fluid under pressure enters the bore 138 and forces the plunger 140 against the end of the screw 118. This produces a force on the screw 118fwhich holds a fiange 142 of the screw 118 firmly against the bearing 128 and takes up any inherent looseness in the longitudinal reception of the screw 118 in the wheelhead 10. The )fluid is introduced into the bore 114 when wheel truing is performed and the reaction forces between the truing mechanism and the wheel 28 -are firmly applied to the bearing 120 to give rigidity to the system. When the pressure is relieved from the cylinjusting knob 152 is rotatably received thereon. The knob 152 has a detent 154 to hold it in a selected position. Extending from the knob 152 is a stop shaft 155 from which a stop pin 156 extends. As the knob 152 is angularly adjusted, the stop pin 156 is angularly adjusted. The top of the piston v148 is adapted to engage the stop pin 156 when iiuid under pressure is introduced through a iiuid line 1518 to the lower end of the cylinder 146. The top of the piston -l148 Varies in elevation by steps, the surface 160` being the top step while the surface 162 is the lower step. If the pin 156 is in the position shown, the surface 160 would engage the stop pin 156 on the upward stroke of the piston 148 and the stroke length would be short. If the pin 156 were adjusted through degrees, the surface 162 would engage the pin 156 andthe stroke of the piston 148 would be longer. The piston 148 is returned to its lower position when pressure is relieved in line 158 by a spring 164 received between the shaft 155 and the piston `148.

The piston 148 has a rack 166 integral therewith which is engaged by the sector gear 168 pivotally received around the screw 118. As the piston 148 moves up and down, the sector gear 168 is rotated. [Fixed to the screw 118 is a ratchet wheel (not shown) which is engaged by apawlV (notshown) fixed to the sector gear 168 for limited pivotal movement relative thereto. On the upward stroke, the piston 148 causes the screw 118 to be rotated to effect movement of the piston 116 (F1G. 1.).an incremental amount toward the grinding wheel 20. 'Ilhe ratchet pawl may be released for rotation of the screw 118 by a handwheel, not shown, to return the piston 116 to a position to allow for a new grinding Wheel after a previous wheel has been used up.

The hydraulic circuit to operate the truing mechanism is shown schematically in FIG. 6. A counter selector switch SW1 is set for a predetermined number of grind operations between truing operations. At the end of a preset number of grinding operations, a signal from thel counter represented by switch SW1 is connected through a conductor 17!) to an electrical unit 172 which includes a source of control voltage and a delay timer. Immediately, a solenoid 1SOL is energized through a conductor 174 and the plunger of a valve 176 shifts to the left and connects the main pressure line 178 to a fluid line 180. Fluid line 180 connects with the fluid passage 138 in communication with the fixed stroke motor cylinder bore 114. The slide member 76 is moved toward the grinding wheel a fixed amount. At the same time pressure from line 180 is connected to the lower end of the cylinder 146 to move the piston 148 upward to engage the stop pin 156. The movement ofthe piston 148 turns the sector gear 168 engaged with the rack of piston 148 which turns V r to compensate for grinding wheel attrition.

After a timed delay determined by the electrical unit 172 to allow for completion of the iixed stroke and `compensation movements, control voltage is connected to a conductor 186 to energize a second solenoid 2SOL and shift the plunger of a pilot valve 188 to the left. lFluid line 178, the main pressure line, is connected to a uid line 19) and the plunger of a reversing valve 184 is caused to shift to the left. Pressure line 178 is then connected to a line 182 and uid under pressure is .connected to the cylinder 66 and the plunger 46 moves down to cause rotation of the pinion 44 which swings the yoke 24 (FIG. l) of the truing attachment. the cylinder 68 moves through a line 192 to valve 134 where is connects to a line 194 which connects to a throttle valve 196 by which the truing rate is set. From throttle valve 196 the uid is returned to the reservoir 198 by way of a line 200, the main return line. rl'ihe piston 48 in the cylinder 68 is moved upward by the drive from thepiston 46 through the pinion 44.

As the

pistons

46 and 48 move, a limit switch ZLS is first released and at the end of swing of the yoke 24, a limit switch 1LS is operated by the piston 46. Conductors 202, 204 connect limit switches 1LS and ZLS, respectively, to the electrical unit 172. When the limit switch 1LS is operated after the limit switch ZLS has been released, the electrical unit causes the solenoid ZSOL to be deenergized. The plunger of the valve 188 shifts back to the position shown. Fluid line 190 is connected to the main return line 280. 'Ihe plunger of valve 184 then shifts back to the position shown and line 182 is connected to the line 194 which connects through the throttle valve 196 to the main return line 200. Line 192 is connected to pressure line 178 through the valve 184. The

pistons

46 and 48 are returned to the position shown, and the yoke24 (FIG. l) is swung back'to its starting position. At the end of the swing the limit switch ZLS is operated, limit switch 1LS having been realeased at the start of the return swing. Y When limit switch BLS is operated now, solenoid 1SOL is deenergized and the plunger of valve 176 shifts back to the position shown. Fluid line 180 is connected to the main return, and the piston 148 is returned to the position shown, the screw 118 (FIG. 1) not being reversely turned, however, since the sector gear 168 (FIG. 5

acts in a ratchet fashion as described. The fixed stroke mechanism returns the slide member 76 back away from the wheel, being motivated by the force produced in the spring 134 (FIG. l), as described, when the uid passage 136 is connected to the main return line 200.

The truing cycle is now completed, with the truing tool retracted from the grinding wheel. The present retracted position has been altered from the previous retracted position by an incremental advancement toward the grinding wheel determined by the length of the stroke of the piston 148 in the cylinder 146 (FIGS. 4, 6).

What is claimed is:

l. In a precision grinding machine, the combination comprising, a grinding wheel rotatably mounted in the machine, a truing tool, a first motor connected to the truing tool and operable for advancement thereof a predetermined amount relative tothe grinding wheel to compensate for grinding wheel attrition, a second motor connected to the truing tool, and operable through a fixed stroke, means to operate said second motor land advance the truing tool a fixed distance to eliminate clearance between the truing tool and the grinding wheel, means to swing the truing tool to true an arc of a circle on the cutting surface of the grinding wheel, and means to reversely operate said second motor and retract the truing tool said fixed distance from the grinding wheel to provide clearance therebetween.

2. In a precision grinding machine having a wheel-head and a grinding wheel rotatably mounted therein, the combination comprising, a truing tool received in the wheelhead, a motor connected to the truing tool reversibly operable to advance the truing tool toward and retract the truing tool from the grinding wheel to eliminate and provide, respectively, clearance therebetween, compensation means operable to move said truing tool and motor to- Y ward the grinding wheel to compensate for grinding wheel At the same time, iiuid from attrition, and means to swing the truing tool to true an arc of a circle on the cutting surface of the grinding wheel when the truing tool is advanced.

3. In a precision grinding machine having a wheelhead yand a grinding wheel rotatably mounted therein, the combination comprising, a truing tool received in the wheelhead, a clearance motor selectively operable to advance the truing tool toward and to retract the truing toolpfrom the grinding wheel to eliminate and provide, respectively, clearance therebetween, a compensation motor operable as said truing tool is advanced to move said clearance motor and truing tool toward the grinding wheel to compensate for grinding wheel attrition, and reversibly operable means to swing the truing tool to true an arc of a circle on the cutting surface of the grinding wheel when said truing tool is advanced.

4. In a precision grinding machine having a wheelhead and a grinding wheel rotatably mounted therein, the combination comprising, a single point truing tool received in the wheelhead, a xed stroke clearance motor operable when energized to `advance the truing tool toward the grinding wheel to eliminate clearance therebetween, a compensation motor operable whenl energized to move said clearance motor .and truing tool toward the grinding wheel a predetermined amount to compensate for grinding wheel attrition, means to simultaneously energize the clearance and compensation motors, means to reciprocally swing the truing ltool 4around an arc when said truing tool has been advanced to true an arc of a circle on the cutting surface of the grinding wheel, and means to reversely operate said clearance motor to retract the truing tool when said truing tool has been reciprocally swung around its arc of movement.

5. In a precision grinding machine having a wheelhead l and a grinding wheel rotatably mounted therein, a truing mechanism to true an arc tangent to two surfaces of the grinding wheel, comprising a truing carriage received in said wheelhead for advancement toward and retraction away from the grinding wheel, a single point truing tool received in said carriage for swinging in an arc, said truing tool `adapted to engage the cutting surface of the grinding wheel when said carriage is advanced, `a fixed stroke mechanism selectively 4operable to advance the carriage from and return the carriage to a retracted position, means to adjust the retracted position to compensate for grinding wheel attrition, and means to swing said truing tool when the truing 4carriage is advanced to true said arc on the grinding wheel cutting surface.

6. In a precision grinding machine having a wheelhead and a grindingpwheel rotatably mounted therein, the combination comprising, a truing carriage received in said i wheelhead for `advancement toward and retraction away from the grinding Wheel, a rotatable compensation screw axially fixed in the wheelhead, a piston threadedly engaged on said compensation `screw and axially movable thereon relative to the wheelhead when ythe compensation screw is rotated, a cylinder bore in said carriage adapted to receive said piston, bias means to effect relative positioning of the piston at one end of the cylinder bore to hold the carriage retracted, means selectively supplying iiuid under pressure to the cylinder bore to overcome said bias meansY to effect relative positioning of the piston at the other end of the cylinder bore and advance the truing carriage, a single point truing tool received in said truing `carriage for swinging in lan arc, said truing tool adapted to engage the cutting surface of the grinding wheel when said carriage is advanced, means to reciprocally swing said truing tool when said carriage is in the advanced position, and means to incrementally rotate the compensation screw to adjust said piston relative to the grinding wheel and compensate for grinding wheel attrition.

, 7 7. In a precision grinding machine hav-ing a wheel,- head and a grinding wheel rotatably mounted therein, 'the combination comprising, 'a truing carriage received inV said wheelhead foritadvancement toward and retraction from the grinding Wheel, a rotatable compensation screw axially spring received between said carriage and said piston to effect relative positioning of the piston at one end of the cylinder bore to hold the carriage retracted, means selec- 15 tively supplying uid under pressure to effect relative positioning of the piston at the other end of the cylinder bore and adv-ance the tming carriage, `said plunger being forced against the compensation screw by said uid to take up axial play between said screw and the wheelhead, a single point truing tool received in said carriage for swinging in an arc, said truing tool adapted to engage the cutting surface of the grinding Wheel when lsaid carriage is advanced, means to reciprocally swing said truing tool when said carriage is in the .advanced position, and means to incrementally rotate the compensation screw to` adjust said piston relative to the grinding Wheel and compensate for grinding wheel attrition.

References Cited in the le of this patent UNITED STATES PATENTS 2,665,681 Haas et al. Jan. 12, 1954 2,907,315 Hill Oct. 6, 1959 FOREIGN PATENTS 893,455 France Jan. 31, 1944 1,096,681 'France Feb. 2, 1955

Claims

1. IN A PRECISION GRINDING MACHINE, THE COMBINATION COMPRISING, A GRINDING WHEEL ROTATABLY MOUNTED IN THE MACHINE, A TRUING TOOL, A FIRST MOTOR CONNECTED TO THE TRUING TOOL AND OPERABLE FOR ADVANCEMENT THEREOF A PREDETERMINED AMOUNT RELATIVE TO THE GRINDING WHEEL TO COMPENSATE FOR GRINDING WHEEL ATTRITION, A SECOND MOTOR CONNECTED TO THE TRUING TOOL, AND OPERABLE THROUGH A FIXED STROKE, MEANS TO OPERATE SAID SECOND MOTOR AND ADVANCE THE TRUING TOOL A FIXED DISTANCE TO ELIMINATE CLEARANCE BETWEEN THE TRUING TOOL AND THE GRINDING WHEEL, MEANS TO SWING THE TRUING TOOL TO TRUE AN ARC OF A CIRCLE ON THE CUTTING SURFACE OF THE GRINDING WHEEL, AND MEANS TO REVERSELY OPERATE SAID SECOND MOTOR AND RETRACT THE TRUING TOOL SAID FIXED DISTANCE FROM THE GRINDING WHEEL TO PROVIDE CLEARANCE THEREBETWEEN.