US3641714A

US3641714A - Machine tool provided with apparatus for compensating the wear of grinding wheel

Info

Publication number: US3641714A
Application number: US39604A
Authority: US
Inventors: Hiroaki Asano
Original assignee: Toyoda Koki KK
Current assignee: Toyoda Koki KK
Priority date: 1969-05-30
Filing date: 1970-05-22
Publication date: 1972-02-15
Anticipated expiration: 1989-02-15
Also published as: DE2026384A1

Abstract

A grinding machine is provided with first feeding means for moving a wheel slide toward and away from a workpiece, a dressing tool arranged to be moved transversely of the face of the grinding wheel to dress the grinding wheel, second feeding means for moving the dressing tool toward and from the surface of the grinding wheel, detecting means for sensing the engagement between the dressing tool and the surface of the grinding wheel, and control means adapted to control the first and second feeding means so as to advance the wheel slide and the dressing tool until the detecting means detects the engagement between the dressing tool and the surface of the grinding wheel.

Description

United States Patent Asano 1 Feb. 15,1972

[54] MACHINE TOOL PROVIDED WITH APPARATUS FOR COMPENSATING THE WEAR OF GRINDING WHEEL 21 Appl. No.: 39,604

3,517,659 6/1970 Stewart ..51/165 R X 3,500,811 3/1970 Perkins ..l25/11 3,457,678 7/1969 Temple..... 51/165 X 3,404,670 10/ 1 968 Gluchowicz. 125/1 1 3,339,317 9/1967 Cleland ..5l/l65 Primary Examiner-Harold D. Whitehead An0rneyBerman, Davidson and Herman [57] ABSTRACT A grinding machine is provided with first feeding means for 0 Foreign Application priority Data moving a wheel slide toward and away from a workpiece, a dressing tool arranged to be moved transversely of the face of May 30, 1969 Japan ..44/42625 the grinding wheel to dress the grinding whee], Second feeding means for moving the dressing tool toward and from the sur- (g1 face of the grinding wheel detecting means for Sensing the gagement between the dressing tool and the surface of the [58] Field of Search ..5l/l65, 165.87, 11625573181, grinding wheel and control means adapted to control the first and second feeding means so as to advance the wheel slide and the dressing too] until the detecting means detects the engage- [56] References cued ment between the dressing tool and the surface of the grinding UNITED STATES PATENTS Wheel 3,155,086 11/1964 Ornehage ..51/l65.68 6Claims,7Drawing Figures U II n] o IL I 5 12 m 2 L, IL 15 ml NI 4 7 1 d f 1111 l, 1 I Mr I II 4 q a 4 g 4 PM,

[ II: /a Ir I! E :1

MACHINE TOOL PROVIDED WITH APPARATUS FOR COMPENSATING THE WEAR OF GRINDING WHEEL BACKGROUND OF THE INVENTION The present invention relates to a machine tool provided with apparatus for compensating for the wear of a grinding wheel, and more particularly to an apparatus which eliminates the degeneration in machining accuracy on a workpiece due to the wear ofa grinding wheel.

Conventionally, the degeneration of machining accuracy caused by thermal deformations of the grinding machine and workpiece, elastic deformation thereof due to the grinding operation, backlash of feed screws in feeding mechanisms, grinding wheel wear, and the like have been eliminated by using a sizing device. The degeneration of machining accuracy due to grinding wheel wear cannot be eliminated except by the use of a sizing device, whereas the degeneration due to the other above-mentioned factors can be substantially reduced by properly arranging the components of the grinding machine. Thus, when a workpiece provided with grooves such as the grooves for a key or spline is required to be ground, high machining accuracy cannot be expected, since the sizing device cannot be easily applied to size the dimension of the workpiece, and also because sizing devices are frequently damaged by the engagement between the grooves and the feeler of the sizing device. Furthermore, a grinding machine provided with such a sizing devices becomes very expensive, since the sizing device itself is quite expensive.

SUMMARY OF THE INVENTION It is therefore a main object of the present invention to provide a grinding machine having an apparatus capable of eliminating the degeneration in machining accuracy on a workpiece due to grinding wheel wear.

Another object of the invention is to provide a grinding machine having an apparatus for compensating for the wear of a grinding wheel and which serves to increase machining accuracy resulting from the use of the machine without requiring the use ofa sizing device.

A still further object of the invention is to provide a grinding machine having an apparatus for compensating for the wear of its grinding wheel, the apparatus being less expensive, simpler in construction, and more reliable in operation than corresponding devices previously employed.

According to the present invention there is provided a grinding machine having an apparatus for compensating for the wear of its grinding wheel. The grinding machine comprises a bed, a work support slidably mounted on the bed to support a workpiece thereon, a wheel slide slidably mounted on the bed and carrying a rotatable grinding wheel, first feeding means for moving the wheel slide toward and from a workpiece on the work support, a dressing tool arranged to be moved transversely of the face of the grinding wheel to dress the grinding wheel, a second feeding means for moving the dressing tool toward and from the surface of the grinding wheel, detecting means for sensing the engagement between the dressing tool and the surface of the grinding wheel, and control means adapted to control the first and second feeding means to advance the wheel slide and the dressing tool until the detecting means detects the engagement between the dressing tool and the surface of the grinding wheel, whereby degeneration of machining accuracy due to the wear of the grinding wheel is compensated for and whereby high machining accuracy may be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects of the present invention will become fully apparent from the following description ofa preferred embodiment of the present invention, with reference to the accompanying drawings, in which:

FIG. 1 is a side view of a numerically controlled grinding machine equipped with an apparatus according to the present invention.

FIG. 2 is a sectional view taken along the line IIII of FIG. 1.

FIG. 3 is a view taken along the line III-Ill in FIG. 2.

FIG. 4 is a sectional view of a vibration detector according to the present invention.

FIG. 5 is a schematic view showing the relationship between the dressing tool and the grinding wheel.

FIG. 6 is an explanatory diagrammatic view including a typical workpiece.

FIG. 7 is a block diagram showing the control system for a numerically controlled grinding machine such as that illustrated in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. 1, a slide base 2 is fixed to a bed I by means of screws 3. A screw shaft 4 is rotatably supported at both of its ends by antifriction ball bearings 5, 6 which are mounted on slide base 2. The screw shaft 4 is restrained from axial movement by means of thrust bearings 7 and 8 at the left end thereof, and at the right end thereof is connected to pulse motor PM-l which is secured to slide base 2. A wheel slide 9 is slidably mounted on the slideways which are formed on the slide base in parallel relationship with respect to screw shaft 4. A feed nut 10 secured to the underside of wheel slide 9 is threadedly engaged with a threaded portion 4a of screw shaft 4 so that wheel slide 9 may be moved toward and from a workpiece 65 by means of pulse motor PM-l. A wheel shaft 11 is rotatably carried by wheel slide 9 and is rotated by means of the grooved pulleys l3 and 14 and V-belt 15 by a motor 12 which is mounted on the rear top portion of wheel slide 9. A grinding wheel 16 is fixedly mounted on wheel shaft 11 by means of a wheel sleeve 17 (FIGS. 2 and 3) and is covered by a wheel guard 18 secured to wheel slide 9 by screws 18a. A bracket 19 provided with a vertical flat surface 19a is fixed on the wheel guard 18 by means of screws 20. An adjustable rest 21 in face contact with the surface 19a and rotatable about a pivot pin 22 is mounted on bracket 19 by means ofa screw 23. A pair of adjusting screws 24 engaged with the top of bracket 19 are threadedly engaged with a projection 21a of adjustable rest 21 which overhangs the bracket 19, whereby the adjustable rest 21 may be turned around the pivot pin 22 so as to ob tain the required position thereof at the required angle with respect to the axis of wheel spindle 11 by suitably turning the screws 24.

Integrally formed on the adjustable rest are a pair of projections 21b and 21c between which two

guide bars

25 and 26, parallel to each other, are connected by nuts 27a, 27b, and 28a, 28b, threadedly engaged on reduced threaded portions 25a, 25b, 26a and 26b at the ends of the guide bars. A dresser slide 29 is snugly and slidably mounted on the

guide bars

25 and 26. A piston rod 32 (FIG. 2) has its right end connected to the side of dresser slide 29 in parallel relationship with respect to the

guide bars

25 and 26, and has its left end connected to a piston 31 which is slidably mounted in a cylinder secured to the adjustable rest 21, whereby the dresser slide 29 is movable concurrently with piston 31. The dresser slide is provided with a vertical bore in which a sleeve 34 is mounted, said sleeve being fixedly secured to dresser slide 29 by screws 35. A cap plate 36 is fixed on the top of the bore and is provided with a second bore in which a bushing 37 has a press fit. A sleeve 38 is rotatably supported by cap plate 36 but is restrained from axial movement by the provision of a flange at the lower end of sleeve 38 and a nut 43 engaged with the sleeve at the upper end thereof, with thrust bearings 39 and 40 and gear 42 interposed therebetween, said gear 42 being connected to the sleeve 38 by a key 41 therebetween. A pulse motor PM-2 is secured to the underside of the cap plate 36. The gear 44 secured to the output shaft of pulse motor PM-Z is meshingly engaged with a larger diameter gear 45a which is fixed to a shaft 45 rotatably mounted on cap plate 36. A smaller diameter gear 45b on the shaft 45 is in turn meshed with gear 42, whereby the sleeve 38 may be rotated by pulse motor I'M-2.

An inner sleeve 46 is disposed within and secured to the sleeve 38. A dressing shaft 47 is provided at the upper end thereof with a threaded portion 470 which is threadedly engaged with a threaded portion on the inner bore of the sleeve 46, and is snugly engaged at its lower portion with the inner bore of the sleeve 34. A key member 49 secured to the dresser slide 29 is slidably engaged with an axially extending long groove 470 at the lower portion of the dressing shaft 47, whereby rotational movement of dresser shaft 47 is prevented but axial movement thereof is allowed. A bracket element 51 having a dressing tool 50 is fixedly secured to the lower end of dresser shaft 47, and a vibration detector 53 is provided at the upper end of said dresser shaft.

The housing 53a of vibration detector 53 is threadedly secured on dresser shaft 47, as shown in FIG. 4. A fastening shaft 53b is axially secured in the housing 53a. Lower electrode 53d, ferroelectric substance 53f, for example barium titanate, and weight member 532, used as an upper electrode, are successively interposed between the lower and upper insulating members 53c and 53h which electrically insulate lower and upper electrodes 53d, 53c and the ferroelectric substance 53f from the surrounding members. A nut 53g is threadedly engaged with the securing shaft 53b to impart a predetermined pressure to ferroelectric substance 53f Thus, when the dressing tool 50 is engaged with the surface of grinding wheel 16, the vibration detector 53 is vibrated through dresser shaft 47, and thus the pressure applied to the ferroelectric substance S3f is changed and is converted into electric voltage changes in accordance with the specific vibration generated by the engagement between dressing tool 50 and grinding wheel 16, whereby the vibration detector 53 acts as a transducer to detect the specific vibrations and to convert them to electric voltage changes, as they occur between the lower and upper electrodes 53d, 532.

Secured to adjustable rest 21 is a bracket 55 on which are mounted limit switches LS,1, LS-2, and LS-3, said limit switches being respectively actuated by an engaging piece 56 (FIG. 3) at the times when dressing tool 50, moving concurrently with engaging pieces 56 is brought to left end position, middle position, or right end position, relative to grinding wheel 16. A changeover valve 57, which changes the direction of pressure fluid supply to the cylinder 30, is connected to the cylinder 30 to control the movement of dresser slide 29. Ports A, B, P and T of changeover valve 57 are respectively connected to right chamber 30R, left chamber 30-L, a pressure fluid supply source (not shown) and a sump through a variable throttle valve 58. A bypass valve 59 is provided in parallel with the throttle valve 58, whereby to enable the dresser slide 29 to move with either a rapid speed or a slow speed. A traverse table 60 is slidably mounted on slideways 1a and lb which are formed on the bed 1 parallel to the axis of the grinding wheel 16. Integrally formed on the under side of the traverse table 60 is a ball nut 61 which is threadedly engaged with a feed screw shaft 62, which in turn is rotatably mounted on the bed 1 but is restrained from axial movement. A pulse motor PM-3 is connected to the feed screw shaft 62 at one end thereof so that traverse table 60 is movable along the slideways 1a and lb. A swivel table 63 is pivotally mounted on traverse table 60, and furthermore a headstock 64 and a footstock (not shown) are mounted on said swivel table for supporting a workpiece, for example a workpiece 65 having longitudinal grooves, such as grooves for splines or key grooves, said workpiece being supported between said headstock and said footstock, between centers, as shown, for example, in FIG. 6.

The control system for controlling the pulse motors PM-l, PM2, PM-3 are shown in FIG. 7. Said motor may be of a conventional type, such as Models EHPM-l/Z-SSSS, lEPM-l09 and EHPM-l-SSSS, respectively manufactured by Fujitsu, Ltd, Tokyo, Japan, suitable information stored in a tape 66 is read by a conventional tape reader 67 and is preset on the counter of a control circuit 68. Tape reader 67 may be of any suitable conventional type, for example, Model 424 made by Tally (Iorporation. Control circuit 68 is one of the modules of a conventional control system such as Fanuc 260, manufactured by Fujitsu, Ltd, Tokyo, Japan. This conventional, commercially available control system also includes most of the additional elements shown in FIG. 7, namely, variable frequency pulse generator 69, gate circuit 70, output control circuit 71, drive units 72a, 72b and 72c, auxiliary circuit 73, main control circuit 74, additional pulse generator 78 and control panel 79.

The control circuit 68 is effective for supplying output control circuit 71 with a selecting signal for selecting the pulse motor or motors to be driven in response to the signal. namely. PM-l, PM-Z, or PM-3. The control circuit also provides a rotational signal for selecting the rotational direction of the pulse motor or motors to be rotated, and the control circuit also furnishes the variable frequency pulse generator 69 with a command signal for specifying the frequency of electric pulses generated thereby. Electric pulses generated by the variable frequency pulse generator 69 are applied to the output control circuit 71 through the gate circuit 70. In accordance with the selection signal from the control circuit 68, the output control circuit 71 applies the directional signal and the electric pulses furnished through the gate 70 and the output control circuit 71 to a drive unit or drive units selected from the drive units 72a, 72b, and 72c, which are respectively associated with pulse motors PM-l, PM-2, and PM-3. The output control circuit 71 also is effective to feed back electric pulses applied to the selected drive unit or drive units, to the control circuit 68. Electric pulses applied to the drive unit or units are referred to as drive pulses hereinafter. The number of drive pulses is subtracted from the number of the command pulses preset on the counter of control circuit 68. When the number stored in the counter becomes zero, the control circuit 68 acts to close the gate 70, to thereby stop the rotation of the selected pulse motor or motors. The auxiliary circuit 73, which controls the auxiliary functions of the numerically controlled machine tool in accordance with information on the tape 66, is connected to the control circuit 68 in the manner schematically indicated in FIG. 7, receiving information from the control circuit 68 and applying the information to a main control circuit 74. A control panel 79 is provided, said control panel having its control elements connected to the main control circuit 74.

In accordance with the present invention, a compensating system is operatively added to the above-mentioned system to compensate for the wear of grinding wheel 16 by operating pulse motors PM-l and PM-Z. Numeral 75 generally indicates the limit switches LS-l, LS-2 and LS-3 which generate signals to confirm the position of dressing tool 50. The vibration detector 53 detects the various vibrations transmitted by the tool and translates these vibrations into changes in electric voltage, forming a signal which is applied to a filter 76. The filter 76 selects a specific voltage change which is generated by the engagement between dressing tool 50 and grinding wheel 16. The selected specific voltage change is supplied to an amplifier 77 and is amplified thereby, and is then furnished to the main control circuit 74. Numeral generally indicates the solenoids of changeover valve 57 and bypass valve 59, which are respectively employed to change the direction and speed of the movement of dresser slide 29. The additional pulse generator 78 generates additional electric pulses which are used to move the wheel slide 9 and the dressing tool 50 for compensating for grinding wheel wear and for dressing the grinding wheel 16 in accordance with the signals supplied from the main control circuit 74.

In case the specific vibration is not detected by the vibration detector 53, even if the limit switch LS-2 is actuated in accordance with the transverse movement of dressing tool 50, the additional pulse generator 78 applies a predetermined number of additional electric pulses to output control circuit 71, because the main control circuit 74 applies a signal to the additional pulse generator 78 to generate additional electric pulses after the left-hand switch LS-l or the right-hand limit switch LS-3 is actuated. At the same time, the main control circuit 74 supplies a control signal to control circuit 68 through auxiliary circuit 73, whereby the control circuit 68 furnishes output control circuit 71 with selective direction signals for pulse motors PM1 and PM2. The output control circuit 71 supplies drive units 72a and 72b respectively associated with pulse motors PM-l and PM-Z with the directional signals and the additional pulses supplied from the additional pulse generators 78, whereby the pulse motors PM-l and PM-2 are rotated, and thus wheel slide 9 and dressing tool 50 are advanced to compensate for the wear of grinding wheel 16.

A typical operation, in which a workpiece having different diameters is ground, is described hereinafter. The feeding data for wheel slide 9, indexing data for traverse table 60, finished diameters d d d of respective portions to be ground, and the like, are programmed on the tape 66 in accordance with the sequence of the operations. At the beginning of the operation, traverse table 60 and wheel slide 9 are retracted to their original positions, and thereafter, the tape reader 67 is placed in operation. The pulse motor PM-l operates to rotate its shaft at high speed and to rapidly advance the wheel slide 9 toward the workpiece, and thus, the wheel slide 9 is advanced at a rapid feed speed V toward the workpiece 65 until the distance between the first portion 65a of the workpiece 65 and the grinding wheel 16 becomes a predetennined amount, for example, 0.05 mm. Meanwhile, the number stored in the counter of the control circuit 68 is subtracted by the number of the drive pulses fed back by the output control circuit 71. When the rapid feed of wheel slide 9 is completed, that is, when the number stored in the counter becomes zero, the tape 66 is fed for next numerical information. The pulse motor PM1 is supplied with lower frequency electric pulses in accordance with the signal then furnished by the control circuit 68, and thus, the wheel slide 9 is advanced at the rough grinding rate V to the first portion 65a to grind the peripheral surface thereof. Meanwhile, the number of drive pulses is subtracted from the number of command pulses newly registered in the counter of control circuit 68. When the predetermined amount is advanced, that is, the rough grinding operation is completed, a third signal is supplied from control circuit 68 to the pulse generator 69, causing it to generate low-frequency electric pulses for slower further rotation of the shaft of the pulse motor PM-l, whereby the wheel slide 9 is fed at a fine feeding rate V to perform the fine grinding operation on the portion 65a. When the fine infeed is completed, spark-out operation is effected for a predetermined period s, and thereafter, wheel slide 9 is retracted at a high retracting speed V This period s for spark-out operation can be manually regulated at control panel 79. When the wheel slide 9 is retracted by a predetermined distance programmed on the tape 66, the data on the tape 66 is read by tape reader 67, and the control circuit 68 then furnishes a signal to the auxiliary circuit 73 to perform the auxiliary operation. At the same time, the auxiliary circuit 73 supplies a command signal to the main control circuit 74 and the solenoids 80a and 80b of changeover valve 57 and bypass valve 59 are energized to change the direction of pressure fluid and to bypass throttle valve 58. The pressure fluid from the pressure source (not shown) is supplied to the left chamber 30-L of cylinder 30 through the P and B ports of the changeover valve. At this time, the fluid in the right chamber 39-R is drained to the reservoir through the A and T ports and thence, through the bypass valve 59. Thus, the piston 31 and the dressing tool 50 is fixed to the lower end of the dressing shaft 47 journaled to the dresser slide are bodily moved to the right, as viewed in FIG. 2, at a higher speed. When the dressing shaft 47 and dressing tool 50 are moved rightwardly of the face of grinding wheel 16, and the limit switch LS-Z is actuated by the engaging piece 56, the vibration detector 53 is fixed at the upper end of the dressing shaft 47 does not detect any vibration caused by the engagement between dressing tool 50 and grinding wheel 16, in the event that the grinding wheel 16 has been worn down by the grinding operations on the first portion 65a of the workpiece 65. Thus, the dresser slide 29 is further moved toward the right and arrives at the right-hand position such as to actuate the limit switch LS-3. Responsive to the signal from the limit switch LS-3, the main control circuit 74 supplies a positioncompensating signal to the additional pulse generator 78 and the command signal to the control circuit 68 through auxiliary circuit 73. Accordingly, the additional pulse generator 78 supplies the predetermined number of electric pulses to output control circuit 71, and control circuit 68 also supplies a selective signal and a directional signal to output control circuit 71 such that it supplies the additional electric pulses furnished by the additional pulse generator 78 and a directional signal to the drive unit 72a and to the drive unit 72b in accordance with the selective signal, whereby the pulse motors PM-l and PM-2 are operated to rotate their shafts so as to advance the wheel slide 9 and the dressing tool 50 by a predetermined amount, for example, 1 micron. When the dressing tool 50 and wheel slide 9 are advanced by said predetermined amount, the changeover valve 57 is operated to change the flow direction of the pressure fluid so as to move the slide 29 leftwards at a rapid speed. During the leftward movement of the dresser slide 29, the limit switch LS-2 is actuated when the dressing tool 50 is located substantially at the midpoint of the face of the grinding wheel, so that the vibration detector 53 can detect the specific vibration which is caused by the engagement between the grinding wheel 16 and the dressing tool 50. However, when the specific vibration is not detected by the vibration detector 53, the slide 29 is further moved leftwards and the limit switch LS-l and the left-end position is actuated, whereby the pulse motors PM-l and PM2 are operated respectively to advance dressing tool 50 and grinding wheel 9 by the predetermined amount previously referred to in the same manner as in the previously described cycle. In this manner, as long as the specific vibration characteristic of the engagement between dressing tool 50 and the face of grinding wheel 16 is not detected by the vibration detector 53 during the actuation of limit switch LS-2, the above-mentioned cycle of performance, that is, the advancement of dressing tool 50 and wheel slide 9 and the transverse movement of the slide 29, is repeated.

When the specific vibration characteristic of said engagement is detected by the vibration detector 53 concurrently with the location of the dressing tool 50 at the midpoint of the face of the grinding wheel, that is, when the limit switch LS-Z is actuated, the transverse movement of the slide 29 is completed at the leftor right-hand end thereof, whereby the wheel slide 9 and dressing tool 50 are advanced only by the amount equal to the wear of grinding wheel 16. Thereafter, the traverse table 60 is shifted by the pulse motor PM-3 (not shown) so that the second position 65b of the workpiece 65 is aligned with grinding wheel 16. In accordance with the data on tape 66, the second portion 65b is ground in the same manner as in the case of the first portion 65a of the workpiece 65. After the grinding operation on the second portion 650, the position-compensating operation is effected in the same manner as above described, and thus, the wheel slide 9 and the dressing tool 50 are advanced by an amount equal to the wear of grinding wheel 16. After that, the third portion 650 of the workpiece 65 is also machined in accordance with the data on the tape 66. When the machining operation on the third portion 65c is completed, the position-compensating operation is effected in the same manner as before.

When a dressing operation for grinding wheel 16 is required, the operator of the associated machine tool pushes a button on control panel 79, whereby the main control circuit 74 supplies a dressing feed signal to the additional pulse generator 78 and a command signal to control circuit 68 through auxiliary circuit 73. Accordingly, the additional pulse generator 78 supplies output control circuit 71 with a predetermined number of electric pulses corresponding to dressing feed of the dressing tool 50, and control circuit 68 furnishes a selective signal and a directional signal to output control circuit 71, which supplies the drive units 72a, 72b with the directional signal and the electric pulses furnished from the additional pulse generator 78 so as to operate the pulse motors PM-l, PM-2, whereby dressing tool 50 and wheel slide 9 are advanced by a predetermined amount, for example, 0.01 millimeter or 0.02 millimeter. With the completion of the advancement of dressing tool 50 and wheel slide 9, the main control circuit 74 issues electric signals to close the bypass valve 59 and to operate changeover valve 57 to change the direction of the pressure fluid. Thus, the fluid flow out of the cylinder 30 is reduced by the variable throttle valve 58, and the slide 29 is transversed at a lower speed so that the surface of the grinding wheel 16 is dressed by the dressing tool 50 carried by the slide 29.

According to the present invention, when the machining operation on every one of the portions 65a, 65b and 65c is completed, the dresser slide 29 is traversed at a rapid speed until the vibration detector 50 detects the engagement between the grinding wheel 16 and the dressing tool 50, and after every transverse movement of the dresser slide 29 the wheel slide 9 and the dressing tool 50 are advanced by the same amount. Thus, degeneration of machining accuracy due to wear of the grinding wheel 16 is eliminated because the wheel slide 9 is advanced by the same amount as the grinding wheel wear. At the same time, a high machining accuracy is obtained in a very inexpensive manner, since in accordance with the present invention the machining accuracy is the same or better than that obtained without using a relatively expensive sizing device. Furthermore, since the advancement movement of the dressing tool 50 in the position-compensating operation for wheel slide 9 is small, for example, 1 micron, the surface of grinding wheel 16 is not damaged by the dressing tool 50, even if the dressing tool 50 is rapidly traversed across the surface thereof. The transverse movement of the dresser slide 29 to compensate for the wear of the grinding wheel 16 may be effected while the wheel slide 9 is being retracted to the original position thereof, while the workpiece is being loaded or unloaded, or while the traverse table is being indexed, since it does not take much time to traverse the dresser slide 29, because of the rapid transverse speed thereof.

While the foregoing description is concerned with a preferred embodiment of the present invention, it will be evident to those skilled in the art that various changes and modifications may be made therein without departing from the basic principle of the invention, and that the appended claims are intended to cover all such changes and modifications as fall within the spirit and scope of the invention.

What is claimed is:

l. A grinding machine provided with an apparatus for compensating for the wear of its grinding wheel comprising; a bed, a work support slidably mounted on said bed to support a workpiece thereon, a wheel slide slidably mounted on said bed and mounting a rotatable grinding wheel for effecting a grinding operation on the workpiece, first feeding means for moving said wheel slide toward and away from the workpiece on said work support, a guide mounted on said wheel slide parallel to the axis of said grinding wheel, a slide slidably mounted on said guide, reciprocating means for moving said slide transversely of the surface of the grinding wheel, a dressing tool holder slidably mounted on said slide and having a dressing tool thereon, second feeding means for moving said holder and dressing tool toward and away from the surface of the grinding wheel, detecting means mechanically connected with said dressing tool and operative to generate an electric signal corresponding to the vibrations produced by the engagement of the dressing tool with the surface of said grinding wheel during the transverse movements of the slide, and control means for automatically operating said second feeding means to advance said holder and dressing tool toward the surface of the grinding wheel a predetermined amount at each transverse movement of the slide until the generation of said electric signal and for simultaneously automatically operating said first feeding means to advance said wheel slide and grinding wheel toward the workpiece the same predetennined amount equal to that of the holder and dressin tool.

2. A grinding machine provi ed with an apparatus for com' pensating for the wear of its grinding wheel as claimed in claim i, wherein speed control means is connected to said reciprocating means and operative to change the moving speed of said slide at slow and rapid speeds, said slide being moved at a slow speed during a wheel-dressing operation and at a rapid speed when the second feeding means is operating to advance the dressing tool and the latter has not yet contacted the grinding wheel.

3. A grinding machine provided with an apparatus for compensating for the wear of its grinding wheel as claimed in claim 1, wherein said detecting means comprises ferroelectric substance sandwiched between a pair of electrodes and is capable of changing a vibration caused by the engagement between said dressing tool and the surface of said grinding wheel into an electric signal.

4. A grinding machine provided with an apparatus for compensating for the wear of its grinding wheel as claimed in claim 1, wherein said guide is pivotally mounted on said wheel slide to vary its angle with respect to the axis of said grinding wheel.

5. A grinding machine provided with an apparatus for compensating for the wear of its grinding wheel as claimed in claim 1, wherein said apparatus is further provided with sensing means for confirming that said dressing tool is located on or above the surface of said grinding wheel, and said detecting means is operable to sense the engagement between the grinding wheel and the dressing tool only at the time when the dressing tool is located against the surface of said grinding wheel.

6. A grinding whee] provided with an apparatus for compen sating for the wear of its grinding wheel as claimed in claim 1, wherein said control means further comprises an additional pulse generator which supplies a predetermined number of electric pulses to said first and second feeding means until said detecting means senses the engagement between said grinding wheel and said dressing tool.

UNITED STATES PATENT ()FFICE CERTIFICATE 0F CORRECTEON Patent No. 3 ,64l,7l4 Dated February 15, 1972 Invent Hiroaki Asano It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 68 "motor" should read motors Column 5, line 2, "with selective direction" should read with selective and directional line 62, "39 -R"'should read 30-R line 64, "SOis fixed" should read 50 fixed line 70, "53 is fixed" should read 53 fixed Column 6, line 29, "LS-l and" should read LS-l at 3 Column 8, line 3, "i" should read l Signed and sealed this 14th day of November 1972o (SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents USCOMM'DC BOE'YG-PGQ U.S. GOVERNMENT PRINTING OFFICE: I969 O-366-334,

Claims

1. A grinding machine provided with an apparatus for compensating for the wear of its grinding wheel comprising; a bed, a work support slidably mounted on said bed to support a workpiece thereon, a wheel slide slidably mounted on said bed and mounting a rotatable grinding wheel for effecting a grinding operation on the workpiece, first feeding means for moving said wheel slide toward and away from the workpiece on said work support, a guide mounted on said wheel slide parallel to the axis of said grinding wheel, a slide slidably mounted on said guide, reciprocating means for moving said slide transversely of the surface of the grinding wheel, a dressing tool holder slidably mounted on said slide and having a dressing tool thereon, second feeding means for moving said holder and dressing tool toward and away from the surface of the grinding wheel, detecting means mechanically connected with said dressing tool and operative to generate an electric signal corresponding to the vibrations produced by the engagement of the dressing tool with the surface of said grinding wheel during the transverse movements of the slide, and control means for automatically operating said second feeding means to advance said holder and dressing tool toward the surface of the grinding wheel a predetermined amount at each transverse movement of the slide until the generation of said electric signal and for simultaneously automatically operating said first feeding means to advance said wheel slide and grinding wheel toward the workpiece the same predetermined amount equal to that of the holder and dressing tool.

2. A grinding machine provided with an apparatus for compensating for the wear of its grinding wheel as claimed in claim i, wherein speed control means is connected to said reciprocating means and operative to change the moving speed of said slide at Slow and rapid speeds, said slide being moved at a slow speed during a wheel-dressing operation and at a rapid speed when the second feeding means is operating to advance the dressing tool and the latter has not yet contacted the grinding wheel.

6. A grinding wheel provided with an apparatus for compensating for the wear of its grinding wheel as claimed in claim 1, wherein said control means further comprises an additional pulse generator which supplies a predetermined number of electric pulses to said first and second feeding means until said detecting means senses the engagement between said grinding wheel and said dressing tool.