US3500811A

US3500811A - Automatically controlled dressing apparatus for a grinding wheel

Info

Publication number: US3500811A
Application number: US575312A
Authority: US
Inventors: Wallace W Perkins
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1966-08-26
Filing date: 1966-08-26
Publication date: 1970-03-17
Anticipated expiration: 1987-03-17

Description

March 17, 1970 w.w. PERKINS AUTOMATICALLY CONTROLLED DRESSING APPARATUS GRINDER CONTROL FOR A GRINDING WHEEL Filed Aug. 26. 1966 TRIGGER? LIFIER ACCELEROMEETER a a--- u 4 PS f INVENTOR. wad/8M2 NPUT ATTORNEY United States Patent Office Patented Mar. 17, 1970 3,500,811 AUTOMATICALLY CONTROLLED DRESSING APPARATUS FOR A GRINDING WHEEL Wallace W. Perkins, West Hartford, Conn., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Aug. 26, 1966, Ser. No. 575,312 Int. Cl. B24b 53/00 US. Cl. 125-11 9 Claims ABSTRACT OF THE DISCLOSURE A grinding wheel dresser with means to monitor the vibrations of the dressing tool as caused by the grinding wheel and to indicate a need for dressing the wheel.

This invention relates an apparatus for shaping the grinding surface on a grinding wheel and particularly such an apparatus including means to automatically terminate the shaping operation after the wheel surface is dressed to a predetermined contour.

The demands of the industry for rapid production at minimum cost usually require that grinding wheels employed in production grinding operations must be operated at a grinding rate which lies as nearly as possible within the maximum efficiency of the grinding wheel. When such grinding wheels are employed in heavy duty grinding operations, they frequently wear to irregular contour, developing grooves, nicks and non-concentric portions due to the wheels encountering edges or uneven portions on the work pieces. It is well recognized that a grinding wheel having imperfections or glazed portions in its grinding face is injurious to the work surface being ground and is a frequent cause of spoiling the work. Consequently, it is the usual practice to periodically reshape and resurface the grinding wheel. To be assured that all nicks and grooves and other imperfections in the grinding wheel surface are removed, present practice is to dress the grinding wheel to the maximum depth at which experience has shown that these imperfections, have occurred. The depth, however, is usually considerably greater than is necessary. As a result, much of the grinding wheel which might be used in production grinding is wasted and much time is lost in this additional unnecessary dressing of the wheel.

It is, therefore, an object of this invention to provide an improved grinding Wheel dressing mechanism which automatically controls the extent of dressing operation on the operative surface of the grinding wheel.

Another object of this invention is to provide an improved grinding wheel dressing mechanism which responds to imperfections in the grinding wheel surface to control the extent of wheel dressing operation.

A further object of this invention resides in the provision of an improved control for a grinding wheel dressing mechanism which automatically terminates the wheel dressing operation when the operative wheel surface has been trued to an accurate surface of revolution.

A still further object of this invention resides in the provision of an improved grinding wheel dressing mechanism which dresses the surface of the grinding wheel to the minimum extent required to bring the wheel surface back into accurate contour and proper operating condition.

To these ends and to improve generally upon devices of this character, this invention consists in the various matters hereinafter described and claimed. In its broader aspects, the invention is not necessarily limited to the specific arrangement selected for illustrative purposes in the accompanying drawings wherein like reference numerals refer to like parts and wherein:

FIGURE 1 illustrates a front view of a dressing apparatus according to the invention,

FIGURE 2 illustrates a partly broken away side view of the apparatus of FIGURE 1,

FIGURE 3 diagrammatically illustrates a truing diamond in position during a truing operation,

FIGURE 4 is a block diagram of the controls for an improved truing mechanism according to the' invention,

FIGURES 5 and' 6 show vibration waveforms in the dressing apparatus for an imperfect and a perfecfgrinding wheel respectively, and

FIGURE 7 schematically shows the circuit of the trigger and relay portions of the circuit of FIGURE 4.

My grinding wheel dressing mechanism may be adapted to a conventional type grinding machine wherein a rotating grinding wheel is fed into a rotating work piece to precisely shape either an internal or an external contour of revolution on the'work piece. In the illustrated embodiment depicted in FIGURES 1 and 2, the grinding wheel 10 is provided with a transversely curved grinding periphery 12 as is common practice for grinding the raceways in the race rings for ball bearings. A typical grinding machine to which my invention is applicable is illustrated in the expired US. patent to Steiner et al. 2,029,511. The grinding wheel 10 is mounted on a suitable driven spindle 14 journalled in a conventional wheelhead slidably mounted on the base of a grinding machine and ar ranged to be fed into and out of a rotatably driven work piece carried by a work slide on a machine base. This general standard construction is not herein illustrated since it is clearly shown in the above noted Steiner patent.

My dressing mechanism has a supporting bracket 16 provided with a flanged base which is suitably fastened as by screws to a work slide 18 that is slidably secured to the base of the grinding machine to bring the dressing mechanism into operative position with respect to the periphery 12 of the grinding wheel 10. The bracket 16 has a pair of upwardly extending spaced arms 24 and 26 provided at their upper ends with coaxial adjustable bearings 28, herein illustrated as conical pivot bearings, which swingably support a yoke member 30 for arcuate movement transversely of the grinding wheel. A dressing tool, herein shown as a rod 32 having a dressing diamond 33 projecting from its end is adjustably secured in a bore through an intermediate portion of the yoke 30 by a set scgew. This dressing tool is preferably mounted in perpendicular relation to the common axis of the adjustable bearings 28, which axis is preferably perpendicular to the plane defined by the axis of the grinding wheel rotation and the tip of the diamond 33. To provide the grinding wheel 10 with a required transverse curvature as herein indicated by the radius R, the dressing tool tip is adjustably positioned at this same distance R from the common axis of the pivot bearings 28.

When it is desired to perform a grinding wheel dressing operation, the work slide 18 is traversed to locate the axis of the pivot bearings 28 in line with the desired center of curvature of the grinding wheel. The grinding wheel slide is thereafter advanced to bring the wheel periphery into position to be dressed by the diamond 33 which is subsequently transversely swung across the rotating grinding wheel periphery by a controlled pivotal swinging movement of the yoke 30 on the bearings 28. This swinging movement may be effected by a link 34 operated by a power driven eccentric as exemplified in the above noted patent to Steiner. The linkage is regulated to control the extent of the swinging movement of the diamond depending upon the width of the grinding wheel 10. Also, if desired, the linkage may be disconnected from its power source and manually operated when it is preferred to hand-operate the dressing mechanism.

Frequently, the grinding wheel 10 is subject to wear conditions which produce nicks or grooves as indicated at 36 in FIGURE 3. In prior automatic grinding wheel dressing operations, it was usual to dress away the grinding wheel to a. much greater radial depth than was necessary to remove such surface imperfection because the depth of these nicks and/or grooves was unknown. Consequently, the dressing operation was continued to a radial depth which exceeded the greatest expected wheel imperfection depth that was likely to occur. Hence, wheel dressing time was excessive; the excessive time displacing premium production time. Also, considerable portions of a grinding wheel which might be effectively used in production were dressed away. Furthermore, this excessive wheel dressing wore away expensive truing diamonds.

The present invention includes provision for automatically controlling the extent of the dressing operation so that it trues the wheel to a depth just sufiicient to remove the surface imperfections. My invention includes an accelerometer or other vibration responsive member 40 which is fastened to the yoke member 30 preferably near the mounting for the dressing tool 32. In this manner, vibrations occasioned by movement of the diamond across the wheel surface are picked up by the vibration sensitive accelerometer 40. These vibrations produce an electrical signal in the accelerometer 40 which is then amplified in an amplifier 42 as shown in FIGURE 4 connected to a trigger circuit control 44, which in turn is connected to a grinder control 46 via relay circuit 47. The circuitry is fed from a power supply 48. A cam 50 is mounted on a hub of the yoke 30 and is arranged to make contact with a mieroswitch 52 supported on the arm 26. The cam is so formed that the mieroswitch 52 is open when the dressing tool 32 is located to the side of the wheel and not in contact therewith, and so that the microswitch is closed shortly after the dressing tool contacts the grinding wheel during its swing across the wheel, and the mieroswitch is opened again just before the dressing tool loses contact with the wheel at the end of its swing.

At the start of a wheel dressing operation, the dressing mechanism is brought into wheel dressing position with the diamond swung to one side of and out of engagement with the grinding wheel. The wheel is advanced towards the diamond to truing position and the reciprocation of the diamond across the wheel is begun. The truing diamond 33 periodically swings back and forth across the wheel and the grinding wheel is periodically advanced by small increments. The contact of the diamond 33 with the grinding wheel surface produces vibrations which are picked up by the accelerometer 40. When the diamond 33 encounters a surface imperfection, as indicated at 36 in FIGURE 3, the diamond will be out of contact with the grinding wheel surface and will not experience any vibrations. The result is that the vibration responsive member 40 produces an interrupted signal as indicated in FIGURE 5 wherein the strong vibration signal 54 indicates contact of the diamond with the wheel and the weak signal 56 in the mid portion of the waveform, indicates contact with the wheel due to the imperfection. The weak signals 58 at the leading and trailing edges of the waveform occur at the beginning and end of each swing across the wheel before and after the diamond is in contact. So long as a broken signal is transmitted from the accelerometer, the dressing mechanism continues to perform its dressing operation removing surface portions of the grinding wheel. However, when the grinding wheel is dressed to a smooth contour so that the diamond 33 is in contact with the grinding wheel surface on its entire dressing swing, the accelerometer 40 produces a uniform unbroken signal as shown in FIGURE 6 and the dressing operation ceases.

The function of distinguishing between the interrupted signal of FIGURE 5 and the uninterrupted signal of FIGURE 6 to the grinder control 46 is performed by the trigger circuit 44 which is shown schematically in FIGURE 7. The relay circuit 47, also shown in FIG- URE 7, responds to the output of the trigger circuit and indicates to the grinder control 46 whether further dressing is required. The trigger circuit includes a silicon controlled rectifier 60, for example, of the type 2N2323, having a relay coil 62 in its anode circuit. Twelve volts AC is supplied to the anode circuit from the power supply 48, the cathore is grounded, and the input to the gate is the amplified signal from amplifier 42. A diode 64 is connected across the relay coil 62 to lessen the dropout time of the relay. The contacts 66 of relay 62 are normally closed when the relay coil 62 is deenergized. In the relay circuit 47, the contacts 66 are in a sepraate circuit 68 fed .by 12 volts DC from the power supply 48 and are in series with the cam operated mieroswitch 52 described previously and with a relay coil 70. The contacts 72 of the relay 70 are in yet another circuit 73 fed by 115 volts from the AC power supply and contains in series with the contact 72 another relay coil 74 which forms the latching coil of a latching relay having a double throw contact 76 which selectively closes with the contact 78 or 80. The unlatching coil 72 for the latching relay is connected to the grinder control 46 such that it will receive an energizing signal at the beginning of every dressing cycle to assure that the contact 76 will be closed with contact 80 at the beginning of each sweep of the dress across the grinding wheel. The contacts 76, 78 and 80 are all connected to the grinder control 46 to provide information to the grinder control as to whether the grinding wheel needs further redressing. If the contact 76 is closed with contact 78, at the end of the dressing cycle, the grinder control 46 with initiate another dressing signal. If, however, the contact 76 should remain closed with contact 80, the grinder control 46 will cease the redressing function and will return the grinding wheel to production operation. Since the grinder control 46 is of a type well known to those skilled in the art, it will not be described herein.

In operation, the SCR will be non-conductive during the negative portion of the AC anode voltage cycle, but will .be conductive during the positive portion of each cycle provided only that the gate voltage is at least 0.8 volt. The amplifier 42 then is so adjusted that the strong signals 54 therefrom will be somewhat greater than 0.8 volt and the

weak signals

56 and 58 will be somewhat less than that value. This is readily accomplished for it has been found in practice that the strong signal amplitude differs from the weak signal amplitude by a ratio of 15 to 1. For the condition where the gate voltage is high, the SCR will conduct, the relay coil 62 will be energized and the relay contact 66 will be open. Due to the inherent dropout time of the relay, the brief non-conducting periods of the SCR during the negative voltage half-cycles will not cause the relay to drop out. However, when a low gate signal occurs, the SCR gate stops conducting entirely so that the relay 62 is deenergized and the contact 66 will be closed. Then, providing that the rnicroswitch 52 is closed, the relay coil 70 will be energized to close contacts 72, which causes relay coil 74 to be energized, thereby closing contacts 76 and 78 of the latching relay to provide a redressing signal to the grinder control 46 to effect continuation of the dressing operation. At the beginning of the next dressing cycle, a reset signal from the grinder control 46 will energize the unlatching relay coil 82 to return contact 76 into engagement with contact 80. If, however, throughout an entire sweep of the dressing tool across the grinding wheel, an uninterrupted signal such as that of FIGURE 6 is received by the SCR, the contact 66 will be held open, the grinder control 46 will not receive a redress signal and at the end of the dressing swing, the redressing activity will be suspended and the grinding wheel will be returned to normal production operation. As described above, in order to send a redress signal to the grinder control 46, microswitch 52 and contact 66 must both be closed. Since microswitch 52 does not close until after the diamond 33 engages the work piece and remains closed until just before the diamond 33 disengages the work piece, the switch will be closed only between points a and b of FIGURES 5 and 6 so that the weak signals 58 generated at the beginning and end of each dressing stroke will not produce a redressing signal. The result thereof of this circuit arrangement is to provide a redress sig nal, when, and only when, a weak signal 56 is generated thus indicating a groove, nick or other grinding wheel imperfection.

It will be seen then that my invention achieves the aforesaid objects. It is not intended that the scope of my invention be limited to the specific embodiment described herein, but rather is to be determined by the scope of the following claims:

I claim:

1. A grinding wheel dresser monitor comprising detecting means adapted to be mechanically coupled with the dresser for detecting the vibrations of the dresser, and having output signals corresponding to the vibrations, the nature of the vibrations being indicative of whether the grinding wheel requires further dressing, means coupled with the detecting means for discriminating between signals indicating need for further dressing and other signals and for rendering an indication of need for further dressing.

2. A grinding wheel dresser monitor as described in claim 1 wherein the detecting means is an accelerometer having an electrical output signal.

3. A grinding wheel dresser monitor as described in claim 2 wherein the means for discriminating between signals is an electrical device.

4. A grinding wheel dresser monitor as described in claim 3 wherein an electronic amplifier is connected between the accelerometer and the means for discriminating to amplify the output signal of the accelerometer.

5. In an apparatus for dressing a grinding wheel comprising a dressing tool, means for moving the dressing tool along the periphery of the grinding wheel in a prescribed path and control means for directing the dressing operation, the improvement consisting of detecting means connected to the dressing tool for detecting the vibrations of the dressing tool during its movement along the grinding wheel wherein an interrupted series of vibrations indicates need for further dressing and means coupled to the detecting means and to the control means for analyzing the vibrations thus detected and for signalling the control means that further dressing is required.

6. In an apparatus as described in claim 5 wherein the means for detecting vibrations comprises an accelerometer having an electrical output signal representative of the vibrations of the dressing tool.

7. In an apparatus as described in claim 6 wherein the means for analyzing the vibrations comprises an electrical trigger circuit which distinguishes between interrupted and non-interrupted signals.

8. In an apparatus as described in claim 7 wherein the trigger circuit is coupled to the accelerometer by an amplifier.

9. In an apparatus as described in claim 7 including switch means responsive to the position of the dressing tool along the periphery of the grinding wheel for controlling the output of the trigger circuit to block signals to the control means when the dressing tool is removed from normal dressing position.

References Cited UNITED STATES PATENTS 2,360,639 10/ 1944 Asimow 73-78 X 3,155,086 1 1/1964 Ornehage 51165 X 3,214,965 11/1965 Wellborn 7378 3,273,293 9/ 1966 Sonderegger. 3,404,670 10/1968 Gluchowicz -11 FOREIGN PATENTS 850,023 9/ 1960 Great Britain.

HAROLD D. WHITEHEAD, Primary Examiner US. Cl. X.R. 73-78 3 3 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,500,811 Dated March 17, 1970 Inventor(s) Wallace kin It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

[ In column 4, line 11, "cathore" should read -'cat'hode --;i1T|

line 26, delete "72" and inert therefor 82 in line 36, delete "with" and insert therefor will SIGNED AND swan AUG 4 .1970

tt 1: A ea IMHII'ITSGHIYIM, JR. Edward M- Fl wh r, J commissioner 0! Patents Arresting Officer