US3113405A

US3113405A - Apparatus for maintaining constant peripheral speed of a grinding wheel to compensatefor wheel wear

Info

Publication number: US3113405A
Application number: US130874A
Authority: US
Inventors: Robert V Schneider; Lennart A Kasparson
Original assignee: Norton Co
Current assignee: Saint Gobain Abrasives Inc
Priority date: 1961-08-11
Filing date: 1961-08-11
Publication date: 1963-12-10
Anticipated expiration: 1980-12-10

Description

Dec. 10, 1963 R. v. SCHNEIDER ETAL 3,

APPARATUS FOR MAINTAINING CONSTANT PERIPHERAL SPEED OF A GRINDING WHEEL T0 COMPENSATE FOR WHEEL WEAR Filed Aug. 11, 1961 /a, le

' AMPU HER ELECTEO -TEANSM ITTER ATTORNEY United States Patent APPARATUS FGR MAiNlAINlNG CGNSTANT PERIPHERAL EEPEED @F A GRINDING WHEEL TC CGMPENSATE FOR WHEEL WEAR Robert V. Schneider and Lennart A. Kasparson, both of Wei-caster, Mass, assignors to Norton Company, Worcester, Mass, a corporation of Massachusetts Filed Aug. 11, 1%1, Ser. No. 139$ 14- Claims. (Cl. 51-1345) This invention relates to grinding machines and has for its principal objects to provide mechanism for automatically maintaining the surface speed of a grinding wheel substantially constant to compensate for wheel wear; to provide a mechanism which will increase the speed of rotation of the Wheel in proportion to its reduction in radius due to wear without overcornpensation; to provide mechanism in which there is means for stopping the wheel in the event of an abrupt change in the mass of the wheel of the order resulting from the breaking-out of a chunk of abrasive material from the wheel, or of failure of some component part of the apparatus, which induces excessive speed without interfering with the means which merely modifies the rotation to maintain a constant surface speed; to provide a mechanism which has maximum and minimum speed limits, so that the machine will fail safe; and to provide mechanism which is adapted to be used in conjunction with conventional grinding machines without extensive alteration thereof.

As herein illustrated, the apparatus comprises a sensing device responsive to a reduction in the radius of the wheel due to Wear to produce a signal of increasing amount, compensating means operable by an increase in the signal to increase the speed of the motor to maintain the surface speed of the wheel constant as the wheel diminishes radius, and means operable, by an increase in speed of the motor which is sufiicient to maintain the surface speed of the wheel constant, to nullify the effect of the increase in the signal until the diameter is further reduced by wear. There is also a safety mechanism disposed at a position adjacent the wheel, but spaced therefrom a predetermined amount, and maintained at said predetermined distance by each increase in the speed of the motor as the latter is speeded-up to maintain the surface speed of the wheel constant, which is movable into engagement with the wheel in the event of an excessive increase in speed caused by failure of a component part of the mechanism, or damage to the wheel, to stop the motor, and there are limit switches to render the mechanism inoperable in the event of too high or too low speeds.

The invention will now be described in greater detail with reference to the accompanying drawings wherein:

FIG. 1 is an elevation of the face of a grinding wheel, showing the sensing means supported at the opposite sides thereof;

FIG. 2 is a wiring diagram of the control circuit; and

FIG. 3 is a diagrammatic illustration of the wheel, the wheel drive motor, and a safety device for rendering the mechanism inoperative in the event of excessive speed.

Referring to the drawings, there is shown a grinding Wheel mounted on a shaft 12 for rotation about a horizontal axis, the shaft being connected to a drive motor M, as diagrammatically shown in FIG. 3.

Grinding wheels of large diameter and high speed, such as are used for snagging large steel billets and slabs wear rapidly and to maintain an efiicient grinding speed, it is necessary to constantly increase the speed of rotation of the wheel in proportion to its reduction in diameter by reason of wear. In accordance with this invention a sensing device is provided for this purpose which, as

shown in FIG. 1, includes a source of radiation 14 mounted at one side of the Wheel and a radiation pick-up device 16 mounted at the opposite side of the wheel. The source of radiation 14a is situated at a radial distance from the axis of rotation, substantially equal to the radius of the wheel prior to wear, and its beam is controlled by an aperture so that it has an angle of spread which, projected on the side of the wheel, is substantially equal to the permissible radial wear of the wheel before the latter has to be renewed, as indicated by the dimension a. The pick-up device 16, which is shielded from the source of radiation by the wheel, is of such a character that it generates a signal which increases in magni tude in proportion to the decrease in radius of the Wheel as the latter is worn down, and thus exposes the device 16 to more and more radiation.

The

parts

14 and 16 of the sensing device are manufactured by the Industrial Nucleonics Corporation of Columbus, Ohio, and are commercially available according to specification. The part 14 comprises a heavy casting provided with a manually operable shutter not illustrated for closing a radiation aperture, en not in use, and contains, as a source 142, two milligrams of radium 226. The part 16 comprises a pipe section within which is mounted a long life halogen-quenched stainless steel shell Geiger-Mueller tube not illustrated, which is operable to convert gamma radiation into electric signals.

For maximum safety in this application, the manually operable shutter provided in part 14 by the manufacturer may be interlocked with the means for securing the cover on the guard enclosing grinding wheel 16) by a suitable linkage so that the shutter is closed automatically when the cover is released. With the provision of such an arrangement, the machine operator is fully protected against radiation automatically whenever the wheel guard is opened for the purpose of changing the grinding wheel.

The electric signal produced by the sensing device is used to control the speed of the variable speed wheel drive motor M by way of a control circuit. shown in FIG. 2. Power is supplied to the circuit from a volt AC. source. The electric current provided by the sensing device is amplified by an amplifier 18 and fed to an electrotransmitter 29. The electrotransrnitter 26 operates to move the slider 21 of a potentiometer 22 from right to left on its resistor 23 as the wheel wears. Since the sensing device operates continuously a speed compensator 26 is provided to stabilize the speed of the motor when the wheel reaches a speed which compensates for the decrease in radius. To this end, the potentiometer resistor 23 is placed in a secondary circuit containing the compensator and is supplied with alternating current from the secondary winding 27 of a transformer, the primary winding of which is shown at 29. The compensator circuit includes a thyratron tube 28, a tachometer generator 35, and a relay CR1. A rectifier is provided for converting the alternating current to direct current, so that when the slide 21 of the potentiometer, which is connected to the grid 30 of the thyratron tube, is moved in a counterclockwise direction in response to an increase in radiation, direct current will be supplied to the grid of the thyra tron tube. By making the grid positive, it conducts current so as to energize the relay CR1. Energizing relay CR1 closes a switch SCR1 of a third circuit which contains the field winding 34 of a rheostat positioning motor 35. The positioning motor 35 drives a rheostat 37 (FIG. 3) which controls the current supplied to the wheel motor M, in a direction to increase the speed of the motor provided that the switch SW1 is set in the run position and the normally closed limit switch LSH is closed. The tachometer generator 36 is also connected to the grid 30 of the thyratron. The tachometer is driven by the motor M so that its speed increases with that of the motor.

Rotation of the tachometer 36 generates a negative current which changes proportional to the increase in the speed of the motor and feeds it back to the grid 39 of the thyratron tube. When the speed of the motor is such that the negative current generated by the tachometer balances the positive current supplied to the grid from the potentiometer, flow of current through the tube is stopped, thereby de-energizing the relay CR1. De-energization of the relay opens the switch SCRl so that the positioning motor 35 comes to a stop and the motor M will continue to run at a constant speed even though the radiation pick-up device contained within part 16 continues to be receptive of radiation from the radiation source 14a. This stabilized condition will continue until more of the surface of the wheel is worn away, thereby increasing the amount of radiation received by the radiation pick-up device, which results in nnbalancing the thyratron tube on the positive side, so as to restart the positioning motor 35 and to move the field rheostat 37 in a direction to further increase the speed of the motor. The circuit explained is in the form of a balancing device or governor.

The normally closed limit switch LS H is controlled by an actuator not illustrated when the slider of the rheostat 37 is rotated into the position which produces the highest permissible speed for the wheel drive motor M so that the run circuit which produces rotation of the positioning motor 35' to increase the speed of motor M is deenergized when motor M reaches this maximum speed.

Similarly, the normally closed limit switch LSL in cluded in the reset circuit for the positioning motor 35 is opened by an actuator not illustrated when the slider of the rheostat 37 is rotated into the position which produces the lowest required speed of the motor M.

A safety device 38 (FIG. 3) is provided for shutting down the apparatus in the event of failure of some component part thereof, or of the wheel itself, which causes excessive speed of the motor M. As shown, this com.- prises an arm 40 fixed to the shaft 42 which connects the position-ing motor 35 to the rheostat 37, so that it is rotated in proportion to the rotation of the rheostat 37. The arm 40 [has pivotally connected to it one end of a link 44, the other end of which is pivotally connected to a rod 46 which is supported with its distal end at a predetermined distance from the surface of the grinding wheel. A limit switch LS1 is mounted at the distal end of the rod 46 and has on it an actuator 48 which is maintained at a predetermined distance from the surface of the wheel during normal operation of the apparatus and is moved toward the wheel in proportion to the reduction in the diameter of the wheel. In the event, however, that the signal produced by the sensing device is not compensated for by the signal produced by the tachometer due to some failure in the circuit or possibly by breakage of the wheel, the unchecked continuing rotation of the positioning motor will move the rod 46 and hence the switch actuator 48 into engagement with the wheel and thus open the limit switch LS1, cutting off the main power supply to motor M and shutting down the grinding machine.

It is within the scope of this invention to employ photoelectric, pneumatic or sonic sensing devices for producing a signal to effect operation of the compensator and correspondingly to employ any electrical, pneumatic, or mechanical equivalent of the compensator to effect control of the motor.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modifications and equivalents which fall within the scope of the appended claims.

We claim:

1. Ina grinding machine, a grinding wheel, a motor for driving the grinding wheel and means for maintaining the surface speed of the Wheel constant as the wheel Wears, comprising an elongated sensing device fixedly secured radially of the grinding wheel and operable, in response to a reduction in the radius of the wheel, to produce a signal of increased magnitude, a compensator responsive to an increase in the signal to increase the speed of the motor, and a feed-back operated by the motor in response to an increase in the speed of the motor sufficient to maintain the surface speed of the wheel constant to nullify the effect of the increase in the signal.

2. In a grinding machine, a grinding wheel, a motor for driving the grinding wheel and means for maintaining e surface speed of the wheel constant as the wheel wears, comprising an elongated sensing device fixedly secured radially of the grinding Wheel and operable, in response to a reduction in the radius of the wheel, to produce a signal of increased magnitude, means operable to increase the speed of the motor, a compensator operable to effect operation of the last-named means, operation of said compensator being effected by an increase in the signal, and a feed-back operated by the motor in response to an increase in the speed of the motor sufiicient to maintain the surface speed of the wheel constant to nullify the effect of the increase in the signal.

3. In a grinding machine, a grinding wheel, a motor for driving the grinding wheel and means for maintaining the surface speed of the wheel constant as the wheel wears, comprising a sensisng device responsive to a reduction in the radius of the wheel to produce a signal of increased magnitude, a thyratron tube, a potentiometer responsive to an increase in the signal to make the thyratron tube conductive, a tachometer operable, by an increase in the speed of the motor, sufiicient to maintain the surface speed of the wheel constant to make the thyratron tube non-conductive, and means operable, when the tube becomes conductive, to elfect an increase in the speed of the motor.

=4. In a grinding machine, a grinding wheel, a motor for driving the grinding wheel and means for maintaining the surface speed of the wheel constant as the wheel wears, comprising sensing means having components fixedly disposed so that they face opposite faces of the wheel, said components including a source of radiation and an elongated sensing element disposed radially of the grinding wheel, said sensing element being responsive to an increase in exposure to said source of radiation by wear of the wheel interposed therebetwcen to produce a signal of increasing amount, a device operable in response to an increase in the signal to increase the speed of rotation of the motor to compensate for the reduction in radius of the wheel, and means driven by the motor operated by an increase in. the speed of the motor sufficient to maintain the surface speed constant so as to neutralize the increased signal.

5. In a grinding machine, a grinding wheel, a motor for driving the wheel and means for maintaining the surface speed of the wheel constant as the wheel wears, comprising sensing means having components fixedly disposed adjacent opposite faces of the wheel consisting respectively of a fixed radiation source and a fixed elongated sensing element disposed radially of the wheel which are increasingly exposed to each other as the radius of the wheel diminishes, said means operating to produce a signal of cumulatively increasing amount as the radius of the wheel diminishes, la rheostat controlling the supply of current to the motor, means operable, in response to each increase in the signal, to move the rheostat in a direction to increase the speed of the motor, and means coupled to the motor operable by an increase in the speed of the motor sufiicient to maintain the surface speed constant to produce a cumulatively increasing compensating signal effective to neutralize the increased signal produced by said sensing means.

6. In a grinding machine, a grinding wheel, a wheel motor for driving the wheel and means for maintaining said surface speed of the wheel constant as the wheel wears, comprising a fixedly mounted sensing device operable to produce a signal of cumulatively increasing magnitude as the wheel diminishes in radius, a field nheostat for supplying current to the motor, a positioning motor for effecting movement of the rheostat, means operable by an increase in the signal to effect operation of the positioning motor and hence movement of the rheostat in a direction to increase the speed of the wheel motor, and means operated by the motor in response to an increase in speed of the wheel motor suflicient to maintain the surface speed of the wheel constant to produce a cumulatively increasing compensating signal effective to neutrailize the increased signal produced by said sensing means.

7. In a grinding machine, a grinding wheel, a motor for dniving the grinding wheel and means for maintaining the surface speed of the wheel constant as the wheel wears, comprising fixedly mounted sensing means operable to produce a signal of constantly increasing magnitude as the wheel wears, a field rheostat for supplying current to the motor, a positioning motor for moving the rheostat, a positioning motor switch, means operable in response to an increase in the signal to close said switch, and means operated by the wheel motor in response to an increase in speed of the wheel motor sufiicient to maintain the surface speed of the wheel constant to produce a signal of opposite kind and of a magnitude sufiicient to neutralize said first-named signal and thereby open said switch.

8. In a grinding machine, a grinding wheel, a motor for driving the grinding wheel and means for maintaining said surface speed of the wheel constant as the wheel wears, comprising sensing means including a fixedly mounted radiation source and a fixedly mounted radiation pick-up disposed adjacent opposite faces of the wheel, said pick-up having a sensitive Zone disposed radially of the wheel and at least as long as the permissible radial wear of the wheel, and said source having a dispersion angle such that its projection on the side of the wheel corresponds in length to the length to the permissible radial wear, said radiation source and said radiation pick-up cooperating to produce a signal which cumulatively increases in magnitude as the radius of the wheel diminishes, means operable in response to each increase in the signal to increase the speed of the motor, and means operated by the motor when the speed of the latter increases sufficiently to maintain the surface speed of the wheel constant to render the last-named means inoperative.

9. In a grinding machine, a grinding wheel, a motor for driving the grinding wheel and means for maintaining said surface speed of the wheel constant as the wheel wears, comprising sensing means including a fixedly mounted radiation source and a fixedly mounted radiation pick-up disposed adjacent opposite faces of the wheel, said radiation source having a point source spaced from the center of the wheel at a radius corresponding to the undiminished radius of the wheel prior to wear and said radiation pick-up having an elongated radiation sensing zone disposed radially of the portion of the wheel worn away in use, said radiation source and radiation pick-up cooperating to produce a signal of cumulatively increas ing magnitude as the radius of the wheel diminshes, means operable in response to each increase in the signal to increase the speed of the motor, and means operated by the motor when the speed of the latter increases sufficiently to maintain the surface speed of the wheel constant to render the last-named means inoperative.

10. In a grinding machine, a grinding wheel, a motor for driving the grinding wheel and means for maintaining the surface speed of the wheel constant as the wheel wears, comprising sensing means including a fixedly mounted radiation source and a fixedly mounted radiation pick-up disposed adjacent opposite faces of the wheel, said radiation source having a point source situated at a distance from the center of the wheel corresponding to the undiminished radius of the wheel prior to wear, and a spread which, projected on the face of the wheel, is at least equal to the permissible amount of radial wear, said radiation pick-up having a sensitive zone disposed in a radial position relative to the wheel which is at least as long as the projection of the spread on the wheel, said components cooperating to produce a signal of cumulatively increasing magnitude as the wheel diminishes in radius, means operable in response to each increase in the signal to increase the speed of the motor, and means operated by the motor when the speed of the latter is increased sufficiently to maintain the surface speed of the wheel constant to render the last-named means inoperative.

11. In a grinding machine, a grinding wheel, a motor for driving the grinding wheel, a source of power for supplying current to the motor and means for maintaining a constant surface speed as the wheel wears, comprising sensing means having components disposed at opposite faces of the wheel which operate to give a continuous signal, the magnitude of which increases as the radius of the wheel diminishes, means operable by an increase in the signal to increase the current flow from said source to said motor, means operable to control the increase in speed of the motor in inverse proportion to the reduction in the radius of the Wheel, means operable by an increase in the speed of the motor sufficient to maintain the surface speed of the wheel constant to render the last-named means inoperative, and a safety device operable by an excessive increase in speed to interrupt the fiow of current to the motor.

12. In a grinding machine, a grinding wheel, a motor for driving the wheel, means for supplying current to the motor including a normally closed switch and means for maintaining a constant surface speed as the wheel wears, comprising sensing means having components disposed at opposite faces of the wheel which operate to give a signal, the magnitude of which increases as the radius of the wheel diminishes, a rheostat controlling the flow of the current from the source to the wheel motor, means operable by an increase in the signal to eifect movement of the rheostat in the direction to increase the current flow to the motor, means responsive to an increase in speed of the motor sufiicient to maintain the surface speed of the wheel constant to terminate operation of the lastnamed means, and means operable by an excessive increase in the speed of the motor to open said normally closed switch.

13. In a grinding machine, a grinding wheel, a motor for driving the wheel, a source of power for supplying current to the motor and means for maintaining a constant surface speed as the wheel wears, comprising sensing means having components disposed at opposite faces of the wheel which operate to give a continuous signal, the magnitude of which increases as the radius of the wheel diminishes, means operable by the signal to increase the current flow to the motor, feed-back means operable by the motor to render the last-named means inoperative when the increase in speed of the motor is sufficient to maintain the surface speed of the wheel constant, a linkage arranged to move linearly toward the surface of the wheel as the speed of the motor increases, and means carried by the linkage operable by contact with the surface of the wheel due to an excessive increase in speed of the motor to interrupt the flow of current from the source to the motor.

14. In a grinding machine, a grinding wheel, a motor for driving the wheel, a source of power for supplying current to the motor and means for maintaining a constant surface speed as the wheel wears, comprising sensing means having components disposed at opposite faces of the wheel which operate to give a continuous signal of increasing magnitude as the radius of the wheel diminishes, means operable by each increase in the magnitude of the signal to increase the flow of current to the motor, feed-back means operable by the motor to render the last-named means inoperative When the increase in speed of the motor is sufficient to maintain the surface speed of the wheel constant, a link including a part situated at a predetermined distance from the surface of the wheel arranged to move linearly toward the surface of the wheel in proportion to the reduction in the radius of the wheel, said part of the linkage being movable into contact with the surface of the wheel if the increase in speed exceeds a proportionate reduction in the wheel, and a switch carried by said part operable by contact with the wheel to interrupt the supply of current to the motor.

References Cited in the file of this patent UNITED STATES PATENTS Price June 23, 1942 -Lonaberger Aug. 8, 1961 FOREIGN PATENTS Great Britain Sept. 30, 1953

Claims

1. IN A GRINDING MACHINE, A GRINDING WHEEL, A MOTOR FOR DRIVING THE GRINDING WHEEL AND MEANS FOR MAINTAINING THE SURFACE SPEED OF THE WHEEL CONSTANT AS THE WHEEL WEARS, COMPRISING AN ELONGATED SENSING DEVICE FIXEDLY SECURED RADIALLY OF THE GRINDING WHEEL AND OPERABLE, IN RESPONSE TO A REDUCTION IN THE RADIUS OF THE WHEEL, TO PRODUCE A SIGNAL OF INCREASED MAGNITUDE, A COMPENSATOR RESPONSIVE TO AN INCREASE IN THE SIGNAL TO INCREASE THE SPEED OF THE MOTOR, AND A FEED-BACK OPERATED BY THE MOTOR IN RESPONSE TO AN INCREASE IN THE SPEED OF THE MOTOR SUFFICIENT TO MAINTAIN THE SURFACE SPEED OF THE WHEEL CONSTANT TO NULLIFY THE EFFECT OF THE INCREASE IN THE SIGNAL.