US3818639A

US3818639A - Apparatus for surface grinding

Info

Publication number: US3818639A
Application number: US00306310A
Authority: US
Inventors: E Dunn
Original assignee: Litton Industries Inc
Current assignee: Litton Industries Inc
Priority date: 1971-09-20
Filing date: 1972-11-14
Publication date: 1974-06-25
Anticipated expiration: 1991-06-25

Abstract

A grinding apparatus comprising abrasive disc means including at least one abrasive disc, means for mounting the abrasive disc for rotative displacement about the axis of the abrasive disc, means for rotationally displacing the abrasive disc, means for mounting a workpiece having at least one surface to be ground by the abrading action of the face of the abrasive disc, means for displacing the mounting means radially across the abrasive disc face from a first radial position proximate the outer periphery thereof to a second radial position proximate the center of the face of the abrasive disc, and means for selectively decelerating the displacing means as the mounting means is displaced from the first position to the second position.

Description

United States Patent [191 Dunn [ June 25, 1974 Related U.S. Application Data [63] Continuation-in-part of Ser. No. 181,746, Sept. 20,

1971, abandoned.

[52] U.S. Cl 51/112, 51/118, 51/l65.77,

5l/l65.9, 51/215 UE [51] Int. Cl. B24b 7/16, B24b 51/00 [58] Field of Search 51/111-116,

51/118, 165.77,165.9, 165.78, 281,122, 124 R, 121, 21 S, 21 UE 3,299,579 1/1967 Jacobson 51/327 X 3,382,622 5/1968 Dunn 51/118 X FOREIGN PATENTS OR APPLICATIONS 1,036,693 8/1958 Germany 51/112 Primary Examiner0thell M. Simpson Assistant Examiner-Nicholas P. Godici Attorney, Agent, or Firm Spencer T. Smith [57] ABSTRACT A grinding apparatus comprising abrasive disc means including at least one abrasive disc, means for mounting the abrasive disc for rotative displacement about the axis of the abrasive disc, means for rotationally displacing the abrasive disc, means for mounting a workpiece having at least one surface to be ground by the abrading action of the face of the abrasive disc, means for displacing the mounting means radially across the abrasive disc face from a first radial position proximate the outer periphery thereof to a second radial position proximate the center of the face of the abrasive disc, and means for selectively decelerating the displacing means as the mounting means is displaced from the first position to the second position.

13 Claims, 11 Drawing Figures PATENTEUJUNZSIQM $818,639

END OF GR ND 9 ,5 I 'i i 26 .START GRIND 23c 23A LOADING POSITION wDRKPIEcE/IaRAsIvE RELATIONSHIP WORKPIECE 8 I LOADED ABRASIVE FPM 7 WORKPIECE TR'AVERSE SPEED IPM ENCODER 92 e A LOGIC cIRcuIT 5 V) J/ I; 94

PULSE RATE E RATE 0 4 MULTIPLIER D 0 g B x g 3 v STEPPING MOTOR a D i I I 5 2 D g I .R 97/ I Fig-6 l ANGULAR POSITION 0F WORKPIECE (t BELOW HORIZONTAL t 1 APPARATUS FOR SURFACE GRINDING This application is a continuation-in-part of my copending application Ser. No. 181,746, filed'Sept. 20, 1971, now abandoned.

This invention relates in general to an improved method and apparatus for grinding opposed faces of workpieces which are ground on horizontal double disc grinders.

Since the surface speed of a rotating abrasive disc is a direct function of radial location the abrasive forces are greatest in the outer peripheral zone of the abrasive disc. Even though the abrasive disc has more abrasive grains in this outer peripheral zone, excessive wear results therein and such uneven wear shortens the life of the abrasive discs which must be frequently redressed.

In grinding machines wherein a workpiece makes a single pass through the grinding zone and is advanced from a position beyond the outer periphery of the abrasive disc this problem of excessive wear is compounded since the workpiece has its maximum size at the point of entry. Additionally, since the load on individual grains varies with the amount of stock removal per unit of time, greater deflection of the abrasive grains occurs in the outer peripheral area than occurs in the inner peripheral area of the disc.

Attempts have been made to achieve uniform abrasive disc wear by designing abrasive discs which have harder abrasive grains in the outer peripheral areas than in the intermediate or central portion or zone of the face. Additionally, the abrasive bond has been varied so that the abrasive grains will be more readily released at the central portion of the face. None of these approaches have been entirely satisfactory because each attempt has sacrificed normal grain life.

A primary object of the present invention is to provide a double disc grinding machine wherein the abrasive discs will be uniformly worn whereby the frequency of the abrasive disc dressing operations will be reduced with a concomitant reduction in machine downtime.

Another object is to grind the parallel sides of workpieces to lapping tolerance limits at a continuous high production rate and still maintain the grinding of each workpiece individually one-at-a-time.

Another object is to direct the workpieces to enter the machine below the horizontal centerline of the abrasive discs and near to the neutral axis of the machine base, to reduce the deflection of the abrasive discs during the initial portion of the grinding cycle and thereby provide more even wear on the faces of the abrasive discs.

Among the advantages of the present invention is the provision of a grinding machine wherein abrasive discs having uniform abrasive characteristics can be utilized.

cordance with the teachings of the present invention;

FIG. 2 is a left-hand end view of the horizontal double disc grinder illustrated in FIG. 1 showing the workpiece locations in the carrier and the relative position of the carrier to the abrasive discs;

FIG. 3 is a left-hand end view of the variable speed drive control unit which governs rotation of the carrier illustrated in FIG. 2;

FIG. 4 is a fragmentary sectional view taken along the line 44 of FIG. 3;

FIG. 5 is an enlarged fragmentary view of the work carrier illustrated in FIG. 2;

FIG. 6 is a chart showing for the first preferred embodiment the resultant effect of the automatic traverse speed reduction compared to a conventional constant traverse speed of a workpiece;

FIG. 7 is a wiring diagram showing the control circuit for operating the automatic cycle of the disc grinder having the first preferred embodiment;

FIG. 8 is a plan view of the disc grinder having the first preferred embodiment showing the pneumatic circuit for controlling the loading and unloading of the workpieces;

FIG. 9 is a block diagram showing a modified drive control mechanism for rotating a fixture or work holder having the first preferred embodiment;

FIG. 10 is an enlarged elevational view of a portion of a grinding apparatus having a second preferred embodiment; and

FIG. 11 is a schematic diagram illustrating the hydraulic controls for the second preferred embodiment.

A horizontal double disc grinding machine 10 having a first preferred embodiment is illustrated in FIGS. 1 and 2. The grinding machine includes an opposing pair of grinding heads 11L and HR which are slidably mounted on the machine base 12. The grinding heads 11L and 11R include

horizontal spindles

13L and 13R (FIG. 8) which carry abrasive discs 14Lv and 14R. The

abrasive discs

14L and 14R are mounted in a conventional manner for rotation about a horizontal axis and for movement toward and away from one another in unison as shown, for example, in US; Pat. No. 3,561,164, granted Feb. 9, 197]. The

abrasive discs

14L and 14R are housed within a wheel hood 15 which is pivotably mounted to the machine base 12 as shown in FIG. 2, whereby worn

abrasive discs

14L and 14R may be easily replaced. The

abrasive discs

14L and 14R are driven through suitable connections by

motors

16L and 16R which are normally arranged to rotate the

abrasive discs

14L and 14R in opposite directions but which may be arranged to rotate these discs in the same direction.

A rotary carrier assembly 17 (FIGS. 1 and 2) includes a housing 18 which is secured to the machine base 12 through a hinge pin bracket 19. The bracket 19 is positioned to align a rotary work carrier 21 with the center of the grinding machine 10. The work carrier 21 is mounted on a horizontal spindle '22 which is rotatably journaled in bearings 20 and 20' (FIG. 4) within the housing 18. The work carrier 21 has a series of work holding stations or

openings

23A, 23B and 23C, each of which is selectively sized to receive a workpiece W. The carrier 21 is rotatably driven by a carrier drive motor 29 and the speed of the motor 29 is governed by a variable speed drive control mechanism 24 which is protected by a guard 25. Rotation of the carrier 21 advances the workpieces W between the

abrasive discs

14L and 14R in an arcuate path.

The

openings

23A, 23B and 23C are geometrically spaced near the periphery of the work carrier 21 at sufficient angular intervals so that no two workpieces are ever in the grinding zone between the

abrasive discs

14L and 14R at the same time. This enables the workpieces W to be ground on a continuous one-at-a-time basis. The carrier 21 is rotated in a clockwise direction as viewed in FIG. 1 to direct the unground workpieces W into the grinding zone 26 below the axis of rotation of the

abrasive discs

14L and 14R. The entry position 27 is such that the

abrasive discs

14L and 14R will accept the workpieces W and will only separate slightly from the initial grinding pressure. The ground workpieces W are discharged from the grinding zone 26 at eye level and at a position 28 which is above the axis of rotation of the

abrasive discs

14L and 14R.

The carrier spindle 22 is rotated by a motor 29 at a rapid speed through a gear drive mechanism 35, which may include a built-in-safety clutch. Referring now to FIGS. 3 and 4, it can be seen that rotation of the spindle 22 rotates a geared pulley 30 which is secured to the spindle 22. The pulley 30 drives a geared pulley 31 by a positive drive belt 32. The geared

pulleys

30 and 31 have a 3:1 ratio so that the pulley 31 rotates three times for every rotation of the spindle 22.

The pulley 31 is secured to a shaft 33 which is journaled in

bearings

34 and 36 within abore 37 of a gear block 38. A segment gear 39 is secured to the shaft 33 and includes a predetermined number of teeth 40 which extend over a predetermined arc and selectively mesh with teeth 41 of a spur gear 42.

The spur gear 42 is mounted on one end of a shaft 43 and a potentiometer 44 is mounted on the other end thereof. The shaft 43 is journaled in

bearings

46 and 47 which are housed within the gear block 38. Rotation of the segment gear 39 and the spur gear 42 causes rotation of the potentiometer 44 as each workpiece W passes through the grinding zone 26. The potentiometer 44 is electrically connected to the drive motor 29 so as to selectively gradually reduce the field voltage thereto each time the potentiometer 44 is rotated, and thereby reduce the traverse speed of the workpiece W.

The segment gear 39 is selectively positioned on the shaft 33 so that the teeth 40 commence engagement with the teeth 41 of the spur gear 42 as the workpiece W enters between the

abrasive discs

14L and 14R (FIG. 3). The segment gear 39 rotates in a clockwise direction as shown by the arrow, and the spur gear 42 is rotated counter-clockwise until the last tooth 40 on the segment gear 39 disengages from the last tooth of the spur gear 42. At this time, the workpiece W is at the end of the grind position 48 (FIG.

Once the segment gear teeth 40 have disengaged from the teeth 41 of the spur gear, the segment gear 39 continues to rotate with the pulley 31 and the spindle 22. In order to reset the potentiometer 44 to its original position a grooved pulley 49 is secured to the shaft 43. The pulley 49 carries one end of an extension spring 50 which is secured thereto by a fastener 51. The other end of the spring 50 is anchored to a bracket 52 which is secured to the lower end of the gear block 38. This arrangement will reset the spur gear 42 and the potentiometer 44 in a clockwise direction (FIG. 3) whenever the spur gear 42 becomes disengaged from the teeth 40 of the segment gear 39. The pulley 49 will rotate in a clockwise direction until a pin 53 thereon contacts a stop pin 54 which is secured to the gear block 38.

The potentiometer 44 is retained at a predetermined value at a minimum resistance level when the pulley 49 is reset. The force of the spring 50 is absorbed by the pin 54, and the angular position of the potentiometer 44 is restored.

The work carrier 21 will rotate at a rapid speed whenever the teeth 40 of the segment gear 39 become disengaged from the teeth 41 of the spur gear 42, and the ground workpiece W will be discharged from the grinding zone 26 at a rapid rate.

The portion of the segment gear which is provided with the teeth 40 is directly related to the length of the arc of the grinding zone 26. The following formula shows, in general, the manner of calculating the length of the toothed arc of the segment gear 39, assuming that the work carrier 21 has three workpieces spaced at intervals:

where S, is the arc of the segment gear 39 having teeth 40; and G is the arc of the grinding zone 26, which can be determined by various means.

The are of the grinding zone 26 will vary depending on such things as the diameter of the

abrasive discs

14L and 14R, the point on the periphery of the

abrasive discs

14L and 14R at which the workpiece W enters and the number of workpieces carried by the carrier.

It may be desirable to have workpiece traverse speed reduction over less than the entire grinding zone 26. For example, it is possible to delay the commencement of the speed reduction until after an initial portion of the grinding cycle has taken place in order to increase the output of the machine. Each of the above must be considered in determining the portion of the segment gear 39 which is provided with teeth 40.

For ease of loading and unloading workpieces W into and from the work carrier 21, a loading chute 55 and loader mechanism 56 are secured to a support bracket 57 (FIG. 8) which is secured to the machine base 12 on one side of the work carrier 21. The loading chute 55 directs the flow of unground workpieces W into the loader mechanism 56 which advances successive workpieces W into the

openings

23A, 23B, or 23C. Each finish ground workpiece W is measured by a gage mecha nism 61 in conventional manner prior to being extracted from the work carrier 21 at a discharge station 58. The ground workpiece W is directed into an unloading chute 62 which is shown positioned to the left of the work carrier 21 and in alignment to accept the workpieces W being extracted. The workpieces W are withdrawn from the

openings

23A, 23B, and 23C by a work ejector 59 which may have a magnetic extractor 63.

It should be noted that necessary entry guides 64 and exit guides 66 are provided to assist in retaining the workpieces W in the proper axial position for entrance or discharge from the

abrasive discs

14L and 14R in a conventional manner. Spray guards 68 and 69 are also provided to protect the operator from any coolant being discharged from between the abrasive discs 14L by a nozzle 71 and to both sides of the work carrier 21 by a nozzle 72. A high volume of coolant is required to flush swarf from the grinding zone 26 and to provide a cooling effect to prevent overheating and distortion of the workpieces W'during the grinding operation.

It is well known that the cutting efficiency of the abrasive grains is greater near the outside periphery of the abrasive discs than it is near the central area thereof. Curves A and B FIG. 6) each represent a comparison of the speed of the abrasive grains (feet per minute) to the workpiece traverse speed (inches per minute) as the workpiece W is advanced through the grinding zone 26, starting at the entry position 27 and ending at end of the grind position 48. Curve A depicts a typical curve utilizing the instant invention; whereas, curve B depicts a typical curve as taught in the prior art where there was no reduction of the workpiece traverse speed. As can be seen in curve A, there is a nearconstant relationship between the speed of the workpiece and the abrasive grains for approximately the first (from 38 to 18) of the grinding zone 26 (FIG. 5). The slow down of the workpiece traverse speed then becomes much more pronounced, resulting in a higher stock removal quotient. This results from the fact that a linear wound potentiometer 44 was used which provided a nearly linear speed reduction; whereas the workpiece W does not approach the center of the

abrasive discs

14L and 14R nearly as fast during the latter portion of the grinding cycle due to the geometry of the situation. Thus, the slope of curve A increases sharply I toward the end of the grinding zone 26. Curve A shows that a nearconstant amount of abrasive grain per unit of time passes the workpiece W as the workpiece passes through the first 20 or so of the grinding zone 26, and further that an increasing amount of abrasive grain per unit of time passes the workpiece W as it approaches the horizontal centerline position, where abrading efficiency is at its lowest value. It should be apparent that this increase provides more time for the less efficient grains near the center of the abrasive disc 14R to erode in order to maintain abrasive disc flatness. The slower traverse speed of the workpiece W, while in the slow speed zone, provides a lapping effect which improves a fine surface finish on the workpiece W.

lt is not possible to predict the ideal shape of curve A for every type of grinding operation. It is believed that the best results are obtained if curve A is either flat or has a possitive slope, as shown in FIG. 6. Curve A can be flattened by using a non-linear potentiometer or any other type of control device, such as a variable speed hydraulic motor or an electric or electronic circuit for varying the voltage to the drive motor 29. It is also possible to provide a workpiece traverse speed reduction and still have a negative slope. This invention contemplates such a situation, although it is not believed to be the preferred manner of practicing the invention.

As can be seen, curve B has a steep negative slope due to the rapid decrease in abrasive grain speed as the center of the abrasive disc is approached. This results in less wear in the central area of the abrasive discs than that at the outer areas, with the concomitant problems caused thereby. Comparison of the total area under the two curves (FIG. 6) shows that curve A permits approximately 73 percent more abrasive grains to pass the center (reference point) on the workpiece W.

Actual tests have been conducted that demonstrate the results of using a variable rotating speed of the work carrier 21 which enables up to 450 workpieces to be ground per hour. Stock removal of 0.006 inch total was removed from the opposite parallel sides of workpieces (0.003 inch from each side) having a diameter of 4 inches. The grinding results included a flatness of 0.00015 inch, parallelism of 0.0002 inch, size uniformity of 0.0005 inch, and a surface finish of 30 RMS (Root-Mean-Square Average) inches.

Other actual tests have demonstrated the capability to grind 600 workpieces per hour utilizing this invention, removing 0.0015 inch total stock while maintaining final surface flatness within 0.000030 inch to 0.000060 inch T.l.R. (Total Indicator Reading), and a surface finish of 6 to 10 RMS inches.

The grinding machine 10 includes a feed system for advancing the

abrasive discs

14L and 14R inwardly to a preset position which is effected by an electrical or digital control system. Variations from the preset positions are made to compensate for wheel wear and for variations beyond the size tolerance limits which are determined by the gage mechanism 61 (FlG. 2). A rapid face cutting approach and retraction rate may be synchronized with the operation of the work carrier 21 when relatively large amounts of stock removal are required.

The described method of grinding enables a continuous flow of workpieces W to be ground to lapping tolerances on a one-at-a-time basis. This is accomplished during the automatic cycle of the machine, as the work carrier 21 is rotated at variable speeds to direct unground workpieces W between the

abrasive discs

14L and 14R.

When a three-station work carrier 21 is used, workpieces W are loaded and unloaded simultaneously while the grinding operation is completed on a third workpiece W which is positioned near the central area of the

abrasive discs

14L and 14R. The work carrier 21 rotates at a slow traverse speed when the workpiece is located proximate the inner periphery of the grinding discs whereby a lapping finish will be achieved. The work ejector 59 will unload the previously ground workpiece W from the opening 23C and the loader mechanism 56 will advance an unground workpiece W into the opening 23A. The work carrier 21 is then rotated at a rapid speed and the cyclic grinding of the workpieces W on a continuous one-at-a-time basis is continued.

The grinding heads 11L and 11R are advanced inwardly during set-up to position the

abrasive discs

14L and 14R at the innermost or grind position prior to starting the automatic cycle. A workpiece W is advanced into the opening 23A by actuating the loader mechanism 56 during the set-up operation.

The automatic cycle is started by depressing the automatic cycle push button 12PB which energizes an automatic cycle relay CRA, as a circuit is completed through a normally closed reset push button 1 lPB, and through a normally closed contact CRl-ll which is an interlock for the manual cycle. The automatic relay contacts CRAl, CRA2, CRA3, and CRAS, CRA6, CRA7 and CRAS are closed by the energization of the relay CRA. Y

The closing of the contact CRAl provides a holding circuit around the automatic cycle push button 12PB which may now be released. The abrasive'disc 14L is rotated by depressing a push button 2PB and a circuit is completed through a contact CRMl, the contact CRA2, and through a normally closed push button lPB to energize the DC control circuit 73, and rotation of the abrasive disc 14L is effected. The contact CRMl is closed when the hydraulic pump (not shown) is energized at the start of the cycle.

The abrasive disc 14R is rotated by depressing a push button 4PB and a circuit is completed through a contact CRMZ, the contact CRA3, and a normally closed push button SP3, to energize the DC control circuit 74 to actuate rotation of the abrasive disc 14R.

A coolant start push button switch ISPB is depressed and held to complete a circuit through a normally closed push button 14PB, the contact CRA4 and through the normally closed contacts 7CR1 and SCRl to energize the coolant pump relay 4M. The energization of the relay 4M closes contacts 4M1 and 4M2. The closing of the contact 4M1 provides a holding circuit around the push button switch 15PB which may now be released. Coolant is directed into the grinding zone 26 through the

coolant nozzles

71 and 72 in a conventional manner.

The work carrier 21 is rotated by depressing the carrier start switch SPBl to complete a circuit to the DC control circuit 76 through the contact CRAS. A switch member 5PB2 is automatically closed when the switch SPBl is depressed and a circuit is completed through a normally closed switch member 6PB, the contact CRA6, and through a contact llCRl, which is closed when the dresser (not shown) is in the retracted position, and the carrier run relay IOCR is energized.

The energization of the relay 10CR closes a contact 10CRl to provide a holding circuit around the switch member 5PB2, and a contact 10CR2 is closed to provide a holding circuit around the switch SPBI. A contact 10CR3 is closed which completes a circuit through the switch member SPBl, the contact 4M2, a timed contact ZTR, a contact 11CR2, and the carrier stop switch 6PBl which is normally closed to energize the carrier start relay lCR. The work carrier 21 is rotated in a clockwise direction (FIGS. 1 and 2) at a speed controlled by the drive motor 29 (FIG. 3) and the workpiece W within the opening 23A is advanced toward the

abrasive discs

14L and 14R at a rapid rate.

Rotation of the work carrier 21 advances the unground workpiece W into the grinding zone 26 between the

abrasive discs

14L and 14R at a rapid rate. The speed of the work carrier 21 is gradually reduced as the workpiece W approaches the central area of the

abrasive discs

14L and 14R to maintain a near-constant work-abrasive speed ratio over a substantial portion of the grinding operation for each workpiece W. The rotation of the work carrier 21 returns to a rapid speed automatically to remove the ground workpiece W from the grinding zone 26 when the grinding operation is completed, as shown at the end of the grind position 48.

The reduced speed of rotation is automatically effected by the variable speed drive control mechanism 24 which actuates the potentiometer 44. The potentiometer 44 alters the field voltage to the drive motor 29. This occurs only when a workpiece W is in the grinding zone 26 and as a workpiece W approaches the central portion of the abrasive discs ML and 14R.

The contact CRA7 was closed by the energization of the relay CRA and a circuit was completed through the switch member 3LSB, a timed contact 3TRl, and a switch 3SWA2 to energize a workpiece inserter relay 9CR. A contact 9CR1 is closed which energizes a solenoid SOL B, and a valve 77 (FIG. 8) is shifted to the right. Air pressure is directed through the valve 77 to the head end of a cylinder 78. A piston 79 and a ram head 81 is advanced to the right. The unground workpieces W may now be loaded in the loading chute 55.

It can be seen in FIG. 2 that when a workpiece W within the opening 238 being ground is at the end of the grinding zone 26, an opening 23A is in alignment with the loader mechanism 56. A limit switch 3LSA is momentarily closed by a cam (not shown) on the periphery of the work carrier 21, and a limit switch 3LSB is opened momentarily which deenergizes the workpiece inserter relay 9CR. The contact 9CR1 opens which deenergizes the solenoid SOL B. The valve 77 (FIG. 8) is shifted to the left and air pressure is directed to the rod end of the cylinder 78 which retracts the piston 79 to the left, to enable a workpiece W to be advanced into a preloading position 82.

The closing of the switch 3LSA energizes a workpiece inserter delay relay 3TR and the contact 3TR1 opens. The contact 9CR1 is opened to deenergize the solenoid SOL B, and the piston 79 is retracted to allow the next unground workpiece W to be lowered into the preloading position 82.

The contact 3TR1 will close after a timed interval which will energize the relay 9CR. The contact 9CR1 is closed and the solenoid SOL B is energized which shifts the valve 77 to the right and air pressure is directed to the head end of the cylinder 78. The piston 79 and the ram head 81 are advanced to the right to load the unground workpiece W into the opening 23C.

The finished ground workpiece W is unloaded from the work carrier 21 by the work ejector 59 and a workpiece W is unloaded down the unloading chute 62. This occurs when the limit switch 4L8 is momentarily closed by a cam (not shown), which completes a circuit to energize the ejector delay relay 4TR. A timed contact 4TR1 is closed which completes a circuit through the contact CRA7 and the normally closed switch 4SWA2 to energize the workpiece ejector relay l2CR. A contact l2CRl is closed to energize a solenoid SOL C which shifts a valve 83 to the right. Air pressure is directed tothe head end of a cylinder 84, the piston 86 and the magnetic extractor 63 are advanced to the right (FIG. 8). The magnetic extractor 63 contacts a finish ground workpiece W in one of the

openings

23A, 238, or 23C.

The contact 4TR1 will open after a time delay which deenergizes relay 12CR. The contact l2CR1 opens and the solenoid SOL C is deenergized. The valve 83 is shifted to the left and air pressure is directed to the rod end of the cylinder 84. A piston 86 and the magnetic extractor 63 are retracted to the left, and one of the finish ground workpieces W is retracted from one of the

openings

23A, 238, or 23C and discharged down the unloading chute 62.

The operation of a continued grinding cycle will continue until a predetermined number of workpieces W have been ground. When the preset count has been registered, automatic loading of the work carrier 21 is discontinued, but carrier rotation and unloading continues until all of the

openings

23A, 23B, and 23C are emptied. A dressing operation would then be initiated and the grinding cycle would normally be repeated.

As previously described, it is desirable that the work carrier 21 is arranged to retain a least three workpieces W which are evenly spaced in or near the periphery of the work carrier 21. When this arrangement is used, the potentiometer 44 is actuated in a positively timed relationship with the movement of the work carrier 21. The potentiometer 44 is operated three times for each revolution of the work carrier 21 to reduce the speed of the work carrier 21 as each of the three workpieces W approaches the central portion of the

abrasive discs

14L and 14R. There may be other instances where it may be more practical to use more than or less than three openings in the work carrier 21. The potentiometer 44 and the drive control mechanism 24 would operate a respective number of times for each revolution of the work carrier 21.

While the invention is described in detail with reference to a speed reduction mechanismofan electromechanical nature, using a potentiometer 44 to control a DC motor, a solid state transducer or other control device could also be used to control the motor.

Various other drive mechanisms and control devices can be used. For example, an adjustable speed hydraulic motor could be utilized to control the rotation of the work carrier 21 and the advance of the workpiece W between the

abrasive discs

14L and 14R or an AC motor could be used to drive the work carrier 21, wherein the reduced speed of advance of the workpiece W would be obtained by decreasing the excitation frequency of the signal to the motor.

As shown in FIG. 9, a stepping motor 91 could also be used to drive the work carrier 21. In this embodiment, a positional encoder 92 sends a signal to a logic circuit 93 which is indicative of the angular position of the work carrier 21 and the workpieces W. The logic circuit 93 generates a signal which is converted by a rate multiplier 94 into pulses 96 which are sent to a driver 97 and pulse signals are directed into the stepping motor 91. The frequency of the pulses 96 determines the rate at which the stepping motor 91 rotates. Therefore, in order to reduce the speed of rotation of the work carrier 21 as the workpiece W approaches the center of the

abrasive discs

14L and 14R, the pulse rate is reduced. Once the workpiece W passes the centerline of the

abrasive discs

14L and 14R, the logic circuit 93 can then generate a signal to increase the pulse rate to provide a rapid withdrawal of the workpiece W from the

abrasive discs

14L and 14R.

In the second preferred embodiment the horizontal double disc grinder has an arm 200, which is pivotably mounted on a rock shaft 202. The rock shaft is journaled in bearings which are housed by support brackets secured to the front of the bed (not shown). A work holding paddle 204, including an opening 206 for receiving a retaining frame 208 for securely holding a workpiece W in a predetermined position, is secured to the arm 200.

The arm 200 is selectively displaceable from a fully retracted position P, whereat the workpiece can be conveniently secured within the workframe 208 to an intermediate partially advanced position P; whereat the surfaces of the workpiece W which are to be ground only partially overlap the abrading faces of the abrasive discs proximate the outer periphery 210 thereof and then to a fully advanced position P whereat the surfaces of the workpiece W which are to be ground only partially overlap the abrading faces of the abrasive discs at the inner periphery 212 thereof.

A hydraulic motor 214, which is secured to the machine bed includes a piston rod 216 which is connected to the arm 200 by a clevis bracket. Reciprocation of piston rod 216 oscillates the arm 200 along an arcuate path between the fully retracted position P and the fully advanced P position.

After the workpiece has been mounted within the retaining frame the arm is rotativelydisplaced to the partially advanced (partially retracted) position P, and is then repetitively oscillated between positions P and P until the workpiece surfaces are completely ground.

The arm will then be returned to the fully retracted position P to complete the cycle.

Referring to FIGS. 10 and 1 l, a control assembly 220 is secured to the arm 200 by a bracket 222 and switch plate 224 is secured to this bracket. Adjustable trip dogs 226, 228 are mounted on the switch plate 224.

A limit switch 230 is mounted on the machine bed and operating lever 232 of the limit switch 230 is selectively positioned to engage the first trip dog 226 when the arm 200 is partially retracted to position P; and is selectively positioned to engage the second trip dog 228 when the arm is fully advanced to position P The hydraulic system for controlling the oscillation of the arm is disclosed in FIG. 11. This system includes a first two position valve 300 which is controlled by a solenoid 302. When the solenoid 302 is in the unenergized state, spring 304 maintains the valve 300 in a first position, and when the solenoid is first energized through manual pushbutton control (not shown) the valve 300 is displaced against the action of the spring 304 to a second position which causes paddle 204 to advance to position P and reverse. The system additionally includes a two position double channel valve 306 (shown in its first position), a plunger or deceleration valve 308, and the fluid cylinder or motor 214.

When the operating lever 232, during retractive motion of paddle 204, strikes the first trip dog 226 at position P,, the solenoid 302 is actuated. Fluid under pressure is directed from a source 310 through

fluid lines

312, 314 to the two position valve 300 which has been shifted to its second position. The pressurized fluid is passed through the valve to fluid line 316 to the second valve 306 for urging the displacement of this valve to its second position whereby a circuit will be defined therethrough by

fluid lines

318, 320 into the head end of cylinder 214. Additional pressurized fluid from the source will be directed through lines 312, 322, through the plunger valve 308 and lines .318, 326, and into the rod end of fluid cylinder 214. Piston .324, due to differential areas being pressurized alike, is accordingly displaced to the right thereby rotating the arm 200 in the clockwise direction.

When the operating lever 232 againstrikes the second trip dog 228 at the fully advanced position P,,, the solenoid is deenergized and the two position valve is displaced by spring 304 to the first position whereby the pressurized fluid will be directed from the source

3l0through lines

312 and 314, valve 300, and line 324 to the second valve 306. This valve is displaced to its first position whereby a circuit is defined therethrough by

lines

320 and 327. Pressurized fluid is also directed through lines 312, 322, through plunger valve 308 through

lines

318 and 326 to the rod end of the cylinder 214. The circuit now functions to permit the passage of fluid from the head end of the cylinder through

lines

320 and 327 into a fluid reservoir 328. The piston is accordingly displaced towards the left and the arm is rotated in the counter clockwise direction.

Throttle valves

330, 330 are provided to control the rate at which the pressurized fluid is directed to the cylinder.

In order that the grinding surfaces will be uniformly worn, the rotational velocity of the oscillating arm should vary with its angular position and the ratio of the rotational velocity of the arm 214 when the workpiece W is at P, to the rotational velocity of the arm 214 when the workpiece W is at P, should approximately be equal to (2R w)/(2R, w) where w is the width of workpiece W and the rotational velocity of the arm should vary substantially linearly therebetween.

Plunger or deceleration valve 308 includes a plunger element 332 which is selectively displaceable from a retracted position to an advanced position. As this piston is advanced, the pressure drop through the valve is increased whereby the pressure acting on the cylinder will be selectively reduced.

A cam support rail 340 is secured at one end to the oscillatable arm and a pin element 342 which is secured to the housing is located within a slot 344 defined in the other end of the cam support rail 340 which extends in a direction parallel to the piston rod.

This cam support rail 340 includes a wedge-shaped element 348 having a substantially linear camming surface selectively inclined so that as the workpiece is displaced from P, to P the plunger element will be advanced from its retracted to its advanced position to achieve the desired velocity gradient of the fluid motor and hence the arm 214.

The arm will be fully retracted when a predetermined number of oscillations are completed and the limit switch 340 will be closed to complete the grinding cycle for a single workpiece W. The right-hand and left-hand abrasive discs may be rapidly retracted by feed means 322, 322' either when the counter (not shown) times out, or when the limit switch 340 is closed.

The principles of the present invention are applicable to single as well as double disk grinders and is applicable to such grinders whether the workpiece is linearly or arcuately displaced across the abrading discs. Additionally, the principles of the present invention are applicable to grinding machines wherein the workpiece is a single object having two opposing surfaces or is two objects each having a single surface to be ground.

Having thus described my invention, I claim:

1. A grinding apparatus comprising abrasive disc means including at least one abrasive disc,

means for mounting said abrasive disc for rotative displacement about the axis thereof,

means for rotationally displacing said abrasive disc,

means for axially displacing said abrasive disc towards a workpiece surface to be ground,

means for mounting a workpiece having at least one surface to be ground by the abrading action of the face of said abrasive disc,

hydraulic means for displacing said mounting means transversely across said abrasive disc face from a first position whereat the workpiece surface is proximate the outer periphery thereof to a second position whereat the workpiece surface is proximate the center thereof,

a source of pressurized fluid,

conduit means for directing the pressurized fluid to said hydraulic means for selectively displacing said mounting means, and

means for selectively incrementally reducing the pressure of the fluid flowing through said conduit means from a first pressure to a second pressure as said mounting means is displaced from said first position to said second position to selectively reduce the rate of displacement of said mounting means so that the effective area of the face of the abrasive disc abrading the workpiece will be substantially equal for all radial positions of the workpiece surface.

2. A grinding apparatus according to claim 1, wherein said abrasive disc means comprises a pair of coaxial discs and said hydraulic displacing means selectively displaces said mounting means intermediate said discs.

3. A grinding apparatus according to claim 1, wherein said mounting means includes an arm member and means for supporting said arm member for pivotal displacement.

4. A grinding apparatus according to claim 1, wherein said hydraulic means includes a fluid cylinder having a piston operatively connected to said mounting means and said conduit means includes a deceleration valve having a plunger element advanceable from a first position to a second position whereby the pressure of the fluid flowing through said conduit means can be reduced from said first pressure to said second pressure, and said reducing means comprises means for selectively advancing said plunger element from said first position to said second position as said mounting means is displaced from said first position to said second position.

5. A double disc grinding machine having a pair of spaced, rotating abrasive discs for grinding opposite faces of a workpiece comprising means for advancing a workpiece in a path between said discs from an entrance position on the periphery of the discs toward the center of the discs through a grinding zone and then toward an exit position on the periphery of the discs, said advancing means including a rotary work carrier having means for supporting a plurality of workpieces in equally spaced relationship about the periphery thereof, the spacings being selectively determined so that only one workpiece will be in the grinding zone at any given time, and

electric motor means operatively driving said rotary carrier, and

means for gradualy reducing the speed of said rotary carrier as a workpiece is displaced from the entrance position towards the center of the discs including a potentiometer for varying an electrical signal to said electric motor means, and

a gear mechanism mechanically linking said rotary carrier to said potentiometer for actuating said potentiometer a predetermined number of times for each rotation of said rotary carrier equal to the number of workpieces received in said carl'lf..

6. A double disc grinding machine according to claim 5, wherein said advancing means further includes means for rapidly increasing the speed of said rotary carrier after a workpiece has passed through said grinding zone.

7. A double disc grinding machine for grindingthe opposite faces of a workpiece comprising a pair of spaced rotatable abrasive discs,

means for rotating said abrasive discs,

a rotary work carrier positioned in overlapping relationship with said discs and having angularly spaced openings for receiving a plurality of workpieces to be ground,

means including an electric motor for rotating said rotary carrier to advance a workpiece along an arcuate path between said discs from an entrance point on the periphery of said discs toward the center of said discs through a grinding zone, and then away from the center of said discs toward an exit point on the periphery of the discs, and

means for gradually reducing the speed of rotation of said rotary carrier as a workpiece is displaced from said entrance point toward the center of said discs through the grinding zone to provide a more even wear pattern on the faces of said discs including a potentiometer for varying an electrical signal to said electric motor; and

a gear mechanism for mechanically linking said carrier to said potentiometer, said gear mechanism including means for actuating said potentiometer a predetermined number of times for each rotation of said carrier equal to the number of workpieces received in said carrier at any given time and said gear mechanism further including means for energizing said actuating means only as a workpiece is progressing through said grinding zone.

8. A double disc grinding machine as recited in claim 7 which further includes:

means for rapidly increasing the speed of rotation of said carrier once the workpiece leaves the grinding zone and begins movement away from the center of said discs.

9. A double disc grinding machine as recited in claim 7, wherein said carrier advances the workpieces through the grinding zone one-at-a-time.

10. A double disc grinding machine as recited in claim 7, wherein said discs are mounted on a horizontal axis and wherein, said carrier advances the workpieces in an upward direction between said discs and the grinding cycle is substantially complete once the workpiece reaches the centerline of said discs to minimize the deflection of said discs.

1 l. A disc grinding machine having at least one rotatable abrasive disc for grinding a face of a workpiece comprising a rotary work carrier including means for supporting a plurality of workpieces in equally spaced relation about the periphery thereof for sequentially advancing workpieces through a grinding zone from an entrance position on the periphery of the disc to a location proximate the center of the disc, the spacings being predetermined so that only one workpiece will be in the grinding zone at any given time,

electric motor means for rotatably driving said rotary work carrier at a predetermined speed,

potentiometer means for supplying a signal to said electric motor means, said signal being selectively variable from a first value whereat said electric motor means rotatably drives said rotary work carrier at said predetermined speed to a second value whereat said electric motor means rotatably drives said rotary work carrier at a second substantially slower speed,

means for gradually and incrementally varying said potentiometer signal from said first value to said second value during an interval of time predetermined to equal the time required for a workpiece to be displaced through said grinding zone, and

means for energizing said varying means when each one of said supporting means advances a workpiece to the entrance position.

12. A disc grinding machine according to claim 11 wherein said selectively varying means comprises a spur gear,

means for interconnecting said spur gear and said potentiometer means whereby rotation of said spur gear from a first predetermined orientation in a selected direction to a second predetermined orientation incrementally varies the value of the signal generated by said potentiometer means from said first to said second value, and said energizing means comprises a segment gear coaxial with and rotating in unity with said rotary work carrier and operatively associated with said spur gear, said segment having a selected peripheral length and location so that said spur gear will be displaced from said first orientation to said second orientation as each one of the workpieces is successively displaced through said grinding zone.

13. A disc grinding machine according to claim 12,

further comprising means for returning said spur gear to said first orientation after said segment has displaced said spur gear to said second orientation.

Claims

1. A grinding apparatus comprising abrasive disc means including at least one abrasive disc, means for mounting said abrasive disc for rotative displacement about the axis thereof, means for rotationally displacing said abrasive disc, means for axially displacing said abrasive disc towards a workpiece surface to be ground, means for mounting a workpiece having at least one surface to be ground by the abrading action of the face of said abrasive disc, hydraulic means for displacing said mounting means transversely across said abrasive disc face from a first position whereat the workpiece surface is proximate the outer periphery thereof to a second position whereat the workpiece surface is proximate the center thereof, a source of pressurized fluid, conduit means for directing the pressurized fluid to said hydraulic means for selectively displacing said mounting means, and means for selectively incrementally reducing the pressure of the fluid flowing through saiD conduit means from a first pressure to a second pressure as said mounting means is displaced from said first position to said second position to selectively reduce the rate of displacement of said mounting means so that the effective area of the face of the abrasive disc abrading the workpiece will be substantially equal for all radial positions of the workpiece surface.

5. A double disc grinding machine having a pair of spaced, rotating abrasive discs for grinding opposite faces of a workpiece comprising means for advancing a workpiece in a path between said discs from an entrance position on the periphery of the discs toward the center of the discs through a grinding zone and then toward an exit position on the periphery of the discs, said advancing means including a rotary work carrier having means for supporting a plurality of workpieces in equally spaced relationship about the periphery thereof, the spacings being selectively determined so that only one workpiece will be in the grinding zone at any given time, and electric motor means operatively driving said rotary carrier, and means for gradualy reducing the speed of said rotary carrier as a workpiece is displaced from the entrance position towards the center of the discs including a potentiometer for varying an electrical signal to said electric motor means, and a gear mechanism mechanically linking said rotary carrier to said potentiometer for actuating said potentiometer a predetermined number of times for each rotation of said rotary carrier equal to the number of workpieces received in said carrier.

7. A double disc grinding machine for grinding the opposite faces of a workpiece comprising a pair of spaced rotatable abrasive discs, means for rotating said abrasive discs, a rotary work carrier positioned in overlapping relationship with said discs and having angularly spaced openings for receiving a plurality of workpieces to be ground, means including an electric motor for rotating said rotary carrier to advance a workpiece along an arcuate path between said discs from an entrance point on the periphery of said discs toward the center of said discs through a grinding zone, and then away from the center of said discs toward an exit point on the periphery of the discs, and means for gradually reducing the speed of rotation of said rotary carrier as a workpiece is displaced from said entrance point toward the center of said discs through the grinding zone to provide a more even wear pattern on the faces of said discs including a potentiometer for varying an electrical signal to said electric motor; and a gear mechanism for mechanically linking said carrier to said potentiometer, said gear mechanism including means for actuating said potentiometer a predetermined number of times for each rotation of said carrier equal to the number of workpieces received in said carrier at any given time and said gear mechanism further including means for energizing said actuating means only as a workpiece is progressing through said grinding zone.

8. A double disc grinding machine as recited in claim 7 which further includes: means for rapidly increasing the speed of rotation of said carrier once the workpiece leaves the grinding zone and begins movement away from the center of said discs.

11. A disc grinding machine having at least one rotatable abrasive disc for grinding a face of a workpiece comprising a rotary work carrier including means for supporting a plurality of workpieces in equally spaced relation about the periphery thereof for sequentially advancing workpieces through a grinding zone from an entrance position on the periphery of the disc to a location proximate the center of the disc, the spacings being predetermined so that only one workpiece will be in the grinding zone at any given time, electric motor means for rotatably driving said rotary work carrier at a predetermined speed, potentiometer means for supplying a signal to said electric motor means, said signal being selectively variable from a first value whereat said electric motor means rotatably drives said rotary work carrier at said predetermined speed to a second value whereat said electric motor means rotatably drives said rotary work carrier at a second substantially slower speed, means for gradually and incrementally varying said potentiometer signal from said first value to said second value during an interval of time predetermined to equal the time required for a workpiece to be displaced through said grinding zone, and means for energizing said varying means when each one of said supporting means advances a workpiece to the entrance position.

12. A disc grinding machine according to claim 11 wherein said selectively varying means comprises a spur gear, means for interconnecting said spur gear and said potentiometer means whereby rotation of said spur gear from a first predetermined orientation in a selected direction to a second predetermined orientation incrementally varies the value of the signal generated by said potentiometer means from said first to said second value, and said energizing means comprises a segment gear coaxial with and rotating in unity with said rotary work carrier and operatively associated with said spur gear, said segment having a selected peripheral length and location so that said spur gear will be displaced from said first orientation to said second orientation as each one of the workpieces is successively displaced through said grinding zone.

13. A disc grinding machine according to claim 12, further comprising means for returning said spur gear to said first orientation after said segment has displaced said spur gear to said second orientation.