US3274738A

US3274738A - Grinding machine

Info

Publication number: US3274738A
Application number: US344653A
Authority: US
Inventors: Martin L Kuniholm
Original assignee: Heald Machine Co
Current assignee: Heald Machine Co
Priority date: 1964-02-13
Filing date: 1964-02-13
Publication date: 1966-09-27
Anticipated expiration: 1983-09-27

Description

Sept. 27, 1966 M. KUNIHOLM GRINDING MACHINE 2 Sheets-Sheet 1 Filed Feb. 13, 1964 INVENTOR martin L. Kunz'holm h 2 Sheets-Sheet 2 INVENTOR.

H oTne y Sept. 27, 1966 1.. KUNIHOLM v GRINDING MACHINE Filed Feb. 15, 1964 Martin L. ffunl'holm A. E MM United States Patent 3,274,738 GRINDING MACH[NE Martin L. Kuniholm, Worcester, Mass., assignor to The Heald Machine Company, Worcester, Mass, a corporation of Delaware Filed Feb. 13, 1964, Ser. No. 344,653 6 Claims. (Cl. 51165) This invention relates to a grinding machine and, more particularly, to apparatus arranged to finish a surface of revolution of a workpiece by the abrasive process.

In finishing annular surfaces of revolution by grinding, there are many advantages to be obtained by pressing the rotating abrasive wheel against the surface with a constant, pre-determined force. This force is usually selected to be at a very high value but, nevertheless, always below the force which would result in the destruction of the wheel. The key advantage to this method, of course, is that the finishing operation is carried out at the highest possible material-removal rate, so that the high capital investment in the grinding machine is occupied with one workpiece for as little time as possible. Furthermore, many unobvi-ous advantages are obtained by the use of this so-called controlled force system of grinding, among them being that the geometry and finish of the surfaces are of considerably greater quality than when the workpiece is finished by the feed rate system of grinding. Maintaining the force at a constant, optimum value is, however, a difiicult matter, but is, nevertheless, important because the upper limit of the force that is available is determined by the tolerance on the force; that is to say,

the operator does not dare make the force too high for fear that, during fluctuations of the grinding force, it may exceed the destruction force of the wheel. These and other difficulties experienced with the prior art devices have been obviated in a novel manner by the present invention.

It is, therefore,.an outstanding object of the invention to provide a grinding machine using the controlled-force method of grinding in which the pre-determined force is maintained at a constant value within very close limits.

Another object of this invention is the provision of a grinding machine having a novel means for measuring the grinding force and using this measurement to regulate the grinding force.

A further object of the present invention is the provision of an internal grinding machine using the controlled-force method, having a simple, rugged arrangement for measuring the force between the wheel and the workpiece, and using this measurement to regulate the amount of the controlled force.

With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, may be best understood by reference to one of its structural forms, as illustrated by the accompanying drawings in which:

FIG. 1 is a generally schematic view of a grinding machine embodying the principles of the present invention,

FIG. 2 is a somewhat enlarged view of a portion of the machine, and

FIG. 3 is a vertical sectional view of a valve forming part of the machine.

Referring first to FIG. 1, wherein are best shown the general features of the invention, the grinding machine, indicated generally by the reference numeral 10, is shown as being of the internal type having a workpiece support 11 carrying a workpiece 12 and mounted on a fixed base 13. Also mounted on the base 13 is a wheelhead table 14 on which is mounted a wheelhead 15 having a spindle 16 on the outer end of which is carried an abrasive wheel 17.

Extending upwardly from the upper surface of the base 13 is an abutment 18 from which extends in a horizontal, transverse direction a piston rod 19. The piston rod is provided at its end with a piston 21 which is slidably mounted in a cylinder 22 carried by the workpiece support 11. Extending axially through the piston rod 19 and the piston 21 is a passage 23 to which is attached a conduit 24 leading to an electro-hydraulic servo valve 25. Also attached to the valve 25 is a conduit 26 leading from the outlet of a pump 27 whose inlet is connected to a tank 28 of hydraulic fluid. A conduit 29 is connected to the conduit 24 and is connected through a dumping valve 31, the other side of which is connected by a conduit 32 to the tank 28 of hydraulic fluid. The valve 3-1 is provided with an operating plunger 33 movable by the passage of electricity through an actuating coil 34. A strong coil spring 35 resides within the cylinder 22 behind the piston 21.

The wheelhead table 14 is connected to the upper surface of the base 1-3 by a spring means, indicated generally by the reference numeral 36 and shown in detail in FIG. 2. The spring means consists of a plate 37 and a plate 38 which are bolted to the upper surface of the base 13, as well as a central plate 39 which is bolted to the undersurface of the table 14. The spring means is also provided with a leaf spring 41, which connects the plate 37 to the plate 39 and a leaf spring 42, which connects the plate 38 to the plate 39. These leaf springs are located at substantially the same angle to the axis of the spindle 16 to permit the table 14 and the wheelhead 15 to pivot about the center of gravity of the wheelhead.

The plate 38 is provided with a vertical surface 43 which extends longitudinally of the machine and parallel to the normal axis of the spindle 16. The plate 39 is provided with a transverse surface 44 which extends at a right angle to the surface 43, these two surfaces being located on opposite sides of the centerline of the wheelhead 15. The spring means 36 is provided with a rectangular bar 45 formed of metal, one end of which is bolted to the surface 43 of the plate 38 and one side of which is bolted to the plate 39. The bar is provided with a vertical aperture 46 located adjacent the end which is bolted to the surface 43 of the plate 38 and another aperture 47 located adjacent the end which is bolted to the surface 44 of the plate 39. The apertures are joined by a slot 48 defined by two parallel vertical

transverse surfaces

49 and 51. Mounted on the side of the bar 45, which is bolted to the surface 44 of the plate 39, is mounted a strain gage 53 having two

electrical leads

54 and 55. The strain gage is of the type known as an SR-4 gage and has the faculty of presenting an electrical resistance value from the lead 54 to the lead 55 which is in direct proportion to the amount of strain to which it is subjected. Similarly, a strain gage 56 is mounted on the surface 51 of the slot 48 and is provided with

leads

57 and 58. A strain gage 59 is mounted on the surface 49 of the slot 48 and is provided with leads 61 and 62. Lastly, a side 63 of the bar 45 is provided with a strain gage 64 having leads 65 and 66. The strain gages 53, 56, 59 and 64 are connected to form a Wheatstone bridge, the lead 54 of the strain gage 53 being connected to the lead 65 of the strain gage 64,

lead 65. Similarly, the other side of the source 67 is connected by a lead 69 to the junction between the lead 57 and the lead 61. The common point between the lead 66 and the lead 62 is joined by a lead 71 to an input binding post of an amplifier 72. Similarly, the common point between the lead 55 and the lead 58 is connected by a lead 73 to another input binding post of the amplifier 72. This amplifiers output is connected to either side of a coil 74 forming part of the servo valve 25, as will be described hereinafter.

Y Referring to FIG. 3, it can be seen that the electrohydraulic servo valve 25 consists of a lower housing 75 and an upper block 76. Bolted in the lower part of the housing 75 is an actuating armature 77 in the form of a steel plate, one side of which is fastened by a bolt 78 to the housing and being free to move pivotally or hinge relative to the connection. A heavy iron block 79 is fastened to the plate to move with it. Extending through the plate and block is an operating rod 81 extending generally centrally of the valve. The coil 74 is mounted in the housing 75 and consists of two

portions

82 and 83 mounted, respectively, on

cores

84 and 85 which are firmly fastened relative to the housing 75. The

portions

82 and 83 are connected electrically in series to form the coil 74 to the ends of which are attached the output leads of the amplifier 72. The leads are indicated in FIG. 3 as being attached to binding

posts

86 and 87 extending into the housing in a dust-proof manner.

Extending through the block 76 concentric with the rod 81 is a bore 88 in which is slidably carried a spool 89 mounted on the end of the rod 81. Part of the bore 88 is occupied by a plug 91 having a central bore 92 leading to an outlet passage 93 which is connected to the output conduit 24. The conduit 26 is connected to an inlet passage 94 formed in the block 76. The inlet passage 94 extends transversely and is joined to a longitudinal bore 95 which carries a restriction element 96 in the form of a threaded rod around which hydraulic fluid must pass and which presents a pre-determined restriction to such passage. The inner end of the longitudinal bore 95 is connected to a groove 97 formed in the side of the bore 88. The spool 89 is also provided with a groove 98 and a transverse bore 99 extends through the spool and lies in the groove 98. The bore 99, in turn, communicates with a central bore 101 extending through the spool and opening at the end opposite the end to which the rod 81 is attached, this being the end which faces toward the plug 91.

Observation of FIG. 3 will show that the distance between the face of the armature block 79 and the flat ends of the

cores

84 and 85 associated with the coil 74 is very small (about .025 inch). Similarly, the distance between the adjacent corners of the groove 98 on the spool 89 and the groove 97 in the bore 88 is a little less than that same distance, so that as the armature moves toward the cores, the grooves become slightly co-extensive to permit the passage of the hydraulic fluid and to give very sensitive control. The plug 91, incidentally, is slidable in the bore, but is stopped from entering the bore too far by a shoulder 102; it is pressed into the bore by a coil spring 103 so that the shoulder acts as a stop.

The operation of the invention will now be readily understood, in view of the above discussion. With the wheelhead operating, the abrasive wheel 17 also Iotates; for the purpose of the present invention, the electric motor is contained in the wheelhead and the shaft 16 is an extension of its rotating element. The workpiece 12 is moved toward the abrasive wheel 17 by movement of the workpiece support 11 transversely of the axis of the spindle 16 over the top surface of the base 13. This is brought about by introducing oil into the cylinder 22 in front of the piston 21. Oil pressure is obtained by the use of the pump 27 pumping oil from the body 28 into the conduit 26. The hydraulic fluid passes through the valve 25 and through the conduit 24 into the passage 23 extending through the piston rod 19. The hydraulic fluid leaves the inner end of the passage and forces the piston 21 rearwardly; in other words, since the piston is fixed to the base 13 through the abutment 18, the workpiece support 11 moves forwardly, bringing the workpiece 12 into contact with the rotating abrasive wheel 17. The workpiece itself will be rotated in a manner well known in this art by use of a rotating platen or rotating rolls which engage the outer periphery. The oil, in pressing the cylinder forwardly, compresses the spring 35 between the back of the piston 21 and the other end of the cylinder. After the grinding operation has been completed, as is indicated by a process gage (not shown) operating on the workpiece 12, electric power is passed through the coil 34 which operates the plunger 33 and opens the dumping valve 31. Since the spring 35 is always under compression and tends to cause the piston to move forward in the cylinder (or to cause the cylinder to move rearwardly relative to the piston), the oil is squeezed out through the passage 23, through the conduit 29 and the dumping valve 31, and through the conduit 32 into the sump tank 28.

During the grinding operation, the oil operating in the cylinder 22 brings about a pressure between the surface of the workpiece 12 which is to be finished and the surface of the abrasive wheel '17. This has the effect of producing a torque on the spindle 16 and on the wheelhead =15. The result is that the spring means 36 is stressed and the wheelhead -15 is permitted to rotate about its center of gravity, the spring elements being selected so that the rotation takes place in that particular portion of the wheelhead.

From an examination of FIG. 2 it will be understood that the torque due to the grinding force operates on the wheelhead and is passed down through the wheelhead table 14 to bear on the plate 39. The plate (in the preferred embodiment) tends to rotate counter-clockwise. The torque bends the springs 42 and 4-1, among other things, and also serves to bend the bar 45. Bending of the bar 45 is accentuated by the apertures 46 and 47 and the slot 48 extending between them. The result is that the strain gages 53, 56, 59, and 64 are subjected to a. considerable strain because of the bending of the surfaces on which they are mounted. All four strain gages are mounted on a line which is in alignment with the axis of the wheelhead. The greater the strain in the strain gages, the greater the signal which will appear on the output ends of .the Wheatstone bridge formed by them and which is introduced to the amplifier 72. This signal is increased in power by the amplifier 7 2 and then appears on the coil 74 of the servo valve 25. When the signal is very great, indicating that the wheel pressure against the workpiece is greater than a pre-determined amount, the signal on the coil 74 will be great and will draw the armature 77 closer to the cores 8'4 and 85. This will cause the spool 89 .to take a position further into the .bore 88 so that-the groove 98 and the groove 97 are co-extensive, permitting oil to pass from the conduit 26 to the conduit 24 with a rather rapid flow. This will cause a rapid feeding of the workpiece support 111 forwardly and will cause 1 an increase in '.the pressure of the wheel against the workpiece. If, on the other hand, the force between the wheel and the workpiece is greater than a pre-determined amount, the voltage passing out of the Wheatstone bridge and through the amplifier to energize the coil 74 will be less, so that the spool will not permit as much fluid to flow through the valve. It is a simple matter to select the threads on the outside surface of the restrictor element 96 in such a manner as to introduce a restriction at all times in the flow of fluid to reduce hunting, vibration, and variations in oil pressure for various reasons.

It can be seen, then, that, by use of the present invention, it is possible to maintain and control the force between the wheel and the workpiece and to carry on the grinding operation with a constant force at all times. This means, of course, that the rate of feed of the workpiece toward the wheel will vary from time to time, depending on the various conditions, but the important factor is that the force remains constant and that the force can be selected at the greatest value consistent with good grinding, quality of sunface, and long life of the wheel.

It is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The invention having been thus described, what is claimed as new and desired to secure by Letters Patent is:

1. An internal grinding machine, comprising (a) a base,

('b) a workpiece support adapted .to hold a workpiece, the said support being mounted on the base for transverse sliding motion thereover,

(c) a wheelhead adapted to carry an abrasive wheel pivotally mounted on the base.

(d) a hydraulic linear actuator for bringing about the sliding motion between the support and the base to bring about engagement between the wheel and the workpiece,

(e) a strain gage means associated with the wheelhead for indicating the force between the wheel and the workpiece, and

(-f) a control including an electrohydraulic servo valve responsive to a signal from the strain gage means for regulating the feed means to maintain the force between the wheel and the workpiece at a predetermined constant value.

2. An internal grinding machine as recited in claim '1, wherein pivotal movement of the wheelhead is resisted by a spring means and the strain gage means is mounted on the spring means to measure the strain therein.

3. An internal grinding machine as recited in claim 2, wherein the spring means consists of a rectangular block of metal having two spaced apertures therethrough and a narrow slot joining the apertures.

4. An internal grinding machine as recited in claim 3, wherein the strain gage means consists of four strain gage elements, two elements of which are mounted on the sides of the block in the vicinity of the slot and the other two are mounted on opposite surfaces of the slot in the vicinity of the first-named two elements.

5. An internal grinding machine as recited in claim 4 wherein the four strain gage elements are electrically connected to form a Wheatstone bridge, the input of the bridge being connected to a source of electrical power and the output being connected to deliver to the valve a signal proportional to any imbalance of the bridge.

6. An internal grinding machine as recited in claim 1, wherein the valve is provided with two spaced parallel coils electrically connected to the control, an armature extending transversely across both coils and resiliently biased to a position away from the coils, an operating rod fastened at one end to the armature and passing longitudinally between the coils, and a flow-regulating spool fastened to the other end of the rod.

References Cited by the Examiner UNITED STATES PATENTS 2,168,596 8/ 1939 Hall. 3,131,517 5/1964 Townsend et a1. 51-165 3,197,921 8/1965 Hohler et al 511-65 X 3,209,498 10/1965 Dall 51165 LESTER M. SWINGLE, Primary Examiner.

Claims

1. AN INTERNAL GRINDING MACHINE, COMPRISING (A) A BASE, (B) A WORKPIECE SUPPORT ADAPTED TO HOLD A WORKPIECE, THE SAID SUPPORT BEING MOUNTED ON THE BASE FOR TRANSVERSE SLIDING MOTION THEREOVER, (C) A WHEELHEAD ADAPTED TO CARY AN ABRASIVE WHEEL PIVOTALLY MOUNTED ON THE BASE, (D) A HYDRAULIC LINEAR ACTUATOR FOR BRINGING ABOUT THE SLIDING MOTION BETWEEN THE SUPPORT AND THE BASE TO BRING ABOUT ENGAGEMENT BETWEEN THE WHEEL AND THE WORKPIECE,