US3691698A

US3691698A - Abrasive element dimension sensing mechanism

Info

Publication number: US3691698A
Application number: US91636A
Authority: US
Inventors: Robert L Schaller
Original assignee: Sundstrand Engelberg Inc
Current assignee: Acme Manufacturing Co Inc; Sundstrand Engelberg Inc
Priority date: 1970-11-23
Filing date: 1970-11-23
Publication date: 1972-09-19
Anticipated expiration: 1989-09-19

Abstract

A transducer feedback mechanism for sensing the precise position of a rotating abrasive element and moving it towards or away from a workpiece to compensate for a change in radius due to wear or expansion. The sensing device includes a carbide pad in engagement with the grinding surface of the abrasive element, in radial alignment with the center thereof, and any movement of the pad causes a sensing transducer to signal a servo-amplifier or computer which controls the position of the element relative to the workpiece. Since the sensing pad is itself subject to wear, means are also provided to periodically re-zero the sensing transducer to compensate for such wear.

Description

United States Patent Schaller 51 Sept. 19, 1972 Schaller ..51/238 R Schaller et a1. ..51/135 R Primary Examinerl-larold D. Whitehead Attorney-Bruns & Jenney [57] ABSTRACT A transducer feedback mechanism for sensing the precise position of a rotating abrasive element and moving it towards or away from a workpiece to compensate for a change in radius due to wear or expansion. The sensing device includes a carbide pad in en gagement with the grinding surface of the abrasibe element, in radial alignment with the center thereof, and any movement of the pad causes a sensing transducer to signal a servo-amplifier or computer which controls the position of the element relative to the workpiece. Since the sensing pad is itself subject to wear, means are also provided to periodically re-zero the sensing transducer to compensate for such wear.

11 Claims, 6 Dnwing Figures [72] Inventor: Robert L. Schaller, Syracuse, N.Y.

[73] Assignee: Sundstrand-Engelberg, Inc., Liverpool, N.Y.

[22] Filed: Nov. 23, 1970 [21] Appl. No.: 91,636

[52] US. Cl. ..5l/l65.88, 51/103 R, 51/135 R [51] Int. Cl. ..B24b 49/00 [58] Field of Search ..5l/165.88, 165.87, 103 R, 135 R [56] References Cited UNITED STATES PATENTS 980,164 12/1910 Nichols ..51/165.88 1,549,600 8/1925 Mueller ..5l/l65.88 2,647,347 8/1953 Blanchette ..51/103 R X 3o l Y IO X 2| 2 PATENTEBssmmz 3,691,698

sum 2 BF 3 ROBERT L. SCHALLER INVENTOR.

P'A'TE'N'TEDSEP 19 I972 SHEET 3 [1F 3 INVENTOR. ROBERT L. SCHALLER ABRASIVE ELEMENT DIMENSION SENSING MECHANISM BACKGROUND OF THE INVENTION This invention relates generally to grinding machinery, and has particular reference to a novel mechanism for sensing the precise position of a rotating abrasive element.

As is well known in the art, abrasive elements used in grinding constantly undergo changes in the radial dimension due to wear, heat and, in the case of an abrasive belt, centrifugal force acting on the belt and the soft covering on the contact wheel. Such variations, of course, affect the accuracy of the grinding operation and to offset this, sensing devices have been developed to detect the variations and then move the abrasive element relative to the workpiece the distance required to compensate.

Heretofore, the sensing devices have generally been in the form of hardened pads which ride on the surface of the abrasive element or fluid type sensors which have the advantage that the sensing fluid is not itself subject to wear. The contacting pads, even though provided with a lubricant, are subject to wear and in most devices means are not provided to accurately adjust for such wear which introduces an error in the abrasive element variations detected by the sensor. This, of course, is undesirable where very close tolerances are required in the workpiece. The fluid type sensors, on the other hand, have not proved to be a complete solution to the problem since, by the very nature of the sensing medium, they are subject to inaccuracies that may be detrimental to precision grinding.

SUMMARY OF THE INVENTION In the present invention the sensing mechanism is particularly adapted for use with centerless and cam grinders wherein the abrasive element support is movable linearly towards or away from a workpiece, the center of which always coincides with a predetermined, fixed centerline. The sensing member is a hardened pad in engagement with the abrasive element operating surface and mounted for linear movement along a radius of the abrasive element. The sensing pad forms the extremity of a precision transducer device that is pre-set to a zero reference point, and any movement of the pad due to variations in the radius of the abrasive element causes a deviation from the zero reference point in the transducer. These deviations are transmitted electronically to precision movement actuating means for the abrasive element support whereby the latter is moved relative to the workpiece to compensate for the change in radius that has been detected.

To solve the problem of wear on the sensing pad which can introduce error in the readings of the transducer, the invention provides a transducer zero reset mechanism in the form of a pad wear indicator. This comprises a fixed reference surface that is totally independent of the abrasive element and with which the sensing pad is initially brought into contact to establish the transducer zero reference point. Thereafter, in the course of the grinding operation, the sensing pad is periodically brought into contact with the reference surface and any wear on the pad will show as a deviation from the zero reference point enabling the transducer device to be re-zeroed in accord therewith.

2 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially diagrammatic side elevation, with parts being shown in section, of a centerless grinder and sensing mechanism of the invention;

FIG. 2 is a horizontal section taken on line 2-2 of FIG. 1;

FIG. 3 is an enlarged side elevation of the sensing mechanism of FIG. 1 with certain parts shown in section to better illustrate the construction and arrangement of the parts;

FIG. 4 is an enlarged front elevation of the sensing mechanism; and

FIGS. 5 and 5A are diagrammatic illustrations to show how the sensing mechanism can be moved transversely with respect to the abrasive element, to different points across its width, in straight and curved surface grinding operations, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENT.

With reference to FIG. 1 of the drawings, 10 indicates a workpiece such as a bar or tube, 11 is the regulating wheel and 12 is the contact wheel of a centerless grinding machine. The contact wheel is motor driven in a conventional manner and carries an abrasive belt 14 which also passes over an idler pulley 15. The sensing mechanism to be described can be used with either a disc or belt type abrasive element but because the sensing problems are more difficult with a belt, the description will be directed to a machine in which an abrasive belt is employed.

The contact wheel 12 and idler 15 are mounted in a grinding column 16 forming a part of the grinding head, generally indicated by the reference number 17. The grinding head includes a sub-base 18 containing a set of ways (not shown) by means of which the head can be moved linearly towards or away from the workpiece 10 along the horizontal center line 19. A plate 20 supports the grinding column 16 and is pivotally connected to the sub-base at 21 to permit the grinding element to be moved angularly with respect to the workpiece for a purpose to be described hereinafter. In this connection, it will be seen that the axis of the pivot 21 is in vertical alignment with the center of the contact wheel 12.

To accommodate workpieces of different diameters, the regulating wheel 1 1, as well as the grinding head 17 can be moved linearly along the horizontal center line 19 by conventional means. Similarly, the work rest blades (not shown) are movable as a single unit along a linear path disposed at an oblique angle to the vertical line 22 through the center of the workpiece. For a detailed description of the work rest positioning means, reference may be had to US. Pat. No. 3,466,810 granted Sept. 16, 1969 to the applicant herein.

The sub-base 18 on which the grinding head 17 is mounted can be moved toward or away from the workpiece by means of a precision ball screw 24 and nut 25. Movement actuating mechanisms of this type have developed to such a degree that they are capable of accurate positioning within a tenth of a thousandth of an inch. Accordingly, the distance X in FIG. 1, which is the distance between the centers of the workpiece and contact Wheels, can be very accurately controlled as by a computer or other electronic means. In this connection, it should be noted that in centerless grinders of the type disclosed herein the vertical center line 22 through the center of the workpiece is a predetermined passline with reference to which all movable grinding components are positioned in a linear manner.

The distance from the center of the contact wheel 12 to the operating surface of the abrasive belt 14, designated R in FIG. 1, is as previously noted subject to variations due to wear, centrifugal force or other factors. This in turn affects the dimension Y, which is the distance between the belt surface and workpiece center, and thus affects the accuracy of the grinding operation. The relationship of X, R and Y can be expressed by the formula Y X R, where Y is the dimension that should be held constant in any given grinding operation to maintain uniformity.

To keep dimension Y constant, it is necessary to determine exactly what the variable dimension R is at all times and feed this information back to the grinding head positioning means whereby the distance X is changed to compensate for variations in R. The information as to R variations can be fed back to a servoamplifier or computer (not shown), which do not per se play a part of the present invention, and provide a signal to a positioning motor 26 which actuates the ball screw 24 to move the grinding head 17 linearly towards or away from the workpiece. The exact position of the grinding head at any time is determined by a positioning read-out transducer 27 of a known type.

Having reference now to FIG. 3, it will be seen that the contact wheel 12 is provided with a covering 28 over which the abrasive belt 14 passes, the covering being of a resilient material such as polyurethane or neoprene. The factors which cause variations in the dimension R include the expansion of this covering due to heat, high speed centrifugal forces which tend to throw the belt outwardly and the wear that occurs on the belt itself, particularly in the first few minutes of direct use. In accord with the invention, these dimensional variations are sensed by a sensing member 29 which is centered on a radius of the contact wheel and is movable linearly along that radius with changes in the dimension R.

The sensing member 29, shown in retracted position in FIGS. 3 and 4, is preferably a carbide pad that in operation is held in contact with the belt surface by a light spring force (not shown). The carbide pad is well adapted to withstand the abrasiveness of the abrasive element, and wear on the pad is reduced to some extent by a coolant which also provides lubrication.

The pad 29 forms the outer extremity of a transducer device 30 which, in the embodiment of the invention disclosed, is a commercially available linear variable differential transformer. In this highly sensitive device, the sensing pad is operatively connected to an iron slug positioned in a magnetic field within the transducer, and any change in the position of the pad is reflected by the slug which results in a change in the output signal of the transducer. The transducer output is fed back through electronic means to the grinding head position ing motor 26, as indicated above. When in belt contacting position, the sensing pad passes through a bore 31 in a guard member 32, the latter being provided to protect the delicate transducer device against damage due to belt breakage or a similar mishap.

The transducer device 30, which can accurately sense a dimensional change of up to a half inch, is

secured by a pair of brackets 34 to a slide 35. In setting I up the apparatus, the transducer is mechanically positioned in approximately correct operating position, secured in place by tightening the bracket bolts 36 and then any further adjustment that is necessary is made electronically. Should the electronic adjustments go beyond the capacity of the transducer, it is only necessary to loosen the bracket bolts and make a further mechanical adjustment.

The transducer carrying slide 35 is reciprocably movable on ways 37 which form a part of a second slide 38, and the slide assembly in disposed so that the axis of the transducer is colinear with a radius 39 of the contact wheel and movement of the sensing pad 29 is linear on this radius. Movement of slide 35 is effected by a precision ball screw 40 and nut 41, the ball screw being driven by an in-feed servo-controlled motor 42. The exact position of the slide at any time is determined by a resolver or positioning read-out transducer 44.

The second slide 38 is reciprocably movable on ways disposed at right angles to the ways 37 whereby slide 38 permits movement of the sensing mechanism transversely with respect to the abrasive belt. The ways 45 form a part of a bracket 46 that is secured to the grinding column 16 by bolts 47. Like the slide 35, movement of slide 38 is effected by a precision ball screw and

nut

48, 49 with the screw being actuated by a control motor 50, FIG. 4, similar to motor 42 and the exact position of the slide being determined by a resolver transducer 51.

In order to accurately detect variations in the R dimension, it is necessary to set the transducer device 30 to a zero reference or null point. This can be accomplished by moving a new carbide pad into contact with a new abrasive belt while the latter is stationary on the contact wheel. This will position the iron slug at a particular point in the transducer magnetic field and will give a reading that will be the zero reference point. Thereafter, with the apparatus performing a grinding operation, any increase in the R dimension due to heat expansion or centrifugal force or any decrease in R due to belt wear will result in corresponding movement by the sensing pad and slug, and movement of the latter away from the zero reference point in either direction will be sensed by the transducer which will signal the grinding head positioning motor 26 as previously described.

However, the carbide pad 29 is also subject to wear, and as this wear occurs the pad will move closer to the center of the contact wheel causing a deviation from the zero reference point entirely independent of deviations caused by changes in the R dimension. This, of course, introduces an error in the signals that are fed back to the control motor 26 and thus affects the accuracy of the grinding operation. To solve this problem, the sensing mechanism of the invention is provided with means for detecting wear on the sensing pad and for resetting the zero reference point should this be necessary.

The sensing pad wear detecting mechanism includes a pin 52, FIG. 3, the outer end of which is guided for reciprocable movement by a bushing 54in the slide 38. The inner end of the pin terminates in a piston 55 located in a cylinder assembly 56 secured to the back of slide 38. By means of an air inlet passage 57, air can be admitted to drive the piston to the opposite end of the cylinder, against the bias of spring 58, whereby pin 52 is thrust out into the path of the previously retracted sensing pad.

The pin 52, which in projected position provides a fixed reference surface totally independent of the belt and contact wheel, will be initially projected when it is known that there is no wear on the sensing pad and the pad brought into engagement therewith. This will give a transducer reading that can be recorded as the sensing pad null point. After a period of grinding, during which pin 52 is retracted, the sensing pad can again be brought into engagement with the pin, and any wear on the pad will show as a deviation from its null point. The zero reference point for the transducer will then be changed by the amount of this deviation (re-set) so that the wear on the sensing pad is not a factor in the variations it detects in the dimension R. Since the wear on the pad is normally very small and is checked frequently, the possibility of consequential error due to such wear is negligible.

After each use of the pin 52 to detect wear on the sensing pad, the air in the cylinder is allowed to escape and spring 58 moves piston 55 and the pin back into their normal, retracted position. A second pin 59, which projects from the piston on its side opposite pin 52, passes through the end wall of the cylinder and engages a microswitch 60 when pin 52 is retracted. The microswitch is connected by simple circuitry to an interlock (not shown) which prevents movement of the sensing pad into contact with the abrasive belt if pin 52 is in its outwardly projecting position.

In FIG. 5 there is a diagrammatic illustration of the manner in which the sensing mechanism can be moved transversely with respect to the abrasive belt 14 to points such as A, B, C, D and Eby means of slide 38, FIGS. 3 and 4, and its previously described movement actuating means. In addition, the plate 20, FIG. 1, can be pivoted about its pivot point 21 to permit the grinding element to be moved angularly with respect to the workpiece, such movement being actuated by a precision ball screw 61 in mesh with an arcuate rack 62 on the plate. The ball screw is driven by an angle positioning motor 64, and the exact angular position of the plate at any time is determined by an angle position transducer 65. With the grinding head being pivotally moved in this manner, as for example to grind cams or large paper mill rolls, it is very important to sense the grinding element at the exact point at which the grind occurs. This can be accomplished by moving the sensing mechanism to points such as are indicated at A, B, C, D and E in FIG. 5A by means of slide 38 and its movement actuating means.

In their present state of development, the seam or joint in most continuous abrasive belts is no thicker than the belt itself. However, if the seam were thicker, it could cause the transducer to give a false signal and in such a situation the invention contemplates the provision of circuitry to nullify transducer signals of very short duration.

From the foregoing description, it will be apparent that the invention provides a novel and very useful mechanism for sensing the precise position of a rotating abrasive element. As will be understood by those familiar with the art, the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof.

I claim:

1. A mechanism for sensing the dimension of a rotating abrasive element movable linearly toward and from a workpiece comprising a sensing member in contact with the abrasive element, the sensing member forming a part of a transducer device initially set to a zero reference point, the sensing member being moved radially of the abrasive element upon any change in the radial dimension thereof, said movement causing a deviation from the zero reference point in the transducer device, circuit means responsive to the transducer device deviations to move the abrasive element linearly relative to the workpiece to compensate for the i change in radial dimensions.

2. A sensing mechanism as defined in claim 1 incl uding means to set the transducer device to a new zero reference point when wear occurs on the sensing member.

3. A sensing mechanism as defined in claim I wherein said transducer device produces a linear output signal.

4. A sensing mechanism as defined in claim 1 wherein said transducer device is mounted on a slide movable radially of the abrasive element for initial positioning of the sensing member relative to the abrasive element.

5. A sensing mechanism as defined in claim 1 wherein said transducer device is mounted on a slide movable transversely relative to the abrasive element for sensing changes in the radial dimension thereof at selected points thereacross.

6. In a mechanism for sensing the precise position of a rotating abrasive element having an operating surface, the abrasive element being movable linearly towards or away from a workpiece, the improvement comprising a hardened sensing pad adapted to continually contact the operating surface of the abrasive element, the sensing pad forming an extremity of a transducer device set to a zero reference point and being movable along a radius of the abrasive element to maintain contact therewith upon any change in its radial dimensions, the movement of the sensing pad causing a corresponding deviation from the zero reference point in the transducer device, and circuit means responsive to such transducer deviations to move the abrasive element linearly towards or away from the workpiece to compensate for the change in radial dimensions, said transducer device being mounted on slide means movable transversely with respect to the abrasive element operating surface to permit changes in the radial dimensions thereof to be sensed at any desired point thereacross.

7. A sensing mechanism as defined in claim 5 together with means cooperable with the sensing pad for setting the transducer device to a new zero reference point when the pad becomes worn.

8. A sensing mechanism as defined in claim 5 wherein said transducer device produces a linear output signal.

9. In a mechanism for sensing the precise position of a rotating abrasive element having an operating surpoint in the transducer device, circuit means responsive to such transducer deviations to move the abrasive element linearly towards or away from the workpiece ,to compensate for the change in radial dimensions,

means to move the transducer device radially of the abrasive element to withdraw the sensing pad from contact with element operating surface, and normally retracted means movable into the radial path and engageable by the pad, said normally retracted means providing a fixed reference point for enabling sensing pad wear to be detected whereby the transducer device can be set to a new zero reference point to compensate for the pad wear.

10. A sensing mechanism as defined in claim 8 wherein said transducer device produces a linear output signal.

11. A sensing mechanism as defined in claim 8 wherein said transducer device and its radial movement means are mounted on a slide movable transversely to the abrasive element operating surface for sensing changes in the radial dimension thereof at selected points thereacross.

Claims

1. A mechanism for sensing the dimension of a rotating abrasive element movable linearly toward and from a workpiece comprising a sensing member in contact with the abrasive element, the sensing member forming a part of a transducer device initially set to a zero reference point, the sensing member being moved radially of the abrasive element upon any change in the radial dimension thereof, said movement causing a deviation from the zero reference point in the transducer device, circuit means responsive to the transducer device deviations to move the abrasive element linearly relative to the workpiece to compensate for the change in radial dimensions.

2. A sensing mechanism as defined in claim 1 including means to set the transducer device to a new zero reference point when wear occurs on the sensing member.

3. A sensing mechanism as defined in claim 1 wherein said transducer device produces a linear output signal.

9. In a mechanism for sensing the precise position of a rotating abrasive element having an operating surface, the abrasive element being movable linearly towards or away from a workpiece, the improvement comprising a hardened sensing pad adapted to continually contact the operating surface of the abrasive element, the sensing pad forming an extremity of a transducer device set to a zero reference point and being movable along a radius of the abrasive element to maintain contact therewith upon any change in its radial dimensions, the movement of the sensing pad causing a corresponding deviation from the zero reference point in the transducer device, circuit means responsive to such transducer deviations to move the abrasive element linearly towards or away from the workpiece to compensate for the change in radial dimensions, means to move the transducer device radially of the abrasive element to withdraw the sensing pad from contact with element operating surface, and normally retracted means movable into the radial path and engageable by the pad, said normally retracted means providing a fixed reference point for enabling sensing pad wear to be detected whereby the transducer device can be set to a new zero reference point to compensate for the pad wear.