US2826875A - Grinding machine - Google Patents

Description

March 18, 1958 A, F, TOWNQEND. 2,826,875

GRINDING MACHINE Filed Feb. 27, 1956 4 Sheets-Sheet 1 INVENTOR. Hlmon Ff Townsend A. F. TOWNSEND 2,826,875

GRINDING MACHINE March 18, 1958 4 Sheets-Sheet 2 Filed Feb. 27, 1956 INVENTOR.

H lmon F. Townsend March 18, 1958 A. F. TOWNSEND 2,826,875

' GRINDING MACHINE Filed Feb. 27. 1956 4 Sheets-Sheet 3 INVENTOR. Hlmon F Tbwnsencl March 18, 1958 A. F. TOWNSEND 2,826,875

GRINDING MACHINE Filed Feb. 27, 1956 4 Sheets-Sheet 4 I l I I l I 35 ea -sz' z INVENTOR. HZmon F Townsend BY )ftnfggq United States Patent ontNmNo MACHINE Almon F. Townsend, Worcester, Mass, assignor to The Heald Machine Company, Worcester, Mass a corporation of Delaware Appiication February 27, 1956, Serial No. 567,783

7 Claims. (Cl. 51-165) This invention relates to a grinding machine and more particularly to apparatus arranged to size accurately a surface of rotation formed by a-brading.

It has been a common practice in the past to control the operation of a grinding machine by means of a gage contacting the workpiece during the abrasion process. For instance, in the patent to Blood et al., No. 2,011,705, the grinding operation is terminated when the gage indicates that the surface being finished has reached a predetermined size. One of the principal difliculties experienced with this type of machine is that changes in the finished sizes of the successive workpieces occur over a long operating period; these errors are due largely to thermal effects. For instance, changes occur in the machine gage, especially if its is in contact with coolant, the temperature of which varies gradually during operation. Other errors may occur due to wear of the machine gage. Attempts have been made to avoid these difficulties by gaging the workpiece after the abrading process is finished and then making adjustments in the crossfeed mechanism to compensate for variations from a predetermined size. Such an apparatus is shown in the patent to Arms No. 2,245,894. This method of control proves inaccurate because of inaccuracies in the response to the feed mechanism of the member controlled by it and because variations in the rough sizes of the workpieces cause changes in deflections and variations in the final size which is controlled by the cross feed. Such variations from piece to piece cannot be corrected by a gage which measuresa workpiece only after the grinding has been completed. Furthermore, it has been considered impossible to employ an after gage to feed back signals to adjust the work size in a grinding machine in which the work size is determined by entry of a solid non-adjustable plug gage into the Work. The present invention obviates the difficulties of the prior art in a novel manner.

It is therefore an outstanding object of the invention to provide a gage-controlled grinding machine in which inaccuracies due to thermal effects have been minimized.

Another object of this invention is the provision of an automatic machine having a work gage and an after gage, including means for correlating the indications of the gages.

A still further object of the invention is the provision of an automatic machine in which the machining operation is regulated primarily by a gage which is associated with the work-piece during the machining, the degree of such regulation being affected also by another gage which is associated with each work-piece after the machining operation has been concluded.

Although the novel features which are believed to be characteristic of this invention will be particularly pointed out in the claims appended hereto, the invention itself, as to its objects. and advantages, the mode of its operation and the manner of its organization maybe better'understood by referring to the following description taken in connection-with the accompanying drawings forming a part thereof, in which: i

- Patented Mar. 18, 1958 Figure 4 is a plan view of the apparatus shown in Figure 2, and

Figure 5 is a schematic view of control apparatus associated with the machine.

All directions used in the description that follows relate to the operator standing in his proper position facing the machine so that it appears as shown in Figure 1. For instance, rearward means away from the operator and left hand means in the direction of the operators left hand. i

In accordance with the invention, the machine is arranged to remove a small amount of material after a signal is received from the machine gage, the amount being adjustable automatically in accordance with a signal from an after-gage. That is to say, a device is interposed between the machine gage and the controls which terminate the operation, this device being adapted to control the amount of material to be removed. Means is provided to convey each workpiece, after it has been finished, to the after-gage which then detects errors in the workpiece and causes suitable adjustments to be made in the aforementioned device. Thus, if the bore of a finished workpiece exceeds a predetermined diameter, the after-gage will act to reduce the material removed in the finishing operation on the next workpiece; the reverse is true if the diameter is less than the predetermined diameter.

Referring first to Figure 1, wherein are best shown the general features of the invention, a machine, indicated generally by the reference numeral 10 is shown as an internal grinding machine for purposes of illustration,

is provided with a base 11 on which are supported a work-' head 12. and a slidable table .13. The table 13 supports cross-feed slide me- nbers 14 and 15; the cross-slide member 15 is movable by a screw 16 turned by a conventional feed mechanism, not shown. A motorized wheel head 17 is mounted on the slide member 15 and carries a tool 18, such as an abrading wheel, which during the grinding operation is coextensive with the workpiece and may reciprocate therein. Alternatively, the invention may be incorporated in a machine such as is shown in the co pending patent application of Almon F. Townsend, Serial Number 473,650.

An annular workpiece 19 having a bore to be finished is supported by a shoe 2% and may be rotated by a magnetic chuck 21 on the spindle of the workhead 12. The machine has incorporated therein a work gage to give a signal when a predetermined work size of the bore is reached. A satisfactory apparatus is illustrated by a work gage 22 of the plug type mounted on a rod 23,

passing through the spindle of the workhead 12 and urged toward the work by a spring 24. Another suitable gage apparatus is the pneumatic type shown in the patent to Schmidt et al., No. 2,771,714. A bell crank 25 engages a collar 25 on the rod 23 and holds the gage away from the work when the end of the crank is raised by a table cam 27 with the table in the loading position, 'as shown, or when raised by a table cam 28 to clear the wheel 18 in its extreme left position. A switch 29 is provided on the base underlying the horizontal arm of the bell crank 25 for a purpose to be explained hereinafter.

A chute 31 underlies the rearward part of the work- 7 ing area and extends rearwardly and downwardly thereverselyl of an intermediate portion of the micro-switch 35 is mounted on the wall adjacent the pin so as to be actuated by a workpiece 19 when at rest against the pin. The lower end of the chute 31 is provided with an'inclined diverting spout 36 which is pivitally connected at its upper forward end to the chute my beans of a hinge pin 37. The spout is provided with sidewalls 38 and 39 and a bar 41 extending across its intermediate portion. To the ends of the bar are pivotally connected the plungers of solenoids 42 and 43 mounted on the chute 31. Adjacent the lower or discharge end of the spout 36 is located a bin 44 having an undersize compartment 4-5, an on-size compartment 46, and an oversize compartment 47 adapted to receive the finished workpieces, segregated according to their ac ceptability as to size.

Associated with the chute 31 is a pneumatic gage head 48 of cylindrical form and having small nozzles d9 which are connected by a conduit 51 to a control box 52 which, in turn, is connected by a conduit 53 to a source of pressure. air, not shown. The control box contains regulatingvalves and the like of the usual type, whereby air is delivered to the nozzles 49 and the pressure in the conduit 51 is determined by the rate of leakage from the nozzles when the gage head 48 is surrounded by a work-piece. The gage head is mounted on a vertical plate 54, as is the pin 34, and apertures are formed in the wall of the chute to permit them to move axially therethrough. From the lower end of the plate 54 extends a horizontal bar 55 which passes through a box 56 and is mounted for sliding but non-rotative movement therein. The box is mounted under the chute 3i and has mounted within it a geared motor '7, on the output shaft of which is mounted an eccentric cam 58. A coil spring 59 extends between a vertical wall of the box and a projection 61 on the bar 55. A roller type can follower 62 is pivotally mounted on the bar 55 and is forced into continuous contact with the cam by the pressure of the spring 59. A microswitch 63 is mounted on the box 56 under the gage head 48 in position to be actuated by the plate 54 when it is in a position close to the chute 31.

Referring next to Figure 5, which shows the electrical circuit used in the machine of the invention. two power lines 71 and 72 are connected to a source of electricity. The line 71 is conected to one side of the switch 35, which is the switch located in the chute 31; the other side of the switch 35 is connected to one side of the microswitch 63, the other side of which is connected to a terminal 87 on the control box 52. Another terminal 88of the control box is connected through the coil of the spout solenoid 43 to the line 72, while another terminal 89 is connected to the line 72 through the coil of the spout solenoid 42. Another terminal 91 on the control box is connected to one side of the coil of a solenoid 85', while a terminal 92 is connected to one side of the coil of a solenoid 86;. the other sides of these last coils are connected together and to the line 72. Within the control box the terminal 87 is connected through a switch 78 to the terminal 91, the switch 78 being closed when the gage head 48 indicates that the bore in the workpiece is too small. The terminal 87 is also connected through a switch 79. to the terminal 92, the other devices in the control box 52 causing the switch '79 to close w' en the gage head 48 indicates that the bore in the we being measured is above a predetermi ed value. the terminal 87 is also connected within the box to the terminal 88. through a switch 84, which is closed when the gage head. 48 indicates that the bore in the workpiece is too small. In a similar manner, the terminal 87 is connected within the box to the terminal 39 through a switch 83 which is closed by the other controls in the box when the gage head 48 indicates the size of the bore in the workpiece is larger than a predetermined The chute and a 4 gage head may be electrical or, as illustrated, may be pneumatic, in which latter case the switches 78, 34, 79 and 83 may be pressure switches responsive to the pres sure in the conduit 51 and may be of the type described in the patent to Schmidt et al.,N o. 2,771,714. The predetermined size necessary to operate the switch 78 may be the same or quite different from that used with the switch S4 and the same may be true of the switches 79 and 83, reflecting different permissible errors above and below a normal size. Attached to the plungers of the solenoids and 86 are pawls S1 and 82, respectively, each adapted to engage and rotate a toothed adjusting wheel 83 or a period-determining device, such as a timer 73. The line 71 is connected through the switch 29 to a terminal 93 of the timer 73; a terminal 94 is connected directly to the line 72. The timer 73 contains a switch 74- which is connected in such a manner that, when an electrical impulse is impressed on the terminals 93 and 94 by the closing of the switch 29 and a predetermined number of impulses are received thereafter from :1 normally-open, spring-biased switch operated by a dog 191 on the table 13, the switch. '74 will close. Although the timer '73 is shown in the preferred embodiment as an electronic counter which counts pulses originating in the switch ltlti and closes the switch 74 after the passage of a period of time determined by a certain number of table reciprocations, it is to be realized that this period of time may be determined by a conventional electronic or mechanical timer or by a timer which operates by measuring the amount of cross-feed taking place. In every case, the timer must use as its reference some constant associated with the machine; in the preferred embodiment, the reference is the constant rate of table reciprocation. In the case of the electronic timer, the reference would be the voltage build-up of a capacitor contained in the timer; the mechanical timer would use as a reference, the rate of rotation of an electric motor or the rate of escape of a gas from an aperture. in the case of the timer opcrat ing from feed, the constant reference might be the constant rate of feed motion of the wheelhead across the table. The period of time at which the switch '74 will close after the closing of the switch 29 can be adjusted over a considerable range of values by the rotation of the wheel 83. One sideof the switch '74 is connected directly to the line 71, while the other side is connected to the line 72 through the coil of a solenoid 75. The solenoid 75 is of the conventional type used in machines of this kind to terminate the grinding operation and to move the wheel away from the workpiece, for example, pushing a latch lift 102 upwardly causing a dog latch 193 to ride over a reverse lever 104. The details of the machine mechanism which accomplishes this are well known in the art and do not form a part of this invention. The switch 35 is also connected to the line 71 on one side and through the motor 57 to the line 72 on the other side. The switch 76, which, as is evident in Figure l, is opened and closed by dogs on the table 13, is connected .to the line 71 on one side and on the other side to the line 72 through the coil1of the solenoid 33.

The operation of the apparatus of the invention will now be readily understood in view of the above description. A workpiece 19 arrives in the shoe 20 by automatic means, not shown, and is rotated by the magnetic chuck 21. The tool 18 is rotated at a high rate of speed by the motorized wheel head 17. The table 13 moves to the leftcarrying the wheel head and tool with it, until the tool lies generally within the bore in' the workpiece. Then, the internal mechanism of the machine causes the table and tool to reciprocate longitudinally, so that the tool moves in and out of the bore. At the same time, the screw 16 is rotated by the feed mechanism, so that the wheel head and tool are advanced laterally. Eventually, the tool engages the surface of the bore and begins to remove metal.

Every time the table 13 moves to theright to withdraw the tool from the bore, the gage 22 is permitted to press against the portion of the workpiece surrounding the bore. In time, the bore is enlarged to the point where the gage may enter the bore; when this happens the bell crank 25 strikes the switch 29 and closes it. Referring to Figure 5, the closing of the switch 29 permits an actuating current to pass through and start the timer 73. After a number of reciprocations of the table, determined by the setting of the wheel 83, the timer closes the switch 74. This permits current to pass through the coil of the solenoid 75 and sets in motion the internal mechanism of the machine which causes the tool to retract completely from the workpiece and to occupy a position at the extreme right of the machine. As the table 13 moves to this extreme position, the dogs attached thereto engage and close the switch 76. Current then is permitted to pass through the coil of the solenoid 33 which, as is evident in Figure 2, acts through the pin 32 to eject the workpiece 19 from the shoe 20 into the chute 31.

The workpiece rolls down the chute until it strikes the pin 34 which extends across the chute at that time, as is evident in Figure 3. In this position the worktpiece 19 also strikes the microswitch 35 and closes it. The closure of this switch permits current to pass through the geared motor 57 and it begins to rotate slowly, carrying the cam 58 with it. In its stopped condition, the cam 58 is always situated so that a portion a little past the point of maximum throw presses against the cam follower 62. As the cam rotates, the bar 55 is moved to the right in Figure 3. The plate 54 moves toward the chute 31 until, eventually, at the point of minimum throw of the earn, the gage head 48 has advanced into the bore in the workpiece and is sending an indication of the bore size through the conduit 51 to the control box 52. At the same time, the plate 54 presses against the microswitch 63. Then, it is evident that both switches 35 and 63 are closed and the circuit to the binding post 87 from the line 71 is closed. If the bore of the workpiece is below a predetermined size, which might be called the adjustment limit,'the gage 48 will indicate such and the mechanism in the control box 52 will close the switch 78. This will permit current to pass into the coil of the solenoid 85, causing the plunger and the pawl 81 to move to the right. The pawl will engage the teeth on the wheel 83 and turn the wheel clockwise. This will lengthen the period of delay introduced by the timer and the grinding operation will continue for a greater number of table strokes or for a slightly longer time than during the preceding cycle. The result will be a larger bore which is closer to the desired size. If the under sized bore in the workpiece just described is smaller than a second predetermined size, which may be called the discard limit, the mechanism in the control box will cause the switch 83 to close. When this happens, current passes throughthe coil of the solenoid 42 and its plunger pulls the diverting spout 36 in such a direction that it overlies'the under-size compartment 45 of the bin 44. Eventually the motor 57 rotates the cam 58 back to its original position and the plate moves away from the chute 31 and releases the switch 63. The gage 48 is withdrawn from the workpiece and the pin 34 is withdrawn entirely from the chute. The workpiece, thus released, rolls down the chute, through the spout and into the bin. In this case, where the bore is undersized, it lands in the undersize compartment for discard or re-grinding. The switch 35 is released, opens, and the motor 57 stops, but only after the cam has gone slightly past its maximum throw so that the pin 34 is allowed to return to a position extending across the chute. It will be realized that, if the bore in the workpiece is larger than a predetermined size, themechanism in the control box 52 will close the switch 79, thus actuating the solenoid 36, the pawl 82, and rotating the adjusting wheel 83 counterclockwise; the timer 73 will be adjusted to give a shorter interval of grinding between the end of the first interval determined by the neither of the solenoids 42 and 43 is energized, the spout 36 will maintain a neutral position overlying the compartment 46 of the bin.

While certain novel features of the invention have been shown and described and are pointed out in the annexed claims, it will be understood that various omissions, substitutions and changes in the forms and details of the device illustrated and in its operation may be made by those skilled in the art without departing from the spirit of the invention.

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

l. A machine comprising a workhead for holding and rotating a workpiece having a surface of revolution to be finished, a cutting tool, a tool holder for holding and rotating the cutting tool, means for feeding the workhead and tool holder relative to each other transversely of the axis of the said surface or" the workpiece to' bring about a material removing operation of the cutting tool on the workpiece, a gage operative on the workpiece during the material-removing operation to determine a first period of the operation, which first period is terminated when a predetermined condition exists between the gage and the said surface, automatically adjustable means for terminating the material-removing operation 7 at the end of a second period after the termination of the first period, means for removing the workpiece from the workhead after the material-removing operation has been so terminated, measuring means for determining the size of the said surface of the workpiece after it has been removed from the workhead, and means responsive to the said measuring means when there is a variation of the said surface of the workpiece from a predetermined size for changing the said adjustable means to change the said second period in a direction to compensate for the said variation.

2. A grinding machine comprising a workhead for holding and rotating a workpiece having a surface of revolution to be finished, an abrading wheel having a working surface of revolution, a wheelhead for holding and rotating the wheel, the workhead and the wheelhead holding the workpiece and the wheel with the axes of their said surfaces parallel to each other, means for feeding the workhead and wheelhead relative to each other transversely of the said surface axes to bring about a grinding operation of the wheel on the workpiece, a gage operative on the workpiece during the grinding operation to determine a first period of the grinding operation, which first period is terminated when a predetermined condition exists between the gage and the said surface, automatically adjustable means for terminating the grinding operation at the end of a second period after the termination of the first period, means for removing the workpiece from the workhead after'the grinding operation has been so terminated and for replacing it with an unfinished workpiece, measuring means for determining the size of the said surface of the workpiece after it has been removed from the worlrhead, and means responsive to the said measuring means when there is a variation of the finished workpiece from a predetermined size for regulating the said adjustable means to change the said second period in a direction to compensate for the said variation.

3, An internal grinding machine comprising a workhead for holding and rotating a workpiece having a bore to be finished, an abrading wheel havinga cylindrical working surface, a wheelhcad for holding and rotating the wheei,the workhead and the wheelhead holding the workpiece and the wheel with the axes of the bore and Working surface parallel to each other, means for feeding the workhead and wheelhead relative to each other transversely of the said axes to bring about a grinding operation of the wheel on the/workpiece, a machine gage operative on the workpiece during the grinding operation to deterimne a first period of the grinding operation, whichfirst period is terminated when a predetermined condition exists between the gage and the said here, automatically adjustable means for terminating the grinding operation at the end of a second period after the termination of the first period, means for removing the finished workpiece from the workhead after the grinding operation has been so terminated, an after-gage for determining the size of the said bore of the workpiece after it has been removed from the workhead, and means to sponsive to the said after-gage when there is a variation of the finished workpiece from a predetermined size for adjusting the said adjustable means to change the said second period in a direction to compensate, for the said variation.

4. An internal grinding machine comprising a workhcad for holding and rotating a workpiece having a surface of revolution to be finished, a wheelhead for holding and rotating an abrading wheel having a working surface of revolution, the workheacl and the wheelhead holding the workpiece and the wheel with the axesof their said surfaces parallel to each other, means for feeding the workhead and wheelhead relative to each other transversely of the said surface axes to bring about a grinding operation of the Wheel on the workpiece, a machine gage operative on the workpiece during the grinding operation to determine a first period of time of the grinding operation, which first period is terminated when a predetermined condition exists between the gage and the said surface, an automatically adjustable timer for terminating the grinding operation at a second period after the end of the first period, means for removing the finished workpiece from the workhead after the grinding operation has been so terminated and for replacing it with an unfinished workpiece, an after-gage for determining the size of the said surface of the finished Work piece after it has been removed from the workhead, and means responsive to the said after-gage when there is a variation of the finished workpiece from a predetermined size for changing the said timer to change the said second period of time in a direction tending to compensate for the said variation.

5. An internal grinding machine comprising a workhead forholding and rotating a workpiece having a surface of revolution to be finished, a wheelhead for holding and rotating an abrading wheel having a working surface of revolution, the workhead and the wheelhead holding the workpiece and the wheel with the axes of their said surfaces parallel to each other, means for feed ing the workhead and wheelhead relative to each other transversely of the said surface axes to bring about a grinding operation ofthe wheel on the workpiece, a gage operative on the said surface of the workpiece duringthe grinding operation to determine a first period of the grinding operation, which first period is terminated when, a predetermined condition exists between the gage and the said surface, a timer connected to the machine to terminate the grinding operation at a second period after the end of the first period, the timer having an adjusting wheel which determines its timing period, means for removing the finished workpiece from the workhcad after the grinding operation has been so terminated and for replacing it with an unfinished workpiece, measuring means for determining the size of the said surface of the finished workpiece after it has been removed from the worlrhead, and, means responsive to the said measuring means when there-is a variation of the finished workpiece from a predetermined size to rotate the adjustable wheel of the timer to change the said second period in a direction tending to compensate for the said variation.

6. A grinding machinehaving a work support for holding a bored workpiece, an abrading tool, means for relatively reciprocating and feeding the tool in the bore of the workpiece for a grinding operation, a plug gage mounted for reciprocation, means urging the gage against the workpiece and into the bore when the bore has been sufiiciently enlarged to permit entry of the gage, an adjustable timer for counting the number of strokes made by the tool relative to the workpiece after the entry of the gage, means responsive to the timer for terminating the grinding operation, an after-gage located away from the support and the tool for measuring successive workpieces, means effective after termination of the grinding operation on a particular workpiece to transfer the workpiece from the support into operative relation to the aftengage, and means responsive to the after-gage to adjust the timer.

7. A grinding machine having a work support for holding a workpiece having a surface to be finished, an abrading tool, means for relatively reciprocating and feeding the said tool against the surface of the workpiece for grinding operation, a gauge mounted for measurement of the said surface of. the workpiece, means urging the gauge against the workpiece and into a terminating position when the surface has been sufficiently ground, an adjustable timer for determining the number of reciprocations made by the tool relative to the workpiece after the gauge caches the terminating position, means responsive to the timer for endingthe grinding operation, an after-gauge located away from the support and the tool for measuring successive workpieces, means effective after the ending of the grinding operation on a particular workpiece to transfer the workpiece from the support into operative relation to the after-gauge, and means responsive to the after-gauge to adjust the timer.

References Cited in the file of this patent UNITED STATES PATENTS 1,891,662 Booth et al. Dec. 20, 1932 2,267,391 Astrowski Dec. 23, 1941 2,502,862 Ljunggren m Apr. 4, 1950 2,751,720 Foster June 26, 1956

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