US2782798A

US2782798A - Hydraulic drives for machine tools

Info

Publication number: US2782798A
Authority: US
Inventors: Albert A Ericson
Original assignee: FARMINGDALE CORP
Current assignee: FARMINGDALE Corp
Priority date: 1948-03-18
Filing date: 1949-10-20
Publication date: 1957-02-26
Anticipated expiration: 1974-02-26

Description

Feb. 26, 1957 A. A. ERICSON 2,782,798

HYDRAULIC DRIVES FOR MACHINE TOOLS Original Filed March 18, 1948 3 Sheets-Sheet 1 ACTI/A 70.? C Y4 lNDE/Q 74 .25.

x Ifnventor v? flfif 4. 54 /650 Feb. 26, 1957 A. A. ERICSON HYDRAULIC DRIVES FOR MACHINE TOOLS Original Filed March 18, 1948 3 Sheets-Sheet 2 6 4% 4 0 2 4 6: m y 6 3 .U M

4 4 I. I w 0 w a 2 ll 5 8 III I/III III. a 2 0 a 4 M m 0% 9 m 9 ited States HYDRAULIC DRIVES FOR MACHINE TOOLS Albert A. Ericson, Glenwood Landing, N. Y., assignor to The Farmingdale Corporation, a corporation of New York 3 Claims. (Cl. 137-505.22)

This invention relates to hydraulic drives for machine tools. Hydraulic drives present many advantages over the mechanical drives more commonly used, in that they present greater mechanical simplicity, require less parts, result in saving power due to elimination of friction of gears, feed screws, etc., provide for simplicity of control thereby reducing operator fatigue, and also permit of an infinite number of rates of feed depending upon the adjustment of the control valve as distinguished from the limited number of feeds obtainable by mechanical means such as change gears, or other rate of feed adjusting devices. The potential advantages inherent in hydraulic feeds have not, however, been fully secured in existing hydraulic feed devices, because satisfactory feed control has not been achieved by such devices. This has been due in part to the fact that the liquid medium used for transmitting the hydraulic power is substantially incompressible resulting in over rigidity of drive, and to the fact that if excess pressure were provided, as is necessary to permit of eflicient operation, such pressure could not be satisfactorily controlled or prevented from building up to a point resulting in breakage and injury to tools, machines or parts whenever any abnormality in operating conditions occurred.

The objects of the present invention are to overcome the defects heretofore encountered in utilizing hydraulic feeds for machine tools to enable the full advantage to be taken of'the greater flexibility and simplicity of hydraulic feeding means and to greatly increase rates of machining over what has been possible heretofore by the use of either mechanical or hydraulic feeds.

It is a more specific object of the invention to provide improved control means for controlling the action of the machine tool.

It is a further object of the invention to provide an improved restrictor valve mechanism for controlling the inlet and discharge orifices to and from the actuator during the actual working part of the cycle.

atent planets, shapers, and other types of tools.

these tools, the cutter is rotated and the work fed into It is known that in the operation of most machine tools fore, lack the sensitivity of the hand of the skilled operator. -Iu accordance with the present invention, a sensitive hydraulic feed is provided which simulates in its action the sensitiveness of the operators hand, but acts more rapidly and more regularly than the hand so as to instantly respond to any change in the work resistance, increasing the rate of feed to take advantage of any reduction in such resistance and instantly slowing down the feed if the resistance is increased so as to prevent breakage or injury to the tool or work.

ice

The above and other objects of the invention are accomplished by the instrumentalities and in the manner described in detail in connection with a preferred embodiment of the invention shown to illustrate the principles thereof.

The improvements in hydraulic drives for machine tools disclosed herein utilize features of the inventions described and claimed in applications for patent filed by me, Serial No. 567,438, filed December 9, 1944, now Patent No. 2,647,371, issued August 4, 1953, and Serial No. 650,073, filed February 25, 1946, now abandoned.

As described and claimed in application Serial No. 650,073 above referred to, it is preferred to use a hydraulic liquid which is rendered elastic to the extent desired by the introduction thereinto of a gas such as air, the liquid and gas mixture being maintained during use under a high pressure. This liquid gas mixture is utilized in a system including an actuator which may be used to drive either the tool or the workpiece, or both. The form of actuator usually employed is a standard piston and cylinder actuator used in many hydraulic machine tool drives. The hydraulic system also includes an accumulator properly proportioned in size in accordance with the size of actuator used and located sufficiently close to the actuator to be responsive to changes in pressure conditions caused in the latter by resistances encountered during the relative feed between the tool and work. The

system also includes a suitable control valve means for regulating the flow of the hydraulic fluid to and from the actuator.

The invention is particularly applicable to machine tools for the working of metals, although it may also be applied to tools for working upon plastics or other materials. The inve ntion may be practiced in connection with power-drivenmachine tools of various types,-such as milling machines, breaching machines, lathes, drills, In some of contact therewith, while in others the work and the tool may be moved relatively to one another as in the broaching machine, planer" and shaper; while in some instances, the work may be rotated and the tool moved relatively thereto as in a lathe. The invention finds particular utility in connection with machines of the milling machine type in which the hydraulic feed is used to bring the work into contact with arotary multi-toothed cutter.

A characteristic advantage of the hydraulic drive of the present invention is that by its use it is possible to employ tools with more acute edges, that is, with greater rake, clearance angles, etc. than it is possible to use for similar work under present practice. This enables the tools to operate more effectively and to do the same work with less expenditure of power.

In the accompanying drawings in which one preferred embodiment of the invention is illustrated in connection with milling machines: Fig; l'is a diagrammatic view of a hydraulic system applied to a milling machine, also showing the wiring diagram of electrical controls which may be employed; Fig. 2 is a vertical section showing an accumulator and connections thereto on a larger scale than Fig. 1, parts being broken away;

. Fig, 3 is .a sectionalview of a restrictor. valve taken on line.:3.--3. of Fig. 4 and showing portions broken away;

Fig. 4 is a vertical central section of the restrictor valve on a plane at right angles to the section of Fig. 3';

Fig. 5 is a'horizontal section of the restrictor valve on line-5-5 of Fig. 4; and

Fig. 6 is a perspective view on an enlarged scale of a portion of the valve plunger. 0

Referring to the drawings in detail:

Fig. 1 shows for purposes" of illustration a conventional milling machine an; ill 25 55;; "whi'liis' marines a workpiece 12 which is adapted to be brought by movementofithe table. 10 into contact with arotary toothed c te 4 ou t on. hev arbo P millina hine..-..A e ipro a u to a idcd which i shownin the form of acylinder mounted on the b ase of the milling machine (not shown) under the tableltl, in which works. a piston 22 carried hy a piston rod 24 whi h is t a s to :t ta le-v Conn c d t the s of the cylinder arepipes 26 and 28.through which fluid is alternately admitted so as to move the table back and forth and; feedthe workpiece into contact with the cutter.

Any suitablesourceof fluidunder pressure is provided ,As shown, a sump 30 is partly filled with a body of hydraulic liquid 32 which is pumped out of the sump by the. pump 34 and forced at,high pressure through the pipe 36. A spring. loaded reliefvalve 38 which may be of any conventional typeis connected to the pipe 36. The overflow from therelief valve discharges into a pipe 40 which has a spray head 42 atits lower end through which any excess .oil is forcibly sprayed into the oil in the sump... The discharge of theoil into the sump in this manner results in the entrainment of air which is carried into the oil in the sump in the form of very small bubbles so that the oil in the sump is maintained in an aerated condition and constantly filled with 'the small air-bubbles which are picked up by the pump along with theoil and pumped throughout the system.

The pipe 36 discharges into a T-connection 44 shown on an enlarged scale in Fig. 2. The T-connection 44 is preferably of substantially larger. diameter than the pipe 36 so as to form an enlarged storage or turbulence chamber within it. Between the pump and the T-connection there is a restriction in the. pipe 36 constituting a hydraulic resistance. In the construction shown in Fig. 2, this-resistance is provided by a reducing nipple 46 whichhas a holefl48 therethr ough substantially smaller in diameter than pipe 36. Asanexample of dimensions which may be used for these parts but without restricting the invention in any way to such dimensions, the pipe- 36 may be a 2A" pipe. The I -connection 44 ,may have a. boreof 2" andthe" restricted orifice inthe. nipple mayhavea length of about 1.", and an insideldiameter of about A". Connected tothe other side ofthe T-connectionis a power line 52 which may comprise a pipe Oil/2" or size having an inside diameter. of, say 7A Mountedon the. sideof the T-connection is anaccumulator 54 which in the instanceshown. is a chamber closed at its upperend having an inside diameterof about 4" and a lengthof about .28 5, being connected to theT-connectiol by a nipple 56 having in the particular example illustrated anninsidevdiameter of about ll z'fl. "The dimensions of the accumulator both as to length and .diameter will be varied inaccordance with the size of the actutaor cylinder 20. In the particular. example illustrated, the actuator comprises. a cylinderof 2'...inside diameter and about 22". long. .This is a conventional size and the dimensions given forthe. accumulator are suitable. for an accumulator to. bensed. with this sizeactuator- If the cylinder of theactuator is larger or smaller, an accumulator of corresponding size should preferably be employed to obtain the .best results. A pipe 60 is provided for the return flow ofliquid. from the actuator 52 is connected through the .reversingvalvetothe pipe 26, then the actuator pistonismoved to.the leftin Fig. 1.and.the work is-brought into. contact with. the cutter. This will be referred to as the power stroke. At this time'the -tlischaffge from the cylinder takes place through the pipe 28 and the pipe '60. When the power line 52 is connected to the pipe 28, then the milling machine table is moved to the right. This will be referred to as the return stroke. The valve 62 is a three-position valve. When in neutral position, as shownin Fig. .1, both

lines

26 and 28 are cut off from communication with lines 52 and 60 so that operation is stopped. When the valve is moved to the down position, then line 52 is connected to line 26 and the table'is moved towards the left on the power stroke. When the valve is in uppermost position, line 52 is connected to line 28 and the return'stroke is taking place. The passages in valve 62 are preferably of such size as to permit a rapid traverse of the milling machine table. The speed of traverse is made as rapid as is consistent with good practice and is determined by the size of .the ports in the valve 62 and by the size of the restriction 48. The full speed thus permittedmay be used on theentire return stroke of the table an is preferably employed on. those parts of the powerstroke except .the part of the stroke in whichthe workpiece is actually being operated upon by thecutter. During this p'art of the stroke, the speed of movement of the table must be r educed to the speed at which the material can be safely removed by the cutter.

I order to regulate the speed of traverse during the cutting part of the stroke, a restrictor valve mechanism is utilized as follows; a two-position cutoii valve 70 is provided which may be of any suitable construction and is preferably designed to stop flow through both of the

pipes

26 and 28. As shown, the valve 70 is of a reciprocating .typehaving two passages therethrough. If the valveisin position shown in Fig. 1 an uninterrupted flow 1 permitted through the valve passages so that

pipes

26 and 28 are open from end to end. In the other position, both pipcs 26 and '28 arecut off. When the valve 70 is in this latter position, restricted flow takes place through

thefbypass pipes

74 and 76, .74 passing from pipe 26 at pnesideot' the valve 70 to the same pipe. at the opposite side ofthe'valve, while pipe 76 bypasses thereturn pipe 28 aroundthev-alve 70. The valve 70 is so manipulated marten closed during traverseoi' the workpiece past the cutterso that during this time the hydraulic fluid for operating'the feed passes through the

pipes

74 and 76.

' For controlling the flow through the

pipes

74 and 76, andijtherefore, the actual rate of feed during the cutting part of the stroke, a restrictor valve 80 is provided. A preferred form of restrictor valve is shown in Figs. 3, 4 and and it comprises a casing 82 having a longitudinal bore 84 therethrough in which is permanently fitted a sleeve 86. The sleeve 86 has a pair of ports 88 therein whichcomrnunicate with horizontal bores 90 in the casing wallithese bores being connected to the two sections of the pipe 74 at the opposite sides of the restrictor valve. Thesleeve 86 also has two-ports 92 therein which communicate with horizontal bores 94 in the valve casing, suchbores being. connected with portions of the pipe 76 at each side of the restrictor valve. By providing the ported sleeve 86 fitting in the casing with the horizontal bores. therein communicating with the ports in the sleeve, a port construction is provided in the casing in which the actualports are formed in the sleeve and it is only necessary to bore the four holes 90 and.94-, respectively, transverselylof the casing, so as to introduce fluid to the

ports

88 and 92.

As'in the construction shown, the actual cutting is done only on the stroke of the milling machine table from right to left, it will be seen that the high pressure from the pump is conducted to the actuator through the

pipes

26, 52 and 74 so that the ports 88 constitute the high pressure ports while ports 92 constitute return ports. I I

For. controlling the flow of fluid through the restrictor .valve; avalve plunger is provided which is capable of limited endwise movement in thesleeve 86. The plunger 100 has a transverse bore 102 adapted to connect the high pressure ports 88 and a transverse bore 104 adapted to connect the low pressure ports 94. Preferably, the bores 102 and 104 are of the same diameter as the ports so that if the plunger were moved to bring the bores into alignment with the ports there would be unrestricted fiow. Under normal conditions however it is necessary to restrict the how very substantially so as to bring about a proper rate of feed for the table. Normally, therefore, the plunger is displaced downwardly in the valve casing so that the flow through both the high pressure and low pressure ports is greatly reduced.

In order to make possible an accurate metering of the flow, means are provided whereby the plunger may be moved longitudinally for considerable distancesfor very small changes in the rate of flow. In the construction shown, this is accomplished by providing notches 106 in the plunger at each end of the bore 132 and similar notches 108 at the opposite ends of the bore These notch-es are preferably of right angle section at the bottom as shown in Fig. 6 and are inclined from maximum depth at their ends where they open into the bores to zero Where comparatively small change in the effective size of the orifices. Actually, the variation of size of the orifices will vary approximately as the square root of the distance moved by the plunger. This permits a very accurate adjustment of the flow and corresponding regulation of speed of the feed of the work.

For adjusting the position of the plunger longitudinally in the valve casing so as to determine the normal maximum speed of cutting feed, the plunger is held between the cam surface 110 of a cam 112 which engages one end of the plunger and a heavy spring 114 which engages the other end of the plunger and at all times urges the plunger towards the cam. The plunger has a reduced end 120 adapted to lit in the end of the spring 114 the plunger near its lower end being provided with a suitable packing to prevent leakage. As shown, this packing comprises an O-ring 122 mounted in a groove 124 in the plunger. The other end of the plunger has a stern 126 of reduced diameter which fits with a close sliding fit in a sleeve 128 having a press fit in the bore of thecasing. The stem 126 of the plunger is provided with a groove 130 in which is a packing such as a rubber O-ring 132. The spring -114 is contained within a housing or cap 134 which is secured to the lower end of the valve casing in any suitable manner as by screws-136. The lower end, of the spring engages an adjustable abutment 138 which is mounted on an adjusting screw 140 screwed through the =lower end of the housing and locked in adjusted position by a -lock nut 142.

The-upper end of the stem 126 of the valve plunger normally bears against the cam surface 110. In the particular construction shown, the upper end of this stem is shown as bifurcated by a slot 144 and the cam surface is divided into two parts by a disc 146 which is circular .in outline and which fits in the slot 144. This engage- 'ment of the disc with the slot serves to hold the plunger against turning.= Obviously, any other means for prevent- -ing the plunger from turning may be employed: The cam 112 is keyed to a shaft 150 which is rotatively mounted in bushings-152 in the valve casing. The upper end of the valve casing is provided with a transverse recess- I 154 to receive the cam and the projecting end of the plunger. Mounted on the end of shaft at the front ,of .the valve casing is a knob 156, preferably having graduations 158' marked on its surface. The knob is shown as provided with a knurled head 160 and a crank handle 162. A suitable zero mark 164 is provided on the face of the valve casing; In case it is desired to lock the setting of the knob 156 and earn 112, a locking shoe 166 is provided which has a curved inclined surface 168 for engagement with a beveled flange 170 on the knob 156. A knurled headed clamp screw 172 is provided for clamping the shoe against the knob.

From the construction described it will be seen that manually adjustable means are provided for the initial accurate adjustment of the orifices in the restrictor valve. When the knob is turned to the right as seen in Fig. 3, the cam will force the plunger down against the pressure of spring 114 thereby reducing the flow through the notches 106 and 108. This slows down the feed of the carriage and produces a finer cutting action. When the knob is rotated in the opposite direction, the cam will permit the plunger to be moved upwardly by the spring 1114, thereby increasing the effective size of the orifices and the rate of feed, resulting in a coarser cut.

The restrictor valve in the construction shown performs a very important function besides mere manual regulation of the rate of feed. It is so constructed'as to act as an automatic regulating valve simultaneously controlling both the power flow to the actuator and the return flow therefrom, the regulation being automatically brought about by variation of pressure in the system, preferably in the power or high pressure line. The construction shown for this purpose comprises a passageway formed in the valve casing and connecting one of the high pressure bores 90 with the space 192 above the shoulder formed on the valve plunger between the main body thereof and the stem 126. As shown, the passageway 190 communicates with the space 192 through the notches 194 formed in the end of the sleeve 128. It will be seen that if the pressure in the high pressure line rises to a point where the pressure on the shoulder 195 is sufficient to overcome the resistance of the spring '114, then the plunger will be moved down slightly away from its position as determined by the setting of the cam 112. This downward movement of the plunger will at once reduce the flow through the metering notches 106 and 108 and will restrict the flow to and from the actuator which will reduce the rate of feed of the table.

The described automatic regulative action of the restrictor valve is very important. Assuming that the normal setting of the valve is such as to give a feed during the cutting stroke as high as is safe under optimum conditions of tool and workpiece, if an increased resistance is encountered the resulting slowing up of the table movement will permit the pressure to build up which will cause the plunger to be moved down sufficiently to check the flow so that the work will not be driven against the tool in such manner as to cause damage. Any forward surge immediately after the hard spot is passed will also be prevented. When, however, the resistance to the feed of the work against the tool is decreased, the pressure will fall and the plunger will move upward so as to increase the flow and increase the rate of feed.

Suitable means are provided for controlling the operation of the system. Preferably, these include manual devices for starting and stopping and which may also be used for reversing and for changing the rate of feed from rapid traverse to controlled traverse. In addition to such 'rnanual controls, mechanism is preferably provided for reversingthe traverse of the carriage and, for'changing from rapidjtraverse to controlled traverse during'the part I of the power stroke when the actual cutting is to beperprovided.

Referring particularly to Fig. 1, the stem 200 of the valve 62 carries cores 201 located in the solenoid coils 202fand 204; Wh'enthe coil 202 is-energized,*t he, valve is moved into position for return traverse,";while :when the coil 204 is energized, the traverse will be forward. An arrangement ,for biasing the valve to a neutral position is provided so that'when neither coil is energized the valve is in the position shown in Fig. 1 with all flow of fluid cut off and the machine stopped. A typical arrangement of biasing springs is illustrated comprising two springs 206 mounted on the stem 200 and engaging opposite sides of a cross plate 208 fixed on the stem. The springs are contained in a stationary box 210 so that whenever the valve is moved to one or the other of its limit positionsjby one of the solenoids one or the other of these springs'206 is stressed.

The valve stem 212 of the shutofi valve 70 is controlled by two solenoids 214 and 216. The valve 70 is not spring biased but will stand in either one of its limit positions to which it may be moved by one'of the solenoids until it is thrown into its otherposition by the action of the other solenoid. The solenoid 214 will move the valve to the position'it will occupy throughout the rapid traverse part of the cyclewhich includesall of the'return stroke and part of the forward stroke. When the solenoid 21.6 is energized, the valve is then thrown to the position in which it cuts the direct flow through the

pipes

26 and 28, thereby causing the. flow to take place through the

bypass pipes

74 and 76 and resistor valve 80. This causes the traverse during the period of actual cutting to be con trolled by the setting of the restn'ctor valve as already described.

For starting and stopping the machine and for any other manual control desired, the series of manual control switches indicated generally at 220 is shown. These operate through a series of holding relay circuits indicated generally at 236 to control the action of the valves. For automatic reversal and shifting from rapid traverse to controlled traverse, three

switches

240, 242 and 244 are provided These are actuated by

trippers

246, 248 and 250 which are adjustably mounted on the carriage or table of the milling machine. These switches are arranged to control the action of the valve operating solenoids through the holding relay means indicated at 230. The circuits and holding relay means are of conventional construction and a're"not, therefore, described'in detail.

Briefly, the operation of the control mechanism is as follows: Assuming that just after the machine is started by operation of the proper manual control switches,'the table ltl'reaches the end of the return traverse, that is, the position' furthest to the right in Fig. 1. At this time it trips the switch 242. This will result in closing the circuit'through the solenoid 204 which will place and hold the valve 62 in position for forward traverse. During the return stroke, the valve 70 has remained in the rapid traverse position already described and it stays in this posi- .tion during the rapid traverse part of the forward stroke.

Priorto the actual'eng'ageme nt of the work 12 with the cutter'14,*however, the tripper 250, having been properly adjusted in position for that purpose, comes into action and'trips the s'witch244. The tripping of this switch results in temporary 'energization of the solenoid 216 which willmove the valve 79 so as to cut off the direct flow through'the pipes '26 and 28, thereby causing the fiow to take'place through the bypass in which the restrictor valve' i s located. The remainder of the forward stroke of thetab'le is, therefore, controlled by the restrictor'valve.

neutral position, one or the other' of the solenoids' 2 02 and 204 which'operate it mustbe'kept'energized throughout the operation. This is accomplished by a suitable arrangement of the holding relay circuits. The valve 70, how. ever, not beingspring biased will stand in whatever posi tion it isset. Therefore, the solenoids 214.and.2l6 are cnergizedmomentarily at proper points in the cycle to shift the valve 70 from one of its positions to the other. This momentary energizing ofone or the other solenoids 214, 216 is also accomplished by the arrangement of the holding relay circuits.

I claim:

1. In a hydraulic feed for machine tools, a-restrictor valve comprising a casing having a longitudinal bore therein having portions of larger and smaller diameter, a valve plunger mounted for endwise movement in said bore, said plunger having a portion of larger diameter fitting the larger diameter of the bore, and a neck of reduced diameter fitting the smaller diameter of the bore, said plunger portion of larger diameter having a shoulder thereon surrounding said neck of reduced diameter,'said plunger being in sealing relation to the bore, said casing having pairs of ports therein at opposite sides of said plunger, metering passages in theplunger connecting the ports of respective pairs, a fluid connection from a port in the casing to the space in the bore in the casing above the shoulder on the plunger and spaced from the bore wall for admitting pressure to said space for urging the plunger in one direction and spring means for urging the plunger in the other direction.

2. In a hydraulic feed for machine tools, a restrictor valve comprising a casing having a longitudinal bore therein having portions of larger and smaller diameter, a valve plunger mounted for endwise movement in said borc, said plunger having a portion of larger diameter fitting the larger diameter of the bore, and a neck of reduced diameter fitting the smaller portion of the bore, said plunger portion of larger diameter having a shoulder thereon surrounding said neck of reduced diameter, said plunger being in sealing relation to the bore said casing having pairs of ports therein at opposite sides of said plunger, metering passages in the plunger connecting the ports of respective pairs, a fluid connection from a' port to the space in the bore in the casing above the shoulder on the plunger and spaced from the bore wall for'admitting pressure to said space for urging the plunger in one direction, spring means for urging the plunger in the other direction, and manual adjusting means for moving said plunger against the force of said spring means.

3. In a hydraulic feed for machine tools, a restrictor valve comprising a casing having a longitudinal bore therein having portions of larger and-smaller diameter, a valve plunger mounted for endwise movement in said here, said plunger having a portion of larger diameter fitting the larger diameter of the bore, and a neck of reduced diameter fitting the smaller portion of the bore, said plunger portion of larger diameter having a shoulder thereon surrounding said neck of reduced diameter, said plunger being in sealing relation to the bore, said casing having pairs of ports therein at opposite sides of said plunger, metering passages in the plunger connecting the ports of respective" pai'rs,'a fluid connection from a port to the'space in the bore in the casing above theshoulder on the plunger and spaced from the bore wall for admitting pressure to saidspace for urging the plunger in one direction, spring means for urging the plunger in the other direction,' and manual adjusting 'means for moving said -plunger against-the force of said spring means,'said manual adj'usting'means comprising a cam engaging the endrof the plunger and mounted for rotation about an axis transverse to the axis' of the plunger and manual means for rotating said cam through determinate angles.

References Citedin the file of this patent UNITED STATES PATENTS "r ldsley Oct. 6, 139s (Other references on following page) 9 UNITED STATES PATENTS Sellers Feb. 27, 1900 Gillin Dec. 8, 1903 Sankey Mar. 1, 1904 Nethery June 23, 1908 Brady Oct. 20, 1908 OBrien Apr. 22, 1913 Masterson June 16, 1914