|Publication number||US3684395 A|
|Publication date||Aug 15, 1972|
|Filing date||Dec 14, 1970|
|Priority date||Dec 9, 1969|
|Publication number||US 3684395 A, US 3684395A, US-A-3684395, US3684395 A, US3684395A|
|Original Assignee||Mitsubishi Heavy Ind Ltd|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (2), Referenced by (10), Classifications (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
United States Patent Nurakami  HEADSTOCK BALANCING CONSTRUCTION FOR MACHINE TOOLS  Inventor: Akira Nurakami,
Japan  Assignee: Mitsubishi Jukogyo Kaisha, Tokyo, Japan 22 Filed: Dec. 14,1970 21 Appl.No.: 97,724
Kabushiki  Foreign Application Priority Data Primary ExaminerGil Weidenfeld Attorney-McGlew and Toren 1451 Aug. 15, 1972  ABSTRACT the column while being guided by the headstock. The
saddle is connected to a respective balance weight by a pair of flexible connecting elements trained over pulleys on the opposite ends of a pair of arms supported on top of the column. A pair of suspension arms are mounted-on the upper end'of the column for oscillation in a horizontal plane about a vertical pivot axis at one end of each suspension arm, the pivot axis including a tubular pivot. Respective conical rollers support each suspension arm for rolling over the top of the column during the horizontal oscillation, and the two arms are interconnected for movement parallel to each other. Each arm has a pulley at each end, and a pair of flexible connectors are trained over these pulleys to connect the headstock to a respective balance weight movable vertically of the column. These latter flexible connecting elements extend vertically through the tubular pivot axes of the respective arms. A synchronizing mechanism interconnects the headstock to the two suspension arms to synchronize the horizontal oscillation of the suspension arms with a lateral displacement of the headstock.
10 Claims, 18 Drawing Figures PATENTEDAUB 15 m2 SHEET 1 [IF 7 FIG. IB
INVENTOR. AKIRA MURAKAMI PATENTEmus 15 m2 SHEEI 2 OF 7 FIG. 2
lllll INVENTOR RA MuRAKAm PAIENTED AUG 15 m2 SHEET 3 [IF 7 g 0 5 mm 8 INVENTOR. Am RA MURAKAVH PATENTEDAIJG 15 1912 FIG.?
INVENTOR. AK\RA MURAKAt u BY I-IEADSTOCK BALANCING CONSTRUCTION FOR MACHINE TOOLS BACKGROUND OF THE INVENTION Machine tools, such as horizontal boring machines, horizontal milling-boring machines, profiling machines, and the like, comprise an upright column movable horizontally along a bed, a sliding element, called a saddle, which is movable vertically along a guide sur- 1 face of the column, and a headstock or ram which is di'splaceable horizontally or laterally of the column while being guided by the saddle. In machine tools having such a construction, the supporting conditions are changed when the headstock or the ram is displaced laterally of the column. As a result of such displacement, not only is the sliding element displaced and distorted, but also other adjacent sliding elements may be displaced or distorted.
To overcome this disadvantageous condition, various balancing arrangements have been proposed as illustrated in FIGS. 1A through 1E. For example, in the balancing arrangements shown in FIGS. 1A and 1B, saddle b is counterbalanced by counterweight w through either one or two connecting elements a, such as chains or ropes. In FIG. 1A, headstock c is suspended by saddle b, and thus saddle b is tilted about the suspension point as a center in'accordance with the displacement of headstock c. Consequently, there results torsion in the narrow guide between the saddle and the column, and headstock c is displaced to a large extent.
In FIG. 1B, saddle b is suspended by two connecting elements, in a manner such that the overall center of gravity of saddle b and headstock c is positioned between the suspension points of the two connecting elements a, so that excessive tilting of saddle b and headstock can be prevented, as compared with the arrangement shown in FIG. 1A. However, tilting of saddle b and displacement of headstock 0, due to stretching of a connecting element a resulting from a change in tension, cannot be prevented.
In FIG. 1C, stretching of one connecting element a is compensated by means of an oil hydraulic device d. In FIG. 1D, tilting of saddle b with displacement of headstock c is compensated by means of cam e mounted on saddle b and roller f on headstock c.
In all of the arrangements shown -in FIGS. 1A through 1D, the weight of headstock c is suspended or supported by saddle b. Consequently, when headstock c is displaced, one or both of the sliding surfaces of saddle b or headstock c is displaced, due to the change in load distribution thereon, as a result of which straight and smooth displacement of headstock 0 cannot be assured. This drawback of the arrangements in FIGS. 1A through 1D, wherein the weight of the headstock or ram is supported by a saddle, can be obviated, for example, by installing roller f directly below the center of gravity of the headstock, as shown in FIG. 1E, so that it can roll on a plate g mounted on saddle b. In the construction of FIG. 1E, the supporting condition of headstock c per saddle, can be maintained constant, but it becomes necessary to install cylinder h and piston rods i on the upper and lower surfaces of saddle b in two places, to control the deformation of saddle b by adjusting the hydraulic pressure in cylinder h in accordance with displacement of headstock c. Additionally, it is I necessary to include the oil hydraulic device d to correct stretching of a connecting element a due to the change in tension. Not only is this arrangement complicated, but it is not possible to obtain complete correction therewith.
SUMMARY OFTHE INVENTION This invention relates to an improved headstock 0 balancing arrangement for machine tools and, more in a horizontalplane about vertical pivot axes at'firstv ends thereof. Conical rollers, rotatably mounted on each arm at substantially the midpoint thereof, support the suspension armson the upper end of the column. Respective flexible connecting elements are supported to extend longitudinally and centrally of each suspension arm, and one end of each connecting element, such as a chain or rope, is connected to a balance weight conforming to the weight of the headstock and the other end is connected to the headstock. The end of each connecting element connected to the headstock extends vertically of the column and coaxially of the pivot axis of the associated suspension arm.
A synchronizing mechanism is provided between the arms and the headstock, to synchronize the oscillation of the arms with the lateral displacement of the headstock. A second pair of flexible connecting elements, such as chains or ropes, are trained over pulleys on the upper end of the column and have first ends connected to another balance weight, conforming to the weight of the saddle, and second ends connected to the saddle at points symmetrical with the overall center of gravity of the saddle. With this arrangement, smooth motion of each component, as well as complete correction, is provided without complicating the construction.
In-the balancing arrangement of the invention, the weights of the headstock and the saddle are independently counterbalanced, with the saddle being counterbalanced by a counterweight conforming to the weight thereof through two connectors and the headstock being counterbalanced by another counterweight, conforming to the weight thereof. Thus, when the headstock is displaced, the two flexible connectors suspending the headstock are moved in parallel and in synchronism with the displacement of the headstock. As a result, there is no change in the relative condition between the headstock and the saddle from the vertical movement of the saddle or the lateral displacement of the headstock, and a straight and smooth movement of the headstock can be obtained.
As mentioned, the two connectors suspending the headstock are connected to the associated balanceweight by being trained over respective suspension arms, and the balanceweight is positioned at the opposite side of the column with respect to the headstock. Thus, each arm oscillates about a vertical pivot axis passing through the suspension point of the, balanceweight, in accordance with displacement of the headstock. Consequently, the length of each arm can be intical lines passing through the suspension points of the upper surface of the column, and is located at a midpoint of the respective suspension arm near the suspension pointof the headstock. Additionally, a generating line of the conical surface of the conical roller rolls on the surface of the upper end of the column parallel to the associated arm, and the extended axis of the roller intersects the pivoting axis of the associated arm. Consequently, each arm is supported at the upper surface of the. column during oscillation, and this support is completely a rolling support without any slipping, so that each arm is moved smoothly.'Since displacement of the headstock is synchronized with the oscillations of the arms, smooth displacement of the headstock is assured.
An object of the invention is to provide an improved balancing arrangement for the headstock and saddle of a machine tool.
Another object of the invention is to provide such a balancing arrangement which is free of the disadvantages of prior art balancing arrangements.
A further object of the invention is to provide such a balancing arrangement assuring smooth motion of each component as well as complete correction with respect to displacement of the saddle and headstock.
Another object of the invention is to provide such a balancing arrangement which is simple in construction;
For an understanding of the principles of the invention, reference is made to the following description of a typical embodiment thereof as illustrated in the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWING In-the Drawing:
FIGS. 1A through 1E are schematic perspective views of known headstock balancing constructions;
FIG. 2 is a schematic perspective view of a balancing arrangement embodying the invention;
FIG. 3 is a longitudinal sectional view through a suspension arm forming part of the balancing arrangement;
FIG. 4 is a somewhat schematic perspective view illustrating the relation of a conical supporting roller to the upper surface of a machine column and to the pivot axis of the associated suspension arm;
FIG. 5 is a vertical sectional view of a suspension position adjusting mechanism;
FIG. 6 is a horizontal sectional view taken along the line A-A of FIG. 3;
FIG. 7 is a longitudinal sectional view taken along the line B-B of FIG. 3;
FIG. 8 is a diagrammatic illustration of the conditions when a suspension arm is moved in synchronism with displacement of the headstock;
FIG. 9 is a diagrammatic illustration of the suspended condition of the headstock; and
FIGS. 10 through 12 are diagrammatic illustrations of the forces acting on the parts and the positions of the parts, for explanatory purposes.
DESCRIPTION OF THE PREFERRED EMBODIMENT As stated, FIGS. 1A through 1E represent known or prior art headstock balancing arrangements.
Referring to FIG; 2, a bed 1 of a machine tool movably supports a vertical column 2 on whicha' s'addie-3 is vertically displaceable in guided relation. A headstock 5, supporting a spindle 4, is embraced by saddle 3 and is displaceable vertically of column 2 as well as being displaceable laterally thereof. Two arms 6, mounted on the upper surface of column 2, carry respective pairs of pulleys 7, one at each end, over which there extend respective flexible connectors 8, such as cables or chains. Connectors 8 have first ends connected to a balanceweight 9 which is movable vertically of an inner space between saddle 3 and column 2. Hangers 10 of connectors 8, at the saddle ends thereof, are spaced equal distances from a vertical line passing through the center of gravity of saddle 3, and hangers 1 1, at the balanceweight side of connectors 8, are also spaced equal distances from the vertical line passing through the center of gravity of balanceweight or counterweight, 9.
A pair of brackets 12 are secured to the upper end surface of column 2, and project outwardly from column 2 in a direction opposite to headstock 5, brackets 2 carrying pivot axes for respective arms 13 and 14 which are oscillatable in a horizontal plane. Each arm 13 and 14 has a pair of pulleys 15, each rotatably supported at the respective end of the arm, and connectors 16 are trained over pulleys 15 to connect headstock 5 with a balanceweight or counterweight 17 positioned beneath brackets 12 and movable vertically along column 2. Connectors 16 extend coaxially through tubular pivot axes of arms 13 and 14. Hangers l8 connect the headstock ends of connectors 16 to headstock-5 at points spaced equal distances from the vertical line passing through the center of gravity of the headstock, and hangers-l9, at the counterweight ends of connectors 16, connect connectors 16 to counterweight 17 at points spaced equal distances from the vertical line passing through the center of gravity of counterweight 17.
When headstock 5 is displaced laterally, arms 13 and 14 oscillate in a horizontal plane in synchronism with the displacement of the headstock, through the medium of a synchronizing means described hereinafter. During such horizontal oscillation of arms 13 and 14, respective conical rollers 20 rotatably mounted adjacent the lower surfaces of arms 13 and 14 roll along respective rails 21, mounted on the upper end surface of column 2, while carrying the load of the respective arms 13 and 14. Opposite ends of a connecting rod 12 are pinned to the lower surfaces of arms 13 and 14 and, as the distance between the pin connections is equal to the distance between the pivot axes of arms 13 and 14, these arms oscillate in parallel with each other.
A rack 23 is mounted at the back side of headstock 5 and this is engaged with an idle gear rotatably mounted in a gear box 24 secured to saddle 3, and idle gear 25 engages a pinion 26.-A bevel gear is secured to the upper end of a splined shaft 29 supported, in vertical orientation, at the bottom and top of column 2 by respective brackets 27 and 28, the bracket 28 being indicated in broken lines. Bevel gear 30 meshes with a bevel gear 32 on one end of a horizontal shaft 31 rotatably supported by bracket 28, and a sprocket 33 is secured to the opposite end of shaft 31. Splined shaft 29 extends, in splined engagement, through pinion 26.
Guide brackets 34 and 35 on the upper end surface of column 2 support a pair of parallel guide bars 36 for a slide 37. A roller 38 rotatably mounted at the lower surface of arm 14, so that it extends from this arm, projects into an aperture in the upper surface of slide 37. As best seen in FIG. 6, the opposite ends of a chain 39 are secured to surfaces of slider 37 which are perpendicular to the moving direction of this slide, and chain 39 is engaged with a sprocket 41, supported by a bracket 40 on the upper surface of column 2, and with sprocket 33.
Idle gear 25, meshing with rack 23, rotates in accordance with the lateral displacement of headstock 5, and this rotation is transmitted to pinion 26, splined shaft 29, bevel gear 30, bevel gear 32, shaft 31 and sprocket 33. When sprocket 33 is rotated, slide 37 is moved by chain 39, thus oscillating arm 14 through the medium of roller 38 and in synchronism with the direction of displacement of headstock 5. Arm 13 is oscillated by connecting rod 22 in synchronism with the oscillation of arrn 14.
Referring to FIG. 3, a housing 42 is bolted to the upper surface of headstock 5 and a cover 43 is bolted to this housing. A slide 44 is positioned in a space defined by housing 42 and cover 43, and is slidable longitudinally of housing 42. A spherical bearing 45, capable of supporting a radial load as well as a bilateral thrust load simultaneously, and having self-aligning properties, is inserted into an aperture in slider 44, and hanger 18, in the form of a shaft, is inserted through bearing 45. A nut 46 is threaded onto a male thread at the lower end of hanger 18, and one end of a connector chain 16 is secured to hanger 18. Connector 16 is guided by the roller 15 which are rotatable about shafts or pivots 47 secured to arm 14.
The other end of connector 16 is secured to hanger 19 of headstock counterweight 17. A thrust bearing 49 and a bush 50 are inserted into an aperture in a cover 48 bolted to counterweight 17, and hanger 19, in the form of a shaft, is inserted into bearing 49 and bush 50, with a nut being threaded on a male thread at the lower end of hanger 19. A thrust bearing 52 and two radial bearings 53 are mounted in a tubular formation in the projecting portion of bracket 12 bolted to the upper surface of column 2, and a hollow or tubular pivot, forming a part of arm 14, is inserted into bearings 52 and 53. Connector 16 extends coaxially through the interior of the hollow shaft or pivot.
Connecting rod 22, interconnecting arms 13 and 14, is oscillatably connected to these arms by pins 55, at its opposite ends, extending through apertures in the arms and secured by nuts 54. A hardened steel plate 56 is bolted to the upper surface of rail 21 which is, in turn,
bolted to the upper end surface of column 2. A roller shaft is inserted into a bracket 59 whose rotation is restricted by means of a key 58 engaged in a shaft 57 secured to arm 14, and whose axial movement is restricted by the opposite sides of arm 14. Conical roller 20 is mounted in this portion, thus supporting radial and thrust loads through roller shaft 50 and is restrained against axial movement by a nut 61. Roller 20 engages steel plate 56 at its generating line, and shaft 60 and bracket 59 are so positioned, relative to arm 14, that the center axis of roller 20 intersects the pivot axis of am 14. The principle of this relation is illustrated in FIG. 4.
As stated, slide 37 is slidable at right angles to the plane of FIG. 3 while being guided by guide bars 36 secured to guide brackets 34 and 35 bolted to the upper end surface of column 2, only bracket 34 being shown-in FIG. 3, and the two brackets being parallel with each other. A roller shaft 62, mounted in an aperture in the lower surface of arm 14, as well as a roller 38 rotatable on shaft 62, extend into an elliptic aperture in slide 37.
Referring to FIG. 5, rack 23 is seated in the groove formed in the back of headstock 5 and extending parallel to the direction of displacement of the headstock, rack 23 being retained by guide plate 64 bolted to headstock 5. Rack 23 engages idle gear 25 in gear box 24, and gear 25, in turn, meshes with pinion 26 having a hub formed with a splined bore receiving splined shaft 29. At-the lower end of shaft 29, the radial load is carried by a radial bearing 65 seated in an aperture in bracket 27 bolted to column 2 and, at the upper end of shaft 29, the radial load, as well as the downward thrust, are carried by bearing 66 secured in bracket 28 bolted to the upper part of column 2. Bevel gear 32 on horizontal shaft 31, rotatably mounted in bracket 28, meshes with bevel gear 30 on the upperend of shaft 31, and sprocket 33 is secured to the other end of shaft 31.
Referring to FIG. 6, bracket 28 and sprocket 33 are shown at the left end, and shown at the right end in FIG. 6 is sprocket 41 rotatably mounted in bracket 40 bolted to the upper surface of column 2. FIG. 6 also illustrates chain 39 whose opposite ends are secured to opposed surfaces of slide 37 guided by guide bars 36, chain 39 being trained over sprockets 33 and 41.
' Referring to FIG. 7, which is a longitudinal sectional view on the line BB of FIG. 3, a bracket 67 is bolted to the end surfaces of housing 42 and cover 43, and a part of this bracket projects into the rectangular space defined by housing 42 and cover 43. A motor 68, with a reduction gear, is mounted on bracket 67, and the projected portion of bracket 67 supports the radial load and the thrust load of a screw shaft 69. One end of shaft 69 is inserted into the output shaft of the reduction gearing of motor 68, with the torque of motor 68 being transmitted to shaft 69 through a key 70. The other end of shaft 69 is threaded into a female thread at the end of slide 44, which is connected to another slide 72 by a connecting rod 71. Slide 44 and slide 71 mount hangers 18, 18, respectively.
A rack 73 is bolted to the lower surface of slide 44 and is engaged with a pinion 75 supported by two bearings 74 mounted in an aperture in the upper surface of headstock 5. A sprocket 76 is fixed on the hub of pinion 75, and a sprocket 79 is fixed on the end of a shaft 78 supported by two bearings 77 inserted into an aperture in the inner projection at the back of headstock 5. A chain 80 is trained over sprockets 79 and 76 but, because of space limitations, chain 80 is illustrated in parallel with the plane of FIG. 7 rather than perpen dicular thereto. A pinion 81 is fixed to the lower end of shaft 78. The rack 23, previously described in connection with FIG. 5, is partially provided with a series of teeth r on the opposite side of the rack from a series of teeth r which latter series meshes with idle gear 25. Pinion 81 meshes with teeth r A cover 82 on cover 43 covers the elliptic aperture in cover 43, and hangers 18 project through this aperture, cover 82 being movable with movement of hangers 18. In addition, two brackets 83 are mounted on the upper surface of cover 43 and mount respective limit switches 84. A plurality of dogs 85 can be mounted on cover 82 for movement in the direction of displacement of headstock 5. The upper surface of cover 82 is marked with graduation lines corresponding to the kind of at-. tachments required for the balancing mechanism, and which will be described hereinafter, and the mounting position of dogs 85 is determined in accordance with these graduation lines.
The operation of the balancing mechanism will now be described. Referring to FIG. 2, the weights of saddle 3 and headstock 5 are independently counterbalanced by the respective counterweights 9 and 17. Headstock balancing or suspension arms 13 and 14 are supported by the respective brackets 12 at first ends thereof and are oscillatable about respective vertical pivot axes at these first ends. The horizontal movement of arms 13 and 14 is guided, and the load thereof is carried, at positions near the opposite ends thereof, by the hardened steel plate 56 provided on the upper surface of rail 21 and through the mediumof the conical rollers 20.
The lateral displacement of headstock 5 results in rotation of gear 25 and pinion 26 by rack- 23 through teeth r Thus, splined shaft 29, bevel gears 30 and 31, shaft 32 and sprocket 33 are rotated. Since chain 39, secured to slide 37 at its opposite ends, is trained over sprockets 33 and 34, slide 37 is guided by guide bars 36 for movement in the same direction and parallel to the direction of lateral displacement of headstock 5. This moves arm 14 through roller 38, resulting in movement of arm 13 through connecting rod 22, so that the horizontal oscillation of arms 13 and I4 is synchronized with the lateral displacement of headstock 5. This relationship is further described with reference to FIG. 8, in which the distance H of the displacement of the headstock is exaggerated with respect to the length A of the arms.
Referring to FIG. 8, when headstock 5 is positioned at the center of its lateral displacement, arm 14 extends perpendicularly to the direction of such displacement and the drop point of the chain at the end of arm 14 is on the perpendicular line above the center Q of one of the two hangers 18 for headstock 5.
When headstock 5 has been displaced to point Q, i
which represents the maximum linear movement or displacement H to one side'of center, arm 14 pivots so 7 center point p of roller 38 on arm 14 has moved to the distance h, while being guided by slide 37. During this time, the synchronizing mechanism selects the values A, a, m, Z Z Z and D so that the distance h through which slide 37 is moved by chain 39 by pinion 25 having the module m and the number of teeth 2,, the bevel gears 30 and 32 having the numbers of teeth Z and Z respectively, and sprocket 33 having an effective diameter D, during displacement of rack 23 through the distance H, is represented by the following equation:
When the movement of arm 14 is regulated or controlled as described above, chain 16 is tilted due to the difference between the linear displacement of headstock 5 and the pivotal displacement of arm 14. However, as point P falls on the line 00', there is no unfavorable or disadvantageous torsion imparted to chain 16. When chain 16 is tilted due to the difference between the linear displacement of headstock 5 and the pivotal motion of arm 14, a horizontal component force F is developed in headstock 5 in addition to the force acting vertically upwardly. p FIG. 9 illustrates the most unfavorable condition, where headstock 5 has been displaced the maximum amount. Even under this condition, 1 min. is far larger than the difference between the linear displacement and the pivotal motion. Additionally, the difference itself is small, because the length A'of arm 14 is greater than the maximum displacement distance H which is one-half of the total travel of headstock 5. In theillustrated embodiment of the invention, in which balanceweight 17 is positioned the furthest from headstock 5 with respect to column 2, the length A can be made larger than the displacement distance H. Consequently, the horizontal component force is small, considered from the practical standpoint.
Referring now to FIGS. 3 and 4, there will be considered the load applied to conical roller 20. In FIG. 20, the weight of the headstock 5 and the counterweight 17 is W, the load to be applied to two rollers 20 is R and the load to be applied to two oscillating shafts is R Under these conditions, the following relationship will hold:
Thus, R is larger than W/2.
Consequently, the resistance to be encountered in the oscillation of arms 14 and 13 horizontally by the synchronizing mechanism should be small in order to improve the synchronization of these arms without transmitting any unreasonable force to the synchronizing mechanism. Thus, the rolling surface of conical roller 20 coincides with the generating line of this conical roller, and the axis of the roller intersects the pivot axis of the arm, thus assuring only rolling motion of the roller without slipping during horizontal oscillation of arms 13 and 14. As a result, the resistance of arms 13 and 14 to such horizontal oscillation becomes quite small.
Referring again to FIG. 3, the spherical bearing 45 is provided between hanger 18 and slide 44, and thus hanger 18 is able to follow the rotation of chain 16 about the center line due to the difference between the linear displacement of headstock 5 and the pivotal motion of arm 14, whereby any torsion in chain 16 is I eliminated. Furthermore, as thrust bearing 49 and bush 50 are provided between hanger l9 and cover 48, hanger 19 is able to follow the angular displacement of chain 16 about its center line due to the oscillation of arms 13 and 14, thus eliminating torsion in chain 16. Finally, since the pivot axes of arms 13 and 14 are tubular and chain 16 passes coaxially of these pivot axes, counterbalance 17 is not moved when arms 13 and 14 oscillate. As a result, the guiding means for counterweight 17, which has not been shown because of its simplicity of construction, can be made simple in practice, because the factor to be considered is only the vertical movement of counterweight 17.
The distance between the pinned ends of connecting rod 22 is equal to the center-to-center spacing of the two pivot axes of the arms 13 and 14, respectively, and the distance between each pivot axis and the point of connection of rod 22, for each arm, is equal to that of the other arm. Consequently, the pivot axis is positioned at the top of the parallelogram, assuring parallel oscillation of arms 13 and 14 as well as smooth lateral displacement of headstock 5. By virtue of connecting rod 22, only one slide 37 is necessary for the synchronizing mechanism of arms 13 and 14.
Referring to FIG. 5, the synchronizing mechanism is operated through meshing of rack 23 with idle gear 25, and such operation is effected by displacement of headstock itself so that no separate driving source is required. With reference to FIG. 6, the elliptic aperture in slider 37 is provided in order to permit arm 14 to execute a circular motion while slide 37 slides parallel with the linear displacement of headstock 5.
FIG. 11a illustrates the condition where the center between two ropes or chains 16 for balancing headstock 5, as spaced equal distances from both connectors 16, passes through the center of gravity G of headstock 5 which is suspended with a horizontal orientation. FIG. 11 b illustrates the condition when an attachment is mounted at the front end of headstock 5, as a result of which headstock 5 is inclined forwardly and downwardly. FIG. 11c illustrates the condition where headstock 5 is again suspended with a horizontal orientation by moving the two connectors 16 toward the attachment end of the headstock and through the distance x. In these figures, if the distance between the front end of headstock 5 and the center of gravity G thereof is L, the distance between such front end and the center of gravity g of the attachment e, and the respective weights of headstock 5 and the attachment are W and w, headstock 5 will become horizontal when the following relationship is established:
FIG. 7 illustrates the balancing mechanism for maintaining the headstock balance when an attachment is mounted thereon. When motor 68, with its reduction gear, is driven, and screw shaft 69 is rotated, slide 44 moves parallel to the direction of displacement of headstock 5 along the guide surface formed by housing 42 and cover 43, due to its threaded engagement with shaft 69. At the same time, slide 72 is displaced in synchronism through the medium of connecting rod 71, so that both hangers 18, one connected to slide 44 and the other connected to slide 72, are moved without any change in the spacing therebetween. When slide 44 moves, rack 23 is moved a distance equal to the distance through which slide 44 moves, by the means of teeth r of rack 23, through rack 73, pinion 75, sprocket 76, chain 80, sprocket 79 and pinion 81. When rack 23 moves, idle gear25 is rotated, thus oscillating arms 13 and 14 in the manner described. This effect corresponds to sliding movement of slide 44 and the movement of headstock 5, and therefore arms 13 and 14 are moved in synchronism with the movement of hangers 18.
Dogs 85, mounted on' cover 82 which is movable with'hangers 18, are positioned in accordance with the graduation lines conforming to the kind of attachment mounted on the headstock, these graduation lines being marked on the upper surface of cover 82. The motor 68 is driven under the control of dog 85 and limit switch 84, and is stopped automatically upon completion of the movement of hangers 18 conforming to the kind of attachment. Housing 42 and cover 43 are provided with reliefs for the movement of hangers l8 and rack 73. In order to put the synchronizing mechanism into operation in accordance with displacement of headstock 5 when the balancing mechanism is not being operated, it is necessary to eliminate the relative motion of rack 23 with respect to headstock 5. For this purpose, the threading of screw shaft 69 into slider 44 serves as a self-locking thread, and chain 80 is provided with a tension adjusting means (not shown) in order to eliminate play in the balancing mechanism due to stretching of chain 80.
The reason why saddle 3 and headstock 5 are suspended by two connectors is that, as explained with reference to FIGS. 1A and 1B, suspension by two connectors is more stable with respect to load variations than is suspension by a single connector. In addition, local deformation, caused by the concentration of stressaround the suspension point, can be decreased by the distribution of the load. The headstock is comparable to a beam having a uniform cross-section. When such a beam is suspended at two points which are spaced by one-third of the beam length, the deflection due to gravity is about one-half that in the case of suspension by a single connector at its center. It is known that, if the beam is suspended at a point near the Bessel pointby two connectors, the deflection due to gravity will become almost zero.
Thus, in the invention arrangement, the load condition is not changed, owing to the action of the balancing mechanism, when the saddle is moved vertically or the headstock is displaced horizontally in the lateral direction. Consequently, straight and smooth movement of the headstock is assured. If the counterweight of the headstock is positioned at the opposite side of the column, with respect to the headstock, the center of gravity of all the moving loads above the column base and others can be coincide with the center of the column base. Consequently, the surface pressures of the sliding surfaces of the column base and bed are balanced, and smooth movement of the column base is assured. The length of the headstock balancing or suspending arms can be increased to the maximum by positioning the counterweight of the headstock at the side of the column opposite the side carrying the headstock, and therefore inconveniences resulting from the difference between the linear displacement of the headstock and the circular or pivotal motion of the supporting arms, can be minimized. Moreover, since the suspension point of the chain is on the extended center line of the arm, no unfavorable torsion of the chain is caused, even if a difference is developed between the linear displacement of the headstock and the circular or pivotal motion of the suspension arms.
Furthermore, although the headstock balancing arms are oscillated, the counterweight of the headstock is not moved at all in the horizontal plane, and thus the guide mechanism for vertical movement can be made simple. In addition, the loads applied to the balancing or suspension arms are supported not only by the pivot shafts but also by the conical rollers. Although the arms execute a circular or pivotal motion, the conical roller executes only rolling motion and without slipping. Consequently, the movement of the arms is quite smooth. The arms are oscillated in synchronism with the dis placement of the headstock, and the synchronizing mechanism assures smooth displacement of the head stock. This synchronizing mechanism is driven directly by displacement of the headstock, and does not require separate driving means.
As the invention arrangement is provided with a motor-driven balancing mechanism, to prevent the headstock from tilting when an attachment is installed at its front end, the headstock can be held in a horizontal condition even when such an attachment is installed. In order to actuate the balancing mechanism, the headstock suspension arms should be moved in synchronism with the displacement of both hangers 18. In accordance with the invention, the synchronizing mechanism can be utilized for driving the balancing mechanism, and therefore the entire arrangement can be simplified. Additionally, the balancing mechanism can be remotely controlled due to the provision of dogs at locations conforming to the kind of attachments to be used, thus facilitating adjustment of the balance. The saddle and the headstock are suspended by two conductors each, and therefore are better stabilized, with respect to changes in load, than in the case of suspension by single conductors, and local deformation around the suspension point is decreased, thus minimizing the deflection of the headstock due to gravity.
Furthermore, housing 42 and cover 43 on the upper surface of the headstock, to protect the balancing mechanism, are of strong box-like construction and are securely attached to the headstock by bolts extending throughout the longitudinal or moving direction of the headstock. Thus, the upper surface of the headstock is reinforced, resulting in a further decrease in local deformation.
It will be understood that variations may be made in the illustrated embodiment without departing from the principles of the invention. For example, the suspension of the headstock by two connectors can be modified to suspension by a single connector in dependence on the situation, but particularly in the case of small machine tools. In this latter case, the suspension point lies on the vertical line extending to the center of gravity of the headstock and in this neighborhood, and thus the use of one headstock suspension arm 13 is obviated and only the arm 14 is used. Furthermore, while the description has pertained to two suspension points which are spaced equally from the vertical line passing through the respective center of gravity when the headstock and saddle are suspended by two connectors, the latter can be suspended by two connectors in the arrangement shown in FIG. 12, whereby each connector is at a different distance from the vertical line extending through the center of gravity of the headstock, and at a corresponding different distance from the vertical line extending through the center of gravity of the corresponding counterweight, the proportion between the spaced distances on the headstock or saddle being equal to the proportion of the two spacings on the associated counterweight. In FIG. 12, if A is equal to B and a is equal to b, the condition is the same as described in detail.
While a balancing mechanism has been shown and described, it can be eliminated in the case when no attachment is installed or when an installed attachment is not heavy enough to cause tilting of the headstock. While the balancing mechanism has been described as being driven by a motor with a reduction gear, it can be driven by a hydraulic actuator or by other means, for example, by changing over the spindle driving mechanism of the headstock itself or the feed driving mechanism. While the synchronizing mechanism has been described as being driven by mechanical connection as a result of displacement or feed of the headstock, it can be driven electrically or hydraulically by signals resulting from change in displacement or position of the headstock, or by receipt of command signals for feeding of the headstock.
The connectors used for suspending the headstock and the saddle are not limited to chains, but may be ropes. The combination of the headstock and the saddle can be replaced by the'combination of the headstock, sometimes referred to as the spindle, carriage, or the like, and a ram or quill.
While a specific embodimentof the invention has been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from'suchprinciples.
What is claimed is:
1. In a machine tool of the type including an upright column movably supported on a bed, a saddle movable vertically along a guide surface of the column, and a headstock displaceable laterally of the column while being guided by the saddle, an improved balancing arrangement, for the headstock and saddle, comprising, in combination, at least one suspension arm mounted on the upper end of said column for oscillation in a horizontal plane about a vertical pivot axis at one end thereof; a conical roller rotatably mounted at substantially the midpoint of each arm and having rolling bearing engagement with said column; a first flexible connecting element supported to extend centrally along each arm and connected at one end to said headstock, the other end of each first connecting element extending vertically of the column and coaxially of the pivot axis of the associated arm; a first balance weight, conforming to the weight of said headstock, movable vertically of said column and having the other end of each first connecting element connected thereto; synchronizing mechanism interconnecting said headstock and each arm and synchronizing the horizontal oscillation of each arm with the lateral displacement of said headstock; a second balanceweight conforming to the weight of said saddle; and at least one second flexible connecting element supported on said column and connecting the center of gravity of said saddle to said second balanceweight.
2. A balancing arrangement for the headstock and saddle of a machine tool, as claimed in claim 1, including two said suspension arms mounted on the upper end of said column for oscillation in a horizontal plane about respective vertical pivot axes at one corresponding ends thereof; said first flexible connecting elements being connected to said headstock at positions spaced in opposite directions from the center of gravity of said headstock, and being connected to said first balanceweight at positions spaced in opposite directions from the center of gravity of said first balanced weight.
3. A balancing arrangement for the headstock and saddle of a machine tool, as claimed in claim 2, including a connecting link articulated to each of said arms at points thereon spaced from said pivot axes; the distance between the connections of said link to said arms being equal to the distance between said pivot axes.
4'. A balancing arrangement for the headstock and saddle of a machine tool, as claimed in claim 2, including a bearing member on the upper end of said column engaged by said conical rollers; each conical roller having its generatrix in engagement with said bearing member and its axis intersecting its generatrix at the vertical pivot axis of the associated suspension arm, whereby each conical roller has only rolling engagement with said bearing member.
5. A balancing arrangement for the headstock and saddle of a machine tool, as claimed in claim 2,.in which said synchronizing mechanism includes a rack on said headstock displaceable with said headstock, gearing meshing with said rack for rotation responsive to lateral displacement of said headstock, and means connecting said gearing to at least one suspension arm and operable to pivot said suspension arm in correspondence with the lateral displacement of said headstock.
6. A balancing arrangement for the headstock and saddle of a machine tool, as claimed in claim 5, in which said headstock is constructed and arranged for securement of a machining attachment to one end thereof; said rack having teeth on opposite surfaces, with the teeth on one surface being engaged with said gearing; further gearing engaged with the teeth on the opposite surface of said rack; remotely controlled means on said headstock operable to shift the points of connection of said first flexible connection elements longitudinally of said headstock to re-balance said headstock when an attachment is secured to the end thereof; said further gearing driven by said remotely controlled means and engaged with the teeth on the other surface of said rack to shift said rack longitudinally of said headstock in accordance with the displacement of said connection points of said first flexible connecting elements to said headstock.
7. A balancing arrangement for the headstock and saddle of a machine tool, as claimed in claim 2, in which each of said vertical pivot axes comprises a tubular pivot; the ends of said first flexible connecting elements connected to said first balancewelght extending coaxially through the respective tubular pivots.
8. A balancing arrangement for the headstock and saddle of a machine tool, as claimed in claim 2. in which said first flexible connecting elements are connected to said headstock at points spaced equal distances to opposite-sides of the center of gravity of said headstock, and are connected to said first balanceweight at points spaced equal distance to opposite sides of the center of gravity of said first balanceweight.
9. A balancing arrangement for the headstock and saddle of a machine tool, as claimed in claim 2, in which said first flexible connecting elements are connected to said headstock at points-spaced unequal distances from the center of gravity of said headstock, and are connected to said first balance weight at points spaced unequal distances from the center of gravity of said first balanceweight; the ratio of the spacings of the connecting points to said headstock being equal to the ratio of the spacings of the connecting points to said first balanceweight.
10. A balancing arrangement for the headstock and saddle of a machine tool, as claimed in claim 5, in which'said synchronizing mechanism includes a slide mounted on the upper end of said column for displacement parallel to the direction of displacement of said headstock; said synchronizing mechanism including a pair of rotatable sprockets driven from said rack through said gearing and a chain trained over said sprockets and connected at opposite ends to opposite ends of said slide; said slide having an elongated slot in its upper surface extending perpendicular to the direction of motion of said slide; and a roller rotatably mounted on at least one of said suspension arms and engaged in said slot for movement of said suspension arms responsive to displacement of said slide corresponding to displacement of said headstock.
PC4050 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIN I Patent No. 3 Dated s hud 15th, 1972 Inventor) AK RA MURAKAMI It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
' The inventors name was mispell-ed in the Letters Patent as AKIRA NURAKAMI It should read AKIRA -EURAKAMI.
ned and seal r h ed thvlS 9th day f January 1973' (SEAL) Attest:
RIELIQRIQM.FSETCHERJR. I ROBTR 8 mg :fiCer r 1 T GOTTSCHAL Commissioner of atents
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|GB885426A *||Title not available|
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|U.S. Classification||408/235, 409/237|