GB2172530A - Apparatus for exchanging workpieces in machine tools - Google Patents

Abstract

A work changing apparatus for use in a grinding machine has two grippers 7, 8 which are disposed one behind the other, as considered in the direction of the axis 9 of the workpiece W1 at the material removing station. Each gripper can releasably hold a discrete workpiece and is rotatable about a vertical or non-vertical axis 11 which intersects and is normal to the axis 9 of the workpiece at the material removing station. In addition, each gripper is movable in the direction of the respective vertical or non-vertical axis 11. The grippers are rotatable and movable longitudinally by pairs of fluid- operated motors, and all such motors are mounted in a carriage which is movable in parallelism with the axis 9 of the workpiece at the material removing station. <IMAGE>

Description

SPECIFICATION Apparatus for exchanging workpieces in machine tools The present invention relates to apparatus for manipulating workpieces in work processing machines, especially in machine tools (such as grinding machines). More particularly, the invention relates to improvements in apparatus for exchanging workpieces in machine tools and like machines by means oftwo work gripping or engaging devices each of which has means (e.g., claws, jaws, prongs, arms, fingers or like parts) for engaging and releasably holding a workpiece, e.g., a substantially cylindrical, ring-shaped or otherwise configurated workpiecewhich is normally rotated during removal of material therefrom while it is held between the centers of a headstock and a tailstock or in any other suitable way for rotation about a predetermined axis.

Automatic removal of finished workpieces and automatic delivery of raw or unfinished workpieces (blanks) is particularly important in a massproducing automatic machine, e.g., in a numerically controlled grinding machine. Reference may be had to German Offenlegungsschrift No. 29 42 060 which discloses an apparatus for automatic delivery of blanks to and for automatic removal of finished workpieces from a turning machine. The apparatus comprises two gripping devices which are disposed in a plane extending at right angles to the axis of rotation of the workpiece in the turning machine and are reciprocable in directions making an acute angle.

A drawback of the just discussed apparatus is that their space requirements are rather pronounced so that they cannot be installed in all types of machine tools. Thus, in many machine tools the space which is available to allow a blankto bypass a finished workpiece orviceversa is very limited due to the provision of so-called interfering contours at both sides of the path of movement of blanks toward and offinished workpieces away from the material removing station. For example, and referring to a numerically controlled grinding machine, the blanks and the finished workpieces must be advanced along a narrow path which is flanked by the grinding wheel orgrindingwheelsatonesideand by one or more work rests, measuring heads, shrouds and/or other machine parts at the other side.Nevertheless, the problem can still be solved if the machine is designed or set up for the treatment ofslenderworkpieces having relatively small diameters. Suchworkpieces can be manipulated while the respective gripping devices perform.relatively short strokes. However, the situation is aggravated if the machine is designed or is set up forthetreatment of relatively bulky workpieces (e.g., ring-shaped, flange-like or barrelshaped parts). Under such circumstances, the gripping devices must perform very long strokes with attendant unacceptably long work exchange intervals.

In accordance with certain other prior proposals, workpieceswhich are to be treated in agrinding machine can be moved to orfrom the position for removal of material therefrom only upon retraction of the grinding wheel or grinding wheels from their operative positions. This is a time-consuming operation which necessitates the provision of additional controls and contributes excessively to the initial and maintenance cost of the machine.

The invention resides in the provision of an apparatus which can be used as a means for exchanging workpieces in machine tools and/or otherworktreating machines, particularly in grinding machines, wherein the workpieces are treated while rotating about a predetermined axis (e.g., about an axis which is defined by the centers of a tailstock and a headstock in a surface grinding machine). The apparatus comprises a first and a second work gripping device each of which has meansfor engaging and releasably holding a discrete workpiece (e.g., an elongated cylindrical workpiece).The two work gripping devices are disposed one behind the other as considered in the direction of the predetermined axis, and the apparatusfurther comprises first drive means for imparting to each device a translatory movement, and second drive means for imparting to each device an angular movement. The second drive means can comprise means for rotatingtheworkgripping devices about axes which are preferably parallel to each other a nd i ntersect the p redetermi ned axis. ihe axes about which the work gripping devices rotate can be vertical or non-vertical.

The first drive means preferably comprise means for moving the first d nd second gripping devices in the directions of their respective axes of rotation.

Each drive means can comprise a discrete motorfor each of the two work gripping devices, and at least one ofthe four motors can constitute a fluid-operated (hydraulic or pneumatic) motor.

The apparatus can further comprise means (e.g., a reciprocable carriage in the form of or including a gantry wagon) for moving the two work gripping devices jointly in the direction of the predetermined axis.

If the workpieces are relatively small, each ofthe work gripping devices preferably comprises a crank with a th row which equals or approximates halfthe distance between the axes of rotation of the first and secondworkgripping devices.

The novel features which are considered as characteristic of the invention are setforth in particular in the appended claims. The improved apparatus itself, however, both as to its construction and its mode of operation, together with additional features and advantag es th ereof, wi II be best understood upon perusal ofthefollowing detailed description of certain specific embodiments with reference to the accompanying drawing.

FIG. 1 is a fragmentary partly side elevational and partly vertical sectional view of an apparatus which embodies one form of the invention and wherein the two work gripping devices are rotatable about vertical axes; FIG. 2 is a partly front elevational and partly vertical sectional viewofthe apparatus; FIG. 3 is a horizontal sectional view as seen in the direction of arrows from the line Ill-Ill of FIG. 2; FIG. 4 is a fragmentary partly side elevational and partly vertical sectional view of a second apparatus wherein the work gripping devices are rotatable about non-vertical axes; FIG. 5 is a horizontal sectional view of a third apparatus with cranked work gripping devices; FIGS. 6a to 6h illustrate different steps of a twostage treatment of workpieces in a machine embodying the apparatus of FIGS. 1 to 3;; FIGS. 7a to 7c illustrate the manner in which the improved apparatus can be used for two-stage treatment of workpieces in two different machines; and FIG. 8 shows the details of one form of presently preferred drive means for rotating and simultaneously reciprocating a gripping device.

The apparatus which is shown in FIGS. 1 to 3 is installed in a grinding machine wherein a workpiece W1 is treated while rotating at a material removing station 3 between the center 4 of a headstock and the center 6 of a tailstock. The grinding wheel is shown at 1, and the axis of rotation of the workpiece W1 (i.e., the common axis of the centers 4 and 6) is shown at 9. The phantom line 2 denotes the outline or contour of an interfering body (obstacle), e.g., of a work rest, a measuring head or a shroud which is disposed in front of or around the material removing station 3. The workpiece W1 is an elongated cylinder whose peripheral surface is to be treated by the working surface of the rotating grinding wheel 1.

The improved work changing apparatus comprises two work gripping devices 7 and 8 which are disposed one behind the other, as considered in the direction of the axis 9, and each of which has two jaws which are movable relative to each other in response to signals from the numerical controls of the grinding machine so as to release orto releasably hold the workpiece W1 or another workpiece (see the workpiece W2). The gripping devices 7 and 8 are respectively rotatable about vertical axes 11 each of which intersects the axis of the workpiece W1 between the centers 4, 6.

The apparatus further comprises drive means 12, 14 which are respectively designed to impart to the gripping devices 7 and 8 linear (translatory) movements in the directions of the respective axes 11 (i.e., to move the grippers above and away from or toward the axis 9), and drive means 13 and 16 which are designed to rotate the gripping devices 7 and 8 about the respective axes. The arrangement is such thatthe drive means 12, 13 can simultaneously rotate and move the gripping device 7 linearly, and that the drive means 14, 16 can simultaneously rotate and move the gripping device linearly along the respective axis 11. In addition, the drive means 12, 13 and 14, 16 can move the respective gripping devices linearly and/or angularly relative to each other and the linear movement of the gripping device 7 or 8 can precede or follow its angular movement.

Each of the four drive means 12, 13, 14, 16 can include a fluid-operated (hydraulic or pneumatic) unit, an electrically operated unit, an electromagnetically operated unit, a mechanically operated unit or a combination of two or more differently operated units. In the embodiment of FIGS. 1 to 3, each ofthe drive means 12, 13, 14, 16 is assumed to be a hydraulically operated motor. Each of the drive means 112, 14 has an elongated doubleacting cylinder for a vertically reciprocable piston 18, and the piston rods 17 of the drive means 12, 14 are rotatable by the respective drive means 13,16 each of which can include a rotary cylinder and piston unit of any known design.It suffices to say that the drive means 12 can move the gripping device 7 independently of or simultaneously with the drive means 14, and vice versa, and the same holds true forthe drive means 13 and 16. The details of operative connections between the drive means 12, 13, 14, 16 and the numerical control system NC of the grinding machine are not shown in the drawing. The axes of the two piston rods 17 coincide with the axes 11 of the respective gripping devices 7,8.

It is further within the purview of the invention to synchronize the operation of the drive means 13 with that of the drive means 12 and/or to synchronize the operation of the drive means 16 with that of the drive means 16. As shown in FIG. 8, the drive means 14 comprises a double-acting cylinder 14A for the piston 18 (not shown) which is fixedly mounted on a platform 19 and whose piston rod 17 is reciprocable in directions indicated by a double-headed arrow 17A. The cylinder 14A is confined in and is affixed to a casing or housing H of the carraige 19. The lower end portion of the piston rod 17 is affixed to a plate 117 having a circular opening 1 17A for a smaller-diameter portion 108A of a tubular member 108 which carries the mobile jaws of the gripping device 8.The tubular member 108 and the gripping device 8 are rotatable as a unit relative to the plate 117. The hollow cylindrical head 108B at the upper end of the tubular member 108 forms part of the drive means 16. This head is located in the housing H and has a radially inwardly extending roller follower 108C extending into a partly straight and partly helical groove 208A machined into the peripheral surface of a fixed cylindrical cam 208 which is mounted in the housing H. The head 108B is rotatable in an enclosure 308 which is movable up and down (arrow 398A) along one or more vertical guide rods 408 in the housing H.

When the piston in the cylinder 14A is displaced in response to admission of a pressurized (gaseous or hydraulic) fluid into the upper or lower cylinder chamber, the piston rod 17 causes the plate 117 to move down (to the illustrated lower end position) or up and to thus move the tubular member 108 and the gripping device 8 in the same direction. The head 108B entrains the enclosure 308 and simultaneously rotates in the enclosure which latter travels along the guide rod or rods 408. The tubular member 108 compels the gripping device 8to rotate about the respective axis 11 because the follower 108C tracks the partly helical groove 208A of the stationary cam 208 in the housing H.

In orderto relieve the piston rod 17 of bending stresses, the housing H can carry one or more downwardly extending guide rods or tie rods (not shown but similar to the illustrated guide rod 408) to hold the plate 117 against rotation with the tubular member 108.

The construction of the drive means 12, 13 for the gripping device is or can be identical with or analogous to the construction of the drive means 14, 16 of FIG. 8. Other means for establishing a predetermined relationship between the extent of axial and angular movements of the gripping devices 7 and 8 can be used with equal or similar advantage. For example, the cylinder 14A of FIG. 8 and its piston can be replaced with a rack and pinion drive for the piston rod 17.

The carriage 19 (e.g., in the form of a gantry wagon) is movable in parallelism with the axis of the workpiece W1 at the material removing station 3 and carries the drive means 12, 13 and 14, 16 for the gripping devices 7 and 8. This contributes to greater versatility of the improved apparatus.

As shown in FIG. 1, the carriage 19 has an extension 119 which carries a reversible electric motor 219 and is reciprocable (in parallelism with the common axis 9 of the centers 4,6 and the workpiece W1 therebetween) along one or more stationary guide rails 319.

The treatment of the workpiece W1 which is shown in FIG. 1 is already completed, and this workpiece is held by the jaws of the gripping device 7. The jaws of the second gripping device 8 hold the other (untreated) workpiece W2 which is about to be treated at the material removing station 3 between the centers 4 and 6. The plane of the jaws which form part of the gripping device 8 is turned through an angle of 90 degrees with reference to the plane of the jaws (of the gripping device 7) which hold the freshly treated workpiece W1, i.e., the axis of the untreated workpiece W2 makes an angle of 90 degrees with the common axis 9 of the centers 4 and 6.

As soon as the treatment of the workpiece W1 by the working surface of the illustrated grinding wheel 1 is completed, the finished workpiece W1 is engaged by the two jaws of the gripping device 7 which has been caused (e.g., by a combination of two cooperating drive means of the type shown in FIG. 8 or by analogous drive means) to descend to the position of FIGS. 1 to 3 in response to actuation of the respective drive means 12. In the course of the next step, the drive means 12 and 13 are actuated, either simultaneously or one after the other, so as to lift the finished workpiece W1 above and away from the material removing station 3.The movements of the gripping device 7 are regulated by the numerical control system NC in such a way that the workpiece W1 bypasses the gripping device 8, the untreated workpiece W2 as well as the obstacle which is denoted by the phantom line 2. Sooner or later, the treated workpiece W1 assumes an orientation in which its longitudinal axis is parallel or substantially parallel to the axis of the untreated workpiece W2.

The removal of finished workpiece W1 from the station 3 is followed by combined angular and translatory movement of the workpiece W2 through the medium of the respective gripping device 8 whose drive means 14, 16 receive signals from the control system NC. The arrangement is preferably such that the workpiece W2 is rotated in the direction in which the workpiece W1 was rotated during or preparatory to removal from the material removing station 3. Again, the drive means 14,16 receive control signals of such nature that the workpiece W2 does not collide with the gripping device 7, with the workpiece W1 and/or with the obstacle 2 during transfer from the position of FIG. 1 to the station 3.As can be seen in the drawing, each of the workpieces W1, W2 is gripped at a location close to one of its axial ends so that it can be moved to or from the station 3 without any lateral or other movement of the carriage 19.

If each of the workpieces W1, W2 is to be treated twice in one and the same machine, first at one end and thereupon at the opposite end, such workpieces are not only manipulated by the respective gripping devices 7,8 but also transported by the carriage 19 in a manner as shown in FIGS. 6a to 6h. In addition, the grinding machine then comprises a depository for temporary storage of workpieces adjacent to the path of movement of the carriage 19. The arrangement is such that the carriage 19 is moved sideways (i.e., in the direction of the axis 9) and that each of the workpieces W1, W2 is manipulated first by one and thereupon by the other gripping device.

FIG. 6a shows the workpiece W1 between the centers 4,6 upon completed grinding of one end portion (at one side of the collar CO1). FIG. 6b shows the next step, i.e., the workpiece W1 was lifted by the gripping device 7 and was moved to a position of parallelism with the workpiece W2 one end portion of which is held by the gripping device 8 at one side of the collar C02. The other end portion of the workpiece W2 has already undergone a treatment by the grinding wheel 1.In the next step, the gripping device 8 is caused to perform a translatory and angular movement so as to lower the workpiece W2 to the material removing station 3 between the centers 4, 6 (see FIG. 6c). The gripping device 8 is then lifted above and away from the station 3 and the shorter end portion (which was previously held by the jaws of the gripping device 8) is treated by the grinding wheel 1 (see FIG. 6d).

During such treatment of the workpiece W2 at the station 3, the carriage 19 is moved in the direction of the common.axis 9 of the centers 4, 6 so as to advance the gripping device 7 and the workpiece W1 (which is held by the device 7) to a depository (e.g., a pallet P or a belt or chain conveyor, not shown), and the gripping device 7 is caused to deposit the workpiece W1 on the pallet P (note FIG.

6e). In the next step (FIG. 6f), the carriage 19 moves relative to the pallet P so that the workpiece W1 can be lifted off the pallet by the gripping device 8. The carriage 19 is then caused to move in the direction of the axis 9 so as to move the gripping device 8 and the workpiece W1 to a level above the station 3 (FIG.

6g) where the gripping device 8 is caused to perform a combined angular and translatory downward movement in order to turn the workpiece W1 through another 900 and to lower the workpiece so that the total angular displacement of the workpiece W1 amounts to 1800 and the grinding wheel 1 then removes material from the other (shorter) end portion of the workpiece W1 in a manner as shown in FIG. 6h.

While the workpiece W1 is treated at the station 3 (FIG. 6h), the carriage 19 transports the finished workpiece W2 to a conveyor (not shown) which accepts and removes finished workpieces, and the gripping device 7 then accepts a fresh (untreated) workpiece from a further conveyor (not shown). The procedure is thereupon repeated in the above described sequence.

The carriage 19 can be reciprocated by a tiuid- operated motor, by a chain conveyor or in any other suitable way so that its drive can receive signals from the control system NC.

FIGS. 7a to 7c show the treatment of workpieces Win two stages but in two discrete grinding machines 21 and 23. The first machine 21 has a grinding wheel 1 which is used to remove material from the longer portion of each of a series of successive workpieces W at one side of the respective collar CO. The carriage (not shown in FIGS. 7a-7c) is then caused to move such workpieces to a depository or magazine 22 which is disposed between the two grinding machines 21,23 and wherein the partially treated workpieces W are temporarily stored preparatory to transfer into the second machine 23 for treatment by a second grinding wheel 1'.The transfer of successive partially treated workpieces W from the machine 21 to the magazine 22 takes place simultaneously with angular displacement of such workpieces through 90 . Additional angular displacement of workpieces W, again through 90 , takes place during transport from the magazine 22 to the material removing station of the machine 23. The grinding wheel 1' removes material from the other (shorter) end portions of the workpieces W after each such workpiece has been turned end-for-end.

FIG. 4 shows a portion of a further apparatus wherein the axes 11 of the piston rods 17 are nonvertical, e.g., they can be parallel or nearly parallel to the adjacent portion or side of the obstacle 2. The selection of orientation of the axes 11 will depend on the availability of space in a particular machine and on certain other variables. All that counts is to ensure that the workpiece W1 and/or W2 can be moved to and from the material removing station 3 without colliding with the other workpiece, with the gripping device for the other workpiece, with the grinding wheel 1 and/or with the obstacle 2.

FIG. 5 shows a further embodiment which is particularly suited for the manipulation of relatively small (e.g., ring-shaped) workpieces W1' and W2'.

Each of the two work gripping devices 7", 8" has a crank 24 whose throw k equals half the distance between the parallel axes 11 of the two piston rods 17. Such construction of the gripping devices enables them to accurately position small ringshaped or similar workpieces with reference to the Z-axis of a grinding machine, i.e., to properly select the orientation of the longitudinal axis of the workpiece at the material removing station.

An important advantage of the improved apparatus is that, if desired, the workpiece W1 or W1' can be replaced with the workpiece W2 or W2' or vice versa without any shifting of the carriage 19 in the direction of the axis 9 and/or in any other direction.

It has been found that the workpieces W1 or W1' and W2 or W2' can be caused to readily bypass each other in a small area if the one or the other workpiece is turned through 90 prior to moving along the other workpiece. If the workpieces are to be treated in two stages, e.g., in a manner as described with reference to FIGS. 6a-6h or 7a-7c, it is necessary to turn each workpiece through 180 by resorting to a depository, such as the pallet P or the magazine 22, and by moving the carriage 19 in the direction of the axes of workpieces at the material removing station or stations. The provision of a depository renders it possible to manipulate each workpiece first by the gripper 7 and thereupon by the gripper 8, or vice versa.

All embodiments of the improved apparatus exhibit the advantage that the time for replacement of workpieces in a grinding machine or in another material removing machine can be reduced to a fraction of the time which is needed by using a conventional apparatus. In addition, the improved apparatus occupies little room and can be designed to deliver or remove workpieces along narrow paths extending between the material removing station and the station for reception of fresh workpieces and delivery of treated workpieces. This is accomplished in that each of the two work gripping devices is movable axially as well as angularly about its axis to thus allow for manipulation of short, long, large-diameter, small-diameter, heavy, lightweight, simple or complex workpieces with a heretofore unmatched degree of facility. Moreover, the operation of drive means for each of the two gripping devices can be automated in a simple and efficient way by using controls which are already provided in an automatic machine tool.

Claims (11)

1. Apparatus for exchanging workpieces in machine tools and the like, particularly in grinding machines, wherein the workpieces are treated while rotating about a predetermined axis, comprising a first and a second work gripping device each of which is arranged to engage and releasably hold a discrete workpiece, said devices being disposed one behind the other as considered in the direction of said axis; first drive means for imparting to said devices translatory movements; and second drive means for imparting angular movements to said devices.

2. The apparatus of claim 1, wherein said second drive means include means for rotating said devices about axes which intersect said predetermined axis.

3. The apparatus of claim 1, wherein said second drive means comprise means for rotating said devices about substantially vertical axes.

4. The apparatus of claim 1, whereinsaid second drive means comprise means for rotating said devices about non-vertical axes.

5. The apparatus of claim 1, wherein said second drive means comprise means for rotating said first and second devices about discrete first and second axes, said first drive means comprising means for respectively moving said first and second devices the direction of said first and second axes.

6. The apparatus of claim 5, wherein at least one of said drive means comprises at least one fluidoperated motor.

7. The apparatus of claim 1, further comprising means for moving said devices jointly in the direction of said axis.

8. The apparatus of claim 7, wherein said means for moving said devices jointly in the direction of said axis comprises a reciprocable carriage.

9. The apparatus of claim 8, wherein said carriage comprises a gantry wagon.

10. The apparatus of claim 1, wherein said second drive means comprise means for rotating said devices about parallel axes and each of said devices comprises a crank having a throw which equals half the distance between said parallel axes.

11. Apparatus for exchanging workpieces in machine tools and the like, substantially as herein described with reference to the accompanying drawings.