GB2085787A - A machine tool, for example, an automatic lathe - Google Patents

Abstract

A machine tool has several carriages (22, 24, 26, 28) which are each controllable by a respective cam (38) and displaceable by means of a respective working cylinder (60). A servo control cylinder (56) which senses the associated cam and which is connected to the working cylinder via a working pressure line (58, 80) is associated with each carriage. Each servo control cylinder has a control piston slidable therein and a valve slide arranged to be actuated by the respective cam by way of a sensing device (54,50). The valve slide controls communication between a pressure medium source and a primary side of the control piston and between this primary side and an outlet. The secondary side of the control piston communicates with the working pressure line (58). <IMAGE>

Description

SPECIFICATION A machine tool, for example, an automatic lathe The present invention relates to a machine tool, for example, an automatic lathe, having several carriages, such as cross-slides and turret carriages, controllable by cams.

In known machine tools of this type, three systems for actuating the carriages are employed in practice.

In a first, purely mechanical construction, the movements of the rotating cams are transmitted to the carriages associated with the individual cams by means of levers, rods, toothed segments, and the like. However, in the case of machines having a large number of carriages this system requires that the cams are not centralised, and, instead, that the cams are arranged near to the carriages with which they are associated. Accordingly, several control shafts connected to one another by gears and supporting the cams are required. A control shaft common to all the cams would of course lead to an extraordinarily complex transmission mechanism which would be greatly affected by high friction and low rigidity.

In ano#ther known construction, hydraulic rods are inserted between the cams and the carriages. Such a hydraulic rod linkage consists of a control cylinder which is actuated by the respective cam and out of which the cam displaces hydraulic fluid which is conveyed via a flexible connecting line into a working cylinder arranged to move the carriage associated with the cam. Since only one connecting line is required from each cam to the respective carriage, it is possible to combine all the cams on one control shaft, without thereby creating restrictions on the arrangement of the carriages or processing units of the machine tool.However, this system also has the disadvantage, above all in the case of carriages which are difficult to move, that considerable forces arise between the cams and the cam followers of the control cylinders which sense these, as a result of which relatively high drive powers are required for the control shaft. Furthermore, the "rigidity" of the transmission mechanism is not particularly great, that is, the distance covered by a carriage does not correspond exactly to the movement predetermined by the associated cam.

In a third known construction, the cams actuate hydraulic copying valves which, in turn, actuate the carriages in the manner of a follow-up control. This technique requires a mechanical return between each carriage and the associated copying valve, which means, in turn, that the carriage, the copying valve and the cam associated with the carriage have to be arranged relatively close to one another, so that it is not possible to central iso the cams in the case of a relatively large number of carriages.

However, the powers required for driving the control shaft or the control shafts are small, and because of the return there are no "rigidity problems".

According to the present invention there is provided a machine tool comprising a plurality of cam controlled carriages, at least one of said carriages being displaceable by means of a hydraulic working cylinder, and at least one servo control cylinder connected via a working pressure line to said working cylinder, said servo control cylinder being actuable by way of a sensing device by the cam associated with said one carriage, wherein the servo control cylinder has a control piston slidable therein and a valve slide arranged to be actuated by the sensing device, said valve slide controlling communication between a pressure medium source and a first, primary side of the control piston, and between the primary side of the control piston and an outlet, and wherein the secondary side of the control piston communicates with the working pressure line.

An embodiment of the invention has the adman tage that it is possible to centralise the control cams on a single control shaft without restricting the arrangement of the carriages or processing units. In addition, higher processing accuracies than those of the known constructions described above are possible. Furthermore, a lower outlay in comparison with known machines having a hydraulic rod system may be achieved.

Embodiments of the present invention not only allow the control cams to be centralised on a single control shaft, but, since only small forces are required to actuate the control cylinders, only a little power is needed to drive this control shaft. Thus, it is possible to use for the control shaft drive a lowpower variable direct-current motor which covers without change gears, the entire time range defined by the processing times for the workpieces. In addition, because of the low forces arising during the sensing of the control cams it is not necessary to provide large rollers, on the cam followers of the control cylinders. Such large rollers have hitherto been necessary in machines with a hydraulic rod system.In embodiments of the present invention tracer pins with small diameters are sufficient as cam followers and as a result of the virtually point-by-point sensing of the cams which is thereby achieved, high accuracies can be achieved and the directions of movement of the carriages can be changed abruptly without loss of time. Moreover, the control cams can be thin or can be made of cheap materials, such as, for example, plastics laminated fabric, and the like. This has the advantage that many cams can be accommodated on a single control shaft, without the danger that the control shaft will sag and thus that the processing accuracy will be reduced.Finally, the total efficiency of the carriage control is substantially higher than in the known constructions, and a carriage can even be moved by hand, for example, to disengage the tool supported by the slide, by displacing manually the tracer pin or cam follower sensing the associated cam.

The basic idea of the present invention, namely the use of a hydraulic rod system with a servo control cylinder, leads, however, not only to greater processing accuracies because the theoretical cam shape can be reproduced more exactly, but also presents the possibility of compensating for deviatins from total rigidity which is never actually provided, of the control cam/transmission mechanism/carriage system. It is proposed, in an embodi ment of the invention, to provide, on a machine tool with a hydraulic rod system, a pressure detector in the working-pressure line between the control cylinder and working cylinder, as well as a servo control cylinder controlled by the pressure detector, for feeding additional pressure medium into the working-pressure line when the working pressure rises.

Flexibilities in the control of the carriages can be compensated by means of appropriate characteristics of the transmission mechanism between the pressure detector and servo control cylinder. Basically, the servo control cylinder controlled by the pressure detector could be the cylinder controlled by the cam, so that two control movements are superimposed, namely that caused by the cam and that caused by the pressure detector. However, it is more expedient, for various reasons, to provide a further servo control cylinder, in order to feed additional pressure medium into the working-pressure line when the working pressure rises in the latter.

Although there are, of course, various possibilities for designing the pressure detector, it is recommeded, for the sake of simplicity, to design the pressure detector as a piston actuating the valve slide of the servo control cylinder.

However, the basic inventive idea of using servo control cylinders in hydraulic rod systems of machine tools also provides a way, in the case of machines with toolholder turrets, of correcting the position of each tool individually, without having to change the cam assigned to the turret carriage. In automatic lathes with a toolholder turret located on a turret carriage and with a hydraulic rod system between the turret and the associated control cam, an adjustable stop can be associated to each of the working positions of the toolholder turret, and the stops can move, according to the rotation of the toolholder, past a tool position detector for sensing the stops. Furthermore, a servo control cylinder controllable by this detector is provided for feeding additional pressure medium into the workingpressure line of the hydraulic rod system.Even this servo control cylinder could, again, be the servo control cylinder sensing the cam belonging to the turret carriage, but it is recommended, to provide a further servo control cylinder for feeding additional pressure medium into the working-pressure line.

The invention thus makes it possible to work with preset tools, even when the cam associated with the turret carriage has been produced incorrectly. In theory, the adjustable stops assigned to the various tools could be located directly on the toolholder turret head, but, in a preferred embodiment of the invention, a further drum which supports the stops and which is reversed synchronously with the toolholder turret head is provided.

An embodiment of the present invention will hereinafter be described, by way of example, with reference to the accompanying drawings, in which :- Figure 1 shows diagrammatically a side view of an automatic lathe of the present invention, Figure 2 shows a view of the cross-slides of the automatic lathe, seen in the direction of its working spindle, and a diagrammatic representation of the transmission mechanism between one of the crossslides and the associated control cam; Figure 3 shows a representation, corresponding to Figure 2, of the turret carriage of the automatic lathe; Figure 4 shows a side view of the parts shown in Figure 3, taken in the direction of arrow X in Figure 3; Figure 5 shows a partial section through the automatic lathe taken along the line 5-5 of Figure 4; Figure 6shows an operating diagram for the hydraulic drives;; Figure 7shows a cut-out from Figure 2 to illustrate, on a larger scale, the parts transmitting the movements from the cam plate to the associated servo control cylinder; Figure 8 shows a side view of the double-armed transmission lever shown in Figure 7; Figure 9 shows a partial section through this transmission lever taken along the line 9-9 of Figure 7; Figure 10 shows a further partial section through this transmission lever taken along the line 10-10 of Figure 7; Figure 11 shows a diagrammatic section through a servo control cylinder controlled by a cam; and Figure 12 shows a similar diagrammatic section through a further servo control cylinder for compensating mechanical flexibilities in the control cam/ carriage transmission system.

Figure 1 shows diagrammatically a side view of an automatic lathe having a base frame 10 and an upper frame 12 which houses in an easily accessible manner a rotatably supported control shaft 14. The control shaft 14 is driven by a variable direct-current motor 16 via a gearing (not shown). A working spindle 18 is also rotatably supported by the upper frame 12 and is driven by a motor (not shown). At its front end the spindle 18 is provided with a clamping chuck 20 for clamping workpieces to be machined.

As shown in Figures 1 and 2, the lathe has several cross-slides 22, 24, 26 and 28 which are displaceably guided on the upper frame 12. In addition, a turret carriage 30 is displaceably mounted on the upper frame 12. In known manner, all these carriages can be advanced in the direction of the workpiece to be machined and retracted again. The cross-slides carry, for example, individual tools (not shown), whilst the turret carriage 30 is equipped with a toolholder turret head 32 which is rotatable about an axle 32a and which carries several, for example eight, radially arranged tools (not shown).

A cam disc for each carriage is fastened on the control shaft 14. Thus, in the embodiment illustrated four cam discs 34,36,38 and 40 are provided for the four cross-slides and one cam disc 42 is provided for the turret carriage 30. Each of these cam discs is sensed by a servo control cylinder, the secondary side of which is connected via a working-pressure line to a working cylinder for displacing the carriage associated with the cam disc. This can be seen in Figure 2 which illustrates the cam disc 38 associated with the cross-slide 26. This cam disc 38 is sensed by a double-armed sensing lever 50 which is pivotable about an axle 48 rigidly fixed to the upper frame and which supports, at its end facing the cam disc, a tracer pin 52 running on the periphery of the cam disc 38.The other end of the sensing lever 50 is pivotally connected to a valve cam follower 54 of a servo control cylinder 56 which is described in more detail below. From the secondary side of this servo control cylinder 56 a working-pressure line 58 leads to a working cylinder 60 which is arranged to displace the cross-slide 26. The working cylinder 60 has a double-acting piston 62 and a piston rod 64 which is connected to the cross-slide 26 via a driver 66. When hydraulic fluid, for example, oil, is forced into the working-pressure line 58 by the servo control cylinder 56, the piston 62 and hence the cross-slide 26 are pushed to the right as shown in Figure 2, that is, the cross-slide 26 is advanced. The cross-slide 26 is retracted in a simple manner.Thus, on the side of the piston 62 on the right in Figure 2, there is always a certain pressure which is supplied via a restoring-pressure line 70 and which, when the cross-slide is advanced, is overcome by the working pressure generated on the secondary side of the servo control cylinder 56. However, when the working-pressure line 58 is relieved the restoring pressure at the right of piston 62 is sufficient to retract the cross-slide 26, that is, to move it to the left as shown in Figure 2.

As the other cross-slides 22, 24 and 28 are displaced in the same manner, the working cylinders and servo control cylinders associated therewith are not illustrated. The displacement of the turret carriage 30, which takes place in the same way, will be discussed briefly with reference to Figure 3. As is shown in Figure 3, the cam disc 42 for the turret carriage 30 is sensed by a sensing lever 74 which is pivotable about the axle 48 and which is articulated to a valve cam follower 76 of a servo control cylinder 78. The secondary side of this servo control cylinder is connected by means of a working-pressure line 80 to one side of a working cylinder 82, the piston rod 84 of which actuates an advancing lever 88 pivotable about an axle 86 rigidly fixed to the upper frame.

This advancing lever 88 is held in contact with the end of the piston rod 84 on the left as seen in Figure 3, by means of a hydraulic spring 90 designed as a hydraulic cylinder. A driver 92 is pivotally connected to the upper end of the advancing lever 88 and is, in turn, connected to the turret carriage 30 via an adjusting spindle 94.

A preferred embodiment of a servo control cylinder will now be described with reference to Figure 11 which shows a cam-controlled servo control cylinder, the servo control cylinder 56 of Figure 2 being chosen as an example.

The servo control cylinder 56 has a cylinder housing 100 with a longitudinally extending bore 102 in which a control piston 104 is displaceably arranged. The piston 104 has a primary side 106, a secondary side 108, a receiving space 110 for a piston-shaped valve slide 112, and a guide projection 114. The valve cam follower 54 is displaceably arranged in a longitudinal bore 116 of the guide projection 114 and abuts the valve slide 112. As described above, the valve cam follower 54 is actuated by the sensing lever 50. To ensure that the valve slide 112 rests against the valve cam follower 54 a valve-slide pressure spring 120 is engaged in a blind hole 122 in the valve slide 112 and which is supported on the bottom of this blind hole 122 in the valve slide 112, and on the upper end of the receiving space 110 in the control piston 104.

The valve-slide pressure spring 120 is arranged such that, when the lowest point of the cam disc 38 is sensed, the spring 120 presses the valve cam follower 54 downwardly until the cam follower 54 lifts a control rod 126 byway of a double-armed intermediate lever 124 when the control rod 126 is lifted it opens a leak valve 128 comprising a valve seat 128a, a valve body 128b and a closing spring 128c, so that hydraulic fluid, such as oil, from a hydraulic fluid source which is under relatively low pressure can flow, via an inlet bore 130 in the cylinder housing 100, the leak valve 128 and a further bore 132, into a working-pressure space 134 located on the secondary side 108 of the control piston 104.

When the sensing lever 50 lifts the valve cam follower 54 during rotation of the cam disc 38, the leak valve 128 is first closed. Thereafter, as the valve slide 112 is further lifted, a working control edge 11 2a of the valve slide permits a throughflow between a lower annular space 138 and a central annular space 140. The lower annular space 138 is connected via bores 142 and 144, a restoringpressure space 146 and a bore 148 to a channel 150 is connected to a source (not shown) of a pressure fluid, for example, oil, for generating the working pressure. The central annular space 140 is connected via a bore 152 and an annular space 154 to the primary side 106 of the control piston 104.Conse- quently, when the lower annular space 138 is in communication with the central annular space 140 as a result of lifting of the valve slide 112, the pressure fluid fed via the channel 150 into the servo control cylinder flows under the primary side 106 of the control piston 104 and lifts the piston 104 until, as a result of the displacement of the control piston 104 relative to the valve slide 112, communication between the annular spaces 138 and 140 is prevented by the working control edge 112a. It is essential, here, that the area of the restoringpressure space 146 which is effective in respect of the control piston 104 is less than the effective area of the primary side 106 of the control piston. It should also be added than an equalising bore 158 connecting the blind hole 122 to the underside of the valve slide 112 is provided in the valve slide 112.

Hydraulic fluid is forced out of the workingpressure space 134 as a result of the lifting of the control piston 104, and, since the leak valve 128 has already been closed, this fluid is flowed via a working-pressure channel 160 into the delivery line 58 which is connected to the channel 160.

The servo control cylinder described above therefore operates in the manner of a follow-up control.

When the height of the cam disc 38 is reduced, the pressure spring 120 presses the valve slide 112 downwardly such that a relieving control edge 112b of the valve slide allows communication between the central annular space 140 and an upper annular space 164. The upper annular space 164 is connected via a bore 166 and an annular space 168 to an equalising bore 170 connected to a tank (not shown) for hydraulic fluid. Because of the pressure prevail ing in the restoring-pressure space 146, the control piston 104 is then moved downwardly until the relieving control edge 112b once again separates the annular spaces 140 and 164 from one another. Since the working-pressure space 134 is enlarged when the control piston 104 moves downwardly the cross-slide 26 can be retracted under the effect of the pressure prevailing in the restoring-pressure line 70.

The restoring-pressure space 146 could even be omitted, since the return of the slide 26 and, consequently, of the associated working cylinder 60 results in a sufficient pressure in the workingpressure space 134 to move the control piston 104 downwardly.

The transmission of the height of a cam disc to the valve cam follower of the associated servo control cylinder will now be described in rather more detail with reference to Figures 7 to 10, again specifically in respect of the cam disc 38 and the servo control cylinder 56 of Figure 2.

The double-armed sensing lever 50 consists of two arms 50a and 50b which are pivotable relative to one another and which are normally pivoted as a unit about the axle 48 by means of the cam disc 38. So that the cam disc can always be made with the largest maximum radius, however, the second arm 50b can be pivoted relative to the first arm 50a and then locked again; for this purpose, the first arm 50a has a slot 50c, through which passes a locking screw 50d attached to the arm 50b.

The double-armed sensing lever is also designed such that, in the case of overloading of the cam disc/servo control cylinder transmission mechanism, it has a lost motion which can be used to switch off the machine; In the embodiment illustrated, a flange 50e carrying a wrist pin 50f is fastened to the axle 48.

The first arm 50a is pivotable about this wrist pin, specifically because it surrounds the axle 48 with play, this play being designed by 50g in Figure 8. So that this play remains ineffective during normal operation, a centering pin 50h is fastened to the first arm 50a (see Figure 9) and is located between a stop screw 50i attached in the flange 50e and a centering spring 50k. The centering pin 50h can be deflected to the right as seen in Figure 9 counter to the effect of the centering spring 50k only when the transmission mechanism is overloaded. When the centering pin 50h is deflected to the right the arm 50a pivots about the wrist pin 50f in a clockwise direction.A trip lever 501 for actuating a limit switch 50m rests against the arm 50a, specifically in a region which forms an arc of a circle concentric to the axle 48, so that normal pivoting of the double-armed sensing lever 50 as a unit has no influence on the limit switch 50m.

However, when the arm 50a pivots about the wrist pin 50f, the trip lever 501 is pivoted in an anticlockwise direction, under the influence of the pressing force exerted by the limit switch 50m so thatthe limit switch switches off the machine tool.

Figure 10 shows a further advantageous feature of the sensing lever 50. As shown in Figure 10, the tracer pin 52 has two grooves 52a and 52b which interact with a sprung ball catch 52c. Whilst Figure 10 illustrates the tracer pin in its normal operating position, it can be displaced in the arm 50a to the left as seen in Figure 10, until the ball catch 52c drops into the second groove 52b. In this position, the tracer pin 52 no longer rests against the periphery of the associated cam disc. The slides can therefore be stopped individually, without a cam having to be removed.

A correcting servo control cylinder can be connected to one or to each of the working-pressure lines, for example to the working-pressure lines 58 and 80 shown in Figures 2 and 3, in order to compensate for deviations in the respective transmission system and of the actuated components from ideal complete rigidity. Such a correcting servo control cylinder is illustrated by way of example in Figure 3, specifically for the working-pressure line 80 associated with the turret carriage 30. This correcting servo control cylinder 200 will now be described in rather more detail with reference to Figure 12.

However, since its basic design is no different from that of the servo control cylinder 78 shown in Figure 11, but, merely has additional elements, the following description will be restricted to explaining these additional elements.

The servo control cylinder 200 has, in a cylinder housing 202, a control piston 204 and a valve slide 206 which is actuated by a valve cam follower 208. A pressure-measuring cylinder 212 with a sprung pressure-measuring piston 214 communicates with the working-pressure space 210, located on the secondary side (upper side) of the control piston 204, such that the length of the part of the piston 216 of the pressure measuring cylinder 212 projecting from the cylinder housing 202 is a measure of the pressure prevailing in the working-pressure space 210 and, consequently, in the working-pressure line 80.

As is evident from Figure 5, a template 220 is fastened to the piston rod 216 of the pressuremeasuring cylinder 212, and this template has a transmission face 220a which is sensed, under the effect of a pressure spring 222, by a sensing cam follower 224. A double-armed transmission lever 228 pivotable about an axle 226 and articulated to the sensing cam follower 224 transmits the movement of the piston rod 216 to the valve cam follower 208 of the correcting servo control cylinder 200, but allowing for the transmission function defined by the transmission face 220a.

If it is assumed that flexibilities in the system as a whole become more significant when the working pressure rises, it will be seen that the lack of rigidity of the system as a whole can be compensated by the correcting servo control cylinder 200. Thus, the higher the pressure in the particular workingpressure line, the more the piston rod 216 is moved to the right as seen in Figure 5, resulting in an upward movement of the valve cam follower 208 and, consequently, in the further conveyance of pressure fluid into the working-pressure line in question, since the working-pressure space 210 is connected via bores 230,232 and 234 to the respective working-pressure line, in the embodiment illustrated to the working-pressure line 80 in Figure 3.

Figures 3 and 4 show a correcting drum 300 which is rotated synchronously with the turret head 32 by drive means (not shown). This drum has as many stop screws 302 with stop nuts 304 as the number of tools which the turret head 32 can hold, that is, eight stop screws in the embodiment illustrated. The position of the respective stop nut 304 is sensed by a correcting feeler 308 which is biased towards the stop nut 304 by a spring 306. The feeler 308 is fastened to a transmission shaft 312 which is rotatably mounted in stationary bearings 310 and to the lower end, as seen in Figure 4, of which a supporting arm 314 is attached. The arm 314 supports the axle 226 and hence the transmission lever 228 articulated to this axle (see Figure 5).

By means of the stop screws 302 or stop nuts 304, it is possible to correct errors in the cam disc 42 and/or individual incorrect positions of the tools supported by the turret head 32. However, the working positions of the tools can also be adjusted individually, after they have been fastened in the turret head 32, without the cam disc 42 having to be changed, since it is merely necessary to displace the stop screws or stop nuts for this purpose.

This tool correction could be carried out via a separate servo control cylinder, but it is especially appropriate to superimpose on one another the correcting movements of the correcting feeler 308 and of the piston rod 216 of the pressure-measuring cylinder 212 and to make these movements act on the same servo control cylinder which, moreover, could also be the servo control cylinder controlled by the cam disc; in the latter case, three movements would be superimposed, namely the sensing movement of the cam disc and the correcting movements of the correcting feeler 308 and of the piston rod 216.

Figure 6 shows diagrammatically part of the hydraulic system of the automatic lathe illustrated.

Since the individual components of this hydraulic system have been explained above with reference to the other Figures, there is no need for a further description of the circuit diagram according to Figure 6. It goes without saying, however that a correcting servo control cylinder and a pressuremeasuring cylinder corresponding to the units 200 and 212 could also be connected to the workingpressure line 58.

The restoring spring of the pressure-measuring piston 214 (see Figure 12) and the transmission face 220a of the template 220 are respectively dimensioned and shaped so that the total characteristic of the correcting system corresponds to the rigidity of the respective parts of the machine.

Claims (8)

1. A machine tool comprising a plurality of cam controlled carriages, at least one of said carriages being displaceable by means of a hydraulic working cylinder, and at least one servo control cylinder connected via a working pressure line to said working cylinder, said servo control cylinder being actuable by way of a sensing device by the cam associated with said one carriage, wherein the servo control cylinder has a control piston slidable therein and a valve slide arranged to be actuated by the sensing device, said valve slide controlling communication between a pressure medium source and a first, primary side of the control piston, and between the primary side of the control piston and an outlet, and wherein the secondary side of the control piston communicates with the working pressure line.

2. A machine tool as claimed in Claim 1, wherein a restoring spring is provided for the control piston.

3. A machine tool as claimed in Claim 1 or 2, wherein a pressure detector is provided in the working pressure line and is arranged to control a further servo control cylinder to feed additonal pressure medium into the working pressure line when the working pressure rises.

4. A machine tool as claimed in Claim 3, wherein the pressure detector comprises a piston arranged to actuate the valve slide of the further servo control cylinder.

5. A machine tool as claimed in Claim 4, wherein a cam defining a transmission function is located in the transmission distance between the pressure detector piston and the further servo control cylinder.

6. An automatic lathe as claimed in any of the preceding claims, having a toolholder turret located on a turret carriage, wherein an adjustable stop is associated with each of the working positions of the toolholderturret, each of said stops being movable, according to the rotation of the tool-post, past a tool position detector for sensing the stops, and wherein a further servo control cylinder controllable by the detector is provided for feeding additional pressure medium into the working pressure line associated with the turret carriage.

7. An automatic lathe as claimed in Claim 6, wherein a second servo control cylinder controllable by the pressure detector and the tool position detector is provided.

8. An automatic lathe substantially as herein be fore described with reference to and as illustrated in the accompanying drawings.